DE2400040C3 - Molding compounds based on organopolysiloxanes which can be hardened under heat to give elastomers - Google Patents

Description

25th

The invention relates to an improvement in the molding compositions which can be hardened under heat to give elastomers Based on organopolysiloxanes. The improvement is achieved through a content of the molding compounds special metal stannates as agents for reducing the compression set and the so-called Reversion achieved.

Conventional organopolysiloxane elastomers are generally stable at temperatures up to about 150.degree. Although you can short-term temperatures up to withstand up to around 260 ° C and even up to 315 ° C. But if they have temperatures over long periods of time If exposed to temperatures above 200 C, they have a tendency to be destroyed quickly. But there are many Areas of application require the use of organopolysiloxane elastomers at elevated temperatures, this tendency to destruction is a very undesirable property.

To improve the resistance to heat aging, red iron oxide has already been used in thermosetting organopolysiloxane compositions incorporated. However, in order to achieve effective heat aging resistance fairly large amounts of iron oxide are required, which gives the cured elastomers a vigorous be red in color which makes them unsuitable for many uses.

It has now been found that by incorporating certain inorganic stannates, the thermosetting Organopolysiloxane compositions have significantly improved color properties that are easily pigmented can be, and that the cured elastomers, moreover, a considerably improved Have resistance to steam, heat aging and reversion.

Compared to the previously known compounds based on organopolysiloxane which can be hardened in the heat to form elastomers, have the molding compositions according to the invention, which can be hardened under heat to give elastomers, in particular the advantages that the cured elastomers have better heat stability and less Have compression set. In addition, these show an improved resistance to embrittlement with heat aging and against so-called enclosed reversion, which is to be understood by this is that the elastomers become liquid or soften inside when heated, although they do mostly remain solid at the edge of the cross-section, but also the more or less thin one that remains Skin is often sticky. This reversion is particularly pronounced when the heating of the elastomers' under there is little or no air admission, d. h .. if the elastomers when heated in a partially or fully closed system.

The invention is therefore in the Molding compositions based on organopolysiloxanes which can be cured to give elastomers by heat, in particular with organic peroxy compounds as hardeners, optionally fillers and other common ones Additions, which are characterized in that they metal stannates with metals from the groups Ha and lib, IHa, including the lanthanides and actinides, and VIII of the long-period system as Contains heat stabilizers.

The inventive content of these metal stannates in the molding compositions based on organopolysiloxane is particularly advantageous when the elastomers are exposed to heat aging, in order to prevent the possible degradation and reversion.

The organopolysiloxanes forming the basis of the molding compositions according to the invention can be be the same as those previously used for the preparation of masses that can be hardened in the heat to form elastomers of organopolysiloxanes could be used as the basis forming or <> anopolysiloxanes. Preferably they have a Williams plasticity of 50 to 250 mm and repeating units the general formula

R _n SiQ

'4-η

in which R denotes identical or different, monovalent, optionally substituted hydrocarbon radicals and / 1 is an average of 1.9 to 2.2, in particular 1.98 to 2.2.

The hydrocarbon radicals R are mostly alk \ l-. Alkenyl, aryl, aralkyl or alkaryl radicals. The substituted ones Hydrocarbon radicals R are mostly halogenated hydrocarbon radicals, e.g. B. halogenated Aryl, cyanoalkyl or cyanaryl radicals.

In particular because of the easier accessibility are preferably at least 50% of the number of R radicals are lower alkyl radicals. preferably alkyl radicals with 1 to 4 carbon atoms. Particularly preferred is the methyl radical. The remaining radicals R which may be present are preferably phenyl and or Vinyl scraps. At least 98% of the silicon atoms are expediently the basis of the molding compositions organopolysiloxanes that form two organic radicals SiC-bonded. Exemplary for the basis of Organopolysiloxanes which form molding compounds are those composed of dimethylsiloxane units and / or those composed of Dimethylsiloxane units and methyl phenylsiloxane and / or methylvinylsiloxane units. z. From 99.65 to 99.99 mole percent dimethylsiloxane and 0.01 to 0.35 mole percent methylvinylsiloxane units.

Examples of organic peroxy compounds are Benzoyl peroxide, tert-butyl perbenzoate. Bis- (2,4-dichlorobenzoyl) peioxide, dicumyl peroxide. Di-

(ρ - chlorobenzoyl) - peroxide or Djalkylperoxyd, vie di -tert-butyl peroxide or 2,5 - di - tert. - butylperoxy - 24 - dimethylhexane. These hardening agents can be used in the molding compositions in the conventional amounts, ie 0.1 to 8 percent by weight or even Eiehr, e.g. B are present in amounts of 4 percent by weight, based in each case on the weight of the organopolysiloxanes forming the basis of the molding compositions. Mixtures of different hardeners can be used.

The metal stannates contained according to the invention, which are crucial for resistance to heat aging of the organopolysiloxanes cured to give elastomers include, by definition, in particular such with metals from the group of rare earths, including in accordance with the present common form of the »long period system« (according to the textbook of the »Inorganischen Chemistry «by F. Albert Cotton and Geoffrey Wi 1 k i η s ο η, 2nd edition 1968, Verlag Chemie GmbH, Weinheim / Bergstrasse) including the IHa group of lanthanides and actinides are to be understood. Examples are cerium, lanthanum, neodymium, praseodymium. Samarium, gadolinium, yttrium, thorium or mixtures thereof, and also those with metals from the Groups Ila and Hb, such as calcium, barium, magnesium. Strontium or cadmium or those with Group VIII metals such as cobalt, nickel or iron. Preferred metal stannates are cerium stannate or barium stannate.

These metal stannates are expediently used in amounts of at least 0.1% based on weight the organopolysiloxanes which form the basis of the molding compositions are used. More than 10% based on the weight of the organopolysiloxanes, which form the basis of the molding compositions, of metal stannate no additional benefit. 1 to 7% are preferred. based on the weight of the base of the organopolysiloxanes which form molding compounds, on these metal stannates.

In addition to the organopolysiloxanes, metal stannates and curing agents forming the basis of the molding compositions, the molding compositions according to the invention can contain substances based on organopolysiloxanes which are conventionally present in compositions based on organopolysiloxanes and which can be hardened to give elastomers in the heat. Examples of such additional substances are reinforcing and non-reinforcing fillers with a surface area in the range from 50 to 500 m ^{2 /} g, agents to prevent the compositions from becoming taut or "crepe-aging" before the final shaping of the molding compositions, plasticizers, pigments, soluble Dyes and flame retardants.

Examples of door reinforcing and non-reinforcing fillers with a surface area as specified The range is asbestos, clays, hydrated calcium silicate, zinc sulfide, pyrogenic silicon dioxide, Silica hydrogel, barium titanate, glass fibers, glass flakes, dehydrated while maintaining the structure, Iron oxide, bentonite, zinc oxide, nickel oxide. Magnesium oxide, graphite powder, slate powder, mica powder, Diatomaceous earth, lead dioxide, lead monoxide, galena, aluminum oxide, calcium carbonate as well hydrated or dehydrated titanium dioxide.

Mixtures of reinforcing and / or non-reinforcing fillers in the specified range can be used can be used.

Depending, for example, on the respective intended use of the molding compounds or the elastomers produced therefrom, on the type of filler used, e.g. B. its density and the type of organopolysiloxanes used, forming the basis of the molding compounds, the reinforcing and / or non-reinforcing fillers can be used in amounts of 10 to 300 percent by weight, based on the weight of the diorganopolysiloxanes forming the basis of the molding compounds. Examples of means for preventing the molding compositions from becoming lumpy before their final shaping or for plasticizers are water, silanols such as diphenylsilanediol or methylphenylsilanediol, each having a viscosity of 30 to 100 cSt at 25 ^L C, siloxanols, e.g. B. of dimethylsiloxane and / or methylphenylsiloxane and / or diphenylsiloxane units, furthermore dimethylpolysiloxanes end-blocked by trimethylsiloxy groups with a viscosity of 30 to 100 cSt at 25 "C., alkoxypolysiloxanes liquid at room temperature, phosphoric acid esters liquid at room temperature, such as tripropyl phosphate or tributylphosphate Such as ethylene glycol or propylene glycol, carboxylic acid esters or anhydrides of dicarboxylic acids, such as phthalic anhydride Mixtures of different substances of the type indicated above can be used.

The agents for preventing the tautness are generally used in amounts of 2 to 30 percent by weight, in particular 5 to 20 percent by weight, each based on the weight of the basis of the Organopolysiloxanes which form molding compounds. used.

The molding compositions can be prepared in many ways. The contained according to the invention Metal stannates can be mixed with the organopolysiloxanes on which the molding compositions are based. while or after the addition of the reinforcing and / or non-reinforcing fillers and the optional used: i other substances are mixed.

The shaping of the molding compositions according to the invention, for. B. by compression molding or extrusion, and their curing can be done in any conventional manner. The curing temperatures can thus in particular be 100 to 200 C, the curing times 5 to 30 minutes or more and the pressure applied during the shaping can be about 0.70 to 70.3 kg · cm ² . After shaping, the products are advantageously subjected to post-curing for about 1 to 24 hours at temperatures in the range from 150 to 250.degree.

Elastomers from the molding compositions according to the invention can have temperatures of 150 to for a long time 300 "C and considerable times even higher temperatures without loss of their properties. This makes them particularly valuable for their use as insulation in electrical conductors and in Form of moldings exposed to higher temperatures. like tubes. Hoses. Plates or gaskets.

The highly viscous diorganopolysiloxane used as the basis for the molding compositions in each of the following examples was obtained by heating a mixture of octamethylcyclotclrasiloxane at 150 ° C. for 5 hours and triacethylletravinylcyclotetrasiloxane in a molar ratio of 99.8: 0.2 in the presence of 0.001 percent by weight, based on weight this mixture. Potassium hydroxide made.

In the following examples, all parts are based on weight, if nothing otherwise stated.

example 1

The highly viscous diorganopolysiloxane produced by the process described was mixed with the amounts of additives listed in Table 1 in four batches. Each of the batches was then cured for 5 minutes at 115 ° C. under a pressure of 42.2 kg / cm ^2.

Table I.

Subjected to heating to 249 ° C. The physical properties of the elastomers thus obtained are compiled in the following Table IV.

Table IV

Physical properties approaches A B

Tensile strength in kg / cm ² 42.2 47.1

Strain, %
Hardness, Shore A

270
43

275 40

C D

49.2 brittle 300

45

Components

Approaches A B

(We (We (We (Weight- weight- weight- weight parts) parts) parts) parts)

High viscosity poly 70 70 70 70 siloxane (example 1) Terminal ones 12.5 12.5 12.5 12.5 Have OH groups sending polydimethyl siloxane (50cSt / 25 ° C) Pyrogen-derived 17.5 17.5 17.5 17.5 SiO ₂ (Cab-0-SiI) Bis- (2,4-dichloro- 1.4 1.4 1.4 1.4 benzoyl) peroxide Titanium dioxide (pyrogen 3.0 won) Iron oxide 2.0 Cerstannate 2.0

The physical properties of the elastomers thus obtained are shown in Table II.

Table II

Physical properties approaches
AWAY

Tensile strength in kg / cm ²
Strain. %
Hardness, Shore A

56.2 49.2 56.2 51.0 460 450 430 450 39 38 38 37 Any of the approaches in Table I that are as above post-cured, were then heat-aged for 168 hours Subjected to heating to 316 ° C. The approach that according to the invention contained the cerstannate additive, was still flexible thereafter.

It can be seen from the values in the tables given above that the elastomers containing cerium stannate are heat-stable at temperatures above 300 ° C. In addition, the molding compositions according to the invention can easily pigmented in the desired color.

Example 2

The following batches were each made by mixing 70 parts by weight of the highly viscous diorganopolysiloxane produced as the base resin, 12.5 parts by weight of a polydimethylsiloxane containing terminal hydroxyl groups (50cSt / 25 ° C), 17.5 parts by weight of a pyrogenic silicon dioxide and 1.1 parts by weight of bis- ( 2,4-dichlorobenzoyl) peroxide, each made with different amounts of cerium stannate. These batches were cured for 5 minutes at 115 ° C. and a pressure of 42.2 kg / cm ² , then post-cured for 24 hours at 249 ° C. in a convection oven and heat-aged for 168 hours at 249 ° C. in a convection oven. The physical properties of the pressure cured, post cured and heat aged elastomers are summarized in Table V below.

Table V

Physical properties cerium stannate

Each of the batches in Table I which were pressure cured as described above were used then post-cured for 24 hours at 249'C in a convection oven. The physical properties the elastomers obtained in this way are listed in Table III.

Table III

Physical properties approaches
AWAY

Tensile strength in kg / cm ²
Strain, %
Hardness, Shore A

60.8 61.5 62.6 33.7 380 410 375 130 43 39 39 50

Each of the approaches according to Table 1, which have been re-trimmed as described above, were then followed heat aging by 168stiindigcs

kg / cm ² I Ge 2 Ge 4 Ge 8 Ge "C weight weight weight weight C. part share share share Tensile strength in C. 55 5min / 115 58.0 56.2 52.7 49.2 24 hours a day C. 59.8 62.6 55.2 52.7 I68h / 249° C. 38.7 49.2 42.9 42.2 Strain, % C. ⁶⁰ 5min / 115 445 430 460 475 24 hours / 249 " C. 325 375 350 330 168h / 249 ' C. 125 300 240 230 Hardness, Shore A C. ⁵⁵ 5 min./Il5 37 38 39 37 24h / 249 ' 39 39 40 3 K 168h / 249 62 45 45 45

The data in the table show that cerium stannate already in a concentration of 1% die Improved heat stability of the elastomers. Components

B e i s ρ i e 1 3

70 parts by weight of the highly viscous diorganopolysiloxane produced as the base resin were added 12.5 parts by weight of a terminal hydroxyl group containing polydimethylsiloxane (5OcSt'25 C). 17.5 parts by weight of a pyrogenically obtained silicon dioxide and 1.4 parts by weight of bis- (2,4-dichlorobenzoyD-peroxide and additionally with each different Amounts of barium stannate mixed together.

The mixtures were cured for 5 minutes at 115 C under a pressure of 42.2 kg / cm ^2, then post-cured for 24 hours at 249 ^C C. The post-cured mixtures were heat aged for 24 hours at 316 ^U C in a convection oven. The physical properties of the elastomers are summarized in Table VI below.

Table Vl

Approaches A B

(Ge (Ge iGe- | Weighted weight parts share share share '

Physical Properties

Tensile strength, kg 'cm ²
Pressure hardening
(5 min./115 ° C)
Post-curing
(24h / 249 ° Q
Heat aging
(24h / 316 C)

Strain, %
Pressure hardening
(5 min. 115 C)
Nachhürtuna
(24h / 249'C)

Heat aging
(24h 316C)

Hardness. Shore A
Pressure hardening
(5min. 15 C)

Post-curing (24h / 249 C) Heat aging (24h / 316 C)

Barium stannal

2 parts by weight 4 parts by weight

45.7 47.1

41.5 35.2

flexible flexible

525 500

270 280

flexible flexible

39 39

42 41

68 65

H igh viscous poly- 70 70 70 70 siloxane

Final 12.5 12.5 12.5 12.5

Polydimethylsiloxane containing OH groups (50cSt / 25'C)

Pyroids recovered 17.5 17.5 17.5 17.5 SiO ₂

Peroxide analyzer 1.4 1.4 1.4 1.4

50% bis (2,4- "dichlorobenzoyl) peroxide -
50% dimethyl silicone oil
Cerium stannate 4

Cerium (IV) oxide 4

Cerium (III) oxide \

Cerium (IV) oxide I ' ⁴

Control *) Cerium oxide mixture of different valency levels.

Approach A = according to the invention.

Salts B. C and D are used for comparison.

Each of these approaches was 5 minutes at 115 ° C

cured while shaping at a pressure of 42.2 kg cm ^2. The physical properties of the elastomers obtained in this way are summarized in tables.

35 posed:

Table!!

40

l'hysical properties approaches B. C. D. A. 68.6 52.7 35.2 Tensile strength in kg cm * 55.5 450 390 300 Strain. % 375 35 36 35 Shorc A hardness 35

45 Each of the batches was then subjected to heat aging by heating at 316 ° C. in a forced air oven for 24 hours. The physical properties of elastomers thus obtained are summarized in the following Table III:

Table III

When the highly viscous methylvinylpolysiloxane is replaced by other organopolysiloxanes that are 0.01 to 0.35 mole percent of methylvinylsiloxane units was replaced, elastomers with practical get the same properties. These properties remained practically unchanged when others were used Anti-structural agents and other metal stannates. the Elastomers each had excellent heat stability, which was also maintained over long periods of time remained, and improved resistance to reversion.

Test ^{report 6s}

Thermosetting compounds were produced from the following components:

Physical Properties

Tensile strength in kg / cm ²

Elongation in% Shore A hardness

Approaches A B

40.1 brittle 21.1 brittle 275 90 28 51

These comparative tests clearly show that the metal stannates used according to the invention, in particular cerium stannate (batch A), give the organopolysiloxane elastomers better heat stability than ceria and cerium oxide mixtures according to the prior art (batch B and C); Approach D did not contain any. 2 "-sat5 and serve! - does control.

£ 09 629/321

Claims (3)

5 claims: 1. Molding compounds based on organopolysiloxanes that can be hardened under heat to form elastomers, with organic peroxy compounds as hardeners, optionally fillers and others customary additives, characterized in that they are metal stannates with metals from the Groups Ha and Hb, IHa, including the lanthanides and actinides, and VIII of the long-period system included as heat stabilizers. 2. Molding compositions according to claim 1, characterized in that they contain these metal stannates in Amounts from 0.1 to 10%, based on the weight of the basis of the molding compositions Organopolysiloxanes contain. 3. Molding compositions according to claim 1 or 2, characterized in that they are as such metal stannates, Contains cerium stannate or barium stannate.