DE1137862B - Process for the production of elastomeric molded parts by heat curing organopolysiloxane molding compounds - Google Patents

Description

Process for the production of elastomeric molded parts by heat curing of organopolysiloxane molding compositions It has been found that elastomeric moldings can be produced by thermosetting molding compounds, the organopolysiloxanes, in which the organic Groups are monovalent hydrocarbon groups or halogenated aryl groups, with 1.98 to 2.1 organic groups meeting each silicon atom, catalysts as well as fillers, can be produced when a molding compound is cured, the except for the organopolysiloxane 1 to 20%, based on the weight of the organopolysiloxane, contains a liquid organopolysiloxane, one by an aliphatic radical contains silicon-bonded nitrile group and in which the remaining silicon valences, which do not participate in the structure of the siloxane chain, by alkyl, aryl, aralkyl and / or Alkaryl groups are saturated.

Organopolysiloxanes containing nitrile groups are available as chemical compounds already known. According to the invention, however, silicone molded parts with elastic ones are obtained Properties and with amazingly improved physical characteristics, e.g. B. tear resistance, Elongation and tensile strength when curing polysiloxanes in the presence of the liquid polysiloxanes containing nitrile groups takes place, but only as physical Addition to the organic polysiloxane.

Cured, elastomeric organopolysiloxanes have found widespread use found everywhere where a resistance to high temperatures of about 125 to 175 ° C is required for longer periods. It's surprising that the addition according to the invention of the organopolysiloxane containing nitrile groups, below for the sake of brevity referred to as cyanoalkylpolysiloxane «, the thermosetting Organopolysiloxanes (except the usual fillers) in one before heat curing Amount of less than 20 percent by weight, based on the weight of the organopolysiloxane, admitted, so fundamental improvements result.

As a rule, there is quite a considerable improvement in the physical properties of the cured organopolysiloxane when added of only 1 weight percent cyanoalkylpolysiloxane based on the weight of the thermoset Organopolysiloxane (i.e. excluding filler, curing agent, or others possibly present modifiers).

Curable organopolysiloxanes which can be used in the context of the invention can e.g. B. be substituted by the following organic groups: methyl, Ethyl, propyl, vinyl, allyl, phenyl, tolyl, xylyl, benzyl, phenylethyl, Naphthyl groups; halogenated aryl groups, e.g. B. chlorophenyl, tetrachlorophenyl, Difluoronaphthyl groups; both alkyl and aryl groups, e.g. B. methyl and phenyl groups, all of which are bonded to silicon atoms by a carbon-silicon bond. Other mixtures of organic groups, e.g. B. Mixtures of methyl, phenyl and Vinyl radicals are not excluded.

At least 75% of the organic groups are preferably methyl groups. The presence of up to 2 mole percent (e.g. 0.05 to 0.6 mole percent) of silicon bound vinyl radicals is not excluded.

These organopolysiloxanes can also be copolymerized up to 0.5 mol percent Triorganosiloxy units, e.g. B. trimethylsiloxy, or terminal, on silicon contain bound hydroxyl groups. All siloxane units can be present in the polysiloxane (CH3) 2SiO units, or the siloxane can be a copolymer of dimethylsiloxane and a minor amount (e.g., 1 to 25 mole percent or more) of one or more of the following units C6H5 (CH3) SiO and (C6H5) 2SiO.

A small amount of a curing accelerator is added to the polysiloxane to cure it, z. B. benzene peroxide, tertiary butyl perbenzoate, ditertiary butyl peroxide, bis- (2, 4-dichlorobenzoyl) peroxide etc., one incorporated. The amount of used Curing agent can vary within wide limits and can, for. B. about 0.1 to about 8% or more and preferably about 0.75 to 6% based on the weight of the curable organopolysiloxane.

The term "cyanoalkyl radical" refers to radicals of the formula wherein R is hydrogen or an alkyl radical, e.g. B. a methyl, ethyl, propyl, butyl radical, etc., and m is an integer from 0 to 5 inclusive, preferably from 0 to 3 inclusive.

The cyanoalkylpolysiloxanes used according to the invention thus include the siloxanes of the formula wherein R and m have the meaning given above. The various R 'groups are the same or different as listed for R, e.g. B.

Phenyl, naphthyl, diphenyl, halogenated aryl, benzyl, phenylethyl, tolyl, xylyl, cyclopentane, cyclohexane groups as well CN I. - (CH2) mCHR groups wherein R has the meaning given above.

Preferably only one of the R 'groups is one CN i - (CH2) mCHR group.

Linear and cyclic cyanoalkylpolysiloxanes to be used according to the invention contain the siloxane unit individually or recurring or inter-condensed with siloxane units of the structure wherein R, R 'and m are as defined above, n and p are integers, namely at least 1, e.g. B. 1 to 100 or more.

The cyanoalkylpolysiloxane can also have units of the formula contain, in which R and m have the meaning given above. Such trifunctional units can be intermediately condensed with siloxy units (3) and (4) either individually or several times.

The cyanoalkylpolysiloxane only needs to be mechanically combined with the curable Organopolysiloxane to be mixed in the desired proportions, one gives Fillers (e.g. silica airgel, finely divided silica, precipitated silica, finely divided diatomaceous earth, etc.), together with any of the known ones Hardener for curable organopolysiloxanes and heats the mixture of ingredients to a temperature between about 125 and 200 ° C. For compression deformation, pressures on the order of about 35 to 70 kg / cm2 or higher for about 5 to 30 minutes or longer, depending on the intended use.

The following are manufacturing processes for the starting materials described. No protection is claimed here for these processes.

A flowable cyanoalkylpolysiloxane was made by mixing 230 g cyanoethyltrichlorosilane, 464 g trimethyldichlorosilane, 138 g trimethylchlorosilane and about 1500 ccm of ethyl acetate, hydrolysis of the silane mixture with an excess of water, Washing out the organic layer until neutral, distilling off the solvent and the lower boiling components and heating the mixture to 2% 85% Sulfuric acid to achieve an equilibrium with the introduction of a chain termination effecting trimethylsiloxy units, neutralization of the reaction product with sodium bicarbonate and distilling off all addicts obtained at about 200 ° C and 25 mm Hg.

This cyanoalkylpolysiloxane is hereinafter referred to as »cyanoethylpolysiloxane No. 1 «.

Another cyanoalkylpolysiloxane called "Cyanoethylpolysiloxane No. 2" was obtained by joint hydrolysis of a mixture of 60 mole percent dimethyldichlorosilane and 40 mole percent cyanoethyltrichlorosilane in ethyl acetate, essentially as above described, received. The joint hydrolysis product was washed out, and the ethyl acetate was removed, one consisting of dimethylsiloxy units and Cyanoethylsiloxy units (CNCH2CH2SiOg, 2) obtained from existing polymer.

An organopolysiloxane was obtained by copolymerizing 0.23 parts Tetramethyltetravinylcyclotetrasiloxane, 15 parts octaphenylcyclotetrasiloxane, 100 Parts of octamethylcyclotetrasiloxane and about 0.075 parts of decamethyltetrasiloxane with a small amount of e.g. B. about 0.001% KO H, based on the weight of the Siloxanes, at temperatures of about 145 to 175 ° C for about 6 hours up to Achievement of a highly viscous, benzene-soluble, curable methylphenylvinylpolysiloxane obtain. This curable methylphenylvinylpolysiloxane was then made freed from lower boiling components. The composition obtained is hereinafter referred to as)> curable methylphenylpolysiloxane ".

Another curable organopolysiloxane was made by heating Octamethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane with about 0, 001 ° / o KOH for 4 to 5 hours at 140 to 150 ° C essentially to the above way described. The product was obtained with a high viscosity Mass distilled containing about 0.2 mole percent of silicon-bonded vinyl groups.

This composition is known as "curable methylpolysiloxane".

In the following examples, all parts are parts by weight.

It should be noted that in the following examples diphenylsilanediol is present as a means of degrading the structure. The diphenylsilanediol improved the machinability of the material by changing it in a much shorter time can be processed.

It has no influence whatsoever on the properties of the hardened material from which is why it is not an essential component of the molding compositions obtained according to the invention forms.

The use and effects of diphenylsilanediol is in the French Patent 1115375 described in detail.

Example 1 A mixture of the following ingredients in those given Quantities by weight were prepared: Ingredients: parts by weight; Curable methylpolysiloxane ........ 100 Finely divided silica 55 Diphenylsilanediol .................. 8 Bis- (2,4-dichlorobenzoyl) peroxide in the form of a dispersion containing 50% solids in a methyl silicone oil ...

Cyanoalkylpolysiloxane No. 1 6 This mixture as well as a no cyanoalkylpolysiloxane Mixture containing No. 1 was heated for 15 minutes at 150 ° C under a pressure of about 35 kg / cm2 pressure deformed and then first 1 hour at 150 ° C, then 24 hours heat aged at 250 ° C and then heat aged for an additional 96 hours at 250 ° C, each of these He- heat treatments were carried out in an oven with air flowing through it. The following Table 1 shows the properties of the two compositions according to the different ones Heat treatments.

Table 1 No Cyano-6 Tefle alkylpolysil-CYanopoly- oxane enthal-siloxane holding sample sample 1 hour at 150 ° C hardens Tensile strength, kg / cm2. 63.5 84.8 Elongation, ° / 0 200 410 Tear strength, kg / cm2 ... 9.38 19.47 24 hours at 250 ° C hardens Tensile strength, kg / cm2 ... 52.5 52.4 Elongation, 200 240 Tear strength, kg / cm2 ... 8.32 10.62 96 hours at 250 ° C hardens Tensile strength, kg / cm2 49.0 50.6 Elongation, ° / 0 170 210 Tear strength, kg / cm2 ... 7.25 12.03 Example 2 In this example, the curable methylphenylpolysiloxane described above was mixed with finely divided silica, diphenylsilanediol and bis (2,4-dichlorobenzoyl) peroxide, whereupon the above-described cyanoalkylpolysiloxanes No. 1 and 2 were added to this mixture in various amounts. A control sample containing no cyanoalkylpolysiloxane was also prepared. The following Table 2 shows the various proportions of the ingredients and the properties of the cured, similar to Example 1, compression-molded and heat-treated product. Cyanoethylpolysiloxane No. 1 was used in the following Samples Nos. 4 to 7 and cyanoethylpolysiloxane No. 2 was used in Samples 8 and 9. All values in the table mean parts by weight in Table 2 Sample number 3 4 5 6 7 8 9 Curable methylphenylpolysiloxane 100 100 100 100 100 100 100 Finely divided silica ........... 40 40 40 40 40 40 40 Diphenylsilanediol ................. 8 8 8 8 8 8 Bis (2,4-dichlorobenzoyl) peroxide * .. 1 1 1 1 1 1 Cyanoethylpolysiloxane 0 6 4 6 8 4 8 Cured for 1 hour at 150 ° C Tensile strength, kg / cm2 118 126 125 112 121 120 132 Elongation, 695 860 830 940 960 790 900 Tear strength, kg / cm2 42.5 54.0 53.1 54.8 47.8 49.6 50.4 Cured for 24 hours at 250 ° C Tensile strength, kg / cm2 36.9 39.4 45.0 51.3 42.9 44.3 57.7 Elongation, 205 230 230 310 280 270 340 Tear strength, kg / cm2 14.2 18.6 15.0 13.3 16.8 18.6 22.1 * In the form of a 50% by weight dispersion in an inaccessible methylpolysiloxane.

The amount of filler used can vary within wide limits and can e.g. B. about 10 to 300 percent by weight, based on the curable organopolysiloxane, be. The actual amount of filler used depends on factors such as B. Art the filler, the curable organopolysiloxanes, the intended use of the cured product, the proportion of the cyanoalkylpolysiloxane, etc. A an advantageous quantity range is between 0.2 and 3 parts of filler per part of curable Organopolysiloxane.

Claims (1)

PATENT CLAIM: Process for the production of elastomeric molded parts by thermosetting molding compounds, the organopolysiloxanes, in which the organic groups are monovalent hydrocarbon groups or halogenated aryl groups, where 1.98 Up to 2.1 organic groups meet on each silicon atom, catalysts and fillers contain, characterized in that a molding compound is cured, the except the organopolysiloxane 1 to 20%, based on the weight of the organopolysiloxane, contains a liquid organopolysiloxane, one by an aliphatic radical contains silicon-bonded nitrile group and in which the remaining silicon valences, which do not participate in the structure of the siloxane chain, by alkyl, aryl, aralkyl and / or Alkaryl groups are saturated. Documents considered: French patent specification No. 1 154 331.