JP2000248006A - Production of emulsion polymerized rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain emulsion polymerized rubber not generating nitrosamine and controllable of curing rate. SOLUTION: In a method for producing emulsion polymerized rubber by emulsion polymerizing a conjugate diene compound, sodium or potassium salt of mercaptobenzothiazole is added before coagulation as an auxiliary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an emulsion polymerized rubber.

[0002]

2. Description of the Related Art In recent years, in a rubber product manufacturing process,
A vulcanization accelerator having a skeleton of a secondary amine is decomposed and reacts with a nitrosating agent such as NO _x to form a nitrosamine (hereinafter “NA”).
That. ) Is reported. Originally, NAs are chemicals that are widely produced and present in our immediate surroundings, and are detected even in foods such as bacon and even in the internal organs of humans, but certain NAs may cause carcinogenicity to animals. . Therefore, first of all, the regulation of NA in rubber products was implemented in Germany.

[0003] Also in Japan, vulcanization accelerators having a secondary amine skeleton and easily forming NA (eg, N-oxydiethylene-2-benzothiazolesulfenamide, tetramethylthiuram disulfide, etc.) are mainly used by tire manufacturers. Has been discontinued, and switching to an accelerator that does not produce NA has been promoted. On the other hand, in the production of emulsion-polymerized rubber, an inexpensive and efficient dialkyldithiocarbamate (the alkyl group is C ₁ -C ₄ , usually a methyl group) is used as a polymerization terminator. These salts are water-soluble, but when they are coagulated by addition of an acid, they remain partially in the rubber and partly change into water-insoluble thiuram, which is incorporated into the rubber crumb. These components can be precursors of NA. Therefore, in order to prevent the generation of NA compounds from precursors caused by these polymerization terminators,
A lot of effort has been made.

[0004]

Further, measures such as not using these dithiocarbamates have been studied. However, since dithiocarbamic acid and thiuram, which have a vulcanization accelerating effect, do not remain in the rubber, the rate of vulcanization of the rubber compound becomes slow, and changes such as a decrease in tensile stress occur. For this reason, it is necessary to adjust the compounding of the vulcanization system, which requires a great deal of work, and may not achieve the desired vulcanization pattern.

[0005]

Means for Solving the Problems Accordingly, the inventors of the present invention have made NA
As a result of intensive studies to provide an emulsion-polymerized rubber that does not produce a compound and that can control the vulcanization rate, sodium or potassium salts of mercaptobenzothiazole having no possibility of producing an NA compound are added before or during coagulation. The addition has led to the completion of the present invention. That is, the gist of the present invention is characterized in that a sodium or potassium salt of mercaptobenzothiazole is added before coagulation of the emulsion-polymerized rubber in the method for producing an emulsion-polymerized rubber by emulsion-polymerizing a conjugated diene compound. A method for producing an emulsion polymerized rubber.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, the emulsion-polymerized rubber in the present invention is a diene-based emulsion-polymerized rubber obtained by emulsion-polymerizing a conjugated diene compound. The emulsion polymerization itself can be carried out by a conventional method, such as styrene-butadiene rubber (SBR) which is a copolymer rubber of butadiene and styrene, butadiene rubber (BR) obtained by polymerization of butadiene, and a copolymer of butadiene and acrylonitrile. Acrylonitrile butadiene rubber (NB
R) and chloroprene rubber obtained by polymerizing chloroprene.

For example, in the case of SBR, the amount of water used for the polymerization reaction is 100 parts by weight per 100 parts by weight of the monomer.
To 250 parts by weight, preferably 150 to 200 parts by weight. Examples of the emulsifier include anionic surfactants such as fatty acid soap, rosin soap, sodium naphthalenesulfonate formalin condensate, and sodium alkylbenzenesulfonate, and nonionic surfactants such as polyoxyethylene alkyl ether. Can be These emulsifiers are used in an appropriate combination, and the amount is usually 2 to 8 parts by weight per 100 parts by weight of the monomer as a total amount of the emulsifier.

As a polymerization initiator, potassium persulfate is used in a so-called hot rubber formulation in which polymerization is carried out at a high temperature of 30 to 60 ° C., and its use amount is usually 0.03 to 3.0. 0 parts by weight. Also 0-20
In a so-called cold rubber formulation in which polymerization is carried out at a low temperature of ° C, a redox initiator generally called a sulfoxylate formulation is used. As a redox initiator, an organic peroxide such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, or paramenthane hydroperoxide is used in combination with ferrous sulfate. The amount of the organic peroxide and ferrous sulfate used is 0.01 to 0.1 part by weight, per 100 parts by weight of the monomer, respectively.
0.005 to 0.07 parts by weight. In the sulfoxylate formulation, it is chelated with sodium ethylenediaminetetraacetate and added with a reducing agent such as sodium formaldehyde sulfoxylate. The amount of the reducing agent used at this time is usually 0.01 to 0.5 part by weight per 100 parts by weight of the monomer.

An electrolyte such as potassium chloride or tripotassium phosphate used for preventing gelation of the latex is usually selected from the range of 0.2 to 0.5 parts by weight per 100 parts by weight of the monomer. The molecular weight is adjusted by adding t-dodecyl mercaptan, t-nonyl mercaptan, or the like to the polymerization system.
It is selected from the range of 0.05 to 0.5 parts by weight based on parts by weight.

In emulsion polymerization of BR or the like, basically the same method as in the case of the emulsion polymerization of SBR can be adopted. The present invention is characterized in that, in the process for producing the emulsion polymerized rubber, a sodium or potassium salt of mercaptobenzothiazole is added before coagulation. The sodium or potassium salt of mercaptobenzothiazole is used as an aqueous solution in the process,
It is suitable. That is, the latex obtained by emulsion polymerization is added with a salt such as salt and sulfuric acid, coagulated, washed with water, dehydrated and dried to obtain a solid rubber,
By being added to the latex in advance before coagulation or as an auxiliary during coagulation, it can be blended well with rubber latex without mechanical kneading. At this time, the sodium or potassium salt of mercaptobenzothiazole is preferably blended with latex before adding sulfuric acid. Then add sulfuric acid,
When coagulating under acidic condition of pH 7 or less, sodium or potassium is replaced by hydrogen to form mercaptobenzothiazole. Since this is insoluble in water, it can be left in the rubber (crum) without being discharged together with water in the coagulation step. The amount of the mercaptobenzothiazole-sodium or potassium salt can be appropriately selected so as to attain a target vulcanization rate. Used in the range of parts. Further, in the method of the present invention, it is preferable to add sodium or potassium nitrite or sodium or potassium nitrate in combination. The amount of these additives is 0.04 per 100 parts by weight of the monomer of the emulsion polymerized rubber.
It is used in the range of 1.0 to 1.0 parts by weight. By adding in combination
Further, since the vulcanization rate can be increased, the addition amount of mercaptobenzothiazole sodium or potassium salt can be reduced, and the cost and cost can be reduced.

In the coagulation, an oil masterbatch or a carbon masterbatch can be directly produced by coagulation with process oil or carbon black. When the sodium or potassium salt of mercaptobenzothiazole is used as a coagulant or coagulation,
By adding the latex to the latex, an emulsion-polymerized rubber which does not generate an NA compound and whose vulcanization rate can be adjusted is obtained.

[0012]

The present invention will be described in more detail with reference to the following examples. Example 1 Emulsion polymerization of styrene-butadiene rubber was carried out as follows in accordance with the polymerization recipe shown in Table 1.
After the inside of the polymerization tank is sufficiently purged with nitrogen, a predetermined amount of each component shown in Table 1 is added under a nitrogen atmosphere except for ferrous sulfate as an activator and ethylenediaminetetraacetic acid / tetrasodium. Next, a refrigerant is circulated through the jacket of the polymerization tank under stirring to adjust the temperature in the polymerization tank to 5 ° C. When the temperature reached a predetermined temperature, the above-mentioned activator was added to start polymerization, and when the polymerization reaction rate reached 60%, diethylhydroxyamine was added to stop the polymerization.

Next, the unreacted monomer was stripped off to obtain a styrene-butadiene rubber. Sodium mercaptobenzothiazole was added to the rubber latex thus obtained in an aqueous solution at a ratio of 0.5 part by weight and sodium nitrite at a ratio of 0.22 part by weight based on 100 parts by weight of all monomers. Was added. After 1.2 parts by weight of an antioxidant was emulsified and added thereto, sulfuric acid and sodium chloride were added to carry out a coagulation treatment. After separating the produced rubber (rubber crumb) from the serum water, it is washed with water and dehydrated.
It was dried with hot air at 80 ° C. so that the water content was 0.3% by weight or less. The rubber thus obtained was made into a compound according to the compounding recipe shown in Table 2, and then vulcanized at 145 ° C. for 50 minutes.

The extraction of NA and nitrosatable amine from the vulcanized rubber was carried out in water at 20 ° C. for 72 hours, dried at 70 ° C., and analyzed for NAs. The analysis is as follows: GC-MS (gas chromatography-mass spectrometry)
Performed by the method. That is, a sample is cut into about 2 mm square, and 15 g
Was weighed and subjected to Soxhlet extraction (10 hours) with 100 ml of acetone.

[0015] The extract is transferred to a rotary evaporator (about 3).
After concentrating at 00 mmHg), acetone was added to make the volume to 25 ml, and GC-MS (MID) measurement was performed. GC-M
The S measurement was performed using the following device: "M-80B Hitachi Double Convergence GC-M
S "under the following conditions.

[0016]

Table 1 Column: DB-1, 0.53 mmid × 30 m Column temperature: 60 ° C. Carrier: He 20 ml / min Slit width: output slit 800 μm collector slit 400 μm Multiplier voltage: 1500 V Ionization voltage: 70 eV Injection amount: 1 μl MID- m / e: 74 The lower limit of NA detection by this assay is 300 ppb.

Table 3 shows the detection effects of NA and nitrosatable amines. The case where detection was performed was indicated by x, and the case where detection was not performed (300 ppb or less) was indicated by ○. In addition, 90% torque time of "rheometer" of unvulcanized compound, which is an index of vulcanization rate (T90, measuring temperature 160 ° C)
Are also shown in Table-3.

Comparative Example 1 The same experiment as in Example 1 was performed, except that the sodium salt of mercaptobenzothiazole and sodium nitrite were not added to the latex before coagulation. Table 3 shows the evaluation results.

Comparative Example 2 Instead of diethylhydroxyamine, sodium dimethyldithiocarbamate was used as a polymerization terminator in an amount of 0.15 part by weight per 100 parts by weight of all monomers, and sodium nitrite was used in an amount of 0.04 part by weight. The same experiment as in Example 1 was performed, except that the respective parts were added as aqueous solutions, and the sodium salt of mercaptobenzothiazole and sodium nitrite were not added to the latex before coagulation. Table 3 shows the evaluation results.

[0020]

[Table 2]

[0021]

[Table 3] * 1) "IRB ^{# 6} " * 2) N-tert-butyl-2-benzothiazolesulfenamide

[0022]

[Table 4]

[0023]

According to the present invention, an emulsion-polymerized rubber which does not generate nitrosamine and whose vulcanization rate can be adjusted can be obtained.

Claims (2)

[Claims] 1. A method for producing an emulsion-polymerized rubber by emulsion-polymerizing a conjugated diene compound, wherein a sodium or potassium salt of mercaptobenzothiazole is added before the emulsion-polymerized rubber is coagulated. Production method. 2. The process according to claim 1, wherein a sodium or potassium salt of mercaptobenzothiazole is used in combination with sodium or potassium nitrite or sodium or potassium nitrate.