DE1141082B - Process for the production of elastomeric molded parts from organopolysiloxane molding compounds - Google Patents

Description

Process for the production of elastomeric molded parts from organopolysiloxane molding compounds Ever since there have been nuclear reactors and similar systems that have generated intense ionizing radiation, such as gamma rays, x-rays or atomic particles, e.g. B. electrons, neutrons or protons, it is known that it has become more and more important to send substances develop that are resistant to such rays. It is particularly acute Ask where a substance is exposed to simultaneous exposure to radiation and high temperatures of 1000 C and above. Under these conditions, degradation occurs most organic substances.

Previously were for use at high temperatures and simultaneous Radiation exposure is best with organopolysiloxanes with a high phenyl group content suitable.

The invention now relates to such an improvement in radiation resistance of siloxane elastomers that these in the form of electrical insulation under the Conditions of intense radiation and high temperatures are relatively permanent are e.g. B. radiation doses over 200 megarads at 200 ° C, can withstand.

According to the invention, elastomeric molded parts which are resistant to radiation are made by curing such organopolysiloxanes with a viscosity of at least 500cSt / 25 ° C and an average of 1.9 to 2.01 methyl, phenyl, vinyl or 3,3,3-trifluoropropyl radicals per Si atom, of which at least 250/0 are methyl radicals, as well as other common constituents containing molding compositions produced, which in addition up to 10 percent by weight, based on the organopolysiloxane, N-dihydro-anthraquinone azine, phthalocyanine, chelated Contain metal complexes of phthalocyanine or diphenylbenzene.

According to the invention, the masses are made by conventional methods Elastomers hardened, for example by heating with organic peroxides, such as di-tert-butyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, dichlorobenzoyl peroxide and dicumyl peroxide, or with sulfur hardeners, such as sulfur or the various Sulfur accelerators, which are common in the sulfur curing of elastomers.

Curing can also be carried out at room temperature by mixing the masses with orthosilicic acid esters or polysilicic acid esters, such as silicic acid methyl ester, Polysilicic acid ethyl ester, orthosilicic acid propyl ester, polysilicic acid allyl ester and, B-silicic acid methoxyethyl ester, or with compounds containing ~ SiH groups, such as methylhydrogensiloxane and phenylhydrogensiloxane. Using the silicic acid ester or of the compounds containing SiH groups contains the siloxane polymer hydroxyl radicals preferably bonded to some of the Si atoms. The hardening takes place here in the presence of catalysts, for example metal salts of carboxylic acids, such as dibutyltin diacetate, dibutyltin dilaurate, lead octoate, tin octoate, or amines, such as hexylamine, methylamine or ammonia.

The compositions to be cured according to the invention can optionally be any inorganic fillers such as synthetic silicas, for example pyrogenic in the gas phase recovered silica, while maintaining the structure dehydrated silica hydrogel, precipitated silicas, or natural silicas such as diatomaceous earth or ground Quartz, metal oxides such as titanium dioxide, zinc oxide, iron, aluminum or magnesium oxide, Soot, or silicates such as glass fibers, asbestos, clay, aluminum or magnesium silicate, contain. These fillers can be pretreated with silanes or siloxanes, to have organosilyl groups attached to the surface.

The grain size of the additives according to the invention to improve the Radiation resistance is not critical, but preferably should be the Have the form of fine powder. Phthalocyanine can be used in any form, for example as phthalocyanine per se or as any metal chelate with polyvalent ones Metals such as copper, iron, aluminum, chromium, nickel, cobalt or magnesium phthalocyanine. Even any isomer of diphenylbenzene is suitable; i.e., the terminal phenyl groups can be ortho, meta or para to one another on the central phenyl group sit.

The compositions obtained according to the invention can be any Type and shape of organopolysiloxane elastomers, such as pressed parts, extrusions or films, processed on fabrics. They serve as electrical insulating means, Seals, or similar, used in the organopolysiloxane elastomers can be used for applications under the influence of high temperatures and more severe Irradiation.

The superiority of the masses obtained according to the invention known organopolysiloxane elastomers were determined in the following way: The masses with and without additives were irradiated with a cobalt-60 source at 200.degree.

The total amount of radiation (measured in megarads) required was the absolute elongation of the additive-free organopolysiloxane elastomers to 500/0 to reduce was determined. Then an additive was made according to a similar mass added to the invention and the product under the same conditions of the same Exposure to radiation dose.

The elongation of the additional sample was now determined. You proved In any case, it turned out to be far greater than 500/0 and thus showed the beneficial effect the additive to prevent the degradation of organopolysiloxane elastomers.

The siloxanes used according to the invention can be any desired siloxanes with a viscosity of at least 500 cSt / 25 "C, in which the substituent groups are essentially all methyl, vinyl, phenyl or 3,3,3-trifluoropropyl radicals. Examples of suitable siloxanes are: dimethyl, diphenyl, bis-3,3,3-trifluoropropyl, Divinyl, methylvinyl, phenylmethyl, 3,3,3 -trifluoropropylmethyl, phenylvinyl, Phenyl-3,3,3-trifluoropropyl and 3,3,3-trifluoropropylvinylsiloxane. The siloxanes can Homopolymers or copolymers of the units mentioned, but must be at least 250/0 of the total organic substituent groups present in the siloxane Be methyl radicals, and the total number of organic radicals present per Si atom must be between 1.9 and 2.01 inclusive. The siloxanes can therefore be limited Amounts of units of the formulas RSiO3 / 2 and R3SiOl / 2, where R is any of those described above May be residues.

In addition, however, the starting siloxanes can contain other substances, such as those containing hydroxyl groups Low viscosity siloxanes to prevent premature hardening of the mixtures made of polymer and filler, additives to reduce permanent deformation, Contain antioxidants, colorants and other commonly used substances.

In the examples, all parts given are parts by weight and all Viscosities measured at 25 ° C.

Example 1 100 parts of a highly viscous dimethylpolysiloxane, 35 Parts pyrogenic silica obtained in the gas phase, 8 parts of a hydroxyl group-containing Dimethylsiloxane of 50 cSt and 3 parts ditert. -Butyl peroxide are rolled and Heated for 112 hours to 175 to 185 "C. The resulting elastomer has a tensile strength of 69.58 kg / cm2 and an elongation at break of 9320/0.

The same mixture is made again with the addition of 3 parts of N-dihydroanthraquinone azine manufactured. The hardening takes place as described above.

The resulting elastomer has a tensile strength of 32.13 kg / cm2 and an elongation at break of 4560/0.

Each of the elastomers is then heated to 200 "C while simultaneously is irradiated with a cobalt-60 source. The elastomer without the addition of N-dihydroanthraquinone azine shows a reduction in elongation to 500wo with a dose of 17 megarads. the however, this containing mass has an elongation of 2300/0 after 17 megarads.

An equally strong improvement in radiation resistance will be achieved when instead of the highly viscous dimethylsiloxane a copolymer is made 99.5 mole percent 3,3,3-trifluoropropylmethylsiloxane and 0.5 mole percent vinylmethylsiloxane units is used.

Example 2 100 parts of a highly viscous phenylmethylpolysiloxane, 30 parts of pyrogenic silica obtained in the gas phase, 8 parts of a hydroxyl-containing silica Dimethylpolysiloxane of 50 cSt and 5.6 parts of dibenzoyl peroxide are rolled and Cured for 5 minutes at 125 to 135 ° C. The resulting elastomer exhibits tensile strength of 44.66 kg / cm2 and an elongation at break of 4830/0.

The same mass is obtained with the addition of 3 parts of N-dihydroanthraquinone azine manufactured and cured as above. The resulting elastomer has tensile strength of 43.12 kg / cm2 and an elongation at break of 4690 / o.

Then the two elastomers are treated with a cobalt-60 source irradiated at 2000 C. The elongation of the elastomer free of N-dihydroanthraquinone azine is reduced to 500/0 by a dose of 80 megarads that contains this Elastomer, on the other hand, has an elongation of 1400/0 after the same dose.

Example 3 100 parts of a copolymer of 99.5 mol percent phenylmethylsiloxane and 0.5 mole percent methylvinylsiloxane units, 30 parts pyrogenic in the gas phase recovered silica, 5 parts of a hydroxyl-containing dimethylsiloxane of 50 cSt and 1 part ditert. -Butyl peroxide are rolled and 1/2 hour at 175 to 185 "C cured. The tensile strength of the resulting elastomer is 43.75 kg / cm2, its elongation at break 1160/0.

The same mass is made with the addition of 6 parts of diphenylbenzene. The mixture is cured as described above and shows a tensile strength of 45.78 kg / cm2 and an elongation at break of 1960/0.

Each of the elastomers is made with a cobalt-60 source at 2000C irradiated. The elongation of the diphenylbenzene-free sample is determined by a dose of 53 megarads reduced to 500/0, while the stretching of the diphenylbenzene-containing Sample under the same conditions is 8001o.

Example 4 100 parts of a copolymer of 20 mol percent diphenylsiloxane, 0.3 mole percent methylvinylsiloxane and 79.7 mole percent phenylmethylsiloxane units, 30 parts of pyrogenic silica obtained in the gas phase and 3.2 parts of di-tert-butyl peroxide are rolled and heated to 175 to 185 "C for 1/2 hour. The tensile strength of the The resulting elastomer is 70.98 kg / cm2, its elongation at break is 477 ° 10.

The same mass is made with the addition of 3 parts of copper phthalocyanine manufactured and cured under the same conditions. The resulting elastomer has a tensile strength of 56.14 kg / cm2 and an elongation at break of 4310/0.

Now the mass is again with the addition of 3 parts of N-dihydroanthraquinone azine produced and cured under the same conditions as the first mass. That The resulting elastomer has a tensile strength of 67.83 kg / cm2 and an elongation at break from 3300/0.

Each of the elastomers is irradiated with a cobalt-60 source and heated to 200 "C at the same time.

After 90 megarads of irradiation, the first elastomer shows one Elongation at break of 500/0; the elongation at break of the phthalocyanine-containing elastomer is 100% and that of the N-dihydroanthraquinone azine containing elastomer is 1500/0. The latter is still effective after exposure to more than 250 megarads at 200 ° C.

Equivalent results are obtained when the copper phthalocyanine is replaced by phthalocyanine and magnesium phthalocyanine.

Example 5 The radiation resistance is increased when a mixture from 100 parts of one having hydroxyl groups end-blocked dimethylpolysiloxane of 5000 cSt, 100 parts of diatomaceous earth, 2 parts of polysilicic acid ethyl ester, 0.2 parts Dibutyltin diacetate and 9 parts of N-dihydroanthraquinone azine at room temperature an elastomer is cured.

The preceding examples show the improvement achieved in Irradiation of the elastomers used according to the invention with a cobalt-60 source.

Equivalent results are obtained when the elastomers are the Irradiation from other sources, such as X-ray machines, Van-de-Graaff machines, Atomic burners and linear accelerators.

Claims (1)

PATENT CLAIM. Process for making elastomeric radiation resistant Molded parts by curing molding compounds, the organopolysiloxanes with a viscosity of at least 500 cSt / 2S "C and an average of 1.9 to 2.01 methyl, phenyl, Vinyl or 3,3,3-trifluoropropyl radicals per Si atom, of which at least 250/0 are methyl radicals, as well as other usual constituents, characterized in that one masses hardens, the additional up to 10 percent by weight, based on the organopolysiloxane, N-dihydroanthraquinone azine, phthalocyanine, chelated metal complexes of phthalocyanine or diphenylbenzene. Documents considered: German Patent No. 1 019 462.