JP3183384B2 - Optical resin composition and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical resin composition which is less deteriorated and less thermally colored even during molding at high temperatures, and is excellent in heat resistance, low moisture absorption and low birefringence, and a method for producing the same.

[0002]

2. Description of the Related Art Materials used for optical elements such as substrates for optical information recording media, optical fibers, camera lenses, pickup lenses, and fθ lenses generally require heat resistance, low moisture absorption, and low birefringence. You. Methacrylic resin is a resin with excellent transparency, weather resistance, and excellent balance of mechanical strength and molding process, but has a higher moisture absorption rate than resins such as polycarbonate, polystyrene, and amorphous polyolefin. In a field where high heat resistance is required, such as a pickup lens of a compact disc player, there is a problem that heat resistance is insufficient. It is known that the birefringence of methacrylic resin is lower than that of polycarbonate or polystyrene.However, in recent years, the performance of pickup lenses has been required to be higher due to the higher density of optical discs. Materials with low birefringence are desired.

To meet these requirements, a methacrylic resin obtained by copolymerizing an N-substituted maleimide and cyclohexyl methacrylate has been proposed (JP-A-61-95011).
JP, JP-A-61-162509, JP-A-64
JP-A-62314, JP-A-1-215810). These resins have excellent transparency and mechanical properties equivalent to those of conventional methacrylic resins, and have excellent heat resistance, low hygroscopicity, and low birefringence that methacrylic resins could not have. is there.

However, methacrylic resins containing N-substituted maleimide and cyclohexyl methacrylate are more likely to deteriorate at 200 ° C. or higher than ordinary methacrylic resins at high temperatures of 200 ° C. or higher. There is a problem that the altered substance becomes a foreign substance and is mixed into the molded product during the melt molding. This is presumed to be due to the fact that the side chains of cyclohexyl methacrylate in the copolymer are eliminated at a high temperature and a cross-linking reaction occurs between the polymer chains, so that foreign substances such as dust in the copolymer are reduced. Even so, a foreign material is formed in the molding machine, so that it is not suitable as a material for an optical element. Also, N
-A methacrylic resin containing a substituted maleimide is optically unpreferable because when exposed to a high temperature of 200 ° C. or more, such as during injection molding, the resin tends to be colored and the polymer turns yellow.

[0005] In order to reduce the heating yellowing of a methacrylic resin containing an N-substituted maleimide, a method of containing a compound having a phosphorus atom (phosphite compound) has been proposed (Japanese Patent Application Laid-Open No. 3-167245). In this method, there is no effect of suppressing the deterioration of the polymer at high temperatures.

On the other hand, when a general phosphite-based antioxidant added for the purpose of suppressing thermal coloring is dissolved in a monomer mixture before the aqueous suspension polymerization, and the polymerization is carried out, the suspension is prepared at a later stage of the polymerization. As the viscosity increases, the particles begin to fuse together,
Leads to solidification. Therefore, generally, the amount of the dispersant is increased, and measures are taken to maintain the stability of the suspended particles.However, since the dispersant is not compatible with the methacrylic resin, the content of the dispersant increases in the copolymer. This increases the amount of foreign matter, and is not suitable as an optical element. Therefore, a means is employed in which the antioxidant is blended with the obtained copolymer and shaped into pellets. However, this method not only increases the number of steps for blending, but also results in entrainment of extraneous dust by blending.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above background, and has as its object to reduce the deterioration and thermal coloring of a resin even at a high temperature during molding.
An object of the present invention is to provide an optical resin composition having excellent heat resistance, low moisture absorption, and low birefringence, and a method for producing the same.

[0008]

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

That is, the present invention relates to a method for preparing a methacrylate unit comprising 10 to 70% by weight of a methyl methacrylate unit and 5 to 3% of an N-substituted maleimide unit.
0% by weight, cyclohexyl methacrylate unit 15 to 85
% By weight and 100 parts by weight of a copolymer (A) composed of 0 to 30% by weight of other copolymerizable monomer units, the following general formula (I)

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

Embedded image A compound represented by the formula (C): more than 0 and 0.5 parts by weight or less ;
And a resin composition for optical use, characterized by comprising:

[0010] The present invention also relates to methyl methacrylate 10
To 70% by weight, 5 to 30% by weight of an N-substituted maleimide, 15 to 85% by weight of cyclohexyl methacrylate and 0 to 30% by weight of a copolymerizable monomer, 100 parts by weight of the following: General formula (I)

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

Embedded image A compound represented by the formula (C): more than 0 and 0.5 parts by weight or less ;
Is dissolved and subjected to suspension polymerization to produce a resin composition for optical use.

[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,
It comprises a substituted maleimide unit, a cyclohexyl methacrylate unit and other copolymerizable monomer units.

The methyl methacrylate used to constitute the copolymer (A) of the present invention is a component that imparts transparency, weather resistance, mechanical properties, and the like 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 that imparts heat resistance and low birefringence to the optical resin composition. The N-substituted maleimide that can be used is not particularly limited, but preferred examples include N-cyclohexylmaleimide, N-isopropylmaleimide, and N-phenylmaleimide. The content of the N-substituted maleimide unit in the copolymer (A) is in the range of 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, it is not possible to sufficiently improve the heat resistance and lower the birefringence of the optical resin composition.
If it exceeds 30% by weight, the birefringence of the optical resin composition will increase and the mechanical strength will decrease.

Further, cyclohexyl methacrylate used for constituting the copolymer (A) of the present invention is a component for imparting low hygroscopicity to the optical resin composition. The content of the 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 obtained optical resin composition has high hygroscopicity, and when the content exceeds 85% by weight, the mechanical strength of the optical resin composition decreases. .

Further, other copolymerizable monomers used as an optional component to constitute the copolymer (A) of the present invention include, for example, aromatic vinyl compounds such as styrene and α-methylstil, and acrylic monomers. Methyl acrylate, ethyl acrylate, acrylates such as cyclohexyl acrylate, ethyl methacrylate, isobornyl methacrylate,
Examples include methacrylates such as phenyl methacrylate and dicyclopentanyl methacrylate. The content of other copolymerizable monomer units in the copolymer (A) is
The range is 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 decrease, and Depending on the type of monomer used, birefringence is increased.

Compound (B) used in the present invention
Is a phenolic antioxidant represented by the above general formula (I). The 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 more. The amount of the compound (B) to be used depends on the copolymer (A) 10
The amount is in the range of 0.05 to 0.5 part by weight with respect to 0 part by weight, and when the amount is less than 0.05 part by weight, the deterioration of the copolymer at a high temperature cannot be prevented. If the amount exceeds 5 parts by weight, the heat resistance of the obtained optical resin composition is lowered, and no improvement in the effect of preventing 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, but it is preferable to dissolve the monomer before the polymerization and then perform the polymerization from the viewpoint of contamination. A phenolic antioxidant other than the above general formula (I),
Some of them can exert their effect at lower temperatures, but those having a deteriorating effect at high temperatures of 200 ° C. or higher have not yet been found other than the above general formula (I). Some methacrylic resins include 200
Although some resins can be injection molded below ℃, the polymer containing N-substituted maleimide and cyclohexyl methacrylate,
For optical use, it is molded at high temperature to reduce internal strain as much as possible. Therefore, it is important to prevent deterioration at a high temperature of 200 ° C. or higher.

[0018] Te present invention smell, added pressure the compound (C) is an antioxidant of the phosphorus system represented by the above general formula (II). The compound (C) is added to suppress coloring of the optical resin composition during heating.
For example, a lens that only needs to transmit a specific wavelength, such as a pickup lens that uses a semiconductor laser as a light source, is not necessary because the coloring of the material does not affect it. Required. The amount of the compound of for such purpose (C) is the copolymer (A) 100 parts by weight of in the range of 0.5 parts by weight or less than 0, the amount is zero. If the amount exceeds 5 parts by weight, the heat resistance of the obtained optical resin composition decreases, and no improvement in the effect of suppressing coloring is observed, which is economically disadvantageous.

The compound (C) may be shaped after blending with the copolymer (A). However, there is a possibility that foreign matter from outside the system may be mixed during the blending. It is more preferable to carry out polymerization after dissolving in water. General formula above
When a phosphite-based compound other than the compound represented by the formula (II) is dissolved in a monomer and polymerized, it can be used without being solidified during suspension polymerization.

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 are possible, but the suspension polymerization method is preferable because of easy handling.

When the optical resin composition of the present invention is produced by a suspension polymerization method, first, the above-mentioned methyl methacrylate, N-substituted maleimide, cyclohexyl methacrylate and other copolymers used if necessary a monomer mixture consisting of monomers capable of a compound represented by the above general formula (I), a compound represented by the above general formula Symbol (II), dissolving the polymerization initiator and chain transfer agent.

Next, the obtained homogeneous mixture is suspended in an aqueous medium in which a dispersion stabilizer is present, and 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, washing, and drying the substance.

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

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

Examples of the dispersion stabilizer used in the suspension polymerization include polyvinyl alcohol, an alkali metal salt of a homopolymer or copolymer of (meth) acrylic acid, and a sodium salt of methyl methacrylate and 2-sulfoethyl methacrylate. Copolymers, carboxycellulose, gelatin, starch, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, calcium phosphate and the like can be mentioned. 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, and manganese sulfate can be used together with these dispersants.

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

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

To the optical resin composition of the present invention, known additives such as coloring agents such as dyes and pigments, plasticizers, release agents, and light stabilizers such as ultraviolet absorbers may be added according to the purpose. You can do it.

[0029]

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

(1) Heat Deformation Temperature (HDT) Resin pellets are molded under pressure (200 ° C., 20 kg / c).
m ² ), a sample of 127 mm × 6.4 mm × 13 mm (thickness) was prepared, and a load of 18 was measured in accordance with ASTM-D648.
It was measured at 20 KPa.

(2) Coloring test 100 mm × 50 mm × 2 mm using resin pellets
(Thickness) flat plates were produced by injection molding at 230 ° C. and 270 ° C. under the following molding conditions, and the difference in coloring was evaluated according to the following criteria. ：: No difference is observed between the molded product at 230 ° C. and the molded product at 270 ° C. Δ: The 270 ° C molded product slightly yellowed compared to the 230 ° C molded product. ×: The 270 ° C molded product is significantly yellowed compared to the 230 ° C molded product.

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

(3) Alteration test 1 g of resin pellets were placed in an oven at 230 ° C. and 250 ° C.
After heating at each temperature of 270 ° C. for 1 hour, each was 25 ml
In acetone, and the presence or absence of acetone-insoluble components was examined. When the copolymer is deteriorated by heating, it becomes insoluble in a solvent. ：: No insoluble content. Δ: Some insolubles were found. ×: There are considerable insolubles.

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

Embedded image (ADK STAB AO-50, manufactured by Asahi Denka Kogyo KK) Compound (IV): a compound represented by the following general formula (IV)

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

Example 1 Methyl methacrylate 60% by weight, N-cyclohexylma
22% by weight of reimide , cyclohexyl methacrylate 18
100 parts by weight of the monomer mixture mixed in a ratio of
0.15 part by weight of n-octyl mercaptan as a chain transfer agent, 0.3 part by weight of 1,1-di-t-butylperoxy-2-methylcyclohexane as a polymerization initiator, 0.2 part by weight of stearyl alcohol as a release agent Parts, 0.1 parts by weight of a compound represented by the above general formula (I) (Adeka Stab AO-60, manufactured by Asahi Denka Kogyo KK) as an antioxidant and a compound represented by the above general formula (II) (Asahi Denka Kogyo Co., Ltd.) 0.1 parts by weight of Denka Kogyo Co., Ltd., Adekastab 1500) was added and dissolved to prepare a uniform mixed solution.

Then, 0.02 parts by weight of a copolymer of methacrylic acid and sodium salt of 2-sulfoethyl methacrylate as a dispersion stabilizer, 0.15 parts by weight of sodium sulfate as a dispersing aid, and a dispersion medium Into a 50 liter polymerization reaction pressure vessel equipped with a stirrer and containing 200 parts by weight of pure water,
and stirred for 15 minutes. Thereafter, the mixture was heated to 85 ° C. in a nitrogen atmosphere to start polymerization, and after the peak of the exothermic polymerization, 120 ° C.
For 1 hour. Thereafter, the mixture was cooled, filtered, washed with water, and dried to obtain a beaded resin composition. The obtained beaded resin composition is twin-screw extruder (PCM-30, manufactured by Ikegai Corporation).
At 250 ° C. and pelletized. Various physical properties were evaluated using the resin pellets. Table 1 shows the obtained results.

Example 2 , Comparative Examples 1 to 6 Various resins were prepared in the same manner as in Example 1 except that the monomer charge composition and the type and amount of the antioxidant were changed as shown in Table 1. A composition was prepared. Table 1 shows the evaluation results of the physical properties of the obtained resin composition.

[0038]

[Table 1]

[0039]

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 moisture absorption 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.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C09K 15/32 C09K 15/32 C G02B 6/00 391 G02B 6/00 391 (56) References JP-A-63-304045 (JP, A) JP-A-5-209102 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 33/08-33/12 C08K 5/103 C08K 5/524 C09K 15/08 C09K 15 / 32 G02B 6/00 391

Claims (4)

(57) [Claims] 1. 10 to 70% by weight of methyl methacrylate units, 5 to 30% by weight of N-substituted maleimide units, 15 to 85% by weight of cyclohexyl methacrylate units and 0 to 30% of other copolymerizable monomer units. % Of the copolymer (A) of the following general formula (I): 0.05 to 0.5 parts by weight of a compound (B) represented by the following formula (II): A compound represented by the formula (C): more than 0 and 0.5 parts by weight or less ;
An optical resin composition comprising: 2. The optical resin composition according to claim 1, wherein the content of the compound (C) represented by the general formula (II) is 0.1 to 0.5 part by weight. 3. 10 to 70% by weight of methyl methacrylate,
To 100 parts by weight of a monomer mixture comprising 5 to 30% by weight of an N-substituted maleimide, 15 to 85% by weight of cyclohexyl methacrylate and 0 to 30% by weight of other copolymerizable monomers, the following general formula (I) Embedded image And 0.05 to 0.5 parts by weight of a compound (B) represented by the following general formula (II): A compound represented by the formula (C): more than 0 and 0.5 parts by weight or less ;
A method for producing an optical resin composition, comprising: 4. A compound (C) represented by the general formula (II)
The method for producing an optical resin composition according to claim 3, wherein 0.1 to 0.5 part by weight is dissolved.