DE2009999A1 - Polybutadiene rubber/urea mixtures to prevent frosting - Google Patents

Abstract

0.1-3 wt.% (referred to rubber) of urea is added to blend before vulcanisation to prevent frosting in coloured vulcanisates of butadiene homo- and co-polymers and usual additives. Relatively small amount of additive is sufficient and it does not increase cost of blend. Urea causes no discoloration in light and can be used in blends coming into contact with foodstuffs, being physiologically harmless.

Description

Method for preventing frosting of colored rubber articles The invention relates to a method for preventing frosting in colored Vulcanized products made from homo-bait copolymers of butadiene and customary mixing additives.

The one taken from the English language and commonly used The term "frosting" describes a phenomenon that occurs with many rubber articles occurs. It manifests itself in the fact that an oxidation occurs on the surface gray coating is generated. This phenomenon shows up on microscopic examination than a variety of microcracks. This coating is undesirable because it is the exterior Appearance of the rubber article impaired. This frosting problem is in the literature in 11Kautschuk und Gummi "1959, page 68 WT ff. already described.

There are already a number of ways to prevent frosting in vulcanizates of substances have been described as suitable. However, these substances partially lead changes in the physical properties of the finished article. Additions where The primary aromatic amines involved are not physiological harmless. It has also been shown that with light, sensitive color settings and with a low dosage of these amines after longer exposure it still discolors can occur.

The object of the invention is specifically for homopolymers and copolymers of butadiene to find a substance that has the above-mentioned disadvantages avoids. The addition should be relatively small and the rubber mixture should not be made more expensive entail.

According to the invention, this object was surprisingly achieved in this way be that the mixture before vulcanization based on rubber 0.1 to 3 weight X urea is added. As the examples below show, In this way, rubber items are definitely discolored when exposed to light locked out. Furthermore, the rubber articles made in this way are physiological harmless, so that they are also suitable for objects that contain foodstuffs come into contact. The intended additional amounts of urine are different and are based on the types of rubber used. For example, it is at Butadiene acrylonitrile mixed polymer requires a higher dosage than for other polybutadienes.

The invention is illustrated by means of the following examples. For Example 1 is a mixture of the following structure: NBR N 2807 or 2818 100 parts of stearic acid 1 n zinc oxide 5 "Haikaolin 5 °" Ultrauarin blue 5 II carbon black o, 8 "Sulfur 2 1? Benzothiazyl-2-cyclohexylsulfenamide 1" Diphenylguanidine 0.5 "165.3 Parts NBR N 2807 or 2818 means: butadiene acrylonitrile mixed polymer with an acrylonitrile content of 28% and a defo value of 700 or 1800.

Increasing amounts of urea are also added to this mixture. Table 1 shows the minimum amount of urea added at which frosting occurs is suppressed.

Table I. Mixture number / addition of urea in% by weight on elastomer Rubber 0 0.1 0.3 0.5 1 2 3 I NBR N 2807 + + + + + - II NBR N 2818 + + + + + + ~ Example II Buna 1551, 1712, CB 100 parts stearic acid 1 zinc oxide 5 "hard clay 50" ultramarine blue 5 "carbon black 0.8" sulfur 2 "benzothiazyl-2-cyclohexylsulfenamide 1" diphenylguunidine 1 11 165.8 parts under Buna 1551, 1712, CB the following is to be understood: 1551: Copolymer of butadiene and styrene with a styrene content of 23.5 and a Mooney viscosity of 50 (ML 4 at 100 ° C.), non-discolouring stabilized.

1712: Copolymer of butadiene and styrene with 23.5% styrene and 37.5% oil (based on rubber) and a Mooney viscosity of 49 discolouring stabilized.

CB: Stereospecific polybutadiene produced by solution polymerization is produced in the presence of organometallic catalysts.

In Example II a different mixture formulation is given. Here too urea is added according to Table I in increasing amounts. It turns out that even with an additional amount of 0.1 or 0.3% by weight of urea on elastomer a frosting phenomenon is prevented.

Table II Mixture number / addition of urea in% by weight on elastomer Rubber oo 1. Buna 1551 + ~ Buna 1712 + + - Buna CB + - Table III illustrates the testing of the rubber articles in question under a xenon lamp. The vulcanization of the mixtures specified in the recipes takes place for b minutes at 1550 C. Plates are cut from the vulcanizates and subjected to a frosting test. The test is carried out in a drying cabinet at 450 ° C.

Table III Type of exposure Dosing of urea in% by weight on elastomer 0 1 3 100 xenon - - -

Claims (1)

P a t e n t an s p r u c h Procedures for preventing frosting in the case of colored vulcanizates from Hoo- and copolymers of butadiene and the usual Additives, characterized in that the mixture is obtained before vulcanization on rubber 0.1-3% by weight of urea is added.