JPH0587532B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a resin composition having particularly excellent heat resistance among α-methylstyrene-acrylonitrile copolymers. Conventionally, styrene-acrylonitrile copolymer, so-called AS resin, and rubber-modified AS resin have been used.
ABS resin, AES resin, AAS resin, etc. are widely used. In order to improve its heat resistance, it has been proposed to replace the styrene component with α-methylstyrene. Various proposals have been made regarding copolymer compositions of α-methylstyrene (hereinafter referred to as αMS) and acrylonitrile (hereinafter referred to as AN). Regarding the synthesis method of the composition, in order to increase the polymerization rate, styrene and AN are added and reacted in the latter half of the polymerization.
33661), a method of emulsion polymerization of αMS and AN, in which αMS is polymerized at a high concentration in the first stage polymerization, and AN is further added in the second stage polymerization to complete the polymerization (Japanese Patent Application Laid-Open No. 1983-1999-
78043) etc. have been presented. However, the heat resistance of resin compositions obtained by these methods is still not sufficient. Regarding the copolymerization of αMS and AN, as stated in Japanese Patent Publication No. 45-33661,
From αMS:AN≒70:30 (azeotrope composition), as the amount of αMS increases, the polymerization rate decreases. Therefore, in order to obtain a copolymer with high heat resistance,
Even if a copolymer with a high αMS content is synthesized by performing polymerization with a composition exceeding the azeotrope content of αMS, the polymerization conversion rate will be low with a monomer composition with a high αMS content as described above. The resin obtained through the normal recovery process has a large amount of unreacted monomer remaining, so a resin composition with high heat resistance cannot be obtained. for example,
In order to obtain a high polymerization rate with a composition exceeding the azeotrope content of αMS, the concentration of unreacted unsaturated nitrile relative to all unreacted monomers in the polymerization system at the end of monomer addition must be kept above a certain value. A method has been proposed (Japanese Unexamined Patent Publication No. 57-2310) in which monomers are added after adjusting the amount. However, since the resin composition obtained by this method also contains nearly 1% by weight of unreacted monomers, it cannot be expected to have any higher heat resistance.
Similarly, with a composition exceeding the azeotrope content of αMS, polymerization is performed until unreacted acrylonitrile becomes 3% by weight or less, and steam is blown into the resulting copolymer latex to remove remaining unreacted monomers. A separation method (Japanese Unexamined Patent Publication No. 8209/1983) has been proposed. However, the αMS content of the resin composition obtained by this method is not clear, nor is the content of residual monomers, so it cannot be expected to have heat resistance beyond a certain level. Therefore, there is a limit to the heat resistance of a thermoplastic resin obtained by mixing the copolymer of αMS and AN as described above with a rubber-modified thermoplastic resin. The present inventors have found that an αMS-AN copolymer composition with a high αMS content and high heat resistance can be obtained when made into a resin composition, and that the above αMS-AN copolymer composition can be used in a rubber-modified thermoplastic resin. The present invention was arrived at as a result of intensive studies to obtain a product with high heat resistance when mixed. That is, the present invention has αMS75 to 82% by weight, AN18
~25% by weight, and continued emulsion polymerization while keeping the concentration of unreacted monomers in αMS at 90% by weight or more based on the total unreacted monomers, resulting in a polymerization conversion rate of 85 to 95% by weight. Thermoplastic resin (A) and rubbery polymer 20 to 60
40 to 80 parts by weight of an aromatic vinyl monomer, a vinyl cyan monomer, and a monomer copolymerizable with these monomers
and the graft copolymer (B) obtained by polymerizing parts by weight to reduce the rubbery polymer content in the mixture to 10%.
The present invention relates to a method for producing a thermoplastic resin composition, characterized in that the residual monomer content is 30% by weight or less and the residual monomer amount is 2000 ppm or less. The present invention will be explained in detail below. In the present invention, the thermoplastic resin (A) is produced as follows. In order to obtain a copolymer having a composition ratio of 75 to 82 parts by weight of αMS and 25 to 18 parts by weight of AN, the concentration of unreacted monomers in the emulsion polymerization system is maintained at 90% by weight or more of αMS, Polymerization is carried out by controlling the addition of In the copolymerization of αMS and AN, in a monomer composition containing more αMS than the azeotrope composition, the conversion rate of AN monomer to a polymer is faster than the conversion rate of αMS monomer,
Sequential or continuous addition of monomers is controlled so as to maintain the monomer concentration ratio in the polymerization system within a certain range. However, as the absolute concentration of monomers in the polymerization system decreases, the polymerization rate slows down, and αMS
It becomes difficult to maintain a high concentration of polymerization. Unreacted monomer in the polymerization system is 15% of the total monomer used.
Emulsion copolymerization is stopped when the amount reaches ~5% by weight. Then, the monomer is removed from the polymerization system by stripping or the like to reduce the unreacted monomer content to 2 to 5% by weight. The obtained copolymer latex was
After salting out at a temperature of ~130℃ and drying by evaporation of water, αMS
- Obtain a powder of AN copolymer. Further, residual monomers are removed from the powder. In this method, an αMS-AN copolymer thermoplastic resin having a residual amount of unreacted monomer of 2000 ppm or less can be obtained by pelletizing while degassing in a vented extruder. The thermoplastic resin obtained by the present invention is
It has extremely high heat resistance, and by mixing and using this resin with a rubber-modified resin, a thermoplastic resin with excellent heat resistance and impact resistance can be obtained. The mixture with the rubber reinforced thermoplastic resin (B) is the αMS obtained above,
It may also be used by mixing with AN copolymer pellets and mixing again in an extruder, or by mixing αMS-AN copolymer powder that has not been processed in the extruder with a rubber-reinforced thermoplastic resin and then venting. Pelletized while degassing with an extruder, the amount of unreacted monomer remaining is 2000ppm
The following heat-resistant rubber-modified thermoplastic may be used. In the present invention, in αMS and AN emulsion copolymerization, the polymerization conversion rate is 85 to 95% by weight, preferably 85 to 92%. If it is less than 85%, the amount of monomer to be recovered is large, which is inappropriate from the viewpoint of economy and productivity, and if it exceeds 95% by weight, the reactivity deteriorates and is not practical. In the process of recovering the obtained emulsion copolymer latex, if it is left untreated, it will be difficult to remove the monomer in the subsequent process, so the amount of residual monomer in the latex can be reduced to 5% by weight or more, preferably 5 to 2% by weight, by stripping or the like. It is necessary to do so. Regarding the further removal of monomers from the latex, if the amount is less than 2% by weight, the powder in the salting out step becomes fine, making the recovery operation difficult and the efficiency of monomer removal extremely poor. A copolymer latex containing 2 to 5% by weight of residual monomers was salted out and recovered, and the powder was further pelletized while removing monomers using a vented extruder, etc., to reduce the residual amount of unreacted monomers to 2000 ppm. Obtain thermoplastic resin. Thermoplastic resins containing more than 2000 ppm of unreacted monomers lead to a decrease in heat resistance, which is the objective of the present invention, and are inferior in moldability due to a large amount of gas being scattered during molding. The αMS,AN copolymer is preferably produced by emulsion polymerization. Emulsifiers used in emulsion polymerization include higher fatty acids such as lauric acid and oleic acid, sodium salts and potassium salts of rosin acid, sodium salts and potassium salts of alkylbenzenesulfonic acids, and sodium and potassium salts of sulfuric esters of higher alcohols. , polyethylene oxide alkyl ether sulfate, polyethylene oxide alkyl phenol ether sulfate, etc., or a mixture of two or more thereof can be used. Furthermore, nonionic surfactants can be used alone or in combination with anionic surfactants. Polymerization catalysts include persulfates, organic peroxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and para-menthane hydroperoxide, sugar-containing pyrophosphoric acid formulations, and sulfoxylate formulations. It is possible to use redox catalysts in combination with cyclic agents. As for other molecular weight regulators, polymerization stabilizers, etc., those commonly used in emulsion polymerization can be used. αMS 75 to 82 parts by weight as a copolymer composition,
AN25-18 parts by weight Preferably αMS78-82 parts by weight
Although the composition contains 22 to 18 parts by weight of AN, it is also possible to substitute a portion of AN with other copolymerizable monomers, such as styrene or methyl methacrylate. The rubber-modified thermoplastic resin (B) used by mixing with the above heat-resistant thermoplastic resin contains polybutadiene, styrene-butadiene copolymer, ethylene-propylene copolymer, ethylene-propylene-ethylidenenorbornene copolymer as a rubber component. , 20 to 60 parts by weight of acrylic rubber, etc. can be copolymerized with aromatic vinyl monomers such as styrene and α-methylstyrene, nitrile monomers such as acrylonitrile, and these monomers such as methyl methacrylate. A graft copolymer of monomers is used. A thermoplastic resin composition with good heat resistance and impact resistance can be obtained by mixing and using the rubber components so that the rubber component content after mixing is 10 to 30% by weight. In order to reduce the amount of residual monomer contained in the resin to 2000 ppm or less, the mixed resin with a heat-resistant thermoplastic resin and a rubber-modified thermoplastic resin is processed using a vented extruder, preferably having 2 to 3 vent ports. Pelletization is performed using an extruder with excellent surface renewal and deaeration ability, such as a co-rotating twin-screw extruder. In some cases, it may be possible to increase the efficiency of degassing the remaining monomer by injecting water into the barrel.
Although not particularly restricted by the above method,
In the process of turning the powder into the final pellet shape,
It is necessary to remove the residual monomer to obtain a thermoplastic resin with a residual monomer content of 2000 ppm or less. Next, the present invention will be explained in more detail with reference to Examples. Example 1 180 parts by weight of ion-exchanged water, 2" parts of potassium stearate, 75" parts of α-methylstyrene, 7" parts of acrylonitrile, and 0.2" parts of tertiary dodecyl mercaptan were placed in a reactor equipped with a nitrogen-substituted stirrer. Prepared and emulsified. Increase the temperature to 60°C while stirring under a nitrogen stream.
After raising the temperature to ℃, a solution of 0.2" part of sodium pyrophosphate, 0.4" part of glucose, and 0.01" part of ferrous sulfate dissolved in 16" parts of ion-exchanged water and 0.1" part of cumene hydroperoxide were added and polymerized. The reaction was started. After the jacket temperature of the reaction vessel was controlled at 70°C and polymerization was continued for 1 hour, a solution of 18" parts of acrylonitrile emulsified in 50" parts of ion-exchanged water and 0.5" parts of potassium stearate was added. Additions were made continuously over time. The polymerization reaction was continued for 1 hour after the addition was completed. The total monomer conversion to polymer was 88% by weight. The obtained latex is
Demonomerization was carried out for 3 hours using the apparatus shown in the figure, resulting in a latex containing 4.5% by weight of unreacted monomers. The latex was added to an aqueous calcium chloride solution kept at 120° C. with stirring, and coagulated and recovered. The obtained water-containing powder was dried in a fluidized fluid dryer (85° C., 1 hour) to obtain a resin powder. The particle size of the powder was 2% by weight, which was good enough to pass 200 mesh (74μ). The unreacted monomer contained in the powder was 1.8% by weight. The amount of acrylonitrile determined by Coleman nitrogen analysis of the powder was 22% by weight. The obtained powder was processed using a vented extruder (Toshiba Machine Co., Ltd.)
The pellets were pelletized while degassing and removing monomers using a TEM50A (3-stage vent). The amount of residual monomer in the pellet was 1300 ppm. The pellet softening temperature (ASTMD1525) was 144°C.
FIG. 2 shows the results of measuring the Vikato softening temperature of samples obtained by changing the removal efficiency of the residual monomer amount using a vented extruder. As is clear from FIG. 2, by controlling the amount of residual monomer to 2000 ppm or less, a thermoplastic resin with excellent heat resistance can be obtained. On the other hand, the copolymer latex obtained after the polymerization was kept at a jacket temperature of 95° C. for 12 hours to remove the monomer using the apparatus shown in FIG. 1, to obtain a latex containing 0.8% by weight of unreacted monomers. The latex was added to an aqueous calcium chloride solution kept at 130° C. with stirring, and coagulated and recovered. The particle size of the powder obtained by drying was 38% by weight that passed 200 meshes (74μ), and the amount of fine powder was extremely large, making it impossible to process it in normal work processes. Example 2, Comparative Examples 1 to 4 Emulsion copolymerization of α-methylstyrene and acrylonitrile was carried out using the same production method as in Example 1.
Compositions with different contents of α-methylstyrene were obtained. The post-treatment step was carried out in the same manner, and the Vicat softening temperature of the resulting pellet molded product was measured.

[Table] *Measured by alcohol coagulation The composition ratio of α-methylstyrene and acrylonitrile shows that if the α-methylstyrene content is less than 75% by weight, the heat resistance is low, and after the completion of polymerization to obtain a composition of 82% or more by weight. It can be said that it is not practical due to the large amount of residual monomer and the low conversion rate to polymer. Examples 3 to 7, Comparative Examples 5 to 8 The rubber-modified thermoplastic resin and the pellets obtained in Examples 1 and 2 and Comparative Examples 1 to 4 were mixed to obtain various pellets using an extruder. Table 2 shows the properties of various thermoplastic mixed resins.

[Table] As shown in this example, by using the α-methylstyrene and acrylonitrile copolymer obtained in the production process of the present invention and controlling the residual monomer to 2000 ppm or less, heat resistance or heat resistance, It can be seen that a thermoplastic resin composition with excellent impact resistance can be produced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the monomer removal apparatus, and FIG. 2 is a graph showing the relationship between the amount of residual monomer and the Vicat softening temperature.

Claims (1)

[Claims] 1. 75 to 82% by weight of α-methylstyrene and 18 to 25% by weight of acrylonitrile were added to reduce the concentration of unreacted monomers of α-methylstyrene to 90% by weight based on the total unreacted monomers.
Heat-resistant thermoplastic resin (A) with a polymerization conversion rate of 85 to 95% by weight by continuing emulsion polymerization while maintaining the concentration above 85% to 95% by weight.
and a graft obtained by polymerizing 20 to 60 parts by weight of a rubbery polymer with 40 to 80 parts by weight of an aromatic vinyl monomer, a vinyl cyan monomer, and a monomer copolymerizable with these monomers. A thermoplastic resin composition characterized in that it is mixed with a copolymer (B) so that the rubbery polymer content in the mixture is 10 to 30% by weight, and the residual monomer amount is 2000 ppm or less. manufacturing method.