JPH0510375B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an industrially advantageous method for producing expandable thermoplastic copolymer particles having excellent heat resistance and solvent resistance, and good foamability and moldability.
As expandable polymer particles, expandable polystyrene resin particles are well known, and by using these particles, a molded foamed article can be easily obtained at low cost. However, since the monomer constituting the polymer is styrene, the foam molded product has poor heat resistance for use in relatively high-temperature pipe insulation materials, roof insulation materials, automobile parts, solar system insulation materials, etc. There are drawbacks that prevent it from being used for the required purpose. In addition, when used in combination with other materials, particularly in automobile parts, etc., it also has the disadvantage that it is difficult to select an adhesive because of its poor solvent resistance. The present inventors found that in order to obtain expandable thermoplastic polymer particles having sufficient heat resistance and solvent resistance for practical purposes, the monomer composition constituting the polymer should be 10% alpha methylstyrene. It was considered necessary to obtain copolymer particles containing 5% or more of acrylonitrile as described above, and to incorporate an easily volatile blowing agent into the resin particles. However, based on this viewpoint, in order to obtain a copolymer with excellent heat resistance by suspension polymerization using a large amount of alphamethylstyrene as described above, t-butyl peroxybenzoate, di-t-butyl peroxybenzoate, di-t-butyl peroxybenzoate, etc. oxide, t-
There are methods using organic peroxides such as butyl peroxyacetate as polymerization initiators, but in methods using these initiators, it is necessary to use extremely large amounts regardless of the polymerization temperature. The resulting copolymer has an extremely low degree of polymerization, and the copolymer particles impregnated with an easily volatile blowing agent to form expandable thermoplastic resin particles have extremely poor foamability and are unsatisfactory. Not only is it difficult to obtain a foamed molded product, but the molded product also becomes weak. Furthermore, if the amount of these initiators used is reduced in order to increase the degree of polymerization, so-called dead end polymerization will occur, making it impossible to obtain a high conversion rate industrially, and therefore making it difficult to obtain a satisfactory foamed molded product.
Furthermore, if an organic peroxide such as benzoyl peroxide is used, it is impossible to obtain a copolymer with a high conversion rate that can be used industrially even at an appropriate polymerization temperature. On the other hand, emulsion polymerization is a method for obtaining alphamethylstyrene-acrylonitrile copolymers with a high degree of polymerization and a high conversion rate, but in order to produce expandable thermoplastic polymer particles by this method,
As seen in Japanese Patent Application Laid-Open No. 57-65735, an extremely complicated process of emulsion polymerization, coagulation, pelletization, and impregnation of the resulting pellets with a blowing agent is required, which not only increases production costs but also increases production costs. However, since the resulting resin contains a large amount of emulsifiers, coagulants, etc., it has the disadvantage that only products with poor foamability, strength, etc. can be obtained. As a result of intensive research in view of these drawbacks, the present inventors have found that by using a specific azo initiator and acrylonitrile in combination, a high degree of polymerization and high conversion can be achieved even when using a large amount of alpha methylstyrene. discovered a suspension polymerization method that yields a copolymer with a
By impregnating the resulting copolymer particles with an easily volatile foaming agent, they succeeded in obtaining expandable thermoplastic copolymer particles with excellent heat resistance, and have completed the present invention. That is, the present invention provides alpha methyl styrene 10
~80% by weight, 5~50% by weight of acrylonitrile, and further styrene, chlorostyrene, paramethylstyrene, t-butylstyrene, acrylic ester,
At least one selected from methacrylic acid esters
1,1'-Azobiscyclohexane-1- with monomers used in a proportion of 0 to 70% by weight of the species compound.
Polymerization at a temperature of 80 to 150°C using one or more selected from carbonylitrile, 2-t-butylazo-2-cyanopropane, 2-t-butylazo-2-cyanobutane, and 1-t-butylazo-1-cyanocyclohexane as an initiator. The gist of the present invention is a method for producing expandable thermoplastic polymer particles, which comprises copolymerizing and impregnating an easily volatile blowing agent during or after the polymerization. The amount of alphamethylstyrene used in the present invention is in the range of 10 to 80% by weight, and is determined depending on the desired heat resistance and expansion ratio, but if it is less than 10% by weight, the effect of improving heat resistance is not observed. When it exceeds 80% by weight, the polymerization conversion rate decreases and a large amount of monomer remains in the resin, resulting in poor heat resistance. In order to obtain heat resistance of 100℃ with a 50x foamed molded product, it is necessary to use 20 to 50% by weight of alpha methylstyrene.
In order to obtain heat resistance of 110° C. in a 5-15 times foamed product, it is necessary to use 50-80% by weight of alpha methylstyrene. Furthermore, the acrylonitrile used in the present invention is
It is necessary to improve the polymerization conversion rate of the composition and to exhibit oil resistance. The amount is 5% by weight
If it is less than this, the polymerization conversion rate of the composition will be low and the oil resistance will not be effective, which is not preferable. Further, even if it is used in an amount exceeding 50% by weight, the polymerization conversion rate will not change and the resin will be colored yellowish brown, which is not preferable. Monomers other than alphamethylstyrene and acrylonitrile include styrene, various substituted styrenes such as chlorostyrene, paramethylstyrene, and t-butylstyrene, acrylic acid esters such as methyl acrylate, ethyl acrylate, and butyl acrylate, methyl methacrylate, One or more types of methacrylic acid esters such as ethyl methacrylate and butyl methacrylate can be used as appropriate. Selection of the initiator used in the present invention is important in order to efficiently obtain a polymer with a high degree of polymerization and a high polymerization conversion rate. Polymerization conversion rate is low and monomer is 5
% or more remaining in the resin, it is difficult to obtain a satisfactory foamed molded product, and even if a foamed molded product can be obtained, it will have extremely poor heat resistance. From this point of view, initiators to be used include, in particular, 1,1'-azobiscyclohexane-1-carbonitrile, 2-t-butylazo-2-cyanopropane, 2-t-butylazo-2-cyanobutane, 1-t-butylazo-
1-cyanocyclohexane is employed. The amount of these initiators used is 0.05% based on the monomer used.
~3.0% by weight is preferred. If it is less than 0.05% by weight, an industrially practical polymerization conversion rate cannot be obtained at all, or it will take a long time, resulting in extremely poor productivity, and if it is more than 3.0% by weight, the molecular weight will decrease significantly. However, satisfactory foam molding cannot be carried out, or even if foam molding can be carried out, the result is only a foam molded product whose strength is significantly inferior. The polymerization temperature when using an initiator in the present invention is 80 to 150°C. If it is less than 80°C, the polymerization conversion rate will be extremely low, and if it exceeds 150°C, the molecular weight will decrease and it will be difficult to obtain a satisfactory foam molded product. In the present invention, a suspension polymerization method is employed as a method for obtaining such expandable thermoplastic copolymer particles. As mentioned earlier, in the emulsion polymerization method, there is an increase in cost due to the complexity of the process and a decrease in quality due to the contamination of emulsifiers and coagulants.In the bulk polymerization method, pelletization is performed after polymerization. It is inferior to the suspension polymerization method in terms of the complexity of the process, which requires impregnation with a blowing agent afterwards. As dispersants used in suspension polymerization, organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose; inorganic dispersants such as tricalcium phosphate, calcium pyrophosphate, sodium silicate, zinc oxide, and magnesium carbonate can be used. However, when using an inorganic dispersant, sodium alkylbenzenesulfonate, α-
By using an anionic surfactant such as sodium olefin sulfonate, the effect of the dispersant is significantly improved. When trying to obtain copolymer particles with the above composition by suspension polymerization using a dispersant, the particle size tends to become very small, and it is difficult to reduce the amount of the dispersant in order to obtain relatively large particles. For example, suspension abnormalities occur in the latter half of polymerization, making it difficult to obtain particles with a relatively large particle size as desired. Therefore, in order to obtain particles with a desired particle size, it is preferable to carry out the polymerization using a small amount of dispersant at the beginning of the polymerization, and to add the dispersant at the latter half of the polymerization. Easily volatile foaming agents used in the present invention include:
Aliphatic hydrocarbons such as propane, butane, and pentane; cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane; and trichlorofluoromethane, dichlorofluoromethane, dichlorodifluoromethane, methyl chloride, and dichloride. Examples include halogenated hydrocarbons such as tetrafluoromethane and ethyl chloride. The amount of these blowing agents to be used varies depending on the desired expansion ratio of the foam molded product, but ranges from 2% by weight to 15% by weight.
By containing it, it is possible to obtain a foamed molded product from 2 times to 100 times larger. These blowing agents may be added either during or after polymerization. On the other hand, in the present invention, when the purpose is a highly foamed molded article, solvents such as toluene, xylene, ethylbenzene, heptane, and octane; monomers such as styrene, alphamethylstyrene, and acrylonitrile; or phthalate esters It is preferable that the expandable thermoplastic copolymer particles contain a plasticizer such as adipic acid ester or the like. Methods for incorporating these solvents, monomers, and plasticizers include a method in which they are mixed with the monomers in advance and polymerized, a method in which they are impregnated simultaneously with the impregnation with the blowing agent, and the like. Furthermore, the method of containing monomers leaves unreacted monomers after polymerization, but it is difficult to control the remaining amount. The amount of these solvents and plasticizers used is preferably 3% by weight or less. The expandable thermoplastic resin particles thus obtained are
After pre-foaming to a desired magnification with a heating medium such as steam or hot air, the foam is filled into a mold that can be closed but cannot be sealed, and heated again with a heating medium such as steam to form the desired foam. It can be made into a heat-resistant foam having a shape. The present invention will be explained below with reference to Examples. Example 1 110 parts by weight of water, 0.08 parts by weight of tribasic calcium phosphate, 0.003 parts by weight of sodium dodecylbenzenesulfonate, and 0.2 parts by weight of sodium chloride were placed in an autoclave equipped with a stirrer, and then stirred for 1.
A mixed monomer consisting of 0.5 parts by weight of 1'-azobiscyclohexane-1-carbonitrile, 30 parts by weight of alphamethylstyrene dissolved in 1.0 parts by weight of toluene, 20 parts by weight of acrylonitrile, and 50 parts by weight of styrene was introduced into the system. The suspension was made into a suspended state, and the temperature was immediately raised to 100°C, and after 3 hours, 0.3 parts by weight of tribasic calcium phosphate was added. After that, polymerization was carried out for an additional 4 hours, and then the temperature was further raised to 115°C, and post-polymerization was carried out for 3 hours. The polymerization conversion rate of the obtained resin was 99.4%. Then lower the temperature to 100 °C and add butane 10
Parts by weight were added and impregnated with a blowing agent for 8 hours at 100°C. The obtained expandable thermoplastic polymer is pre-foamed to an apparent magnification of 50 times by heating with steam, then filled into a mold that can be closed but cannot be sealed, and heated with steam to form a mold of 45 cm x 30 cm x A 2 cm plate-shaped foam molded product was obtained. After this molded body was left in a hot air soaking dryer at 100°C for one week, the dimensional change rate with respect to the initial size was -1.5%. Examples 2 to 4 The same procedure as in Example 1 was carried out except that 1,1'-azobiscyclohexane-1-carbonitrile was changed to the substance and polymerization temperature shown in Table 1, respectively. The results are shown in Table-1. Comparative Example 1 In Example 1, 1,1'-azobiscyclohexane-1-carbonitrile was changed to benzoyl peroxide and polymerization was carried out at 90°C for 7 hours, but the polymerization addition rate increased only to 78%. However, it was not possible to obtain a foamed molded product. Example 5 A foam molded product was obtained in the same manner as in Example 1 except that the monomer composition was 50 parts by weight of alphamethylstyrene, 25 parts by weight of acrylonitrile, and 25 parts by weight of styrene. After this molded body was left in a hot air soaking dryer at 100°C for one week, the dimensional change rate with respect to the initial size was -1.8%.

[Table] * Because the polymerization conversion rate was low, impregnation with a blowing agent was not performed. Therefore, no molded product was obtained and no heat resistance test was conducted.

Claims (1)

[Claims] 1 10 to 80% by weight of alphamethylstyrene, 5 to 50% by weight of acrylonitrile, and at least one compound selected from styrene, chlorostyrene, paramethylstyrene, t-butylstyrene, acrylic ester, and methacrylic ester. 70
Using monomers in the proportion of 1,1′-
azobiscyclohexane-1-carbonitrile,
2-t-butylazo-2-cyanopropane, 2-
Copolymerization is carried out at a polymerization temperature of 80 to 150°C using one or more types selected from t-butylazo-2-cyanobutane and 1-t-butylazo-1-cyanocyclohexane as an initiator, and easily volatile during or after the polymerization. A method for producing expandable thermoplastic resin particles, which comprises impregnating them with a blowing agent.