JPH0125482B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a heat-resistant copolymer, especially α-
The present invention relates to a method for producing a heat-resistant copolymer containing an alkyl-substituted aromatic vinyl monomer and a vinyl cyanide monomer as essential components. (Conventional technology) Today, as a thermoplastic resin with excellent impact resistance,
ABS resin, high impact polystyrene, AAS
Rubber-modified thermoplastic resins such as resins and AES resins are widely used. However, in fields that require high heat distortion temperatures, these resins lack heat resistance, which limits their use at relatively high temperatures. especially
Various methods have been proposed to improve the heat resistance of ABS resins. For example, it has been proposed that a resin composition with excellent heat resistance be obtained by blending a copolymer consisting of α-methylstyrene and acrylonitrile. This is described in Japanese Patent Publication No. 18194, Japanese Patent Publication No. 57-603733, Japanese Patent Publication No. 58-23810, etc. (Problems to be Solved by the Invention) However, in order to improve the heat resistance of ABS resin, when producing a copolymer of α-alkyl substituted aromatic vinyl and vinyl cyanide to be blended with it, monomer In conventional techniques, when the amount of α-alkyl-substituted aromatic vinyl monomer in the mixture is increased, the final polymerization conversion rate tends to decrease, resulting in unreacted monomers remaining in the resulting copolymer. I will do it. Moreover, when unreacted monomers are present, it is necessary to remove the remaining monomers since this lowers the heat resistance of the resulting copolymer. In order to remove this large amount of residual monomer, when the resulting copolymer is pelletized using an extruder,
Measures such as lowering the screw rotation speed, using a high vacuum vent, or increasing the cylinder temperature are generally taken. However, such methods result in decreased productivity and increased production costs. Moreover, an excessive increase in cylinder temperature causes thermal decomposition of the copolymer, and conversely increases the amount of residual monomer, resulting in a decrease in heat resistance. Furthermore, when such a copolymer is blended with an ABS resin or the like and extrusion molded, an excessive increase in cylinder temperature causes deterioration of the rubber component, making it difficult to obtain a resin with good impact resistance. (Means for Solving the Problems) As a result of intensive studies in view of the current situation as described above, the inventors of the present invention have devised a co-product by emulsion polymerizing at least an α-alkyl-substituted aromatic vinyl monomer and a vinyl cyanide monomer. The inventors have discovered that the above-mentioned problems can be solved by maintaining the pH within the polymerization system within a specific range until the polymerization conversion rate reaches at least 30% when producing a polymer, and have thus arrived at the present invention. The gist of the present invention is to emulsion polymerize a monomer mixture consisting of 70 to 90% by weight of an α-alkyl substituted aromatic vinyl monomer and 30 to 10% by weight of a vinyl cyanide monomer to produce a copolymer. When manufacturing the
Polymerization is carried out while maintaining the pH in the polymerization system in the range of 9.5 to 11.5 by continuous or intermittent addition of a basic compound until the polymerization conversion rate of the monomer mixture reaches at least 30%. This is a method for producing a heat-resistant copolymer. Examples of the α-alkyl-substituted aromatic vinyl monomer used in carrying out the present invention include α-methylstyrene, α-ethylstyrene, and α-methylstyrene having a halogen or alkyl nuclear substituent. It can be used alone or in a mixture of two or more, but preferably α-
It is methylstyrene. The amount of α-alkyl substituted aromatic vinyl monomer used is preferably 70% by weight or more based on the total monomers,
If it is less than 70% by weight, the heat resistance of the resulting copolymer tends to decrease. Moreover, even if it is used in an amount exceeding 90% by weight, it tends to become difficult to obtain a copolymer with a high polymerization conversion rate. Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, and ethacrylonitrile, which may be used alone or in combination of two or more, with acrylonitrile being preferred. The amount of vinyl cyanide monomer used is 10 out of the total monomers.
It is preferable to use at least 10% by weight, and if it is less than 10% by weight, the final polymerization conversion rate tends to decrease. Furthermore, if it is used in an amount exceeding 40% by weight, the resulting copolymer tends to be colored by heating, and its physical properties tend to deteriorate. Furthermore, in the present invention, in addition to the above-mentioned α-alkyl substituted aromatic vinyl monomer and vinyl cyanide monomer, other vinyl monomers that can be copolymerized with these may also be copolymerized. Other vinyl monomers that can be copolymerized with these include, for example, maleimide monomers such as N-phenylmaleimide and maleimide, acrylic acid, methacrylic acid, acrylic esters,
Acrylic acid monomers such as methacrylic esters,
Also, fumaronitrile, acenaphthylene, etc. can be mentioned, and these can be used alone or in a mixture of two or more kinds. These other copolymerizable vinyl monomers are optional components, but the amount used is preferably up to about 20% by weight based on the total monomers. The most important thing in the present invention is to maintain the pH within the polymerization system in the range of 9.5 to 11.5 until the polymerization conversion rate reaches at least 30% during emulsion polymerization. That is, prior to the start of polymerization, when the pre-prepared components other than monomers such as emulsifiers and polymerization initiation aids are sufficiently dissolved, a basic compound is added to adjust the pH of the polymerization system to a range of 9.5 to 11.5. Adjust. After that, monomers are charged and polymerization is started. As the polymerization progresses, the PH in the polymerization system will decrease, but the PH in the polymerization system should be kept low until the polymerization conversion rate is at least 30%.
It is important to further add a basic compound to maintain the range of 9.5 to 11.5. The method of adding the basic compound is not particularly limited and may be added continuously or intermittently. When the polymerization conversion rate is less than 30%, the PH in the polymerization system is
If it is less than 9.5, the decomposition rate of the polymerization initiator tends to decrease, resulting in a decrease in the polymerization rate and a decrease in the final polymerization conversion rate. In addition, if the PH in the polymerization system exceeds 11.5 when the polymerization conversion rate is less than 30%, the polymerization initiation aid etc. will rapidly decompose, inhibiting the smooth progress of polymerization, and tending to cause a decrease in the final polymerization conversion rate. Each of these is unfavorable. When carrying out the present invention, as the basic compound added for the purpose of adjusting the PH in the polymerization system, those normally used for adjusting the PH can be used, and preferred ones are sodium hydroxide and potassium hydroxide. , etc. Emulsion polymerization can be carried out by conventional methods. That is, commonly known anionic emulsifiers, polymerization initiators, polymerization initiation aids, and polymerization degree regulators can be used as appropriate, and there are no particular limitations on their types and amounts added. After the polymerization is completed, the copolymer is coagulated by a conventional method to obtain the desired copolymer powder. The copolymer obtained by the above method has a high polymerization conversion rate, has very little residual monomer, and has excellent heat resistance, and can be used alone. It may also be used in blends with other polymers. The polymer to be blended can be selected as appropriate depending on the purpose of use, but heat resistance can be improved by blending with a rubber-modified graft copolymer containing a rubber component such as ABS resin, AAS resin, or AES resin. A thermoplastic resin composition with excellent impact resistance is obtained. (Example) The present invention will be specifically described below with reference to Examples.
In addition, "part" in each example and reference example represents "part by weight." The various measurement methods were as follows. Measurement of PH: Measurement was carried out by a colorimetric method using test paper impregnated with the following indicator. PH measurement range Phenol Red 6.8 ~ 8.4 Thymol Blue 8.0 ~ 9.6 Mixed phenolphthalein and thymonol phthalein 9.6 ~ 10.0 Nile Blue 10.0 ~ 11.0 Alizarin Yellow R 10.2 ~ 12.0 Tropeolin O 11.0 ~ 13.0 Polymerization conversion rate during polymerization: Polymerization The latex collected during the test was coagulated with isopropanol, and the solid content was calculated. Final polymerization conversion rate: Calculated by quantifying the amount of remaining monomer by gas chromatography. Amount of residual monomer in pellets: After dissolving the pellets obtained by extrusion molding the copolymer powder obtained by polymerization in dimethylformamide, the amount of remaining monomer was determined by gas chromatography. Calculated. Vikatsu softening temperature: Measured by JISK-7206 method B (load: 5 kg). Notched Izod impact strength: Measured according to JISK-6871. Example 1 A 5 capacity stirred reactor was charged with the following materials. Water 200 parts Potassium laurate 2.5 parts Dextrose 0.5 part Ferrous sulfate (FeSO _{4.7H 2} O) 0.005 part Sodium pyrophosphate 0.1 part The pH was 10.0 at the time the above substances were charged.
When 0.01 part of potassium hydroxide was added to this, the pH of the system rose to 10.8. Next, after heating and stirring at 60℃ in a nitrogen stream, α-
After 80 parts of methylstyrene and 4 parts of acrylonitrile were charged and thoroughly emulsified, 0.5 part of cumene hydroperoxide was added, and then acrylonitrile was added.
16 parts were continuously added dropwise for 2 hours. During the dropwise addition of this acrylonitrile, the polymerization conversion rate and pH of the polymerization system were measured at appropriate times as described below, and potassium hydroxide was added to adjust the pH. That is, when the polymerization conversion rate was 10%, the PH of the polymerization system reached 9.5%, so when 0.01 part of potassium hydroxide dissolved in 0.5 part of water was added, the PH of the polymerization system rose to 1.04. When the polymerization conversion rate was 18%, the PH of the polymerization system was 9.6, so 0.01 part of potassium hydroxide dissolved in 0.5 part of water was added, and the PH of the polymerization system rose to 10.4. When the polymerization conversion rate was 27%, the PH of the polymerization system was 9.5 parts, so when 0.01 part of potassium hydroxide dissolved in 0.5 part of water was added, the PH of the polymerization system rose to 10.3. The pH of the polymerization system was 10.0 when the polymerization conversion rate was 30%. After the dropwise addition of acrylonitrile was completed, stirring was further continued at 60°C for 1 hour, and then the polymerization was completed. The final polymerization conversion rate at the end of polymerization was 97%. The produced copolymer latex was coagulated with a 1% aqueous magnesium sulfate solution, washed and dried to obtain a white powdery copolymer. This white powdery copolymer was extruded into pellets using a 25 m/m extruder at a cylinder temperature of 230°C and a vent pressure of 40 mmHg (absolute pressure). The residual monomer content in the pellet was measured and found to be 0.03% α-methylstyrene and 0% acrylonitrile. The above pellets were injection molded using a screw-type injection molding machine (cylinder temperature: 230°C, mold temperature: 60°C) to prepare test pieces for measuring the softening temperature of Vikatsu.
The Vikatsu softening temperature was 134°C. Example 2 Polymerization, coagulation, pelletization, and molding were carried out under the same conditions as in Example 1 except that the pH was adjusted as described below. The pH of the system before the start of polymerization was 10.0. The pH was adjusted by dissolving 0.04 part of potassium hydroxide in 1 part of water and continuously dropping the solution over 30 minutes from the start of polymerization. The PH of the polymerization system at a polymerization conversion rate of 10% and 20% was 10.3 and 10.2, respectively. In addition, the polymerization conversion rate at the end of dropping the potassium hydroxide aqueous solution was 33
%, and the pH of the polymerization system was 10.2. The final polymerization conversion rate at the end of the polymerization was 8%. Further, the amount of residual monomers in the pellet was measured and found to be 0.03% of α-methylstyrene and 0% of acrylonitrile.
Furthermore, the Vikatsu softening temperature was 134°C. Comparative Example 1 Polymerization, coagulation, pelletization, and molding were carried out under the same conditions as in Example 1, except that the pH was not adjusted using potassium hydroxide before and during the polymerization. In this case, the pH of the system before the start of polymerization was 10.0. In addition, the pH of the polymerization system at a polymerization conversion rate of 10% is 9.2,
The PH of the polymerization system at a polymerization conversion rate of 20% was 8.8, and the PH of the polymerization system at a polymerization conversion rate of 30% was 8.4. The final polymerization conversion rate was 83%, and the amount of residual monomer in the pellets was determined to be α-methylstyrene.
0.9%, acrylonitrile 0.2%, Vikatsu softening temperature was 121°C. Examples 3 to 8 Polymerization, coagulation, pelletization, and molding were carried out under the same conditions as in Example 1 or 2, except that the type of emulsifier and the amount of monomer charged were changed. . The pH adjustment method for sequential addition was the same as in Example 1, and for the continuous addition, the same method as in Example 2 was used. These results are shown in Table 1. Comparative Examples 2 to 6 Polymerization was carried out under the conditions of Example 1 by changing the type of emulsifier and the amount of monomer charged. However, the PH of the system before the start of polymerization was adjusted as shown in Table 2 using an aqueous potassium hydroxide solution, and the PH of the system during polymerization was not adjusted. These results are shown in Table 2.

【table】

【table】

[Table] Reference Example Production of diene-based rubber-modified graft copolymer The following materials were charged into a reactor with a capacity of 25 and equipped with a stirrer. Water 140 parts Dextrose 0.3 parts Ferrous sulfate (FeSO _{4.7H 2} O) 0.005 parts Sodium pyrophosphate 0.2 parts Polybutadiene latex 120 parts (Solid content 50%, average particle size 0.3 μm) The above substances were mixed in a nitrogen stream for 60 minutes. After heating and stirring at °C,
28 parts of styrene, 12 parts of acrylonitrile and 0.3 parts of cumene hydroperoxide were continuously added dropwise for 2 hours. After the dropwise addition was completed, the mixture was stirred at 60° C. for an additional hour, and then the polymerization was completed. Two parts of butylated hydroxytoluene was added as an antioxidant to the obtained graft copolymer latex, and the mixture was coagulated with a 5% aqueous sulfuric acid solution.
After washing and drying, a white powdery graft copolymer was obtained. The obtained diene-based rubber-modified graft copolymer and the copolymers obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were mixed at the weight ratio shown in Table 3, and each of these was added with a phosphorescent stabilizer. After mixing with a Henschel mixer at 3000 rpm for 5 minutes, extrusion was carried out at a cylinder temperature of 230 DEG C. to pelletize samples 1 to 7. Each of these pellet samples was put into a screw-type injection molding machine (cylinder temperature
(230°C, mold temperature 60°C) to prepare notched Izod impact measurement test pieces and Vikat softening temperature measurement test pieces, and the notched Izod impact strength and Vikat softening temperature were measured. These results are shown in Table 3. The results in Table 3 show that a molded article having excellent heat resistance can be obtained by blending the copolymer obtained by the method of the present invention with the diene rubber-modified graft copolymer.

[Table] (Effects of the invention) In producing an α-alkyl-substituted aromatic vinyl copolymer, the present invention achieves a polymerization conversion rate of at least
By keeping the PH in the polymerization system within a specific range until the pH reaches 30%, it has the excellent effect of producing a copolymer with excellent heat resistance at a high polymerization conversion rate.

Claims (1)

[Claims] 1 α-alkyl substituted aromatic vinyl monomer 70-90
wt% and vinyl cyanide monomer 30-10wt%
When producing a copolymer by emulsion polymerization of a monomer mixture consisting of: By adding
A method for producing a heat-resistant copolymer, characterized in that polymerization is carried out while maintaining the molecular weight within the range of 9.5 to 11.5.