BORON NITRIDE/SILICA CATALYZED POLYSILOXANE RESIN AND LAMINATED ARTICLES FORMED THEREFROM

Abstract: A polysiloxane resin blend including boron nitride and silica and laminated articles formed from the resin blend wherein the catalysis of the blend is regulated by silica and the blend has a concentration of boron nitride of between about 12 and 75 weight %.

Description: Boron Nitride/Silica Catalyzed Polysiloxane Resin and Laminated Articles Formed Therefrom Background of Invention Field of Invention This invention relates (1) to the use of a catalyzed combination of silica (Si0 2 ), as an inhibitor, and boron nitride (BN), to control the polymerization reaction under heat and pressure of polysiloxane resin formulations and (2) to laminated articles formed therefrom. References Cited 1. U.S. Patent 5,552,466 09/03/96 Beckley et al 2. U.S. Patent 4,927,587 05/22/90 Masaharu et al 3. U.A. Patent 60/024,357 08/20/96 Clarke 4. Preparative methods of Polymer Chemistry, Sorenson, .R. and Campbell, T.W. John Wiley and Sons, pp. 383-390 (1961). 5. Inorganic and organometallic Polymers "Recent Advances in organosiloxane Copolymers" Summers J.D. et al., American Chemical Society, pp. 180-197 (1988). 6. U.S. Patent 5,562,966 10/08/96 Clarke Description of the Previously Published Art A variety of polysiloxane oligimers that are well known in the art (currently supplied by Dow Corning and GE Silicones, et al.) can be used to formulate polysiloxane resins containing catalyst and additives for composite processing. Conventional curing of polysiloxane resin formulations is well documented in the literature (Ref. 1, 2 and 3). the polysiloxane blends employ conventional means, such as chemical curing or heat curing. Condensation catalysts are among the typical catalysts used to crosslink silicone polymers. Depending upon the silicon polymer's reactive groups, other catalysts and initiators can also be employed. Free radical catalysts, such as peroxide catalysts, may be used when silicone polymers contain a vinyl group. Ultraviolet light radiation and silane-olefin addition (hydrosilation) may be used when silicone polymers have terminal double bonds or silicone hydride groups in the terminal positions. Silicone compounds with hydroxy groups can also be catalyzed with heat. In the described processes (Ref. 1, 4 and 5) for forming a resin blend of polysiloxane, the use of boron nitride as a filler in combination with the above described typical catalysts has been mentioned. However, the method of controlling the polymerization is with conventional catalysts and heat. Most prior art has concentrated upon quartz and related ceramic additives for enhancing the ceramic yield, while using conventional catalysts for controlling the polymerization process. Conventional, e.g. organo-zinc catalyst agents (Ref. 1), for polysiloxane polymerization reactions commonly utilize an organic or organometallic agent generally provided in a small quantity at less than 1% of the resin weight. Once a conventional catalyst has been spent in assuring the polymerization reaction, little is offered from the remnants of the catalyst for the final product advantages. 3ecause it creates a multiple reaction rate control problem, a combination of an accelerator conventional catalyst with boron nitride is less desirable. Objectives of the Invention The objectives of the invention are to: Provide ceramic catalyst (BN or BN/Si0 2 ) which can be adjusted in weight and particle size to assure the resin formulation will gel when heated at 350°F within 4 to 10 minutes with a preferred time of 5 to 7 minutes. Provide catalyst that will increase resin formulation's ceramic yield. Increase amount of boron nitride resin loading capability beyond 12 BN wt% by adding silica (Figure 2) to inhibit the otherwise high resin reaction rate. Provide BN or BN/Si0 2 catalyzed resin formulations which will thoroughly impregnate fabric reinforcement (typically as thick as .010 inches (.25 mm) with a real weight of 8.7 oz/yd 2 (300 gm/m 2 ) at ambient temperature with minimal to no solvent. Enable the fiber reinforced ceramic products produced from the resin formulation to achieve higher mechanical strength properties at high temperatures (1830°F, 1000°C) through increased ceramic matrix lubrication of the fiber to matrix interface within the composite structures. Enable laminates made from the above described formulation to be cut with laser technology (C0 2 , YAG, etc.) forming products with a glass sealed (borosilicate ) edge superior in mechanical properties to die cut parts. Provide catalyst with nonmetallic elements for producing high dielectric electrical application products. Provide a ceramic catalyst alternative to conventional organic and organometallic catalysts. Typical catalyst compositions are provided in Table 1 for the BN weight % determined for different parts Si0 2 (see Figure 3a) in a BN+SiO 2 +100R mixture. Table 1 Boron Nitride Weight Percent For Different Si0 2 Resin Loading Levels For Preferred Gel Times (minutes) at 350°F (177°C) (Where BN wt%=[BN/ (BN+SiO 2 +100 R]xl00%) Resin Gel Time Different SiQ 2 Loading Levels (see Figure 3a) heating @350°F (no Si0 2 ) (2.5 Si0 2 ) (10SiO 2 ) (15Si0 2 ) (20 Si0 2 ) response (minutes) BN(wt%) slow >10 <3 <5 <1 <16 <20 10-7 3-5 5-10 14-22 16-26 20-30 preferred 7-5 5-8 9-11 21-23 25-27 29-31 5-4 8-12 10-17 22-32 26-37 30-41 <4,>2 13-30 17-40 32-61 37-67 41-7 fast <2 30-50 >40 >61 >67 >72 When only very low levels of boron nitride are desired within the resin blend (i.e., <3 weight percent boron nitride), the use of submicron Al 2 0 3 at <0.25 wt% will facilitate the polymerization reaction. Since submicron Al 2 0 3 is highly reactive, only a trace amount is needed to assure the reaction. When BN is used without Si0 2 (Table 1), the most preferred gel time is 4 to 7 minutes which is controlled by using the BN at a limited concentration of 5 to 12 wt%. when higher BN concentrations are needed, the use of Si0 2 to regulate the gel time (Figure 3a ) is preferable. This is an essential consideration, since the boron nitride reaction time becomes too fast for practical resin processing at higher concentrations. Table 2 demonstrates how silica can be used for regulating the gel time at 5 to 7 minutes at 350°F for increasing concentrations of BN as shown in Figure 3a. Table 2 Parts BN wt% Silica B 3NN BBNN//SSii00 22 RReessiinn Gel Time @ 350°F (minutes ' 13 none 14.9 not applicable <4 (when>13%, reaction too fast) 10 2.5 11.4 4.6/1 5-7 (preferred) 22 10 31.0 3.1/1 5-7 (preferred) 26 15 40.4 2.7/1 5-7 (preferred) 30 20 51.4 2.6/1 5-7 (preferred) It is the further objective of this invention to provide a practical method of processing the preferred polysiloxane resin blend into impregnation blends with a high quality uniform dispersion of submicron boron nitride. When added to polysiloxane blends during "hot melt" processing, submicron ceramic particles tend to "clump" together in high-speed mixing. This approach also limits the concentration of BN to roughly 20%. Because it diminishes the available surface area, this condition also renders the boron nitride less precise as an effective controlling catalyst. The preferred processing approach is to disperse the submicron boron nitride into the polysiloxane resin blend; using anhydrous acetone to facilitate an even distribution with minimal to no particle agglomeration or clumping observed. The use of anhydrous acetone allows for easy acetone removal, and thoroughly dissolves all polysiloxane blend constituents without leaving water contamination. It is the further objective of this invention to produce a variety of high-temperature non-metallic composite products. the products may be cut from flat composite laminates, molded from various ceramic fabrics and fiber reinforcements with a preferred S-glass, 8 harness satin (8HS), style 6781 fabric. They are, then, impregnated with the preferred polysiloxane formulation loaded with boron nitride and quartz filler. The preferred prepeg produced from impregnation processing is catalyzed with boron nitride and silica within the concentration range given in Figure 3a. This invention allows optimal control of submicron boron nitride and silica loaded polysiloxane resin blends for all major methods of prepreg processing. SUMMARY OF THE INVENTION In order to produce highly reliable polysiloxane resin for hot melt, wet impregnation, or resin transfer molding of ceramic reinforcements, a unique blend of resins and additives has been formulated. The catalyst used throughout is a combination of submicron boron nitride and silica, which is blended within the preferred polysiloxane blend with anhydrous acetone. To retain the control of the polymerization rate at practical level for optimal impregnation processing and molding, the BN catalyst is blended with silica. This also facilitates the practical use of high speed mixing equipment without the use of acetone. However, for preferred uniform dispersion and low temperature processing advantages, the anhydrous acetone is preferred. Other fillers include, mica, quartz, silicon hexaboride, silicon carbide, and related whisker materials including carbon whiskers. The preferred fabric is 8 HS, S-glass, style 6781 fabric. Other fabrics and fibers and E-glass, alumina-silica, fused silica and zirconia. Utilizing boron nitride and silica as the catalysts, the resins are blended together. Then, the resin blend is used to impregnate ceramic fabric; preferably from a resin impregnation process at a temperature not to exceed 200°F(93°C). Although the near ambient temperature process is preferred, a wet process in acetone can also be utilized. Using anhydrous acetone minimizes the amount of acetone required, and assures a uniform submicron ceramic catalyst (BN and SiO 2 ) dispersion. In preparing the polysiloxane blend for ambient temperature fabric impregnation, the anhydrous acetone is easily removed. The resin impregnated fabric is molded into flat laminates utilizing autoclaves and presses for high volume production to heat process the fabric at pressures from 100 to 200-psi at a temperature of 400°F (204°C) . The laminates can be cut into various high temperature gaskets using lasers or cutting dies. The boron nitride catalyzed polysiloxane matrix produces high temperature non-metallic gaskets, which are capable of sealing hot gases at temperatures of 1832°F ( 1000C) . Due to the high ceramic yield of the ceramic catalyzed resin formulation, the laser cut gaskets are formed with glass sealed edges. High temperature head gaskets made from the combination of BN and Si0 2 catalyzed resin, and reinforced with S-glass fabric has been tested in 2-cylinder, 2.5 horse power Kohler command IC engines. After the gasket was installed, the gasket was found to successfully seal hot combustion chamber gases, at exhaust temperatures of 1000-psi and 1500°F( 816°C) , for three months extensive durability testing. When BN and Si0 2 are used in combination (Figure 1), the addition of Si0 2 can be used to regulate the reactivity of BN catalyzed polysiloxane reactions. This synergistic advantage of using Si0 2 in combination with BN is not obvious and it is significant in allowing polysiloxane resin formulations to be produced with high concentrations (>12 to 75 wt%) of BN. Even when heated to 350°F, mixing silica with polysiloxane resins is essentially non-reactive. When conventional (Ref. 1), e.g. organo-zinc, catalysts are used, the silica performs as a filler, which neither activates nor inhibits the reaction. As shown in Figure 2, boron nitride is, however, thermally reactive with polysiloxane resins. Figure 2 shows the "gel" times measured at 350°F(177°C) for different BN concentrations. For most practical applications, when BN is used as a catalyst without Si0 2 , it is limited to a concentration from 4 to 12 wt%. The reactivity of BN at 350°F if too slow at less than 4 and too fast at greater than 12 wt%. While constantly stirring at 350°F (177°C), the "gel" time for different concentrations of a catalyst in a polysiloxane resin can be observed precisely at the time when the polymerizing resin mixture suddenly loses fluidity; e.g., after bubbles no longer rise in it, and the liquid phase suddenly changes to a high viscosity rubber or solid. When slower rates of reaction are desirable, the gel may be determined at lower temperatures, such as 250°F and 150°F. Using a conventional catalyst with Si0 2 , the Si0 2 is non- reactive and serves essentially as a filler. When a conventional accelerator catalyst is used with BN, the reaction time generally becomes too fast for most practical applications. By using an inhibitor catalyst with BN, which is the preferable technique, BN may be used at high concentrations. Combining Si0 2 with BN, the ceramic yield is greater than achievable by BN with non-ceramic catalysts . The relative amount of Si0 2 needed to regulate the BN catalyzed reaction, within practical gel time limits, is revealed in Figure 3a. When low BN catalyst concentrations are needed, only low levels of Si0 2 are required to regulate the reaction (see Figure 3a) . Correspondingly, when high BN concentrations are required, higher levels of Si0 2 are needed to regulate the reaction time within practical limits. The practical gel time at 350°F (177°C) typically is from 2 to 12 minutes (Figure 3a) , with the preferred range at 4 to 10 minutes. Figure 3b reveals the BN wt% catalyst concentrations and gel times most preferred for composite applications . A target gel time of 5 to 7 minutes is preferred for fiber reinforced composite product applications. When higher boron nitride loading levels are desired, adding silica (see Figure 2 and 3) will allow higher boron nitride loading capability within easy to control resin processing times. Each ceramic catalyst remnant, upon pyrolysis, enhances the ceramic yield. After pyrolysis, the ceramic yield is in excess of 90% for fiber-reinforced ceramic product applications in the thermal range of 1000 to 2000°F. Beyond the capabilities of the common conventional catalysts, the ceramic catalysts provide significant high temperature, high yield, electrical and product performance advantages not achieved before. When ceramic catalysts are used, the physical surface area of the ceramic particulate is a controlling factor. The smaller the particulate size the greater the surface area. For both boron nitride and silica, a submicron particle size is preferred. The boron nitride particulate is also porous, which increases the reactive surface area. All considerations to assure the particulate surface is contaminant free and dry for polymer processing are undertaken in preparing the resin blends. The selection of particulate sizes also affords a method of controlling the reaction, larger particulate sizes slow the reaction down, while finer sizes increase the rate of reaction. To further modify the reactivity of the polymer resin blends, colloidal silica solutions have been used in combination with submicron boron nitride. A purity of 99% or greater for the ceramic particulate is preferred. Metallic contaminants are avoided when selecting the ceramic particulates , especially in electrical applications. The invention describes the necessary controlling processes for preparing the resin formulations. These processes enable the resin to thoroughly impregnate the fabric, while it is heavily loaded with filler materials. The enabling technology of this invention allows a minimal-solvent to solventless resin formulation to be used at ambient temperature for high speed resin impregnation of fabric. Compared to conventional "wet" (high solvent) and hot melt (low filler levels) resin formulations, this approach assures a clean, pollution-free environment and offers the lowest cost in producing prepreg materials. Also, the heat treatment and densification processes are described for producing composite products with high ceramic yields from the prepreg materials. Brief Description of Drawings Fig. 1 is a histogram showing silica capacity to inhibit boron nitride catalyzed polysiloxane reactions. Fig. 2 is a graph showing resin system gel times verses boron nitride catalyst. Fig. 3a is a graph showing resin system gel time verses boron nitride and silica and catalyst concentrations. Fig. 3b is a graph showing the preferred range of boron nitride and silica catalyst concentrations based on Fig. 3a data. Fig. 4a is a graph showing resin system gel time verses boron nitride-silica ratios. Fig. 4b is a graph showing the preferred boron nitride-silica ratio range for resin system gel times verses boron nitride-silica ratios . Description of the Preferred Embodiments The unique resin employed is blended from three different molecular weight silicone resins, the primary component is a solid resin, such as methylphenylsesquisiloxane, which is preferably dissolved into two lower-molecular weight liquid resins; one is dimethyl polysiloxane silanol, and the other is a methylsiloxane resin. To facilitate the thorough mixing of the resin blend, a solvent such as anhydrous acetone may be added to initially dissolve the methylphenylsesquisiloxane. A typical resin blend with a preferred additive system is given in Table 3. Table 3 Resin/Additive Formulation Parts by Weight In General Preferred (1) Methylphenylsesquisiloxane 50 65 (2) boron nitride catalyst, 5-14 8 quartz, 1-2 1.3 (3) Dimethyl polysiloxane silanol 10-50 25* (4) Methylsiloxane resin 5-50 10 ♦ Approximate amount since commercial formulation will have other ingredients. Table 4 displays the formulation using preferred commercially available resins. Table 4 Formulation Using Commercial Resins Parts by Weight In General Preferred (1) GE Silicones SR 355 silicone 65 65 resin (high MW) (2) boron nitride catalyst 5-14 8 quartz, 1-3 1.3 (3) GE Silicones TPR 178 10-50 25 (4) GE Silicones TPR 179 5-25 10 For the above resin formulation based on 100 parts by weight of the silicone resin, typically for a practical 4-7 minute gel time at 350°F, the boron nitride/silica catalyst ratio is 6:1. See Figure 4a for greater detail. Alternatively, Dow Corning materials can be used for some of the equivalent GE silicone resins. As set forth in Table 5, the range of products obtained is directly related to the cure temperature. Table 5 Products Obtained Cure Temperature Rubber Products 300-400°F High vacuum sealing products 400-500°F High mechanical strength products 500-750°F Green ceramic products 800-1250°F Hard ceramic products 1250-2350°F These resin formulations are most effective when used to impregnate refractory fibers, such as: S-glass, E-glass, quartz, silica, alumina and alumina-silica fibers, fabrics or braided preforming materials. According to Owens Corning, there are two grades of glass fiber used in the composites industry: E-glass or electrical grade, and Owens Coming's patented S-2 Glass R high-strength fiber. S2- Glass R fiber is said to provide higher strength and corrosion resistance than E-glass. It is used in the more demanding applications, which require added strength, lighter weight or both. Both E-glass and S-2 Glass R fiber compete against exotic fibers like ara id, carbon, and boron. Due to cost performance advantages, Owens Corning claims that 99% of all fibers used within the composites industry are glass fibers. When these refractory fibers are used with this polymer blend to produce fiber-reinforced composites, the parts produced have superior ceramic yield, ease of laser cutting, mechanical gasket sealing at high temperature, thermal insulating, dielectric, and reduced friction properties. Table 6 provides typical combinations of the resin blend for specific fibers and molded composite performance temperatures. Table 6 Silica Fiber Reinforced Composite Primary Structure Materials for Different Temperatures *Note: The fiber sizing coating was <1% of the fiber weight and the coating was a low mw polysiloxane with 10 wt% boron nitride. For the various fiber-to-matrix additive relationships set forth in Table 4, it is seen that, for all of the high-temperature ceramic products, BN is the specified fiber coating to assure highest performance. The boron nitride, BN and silica Si0 2 is best employed in particles sizes of 1 micron or less. This BN is available from CERAC, Inc. as item #B-1084. Si0 2 is preferred as quartz. Table 7 BN/SiO 2 Resin Formulation (Figure 4a and 4b) Resin formulation Parts by Weight (1) Methylphenylsesquisiloxane 65 (2) boron nitride (98% submicron) 5-14 (3) Quartz (submicron) 1-2.5 (4) Dimethyl polysiloxane silanol 25* (5) Methylsiloxane resin 10 ♦ Approximate amount since commercial formulation will have other ingredients . When the fiber reinforced composite is molded from the above resin, it is heated to high temperatures to produce ceramic products. One of the key features of this invention is to use a slow controlled heat schedule in this procedure. Below is an example of such a schedule. Slow Controlled Heat Schedule After two hours under 200-psi pressure and 350°F (177°C), a typical 1/8-inch thick fiber-reinforced molded panel is heat- treated on the following heat schedule for optimal ceramic performance properties: • Heat from 350°F (177°C) to about 960°F (515°C) at about 212°C)/hour. .Then hold at about 960°F for about 48 hours. .Then raise from 960°F to 2000°F (1093°C) at about 50°F (10°C)/hour. .Then hold for about 2 hours. .Then raise from about 2000°F (1093 C C) to about 2300°F (1260°C). .Then hold for about 2 hours at about 2300°F (1260°C). .Then cool at not more than about 212°F/hour. To formulate the polysiloxane resin containing the BN and Si0 2 , and to impregnate the ceramic fibers or fabric for composite molding and ceramic processing, a variety of polysiloxane oligomers, which are well known in the art, can be used. These polysiloxane oligomers include those commercially available from Dow Corning, General Electric and others. The silicon matrix used in this invention is essentially an elastomer when heat treated to 350°F (177°C), thermoset to 700°F (371°C), a green ceramic to 1300°F (704°C) and a ceramic to 2300°F (1260°C). Depending upon the temperature to which the composite is heat treated, its properties fall between those of elastomers and ceramics. The formulation is adjusted to provide fiber impregnation and composite molding advantages. With no apparent processing problem, the resin may be stored for a multitude of weeks at ambient temperature. Until it is released at the appropriate processing cure temperature, the polymer reaction is so slow at ambient temperatures that it provides a very practical "out time" level. The initial reaction in the heat cure of the resin formulation initially involves condensation of methoxysilane and silanol end groups. This condensation reaction has a methanol by-product. As the temperature is raised from 300°F (149°C) to 550°F (228°C), it is followed by a cross-linking polymerization reaction. The cross- linking at the higher temperatures forms a dense thermoset polymer network with the evolution of formaldehyde and methanol . This is followed by the decomposition of the polysiloxane matrix from 802°F (428°C) to 1050°F (564°C). In the 937°F (503°C) to 1220°F (660°C) range, the methylsiloxane component decomposes evolving methane. Many polymer combinations can create polysiloxane polymers. One family of polysiloxane formulations are called "rigid" silicone resins; which are prepared from cohydrolyzed organochlorosilane mixtures, containing high functionality in desired ratios to form resin intermediates high in reactive silanol groups. The resin intermediate is subsequently partially condensed to form a complex polysiloxane polymer. The prepolymer is still solvent-soluble and in a usable form. In the presence of heat and/or catalyst, the remaining silanol groups of the prepolymer condense further to fully cure the resin, the by-product of the cure is a small amount of water and methanol from condensed-OH groups. Depending on the choice of the predominately methyl and phenyl radicals, resins of this type may vary widely in physical form and handling characteristics. To provide a blend having these characteristics, members from the appropriate polysiloxane polymers, which are well known in the art, are chosen. The rigid polysiloxane polymer is both chain extended, branched and may also be cross-linked. Boron nitride has been found to perform well as a thermal- activated catalyst (accelerator). Figure 2 provides the gel times which are comparable for typical curing agents , such as the peroxide or metallic hexanoate and aliphatic hexanoic acid catalysts. These organic catalysts are used typically at <1% by weight of the resin blend with no ceramic yield. The invention provides the opportunity for producing superior ceramic filled matrix composite parts. It may be used to produce the following: industrial gaskets (including internal combustion engines, chemical pumps, etc.), valves, pistons, push rods, engine blocks and heads, seal rings, turbine engine combustion liners and blades and composite industry autoclave tooling, press tooling, glass industry mold-forming tooling and high temperature fasteners, and super plastic forming tools. The mechanism for the superior parts to be produced is directly related to the preferred use of boron nitride and silica as the catalysts for the polysiloxane polymerization. This is achieved in two ways . The first method utilizes the boron nitride and silica at less than 1 micron particulate size, with a preferred concentration shown in Figure 3b. The concentration is most desired for controlling the impregnation hot melt process at less than 200°F (93°C) with sufficient process time for long prepreg processing runs. The gel times have been found to produce the polymerization of polysiloxane with excellent control of the reaction when using a combination of submicron boron nitride and silica (see Figure 3a) . The second method uses anhydrous acetone to uniformly disperse the submicron boron nitride and silica throughout the polymer blend without "clumping", and allows an ease of removal of the acetone with minimal use of the solvent. The boron nitride lubricates the interface between the fiber and matrix; this increases the load bearing capability of the composite systems so that the higher mechanical properties can be realized for parts requiring high temperature performance conditions, such as internal combustion engine non-metallic composite head gaskets. By using the formulations and the slow heating cycles of this invention, component parts can be processed to 1500°F (816°C) so as to provide total removal of residual organic by-products. Parts made in this manner should produce more reliable performing CMC valve products . Laser cut tensile specimens have been found to have 43% higher strength than die cut specimens. The glass edge created from the laser is less notch sensitive than die cut edges. The ceramic filled matrix composite products may be formed by the method described in the co-pending United States patent application serial number 08/962,783 filed November 3, 1997, which is incorporated herein by this reference. Basically the method comprises the steps of impregnating the fibers of a fabric such as a ceramic fabric (e.g. ceramic fibers woven into a fabric such as eight harness satin style 6781) with a resin according to the present invention, rebulking the impregnated fabric by heating under vacuum conditions (e.g. 235°F for one hour), coating the fabric with a sealant, impregnating a second layer of fabric with resin and layering it on the first layer of fabric and repeating the rebulking, coating and impregnating processes for each additional layer of fabric desired for the final product. Then coating the outer layers of the product with boron nitride and curing the product at an elevated temperature and pressure (e.g. 450°F for one hour) . Alternatively, during the impregnating process, the outer surface of the fabric may be coated with a silicon sealant such as that described in the concurrently filed United States patent application Serial Number 09/185,281 filed November 3, 1998 and entitled "High Temperature Silicon Sealant". Preferably, the foregoing method is utilized to produce gaskets, washers and other laminated sheet-like articles which may be die cut in a conventional manner from panels of the laminate. Preferably, however, it has been discovered that when such articles formed of the resin material of the present invention are cut from panels using a laser, glass sealed edged are formed which are vastly superior to the edges formed by die cutting and result in about a twenty-five percent increase in the tensile strength of the resulting article. It is believed that such increased tensile strength is due to the "picture frame" like structure that is formed along the outer edges and around the interior holes cut in the panel by the laser in the forming of the gasket and washer like articles. In such a laser cutting, the resin material of the present invention used in forming the laminate is vaporized in the cutting regions and upon cooling forms the glass like sealed edges. Further, with respect to such laser cutting, it has been found that the preferred method of laser cutting is with a carbon dioxide laser set at about 200 to 250 watts of power with a nitrogen gas purge in the area of the laser cut. The purge with nitrogen is accomplished by nitrogen at a positive pressure being directed through a shroud around the laser beam at an area surrounding the cutting region to saturate the cutting region with nitrogen thereby removing undesired carbon from the vicinity of the resulting glass sealed edge. The unexpected advantages of using a laser cutting process with articles formed with resin materials according to the present invention are: 1. Glass sealed edges on the article which is particularly important for containment of hot combustion gasses in automotive applications. 2. Glass sealed edges for chemically inert containment of engine transmission, clutch, brake and other automotive fluids requiring fluid containment. 3. Increased tensile strength, as previously described. 4. Increased modulus of elasticity for delicate articles such as thin automotive gaskets. 5. Cost reduction in the manufacture of the resulting articles. 6. Finally, for hybrid laminate articles, the laser results in a "marrying" of thermally insulating and thermally conductive portions of the article. In this regard, such hybrid articles including gaskets are formed as previously described starting however with a metallic substrate material such as an aluminum sheet which is cleaned as with acetone prior to the application of the resin sealant to its opposite surfaces and the coating with the resin material. Then the layers of fabric material, such as a porous Teflon sheets, are added in the previously described manner. In the laser cutting, the aluminum sheet is cut with the balance of the material (silicone laminate) allowing for high torque retention and thermal conductivity, the resulting microstructure produced at the laser cut interface is made up of silicon and aluminum at the external edge. Within the S-glass film, the composition is about: 65% Silicon dioxide 25% Aluminum dioxide 10% Magnesium oxide When the metal core is Invar, the composite sealant is used to bond the composite laminate has preferably made up of S-glass fabric. The resulting hybrid laminate has a low coefficient of expansion for high temperature diesel engine spacing head gasket applications with minimal thermal stresses. When the resulting articles are washers, several unexpected advantages have been discovered, as follows: 1. the washer performs a "Bellville" washer functions as an "elastomeric" washer with minimal metal brinnelling. 2. The washer retains bolt torque load through elastomeric rebound to compensate for metal brinnelling. 3. The washer substantially reduces metal bolt flatness of mating surfaces. 4. The washer as a rubber washer performs load spreading function at high temperatures. 5. The washer functions as a sound dampener such as when the washer is located around fuel injectors in diesel engines. The different functions as set forth above depend upon the curing temperature to which the washer is subjected as set forth below: Temperature Function 70-450°F Rubber washer with rebound 450-700°F Load spreading washer 700-1200°F Preceramic washer transformation 1200-2000°F Ceramic washer transformation It is understood that the foregoing detailed description is given merely by way of illustration, and that many variations may be made therein without departing from the spirit of this invention.

Claims: Claims 1. A polysiloxane resin blend including boron nitride and silica wherein catalysis of the blend is regulated by the silica and the blend has a concentration of boron nitride of between 12 and 75 weight %. 2. The resin of claim 1 wherein the blend is between about 2 to 20 parts silica to about 20 to 50 parts boron nitride. 3. The resin of claim 1 blended from a solid silicon resin and two lower molecular weight liquid silicon resins. 4. The resin of claim 3 wherein the solid resin is methylphenylsesquisiloxane and the liquid resins are dimethyl polysiloxane silanol and a methylsiloxane. 5. The resin of claim 4 wherein anhydrous acetone is added to initially dissolve the solid resin. 6. The resin of claim 1 in a laminated article. 7. The combination of claim 6 wherein the article is a gasket. 8. The combination of claim 6 wherein the article is a washer. 9. The combination of claim 6 wherein the article is formed from a laminated panel and is cut therefrom using a laser to form glass sealed edges on the article.

Inventors: CLARKE WILLIAM A, CLARKE, WILLIAM, A.
Applicants: GASKET KING LLC, THE GASKET KING, LLC
Application year: 1999
Main classification: C08G77
IPC codes: B32B27, C08G77, C08K3, C08L83