The present invention is directed to a resin ceramic composition that includes a ceramic filler in an amount effective for providing a single composition with a magnetic field of at least one gauss.

1. Field of the Invention
The present invention relates to resin ceramic compositions. More particularly, the resin ceramic compositions of the invention include a ceramic that provides the composition with magnetic properties.
2. Description of the Prior Art
A variety of resins are used in connection with devices having magnetic or electronic uses. Often the resin serves as a package or as a support structure onto which other devices are attached. Hence, the resin must be further processed to provide a finished product.
Semiconductor devices are packaged and encapsulated in a variety of resinous materials, including epoxy. Epoxy resins have excellent heat resistance, moisture resistance, electrical characteristics and adhesion properties, and they can acquire various characteristics with the addition of modifying agents. Accordingly, epoxy resins are used for packaging microelectronic components, such as integrated circuits.
The epoxy compositions used in electronic applications may include a hardener and fillers. The fillers are utilized to provide the epoxy resin with desirable characteristics such as a low coefficient of thermal expansion and high thermal conductivity. Commonly used fillers include inorganic fillers used in combination with epoxy include silica, quartz, alumina, fiber glass, calcium silicate, a variety of earths and clays, and combination thereof. Examples of epoxy compositions which include various types of fillers which are used in electronic applications are described in U.S. Pat. No. 4,042,550.
One type of semiconductor device which utilizes epoxy compositions, are proximity sensing devices, such as a Hall effect sensor. A Hall effect sensor relies on a change of magnetic flux density applied to a sensing plane of a Hall effect element. A detailed description of Hall effect sensors is set forth in U.S. Pat. Nos. 5,729,130, 5,694,038, 5,650,719, 5,389,889 and 4,970,463, and the operation of a number of different Hall effect type sensors is described in Allegro (formerly Sprague) Data Book SN-500.
In a representative Hall effect sensor as shown in U.S. Pat. No. 4,970,463, a magnet is mounted a fixed distance from a sensing plane of a Hall effect sensor element, defining an air gap and forming an assembly. The manufacture of such assemblies requires that the magnet be mounted in a particular orientation relative to the sensing plane. Various techniques are known for fixing the position of the Hall effect sensor, such as potting or overmolding. In one known overmolding technique, the magnet is overmolded onto an existing semiconductor which is already encapsulated in a package. The addition step of adding or overmolding a magnet to the semiconductor increases the complexity and cost of manufacture of such devices.
In addition to the increased manufacturing cost, a common shortcoming of such sensing devices is the dependence of the output of the device on the airgap between the device and the magnet which may vary on a part to part basis. More specifically, as the air gap between the magnet and the semiconductor increases, the maximum output range of the device decreases, decreasing the sensitivity of the sensor. Thus, there is a need to provide a reduced cost Hall effect sensor with relatively consistent repeatable output characteristics.
Briefly, the present invention relates to a resin ceramic composition and provides a number of properties heretofore not available in a single composition. In an important aspect of the invention, the resin ceramic composition is capable of providing a magnetic field. Hence, the use of the resin ceramic compositions of the invention eliminates the need to use a separate magnet and thus significantly reduces the cost of such devices requiring external magnet fields.
In one aspect of the present invention, the resin ceramic composition is an epoxy ceramic composition suitable for encapsulating an integrated circuit. Two embodiments of this aspect the invention are contemplated. In one embodiment the composition is overmolded over an already encapsulated integrated circuit. In another embodiment of the invention, the composition is used as the only encapsulation for the integrated circuit die. In both embodiments, the use of the composition eliminates the need for an external magnet, significantly reducing the cost of the sensor and providing relatively consistent repeatable output characteristics. Further, the use of the resin ceramic composition of the invention as a package or overmold provides a relatively repeatable and consistent air gap, and thus, increases the sensitivity of the device used with a similar type magnetic material. Since the magnetic field strength is temperature dependent in one aspect of the invention, the composition may be based on a resin that is able to provide suitable output over an anticipated temperature range of xe2x88x9240xc2x0 C. to 150xc2x0 C., which makes the composition attractive for sensors used in automotive applications.
The composition of the invention includes a resin, and an amount of ceramic filler effective for providing the composition with a magnetic field strength of at least about 1 gauss. The ceramic filler may include strontium ferrite, barium ferrite, or mixtures thereof. When the resin is an epoxy, and the epoxy ceramic composition is used to encapsulate an integrated circuit, the ceramic filler may have a particle size of about 1.5 microns or less. The relatively small particle size and shape provides an additional advantage in that it provides less stress on the semiconductor than other compositions used for encapsulation.
The present invention also provides a process for preparing a resin ceramic composition. In accordance with the process of the present invention, a resin is blended with a ceramic filler in an amount effective for providing the resulting composition with a magnetic field of at least about 1 gauss. The resin ceramic filler blend is exposed to a magnetic field to orient magnetic dipoles within the composition.
The present invention also provides a process for preparing a resin molding composition capable of conversion to a thermoset condition upon application of heat which is suitable for encapsulating semiconductor devices. The process provides a composition having properties compatible for use with semiconductor device, and a magnetic field of at least about 1 gauss. In accordance with this aspect of the present invention, a resin composition is blended with a hardener, if necessary, and a ceramic filler in an amount effective for providing the resulting composition with a magnetic field of at least about 1 gauss. In an important aspect of the invention, the ceramic filler may include a dielectric that has magnetic properties such as barium ferrite, strontium ferrite, and mixtures thereof. The resin/hardener/ceramic filler blend is heated to a temperature for a predetermined time effective for crosslinking the composition. The resin/hardener/ceramic filler blend may be isotropic or anisotropic (i.e. non-magnetically oriented or magnetically oriented).
The present invention provides a resin having magnetic properties. In one aspect of the invention, the resins may be used in connection with various types of magnetic responsive sensors. Examples of magnetic flux responsive sensors include Hall effect sensors, discrete, hybrid or integrated circuits which include Hall effect sensors such as application specific integrated circuits (ASIC), reed switches, magneto resistive sensors (MRS) such as a hybrid, discrete or integrated circuit including an MRE, and magnetic axial contact switches and the like as generally described in U.S. Pat. No. 4,970,463, herein incorporated by reference. Any sensor which provides an output signal in response to a change in magnetic flux density can be fabricated by the method in accordance with the present invention.
Resins useful in the present invention may include thermoplastic and thermoset resins. Representative examples of resins that may be used in the present invention include epoxy, polyester, polypropylene, polyethylene, polybutylene, polycarbonate, styrene, sulfone based resins, and polyamide-imide.
The particular resin utilized depends on the application, in particular, resins have known characteristics selected for the application in which the resin is used. Since the invention is directed to the addition of magnetic materials to form a magnetic resin, a specific embodiment of a single resin, epoxy, is describe by way of example. The selection and application of other resins without magnetic properties are with the ordinary skill in the art. These resins can be formulated into magnetic resins in accordance with the present invention.
In one aspect of the invention, the resin is an epoxy and the epoxy composition of the present invention provides a single composition for encapsulating semiconductor devices either by overmolding an already encapsulated integrated circuit or as the only encapsulation for the integrated circuit die. In both embodiments, the use of the composition eliminates the need for a discrete magnet, significantly reducing the cost of the sensor and providing relatively consistent repeatable output characteristics.
The epoxy composition in accordance with one aspect of the present invention may be selected to provide certain properties that make it compatible and appropriate for use in semiconductor devices. In this aspect of the invention, the resinous material applied to the electronic device is compatible with the electronic device such that the material does not chemically or physically interfere with the device. For example, the resinous composition is relatively free of ions, such as chlorine, bromine, and fluorine, which may chemically react to form corrosive compounds. As used herein, xe2x80x9cRelatively free of ionsxe2x80x9d means that the epoxy composition has less than typical amount chlorine, bromine, fluorine or any combination thereof typically used for encapsulation of semiconductor dies. Further, the epoxy composition provides adequate sealing of leads to prevent penetration of moisture and ionic contaminants which can also promote degradation of the semiconductor device.
In another important aspect, the resin composition of the invention may provide a low coefficient of thermal expansion when this property is needed. Due in large part to the increasing complexity of semiconductors, such semiconductors have become more vulnerable to thermally-induced stress. The use of an encapsulant composition which does not have a low coefficient of thermal expansion can cause premature failure due to cracking of chips, wire breakage and parametric shift. The resin composition of the present invention is effective for use in semiconductors where large thermally induced internal stress might normally occur due to applications subject to relatively wide temperature ranges.
In addition to a low coefficient of thermal expansion, the resin composition may also be formulated to provides a high thermal conductivity for those applications where this property is important. Semiconductor devices of high circuit density generate more heat per unit area than devices of low circuit density, requiring the rapid dissipation of heat through the encapsulant in order to insure cooler operation and a long operating life. It is widely accepted in the electronics industry that a increase of 10xc2x0 C. in junction temperatures decreases the life expectancy of a semiconductor device by one half. Therefore, the property of high thermal conductivity, i.e. rapid dissipation of heat, is necessary to the efficient operation and long life of a microelectronic device.
Epoxy Resin
In one aspect, the epoxy resin component of the compositions of the present invention are those having more than one epoxide group and may be of any of those used in molding compositions, such as the diglycidyl ethers of bisphenol A, Glycidyl ethers of phenol-formaldehyde resins, aliphatic, cycloaliphatic, aromatic and heterocyclic epoxies.
Some commonly used epoxy resins include epoxies prepared by the reaction of epichlorohydrin with bisphenol A, or with hydrogenated bisphenol A, or with bisphenol F, or with Novolac phenolic resins, or with polyols such as glycerol, sorbitol, polyethylene or polypropylene glycol. As an example the structure of polyethylene glycol diglycidal ether is shown below.
Epoxy resins useful in the present invention are commercially available under a variety of trademarks, such as xe2x80x9cEponxe2x80x9d, xe2x80x9cEpi-Rezxe2x80x9d, xe2x80x9cGenepoxylxe2x80x9d and xe2x80x9cAralditexe2x80x9d, to name a few. Epoxylated novolac resins are also useful in this invention and are available commercially under the trademarks xe2x80x9cCiba ECNxe2x80x9d and xe2x80x9cDow DENxe2x80x9d.
Hardeners, also known as curing agents, which may be used herein are any of those commonly used for the purpose of cross-linking the epoxy resin and causing it to form a hard and infusible mass. These hardeners are well known in the art and the use of any particular one or combination thereof and is acceptable. Examples of hardeners or curing agents which may be used include anhydrides such as phthalic anhydride, tetrachlorophthalic anhydride, benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), the dianhydride of 1,2,3,4-cyclopentanetetracarboxylic acid (CPDA), trimellitic anhydride, trimellitic double anhydride, and nadic anhydride; novolacs; and amines such as diamines, aromatic amines, methylene dianiline, m-phenylene diamine, and m-tolylene diamine.
Generally, the amount of hardener added to the epoxy will depend upon the desired properties of the end product. For example, about 10% or more of hardener is used, based on the stoichiometric amount of the epoxy groups present.
Fillers
The ceramic fillers of the present invention may be blended with any resin as described herein. The ceramic filler may be blended with the resin and/or the hardener before the composition is allowed to harden and also before curing in the presence of a magnetic field for orienting magnetic dipoles in the composition. In an important aspect of the invention, the epoxy/hardener is blended with a magnetic ceramic filler.
Magnetic ceramic fillers useful in the present invention are dielectric ceramics which act as electric insulators and are thus not electrically conductive. The magnetic ceramic fillers of the invention provide a magnetic field of at least about 1 gauss and can provide a magnetic field of up to at least about 150 gauss and up to 600 gauss and higher depending upon the percentage of magnetic ceramic filler. The magnetic field provided by the composition is at least about 1 gauss at a temperature range from about xe2x88x9240xc2x0 C. to about 150xc2x0 C. In particular, the magnetic temperature co-efficient for the composition is about xe2x88x920.19%/xc2x0 C. In other words, the magnetic flux is reduced by 0.19% for each degree of temperature change relative to 25xc2x0 C. Thus at a 150xc2x0 C., the gauss output of the composition will be reduced by about 24%.
In a very important aspect, ceramic fillers of the present invention include strontium ferrite, barium ferrite and any equivalents. In another very important aspect, when the composition is used with semiconductor devices, the ceramic has a particle size of about 1.5 microns. The small particle size allows for adequate dispersion of the ceramic filler in the epoxy resin and provides the resin with the desired properties of thermal expansion and conductivity. Further, smaller particle size results in less stress on the integrated circuit die.
Additives
A variety of adjuvants may be added to the epoxy molding composition to provide special properties. Thus, catalysts, mold release agents, pigments, flame retardants, and coupling agents are generally employed in addition to the epoxy resin, hardener and filler.
Preparation of Semiconductor Devices with Epoxy Overmold or Potting
In one important aspect of the invention, epoxy resin as described above is blended with hardener and with a magnetic ceramic filler. The blend will contain an amount of ceramic filler effective for providing the final composition with a desired magnetic field of at least about 1 gauss. In one very important aspect, the blend will contain from about 40 to about 65 percent by weight preferably 50 percent by weight, ceramic filler, based on the weight of the resin/hardener/ceramic filler blend.
The resin/hardener/ceramic filler blend is overmolded or potted onto a semiconductor which is already packaged. Hardening or cross-linking of the epoxy resin is then effected by heating the composition. In an important aspect, heating is conducted at about 115xc2x0 C. about 60 minutes.
The resin/hardener/ceramic filler blend may be isotropic or anisotropic (i.e. non-magnetically oriented or magnetically oriented). In an anisotropic embodiment, curing of the epoxy is done in the presence of a magnetic field. Magnetic orientation may be effected by application of a suitable magnetic field, well known within the ordinary skill in the art.
Encapsulation of Semiconductor Die
In another important aspect of the invention, the compositions of the present invention are used to encapsulate a semiconductor die. As used herein, a semiconductor die is a portion of a semiconductor wafer formed by conventional integrated circuit techniques. Such dies normally include bond pads for connection to internal electrical circuits. In particular, various known methods are known for connecting the bonds on bond frames. The die and bonds are encapsulated in a package, normally an epoxy composition.
In an important aspect of the present invention, epoxy compositions normally used to encapsulate a semiconductor are substituted with the composition in accordance with the present invention by known techniques. The method of the present invention provides a device having a decreased or zero air gap. This method reduces the internal air gap between the die and the magnetic fields.

Resin ceramic compositions having magnetic properties


An apparatus and method for a centrifugal fluid pump for pumping sensitive biological fluids, which includes (i) an integral impeller and rotor which is entirely supported by an integral combination of permanent magnets and electromagnetic bearings and rotated by an integral motor, (ii) a pump housing and arcuate passages for fluid flow and containment, (iii) a brushless driving motor embedded and integral with the pump housing, (iv) a power supply, and (v) specific electronic sensing of impeller position, velocity or acceleration using a self-sensing method and physiological control algorithm for motor speed and pump performance based upon input from the electromagnetic bearing currents and motor back emfxe2x80x94all fitly joined together to provide efficient, durable and low maintenance pump operation. A specially designed impeller and pump housing provide the mechanism for transport and delivery of fluid through the pump to a pump output port with reduced fluid turbulence.

1. The Field of the Invention
This invention relates to magnetically supported and rotated rotors and, more particularly, to a centrifugal pumping apparatus and method whose disk-like impeller is magnetically suspended and rotated in a contact-free manner, the rotation speed of the impeller being controlled and changed electronically by fluid pressure and impeller positioning algorithms.
2. The Relevant Technology
Historically, fluid pumps are of many and varied types and configurations, all performing essentially the same end result, namely, to provide fluid movement from one point to another. All pumps have a similar characteristic in that fluid is drawn into the pump through a vessel or pipe by a vacuum created by pump operation. In addition to the primary force of vacuum, secondary forces such as gravity, impeller inertia, or existing pipe/vessel fluid pressures also have an effect on fluid flow. Operation of the pumping mechanism creates a fluid pressure and/or fluid velocity which subsequently creates the vacuum that draws fluid into the pump through a pump inlet port. Fluid from the inlet port is transported throughout the pump by the pump mechanism which subsequently directs fluid to a pump outlet port.
Fluid pump configurations vary mostly by adaptation to function. For example, lift and force pumps utilize a reciprocating motion to displace fluid, whereas vacuum pumps create a vacuum that is used to displace fluid. Rotating axial-flow pumps utilize propeller-like blades attached to a rotating shaft to accomplish the displacement of fluid. Jet pumps utilize a steam-jet ejector which enters a narrow chamber inside the pump and crates a low-pressure area that correspondingly creates a suction that draws the fluid into the chamber from an inlet port. Although, other pump types could be specified, more specific reference will be made hereafter to fluid pumps for a sensitive fluid such as blood which are more easily adaptable to environments where size and geometry of the pump are critical.
The rotating centrifugal pump is, by nature, more tightly configured and readily adaptable to pumping of sensitive fluids. Blood flow pumps have relatively low flow rate performance characteristics compared to many ordinary industrial applications yet have significant pressure rise requirements. Centrifugal pumps are well suited to such applications rather than axial flow pumps or other designs. This leads to the use of a centrifugal pump design for the preferred embodiment of this invention. The pump includes several ribs or vanes mounted to an impeller whose rotational force impels fluid toward the outside of the rotor by centrifugal force. Centrifugal pumps traditionally possess a shaft-mounted impeller immersed in the fluid, where the shaft extends through a seal and bearing apparatus to a drive mechanism. Revolving vanes of the impeller create a partial vacuum near the center of the axis of rotation which correspondingly draws in fluid through the intake opening of the pump. A smooth pump volute is located in the pump stationary component to assure the smooth flow of pumped fluid from the exit of the impeller to the pump exit passage. The volute accumulates the pump flow as it exits the pump impeller and performs the function of increasing the fluid pressure (head) by converting fluid kinetic energy (velocity) to potential energy (pressure or head). Although centrifugal pumps do not require valves for movement of fluid, pump geometry must be such that fluid drawn in through the input opening will continue through the pump mechanism and on to the outlet port without significant internal fluid leakage or inefficiencies.
These prior art pumps are known to have problems. For example, it is well documented that shaft seals as configured in conventional centrifugal pumps are notoriously susceptible to wear, failure, and even attack by certain fluids, thus resulting in leakage problems. It is also well known that pumps for some fluids require more careful design consideration and require specific pumping techniques in order to avoid fluid damage, contamination, and other undesirable conditions. For example, fluids such as corrosive fluids (acids or caustics) or sensitive fluids such as blood, require special consideration such that seals do not leak and thereby lose integrity of the fluid. Pumping of sensitive fluids, such as blood, by continuous flow pumps requires highly reliable and non-damaging bearings to support the rotating impeller. Prior art pumps have very significant problems with bearings needed to support the impeller as it rotates. Ball and other rolling element bearings can only be employed if isolated from the sensitive fluid (blood) by shaft seals and lubricated with non-body fluids. In this situation, all of the sealing problems indicated above apply. If the conventional ball or other rolling element hearings employ the sensitive fluid as a lubricant, the sensitive fluid living properties, such as red blood cells in blood, are destroyed in a short period of time due to being ground between the rolling components in the bearings. Thrust and radial fluid film bearings, lubricated with the sensitive fluid, have been employed in some prior art pumps. These have been subject to poor performance and/or many failures due to seizure of the rotating component in the stationary component, production of thrombosis (clotting), damage to the sensitive fluid due to hemolysis (high shear), and other problems.
Fluid film bearings also do not provide any information on the instantaneous pump pressures and flow rates that can be employed for speed control of the motor to match physiological needs to future pump performance. Conventional ball bearings and fluid film thrust and radial bearings do not have the long term reliability required for pumps in which fluid stasis and high fluid shear stress must be avoided, such as blood pumps. Furthermore, ball bearings have a limited life when employed in the pumping of sensitive fluids and often must be lubricated by an external lubricating fluid which requires seals to contain the lubricating fluid. Transport and containment of lubricating fluid for bearings increases the overall size of the pump housing as well as increasing complexity of operation due to extra vessels and mechanisms used to deliver and cool lubricating fluid, thereby making pump apparatus non-implantable infused to replace natural heart functions. Therefore, the relatively short life of fluid pumps with shafts and conventional bearings makes them unsuitable for implanting in body cavities for the long term replacement of natural heart functions.
Furthermore, pumping of blood involves specific known hazards typically associated with shaft seals for impeller-type blood pumps due to pockets of fluid being susceptible to stagnation and excessive heat. Further still, pumping sensitive fluids, such as blood, requires careful consideration of geometry of impeller vanes and pump housing. Excessive mechanical working and heating of blood causes blood components to breakdown by hemolysis and protein denaturization, which leads to blood coagulation and thrombosis.
Avoidance of blood damaging effects of pump operation is best accomplished by natural heart function. The natural heart has two basic functions, each side performing a different pumping function. The right side of the natural heart receives blood from the body and pumps it to the lungs, whereas the left side of the natural heart collects blood from the lungs and pumps it to the body. The beating of the natural heart, in combination with heart valves, provides blood pumping action in a pulsatile, remarkably smooth and flowing manner. Blood flow (cardiac output) of the natural heart is primarily regulated by venous return, otherwise known as pump preload. However, due to diseases or accident, natural heart functions can be partially or totally lost. Mechanical apparatus developed to replace natural heart functions historically ranged in size from extremely large in the earliest heart-lung or pump oxygenator apparatus to more recent apparatus whose size and function more closely resembles that of the natural heart.
In addition to total heart replacement, development of other mechanical apparatus focuses on replacement of a portion of the function of the natural heart, such as a ventricular assist device that aids a failing left ventricle weakened by disease or other damage. A primary consideration for natural heart function replacement, whether partial or total, is that blood must be pumped throughout the entire apparatus in a gentle, low thermal, and non-destructive manner. For example, if a pump impeller supported by mechanical bearings comes in contact with blood, relative movement between parts of the bearings results in excessive mechanical working of the blood which causes blood cells to rupture, resulting in hemolysis. Another mechanical effect that can injure blood is formation of regions within the pump where blood is semi-stagnant or where blood will eddy without sufficient blood exchange, thereby creating the equivalent to blood stagnation. The result of blood stagnation often is coagulation of the blood (thrombosis), which correspondingly causes blood to cease to flow at all. Yet another effect that can injure blood is excessive heating due to friction of a sidewall of the pump or other pumping mechanisms as blood passes through the pump. Specifically, side wall friction caused by abrupt angular changes of internal pump geometry requires blood to follow harsh changes of direction and thereby creates excessive mechanical working of blood which causes blood cell rupture or activation of blood platelets and corresponding hemolysis and thrombosis. Yet another effect that can injure blood is caused by inefficient pump operation whereby a large part of the energy supplied to the pump appears as heat discharged into the blood which damages blood by overheating and coagulation. Notably, because blood albumen begins to denature at 42 degrees Centigrade, inefficiencies in pump operation which result in overheating of the blood will cause a very serious and life threatening condition.
The before mentioned conditions of stagnation, harsh pump geometry, turbulence and/or heating will activate blood platelets and/or damage oxygen-carrying red blood cells. Damage to blood starts a chain reaction that forms a thrombus with potential to block blood vessels, starving the tissues it nourishes, and leading to a serious, life threatening condition. Numerous attempts to avoid the foregoing problems associated with pumping blood have been made using flexible diaphragms and collapsible tubing in roller pumps However, the continual flexing of the diaphragm and/or tubing material is known to change the blood-contacting properties of the material resulting in material fatigue, dislodged fragments of the internal wall of the flexible material, and emboli passed into the bloodstream by the fragments.
In addition to the above mentioned conditional requirements for pumping blood, the rate of impeller rotation has a significant effect on stability and structure of sensitive vessels. Impeller rotational operation that is not regulated by pump preload pressure will cause atrial suction in sensitive vessels just prior to the pump inlet port, wherein blood vessels collapse when impeller rotation exceeds blood vessel wall rigidity. Prior art pumping apparatus has not provided adequate integration of controls to insure that rapid adjustments to impeller rotational speed does not have a negative effect.
Kletschka ""005 (U.S. Pat. No. 5,055,005) discloses a fluid pump levitated by opposing fluid. Stabilization of impeller by opposing fluid alone is not sufficient to maintain impeller in precise position within pump housing, as well as high pressure fluid jets subject blood to the before mentioned blood coagulation caused by mechanical working of blood.
Kletschka ""877 (U.S. Pat. No. 5,195,877) discloses a fluid pump with a magnetically levitated impeller utilizing a rigidly mounted shaft surrounded by a magnetically levitated rotor which serves as an impeller for fluid. The shaft of this invention introduces a requirement for a hydraulic bearing and seal at the juncture of the shaft and the rotating impeller which subjects blood, or other sensitive fluids, to thermal and stagnation conditions at the region of the bearing.
For more than 25 years, those skilled in the art have studied pumps that are used as total artificial hearts and experimentally implanted in animals. These studies have provided useful feedback of the relative effectiveness of blood pumping apparatus. These pumps can be categorized a, producing pulsatile or non-pulsatile flows. The pumps producing pulsatile fluid motion (positive displacement pumps) more closely resemble fluid motion as provided by the natural heart. Information to date has not yet determined if pulsatile fluid movement is needed to provide a necessary physiological benefit, or if the pulsatile fluid motion is primarily due to the non-rotary nature of heart muscle. Most pulsatile pumps universally require valves (mechanical or tissue) with inherent mechanical problems and limitations. valve systems are not required in prior art non-pulsatile pumps, the non-pulsatile pumps require rotating shafts passing through various bearings and seals. These shafts create inherent problems of blood stagnation, contamination and undesirable thermal conditions, thereby making long term use of the pumps as a replacement for natural heart function unfeasible. Most early prior art rotating non-pulsatile systems were installed outside of the body for short-term cardiac assistance and experienced a moderate amount of success.
One blood pumping apparatus is the total artificial heart. The total artificial heart has been used in five patients as a permanent replacement for pathological, irreparable ventricles; and in 300 patients as a temporary bridge to cardiac transplantation. The longest support on the total artificial heart has been 795 days. Other blood pumping apparatus, e.g., ventricular assist devices, have been used in patients unweanable from cardiopulmonary bypass during cardiac surgery or those whose one ventricle only has failed. The most common mechanical replacement of natural heart function is a temporary bridge to cardiac transplantation by a ventricular assist device with over 1250 patients receiving such temporary ventricular assist apparatus.
Historically, blood pumping apparatus have presented many problems. For example, the pumping mechanism of reciprocating (diaphragm) total artificial hearts has been energized with gases (pneumatic systems), electricity (motors, solenoids, etc.), and skeletal muscles. The energy sources and associated convertor systems possess additional components that increase complexity of the total system and thereby contribute to overall unreliability. Also, the size of prior art systems for total artificial hearts is very restrictive to patient mobility and not conducive to quality of life of the recipient. Another constraining factor not fully met by prior art apparatus is that the excessive size and complexity of energy conversion systems, as well as overall pump design exceeds the available anatomical space. Furthermore, most of these prior art reciprocating systems exhibit excessively high (i) noise characteristics, (ii) vibration, and (iii) recoil (thrust) levels.
Many of the problems of the prior art rotating pumps have been addressed by those skilled in the art through pump adaptation with capability to meet the above mentioned requirements for pumping sensitive fluids (such as blood). These pump adaptations can be accomplished bag support of the impeller through electromagnets located on the impeller and the housing such that the impeller can be rotated without shafts, seals or lubricating systems. Permanent magnets without some form of additional support cannot entirely suspend an object, such as an impeller, but require additional adjustable support or force in some axis to achieve stabilized suspension. This is based on Earnshaw""s theorem which indicates that suspension systems comprised solely of permanent magnets will not be stable. However, actively controlled electromagnets can be used to stabilize and support an object with respect to all degrees of freedom of movement. Additionally, one electromagnet with a feedback position sensor can provide stable suspension of an object (or impeller in the case of the centrifugal fluid pump). The only expenditure of energy in hybrid magnetically supported impellers is electromagnetic energy utilized for stabilizing and rotating the impeller. Permanent magnets and one electromagnet for impeller suspension and rotation create a stable and efficient pump operation.
Within the past decade, prior art patents have disclosed magnetically suspended and rotated rotors which have exhibited a limited degree of success. These prior art configurations utilize partial magnetic suspension to reduce hazards to blood. Although magnetically suspended prior art devices successfully reduce some of the friction hazard of the rotary shaft, the prior art devices are still impractical for implantation in total heart replacement due to size, complexity, and less than optimal impeller positioning, position sensing, and speed control. The excessive size and difficulty in maintaining precise impeller positioning and speed of these prior art inventions is due mostly to geometric configuration of the impeller, which is cylindrical, spherical, or otherwise mostly three dimensional in nature.
In view of the foregoing, it would be a significant advancement in the art to provide improvements in magnetically suspended and rotated centrifugal pumping apparatus to thereby allow for reduced size and increased accuracy in impeller positioning and speed controls. It would also be an advancement in the art to provide a centrifugal pumping apparatus that would be free of shafts, rolling element or fluid film bearings, mechanical seals, or physical proximity sensors, thereby allowing for a fully integrated pump design without mechanical contact, wear, failure due to seizing up of fluid bearings, and generation of thrombosis or shear damage. An even further advancement in the art would be to provide a centrifugal pumping apparatus with geometry of impeller and pump housing such as would provide efficient and low-turbulence transport of fluid throughout pump mechanisms including the pump output port. Further still, it would be an advancement in the art to provide a versatile centrifugal pumping apparatus that could operate in either pulsatile or non-pulsatile mode.
It is a primary object of the present invention to provide improvements in rotating centrifugal fluid pumps for sensitive fluids.
It is another object of the present invention to provide improvements in fluid pumps using a combination of permanent magnets, efficient non-contact electromagnetic bearings, and an efficient motor.
It is also an object of the present invention to provide a centrifugal pumping apparatus of relatively compact size to enable anatomical implantation.
It is a further object of the present invention to provide a centrifugal pumping apparatus and method to provide a long product life and which requires minimal maintenance.
It is an additional object of the present invention to provide improvements in centrifugal fluid pumps which are used for partial or total heart function replacement.
It is still another object of the present invention to provide a centrifugal pumping apparatus and method whose pump design geometry provides efficient and low-turbulence transport and output of sensitive fluid throughout the pump, including low-turbulence output just beyond the outlet port.
It is yet another object of the present invention to provide a centrifugal pumping apparatus and method whereby fluid pressure and output fluid volume are controlled and changed electronically via specific fluid pressure and positioning algorithms.
It is another object of the present invention to provide a centrifugal pumping apparatus and method that is capable of operation in either pulsatile or non-pulsatile mode.
It is yet another object of the present invention to provide a centrifugal pumping apparatus and method that is adaptable as either a ventricular assist device or paired to provide a total heart replacement.
The above objects and others not specifically recited are realized through an apparatus and method for a centrifugal fluid pump for pumping sensitive biological fluids, which includes (i) an integral impeller and rotor which is entirely supported by an integral combination of permanent magnets and electromagnetic bearings and rotated by an integral motor, (ii) a pump housing and arcuate passages for fluid flow and containment, (iii) a brushless driving motor embedded and integral with the pump housing, (iv) a power supply, and (v) specific electronic sensing of impeller position, velocity or acceleration using a self-sensing method and physiological control algorithm for motor speed and pump performance based upon input from the electromagnetic bearing currents and motor back emfxe2x80x94all fitly joined together to provide efficient, durable and low maintenance pump operation. A specially designed impeller and pump housing provide the mechanism for transport and delivery of fluid through the pump to a pump output port with reduced fluid turbulence.
These and other objects and features of the present invention will become readily apparent from the following description in which preferred and other embodiments of the invention have been set forth in conjunction with the accompanying drawings and appended claims.
The underlying rationale for a rotating centrifugal pump with an impeller, fully supported by a combination of permanent magnets and electromagnetic bearings and rotated by an electric motor, is to prevent damage to blood or other sensitive fluid due to conditions of (1) excessive heat, (2) stagnation, (3) coagulation (thrombosis), or (4) high shear of fluid or blood components (hemolysis) due to fluid instability caused by turbulence or mechanical working of fluid due to harsh pump mechanism or geometry. Furthermore, the apparatus size of this invention is capable of fitting into available anatomical space if used for total natural heart replacement or ventricular assistance.
To be suitable as a blood pump, the pump must be able to adequately meet physiological perfusion needs of a ventricular or biventricular assist device for total heart replacement. As a total heart replacement device, the pump must be of sufficiently small size and mass to be implantable within available anatomical space and not cause any negative effects on surrounding organs due to excessive apparatus weight. Furthermore, the disc-like shape of the impeller of this invention significantly reduces size and complexity of the pumping apparatus. The pumping apparatus of the invention can be used singularly as a ventricular assist device that assists or replaces partial heart function or a pair of devices can be combined to form a total mechanical heart replacement. The combined size of two devices in a total mechanical heart replacement is approximately the size of a natural heart, thereby enabling implantation within existing anatomical space.
The impeller of this invention is entirely suspended and enclosed within its pump housing, thereby providing contact-free operation between pump impeller and any other portion of the pump. The pump impeller is magnetically suspended with a combination of permanent magnets and electromagnetic bearings. The permanent magnets are configured in reverse polarity which provide positive radial stiffness while being employed in the radial gaps inherent in disk-shaped impellers unlike the repulsive permanent magnet rings cited in the prior art patents which can only be employed in axial gap configurations. This reverse polarity permanent magnet configuration is required for a disk-shaped impeller geometry. It is enclosed within its pump housing, thereby providing contact-free operation between pump impeller and any other portion of the pump. The pump impeller is suspended by a combination of permanent and electromagnetic forces. An electric motor rotates the pump impeller to perform the pumping function of fluid. The notable absence of shafts, ball bearings, shaft seals or other sources of contamination make possible significantly extended product life of the pumping apparatus of this invention, thereby enabling long term natural heart replacement.
The pump impeller rotates about an axis and the term xe2x80x9caxial directionxe2x80x9d is employed here to denote the direction parallel to the axis of rotation of the pump impeller. The term xe2x80x9cradial directionxe2x80x9d is used here to denote directions perpendicular to the axial direction. The invention consists of permanent and electromagnetic bearings, comprising magnetic and other materials, activated by electrical currents in coils wound around the bearing magnetic components, which develop axial forces and provide adjustments to impeller positioning relative to pump housing. A multiplicity of magnetic bearings, in a suitable configuration arranged around the impeller, is required to center the impeller during operation of the pump and to avoid contact between the rotating and stationary components. Six impeller degrees of freedom: three translations and three rotations, must be controlled. This non-contacting operation allows the bearings to operate without wear or friction losses.
A feedback electronic controller is provided in the suspension system to automatically adjust the activating (thrust) bearing coil currents which, in turn, adjust the control forces exerted by the magnetic bearings on the rotating impeller in response to the applied forces. Such electronic controller is continuously provided with an electronic signal which is related to the position or velocity or acceleration or a combination of position, velocity and acceleration, of the rotating impeller in the available clearance space inside the pump frame during operation. Switching or direct current power amplifiers and power supplies necessary to operate the electromagnetic actuators in the magnetic bearings are provided in the invention.
Impeller position and rotational speed of this invention are controlled by specific algorithms which sense fluid pressure and the axial location of pump impeller within pump housing, correspondingly making adjustments to rotational speed and/or impeller position to provide a fully integrated system of physiological control. Impeller rotational speed is adjusted to correspond to fluid pressure at pump preload pressure (inlet pressure) and/or exit pressure to match bodily needs for increased or decreased pump flow rate or pressure rise. This also avoids excessive rpm and thus suction thereby avoiding excessive pressure.
The geometric design of the pumping apparatus of this invention provides fluid movement throughout the entire pump mechanism in a smooth, non-turbulent, and low thermal manner. Impeller rotation causes fluid to move centrifugally by specially curved impeller vanes which emanate from the epicenter of the disc-like impeller and extend toward the outside of the impeller, and simultaneously create a partial vacuum at the region near the impeller""s axis of rotation that draws additional fluid into the inlet port. Blood, or other sensitive fluid, does not stagnate at any location within the pumping apparatus due to return fluid flow along the side of the impeller which returns fluid to the impeller epicenter without flow interference from stagnation pockets, bearings or seals. Importantly, the geometry of the pump housing, the impeller vanes, the outlet port, and all other aspects of the pumping apparatus of this invention are such that sensitive fluids are protected from damage otherwise caused by stagnation, excessive heat, turbulence, and excessive mechanical working of the fluid.
The fluid is transported throughout the entire pumping apparatus without harsh angular redirection to flow. The configuration of pump housing is designed with a spiral volute curve such that the same curve slope throughout the pump housing enables fluid to be transported within the pump housing with no net abrupt angular change of direction, nor corresponding net increase in thermal friction and energy loss due to friction from the pump side wall.
Another important feature of the pumping apparatus of this invention is the capability of operation in either pulsatile or non-pulsatile mode. Cyclic variance of impeller rotational speed will cause the pump to operate in a pulsatile mode, which more closely resembles pumping action by the natural heart, whereas uniform impeller rotational speed operates the pump in non-pulsatile mode. Operational mode change from pulsatile to non-pulsatile or vice versa is accomplished through changes to the pump operation settings, thereby avoiding trauma associated with replacing the total pumping apparatus when a change from either pulsatile or non-pulsatile is determined to be the preferred operation mode.
One aspect of this invention, unlike prior art devices, is that means or structure are provided in the magnetic suspension system to generate the electronic feedback signal related to the position, velocity or acceleration of the rotating impeller either via a physical medium such as an eddy current, induction, optical, capacitance or other approach, or via a self-sensing electronic signal obtained from the current or voltage wave form, or a combination of the current and voltage wave form provided to the activating coils in the magnetic bearings. In the case of a physical sensor device placed in the pump frame near the clearance gap between the frame and the rotating impeller, the gap between the frame and the rotating impeller, the electronic position, velocity, or acceleration signal, is obtained from signal conditioning electronics. Wiring is provided for input of the signal into the electronic controller for the magnetic bearings. In the preferred embodiment, a self-sensing signal is used and the signal conditioning is provided for determining the position, velocity, or acceleration of the rotating impeller without a physical device, which allows for a minimum number of wires required in the wiring pathways between the electromagnetic actuators and the electronic controllers.
The electromagnetic bearings and their control electronics possess a physical sensor or self sensing signal such that forces (velocity, or acceleration) attempting to displace the impeller are immediately sensed and the current delivered to the coils is altered, thus avoiding impeller displacement resultant from those forces.
The flow (cardiac output) of the natural heart is primarily regulated by the venous return (preload). Another very important feature of the invention, named the physiologic controller, provides a signal which is used to determine changes in the preload or filling pressure to the pump. The controller sends a signal from monitoring changes in current flows in the thrust bearing. This information is employed to control the rotational speed of the impeller, to regulate pump suction pressure, and to regulate the needed pump outputs. This unique feature of the magnetically suspended pump allows for sensing of the inflow pressure (preload) and thus the flow (cardiac output) consistent with the physiologic needs of the recipient as a ventrical assistance device (VAD). When two pumps are used as a total artificial heart (TAH) the rotational speed of each pump will be regulated independently and each pump will be sensitive to the preload thus providing changes in flow and balance consistent with the changing physiologic needs of the recipient. This feature allows the pumps to be used without the need of the complexities associated with volume displacement chambers required with pulsatile pumps.
The invention provides for a motor to impart the necessary torque and rotation to the rotor. This is a three phase brushless DC motor controlled by using back EMF. The motor is in the shape of a disc located in the base of the housing frame and near the center of rotation of the impeller. Commutating the motor with back EMF allows effective start-up and precise control of the speed of rotation. Changes in the rotation speed are predicated on the preload as described above in the form of a physiologic controller.

Hybrid magnetically suspended and rotated centrifugal pumping apparatus and method

University of Virginia Patent Foundation


The present invention relates to ink-jet recording media having an ink-receptive coating comprising silica, water-dispersible alumina and a hydrophilic, water-insoluble polyurethane resin. The polyurethane resin is capable of absorbing at least 200% by weight of water. The media provide images having good color gamut, color density and water-fastness.

1. Field of the Invention
The present invention relates to ink-jet recording media having an ink-receptive coating comprising a hydrophilic, water-insoluble polyurethane resin, silica and water-dispersible alumina. The media are capable of absorbing large volumes of aqueous-based ink to provide images having good color gamut, color density and water-fastness.
2. Brief Description of the Related Art
Recently, it has become more popular to used wide format ink-jet printers for printing large format materials such as signs, posters, banners, and advertising displays for indoor and outdoor applications. Typically, the recording medium comprises a base substrate coated with an ink-receptive coating. If the printed image or text is intended for viewing by reflected light, the substrate is typically an opaque paper or film. If the printed image or text is intended for viewing by transmitted light, the substrate is typically a transparent or translucent film.
xe2x80x9cBack-litxe2x80x9d films are typically translucent films, where the image (and text) is viewed by means of a light source placed behind the imaged surface of the films. Back-lit films are commonly used for high impact lighted signs, vending and game machine displays, and trade-show displays. For these applications, it is important that the substrate and coatings be durable and have good weather-resistance, particularly water-fastness and light stability.
Traditionally, most inks used in ink-jet printing devices have consisted of molecular dyes carried in an aqueous-based solvent or ink vehicle containing a substantial amount of water. Water-miscible solvents and trace amounts of high-boiling solvents such as glycol or glycol ethers may also be present in the fluid. During imaging (i.e., printing), molecular dyes from the ink penetrate into the ink-receptive coating, leaving solvent to evaporate off the surface of the imaged media. Today, pigmented inks are replacing molecular dye-based inks. Pigmented-based inks have better light stability than molecular dye-based inks which is important for imaged media that are displayed outdoors. Pigmented inks comprise a pigmented colorant carried in an aqueous-based ink vehicle. Unlike molecular dyes, pigmented colorants generally bind to the surface of the film or paper, i.e., recording medium. In order to obtain an image having good color gamut and high color density that does not smear, the recording medium should absorb the ink quickly, while retaining or insolubilizing the colorants on its surface.
The industry is constantly seeking to develop ink-jet recording media having improved ink-receptive coatings.
For example, Viola, U.S. Pat. No. 4,578,285 discloses a transparent ink-jet printing substrate comprising a transparent support carrying an ink-receptive layer comprising at least 70 weight percent polyurethane and 5 to 30 weight percent of a polymer selected from the group consisting of poly(vinyl pyrrolidone), vinyl pyrrolidone/vinyl acetate copolymer, poly(ethylene oxide), gelatin, and poly(acrylic acid). The patent further discloses that in order to prevent front-to-back blocking of the printing substrates and to improve slippage in the printer, the ink-receptive layer may contain about 0 to 0.5% by weight silica.
Romano et al., U.S. Pat. No. 5,605,750 discloses an opaque image-recording element for an ink-jet printer comprising an opaque substrate having on its surface a lower layer of a solvent-absorbing microporous material and an upper layer of a porous, pseudo-boehmite. The microporous layer comprises: (a) a matrix of a substantially water-insoluble thermoplastic organic polymer such as, for example, polyolefins, polyesters, polyamides, polyurethanes, polyureas, poly(vinyl halides), poly(vinylidene halides), polystyrenes, poly(vinyl esters), and polycarbonates; (b) finely divided substantially water-insoluble filler particles such as, for example, silica, mica, and clay; and (c) a network of interconnecting pores.
It would be desirable to have an ink-jet recording medium with an ink-receptive coating that could absorb large volumes of aqueous-based pigmented ink to form an image having good color gamut, color density and water-fastness. The present invention provides such ink-jet recording media.
The present invention relates to an ink-jet recording medium comprising a substrate having an ink-receptive layer coated thereon. The ink-receptive layer comprises silica, water-dispersible alumina and a hydrophilic, water-insoluble polyurethane resin capable of absorbing at least 200% by weight of water based on the weight of said resin. Preferably, the layer further comprises a metal salt.
Typically, the polyurethane resin comprises at least 25 wt. % the silica particulate comprises at least 25 wt. % and the water-dispersible alumina particulate comprises about 1 to about 10 wt. % of the layer based on the weight of the layer. Preferably, the layer comprises about 30 to about 60 wt. % polyurethane resin and about 30 to about 70 wt. % silica particulate.
Preferably, the silica particulate has a particle size in the range of about 4 to about 10 microns and a surface area of at least 300 m2/g. Preferably, the water-dispersible alumina comprises at least 90 wt. % aluminum hydrate.
The substrate may be a paper or film. Translucent films are preferred for use as back-lit films.
The present invention relates to an ink-jet recording medium comprising a substrate having an ink-receptive coating prepared from an aqueous-based solution.
The porous ink-receptive coating comprises a hydrophilic, water-insoluble polyurethane resin that is capable of absorbing at least 200% by weight water based on the weight of the resin.
Suitable hydrophilic, water-insoluble polyurethanes include, for example, carboxylated, polyester-type, and polyether-type polyurethanes that are capable of absorbing at least 200% by weight water. As shown in the following examples, it has been found that not all polyurethane resins are suitable for use in the present invention. Suitable polyurethanes may be in the form of a dispersion or solution having a solids content of about 20% or greater. Commercially-available suitable polyurethane resins include IJ-40 and IJ-150 available from Espirit Chemical Company (Sarasota, Fla.).
Silica particles useful in the present invention include amorphous precipitated silica and silica gel particles. The polyurethane resin may be filled with silica particulate, i.e., it may be commercially produced and sold with silica particulate dispersed within the resin. Alternatively, the silica particulate may be added to the ink-receptive coating formulations of this invention as a separate ingredient. Typically, the size of the silica particles is in the range of about 2 xcexcm to about 15 xcexcm. Preferably, the silica has a particle size of about 4 to about 10 xcexcm and a surface area of at least 300 m2/g. Suitable silica particles are commercially available, for example, GASIL IJ-35 silica gel available from Crossfield Company (Joilet, Ill.) may be used. Silica particles having relatively high surface areas should be used to enhance the ink absorption capabilities of the coating.
The ink-receptive coating further contains water-dispersible alumina to enhance image quality. The alumina also improves the strength and water-fastness of the coating. Preferably, the water-dispersible alumina comprises at least 90 wt. % aluminum hydrate. As shown in the following examples, when no water-dispersible alumina is present in the coating, the quality of the image is only fair with significant inter-color bleeding and ink cracking visible. Suitable water-dispersible alumina include DISPERAL SOL P2, available from CONDEA Vista Company (Houston, Tex.).
As shown in the following examples, it is important that the ink-receptive coating contain a polyurethane resin having a water-absorption capacity of at least 200 wt. %, silica and water-dispersible alumina in order to obtain high quality prints having good color gamut, color density and water-fastness.
Typically, the hydrophilic, water-insoluble polyurethane resin comprises at least about 25% by weight and is preferably about 30 to about 60 wt. % of the ink-receptive coating based on the weight of the coating. Typically, the silica comprises at least about 25% by weight and is preferably about 30 to about 70 wt. %. The alumina particulate comprises about 1 to about 10% by weight of the coating.
In addition, the ink-receptive coating may contain various polymeric binders for enhancing image quality. For example, water-soluble polymeric binders, such as poly(2-ethyl-2-oxazoline), poly(vinyl pyrrolidone), vinyl pyrrolidone copolymers, poly(ethylene oxide), starch, casein, sodium alginate, gelatin, gum arabic, and cellulose derivatives may be used. In addition, water-dispersible resins such as polyacrylates, polymethacrylates, polyvinyl acetate, polyvinyl chloride, styrene, styrene and maleic acid anhydride copolymers may be used. METHOCEL K3, a water-soluble cellulose ether available from Dow Chemical, is an example of a suitable cellulose derivative that can be used.
Various additives may also be employed in the ink-receptive coating. These additives include surface active agents that control the wetting or spreading action of the coating solution, antistatic agents, suspending agents, acidic compounds to control the pH of the coating, optical brighteners, UV blockers/stabilizers, and the like. In addition to the above-described silica particles, other particulate may be used, for example, alumina, kaolin, glass beads, calcium carbonate, titanium dioxide, polyolefins, polystyrene, starch, poly(methyl methacrylate), and poly(tetrafluoroethylene).
The ink-receptive coating can further include metal salts of the formula, MeX to improve ink absorption. The metal can be Na, K, Mg, Zn, Ca, Cu, and the like, and X can be Cl, Br, SO4, and the like. The metal salt may be be used in an amount up to about 10% by weight based on the weight of the coating to enhance the ink capacity of the coating without harming coating strength.
The ink-receptive coating has a high void content due to the high concentration of silica dispersed in the polyurethane resin-based coating. The porous nature of the ink-receptive coating allows aqueous-based pigmented ink to penetrate the coating and be rapidly absorbed in the spaces between the silica. Further, the silica particles have a high surface area and are capable of absorbing the ink. In this manner, images having good smear and water-resistance are produced. At the same time, the pigmented colorants in the ink tend to bind to the coating at or near its surface, thereby providing an image having good color gamut and high color density.
The ink-jet recording media of this invention can be made using any suitable substrate such as a polymeric film or paper. Examples of suitable polymeric films include films made of polymers selected from the group consisting of polyesters, cellulose esters, polyimides, polystyrenes, polyolefins, poly(vinyl acetates), polycarbonates, and fluoropolymers, and mixtures thereof. Examples of suitable papers included plain papers, clay-coated papers, and resin-coated papers. Polyester and vinyl films are particularly preferred film substrates. Polyethylene-coated papers are particularly preferred paper substrates. The thickness of the base substrate may vary, but is typically in the range of about 1 mil to about 20 mils, and most typically in the range of about 3 to about 9 mils. The base substrate may be treated with a conventional adhesion promoting layer on its imaging surface as is known in the art. As discussed above, the ink jet recording media of this invention are particularly suitable for use as xe2x80x9cback-litxe2x80x9d films.
Conventional coating and drying methods may be employed including roller coating, blade coating, wire bar coating, dip coating, extrusion coating, air knife coating, curtain coating, slide coating, doctor coating, gravure coating, or slot-die coating, and the coating may be dried by hot forced air in an oven.
The invention is further illustrated by the following examples using the below test methods, but these examples should not be construed as limiting the scope of the invention.
Test Methods
Color Density
The ink-jet recording media were imaged with multiple colors using HPUV ink from a HP 2500CP printer in D best mode, and the color density of the imaged medium was determined. The black pigment ink density (KOD) of the imaged surface was measured on a densitometer (Macbeth TD904 available from Macbeth Process Measurements, Newburgh, N.Y.) following the manufacturer""s standard recommendations. Samples having high ink density values exhibit images having better quality and higher resolution than samples having low ink density values.
Water Absorption Capacity
A polyurethane resin was coated onto the surface of a polyester film and dried. A 3 inch by 4 inch sample of the coated film was then weighed (W0). The film sample was then immersed in a tray of water for about twenty (20) minutes and then removed. A blotting paper was used to remove excess amounts of water from the film sample, and the wet film sample was weighed (W2). The polyurethane coating was then removed from the wet film sample by scraping the sample with a sheet of paper, and the film was weighed (W1).
The water absorption capacity of the polyurethane resin was determined according to the following formula:   A  =                    W        2            -              W        0                            W        0            -              W        1
Coating Strength
The strength of the ink-receptive coating on the substrate was evaluated in the following manner. A piece of scotch tape was placed firmly on a non-imaged medium and then quickly peeled off. The tape was then inspected to determine whether or not any coating residue was on the tape. For coatings having excellent strength, no coating residue, or only a minimal amount, was observed on the tape.

Ink-jet media having high aqueous-based ink absorption capacity