DD219201A1 - METHOD FOR REDUCING THE ANVULCANIZATION TILT OF RUBBER MIXTURES - Google Patents

Abstract

The invention relates to a method for reducing the scorching tendency and for improving the processing behavior of rubber mixtures of natural or synthetic rubber or of blends thereof by addition of low molecular weight polybutadiene dicarboxylic acids. The low molecular weight polybutadienedicarboxylic acids have a multiple effect in the mixtures and vulcanizates: the carboxylic acid group reduces the risk of scorching in the course of the preparation and processing of the rubber mixtures; the low molecular weight polybutadiene acts as a temporary plasticizer during compounding and processing, which is additionally reduced by lowering the process temperatures the scorch tendency is reduced and incorporated into the network as a type of plasticizer during the vulcanization process. As a result, this plasticizer is not extractable and does not migrate during use of the rubber article. This is especially important for multi-layered articles. Since the polybutadienedicarboxylic acids are not volatile, they do not cause pore formation during the vulcanization process and are therefore also suitable for high-temperature vulcanization.

Description

Title of the invention

Process for reducing the scorching tendency of rubber compounds.

Field of application of the invention

The invention relates to a method for reducing the scorching tendency and for improving the processability of natural rubber or synthetic rubber blends or blends of both by addition of suitable substances.

1-5. NGY19-3 3 * 12 9 52 ^

Characteristic of the known technical solutions

It is known that in order to achieve the usual in the rubber industry today high operating speeds even with the use of vulcanization accelerators with delayed use of the mixtures substances must be added>, leading to the reduction of scorch tendency and thus to reduce mixing waste by premature vulcanization. These substances include z. As N-nitrosodiphenyl, N-cyclohexylthiophthalimide and certain carboxylic acids, such as ζ. Β. Salicylic and benzoic acid. The effective with respect to the delay in the scorching component of the carboxylic acids, the carboxyl · In addition to the desired delayed _(effect the carboxylic acids alter some vulcanizate, as ζ hardness, undesirably '..' - - '' .. A. Another possibility for achieving higher working speeds in the production and processing of rubber compounds is the addition of suitable plasticizers, at the same time improving the filler distribution, but certain vulcanizate properties are adversely affected by the plasticizer addition, modulus 300 and abrasion behavior Plasticizer is the tendency of the latter to diffuse from the higher plasticizer-concentration blends into adjacent lower-plasticizer blends in rubber articles made up of different blends having different plasticizer levels and to be undesirable there hte to cause property changes. In the context of diffusion, the migration of the plasticizers to the mixing surface is too

see, which often leads to Verschweißstörungen. Furthermore, most of the plasticizers are volatile at higher temperature so that they cause pore formation in the vulcanizate during the vulcanization process.

For the effect of Vulkahisationsverzögerern and plasticizers in rubber compounds see Kleemann "mixtures for the, Elastverarbeitung", VEB German publishing house for the basic industry, Leipzig, 1982, chapter 11 and 5 respectively.

Object of the invention

The aim of the invention is to reduce the scorch tendency of blends of natural or synthetic rubber or blends thereof and to improve the processing behavior of the rubber blends without undesirably altering the vulcanizate properties.

Explanation of the essence of the invention

The invention has for its object to zu.entwickeln a process for reducing the scorch tendency and improving the processability of mixtures based on natural and synthetic rubber or blends thereof, wherein the rubber mixtures sulfur and conventional vulcanization and fillers and auxiliaries and in Temperatures of 373 K to 453 K can be vulcanized within 10 to 240 min.

The object is achieved according to the invention by adding a low molecular weight diene polymer having carboxyl groups to the rubber mixtures. The low molecular weight diene polymer having carboxy groups added as the diene component contains homopolymers of butadiene or isoprene or copolymers thereof with styrene or acrylonitrile having molecular weights of 500 to 5000 g / mol , The carboxyl groups are either at the ends of the polymer chain or are randomly distributed over them. The product used according to the invention is a viscous liquid of light yellow color which can be easily metered and easily incorporated into the rubber mixtures on the known mixing equipment of the rubber industry. In order to achieve the desired effects, an addition of 5 to 20 phr is required. "The physico-mechanical properties of the vulcanizates are thereby influenced predominantly positively. By reducing the scorching tendency, fewer losses occur due to premixed, vulcanized mixtures, and the production rate on the processing units, such as extruders and calenders, can be markedly increased. The softening effect of the diene polymers used according to the invention reduces the processing temperatures and thus also allows higher processing speeds. Since the diene polymers react with the sulfur during the vulcanization process in contrast to the usual plasticizers by the double bonds present and are thus firmly incorporated into the resulting network, their plasticizing effect is only temporary.

The adversely influencing the vulcanizate properties when using customary plasticizers is thus largely avoided.

By incorporating the polybutadienedicarboxylic acids used according to the invention into the network, extraction from the vulcanizate is not possible. In addition, migration is avoided, which is of importance in particular for more layered rubber articles. Since the substance used according to the invention is not volatile, vulcanization can also be carried out at high temperatures without pores forming in the article.

By the described advantages better utility properties of the rubber products are obtained. The invention will be explained in more detail by embodiments.

Exemplary embodiments Example 1

The influence of polybutadiene dicarboxylic acids on the vulcanization behavior of synthetic rubber mixtures was investigated on filler-free mixtures, which show this effect particularly clearly. The amount of sulfur was varied to determine if the proportion of polybutadiene dicarboxylic acids incorporated into the network is altered thereby. The mixtures were prepared on a laboratory roll mill according to the recipes listed below and the vulcanization of test flaps in a hydraulic press under the specified conditions.

Hischungs no.

Styrene-butadiene copolymer with 23 % styrene content 100 100 100 100 sulfur 2.0 2.0 2.4 2.8 Zinc oxide: 3 3 3 3 stearic acid 1 1 1 1 Vulcazite CZ 1 " 1 1 1 Polybutadiendicarboxylic acid tm 20 20, I 20

All information in parts by weight

 Vulkahisationsbedingungen: 60 min heating time at 145 C.

Mixing characteristics:

Monsanto 750 (VuIkämete r) 2.5 • * Basic mix 4.9 5.1 4.4 Scorch time t ₂ , min at 180 ⁰ C. 1.3 Vulkanisateigeηschäften 245 1 2 3 Mix no. 62 1.4 2.0 1.8 Tensile strength, MPa 45 470 485 395 Elongation at break, % 0,124 43 45 48 Hardness Shore A 8.4 41 41 , 43 Impact resilience, % 0,111 0.114 0.116 ν «-We rt 13.7 11.9 9.9 Sol percentage, %

The influence of Polybutadiendicarbonsäurezusatzes on the Anvulkanisationsverhalten (t ^ time) can be clearly seen, the t ₂ time is extended from 2.5 min to 4.9 min. This results in a significant improvement in processing safety. The increasing addition of sulfur causes only a slightly shortened

Scorch time (from 4.9 to 4.4 min). The V values show that with the addition of polybutadienedicarboxylic acids, a drop occurs compared with the base mixture, which is partially compensated by the increasing sulfur addition. The proportion of extractable material is greater than that of the basic mixture when an addition of the substance according to the invention takes place. At a sulfur dosage of 2.8 % , the sol proportion of the basic mixture is almost reached again. This proves that the polybutadienedicarboxylic acid is almost completely incorporated into the network.

Example 2

In this example, it is examined * how the addition of increasing amounts of polybutadienedicarboxylic acid has an effect on the scorching behavior and the processability of soot-containing synthetic rubber mixtures. The mixtures were prepared according to the formulations listed below and the vulcanization was carried out according to Example 1.

Mix no.

Styrene-butadiene copolyer with 23% S'tyrengeha.lt 100 100 100 100 100 PM PM 75 50 50 50 50 50 sulfur 2 2 2 2 2 zinc oxide 3 3 3 3 3 stearic acid 1 1 1 1 Vulcazite CZ 1 1 1 1 1 Polybutadiendicarbonsäure - 5 '. 10 15 20

All information in parts by weight.

Mix properties: Monsanto 750 (Vulkameter) Scorch time t ₉ , min at 145 ^° C.

11.5

14.0

15.0

17.5

Vulcanizate properties Mixing No. ».

Basic mixture 1 2 3 4 21.9 25.2 21.5 17.6 15.7 ^v 330 415 460 555 630 69 67 66 61 60 42 39 37 35 32 0.307 0,288 0.265 0.225 0.204 3.3 4.0 4.3 6.8 6.9 19.6 16.1 12.0 7.4 5.6 22.5 / 26 21/23 19/23 13.9 / 22 12.5 / 2 76 68 61 42 40 82 80 77 76 74

Tensile strength, MPa Elongation at break, % Hardness Shore A Impact resilience, %

Sol fraction, % modulus 300, MPa

Mixture deficit DH / DE, N / mm * 10

Mix Mooney, ME Fuel Oil Temperature, ⁰ C

In this example too, the influence of the polybutadienedicarboxylic acid on the scorching behavior is clearly recognizable. Compared with the basic mixture, the addition of 20 phr almost doubles the t ₂ time. The v _r value decreases with increasing polybutadienedicarboxylic acid amount and the sol fraction becomes larger. As shown in Example 1, by increasing the amount of sulfur, the crosslinking density can be increased, whereby the crosslinking state of the starting mixture can be achieved.

The softening effect of the polybutadienedicarboxylic acid can be clearly recognized by the decreasing defoaming and the lower Mooneey values with increasing metering. The lower defoelasticities indicate a better processability of the mixtures. This is confirmed by the lower spraying temperatures. -

Claims (3)

10 invention claim 1, "method of reducing the Anvulkanisationsneigung and for improving the processability of rubber compounds from natural or synthetic rubber or blends thereof, which fillers and auxiliaries, as well as sulfur and accelerator ^corresponds: holding and taking in the rubber industry standard conditions produced, processed and cured , characterized in that 5 to · 20 phr of a low molecular weight diene polymer having carboxyl groups with a molecular weight of 500 to 5000 g / mol are added to the mixture. 2. The method according to item 1, characterized in that as low molecular weight diene polymers with carboxyl groups homopolymers of butadiene or isoprene or their copolymers with styrene or , Acrylonitrile can be used. 3. Process according to "Points 1 and 2, characterized in that the rubber mixtures comprise polymers of conjugated dienes, for example 1,4-cis-polybutadiene, natural or synthetic polyisoprene or copolymers such as butadiene-styrene and butadiene Acrylonitrile copolymers.