JP2007224255A - 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 and has a small birefringence. <P>SOLUTION: The optical molded item is obtained by using a styrene-butadiene block copolymer comprised of 75-60 mass% of a styrene monomer unit and 25-40 mass% of a butadiene monomer unit, and contains 0.01-2 pts.mass of at least one heat-resistant stabilizer or 0.01-2 pts.mass of at least one light-resistant stabilizer or both of these (each based on 100 pts.mass of the styrene-butadiene block copolymer). The optical molded item is suitable for a base film for optical films. <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 was difficult to say that the problems of birefringence and light resistance were 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 and low birefringence.

That is, the present invention is an optical molded body using a styrene-butadiene block copolymer composed of 75 to 60% by mass of styrene monomer units and 25 to 40% by mass of butadiene monomer units, Light resistance selected from 0.01 to 2 parts by mass of one or more heat-resistant stabilizers selected from hindered phenol compounds, lactone compounds, phosphorus compounds and sulfur compounds, or hindered amine compounds and benzotriazole compounds. 1. Optical stabilizer characterized by containing 0.01 to 2 parts by weight of one or more light stabilizers or both of them (provided that each part is 100 parts by weight of a styrene-butadiene block copolymer). The body is a base film for optical films.

The optical molded body of the present invention is suitable for use as a base film for optical films such as retardation films and antireflection films because it has good transparency, hue, impact resistance, and low birefringence. is there.

The styrene-butadiene block copolymer used in the present invention is not particularly limited as long as it is obtained by living anionic polymerization from a styrene monomer and a butadiene monomer. The block part may be a block copolymer comprising a block part mainly composed of a styrene monomer and a block part mainly composed of a butadiene monomer, and each block part may be composed of a styrene monomer and a butadiene monomer. It may be a block copolymer which is a so-called tapered block part in which the composition ratio of the monomer gradually changes, and each block has a constant ratio of the composition ratio of the styrene monomer and the butadiene monomer. The block copolymer which is what is called a random block part may be sufficient. Further, it may be a block copolymer in which a plurality of these block portions are the same, or a block copolymer in which a plurality of different block portions exist, and the molecular structure may be linear or so-called star-shaped.

The weight average molecular weight (Mw) of the matrix of the styrene-butadiene block copolymer resin is not particularly limited, but is preferably 50,000 to 300,000, more preferably 70,000 to 250,000. In addition, the weight average molecular weight (Mw) of this invention is the weight average molecular weight (Mw) of polystyrene conversion measured by GPC, and was 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.

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.

Examples of the butadiene monomer used in the present invention include 1,3-butadiene and 2-methyl-1,3-butadiene. Among these, 1,3-butadiene is preferable.
Furthermore, the proportion of 1,2-vinyl unsaturated bonds based on the butadiene monomer in the polymer chain of the styrene-butadiene block copolymer is preferably 20 mol% or less based on the total amount of the butadiene monomer. 15 mol% or less is more preferable. The proportion of the 1,2-vinyl unsaturated bond can be controlled by selecting a polymerization solvent, and can be reduced by using a nonpolar solvent.

The styrene-butadiene block copolymer is characterized in that the proportion of monomers constituting it is 75 to 60% by mass of styrene monomer units and 25 to 40% by mass of butadiene monomer units. The monomer ratio is preferably 73 to 62% by mass of styrene monomer units and 27 to 38% by mass of butadiene monomer units, 71 to 64% by mass of styrene monomer units, and a single amount of butadiene monomers. The body unit is more preferably 29 to 36% by mass. When the composition of the copolymer resin is within this more preferable range, the resulting resin composition is particularly excellent for a soft optical molded article.
If the styrenic monomer unit is less than 60%, the resulting optical molded article is too soft and difficult to use, and deformation may be a problem. If it exceeds 75% by mass, birefringence increases, which is not preferable.

The styrene-butadiene block copolymer may contain a heat-resistant stabilizer or may contain a light-resistant stabilizer. Moreover, it is more preferable when both are included.
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.

Although a light-resistant stabilizer will not be specifically limited if it has the effect, For example, a hindered amine type compound and a benzotriazole type compound are mentioned. 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.
In addition, the resin composition may contain additives such as lubricants, plasticizers, colorants, antistatic agents, mineral oil, etc., but there is a possibility that transparency may be hindered, and the amount added is small. Is preferred.

The blending and granulation method of the resin composition are not particularly limited, and a known method can be employed. For example, a styrene-butadiene block copolymer, a heat stabilizer, a light stabilizer, and additives to be used as needed are uniformly mixed in advance with a tumbler or a Henschel mixer, and then a single screw extruder or a twin screw extruder. If the solvent removal and granulation are carried out on the same line after polymerization, the heat stabilizer, light stabilizer and additives used as needed are added to the system at the final stage. There is a method of granulating after adding and mixing.

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

[Example 1]
(1) Take 480 kg of cyclohexane containing 150 ppm of tetrahydrofuran in a sealable pressure-resistant container having an inner diameter of 1.0 m, a volume of 1.3 m ³ and a Max Blend blade (manufactured by Sumitomo Heavy Industries-60 rpm), and then n-butyl 1490 mL of a cyclohexane solution (hereinafter referred to as initiator) containing 10% by mass of lithium was added, and the liquid temperature was kept at the outside air temperature (about 20 to 30 ° C.).
(2) After 16.0 kg of styrene monomer was added thereto, the temperature inside the can was raised to 70 ° C. for anionic polymerization of the styrene monomer. Thereafter, the temperature inside the can was cooled to 40 ° C.
(3) Next, 96.0 kg of styrene monomer and 48.0 kg of butadiene were added simultaneously, the temperature was raised again, and the reaction was continued. In the anionic polymerization reaction, when water is present, the polymerization active terminal is deactivated. Therefore, a solvent and a raw material monomer with moisture kept at 5 ppm or less were used.
(4) After completion of the reaction, the temperature in the can was cooled to 70 ° C., and then the polymerization solution was transferred to another container and 110 g of water was added to deactivate the solution, thereby obtaining a solution containing the polymer of Reference Example 1.
(5) Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) as a heat-resistant stabilizer per 100 parts by mass of the total charge of monomers (ie, styrene monomer and butadiene) in the polymerization solution of Reference Example 1 ) 0.2 parts by mass of propionate (IRGANOX1076 manufactured by Ciba Specialty Chemicals) was dissolved. Each of these polymerization solutions was pre-concentrated, and further devolatilized and extruded with a twin-screw extruder equipped with a vacuum vent to obtain pellet-shaped block copolymers.

[Examples and Comparative Examples]
Using the same apparatus as in Example 1, polymerization was performed so that the amounts of styrene and butadiene shown in Table 1 were obtained. The initial amount of styrene charged was the same as in Example 1.
In Examples 1 to 4 and Comparative Examples 1 and 2, bis (2,2,6,6-tetramethyl) was added as a hindered amine compound as a light-resistant stabilizer to 100 parts by mass of a styrene-butadiene block copolymer. -4-piperidyl) sebacate, 2- (2H-benzotriazol-2-yl) -4,6-di-t-pentylphenol as a benzotriazole-based compound was mixed with 0.1 parts by mass of each Henschel mixer, A resin composition was obtained by melt kneading at a cylinder temperature of 220 ° C. using a shaft extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.).
An optical disk having a diameter of 180 mm, a center hole of 15 mm, and a thickness of 1.2 mm is obtained by injection molding the resin prepared as described above at a molding temperature of 250 ° C. and a mold temperature of 60 ° C. with an injection molding machine MDM-I manufactured by Meiki. A substrate was obtained. Next, the characteristics of the obtained optical disk substrate were evaluated. The evaluation results are shown in Table 1.

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) 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.

Thus, a styrene-butadiene block copolymer in which a styrene monomer and a butadiene monomer are in a specific ratio is preferable, and a ratio of styrene monomer / butadiene monomer (mass basis) is particularly preferable. When the ratio is 1.5 times to 2.3 times, Re becomes small, which is particularly preferable.

Claims (4)

An optical molded article using a styrene-butadiene block copolymer composed of 75 to 60% by mass of a styrene monomer unit and 25 to 40% by mass of a butadiene monomer unit. 0.01 to 2 parts by mass of one or more heat-resistant stabilizers selected from hindered phenol compounds, lactone compounds, phosphorus compounds and sulfur compounds (provided that 100 parts by mass of a styrene-butadiene block copolymer) The molded article for optics according to claim 1, wherein   Contains 0.01 to 2 parts by weight of one or more light stabilizers selected from hindered amine compounds and benzotriazole compounds (provided that the styrene-butadiene block copolymer is 100 parts by weight). The optical molded body according to claim 1 or 2, wherein The optical molded body according to any one of claims 1 to 3, wherein the optical molded body is a base film for an optical film.