JP2000248007A - Production of emulsion polymerized rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing emulsion polymerized rubber having no possibility generating a nitrosamine compound. SOLUTION: In a method for producing emulsion polymerized rubber by emulsion polymerizing a conjugate diene compound, a dithiocarbamate expressed by the general formula (R1 and R2 are each a >=5C hydrocarbon residue; M is Na, K or quaternary ammonium salt) is added as a terminator of the emulsion polymerization or an auxiliary in coagulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

In recent years, in the production process of the rubber, forming a vulcanization accelerator is decomposed with the secondary amine skeleton, nitrosamines by reaction with nitrosating agent such as NO _x (hereinafter referred to as "NA".) It has been reported that Originally NA
Classes are chemicals that are widely produced and present in our immediate surroundings, and are detected in foods such as bacon and even in the internal organs of humans, but certain NAs pose a risk of carcinogenicity to animals. So, first of all, in Germany,
Regulations have been enforced.

[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 adding an acid, they remain partially in the rubber and partially change to water-insoluble thiuram and are taken up in the oil-extended rubber (rubber crumb). These components can be precursors of NA. Therefore, much effort has been made to prevent the formation of NA compounds from precursors caused by these polymerization terminators.

[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, there is a difference in the easiness of formation of NA and its precursor depending on the type of dithiocarbamic acid. The present invention has been completed by noting that a dithiocarbamate is not used to generate an NA compound. That is, the gist of the present invention is to provide a method for producing an emulsion-polymerized rubber by emulsion-polymerizing a conjugated diene compound, wherein the dithiocarbamate represented by the following general formula (I) is provided.

[0006]

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[0007] (wherein, R ^1, R ² is, C ₅ or more hydrocarbon residue, M is Na, K or an quaternary ammonium salt.) The emulsion polymerization terminator or as clotting time auxiliaries And a method for producing an emulsion polymerized rubber.

[0008]

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 above-mentioned emulsion polymerization of SBR can be employed. The present invention is characterized in that in the emulsion polymerization, a dithiocarbamate represented by the general formula (I) is added as a terminator for the emulsion polymerization or as an auxiliary during coagulation. R ¹ and R ^{2 each} represent a C ₅ or more hydrocarbon residue, and the hydrocarbon residue may be any of a fatty acid, an alicyclic group and an aromatic group, and is preferably a C _{6 to} C ₁₂ alkyl group. Or it is a benzyl group.

If at least ^one of R ¹ and R ² is less than C ₅ , it is inappropriate because an NA compound or a nitrosatable amine can be detected. The dithiocarbamate represented by the general formula (I) is preferably used in an aqueous solution in the form of an aqueous solution. And quaternary ammonium salts.

That is, by adding it as an aqueous solution as a terminator for emulsion polymerization or as an auxiliary during coagulation, it can be blended well with rubber latex without mechanical kneading and can be manufactured at low cost. The amount of the dithiocarbamate represented by the general formula (I) can be appropriately selected so as to achieve a target vulcanization rate.
Usually, 0.0 parts per 100 parts by weight of the monomer of the emulsion polymerized rubber
It is used in the range of 2 to 1.0 part by weight.

After the reaction is stopped, unreacted monomers are recovered and removed to obtain a latex. The resulting latex can be coagulated by adding an acid such as salt and sulfuric acid, washed with water, dehydrated and dried to obtain a solid rubber. In the present invention, as described above, the dithiocarbamate represented by the general formula (I) can be added as an auxiliary during coagulation.

In this coagulation, an oil masterbatch or a carbon masterbatch can be directly produced by co-coagulation with a process oil or carbon black. Furthermore, in the method of the present invention, sodium nitrite (or potassium) or sodium nitrate (or potassium) is added in combination, and coagulation under acidic condition of pH 6 or less promotes the production of thiuram. And the vulcanization rate can be controlled. These addition amounts are usually used in the range of 0.005 to 0.5 parts by weight per 100 parts by weight of the monomer of the emulsion polymerized rubber. When these are not added together, since the dithiocarbamate is water-soluble, a part of the dithiocarbamate is discharged together with water in the step of producing a solid rubber by coagulation, and the remaining amount in the solid rubber becomes unstable. It easily causes vulcanization speed to fluctuate. Therefore, it is preferable to add them together.

As described above, most preferably, R ¹ and R ²
Is formed by adding a dithiocarbamate represented by the general formula (I), which is either a hexyl group or an octyl group, and sodium nitrite as a polymerization terminator or to a latex during coagulation to form an NA compound. An emulsion-polymerized rubber having no vulcanization rate and an adjustable vulcanization rate can be obtained.

[0018]

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 was sufficiently purged with nitrogen, a predetermined amount of each component shown in Table 1 was used as an activator, such as ferrous sulfate and ethylenediaminetetraacetic acid.
Except for tetrasodium, it is added under a nitrogen atmosphere. 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 initiate polymerization, and when the polymerization reaction rate reached 60%, sodium dihexyldithiocarbamate was added in an amount of 0.15 parts by weight per 100 parts by weight of all monomers. In each case, sodium nitrite was added as an aqueous solution at a ratio of 0.04 parts by weight to terminate the polymerization.

Next, unreacted monomers were stripped off to obtain a styrene-butadiene rubber. The amount of sodium dihexyldithiocarbamate per 100 parts by weight of solids in the latex is 0.25 parts by weight as a result of removing unreacted monomers. After 37.5 parts by weight of an aromatic process oil and 1.2 parts by weight of an antioxidant were emulsified and added to the rubber latex thus obtained, a coagulation treatment was carried out by adding sulfuric acid and salt. After separating the generated oil-extended rubber (rubber crumb) from the serum water, washing and dewatering,
Drying was performed with hot air at 70 to 80 ° C. so that the water content was 0.3% by weight or less. The oil-extended rubber thus obtained was compounded according to the formulation shown in Table 2 and then 145.
A vulcanization treatment was performed at 50 ° 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.

[0021] The extracted solution is put on 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.

[0022]

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 250 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 (250 ppb or less) was indicated by o. Table 3 also shows the "vulcanizing compound" 90% torque time (T90) of the unvulcanized compound as an index of the vulcanizing rate.

Example 2 The same experiment as in Example 1 was carried out except that sodium dibenzyldithiocarbamate was used instead of sodium dihexyldithiocarbamate. Table 3 shows the evaluation results.

Example 3 The same experiment as in Example 1 was conducted except that sodium dioctyldithiocarbamate was used instead of sodium dihexyldithiocarbamate. Table 3 shows the evaluation results.

Comparative Example 1 The same experiment as in Example 1 was performed except that sodium dimethyldithiocarbamate was used instead of sodium dihexyldithiocarbamate. Table 3 shows the evaluation results.

Comparative Example 2 The same experiment as in Example 1 was performed except that sodium dibutyldithiocarbamate was used instead of sodium dihexyldithiocarbamate. Table 3 shows the evaluation results.

[0028]

[Table 2]

[0029]

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

[0030]

[Table 4]

[0031]

According to the method of the present invention, an emulsion-polymerized rubber whose vulcanization rate can be adjusted can be produced without producing a nitrosamine compound.

Claims (4)

[Claims] In a method for producing an emulsion-polymerized rubber by emulsion-polymerizing a conjugated diene compound, a dithiocarbamate represented by the following general formula (I) is used: (Wherein R ¹ and R ² are hydrocarbon residues of C ₅ or more, and M is Na, K or a quaternary ammonium salt). Addition as a terminator for emulsion polymerization or as an auxiliary during coagulation. A method for producing an emulsion polymerized rubber, which is characterized by the following. 2. The emulsion polymerization according to claim 1, wherein the dithiocarbamate represented by the general formula (I) of claim 1 and sodium or potassium nitrite or sodium or potassium nitrate are added in combination. Rubber manufacturing method. 3. The dithiocarbamate represented by the general formula (I) according to claim ¹ , wherein R ¹ and R ² are a C ₆ -C ₁₂ alkyl group or a benzyl group. The method for producing the emulsion polymerized rubber according to the above. 4. The emulsion polymerized rubber according to claim ¹ , wherein R ¹ and R ² of the dithiocarbamate represented by the general formula (I) are hexyl or octyl. Production method.