DE1216541B - Heat-curable polysiloxane molding compound that can be vulcanized into cell bodies - Google Patents

Description

Thermosetting polysiloxane molding compound that can be vulcanized to form cell bodies It is known by curing a mixture of diorganopolysiloxanes with a Filler silicone elastomers as a solid with a certain volume and more uniform Establish density.

It is also known to add a propellant to the masses prior to curing incorporated, whereby foams from silicone elastomers are obtained. Such Foamed elastomers do not have a uniform density and stretch during of hardening.

It is therefore very difficult to determine the volume of the finished foamed To control elastomers.

The known foams are known to be produced by the following process steps: melting the silicone, mixing with catalysts, blowing agent and optionally fillers, the course of the foaming reaction, pre-curing and post-curing and further temperature treatment.

The vulcanizable to cell bodies, fillers and optionally Thermosetting polysiloxane molding compositions containing heat-curing catalysts are characterized according to the invention in that it consists of a mixture (1) of organopolysiloxanes, (2) from 20 to 50 parts by weight of a reinforcing filler per 100 parts by weight Organopolysiloxane; and (3) from 10 to 500 parts by weight of solid particles of a void generating Substance per 100 parts by weight of organopolysiloxane and filler consist, wherein the void-generating substance at the curing temperature of the organopolysiloxane is in the solid state, is insoluble and inert in the organopolysiloxane and a water-soluble, solid substance or one at temperatures above the curing temperature of the organopolysiloxane and below 260 "C volatile solid substance represents.

The formation of cells therefore takes place from the molding compositions according to the invention in a much simpler way than was previously the case, with as a special one Advantages to be emphasized are that moldings with good dimensional stability and extraordinary small tolerances can be produced. It was also surprising that an inert, cell-forming material from the cured polysiloxane only by treatment can be practically completely removed with water.

The finely divided, solid, void-creating substance is in the Rubber is insoluble and cannot react with it, it is infusible and decomposes does not change at the curing temperature of the rubber, but can follow from the mass easily removed after curing to elastomer, e.g. B. by washing with water, by heating and simultaneous Decomposition or evaporation. Here stay behind in the cured elastomer there are voids corresponding to the particle size of the solid particles correspond. The cavity-containing elastomer can then undergo post-curing Stabilization of the elastomer by removing the volatile, low molecular weight siloxanes removed.

The dimensionally stable, cell-containing silicone elastomers have a density of 0.35 to 1.00 g / cm3, depending on the particle size and the amount of solid particles that were incorporated into the siloxane rubber composition before curing.

The thermosetting polysiloxane molding compounds can, in addition to the organopolysiloxane rubber, the filler and the void-creating substance are hydroxy or ethoxysilicon compounds contain.

They make the masses easier to soften after standing. The compositions also contain a hardening agent.

The curable polysiloxane molding compounds are mixed at room temperature, in any case below the curing temperature, with the ingredients described above produced to a uniform dispersion. It is preferable to mix first all components with the exception of the solid, void-creating particles. You get such a uniform dispersion which, when mixing is continued, creates a cavity Material is mixed in.

If you have the voiding material at the same time with admits the other substances, it is generally difficult to obtain a uniform To obtain dispersion, so that the cell structure of the elastomer made from it is not uniform.

Suitable devices for mixing and processing the components are roller mills, the rollers of which run at different speeds, as well Banbury mixer. The organopolysiloxanes are placed on the rollers and become one rolled out into an even layer. Then the filler is added, rolling continued until the filler is evenly distributed in the organopolysiloxane. Other Additives, e.g. B. plasticizers such as a hydroxy or alkoxysilicon compound and optionally coloring, are added and rolling continued until one a uniform dispersion is obtained again. The molding compositions according to the invention contain a curing catalyst.

Such dispersions are made from an organopolysiloxane filler usually referred to as "silicone rubber compounds". After that, under continuation of mixing, the divided, void-creating solid substance is added until a uniform dispersion is obtained.

The curable siloxane rubber composition is then by conventional means Production of silicone elastomers known process in the heat to a silicone elastomer hardened containing the solid void-creating particles. The molding compound can can also be cured to elastomers by z. B. rolled in an organic peroxide and then the resulting mixture is heated so high that the peroxide is hardened decomposed the molding compound to an elastomer. The hardening process must be followed make sure that the temperature is lower than the one used to vaporize, Decomposition or dissociation of the solid, void-creating particles is required.

This silicone elastomer then becomes the solid cavity-producing one Substance removed, creating a dimensionally stable, cell-containing elastomer in which the cells have practically the same dimension as those removed from them have solid particles.

If the voiding substance is water soluble, it can removed by leaching the cured elastomer; volatile or decomposable, Void generating substances are produced at temperatures between the curing temperature and 2600 C, at which the void-generating material is volatile, sublimates or decomposes and diffuses out of the cured elastomer, removed.

When removing the water-soluble solid particles, the hardened Elastomers are alternately exposed to pressure and relaxation, creating the solid Substance is broken into finer particles that are more easily dissolved by the water will.

The elastomer is then leached with water in 2 to 48 hours. When removed by evaporation, sublimation or decomposition into gaseous products the cured elastomer is placed in an oven running on a for 4 to 48 hours Maintained temperature above the curing temperature of the elastomer up to 260 "C will. The void-creating substance is thereby made of the cured elastomer removes and leaves behind a dimensionally stable cell body, the cells of which are essentially the same size as the particles of the removed void-creating substances own.

The above-mentioned post-curing is carried out at temperatures of 177 "C, preferably at 249 "C, carried out in the course of 24 hours in a hot air oven. The post-curing serves to generate cell bodies and also stabilize the physical Properties of the cell body and also to improve its compression properties.

These treatments have no adverse effect on the others Properties of the cell body.

The amount of the void generating substance in the curable siloxane rubber compositions can preferably from 25 to 225 parts by weight per 100 parts by weight of organosiloxane and reinforcing filler vary. Your average particle size can be from 2 microns to 3.2 mm in diameter, the selected particle size being depends on the size of the cells you want.

The density of the cell body depends of course on the amount and particle size the cavity-producing substance. For example, if elastomers with a density from 0.75 to 1.00 are desired, small amounts of larger particles must be voiding Substance can be used while on the other hand in cell bodies with a density from 0.35 to 0.75 major amounts of small particles of the void-creating substance should be used. Mixtures of large and small particles can also be used be used; this gives a maximum packing effect and a low one Density.

The molding compositions according to the invention contain the cavity-producing Substances as crystalline or amorphous solids, which compared to the rubber mass, in particular are inert to curing.

Examples of the water-soluble void-generating substances are inorganic compounds such as the halides of lithium, sodium, or potassium from the ammonium ion, the sulfides of lithium, sodium or potassium, salts of organic Acids such as potassium acetate, sodium acetate, sodium benzoate and organic compounds, such as cane sugar, urea or tartaric acid.

Examples of cavity-creating substances that can be produced by heating Temperatures above the curing temperature of the elastomer and below 260 "C can be removed are sublimable solids, such as oxalic acid, oc-aminoanthraquinone, o-anthranilic acid, chloranthraquinone, chlorobenzoic acid, dichloroanthraquinone or Isatin. Solids that melt or evaporate somewhat are urea, phthalic anhydride, Citric acid, tartaric acid, adipic acid or p-naphthol.

Examples of void-creating substances that when heated above dissociate the curing temperature are ammonium chloride or ammonium format.

The organopolysiloxanes to be used as starting material are both homopolymeric and copolymeric organopolysiloxanes. These organopolysiloxanes contain siloxane units of the formula in which R and R 'represent monovalent organic radicals, such as monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals, cyanaryl radicals, cyanoalkyl radicals in which the cyano group is bonded to the silicon atom via at least 2 carbon atoms, and nitroaryl radicals. The ratio of the organic radicals to the silicon atoms in the organopolysiloxane is 1.95 to 2.05.

Examples of the monovalent organic radicals represented by R 'in formula (1) are the olefinically unsaturated monovalent hydrocarbon radicals, such as alkenyl radicals, e.g. B. the vinyl or the allyl radicals, the cycloalkenyl radicals, e.g. B. the cyclohexenyl radical. The preferred monovalent, olefinically unsaturated hydrocarbon radical is the vinyl residue.

Examples of monovalent organic radicals represented by R and R 'in formula (1) are alkyl radicals, such as methyl, ethyl or propyl radicals, aryl radicals, such as phenyl or toluyl radicals, aralkyl radicals, such as benzyl or phenylethyl radicals or Cycloalkyl radicals, such as cyclohexyl or cyclopentyl radicals.

Examples of the halogenated monovalent hydrocarbon radicals which represented by R and R 'in formula (1) are: chloromethyl, trichloromethyl, Chloropropyl, chlorophenyl, bromophenyl, trifluoromethylphenyl radicals or the perfluoroalkyl radicals, like 2-trifluoromethylpropyl-, hexafluorisohexyl-, 3,3, 3-trifluoropropyl-, 5,5, 5-trifluoro-2- (trifluoromethyl) -amyl- or 5,5,6,6,6-pentafluoro-2- (pertluoroethyl) -hexyl radicals.

Examples of the cyanaryl groups represented by R and R 'in formula (1) are cyanophenyl radicals, such as p-cyanophenyl, o-cyanophenyl or m-cyanophenyl radicals, or cyanophenyl bromide radicals, such as 2-bromo-2-cyanophenyl-, 2,5-dibromo-4-cyanophenyl- or Bromo-2,4-dicyanophenyl radicals.

Examples of the nitroaryl radicals represented by R and R 'in Formula (1), are nitrophenyl or nitronaphthyl radicals.

Usable organopolysiloxanes can contain siloxane units, in which either the same organic radicals are bonded to the silicon atoms are e.g. B. the dimethylsiloxy, diphenylsiloxy or diethylsiloxy or in which there are various organic radicals on the silicon atoms, e.g. B. the Methylphenylsiloxy-, Phenyläthylmethylsiloxy-, Äthylphenylsiloxy-, Methylvinylsiloxy- or phenylvinylsiloxy units.

If olefinically unsaturated, monovalent hydrocarbon radicals in the Organopolysiloxane are present, it is preferred that they be present in an amount of 0.037 up to 0.74% of the monovalent organic radical are present.

Any filler can be used in the production of the molding compositions according to the invention of the strongly reinforcing type such as carbon black or inorganic compounds, as well as any suitable combination of fillers incorporated using the usual methods will. Finely divided fillers are preferred among the inorganic fillers of the strongly reinforcing silica-based type; they are characterized by Particle diameters of less than 500 millimicrons and larger due to surfaces than 50 m21g. Inorganic fillers of a composition or a particle diameter and a surface that does not match the preferred can be in combination can be used with preferred fillers with good results. examples for such fillers are titanium dioxide, iron oxide or aluminum miniumoxide as well as the well-known inert inorganic fillers such as kieselguhr, calcium carbonate or quartz, which are preferred can be used in conjunction with highly reinforcing silica fillers.

In the hydroxy group-containing silicon compounds, which are for suitable for the production of the molding compositions according to the invention, they are preferably to organosubstituted hydroxysilanes or hydroxypolysiloxanes. While the silanes usually only have a single silicon atom, the polysiloxanes in which the silicon atoms are bonded via oxygen atoms, from 2 to 35 and more silicon atoms contained in the molecule. When using polysiloxanes, those with linear Structure preferred; however, you can also use branched polysiloxanes that contain no more than 35 silicon atoms in the molecule. The preferred siloxanes include four to twenty diorganosiloxy units in the molecule.

The hydroxyl-containing silicon compounds which can be used contain at least one and preferably two hydroxyl groups in the molecule. Typical hydroxysilanes are the saturated hydrocarbon-substituted hydroxysilanes, such as diphenyldihydroxysilane, Trimethylhydroxysilane or phenyldimethylhydroxysilane, the silicates, such as partial hydrolyzed tetraethylsilicate, as well as the condensed polymers thereof, furthermore Silicates such as diethoxy-di- (2-ethylhexanediol-1,3) -silicate or diethoxy-o, o-di- (2-ethylhexanediol-1,3) -silicate.

In most cases the polysiloxanes can be two to six and contain more hydroxyl groups in the molecule. Hydroxy-containing, organosubstituted polysiloxanes obtained by hydrolysis and condensation of the aforementioned organosubstituted hydroxysilanes have been obtained.

The terminally hydroxyl-substituted polysiloxane oils have a relatively low molecular weight, the polymer chains having at least 2 and up to about 35 and more diorganosiloxy units (R2SiO) in the molecule and on average at least one hydroxyl group on each of the terminal silicon atoms of the molecule. Such polysiloxanes can be represented by the general formula: in which R has the above meaning, a has a value from 0 to 2, b has a value from 0 to 3 and x has a value from 2 to 35.

The suitable alkoxy group-containing silicon compounds are preferred organosubstituted alkoxysilanes or alkoxypolysiloxanes. While the silanes usually Contain only a single silicon atom, the polysiloxanes, in which the silicon atoms Are connected to each other via oxygen atoms, from 2 to 35 and more silicon atoms contained in the molecule. When using polysiloxanes, they should preferably be linear Possess structure. However, one can also use branched substances that are not contain more than 20 silicon atoms in the molecule. The preferred polysiloxanes contain two to twenty diorganosiloxy units in the molecule; The alkoxy-containing Silicon compounds contain at least one, preferably at least two, alkoxy groups in the molecule. Such silanes have the general formula: RnSi (ORtt) o-n - where R has the above meaning, R "is an alkyl or aryl radical and n has a value of 0 to 3 has.

Polysiloxanes with terminal alkoxy groups have the general formula: where R and R "have the above meaning, a has a value from 0 to 2, b has a value from 0 to 3 and x has a value from 2 to 35. R and R" can represent different radicals in one molecule. R "preferably denotes an alkyl radical having 1 to 6 carbon atoms. Examples of such alkyl radicals R" are methyl, ethyl, propyl, octyl or octadecyl radicals.

Examples of aryl radicals R ″ are phenyl, toluoyl: xylyl or naphthyl radicals.

Typical alkoxysilanes are: Saturated hydrocarbon-substituted ones Alkoxysilanes, e.g. B. Trimethyläthoxysilan, Dimethyldiäthoxysilan, Methyltriäthoxysilan, Ethyltriethoxysilane, diethyldimethoxysilane, triethylpropoxysilane, phenyltriethoxysilane, Diphenyidiäthoxysilan, Triphenyläthoxysilan, and mixed saturated hydrocarbon-substituted Alkoxysilanes, such as methylethyldipropoxysilane or methylphenyldiethoxysilane, unsaturated hydrocarbon-substituted alkoxysilanes, e.g. B. Vinyltriäthoxysilan, Äthylvinyldiäthoxysilan, Phenylvinyldiethoxysilane, divinyldipropoxysilane, allyltriethoxysilane, methylallyldiethoxysilane or ethylcyclohexenyl diethoxysilane, halogen-substituted hydrocarbon alkoxysilanes z. B. o; -Chlormethyltriäthoxysilan, y-Chlorpropyltriäthoxysilan, y-Chlorpropylmethyldiäthoxysilan, y-8-dichlorobutyltriethoxysilane, p-chlorophenyltriethoxysilane or o-p-dichlorophenyltriethoxysilane, the cyanoalkylalkoxysilanes, e.g. B. ß-Cyanoäthyltriäthoxysilan, y-Cyanopropylmethyldiäthoxysilan or d-cyanobutylphenyldipropoxysilane, the organic silicates, e.g. B. Tetraethylsilicates and its condensed polymers, or organic silicates, such as diethoxy-di- (2-ethylhexanediol-1,3) silicates, or diethoxy-d- (triethanolamine) silicate.

The alkoxy-containing organosubstituted polysiloxanes in the molding compositions according to the invention are contained, contain at least one alkoxy group, preferably at least two alkoxy groups in the molecule. In most cases you can such polysiloxanes contain two to six or more alkoxy groups in the molecule. Those alkoxy-containing, organosubstituted polysiloxanes are particularly suitable, those by hydrolysis and condensation of the above-mentioned organosubstituted alkoxysilanes have been manufactured.

As curing agents, the molding compositions contain all substances that have already been used in the heat curing of silicone elastomers. It can Thus, for example, the hardening agents are an organic peroxide.

The following examples serve to illustrate the invention. if unless stated otherwise, they are always parts by weight.

Preparation of a Typical Silicone Rubber Compound A rubbery one Silicone compound was made by rolling 100 parts of a rubbery one Dimethylpolysiloxane containing 0.20 parts of combined methylvinylsiloxy units, 30 parts of a mixture of finely divided reinforcing - silica filler and 10 parts of an ethoxy-terminated dimethylpolysiloxane (ethoxy content 12 percent by weight) at room temperature until a uniform dispersion was obtained.

Example 1 a) Production of the molding compound The compound described above (100 parts) was placed on a 2-roll differential rubber roller and kept at room temperature rolled out into a uniform layer. To this layer 1 became part of a 40 weight percent mixture of 2,4-dichlorobenzoyl peroxide in a dimethyl silicone oil given and thus at a temperature below 50 "C up to a uniform Rolled dispersion. .100 parts of oxalic acid dried at 100 "C for 16 hours and had a particle size of less than 0.074 mm were during rolling added and rolling continued below 50 "C until a uniform dispersion was obtained. b) Application of the molding compound The resulting mixture was applied as a layer Taken from the roller and placed in a plate measuring 15.24 15.24 0.20 cm shaped. The plate was placed between layers of polyethylene sterephthalate and in a standard form (15.24 15.24 1.91 cm) for 15 minutes to an elastomer cured by heating to 121 "C. A sample of the cured elastomer was in heated in an air oven to 1490 C for 24 hours until the oxalic acid evaporates and then a further 24 hours at 249 "C. The resulting dimensionally stable, cellular silicone elastomers contained small cavities or

Cells with substantially the same dimensions as the particles of the Oxalic acid. The voids were uniform in the dimensionally stable cellular silicone elastomer distributed. The density of the elastomer was 0.82 on 3.

A second sample of the cured elastomer was used for 6 hours Oven heated to 149 "C and then heated to 204" C for 18 hours. A dimensionally stable one was obtained cellular silicone elastomer with a density of 0.77 glcm3, a tear strength of 7.1 kg / cm2 and an extensibility of 240010.

The dimensions of the cured sample were 15.24 15.24 91 cm.

A silicone elastomer made from this silicone mass without Using oxalic acid had a density of 1.2 gicm3.

Example 2 a) Production of the molding compound To 100 parts of the above Silicone mass was 1 g of a 40 weight percent mixture of 2,4-dichlorobenzoyl peroxide given in a dimethylsiloxane oil and the mixture at room temperature to a rolled uniform dispersion. 100 parts of urea were added to this mixture (Particle size 0.59 mm and smaller) and mixing at one temperature continued below 50 "C until there is a uniform dispersion of the urea received. b) Application of the molding compound The resulting compound was sandwiched between layers of polyethylene terephthalate placed in a standard mold and cured to an elastomer at 121 "C for 15 minutes. Samples of this elastomer were treated as follows: (a) The urea became off remove the elastomer by immersing it in boiling water for 48 hours, the boiling water was frequently renewed. The elastomer was then in one Air circulation oven heated to 149 "C for 1 hour and then to 249" C for 48 hours, wherein one is a dimensionally stable cellular silicone elastomer with a tensile strength of 10.55 kg / cm2, an extensibility of 28001o and a density of 0.71 g / cm3 received.

(b) The urea was removed from the elastomer by removing it At 1490 C for 18 hours, 204 "C for 6 hours, and finally 48 hours Long heated to 249 ° C. A dimensionally stable cellular silicone elastomer was obtained with a tensile strength of 10.55 kg / cm2, an elongation of 300 ° / 0 and a density of 0.69 g / cm3.

Example 3 a) Production of the molding compound To 100 parts of the above Silicone compound was 1 g of a 40 percent by weight mixture of 2,4-dichlorobenzoyl peroxide given in a dimethylsiloxane oil and the mixture at room temperature to a rolled uniform dispersion.

100 parts of ammonium chloride (particle size between 0.59 and 0.25 mm) and rolling continued at below 50 "C, until you get a uniform dispersion of ammonium chloride and silicone rubber received. b) Application of the molding compound The molding compound formed was sandwiched between layers of polyethylene terephthalate placed in a standard mold and heated to 121 "C for 15 minutes to form an elastomer hardened. Samples of the elastomer were treated as follows: (a) The ammonium chloride was removed from the elastomer by placing it in boiling water for 24 hours dived and changed the water frequently.

The elastomer was then heated to 149 "C for 1 hour and then 2490 C for 24 hours.

The dimensionally stable cellular silicone elastomer obtained had a tensile strength of 14.06 kg / cm2, an elongation of 3500 / o and a density of 0.75 g / cm3.

(b) The ammonium chloride was removed from the elastomer by it was heated to 204 "C for 6 hours and to 249" C for 24 hours. A dimensionally stable, cellular silicone elastomer with a tensile strength of 9.84 kg / cm2, an extensibility of 3500in and a density of 0.71 g / ccm.

A similar batch was made using 100 parts Ammonium format (particle size between 0.59 and 0.25 mm) instead of ammonium chloride. After curing to an elastomer, it was at 149 "C for 18 hours and 48 hours heated to 249 "C. A dimensionally stable, cellular elastomer with a Obtained density of 0.77 g / ccm.

Example 4 a) Production of the molding compound To 100 parts of the above Silicone compound was 1 g of a 40 percent by weight mixture of 2,4-dichlorobenzoyl peroxide added in a dimethylsiloxane oil and the mixture into a uniform dispersion rolled. The rollers were adjusted to give a 3.2 mm overlay.

150 parts of urea particles were added to this mixture (im essentially in the form of spherical particles with a diameter of 3.2 mm and smaller). Rolling was continued below 50 "C until uniform Dispersion of urea and silicone received. During the rolling were individual urea globules broken. b) Application of the molding compound The resulting Molding compound was placed in a conventional mold between layers of polyethylene terephthalate and hardened to an elastomer by heating to 121 "C for 15 minutes. The urea was removed from the elastomer by leaving it at 149 "C for 18 hours and 24 hours heated to 249 "C.

A dimensionally stable cellular silicone elastomer was obtained, with a tensile strength of 3.51 kg / cm2, an extensibility of 150 0in and one Thickness of 0.60 g / cm3.

Example 5 a) Production of the molding compound To 100 parts of the above Silicone compound became part of a 40 weight percent mixture of 2,4-dichlorobenzoyl peroxide added in a dimethylsiloxane oil and the mixture to a uniform dispersion rolled. This mixture was mixed with 200 parts of phthalic anhydride (commercially available Flakes with a particle size of 3.2 mm in diameter and 254 microns thick) and continue mixing below 500 C until a uniform dispersion is obtained of phthalic anhydride and silicone. During the rolling were some flakes broken into smaller particles. b) Application of the molding compound Die resulting molding compound was between polyethylene terephthalic acid layers in a Placed in the usual form and hardened by heating to 121 "C for 15 minutes. The phthalic anhydride was removed from the elastomer by heating it to 149 "C for 64 hours and then to 2490 ° C. for 24 hours. A dimensionally stable cellular silicone elastomer was obtained with a tensile strength of 2.1 kg / cm2, an elongation of 3500 / o and a Density of 0.61 g / cm3.

Example 6 a) Production of the molding compound To 150 parts of the above Silicone compound became part of a 40 weight percent mixture of 2,4-dichlorobenzoyl peroxide in a dimethylsiloxane oil and the mixture below 50 "C to a uniform Rolled dispersion. The rollers were adjusted to form a 3.2 mm ply. 210 parts of urea particles (essentially spherical in shape) were added to this mixture Particles with a diameter of 3.2 mm and smaller) and rolling continued below 50 ° C to a dispersion of urea and the silicone. b) Use of the molding compound The molding compound formed was sandwiched between layers of polyethylene terephthalate brought into a usual shape and by heating for 5 minutes to 121 "C to an elastomer hardened. The urea was removed from the elastomer by heating for 24 hours at 1490 C for a long time and then at 2490 C for 24 hours. A dimensionally stable one was obtained cellular silicone elastomer with a density of 0.55 g / cm3.

Example 7 a) Production of the molding compound To 50 parts of the above-described Rubber mass was 0.5 g of a 400 weight percent mixture of 2,4-dichlorobenzoyl peroxide given in a dimethylsiloxane oil and the mixture below 500 C to a uniform Rolled dispersion.

125 parts of urea (particle size between 0.59 and 0.149 mm) and the rolling below 500 C until a uniform Dispersion of urea and silicone continued. b) Application of the molding compound The resulting molding compound was between polyethylene terephthalate layers in a given the usual shape and in the course of 15 minutes at 121 "C to an elastomer hardened. The urea was made from the elastomer by heating it at 1490 ° C. for 18 hours removed for a long time and then at 2490 C for 24 hours. A dimensionally stable, cellular silicone elastomer with a density of 0.5 g / cm3.

If one uses the dimethylpolysiloxane in the preceding examples containing 0.2 weight percent combined methylvinylsiloxy units replaced by a dimethylpolysiloxane containing 0.2 weight percent combined methylvinylsiloxy units and containing 12 weight percent diphenylsiloxy units gave similar results obtain.

Dimensionally stable, cellular silicone elastomers were also obtained, if you use a methylethylpolysiloxane instead of the dimethylpolysiloxane with 0.2 percent by weight combined methylvinylsiloxy units were used in the previous examples.

It should be noted that when rolling, the outermost particle size the solid voiding substance depends on several factors, e.g. B. from the fragility of the dispersed substance, of the rolling duration and the dimensions of the roll gap of the rolls.

The dimensionally stable, Cellular silicone elastomers are characterized by the fact that they have cavities or Cells with essentially the same dimensions as before the particles of the solid possess void generating substance used in their manufacture, and that the dimensionally stable, cellular silicone elastomer dissolves upon removal of the solid void-creating particles does not expand, but at most one Volume contraction is subject to the extent that it is usually the case with the usual Silicone elastomers occurs, d. H. that the external dimensions of the dimensionally stable, cellular silicone elastomers remain essentially constant or a conventional, linear shrinkage up to 100 / o are subject.

In the preparation of the molding compositions according to the invention, preference is given to the use of a hydroxylated silicon compound or an alkoxysilicon compound or a filler compounded with a trihydrocarbylchlorosilane such as trimethylchlorosilane or with alcohol.

Using such a modified system one can get larger Incorporate quantities of the solid void-creating particles into the masses and add to this way dimensionally stable, cellular silicone elastomers with lower density obtain.

The elastomers produced from the molding compositions according to the invention are suitable as sealing rings or washers for use with high and low Temperatures as well as suspension or

Upholstery material, especially if flexibility at both high as well as at low temperatures.

Claims (1)

Claim: Vulcanizable to cell bodies, fillers and optionally Thermosetting polysiloxane molding compositions containing hot-curing catalysts, thereby characterized in that it consists of a mixture (1) of organopolysiloxane, (2) of 20 to 50 parts by weight of a reinforcing filler per 100 parts by weight of organopolysiloxane and (3) from 10 to 500 parts by weight of solid particles of a void generating Substance per 100 parts by weight of organopolysiloxane and filler consist, wherein the void-generating substance at the curing temperature of the organopolysiloxane is in the solid state, is insoluble and inert in the organopolysiloxane and a water-soluble, solid substance or one at temperatures above the curing temperature of the organopolysiloxane and below 260 "C volatile solid substance represents. Documents considered: British Patent No. 766 139; No 11, »Chemistry and Technology of Silicones«, Weinheim, 1960, p.264 / 265, Special print »Rubber and Asbestos« - Plastic Masses, from Issue 7 to 10, 1955, A. W. G e n tu er Verlag Stuttgart, p. 4, left column, and p. 12, right column.