Silicone rubber surfaces for biometric print TIR prisms

Molded silicone rubber sheets with optical quality surfaces and methods for making the same. The silicone rubber sheets are made by molding liquid silicone rubber in a mold. In embodiments, the mold forms parallel optical quality flat surfaces. In one embodiment, a stiffening plastic is molded in the middle of the silicone rubber sheet between the parallel optical quality flat surfaces. In another embodiment, the mold forms one optical quality flat surface while the surface parallel to the optical quality flat surface is bonded to a prism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of biometrics.

2. Background Art

Biometrics is a science involving the analysis of biological characteristics. Biometric imaging captures a measurable characteristic of a human being for identity purposes. See, e.g., Gary Roethenbaugh,Biometrics Explained, International Computer Security Association, Inc. (1998), pp. 1-34, which is incorporated herein by reference in its entirety.

Fingerprint scanners and palm scanners are two types of biometric imaging systems for acquiring fingerprint images and palm print images, respectively. Many fingerprint and palm print scanners include glass platens that result in latent prints. Latent print images are images of prints that remain on the platen after a person's finger or palm have been removed and may show up on subsequent images of fingerprints or palm prints acquired thereafter. To eliminate latent print images, glass platens have been replaced by platens made of silicone rubber sheets.

Commercially available silicone rubber sheets are often manufactured using a process known as calendaring. Calendaring is a rolling process in which a machine with rollers, known as a calendar, is used to form thin sheets from plastic, paper, or other materials. For silicone rubber sheets, liquid silicone is poured on rollers of the calendar with a catalyst and mixed. The rollers rotate several times. As the temperature is changed from cold to hot, the mixture begins to form a rubber sheet. The rubber sheet is then passed through another set of rollers that are very hot. The rubber sheet is then released and hardens almost instantly.

Silicone rubber sheets manufactured using calendaring often have problems associated with them. For example, they may not be completely flat, and often have inclusions and striations that cannot be removed. The silicone rubber sheets may also be cloudy in color. For many applications these characteristics may not be a problem. But in applications where the silicone rubber sheets need to be of optical quality, such as biometric imaging, commercially available silicone rubber sheets produced from calendaring do not provide adequate surface quality or finish to optimize image enhancement.

Silicone rubber molding is another process used to produce many products. However, conventional methods for molding silicone rubber also do not provide the optical quality needed for biometric imaging.

What is needed is an optical quality silicone rubber sheet that provides adequate surface quality or finish to optimize image enhancement. What is further needed is a method for making the same.

BRIEF SUMMARY OF THE INVENTION

The present invention solves the above-mentioned needs by providing silicone rubber sheets with optical quality surfaces and methods for making the same. The silicone rubber sheets are made by molding liquid silicone rubber in a mold. In embodiments, the mold forms parallel optical quality flat surfaces. In one embodiment, a stiffening plastic is molded in the middle of the silicone rubber between the parallel optical quality flat surfaces. In another embodiment, the mold forms one optical quality flat surface while the surface parallel to the optical quality flat surface is bonded to a prism during the molding process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides optical quality silicone rubber sheets and methods for making the same. The optical quality silicone rubber sheets are produced using molding methods that provide adequate surface quality or finish to optimize image enhancement for many applications, such as biometric imaging.

Silicone Rubber Sheet

FIG. 1is a diagram100illustrating an optical quality silicone rubber sheet for a biometric TIR prism.FIG. 1shows a prism102and an optical quality silicone rubber sheet104attached to prism102. An enlarged view108of a portion106of silicone rubber sheet104is also shown inFIG. 1. Enlarged view108shows the components of silicone rubber sheet104. The components of silicone rubber sheet104include a silicone rubber compound110and two parallel optical quality molded surfaces112.

In one embodiment, silicone rubber compound110is comprised of liquid silicone. In another embodiment, silicone rubber compound110is comprised of liquid silicone diluted with a thinning solution. The dilution may range from 10 to 40 percent.

At least one of the optical quality molded surfaces112enables optical contact with prism102. In other words, when silicone rubber sheet104is applied to the surface of prism102, silicone rubber sheet104adheres to prism102without any separation between prism102and silicone rubber sheet104. Quality molded surfaces112have a surface flatness of 4 to 6 waves of light per inch. In an embodiment, one of the quality molded surfaces112is used to make optical contact with prism102. The other quality molded surface is used as a TIR (Total Internal Reflection) platen surface.

The thickness of silicone rubber sheet104may range from 30 to 60 mils. The thickness of silicone rubber sheet104is dependent on the application in which it is used. For example, in the application of biometric imaging, the thickness of silicone rubber sheet104is dependent upon the size of prism104. The smaller the prism, the smaller the thickness of silicone rubber sheet104. The larger the prism, the larger the thickness of silicone rubber sheet104. For example, a fingerprint scanner may use a smaller prism than a palm print scanner. The fingerprint scanner with the smaller prism may therefore require silicone rubber sheeting that is closer to the lower range of thickness, that is 30 mils, while the palm print scanner with the larger prism may require silicone rubber sheeting that is closer to the higher range of thickness, that is 60 mils.

In an embodiment, RTV (Room Temperature Vulcanization) liquid silicone manufactured by General Electric is used. RTV is a very clear liquid silicone. RTV is comprised of two parts that when mixed together cause it to vulcanize at room temperature. As its name implies, RTV may be cured at room temperature. RTV is not limited to curing at room temperature. RTV may also be cured by heating to accelerate the curing process.

FIG. 2is an exemplary mold200for making optical quality silicone rubber sheet104. Mold200is comprised of a mold cavity202, a plurality of spacers204, two plates206, and two clamps208. Spacers204are located at three edges of mold cavity202. The two plates206may be a glass or plastic plate for visibility. In one embodiment, the two plates206are two pieces of float glass. Float glass provides optically flat surfaces. In other words, the surface flatness of float glass is within 4 to 6 wavelengths of light per inch. In an embodiment, each float glass plate206may be ¾ inch thick. The present invention is not limited to using float glass. Other types of plates206, such as plastics or optically polished materials, may be used that allow for visibility, provide for optically flat surfaces, and do not stick to rubber. For example, such plastics as acrylic, polycarbonate, polypropolene, polyethylene, teflon, etc. may be used if they meet the optically flat standard of at least 4 to 6 wavelengths of light per inch.

Once the molding process for a given configuration is developed, the molds may be made of opaque materials that are compatible with silicone rubber.

The two plates206are separated by spaces204. The thickness of spacers204are equivalent to the desired thickness of the silicone rubber sheet to be molded. Clamps208are U-shaped and adjustable, and are used to hold the two pieces of float glass206together. Clamps208are applied with enough force to prevent leakage of silicone rubber compound110. Mold cavity202is used to hold the liquid silicone compound for making silicone rubber sheet104.

FIG. 3is a method300for making optical quality silicone rubber sheet104according to an embodiment of the invention. The process begins with step302, where the process immediately proceeds to step304.

In step304, silicone rubber compound110is prepared. As previously stated, silicone or RTV is in two parts and the two parts must be mixed together. In one embodiment, silicone rubber compound110is comprised of 100 percent RTV. In another embodiment, RTV is diluted between 10 to 40 percent with Toluene to produce silicone rubber compound110. Toluene is a solvent to silicone rubber and may be purchased at any hardware store. General Electric recommends that Toluene be used to thin RTV, if desired. The process then proceeds to step306.

In step306, silicone rubber compound110is out gassed. Silicone rubber compound110is placed in a vacuum chamber to get all of the entrapped air out of silicone rubber compound110.

In step308, silicone rubber compound110is injected into mold cavity202. The process then proceeds to step310.

In step310, silicone rubber compound110is cured in mold cavity202. Mold200is placed into a temperature controlled oven. Silicone rubber compound110is cured for a certain amount of time at a specific temperature. Table 1 shows the recommended temperature vs. cure time for curing silicone rubber compound110. The temperatures and cure times are recommended by General Electric, the manufacturer of a specific variety of RTV.

TABLE 1Temperature° C. (° F.)Cure Times25 (77)6 to 7days65 (149)4hours100 (212)1hour125 (257)45minutes150 (302)15minutes
In one embodiment, silicone rubber compound110is cured for 1 hour at temperature 100° C. (212° F.). Other cure times and temperatures shown in Table 1 may be used without departing from the scope of the invention. At the end of the desired cured time, mold200is removed from the temperature controlled oven. Curing silicone rubber compound110causes the float glass surface of plates206to be replicated on the surface of silicone rubber compound110that forms a TIR surface for the resulting silicone rubber sheet104. The process proceeds to step312.

In step312, the mold is taken apart in order to remove silicone rubber sheet104. Clamps208are removed and plates206are separated. Silicone rubber sheet104is peeled from one of plates206. The plate206in which silicone rubber sheet104is peeled from depends on which one of the two plates are easily separated from silicone rubber sheet104. The plate206that is hardest to remove requires that silicone rubber sheet104be peeled off. The process then proceeds to step314.

In step314, silicone rubber sheet104is cut to the desired dimensions for its particular application. Silicone rubber sheet104may be cut with a die cutter. Other cutting devices may also be used, such as an exacto knife, shears, etc. The process then proceeds to step316, where the process ends.

Integrally Molded Silicone Rubber Surface

Silicone rubber sheets104produced using molding process300provide optical clarity and flatness without striations (induced stress in the silicone) and inclusions that result from commercial silicone rubber sheets that are produced using the calendaring process. Although silicone rubber sheet104produced using molding process300provides a precise optical quality silicone rubber layer, silicone rubber sheet104may be difficult to install reliably and quickly on the surface of prism102without inducing distortion and strain in the silicone layer and anomalies in the interface between the surface of prism102and the silicone rubber sheet104. These distortions, strains, and anomalies may cause unacceptable optical images. If the placement of silicone rubber sheet104on prism102is anything except perfectly flat, any distortions, strains, or anomalies will be displayed on an image.

In another embodiment of the invention, in-situ molding on a prism surface takes advantage of the precision qualities of the molding process while avoiding installation problems that cause distortion and strain in the silicone layer and interfacing anomalies between the prism surface and the silicone rubber sheet.FIG. 4is a diagram illustrating an optical quality silicone rubber sheet that is bonded to a biometric TIR prism according to an embodiment of the invention.FIG. 4shows prism102with an optical quality silicone rubber sheet402bonded to prism102using a binder. An enlarged view406of a portion404of silicone rubber sheet402is also shown inFIG. 4. Enlarged view406shows the components of silicone rubber sheet402. The components of silicone rubber sheet402include silicone rubber compound110, one optical quality molded surface408, and a binder410.

Quality molded surface408has a surface flatness of 4 to 6 waves of light per inch. Quality molded surface408is used as a TIR (Total Internal Reflection) platen surface on which a biometric image is formed. Binder410is the material used to bond silicone rubber sheet402to the surface of prism102. Thus, in this embodiment, one does not have to attach or worry about attaching silicone rubber sheet402to prism102because silicone rubber sheet402is permanently bonded to the surface of prism102.

In one embodiment, a liquid silicone primer, SS4120, manufactured by General Electric, is used to bond silicone rubber sheet402to prism102. SS4120 is a very thin material with a viscosity of alcohol. SS4120 has an approximate curing time of one hour before one can use it. Other silicone primers that are clear and remain clear after the primer cures may also be used.

FIG. 5is an exemplary mold500for making optical quality silicone rubber sheet402bonded to biometric TIR prism102according to an embodiment of the invention. Mold500is comprised of a mold cavity502, a plurality of spacers504, two clamps508, and two plates206and506, respectively. Plate206may be a glass or plastic plate for visibility. In one embodiment, plate206is a piece of float glass for providing an optically flat surface. Plate506may be any type of plate built to hold prism102.

Spacers504are located along three sides of mold cavity502. Spacers504are used to separate prism102from plate206. The thickness of spacers504are equivalent to the desired thickness of the silicone rubber sheet to be molded. Clamps508are U-shaped and adjustable, and are used to hold the two plates206and506together. Other types of clamps may be used to hold mold500together. Clamps508are applied with enough force to prevent leakage of silicone rubber compound110. Mold cavity502is used to hold the liquid silicone rubber compound110for making silicone rubber sheet402.

FIG. 6is a method for making an optical quality silicone rubber sheet that is bonded to a biometric TIR prism according to an embodiment of the invention. The process begins with step602and immediately proceeds to step604.

In step604, the surface of prism102is coated with a liquid silicone primer or binder410. A thin layer of silicone is applied to the liquid silicone primer as a sealer. Then the liquid silicone primer and thin layer of silicone are cured. In one embodiment, curing time is one hour. Binder410enables silicone rubber sheet402to adhere to prism102. The process then proceeds to step606.

In step606, silicone rubber compound110is prepared. As previously stated, silicone is provided in two parts and the two parts must be mixed together. As previously stated, the present invention uses a liquid silicone, RTV, manufactured by General Electric. In one embodiment, silicone rubber compound110is comprised of 100 percent RTV. In another embodiment, silicone rubber compound110is silicone, RTV, diluted with a thinner. One embodiment dilutes the silicone with 10 to 40 percent of Toluene to produce silicone rubber compound110. The process then proceeds to step608.

In step608, silicone rubber compound110is out gassed. Silicone rubber compound110is placed in a vacuum chamber where all of the entrapped air is removed from silicone rubber compound110. The process then proceeds to step610.

In step610, silicone rubber compound110is injected into mold cavity502. The process then proceeds to step612.

In step612, silicone rubber compound110in mold cavity502is cured. Mold500is placed into a temperature controlled oven. Silicone rubber compound110is cured for a certain amount of time at a specific temperature. Table 1 shows the recommended temperature vs. cure time for curing silicone rubber compound110. The temperatures and cure times are recommended by General Electric, the manufacturer of RTV.

In one embodiment, silicone rubber compound110is cured for 1 hour at temperature 100° C. (212° F.). Other cure times and temperatures shown in Table 1 may be used without departing from the scope of the invention. At the end of the desired cured time, mold500is removed from the temperature controlled oven. Curing silicone rubber compound110causes the float glass surface of plate206to be replicated on the surface of silicone rubber compound110. The replicated float glass surface forms a TIR surface for the resulting silicone rubber sheet402. In biometric imaging applications, this surface is used as the TIR platen surface. The process proceeds to step614.

In step614, prism102, now having a bonded silicone rubber sheet402adhered to it, is removed from mold500. Clamps508are removed and plate206is separated from silicone rubber sheet402. Prism102is then removed from plate506. The process then proceeds to step616, where the process ends.

Reinforced Silicone Rubber Sheet

In one embodiment of the present invention, a plastic stiffening material is embedded approximately in the center of two layers of silicone to form a reinforced silicone rubber sheet. The reinforcement serves to both prevent distortion strain during application of the reinforced silicone rubber sheet and to assist with application of the reinforced silicone rubber sheet by the attraction of optically flat surfaces whose flatness is maintained by the stiff reinforcement. These factors, combined with the natural affinity of silicone rubber to a smooth surface, allow adequate optical contact to be achieved by simply placing the reinforced silicone rubber sheet on an adequately clean surface. The attraction between the silicone rubber, the stiff plastic material and glass causes the reinforced silicone rubber sheet to make optical contact with a clean surface, such as a TIR platen surface, almost entirely on its own. When placed on a TIR platen surface, the reinforced silicone rubber sheet becomes an image enhancing, resilient surface with no optically degrading strains or interface irregularities being induced or incurred.

FIG. 7is a diagram illustrating an optical quality reinforced silicone rubber sheet according to an embodiment of the invention.FIG. 7shows a prism102and an optical quality reinforced silicone rubber sheet702attached to, yet separate from, prism102. An enlarged view706of a portion704of reinforced silicone rubber sheet702is also shown inFIG. 7. Enlarged view706shows the components of reinforced silicone rubber sheet702. The components of reinforced silicone rubber sheet702include a stiff plastic material708positioned between two layers of silicone rubber compound110, two binder layers710, and two parallel optical quality molded surfaces112. Binder layers710bind the two layers of silicone rubber compound110with stiff plastic material708. One of the two parallel optical quality mold surfaces112is used to make optical contact with prism102. The other parallel optical quality mold surface112may be used as a TIR platen surface on which a biometric image, such as a fingerprint, a palm print, etc., is formed.

In an embodiment, polycarbonate may be used for stiff plastic material708. Polycarbonate is a high temperature plastic having high strength. Polycarbonate is very clear, has a high index refraction, and is readily available in thicknesses of 5 to 60 mils. Other types of stiff plastic material that bond to silicone rubber and exhibit good optical quality may be used. Such plastics may include acrylic, CR39, styrene, etc.

The overall thickness of reinforced silicone rubber sheet702is directly related to the size of the surface on which it is to be applied. For example, on an approximately 3 by 2 inch surface of a prism for a fingerprint scanner, the thickness may be in the range of 25-30 mils. On an approximately 4 by 6 inch surface of a prism for a palm scanner, the thickness may be in the range of 40-60 mils. Thus, the larger the surface on which reinforced silicone rubber sheet702is to be applied, the larger the thickness of reinforced silicone rubber sheet702. In one embodiment, the overall thickness of reinforced silicone rubber sheet702may range from 25 to 100 mils. The thickness of stiff plastic material708may range from 5 to 60 mils while the two layers of silicone rubber compound110may range from 5 to 50 mils. In one embodiment, the two layers of silicone rubber compound110and stiff plastic material708are of equal thickness. In another embodiment, the thickness of stiff plastic material708may be 50 mils while each layer of silicone rubber compound110may be 25 mils. Yet, in another embodiment, the thickness of stiff plastic material708may be 10-20 mils while one layer of silicone rubber compound110may be 5-15 mils and the other layer of silicone rubber compound110may be 10-30 mils.

FIG. 8Ais a side view of an exemplary mold800for making optical quality reinforced silicone rubber sheet702according to an embodiment of the invention. Mold800comprises a base802, a first clamp804fixed to, and on one side of, base802, a post806fixed to base802on the side opposite of first clamp804, a spring808, a moveable clamp810, a pair of parallel plates812, a pair of clamps814on each side of parallel plates812, a pair of parallel mold cavities (not shown) for injecting silicone rubber compound110, and spacers (not shown) located on each end of the pair of mold cavities for indicating the thickness of the two layers of silicone rubber compound110. As previously indicated, the thicknesses of the two layers of silicone rubber compound110may not be equal.

Spring808, clamps804and810, and post806form a tensioning device for tensioning stiff plastic material708. Parallel plates812may be glass or plastic plates for visibility. In one embodiment, parallel plates812are pieces of float glass for providing an optically flat surface. Clamps814are used to hold the two pieces of float glass812together. Clamps814are applied with enough force to prevent leakage of the two layers of silicone rubber compound110. The parallel mold cavities (not shown) are used to hold the liquid silicone compound for making reinforced silicone rubber sheet702.

FIG. 8Bis a top view of mold800for making optical quality reinforced silicone rubber sheet702.FIG. 8Bindicates the location of spacers818.

FIG. 9is a method for making an optical quality reinforced silicone rubber sheet according to an embodiment of the invention. The process begins with step902, where the process immediately proceeds to step904.

In step904, a binder is applied to a plastic stiffening layer. In one embodiment, the binder is a silicone primer, SS4120, manufactured by General Electric Company. Then a sealer coat of silicone is applied. In one embodiment, the plastic stiffening layer is dipped into the silicone. The plastic stiffening layer is then cured for approximately 1 hour. The process then proceeds to step906.

In step906, after curing, the plastic stiffening layer is placed in the tensioning device of mold800between plates812. Each end of the plastic stiffening layer is attached to mold800via clamps804and810. To prevent the silicone, in which the plastic stiffening layer was sealed, from being attracted to plates812(wherein plates812are made of glass), enough tension must be applied to the plastic stiffening layer to prevent it from attaching itself to glass plates812. Thus, the spring is used to stretch the stiffening layer by a necessary amount to prevent the stiffening layer from attaching itself to one of glass plates812and to maintain its position within mold800. The process then proceeds to step908.

In step908, silicone rubber compound110is prepared. As previously stated, silicone or RTV is in two parts and the two parts must be mixed together. In one embodiment, silicone rubber compound110is comprised of 100 percent RTV. In another embodiment, silicone rubber compound is comprised of RTV diluted with a silicone thinner, Toluene. RTV may be diluted by 10 to 40 percent to produce silicone rubber compound110. The process then proceeds to step910.

In step910, silicone rubber compound110is out gassed. Silicone rubber compound110is placed in a vacuum chamber to get all of the entrapped air out of silicone rubber compound110.

In step912, the spacers are adjusted for the appropriate thickness of the mold cavities. Silicone rubber compound110is injected into the two mold cavities for mold800. The process then proceeds to step914.

In step914, silicone rubber compound110is cured in mold800. Mold800is placed into a temperature controlled oven. Silicone rubber compound110is cured for a certain amount of time at a specific temperature as shown in Table 1.

In one embodiment, silicone rubber compound110is cured for 1 hour at temperature 100° C. (212° F.). Other cure times and temperatures shown in Table 1 may be used without departing from the scope of the invention. At the end of the desired cured time, mold800is removed from the temperature controlled oven. Curing silicone rubber compound110causes the float glass surfaces of plates812to be replicated on each outside surface of silicone rubber compound110. The top surface of silicone rubber compound110forms a TIR surface for the resulting reinforced silicone rubber sheet702. The bottom surface of silicone rubber compound110enables reinforced silicone rubber sheet702to make optical contact with a surface on which it attaches. The process proceeds to step916.

In step916, mold800is taken apart in order to remove reinforced silicone rubber sheet702. Clamps814,804, and810are removed and plates812are separated. The process then proceeds to step918.

In step918, reinforced silicone rubber sheet702is cut to the desired dimensions for its particular application. Silicone rubber sheet702may be cut with a die cutter. Other cutting devices may also be used, such as an exacto knife, shears, etc. The process then proceeds to step920, where the process ends.

FIG. 10Ais an exemplary diagram illustrating a reinforced silicone rubber sheet1002for a fingerprint scanner. Reinforced silicone rubber sheet1002is comprised of two layers of clear silicone rubber1004and one layer of clear polycarbonate1006inserted between the two layers of clear silicone rubber1004. A molded surface is formed on the outside surface of the two layers of clear silicone rubber1004. A primer/binder binds the inside surface of the two layers of clear silicone rubber1004to the layer of clear polycarbonate1006. Reinforced silicone rubber sheet1002is approximately 3.24±0.010 inches by 2.11±0.010 inches and has a thickness of approximately 30±2 mils. Each layer of clear silicone rubber1004is 7.5±0.75 mils thick. The layer of clear polycarbonate1006is 15±0.75 mils thick. Notes for reinforced silicone rubber sheet1002are found in Table 2.

FIG. 10Bis an exemplary diagram illustrating a reinforced silicone rubber sheet1012for a palm print scanner. Reinforced silicone rubber sheet1012is comprised of two layers of clear silicone rubber1014and one layer of clear polycarbonate1016inserted between the two layers of clear silicone rubber1014. A molded surface is formed on the outside surface of the two layers of clear silicone rubber1014. A primer/binder binds the inside surface of the two layers of clear silicone rubber1014to the layer of clear polycarbonate1016. Reinforced silicone rubber sheet1012is approximately 5.75±0.010 inches by 5.06±0.010 inches and has a thickness of approximately 45±2 mils. The two layers of clear silicone rubber1014are not of equal thickness. One layer of clear silicone rubber1014is 10±0.75 mils thick while the other layer of clear silicone rubber1014is 20±0.75 mils thick. The layer of clear polycarbonate1016is 15±0.75 mils thick. Notes for reinforced silicone rubber sheet1012are found in Table 2.

TABLE 2NOTES1.MOLDED OPTICALLY CLEAR SILICONE RUBBER WITH REINFORCED LAYER OF CLEAR POLYCARBONATEFILMA)OPTICALLY CLEAR SILICONE RUBBER:MECHANICAL PROPERTIES AFTER CURING:HARDNESS: SHORE A DUROMETER: 44-46TENSILE STRENGTH: 920 PSIELONGATION: 120%SHRINKAGE: 0.20%REFRACTIVE INDEX: 1.40COEFFICIENT OF EXPANSION: 15.3 × 10−6IN/IN/° F.B)CLEAR POLYCARBONATE FILM:GRADE: GRAPHICS QUALITYREFRACTIVE INDEX: 1.588LIGHT TRANSMISSION: 88% MINIMUMHARDNESS: ROCKWELL R 118YIELD STRENGTH: 8.500 PSIULTIMATE STRENGTH: 9.000 PSICOEFFICIENT OF EXPANSION: 37.5−6IN/IN/° F.VISUAL DEFECTS: NONE PERMITTEDVISUAL SCRATCHES: NONE PERMITTEDC)PRIMER/BINDER:OPTICALLY CLEAR PRIMER/BINDER WHICH WILL NOT REDUCE THE OPTICALLYCLEARNESS AND TRANSMISSIVITY OF THE FINAL LAMINATE.A BOND STRENGTH OF 4-10 PSI IN A PEEL CONFIGURATION AND 200-800 PSI IN LAPSHEAR IS REQUIRED.D)MOLDED SURFACES:TOOLING MOLD SURFACES MUST BE FLAT WITHIN 6-10A PER INCH MAXIMUM, VISIBLELIGHT AND HAVE A SURFACE QUALITY OF 80-50 (EQUIVALENT TO COMMERCIAL QUALITYFLOAT GLASS).E)CLEANLINESS:MAINTAIN A CLASS 100 (M3.5) HEPA ENVIRONMENT THROUGHOUT COMPLETEFABRICATION; MOLDING PROCESS, TRIMMING TO SIZE, AND FINAL PACKAGING.F)ACCEPTANCE TESTS:VISUAL TEST: NO BUBBLES, INCLUSIONS, OR STRIATIONS PERMITTED.TRANSMISSIVITY TEST PER (TBD) METHOD: MINIMUM TRANSMISSIVITY OF (TBD)%OVER VISIBLE SPECTRUM.FUNCTIONAL TEST: MOLDED SILICONE PAD (AFTER TRIMMING) MUST OPTICALLYCONTACT, TO PRODUCE A VISUALLY TRANSPARENT INTERFACE WITH A CLEAN GLASSSURFACE. THIS MUST OCCUR OVER 100% OF THE PAD SURFACE AND WITHIN 30 SECONDS,AFTER PLACING PAD ON THE GLASS SURFACE, WITHOUT ANY ADDITIONALFORCE/PRESSURE OR WETTING AGENTS.GLASS SURFACE MUST CONFORM TO THE SAME SPECIFICATIONS AS SPECIFIED FOR THEMOLD SURFACES IN NOTE ID.BOND TEST: (TBD) TEST METHOD TO VERIFY PRIMER/BINDER BOND STRENGTH ASSPECIFIED IN SECTION 1C.2.APPLY PROTECTIVE FILM TO BOTH MOLDED SURFACES PRIOR TO TRIMMING PER NOTE 3.3.ALL EDGES TO BE CLEANLY TRIMMED WITHOUT DISTORTIONS, BURRS, OR TRIMMING DEBRIS; TOINSURE FUNCTIONAL ACCEPTANCE TEST PER NOTE IF WILL BE MET.4.PACKAGE INDIVIDUALLY TO MAINTAIN CLEANLINESS, FLATNESS AND MOLDED SURFACE QUALITY.5.SAMPLES MUST BE APPROVED.6.PRODUCTION LOT INSPECTION:AN AQL LEVEL SAMPLE WILL BE PERFORMED BY THE QUALITY DEPT. TO VERIFY CONFORMANCETO THE ACCEPTANCE TESTS SPECIFIED IN NOTE 1F.

Although the present invention has been described using silicone, the present invention may also be made using vinyl. In another embodiment of the invention, color, such as a faint red or blue, is added to the silicone rubber and/or stiffening layer to provide an optical bandpass filter for improving ambient light. In yet another embodiment of the invention, once the silicone rubber sheet makes optical contact with a surface, such as, for example, a prism surface, the silicone rubber sheet changes in color.

CONCLUSION

The present invention is not limited to the embodiment of a biometric scanner. The present invention can be used with any system that utilizes a silicone rubber sheet. The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.