JPH0221402B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a copolymer having excellent heat deformation resistance, and more specifically, to a highly practical copolymer having excellent heat decomposition resistance, moldability, transparency, and heat deformation resistance. The present invention relates to a method for producing a methacrylic resin. [Prior art] Generally, polymethyl methacrylate resins or resins containing methyl methacrylate as a main component are widely used in automobile parts, electrical parts, displays, etc. due to their excellent properties such as transparency, surface gloss, mechanical strength, and moldability. used in the field. However, its heat resistance is not necessarily sufficient, and its use is limited in applications where shape stability at high temperatures is required. Therefore, research on improving the heat deformation resistance of methyl methacrylate resins has been widely conducted, and several reports and proposals have been made. A copolymer of methyl metharylate and O-methylphenylmaleimide is disclosed in Japanese Patent Publication No. 9753/1983. [Problem] The copolymer obtained by this patent has a 2.0 to 5.0
Contains % by weight of unpolymerized monomers, which causes poor surface appearance (silver), poor coloring, etc. during high temperature injection molding. For this reason, its use is limited to general use, and it cannot be used in high-temperature injection molding applications, particularly in disc disks and the like. (Means for Solving the Problems) The present inventors used an industrially possible process for copolymers of methyl methacrylate and O-methylphenylmaleimide to obtain copolymers with extremely low residual monomers. As a result of extensive research, we discovered that this can only be achieved by satisfying specific polymerization and deaeration conditions. [Structure of the invention] That is, the present invention provides methyl methacrylate units
In a method of producing a copolymer consisting of 60 to 97.5% by weight and 2.5 to 40% by weight of O-methylphenylmaleimide units by suspension polymerization, the 10-hour half-life is 55 to 80°C.
0.1 to 100 parts by weight of the above monomers
Using 0.5 parts by weight at a temperature of 50°C to 85°C for 2 to 10 hours,
The first stage polymerization was carried out at a temperature of 90 to 100°C for 1 to 5 hours, and the beads obtained by the second stage polymerization were heated at a temperature of 260 to 300°C under the vacuum of a vent. The present invention relates to a method for producing an acrylic resin, which is characterized by degassing and removing volatile components under conditions of 10 mmHg. The polymer of the present invention has methyl methacrylate units
It is necessary to contain 60 to 97.5% by weight, preferably 70 to 90% by weight. If the content of methyl methacrylate units is less than 60% by weight, the transparency and mechanical strength will be significantly reduced, which is a practical problem. It is necessary to contain the O-methylphenylmaleimide unit, which is a copolymerization component, in an amount of 2.5 to 40% by weight, preferably 10 to 30% by weight. If the O-methylphenylmaleimide unit is less than 2.5% by weight, one of the effects of the present invention, which is improved heat deformation resistance, cannot be achieved, and if it exceeds 30% by weight, residual O-methylphenylmaleimide units remain. It becomes very difficult to reduce the amount of monomer, and as a result, there are problems such as inability to perform high-temperature molding and significant discoloration, making it impossible to put it to practical use. The copolymer of the present invention is produced by suspension polymerizing beads at a temperature of 50°C to 100°C and then heating the beads to 260°C to 300°C.
It can be obtained by extruding at a temperature of 50 mmHg or less at a vent vacuum level of 50 mmHg or less. Particularly preferable degassing conditions are 290°C to 315°C, and the degree of vacuum is 30mmHg.
It is as follows. If the deaeration temperature is less than 260°C, no matter how good the degree of vacuum is, it will have little effect in reducing residual monomers. Furthermore, when the degree of vacuum exceeds 50 mmHg, no matter how high the temperature is, the effect of reducing residual monomers is small. As suspension aids used in suspension polymerization, aluminum hydroxide, magnesium hydroxide, etc. are used as inorganic suspending agents, and polypotassium methacrylate, polyvinyl alcohol, etc. are used as organic suspending agents. The reaction temperature is preferably 50 to 100°C, particularly preferably 50 to 85°C, after 2 to 10 hours of polymerization.
It is necessary to polymerize at 90-100°C for 3-5 hours. As an initiator that can be used in the present invention, 10
It is necessary that the time half-life is 55-80℃,
Such initiators include azo initiators such as azobisisobutyronitrile, 2,2azobis(2,4-dimethylvaleronitrile), benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, etc. peroxide etc. can be used. Further, in the copolymerization, it is preferable to use a chain transfer agent, and examples thereof include alkyl mercaptans such as butyl mercaptan and octyl mercaptan. The copolymerization component used in the present invention is O-methylphenylmaleimide, but the effects of the present invention will not be exhibited even if other N-substituted maleimides are used. For example, when copolymerizing with phenylmaleimide, chlorophenylmaleimide, nitrophenylmaleimide, butyl phenylmaleimide, etc., the copolymerization property is poor and it is difficult to achieve the effect of increasing the heat deformation resistance temperature, and the color becomes reddish-yellow. This causes problems such as discoloration. It also has a political flaw in that it cannot be molded at high temperatures. As the copolymerization component used in the present invention, copolymerizable monomers such as acrylic esters and styrene can be used as the third component within a range that does not reduce the effects of the present invention. Example 1 A monomer solution consisting of 90 parts by weight of methyl methacrylate, 10 parts by weight of O-methylphenylmaleimide, 0.25 parts by weight of t-butylperoxy 2-ethylhexanoate, and 0.26 parts by weight of octyl mercaptan,
It was suspended in a suspension phase consisting of 250 parts by weight of water and 1 part by weight of potassium polymethacrylate in a polymerization machine equipped with a jacket, and heated water was passed through the jacket to increase the polymerization temperature to 80°C.
Polymerization was started. The polymerization temperature was raised to 95°C 120 minutes after the start of polymerization, and the reaction was continued for an additional 300 minutes to complete the reaction. The obtained polymer was cooled, washed, and dried to obtain beads with a diameter of 0.3 mm. This bead is 65mmφ
The mixture was pelletized using a vented extruder at an extrusion temperature of 305°C and a vent vacuum of 10 mmHg. The obtained pellets were injection molded using an injection molding machine (IS-75 manufactured by Toshiba Machine) to prepare test pieces for measuring heat distortion temperature (HDT). The test results are shown in the table. The injection molding temperature was 260°C. Examples 2 to 8 and Comparative Examples 1 to 7 Copolymers having various monomer compositions shown in the table were produced in the same manner as in Example 1. The experimental results of copolymers according to the present invention (Examples 2 to 8) and copolymers different from the present invention (Comparative Examples 1 to 7) are shown in the table. Comparative Example 8 The beads obtained in Example 1 were pelletized using a 60 mmφ vented extruder. Normal extrusion conditions: Vent vacuum degree is 50mmHg, extrusion temperature is
It was 250℃. The residual monomer content of the resulting pellets was 1.75% by weight. A test piece was prepared by injection molding in the same manner as in Example 1. The evaluation results are shown in the table. [Effects] According to the present invention, a copolymer with a residual monomer content of 1.0% by weight or less can be obtained, and the obtained copolymer has excellent heat deformation resistance, heat decomposition resistance (for example, generation of silver),
It is a copolymer with excellent high-temperature moldability, low intrinsic birefringence, and extremely high transparency.

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Claims (1)

[Claims] 1 60-97.5% by weight of methyl methacrylate units,
In a method for producing a copolymer consisting of 2.5 to 40% by weight of O-methylphenylmaleimide units by suspension polymerization, an initiator with a 10-hour half-life of 55 to 80°C is added to 100 parts by weight of the above monomer. Use 0.1-0.5 parts by weight
The first stage polymerization was carried out at a temperature of 50 to 85 °C for 2 to 10 hours, and then at a temperature of 90 to 100 °C for 2 to 5 hours.
The second stage of polymerization was carried out, and the obtained beads were
A method for producing an acrylic resin, which comprises degassing and removing volatile components at a temperature of 315°C to 315°C and a vent vacuum of 50 mmHg or less.