DE1282968B - Heat-vulcanizable organopolysiloxane molding compounds - Google Patents

Description

Heat-vulcanizable organopolysiloxane molding compounds become vulcanizable Organopolysiloxanes mixed with certain fillers, especially finely divided ones High reinforcing capacity silica products such as pyrogenic Silicon dioxide, silicon dioxide aerogels and silicon dioxide obtained by precipitation, this makes the resulting mixtures of substances tough and difficult to process. It can be assumed that this toughness is due to the action of silica on the organopolysiloxane comes about, and they are usually called "structure". It is already known that structure formation in such mixtures of substances thereby to eliminate the possibility of low molecular weight organosilicon compounds in the mixtures incorporated containing hydroxyl or alkoxy groups. The use of such organosilicon additives contributes noticeably to the suppression of structure formation in the substance mixtures and makes them easier to process and also gives them a better shelf life. However, the use of such structure-reducing additives often leads to undesirable plasticizing effects insofar as the approaches become sticky and are difficult to use. It is also still known, instead of or preferably next to the finely divided silicon dioxide product: t and next to those mentioned above Organosilicon additives other fillers, especially those based on naturally occurring ones Add silicates such as diatomaceous earth or quartz to reduce structure formation.

Surprisingly, it has now been found that fiddling with the vulcanizable organopolysiloxane molding compositions of the type mentioned above and their Processability can be improved considerably by using a synthetic in it Metal silicate incorporated.

Even more surprising was the finding that the incorporation of the synthetic silicate mentioned to reduce the permanent compression set of the vulcanized elastomer produced from the molding compound can lead. the The improvement achieved in this way with regard to the permanent compression set imparts the silicone rubbers from an economic point of view of greater importance because they are their usefulness increased for applications where such a property is important, for example in the manufacture of high-temperature-resistant seals.

Accordingly, the invention relates to heat or high energy radiation vulcanizable organopolysiloxane molding compounds based on (1) in the solid, elastic state convertible organopolysiloxanes, (2) triggering structure formation Silicon dioxide fillers with an effective surface area of at least 50 times g, (3) liquid, structure-reducing additives of the organosilicon compound type and (4) Si-based fillers, with the characterizing feature that as (4) 1 to 20 parts by weight of a powdered synthetic metal silicate per 100 parts by weight of the convertible organopolysiloxane (1).

Organopolysiloxanes that can be converted into a solid, elastic state are, belong to the state of the art and consist of polysiloxanes, the primary Contain diorganopolysiloxane units, but also small amounts of triorganosiloxane, May contain monoorganosiloxane and SiO2 units. The preferred one in question Coming convertible organopolysiloxanes are essentially linear in nature and have a ratio of organic substituents to silicon atoms of about 1.98: 1 to about 2.0: 1 and more, preferably 1.99: 1 to 2.005: 1.

Organic substituents can be used in the convertible organopolysiloxanes monovalent hydrocarbon radicals and monovalent substituted hydrocarbon radicals to be available. However, it is advantageous if at least 50% of the total organic Substituents are methyl radicals; the remaining radicals, for example, alkyl radicals can be, such as ethyl, propyl, butyl or octadecyl radicals, and also alkenyl radicals, such as vinyl or aryl radicals, aryl radicals, such as phenyl, naphthyl or diphenylyl radicals, substituted hydrocarbon radicals, e.g. B. the Trifluorpropyfrest, or Cyanalkylreste can represent.

If the convertible organopolysiloxane contains alkenyl radicals, e.g. B. vinyl residues, so it is recommended that these residues in an amount of less than 10.10, the total amount of organic substituents present in the organopolysiloxane are.

The organopolysiloxanes can be homopolymers or copolymers and can vary in consistency from viscous liquids to stiff, high-molecular rubber-like substances.

The organopolysiloxanes which can be used, for example, include consequently dimethylpolysiloxanes, copolymers of: dimethylsiloxane units and vinyl methylsiloxane units, copolymers of diphenylsiloxane units, Dimethylsiloxane units and methyl vinylsiloxane units or copolymers of dimethylsiloxane units and trifluoropropylmethylsiloxane units.

Silica fillers which trigger the formation of the structure can be used. any finely divided, highly reinforcing silicon dioxide products are used, which have an effective surface area of at least 50 m2 / g and preferably one effective surface area of more than 100 m2 / g, as determined by nitrogen adsorption according to the method used in the »A.S.T.M. Special Technical Bulletin «, issue 50, p. 95 ff. (1941). Among the silica fillers that can be used in accordance with the invention are included, include z. B. the silicon dioxide products obtained on pyrogenic W. egeX, silicon dioxide aerogels and d silicon dioxide products obtained by precipitation. That Reinforcing silica is preferably in an amount of from about 10 to about Contain 70 parts by weight per 100 parts by weight of the convertible organopolysiloxane.

In addition to the reinforcing silica fillers, can the vulcanizable molding compositions according to the invention also contain other fillers, as they are usually used in the manufacture of siloxane elastomers. These other fillers include metal oxides such as titanium dioxide, zinc oxide, and ferric oxide or magnesium oxide, fibrous fillers such as asbestos or glass fibers, or those containing silicon dioxide Fillers such as diatomaceous earth or quartz flour.

As a structure-reducing additive, the component (3) of the constitutes the above-mentioned mixtures of substances according to the invention, can be any of those Organosilicon compounds are used, which are already known for such purposes are and after their incorporation in the mixture a plasticizing or have a softening effect on the vulcanizable mixture of substances. Such organosilicon compounds can be monomeric or polymeric and are usually characterized in that she in the molecule groups, such as alkoxy or hydroxyl groups, contain are reactive with the finely divided silica.

The organosilicon liquids which are preferred for the purposes of the invention are those of the general formula correspond, where R is a monovalent hydrocarbon radical or a halogenated monovalent hydrocarbon radical, which is preferably a low molecular weight alkyl radical, e.g. B. is a methyl radical or a phenyl radical, and wherein p is a number from 1 to 30.

The amount of the structure-reducing additive in the substance mixtures is present, can fluctuate within a wide range and depends on factors like the nature of the additive, the type of vulcanizable organopolysiloxane and the amount of silica filler present. Usually the Amount of the additive in the range that is normally found when mixing of vulcanizable organopolysiloxane mixtures, a. i.e., it lies between about 4 and about 30 parts by weight, preferably between 5 and 15 parts by weight, each related. per 100 parts by weight of the convertible organopolyiloxane.

Component (4) of the molding compositions according to the invention consists of one or several synthetic metal silicate powders, such as calcium silicate or Magne, -, silicon silicate. These synthetic silicates can thereby. hydrothermal conversion a silica material such as diatomaceous earth silica with a metal oxide or hydroxide, and they are characterized by a high absorption capacity for liquids while maintaining their character as dry, flowable Powder excellent. -The synthetic silicates of this type are commercially available Materials, and they can be, as, powders, with, different effective surfaces obtain.

For the purposes of the invention, synthetic ones are particularly advantageous Silicates can be used, which have the ability to reduce the structure of the liquid To absorb additive in an amount that is at least two times its weight : of the synthetic silicate.

Be on 100 parts by weight of the convertible organopoly, oxane 1 to 20 parts by weight of the synthetic metal silicate used. Even if one some improvement. the permanent compression deformation of the rubber already. achieved if you use component (4) in an amount down to 1 part by weight is used, a technically more satisfactory improvement in this property is achieved ; but then achieved when the proportion of the.

Silicates is about 2 to about 10 parts by weight. A certain Improvement in processability can be achieved if-the amount of silicate is increased beyond this amount, but it can also worsen the physical properties of the finished elastomer.

The molding compositions according to the invention can be used in any known manner getting produced. So can for example the structure-reducing one Additive to be incorporated into the synthetic silicate to obtain a product which is generally a free-flowing powder. This powder can then mixed with the other ingredients in a rubber mixer or roller mill will. Deviating from this, the structure-reducing additive can, if desired and the synthetic silicate can be incorporated separately into the substance mixtures.

The vulcanizable molding compositions according to the invention can be prepared by heating with organic peroxides, such as benzoyl peroxide, dichlorobenzoyl peroxide, tert-butyl perbenzoate, Dicumyl peroxide or tert-butylcumyl peroxide, or by being one of the energetic ones Exposure to radiation can be converted into silicone elastomers.

In addition to the essential components and something beyond that The vulcanizable molding compositions according to the invention can be added fillers also contain additives such as are commonly used in silicone compounds, e.g. B. Pigments, flame retardants and heat stabilizers.

The following examples in which the indicated parts are parts by weight mean, are intended to explain the invention in more detail.

Example 1 A rubber mixer was used to mix 100 parts one of 99.8 mole percent dimethylsiloxane and approximately 0.2 mole percent methyl vinylsiloxane units existing mixed polysiloxane with 35 parts of a finely divided silica filler and 2 parts of zinc oxide to mix together. This mixture was then made up of 15 parts given a free-flowing powder, which by mixing a synthetic Calcium silicate with a low molecular weight, hydroxyl radical on the terminal silicon atom containing dimethylpolysiloxane mixture had been prepared, the mixture 1 part of synthetic silicate for every 3 parts of dimethylpolysiloxane mixture. After the free-flowing powder had been thoroughly dispersed, 1.75 parts of 2,4-dichlorobenzoyl peroxide were obtained incorporated into the mixture as a vulcanizing agent. The mixture thus obtained was not sticky and easy to handle. It became the plasticity of the mixture determined according to W i 11 i a m s; it was 270. An equal mixture of substances, which through Incorporation of 11 parts of the low molecular weight dimethylpolysiloxane, but without The addition of the above-mentioned silicate was found to be touched as sticky and its Williams plasticity was determined to be 220.

The permanent compression set was determined using the »BS 903, part A6, 1957 «(without sandpaper) on test samples of type 1 after vulcanization in one Press determined with subsequent 4-hour post-curing at 250 ° C. The measured values for the permanent compression set were applied to the samples under constant tension, for a period of 24 hours at 150 "C and 24 hours at 200" C, certainly. The values obtained for the samples containing the synthetic silicate were 14 and 4101o, respectively. If the control samples were tested in the same way, permanent compression deformations of 44 or 70%.

Example 2 A vulcanizable composition was used the approach described in Example 1 produced with the difference that 11 Parts of the low molecular weight dimethylpolysiloxane and 4 parts of the synthetic metal silicate instead of 15 parts of the mixture of these two ingredients in the mixture were mixed in separately. The mixed mixture was easy to handle, and it had a Williams plasticity of 270.

The compression set of the vulcanized rubber was determined in the manner described in Example 1; it was 170 per cent after 24 hours at 150 "C and 43010 after 24 hours at 200" C.

Was the above vulcanizable composition with 5 parts of diatomaceous earth instead of the 4 parts of the silicate contained in the molding composition according to the invention produced, values for the permanent compression set of 24% are obtained 24 hours at 150 "C and from 62 ovo after 24 hours at 2000 C.

These values are much higher than those obtained with the molding compositions according to the invention obtained, and the vulcanized silicone elastomer obtained is therefore that according to the invention received inferior. Diatomaceous earth is essentially silica and not a silicate (see.

R ö m p p, Chemielexikon, 4th edition, p. 2274).

Claims (2)

Claims: 1. Vulcanizable by heat or high-energy radiation Organopolysiloxane molding compounds based on (1) in the solid, elastic state convertible organopolysiloxanes, (2) structure-inducing silica fillers with an effective surface area of at least 50 m2 / g, (3) liquid, structure-reducing Additives of the organosilicon compound type and (4) Si-based fillers, characterized in that as (4) 1 to 20 parts by weight of a powdery synthetic metal silicate based on 100 parts by weight of the convertible organopolysiloxane (1), are included. 2. organopolysiloxane molding compositions according to claim 1, characterized in that that they contain a synthetic metal silicate produced by hydrothermal conversion of a silica with a metal oxide or hydroxide. Documents considered: German Auslegeschrift No. 1,136,106; British Patent No. 859 284.