JPH11181018A - Production of transparent resin for optical material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing foreign matter of a resin suitable for optical material uses. SOLUTION: This method for producing a transparent resin for optical materials comprises producing a resin in which a foreign matter having >=5 μm size is contained in an amount of <=2,000 /g in the copolymer and total residual monomer content is <=3,000 ppm by passing an aromatic vinyl-based copolymer obtained by copolymerizing 95-30 wt.% aromatic vinylic monomer with 5-70 wt.% (meth)acrylic acid alkylester-based through a sintered metal filter in a melted state in a method for producing a transparent resin for optical materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a transparent resin for optical materials.

[0002]

2. Description of the Related Art In recent years, resin materials have been used for video recording devices such as a camera and a video camera for the purpose of improving productivity and reducing the weight. The material is also made of resin. The resin used for such an optical material is required to be transparent and to have excellent optical characteristics, and to remove foreign particles such as polymethyl methacrylate, polycarbonate, and polystyrene / polyphenylene ether alloy resin. Things are used.

Japanese Patent Application Laid-Open No. 61-90345 discloses that a transparent resin such as an acrylic resin having a limited number of foreign substances and an aromatic vinyl resin obtained by using methacrylic acid ester and styrene as a comonomer is suitable for an optical disk. JP-A-57-162135, JP-A-57-33446 and JP-A-58-88843 particularly disclose methacrylic acid esters and vinyl monomers copolymerizable therewith. It is disclosed that such a copolymer is suitable for a high-density record carrier because of its excellent fluidity and the like. However, these publications hardly describe how to produce a resin having excellent transparency and fluidity, and Japanese Patent Application Laid-Open No. 61-90345 discloses a method for reducing the amount of foreign matter. It describes only a method of filtering raw materials (monomers and the like) used, and does not mention the conditions at all.

On the other hand, Japanese Patent Application Laid-Open No. 63-57613 discloses that in a method for producing a methyl methacrylate polymer, an inert gas is introduced into a monomer solution of a raw material to reduce dissolved oxygen to 1 ppm or less. A method is disclosed in which a foreign substance is filtered with a filter of 5 μ or less and then supplied to a reaction zone. However, since a methyl methacrylate polymer has poor fluidity, it cannot be said to be a molding material suitable for obtaining a small molded product often used for an optical material. Further, Japanese Patent Application Laid-Open No. Sho 63-5
The production method disclosed in No. 7613 is a method in which devolatilization treatment is carried out before the polymerization conversion rate becomes high, which is not economical in terms of equipment for industrial implementation. There are drawbacks such as the inability to remove foreign matter generated in the volatile process.

Japanese Patent Application Laid-Open No. 63-91231 discloses a method for manufacturing an optical element in which foreign substances in a molten mixed resin composed of polystyrene and polyphenylene ether are limited to foreign substances of 1 μm or more using a burning metal filter. Have been. However, this resin also has the drawback that the flowability is very poor, the moldability is extremely poor, and the weather resistance is also poor because the main chain contains oxygen.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides transparency, optical properties and dimensional stability obtained by copolymerizing an aromatic vinyl monomer and an alkyl methacrylate monomer. When an aromatic vinyl copolymer having excellent moldability is used as a resin for optical materials such as lenses and prisms, it is an object of the present invention to provide a method for removing foreign matters in the resin by a relatively simple method. Is what you do.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that an aromatic vinyl monomer and an alkyl group having 1 to 2 carbon atoms (meth) acrylic acid. By passing an aromatic vinyl copolymer obtained by copolymerizing an alkyl ester monomer through a sintered metal filter in a molten state, it is possible to obtain the desired transparent resin for optical materials such as lenses and prisms. As a result, the present invention has been completed.

That is, the present invention provides a method for producing a transparent resin for an optical material, wherein the transparent resin for an optical material comprises 95 to 30% by weight of an aromatic vinyl monomer and an alkyl group having 1 to 2 carbon atoms. An aromatic vinyl copolymer obtained by copolymerizing 5 to 70% by weight of a (meth) alkyl acrylate monomer, wherein the aromatic vinyl copolymer is a sintered metal filter in a molten state. , To obtain a resin having 2000 / g or less foreign matters of 5 μm or more in the copolymer and a total residual monomer content of 3000 ppm or less.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The transparent resin for optical material referred to in the present invention is an aromatic resin obtained by copolymerizing an aromatic vinyl monomer and an alkyl (meth) acrylate monomer having an alkyl group having 1 to 2 carbon atoms. Refers to a vinyl copolymer.

Here, the aromatic vinyl monomer includes:
Styrene, α-methylstyrene, m-methylstyrene,
Examples thereof include p-methylstyrene, o-chlorostyrene, and p-chlorostyrene, and these can be used alone or in combination of two or more.

The alkyl methacrylate monomer having an alkyl group having 1 to 2 carbon atoms includes methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate. These may be used alone or in combination of two or more.

When polymerizing an aromatic vinyl copolymer used for a transparent resin for an optical material, the proportion of each constituent component is 95 to 30% by weight of an aromatic vinyl monomer, It is necessary that the alkyl (meth) acrylate monomer having 1 to 2 carbon atoms in the group is in the range of 5 to 70% by weight.

If the range of the aromatic vinyl monomer used exceeds 95% by weight, optical properties such as heat resistance and light transmittance are remarkably deteriorated. It is not preferable because the moldability such as moldability, mold transferability and the like and the moisture absorption property are inferior. The range of the aromatic vinyl monomer is 90 to 40% by weight, and the range of the alkyl (meth) acrylate-based monomer is 10 to 60% by weight for achieving a good balance between optical properties, moldability, and water absorption properties. %, And this range is preferable for the above-mentioned reason.

In the present invention, it is necessary that the polymerized aromatic vinyl copolymer is passed through a sintered metal filter in a molten state. Here, the sintered metal filter is preferably a thickness filtration type filter in which metal fibers (metal fibers), other furnace materials, and the like are sandwiched between meshes of the protective layer and the support layer and simultaneously sintered to be completely integrated, and in particular, The material is not particularly limited as long as it is excellent in heat resistance, pressure resistance and corrosion resistance and has a capability of removing a certain amount of foreign matter, but at least foreign matter of 5 μm or more in the resin after filtration is 2,000. / G or less, so that the filtration accuracy (the value of the particle size indicating the size at which the contaminants are removed by the sintered metal filter when the molten resin passes through the filter) is reduced. It is preferable to use 30 μm or less, particularly 20 μm or less, more preferably 5 to 2 μm.
It is desirable to use one having a thickness of 0 μm. Increasing the filtration accuracy can reduce the amount of foreign matter, especially fine foreign matter, but if the filtration accuracy is too high, the pressure loss of the sintered metal filter will increase and the productivity will decrease. Accuracy is not preferred.

In the present invention, the shape of the sintered metal filter is appropriately selected from the group consisting of a cylinder, a disk, a disk, and a tube. The installation place is not particularly limited, but the polymer including the aromatic vinyl copolymer is
When exposed to high heat history, foreign substances such as contamination are likely to be generated, so after removing residual volatile components with high heat history
(After the devolatilization step). When an extruder is used in the devolatilization step or the kneading of the additives, the extruder can be installed at the tip of the extruder. Also, during or after polymerization, or after completion of devolatilization, a part or all of the aromatic vinyl copolymer is withdrawn (to a branch pipe) and passed through a sintered metal filter in the same manner to remove foreign matter. It is also possible to remove it.
In particular, the aromatic vinyl copolymer pelletized through a devolatilization step without removing foreign matter with a sintered metal filter is extruded with a sintered metal filter installed at the tip at the stage of forming a molded pellet for an optical material. It is also possible to remove foreign matter by passing through a machine.

In the present invention, when the aromatic vinyl copolymer is passed through a sintered metal filter in a molten state to remove foreign matter, the melting temperature is 300 ° C. or less, preferably 180 to 260 ° C., and most preferably. Is in the range of 200-240 ° C. If the melting temperature is too high, a part of the aromatic vinyl copolymer is decomposed to increase the volatile content and the yellowness of the resin is undesirably increased. On the other hand, when the temperature is lower than 180 ° C., the fluidity when passing through a metal filter is deteriorated, and the pressure loss in the sintered metal filter is increased, which hinders the removal of foreign substances.

In order to allow the aromatic vinyl copolymer to pass through the sintered metal filter in a molten state, it is preferable to use an extruder. The extruder used in this case is not particularly limited, such as a single screw extruder, a twin screw extruder, and other extruders. Further, for the purpose of stabilizing the feed, a gear pump or the like can be combined with the above method. Among these methods, a method in which a sintered metal filter is installed at the extruder tip and the resin is passed through the sintered metal filter in a molten state to obtain molding pellets is also preferable from a simple and economical viewpoint. .

In the present invention, the amount of foreign matter in the aromatic vinyl copolymer after passing through the sintered metal filter is 5%.
It is necessary for the optical material having excellent transparency and light transmittance especially for lenses and prisms to have 2000 μm / g or less of foreign substances having a size of μm or more. The amount of foreign substances in the aromatic vinyl copolymer was determined by washing the pellet-shaped copolymer with methanol, dissolving with methyl ethyl ketone to obtain a 10% solution, and then using a particle counter to measure 5 μm.
It can be measured by counting the number of foreign substances described above.

Further, the total residual monomer content in the copolymer must be not more than 3000 ppm,
It is preferably at most 0 ppm. If the total residual monomer content in the copolymer exceeds 3,000 ppm, silver, mold wetting, fogging, and the like are liable to occur when molded, which is not preferable because the material is not suitable for optical material applications.

The transparent resin for optical materials produced in the present invention preferably has a yellowness of 2 or less. When the yellowness becomes 2 or more, it is used as a resin for optical materials.
Not only does the yellowness of the resin increase to impair the aesthetic appearance, but also causes a decrease in light transmittance, and when the resin according to the present invention is used for optical applications, its use range is limited. In particular, in order to maintain the yellowness at 2 or less, it is desirable to appropriately maintain the temperature condition in the molten state within the above-mentioned temperature range. Here, the yellowness referred to in the present invention refers to a value obtained by measuring a test piece having a thickness of 3 mm manufactured by injection molding according to JIS-K7103.

[0021]

EXAMPLES The present invention will be described in more detail with reference to specific examples below, but the present invention is not limited to these examples. The method of analyzing the resin in Examples and the like is as follows.

(1) Measurement of the number of foreign substances After washing the resin pellets with methanol, dissolving them with methyl ethyl ketone to make a 10% solution, the number of foreign substances of 5 μm or more was measured using a particle counter. (2) Measurement of total residual monomer A sample is dissolved in dimethylformamide and quantified by gas chromatography. (3) Measurement of Moisture Absorption A weight change was measured when a 3 mm-thick test piece manufactured by injection molding was saturated with water at 45 ° C. × 95%. The lower the moisture absorption, the better. (4) Change in surface accuracy due to moisture absorption Moire fringes were visually observed as surface accuracy of the test piece before and after the moisture absorption measurement, and the change in the change surface accuracy was judged by △, Δ, ×.

(5) Yellowness A 3 mm thick test piece produced by injection molding was measured according to JIS-K7103. The lower the yellowness, the better. (6) Mold transferability A hairline mold was used as a mold transferability test piece.
The transferability of the hairline of the test piece obtained by injection molding was visually observed, and evaluated by △, Δ, and ×. (7) Melt flow index MI As an index of moldability, it was measured under the conditions of a cylinder temperature of 200 ° C. and a load of 5 kg according to JIS-K7210. The higher the MI, the better the moldability.

Example 1 80 parts by weight of styrene (SM) and 20 parts by weight of methyl methacrylate (MMA) were used as polymerization monomers, and styrene-methyl methacrylate copolymer resin (MS resin) pellets were obtained by continuous bulk polymerization. Was. Using a single-screw extruder in which the pellets are provided at the tip with a sintered metal filter (filtration accuracy 5 μm) using stainless steel metal fiber as a filter material.
Removal of foreign matter and pelletization were performed at a temperature of 0 to 240 ° C. Table 1 shows the analysis results of the pellets.

Example 2 A styrene-methyl methacrylate copolymer resin was prepared in the same manner as in Example 1 except that 40 parts by weight of styrene (SM) and 60 parts by weight of methyl methacrylate (MMA) were used as polymerization monomers. Obtained. Table 1 shows the analysis results of the pellets.

Example 3 A styrene-methyl methacrylate copolymer resin was obtained in the same manner as in Example 1, except that a sintered metal filter having a filtration accuracy of 10 μm was used. Table 1 shows the analysis results of the pellets.

Comparative Example 1 A styrene-methyl methacrylate copolymer resin was prepared in the same manner as in Example 1 except that 20 parts by weight of styrene (SM) and 80 parts by weight of methyl methacrylate (MMA) were used as polymerization monomers. Obtained. Table 1 shows the analysis results of the pellets.

Comparative Example 2 A styrene-methyl methacrylate copolymer resin was obtained in the same manner as in Example 1 except that the filtration accuracy of the sintered metal filter was 30 μm. Table 1 shows the analysis results of the pellets.

Comparative Example 3 A styrene-methyl methacrylate copolymer resin was obtained in the same manner as in Example 1 except that the temperature condition of the extruder was 240 to 300 ° C. Table 1 shows the analysis results of the pellets.

Comparative Example 4 A styrene-methyl methacrylate copolymer resin was obtained in the same manner as in Example 1 except that no sintered metal filter was used. Table 1 shows the analysis results of the pellets.

[0031]

[Table 1]

[0032]

According to the present invention, transparency with less foreign matter,
A transparent resin for an optical material having excellent optical characteristics, dimensional stability, and moldability can be produced, and it can be widely used especially for optical components such as lenses and prisms, taking advantage of the characteristics. Further, the transparent resin for optical materials obtained according to the present invention has a low water absorption, so that it is less likely to generate silver and can be applied to a wide range of molding conditions.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeru Ituno 80-46, Hama, Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Chemical Co., Ltd.Kyushu Works (72) Inventor Isao Tanaka Chuo-ku, Tokyo 2-31-1 Shinkawa Inside Nippon Steel Chemical Co., Ltd.

Claims (3)

[Claims] 1. A method for producing a transparent resin for an optical material, wherein the transparent resin for an optical material comprises an aromatic vinyl monomer 95
(Meta) having 30 to 30% by weight and an alkyl group having 1 to 2 carbon atoms
An aromatic vinyl-based copolymer obtained by copolymerizing 5-70% by weight of an acrylic acid alkyl ester-based monomer,
By passing the aromatic vinyl copolymer through a sintered metal filter in a molten state, the number of foreign substances having a size of 5 μm or more in the copolymer is 2,000 / g or less, and the total residual monomer content is 3000 ppm or less. A method for producing a transparent resin for an optical material, comprising obtaining a resin. 2. The process for producing a transparent resin for optical materials according to claim 1, wherein the aromatic vinyl copolymer is passed through a sintered metal filter in a molten state using an extruder provided with a sintered metal filter at the tip. Method. 3. The sintered metal filter has a filtration accuracy of 5 to 5.
The method for producing a transparent resin for an optical material according to claim 1 or 2, wherein the resin having a thickness of 20 µm is used.