CS205674B1 - Method pf preparation of the thermoplastic mixtures containing wholly sieved rubber - Google Patents

Description

The invention relates to a process for the preparation of thermoplastic compositions comprising fully crosslinked rubber and a low content of high melt index polyethylene.

For example, U.S. Pat. No. 3,835,201, U.S. Pat. No. 4,031,169, U.S. Pat. No. 4,036,912, U.S. Pat. No. 4,046,840 disclose processes for the preparation and composition of mixtures of rubbers and plastics suitable for the manufacture of technical articles which can be processed by forming at higher temperatures. However, the materials prepared in this way are characterized by low thermal stability due to the presence of uncrosslinked rubber and plastic such as polyethylene. Certain improvements to the above properties can be achieved by partially crosslinking the rubber-plastics blends already in production; preferably the principle of the so-called dynamic vulcanization as described in U.S. Pat. No. 3,037,954 has been used. Partial crosslinking, as disclosed, for example, in U.S. Pat. Nos. 3,758,643 and 3,862,106, does not yet achieve the maximum mechanical values of the compositions. _of

Complete dynamic vulcanization requires kneading rubber mixtures with plastics or thermoplastic materials in high-speed mixers at 100 rpm. per minute (such as a Corder Brabender PLV 151 Casing Laboratory Mixer with a working chamber content of 0.05 L) and at temperatures around 180 ° C. The method of preparation is described, for example, in U.S. Patent 1493,951. On large operational rubberized kneading machines where the rotational speed of the rotors is lower, it is not possible to obtain materials which are technically usable by complete dynamic vulcanization. The resulting products are crushed and unprocessable. '

These drawbacks are overcome by the object of the present invention, which is a process for preparing thermoplastic compositions containing fully crosslinked rubber, characterized in that it is prepared by kneading in a high-pressure kneading machine 15 to 50 wt. % of an ethylene propylene terpolymer containing 55 to 90 wt. % of ethylene or as mixtures with butadiene-styrene rubber in a weight ratio of 1: 2 to 12: 1, 1 to 9.5 wt. % polyethylene having a melt index of 20 to 200, 10 to 50 wt. % Of reinforcing fillers, 1 to 10 wt. % of plasticizers, 0.75 to 2.5 wt. % zinc oxide, 0.15 to 1.0 wt. % stearic acid, 0.03 to 2.5 wt. % tetramethylthiurammonosulfide and 0.02 to 1.0 wt. % sulfur.

Surprisingly, it has been found that the complete dynamic vulcanization of EPDM-based mixtures, possibly in combination with SBR, can be carried out on commercially available rubber kneading machines in the presence of a small amount of polyethylene with a high melt index determined e.g. Very good results have been achieved with an accelerator system containing sulfur as the vulcanizing agent and a zinc oxide activator and stearic acid. Satisfactory results were also achieved with sulfur-free systems. The work done so far has been carried out with isotactic polypropylene or polyethylene with melt index values from 0.1 to 1, with an optimum plastic content in the mixture of about 50 wt. Although the strength of the high melt index polyethylene used as well as its heat resistance is low, the resulting blends have high mechanical properties and excellent flexibility.

For economic reasons, the blends can be treated directly with the blending process with fillers and plasticizers, extenders, and the like, as is customary with vulcanizates produced by commercial methods. The mixtures can be processed at temperatures around 150 ° C, for example by rolling, extrusion, etc., and the resulting waste can be reprocessed.

Example 1

Basic mechanical properties

Tensile strength

Module 200%

Ductility

Elesticity

Hardness

Ductility

Crescent structural strength at 25 ° C

9.0 MPa 7.3 MPa 330%%

Sh A 50 ° / o

N. mm ^-1

Example 2

The mixing procedure is the same as in Example 1, except that sulfur was added to the mixture simultaneously with the vulcanization accelerator during kneading.

Rubber, zinc oxide and stearic acid were introduced into a Banbury-Bridge kneading machine having a working chamber volume of 60 liters at an initial temperature of 25 ° C. After 1 to 2 minutes kneading, high melt index polyethylene, soot, plasticizer was added, after 4 minutes the temperature at the control sensor reached 13 ° C, the vulcanization accelerator was added. Within 2 minutes, the temperature rose to 150 ° C and the driveline current consumption was increased by 10-15%. After a further 2 minutes the power take-off of the drive unit dropped to its original value and kneading was stopped. The film was rolled from the mixture at 150 ° C, from which the bodies were punched to determine the basic mechanical properties.

Used recipe mass. %

Ethylene-propylene terpolymer 42.5

Butadiene-styrene rubber 7.5

Polyethylene of melt index 200 5

Carbon black 38

Plasticizer 2.5

Zinc oxide 2,5

Stearic acid 0,75

Tetramethylthiurammonosulfide 0.25

Sulfur 1

Basic mechanical properties

Mass recipe used,%

Ethylene-propylene terpolymer 40

Polyethylene of Melt Index 20 8

Saze 44

Emollient 4

Zinc oxide 2

Stearic acid 0,8

Tertramethylthiurammonosulfide 1,2

Tensile strength

Module 200%

Ductility

Elasticity

Hardness

Ductility

Crescent structural strength at 25 ° C

MPa,

8.5 MPa 280%%

Sh A 40%

N. mnr ¹

Claims (2)

Process for preparing thermoplastic compositions comprising fully crosslinked rubber, characterized in that it is kneaded in a high-pressure kneading machine of 15 to 50 wt. % ethylene-propylene terpolymer containing 55 to 90 wt. % ethylene or a mixture thereof with butadiene-styrene rubber in a weight ratio of 1: 2 to 12: 1, 1 to 9.5 wt. % of polyethylene having a melt index of 20 to 200, 10 to OF THE INVENTION 50 wt. % of reinforcing fillers, 1 to 10 wt. % of plasticizers, 0.75 to 2.5 wt. % zinc oxide, 0.15 to 1.0 wt. % stearic acid, 0.03 to 2.5 wt. % tetramethylthiurammonosulfide. 2. A process for the preparation of the thermoplastic compositions according to claim 1, characterized in that 0.02 to 1.0 wt. % sulfur.