JPH0132842B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for thickening synthetic rubber latex. Synthetic rubber latex can be easily obtained by emulsion polymerization, and the emulsifier is usually 0.5 to 5% of the monomer.
The amount of rubber particles in the polymer latex obtained with this formulation is approximately 1 part by weight.
It is in the range of about 0.05 to 0.18μ. However, synthetic rubbers with even larger particle diameters are required for various uses, and large particle rubbers have industrially important and wide-ranging uses. Many methods have been known so far for enlarging latex-like rubber particles, and they can be broadly divided into two methods. One method is to achieve enlargement during the rubber polymerization stage, and the other is to achieve enlargement through post-treatment after polymerization. Methods for enlarging the rubber during the polymerization stage include polymerizing with as little emulsifier as possible, using a special emulsifier, seed polymerization, and increasing the monomer concentration and stirring at high speed during polymerization. Methods of coagulating and enlarging the particles are known.
Further, as methods for enlarging ordinary latex through post-treatment, there are known enlarging methods using acids, enlarging methods using salt, ammonia soap methods, freezing methods, enlarging methods using special solvents, etc. However, each of these known methods has major drawbacks. The biggest drawback of the method of enlarging the rubber during the polymerization stage is that it requires an excessive amount of polymerization time.On the other hand, with the method of enlarging the latex through post-treatment, stabilization of the latex during enlargement is a major problem. However, it is usually difficult to prevent the formation of agglomerates in which oversized particles have grown. The present applicant first added a latex with a pH of 4 or higher obtained by polymerizing a mixture of an alkyl acrylate and an unsaturated acid in the presence of at least one anionic surfactant to a synthetic rubber latex adjusted to a pH of 7 or higher. An epoch-making method was proposed for enlarging the particle size of the synthetic rubber latex, which greatly improved the drawbacks of the previously known enlarging methods (Japanese Patent Publication No. 45921/1983). The present inventors conducted a more detailed study on enlargement agents, and found that in the method of obtaining an unsaturated acid-containing copolymer, by using a conjugated diene monomer, a monomer group containing no unsaturated acid can be obtained. It has been discovered that the particle size of the synthetic rubber can be effectively enlarged with a very low unsaturated acid content by employing a two-stage polymerization method in which the monomer group is polymerized and then the remaining monomer group is polymerized, and the present invention completed. That is, in the present invention, at least one unsaturated acid selected from the group of acrylic acid, methacrylic acid, itaconic acid, and crotonic acid is added to 100 parts by weight (as solid content) of synthetic rubber (A) latex adjusted to a pH of 7 or higher. 0.1
~20% by weight, 99.9 to 40% by weight of at least one conjugated diene monomer, and 0 to 47% by weight of at least one other monomer copolymerizable with these, obtained by emulsion polymerization. When enlarging the synthetic rubber by adding 0.01 to 10 parts by weight (as solid content) of the unsaturated acid-containing copolymer (B) latex, Obtained by polymerizing 5 to 90% by weight of the monomer group and not containing the unsaturated acid, and then polymerizing the remaining 95 to 10 weight% of the monomer group containing the unsaturated acid. , a method for enlarging synthetic rubber characterized by using a copolymer latex having an average particle diameter of 0.05 to 0.2μ. The synthetic rubber used in the present invention includes polybutadiene, a copolymer of 50% by weight or more of butadiene and 50% by weight or less of at least one vinyl monomer copolymerizable therewith, chlorobrene and its copolymer, and acrylic acid. Ester homopolymer or 50
Included are copolymers comprising at least 50% by weight of alkyl acrylate and 50% by weight or less of a vinyl monomer copolymerizable therewith. These can be easily obtained by ordinary polymerization methods and have a particle size of about 0.05 to 0.2μ. These synthetic rubbers do not require particular restrictions on polymerization conditions, and may be crosslinked with divinyl compounds or the like. Enlargement of rubber particles can be achieved simply by adding the unsaturated acid-containing polymer (B) latex to this synthetic rubber (A) latex.
Here, the synthetic rubber (A) latex needs to have a pH of 7 or higher. For example, polybutyl acrylate rubber latex polymerized with sodium octylsulfosuccinate as an emulsifier and potassium persulfate as a catalyst has a pH of 2 to 3, but even if an unsaturated acid-containing polymer latex is added to this latex, no No hypertrophy occurs. However, if a small amount of alkali such as potassium hydroxide is added to raise the pH to 7 or higher, rubber with a large particle size can be easily obtained. The unsaturated acid-containing copolymer used to enlarge the synthetic rubber in the present invention must be in the form of a latex, and must be composed of a specific unsaturated acid and a conjugated diene monomer. are essential conditions, and if necessary, other monomers copolymerizable with these may be copolymerized. The unsaturated acids constituting the unsaturated acid-containing copolymer are selected from the group of acrylic acid, methacrylic acid, itaconic acid, and crotonic acid, and these unsaturated acids are used alone or in combination. The constituent amount of the above unsaturated acid in the unsaturated acid-containing copolymer is 0.1 to 20
It is necessary that the amount is % by weight. If the amount is less than 0.1% by weight, the enlarging ability will be low, and if the amount is more than 20% by weight, the enlarging ability will be too strong and excessive particles will be produced, which is not preferable. On the other hand, the conjugated diene monomers constituting the unsaturated acid-containing copolymer include butadiene, chloroprene,
Isoprene and the like are used alone or in combination. The content of the conjugated diene monomer in the unsaturated acid-containing copolymer is from 99.9 to 40% by weight, and if it deviates from this range, the effects of the present invention cannot be sufficiently achieved. Other copolymerizable monomers that may be used if necessary to form the unsaturated acid-containing copolymer include unsaturated aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; acrylonitrile, and methacrylonitrile. Unsaturated nitrile compounds; examples include alkyl (meth)acrylates in which the alkyl group has 1 to 12 carbon atoms, and these may be used alone or in combination. The amount of the other copolymerizable monomer in the unsaturated acid-containing copolymer is 0 to 47% by weight.
If it exceeds 47% by weight, the effects of the present invention will not be achieved. In the present invention, the unsaturated acid-containing copolymer (B) latex is prepared by first selecting the monomer group consisting of the unsaturated acid, the conjugated diene monomer, and other copolymerizable monomers in the specified range. After polymerizing the portion having a weight of 5 to 90% and not containing the unsaturated acid, the remaining 95 to 10% by weight of the monomer group containing the unsaturated acid is subsequently polymerized to obtain a latex having a two-layer structure. Therefore, the effect of enlarging the synthetic rubber becomes extremely large. On the other hand, it is also possible to simultaneously polymerize a monomer group consisting of other monomers copolymerizable with unsaturated acids and conjugated diene monomers, but in this case it is not preferred because the enlarging effect is small. In addition to the above, unsaturated acid-containing monomers or similar monomers include cinnamic acid, maleic anhydride, butenetricarboxylic acid, etc., but these are not practical due to their low enlargement ability. Not on point. Further, when producing the unsaturated acid-containing copolymer, it is preferable to use an anionic surfactant as an emulsifier, but a nonionic surfactant may also be used. The particle size of the unsaturated acid-containing copolymer latex greatly affects its enlargement ability, and the average particle size of 0.05
A material in the range of ~0.2μ is used. This unsaturated acid-containing copolymer is added in the form of a latex to a synthetic rubber latex, and at this time, by simultaneously adding an inorganic electrolyte, the particle size of the synthetic rubber can be enlarged extremely efficiently and stably. The amount of the unsaturated acid-containing copolymer latex added is 0.01 to 10 parts by weight (as solid content), particularly preferably 0.1 to 5 parts by weight, per 100 parts by weight (as solid content) of the synthetic rubber latex. Also, the amount of inorganic electrolyte added is 100% synthetic rubber.
0.05 to 4.0 parts by weight, particularly preferably 0.1 parts by weight
Up to 1.0 part by weight is sufficient, and such a small addition effectively enlarges the synthetic rubber. As the inorganic electrolyte, neutral inorganic salts such as potassium chloride, sodium chloride, and sodium sulfate can be suitably used. Further, this inorganic electrolyte can be added in advance during the polymerization of the synthetic rubber latex, and the same effect as when added at the time of enlargement is achieved. As described above, an unsaturated acid-containing copolymer latex for enlargement is produced by using a conjugated diene monomer in the first stage of polymerization, and by polymerizing an unsaturated acid-containing monomer group in the second stage of polymerization. By using the product obtained by this method, it is possible to effectively enlarge the particle size of the synthetic rubber with a very low unsaturated acid content. The particle size of the enlarged rubber obtained by the method of the invention is 0.07-5μ. Furthermore, by using the enlarged rubber, it is possible to obtain a thermoplastic resin that has even better impact resistance than conventional ones. Hereinafter, the present invention will be specifically explained with reference to Examples. In the examples, "parts" and "%" mean "parts by weight" and "% by weight," respectively. Example 1 [Synthesis of synthetic rubber] (A-1) 1,3-butadiene 66 parts Butyl acrylate 9 parts Styrene 25〃 Potassium oleate 1.0〃 Potassium rosinate 1.0〃 Diisopropylbenzene hydroperoxide
0.2〃 Ferrous sulfate 0.005〃 Sodium pyrophosphate 0.5〃 Dextrose 0.3〃 Water 200〃 Using a mixture of the above composition, polymerization was carried out at 50°C in a 100° autoclave. Polymerization was almost completed in 9 hours, and a rubber latex with a conversion rate of 97%, a particle size of 0.08 μm, and a pH of 9.0 was obtained. [Synthesis of unsaturated acid-containing copolymer latex for enlargement] (B-1) 1,3-butadiene 60 parts Styrene 20〃 Potassium oleate 0.8〃 Potassium rosinate 0.8 parts Diisopropylbenzene hydroperoxide
0.16〃 Ferrous sulfate 0.004〃 Sodium pyrophosphate 0.4〃 Dextrose 0.24〃 Water 160〃 Using a mixture of the above composition, polymerization was carried out at 50°C in a 100° autoclave. Polymerization was almost completed in 9 hours, and a rubber latex with a conversion rate of 97% and a particle size of 0.08 μm was obtained. To this copolymer, potassium oleate 1 part dioctyl sodium sulfosuccinate 3 cumene hydroperoxide 0.1 sodium formaldehyde sulfoxylate
0.3〃 10〃 of water was added and the temperature was raised to 70℃, and a mixture consisting of 17 parts of n-butyl acrylate, 3 parts of methacrylic acid, and 0.3〃 of cumene hydroperoxide was added thereto over 1 hour.
Stirring was continued for hours to obtain a copolymer latex with a conversion rate of 98%. 100 parts (solid content) of the rubber latex (A-1) was placed in a container, and various amounts of the latex (B-1) were added thereto at room temperature while stirring. This latex was sampled immediately after stirring for 30 minutes, and sampled after being left for 5 days.The latex was treated with osmium tetroxide and its particle size was measured using an electron microscope. Furthermore, the stability of the enlarged latex after being left for one month was also evaluated. These evaluation results are shown in Table 1. For comparison, a similar evaluation was also conducted using a latex (B-2) obtained by one-step emulsion polymerization using the method described below. These evaluation results are also shown in Table 1. (B-2) 1,3-butadiene 60 parts Styrene 20 n-butyl acrylate 17 methacrylic acid 3 Sodium dioctyl sulfosuccinate 2 Diisopropylbenzene hydroperoxide 0.2 Ferrous sulfate 0.005 Sodium pyrophosphate 0.5 Dextrose 0.3〃 Water 200〃 Using a mixture of the above composition, polymerization was carried out at 50°C in an autoclave. Polymerization was almost completed in 9 hours, and a rubber latex with a conversion rate of 97% and a particle size of 0.07 μm was obtained.

[Table] As is clear from Table 1, by using a conjugated diene monomer in the first stage and copolymerizing methacrylic acid in the second stage, the unsaturated acid-containing latex for enlargement has a very low amount of methacrylic acid. The thickening effect is high depending on the content, and the stability of the obtained thickened latex is also good. Example 2 A latex (B-3) containing 75 parts of 1,3-butadiene in the first stage and 21 parts of butyl acrylate and 4 parts of methacrylic acid in the first stage as a thickened unsaturated acid-containing copolymer latex. Example 1 (B
-1) Synthesized using the same formulation, and examining the enlargement behavior of various synthetic rubbers, the results are shown in Table 2.

【table】

Claims (1)

[Claims] 1 Synthetic rubber (A) latex adjusted to PH7 or higher
Acrylic acid, per 100 parts by weight (as solid content)
0.1 to 20% by weight of at least one unsaturated acid selected from the group of methacrylic acid, itaconic acid, and crotonic acid, and at least one conjugated diene monomer
Unsaturated acid-containing copolymer (B) latex obtained by emulsion polymerization of a monomer group consisting of 99.9 to 40% by weight and 0 to 47% by weight of at least one other monomer copolymerizable with these 0.01 ~10 parts by weight (as solids)
When enlarging the synthetic rubber by adding, as the unsaturated acid-containing copolymer (B) latex, a portion containing 5 to 90% by weight of the monomer group and not containing the unsaturated acid. and then polymerize the remaining 95 to 10% by weight of the monomer group containing the unsaturated acid, with an average particle diameter of 0.05.
A method for enlarging synthetic rubber, characterized by using a copolymer latex of ~0.2μ.