JP2005105102A - Resin composition for light-guiding element of high non-hygroscopicity and light-guiding element product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-guiding element product excellent in fluidity and non-hygroscopicity enabling thin-wall formation at relatively low temperatures, suppressed in the warpage/deformation of the product under high-temperature and high-humidity conditions, and having high light resistance. <P>SOLUTION: A resin composition for the light-guiding element comprises (A) an acrylic copolymer made from 50-75 wt.% of an acrylic monomer and 25-50 wt.% of an aromatic vinyl monomer and having a weight-average molecular weight of 30,000-200,000 and a molecular weight distribution of 2.0-3.0 and (B) an ultraviolet light absorber master batch, wherein the ultraviolet light absorber master batch(B) is a pelletized master batch comprising 50-99 wt.% of the acrylic copolymer(A) and 1-50 wt.% of an ultraviolet light absorber. The light-guiding element product molded using this composition is also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light guide resin composition and a light guide product that are excellent in initial colorability and have good hygroscopicity and light resistance.

  Acrylic resins are widely used in outdoor applications such as automobile exterior parts and exterior products because of their excellent transparency, light resistance, and surface hardness. Acrylic resin is one of the plastics that is optically very excellent because it has a light transmittance in the visible light region that is more than that of glass and has a small birefringence after molding. For this reason, acrylic resins have been conventionally used as various optical materials, and their application as optical plastic lenses, optical discs, and the like are progressing.

  For this reason, acrylic resins have been conventionally used as various optical materials, but recently, their use as backlights for liquid crystal displays has increased. The backlight light guide refers to a unit that propagates and diffuses light incident from a certain direction and emits light on the liquid crystal unit surface side. There are two types of backlight methods: a direct type with a light guide sandwiched between a light source and a liquid crystal unit, and an edge light method with a light source arranged at the edge of the light guide. Due to the demand for weight reduction, the thinning of the light guide is an issue, and the edge light system has become the mainstream. In the edge light method, the light transmission distance in the light guide is longer than that in the direct type. Therefore, in order to prevent light loss in the light guide, the material used for the light guide has a high light transmittance. It is essential to have In addition, it is necessary to design the light guide so that light incident from the edge is emitted to the entire side surface of the liquid crystal unit of the light guide.

As a method for uniformly emitting light incident from the edge of the light guide to the entire surface of the light guide, dot gradation printing is performed on one side (Japanese Patent Laid-Open Nos. 6-194526 and 63-62104). ), A method of forming irregularities for diffusing light on one side (Japanese Patent Laid-Open No. 61-127506), a method of attaching a film with gradation, and the like. In general, an injection molding method is used for forming a thin and precise light guide plate and unevenness for diffusing light.
In this case, it is necessary to improve the moldability and fluidity of the acrylic resin. For this purpose, a method of reducing the molecular weight of the resin or copolymerizing a comonomer having an internal plasticizing effect is generally used. It is. Recently, products called front covers (panels) such as light guides, lenses, and liquid crystals have become larger. As products become larger, warping and deformation of products due to moisture absorption by acrylic resins are becoming a problem. For this reason, it is necessary to improve the hygroscopic properties of the acrylic resin, and as a technique for this, it is common to copolymerize a low-hygroscopic comonomer. However, an acrylic resin simply improved in hygroscopicity by increasing the amount of a low-hygroscopic comonomer is not desirable because optical properties and light resistance are lowered.

Furthermore, since the liquid crystal display has a larger size, improved screen brightness, and a longer life, the performance required of recent light guides is required to have a very high light resistance level. Yes. As a means for improving the light resistance of acrylic resins, it is generally known to add ultraviolet absorbers. However, once an ultraviolet absorber is kneaded into a pelletized acrylic resin, multiple thermal degradation and ultraviolet rays are introduced. There is an initial colorability problem that the color of the absorbent is yellowish and the transmittance in the short wavelength region is lowered.
JP 2003-165895 A

  An object of the present invention is to provide a light guide resin composition and a light guide product that are excellent in initial colorability, moisture absorption, and light resistance.

As a result of intensive studies in view of such problems, the present inventors have found that the above object can be achieved by using a specific copolymer and selecting a method for adding an ultraviolet absorber. Has been reached.

It is possible to provide a light guide product having high light resistance, which has excellent fluidity and moisture absorption characteristics that enable thin-wall molding at a relatively low temperature, and is suppressed from warping and deformation of the product under constant temperature and high humidity. .

  That is, the present invention comprises 50 to 75% by weight of an acrylic monomer and 25 to 50% by weight of an aromatic vinyl monomer, has a weight average molecular weight of 3 to 200,000, and a molecular weight distribution of 2.0 to 3 A resin composition for a light guide comprising an acrylic copolymer (A) in the range of 0.0 and an ultraviolet absorber masterbatch (B), wherein the ultraviolet absorber masterbatch (B) is an acrylic copolymer. The present invention provides a resin composition for a light guide, which is a pellet-shaped masterbatch comprising 50 to 99% by weight of combined (A) and 1 to 50% by weight of an ultraviolet absorber.

The resin composition for a light guide in the present invention comprises 50 to 75% by weight of an acrylic monomer and 25 to 50% by weight of an aromatic vinyl monomer, has a weight average molecular weight of 3 to 200,000 and a molecular weight distribution. Is made of an acrylic copolymer (A) in the range of 2.0 to 3.0 and an ultraviolet absorber masterbatch (B).

Examples of the acrylic monomer constituting the acrylic copolymer (A) include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth ) Phenyl acrylate, benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and the like.
Here, (meth) acrylic acid is acrylic acid or methacrylic acid, and one or more of the above-mentioned acrylic monomers can be selected and used.

Examples of the aromatic vinyl monomer constituting the acrylic copolymer (A) include styrene, α-methylstyrene, paramethylstyrene, and the like, and one or more types are selected and used. be able to. Of these, styrene is particularly preferred.

When the acrylic monomer constituting the acrylic copolymer (A) is less than 50% by weight, the optical properties are inferior and the light resistance is inferior. On the other hand, when the acrylic monomer is 75% by weight or more, the hygroscopic property is inferior and the product is warped and deformed.

When the weight average molecular weight of the acrylic copolymer (A) is less than 30,000, the impact strength is inferior, and cracking may occur during product transportation or cracking / cracking during release. Further, if the weight average molecular weight exceeds 200,000, it is not preferable because productivity is lowered and economical efficiency is deteriorated, and fluidity is lowered and a thin molded product is hardly obtained. Preferably it is 5 to 150,000.

Furthermore, when the molecular weight distribution of the acrylic copolymer (A) is less than 2.0, it is necessary to suppress the polymerization conversion rate, which is inferior in economic efficiency. On the other hand, if it exceeds 3.0, the fluidity is lowered, and it is difficult to obtain a thin molded product.

In addition, as a method of adjusting the weight average molecular weight and molecular weight distribution of the acrylic copolymer (A), when polymerizing the acrylic copolymer (A), the polymerization method, polymerization temperature, or polymerization used It can be adjusted by appropriately setting the amount of initiator and molecular weight regulator used.
Moreover, about the weight average molecular weight and molecular weight distribution of this acrylic copolymer (A), after melt | dissolving this acrylic copolymer (A) in tetrahydrofuran, it is polystyrene using Shimadzu high performance liquid chromatography (HSG column). From the converted molecular weight, the weight average molecular weight and molecular weight were measured.

  The acrylic copolymer (A) can be produced by a known polymerization method, among which a solution polymerization or a bulk polymerization method is preferable, and a continuous block or solution polymerization method is more preferable. More specifically, a raw material in which an acrylic monomer and an aromatic vinyl monomer and, if necessary, a solvent such as ethylbenzene, toluene, and methyl ethyl ketone are mixed is supplied to the polymerization step, and the monomer is polymerized. And after the step, the mixed liquid containing the polymer, the unreacted monomer and / or the solvent is heated, and simultaneously or after the heating, the mixture is introduced into the decompression chamber to remove the unreacted monomer and / or the solvent into the polymer. From the granulation step, which is pelletized by adding and granulating additives such as colorants, antioxidants, and fillers to the polymer discharged from the recovery step as necessary It is preferable to become. The acrylic copolymer thus obtained preferably has a volatile component of 3000 ppm or less from the viewpoint of optical properties and light resistance. As a method for reducing the volatile component, for example, it may be reduced by an operation such as a polymerization temperature at the time of the polymerization, a polymerization initiator to be used, an addition amount of a chain transfer agent, or devolatilization by an extruder in a granulation step. Is possible. Further, the content of the volatile component in the copolymer can be measured with a gas chromatograph by dissolving the sample in dimethylformamide.

  The ultraviolet absorbent master batch (B) can be produced by a known method. For example, an acrylic copolymer (A) and an ultraviolet absorbent are mixed at a predetermined ratio, and a general extruder is used. It can be obtained by melting and kneading. Preferably, the resin composition excellent in the initial colorability can be obtained by lowering the temperature as much as possible at the time of preparing the ultraviolet absorbent master batch (B).

  Examples of the ultraviolet absorber constituting the ultraviolet absorber masterbatch (B) include benzophenone series, benzotriazole series, propandioc acid series, and oxalanilide series ultraviolet absorbents, and two or more kinds of these ultraviolet absorbents can be used in combination. . Among these, particularly, a propandiocic acid-based and / or oxalanilide-based UV absorber is preferable, and 2-ethyl, 2′-ethoxy-oxylanilide and / or propandioc acid, [(4-methoxyphenyl) -methylester is a main component. And the compound.

  Moreover, the said ultraviolet absorber masterbatch (B) is mix | blended in the ratio of 1-50 weight% of ultraviolet absorbers with respect to acrylic copolymer (A) 50-99 weight%. If the blending ratio of the ultraviolet absorber is less than 1% by weight, the initial colorability upon thermal degradation is inferior, and if it exceeds 50% by weight, the dispersibility decreases, which is not preferable.

The resin composition for a light guide according to the present invention is composed of the acrylic copolymer (A) and the ultraviolet absorber masterbatch (B), and the blending ratio is not particularly limited, but various physical property balances. From the surface, the amount of the ultraviolet absorbent master batch (B) is about 0.1 to 10 parts by weight with respect to 100 parts by weight of the acrylic copolymer (A).

Moreover, the resin composition for light guides of this invention can be made to contain various additives in the range which does not impair the characteristic. Examples of the additive include a lubricant, a release agent, an antioxidant, an antistatic agent, an organic light diffusing agent, and an inorganic light diffusing agent.

Furthermore, it is preferable that the resin temperature at the time of shape | molding a light guide product using said resin composition for light guides is 200-320 degreeC. If the resin temperature at the time of molding the light guide is less than 200 ° C., molding distortion tends to remain, causing warpage and deformation. On the other hand, if it exceeds 320 ° C., it reaches the decomposition temperature region of the resin composition for the light guide, and this causes an appearance defect due to silver streak or burning, which is not preferable.

Moreover, various shapes, such as a plate-shaped molded product and a tubular molded product, are mentioned as a light guide product which consists of the resin composition for light guides of this invention.

〔Example〕
-Acrylic copolymer (A)-
A-1: A styrenic resin was produced using a continuous polymerization apparatus consisting of one fully mixed reaction tank having a capacity of 20 liters. Styrene was used as the styrenic monomer, and methyl methacrylate was used as the (meth) acrylic acid alkyl ester. Further, t-butyl peroxy (2-ethylhexanoate) was used as a polymerization initiator. A polymerization raw material consisting of 55 parts by weight of styrene, 35 parts by weight of methyl methacrylate, 10 parts by weight of ethylbenzene, 0.05 part by weight of t-dodecyl mercaptan, and 0.015 part by weight of a polymerization initiator at 13 kg / h using a plunger pump. Polymerization was carried out by continuously supplying the reaction vessel, and the polymerization temperature was adjusted so that the polymerization conversion rate at the outlet of the reaction vessel was 53.5% by weight. The polymerization temperature at this time was 150 ° C. The number of revolutions in the reaction vessel was 150 rpm, and the polymerization temperature was measured by inserting thermocouples in the upper, middle, and lower portions of the reaction vessel. The temperature at the three locations was an average value of ± 0.2 ° C. It is considered that the polymerization liquid is uniformly mixed. Following the polymerization, the polymerization solution continuously drawn out from the reaction vessel is supplied to a devolatilizer to separate volatile components such as unreacted monomers and organic solvents, and then the resin is passed through an extruder. Pelletized. The content of volatile components in the copolymer was 2200 ppm. The acetone-soluble part had a weight average molecular weight (Mw) of 140,000 and a molecular weight distribution (Mw / Mn) of 2.3.

A-2: A styrenic resin was produced using a continuous polymerization apparatus consisting of one fully mixed reaction tank having a capacity of 20 liters. Styrene was used as the styrenic monomer, and methyl methacrylate was used as the (meth) acrylic acid alkyl ester. Further, t-butyl peroxy (2-ethylhexanoate) was used as a polymerization initiator. A plunger pump is used as a polymerization raw material comprising 37 parts by weight of styrene, 40 parts by weight of methyl methacrylate, 3 parts by weight of butyl acrylate, 20 parts by weight of ethylbenzene, 0.13 parts by weight of t-dodecyl mercaptan, and 0.04 parts by weight of a polymerization initiator. Was continuously fed to the reaction vessel at a rate of 13 kg / h to carry out the polymerization, and the polymerization temperature was adjusted so that the polymerization conversion rate at the outlet of the reaction vessel was 48.5% by weight. The polymerization temperature at this time was 135 ° C. The number of revolutions in the reaction vessel was 150 rpm, and the polymerization temperature was measured by inserting thermocouples in the upper, middle, and lower portions of the reaction vessel. The temperature at the three locations was an average value of ± 0.2 ° C. It is considered that the polymerization liquid is uniformly mixed. Following the polymerization, the polymerization solution continuously drawn out from the reaction vessel is supplied to a devolatilizer to separate volatile components such as unreacted monomers and organic solvents, and then the resin is passed through an extruder. Pelletized. The content of volatile components in the copolymer was 1800 ppm. The acetone-soluble part had a weight average molecular weight (Mw) of 150,000 and a molecular weight distribution (Mw / Mn) of 2.2.

A-3: A styrenic resin was produced using a continuous polymerization apparatus consisting of one fully mixed reaction tank having a capacity of 20 liters. Styrene was used as the styrenic monomer, and methyl methacrylate was used as the (meth) acrylic acid alkyl ester. Further, t-butyl peroxy (2-ethylhexanoate) was used as a polymerization initiator. A polymerization raw material consisting of 24 parts by weight of styrene, 66 parts by weight of methyl methacrylate, 10 parts by weight of ethylbenzene, 0.45 parts by weight of t-dodecyl mercaptan, and 0.016 parts by weight of a polymerization initiator at 13 kg / h using a plunger pump. Polymerization was carried out by continuously supplying the reaction vessel, and the polymerization temperature was adjusted so that the polymerization conversion rate at the outlet of the reaction vessel was 47.8% by weight. The polymerization temperature at this time was 150 ° C. The number of revolutions in the reaction vessel was 150 rpm, and the polymerization temperature was measured by inserting thermocouples in the upper, middle, and lower portions of the reaction vessel. The temperature at the three locations was an average value of ± 0.2 ° C. It is considered that the polymerization liquid is uniformly mixed. Following the polymerization, the polymerization solution continuously drawn out from the reaction vessel is supplied to a devolatilizer to separate volatile components such as unreacted monomers and organic solvents, and then the resin is passed through an extruder. Pelletized. The content of volatile components in the copolymer was 850 ppm. The acetone-soluble part had a weight average molecular weight (Mw) of 76,000 and a molecular weight distribution (Mw / Mn) of 2.5.

Ai: A styrenic resin was produced using a continuous polymerization apparatus comprising one fully mixed reaction tank having a capacity of 20 liters. Styrene was used as the styrenic monomer, and methyl methacrylate was used as the (meth) acrylic acid alkyl ester. Further, t-butyl peroxy (2-ethylhexanoate) was used as a polymerization initiator. A polymerization raw material comprising 80 parts by weight of styrene, 16 parts by weight of methyl methacrylate, 3.5 parts by weight of ethylbenzene, and 0.034 parts by weight of a polymerization initiator is continuously supplied to the reaction tank at 13 kg / h using a plunger pump. Then, the polymerization was carried out, and the polymerization temperature was adjusted so that the polymerization conversion rate at the outlet of the reaction vessel was 45.6% by weight. The polymerization temperature at this time was 135 ° C. The number of revolutions in the reaction vessel was 150 rpm, and the polymerization temperature was measured by inserting thermocouples in the upper, middle, and lower portions of the reaction vessel. The temperature at the three locations was an average value of ± 0.2 ° C. It is considered that the polymerization liquid is uniformly mixed. Following the polymerization, the polymerization solution continuously drawn out from the reaction vessel is supplied to a devolatilizer to separate volatile components such as unreacted monomers and organic solvents, and then the resin is passed through an extruder. Pelletized. The content of volatile components in the copolymer was 1250 ppm. The acetone-soluble part had a weight average molecular weight (Mw) of 150,000 and a molecular weight distribution (Mw / Mn) of 2.5.

-UV absorber masterbatch (B)-
It mix | blended and mixed in the ratio shown in Table 1, and melt-kneaded at 220 degreeC using the 40 mm twin-screw extruder, and obtained the ultraviolet absorber masterbatch (B) pellet.

-UV absorber-
Benzotriazole UV absorber (b-1); TINUVIN P manufactured by Ciba Specialty Chemicals Co., Ltd.
Propanedioc acid type ultraviolet absorber (b-2); Sanduvor PR-25 manufactured by Clariant Japan Co., Ltd.
Oxalanilide UV absorber (b-3); manufactured by Clariant Japan Co., Ltd. Sanduvor VSU

Polystyrene (PS); Nippon Polystyrene Co., Ltd. GPPS G637R
Polymethylmethacrylate (PMMA); Sumipex MGSS manufactured by Sumitomo Chemical Co., Ltd.

-Hindered amine light stabilizer-
HALS; bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate: TINUVIN 770 manufactured by Ciba Specialty Chemicals Co., Ltd.

[Examples 1-6, Comparative Examples 2-5]
About each said component, after dry-drying the dry blend pellet mixed in the ratio shown in Table 2 at 80 degreeC, HP-100 injection-molding machine made from Hayabusa Iron Works, Ltd. and MD450S-made by Niigata Seiko Molding Machine Co., Ltd. Various test pieces were obtained at a resin temperature of 200 to 320 ° C. using IV AP.
[Comparative Examples 1 and 6]
About each said component, it mixed in the ratio shown in Table 2, and the predetermined | prescribed pellet was obtained with the single screw extruder which made the cylinder temperature 220 degreeC. After pre-drying the obtained pellets at 80 ° C., a resin temperature of 200 to 320 ° C. is used by using an HP-100 injection molding machine manufactured by Hayabusa Iron Works and MD450S-IV AP manufactured by Niigata Seiko Molding Machine Co., Ltd. Various test pieces were obtained in the range.
The results are shown in Table 1. Various test conditions are as follows.

Color difference : Using a test piece having a thickness of 3 mm, yellowness YI (transmitted light) was measured with CMS-35SP manufactured by Murakami Color Research Laboratory. It shows that the smaller the YI value, the better the yellowness.

Light resistance : Using a test piece with a thickness of 3 mm, Ubucon (Toyo Seiki Seisakusho Co., Ltd., irradiation intensity: 2.5 mW / cm ² , black panel temperature: 60 ° C., irradiation time: 300 hours) The yellowing degree difference ΔYI (transmitted light) was measured with CMS-35SP manufactured by Murakami Color Research Laboratory.

Hygroscopicity : A 300 mm x 250 mm light guide plate molded product with a thickness of 4 mm is absorbed for 300 hours in an environment of 60 ° C and 95% humidity using a constant temperature and humidity chamber manufactured by Tabai Espec Co., Ltd. The amount of deformation was measured. Unit: mm.

Transparency (haze) : Measured with a reflection / transmittance meter HR-150 manufactured by Murakami Color Research Laboratory Co., Ltd. using a test piece having a thickness of 3 mm.

The resin composition for a light guide according to the present invention is a light guide product that satisfies the recent market needs of high light resistance and has excellent initial (before light resistance deterioration) colorability, and has a relatively low temperature. Because of its fluidity that enables thin-wall molding at low temperatures and excellent moisture absorption characteristics, the use of this resin composition can suppress warping and deformation of products under constant temperature and high humidity. A compatible light guide product can be obtained.

Claims (4)

It consists of 50 to 75% by weight of acrylic monomer and 25 to 50% by weight of aromatic vinyl monomer, and has a weight average molecular weight of 3 to 200,000 and a molecular weight distribution of 2.0 to 3.0. A resin composition for a light guide comprising an acrylic copolymer (A) and an ultraviolet absorber masterbatch (B), wherein the ultraviolet absorber masterbatch (B) is an acrylic copolymer (A) 50- A resin composition for a light guide, which is a pellet master batch comprising 99% by weight and 1 to 50% by weight of an ultraviolet absorber. The resin composition for a light guide according to claim 1, wherein the acrylic copolymer (A) is an acrylic copolymer having a volatile component of 3000 ppm or less obtained by a bulk polymerization method or a solution polymerization method. The resin composition for a light guide according to claim 1 or 2, wherein the ultraviolet absorbent masterbatch (B) comprises an ultraviolet absorbent mainly composed of propanedioc acid and / or oxalanilide and an acrylic copolymer (A). . The light guide product obtained by shape | molding the resin composition for light guides in any one of Claims 1-3 at resin temperature 200-320 degreeC.