JPH026777B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition, and more particularly to an unsaturated rubber composition that is free from bloom in its vulcanizate and has excellent vulcanization properties such as heat aging resistance and compression set resistance. Usually, unsaturated rubbers such as natural rubber and diene-based synthetic rubber are vulcanized using a compounding system consisting of sulfur, a vulcanization accelerator, and zinc oxide. However, as is well known, the crosslinks between rubber molecules when sulfur is used as a vulcanizing agent are polysulfide bonds, which are unstable to heat and easily form S-S bonds. As a result, the sulfur vulcanizate has poorer heat aging resistance than before, and this is a cause of increased compression set. In order to improve the heat aging resistance of such sulfur vulcanizates of unsaturated rubber, thiuram-based vulcanizates such as tetramethylthiuram disulfide and tetraethylthiuram disulfide have traditionally been used without using sulfur as a vulcanizing agent. A so-called sulfur donor vulcanization method is often adopted, in which a compound is used as a crosslinking agent to form monosulfide bonds between rubber molecules for crosslinking. However, even in this method, if 1.5 parts by weight or more of a thiuram compound is added to 100 parts by weight of rubber, reaction products of the thiuram compound and zinc oxide etc. will bloom on the surface of the vulcanizate.
When more than 1 part by weight is added, bloom becomes extreme and the appearance of the rubber product is significantly deteriorated. The present invention has been made in view of the above, and includes:
An object of the present invention is to provide an unsaturated rubber composition that does not cause blooming in a vulcanizate even when crosslinked using a thiuram compound as a crosslinking agent, and has excellent physical properties such as heat aging resistance and compression set. . The rubber composition according to the present invention comprises (a) 100 parts by weight of natural rubber, diene-based synthetic rubber, or a mixture of two or more thereof, and (b) the general formula (However, each R ¹ independently represents an alkyl group, an aryl group, or a nitrogen-containing carbon ring formed by two R ^1s together with nitrogen, and x represents an integer of 1 to 6.) Thiuram compounds 1 to 1 represented by 15 parts by weight, (c) general formula (However, R ² is each independently an alkyl group,
Aryl group, cycloalkyl group or two ^R2
indicates a nitrogen-containing carbon ring formed with nitrogen. ) and the general formula (However, R ³ represents an alkyl group.) It is characterized by containing 0.05 to 5 parts by weight of at least one nickel salt selected from nickel xanthates represented by the following. In the present invention, diene-based synthetic rubber includes styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), polyisoprene rubber, ethylene-propylene-diene rubber, etc. Rubbers are sometimes collectively referred to as unsaturated rubbers. The thiuram compound used in the present invention is represented by the above general formula (), where preferably R ¹
are an alkyl group having 5 or less carbon atoms, and 8 carbon atoms, respectively.
Indicates the following aryl group or a nitrogen-containing carbon ring with 10 or less carbon atoms formed by two R ¹ together with nitrogen, x
represents an integer from 2 to 4. Therefore, preferred specific examples include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, dipentamethylenethiuram tetrasulfide, and the like. Such thiuram compounds are used for unsaturated rubbers.
For 100 parts by weight, 1 to 15 parts by weight, preferably
1.5 to 5 parts by weight are used. When too many thiuram compounds are blended, scorch occurs very quickly, making it difficult to put it to practical use.
If it is too small, crosslinking will not be done sufficiently,
This is because the desired vulcanized physical properties cannot be obtained. As mentioned above, when unsaturated rubber is crosslinked with a thiuram compound, bloom is generally severe, but according to the present invention, nickel dithiocarbamate represented by the general formula () and xanthogen represented by the general formula () By using in combination 0.05 to 5 parts by weight of at least one selected from acid nickel based on 100 parts by weight of rubber, blooming does not substantially occur in the vulcanizate. However, when added in too large a quantity, these nickel salts are undesirable because they retard crosslinking and cause a decrease in physical properties such as modulus and TB, and are also economically disadvantageous. Particularly preferably 0.1 to 2 parts by weight. In the nickel dithiocarbamate represented by the general formula (), R ² preferably represents an aryl group or arylalkyl group having 8 or less carbon atoms, or a nitrogen-containing carbon ring formed by bonding two R ² together with nitrogen, Preferred specific examples include nickel dimethyldithiocarbamate, nickel diethyldithiocarbamate, nickel di-n-butyldithiocarbamate, nickel pentamethylenedithiocarbamate, nickel cyclohexylethyldithiocarbamate, nickel dibenzyldithiocarbamate, nickel lupetidine dithiocarbamate, and ethyl fluoride. Examples include nickel dithiocarbamate. Further, in the nickel xanthate represented by the general formula (), R ³ is preferably an alkyl group having 2 to 5 carbon atoms, and specific examples include isopropyl nickel xanthate, butyl nickel xanthate, and ethyl nickel xanthate. etc. can be mentioned. Further, in the present invention, sulfur may be used in combination with the above-mentioned thiuram compound as a crosslinking agent, or morpholine disulfide, selenium diethyldithiocarbamate, etc. may be used in combination as a crosslinking agent. In addition, it is of course possible to appropriately contain compounding agents normally used for unsaturated rubbers, such as reinforcing fillers, vulcanization accelerators, vulcanization aids, softeners, and anti-aging agents. It is. As described above, in the present invention, a thiuram compound is used as a crosslinking agent for unsaturated rubber, and nickel dithiocarbamate and/or nickel xanthate are used in combination with this to prevent blooming while vulcanizing. It can impart excellent heat aging resistance, compression set, etc. to objects. Examples of the present invention are listed below, but the present invention is not limited to these Examples in any way.
In addition, in the following, the testing methods for rubber compositions and vulcanizates are as follows, and parts indicate parts by weight. (1) Mooney viscosity and scorch test JIS K6300 was followed. (2) Preparation of vulcanized rubber test samples Using a mold specified in ASTM D3182-74,
A vulcanized sheet was obtained by pressure vulcanization under the conditions shown in each example. (3) Bloom state The appearance of the sample was visually observed using the method specified in MIL2020, 106c of the vulcanized sheet obtained above. (4) Tensile test The sample obtained in section (2) was tested according to the method specified in JIS K6301. (5) Compression set test The sample obtained in section (2) was heat treated at 100°C for 70 hours at a compression ratio of 25% according to the method specified in JIS K6301. (6) Heat aging test The sample obtained in section (2) was heated at 120℃ using a gear type heat aging tester according to the method specified in JIS K6301.
The rate of change in tensile properties after being left for 168 hours was measured. Example 1 SBR#1500 100 parts Zinc oxide 5 Stearic acid 2 Aroma softener 20 HAF carbon 70 Table 1 shows the test results for a styrene-butadiene rubber composition containing the components shown in Table 1. show. Vulcanization was carried out at 148°C for 25 minutes. The rubber composition according to the present invention, which uses a thiuram compound and a nickel salt in combination, has no bloom and has a small compression set. In addition, comparative example experiment number 1
The rubber composition has no bloom, but has a large compression set. Example 2 The test results for a styrene-butadiene rubber composition containing the same SBR #1500, zinc oxide, stearic acid, softener, and carbon black composition as shown in Example 1, as well as the components shown in Table 2, are shown below. It is shown in Table 2. Vulcanization was carried out at 148°C for 25 minutes. All of the rubber compositions of the present invention are free from bloom and have small compression set. Example 3 NBR1042 100 parts Zinc oxide 4 Stearic acid 0.5 Plasticizer 15 SRF carbon 65

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Table 3 shows test results for acrylonitrile-butadiene rubber compositions having the composition shown in [Table] and further containing the components shown in Table 3. Vulcanization was carried out at 148°C for 30 minutes. The rubber composition according to the present invention is free from bloom and
Compression set is also small. Note that the rubber composition of Comparative Example Experiment No. 4 had no bloom, but had a large compression set. Example 4 Table 5 shows the test results for the rubber compositions shown in Table 4. Vulcanization was carried out at 148°C for 25 minutes. The rubber composition according to the present invention does not bloom.

Claims (1)

[Scope of Claims] 1 (a) 100 parts by weight of natural rubber, diene-based synthetic rubber, or a mixture of two or more thereof; (b) General formula (However, R ¹ each independently represents an alkyl group, an aryl group, or a nitrogen-containing carbon ring formed by two R ^1s together with nitrogen, and x represents an integer of 1 to 6.) 15 parts by weight, (c) general formula (However, each R ² independently represents an alkyl group, an aryl group, a cycloalkyl group, or a nitrogen-containing carbon ring formed by two R ² together with nitrogen.) Nickel dithiocarbamate represented by the following, and the general formula (However, R ³ represents an alkyl group.) A rubber composition characterized in that it contains 0.05 to 5 parts by weight of at least one nickel salt selected from nickel xanthates represented by: