A method of magnetically manipulating a medical device within a body part of a human patient in conjunction with MR imaging includes applying a navigating magnetic field with magnets from the MR imaging device, and changing the magnetic moment of the medical device to change the orientation of the medical device within the body part.

This invention relates to an apparatus for navigating medical devices within the body to sites of treatment delivery, and methods of using this apparatus to achieve this navigation. More specifically, this invention relates to the use of a magnetic field from an MR imaging device to navigate a magnetic medical device within the body.
The need for improved surgical navigation techniques stimulated the development of magnetic stereotaxis as a novel means for guiding a surgical implant, such as a catheter, along nonlinear paths within a body part. In particular, it is useful in intraparenchymal applications within the brain, where linear stereotactic techniques (either framed or frameless) do not permit the probe to follow single-pass curvilinear paths to a target location deep within the brain, as first taught by Howard et al. in U.S. Pat. No. 4,869,247 incorporated herein by reference. Howard et al. subsequently taught magnetic stereotactic techniques for volume-contoured therapy delivery within the brain and elsewhere in the human body in succeeding U.S. Pat. Nos. 5,125,88, 5,707,334, and 5,779,694 incorporated herein by reference. Advanced versions of magnetically guided surgical systems capable of performing magnetic stereotactic procedures in the brain and in other body parts have been disclosed in U.S. patents by Werp et al., U.S. Pat. No. 5,9331,818; Blume et al., U.S. Pat. No. 6,014,580; Werp et al., U.S. Pat. No. 6,015,414; Ritter et al., U.S. Pat. No. 6,128,174; and Blume et al., U.S. Pat. No. 6,157,853. In all of these approaches, as well as in any of the other known techniques for magnetic manipulation of a probe mass or implant located within the body (see Gillies et al., xe2x80x9cMagnetic manipulation instrumentation for medical physics research,xe2x80x9d Review of Scientific Instruments, pp. 533-562 (USA 1994)), incorporated herein by reference, the controlled movement of the probe mass or implant is actuated by a magnetic field created external to the body. In all such arrangements the magnetic component of the implant (typically located at the tip of a catheter) is a passive ferromagnetic or permanent magnetic element of a geometry consistent with that of the catheter""s form and function, and within which there either exists or can be made to exist, adequate magnetic moment to create the forces and torques needed to steer and/or guide the implant within the body part into which it has been inserted.
Magnetic stereotaxis is particularly useful for navigation of medical devices throughout body tissues, cavities, and vessels. Discussion of applications to catheter navigation within the chambers of the heart for electrophysiologic mapping and ablation can be found in Hall et al., U.S. patent application Ser. No. 09/405,314, incorporated herein by reference. Disclosure of navigation of catheters within the myocardial tissue of the heart can be found in Sell et al., U.S. patent application Ser. No. 09/398,686, incorporated herein by reference. Removal of tissues from body lumens and cavities via magnetic navigation of atherectomy tools is disclosed in Hall et al., U.S. patent application Ser. No. 09/352,161, incorporated herein by reference. Catheters for magnetic navigation within the blood vessels of the brain and other body parts are disclosed in Garibaldi, U.S. patent application Ser. No. 60/153,307, incorporated herein by reference.
Four inherent limitations to this general design of magnetic stereotaxis system are the following. First, it is generally unsafe to perform magnetic resonance (MR) imaging studies during or after a magnetic stereotaxis procedures in which the magnetic element of the implant is still resident within the patient, as might be contemplated in situations where updated MR data might be needed for ongoing magnetic stereotaxis navigation requirements. This is because the large fields intrinsic to all types of MR scanners (either standard bore-type systems or the lower-field interventional-style systems) are large enough to cause otherwise uncontrolled displacement of the implant within the patient. The nature of this particular problem is discussed in the broader context of MR-driven forces on implants, by Planert et al., xe2x80x9cMeasurements of magnetism-related forces and torque moments affecting medical instruments, implants, and foreign objects during magnetic resonance imaging at all degrees of freedom,xe2x80x9d Medical Physics, pp. 851-856 (USA 1996) and by Manner et al., xe2x80x9cMR Imaging in the presence of small circular metallic implants,xe2x80x9d Acta Radiological, pp. 551-554 (Denmark 1996), the disclosures of both of which are incorporated herein by reference.
A second limitation of the existing art is that relatively complex arrangements of magnetic field sources external to the patient must be assembled and controlled in order to carry out magnetic stereotactic movement of the implant. A single static background field is virtually always inappropriate for effecting controlled movement of the magnetic element in the implant used in existing magnetic stereotaxis procedures. A third limitation, related to the second, is that a magnetic element left in the brain or another body part can create a significant imaging artifact when that body part is imaged by an MR scanner, most typically rendering that imaging data set useless or of greatly reduced diagnostic and therapeutic value to the clinician and patient.
A fourth limitation is that appreciably and clinically precious time could be lost when carrying out a sequential and reciprocal process of conducting a magnetic stereotaxis procedure that must be interleaved with intra-operative MR imaging studies for diagnostic, therapeutic or navigational purposes. These limitations are not traversed by Kucharczyk et al. in their U.S. patent application Ser. No. 09/174,189 and in their International Application No. PCT/US99/24253, (the disclosure of both of which are incorporated herein by reference), which teach means for serial and reciprocal movement of the patient from a magnetic stereotaxis system to an MR scanner for purposes of updating the imaging information used for the reference portion of the magnetic stereotaxis procedure.
A more nearly ideal situation would arise if it were possible to integrate the form and function of a MR scanner and a magnetic stereotaxis system in such a way that magnetic stereotaxis procedures could be carried out within an MR scanner (or vice versa), and all done in such a way that the form and function of the MR scanning process would not interfere with those of the magnetic stereotaxis process, but that the respective forms and functions would instead complement and/or enhance each other. The subject of the present invention is a means and technique that accomplishes this goal and circumvents the existing limitations by incorporating a triaxial arrangement of miniature electromagnets as the magnetic element at the tip of the medical device or catheter. By externally regulating the electrical currents that pass through each of the independent coils, the torque and force on the tip of the medical device or catheter can be made to react to a static magnetic field of a MR scanner in such a way that the tip of the medical device or catheter can be guided along a preferred path to reach a target location within a brain or other body part. The resulting means and technique will thus exhibit all of the advantages of conventional magnetic stereotaxis (primarily the ability to navigate the medical device or catheter along complex curvilinear paths), while incorporating the further advantages of rapid sequential MR imaging of the patient, without introducing imaging artefacts on the MR images, since imaging is performed during periods when no currents flow through the triaxial coil components.
Medical devices with one or more miniaturized coils on them have been disclosed for a variety of other purposes, but none have been designed for use as the actuator in a combined magnetic stereotaxis and MR imaging process such as the type that is the subject of the present invention. Instead, such coil systems have been limited in function to identifying the location of the probe (in which they are housed) in relation to the body part into which the probe is inserted. Examples of such disclosures include Grayzel, U.S. Pat. No. 4,809,713; Dumoulin et al., U.S. Pat. No. 5,211,165; Twiss et al., U.S. Pat. No. 5,375,596; Acker et al., U.S. Pat. No. 5,558,091; Martinelli, U.S. Pat. No. 5,592,939; Calhoun et al., U.S. Pat. No. 5,606,980; Golden et al. U.S. Pat. No. 5,622,169; Shapiro et al., U.S. Pat. No. 5,645,065; Heruth et al., U.S. Pat. No. 5,713,858; Watkins et al., U.S. Pat. No. 5,715,822; Saad, U.S. Pat. No. 5,727,553; Weber et al., U.S. Pat. No. 5,728,079; Acker, U.S. Pat. No. 5,729,129; Darrow et al., U.S. Pat. No. 5,730,129; Young et al., U.S. Pat. No. 5,735,795; Glantz, U.S. Pat. No. 5,749,835; Acker et al., U.S. Pat. No. 5,752,513; Slettenmark, U.S. Pat. No. 5,758,6670; Polvani, U.S. Pat. No. 5,762,064; Kelly et al., U.S. Pat. No. 5,787,886; Vesely et al., U.S. Pat. No. 5,797,849; Ferre et al. U.S. Pat. No. 5,800,352; Kuhn, U.S. Pat. No. 5,810,728; Young et al., U.S. Pat. No. 5,817,017; Young et al., U.S. Pat. No. 5,819,737; Kovacs, U.S. Pat. No. 5,833,603; Crowley, U.S. Pat. No. 5,840,031; Webster, Jr. et al., U.S. Pat. No. 5,843,076; Johnston et al., U.S. Pat. No. 5,843,153; Lemelson, U.S. Pat. No. 5,845,646, Lemelson, U.S. Pat. No. 5,865,744, Glowinski et al., U.S. Pat. No. 5,868,674; Horzewski et al., U.S. Pat. No. 5,873,865; Haynor et al., U.S. Pat. No. 5,879,297; Daum et al., U.S. Pat. No. 5,895,401; Ponzi, U.S. Pat. No. 5,897,529; Golden et al., U.S. Pat. No. 5,902,238; Vander Salm et al., U.S. Pat. No. 5,906,579; Weber et al., U.S. Pat. No. 5,908,410; Lee et al., U.S. Pat. No. 5,911,737; Bladen et al., U.S. Pat. No. 5,913,820; Snelten et al., U.S. Pat. No. 5,916,162; Lemelson, U.S. Pat. No. 5,919,135; Chen et al., U.S. Pat. No. 5,921,244; Navab, U.S. Pat. No. 5,930,329; Rasche et al., U.S. Pat. No. 5,938,599; Lloyd, U.S. Pat. No. 5,938,602; Ponzi, U.S. Pat. No. 5,938,603; Johnson, U.S. Pat. No. 5,941,858; Cermak. U.S. Pat. No. 9,941,889; Johnson et al., U.S. Pat. No. 5,944,023; Derbyshire et al., U.S. Pat. No. 5,947,900; Beisel, U.S. Pat. No. 5,947,940; Van Vaals et al., U.S. Pat. No. 5,951,472; Lev, U.S. Pat. No. 5,951,566; Rogers et al., U.S. Pat. No. 5,951,881; Wan, U.S. Pat. No. 5,952,825; Rosenberg et al., U.S. Pat. No. 5,959,613; Ponzi, U.S. Pat. No. 5,964,757; Ferre et al., U.S. Pat. No. 5,967,980; Wittkampf, U.S. Pat. No. 5,983,126; Taniguchi et al., U.S. Pat. No. 5,997,473; Mouchawar et al., U.S. Pat. No. 6,002,963; Van Der Brug et al., U.S. Pat. No. 6,006,127; Pflueger, U.S. Pat. No. 6,013,038; Vesely et al., U.S. Pat. No. 6,019,725; Webb, U.S. Pat. No. 6,019,726; Murata, U.S. Pat. No. 6,019,737; Wendt et al., U.S. Pat. No. 6,023,636; and Holdaway et al., U.S. Pat. No. 6,083,166. The disclosures of all of the foregoing are incorporated herein by reference. Other uses for miniature coils or microcoils on catheters include the controlled introduction of local electromagnetic fields during the MR imaging process for the purpose of improving imaging contrast in the tissues adjacent to the catheter or probe, as taught for instance by Truwit et al., U.S. Pat. No. 5,964,705, incorporated herein by reference. Miniature triaxial arrangements for field sensing in medical probes have been disclosed by Acker, U.S. Pat. No. 5,833,608, incorporating herein by reference. Additional publications that document related uses for microcoils on catheters for either tracking or imaging purposes include the papers of Wildermuth et al., xe2x80x9cMR Imaging-guided intravascular procedures: initial demonstration in a pig model,xe2x80x9d Radiology, 578-583 (USA 1997), Bakker et al., xe2x80x9cMR-guided endovascular interventions: susceptibility-based catheter and near-real-time imaging technique,xe2x80x9d Radiology, pp. 273-276 (USA 1997), Rasche et al., xe2x80x9cCatheter tracking using continuous radial MRI,xe2x80x9d MRM, pp. 963-968 (USA 1997), Worley, xe2x80x9cUse of a real-time three-dimensional magnetic navigation system for radiofrequency ablation of accessory pathways,xe2x80x9d PACE, pp. 1636-1645 (USA 1998), Burl et al., xe2x80x9cTwisted-pair RF coil suitable for locating the track of a catheter,xe2x80x9d MRM, pp. 636-638 (USA 1999) and Coutts et al, xe2x80x9cIntegrated and interactive position tracking and imaging of interventional tools and internal devices using small fiducial receiver coils,xe2x80x9d MRM, pp. 908-913 (USA 1998). The disclosures of which are incorporated by reference. Coils in the catheter tip can be used to both locate the tip, and to measure the orientation of the tip in three dimensional space, as discussed by Shapiro et al, U.S. Pat. No. 5,645,065, and Haynor et al, U.S. Pat. No. 5,879,297, the disclosures of which are incorporated by reference.
The invention relates to the interaction between the static magnetic field of an MR scanner and one or more independent magnetic dipole moments created by a plurality of electromagnetic elements that are located within a medical device or catheter within a patient. The concept of utilizing a variable magnetic moment in the tip of a catheter for navigation in a static magnetic field was disclosed by Garibaldi et al., U.S. patent application Ser. No. 09/504,835, which is incorporated herein in its entirety by reference. Garibaldi et al. discusses a variety of permanent and electromagnetic means for generating a variable moment at the catheter tip for navigation in a static field, which may be energized for the purpose of navigation. The present invention employs the static field of an MRI imager, and the combined sequential processes of navigation and MRI imaging. Our discussion focuses on the static field of an MR imager which is always on, and for practical purposes cannot be turned off or otherwise changed or interrupted. For this reason, the present invention cannot employ permanent or inducible magnetic materials within the medical device. Consequently, the variable moment must be generated by coils, and preferably air-core coils.
If a static magnetic field H is acting along the z direction of the bore of a MR imaging, and a magnetic dipole moment m is present in the magnetic element of an implanted probe or catheter, then the vectors representing H and m in a three-dimensional space can be written H=Hk along the z-axis and m=mxi+myj+mzk and the torque experienced by the dipole moment in the field of the MR scanner is xcfx84=mxc3x97H. The x, y, and z components of the moment m are controlled independently, so that the vector m can point in any arbitrary direction in three dimensional space.
Evaluation of the vector cross product produces the components xcfx84x=myH, xcfx84y=xe2x88x92mxH, and xcfx84z=0. The torque acting on the dipole is perpendicular to m and H and in this case has no component about the z-axis along which the magnetic field lies. It is possible, however, to navigate a catheter to points lying in the plane perpendicular to H via successive small displacements of the moment out of this plane. This process can be referred to as compound rotation about the H axis. The first step in the process is to rotate the catheter tip upward out of the x-y plane at an angle which advances the catheter projection on the x-y plane, followed by a second rotation which rotates the catheter back down to the x-y plane, while once again advancing the catheter orientation angle. The net rotation of the catheter tip about the z-axis thus follows a sawtooth or triangular trajectory, each step in the advancement being made up of two allowed out-of-plane rotations.
One can make numerical estimates of the sizes of the torques that can act on the dipole in the presence of the MR scanner field by noting that the magnitude of the torque is given by expanding the cross product xcfx84=mxc3x97H to obtain xcfx84=mH cos xcex8 where xcex8 is the angle between m and H. xcfx84 is a maximum when xcex8=90xc2x0. If the dipole moment is produced by a coil that has N turns of wire windings carrying an electrical current I, and has a cross-sectional area A, then the expression for the torque acting on the coil can be written as xcfx84=NIAB where B=xcexcoH defines the relationship between the magnetic induction B and the magnetic field strength H, with xcexco being the permeability of free space. As a practical example of the application of these principles in a clinically realistic setting, the mechanical torque required to rotate a dipole moment produced by 350 turns of wire carrying 1.4 A of current and having a diameter of 2 mm with associated cross-sectional area of 3.14xc3x9710xe2x88x926 m2 would be 2.3xc3x9710xe2x88x923 N-m or 230 gram-mm in a MR scanner field of 1.5 T. If this coil is 5 mm long, the effective force couple producing the torque is 230/5=46 grams, which is adequately large for catheter navigation.
In the preferred embodiment of the present invention, three miniaturized coils of appropriate length, radius and current carrying capacity are assembled into a triaxial configuration in which the cross-sectional planes of each are orthogonal to those of the others. There are a number of different ways of doing this. In one preferred embodiment, the coils are wound on a common hollow coil form or mandrel in the shape of a rectangular parallelepiped that is made from non-conducting, non-susceptible materials which are MR compatible. In one embodiment, the coils are approximately 1 cm in length, have a diameter of 2 mm and a thickness of 0.25 mm. One transverse coil is wound around a long axis of the parallelepiped mandrel, a second transverse coil is wound along the other long axis perpendicular to the first, and the third (axial) coil is wound around the other two. The latter coil has a similar cross sectional area times number of turns as the transverse coils, so that all three coils have approximately equal dipole moment magnitude for equal energizing currents. This assembly is fixed inside the tip of a supple catheter with the leads from the coils brought down the internal length of the catheter tube to an exit point at which they are connected to three independent power supplies, one for each coil.
Cooling water or some other heat exchange medium can be made to flow through an internal jacket inside the catheter, thus bathing the triaxial coil assembly and carrying away a substantial amount of the heat generated during operation of the independent coils. The amount of cooling power available to the coils limits the level of current flow and ohmic heating that they can sustain; for example 16 W of cooling would establish a limit of 2.3 A maximum per coil assuming that the total resistance of a given coil is approximately 3xcexa9. The pressure driving the flow would ideally be 100 psi or less, with the flow entering the catheter at body temperature and leaving it at some higher temperature governed by considerations of patient safety and comfort.
With the coils being open circuit at the beginning of a procedure, the patient is imaged, and the location of the catheter noted. The coils themselves, rather than being passive open circuit coils, could actually serve as pick up coils for the MRI rf signal, providing an enhanced image at the site of the catheter, as discussed in the cited literature. Following this essentially real time imaging, the coils are energized, following the predictions of a coil-current vs. torque algorithm that would determine the catheter""s directional advancement within the MR scanner""s field, thus permitting the tip of the catheter to be steered along a desired direction. Subsequent imaging sequences are then carried out to verify the new location of the catheter""s tip, and the next movement sequence is then planned and executed.
In some modem MRI machines, the patient can actually be rotated during a procedure relative to a transverse MRI magnetic field residing in a gap between magnets. Such patient rotations may be employed to further enhance navigation. In particular, the patient may be rotated in these machines to ensure that maximum torque can always be applied about directions that would otherwise be parallel with the MRI field.
Using this means and technique, catheters can be manipulated through a body part, for example the brain, and positioned such that the lumen of the catheter is left along a curvilinear path that might be optimized for contoured drug delivery for the treatment of a neurodegenerative disorder intrinsic to the brain. Many other possible scenarios can also be achieved in the same way, for instance the nonlinear stereotactic guidance of an electrode for recording of potentials, ablation of a zone of tissue or deep brain stimulation for pain or tremor control. Likewise, electrophysiological mapping and ablation procedures can be carried out within the chambers of the heart. We note that the cooling required to adequately energize the coils can also cool the electrode tip of an ablation catheter. Such cooling results in larger ablative lesions, with fewer complications associated with clot formation on the electrode tip. Steering of catheters and devices can also be carried out within the endovascular system, for diagnostic and therapeutic purposes.
A host computer can coordinate and control the power supplies used to drive the individual coils, interpreting instruction from a clinician operating an intuitive interface such as a joy stick. The control algorithm requires as input the present orientation of the triaxial coil assembly within the patient, the direction and magnitude of the MR scanner field at the location of the triaxial coil assembly, the desired new angular orientation or curvilinear displacement that is to be taken in the next step in the movement sequence, and any related anatomical or physiological information about the patient as might be required to safely and efficaciously carry out the procedure.

Catheter navigation within an MR imaging device


A sport fishing outrigger assembly is disclosed that includes a boom attachment arm having a distal end portion and proximal end portion, a rotating arm having a distal head portion capable of releasable attachment to the proximal end portion and a handle engagement, an adjuster for adjusting the releasable attachment of the distal head portion to the proximal end portion, an indexing sleeve secured to the rotating arm, a rotator operatively engaged to the rotating arm, and a handle operatively engaged to the handle engagement and the rotator.

This invention relates to the field of sport fishing, and particularly to an outrigger mounting system having a vertically adjustable outrigger mounting arm assembly capable of rotational movement.
Saltwater sport fishing typically consists of anglers positioned on boats that are then dispatched to prolific offshore fishing areas. One useful method of catching gamefish involves a technique known as trolling. Trolling is the practice of baiting hooks that are subsequently lowered and dragged behind the stern of a slow moving vessel by the angler. In order to increase the chances of hooking a fish, it is beneficial to have as many lines in the water as possible. To a gamefish, the wake of a vessel generally creates the appearance of a large school of smaller fish to be preyed upon. The angler can strategically simulate bands of straggling or displaced fish from the school with numerous baited lines. These simulated straggling fish are misinterpreted to be the disadvantaged and weakened fish that gamefish frequently utilize as a food source.
As stated above, an angler will often drag as many baited lines from behind the boat as possible, thereby increasing the chances of hooking a fish. However, as more baited lines are used, the probability of the lines becoming entangled with one another increases. This is a problem that occurs in a variety of situations, such as with a narrow beam boat or any boat that is in the process of being turned. As a result, sport fishing outriggers have been developed to assist in keeping the various lines separated. However, the positioning and lowering of outrigger booms presents additional problems of rotational movement and preventing the booms from contacting the water. This problem has brought forth various attempts to create mechanisms to rotate the boom and that prevent the boom from contacting the water.
Outriggers consist of a long pole, or boom, having one end secured to the boat with deployment resulting from an outward lateral extension of the boom from a side of the boat. Baited fishing lines often have integrated release clips that are attached to the outriggers, thereby providing sufficient separation between the lines to prevent tangling. When a fish is hooked on the bait line, the line clip releases from the outrigger, thus allowing the angler to reel in the fish.
Outriggers are required to be freely stowable to a position beside the boat for close quarters operation and docking. For practicality, the outrigger should be swung laterally outward to its deployed position. The prior art includes various types of mounting schemes including outrigger units for horizontal and vertical mounting, on center consoles, flybridges, half towers, tuna towers, radar arches, and/or T-tops. Prior patents disclose a variety of methods for mounting, deploying, and locking such outriggers into place (see e.g. U.S. Pat. Nos. 5,445,102 and 3,724,791), with each having distinct drawbacks. Such drawbacks include overall mechanical complexity; powered operation; non-durable construction; and/or ineffective position adjustment and locking mechanisms that slip and/or wear out.
Although the prior art discloses a vast array of mechanisms and mounting locations for outrigger mounts, the prior art fails to disclose or otherwise teach a simple and durable outrigger system having an effective boom locking mechanism, a boom stop that prevents excessive lowering, and a positionable arm that allows for both vertical and rotational movement of the boom. This is of particular importance with respect to the excessive forces experienced by an outrigger mount during operation. Both wind and movement (of the boat) impart forces on to a boom, thereby increasing the stresses on the outrigger mount of the boom. Generally, the longer the boom, the greater the stresses at the outrigger mount. If the position adjustment and/or locking mechanism were to succumb to these increases in stress, the outrigger might swing in an unrestricted manner during a critical maneuver or operation, with potentially disastrous or life-threatening results to passengers of the outrigger equipped boat or other surrounding vessels. Accordingly, an outrigger assembly with a novel position adjustment and locking mechanism is disclosed that alleviates this and other shortcomings of the prior art.
As described in the aforementioned prior art, the mounting and operation of a conventional outrigger system can be complicated. Booms of considerable length must be stored in an upright position to allow the vessel to pass beneath low bridges, as well as for close quarters maneuvering. Similarly, should the boat pass under or through an object that limits clearance, the boom must be vertically lowered and/or rotated in from the extended position on a non-vertical plane. Preferably the outrigger mount not only rotates in the non-vertical plane in a 360xc2x0 arrangement from a position on the vessel, but also allows the boom attachment arm to be easily raised and lowered in a vertical plane. Thus, in the operation of a one way of several conventional outrigger booms, the boom is inserted into a vertically adjustable boom attachment arm, usually as part of an elbow, and locked into position with a locking pull pin. The outrigger boom is then rotated in a non-vertical plane to a point determined by the user. Additionally, either before or after the boom is rotated in the non-vertical plane, the user may raise or lower the boom within a vertical plane with respect to the outrigger mount.
Accordingly, what is lacking is an outrigger assembly having an effective boom locking mechanism, a boom stop that prevents excessive lowering, and a positionable arm that allows for both vertical and rotational movement of the boom to eliminate the complicated and problematic outrigger mounts commonly used to support outrigger booms.
The present invention eliminates the above-mentioned needs for an outrigger assembly by providing an outrigger assembly having a positionable arm that allows for both vertical and rotational movement of the boom and a boom stop that prevents excessive lowering.
In accordance with the present invention, there is provided an outrigger assembly. The outrigger assembly includes a boom attachment arm having a distal end portion and a proximal end portion, a rotating arm having a distal head portion capable of releasable attachment to the proximal end portion and a handle engagement, and adjustor for adjusting the releasable attachment of the distal head portion to the proximal end portion, an indexing sleeve secured to the rotating arm, a rotator operatively engaged to the rotating arm, and a handle operatively engaged to the handle engagement and the rotator.
The present invention is further directed to a method for adjusting a boom. The method includes the steps of inserting a boom into an outrigger assembly, securing the boom with a pin, rotationally positioning the boom within a first plane, rotationally positioning the boom within a second plane, and wherein the first plane and the second plane are perpendicular to one another.
Accordingly, it is an objective of the present invention to disclose a sport fishing outrigger assembly that is capable of rotation in a first plane and rotation in a second plane.
A related objective of this invention is to provide an outrigger mount employing a pull-pin to secure the outrigger boom.


A snowmobile having an accessory attachment system and a cargo rack storage compartment. The snowmobile includes a chassis having a front portion, a central portion, and a rear portion. The front chassis portion mounts a pair of steerable skis and includes an engine cradle for mounting an engine that powers a drive track. The central chassis portion includes a drive tunnel having the drive track disposed therein, an operator seat being mounted to the top portion of the drive tunnel, a top portion of the tunnel supporting an operator seat. The rear chassis portion includes a rear close-off that reinforces the drive tunnel and defines a cargo rack storage compartment co-extensive with a portion of the drive tunnel. An optional passenger seat may be removably mounted above a portion of the storage compartment. The rear close-off also includes plurality of mounting points, such as hooks or bracket holes.

The invention relates to a snowmobile, and, in particular, to a snowmobile having an accessory attachment system and an integrated cargo storage rack.
Snowmobiles are popular land vehicles for use in cold and snowy conditions. Snowmobiles may used as transportation vehicles or as recreational vehicles. Although primarily a recreational activity, snowmobiling also provides many useful functions. Snowmobiles may be relied upon by law enforcement units in snowy areas for search and rescue work and emergency missions. During such use, it is frequently necessary to transport a variety of cargo with the snowmobile. Snowmobiles are also used by surveyors, ranchers, public utility employees, environmental and wildlife scientists and others. Ski-touring centers across North America utilize snowmobiles for trail grooming and track setting. Snowmobiles are also widely used by cross country ski race officials, dog sled races, and by ski patrols for rescue purposes. In many uses, the desirability to stow cargo requires ample cargo or storage space in the snowmobile.
In general, a snowmobile has a central frame or chassis on or around which the various components of the snowmobile are assembled. Typically, a pair of skis are mounted at the front portion of the chassis. An engine cradle or bulkhead is defined by a plurality of front structural members of the chassis. The engine drives a ground-engaging endless track disposed in a longitudinally extending drive tunnel formed within the chassis. Generally horizontal footrests extend outwardly laterally from opposite sides of the chassis. The snowmobile suspension generally includes two systems, a front suspension system for the skis and a rear suspension system for the track.
Handling, cornering and ride quality are largely dependent upon the front suspension system of the snowmobile. The skis of a snowmobile may be independently suspended by means of respective suspensions. Some form of stabilizer or sway bar arrangement interconnecting the front skis may be provided to reduce the amount of leaning that occurs during cornering of the snowmobile.
The endless track is driven by an engine located in the bulkhead. In conventional snowmobiles, the track is provided under the chassis in such a manner that the entire length of the track is located beneath the drive tunnel formed by the chassis. A snow guard typically is provided at the rear of the chassis to prevent snow that the track engages from spraying excessively in an upward or rearward direction. The track is supported beneath the chassis by the rear suspension. The rear suspension is designed to provide a comfortable ride and to help absorb the shock of the snowmobile crossing uneven terrain.
The typical snowmobile tunnel is a unitary aluminum construction and is reinforced with braces inside the tunnel. Aluminum is generally used for tunnel construction because of its relatively light weight. Suspension pads are added to the tunnel (usually by riveting) where the suspension mounts to the chassis. The steel suspension pads reinforce the tunnel to prevent the suspension from tearing holes in the aluminum of the tunnel. A rack is separately mounted on the rear of the tunnel. Attaching the braces, pads, and rack is labor intensive, requiring extensive riveting, and can be expensive.
The vehicle body may comprise a seat with a storage compartment disposed generally rearward of the seat. A storage compartment may also be provided underneath the seat. Most snowmobiles require a cushioned seat for the rider to sit on for comfort, as well as safety. For many snowmobiles, weight is also an issue, and reduction in weight is desirable. For example, additional weight on a snowmobile contributes to the track sinking into the snow and stalling the snowmobile. The added weight also reduces fuel efficiency and speed.
Typically, a snowmobile seat comprises a rigid base and a cushion. The base may be formed of metal or plastic and is covered in a softer padding or cushion. The seat is typically formed as a unitary part that is bolted to the snowmobile chassis. Snowmobiles may be provided with a seat for supporting one person or with a seat for supporting two people Touring snowmobiles are often used to carry two individuals (xe2x80x9ctwo-up ridingxe2x80x9d). It may not be preferable to have two seats at all times due to the extra weight of the second seat, the undesirable appearance of the second, empty, seat, and the wasted excess space of the second seat. Therefore, a removable or optional second seat for a passenger may be desirable. Such a removable seat allows the snowmobile to be tailored to one or two-up riding.
A variety of storage components are used with snowmobiles, especially touring snowmobiles. Frequently, a storage compartment is mounted rearward of at least a portion of the seat. Items may be stored in a storage compartment, however, the storage compartment is typically relatively small. Although some oversized storage compartments are available, these are still often inadequate for stowing snowmobile accessories. Further, in many designs, the storage compartment is not available in conjunction with a passenger seat. Another snowmobile configuration incorporates underseat storage, also usually relatively small.
In the place of, or in addition to, such storage compartments, cargo racks are often provided for attachment to the rear of the snowmobile. The storage compartments and/or racks provide storage rooms for cargo and/or snowmobile accessories. An accessory luggage rack (or rear cargo rack) may be attached to the rear of the snowmobile to afford more storage capabilities. A typical rack is relatively large, heavy, and can be expensive. The rack is often sold as an accessory (not as part of the snowmobile) and the snowmobile user must bolt the rack to the machine (generally such that the rack fits onto the backrest assembly and hangs rearwardly off the machine). Traditionally the rear portion of a touring snowmobile has consisted of a tunnel with reinforcement bracing on the inside and an accessory luggage rack attached to the back. However, this can be costly to assemble and adds extra weight.
Further, items may be hooked or attached to the snowmobile. For example, snowmobile accessories, due to their size, may need to be hooked or attached to the snowmobile. In some cases, bungee cords or tie straps are used to attach an accessory or carry-on to the snowmobile. Many accessory racks have places on which to hook a bungee. However, if an accessory rack is not purchased and installed, there is not generally a place on which to hook a bungee. A snowmobile user may then become creative and attempt to hook a bungee to a portion of the snowmobile not intended for such use. This may lead to snowmobile damage such as a portion of the body snapping off under the force of the hook or the hook sliding off because the body is not formed for receiving a hook.
One feature of the invention provides an integrated snowmobile cargo rack/storage compartment and drive tunnel. The drive tunnel, supporting and containing the endless track, is preferably aluminum to provide a lightweight structure. A cargo rack/storage compartment, preferably formed of steel, is preferably mounted to the tunnel, and provides bracing and support for the aluminum tunnel. The cargo rack/storage compartment acts not only as a storage rack but also as tunnel bracing and rear suspension pads, thereby alleviating the need for extra tunnel bracing, suspension pads, etc. normally found with an aluminum drive tunnel. The storage compartment reduces the weight associated with separate braces, suspension pads, and rack attached to a tunnel. The storage compartment is positioned under an optional removable passenger seat.
The invention also provides a passenger seat that may be removable. An abbreviated trunk cover or storage lid may be provided for the covering the rear storage compartment when the passenger seat is attached. Removing the passenger seat expands the accessible area of the covered storage compartment. The snowmobile may be converted into a one-up sled by removing the abbreviated trunk cover or storage lid and passenger seat, and affixing a full-length trunk cover or storage lid. The full-length trunk cover or storage lid creates a sleek one-up look while providing rider comfort and increased accessible storage capacity. Additionally, by removing the second seat completely when the snowmobile is in its one-up configuration, the overall weight of the sled is decreased.
The invention also provides an accessory attachment system. In an embodiment of the snowmobile of the present invention, the storage compartment has several mounting points for mounting cargo to the sled. The mounting points may be mounting locations such as hooks or brackets. The bracket is mounted to the side of a rear side panel of the storage compartment. The bracket has two holes that are designed to accept mounting pins from an accessory to be mounted to the snowmobile. Three hooks are provided on the side panel of the storage compartment and each may be used to mount accessories or tie straps or bungee cords. All of these components may be hidden underneath a plastic cover. The plastic side covers include holes to receive, for example, bungee cords. Bungee cords go through the holes and are attached to cargo hooks hidden under the cover. Thus, accessory attachments may be quickly removed without requiring tools. Optionally, saddlebags may be provided with pins corresponding to the holes on the plastic cover. The pins are designed to go through holes provided on the plastic cover and attach to holes on the bracket on the tunnel.

Snowmobile accessory attachment system and integrated snowmobile cargo rack


A method and apparatus for preventing unauthorized access to information temporarily stored in memory, such as a hard disk drive, associated with a digital document processor, such as a digital copier, printer, or facsimile machine. This invention includes storing information to memory, conducting an operation on the information, and automatically overwriting the information one or more times with a bit mask. Bit masks may be non-random or random sequences of binary values.

The present invention relates generally to a method and apparatus for safeguarding data stored in memory and specifically to a method to prevent unauthorized access to data stored temporarily in a nonvolatile memory, such as a hard disk drive.
Digital copiers, laser printers, facsimile machines, document scanners, computers, cellular telephones, digital cameras, and multifunction devices possess several properties in common. All these devices are capable of processing a digital image of a document ("image," "data," "image data," or "image data file"). If the device is able to "read" a document, it typically includes a scanner component, and if the device is able to print a document, it typically includes a printer component. Additionally, these devices typically incorporate a memory. These devices may be collectively referred to as "digital document processors."
Digital document processors may perform one or more of the following operations: scanning, storing, transmitting, reading, viewing, printing, and deleting. Depending on the particular digital document processor, additional operations may also be performed.
A digital document processor may be able to perform the operation of scanning an original document. The document is illuminated and a charge coupled device or a contact image sensor converts the reflected image into a plurality of electrical signals that together create a digital image of the original document. All or part of the scanned image data is typically stored in a memory.
A digital document processor may be able to perform the operation of printing image data stored in a memory. One type of printing, laser printing, may be accomplished by reading image data from memory in another digital document processor (such as a computer) and using the data to turn a laser beam on and off as the beam scans a charged drum. Where the laser beam strikes the drum, charges are neutralized. Areas not exposed to the beam attract toner powder which is transferred to paper passing over the drum. Pressure applied to the paper as it passes over the drum fuses the toner powder to the paper. The image data stored in memory is thus converted to a physical representation on paper. The image data may also be read from the digital document processor's memory. For example, to accommodate the slower speed of a printer without idling a computer's faster input/output bus, image data in computer memory may be buffered in a printer memory. In addition, confidential or secure image data may be stored in a digital document processor's memory and not printed until an authorized user enters a personal identification number. In this way, a user may send a confidential document to a printer and the document will not print until the user is present.
A digital document processor may be able to perform the operation of copying an original document. By storing image data to memory, multiple copies can be made without repeatedly inputting an original document. In addition, storing image data to memory permits image size, orientation, and page sequence to be modified prior to printing. For example, two original 8½″ by 11″ images stored in memory may be rotated 90 degrees, reduced in size, and printed side-by-side on one side of a single 8½″ by 11″ sheet of paper. As a further example, a large number of original images may be reduced, reoriented, and printed side-by-side on the front and back sides of sheets of paper in a sequence different from the copy sequence in book format.
As exemplified by the scanning, printing, and copying operations, most operations use memory at one or more steps. A transmitting operation, for example, stores image data in a facsimile memory so that an image can be transmitted later or so that images can be simultaneously transmitted and received. In addition, memory is used in digital document processors for other purposes readily apparent to one skilled in the art.
A document may be represented in memory as a bit-mapped image. A bit map is a representation of an original document that consists of rows and columns of dots. The value of each dot may be stored in memory as a single bit to represent a black or white value, or as a byte or several bytes for shades of gray or for colors. Documents may be stored using other storage schemes, but they are all based on a binary code that uses ones ("positives") or zeros ("negatives"). Throughout this document, storage schemes may be discussed in terms of bit mapping, but one skilled in the art could apply the same principles to other storage schemes.
Memory may include both volatile memory and nonvolatile memory. "Nonvolatile memory" means any memory having the property of retaining stored data when electrical power fails or is turned off. Examples of nonvolatile memory include hard disks, floppy disks, optical disks, compact disks ("CDs"), digital versatile disks ("DVDs"), tape drives, and various integrated circuit ("IC") memories, as further defined below.
Nonvolatile memory devices, such as floppy disks, hard disks, magnetic tape, optical disks, CDs, and DVDs, are made from media that can be permanently altered to store a bit of information. In the case of floppy disks, hard disks, and magnetic tape, data is stored by writing a pattern of magnetic fields on a magnetic material. Data is read by sensing the presence of a magnetic field and its direction. In the case of optical disks, CDs, and DVDs, a laser is used to form and read bumps on a plastic media.
IC devices such as erasable programmable read-only memory ("EPROM"), electrically erasable programmable read-only memory ("EEPROM"), flash erasable programmable read-only memory, nonvolatile random access memory ("NVRAM"), and flash memory chips represent another type of nonvolatile memory. In these devices, data is represented by electric charges stored on insulated gates. Another type of IC nonvolatile memory is a static random access memory with a battery backup.
With disk type nonvolatile memory, a portion of each disk may store a directory for the disk. To locate a particular data file, the directory is used to identify the location where the data is stored. The directory is also used to identify "free" locations where new data may be stored. In addition, before a disk can be used it may require formatting to define locations where data may be stored. When a user issues a command to format a disk containing previously stored data, only the directory is updated to indicate locations where data may be stored. Similarly, when a user issues a command to delete a file stored on a disk, only the directory is updated. Alternatively, data on a disk may be stored and retrieved using a linked list data structure instead of a table. When a user issues a delete command, only a pointer to the data is updated. In all three situations, however, data remains on the disk until it is later overwritten.
Even when image data is overwritten with new information, a substantial portion or residual elements of the overwritten information may remain on the disk. First, modern disks commonly use data compression and multibit coding techniques. With these techniques, overwriting all zeros, for example, results in writing a single zero and a follow-on code indicating the length of the run. These techniques may result in substantial portions of the original information remaining on the disk. Second, the pattern of magnetization on a disk is modified when image data is stored. Traces of the modified pattern of magnetization remain even after it is overwritten. Sophisticated techniques have been developed that sense subtle changes in magnetization and enable the overwritten information to be recovered from residual elements.
A disadvantage of nonvolatile memory or storage devices is that the stored data may be viewed by unauthorized persons. Because nonvolatile memory retains stored data when electrical power fails or is turned off, it is possible to remove a nonvolatile memory device from a digital document processor, install the memory in a computing system, and use the computing system to read data stored in the nonvolatile memory. A further disadvantage of nonvolatile storage devices is that even when data has been "erased," it may still be possible to recover and read the information. Data may be recovered and read because only a directory entry or a pointer to the data was erased, because data compression or multibit coding techniques do not overwrite a substantial portion of the data, or because sophisticated techniques may be used to detect residual elements of a magnetic pattern remain on the disk even after an overwrite.
The security risk associated with memory being readable after it is removed from a digital document processor has been recognized, and security solutions for protecting the confidentiality of data stored in memory have been attempted.
Some types of security solutions erase the entire memory. For example, degaussing may be used to neutralize or demagnetize an entire magnetic memory. Physical destruction may be used to prevent access to an entire optical memory. The entire memory of an IC device, such as an EPROM, may be erased by shining an ultraviolet light through a quartz window in the top of the package. In other ICs, such as an EEPROM, the entire memory may be electrically erased by downloading a bit sequence to the device.
Because data is generally recoverable if it is merely "deleted" or "erased" by a software program, the overwriting security solution was developed to obscure or conceal the data. When information is identified as sensitive or a security risk, a specific overwriting instruction is made. Alternatively, data may kept for a predefined period until the memory is needed again and then overwritten.
Overwriting refers to storing new useful data or a meaningless bit pattern at the memory location of the data to be erased. When overwriting is used to conceal information, the overwritten bit pattern may be all ones, all zeros, or any predetermined sequence of binary values. Alternately, the bit pattern may be a random or pseudo-random pattern of binary values ("random bit mask"). A pseudo-random number sequence is so named because an identical sequence of numbers is created each time the generator is invoked, and the sequence eventually repeats. An advantage of overwriting with a random bit mask is that the ability of sophisticated techniques to reconstruct the original data from residual elements is significantly diminished.
Several government agencies have established standards for overwriting data stored on a hard disk drive. Typically, these standards require two or more overwrite operations. The Department of Defense, for example, requires three overwrites: (1) a binary value is written, (2) a complementary binary value is written, and (3) a random value is written.
PowerQuest's DATAGONE™ is a commercially available software program that erases data from a hard disk using overwriting operations. DATAGONE™ erases an entire partition of a hard drive. White Canyon Software's SECURECLEAN™ is another software program that erases data from a hard disk by performing overwrite operations at the file level.
Windmill Software Ltd.'s Windmill Logger is a data acquisition software program that exemplifies the use of an overwriting operation to conserve space on a hard disk drive. To prevent a user's hard disk drive from being filled with data, the user may specify a set of data files that may be reused. For example, seven data files, one for each day of the week, may be specified. When all seven specified files are full, data in the first file is automatically overwritten with new data. On the next day, the second data file is over-written, etc.
U.S. Pat. No. 6,012,145 to Mathers, et al. ("the Mathers reference") discloses another means for securing nonvolatile memory. Specifically, the Mathers reference discloses a password security system for protecting information recorded on the portable hard disk drives that are typically used in laptop portable computers. The Mathers reference requires an additional microprocessor, a keyboard, a display, and an operating system. While the Mathers reference provides a security means for portable hard disk drives, the additional hardware and software required make it expensive and impractical for use with hard disk drives incorporated into digital document processors other than portable laptop computers.
Ukai, et al., U.S. Pat. No. 5,642,199, ("the Ukai reference") discloses a digital copier or a complex copier having a facsimile function with a security function for keeping a record of persons who copied or transmitted images and the dates of copying or transmission. In addition, the type of image may be recorded, or a "thinned" version of the document image may be saved. While the Ukai reference discloses a means for identifying the person who may have had unauthorized access to a document, it does not prevent unauthorized access to a document.

Random bit mask generation for obscuring data on nonvolatile memory device


The present invention relates to a foam, a process for preparing the foam and an article containing the foam. The foam contains a coupled propylene polymer and has a density in of from 9.6 to 801 kg/m3 and has either a foamability factor of more than 1.8 to less than 2.8 and an open cell content less than 20 percent, or a foamability factor of at least 2.8 and less than 15 and an open cell content of less than 50 percent. The process includes heating a coupled propylene polymer having a melt flow rate from 0.2 to 20 g/10 min and a melt strength of at least 39 cN to a molten state to produce a molten polymer material and mixing said molten polymer material with a blowing agent under conditions to produce a foamed material having a density in the range of from 9.6 to 801 kg/m3.

This invention relates to propylene polymer foams, methods for preparing the same, expandable compositions, and foamed articles.
Polypropylene can offer better impact properties than polystyrene, because polypropylene is a semi-crystalline polymer which has a glass transition temperature substantially below room temperature. In addition, polypropylene can offer good temperature stability and high chemical resistance. However, until now, the production of polypropylene foams has been limited because of its low melt strength and melt elasticity and this makes it difficult to be foamed in comparison to the other plastics. If the melt strength and the melt elasticity are too weak, as in the case of polypropylene, the cell walls separating the bubbles will be too weak to bear the extensional force that is generated during the foaming process and the bubbles will rupture very easily. As a result, foamed polypropylene products are generally characterized by high open cell content, which makes them unsatisfactory in many applications.
Extruded closed cell foams of polypropylene having a foamability factor of less than about 1.8 are disclosed in U.S. Pat. No. 5,527,573. Branched or lightly crosslinked polymers, such as may be obtained by chemical or irradiation branching or lightly crosslinking, including high melt strength polypropylene are used therein for making foams. In co-pending U.S. patent application Ser. No. 09/133,576 filed Aug. 13, 1998 and WO-99/10424 in-situ rheology modification of polyolefins is disclosed as applied to, among others, polypropylenes resulting in polypropylenes having advantageous melt processing properties. Foams are mentioned among the possible end uses or applications of such rheology-modified propylene polymers.
There is a continuous demand for propylene polymer foams of a relatively high closed cell content, which do not suffer from the bubble stability problem generally experienced with polypropylene foams. The foams desirably are capable of being manufactured at high foam production rates on conventional foaming equipment while using a relatively low amount of blowing agent.
The present invention is directed in one aspect to a foam comprising a coupled propylene polymer and having a density in the range of from 9.6 to 801 kilograms per cubic meter (kg/m3) (0.6 to 50 pounds per cubic foot (lbs/ft3)) and having either a foamability factor of more than 1.8 to less than 2.8 and an open cell content less than 20 percent (%), or a foamability factor of equal to or more than 2.8 and less than 15 and an open cell content of less than 50%. The invention includes in a further aspect a process for preparing a foam comprising heating a propylene polymer having a melt flow rate from 0.2 to 20 grams per 10 minutes (g/10 min) and a melt strength of at least 39 centiNewtons (cN), optionally mixed with a nucleating agent, to a molten state to produce a molten polymer material, and mixing said molten polymer material with a blowing agent under conditions to produce a foamed material having a density in the range of from 9.6 to 801 kg/m3 (0.6 to 50 lbs/ft3), wherein the propylene polymer is obtained by a coupling treatment carried out before, during or after admixture with the blowing agent. According to yet a further aspect the invention relates to an expandable composition comprising a coupled propylene polymer having a melt strength of xe2x89xa739 cN at a drawability from 15 to 60 millimeters per second (mm/sec), and a melt flow rate from 0.2 to 20 g/10 min, and a blowing agent.
Finally, the present invention relates to articles comprising the foams according to the present invention. It has been found that excellent foams can be obtained from certain propylene polymers which due to their melt strength and melt drawability characteristics provide higher thermal collapse resistance, and therefore less open cell content and lower density than prior art polypropylenes.
As used herein the xe2x80x9cfoam densityxe2x80x9d is determined by weighing a small representative piece of foam and dividing this by the volumetric displacement of the foam.
As used herein the terms xe2x80x9cmelt strengthxe2x80x9d and xe2x80x9cdrawabilityxe2x80x9d refer to polymer melt properties and are measured at 190xc2x0 C. according to the following procedure. Measure melt strength by using a capillary rheometer fitted with a 2.1 millimeter (mm) diameter, 20:1 die with an entrance angle of approximately 45 degrees. After equilibrating the samples at 190xc2x0 C. for 10 minutes, run the piston at a speed of 25.4 millimeters per minute (mm/minute). The standard test temperature is 190xc2x0 C. The sample is drawn uniaxially to a set of accelerating nips located 100 mm below the die with an acceleration of 2.4 millimeters per second per second (mm/sec2). The required tensile force is recorded as a function of the take-up speed of the nip rolls. The maximum tensile force attained during the test (at break) is defined as the melt strength and is expressed in cN. The limiting wheel velocity at break is the melt drawability and reported in units of mm/s. In the case of polymer melt exhibiting draw resonance, the tensile force and wheel velocity before the onset of draw resonance was taken as the melt strength and drawability, respectively.
As used herein the xe2x80x9caverage cell sizexe2x80x9d in millimeters is determined according to American Society for Testing and Materials (ASTM) D3576 Standard Test Method for Cell Size of Rigid Cellular Plastics.
As used herein the term xe2x80x9cmelt flow ratexe2x80x9d refers to the melt flow rate of the polymer measured according to method ASTM D 1238L, at a temperature of 230xc2x0 C. under a weight of 2.16 kg and is expressed in g/10 min.
As used herein the term xe2x80x9cisotacticxe2x80x9d refers to a degree of isotacticity as measured by C13 NMR of at least about 50%.
As used herein, xe2x80x9cpropylene polymerxe2x80x9d means propylene polymer selected from the group consisting of (a) homopolymers of propylene, (b) random and block copolymers of propylene and an olefin selected from the group consisting of ethylene, C4-C10 1-olefins, and C4-C10 dienes, provided that, when said olefin is ethylene, the maximum polymerized ethylene content is less than about 20% by weight, when said olefin is a C4-C10 1-olefin, the maximum polymerized content thereof is less than about 20% by weight and when said olefin is a C4-C10 diene, the maximum polymerized content thereof is less than about 20% by weight, (c) random terpolymers of propylene and 1-olefins selected from the group consisting of ethylene and C4-C8 1-olefins, provided that the maximum polymerized C4-C8 1-olefin content is less than about 20% by weight, and when ethylene is one of said 1-olefins, the maximum polymerized ethylene content is less than about 20% by weight, and d) impact propylene copolymers also referred to as heterophasic propylene copolymers where polypropylene is the continuous phase and an elastomeric phase is uniformly dispersed therein. Advantageously, the impact copolymers have at least about 5 weight percent, preferably at least about 10, preferably up to about 40, more preferably up to about 25 weight percent, and most preferably up to about 20 weight percent ethylene. The C4-C10 1-olefins include the linear and branched C4-C10 1-olefins such as, for examples 1-butene, isobutylene, 1-pentene, 3-methyl-1-buterie, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, and the like. Examples of C4-C10 dienes include 1,3-butadiene, 1,4-pentadiene, isoprene, 1,5-hexadiene, 2,3-dimethyl-1,3-hexadiene, and the like.
The term xe2x80x9cisotactic propylene polymerxe2x80x9d refers to a propylene polymer having preferably no or only a very minor percentage of comonomers polymerized in its structure and has in general an isotacticity of at least 50% as determined by 13C NMR, more preferably an isotacticity of at least 52%, and most preferably of at least 54%. It preferably is a propylene homopolymer.
Surprisingly it has been found that a certain novel combinations of propylene polymer resin properties and final propylene polymer foam product properties produce the increased closed cell foams of the present invention.
The foamability factor is the combination of these properties. This factor is expressed by the following equation:
F=Dn*D*(tan xcex4)0.75
where
F is the foamability factor
Dn is the density of the foam in lbs/ft3 or Dn=Dn*/16.02 wherein Dn* is the density of the foam in kg/m3;
D is the average cell size diameter in millimeters;
tan xcex4 is Gxe2x80x3/Gxe2x80x2; where Gxe2x80x3 is the loss modulus; and Gxe2x80x2 is the storage modulus of the polymer melt using 2.5 mm thick and 25 mm diameter specimens at 190xc2x0 C. (centigrade) at one Radian per second oscillating frequency.
According to the present invention the foams have a foamability factor of more than 1.8 to less than 2.8, preferably from 1.9 to 2.8, more preferably from 2.0 to 2.5 and simultaneously an open cell content of less than 20%. Alternatively, the foams have a foamability factor of equal to or more than 2.8 and less than 15, preferably less than 10, more preferably less than 6, still more preferably less than 5, even more preferably less than 4 and simultaneously an open cell content of less than 50%, preferably of less than 45%.
The parameter tan xcex4 may be determined by using a mechanical spectrometer, such as model RMS-800, available from Rheometrics, Inc. in Piscataway, N.J., USA. In the evaluation of rheological characteristics, such as tan xcex4, Gxe2x80x2 and Gxe2x80x3, of viscoelastic materials, such as polymer melts, a disk-like specimen, measuring 2.5 mm in thickness and 25 mm in diameter is placed between opposed, axially spaced apart, radially-extending surfaces and is coupled to each surface, filling the axial spacing between the surfaces. One of the surfaces then is rotated about the axial direction relative to the other to place the test specimen in shear and the torque resulting from the shear is measured. The shear may be steady shear, in which case the measured torque is constant, or the shear may be dynamic shear, in which case the measured torque changes continuously with time. The measured torque is proportional to the viscous, or loss component of the modulus (Gxe2x80x3) of the material. For the purpose of this invention the shear is steady shear, meaning the measured torque, and thus Gxe2x80x3, is constant at the given temperature. As a result of the nature of the forces applied to the test specimen in this procedure, the test specimen has a tendency to expand axially, thereby placing axially directed forces upon the relatively rotating surfaces to which the specimen is coupled. This axial force exerted upon the surfaces by the test specimen under shear conditions is proportional to the elastic, or storage component of the modulus (Gxe2x80x2) of the material. The parameter tan xcex4 for the present invention is then calculated as Gxe2x80x3 divided by Gxe2x80x2 at the stated temperature and oscillating frequency.
In addition to meeting the foamability factor requirement, the mixture of the blowing agent and propylene polymer material (foaming gel) is cooled down to the optimum foaming temperature, which is easily determined experimentally.
The melt flow rate of the propylene polymer used for preparing the foams according to the present invention is generally from 0.2 to 20 g/10 min, preferably from 0.3 to 10 g/10 min and most preferably from 0.4 to 5 g/10 min as measured by ASTM D1238L at 230xc2x0 C./2.16 kilograms (kg). At melt flow rates below these ranges the polymer will be more difficult to extrude, while above these ranges it will be difficult to make foam having large cross-sections. The propylene polymer in general has a melt strength of at least about 39 cN, preferably at least about 40 cN, most preferably at least about 50 cN, and in some instances at least about 60 cN. The propylene polymer exhibits these melt strength values preferably at a melt drawability of from 15 to 60 mm/sec. The drawability property allows the drawing of the cells to small diameters, whereas the melt strength provides sufficient strength to form closed cells. Propylene polymers having such suitable melt strength and melt drawability properties allow the production of foams of a broad density range and of good mechanical properties with the possibility of controlling cell size and open cell content.
The propylene polymer is obtained from conventional propylene polymers that have been treated to provide the desirable properties melt properties by chemical treatment with coupling or branching agents. Preferred coupling treatments are disclosed in U.S. patent application Ser. No. 09/133,576 filed Aug. 13, 1998 and WO 99/10424 published Mar. 4, 1999 (which are both incorporated by reference herein in their entirety).
The propylene polymers used in the current invention are thermoplastic polymers and not crosslinked polymers. Crosslinking (otherwise known as xe2x80x9cvulcanizationxe2x80x9d) results in a thermoset polymer characterized by high gel levels. Crosslinking is typically evidenced by gel formation which is measured in the case of polypropylene by xylene insolubility, or in the case of films by optically evident gels in a film, for instance as analyzed by a laser gel counter commercially available from Optical Control System, Inc. under the trade designation FS-3.
The polymer materials that are subjected to such a treatment are suitably of any molecular weight distribution (MWD). MWD is calculated as the ratio Mw/Mn where Mw is the weight average molecular weight and Mn is the number average molecular weight. Those skilled in the art are aware that polymers having a MWD less than about 3 are conveniently made using a metallocene or constrained geometry catalyst or using electron donor compounds with Ziegler Natta catalysts. In the practice of the invention, the MWD is preferably at least from about 3.5 to about 15 and more preferably from about 6 to about 9.
The most preferred way of preparing the propylene polymers used for making the foams of the current invention is by a coupling treatment such as disclosed in U.S. patent application Ser. No. 09/133,576 filed Aug. 13, 1998 and WO 99/10424 published Mar. 4, 1999. As used herein, xe2x80x9ccouplingxe2x80x9d refers to modifying the rheology of a polymer by reacting the polymer with a suitable coupling agent. A xe2x80x9ccoupled polymerxe2x80x9d is a rheology modified polymer resulting from a coupling reaction. Coupled polymers are also referred to herein as xe2x80x9cmodified polymersxe2x80x9d or xe2x80x9crheology modified polymers.xe2x80x9d A coupled polymer differs from a crosslinked polymer in that the coupled polymer is thermoplastic and has a low gel level.
According to this preferred treatment, the propylene polymer resin is reacted with a polyfunctional compound capable of insertion reactions into Cxe2x80x94H bonds. Such polyfunctional compounds have at least two, preferably 2, functional groups capable of forming reactive groups that are capable of Cxe2x80x94H insertion reactions. Those skilled in the art are familiar with Cxe2x80x94H insertion reactions and reactive groups capable of such reactions. For instance, carbenes as generated from diazo compounds, as cited in Mathur, N. C.; Snow, M. S.; Young, K. M., and Pincock, J. A.; Tetrahedron, (1985), 41(8), pages 1509-1516, and nitrenes as generated from azides, as cited in Abramovitch, R. A.; Chellathurai, T.; Holcomb, W. D; McMaster, I. T.; and Vanderpool, D. P.; J. Org. Chem., (1977), 42(17), 2920-6, and Abramovitch, R. A., Knaus, G. N., J. Org. Chem., (1975), 40(7) 883-9.
Compounds having at least two functional groups capable of forming reactive groups that are capable of Cxe2x80x94H insertion under reaction conditions are referred to herein as coupling agents. Such coupling agents include alkyl and aryl azides (Rxe2x80x94N3), acyl azides (Rxe2x80x94C(O)N3), azidoformates (Rxe2x80x94Oxe2x80x94C(O)xe2x80x94N3), phosphoryl azides ((RO)2xe2x80x94(PO)xe2x80x94N3), phosphinic azides (R2xe2x80x94P(O)xe2x80x94N3)and silyl azides (R3xe2x80x94Sixe2x80x94N3). Preferably, the coupling agent is a poly(sulfonyl azide). U.S. patent application Ser. No. 09/133,576 filed Aug. 13, 1998 and WO 99/10424 published Mar. 4, 1999 contain additional teaching regarding azides and their use for modifying polymers.
When the poly(sulfonyl azide) reacts with the propylene polymer resin, at least two separate propylene polymer chains are advantageously joined and the molecular weight of the polymer chain is increased. In the preferred case when the poly(sulfonyl azide) is a bis(sulfonyl azide) (hereinafter xe2x80x9cBSAxe2x80x9d), two propylene polymer chains are advantageously joined.
The poly(sulfonyl azide) is any compound having at least two sulfonyl azide groups (xe2x80x94SO2N3) reactive with the propylene polymer. Preferably the poly(sulfonyl azide)s have a structure Xxe2x80x94Rxe2x80x94X wherein each X is SO2N3 and R represents an unsubstituted or inertly substituted hydrocarbyl, hydrocarbyl ether or silicon-containing group, preferably having sufficient carbon, oxygen or silicon, preferably carbon, atoms to separate the sulfonyl azide groups sufficiently to permit a facile reaction between the propylene polymer and the sulfonyl azide, more preferably at least 1, more preferably at least 2, most preferably at least 3 carbon, oxygen or silicon, preferably carbon, atoms between functional groups. While there is no critical limit to the length of R, each R advantageously has at least one carbon or silicon atom between X""s and preferably has less than about 50, more preferably less than about 20, most preferably less than about 15 carbon, oxygen or silicon atoms. Silicon containing groups include silanes and siloxanes, preferably siloxanes. The term inertly substituted refers to substitution with atoms or groups that do not undesirably interfere, at the coupling reaction conditions, with the desired reaction(s) or desired properties of the resulting coupled polymers. Such groups include fluorine, aliphatic or aromatic ether, siloxane as well as sulfonyl azide groups when more than two propylene polymer chains are to be joined. R is suitably aryl, alkyl, aryl alkaryl, arylalkyl silane, siloxane or heterocyclic, groups and other groups that are inert and separate the sulfonyl azide groups as described. More preferably R includes at least one aryl group between the sulfonyl groups, most preferably at least two aryl groups (such as when R is 4,4xe2x80x2diphenylether or 4,4xe2x80x2-biphenyl). When R is one aryl group, it is preferred that the group have more than one ring, as in the case of naphthylene bis(sulfonyl azides). Poly(sulfonyl)azides include such compounds as 1,5-pentane bis(sulfonylazide), 1,8-octane bis(sulfonyl azide), 1,10-decane bis(sulfonyl azide), 1,10-octadecane bis(sulfonyl azide), 1-octyl-2,4,6-benzene tris(sulfonyl azide), 4,4xe2x80x2-diphenyl ether bis(sulfonyl azide), 1,6-bis(4xe2x80x2-sulfonazidophenyl)hexane, 2,7-naphthalene bis(sulfonyl azide), and mixed sulfonyl azides of chlorinated aliphatic hydrocarbons containing an average of from 1 to 8 chlorine atoms and from about 2 to 5 sulfonyl azide groups per molecule, and mixtures thereof. Preferred poly(sulfonyl azide)s include oxy-bis(4-sulfonylazidobenzene), 2,7-naphthalene bis(sulfonyl azido), 4,4xe2x80x2-bis(sulfonyl azido)biphenyl, 4,4xe2x80x2-diphenyl ether bis(sulfonyl azide) and bis(4-sulfonyl azidophenyl)methane, and mixtures thereof.
Sulfonyl azides are commercially available or are conveniently prepared by the reaction of sodium azide with the corresponding sulfonyl chloride, although oxidation of sulfonyl hydazines with various reagents (nitrous acid, dinitrogen tetroxide, nitrosonium tetrafluoroborate) has been used.
The following discussion regarding the coupling reaction mechanism provides the inventors current theories but is not intended to limit the scope of this invention. Sulfonyl azides decompose in several ways, but for the practice of the invention, the reactive species, believed to be the singlet nitrene, as evidenced by insertion into Cxe2x80x94H bonds is desired. Thermal decomposition is reported to give an intermediate singlet sulfonyl nitrene, which will react readily by insertion into carbon-hydrogen bonds. The high temperatures necessary for efficient formation of the sulfonyl nitrene is usually greater than about 150xc2x0 C. When BSA such as, 4,4xe2x80x2-Oxydibenzenesulfonyl azide (DPO-BSA) is used for the coupling agent, polymer stream temperatures of greater than 250xc2x0 C. are preferably avoided while there is significant unreacted azide in the reaction mixture.
The poly(sulfonyl azide) is preferably mixed with the propylene polymer before the resulting mixture is heated to the decomposition temperature of the poly(sulfonyl azide). By decomposition temperature of the poly(sulfonyl azide) is meant that temperature at which a substantial percentage of the azide is converted to the sulfonyl nitrene, eliminating nitrogen and more heat in the process. The decomposition temperature may be determined by differential scanning calorimetry (DSC). For instance, a differential scanning calorimeter (DSC) thermogram of the DPO-BSA shows no change in the heat flow until a sharp endothermic melting peak is observed at 100xc2x0 C. The baseline is flat again (no heat flow) until a broad exothermic peak is observed that begins about 150xc2x0 C., peaks at 185xc2x0 C. (referred to herein as the peak decomposition temperature) and is complete by 210xc2x0 C. The total amount of energy released due to decomposition of the sulfonyl azide groups is about 1500 Joules/gram. Preferably, the poly(sulfonyl azide) is heated to at least the peak decomposition temperature. The poly(sulfonyl azides) used advantageously have a peak decomposition temperature greater than about 150xc2x0 C., preferably greater than about 160xc2x0 C., more preferably greater than about 180xc2x0 C.
The amount of poly(sulfonyl azide) is preferably at least about 50 parts per million by weight (ppm), more preferably at least about 75 ppm, most preferably at least about 100 ppm, and in some instances, preferably at least about 150 ppm. In the practice of the invention, formation of crosslinked networks to an extent that would result in intractable propylene polymer is to be avoided; therefore, poly(sulfonyl azide) is preferably limited to that amount which results in chain coupled or rheology modified (but not substantially crosslinked) propylene polymer, preferably less than about 2000 ppm, more preferably less than about 1500 ppm, most preferably less than about 1300 ppm poly(sulfonyl azide) based on the total weight of propylene polymer. Substantial crosslinking is characterized by the presence of gels of sufficient size or weight percentage such that the processing of the film is detrimentally affected. Such detrimental effects include increased operating amperage, discontinuities in or undispersed materials in the film, increased back pressure, and/or, partial die plugging due to gels or black specs. The amount to be used depends on the melt flow rate of the starting and targeted propylene polymers and can be determined by the skilled person.
The propylene polymer and coupling agent are suitably combined in any manner which results in desired reaction thereof, preferably by mixing the coupling agent with the polymer under conditions which allow sufficient mixing before or during reaction to avoid unnecessary or undesirable amounts of localized reaction. An undesirable amount is an amount that interferes with the purpose of the final product. In a preferred embodiment the process of the present invention takes place in a single vessel, that is mixing of the coupling agent and polymer takes place in the same vessel as heating to the decomposition temperature of the coupling agent. The vessel is most preferably a twin-screw extruder, but preferably a single-screw extruder or advantageously a melt mixer, including a batch mixer. The reaction vessel more preferably has at least two zones of different temperatures into which a reaction mixture would pass.
In the most preferred embodiment, the propylene polymer and the coupling agent are physically mixed at a temperature that is low enough to minimize the reaction between the coupling agent and the polymer. Such physical mixing can occur in any equipment, such as V-blenders, ribbon or paddle blenders, tumbling drums, or extruders, which will mix the coupling agent and the propylene polymer. The term extruder is used for its broadest meaning to include such devices as a device that extrudes pellets as well as an extruder which produces the extrudate for forming into articles, such as a film.
Preferably, this physical mixing occurs in the early stages of an extruder, most preferably a twin screw extruder. In particular, this embodiment may be practiced by simultaneously introducing the propylene polymer resin and the coupling agent into the feed section of an extruder. The extruder is configured to have a first section that physically mixes and conveys the coupling agent and polymer in a manner that minimizes the reaction between the coupling agent and the polymer. The conveying first section is followed by at least a second section where the coupling agent and polymer are rapidly further mixed and sufficient heat is added to cause significant reaction between the coupling agent and polymer.
In another embodiment, the mixing is preferably attained with the polymer in a molten or at least partially melted state, that is, above the softening temperature of the polymer, or in a dissolved or finely dispersed condition rather than in a solid mass or particulate form. Any mixing equipment is suitably used in this embodiment, preferably equipment which provides sufficient mixing and temperature control in the same equipment, but advantageously practice of this embodiment takes place in such devices as an extruder, melt mixer, pump conveyor or a polymer mixing devise such as a Brabender melt mixer. While it is within the scope of this embodiment that the reaction take place in a solvent or other medium, it is preferred that the reaction be in a bulk phase to avoid later steps for removal of the solvent or other medium.
Melt phase mixing is advantageous for forming a substantially uniform admixture of coupling agent and polymer before exposure to conditions in which chain coupling takes place. Conveniently for this embodiment, the formation of a substantially uniform admixture occurs along a temperature profile within equipment such as an extruder. The first zone is advantageously at a temperature at least equal to the softening temperature of the polymer(s) and preferably less than the decomposition temperature of the coupling agents and the second zone is at a temperature sufficient for decomposition of the coupling agent. Especially in the case of propylene polymers, most preferably the propylene polymer(s) and coupling agent are exposed to a profile of melt stream temperatures ranging from about 160xc2x0 C. to about 250xc2x0 C.
Those skilled in the art recognize that a polymer, or mixture thereof, typically melts over a range of temperatures rather than melting sharply at one temperature. For the practice of this embodiment, it is sufficient that the polymer be in a partially melted state. For convenience, the temperature of this degree of melting can be approximated from the differential scanning calorimeter (DSC) curve of the polymer or mixture thereof to be treated.
Conveniently, when there is a melt extrusion step between production of the polymer and its use, at least one step of the process of the invention takes place in the melt extrusion step. The heat produced during the extrusion step provides the energy necessary to cause the reaction between the coupling agent and the target polymer.
For all embodiments, a temperature of at least the decomposition temperature of the coupling agent is preferably maintained for a time sufficient to result in decomposition of at least sufficient coupling agent to avoid later undesirable reaction, preferably at least about 80, more preferably at least about 90, most preferably at least about 95 weight percent of the coupling agent is reacted. Those skilled in the art realize that this time is dependent on whether the temperature is one at which the coupling agent slowly decomposes or one at which it very rapidly decomposes. Preferably, the time will be at least about 5 seconds, more preferably at least about 10 seconds to avoid unreacted coupling agent, and subsequent undesirable reactions, or to avoid the need for inconveniently, possible destructively high temperatures. Conveniently, the reaction time is about 20 seconds.
Additives are optionally included in the propylene polymers. Additives are well within the skill in the art. Such additives include, for instance, stabilizers including free radical inhibitors and ultraviolet wave (UV) stabilizers, neutralizers, nucleating agents, slip agents, antiblock agents, pigments, antistatic agents, clarifiers, waxes, resins, fillers such as silica and carbon black and other additives within the skill in the art used in combination or alone. Effective amounts are known in the art and depend on parameters of the polymers in the composition and conditions to which they are exposed.
In addition, other thermoplastic polymers may be blended with the propylene polymers provided the desired foam properties are achieved. Examples of these include high- and low-density polyethylenes, ethylene-vinyl aromatic interpolymers, polybutene-1,ethylene-vinyl acetate copolymer, ethylene-propylene rubber, styrene-butadiene rubber, ethylene-ethyl acrylate copolymer and the like, that may be mixed into the above-mentioned propylene polymer, so long as the latter is the main component in the resulting mixture and the mixture is of uniform quality.
The foams of the present invention may be prepared by a process comprising heating a propylene polymer having a melt flow rate from 0.2 to 20 g/10 min and a melt strength of at least 39 cN, optionally mixed with a nucleating agent to a molten state to produce a molten polymer material, and mixing said molten polymer material with a blowing agent under conditions to produce a foamed material having a density in the range of from 9.6 to 801 kg/m3 (0.6 to 50 lbs/ft3), wherein the propylene polymer is obtained by a coupling treatment carried out before, during or after admixture with the blowing agent. The molten polymer material is most preferably mixed with a blowing agent under conditions that preclude foaming to form a foamable gel, and then exposing the foamable gel to conditions conducive to foaming to produce a foamed material. A foam is conveniently prepared by heating a propylene polymer having has a melt strength xe2x89xa739 cN at a drawability from 15 to 60 mm/sec, to form a plasticized or melt polymer material, incorporating therein a blowing agent to form a foamable gel, and extruding the gel through a die to form the foam product. Prior to mixing with the blowing agent, the polymer material is heated to a temperature at or above its glass transition temperature or melting point. The blowing agent is optionally incorporated or mixed into the melt polymer material by any means known in the art such as with an extruder, mixer, blender, or the like. The blowing agent is mixed with the melt polymer material at an elevated pressure sufficient to prevent substantial expansion of the melt polymer material and to generally disperse the blowing agent homogeneously therein. Optionally, a nucleator is blended in the polymer melt or dry blended with the polymer material prior to plasticizing or melting. The foamable gel is typically cooled to a lower temperature to optimize physical characteristics of the foam structure. The gel is optionally cooled in the extruder or other mixing device or in separate coolers, preferably to a temperature above, more preferably at least about 5xc2x0 C. above, most preferably up to about 40xc2x0 C. above, the softening point or crystallization temperature of the propylene polymer. The gel is then extruded or conveyed through a die of desired shape to a zone of reduced or lower pressure to form the foam structure. The zone of lower pressure is at a pressure lower than that in which the foamable gel is maintained prior to extrusion through the die. The lower pressure is optionally superatmospheric or subatmospheric (evacuated or vacuum), but is preferably at an atmospheric level. Preferably, the gel is extruded into a zone of atmospheric pressure at a temperature that is about the melting temperature of the polypropylene, or less than the melting temperature, but above the crystallization temperature of the polypropylene. The melting temperature and crystallization temperatures are determined by a DSC test method.
Other suitable processes are a coalesced foam process as described in U.S. Pat. No. 4,824,720 and an accumulating extrusion process described in U.S. Pat. No. 4,323,528, both hereby incorporated by reference.
U.S. Pat. No. 4,824,720, which describes the coalesced (or strand) foam process. This patent describes a method for providing a closed cell foam structure comprising a plurality of coalesced extruded strands or profiles by extrusion foaming of a molten thermoplastic composition utilizing a die containing a multiplicity of orifices. The orifices are so arranged such that the contact between adjacent streams of the molten extrudate occurs during the foaming process and the contacting surfaces adhere to one another with sufficient adhesion to result in a unitary structure. The individual strands of coalesced foam should remain adhered into a unitary structure to prevent strand delamination under stresses encountered in preparing, shaping, and using the foam.
U.S. Pat. No. 4,323,528 describes an accumulating extrusion process. In this accumulating extrusion process low density, elongated cellular bodies having large lateral cross-sectional areas are prepared by: 1) forming, under pressure, a mixture of a thermoplastic polymer and a blowing agent, with the mixture having a temperature at which the viscosity of the mixture is sufficient to retain the blowing agent when the mixture is allowed to expand; 2) extruding the mixture into a holding zone maintained at a temperature and pressure which does not allow the mixture to foam, the holding zone having an outlet die defining an orifice opening into a zone of lower pressure at which the mixture foams, and an openable gate closing the die orifice; 3) periodically opening the gate; 4) substantially concurrently applying mechanical pressure by a movable ram on the mixture to eject the mixture from the holding zone through the die orifice into the zone of lower pressure, at a rate greater than that at which substantial foaming in the die orifice occurs and less than that at which substantial irregularities in cross-sectional area or shape occurs; and 5) permitting the ejected mixture to expand unrestrained in at least one dimension to produce an elongated thermoplastic cellular body.
In the practice of the invention where a propylene polymer is used which is obtained by reaction with a coupling agent, such as a poly(sulfonyl azide), this coupling treatment may be carried out before, during or after admixture with the blowing agent. Conveniently the coupling agent is admixed with the polymer preferably before or optionally during admixture with the blowing agent and the admixture is heated at least to the decomposition temperature of the poly(sulfonyl azide) for a period sufficient to result in coupling before the foam is formed.
Blowing agents (also referred to herein as foaming agents) useful in making the present foam include inorganic agents, organic blowing agents and chemical blowing agents. Suitable inorganic blowing agents include carbon dioxide, nitrogen, argon, water, air, nitrogen, and helium. Organic blowing agents include aliphatic hydrocarbons having 1-9 carbon atoms, aliphatic alcohols having 1-3 carbon atoms, and fully and partially halogenated aliphatic hydrocarbons having 1-4 carbon atoms. Aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, and the like. Aliphatic alcohols include methanol, ethanol, n-propanol, and isopropanol. Fully and partially halogenated aliphatic hydrocarbons include fluorocarbons, chlorocarbons, and chlorofluorocarbons. Examples of fluorocarbons include methyl fluoride, perfluoromethane, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoromethane (HFC-134), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), 1,1,1,3,3-pentafluoropropane (HFC13 245fa), pentafluoroethane, difluoromethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane. Partially halogenated chlorocarbons and chlorofluorocarbons for use in this invention include methyl chloride, methylene chloride, ethyl chloride, 1,1,1-trichloroethane, 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), chlorodifluoromethane (HCFC-22), 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Fully halogenated chlorofluorocarbons include trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113), 1,1,1-trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane (CFC-114), chloroheptafluoropropane, and dichlorohexafluoropropane. Chemical blowing agents include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitrosoterephthalamide, and trihydrazino triazine.
Though the present process optionally employs any known blowing agent, preferred blowing agents are volatile blowing agents having a boiling point temperature range of xe2x88x9250xc2x0 C. to +50xc2x0 C. and include, but are not limited to aliphatic hydrocarbons such as n-pentane, isopentane, neo-pentane, isobutane, n-butane, propane and the like; fluoro-chlorinated hydrocarbons such as dichlorotetrafluoroethane, trichlorotrifluoroethane, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane and the like; and so on. Among them, the non-fully halogenated hydrocarbons are preferable in point of environmental considerations. Particularly preferred among the non-fully halogenated hydrocarbons are partially or fully fluorinated hydrocarbons and non-fully halogenated fluoro-chlorinated hydrocarbons. Examples of these include 1-chloro-1-fluoroethane and 1,1-difluoroethane. Particularly preferred among the aliphatic hydrocarbons are isobutane and isobutane/n-butane mixtures. Also contemplated are combinations of these blowing agents with minor amounts of CO2, H2O, N2 and argon in the mixtures.
In general, incorporation of a greater amount of blowing agent results in a higher expansion ratio (the term xe2x80x9cexpansion ratioxe2x80x9d herein referred to means the ratio (density of resin)/(density of expanded product)) and thus a lower foam density. However care must be taken not to incorporate an amount of blowing agent that causes a separation between resin and blowing agent during the foam conversion process. When this happens, xe2x80x9cfoaming in the diexe2x80x9d occurs, the surface of the expanded product becomes rough and no good expanded product is obtainable. The amount of blowing agent incorporated into the polymer melt material to make a foam-forming polymer gel preferably is from about 0.04 to 6.0 gram-moles per kilogram of polymer, more preferably from about 0.05 to 6.0 gram-moles per kilogram of polymer, and most preferably from about 0.055 to 6.0 gram-moles per kilogram of polymer.
A nucleating agent is optionally added to control the size of foam cells. Preferred nucleating agents include inorganic substances such as calcium carbonate, talc, clay, titanium dioxide, silica, barium stearate, calcium stearate, diatomaceous earth, mixtures of citric acid and sodium bicarbonate, and the like. The amount of nucleating agent employed advantageously ranges from about 0.01 to about 5 parts by weight per hundred parts by weight of a polymer resin. The preferred range is from 0.1 to about 3 parts by weight.
In general, an increased amount of nucleating agent gives a smaller diameter of cell. However, if the amount exceeds 5 parts by weight, agglomeration or insufficient dispersion of nucleating substance occurs, so that the diameter of the cell becomes greater. On the contrary if the amount is less than 0.01 part by weight, the nucleating action is too feeble to decrease the diameter of the cells.
The present foam preferably has a density of from about 9.6 to 801 kg/m3 (0.6 to 50 lbs/ft3) measured according to ASTM D-1622-88, more preferably from about 9.6 to 721 kg/m3 (0.6 to 45 lbs/ft3), most preferably from 9.6 to about 641 kg/m3 (0.6 to about 40 lbs/ft3). Preferred low den foams have a foam density ranging from 16 to 320 kg/m3 (1 to 20 lbs/ft3).
The foam preferably has an average cell size of about 6 mm or less measured according to ASTM D3576-77.
The foam optionally takes any physical configuration known in the art such as bead, sheet or plank or coalesced strands. The foam is particularly suited to be formed by extrusion into a region formed of air, vacuum or partially vacuumed environment, or water.
The foam is optionally closed cell or open cell. A typical amount of closed cells is more than 50 percent. Preferred closed-cell foams have greater than 80 percent closed cell content measured according to ASTM D2856-87.
Various additives are optionally incorporated in the foam structure such as inorganic fillers, pigments, dyes, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids, extrusion aids, and the like.
According to a further aspect the present invention relates to an expandable composition comprising a coupled propylene polymer having a melt strength of xe2x89xa739 cN, a drawability from 15 to 60 mm/sec, and a melt flow rate from 0.2 to 20 g/10 min, and a blowing agent. The expandable composition may comprise the blowing agent, as well as a nucleating agent and other additives as mentioned in this specification, in the amounts described herein.
The foam according to the present invention is particularly suited for use in automotive interior and exterior applications for energy absorption and comfort cushioning, such as automotive headliners, door liners, energy absorption counter measure. It can be used in general cushion packaging and comfort cushioning market. It can be used as thermal insulation foams for insulating tanks, trucks, and cars as well as walls and roofs in residential and commercial buildings, refrigerators, etc. It can be used as sound insulation foams in automobiles as well as in buildings.
Additionally, expanded or expandable beads can be formed that can be subsequently molded into desired shapes for any of the above applications, including impact energy management, cushion packaging, bulk dunnage packaging and the like. The beads can also be molded into panels for use in insulating applications such as for roofing, walls, tanks, and the like.