An electrically conductive surface is combined with a protective surface of glass in order to provide an anode from which electrons can be transferred to seawater for the purpose of generating gaseous chlorine on the surface to be protected. Ambient temperature cure glass (ATC glass) provides a covalent bond on an electrically conductive surface, such as nickel-bearing paint. In this way, boat hulls, submerged portions of outboard motors, and submerged portions of stern drive systems can be protected effectively from the growth of marine organism, such as barnacles. The electrically conductive surface generates electrons into the seawater in order to create chlorine gas at the surface which inhibits and discourages marine growth. The protective coating of glass inhibits the migration of metal ions from the electrically conductive surface into the seawater and therefore inhibits corrosive degradation as a result of galvanic action.

1. Field of the Invention
The present invention is generally related to an apparatus and method for inhibiting the fouling of an underwater surface and, more particularly, to a combination of a metallic coating and a protective glass coating which permits electrons to pass through the protective coating between the metal coating and the seawater while inhibiting the transfer of ions between the metallic coating and the seawater, whereby gaseous chlorine is formed on and in the vicinity of the protective coating to inhibit the growth of organic material on the surface of the underwater object.
2. Description of the Prior Art
Throughout the following discussion of the prior art and the description of the present invention, the unwanted growth on a ship""s hull or other underwater surface will be referred to as fouling. Although fouling is primarily a biological phenomenon, its implications relate to engineering. Due to an increase in the resistance to movement of the hull through water, fouling of the hulls of ships results in a reduction in speed, an increase in the cost of fuel, and losses in both time and money in the application of remedial measures.
Underwater surfaces rapidly absorb organic material, referred to as conditioning films, which may influence the subsequent settlement of microorganisms. Bacteria and diatoms are soon present after immersion in water, resulting in a slime that covers the submerged surface. Following the establishment of the micro fouling slime layer, macro fouling rapidly develops. The macro fouling community is often described as either soft fouling or hard fouling. Soft fouling comprises algae and invertebrates such as soft corals, sponges, anemones, tunicates, and hydroids while hard fouling comprises invertebrates such as barnacles, mussels, and tubeworms.
Various toxic and non-toxic solutions have been attempted. Both ultrasonic (e.g. 14 kHz) and low frequency (e.g. 30 Hz) sound waves inhibit barnacle settlement and may have application to fouling control in certain circumstances. These and many other anti-fouling techniques are described in an article written by Maureen Callow in the publication titled xe2x80x9cChemistry and Industryxe2x80x9d at Section 5, pg. 123, on Mar. 5, 1990.
As described in the Baltimore Business Journal, Vol. 10, No. 47, Section 1, pg. 3 on Apr. 23, 1993, McCormick and Company has discovered that its red pepper extracts are natural repellents of barnacles and zebra mussels. A coating of this type has been tested, and it has been determined that it repels both barnacles and zebra mussels which have become costly nuisances in the Great Lake Region by clogging intake pipes for power plants and water treatment plants. It is estimated that several billion dollars in damage will be caused by zebra mussels before the turn of the century.
U.S. Pat. No. 5,532,980, which issued to Zarate, et al on Jul. 2, 1996, discloses a vibrational anti-fouling system. The system produces vibrations in an underwater structure for the purpose of inhibiting the attachment of aquatic life forms to the structure. The system includes a controller which drives one or more transducers. The transducer comprises a housing, one end of which is closed by a resilient diaphragm. An electromagnet with soft magnetic core is contained in the housing spaced from the unsupported portion of the diaphragm. The unsupported portion of the diaphragm is mounted over an underwater structure. In operation, the electromagnet is excited with a current pulse, which deforms the diaphragm so that the housing moves towards the structure. As the current drops off, the diaphragm is restored to its original shape and the housing moves away from the structure imparting a vibrational force to the structure. The transducer includes an elastic membrane to compensate the changes in temperature and pressure commonly found when working underwater. The magnetic cores positioned in the transducers are saturated by current pulses generated by the controller to eliminate the effects of component variations and allow multiple units to be connected to the controller without changes in sound levels. The system is highly resistant to electrolytic corrosion since, most of the time, there is no voltage difference between the resonators, wires and ground.
U.S. Pat. No. 5,386,397, which issued to Urroz on Jan. 31, 1995, describes a method and apparatus for keeping a body surface, which is in contact with water, free of fouling. A sound wave is generated for keeping a surface free of scale, fouling and dirt by the adherence of organisms such as marine life, the surface being part of the body that is in contact with water. The method comprising of steps of generating and emitting from at least one location of the body, at least one high frequency sound wave train forming, adjacent to the body surface, a vibrating field encircling the body surface. The molecular energy of the water within the field is increased to generate a drastic drop in the density of the water as well as the density of the cells of the organisms entering the vibrating field. This alters the habitat of the organisms and discourages the organisms from adhering to the body surface.
U.S. Pat. No. 4,058,075, which issued to Piper on Nov. 15, 1977, discloses a marine life growth inhibitor device. The device is used for inhibiting marine life on the outer surface of submerged object such as boat. The device includes a controller connected to a source of electrical power and a plurality of speakers electrically connected to the controller and attached at predetermined locations on the interior of the boat""s hull, whereby vibrations may be transmitted through the hull. The controller may also include a transformer for reducing the voltage of the alternating current power source. Each of the plurality of speakers has a speaker diaphragm having first and second speaker diaphragm sides. Each of the speakers is mounted in a speaker housing secured to the hull of the boat for enabling transfer of acoustical energy from both the first and second side of the speaker diagram to the boat hull to inhibit the growth of marine life on the exterior surface of the boat hull. The speakers are selected to produce acoustical vibration in the audible range.
U.S. Pat. No. 5,143,011, which issued to Rabbette on Sep. 1, 1992, discloses a method and apparatus for inhibiting barnacle growth on boats. The system for inhibiting growth of barnacles and other marine life on the hull of a boat includes a plurality of transducers or vibrators mounted on the hull and alternately energized at a frequency of 25 Hertz through a power source preferably the boat battery, and a control system. The system has two selectable operating modes. One is continuous and the other is periodic. Also, when the voltage of the battery falls below a predetermined level, transducers are automatically deenergized to allow charging of the battery after which the transducers are energized.
U.S. Pat. No. 3,241,512, which issued to Green on Mar. 22, 1966, describes an anti-fouling, barnacles, algae, eliminator. The apparatus is intended for boats and, in particular, comprises a pair of copper bus bars or electrodes, or a pair of perforated tubes, or both the electrodes and perforated tubes positioned on opposite sides of the keel of a boat whereby copper ions, chlorine gas or bubbles, or combination of the ions and chlorine gas produced bubbles that float upward from the keel on both sides thereof following the contour lines of the boat hull cleaning the surface thereof and removing barnacles, algae, and other foreign and undesirable matter.
U.S. Pat. No. 3,625,852, which issued to Anderson on Dec. 7, 1971, describes a marine anti-fouling system. The system is intended for use with boat and ship hulls having a keel and sides diverging upwardly therefrom. The anti-fouling system comprises a pair of laterally spaced elongated anode electrode components each mounted externally on one side of the hull substantially adjacent the keel and lengthwise thereof. It also comprises an elongated cathode electrode component mounted externally on and lengthwise of the keel in spaced relationship between the anode electrode components. The system further comprises a source of electrical current and electrical circuit means therefor for energizing the anode electrode components with a positive potential and the cathode electrode components with a negative potential with the cathode electrode component being electrolytically common to the anode electrode components.
U.S. Pat. No. 5,465,676, which issued to Falcaro on Nov. 14, 1995, discloses a barnacle shield. A system for discouraging and inhibiting marine growth onto a boat""s underwater hull surface comprises a plurality of sections of foam filled PVC pipe tied together to form a flotation frame, an envelope of flexible, polyethylene, bubble wrap material, of a size and shape to enclose the underwater part of a boat""s hull, and affixed to and supported by the flotation frame, a sprinkler hose affixed to the flotation frame for injecting fresh water for washing the boat""s underwater hull, and a plurality of drain/check valves mounted in the envelope for eliminating the wash down water in the envelope.
U.S. Pat. No. 4,170,185, which issued to Murphy et al on Oct. 9, 1979, describes a means for preventing marine fouling. The effective antifouling result with respect to marine creatures such as barnacles is achieved by energizing a piezofilm layer carried on the outside of a vessel to cause mechanical vibration of the layer.
U.S. Pat. No. 4,046,094, which issued to Preiser et al on Sep. 6, 1977, discloses an antifouling system for active ships which are at rest. A system for discouraging and inhibiting growth of the entire marine fouling community onto a ship hull while it is at rest in brackish or seawater is described. A pipe or pipes having nozzles distributed therealong, run the length of the keel. Fresh water is supplied to the pipe which flows out the nozzles and up along the hull to create and maintain a moving boundary layer of fresh water. Such movement also serves to inhibit fouling. An enclosure comprising segmented, over-lapping opaque curtains hang down by weights, from the ship-deck. These curtains serve to prevent light from reaching the hull, and to protect the thin boundary layer of fresh water from the disruptive, mixing actions caused by the surrounding currents. Thus the marine fouling community, including tubeworns, barnacles, grass, and algae, may be inhibited from growing and adhering to the hull surface.
U.S. Pat. No. 4,283,461, which issued to Wooden et al on Aug. 11, 1981, describes a piezoelectric polymer antifouling coating. An antifouling coating for marine structures in the form of a film containing piezoelectric polymer material, which, when electrically activated vibrates at a selected frequency to present a surface interfacing with water which is inhospitable for attachment of vegetable and animal life including free-swimming organisms thereby discouraging their attachment and their subsequent growth thereon to the macrofoulant adult stage is disclosed.
U.S. Pat. No. 5,342,228, which issued to Magee et al on Aug. 30, 1994, discloses a marine drive which is provided with a large volume anode, about 30 cubic inches, for. galvanic protection. The anode is a brick-like block member tapered along each of its height, width, and length dimensions. The drive housing has a anode mounting section extending rearwardly therefrom and has a downwardly opening cavity of substantially the same shape and volume as the anode, and receiving the anode in nested flush relation.
U.S. Pat. No. 5,716,248, which issued to Nakamura on Feb. 10, 1998, discloses a sacrificial anode for a marine propulsion unit. The sacrificial anode arrangements for a marine propulsion unit is disclosed wherein the sacrificial anode is juxtaposed to the trim tab and is detachably connected to the lower unit housing by fastening means which can be removed from the upper surface thereof. In one embodiment, the trim tab is detachably connected to the sacrificial anode and is connected to the outer housing portion through the sacrificial anode.
U.S. Pat. No. 5,298,794, which issued to Kuragaki on Mar. 29, 1994, describes an electrical anticorrosion device for a marine propulsion apparatus. The device primarily relates to an electrical anticorrosion apparatus for a marine propulsion arrangement. More particularly, the device relates to an anodic protection arrangement which is suitable for use with an inboard/outboard propulsion unit. According to the description in this patent, an anode and the reference electrode are housed within a housing unit which is mounted upon a propulsion unit mounting bracket. The two electrodes are arranged so that each is essentially equidistant from a point located approximate midway across the lateral width of an outboard drive unit, which unit is secured to the mounting bracket, when the unit is positioned for driving the associated watercraft in a generally forward direction.
U.S. Pat. No. 4,322,633, which issued to Staerzl on Mar. 30, 1982, discloses a marine cathodic protection system. The system maintains a submerged portion of the marine drive unit at a selected potential to reduce or eliminate corrosion thereto. An anode is energized to maintain the drive unit at a pre-selected selected constant potential in response to the sensed potential at a closely located reference electrode during operation. Excessive current to the anode is sensed to provide a maximum current limitation. An integrated circuit employs a highly regulated voltage source to establish precise control of the anode energization.
U.S. Pat. No. 5,052,962, which issued to Clark on Oct. 1, 1991, describes a naval electrochemical corrosion reducing. The corrosion reducer is used with ships having a hull, a propeller mounted on a propeller shaft and extending through the hull, therein supporting the shaft, at least one thrust bearing and one seal. Improvement includes a current collector and a current reduction assembly for reducing the voltage between the hull and shaft in order to reduce corrosion due to electrolytic action. The current reduction assembly includes an electrical contact, the current collector, and the hull. The current reduction assembly further includes a device for sensing and measuring the voltage between the hull and the shaft and a device for applying a reverse voltage between the hull and the shaft so that the resulting voltage differential is from 0 to 0.05 volts. The current reduction assembly further includes a differential amplifier having a voltage differential between the hull and the shaft. The current reduction assembly further includes an amplifier and the power output circuit receiving signals from the differential amplifier and being supplied by at least one current supply. The current selector includes a brush assembly in contact with a slip ring over the shaft so that its potential may be applied to the differential amplifier.
U.S. Pat. No. 4,559,017, which issued to Cavil et al on Dec. 17, 1985, discloses a constant voltage anode system. The marine propulsion unit has a housing exposed to sea water and subject to attack by the sea water. It has a permanent type anode housing with a substantially constant surface characteristic which is mounted on the housing and supplied with constant voltage. Holes under the anode through the housing which extend to interior passages permits the current of the anode to influence and protect the passages.
U.S. Pat. No. 3,497,434, which issued to Littauer on Feb. 24, 1970, discloses a method for preventing fouling of metal in a marine environment. It anodically dissolves metals that are toxic to marine organisms. This is done under controlled conditions to prevent fouling by marine organisms of structures immersed in a marine environment.
U.S. Pat. No. 5,889,209, which issued to Piedrahita et al on Mar. 30, 1999, describes a method and apparatus for preventing biofouling of aquatic sensors. A submersible ultrasonic emitter is integrated with a dissolved oxygen or other aquatic probe so that biofouling of the sensors"" membrane is minimized. Sonification, that is, exposure to ultrasound, precludes the needs to use other biofouling elimination procedures such as water/air jets, chemical treatments, or biocides. The invention can be configured to readily integrate with existing probes from a variety of manufacturers, and eliminates membrane cleaning as the maintenance interval constraint for field or laboratory deployed sensors.
U.S. Pat. No. 5,735,226, which issued to McNeal on Apr. 7, 1998, describes a marine anti-fouling system and method. The system and method is disclosed for inhibiting the growth of marine life on a submerged surface and includes a control box and a number of transducers. The control box further includes an ultrasonic driver board, a magna-polar filter, and a power source. The ultrasonic driver board generates an electrical signal having an ultrasonic frequency which continually varies between 25 KHz and 60 KHz. A portion of this continually varying electrical signal is passed through the magna-polar filter where the signal is enhanced. This enhanced signal is then returned to the ultrasonic driver board where is combined with the electrical signal varying between 25 KHz and 60 KHz. This combined signal is then electrically communicated to a number of transducers which are mounted on the submerged surface to be protected. There, the electrical signal having combined frequencies is translated from electrical energy to acoustic energy which is transmitted to the submerged surface to inhibit the growth of marine life on the submerged surface.
U.S. Pat. No. 5,552,656, which issued to Taylor on Sep. 3, 1996, describes a self-powered anti-fouling device for watercraft. The device comprises a layer of piezoelectric material, preferably a poled plastic material such as a PVDF polymer, for mounting on the hull of a watercraft. The layer has electrodes on opposite major surfaces thereof, and the layers are connected to a power supply comprising a battery and a d.c to a.c. converter. The converter generates an a.c. voltage at a frequency, such as 20 KHz, for causing vibrations of the layer, such vibrations serving to retard the growth of water dwelling organisms in the craft. The layer electrodes are also connected to an a.c. to d.c. converter for converting a.c. energy to d.c. energy suitable for trickle charging the power supply battery. Accordingly, during transit of the craft through the water, water induced hull vibrations cause vibrations of the layer for generating a.c. energy for storage in the battery, which stored energy is used for causing anti-fouling vibrations of the energy generating layer.
U.S. Pat. No. 4,943,954, which issued to Ostlie on Jul. 24, 1990, describes a method and system for counteracting marine biologic fouling of a hull or submerged construction. A system and a method for counteracting marine fouling of a vessel hull are provided. Electro-mechanical vibration transducers are arranged in pairs adjacent to fixed nodal lines on the hull and are driven in an inverted phase relationship in order to provide a water particle movement in a hull parallel direction right outside side nodal lines in addition to the hull perpendicular relative movements right outside the transducers. The invention also comprises a combination of the mechanical system above and a special surface coating which counteracts fouling from other organisms than those influenced by the water particle movement in the infrafrequency range.
U.S. Pat. No. 4,058,075, which issued to Piper on November 15, 1977, describes a marine life growth inhibitor device. The device is used for inhibiting marine life on the outer surface of a submerged object such as a boat. The device includes a controller connected to a source of electrical power and a plurality of speakers electrically connected to the controller and attached at predetermined locations on the interior on the boat""s hull, whereby vibrations maybe transmitted through the hull. The controller may also include a transformer for reducing the voltage of the alternating current power source. Each of the plurality of speakers has a speaker diaphragm having a first and a second speaker diaphragm side. Each of the speakers is mounted in a speaker housing secured to the hull of the boat for enabling transfer of acoustical energy from both the first and second side of the speaker diaphragm to the boat hull to inhibit the growth of marine life on the exterior surface of the boat hull. The speakers are selected to produce acoustical vibration in the audible range.
U.S. Pat. No. 4,092,943, which issued Lund et al on Jun. 6, 1978, describes a marine protection system. An underwater marine protection system for preventing or retarding marine growth on vessels, pilings, in submerged structures in which a boat slip, or the like, has a series of gas diffusers placed under the water located to direct gas towards the bottom of the marine vessel is described. The gas diffusers are connected to an ozone source for direction ozone gas through the diffusers towards the bottom of a boat. Skirts or curtains are connected to the pilings in the boat slip to prevent the free flow of water into and out of the slip where the water has been treated. A special top extends across the slip and around the vessel therein to increase the effectiveness of the ozone. An alternate embodiment has the gas diffusers formed in the bottom of the boat or submarine structure.
U.S. Pat. No. 4,170,185, which issued to Murphy et al on Oct. 9, 1979, discloses a system for preventing marine fouling. The effective antifouling result with respect to marine creatures such as barnacles is achieved by energizing a piezofilm layer carried on the outside of a vessel to cause mechanical vibrations of the layer.
U.S. Pat. No. 3,069,336, which issued to Waite et al on Dec. 18, 1962, discloses a means for protecting ships"" hulls. The system relates to ships and in particular to the protection of metal hulls against corrosion, but it further relates to the protection of ships"" hulls against fouling with barnacles or other similar marine growth and marine vegetation.
U.S. Pat. No. 3,766,032, which issued to Yelser on Oct. 16, 1973, discloses a method for controlling marine fouling. An electrical apparatus and method is disclosed for eliminating the fouling of boat bottoms and the like by marine growth. The underwater surface is sheathed with strips of metal such as stainless steel. An electric current is passed between the adjacent strips or areas, preferably for short periods of time on a regular maintenance schedule (e.g. 30 amperes per square foot for a few seconds every two days). The sheathing may be of 0.020xe2x80x3 stainless steel in 3-inch wide strips spaced 0.100 inches apart. Test panels in sea water are found to remain clean and bright after six months immersion when so energized, while identical panels to which no current is applied become heavily fouled. Ions produced by electrolysis close to the sheathed surface move at relatively high velocities, and are found to kill the small organisms that settle on the surface. No persistent toxic chemicals such as mercury compounds are released into the water, and only minute quantities of dead organic matter are released at any time.
U.S. Pat. No. 3,661,742, which issued to Osborn et al on May 9, 1972, describes an electrolytic method of marine fouling control. The improved method of inhibiting the sustained attachment of marine organisms to metallic surfaces while preventing corrosion of the metallic surfaces by cathodic protection is disclosed. Inhibition of marine organisms attachment takes place when toxic ions are forced into solution by reversing and increasing the current density in the cathodic protection system at periodic intervals for short periods of time.
U.S. Pat. No. 1,021,734, which issued to Delius et al on Mar. 26, 1912, describes a process for protecting ships from barnacles. The invention relates to sea going vessels which have hulls which are either made of metal or sheathed with metal and is intended for protection of vessels from the accumulation of barnacles. This is accomplished by providing a means for electrically destroying the barnacles that may be attached to the ship.
U.S. Pat. No. 4,869,016, which issued to Diprose et al on Sep. 26, 1989, describes a marine biofouling reduction invention. The method provides a substantial reduction of marine corrosion in sea water by micro and macro biofouling. An alternating current is generated of sufficient strength and frequency sufficient to shock marine biofouling organisms and sufficient to upset the normal behavior patterns of the marine biofouling organisms and trained in the sea water passing around or through the structure. The device causes release into the water around or within the structure controlled amounts of chlorine ions and copper ions to produce an environment actively hostile to potential marine biofouling organisms.
U.S. Pat. No. 5,088,432, which issued to Usami et al on Feb. 18, 1992, describes a system for providing anti-fouling for substances in contact with sea water. It comprises a first conductive membrane that is coated on the outer side of the electric insulator mounted at the surface of the substance such as ships and composes thin sheets of metal having low specific resistance or metal oxide, spray-coated membrane, evaporated membrane, or fused membrane. The second conductive anti-fouling membrane has a higher electric resistance than the first conductive membrane.
U.S. Pat. No. 5,820,737, which issued to Kohn on Oct. 13, 1998, describes an anti-fouling laminate marine structure. The structure is submersible in sea water, such as a boat hull, and is electrically activated. The hull is formed of inner and outer skins. The outer skin forms an exposed surface and is coated with a metallic paint defining a cathode electrode. The core is constituted by balsa wood or foam plastic modules. This is attached to an open mesh material that includes conductive fibers to create an electrical grid defining anodic electrode that is embedded in the laminate.
U.S. Pat. No. 6,209,472, which issued to Staerzl on Apr. 3, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. The system for inhibiting marine organism growth on underwater surfaces provides an electric current generator which causes an electric current to flow proximate the underwater surface. A power source, such as a battery, provides electrical power to the electric current generator. The flow of current passes from the underwater surface through the water surrounding the surface or in contact with the surface and a point of ground potential. The point of ground potential can be a marine propulsion system attached to a boat on which the underwater surface is contained.
U.S. Pat. No. 948,355, which issued to Tatro et al on Feb. 8, 1910, describes an expeditious and inexpensive means for removing pests from ship""s bottoms and for protecting from such pests any non-metallic objects located or moving under seawater. The system uses the anode and the cathode of an electric battery and the two poles of the battery must both be in contact with the seawater so that the circuit of the electric current must be completed through the water.
U.S. Pat. No. 6,173,669, which issued to Staerzl on Jan. 16, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. The marine fouling prevention system comprises two conductive surfaces and a device that alternates the direction of the electric current between the two surfaces. The current is caused to flow through seawater in which the two surfaces are submerged or partially submerged. A monitor measures the current flowing from one of the two conduction surfaces and compares it to the current flowing into the other conduction surface to assure that no leakage of current of substantial quantity exists. The system applies a low magnitude current density, of approximately 0.10 to 0.50 milliamperes per square foot, for an extended duration of time of approximately 10 to 20 minutes. By alternating current direction between the two surfaces, both surfaces can be provided with sufficient chlorine bubbles to prevent marine growth from attaching to the surfaces.
U.S. Pat. No. 5,929,159, which issued to Schutt et al on Jul. 27, 1999, describes an oligomeric silicon coating composition, articles coated therewith and method for forming coating composition and coated articles based thereon. Corrosion resistant coatings are provided by aqueous-alcoholic acidic dispersions of the partial condensate of monomethyl silanol (by hydrolysis of monomethyl alkoxysilane) alone or in admixture with minor amounts of other silanol, e.g. gamma-glycidyloxy silanol, phenyl silanol, etc., wherein the dispersions contain divalent metal cations, e.g., Ca+2, in place of all or most of colloidal silica used in prior formulations of this type. The coatings may be applied to boat hulls, including aluminum hulls and are effective in preventing corrosion from salt water for extended periods.
U.S. Pat. No. 3,721,574, which issued to Schneider et al on Mar. 20, 1973, describes silicate coatings compositions. Water resistant and air drying alkali metal silicate coatings contain a base of an alkali metal silicate solution having a high molar ratio of solvated silica to alkali metal oxide. To this base is added colloidal silica in amounts to increase the SiO2:alkali metal oxide mole ratio to as high as 9:1. The compositions are advantageously modified with silane wetting agents and multivalent metal ions, e.g., calcium. Ultimately, the coatings may be modified with various materials such as tetrafloroethylene polymer or zinc.
U.S. Pat. No. 4,162,169, which issued to Schutt on Jul. 24, 1979 describes an alkali-metal silicate binder and methods of manufacture. A paint binder utilizing a potassium or sodium silicate dispersion having a silicon dioxide to alkali-metal oxide mol ratio of from 4.8:1 to 6.0:1, in which the binder exhibits stability during both manufacture and storage is disclosed. The process of making the binder is predictable and repeatable and the binder may be made with inexpensive components. The high mol ratio is achieved with the inclusion of a silicon dioxide hydrogel. The binder, which also employs a silicone, is in the final form of a hydrogel sol.
U.S. Pat. No. 6,187,447, which issued to Stein et al on Feb. 13, 2001, describes a condensation curable silicone foul release coatings and articles coated therewith. Anti-fouling coatings comprise a room temperature vulcanizable polyorganosiloxane composition and a polyorganosiloxane free from silanol groups and comprising at least one hydroxy- or alkoxy-terminated polyoxyalkylenealkyl radical. The latter is capable of blooming to the surface of the cured room temperature vulcanizable composition, thus inhibiting the deposition of marine life on the coated article.
U.S. Pat. No. 6,161,989, which issued to Kotani et al on Dec. 19, 2000, describes an antifouling wall structure for use in pipe and method of constructing the antifouling wall therefor. A wall surface of a structure to be rendered antifouling is covered with antifouling panels caused to firmly adhere thereto and fixed. Not only can this work be conducted easily and quickly but also part of the antifouling panels can be easily replaced. The disclosed antifouling wall structure and the method of constructing the antifouling wall are characterized in that antifouling panels each comprising a base material layer and, formed thereon, an antifouling paint layer are arranged on a wall surface of structure to be rendered antifouling so that the antifouling panels have their side of antifouling paint layer brought into contact with water and detachably fixed by means of fastening members.
U.S. Pat. No. 5,344,531, which issued to Saito et al on Sep. 6, 1994, describes a prevention method of aquatic attaching fouling organisms and its apparatus. The invention relates to a method of preventing or controlling aquatic attaching fouling organisms which comprises covering aquatic organisms attaching portions on the surfaces of submerged structures or intake facilities with a plurality of mutually insulated metallic covers made of iron, magnesium, aluminum or their alloys through an insulating material and a cushion; using each of the metallic covers as an electrode; forming an electric circuit using the metallic covers facing each as a pair, connecting the electrode to a D.C. power supply having a polarity reversal function so as to supply a current between both poles either continuously or intermittently, and reversing the polarity of the current so that when one of the metallic covers is an anode, the surface of the metal constituting the metallic cover is dissolved and activated, and attachment of the aquatic fouling organisms to the surfaces of the metallic covers is prevented or controlled.
World Intellectual Property Organization patent application WO 98/18855, which was filed by Gedeon et al on Oct. 23, 1999 and assigned the International Application number PCT/US97/18964, describes a silicon coating composition. Corrosion resistant coatings are provided by Aqueous-alcoholic acidic dispersions of the partial condensate of monomethyl silanol (by hydrolysis of monomethyl alkoxysilane) alone or in mixture with minor amounts of other silanol (e.g., gamma-glycidyloxy silanol, phenyl silanol, etc.) wherein the dispersions contain divalent metal cations (e.g., Ca+2) in place of all or most of colloidal silica used in prior formulations of this type. The coatings may be applied to boat hull, including aluminum hulls and are effective in preventing corrosion from salt water for extended periods.
U.S. Pat. No. 4,196,064, which issued to Harms et al on Apr. 1, 1980, describes a marine fouling control apparatus. A structure exposed to a marine environment is coated with a coating comprising stainless steel particles such as stainless steel flakes in a coating matrix. Marine growth is removed from the coating by impressing an electrical potential. Marine growth is also prevented. Preferably, the structure is coated with a first coating comprising metallic zinc prior to coating with a second coating comprising stainless steel flakes in an inorganic polymer matrix, and a cathodic potential is impressed.
U.S. Pat. No. 4,297,394, which issued to Wooden et al on Oct. 27, 1981, describes a piezoelectric polymer antifouling coating and method of use and application. An antifouling coating with method of use and method of application on marine structures in the form of a film containing piezoelectric polymer material, which, when electrically activated vibrates at a selected frequency to present a surface interfacing with water which is inhospitable for attachment of vegetable and animal life including free-swimming organisms thereby discouraging their attachment and their subsequent growth thereon to the macrofoulant adult stage.
Certain types of ambient temperature cured glass (ATC glass) is available in commercial quantities from the Adsil Corporation. According to Adsil, the ambient temperature cured glass offers the combined benefits of low toxicity and high protection from most causes of corrosion. It is made from glass and is impervious to nearly all corrosive materials. Covalent bonding allows these glass coatings to permanently adhere with nearly any surface. The silica is absorbed into small gaps in the surface of the material and, according to Adsil, even between molecules. As a result of the unique properties of covalent bonding, these glass coatings permanently adhere to most metals such as copper, aluminum, stainless and galvanized steel, and other metals. It is usable on painted metals, fiberglass, roofing materials, cement, bricks, and tile. The inorganic glass coatings are chemically engineered to form a permanent bond with whatever surface on which it is applied. Described by the term xe2x80x9ccovalent bondingxe2x80x9d, these coatings work their way into minute gaps in the surface. Covalent bonding allows the coating to grip the surface. The coating does not degrade.
The patents described above are hereby explicitly incorporated by reference in the following description.
As described above, fouling of underwater surfaces has been recognized as a problem for many years. Anti-fouling techniques, such as biocidal paints, can contribute to the pollution of waterways. Many other methods simply are not effective. It would therefore be significantly beneficial if a device or method could be developed which does not pollute the environment, but which effectively inhibits the growth of marine organisms on surfaces which are submerged in water such as boat hulls, pipes, pilings, and grates.
The Staerzl patents describe above (i.e. U.S. Pat. Nos. 6,173,669 and 6,209,472) are generally related to systems and apparatus which cause an electric current to flow between submerged conductive materials and other electrodes in such a way that gaseous chlorine is formed on the surface of the material when the electrically conductive material is connected as an anode to a source of power, such as a current source. It has been determined that the production of chlorine gas in this way is effective in inhibiting the growth of organic material, such as barnacles, on the surface.
The conductive material used to create the gaseous chlorine on its surface can be virtually any conductive material. However, the properties of certain conductive materials significantly affect the applicability of those materials for these purposes. For example, the use of an active metal as an anode can result in a degradation of the metallic electrode because metallic ions are typically emitted from the conductive materials into the surrounding seawater. This is a natural result caused by the use of the active metal as an anode in the circuit. Other materials, such as graphite, do not exhibit this tendency to give off ions into the seawater and, therefore, are not eroded in this way. However, materials such as graphite also exhibit a higher resistance to electric current flow because of the manner in which the coating is typically formulated. Other materials, such as silver, gold, and platinum, could serve as effective electrodes for the purpose of producing gaseous chlorine, but these materials are expensive and therefore could not be used in large quantities without being cost prohibitive.
It would therefore be significantly beneficial if an electrically conductive coating, such as a paint, could be used for these purposes in which an active metal such as nickel acts as the electrode. The use of an electrically conductive paint would also allow the system to be used in conjunction with non metallic materials, such as fiberglass hulls of marine vessels. It would also be significantly beneficial if a means could be provided for inhibiting the movement of ions from the electrically conductive material into the surrounding seawater which could otherwise result in the rapid corrosion and degradation of the electrically conductive material.
An apparatus for inhibiting the fouling of an underwater object made in accordance with the present invention, comprises an electrically conductive surface of the underwater object. This electrically conductive surface can be the surface of an electrically conductive material or, alternatively, the electrically conductive surface can be a conductive coating disposed on the surface on the underwater object. The present invention further comprises an electric current source which is connectable in electrical communication with the electrically conductive surface. The electric current source can be a power supply, associated with a battery, that provides a DC current to the electrically conductive surface.
The present invention further comprises a protective coating disposed on the electrically conductive surface. In a particularly preferred embodiment of the present invention, the protective coating is a glass coating which inhibits the flow of ions from the electrically conductive surface into the surrounding water, but readily permits the flow of electrons through the protective coating. The present invention further comprises an electrode which is connectable in electrically communication with the electric current source in order to form an electrical circuit comprising the electrically conductive surface, the electric current source, the electrode, and the water in which both the electrode and the electrically conductive surface are disposed.
The protective coating can be a glass coating and, in a particularly preferred embodiment of the present invention, can be an ambient temperature cure glass such as that is available in commercial quantities from the Adsil Corporation. That type of ambient temperature cure glass (ATC Glass) is described above.
If the underwater object is made of metal, the electrically conductive surface can comprise the same material as the underwater object and, is actually the surface of the underwater object itself. However, the electrically conductive service can also be a conductive coating disposed on the underwater object when the underwater object is non metallic in nature. For example, the electrically conductive surface can be a nickel coating or a graphite coating. The electric current flowing through the electrical circuit described above can be unidirectional or, alternatively, can be periodically reversed with the electrically conductive surface alternatively acting as an anode and a cathode of the electrical circuit.
The protective coating, used in a preferred embodiment of the present invention, discourages ionic transfer between the electrically conductive surface and the water, which is typically seawater, but the protective coating permits electron transfer between the electrically conductive surface and the water. The underwater object can be a boat hull. The electrode of the present invention can comprise a second electrically conductive surface identical to the electrically conductive surface described above. In addition, the second electrically conductive surface can be a surface of a second underwater object. For example, two portions of a boat hull can be electrically isolated from each other and connected only through the electrical circuit described above. In this way, the two surfaces provide first and second electrically conductive surfaces that alternatively are connected as the anode and the cathode in the electrical circuit. Under the various embodiments of the present invention, gaseous chlorine is formed on the protective coating which is, in turn, deposited on the conductive surface.
The method of the present invention for inhibiting the fouling of an underwater object comprises the steps of providing an electrically conductive surface of the underwater object, causing an electric current to flow through the electrically conductive surface, disposing a protective coating on the electrically conductive surface, and connecting an electrode in electrical communication with the electrically conductive surface to form an electrical circuit comprising the electrode, the electrically conductive surface, and the water in which both the electrode and the electrically conductive surface are disposed. The electrode can be a second electrically conductive surface similar to the first, wherein the first and second electrically conducted surfaces are alternatively applied as anode and cathode in the electrical circuit.

System for inhibiting fouling of an underwater surface


An olefin polymerization process is provided comprising contacting an olefin monomer with chromium oxide on a titanium containing silica support having less than about 3 weight percent titanium in combination with an organoboron promoter. Polymers thus produced are useful for blow molding applications.

This invention relates to modified supported chromium oxide olefin polymerization catalyst systems.
It further relates to a method of making ethylene polymers and copolymers.
Supported chromium oxide catalyst systems have been used for many years in the polymerization of olefins. Ethylene can be polymerized by contacting the monomer with a silica-supported chromium oxide catalyst systems, the reaction being carried out in an inert liquid at temperatures below 110xc2x0 C. for producing solid polymer suspended in the liquid or at temperatures above 110xc2x0 C. for solution polymerization. The properties of the resulting polymer depend upon a number of factors, including the type of catalyst system employed and its activation temperature, the reaction pressure, and the reaction temperature. It is generally known that titanium can be added to the supported chromium oxide catalyst systems to produce a polymer having an increased melt index and a broader molecular weight distribution. It is also generally known that certain substances called promoters or adjuvants can be used in combination with chromium oxide catalyst systems to modify the properties of the polymer.
The use of chromium catalyst systems with certain organoboron promoters generally is known to broaden the polymer molecular weight distribution. Use of titanium in the catalyst system support or boron adjuvants in the reactor can result in improvements in the environmental stress crack resistance (ESCR) of the resultant polymers, as well as increased catalyst system productivity. Unfortunately, these modifications can increase the amount of low molecular weight polymer and oligomers that are formed. Low molecular weight polymers and oligomers can contribute smoke and odor during the processing of the polymer, or resin, as it is molded into bottles and other articles of manufacture.
Another important characteristic of a blow molding resin is the swell properties of the resin. Two kinds of swell are critical during blow molding. These are xe2x80x9cweight swellxe2x80x9d and xe2x80x9cdiameter swellxe2x80x9d; the later also is referred to herein as xe2x80x9cdie swellxe2x80x9d. As polymer, or resin, is extruded under pressure through a die opening and into a mold, a polymer has a tendency to swell as it exits the die. This is known as weight swell and can be determinative of the thickness of bottle wall, as well as the overall weight of the resultant blow molded product. For example, a resin which is extruded through a 0.02 inch die gap might yield a bottle wall thickness of 0.06 inches, in which case the weight swell is said to be 300%. A resin that swells too much can produce a bottle with too thick of a wall. To compensate, the die opening, or gap, can be narrowed by manual adjustment. However, any decrease in die gap can increase the resistance to the flow of the resin through the die. Narrower die gaps can result in higher shear rates during extrusion which also can increase melt fracture leading to a rough bottle surface. Thus, a resin which can be described as easily processable must exhibit low weight swell, which allows a wide die gap.
Diameter, or die, swell refers to how much a parison flares out as it is extruded from the die. For example, a resin extruded through a circular die of one (1) inch diameter can yield a parison tube of 1.5 inches in diameter; the die swell is said to be 50%. Die swell is significant because molds usually are designed for a certain amount of flare; too much die swell can interfere with molding of a bottle handle. A high degree of weight swell often causes high die swell because of the narrow die gap. Unfortunately, a narrow gap also increases the resistance to polymer flow. Thus, as used herein, a polymer which is considered easily processable also should exhibit low die swell.
Attempts have been made to obtain ethylene polymers having a broader molecular weight distribution (MWD) and consequent improved environmental stress crack resistance imparted by organoboron promoters and titania-containing catalyst systems. One of the most prevalent problems associated with such attempts is an increase of the amount of swell exhibited by the resin as it exits the die. Swell can be decreased by raising the activation temperature of the catalyst system, however, this also can reduce the polymer ESCR. Swell also can be decreased by lowering the melt index (MI), but this generally makes the resin more difficult to process, as measured by output rate and melt fracture. Swell also can be decreased by adding more chromium to the catalyst system, but this tends to impart a dirty color to the final polymer product. Thus, it has been difficult to produce a resin that maintains good swell and processing characteristics, high ESCR, and a low volatiles content.
It is an object of this invention to provide a process by which high density ethylene polymers and copolymers can be manufactured having a high stress crack resistance are prepared in high yield.
It is a further object of the invention to minimize the production of oligomers and low molecular weight polymer during the polymerization process.
It is a further object of this invention to minimize the amount of die swell and weight swell exhibited by the resin during molding.
It is a further object of this invention to provide a blow molding polymer which processes well in the blow molding machine.
In accordance with one embodiment of the invention, a polymerization catalyst system is provided which comprises chromium oxide on a silica-titania, wherein said support comprises less than about 3 weight percent titanium, in combination with an organoboron promoter. Further according to the invention, an ethylene polymer or copolymer is produced by contacting an ethylene monomer, and an optional comonomer, with an activated catalyst system comprising chromium oxide on a silica-titania, wherein said support comprises less than about 3 weight percent titanium, in the presence of an organoboron promoter. The resulting polymer is produced in high yield and has a combination of improved properties, including high shear response, good environmental stress crack resistance, and high density.
The silica containing substrates, or supports, used in the invention catalyst systems are silica or silica-alumina gels. Such gels conventionally are prepared by mixing an acid such as sulfuric acid with an aqueous solution of an alkali metal silicate such as sodium silicate to produce an aqueous gel, or hydrogel. The silicate preferably is added to the acid, and the reaction mixture is strongly agitated. The mixing temperature can range from about 1xc2x0 C. to about 43xc2x0 C. The resulting hydrogel is approximately 3 to about 12 weight percent SiO2 and has a pH in a range of about 3 to about 9. The hydrogel is aged at a temperature of about 18xc2x0 C. to 98xc2x0 C. for a suitable time, generally more than one hour. Silica gels often have a minor portion, generally not exceeding 20 weight percent, of alumina or other metal oxides, an the support of the invention includes composite silica gels comprising silica and alumina, thoria, zirconia and like substances.
As used in this disclosure, the term xe2x80x9csupportxe2x80x9d refers to a carrier for another catalytic component. However, by no means, is a support necessarily an inert material; it is possible that a support can contribute to catalytic activity and selectivity.
The hydrogel then is washed with water and either an ammonium salt solution or a dilute acid to reduce the alkali metal content of the hydrogel to less than about 0.1 weight percent. The ammonium salt solution is preferably one such as ammonium nitrate or an ammonium salt of an organic acid which volatizes upon subsequent calcination.
Water in the hydrogel can be removed by any conventional method, such as, foe example, by spray drying, vacuum oven drying, or air oven drying at temperatures above 100xc2x0 C. If the hydrogel is dried by heating, it is not necessary to add an agent to the gel to prevent shrinkage of the pores.
The support must comprise titanium. Titanation of the silica can be effected using a variety of methods. The titanated catalyst systems must comprise no more than about 3 weight percent titanium, based on the weight of the catalyst system (not including the organoboron component), after calcining. All or part of the titanium can be supplied by coprecipitation of silica and titania. In the coprecipitation method, a titanium compound, such as, for example, a titanium halide, nitrate, sulfate, oxalate, or alkyl titanate, can be incorporated with the acid or the silicate in an amount such that the amount of titanium present as titanium dioxide in the final calcined catalyst system is less than about 3 weight percent. The amount of titanium in the calcined catalyst system generally will be about 0.5 weight percent to about 3.0 weight percent, preferably within a range of about 0.5 to about 2.6 weight percent. Most preferably, the amount of titanium in the catalyst system support is within a range of 0.8 to 1.5 weight percent. The coprecipitation of titania with silica is disclosed in U.S. Pat. No. 3,887,494, the disclosure of which is hereby incorporated by reference.
Titanation of the catalyst system support alternatively can be effected by impregnation of the hydrogel or xerogel before or after incorporation of the chromium component of the catalyst system. For example, an aqueous solution of a hydrolysis-resistant titanium compound can be incorporated into a silica hydrogel and dried by conventional techniques.
Titanation of the silica support also can be accomplished by adding a titanium compound to the silica xerogel, usually with heat to vaporize the solvent and cause titanium to be deposited on the support.
Particularly advantageous catalyst systems useful in this invention are silica-titanias created by twice aging, as disclosed in U.S. Pat. No. 4,981,831, the disclosure of which is hereby incorporated by reference.
The chromium component of the catalyst system comprises about 0.5% to about 4% weight percent chromium, preferably about 0.8 to about 2.0 weight percent, based on the weight of the calcined catalyst system and most preferably between 0.8 and 1.5% weight percent. The chromium component can be coprecipitated with the silica or the silica-titania or added by means of an nonaqueous solution of a chromium compound such as tertiary butyl chromate to the xerogel, but preferably it is introduced by incorporating an aqueous solution of a water soluble chromium compound into the hydrogel after washing the hydrogel to remove alkali metal ions. Suitable chromium compounds include chromium acetate, chromium nitrate, chromium sulfate, chromium trioxide, ammonium chromate or any other chromium compound which can be converted to chromium oxide by calcination with at least part of the chromium being converted to the hexavalent state. As used herein, the term xe2x80x9cchromium oxidexe2x80x9d, as used to describe the chromium compound present in the catalyst system after calcining, includes fixed surface chromates formed by the reaction of chromium oxide and silica, as discussed in Hogan, J. Poly. Sci. A-1, 8, 2637-2652 (1970). The chromium compound can be employed in any amount so as to provide the desired weight percent chromium in the final catalyst system.
The catalyst system can be activated by calcining at a temperature within the range of about 530xc2x0 C. to about 650xc2x0 C. in a dry atmosphere containing oxygen, usually dry air, for a time of about 10 minutes to 20 hours or longer. Activation can follow titanation of the catalyst system in the activator, as described above, by heating the fluidized catalyst system sample to about 316xc2x0 C., substituting dry air for the nitrogen atmosphere present during titanation, raising the temperature to at least about 400xc2x0 C., and calcining the fluidized catalyst system at this elevated temperature for any appropriate activation time. Following activation, the catalyst system must be stored in a dry, inert atmosphere until used.
Catalyst systems of this invention do not require a reduction step using carbon monoxide or other reducing treatments. In fact, such reduction treatments can be detrimental to this invention because they can narrow the molecular weight distribution and lower the density of the resin beyond that which is desirable for blow molding.
The resultant chromium on silica-titania catalyst system must be of a certain porosity. The pore volume of the resultant catalyst system preferably is within a range of about 0.6 to about 1.4 milliliters per gram and preferably within a range of about 0.7 to about 1.3 milliliters per gram. Most preferably, for best catalyst system activity and most improved polymer product properties, the pore volume of the catalyst system is within a range of 0.8 to 1.1 milliliters per gram. Higher pore volumes tend to give higher swell in the resin, and lower pore volumes destroy the activity of the catalyst system.
The surface area of the catalyst system must be within a range of about 100 m2/gram to about 500 m2/gram, preferably within a range of about 200 m2/gram to about 400 m2/gram. Most preferably, the surface area of the catalyst system, for best catalyst system productivity and best resultant polymer processing properties is within a range of 300 m2/gram to 400 m2/gram.
The resultant pore diameter is important because it can affect the amount of swell in the resin. As used here, the pore diameter is calculated by the equation: Pore diameter=4(Pore Volume)/(Surface Area). The pore diameter must be from about 50 angstroms (xc3x85) to about 150 xc3x85, preferably between 60 xc3x85 and 140 xc3x85, and most preferably between 70 xc3x85 and 120 xc3x85.
Organoboron compounds used as promoters with the silica-titania chromium oxide catalyst systems of the invention can be expressed as BR3, wherein each R is selected independently from hydrogen, alkyl, cycloalkyl and aryl, at least one R in each compound being a hydrocarbon radical having from 1 to 12 carbon atoms, with the total number of carbon atoms not exceeding 30 in each compound. Examples of suitable boron promoters include trimethylborane, triethylborane, tri-n-dodecylborane, tricyclohexylborane, tri(2-methylcyclopentyl)borane, triphenylborane, tribenzylborane, tri(2-ethylphenyl)borane, methyldiethylborane, and like compounds. Boron compounds such as diborane which can form an organoboron compound in-situ, on contact with the olefin monomer(s), also are suitable. Trialkylboranes presently are preferred because of their availability.
The amount of boron compound used is generally within a range of about 0.1 to about 10 weight percent, based on the weight of the calcined catalyst system fed to the polymerization reactor. In a continuous particle form process using a loop reactor, for example, it is convenient to introduce the organoboron compound as a separate stream into the reactor, either continuously or in pulses, as a dilute solution in an inert hydrocarbon, e.g., 0.1 weight percent in isobutane. The concentration of the organoboron compound also can be expressed in parts per million (ppm) based on the diluent used in the polymerization reactor. Weight percent ranges of organoboron compounds should be from about 0.1ppm to about 2 ppm organoboron compound, based on the amount of diluent charged in a continuous particle form process using a loop reactor. Preferably it should be from 0.3 ppm to 1.5 ppm, and most preferably it should be from 0.8 ppm to 1.3 ppm. Higher levels of the boron compound can generate more volatile components, and lower amounts do not give sufficiently high ESCR.
Polymers produced in accordance with the process of this invention are homopolymers of ethylene and copolymers of ethylene and higher alpha-olefin comonomers. Preferably, the ethylene concentration in the polymerization reactor is within a range of from about 2 weight percent to about 20 weight percent, based on the total liquid content of the reactor. Most preferably, the ethylene concentration in the polymerization reactor is within a range of from about 4 to about 15 weight percent. Measured in another manner, ethylene concentration in the polymerization reactor flash gas is within a range of from about 2 weight percent to about 12 weight percent. Most preferably, the ethylene concentration in the polymerization reactor flash gas is within a range of from about 3 to about 8 weight percent. Ethylene concentration in the reactor can significantly affect the molecular weight of the resultant polymer and also catalyst system activity.
Alpha-olefin comonomers used in the present invention must be selected from the group consisting of 1-butene, 1-hexene, and mixtures thereof in order to produce a copolymer with desirable properties as well as ease of use in a loop/slurry polymerization reaction process. The most preferred comonomer is 1-hexene to produce a copolymer with the best product properties. If a comonomer is present during polymerization, the comonomer concentration in the polymerization reactor is within a range of from about 0.1 to about 10 weight percent. Most preferably, comonomer is present within a range of about 0.2 to about 2 weight percent.
Polymerization of the olefin monomer(s) must be carried out under loop/slurry polymerization conditions wherein the temperature is kept below the temperature at which polymer swells. Such polymerization techniques are well known in the art and are disclosed, for instance, in Norwood, U.S. Pat. No. 3,248,179, the disclosure of which is herein incorporated by reference. A light diluent, loop polymerization process is much more preferred than a stirred tank reactor because a stirred tank cannot contain isobutane, which is necessary to produce other commercially popular high density polyethylene polymer product grades. A loop reactor also has an advantage in that isobutane diluent can be flashed off during polymer recovery, eliminating the necessity of separating polymer product from solvent. Additionally, the greater heat transfer surface of a loop reactor offers much more versatility for plant operation, and often less polymer swelling during polymerization.
Polymerization reaction temperature in the reactor, or reaction zone, according to this invention, is critical and is dependant on the type of catalyst system employed. Polymerization reaction temperatures usually must be within a range of about 200xc2x0 F. to about 230xc2x0 F. (93xc2x0 C. to 110xc2x0 C.), preferably within a range of about 210xc2x0 F. to about 225xc2x0 F. (99xc2x0 C. to 107xc2x0 C.). Most preferably, the reaction zone temperature is within a range of 210xc2x0 F. to 220xc2x0 F. (99xc2x0 C. to 104xc2x0 C.). Too high of a reactor temperature can produce a polymer with too low of a molecular weight; or even to a fouled reactor. Too low of a reactor temperature can make the polymerization process inoperable because a lower reactor temperature can be difficult to maintain due to the exothermic polymerization reaction, flashing off reactor diluent can be difficult, and can produce a polymer with a commercially unacceptably high molecular weight.
Polymers produced in accordance with this invention are homopolymers of ethylene and copolymers of ethylene and higher alpha-olefin comonomers. Polymers produced according to this invention are much more easily processed than polymers produced in accordance with different polymerization processes. The high load melt index (HLMI) usually is within a range of about 5 g/10 mins to about 25 g/10 mins, preferably within a range of about 8 g/10 mins to about 20 g/10 minutes. Most preferably, the HLMI of the polymer product is within a range of 10 g/10 mins to 16 g/10 mins. The HLMI/MI ratio of polymers produced in accordance with this invention is relatively high and usually is within a range of about 100 to about 250, preferably within a range of about 140 to about 230; most preferably the HLMI/MI ratio is within a range of 160 to 200.
These polymers also have a broad molecular weight distribution as evidenced by Mw/Mn. Usually the Mw/Mn ratio is within a range of about 15 to about 30, preferably within a range of about 15 to about 26. Most preferably the Mw/Mn ratio is within a range of 18 to 23. These polymers also have a very narrow density range, usually within a range of about 0.950 g/cc to about 0.960 g/cc. Preferably the density is within a range of about 0.952 g/cc to about 0.958 g/cc and most preferably the density is within a range of 0.953 g/cc to 0.957 g/cc.
Polymers produced in accordance with this invention also have a very high environmental stress crack resistance (ESCR). Generally, under Condition A, the ESCR is greater than about 400 hours, preferably greater than about 500 hours and most preferably the ESCR, condition A is greater than 600 hours. The modified Condition B ESCR usually is greater than about 50 hours, preferably greater than about 65 hours, and most preferably greater than 80 hours.
Polymers of this invention also have excellent processing characteristics, as indicated by a high shear rate at the onset of melt fracture. The shear rate at onset of melt fracture is at least about 2000 secxe2x88x921, preferably greater than about 2100 secxe2x88x921, and most preferably greater than 2200 secxe2x88x921. Polymers of this invention also have high output rates from a blow molding machine, at least 1200 grams per minute (g/min), preferably greater than 1300 g/min, and most preferably greater than 1350 g/min.
Polymers of this invention are characterized as having low swell characteristics, too. They usually exhibit less than about 42% diameter swell, preferably less than about 39%, and most preferably less than 35%. The weight swell of polymers of this invention usually is less than about 380%, preferably less than about 350%, and most preferably less than 330%.
Polymers of this invention also are characterized as having a low volatile content, or smoke content. This means that they should contain less than 2% of their weight as oligomeric components having less than 1000 molecular weight. Preferably, these polymers comprise less than about 1.6 weight % below 1000 MW, and most preferably these polymers comprise less than 1.4% material below 1000 in molecular weight. These polymers should also contain less than about 0.7% xylene solubles, preferably less than about 0.65%, and most preferably less than 0.6 % xylene solubles.
The following examples are provided to further assist a person skilled in the art with understanding the invention. The particular reactants, conditions, and other variables are intended to be generally illustrative of these inventions and are not meant to be construed to the unduly limiting the reasonable scope of the invention.
Catalyst systems used for the production of the inventive resins 17-21 and control resin 22, were based on low porosity Cr/silica-titania commercially available from W.R. Grace Company as 965 Sylopore(copyright). It contained 2.5 weight percent titanium as titania and originally 1.0 weight percent chromium. Sylopore(copyright) has a pore volume of about 1.0 cc/g and a surface area of usually about 380 m2/g. Specific measurements may be shown in the Tables that follow. In some Runs, both inventive Runs and control Runs, extra chromium was added through impregnation of a 0.5% methanol solution of chromium nitrate, as indicated in the Tables.
Control resins were made from several other types of commercial catalyst systems commercially available from W.R. Grace. The catalyst 969MS (sometimes also referred to as 1% Cr on Grade 952 silica), used for Runs 1-10, had a pore volume of about 1.6 cc/g and a surface area around 300 m2/g.
Run 11 was made using a HA30 support, from W.R.Grace, having the properties listed in the Tables.
Runs 12-14, were made by a catalyst system described as chromium on HPVSA silica. This silica also was made by W.R. Grace and had a surface area of about 580 m2/g and a pore volume of about 2.2 cc/g.
Another silica support used in Runs 15 and 16, labeled HPV, had a pore volume of 2.5 cc/g and a surface area of 300 m2/g.
Some polymers, or resins, were made from 964 Magnapore(copyright), Runs 23-34, and 963 Magnapore(copyright), Runs 35-48, and which contained 1.0, 2.0 or 3.0 weight percent chromium on a high porosity silica-titania and either 2.5 or 5.0 weight percent titanium, as indicated. 964 Magnapore(copyright) has a pore volume of 2.3 cc/g and a surface area of 540 m2/g. 963 Magnapore(copyright) has a pore volume of 2.6 cc/g and a surface area of 520 m2/g.
The catalyst system used in Runs 49-61 was similar to 963 Magnapore(copyright), but had only one (1) weight percent titania in the support.
Another catalyst system was used in Runs 62-64 and was prepared by W.R.Grace by depositing aluminophosphate (P/Al molar ratio of 0.6) into the pores of silica. This material had a pore volume of 1.3 cc/g and a surface area of 250 m2/g.
Ethylene polymers were prepared using these catalyst systems in a continuous particle form process (also known as a slurry loop process) by contacting a catalyst system with a ethylene and 1-hexene. The medium (diluent) and temperature thus were selected such that the copolymer was produced as solid particles and is recovered in that form. Ethylene that had been dried over activated alumina was used as the monomer.
The reactor was a liquid full 15.2 cm diameter pipe loop having a volume of 23 gallons (87 liters). Liquid isobutane, degassed by fractionation and dried over alumina, was used as the diluent, and occasionally some hydrogen was added to regulate the molecular weight of the polymer product. The reactor pressure was about 3.8 MPa (about 580 psi). The reactor temperature was varied over the range of 180xc2x0 F. to 230xc2x0 F. (82xc2x0 C. to 110xc2x0 C.), as indicated in the Tables below. The reactor was operated to have a residence time of 1.25 hours. Catalyst system was added through a 0.35 cc circulating ball-check feeder. At steady state conditions, the isobutane feed rate was about 46 liters per hour, the ethylene feed rate was about 30 lbs/hr, and the 1-hexene feed rate was varied to control the density of the polymer product. Catalyst system concentrations in the reactor can be such that the catalyst system content ranges from 0.001 to about 1 weight percent, based on the weight of the reactor contents. Polymer was removed from the reactor at a rate of about 25 lbs per hour and recovered in a flash chamber. A Vulcan dryer was used to dry the polymer under nitrogen at about 60xc2x0 C. to about 80xc2x0 C.
Cocatalysts triethylaluminum (TEA) and triethylboron (TEB) sometimes were added, as indicated in the Table below. To prevent static buildup in the reactor, a small amount ( less than 5 ppm of diluent) of a commercial antistatic agent sold as Stadis 450 was usually added.
Density (g/ml): ASTM D 1505-68 and ASTM D 1928, Condition C. Determined on a compression molded sample, cooled at about 15 C per minute, and conditioned at room temperature for about 40 hours.
High Load Melt Index (HLMI)(g/10 min): ASTM D1238, condition E. Determined at 190 C with a 21,600 gram weight.
Molecular Weight Distribution Mw/Mn: Molecular weights and molecular weight distributions were obtained using a Waters 150 CV gel permeation chromatograph with trichlorobenzene (TCB) as the solvent, with a flow rate of 1 mL/minute at a temperature of 140 C. BHT (2,6-di-tert-butyl-4-methylphenol) at a concentration of 1.0 g/L was used as a stabilizer in the TCB. An injection volume of 220 L was used with a nominal polymer concentration of 0.3 g/l (at room temperature). Dissolution of the sample in stabilized TCB was carried out by heating at 160-170 C for 20 hours with occasional, gentle agitation. The column was two Waters HT-6E columns (7.8xc3x97300 mm). The columns were calibrated with a broad linear polyethylene standard (Phillips Marlex(copyright) BHB 5003) for which the molecular weight had been determined. As a measure of volatile oligomeric components, or smoke, the amount of material found in the range of molecular weights from 100 to 1000 are listed in the table below.
Xylene solubles (%): ASTM D5494-94. A measurement of the amount of low molecular weight oligomers and thus, of the potential of the resin to smoke during processing.
A xe2x80x9cQuantachrome Autosorb-6 Nitrogen Pore Size Distribution Instrumentxe2x80x9d was used to determined the surface area and pore volume of the supports. This instrument was acquired from the Quantachrome Corporation, Syosset, N.Y.
Polymer resins obtained by this invention are useful for blow molding applications. In these examples blow molding evaluations were conducted by blowing a one gallon (105.0+0.5 gm) bottle on a Uniloy 2016 single head blow molding machine using a 2.5 inch diameter die, 20 degree diverging die, 32% accumulator position, 8.5 second blow time, 0.10 second blow delay, 0.75 second pre-blow delay and a 45xc2x0 F. mold temperature. A reciprocating screw speed of 45 rpm was used, providing parison extrusion at shear rates greater than 10,000/secxe2x88x921 through the die.
Three measurements of polymer processability during blow molding were determined in the following three tests:
1-Minute Output: Describes the speed at which one part of the blow molding operation was accomplished. For this test, the extruder on the blow molding machine was set at 45 rpm and it was allowed to extrude resin for one full minute at the same die gap used to make the desired bottles. After 1 minute, the test was stopped and extruded polymer was weighed to determine the 1-minute output value. This value provides an indication of the rate of extrusion of the polymer during the blow molding operation.
Processing Rating: A subjective rating given by the machine operator based on their unbiased observations during the test. Each resin was given a rating of from 1 to 5, with 5 being the worts and 1 being the best. The operator considered such factors as head pressure, temperature, cycle time, pinch-off, and difficulties trimming.
Shear Rate at Melt Fracture. The onset of melt fracture of each resin was evaluated on the same Uniloy machine used in the previous two tests, by opening the die gap and extruding the resin. Shear rate was increased steadily by increasing the screw rpm. Onset of melt fracture was the rpm at which the parison showed visible signs of melt fracture, such as a shark skin appearance or a distorted rippled surface.
Percent Weight Swell: Measures the amount the molten resin expands immediately as the resin exits the die. Percent weight swell is a measure of the xe2x80x9cmemoryxe2x80x9d of polymer chains as the chains seek to relax and reform the original polymer shape. Weight swell is important because it measures how tightly the die gap must be adjusted to provide a constant bottle weight. If a resin has high weight swell, the die gap required will be tighter to make the proper part weight. In so doing, higher stress will be required to push the resin through the die than a lower weight swell resin. Weight swell is defined as the ratio of the die gap to the final bottle wall thickness.
Diameter Swell (Die Swell): The ratio of the parison diameter to the die diameter.


An image display device includes a substrate; a sparse array of light emitting elements formed on one side of the transparent substrate, the light emitting element being selectively addressable to form an image; an array of lens-lets located on the opposite side of the substrate, the focal plane of the lens-lets being at the one side of the substrate and the lens-lets being arranged with respect to the light emitting elements such that the light emitted by the light emitting elements is directed by the respective lens-lets to intersect at a common region associated with a predetermined viewing distance; and the sparseness of the array of the light emitting elements being such that the ratio of the light emitting area of the light-emitting element under a lens-let to the total area of the lens-let is less than or equal to 0.25.

The present invention relates to display devices with integrated beam forming lens-lets or micro-lenses. More particularly, the present invention relates to the use of solid state emissive display devices with small lenses placed on or integrated into the display device substrate and associated with each light emitting element or sub-element.
Digital imaging devices are widely known and used in electronic equipment. Solid-state imaging devices, those which are constructed on a substrate which may contain integrated drive circuitry, are very useful for portable imaging applications in which a light, rugged, high-quality display is needed. Such devices often rely on liquid crystal displays or light emitting diodes. In particular, organic light emitting diodes (OLEDs) provide a very thin, high-quality, and low-power technology for color image display with Lambertian emission characteristics providing a wide viewing angle. The OLED technology can be built upon a glass substrate as well as traditional silicon wafers.
Such displays, in general, are capable of reproducing images by writing specific information to a plurality of light emitting elements on a surface. These light emitting elements are generally organized as a rectangular array and are addressed via control lines connected to the display device. Each light emitting element is individually addressable and specific data values representing an amount of light to be produced, can be written to them; each data value then being expressed as an element in the displayed image. For color displays, each light emitting element is generally composed of sub-elements in each of several, usually three, primary colorsxe2x80x94typically red, green, and blue. Since the sub-elements are so small, a human observer will see the additive combination of the primary colors enabling the display of many different colors. Each of these sub-elements elements is individually addressable by the control and data lines of the display device.
Optical technology has now progressed to the point that very small optical elements can be created. These elements can be fabricated in a variety of ways and can be combined into an array of small elements covering a surface. Each lens element affects the light passing through according to that element""s surface profile and its refractive index. The lens element is referred to as a lens-let, micro-lens-let, or micro-lens or in the case of periodic cylindrical lenses: lenticular arrays. This technique of optical design differs from the traditional in that different portions of a beam can be made to pass through different optical elements, enabling a variety of effects. The construction of the lens-lets on a surface also enables the implementation of optical effects using smaller optical elements because each lens-let is very small and the surface on which they are made can be very thin and light-weight. It is also the case that construction techniques for lens-let arrays has progressed to the point that such arrays are well understood and manufacturable (see U.S. Pat. No. 5,867,321, issued Feb. 2, 1999 to Nakama et al., entitled Planar Microlens Array and Method of Making Same). Hence, thin, robust, imaging systems with a wide variety of properties can be created using this technology.
Digital imaging displays have been integrated with micro-lens technology to improve the optical characteristics of the display. Most such implementations rely on laminating a micro-lens array on the surface of a display device. In particular, some liquid crystal display devices include a micro-lens layer to shape the light entering and exiting from each light emitting element in the display so as to improve the viewing angle of the display or otherwise enhance the display characteristics (see EP 0 640 850 A2, published Mac. 1, 1995, Suzuki et al., entitled Microlens Array Sheet for a Liquid Crystal Display, Method for Attaching the Same and Liquid Crystal Display Equipped with the Same; U.S. Pat. No. 5,680,186, issued Oct. 21, 1997 to Watanabe et al., entitled Liquid Crystal Display Device with Microlenses Having a Focal Point Between a Cover Layer and the Liquid Crystal Layer""s Center; and EP 0 615 150 A3 and A2, published Sep. 9, 1994, Borrelli et al., entitled Cover Glass for LCD Panel). It is also possible to integrate a micro-lens directly upon a substrate of display light emitting elements with the use of resins to form the lenses (see EP 0 658 779 A2, published Jun. 21, 1995, Mizuguchi et al., entitled Microlens Substrate). In the first case, a separate substrate or layer must be incorporated into the device, adding manufacturing cost and difficulty. In the second case, the integration of resin materials on a substrate is problematic from both a materials and process perspective. In both cases, the designs are for liquid crystal devices.
Other integrations of light emitting devices and microlenses have also been explored. For example, EP 0 384 849 B1, published Aug. 29, 1980, Shimada et al., entitled A Semiconductor Light Emitting System describes an LED with an integrated micro-lens on the same substrate which radiates parallel to the substrate. Such designs are not suitable for a multi-element display device and require complex photolithography techniques. Micro-lenses are also used in conjunction with solid-state light capturing devices (see EP 0 744 778B1, published Nov. 27, 1996, Sano et al., entitled Solid-State Imaging Device and Method of Manufacturing the Same) and in light-valve displays (U.S. Pat. No. 5,757,124, issued May 26, 1998 to E. Pope, entitled Display Screen Having Amorphous Silica Microspheres with Fluorescence Behavior) using masks and micro-spheres. Cathode ray tubes with a layer of light emitting element level optical micro-lenses are also known (EP 0 957 385 A1, published Nov. 17, 1999, S. Zelitt, entitled 3-D Imaging System) in this case to support three-dimensional (3-D) imaging.
These techniques rely on the use of an additional surface with micro-lenses attached to the surface of a digital image display, the use of a special cover material surface with micro-lenses encapsulating the display, or special process methods to integrate micro-lenses on the base substrate. In the first case, additional materials, components, and process steps are needed to fabricate a solid-state display with micro-optical components. In the second case an existing component must be specially treated and aligned with the other components and, in the third case, difficult materials and non-standard process methodologies must be undertaken which limits the use of the technique. Moreover, many of these methods are limited in application to liquid crystal display devices.
Hence, digital image display systems that are portable, small, and lightweight, are greatly restricted in their ability to integrate optical elements for producing desirable effects. When added to an imaging system, the optical elements are too bulky, lack robustness, or require manufacturing methods and precision, which adds to the cost of the system.
In standard emissive OLED devices the energy is emitted uniformly in all directions. This is an advantage over LCD displays, which are more directional. The disadvantage of this uniform angular emission is that much energy is used for directions that, in many applications, are not useful. It would be desirable to direct the emission directly at the user and spare the energy currently employed away from the user. Another advantage for this would be for security so that other users could not view the screen.
There is a need therefore to provide an improved display that directs the energy to an observer and spares the energy required to transmit to regions away from the viewer.
The need is met according to the present invention by providing an image display device that includes a substrate; a sparse array of light emitting elements formed on one side of the transparent substrate, the light emitting element being selectively addressable to form an image; an array of lens-lets located on the opposite side of the substrate, the focal plane of the lens-lets being at the one side of the substrate and the lens-lets being arranged with respect to the light emitting elements such that the light emitted by the light emitting elements is directed by the respective lens-lets to intersect at a common region associated with a predetermined viewing distance; and the sparseness of the array of the light emitting elements being such that the ratio of the light emitting area of the light-emitting element under a lens-let to the total area of the lens-let is less than or equal to 0.25.
The present invention has the advantage of providing a low-cost, small, and energy efficient display. Another advantage is that the viewer of the display has improved privacy for the subject matter being viewed.

Image display device with array of lens-lets


A corneal punch comprising a base unit having a first annular mating surface surrounding a well in which a donor cornea may be located, and a separate guide unit including an inner annular guide shaft and an outer locating ring connected to the guide shaft and having a second annular mating surface. The base unit and the guide unit may be releasably positioned in registration with each other by way of the first and second mating surfaces such that the guide shaft is substantially coaxial with the well.

1. Field of the Invention
The present invention relates to a corneal punch for cutting corneal grafts from donor corneas prior to transplantation of the grafts to patients with damaged or diseased corneas.
2. General Background of the Invention
In the field of eye surgery, it is sometimes necessary to perform a corneal transplant by replacing a diseased or damaged cornea of a patient with a donor cornea harvested from an immunologically compatible cadaver. This is generally achieved by removing at least a central portion of the diseased or damaged cornea from a patient's eye using a trephine, using a corneal punch to cut an equivalent portion from a donor cornea (this portion being known in the art as a donor graft), and then inserting the donor graft into the space on the surface of the patient's eye left vacant by removal of the diseased or damaged portion of the patient's original cornea.
A known corneal punch comprises a base unit including a well in which a donor cornea may be located, and a guide unit which is then placed on top of the base unit and registered therewith by way of four pins provided on the underside of the guide unit and which locate into four corresponding holes provided on an upper peripheral surface of the base unit. The guide unit is a generally solid block of similar size to the base unit, and includes a central aperture which is located directly over the well of the base unit when the guide unit is in registration therewith. The central aperture is circular, and is sized and shaped so as slidably to receive a corneal trephine. The corneal trephine may be moved up and down within the guide unit in a reciprocating manner so as to allow a donor graft to be cleanly cut from the donor cornea.
This known corneal punch has two significant disadvantages. Firstly, it is difficult to register the guide unit with the base unit because the four pins are difficult to locate within the four holes. Secondly, because the guide unit is substantially solid and opaque, it is not possible for a surgeon or technician to have a clear view of the donor cornea when cutting the donor graft therefrom with a corneal trephine.
According to the present invention, there is provided a corneal punch comprising a base unit having a first annular mating surface surrounding a well in which a donor cornea may be located, and a separate guide unit including an inner annular guide shaft and an outer locating ring connected to the guide shaft and having a second annular mating surface, wherein the base unit and the guide unit may be releasably positioned in registration with each other by way of the first and second mating surfaces such that the guide shaft is substantially coaxial with the well.
Advantageously, the outer locating ring of the guide unit is connected to the guide shaft by way of one or more spokes or webs so as to provide one or more windows in the guide unit. The one or more windows allow the well to be observed when the guide unit is in registration with the base unit. Furthermore, a donor cornea or donor graft may be manipulated through the one or more windows when in the well, for example with a pointed tool or the like, for positioning or other purposes.
The one or more spokes or webs may be provided with corrugations or ridges or the like on upper surfaces thereof so as to provide a good gripping surface for a person's fingers when pushing down on the guide unit so as to ensure it is held firmly in place on the base unit when the corneal punch is in an assembled condition. Alternatively or in addition, the inner annular guide shaft of the guide unit may be provided with peripheral ridges or corrugations, such as a knurled outer edge, for providing a finger grip.
Alternatively, the guide unit or at least a part thereof, preferably a part between the locating ring and the guide shaft, may be made out of a substantially transparent material so as to allow the well to be observed when the guide unit is in registration with the base unit.
In this way, the present invention provides a corneal punch where it is relatively easy to position the guide unit in registration with the base unit, in which the well is visible to a surgeon or technician when the guide unit is in place, and in which access to a donor cornea or donor graft is provided through one or more windows so as to allow the cornea or graft to be manipulated or repositioned when in the well.
The first and second mating surfaces may comprise annular mating flanges and shoulders so as to provide good registration between the base unit and guide unit. The annular mating flange of the first mating surface may fit inside the annular mating flange of the second surface, or vice versa.
The guide shaft is sized and shaped so as slidably and snugly to receive an annular corneal trephine, and to allow a cutting edge of the trephine to be lowered into the well so as to cut a donor graft from a donor cornea located therein.
The base unit may be provided with peripheral finger grips or the like so as to allow it to be held firmly in position on a flat surface when cutting a donor graft from a donor cornea. The finger grips may take the form of corrugations or ridges or the like formed on a surface of the base unit. In some embodiments, the base unit includes a generally planar base plate which allows the corneal punch to be held down on a flat surface in a secure manner. The base plate may include a generally annular cut-out portion in which a corneal trephine may be snugly located for storage purposes.
In preferred embodiments, the present invention is made out of surgical grade stainless steel, although other materials such as plastics or polymers or other metals may be used where appropriate. The guide unit in particular may be made fully or partially out of a substantially transparent plastics material so as to allow the well in the base unit to be observed when the guide unit is in position.
It is preferred that the present invention is a disposable corneal punch, in that it is discarded after use. However, certain embodiments may be sterilised, for example in an autoclave, and then used again.
The well may comprise a generally circular concave dish sunk into a central part of the base unit and adapted to contain a donor cornea.