JPS61272215A - Production of heat-resistant, solvent-resistant acrylic copolymer - Google Patents

Abstract

PURPOSE:To obtain the titled copolymer having improved thermal decomposition properties, causing a few silver streaking, by polymerizing a methacrylic acid alkyl ester, etc., by the use of an azo compound, etc. as a radically polymerization initiator and a polyfunctional mercaptan as a chain transfer agent. CONSTITUTION:(A) 80-95wt% methacrylic acid alkyl ester is polymerized with (B) 0.5-5wt% acrylonitrile, and (C) 2-15wt% methacrylonitrile in the presence of (D) 0.01-2wt% (based on monomers) of a peroxide (e.g., lauroyl peroxide, etc.) or an azo compound (e.g., azobisisobutyronitrile, etc.) as a polymerization initiator and (E) 0.02-3wt% (based on monomer) of a polyfunctional mercaptan (e.g., thioglycolic ester of pentaerythritol, etc.) as a chain transfer agent preferably by suspension polymerization at 60-95 deg.C, to give the aimed copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an uncolored methacrylic copolymer with improved thermal decomposition properties.

More specifically, the present invention relates to a very practical method for producing a methacrylic copolymer having excellent heat decomposition resistance, solvent resistance, transparency, and heat deformation resistance.

(Industrial Application Field) Generally, polymethyl methacrylate resin or methacrylic resin containing methyl methacrylate as a main component has transparency,
Due to its excellent properties such as surface gloss, mechanical strength, and moldability, it is used in a wide range of fields such as automobile parts, electrical parts, and displays. Vacuum-formed, heat-processed or injection-molded methacrylic resin molded products have a beautiful appearance and are widely used for decoration.
When performing secondary processing such as dyeing, cutting, surface finishing, adhesion, bending, interlocking, perforation, and engraving, there are many opportunities for contact with organic solvents in a gas phase, liquid state, or mist. In such cases, depending on the type of solvent used, cracks may occur in the molded product (bi-cracks). , mechanical imbalance that occurs during mold filling, bending, compression, etc., as well as swelling due to moisture absorption and solvent intrusion (2) Strain energy is accumulated on the surface and inside of the molded product. It is thought that the intrusion of solvent into or near this accumulated area breaks the balance between the strength of the base material and this strain energy, causing cracks to occur there.This is what is called environmental stress. This is a phenomenon called a crack.

The present inventors conducted research on a copolymer that has sufficient solvent resistance to cope with all the conditions that acrylic resin molded products are expected to encounter, and has other properties equivalent to that of acrylic resin. He discovered a copolymer made by blending ester and unsaturated nitrile monomers in a specific ratio and filed a patent application. (Patent Application No. Shoj9-/l/g74) However, when this copolymer is injection molded or extruded like conventional methacrylic resins, the molding temperature (22
0-300℃) and thermal decomposition start temperature (0-300℃)
Since these are close to each other, the amount of residual residual particles in the molded product tends to increase due to thermal decomposition, and furthermore, the appearance of the molded product is significantly impaired due to the large amount of silver generated.

An increase in the residual monomer has a plasticizing effect (secondary effect), which lowers the heat deformation temperature of the molded product, and its use is restricted in applications that require shape stability at high temperatures. Due to the large number of parts, problems arise when used for large molded products at high temperatures.

Therefore, in order to improve the heat deformation resistance of this copolymer and eliminate the generation of silver, it is necessary to suppress the thermal decomposition of the methacrylic resin.

(Prior Art) Conventionally, it has been thought that one of the causes of thermal decomposition of methacrylic resins is related to the amount of double bonds at the end of the molecular chain. The double bond at the end of the molecular chain of the obtained methacrylic resin is generated by disproportionation termination in radical polymerization, and is influenced by the type and amount of radical, and polymerization conditions. Therefore, patent applications have been filed regarding the type and amount of peroxide as a technique for improving thermal decomposition properties. (Tokugansho! 3-7♂2da0). However, when using this method, the effect of improving the thermal decomposition properties of the copolymer of the present invention cannot be said to be sufficient.

In addition, usually a small amount of an amine-based or phenol-based additive, or an aromatic mercaptan is blended into a methacrylic resin as an antioxidant, but when using these techniques, C2 is the copolymer of the present invention. This is not preferable because the combined resin will be colored.

(Problems to be Solved by the Present Invention) The present inventors propose a method for producing a copolymer with good thermal decomposition properties, which could not be achieved using conventional techniques.

(Means for Solving the Problems) The present inventors have discovered that thermal decomposability can be dramatically improved by using a specific radical initiator and a polyfunctional mercaptan, and have thus arrived at the present invention.

The present invention also provides a method for producing a copolymer with excellent thermal deformation resistance and less silver generation as a result of improved thermal decomposition.

In other words, the present invention is a methacrylic acid alkyl ester! θ～
Rij Weight Section, Acrylic A Nitrile 0.5~! Weight section methacrylonitrile a~no! When polymerizing a copolymer consisting of 0.0% by weight per monomer weight as a polymerization initiator.
A methacrylic resin characterized in that it is polymerized by adding 0.07 to 2% by weight of a peroxide azo compound and further a polyfunctional mercaptan of 0.02 to 3% by weight per monomer as a chain transfer agent. The present invention relates to a manufacturing method.

As the methacrylic acid ester unit used in the copolymer of the present invention, methyl methacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate are preferred. Particularly preferably, methyl methacrylate is used. The number of methacrylic acid ester units in the copolymer is 10~! It is necessary and especially preferable to be a weight person! In the evening, I was in charge of θ weight.

If it exceeds 95% by weight, it becomes difficult to improve solvent resistance, and if it is less than 0% by weight, colorless transparency and heat deformation resistance are impaired, which is not preferable.

The acrylonitrile unit used in the copolymer of the present invention is 0. T~! It is necessary to have a weight ratio of 1 to 3 weight ratios. If the weight ratio is exceeded, the reddish-yellow color of the molded product will become stronger, which is undesirable. 0. ! If it is less than the weight ratio, no improvement in solvent resistance can be expected.

The number of methacrylonitrile units used in the copolymer of the present invention is 2~/! It is necessary that the ratio is by weight, and particularly preferably 3 to /θ weight ratio.

If it exceeds 75% by weight, polymerization productivity will deteriorate and it will be difficult to supply the product at a low cost industrially, and furthermore, thermal decomposition will be severe during injection molding, resulting in an increase in residual monomer in the molded product.
This is undesirable because it lowers DT.

If the weight ratio is less than 2, no improvement in solvent resistance can be expected.

What is the weight average molecular weight of the copolymer? -200,000, and if it is less than ♂10,000, the mechanical strength will drop significantly and the solvent resistance will not be good. If the value exceeds θ, the melt viscosity becomes too high to be used during injection molding.

Suspension polymerization, emulsion polymerization, and bulk polymerization can be used to obtain the copolymer of the present invention. Although continuous bulk polymerization can be carried out using a high temperature polymerization initiator, suspension polymerization is particularly preferred from the viewpoint of economical efficiency.

As the chain transfer agent, polyfunctional mercaptan is particularly preferred from the viewpoint of molecular weight control effect and thermal stability of the copolymer. When aliphatic mercaptan and thioglycolic acid ester are used, the resulting copolymer has poor thermal decomposition properties. The optimum polymerization temperature for suspension polymerization is ≦θ to 5°C.

Azo-based initiators are suitable as polymerization initiators, and when using peroxides such as lafuroyl peroxide and t-butyl peroxy 2-ethylhexanoate, the effect of improving thermal decomposition is that of azobisisobutyroyl peroxide. Nitrile, dimethyl 2.2'azobisisobutyrate, azobis(2,
4t dimethylvaleronitrile), /, /'azobis/-
It is not as good as azo initiators such as cyclohechitin carbonitrile.

As the chain transfer agent, polyfunctional mercaptan is particularly preferred from the viewpoint of molecular weight control effect and thermal stability of the resin.

When aliphatic mercaptans and thioglycolic acid esters are used, the thermal decomposition properties of the resins obtained are significantly high.

The polyfunctional mercaptan that can be used in the present invention includes at least one type of thioglycolic acid ester selected from pentaerythritol, trimethylolpropane, or ethylene glycol, or at least one type selected from pentaerythritol, trimethylolpropane, or ethylene glycol. It is preferable to use 3-mercaptopropionic acid ester.

Plasticizers, mold release agents, and the like can be used in the resin of the present invention as long as they do not impair the effects of the present invention.

The residual monomers in the copolymer were determined by a conventional gas chromatography method.

The heat distortion temperature (HDT) was measured in accordance with the conditions specified in A8TM-6 G♂.

(Measurement of Molecular Weight by GPC) Molecular weight measurement by GPC is generally carried out as described in the literature [Gel Chromatography (Basic Edition) by Takeda et al., published by Kodansha, pp. 97-72.2].

For example, the molecular weight of the copolymer of the present invention was measured as follows.

As a column, H2O-2θ, Yu0 (manufactured by Takasugi Seisakusho ■),
A calibration curve was created using two standard polystyrene tubes manufactured by Pressure Chemical Co., Ltd. The elution curve obtained using a sample solution in which copolymer 75■ is dissolved in methyl ethyl ketone 3θ- is divided into equal parts, the height at the division points is measured, and Mw is determined by the following formula.

However, Hi is the height of the elution curve at the dividing point (:), Mi (
p) is the molecular weight of standard polystyrene at dividing point i, Q
m and Qp are the Q factors of the copolymer and polystyrene, and are expressed as da0 and g/, respectively.

(Measurement of thermal decomposition index α) Using pyrolysis gas chromatography, the copolymer was decomposed in an N2 atmosphere at 4t-t0°C for 60 minutes (all the decomposed gases decomposed into two were detected and integrated, and this was also 3 at 270℃
Accumulate the gas decomposed and generated in 0 minutes.Let this be Y, and calculate α by setting the thermal decomposition index α=Y/X.

Solvent resistance tests for molded products are carried out at 23°C and relative humidity! 0
The moisture in the molded product is adjusted to 0.3 to 0 in an atmosphere of
．． The concentration was set to 6% by weight.

The specimens were immersed in each solvent at 23° C. for a certain period of time, and the occurrence of cracks was observed.

Example/Methacrylic acid methacrylic acid! , θ parts by weight, θ parts by weight of methacrylonitrile, 7.0 parts by weight of acrylonitrile, t-butylperoxy 2-ethylhexanoate θ, 0 parts by weight, pentaerythritol tetrakis (thioglycolate) 0.4t 3 A monomer solution consisting of 2 parts by weight of water is suspended in a suspension phase consisting of 2 parts by weight of water and 7 parts by weight of potassium polymethacrylate in a jacketed polymerization machine, and hot water is passed through the jacket to maintain the polymerization temperature. Polymerization was initiated at θ°C. 300 minutes after the start of polymerization, the polymerization temperature was raised to 9t°C (2 t°C), and the reaction was continued for another θ minute to complete the reaction. The obtained polymer was cooled, washed, and dried to form beads with a diameter of 0.3 + m. I got it.

As a result of analyzing the copolymer composition in the molded product using gas chromatography, it was found that the weight ratio was 95 methyl methacrylate units, 95% methacrylonitrile units, Q% by weight, acrylonitrile units/, θ weight ratio, which was the same as the seven-mer composition. Met.

These beads were pelletized using a 3θteaf3 vented extruder at an extrusion temperature of 260° C. and a vent vacuum of 30 mHg. The obtained pellet was injection molded using an injection molding machine (M-20θ/♂0θDM manufactured by Taki Seisakusho) to obtain a flat plate-shaped molded product with dimensions /θθ×/θ0×3ffi11. Silver was observed due to thermal decomposition during injection molding.

As a result of measuring the residual upper mass in the molded article, it was found to be 0.3/wt%.

The heat distortion temperature (HDT) was 9°C on September 9th.

The weight average molecular weight Mw is /θ,! 1,000, and the thermal decomposition index α is 1.
It was 0.

(Solvent resistance test) Molded products at 23℃ and relative humidity! Conditions were adjusted in a σ-related atmosphere. The moisture content in the molded product was in the O, S weight ratio. 23℃
5 each for gasoline, isopropyl alcohol, and xylene.
The samples were immersed for 3 hours and 3 minutes, and the occurrence of cracks was observed.

The results are shown in Table/.

Example 2 Polymerization was carried out using the same apparatus and conditions as in Example, except that the copolymer composition, type of chain transfer agent, and temperature were changed, and the results shown in Table 1 were obtained. The thermal decomposition index α of both is! The injection-molded pieces had a relatively small size, and the appearance of the injection molded pieces at 0°C was also good. Solvent resistance evaluation by dipping method also showed good results.

Comparative Example/~j Monofunctional mercaptan (EHTG, n
-OM) results are shown in Table/. The thermal decomposition index α was extremely large, and due to thermal decomposition during molding, there was a large amount of residual slag in the molded piece, and the heat distortion temperature (HDT) was low. Further, silpa streaks were observed in the injection molded piece at 210°C.

Comparative Example 6 When the VAN content in the copolymer composition is less than 3% by weight, the solvent resistance is extremely poor.

Examples 6 to 3 The results of experiments carried out in the same manner as in Examples 6 to 3 are shown in Table 2, except that AIBN was used as the initiator.

In all cases, the thermal decomposition index α was as small as 6°, and the appearance of the injection molded pieces at 2♂θ°C was good.

Comparative example 7~? Table 2 shows the results when monofunctional mercaptan (n-OM) was used as the chain transfer agent. The thermal decomposition index α was large, the amount of residual slag in the molded piece was large, and silver streaks were generated in the injection molded piece at ♂θ°C.

As a comparative example, nitrile monomers (MAN, AN
) General acrylic resins that do not contain these compounds have poor solvent resistance.

(Left below) Reagent list Solvent resistance evaluation A short piece of molded piece is immersed in a solvent for a predetermined period of time, and the occurrence of microcracks is observed and evaluated.

Molding conditions: 240℃ injection molding

Claims (1)

[Claims] 1) 80 to 95% by weight of methacrylic acid alkyl ester,
When polymerizing a copolymer consisting of 0.5 to 5% by weight of acrylonitrile and 2 to 15% by weight of methacrylonitrile, 0.01 to 2% by weight of peroxide or azole per monomer weight is used as a polymerization initiator. A method for producing a methacrylic resin characterized by adding a compound and further 0.02 to 3% by weight of a polyfunctional mercaptan per monomer as a chain transfer agent and polymerizing 2) Pentaerythritol as a polyfunctional mercaptan;
3) The production method according to claim 1, characterized in that at least one thioglycolic acid ester selected from trimethylolpropane or ethylene glycol is used. 3) Pentaerythritol as the polyfunctional mercaptan;
Claim 1, characterized in that at least one type of 3-mercaptopropionic acid ester selected from trimethylolpropane or ethylene glycol is used.
Manufacturing method described in section