JP2007224130A - Optical molded item - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical molded item that exhibits good transparency, hues and impact resistance, is hardly deformed by moisture absorption and has a small birefringence. <P>SOLUTION: The optical molded item is obtained by using a resin composition that comprises a copolymer resin as a main component, which is obtained by bulk continuous polymerization of a styrene monomer and a (meth)acrylic ester monomer in the presence of a butadiene rubber and has a ratio of constituting monomers of 10-38 mass% of a styrene monomer unit, 5-18 mass% of a butadiene monomer unit and 85-44 mass% of a (meth)acrylic ester monomer unit, and a heat-resistant stabilizer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an optical molded body.

Conventionally, methacrylic resins have been widely used for optical molded articles. However, methacrylic resin has good optical properties such as transparency and low birefringence, but has low impact resistance and high hygroscopicity, so deformation due to moisture absorption becomes a problem when it is used as an optical molded body. It was. On the other hand, polystyrene is transparent and has good moldability, low hygroscopicity and little deformation, but has low impact resistance and high birefringence (refraction), so its use in this field is limited.
The following publications relating to such optical molded articles are known, but it is difficult to say that the problems of birefringence and light resistance have been sufficiently solved.
JP 2002-242679 A Japanese Patent Laid-Open No. 2002-243917 JP 2002-284946 A

An object of the present invention is to provide an optical molded article having good transparency, hue, impact resistance, little deformation due to moisture absorption, and low birefringence.

That is, the present invention is an optical molded body using a copolymer resin having the following composition and a resin composition containing a heat resistance stabilizer. This copolymer resin is a copolymer resin obtained by continuously polymerizing a styrene monomer and a (meth) acrylate monomer in the presence of a butadiene rubber, and the copolymer resin is The proportion of the constituent monomers is 10 to 38% by mass of styrene monomer units, 5 to 18% by mass of butadiene monomer units, and 85 to 44% by mass of (meth) acrylate monomer units. The heat resistance stabilizer is at least one selected from a hindered phenol compound, a lactone compound, a phosphorus compound and a sulfur compound, and the total amount thereof is 100 parts by mass of the copolymer resin. It is 0.01-2 mass parts with respect to.
Further, the present invention is an optical molded body, wherein the optical molded body is an optical disk substrate or a light guide plate, a lens, a front plate, an optical sheet base sheet, or an optical film base film.

The optical molded body of the present invention has good transparency, hue, impact resistance, little deformation due to moisture absorption, and low birefringence. For example, an optical disk substrate, a light guide plate, a lens, a front plate, a phase difference It is suitable and useful for base films of optical films such as films and antireflection films, and base sheets of optical sheets such as lenticular lenses and Fresnel lenses.

The copolymer resin used in the present invention is a copolymer resin obtained by continuously polymerizing a styrene monomer and a (meth) acrylic acid ester monomer in the presence of a butadiene rubber. Several methods are known for producing such a ternary resin. However, in the copolymer resin used in the present invention, a butadiene rubber is combined with a styrene monomer and (meth). It is characterized by being obtained by continuous bulk polymerization in a state dissolved in an acrylate monomer. In addition to this bulk continuous polymerization, a method of blending the graft rubber particles obtained by emulsion polymerization with a styrene- (meth) acrylate copolymer resin, or in the presence of a butadiene rubber, a styrene monomer and (meth) acrylic There is a method to obtain acid ester monomer by suspension polymerization after bulk polymerization, but in these cases sufficient transparency cannot be obtained, and if this is used for a light guide plate with a long optical path, light attenuation is seriously problematic It may become.

During the continuous bulk polymerization, a solvent such as ethylbenzene or toluene is preferably 25 parts by mass or less, more preferably 5 to 20 parts per 100 parts by mass in total of the styrene monomer and the (meth) acrylic acid ester monomer. Part by mass can be used. Use of a solvent tends to lower the viscosity at the time of polymerization, making it easier to control the polymerization, and stabilizing the physical properties of the resulting copolymer resin. The polymerization temperature is preferably 80 to 170 ° C, more preferably 100 to 160 ° C. At the time of polymerization, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1- Bis (t-butylperoxy) -cyclohexane, 2,2-bis (4,4-di-butylperoxycyclohexyl) propane, t-butylperoxyisopropyl monocarbonate, di-t-butyl peroxide, dicumylper It is preferable to add a known polymerization initiator such as oxide, ethyl-3,3-di- (t-butylperoxy) butyrate, and particularly when two or more polymerization initiators having different half-life temperatures are used, impact resistance is increased. May improve.

The addition amount of the polymerization initiator is preferably 0.005 to 5 parts by mass, more preferably 0.01 to 100 parts by mass with respect to the total of 100 parts by mass of the styrene monomer and the (meth) acrylate monomer. 1 part by mass. Outside this range, the balance between transparency and impact resistance may be poor.
Further, a known molecular weight modifier such as 4-methyl-2,4-diphenylpentene-1, t-dodecyl mercaptan, n-dodecyl mercaptan may be added during the polymerization.

The weight average molecular weight (Mw) of the matrix of the copolymer resin is preferably 50,000 to 150,000, more preferably 70,000 to 130,000. In addition, the weight average molecular weight (Mw) of this invention is a weight average molecular weight (Mw) of polystyrene conversion measured by GPC, and is measured on the measurement conditions of the following description.
Device name: SYSTEM-21 Shodex (manufactured by Showa Denko)
Column: 3 series PL gel MIXED-B Temperature: 40 ° C
Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2% by mass
Calibration curve: produced using standard polystyrene (PS) (manufactured by PL), and the weight average molecular weight was expressed in terms of PS.

The rubber particle diameter in the copolymer resin is not particularly limited, but is preferably in the range of 0.1 to 1.0 [mu] m, more preferably 0.1 to 0.5 [mu] m. The rubber particle diameter is obtained from the following formula [Equation 1] by measuring the particle diameter Di (equivalent circle diameter) of about 3000 rubber particles in the photograph from an ultra-thin section transmission electron micrograph of the resin. Average particle diameter.

The toluene-insoluble content of the copolymer resin is not particularly limited, but is preferably in the range of 8 to 30% by mass, more preferably 12 to 25% by mass. The toluene insoluble matter is measured as follows.
A sample of 0.35 g was precisely weighed (a) and dissolved in 35 ml of toluene at a temperature of 25 ° C. for 24 hours, and then the lysate was transferred to a centrifuge tube having a mass (b) measured in advance and having a maximum centrifugal radius. Using a 10.7 cm angle rotor, centrifuge at 14,000 rpm for 40 minutes at a temperature of 10 ° C. or less, remove the non-precipitate by decantation, and dry for 24 hours in a vacuum dryer at a temperature of 70 ° C. The mass (d) is measured, and the toluene insoluble matter is calculated by the following formula [Equation 2].

The swelling index of the copolymer resin is preferably 8-20, more preferably 9-17. The swelling index is measured as follows. A sample of 0.35 g was precisely weighed (a) and dissolved in 35 ml of toluene at a temperature of 25 ° C. for 24 hours, and then the lysate was transferred to a centrifuge tube having a mass (b) measured in advance and having a maximum centrifugal radius. Using a 10.7 cm angle rotor, the mixture is centrifuged at 14,000 rpm for 40 minutes at a temperature of 10 ° C. or less, and after removing non-precipitates by decantation, the mass (c) of the centrifuge tube before drying is measured. It is dried in a vacuum dryer at a temperature of 70 ° C. for 24 hours, the mass (d) of the centrifuge tube after drying is measured, and the swelling index is calculated by the following equation [Equation 3].

Examples of the styrene monomer used in the present invention include styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, pt-butylstyrene, and the like. Is preferably styrene. These styrenic monomers may be used alone or in combination of two or more.

As the (meth) acrylic acid ester monomer used in the present invention, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate methacrylate ester, methyl acrylate Acrylates such as ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, etc., preferably methyl (meth) acrylate, or n-butyl acrylate, Methyl (meth) acrylate is preferred. These (meth) acrylic acid ester monomers may be used alone or in combination of two or more.

Further, if necessary, a vinyl monomer copolymerizable with these monomers may be copolymerized. Examples of such monomers include acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, N -Phenylmaleimide, N-cyclohexylmaleimide and the like.

Examples of the butadiene rubber used in the present invention include polybutadiene, styrene-butadiene block copolymer, and styrene-butadiene random copolymer. Of these, a polybutadiene having a 5 mass% styrene solution viscosity at a temperature of 25 ° C. of 100 mPa · s or less and a proportion of 1,2-vinyl bonds of unsaturated bonds based on butadiene of 20 mol% or less is preferable, and 5 mass%. More preferably, the styrene solution has a viscosity of 60 mPa · s or less and the proportion of 1,2-vinyl bonds among unsaturated bonds based on butadiene is 14 mol% or less.

As for copolymer resin, the ratio of the monomer which comprises copolymer resin is 10-38 mass% of styrene-type monomer units, 5-18 mass% of butadiene-type monomer units, (meth) acrylic acid ester-type single quantity The body unit is 85 to 44% by mass. The monomer ratio is preferably 15 to 33% by mass of styrene monomer units, 5 to 17% by mass of butadiene monomer units, and 80 to 50% by mass of (meth) acrylate monomer units. More preferably, the styrene monomer unit is 15 to 30% by mass, the butadiene monomer unit is 7 to 15% by mass, and the (meth) acrylic acid ester monomer unit is 78 to 55% by mass. When the composition of the copolymer resin is in a more preferable range, the resulting resin composition is particularly excellent for a hard optical molded body.
If the styrenic monomer unit is less than 10%, deformation due to moisture absorption of the obtained optical molded product may be a problem. If it exceeds 38% by mass, birefringence increases, which is not preferable. If the butadiene monomer is less than 5%, the impact strength is inferior, and if it exceeds 18%, the viscosity at the time of bulk continuous polymerization becomes too high and the polymerization is not stable. If the (meth) acrylic acid ester monomer unit is less than 44% by mass, the birefringence increases, and if it exceeds 85% by mass, the mold transferability of the obtained copolymer resin tends to be inferior, which is not preferable.

The resin composition contains the copolymer resin described above and a heat stabilizer.
The heat resistance stabilizer is not particularly limited as long as it has the effect, and examples thereof include heat resistance stabilizers such as hindered phenol compounds, lactone compounds, phosphorus compounds, and sulfur compounds. These may be used alone or in combination of two or more. The blending amount is preferably 0.01 to 2 parts by mass, more preferably 0.01 to 1 part by mass with respect to 100 parts by mass of the copolymer resin. The inclusion of a heat-resistant stabilizer is preferable because it can be processed at a high temperature, leading to a reduction in birefringence, and further, an appearance change when exposed to light is reduced.

In addition to this, the resin composition may contain additives such as a light-resistant stabilizer, a lubricant, a plasticizer, a colorant, an antistatic agent, and mineral oil, but there is a possibility that the transparency may be hindered. Less or no addition is preferred. Specifically, the total amount of additives including the heat stabilizer is 20% by mass or less, preferably 90% by mass or less, and more preferably 5% by mass or less.
The light-resistant stabilizer is not particularly limited as long as it has the effect, and examples thereof include hindered amine compounds and benzotriazole compounds. These may be used alone or in combination of two or more. The inclusion of a light-resistant stabilizer is preferable because it reduces the change in appearance when exposed to light, and also reduces the change in appearance during storage.

The blending method and granulation method of the resin composition are not particularly limited, and known methods can be employed. For example, copolymer resin, heat stabilizer, light stabilizer and additives to be used as needed are mixed uniformly in advance with a tumbler or Henschel mixer, and supplied to a single screw extruder or twin screw extruder. There are a method of melt-kneading, a method of adding at the stage of supplying the monomer for bulk continuous polymerization, and a method of adding and mixing in the system at the final stage of polymerization, followed by granulation.

Hereinafter, although detailed content is demonstrated using an Example, this invention is not limited to a following example.

[Example 1]
A first fully mixed reactor having a volume of about 5 liters equipped with a stirrer, a second fully mixed reactor having a volume of about 15 liters equipped with a stirrer, a column type plug flow reactor having a volume of about 40 liters, preheating A devolatilizing tank equipped with a vessel was connected in series. Butadiene rubber (Diene 35AS manufactured by Asahi Kasei Chemicals Co., Ltd .: 5 mass% styrene solution viscosity at a temperature of 25 ° C. is 85 mPa · s, and the proportion of 1,2-vinyl bonds out of unsaturated bonds based on butadiene is 12 parts by mass. Is dissolved in a mixed solution composed of 20 parts by mass of styrene, 68 parts by mass of methyl methacrylate (hereinafter referred to as MMA) and 12 parts by mass of ethylbenzene, and 1,1-bis (t-butylperoxy)- 0.05 part by mass of cyclohexane (Perhexa C manufactured by NOF Corporation), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (IRGANOX 1076 manufactured by Ciba Specialty Chemicals) as a heat stabilizer 0.2 parts by mass was mixed to obtain a raw material solution. This raw material solution was introduced into a first complete mixing type reactor controlled at a temperature of 108 ° C. at 7 kg / hour. The reaction solution was continuously withdrawn from the first complete mixing reactor, and 2.0 g / h of n-dodecyl mercaptan (Kio Co., thiocalcol 20) was added to the reaction solution, and then the temperature was controlled at 130 ° C. It was introduced into the type reactor. The second complete mixing reactor was stirred at 180 rpm. Subsequently, the reaction solution was continuously withdrawn from the second complete mixing type reactor, and 2.0 g / h of n-dodecyl mercaptan and di-t-butyl peroxide (Perbutyl D manufactured by NOF Corporation) were added to the reaction solution at a rate of 0.000 / h. After adding 5 g, it was introduced into a tower-type plug flow reactor adjusted so as to have a gradient of 130 ° C. to 150 ° C. in the direction of flow. While this reaction solution was heated with a preheater, it was introduced into a devolatilization tank controlled at a temperature of 240 ° C. and a pressure of 1.0 kPa to remove volatile components such as unreacted monomers. The resin liquid was extracted with a gear pump and extruded and cut into a strand shape to obtain a pellet-shaped resin composition. The evaluation results are shown in Table 1.
The obtained resin composition was injection-molded at a molding temperature of 250 ° C. and a mold temperature of 60 ° C. using an injection molding machine MDM-I manufactured by Meiki Co., Ltd. Got. Next, the characteristics of the obtained optical disk substrate were evaluated. The evaluation results are shown in Table 1.

[Example 2]
The same operation as in Example 1 was conducted except that 8.5 parts by mass of butadiene rubber was used. The evaluation results are shown in Table 1.

[Example 3]
Ubepol BR13HB manufactured by Ube Industries, Ltd. (viscosity of 5 mass% styrene solution at a temperature of 25 ° C. is 41 mPa · s, and the proportion of 1,2-vinyl bonds out of unsaturated bonds based on butadiene is used as butadiene rubber). Except for this, the same procedure as in Example 1 was performed. The evaluation results are shown in Table 1.

[Example 4]
The same operation as in Example 1 was performed except that the butadiene rubber was changed to 5 parts by mass. The evaluation results are shown in Table 1.

[Example 5]
The same operation as in Example 1 was performed except that the butadiene rubber was changed to 17 parts by mass. The evaluation results are shown in Table 1.

[Example 6]
Styrene butadiene rubber instead of butadiene rubber (Toughden 2000A manufactured by Asahi Kasei Chemicals Co., Ltd .: Viscosity of 5 mass% styrene solution at a temperature of 25 ° C. is 50 mPa · s. This was performed in the same manner as in Example 1 except that 10 parts by mass) and 40 parts by mass of styrene, 60 parts by mass of MMA, and 12 parts by mass of ethylbenzene were used. The evaluation results are shown in Table 1.

[Example 7]
The same procedure as in Example 3 was performed except that 17 parts by mass of the styrene butadiene rubber described in Example 6 was used. The evaluation results are shown in Table 1.

[Example 8]
To 100 parts by mass of the resin composition of Example 1, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate as a hindered amine compound as a light-resistant stabilizer and 2- (2H— as a benzotriazole compound After mixing benzotriazol-2-yl) -4,6-di-t-pentylphenol with 0.1 parts by mass of each Henschel mixer, a twin screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) was used. The resin composition was obtained by melt-kneading at a cylinder temperature of 220 ° C. The evaluation results are shown in Table 1.

[Comparative Example 1]
The same procedure as in Example 1 was performed except that butadiene rubber was not added. The evaluation results are shown in Table 1.

[Comparative Example 2]
The same operation as in Example 1 was carried out except that 23 parts by mass of butadiene rubber was used. The evaluation results are shown in Table 1.

[Comparative Example 3]
The same procedure as in Example 3 was performed except that 5 parts by mass of the styrene butadiene rubber described in Example 6 was used. The evaluation results are shown in Table 1.

[Comparative Example 4]
The same procedure as in Example 1 was conducted except that styrene was 0 parts by mass and MMA was 100 parts by mass. The evaluation results are shown in Table 1.

[Comparative Example 5]
To an autoclave having a capacity of 200 liters, 56 kg of pure water, 400 g of potassium oleate, 1200 g of potassium rosinate, 1.2 kg of sodium carbonate, and 400 g of potassium persulfate were added and dissolved uniformly with stirring. Next, 80 kg of butadiene and 400 g of t-dodecyl mercaptan were added, polymerization was carried out at 60 ° C. for 30 hours while stirring, and the mixture was further heated to 70 ° C. and allowed to stand for 30 hours to complete the polymerization to obtain a butadiene rubber latex.
30 kg of this butadiene rubber latex was weighed in terms of solid content, transferred to an autoclave having a volume of 200 L, added with 80 kg of pure water, and heated to 50 ° C. under a nitrogen stream while stirring. To this was added 2 kg of pure water in which 1.25 g of ferrous sulfate, 2.5 g of sodium ethylenediaminetetraacetate and 100 g of Rongalite were dissolved. A solution in which 120 g of hydroperoxide was dispersed in 8 kg of pure water containing 450 g of potassium oleate was continuously added separately over 6 hours. After completion of the addition, the temperature was raised to 70 ° C., 30 g of diisopropylbenzene hydroperoxide was further added, and the mixture was left for 2 hours to complete the polymerization. Antioxidant is added to the obtained emulsion, the solid content is diluted to 15% by mass with pure water, the temperature is raised to 60 ° C., dilute sulfuric acid is added with vigorous stirring, and salting out is performed. The mixture was heated to 90 ° C. and solidified, and then dehydrated, washed with water, and dried to obtain a powdered emulsion graft.
24 parts by mass of this emulsified graft and 76 parts by mass of the MMA-styrene resin obtained in Comparative Example 1 were mixed with a Henschel mixer, and then cylinder temperature using a twin screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.). It was melt-kneaded at 220 ° C. to obtain a pellet-shaped copolymer resin. The evaluation results are shown in Table 1.

[Comparative Example 6]
The same procedure as in Example 1 was performed except that the heat stabilizer octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate was not added. The evaluation results are shown in Table 1.

Among the samples described above, the optical stability of the optical disk substrates of Examples 1, 8 and Comparative Example 6 was examined for the light stability and the appearance change after storage, and the evaluation results are shown in Table 2.
The light stability was determined by visual inspection of the appearance (yellowishness and transparency) after irradiation for 24 hours using a xenon weatherometer, Atlas CI65A, manufactured by Toyo Seiki Seisakusho, based on the following criteria. The change when this test piece was left in an environment of 60 ° C. and 80% relative humidity for 24 hours was evaluated according to the following criteria. The evaluation results are shown in Table 2.
○: No change △: Some change in appearance ×: Some change in appearance

Using the resin compositions of Example 1 and Example 8 and the copolymer resin of Comparative Example 6, the optical disk substrate was molded by raising only the molding temperature to 270 ° C., and the b value and Re were measured. The evaluation results are shown in Table 3.

The evaluation was based on the following method.
(1) Transparency Based on ASTM D1003, the haze was measured using a haze meter (NDH-1001DP type manufactured by Nippon Denshoku Industries Co., Ltd.), and indicated by the maximum value of haze (unit:%) in the molded product. 1% or less was accepted.
(2) The b value was measured using a hue color difference meter (Σ-80 manufactured by Nippon Denshoku Industries Co., Ltd.), and indicated by the maximum value of the b value in the molded product. 1 or less was accepted.
(3) Impact resistance In accordance with JIS K7211, using a weight with a weight tip of 5R, a weight diameter of 14mmφ, and a mass of 200gf, the weight is dropped to the center hole of the molded product and the middle part on the outside. (Unit: cm) was measured. 20 cm or more was accepted.
(4) The dimensional change rate (unit:%) of the diameter when the hygroscopic deformable molded product was left in an environment of 70 ° C. and 90% humidity for 5 days was measured. A change rate of 0.3% or less was accepted.
(5) Retardation (Re) was measured using a birefringence phase difference measuring apparatus (KOBRA-WR manufactured by Oji Scientific Co., Ltd.) and indicated by the maximum value of Re (unit: nm) in the molded product. 50 nm or less was regarded as acceptable.
(6) Melt mass flow rate (MFR)
Based on JIS K7210, measurement was performed using resin pellets at a temperature of 200 ° C. and a load of 49 N. The measuring machine used was a melt indexer (F-F01) manufactured by Toyo Seiki Seisakusho.

Thus, when the copolymer resin obtained by bulk continuous polymerization is used, the haze value becomes smaller than that obtained by the emulsion polymerization method. The ratio of styrene monomer to butadiene monomer is always higher when the former is higher than the latter, and the former is preferably 1.7 to 2.3 times the latter.

Claims (8)

An optical molded article using a resin composition containing a copolymer resin having the following composition and a heat stabilizer.
Copolymer resin: A copolymer resin obtained by continuous polymerization of styrene monomer and (meth) acrylate monomer in the presence of butadiene rubber, and constitutes copolymer resin The ratio of the monomer to be used is 10 to 38% by mass of styrene monomer units, 5 to 18% by mass of butadiene monomer units, and 85 to 44% by mass of (meth) acrylic acid ester monomer units. Polymerized resin.   The heat resistance stabilizer is one or more selected from hindered phenol compounds, lactone compounds, phosphorus compounds and sulfur compounds, and the total amount is 0 with respect to 100 parts by mass of the copolymer resin. The optical molded body according to claim 1, wherein the copolymer resin is 0.01 to 2 parts by mass.   The optical molded body according to claim 1 or 2, wherein the optical molded body is an optical disk substrate.   The optical molded body according to claim 1 or 2, wherein the optical molded body is a light guide plate.   The optical molded body according to claim 1 or 2, wherein the optical molded body is a lens.   The optical molded body according to claim 1 or 2, wherein the optical molded body is a front plate.   The optical molded body according to claim 1 or 2, wherein the optical molded body is a base sheet for an optical sheet. The optical molding according to claim 1 or 2, wherein the optical molding is a base film for an optical film.