JPH02117946A - Production of methacrylic resin with high thermal stability - Google Patents

Abstract

PURPOSE:To obtain the title resin with no offensive odor by admixing a monomer such as methyl methacrylate with a specified amount of a dithiol compound followed by polymerization. CONSTITUTION:(A) 100 pts.wt. of either methyl methacrylate alone or mixture comprising >=50wt.% of methyl methacrylate and another vinyl compound copolymerizable therewith (e.g., methyl acrylate, maleic anhydride is admixed with 0.01-0.5 (pref. 0.005-0.3) pts.wt. of dithiol compound (pref. glycol dimercapto acetate, glycol dimercapto propionate or dimercapto decane) to effect dissolution, and the resultant system is polymerized using a polymerization initiator (e.g., organic peroxide, azo compound), molecular weight regulator (e.g., aliphatic mercaptan), etc., thus obtaining the objective methacrylic resin with high thermal stability.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a methacrylic resin with excellent thermal stability. The present invention relates to a method for producing a methacrylic resin with improved thermal stability, which involves adding and mixing the methacrylic resin and then polymerizing the resin.

(Prior art) Methacrylic resin is widely used as a resin with excellent transparency, surface gloss, weather resistance, chemical stability, etc., but it has poor thermal stability during molding processing, and it also has problems with molding conditions. Since the decomposition temperatures of the methacrylic resin are close to each other, the moldable area is narrow. The main reason for the poor thermal stability of methacrylic resin is the thermal decomposition of methacrylic resin at molding temperatures, so in order to improve production stability, it is necessary to prevent thermal decomposition of methacrylic resin (mainly the formation of the monomer). It is necessary to take measures to

Conventionally, methods of adding amine compounds, metal soaps, hindered phenol compounds, etc. have been proposed in order to prevent thermal decomposition of thermoplastic resins. When used, there are few practical ones because they have no effect, reduce transparency, weather resistance, etc., or are colored.

(Problem to be Solved by the Invention) There is also a method of adding a certain thio compound to methacrylic resin. For example, in Japanese Patent Publication No. 38-14491, alkyl or aromatic mercaptans are added to methacrylic resin and heated at 100°C or higher. Heat treatment is performed to improve thermal stability, but when molded at a high temperature of 260° C. or higher, there are problems such as insufficient thermal stabilizing effect and strong mercaptan odor. In Japanese Patent Publication No. 52-12739, polyvalent thiols such as trimethylolpropane tris (thioglycolate) and pentaerythritol tetrakis (thioglycolate) are used for heat stabilization, but they cause increased coloration and poor weather resistance. A decrease in Mata Tokko 1987
The use of alkyl disulfides as in No. 9392 and JP-A No. 51-36258 has good thermal stability effects, but has disadvantages such as coloring, producing mercaptan odor during molding, and worsening the working environment. However, the reality is that almost no technology has been put into practical use so far.

Therefore, it is an object of the present invention to provide a method for producing a methacrylic resin that is imparted with thermal stability without impairing the original characteristics of the conventional methacrylic resin described above.

(Means for Solving the Problems) The present inventors have completed the present invention by discovering that by using a specific dithiol compound, it is possible to improve the thermal stability that impairs the characteristics of methacrylic resin.

That is, in the present invention, when polymerizing methyl methacrylate alone or a monomer mixture containing 50% or more of methyl methacrylate, 0.001 to 0.5 of the dithiol compound is added to 1 part by weight of 100 monomers. The present invention relates to a method for producing a methacrylic resin having excellent thermal stability, which involves mixing and dissolving one part of methacrylic resin and then polymerizing the resin.

The methacrylic resin in the present invention is a homopolymer of methyl methacrylate, or contains 50% by weight or more of methyl methacrylate, and contains other copolymerizable vinyl compounds such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, Acrylic acid esters such as cyclohexyl acrylate, methacrylic acid esters such as ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, cyclohexyl methacrylate, inbornyl methacrylate, and acrylic acid, methacrylic acid,
Maleic anhydride, styrene, α-methylstyrene, P-
It refers to a binary or multicomponent copolymer with methylstyrene, acrylonitrile, methacrylonitrile, etc.

To achieve improved thermal stability in the present invention,
Methyl methacrylate alone or 50 methyl methacrylate
Examples of the dithiol compound added to the monomer mixture constituting the copolymer containing % or more include glycol dimercaptoacetate, glycol dimercaptoprobionate, dithiol terephthalate, dimercapto diethyl ether, dimercaptodecane, and dimercapto. Examples include dodecane, and particularly preferred compounds are glycol dimercaptoacetate, glycol dimercaptoprobionate, and dimercaptodecane.

The amount of these compounds to be added is within the range of 0.001 to 0.5 parts per 100 parts of methyl methacrylate alone or a monolayer mixture containing 50% or more of methyl methacrylate. but more preferably 0.005
-0.3 parts by weight. If the amount added is less than 0.001 part by weight, the heat stabilization effect will be poor, while if it exceeds 0.5 part by weight, the heat distortion temperature may be lowered, the molded product may be colored, or a strange odor may be felt during molding. This is not desirable as it may cause

As a method for obtaining the methacrylic resin of the present invention, known polymerization methods such as cast polymerization, suspension polymerization, milk polymerization, Fg liquid polymerization, etc. can be used. A method in which, when methyl methacrylate alone or a monomer mixture containing 50% or more of methyl methacrylate is polymerized by the above polymerization method, dithiols are added to the monomer or monomer mixture, mixed and dissolved, and then polymerized. is taken. In this case, commonly used polymerization initiators such as organic peroxides or azo compounds are used, and aliphatic mercabutane may be used in combination as a molecular weight regulator.

Further, coloring agents such as dyes and pigments, plasticizers, lubricants, ultraviolet stabilizers, etc. can be added at the same time during polymerization or pelletization.

(Effects of the Invention) A remarkable advantage of using the dithiol compound of the present invention is that the resin obtained by the production method of the present invention has excellent thermal stability;
In addition, since the resin does not give off any unpleasant odors, the molding company can easily produce complex and large molded products at higher temperatures without fear of coloring due to thermal decomposition of methacrylic resin, silver streaks, etc. And it can be obtained stably.

(Example) The present invention will be specifically explained below with reference to Examples.

Additives used in the examples are represented by the following abbreviations.

Gelcol dimercaptoacetate (Gr) MA), υ Gelcol dimercaptopropinate (G D M P
)-dimercaptodecane (D M D ) In the examples, % represents 1% by weight, and parts represent parts by weight.

In addition, in the examples, the Jf value of thermal stability was expressed using the following method.

Using an injection molding machine (N-70A type manufactured by J Nikki Steel Works),
Cylinder temperature 260~270°C1 injection pressure 600~
A flat plate of 70 x 200 x 3 (thick) size was molded under the conditions of 1100 ktr/c+&, a mold temperature of 50°C, and a cooling time of 180 seconds, and the remaining monomer lid in this molded product was measured by gas chromatography to determine the remaining monomer cap. 047% or less at cylinder temperature 260°C, cylinder temperature 270°
When the C content was 1.0% or less, it was considered to have a thermal stability effect.

In addition, if the molded product became discolored or silver streaks occurred, it was determined that there was no thermal stability effect.

Example 1 20 kg of a monomer mixture containing lauroyl peroxide and octyl mercaptan with a composition of 99% methyl methacrylate and 1% ethyl acrylate, and 2 kg of GDMAo.
:/B was dissolved and put into 40kr of pure water in which a dispersion stabilizer had been dissolved in advance in a 751 pressure-resistant reaction tank, and suspension polymerization was carried out at 80°C. After the exothermic peak, 125"C"C post-polymerization was carried out. After cooling, the copolymer beads were collected. After the obtained beads were washed and dried, they were transferred to 40 Ill/li Ben 1 using an extruder at a cylinder temperature of 200 to 250°C, a screw rotation speed of 60 ru, and a pen of 1 to (vacuum degree) of 50 +.
Pelletization was performed under +0 conditions. The residual amount of monomer in the pellet was 0.25%.

As a result of evaluating the thermal stability of this pellet, there was no abnormal odor during injection molding, and the molded product was free of silver streaks and coloration. In addition, the amount of residual monomer in the molded product was 0.53% at cylinder temperature of 260°C and 0.62% at 270°C, and the increase in monomer was small, indicating good thermal stability. .

Example 2 Monomer mixture 'Jl containing azobisisobutyroni-1-lyl, octyl mercaptan, and stearyl alcohol with a composition of 99% methyl methacrylate and 1% methyl acrylate.
) 20kf to DMDo, 06kr to lδ,
This was put into a 751 pressure-resistant reaction tank filled with 30 kg of pure water in which a suspension dispersant had been dissolved in advance, and suspension polymerization was carried out at 80 °C. After the exothermic peak, post-polymerization was carried out at 120 °C for 1 hour, and then cooled. Then, the copolymer beads were taken out. The obtained beads were pelletized in the same manner as in Example 1. The residual amount of monomer in the pellet was 0.16%. As a result of evaluating the thermal stability of this pellet, there was no abnormal odor during injection molding, and the molded product was free of silver streaks and coloration.

In addition, the amount of residual monomer in the molded product is determined at cylinder temperature 260
There was almost no decomposition at 0.55% at 270°C and 0.64% at 270°C, and the thermal stability was good.

Example 3 GDMPO was added to 20 kf of a monomer mixture containing tert-butyl peroxy 2-ethyl hexanoate, n-dodecyl mercaptan, and stearic acid monoglyceride with a composition of 98% methyl methacrylate and 2% methyl acrylate.
,001 kg was dissolved and charged into a 751 pressure-resistant reaction tank filled with 30 kg of pure water in which a suspending and dispersing agent had been dissolved in advance, and tlJ polymerization was carried out at 70°C. After the exothermic peak, 12
After polymerization was carried out at 0° C. for 1 hour, the mixture was cooled, and the copolymer beads were taken out and the resulting beads were pelletized in the same manner as in Example 1. Monomer residual 1 in pellet is 0.15
%Met. As a result of evaluating the thermal stability of this pellet, there was no abnormal odor during injection molding, and there were no silver streaks or coloring in the molded product. In addition, the amount of residual monomer in the molded product is 0.58% at a cylinder temperature of 260°C, 27%.
Thermal stability was good at 0.69% at 0°C.

Comparative Example 1 Monomer mixture 2 containing lauroyl peroxide, n-octyl mercaptan, and stearyl alcohol with a composition of 98% methyl methacrylate and 2% methyl acrylate.
0kg in pure water 40k in which suspension dispersant was dissolved in advance
g into a 751 pressure-resistant reactor and heated at 80℃! V
Nurimoto polymerization was performed, exothermic peak 1 & 125°C? After performing the post-polymerization, it was cooled and the copolymer beads were taken out.The obtained beads were pelletized in the same manner as in Example 1.The residual monomer i of the pellets was 0.23%. there were.

As a result of evaluating thermal stability using this pellet, the amount of residual monomer in the molded product was 0.83 at a cylinder temperature of 260°C.
%, 1.24% at 270°C, there was a large increase in monomer, silver streaks occurred frequently in the molded product, and thermal stability was poor.

Comparative Example 2 Monomer mixture 20k containing azoisobutyronitrile, n-octyl mercaptan, and stearyl alcohol with a composition of 99% methyl methacrylate and 1% methyl acrylate.
Dissolve 2 kg of Gr) MAo in g in advance! 9
75" filled with 30" of pure water in which Ji turbidity dispersant was dissolved.
1. Pour this into a pressure-resistant reaction tank and polymerize at 70°C.
After post-polymerization was carried out at an exothermic peak of f & 120° C., the copolymer beads were collected, and the resulting beads were pelletized in the same manner as in Examples. The residual amount of monomer in the pellet was 0.22%. As a result of evaluating the thermal stability using this pellet, it was found that the residual amount of monomer was
0.48% at 60°C, 0.65% at 270°C,
The molded product did not have any defects such as silver streaks, but the molded product was colored yellow and had a mercaptan odor during molding.

Comparative Example 3 After polymerizing and forming berent in the same manner as Comparative Example 2 except that Gl)MAO, 2kf was changed to GDMPo, 0001kir, the thermal stability was evaluated. There was no coloration, but as the cylinder temperature rose, silver streaks tended to occur. The amount of residual monomer in the molded product is determined at cylinder temperature 260
It was 0.81% at °C and 1.15% at 270 °C, and there was almost no thermal stability effect.

Claims (1)

[Claims] Methyl methacrylate alone or 50 methyl methacrylate
When polymerizing a monomer mixture containing % or more, 0.001 parts by weight of the dithiol compound per 100 parts by weight of the monomer.
A method for producing a methacrylic resin having excellent thermal stability, which comprises mixing and dissolving ~0.5 parts by weight and then polymerizing the resin.