JPH09169883A - Optical resin composition and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical resin composition which has a limited tendency to deteriorate and to discolor at a high temp. in molding, a superior heat resistance, low hygroscopicity and low birefringence by making a specific methacrylic resin contain a specific antioxidant. SOLUTION: This optical resin composition contains 100 pts.wt copolymer (A) consisting of 10-70wt.% methyl methacrylate unit, 5-30wt.% N-substd. maleimide unit, 15-18wt.% cyclohexyl methacrylate unit and 0-30wt.% another copolymerizable monomer and 0.05-0.5 pts.wt. compound (B) as represented by formula I (wherein (X) is tert.-butyl) and 0-0.5 pts.wt. compound (C) as represented by formula II (wherein R is a 12-15C alkyl). This composition is obtained by dissolving the components B and C into the mixture of methyl methacrylate, N-substd. maleimide, cyclohexyl methacrylate and another copolymerizable monomer and subjecting the mixture to suspension polymerization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for optics which is less likely to be deteriorated or colored by heat even during molding at a high temperature and is excellent in heat resistance, low hygroscopicity and low birefringence, and a method for producing the same.

[0002]

Materials used for optical elements such as substrates for optical information recording media, optical fibers, camera lenses, pickup lenses and fθ lenses are generally required to have heat resistance, low hygroscopicity and low birefringence. It Methacrylic resin is a resin that is excellent in transparency and weather resistance and has a good balance of mechanical strength and molding processing, but on the other hand, it has a higher moisture absorption rate than resins such as polycarbonate, polystyrene, and amorphous polyolefin, In a field requiring high heat resistance such as a pickup lens of a compact disc player, there is a problem that heat resistance is insufficient. Also, it is known that the birefringence of methacrylic resin is lower than that of polycarbonate or polystyrene, but in recent years, high performance of the pickup lens has been required due to the high density of the optical disc, and it is more difficult than the conventional methacrylic resin. Materials with low birefringence are desired.

To meet these demands, a methacrylic resin obtained by copolymerizing an N-substituted maleimide and cyclohexyl methacrylate has been proposed (JP-A-61-95011).
Japanese Patent Application Laid-Open No. 61-162509, Japanese Patent Application Laid-Open No. 64
-62314, JP-A 1-215810). These resins are excellent resins that have the same excellent transparency and mechanical properties as conventional methacrylic resins, but also have heat resistance, low hygroscopicity, and low birefringence that methacrylic resins cannot have. is there.

However, the methacrylic resin containing N-substituted maleimide and cyclohexyl methacrylate is more likely to undergo alteration of the copolymer at a high temperature of 200 ° C. or higher as compared with a normal methacrylic resin, resulting in injection molding or the like. There is a problem that the deteriorated substance becomes a foreign substance during the melt molding and mixes into the molded product. It is assumed that this is because the side chain of cyclohexyl methacrylate in the copolymer is desorbed at high temperature, and a crosslinking reaction occurs between the polymer chains, so the amount of foreign substances such as dust in the copolymer is reduced. However, since foreign matter is produced in the molding machine, it is unsuitable as a material for optical elements. Also, N
A methacrylic resin containing a substituted maleimide is optically unfavorable because it is easily colored when exposed to a high temperature of 200 ° C. or higher, such as during injection molding, and the polymer yellows.

A method has been proposed in which a compound having a phosphorus atom (phosphite compound) is incorporated in order to reduce yellowing due to heating of a methacrylic resin containing an N-substituted maleimide (JP-A-3-167245). (Japanese Patent Laid-Open No. 6-116331), this method has no effect of suppressing alteration of the polymer at high temperature.

On the other hand, when a general phosphite antioxidant added for the purpose of suppressing thermal coloring is dissolved in the monomer mixture before the aqueous suspension polymerization and the polymerization is carried out, the suspension is obtained at the latter stage of the polymerization. As the viscosity of the particles increases, the particles begin to fuse,
Leading to solidification. Therefore, generally, a means for maintaining the stability of suspended particles by increasing the amount of the dispersant charged is taken, but since the dispersant is not compatible with the methacrylic resin, the content of the copolymer in the copolymer increases as the content increases. The amount of foreign matter increases, which is unsuitable as an optical element. Therefore, the antioxidant is blended with the obtained copolymer and shaped into pellets. However, this method not only increases the number of blending steps, but also results in entrainment of dust outside the system by blending.

[0007]

SUMMARY OF THE INVENTION The present invention has been made against the background described above, and an object thereof is to prevent deterioration and thermal coloring of a resin even at a high temperature during molding.
An object is to provide an optical resin composition having excellent heat resistance, low hygroscopicity, and low birefringence, and a method for producing the same.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a specific amount of a specific antioxidant is added to a methacrylic resin having a specific composition by a specific method. It has been found that the above objects can be achieved by the inclusion, and the present invention has been completed.

That is, according to the present invention, the methyl methacrylate unit is 10 to 70% by weight, and the N-substituted maleimide unit is 5 to 3%.
0% by weight, cyclohexyl methacrylate unit 15-85
To 100 parts by weight of a copolymer (A) consisting of 0 to 30% by weight of other copolymerizable monomer units, and the following general formula (I):

Embedded image 0.05 to 0.5 parts by weight of the compound (B) represented by the following formula (II)

[Chemical 6] An optical resin composition comprising 0 to 0.5 part by weight of a compound (C) represented by

The present invention also provides methyl methacrylate 10
˜70 wt%, N-substituted maleimide 5˜30 wt%, cyclohexyl methacrylate 15˜85 wt%, and other copolymerizable monomer 0˜30 wt% General formula (I)

Embedded image 0.05 to 0.5 parts by weight of the compound (B) represented by the following formula (II)

Embedded image The method for producing an optical resin composition is characterized in that 0 to 0.5 part by weight of the compound (C) represented by

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The copolymer (A) constituting the optical resin composition of the present invention comprises a methyl methacrylate unit, N-
It is composed of substituted maleimide units, cyclohexyl methacrylate units and other copolymerizable monomer units.

Methyl methacrylate used for constituting the copolymer (A) of the present invention is a component which imparts transparency, weather resistance and mechanical properties to the optical resin composition. The content of the methyl methacrylate unit in the copolymer (A) is in the range of 10 to 70% by weight, preferably 20 to 65% by weight. When the content of the methyl methacrylate unit is less than 10% by weight, the mechanical strength of the obtained optical resin composition decreases, and when it exceeds 70% by weight, the low hygroscopicity of the optical resin composition is insufficient. Become.

The N-substituted maleimide used for constituting the copolymer (A) of the present invention is a component which imparts heat resistance and low birefringence to the optical resin composition. The N-substituted maleimide that can be used is not particularly limited, but preferable examples include N-cyclohexylmaleimide, N-isopropylmaleimide, N-phenylmaleimide, and the like. The content of the N-substituted maleimide unit in the copolymer (A) is 5 to 30% by weight, preferably 10 to 25% by weight. When the content of the N-substituted maleimide unit is less than 5% by weight, the heat resistance and the low birefringence of the optical resin composition cannot be sufficiently improved, and
When it exceeds 30% by weight, the birefringence of the optical resin composition increases and the mechanical strength decreases.

Cyclohexyl methacrylate used to form the copolymer (A) of the present invention is a component that imparts low hygroscopicity to the optical resin composition. The content of cyclohexyl methacrylate unit in the copolymer (A) is in the range of 15 to 85% by weight, preferably 15 to 75% by weight. When the content of the cyclohexyl methacrylate unit is less than 15% by weight, the hygroscopicity of the obtained optical resin composition is high, and when it exceeds 85% by weight, the mechanical strength of the optical resin composition decreases. .

Further, other copolymerizable monomers used as an optional component for constituting the copolymer (A) of the present invention include, for example, aromatic vinyl compounds such as styrene and α-methylstill, acryl. Methyl acid, ethyl acrylate, acrylic acid esters such as cyclohexyl acrylate, ethyl methacrylate, isobornyl methacrylate,
Examples thereof include methacrylic acid esters such as phenyl methacrylate and dicyclopentanyl methacrylate. The content of the other copolymerizable monomer unit in the copolymer (A) is
It is in the range of 0 to 30% by weight, preferably 0 to 15% by weight. When the content of the other copolymerizable monomer unit in the copolymer (A) exceeds 30% by weight, the mechanical strength, heat resistance and transparency of the obtained optical resin composition are lowered, and The birefringence is increased depending on the type of monomer used.

Compound (B) used in the present invention
Is a phenolic antioxidant represented by the above general formula (I). This compound (B) is used to reduce the deterioration of the copolymer (A) when the optical resin composition is molded at a high temperature, for example, at a temperature of 200 ° C. or higher. The amount of the compound (B) used is the copolymer (A) 10
0.05 to 5 parts by weight with respect to 0 parts by weight,
If it is less than 0.05 parts by weight, it is not possible to prevent the copolymer from being deteriorated at high temperature, and if it exceeds 0.5 parts by weight, the heat resistance of the obtained optical resin composition is lowered. At the same time, no improvement in the effect of preventing the deterioration of the copolymer at high temperatures is observed, which is economically disadvantageous.

The compound (B) may be blended with the copolymer (A) and shaped. However, from the viewpoint of inclusion of foreign matter, it is preferable that the compound (B) is dissolved in the monomer before the polymerization and then the polymerization is performed. A phenolic antioxidant other than the above general formula (I) at 200 ° C.
Some of them can exert their effects at lower temperatures, but no one having a deterioration inhibiting effect at a high temperature of 200 ° C. or higher has been found so far except the above general formula (I). 200 among common methacrylic resins
Although some resins can be injection-molded at a temperature below ℃, a polymer containing N-substituted maleimide and cyclohexyl methacrylate is
For optical use, it is molded at high temperature for the purpose of reducing internal distortion as much as possible. Therefore, it is important to prevent alteration at a high temperature of 200 ° C. or higher.

Further, in the present invention, the compound (C) optionally added is a phosphorus-based antioxidant represented by the above general formula (II). This compound (C) is added in order to suppress coloring of the optical resin composition during heating, and for example, a lens such as a pickup lens using a semiconductor laser as a light source, which only needs to transmit a specific wavelength. Is unnecessary because the coloring of the material does not affect
It is necessary for applications such as camera lenses and projection lenses that are affected by the color of the lens. The amount of the compound (C) used for such an application is in the range of 0 to 0.5 parts by weight, and the amount of the compound (C) used is 0.5 parts by weight, based on 100 parts by weight of the copolymer (A). When it exceeds, the heat resistance of the obtained optical resin composition is lowered, and the effect of suppressing the coloring is not improved, which is economically disadvantageous.

The compound (C) may be shaped after blending with the copolymer (A), but since foreign substances from the outside of the system may be mixed during blending, the monomer may be added before the polymerization. It is preferable to carry out the polymerization after the solution is dissolved in. The above general formula
A phosphite compound other than the compound represented by (II), which has not been solidified during suspension polymerization when it is dissolved in a monomer and polymerized, has not been found yet.

The method for producing the optical resin composition of the present invention comprises:
Known methods such as a bulk polymerization method, a suspension polymerization method, and an emulsion polymerization method can be used, but the suspension polymerization method is preferable from the viewpoint of easy handling.

When the optical resin composition of the present invention is produced by the suspension polymerization method, first, the above-mentioned methyl methacrylate, N-substituted maleimide, cyclohexyl methacrylate and other copolymers used as necessary. A compound represented by the above general formula (I) is added to a monomer mixture of possible monomers, and the above general formula (II) optionally used.
The compound represented by, the polymerization initiator and the chain transfer agent are dissolved.

Then, the obtained homogeneous mixed solution is suspended in an aqueous medium in which a dispersion stabilizer is present, and then the suspension is maintained at a predetermined polymerization temperature for 1 hour to complete the polymerization. The optical resin composition of the present invention can be obtained by filtering the product, washing with water, and drying.

The polymerization initiator used in the suspension polymerization is, for example, 2,2'-azobisisobutyronitrile,
Azo initiators such as 2,2′-azobis-2,4-dimethylvaleronitrile, benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, 1,1-di-t-butylperoxy-2 Examples thereof include peroxide initiators such as methylcyclohexane. The amount of these polymerization initiators used is in the range of 0.001 to 3 parts by weight with respect to 100 parts by weight of the above monomer mixture.

Examples of the chain transfer agent used in suspension polymerization include t-butyl mercaptan, n-butyl mercaptan, n-octyl mercaptan and n-dodecyl mercaptan. The amount of these chain transfer agents used is in the range of 0 to 3 parts by weight with respect to 100 parts by weight of the monomer mixture.

Dispersion stabilizers used in suspension polymerization include alkali metal salts of polyvinyl alcohol, homopolymers or copolymers of (meth) acrylic acid, and sodium salts of methyl methacrylate and 2-sulfoethyl methacrylate. Examples thereof include copolymers, carboxyl cellulose, gelatin, starch, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, calcium phosphate and the like. These dispersants are based on 100 parts by weight of water.
It is preferable to use it in the range of 0.01 to 5 parts by weight.
If necessary, a dispersing aid such as sodium chloride, potassium chloride, sodium sulfate, potassium sulfate or manganese sulfate may be used together with these dispersants.

The amount of water with respect to the monomer in the suspension polymerization is not particularly limited, but it is preferable that the weight ratio of the monomer / water is 1/1 to 1/10, and more preferably 1 The range is / 2 to 1/4.

The polymerization temperature of the suspension polymerization is not particularly limited, but it is 50 to 150 ° C., preferably 50 to 130.
It is in the range of ° C.

In the optical resin composition of the present invention, known additives such as colorants such as dyes and pigments, light stabilizers such as plasticizers, release agents and ultraviolet absorbers may be added depending on the purpose. You can do it.

[0029]

The present invention will be described below in detail with reference to examples. The evaluation of physical properties in Examples and Comparative Examples was carried out by using the following methods.

(1) Heat distortion temperature (HDT) A resin pellet is pressure-molded (200 ° C., 20 kg / c).
m ² ), a 127 mm × 6.4 mm × 13 mm (thickness) test piece was prepared, and a load of 18 was applied in accordance with ASTM-D648.
It was measured at 20 KPa.

(2) Color test 100 mm × 50 mm × 2 mm using resin pellets
A (thickness) flat plate was prepared by injection molding under the following molding conditions at each temperature of 230 ° C. and 270 ° C., and the difference in coloring was evaluated according to the following criteria. ◯: No difference is observed between the 230 ° C molded product and the 270 ° C molded product. Δ: The 270 ° C molded product is slightly yellowed compared to the 230 ° C molded product. X: The 270 ° C molded product is significantly yellowed compared to the 230 ° C molded product.

Molding conditions Molding machine: injection molding machine PS-60E manufactured by Nissei Plastic Co., Ltd. Cylinder setting temperature: 230 ° C., 270 ° C. Mold setting temperature: 70 ° C. Injection setting pressure: 600 to 1000 kg / cm ² Injection setting speed : 50% Injection time: 18 seconds Cooling time: 23 seconds

(3) Alteration test 1 g of resin pellets was heated in an oven at 230 ° C, 250 ° C,
After heating for 1 hour at each temperature of 270 ℃, 25 ml of each
The mixture was placed in acetone and the presence or absence of acetone insoluble matter was examined, and the following criteria were used for judgment. When the copolymer is altered by heating, it becomes insoluble in the solvent. ○: There is no insoluble matter. Δ: There is some insoluble matter. X: There is a considerable amount of insoluble matter.

The abbreviations in Table 1 represent the following compounds. MMA: methyl methacrylate CHMI: N-cyclohexylmaleimide PhMI: N-phenylmaleimide CHMA: cyclohexylmethacrylate Compound (I): compound represented by the above general formula (I) (Adeka Stab AO-60 manufactured by Asahi Denka Co., Ltd.). ) Compound (II): Compound represented by the above general formula (II) (Adeka Stab 1500 manufactured by Asahi Denka Kogyo Co., Ltd.) Compound (III): Compound represented by the following general formula (III)

Embedded image (Adeka Stab AO-50, manufactured by Asahi Denka Co., Ltd.) Compound (IV): compound represented by the following general formula (IV)

Embedded image (Adeka Stab 2112, manufactured by Asahi Denka Co., Ltd.)

[Example 1] 100 parts by weight of a monomer mixture prepared by mixing 60% by weight of methyl methacrylate, 22% by weight of N-cylohexylmaleimide and 18% by weight of cyclohexyl methacrylate was used as an n-chain transfer agent. 0.15 parts by weight of octyl mercaptan, 1,1 as a polymerization initiator
0.3 part by weight of di-t-butylperoxy-2-methylcyclohexane, 0.2 part by weight of stearyl alcohol as a release agent, a compound represented by the above general formula (I) as an antioxidant (Asahi Denka Kogyo Co., Ltd. ADEKA STAB A manufactured by Co., Ltd.
O-60) 0.1 part by weight and the compound represented by the general formula (II) (Adeka Stub 15 manufactured by Asahi Denka Co., Ltd.).
00) 0.1 part by weight was added and dissolved to prepare a uniform mixed solution.

Next, 0.02 part by weight of a copolymer of methacrylic acid and sodium salt of 2-sulfoethyl methacrylate was used as a dispersion stabilizer, 0.15 part by weight of sodium sulfate as a dispersion aid and a dispersion medium. As a polymerization reaction pressure vessel of 50 liters equipped with a stirrer, containing 200 parts by weight of pure water as a reactor, and replacing the atmosphere with nitrogen to 200 rp.
It was stirred at m for 15 minutes. Then, the polymerization was initiated by heating to 85 ° C in a nitrogen atmosphere, and after the exothermic peak of polymerization, 120 ° C.
Then, it was heated for 1 hour. Then, it was cooled, filtered, washed with water and dried to obtain a bead-shaped resin composition. The obtained bead-shaped resin composition is a twin-screw extruder (PCM-30, manufactured by Ikegai Corp.)
At 250 ° C., and pelletized. Various physical properties were evaluated using this resin pellet. Table 1 shows the obtained results.

[Examples 2 to 3 and Comparative Examples 1 to 5] Various examples were carried out in the same manner as in Example 1 except that the monomer charging composition, the kind and amount of the antioxidant were changed as shown in Table 1. The resin composition of was manufactured. Table 1 shows the evaluation results of the physical properties of the obtained resin composition.

[0038]

[Table 1]

[0039]

EFFECTS OF THE INVENTION The optical resin composition of the present invention has little deterioration and thermal coloring even in molding at high temperature, and is excellent in heat resistance, low hygroscopicity and low birefringence. For example, it is useful as an optical element material such as an optical information recording substrate, an optical fiber, a camera lens, a pickup lens, and an fθ lens.

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Claims (2)

[Claims] 1. Methyl methacrylate units 10-70% by weight, N-substituted maleimide units 5-30% by weight, cyclohexyl methacrylate units 15-85% by weight and other copolymerizable monomer units 0-30% by weight. % Based on 100 parts by weight of the copolymer (A), the following general formula (I): 0.05 to 0.5 parts by weight of the compound (B) represented by the following formula and the following general formula (II): An optical resin composition comprising 0 to 0.5 part by weight of a compound (C) represented by 2. Methyl methacrylate 10 to 70% by weight,
To 100 parts by weight of a monomer mixture consisting of 5 to 30% by weight of N-substituted maleimide, 15 to 85% by weight of cyclohexyl methacrylate and 0 to 30% by weight of other copolymerizable monomer, the following general formula (I) is added. [Chemical 3] 0.05 to 0.5 parts by weight of the compound (B) represented by the following formula and the following general formula (II): A method for producing an optical resin composition, which comprises dissolving 0 to 0.5 parts by weight of the compound (C) represented by