Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/38—Boron-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/06—Preparatory processes
  • C08G77/08—Preparatory processes characterised by the catalysts used
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/04—Polysiloxanes
  • C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
  • C08G77/16—Polysiloxanes containing silicon bound to oxygen-containing groups to hydroxyl groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
  • C08G77/70—Siloxanes defined by use of the MDTQ nomenclature

Definitions

• This invention relates (1) to the use of a catalyzed combination of silica (Si0 2 ), as an inhibitor, and boron nitride
• 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.
• organo-zinc catalyst agents 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.
• the objectives of the invention are to:
• 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.
• 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 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.
• submicron Al 2 0 3 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.
• 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%.
• 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.
• 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.
• anhydrous acetone allows for easy acetone removal, and thoroughly dissolves all polysiloxane blend constituents without leaving water contamination.
• 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.
• the catalyst used throughout is a combination of submicron boron nitride and silica, which is blended within the preferred polysiloxane blend with anhydrous acetone.
• the BN catalyst is blended with silica. This also facilitates the practical use of high speed mixing equipment without the use of acetone.
• the anhydrous acetone is preferred.
• 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.
• 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.
• BN at 350°F if too slow at less than 4 and too fast at greater than 12 wt%.
• 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.
• the gel may be determined at lower temperatures, such as 250°F and 150°F.
• the Si0 2 is non- reactive and serves essentially as a filler.
• a conventional accelerator catalyst is used with BN
• the reaction time generally becomes too fast for most practical applications.
• BN may be used at high concentrations.
• the ceramic yield is greater than achievable by BN with non-ceramic catalysts .
• 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.
• the physical surface area of the ceramic particulate is a controlling factor.
• 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.
• 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.
• 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 .
• 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.
• a solvent such as anhydrous acetone may be added to initially dissolve the methylphenylsesquisiloxane.
• Methylsiloxane resin 5-50 10 ⁇ Approximate amount since commercial formulation will have other ingredients.
• Table 4 displays the formulation using preferred commercially available resins.
• the boron nitride/silica catalyst ratio is 6:1. See Figure 4a for greater detail.
• Dow Corning materials can be used for some of the equivalent GE silicone resins.
• refractory fibers such as: S-glass, E-glass, quartz, silica, alumina and alumina-silica fibers, fabrics or braided preforming materials.
• 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.
• the fiber sizing coating was ⁇ 1% of the fiber weight and the coating was a low mw polysiloxane with 10 wt% boron nitride.
• 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.
• the fiber reinforced composite 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.
• polysiloxane resin containing the BN and Si0 2 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).
• the formulation is adjusted to provide fiber impregnation and composite molding advantages.
• 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.
• 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.
• polysiloxane polymers 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.
• 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.
• FIG. 1 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.
• industrial gaskets including internal combustion engines, chemical pumps, etc.
• 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.
• 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.
• a fabric such as a ceramic fabric (e.g. ceramic fibers woven into a fabric such as eight harness satin style 6781)
• a resin according to the present invention rebulking the impregnated fabric by heating under vacuum conditions (e.
• 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) .
• 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".
• 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.
• 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 laser results in a "marrying" of thermally insulating and thermally conductive portions of the article.
• 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.
• the layers of fabric material such as a porous Teflon sheets, are added in the previously described manner.
• 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.
• the composition is about:
• 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.
• the washer performs a "Bellville” washer functions as an "elastomeric” washer with minimal metal brinnelling.
• the washer retains bolt torque load through elastomeric rebound to compensate for metal brinnelling.
• the washer substantially reduces metal bolt flatness of mating surfaces. 4.
• the washer as a rubber washer performs load spreading function at high temperatures.
• the washer functions as a sound dampener such as when the washer is located around fuel injectors in diesel engines.

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• Chemical & Material Sciences (AREA)
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• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Ceramic Products (AREA)
• Laminated Bodies (AREA)

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• 1999
  • 1999-11-03 EP EP99957494A patent/EP1044236A4/de not_active Withdrawn
  • 1999-11-03 JP JP2000579661A patent/JP2002528616A/ja active Pending
  • 1999-11-03 WO PCT/US1999/025664 patent/WO2000026278A1/en not_active Application Discontinuation

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