JPH0234644A - Rubber composition - Google Patents

Abstract

PURPOSE:To obtain a rubber composition improved in a scorching time and crosslinking rate and giving a vulcanizate improved in ozone resistance, by mixing a specified rubber component with a thiourea and a thiuram. CONSTITUTION:A rubber component is obtained by mixing 50-95wt.% chloroprene rubber with 50-5wt.% hydrogenated NBR obtained by hydrogenating at least 80% of the butadienic double bonds of an acrylonitrile/butadiene copolymer. 100 pts.wt. said component is mixed with 0.1-10 pts.wt. thiourea (e.g., 2- mercaptoimidazoline), 0.1-10 pts.wt. thiuram (e.g., tetra-mehtylthiuram disulfide) and, optionally, a reinforcement, a filler, a vulcanization accelerator, a plasticizer, an antioxidant, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rubber composition. More specifically, the present invention relates to a rubber composition that provides a vulcanizate with excellent ozone resistance and also has an excellent crosslinking speed.

[Conventional technology]

Chloroprene rubber is used as a molding material for various rubber parts, but it has the following drawbacks.

(a) Poor ozone resistance Chloroprene rubber has a structure with double bonds in its main chain, so its ozone resistance is poor.

In order to solve these drawbacks, large amounts of anti-aging agents have been blended into the product, but if the blended anti-aging agents are extracted with oil or the like, the effect of improving ozone resistance is lost.

(b) The scorch time is short and it is difficult to increase the crosslinking rate. Because the scorch time is short, the crosslinking rate cannot be increased, and therefore it is not suitable for short-time crosslinking such as injection molding. In order to lengthen the scorch time, there is a method of using thiurams, which are retarders, but this has the side effect of slowing down the crosslinking rate.

[Problem to be solved by the invention]

The present invention has good ozone resistance, long scorch,
The purpose of this invention is to provide a chloroprene rubber composition with a high crosslinking rate.

[Means for solving division problems]

Such an object of the present invention is to obtain chloroprene rubber of about 50 to 95
This is achieved by a rubber composition in which approximately 0.1 to 10 parts by weight of thioureas and thiurams are blended to 100 parts by weight of a rubber component consisting of approximately 50 to 5 parts by weight of hydrogenated NBR.

Hydrogenated NBR is obtained by hydrogenating the butadiene double bond in an acrylonitrile-butadiene copolymer, and exhibits chemical stability at a hydrogenation rate of approximately 80% or higher, particularly in terms of heat resistance and chemical resistance. It also has the property of having high rubber strength. Regarding heat resistance, the higher the hydrogenation rate, the better the heat resistance, and therefore it is preferable to use one with a hydrogenation rate of 100%, but from the viewpoint of the required degree of heat resistance, cost, etc. Even if a material with a low hydrogenation rate is used, the processability is not affected much.

Such hydrogenated NBR is about 50 to 95 chloroprene rubber.
It is used in a proportion of about 50 to 5% by weight.

If less hydrogenated NBR is used, the effect of improving ozone resistance will not be sufficient, while if it is used in a higher proportion, the characteristics of chloroprene rubber will be lost.

In the rubber composition according to the present invention, each of lithioureas and thiurams is about 0.0% per 100 parts by weight of these rubber components.
It is used in a proportion of 1 to IO parts by weight.

Examples of thioureas include 2-mercaptoimidacillin, N,N'-diethylthiourea, dibutylthiourea, dilaurylthiourea, trimethylthiourea,
Tetramethylthiourea and the like are used. Further, as the thiurams, for example, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram tetrasulfide, etc. are used. The above blending ratio of each of these components is
All are selected from the viewpoint of achieving an appropriate crosslinking rate.

In addition to these essential ingredients, the composition also contains reinforcing agents such as carbon black, graphite, and fine silica, talc,
Fillers such as clay and calcium silicate, vulcanization accelerators such as zinc oxide, titanium oxide, and stearic acid, plasticizers such as dioctyl adipate, dioctyl phthalate, and process oil, diphenylamine, benzoic acid, 2-mercaptobenzimidazole, etc. Anti-aging agents and the like are appropriately blended to obtain practical rubber performance.

The composition is prepared by kneading the ingredients to be used using a closed mixer such as an intermix, a Banbury mixer, or a kneader, or an open roll. The rubber composition thus prepared is vulcanized into a desired shape by heating and pressurizing it using a heat press, an injection molding machine, or the like.

[Action] and [Effects of the Invention] When thioureas are used as a vulcanization accelerator for chloroprene rubber, crosslinking occurs, but when thiurams are used, there is almost no crosslinking, and when both are used in combination, the crosslinking occurs when thioureas alone are used. Slightly reduce speed.

On the other hand, when thioureas are used as vulcanization accelerators for hydrogenated NBR, there is almost no crosslinking, and when thiurams are used, crosslinking occurs, which is completely opposite to the case of chloroprene rubber.

Thus, thioureas act as crosslinking agents in the case of chloroprene rubber and as retarders in the case of hydrogenated NBR, while thiurams act quite the opposite.

When thioureas and thiurams that act in this manner are blended with chloroprene rubber and hydrogenated NBR, the completely unexpected effect of faster crosslinking and longer scorch than in the case of chloroprene alone was obtained. Moreover, the formulation of hydrogenated NBR improves the ozone resistance of chloroprene rubber.

〔Example〕

Next, the present invention will be explained with reference to examples.

Example °1 Chloroprene rubber (electrochemical product DCR31)
75 parts by weight hydrogenated NBR (Nippon Zeon products Zetp
ol 1020) 25 carbon black (
ASTM N550) 40 Zinc oxide 5 Magnesium oxide 5 Anti-aging agent 3 (N-phenyl-N'-isopropyl-ρ-phenylenediamine) 2-Mercaptoimidacillin 1
．． 5 Tetramethylthiuram disulfide
1.0 A rubber composition was prepared by kneading the above blending ratio in a kneader. Regarding this rubber composition, the scorch time was measured using a Mooney viscometer (125° C., using Rotor S), and the crosslinking rate was measured using a curelastometer. Furthermore, a test piece (150X 150
Extension, IHz.

The ozone concentration (50 pphm) was measured.

Comparative Example 1 In Example 1, hydrogenated NBR was not used and the amount of chloroprene rubber was changed to 100 parts by weight.

Example 2 Hydrogenated NBR (Nippon Zeon product Zetpol 2020
) 40 Carbon Black (ASTM N5
50) 40 zinc oxide
magnesium pentoxide
5 Anti-aging agent (same as Example 1) 3 Trimethylthiourea
1.5 Tetraethylthiuram disulfide 1.0 The same measurements as in Example 1 were performed on the formulation with the above blending ratio.

The measurement results for each of the above examples and comparative examples are as follows.

This is shown in the following Table 1 and the graph (torque value measured with a culastometer) in FIG.

Table 1 One lesson Σm One example - Comparative example - Example 2 [Scorch time] t3 (minutes) 12.5 7,3
13.2 tons, (minutes) 15.6
18.1 16.2 [Ozone resistance] After 48 hours No cracks No cracks No cracks After 120 hours Few cracks Many cracks
Few cracks after 240 hours Many cracks Cutting
Innumerable cracks Comparative Example 2 In Comparative Example 1, the amount of anti-aging agent was changed to 10 parts by weight.

For the test pieces of Example 1 and Comparative Example 2, grease at 60°C (Kyodo Yushi Products Morilex 52
) The ozone resistance was measured before and after immersion in the liquid for 70 hours according to the method described above. The results obtained are shown in Table 2 below.

Table 2

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes over time in torque values measured by a culastometer.

Claims (1)

[Claims] 1. About 0.1 to 10 parts by weight of thioureas and thiurams are blended with 100 parts by weight of a rubber component consisting of about 50 to 95% by weight of chloroprene rubber and about 50 to 5% by weight of hydrogenated NBR. Rubber composition.