JPS6328468B2 - - Google Patents

Description

Claim 1 (A) Essentially methyl, vinyl, phenyl,
and 3,3,3-trifluoropropyl, and 10 to 100 parts by weight of treated reinforcing silica filler, with a vinyl group content of 0.01 to 0.1. 100 parts by weight of a mixture which is 1% by weight, 1 pretreated white clay having a surface area of not more than 50 m ² /g whose surface has been treated to contain olefinically unsaturated siloxy groups.
~150 parts by weight 2 and an organic peroxide vulcanizing agent 3 to form an improved silicone elastomer composition, (B) molding the improved silicone elastomer composition, and (C) molding the molded silicone elastomer composition. Thermal stability of a silicone elastomer, characterized in that the vulcanized silicone elastomer has improved thermal stability by heating the silicone elastomer composition at an elevated temperature for a period sufficient to vulcanize the silicone elastomer composition. How to improve sex. 2 Mixture before addition of pretreated white clay
The method according to claim 1, wherein (1) is heated. 3. The method according to claim 1, wherein the vinyl group content of the mixture (1) is 0.025 to 0.1% by weight. 4. The method according to claim 1, wherein the pretreated white clay is kaolin clay having a surface containing vinylsiloxy groups and having an average particle size of 5 microns or less. 5 (i) essentially methyl, vinyl, phenyl,
and 10 to 100 parts by weight of a treated reinforcing silica filler, with a vinyl content of 0.01 to 0.1 parts by weight. (ii) a pretreated white clay having a surface area of not more than 50 m ² /g, the surface of which has been treated to contain olefinically unsaturated siloxy groups;
150 parts by weight, and (iii) a silicone elastomer composition having improved thermal stability when vulcanized. 6. The composition according to claim 5, wherein the vinyl group content of the mixture (1) is 0.025 to 0.1% by weight. 7. The composition according to claim 5, wherein the pretreated white clay is a kaolin clay having a surface containing vinylsiloxy groups and having an average particle size of 5 microns or less. 8. A composition according to claim 5, further comprising a heat-stable pigment. BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method for improving the thermal stability of colorable silicone elastomers that are catalyzed by organic peroxides and thermally vulcanized. Description of the Prior Art Elastomeric materials based on polyorganosiloxane polymers have found utility in part because of their resistance to the effects of high temperatures. Despite the inherent thermal stability of polyorganosiloxane polymers, much work has been done to improve their thermal stability. The majority of heat-stable additives discovered are metal oxides. Iron oxide is the most commonly used metal oxide. Some metal salts are also useful. Because metal oxides and metal salts are themselves coloring in silicone elastomers, many of these additives are not useful if it is desired to color the elastomer. Simpson U.S. Patent No. 1, issued September 12, 1967.
No. 3,341,489 discloses the addition of certain olefinically unsaturated organosilicon materials, such as vinyltriethoxysilane, to organopolysiloxane compositions that can be converted to a cured, solid, elastic state. The resulting formulation could be directly processed into valuable elastic products without the need for elongation and subsequent curing. A brochure published by Union Carbide Corporation and designated F-44715B entitled "Silane Coupling Agents in Mineral-Reinforced Elastomers" describes the use of mineral fillers to improve the mechanical and dynamic properties of elastomers. It has been suggested that fillers such as pyrogenic clays treated with vinyl functional silanes can be added to formulated peroxide cured elastomers, including silicone elastomers. There is no teaching on how to improve the thermal stability of silicone elastomers. Inorganic fillers treated in this way can be used for polyester resin, crosslinked polyethylene, ethylene/propylene rubber, and ethylene/propylene rubber.
It has been used in propylene terpolymers to yield products with improved physical properties. SUMMARY OF THE INVENTION A method has been discovered to improve the thermal stability of colorable silicone elastomer formulations. A silicone elastomer composition having a vinyl group content of 0.01 to 0.1% by weight, a pretreated white clay having a surface area of 50 m ² /g or less and containing olefinically unsaturated siloxy groups on the surface, and an organic peroxide. Mix with vulcanizing agent. An improved silicone elastomer composition is produced and thermally vulcanized. The cured silicone elastomer has improved heat resistance compared to silicone elastomer materials without the addition of pretreated white clay. It is an object of the present invention to provide a method for improving the thermal stability of certain silicone elastomers in a convenient and economical manner. It is an object of the present invention to provide a method of improving the thermal stability of certain silicone elastomer formulations in such a way that the compositions can be colored in a desired color. DESCRIPTION OF THE INVENTION The present invention consists of (A) a polydiorganosiloxane rubber having organic groups selected from the group consisting essentially of methyl, vinyl, phenyl, and 3,3,3-trifluoropropyl; 100 parts by weight of a mixture consisting of 1 part treated reinforcing silica filler with a vinyl group content of 0.01 to 0.1% by weight, 50 m ² / preparing an improved silicone elastomer composition by mixing 1 to 150 parts by weight of a pretreated white clay having a surface area of less than
molding the improved silicone elastomer composition; and (C) heating the molded silicone elastomer composition at an elevated temperature for a period sufficient to vulcanize the silicone composition to obtain an improved vulcanized silicone elastomer. The present invention relates to a method of improving the thermal stability of silicone elastomers comprising thermally stable silicone elastomers. Silicone elastomers are commercialized in part based on their inherent resistance to the effects of high temperature exposure. Since their early commercialization, efforts have been made to improve the thermal stability of silicone elastomers. The method of the present invention provides improved thermal stability for certain silicone elastomers. In addition to improving thermal stability at least as economically as other known methods, the method also has the advantage of producing silicone elastomer compositions that can be colored to any desired color. There is. The method of the present invention to provide a colorable silicone elastomer with improved thermal stability relies on the use of a specific silicone mixture 1 and a specific pretreated white clay. The use of clay 2 in combination with specific silicone mixture 1 resulted in an unexpected improvement in thermal stability for the resulting silicone elastomer. Silicone mixtures useful in the present invention are commercially available in several specific forms. Mixtures of these with an essential vinyl group content of 0.01 to 0.1% by weight are practicable. The mixture contains a polydiorganosiloxane rubber having organic groups selected from the group consisting of methyl, vinyl, phenyl, and 3,3,3-trifluoropropyl, where the organic groups are silicon ions of the polydiorganosiloxane. bonded to atoms. Polydiorganosiloxanes typically have a viscosity of 1000 Pa.s or more to include non-flowing gums. Mixture 1 also contains reinforcing silica filler to improve the physical strength of the polymer. The reinforcing silica filler has a surface area from 150 m ² /g to more than 400 m ² /g. Such reinforcing silica fillers are known and commercially available. The reinforcing silica filler may be treated or may be treated in situ during the manufacture of the mixture. Treated Reinforced silica fillers can be treated by any of the conventional methods disclosed in the prior art, where the treating agents include organosilanes, organosiloxanes, and silazane. Processes for the preparation of treated reinforcing silica are described in U.S. Pat. US patent
No. 3,334,062, Smith, US Pat. No. 3,635,743, issued January 18, 1972, and Hartage, US Pat. No. 3,624,023, issued November 30, 1977. The amount of reinforcing filler starts from 10 parts by weight per 100 parts by weight of polydiorganosiloxane.
It can be varied up to about 100 parts by weight, preferably from 15 to 75 parts by weight. If the reinforcing silica filler is not treated as described above, it is necessary to treat the reinforcing silica in situ during the mixing process to prevent reaction between the polydiorganosiloxane rubber and the reinforcing filler.
The reaction results in a mixture that is too hard to process, a phenomenon known as creep hardening. Reinforced silica can be treated by adding creep inhibitors in situ during mixing of the composition. During the preparation of Mixture 1, the composition may be heated during the mixing step to improve the reaction between the hydroxyl groups on the surface of the reinforcing silica and the creep inhibitor. Effective creep inhibitors are known.
It includes low molecular weight silanes, siloxanes and silazane. Short chain siloxanes, typically end-capped with hydroxyl or alkoxyl groups so that they react with the hydroxyl groups present on the surface of the reinforcing filler, are often used. The organic groups present in the creep inhibitor are the same as those found in polydiorganosiloxane rubbers. Silicone elastomer compositions also handle
It may also contain small amounts of additives to improve properties such as compression set, oil resistance, etc. The additive should not color the formulation unless it imparts the desired color. The pigmentable silicone elastomer formulation may consist of a single polydiorganosiloxane gum or a mixture of different gums. The composition may also contain a single reinforcing silica filler or a mixture of reinforcing silica fillers. Mixture 1 or the combination of mixtures should contain 0.01 to 0.1% by weight of vinyl groups. Vinyl groups may be present in the polydiorganosiloxane, in the creep inhibitor, on the surface of the reinforcing filler, or in other additives in the mixture. Preferred vinyl group content is 0.025-0.1% by weight
It is. Another critical component present in the silicone elastomer formulation used in the process of the invention is a pretreated white clay with a surface area of 50 m ² /g or less. The surface of the clay has been treated to contain olefinically unsaturated siloxy groups. Since the surface area of fillers normally varies with particle size, it is useful to describe the physical properties and small particle size. As the particles become smaller, the surface area increases. Kaolin clay with an average particle size of 4.5 microns has a surface area of 6 to 7 m ² /g, while clay with an average particle size of 0.2 microns has a surface area that varies from about 12 to 20 ^{m 2} /g depending on the degree of particle agglomeration. have. Clays useful in the present invention are prepared clays that do not color the silicone elastomer composition and that allow the silicone elastomer composition to be colored in the desired color. Clays that are themselves highly pigmented are not suitable. Unless the desired color is a shade similar to that produced by colored clay,
Their use in silicone elastomer compositions makes it impossible to achieve the desired color. Suitable clays are commercially mined and refined aluminum silicate minerals for use as fillers in paints, plastics and elastomers.
Clays are further defined as illite, kaolinite, and montmorillonite, all of which are complex aluminum silicate minerals. Kaolinite or kaolin clay is a more preferred clay as it is readily available in white form. For purposes of this invention, "white" is considered to lack a strong enough tint or tone to prevent further coloring of the silicone elastomer composition to the desired color. When a suitable clay is mixed into a silicone elastomer composition, the composition changes to a cream color, but the clay has low hiding power and low color intensity so that it can still be easily colored. Prior to use in the method of the present invention, a white clay having a predetermined surface area is pretreated to contain olefinically unsaturated siloxy groups on the clay surface. The most common siloxy groups are vinylsiloxy and methacryloxy. Pretreated white clays with defined surface areas and surface treatments are commercially available. A typical pretreated clay is vinylsiloxy-treated kaolin produced by treating calcined kaolin with an average particle size of 0.8 microns with vinyl-tris(β-methoxyethoxy)silane in a slurry of water followed by drying. In order to improve the thermal stability of the silicone elastomer of the present invention, as little as 1 part by weight of pretreated white clay is effective. The amount of pretreated white clay for 100 parts by weight of mixture 1
Increasing to 10 or 20 parts by weight further improves thermal stability. Mixtures 1 falling within the requirements of the invention
When 110 parts of pretreated white clay were added, the thermal stability of the resulting silicone elastomer was lower than that formed with untreated quartz powder filler (commonly used in silicone elastomers), which is outside the scope of this invention. This was an improvement over similar compositions. Retention of physical properties was not as high for compositions using higher amounts of pretreated white clay as when using lower amounts. However, it should be noted that the initial properties of the compositions are also different. The preferred amount of pretreated white clay used in the process of the invention depends on the requirements of the cured silicone elastomer as well as the other components used in the silicone elastomer. Adding more clay, for example, increases the durometer hardness of the cured silicone elastomer. If the specified durometer hardness is in the low range, the amount of filler in the silicone elastomer will have to be at a lower level than when the specified durometer hardness is in the high range. Such effects are well known and the optimum amounts of the various components can be readily determined by simple experimentation. The compositions of the present invention containing the pretreated white clay used in the present invention can be colored to any desired or required color since the clay useful in the present invention does not by itself color the composition. .
Many previously known methods of improving the thermal stability of silicone elastomers have relied on the addition of materials that strongly color the composition, severely limiting the color options available. The methods of the present invention thus produce compositions with both improved thermal stability and coloring properties through the use of commercially available and low cost ingredients. It was unexpected that the combination of defined mixture 1 and pretreated white clay 2 would provide such advantages. Optionally, untreated inorganic extender fillers may be added to the compositions used in the method. Since the use of untreated inorganic extender fillers will dilute the effect of the use of pretreated white clay, the relative amounts of clay and untreated inorganic extender fillers will influence their effect on the properties of the cured silicone elastomer. must be determined by. Inorganic extender fillers useful in silicone elastomers are known. The compositions of the present invention can be colored with known pigments useful for use with silicone elastomers. The pigments are heat stable and have little or no effect on the properties of the vulcanized silicone elastomer. The colorant is normally an inorganic oxide or salt and is finely dispersed in the silicone polymer to provide a masterbatch that can be easily dispersed during mixing of the silicone elastomer formulation. The silicone elastomer composition contains an organic peroxide vulcanizing agent suitable for vulcanizing the polydiorganosiloxane in the silicone elastomer mixture. Since polydiorganosiloxane contains vinyl groups, it can be vulcanized with either "non-vinyl" or "vinyl" organic peroxides. Typical organic peroxides for vinyl are di-tert-butyl peroxide and 2,5
-bis-(tert-butylperoxy)-2,5-dimethylhexane. Representative non-vinyl peroxides are benzoyl peroxide, dicumyl peroxide and 2,4-dichlorobenzoyl peroxide. All of these organic peroxide vulcanizing agents are known, and their properties are also known.
The properties of the cured silicone elastomer can vary depending on the type and amount of vulcanizing agent used to cure the formulation. Typical variations in such selection are well recognized in the art.
Vulcanizing agents are generally silicone elastomer based
It is present in an amount of 0.1 to 5 parts by weight per 100 parts by weight, preferably 0.5 to 2.0 parts by weight. The first step of the method of the invention consists of a mixture 1, pretreated white clay 2, organic peroxide vulcanizing agent 3,
and mixing optional ingredients. Common mixing methods in silicone elastomer technology and suitable for the present invention include dough mixers, rubber compounding mills,
or mixing using a Banbury mixer. The order of mixing is not critical. Generally, mix 1 is placed in a mixer, clay 2 and other additives are added and mixed until homogeneous, then the vulcanizing agent is added and mixed until homogeneous. When using pigments to color a silicone elastomer composition to a desired color, the pigments are mixed into clay 2 so that they are well distributed throughout the mixture to provide uniform coloring.
should be added in the same mixing order as other additives. After the improved silicone elastomer formulation is prepared in a mixing process, the formulation is molded into the desired shape. The formulation is formed into a shape by any of the conventional known methods of forming both reinforced and non-reinforced elastomeric curable compositions, such as press molding, injection molding, calendering, and extrusion. be able to. The shaped composition is then cured or vulcanized by heating at an elevated temperature for a time sufficient to cause decomposition of the organic peroxide and subsequent crosslinking of the polydiorganosiloxane. The time and temperature required to cause stock vulcanization are determined by the selected organic peroxide vulcanizing agent,
It depends on the method of heating, the method of molding the composition, and the thickness of the molded article. Suitable temperatures for a given set of conditions are known in the silicone elastomer art.
Typical temperatures are 110°C to 175°C for molding operations
The temperature of the oven used for continuous hot air vulcanization is approximately 300℃. The cured silicone elastomer produced by the method of the present invention is improved when compared to a similar cured silicone elastomer produced by a similar method but without the inclusion of the pretreated white clay used in the method of the present invention. It has thermal stability. It is completely unexpected that the inclusion of as little as 1 part by weight of pretreated white clay in 100 parts by weight of a silicone elastomer composition significantly improves the resistance of the stock to changes in physical properties due to heat exposure. That's true. The effective amount of pretreated white clay and the effectiveness of the pretreated white clay make the method of the present invention a particularly desirable method for improving the thermal stability of silicone elastomers. This method is also useful where the silicone elastomer is of any desired or required color. The silicone elastomer produced by the method of the present invention can be used in molded products, gaskets, and O
- Suitable for conventional uses of silicone elastomers such as rings, diaphragms, tube materials and insulated wires. Insulated wire can be easily colored to match the desired color code. The following examples are intended to illustrate the invention and are not intended to limit the invention, which is adequately described by the appended claims. All parts are parts by weight. Example 1 This example demonstrates the improvement in heat aging properties obtained when a small amount of pretreated white clay is present in a silicone elastomer composition. Mixtures were prepared by mixing 100 parts of a commercially available silicone mixture with various amounts of pretreated white clay as shown in Table 1 on a two-roll rubber mill. Commercially available silicone elastomer mixtures include dimethylvinylsiloxy endblocked topopolydiorganosiloxane gums having both dimethylsiloxy and methylvinylsiloxy units in amounts such that the vinyl groups average about 0.09% by weight of the rubber, a creep inhibitor. and a reinforcing silica filler having a surface area of about 250 m ² /g. The mixture contained approximately 0.07% by weight vinyl groups. The pretreated white clay was calcined kaolin clay and had been treated with about 1% by weight vinyl-tris(β-methoxyethoxy)silane. The clay thus had up to about 0.1% by weight of vinyl groups in the form of surface-bound vinylsiloxy groups.
The average particle size of the treated kaolin was approximately 0.81 microns. Each mixture contained 1 part of catalyst A (2,5-bis-(tert-butylperoxy)-2,
5-Dimethylhexane 50% active powder, vinyl catalyst) or 1.5 parts of catalyst B (2,4-dichlorobenzoyl peroxide 50% active paste, non-vinyl catalyst). Each catalyst mixture was pressed into test slabs to a thickness of approximately 2.54 mm and cured at 171°C for 10 minutes for Catalyst A and 5 minutes at 116°C for Catalyst B. After pre-squeezing, cut the slab into test pieces.
Durometer hardness according to ASTM D2240,
It was also tested for tensile strength and elongation at break according to ASTM D412. The results are shown in Table 1. Furthermore, the test piece was heated to 250℃ in an air circulation oven.
Heat aged for 24 hours and tested as described above. The changes in physical properties caused by heat aging of the test pieces were much less in those containing a small amount of pretreated white clay than in those without pretreated white clay. This improvement in heat aging was unexpected since only a small amount of pretreated white clay was added. The total filler content of the cured elastomer did not change significantly. The amount of vinyl groups on the pretreated white clay was only about 14% or 28% of the vinyl present in the base, depending on the amount of pretreated white clay used. The total amount of vinyl groups remained virtually unchanged. Example 2 The previous example was repeated using a different commercially available silicone mixture. The mixture of this example was the same as in Example 1 except that it contained more reinforcing filler and creep inhibitor, and the mixture contained about 0.064% by weight vinyl groups. Formulations were prepared and tested as in Example 1. The test results, as shown in Table 2, show that the resistance to changes in physical properties caused by heat aging was improved by the addition of a small amount of pretreated white clay. Example 3 An untreated clay similar to that of Example 2 was used to evaluate effectiveness. The filler was calcined kaolin clay, in which at least 70% by weight of the particles were fixed with anhydrous aluminum silicate, Al ₂ O ₃ .2SiO ₂ , with an average particle size of less than 2 microns and about 0.8 microns. . The mixture of Example 2 was repeated except that the pretreated white clay was replaced with the untreated clay described above. Sample preparation and testing were performed as in Example 1. The results are shown in Table 3. The untreated clay did not improve its resistance to changes in physical properties caused by heat aging to the extent that the pretreated white clay of the present invention did. Example 4 The effect of bulk additions of pretreated white clay and untreated extender filler was evaluated. The mixture of Example 1 was mixed with 110 parts of the pretreated white clay described in Example 1. The mixture of Example 1 was also mixed with 110 parts of quartz powder filler, said to have a particle size of 5 microns. This is a commercially available extender filler commonly used in silicone elastomers. The mixture was prepared and tested as in Example 1. The results are shown in Table 4. The changes in properties due to the effects of heat aging were much greater with the untreated extender than with the pretreated white clay. Example 5 The use of a pretreated white clay in a mixture similar to Example 1 but containing higher amounts of reinforcing silica filler and creep inhibitor was evaluated. The mixture used in this experiment contained approximately 0.05% by weight vinyl groups. the mixture, the amount of the pretreated white clay of Example 1 as shown in Table 5, and catalyst A or B.
1 part of either were mixed. Formulations were prepared and tested as shown in Example 1. The results show that the addition of small amounts of pretreated white clay improved resistance to changes in physical properties caused by heat aging. Example 6 This example shows the effect of pretreated white clay added to a mixture having a vinyl group content greater than 0.1% by weight, an amount outside the scope of the claims of the invention. This mixture contained dimethylvinylsiloxy endblocked polydimethylsiloxane gum having about 0.044% by weight vinyl groups. Gum is about 250
m ² /g and was reinforced with fume silica whose surface had been treated with trimethylsiloxy groups. Furthermore, both the dimethylsiloxy unit and the methylvinylsiloxy unit have a vinyl group of 7.55
% by weight of a dimethylvinylsiloxy endcapped polydiorganosiloxane fluid. The vinyl group in this mixture is approximately 0.15
It was in weight%. The formulation comprises the above base and the pretreated white clay of Example 1 in the amounts shown in Table 6.
A combination of catalysts A and B was prepared. A formulation was prepared and tested as in Example 1. Table 6
The results show that the pretreated white clay was not effective in improving the thermal stability of this comparative mixture. Example 7 This example shows the effect of pretreated white clay on other mixtures with a vinyl group content greater than 0.1% by weight which is outside the scope of the claims of the invention. The mixture of this example contained the same dimethylvinylsiloxy end-capped polydiorganosiloxane gum as Example 1. Reinforcement filler is approximately 250m ² /
It was fume silica with a surface area of g. The creep inhibitor was a mixture of a hydroxyl-endcapped polymethylphenylsiloxane fluid and a hydroxyl-endcapped polymethylvinylsiloxane fluid. The mixture contains approximately 0.2% vinyl groups by weight.
It contained. The formulation comprises the above mixture and the pretreated white clay of Example 1 in the amounts shown in Table 7.
A combination of catalysts A and B was prepared. A formulation was prepared and tested as in Example 1. Table 7
The results shown in the table show that the pretreated white clay is catalyst A.
showed no effect on improving the thermal stability of this formulation when used. It is clear that with Catalyst B, the stock did not work properly when pressed and hardened during heat aging.

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