JPS6289710A - Production of methacrylic resin - Google Patents

Abstract

PURPOSE:To obtain the titled resin having little deterioration and coloring at high temperature, by heating a methacrylic polymer composition at high temperature, making it flow in a degassing tank having space at the top to remove a volatile component and reducing a volatile content to <=a specific value by a vented extruder. CONSTITUTION:A methacrylic polymer composition polymerized by a perfect blending polymerizer 1 is heated to 200-300 deg.C by a preheater 3, made to flow in a degassing tank 4 having sufficient space at the top of the tank kept at atmospheric pressure or 20kg/cm<2> gauge pressure, to eliminate most of the volatile component. Then, the composition is fed to an extruder 5 having vents 6, 7 and 8, which is connected to the bottom of the tank to reduce the remaining volatile content of the polymer composition to <=1.0wt% and it is extruded from an extrusion die 9, to give the aimed resin.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a process for producing methacrylic resin molding materials, extruded plates, etc. by solution polymerization or bulk polymerization. More specifically, the present invention relates to a method for removing 70% by weight of unreacted 25S monomer, solvent, and polymerization byproducts contained therein from a methacrylic resin composition produced by solution polymerization or bulk polymerization.

Methacrylic resins are widely used in lighting equipment, signboards, various decorative items, nameplates, etc. due to their excellent transparency, good mechanical properties, workability, and beautiful appearance of molded products. It is also used in automobile parts, tableware, etc.

In particular, its use has recently been expanded to optical applications such as lenses, optical disks, and optical fibers, and in addition to the above properties, it is a material with excellent optical purity, which means a reduction in minute foreign matter, a reduction in volatile components such as residual monomers, and a high molecular weight gel. Minimization is required.

Solution polymerization and bulk polymerization are known as excellent methods for producing methacrylic resins with excellent optical purity.

In solution polymerization and bulk polymerization, it is extremely difficult to remove volatile components from a methacrylic resin composition containing a large amount of unreacted monomers (25 to 70% by weight), solvents, and polymerization reaction by-products. It is an important technology for

(Prior art and problems) The basic method for removing volatile components such as unreacted monomers, solvents, and polymerization reaction by-products is to heat a polymer composition to a high temperature and introduce it into a vacuum atmosphere to volatilize it. This is a method of separation. If the volatile component is less than 10% by weight, it can be efficiently separated using a multi-stage vented twin-screw extruder, etc., and the volatile component remaining in the final methacrylic resin is 10% by weight or less. Therefore, it is possible to obtain a methacrylic resin molding material or an extruded plate with good physical properties.

When the amount of volatile components exceeds 10% by weight, when using a multi-stage vented extruder, the resin foams violently due to the gasification of the volatile components, which often causes problems such as the vent hole being blocked by the foamed polymer. This made it difficult to operate stably for a long time.

In addition, it is difficult to raise the temperature of the polymer composition when a multi-stage vented extruder is not used, the method of transporting the high viscosity fluid after volatile components has been removed, and This causes problems such as deterioration and side reaction products.

Polymer deterioration, coloring, and side reaction products caused by long-term residence at high temperatures are fatal drawbacks to methacrylic resins with excellent optical purity, which is the object of the present invention, and cause problems in industrial use.

Conventionally, methods for producing molding materials by removing volatile components such as unreacted monomers and/or solvents and by-products from polymer compositions produced by bulk polymerization and solution polymerization mainly focus on styrene resins. Discussions are progressing, for example,
It is disclosed in Japanese Patent Publication No. 5-8557, Japanese Patent Publication No. 38-120, Japanese Patent Publication No. 44-20097, Japanese Patent Publication No. 31678-1978, Japanese Patent Application Laid-Open No. 47-27872, etc.

Methacrylic resins are also disclosed in Japanese Patent Publication No. 52-17555 and Japanese Patent Application Laid-open No. 50-88197.

(Means for Solving the Problems) The present invention provides a devolatilization process method that reduces polymer deterioration, coloring, and side reaction products caused by high-temperature and long-term residence.

That is, in the present invention, when removing volatile components from a methacrylic polymer composition, the polymer composition is heated to a temperature of 200°C.
It is heated to ~300℃ and poured into a devolatilizing tank with sufficient space at the stop that is maintained at atmospheric pressure or zOψ back gauge, and after removing most of the volatile components, it is connected to the bottom of the tank. The present invention relates to a method for producing a methacrylic resin, characterized in that the residual volatile content of a polymer composition is reduced to 1.0% by weight or less by feeding the polymer composition into a vented extruder.

The methacrylic polymer composition of the present invention is mainly composed of a methacrylic polymer, unreacted monomers, solvents, and polymerization byproducts, and also contains a decomposed product of an initiator added during polymerization, a chain transfer agent, additives, etc. be.

The methacrylic polymer is obtained by polymerizing methyl methacrylate alone or a monomer mixture containing methyl methacrylate as a main monomer. Preferred monomers other than methyl methacrylate include ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, acrylonitrile, methacrylonitrile, styrene, and the like. Particularly preferably, a combination of methyl methacrylate and methyl acrylate, or a combination of methyl methacrylate and styrene is used.

It is preferable to use methyl methacrylate in an amount of 40% by weight or more. If the amount of methyl methacrylate is less than 40% by weight, it becomes difficult to obtain a colorless and transparent resin, which is a feature of the present invention.

That is, the feature of the present invention is that a first devolatilization zone using a devolatilization tank and a second devolatilization zone using an extruder with a vent are provided in order to reduce thermal deterioration of methacrylic resin and increase the devolatilization rate of residual volatile components. It is to be used together.

In the first devolatilization zone, the polymer composition is heated using a preheater, and the temperature condition of the preheater is set to 200 to 300°C.
Make it.

The heated polymer composition is allowed to flow down through a narrow outlet of the preheater into a devolatilization tank.

The pressure in the devolatilization tank is maintained at atmospheric pressure or ZOkvd gauge to cause instantaneous rapid volatilization and foaming, resulting in the formation of a very large evaporation area and the removal of volatile matter.

Since the foamed polymer composition rapidly expands in volume, the upper space of the devolatilization tank needs to have a volume 3 to 5 times the volume of the polymer composition before foaming.

During casting and falling, the polymer is cooled by latent heat of vaporization,
The temperature will be 180-280℃.

The pressure in the devolatilization tank is controlled as a driving force for removing volatile components and feeding the polymer composition to the vented extruder. Normal atmosphere □ pressure or ZOkC9/cry? Keep it on the gauge and drive. When the pressure is lower than atmospheric pressure, the devolatilization efficiency is too high and the volatile content in the polymer composition is low.
fc results and 1. The viscosity increases, making it difficult and difficult to drain. ?
-Okay! ? /crr? If it exceeds the gauge, the devolatilization efficiency will be insufficient and problems such as vent clogging will occur in vented extruders.

The residual volatile content in the polymer composition discharged from the devolatilization tank is preferably 3 to 10% by weight, and is particularly controlled so as not to exceed 10% by weight. Residual volatile content is 1
If the weight exceeds 0.00, operation of the vented extruder, which is the next step after the devolatilization tank, becomes virtually impossible due to troubles such as clogging of the pent section by a large amount of foamed volatile components. If the amount is less than 3% by weight, the viscosity may change from several thousand voids to several thousand voids, depending on the molecular weight of the resin, and may become extremely viscous, making it extremely difficult to discharge. As a result, the residence time becomes longer, which tends to cause coloring and deterioration of the resin, which poses a problem.

The feature of the present invention is that by providing two stages of devolatilization zones, the residence time of the polymer composition during high-temperature devolatilization in the first stage is shortened as much as possible, and coloration of the resin and generation of polymerization byproducts are prevented. It is in. The residence time is preferably 10 to 30 minutes.

As the vented extruder used as the second devolatilization zone of the present invention, a twin-screw multi-stage vented extruder is preferred. Particularly preferably, a twin-screw extruder with a three-stage vent is used.

The L/D of the extruder is usually 20 to 40.

The extruder in the second devolatilization zone is heated at a temperature of 200 to 220°C at the first stage vent part, and the pressure is between atmospheric pressure and 1.5°C.
o ky/cry? Drive with a gauge. In particular, pressure is necessary to prevent air from leaking from the screw shaft sealing gland, and when operating under negative pressure, oxidative deterioration of the polymer occurs due to air leakage, resulting in coloring of the resulting polymer. Undesirable.

The temperature after the second vent part and third vent part is 230 to 280.
℃, preferably 240-270℃, the pressure is 10 Qt
Rryslig or less is preferable. If the temperature is less than 230°C, the viscosity becomes very high, making it difficult to remove volatile components. If the pressure exceeds 1 g (100 mm), the removal efficiency of volatile matter will be extremely reduced, which is not preferable.

(Effects) The present invention is a devolatilization process method that produces less polymer deterioration, coloring, and side reaction products due to high temperature and long periods of time.

Example 1 Ordinary solution polymerization was carried out using a fully stirred tank 1 as shown in Fig. 1, and the average molecule [1] consisting of 99% by weight of methyl methacrylate and 1% by weight of methyl acrylate was measured by GPC.
50% methacrylic resin, unreacted monomer, initiator,
A polymer composition containing 50% of chain transfer agent residue, decomposition products, and solvent was obtained.

This is regularly taken out by a metering pump 2, heated to 260° C. by a preheater 3, and cast into a devolatilization tank 4. The devolatilization tank has a pressure of 0.8 to 9/crI? The gauge and temperature were maintained at 200°C to remove residual volatile components. The polymer having a residual volatile component of 7.5 mA% is discharged from the lower part of the devolatilization tank and is allowed to fall into the supply section of the twin-screw extruder 5. The first stage devolatilization section 6 of the twin-screw extruder 5 has a pressure of about 0.5φ and a temperature of 220.
℃, and the second devolatilizing section 7 is maintained at so+utl(g, 25
The remaining volatile components were removed under the conditions of 0° C., 301 g in the third devolatilizing section 8, and 250° C. The final residual volatile component of the resin extruded from the extrusion die 9 was 0.34% by weight.

A test piece with a thickness of 3 Im was molded using a 3 oz injection molding machine, and the appearance was colorless and transparent and very good.

Example 2 Ordinary solution polymerization was carried out using the fully stirred tank 1 shown in Figure 1, and 70% by weight of methyl methacrylate and 30% by weight of styrene were used.
A polymer composition containing 45% of a methacrylic resin having a weight average molecular weight of 150,000 as measured by GPC, and 55% of an initiator, residues of chain transfer agents, decomposition products, and a solvent was obtained. This is regularly taken out by a metering pump 2, heated to 240° C. by a preheater 3, and cast into a devolatilization tank 4. The devolatilization tank has a 1.1 Δ gauge and is maintained at 200°C to remove residual volatile components. A polymer containing 9.0% by weight of residual volatile components is discharged from the lower part of the devolatilization tank and dropped into the supply section of the twin-screw extruder 5.

The first stage devolatilizing section 6 of the devolatilizing extruder 5 is maintained at a pressure of about 0.5° C. and the ground temperature is sometimes maintained at 220° C., and the second devolatilizing section 7 is maintained at a pressure of about 0.5° C.
, 250°C conditions, third devolatilization section 8 30mmHg, 25
Remaining volatile components were removed at 0°C.

The final residual volatile component of the resin extruded from the extrusion die 9 was 0.24% by weight.

A test piece with a thickness of 3n was molded using a 3-ounce injection molding machine, and the appearance was colorless and transparent, and the appearance was very good.

[Brief explanation of drawings]

FIG. 1 is a flow sheet of one embodiment of the present invention. In Fig. 1, 1 is a complete mixing polymerization reactor, 3 is a metering pump, 3 is a preheater, 4 is a devolatilization tank, is a twin-screw extruder, 6,
7.8 indicates the extruder ventro (first, second, third), and 9 indicates the strand die.

Claims (2)

[Claims] (1) When removing volatile components from a methacrylic polymer composition, the polymer composition is heated to a temperature of 200 to 300°C, and the upper part is maintained at atmospheric pressure to 20 kg/cm^2 gauge. After the polymer composition is cast into a devolatilization tank having a space of 1.0 mm to remove most of the volatile components, the remaining volatile components of the polymer composition are removed by supplying the polymer composition to a vented extruder connected to the bottom of the tank. A method for producing methacrylic resin characterized in that the content is 0% by weight or less. (2) The methacrylic polymer composition contains 80% by weight or more of methyl methacrylate units and has a molecular weight of 7 to 7 as measured by GPC.
150,000 polymer, and a volatile component consisting of 25 to 70% by weight of unreacted monomers, solvents, and polymerization byproducts (3) The methacrylic polymer composition contains 40 to 70% by weight of methyl methacrylate units and 30 to 6 styrene units.
0% by weight of a copolymer with a molecular weight of 70,000 to 150,000 as measured by GPC, and a volatile component consisting of 25 to 70% by weight of unreacted monomers, solvents and polymerization by-products. Method for producing methacrylic resin described in section 1)