DE1128655B - Process for reducing the build-up of pre-mixed filler-containing organopolysiloxane compounds which can be hardened in the heat to form elastomers - Google Patents

Description

INTERNAT. KL. C 08 g

GERMAN

PATENT OFFICE

W24498IVd / 39b

REGISTRATION DATE: NOVEMBER 21, 1958

• NOTICE THE REGISTRATION ANDOUTPUTE EDITORIAL: APRIL 26, 1962

In order to improve the mechanical values, organopolysiloxane elastomers are produced as is known, so-called "active fillers" or "reinforcing fillers", especially in the gas phase Pyrogenically obtained silica or silica hydrogels dehydrated while maintaining the structure as well as diatomaceous earth is used. In addition to such silicas are used for the same purpose sometimes also carbon black, finely divided y-aluminum oxide with a particle size of less than 100 πΐμ ίο or other fillers commonly used in the rubber industry which are known to be they exert a reinforcing influence on the mechanical properties of the elastomers, such as pyrogenic Oxides of metals, especially titanium, generated in the gas phase are used. The so obtained Elastomers are characterized by excellent resistance to water and aqueous chemicals, through good tensile strength and abrasion resistance and, except when using carbon black, through low dielectric losses.

The uncured organopolysiloxane compositions to which active fillers have been added, however, stick together very strong during storage and must therefore prior to shaping by prolonged rolling into the deformable, plastic state. The time it takes to do this in hereinafter referred to as the “rolling time”, is generally more than 15 minutes for such mixtures. These Times are even longer if the filler content, based on the siloxane, is greater than 20 to 30%. In the case of a higher proportion of filler, which is often desirable in order to achieve higher Shore hardnesses, it is mostly no longer possible at all, these "unvulcanized" mixtures by rolling in the plastic, deformable state.

Elastomers with these active fillers, especially those with pyrogenic in the gas phase obtained silicic acid, furthermore show the disadvantage that the elongation at break during heat aging falls off relatively quickly.

Attempts have already been made to remedy this problem by adding silanols and organosilicic acid esters or to eliminate their linear condensation products. This addition increases the rolling time actually shortened, however, if such mixtures are stored for a long time, it is also an unpleasant one Noticeable tightness. Furthermore, the addition of these substances causes the voltage value the elastomer decreases sharply and the permanent deformation is increased. Also join prolonged storage of such elastomers efflorescence method for reducing

the rigging of ready-mixed

organopolysiloxarim compositions containing fillers, which in the heat to elastomers

are hardenable

Applicant:

Wacker-Chemie G. mb H.,
Munich 22, Prinzregentenstr. 22nd

Dr. Siegfried Nitzsche and Dr. Manfred Wick,

Burghausen (Obb.),
have been named as inventors

that are difficult to remove. Even with these elastomers, the tensile strength is at Heat aging returns faster than organopolysiloxane elastomers with inactive fillers, the but not because of poor electrical and mechanical values for many technical applications are useful.

Also the well-known addition of pinacone or its reaction product with dimethyldichlorosilane is effective only for a limited time and also deteriorates the heat resistance of Elastomers considerably. In addition, these mixtures experience increased shrinkage on curing which must be compensated for by specially constructed shapes.

It has now surprisingly been found that the pre-mixed, filler and a Customary organic peroxide-containing organopolysiloxane compositions, which in a known manner in are curable to elastomers by heat, the rolling time is shortened to about one twentieth and at the same time the elongation at break of the elastomers made from them increases after heat aging can be if the masses are rolled or kneaded at 60 to 200 ° C.

This finding is all the more surprising as it is stated in the literature that ready-to-harden with Mixtures containing hardeners should not be heated to temperatures higher than 50 ° C under any circumstances

209 577/438

because otherwise hardening and rendering of these mixtures useless is to be expected is.

It should also be emphasized that the effect achieved according to the invention does not occur if the same Mixture subjected to a kneading or rolling process in the heat in the absence of hardeners.

It has been shown that an organopolysiloxane compound mixed with an organic peroxide itself then hardened without further addition of peroxide when heated to 80 ° C, if it previously hardened 3 hour kneading or rolling process at 120 ° C was subjected.

example

From 100 g of a dimethylpolysiloxane with a molecular weight of 500,000, 40 g of a pyrogenic silica obtained in the gas phase (surface area, determined by the BET method: 200 m 2 / g) and 2 g of 2,4-dichlorobenzoyl peroxide. This finished mixture ao is divided in half. One half is stored for 4 weeks at room temperature, the other half is rolled immediately after production for 30 minutes at 120 ° C on a rolling mill and then also stored for 4 weeks at room temperature. The non-hot-rolled part of this mixture requires a rolling time of 20 minutes after 4 weeks to convert it into the plastic state, while the hot-rolled part of the same mixture can be converted into the plastically deformable state within one minute. The elongation at break of an elastomer from the cold-rolled part of the mixture is 260% after curing and tempering for 12 hours at 150 ° C and 12 hours at 200 ° C, while the elongation at break of the hot-rolled part of the mixture is also 12 hours at 150 ° C and annealed for 12 hours at 200 ⁰ C, 550 <> / is _0th

If the mixture is rolled or kneaded under the same conditions before the peroxide is added, the peroxide is only added after this rolling or kneading process and the mixture thus produced Also stored for 4 weeks at room temperature, an elastomer with a rolling time is obtained of 30 minutes and an elongation at break of 250% after curing.

Claims (2)

PATENT CLAIMS: 1. A process for reducing the build-up of ready-mixed organopolysiloxane compositions containing fillers which are curable in a manner known per se in the heat to give elastomers, characterized in that the compositions which already contain a conventional organic peroxide as hardener are rolled or rolled at 60 to 200 ° C be kneaded. 2. The method according to claim 1, characterized in that that the organopolysiloxane is rolled for at least 30 minutes. Considered publications:
Belgian patent specification No. 562 036. Legacy Patents Considered:
German Patent No. 1,077,425. © 209 577/438 4.