JP2013087278A - Nitrosamine-free high speed vulcanizable rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high speed vulcanization accelerator corresponding to nitrosamine problems and a rubber composition using the vulcanization accelerator.SOLUTION: The nitrosamine-free and high speed vulcanizable rubber composition is obtained by using a bismuth tris(dibenzyl dithiocarbamate) compound or a bismuth tris(di-2-ethylhexyl dithiocarbamate) compound as a vulcanization accelerator.

Description

  The present invention relates to a vulcanization accelerator which is essential for enhancing the vulcanization activity of rubber and improving physical properties. More specifically, it is possible to achieve both safety and hygiene (nitrosamine free) and productivity (high-speed vulcanization). It relates to a vulcanization accelerator.

  Conventionally, dialkyldithiocarbamates (hereinafter abbreviated as dithiocarbamates) are generally used as vulcanization accelerators for rubber, and are characterized by improving the activity of vulcanizing agents and other vulcanization accelerators against vulcanization reactions. It is said.

  At present, the main dithiocarbamates used as vulcanization accelerators generate nitrosamines having carcinogenic properties, and are therefore regulated by TRGS552 of German law (Non-patent Document 1).

  On the other hand, nitrosamines derived from dibenzylamine with a bulky alkyl group are not considered to be carcinogenic in TRGS552, and nitrosamines derived from di-2-ethylhexylamine are non-volatile and are therefore not subject to regulation. Zinc dibenzyldithiocarbamate, tetrabenzylthiuram disulfide, and tetra-2-ethylhexylthiuram disulfide are on the market (Patent Document 1).

  However, these nitrosamine-free vulcanization accelerators have the disadvantages of low vulcanization activity and slow vulcanization speed because they have a higher molecular weight than conventional vulcanization accelerators under general vulcanization conditions.

  Although tris (dibenzyldithiocarbamate) bismuth represented by Chemical Formula 1 is a known substance, there is no document that has found its use as a rubber vulcanization accelerator (Non-patent Document 2).

  Meanwhile, Robinson Brothers Ltd. Patents relating to dithiocarbamic acid metal salts derived from amines having C5-C18 branched alkyl groups have been filed as nitrosamine-free vulcanization accelerators, but only diisononyl dithiocarbamate salts are described in the examples. No 2-ethylhexyl dithiocarbamate salts related to Chemical Formula 2 are described as examples (Patent Document 2).

JP-A-6-256603 JP-A-6-184363

TRGS552 (N-Nitrosoamine) J. et al. Radioanal. Nucl. Chem. 117 (3), 145-154

  An object of the present invention is to provide a high-speed vulcanization accelerator corresponding to the nitrosamine problem and a rubber composition using the vulcanization accelerator.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention can be accomplished by replacing or using the currently used nitrosamine-free vulcanization accelerators with the specific dithiocarbamates represented by Chemical Formula 1 and / or Chemical Formula 2 to complete the present invention. It has come.

  According to the present invention, a rubber composition which is nitrosamine-free and capable of being vulcanized at a higher speed than before by blending 0.01 to 10 parts by weight of the compound represented by Chemical Formula 1 and / or Chemical Formula 2 with 100 parts by weight of rubber. Can be provided.

The relationship between the scorch time and the vulcanization speed in Examples 1 to 4 and Comparative Example 1 is shown. The relationship between scorch time and vulcanization speed in Examples 5 to 7 and Comparative Example 2 is shown.

Hereinafter, the present invention will be described in more detail with specific embodiments.
The base rubber component in the present invention includes natural rubber (NR), synthetic rubber such as butadiene rubber (BR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butyl rubber (IIR), and nitrile rubber (NBR). ), Chloroprene rubber (CR), ethylene / propylene rubber (EPDM) and the like, and these indicate a single or a mixture of these.

  In order to obtain a vulcanizable rubber composition, a vulcanizing agent (A) and a vulcanization accelerator (B) for improving the vulcanization speed and physical properties of the vulcanized rubber are added.

In the vulcanizing agent (A), for example, sulfur is used, and sulfur includes powdered sulfur, precipitated sulfur, insoluble sulfur and the like, and any of them may be used. In the present invention, addition of 0.1 to 2 parts by weight is preferable.
In addition to sulfur, there are thiuram polysulfide compounds and dialkyl dipolysulfide compounds, which may be used in combination with sulfur in an arbitrary amount, but are limited to nitrosamine-free compounds.

  In the vulcanization accelerator (B), 0.01 to 10 parts by weight of the compound represented by Chemical Formula 1 and / or Chemical Formula 2 is added, and 2-benzothiazole disulfide (MBTS) or N-cyclohexyl-2-benzothiazole sulfate is added. Thiazoles such as phenamide (CBS), thiurams such as tetrabenzylthiuram disulfide (TBzTD) and tetra-2-ethylhexylthiuram disulfide (TEHTD), and dithiocarbamates such as zinc dibenzyldithiocarbamate (ZnBzDC) Any amount of a nitrosamine-free vulcanization accelerator may be used in combination.

  For other compounding agents, depending on the application and performance, in addition to reinforcing agents such as carbon black and silica that are generally used in rubber products, vulcanization acceleration aids such as zinc oxide, process oil and stearic acid are included. It can be included.

  As described above, at least the rubber contains (A) and (B), and the other components are appropriately selected to exhibit the performance in the present invention.

Hereinafter, although an example is given and it explains still more concretely, of course, the present invention is not limited at all by the example.
First, synthesis examples of the compounds represented by Chemical Formula 1 and Chemical Formula 2 are shown.

Synthesis Example of Tris (dibenzyldithiocarbamate) bismuth represented by Chemical Formula 1 14.21 g (72 mmol) of dibenzylamine and 100.5 g of 3% NaOH aqueous solution were mixed and stirred at room temperature. To the aqueous solution, 6.00 g (79 mmol) of carbon disulfide was added dropwise over 20 minutes. Then, it stirred for 1 hour and heated up to 65 degreeC. After adding 55 g of 3% NaOH aqueous solution, a solution obtained by dissolving 4.66 g (10 mmol) of bismuth oxide in 31.2 g of 12 wt% HCl aqueous solution was added dropwise over 1 hour. After completion of dropping, the mixture was further stirred for 30 minutes. After cooling to room temperature, filtering and washing with water, drying was performed to obtain 18.3 g of tris (dibenzyldithiocarbamate) bismuth (yield 89.3%, dark green crystals, mp 139 ° C.).

Synthesis Example of Tris (di-2-ethylhexyldithiocarbamate) bismuth represented by Chemical Formula 2 17.50 g (72 mmol) of di-2-ethylhexylamine and 9.88 g (73 mmol) of 29.7% NaOH were charged into 29.30 g of water. . After 5.80 g (76 mmol) of carbon disulfide was dropped and stirred at room temperature over 50 minutes, 17.7 g of THF was added to dissolve the reaction product (A). The mixture was further stirred for 1 hour. Subsequently, 5.27 g (11 mmol) of bismuth oxide and 105.1 g of water were charged, the temperature was raised to 65 ° C., and 5.20 g (41 mmol) of 73.3% sulfuric acid was added to form bismuth sulfate as a white slurry. After cooling, 75.1 g (68 mmol) of a 30.9% (A) solution was added dropwise over 1.3 hours, followed by stirring at room temperature for 2.5 hours. The organic layer was separated and washed with water, and 100 g of toluene was added to dissolve the oily reaction product, followed by filtration. The toluene solution was concentrated to obtain 25.8 g of tris (di-2-ethylhexyldithiocarbamate) bismuth (yield 98.9%, orange oily substance).

Next, a rubber test result is shown.
Table 1 shows the content of the rubber composition of Test 1.

Each rubber composition in Test 1 is prepared according to a general kneading method using a closed mixer and an open roll mill. Specifically, in a Banbury mixer, chemicals up to step A such as rubber and filler are added and kneaded. Thereafter, the chemicals in step B were added using an open roll mill to obtain each rubber composition.
Examples 1 to 4 are nitrosamine-free vulcanization systems containing the compounds represented by Chemical Formulas 1 and 2 in the present invention. On the other hand, Comparative Example 1 is a conventional nitrosamine-free vulcanization system.

  The physical properties of the unvulcanized rubber of each composition obtained were subjected to a Mooney scorch test and a vulcanization test using a vibration vulcanization tester described in JIS K6300 unvulcanized rubber test method. The results are shown in Table 2.

  As can be seen from Table 2 and FIG. 1, the vulcanization systems of Examples 1 to 4 using the compounds of Chemical Formula 1 and Chemical Formula 2 in the present invention are more suitable for the optimal vulcanization time than Comparative Example 1 ( It was confirmed that t′c (90)) was short, that is, the vulcanization rate was high.

  Table 3 shows the vulcanized physical properties and aging characteristics of each rubber composition.

  In vulcanized rubber physical properties and heat aging resistance, Examples 1 to 4 were equal to or higher than those in Comparative Example 1. Further, in compression set resistance, results exceeding Comparative Example 1 were obtained. Moreover, the bloom resistance related to the design of the rubber was also good.

  Table 4 shows the content of the rubber composition of Test 2.

Each rubber composition in Test 2 was prepared in the same manner as in Test 1 to obtain a rubber composition.
Examples 5 to 7 are nitrosamine-free vulcanization systems containing the compound represented by Formula 1 in the present invention. On the other hand, Comparative Example 2 is a conventional vulcanization system that is not nitrosamine-free.
The physical properties of the unvulcanized rubber of each composition obtained were measured in the same manner as in Test 1. The results are shown in Table 5.

  As can be seen from Table 5 and FIG. 2, Examples 5 to 7 containing the compound represented by Chemical Formula 1 in the present invention are more suitable than Comparative Example 2, which is a conventional vulcanization system that is not nitrosamine-free. It was shown that the vulcanization time (t′c (90)) was short, that is, the vulcanization rate was fast.

  Table 6 shows the vulcanized physical properties and aging characteristics of each rubber composition.

  As can be seen from Table 6, in Examples 5 to 7, good results were obtained in comparison with Comparative Example 2 in physical properties of vulcanized rubber, heat aging resistance and compression set.

Claims (3)

A rubber vulcanization accelerator represented by Chemical Formula 1:

A rubber vulcanization accelerator represented by Chemical Formula 2:

  A rubber composition comprising 0.01 to 10 parts by weight of a compound represented by Chemical Formula 1 according to claim 1 and / or a compound represented by Chemical Formula 2 according to claim 2 with respect to 100 parts by weight of rubber. object.

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