TW202106860A - Edge-light-type light guide plate and edge-light-type surface light source unit - Google Patents

Abstract

Provided are an edge-light-type light guide plate that is easy to manufacture due to having exceptional brightness uniformity and exceptional moldability in light guide plate manufacturing achieved by extrusion and roller transfer, and an edge-light-type surface light source unit in which the light guide plate is used. The present invention provides an edge-light-type light guide plate including a styrene-based resin composition, wherein the surface of the light guide plate has a plurality of lenticular and/or prismatic protrusions, the thickness T of the light guide plate is 1.0-3.0 mm, and the styrene-based resin composition contains a styrene-based resin and a phosphorus-based antioxidant (A) and/or a phenol-based antioxidant (B) and satisfies (1) and/or (2): (1) the height H of the protrusions is 10-500 [mu]m and (2) the pitch P of the protrusions is 30-800 [mu]m.

Description

Edge-emitting light guide plate and edge-emitting surface light source unit

The present invention relates to an edge light type (also called: edge light type) light guide plate and an edge light type (edge light type) surface light source unit.

The backlight of the liquid crystal display includes a direct type backlight in which the light source is arranged on the front surface of the display device and an edge-emitting type backlight in which the light source is arranged on the side. The light guide plate is incorporated into the edge-emitting backlight to guide the light from the side into the liquid crystal panel. It is used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, portable phones, car navigation, etc. . In addition, a backlight using a light guide plate is also used for lighting. It has been proposed that the light guide plate uses a styrene resin that has lower water absorption than acrylic resin represented by PMMA (polymethyl methacrylate), and is less prone to warpage and dimensional changes in molded products (Patent Document 1). In addition, it has also been proposed to use polystyrene for light guide plates.

The light guide plate is a component that has the function of injecting light from the end surface (side surface) of the plate-shaped molded product, and guiding the light to the front surface of the molded product using the reflective pattern formed on the back (non-emitting surface) of the molded product (Emitting surface) to make the surface emit light. In recent years, light guide plates have become larger and thinner. In addition, in order to improve the uniformity of emitted light, it is an industrial mainstream to provide a prismatic pattern on the front surface (light emitting surface) of a plate-shaped molded product. The pattern on the front or back of the plate-shaped molded product can be formed when the plate-shaped molded product is molded. For example, the pattern can be formed by using a mold shape in injection molding, or using roll transfer in extrusion molding. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2003-075648 [Patent Document 2] International Bulletin 2013/094642

[technical problem]

However, in a light guide plate using polystyrene whose optical properties are inferior to that of acrylic resin, the moldability of the pattern is a big issue. When a concave-convex pattern is provided on the front surface (light emitting surface) of the light guide plate, the pattern can be formed by roller transfer during extrusion molding, but during molding, problems such as fat accumulation in the orifice, poor transferability, and poor mold release may occur. Therefore, it is difficult to easily manufacture a light guide plate with uniform brightness. On the other hand, if the pattern molding is insufficient, not only the optical properties are poor, but also the strength becomes low as the wall becomes thinner, and there is a problem that the light guide plate cannot withstand practical use.

The present invention has been completed in view of such problems, and provides an edge-emitting light guide plate that is excellent in uniformity of brightness and has excellent moldability in the production of light guide plates by extrusion molding and roll transfer, and can be easily manufactured and used The edge-emitting surface light source unit of the light guide plate. [Technical means to solve the problem]

According to the present invention, there is provided an edge light type (edge-emitting type) light guide plate containing a styrene-based resin composition, having a plurality of convex lens-shaped and/or prismatic convex portions on the surface of the light guide plate, the light guide plate The thickness T is 1.0-3.0mm, and the styrene-based resin composition contains a styrene-based resin, a phosphorus-based antioxidant (A) and/or a phenol-based antioxidant (B), and satisfies the following (1) and At least one of (2), (1) The height H of the convex part is 10～500μm (2) The pitch P of the convex portions is 30 to 800 μm.

The inventors of the present invention conducted repeated and intensive studies, and found that in an edge-emitting light guide plate containing a styrene-based resin composition, they have discovered that the surface has a plurality of lenses and/or prismatic predetermined patterns of convex portions, and the light guide plate When the styrene-based resin composition contains a specific antioxidant, the edge-emitting light guide plate can be easily manufactured with excellent uniformity of brightness and excellent moldability, thereby completing the present invention.

Hereinafter, various embodiments of the present invention will be illustrated. The embodiments shown below can be combined with each other. Preferably, the height H of the convex portion is 10 to 500 μm, and the pitch P of the convex portion is 30 to 800 μm. Preferably, with respect to 100 parts by mass of the styrene-based resin composition, 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (A) and 0.001 to 0.5 parts by mass of the phenol-based antioxidant (B) are contained. Preferably, the phosphorus antioxidant (A) is selected from 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, Tris(2,4-di-tert-butylphenyl) phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetra Oxa-3,9-diphosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4-diyldiphosphinite At least one of acid ester and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite. Preferably, the phenolic antioxidant (B) is selected from 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra Tert-Butyl dibenzo[d,f][1,3,2]dioxin, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid Ester, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritol tetra[3-(3,5-di-tert-butyl-4- Hydroxyphenyl)propionic acid) ester, 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethyl At least one of oxyethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane. Preferably, the weight average molecular weight (Mw) of the styrene-based resin is 200,000 to 400,000, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.0 to 3.0. Preferably, the average transmittance of the styrene-based resin composition at an initial optical path length of 115 mm and a wavelength of 380 to 780 nm is 80% or more. According to another aspect of the present invention, there is provided an edge light type (edge light type) surface light source unit having the edge light guide plate and a light source that supplies light to the end surface of the edge light guide plate.

Hereinafter, embodiments of the present invention will be described. Various characteristic items shown in the embodiments shown below can be combined with each other. In addition, the invention is realized independently for each characteristic item.

1. Edge-emitting light guide plate [Shape of light guide plate] (Protrusion) The edge-emitting type (side-light type) light guide plate of the present invention has an uneven shape on the surface of the light guide plate. More specifically, as shown in FIG. 1, the surface of the light guide plate 1 has a plurality of convex lens-shaped (FIG. 1A) and/or prismatic (FIG. 1B) convex portions 3. The convex portion is preferably provided on at least one surface of the light guide plate, and particularly needs to be provided on one surface as the front surface (light emitting surface) of the light guide plate. For other surfaces, it can be provided if necessary, but it is more preferable to be provided only on the front surface (light emitting surface) of the light guide plate.

Here, the convex lens-shaped convex part means the arc-shaped convex part 3A shown in FIG. 1A, and the edge shape of a cross section is a circular arc-shaped protrusion body (FIG. 2A). In addition, the prismatic shape refers to the convex portion 3B shown in FIG. 1B, and the edge shape of the cross section is a protruding body with a triangular mountain shape (FIG. 2B ). In addition, the convex portions are formed in a parallel relationship with each other (FIG. 1 ). In addition, the convex portion is preferably formed integrally with the light guide plate.

The plurality of convex portions on the surface of the light guide plate is not limited as long as it is formed in plurality, and it is preferably a periodic pattern.

The pitch P of the convex portions is preferably 30 to 800 μm, more preferably 100 to 600 μm, and still more preferably 200 to 400 μm. If it is within such a range, it is easy to manufacture a light guide plate having excellent extrusion stability, roll transferability and roll releasability, and sufficient strength in molding of the antioxidant-added styrenic resin composition. The pitch P of the convex portions is specifically, for example, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 and 800 μm may be in the range between any two of the numerical values exemplified here. Here, the pitch P of the convex parts means the average value of the distance between the vertices of the adjacent convex parts as shown in FIG. 2. In a specific example, it refers to the average value of the distance between the vertices of adjacent convex portions among 100 consecutive convex portions in an arbitrary range.

The height H of the convex portion is preferably 10 to 500 μm, more preferably 50 to 300 μm, and still more preferably 90 to 200 μm. If it is within such a range, it is easy to manufacture a light guide plate having excellent extrusion stability, roll transferability and roll releasability, and sufficient strength in molding of the antioxidant-added styrenic resin composition. Specifically, the height H of the convex portion is, for example, 10, 20, 21, 25, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500 μm, It may be in the range between any two of the numerical values exemplified here. Here, the height H of the protrusion means the average value of the difference between the lowest position and the highest position of the protrusion as shown in FIG. 2. In a specific example, it means the average value of the difference between the lowest position and the highest position of the convex part among 100 continuous convex parts in an arbitrary range.

The width W of the convex portion is preferably 30 to 800 μm, more preferably 100 to 600 μm, and still more preferably 200 to 400 μm. If it is within such a range, it is easy to manufacture a light guide plate having excellent extrusion stability, roll transferability and roll releasability, and sufficient strength in molding of the antioxidant-added styrenic resin composition. The width W of the convex portion is specifically, for example, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 and 800 μm may be in the range between any two of the numerical values exemplified here. Here, the width W of the convex portion refers to the average value of the distance between the lowest positions of the convex portion as shown in FIG. 2. In a specific example, it refers to the average value of the distance between the lowest positions of the convex portions among 100 consecutive convex portions in an arbitrary range.

The ratio (H/P) of the height H of the convex portion to the pitch P is preferably 0.1 to 1.0, more preferably 0.26 to 0.7, and still more preferably 0.3 to 0.5. If it is within such a range, it is easy to manufacture a light guide plate having excellent extrusion stability, roll transferability and roll releasability, and sufficient strength in molding of the antioxidant-added styrenic resin composition. The ratio (H/P) is specifically, for example, 0.10, 0.15, 0.20, 0.25, 0.26, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.66, 0.67, 0.68 , 0.70, may be in the range between any two of the numerical values exemplified here.

(thickness) The thickness T of the light guide plate is 1.0 to 3.0 mm, preferably 1.5 to 2.5 mm, and more preferably 1.6 to 2.4 mm. If it is within such a range, it is easy to manufacture a light guide plate having excellent extrusion stability, roll transferability, and roll releasability and sufficient strength during molding of an antioxidant-added styrenic resin composition. The thickness T of the light guide plate is specifically, for example, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0mm may be within the range between any two of the numerical values exemplified here.

[Styrenic resin composition] The edge-emitting light guide plate of the present invention is an edge-emitting light guide plate containing a styrene-based resin composition. That is, it is a molded article formed of a styrene-based resin composition.

The styrene-based resin composition contains a styrene-based resin and a phosphorus-based antioxidant (A) and/or a phenol-based antioxidant (B).

(Styrenic resin) The styrene-based resin can be obtained by polymerizing a styrene-based monomer. Styrenic monomers refer to styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, and p-methylstyrene as aromatic vinyl monomers. The singly or a mixture of two or more kinds of tert-butyl styrene and the like is preferably styrene. In addition, it can be copolymerized with monomers other than styrene-based monomers within a range that does not impair the characteristics of the present invention. Examples include acrylic acid, methacrylic acid, butyl acrylate, ethyl acrylate, methyl acrylate, and methyl methacrylate. Acrylic monomers such as esters, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, α,β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid, phenylmaleimide, Imide-based monomers such as cyclohexyl maleimide. The styrene-based resin preferably consists essentially of a styrene-based monomer, and is more preferably a homopolymer of a styrene-based monomer.

The styrene-based resin composition is preferably composed of a styrene-based resin and various additives, and preferably contains a styrene-based resin, for example, 90 to 99.998 parts by mass and 95 to 99.98 parts by mass relative to 100 parts by mass of the styrene-based resin composition. Specifically, the ratio of the styrene-based resin is, for example, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.1, 99.2, 99.3, 99.4 relative to 100 parts by mass of the styrene-based resin composition. , 99.5, 99.6, 99.7, 99.8, 99.85, 99.88, 99.9, 99.98, 99.998 parts by mass, and may be in the range between any two of the numerical values exemplified here.

As a polymerization method of styrene resin, well-known styrene polymerization methods, such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method, are mentioned. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

When the styrene-based resin is polymerized, a polymerization initiator and a chain transfer agent can be used as necessary. As the polymerization initiator, a radical polymerization initiator is preferable, and known and commonly used ones include, for example, 1,1-bis(tert-butylperoxy)cyclohexane, and 2,2-bis(tert-butylperoxy). Peroxy ketals such as butane, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 1,1-bis(tert-amylperoxy)cyclohexane, etc., peroxide Hydroperoxides such as hydrocumene and tert-butyl hydroperoxide, alkyl peroxides such as tert-butyl peroxyacetate, tert-amyl peroxide isononanoate, tert-butylcumyl peroxide, Di-tert-butyl peroxide, dicumyl peroxide, di-tert-hexyl peroxide and other dialkyl peroxides, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxide Peroxy esters such as isopropyl monocarbonate, tert-butyl peroxyisopropyl carbonate, polyether tetra(tert-butyl peroxycarbonate) and other peroxycarbonates, N,N'-azobis (Cyclohexane-1-nitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), N,N '-Azobis[2-(hydroxymethyl)propionitrile] and the like, one kind or two or more kinds of these can be used in combination. As the chain transfer agent, aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene, and the like can be mentioned.

As a polymerization inhibitor for styrene-based monomers used in the polymerization of styrene-based resins, 4-tert-butylcatechol (TBC) is mostly used. Sometimes 4-tert-butylcatechol (TBC) may remain in a small amount. In a styrene resin composition. 4-tert-butylcatechol itself becomes a coloring component and reduces the hue and transmittance. Therefore, it is preferable that 4-tert-butylcatechol is not contained in the styrene resin composition as much as possible, but it is difficult to completely remove it. The preferred range of 4-tert-butylcatechol is 0.001 to 10 μg/g, more preferably 0.01 to 8 μg/g, and particularly preferably 0.1 to 6 μg/g.

In the case of continuous polymerization, first use a well-known complete mixing tank type stirring tank, tower type reactor, etc. in the polymerization step, and use polymerization temperature adjustment to control the polymerization reaction to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate. . The polymerization solution containing the polymer leaving the polymerization step is transferred to the devolatilization step to remove unreacted monomers and polymerization solvent. The devolatilization step consists of a vacuum devolatilization tank with a heater, a devolatilization extruder with vents, and the like. The molten polymer leaving the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded from the porous die into a strand shape, and processed into a pellet shape by a cold cutting method, an air cutting method, and an underwater hot cutting method.

The weight average molecular weight (Mw) of the styrene resin is preferably 200,000 to 400,000, more preferably 220,000 to 380,000, and still more preferably 250,000 to 300,000. By being in such a range, it is possible to achieve both moldability and strength of the light guide plate. If it is less than 200,000, the strength of the molded product is insufficient, and if it exceeds 400,000, the moldability is significantly reduced. The weight average molecular weight (Mw) of the styrene resin is specifically, for example, 200,000, 210,000, 220,000, 230,000, 240,000, 250,000, 260,000, 270,000, 280,000, 290,000, 300,000, 31 10,000, 320,000, 330,000, 340,000, 350,000, 360,000, 370,000, 380,000, 390,000, 400,000, and may be in the range between any two of the numerical values exemplified here. The weight average molecular weight of the styrene-based resin can be controlled according to the reaction temperature, residence time, type and amount of polymerization initiator, type and amount of chain transfer agent, type and amount of solvent used during polymerization, and the like in the polymerization step.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the styrene resin is preferably 1.0 to 3.0, more preferably 1.2 to 2.8, and still more preferably 1.5 to 2.5. If it is within such a range, it is easy to manufacture a light guide plate having excellent extrusion stability, roll transferability and roll releasability, and sufficient strength in molding of the antioxidant-added styrenic resin composition. The ratio (Mw/Mn) of the weight average molecular weight (Mw) of the styrene resin to the number average molecular weight (Mn) is specifically, for example, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 may be in the range between any two of the numerical values exemplified here. The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the styrene-based resin can be based on the reaction temperature, residence time, type and amount of polymerization initiator, and type of chain transfer agent in the polymerization step. It is controlled by the addition amount, the type and amount of the solvent used in the polymerization, etc.

(Phosphorus antioxidant (A)/phenol antioxidant (B)) The styrene-based resin composition may contain any one of the phosphorus-based antioxidant (A) and the phenol-based antioxidant (B), and by using both in combination, higher moldability and strength can be obtained.

The phosphorus antioxidant (A) is preferably contained in an amount of 0.001 to 0.5 parts by mass, preferably 0.01 to 0.4 parts by mass, and more preferably 0.05 to 0.3 parts by mass relative to 100 parts by mass of the styrene resin composition. In addition, the phenolic antioxidant (B) is preferably contained in an amount of 0.001 to 0.5 parts by mass, preferably 0.01 to 0.3 parts by mass, and more preferably 0.05 to 0.2 parts by mass relative to 100 parts by mass of the styrene resin composition. Within such a range, moldability and strength are excellent. The content of the phosphorus antioxidant (A) and the phenolic antioxidant (B) relative to 100 parts by mass of the styrene resin composition are specifically, for example, 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, respectively. 0.06, 0.07, 0.08, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 parts by mass, and may be in the range between any two of the numerical values exemplified here.

Phosphorus antioxidant (A) is, for example, selected from 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, tris( 2,4-di-tert-butylphenyl) phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa -3,9-Diphosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4diyl diphosphonite , At least one of bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite.

The phenolic antioxidant (B) is, for example, selected from 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyl Dibenzo[d,f][1,3,2] dioxaphosphepine, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propane Ester, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl) propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4 -Hydroxyphenyl)propionate) ester, 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1- At least one of dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane. For 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d, f] [1, 3, 2] Dioxaphos (for example, Sumilizer GP manufactured by Sumitomo Chemical Co., Ltd.), a compound having a phosphite structure and a phenol structure in the same molecule is considered to be a styrene resin composition They contain phosphorus antioxidants and phenolic antioxidants. For example, when 0.1 parts by mass of phosphorus-phenolic compounds are contained, it is considered that 0.1 parts by mass of phosphorus-based antioxidants and 0.1 parts by mass of phenolic antioxidants are contained with respect to 100 parts by mass of styrene-based resin composition.

Examples of methods for adding phosphorus antioxidants (A), phenolic antioxidants (B), and other additives include the polymerization step, devolatilization step, granulation step of styrene resin and the method of adding and mixing in the molding process. The method of adding and mixing by extruder, injection molding machine, etc., using non-additive styrene resin to adjust the phosphorus antioxidant (A) and phenol antioxidant (B) to a high-concentration resin composition dilution The method of mixing into the target content, etc. are not particularly limited.

(Other additives) The styrene-based resin composition may contain sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, hindered amine-based stabilizers, antistatic agents, hydrophilic additives, and liquid paraffin within a range that does not impair the effects of the present invention. Various additives such as mineral oil), polyethylene wax, microcrystalline wax, bluing agent, etc.

The styrene resin composition may contain, as additives, higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, stearamide, erucamide, and ethylene distearic acid as additives within the range that does not impair the effects of the present invention. Higher fatty acid amides such as amides, and higher alcohols such as myristyl alcohol, cetyl alcohol, stearyl alcohol, and other mold release agents, but the transmittance may deteriorate, and it is preferable not to contain a mold release agent other than essential. The content of the release agent is preferably 500 ppm or less in the styrene-based resin composition, more preferably 200 ppm or less, and even more preferably 100 ppm or less. From the viewpoint of obtaining high transmittance, the styrene-based resin composition preferably does not substantially contain a mold release agent.

The Vicat softening temperature of the styrene resin composition is preferably 95 to 104°C, and more preferably 97 to 104°C. When the Vicat softening temperature is less than 95°C, the heat resistance is insufficient, and the light guide plate may be deformed due to the use environment.

The haze of the styrene-based resin composition is 5% or less in the case of a molded article having a thickness of 4 mm, and more preferably 1% or less.

The average transmittance of the styrene-based resin composition at an initial optical path length of 115 mm and a wavelength of 380 to 780 nm is preferably 80% or more, and more preferably 84% or more.

The optical path length after the long-term durability test of the styrene resin composition is 115 mm, and the average transmittance at a wavelength of 380 to 780 nm is preferably 80% or more, and more preferably 83% or more.

The initial YI value of the styrene-based resin composition is preferably 7.0 or less, and more preferably 6.0 or less.

The YI value difference (ΔYI) between the initial YI value and the YI value after the long-term durability test is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

The total light transmittance and YI value were measured according to the following procedure. Using pellets of the styrene-based resin composition, injection molding was performed at a cylinder temperature of 230°C and a mold temperature of 50°C to form a plate-shaped molded product with a thickness of 127×127×3 mm. Here, the sample for evaluating the long-term durability (the sample after the long-term durability test) was stored in an oven at 80°C for 1,000 hours. Next, a test piece with a thickness of 115×85×3 mm was cut out from the plate-shaped molded product, and the end surface was polished by buffing to prepare a plate-shaped molded product having a mirror surface on the end surface. For the polished plate-shaped molded product, use the UV-visible spectrophotometer V-670 manufactured by JASCO Corporation, and measure the incident light with a size of 20×1.6mm and a diffusion angle of 0°. The optical path length is 115mm and the wavelength is 350nm～800nm. The spectral transmittance below is calculated based on JIS K7105 for the YI value of the 2° field of view under the C light source. In addition, the average transmittance at a wavelength of 380 nm to 780 nm refers to the total light transmittance.

[Manufacturing method of light guide plate] The edge-emitting light guide plate of the present invention can be obtained by molding the above-mentioned styrene resin composition. As a molding method, known methods such as sheet extrusion molding, injection molding, and compression molding can be used. From the point that it is easy to increase the size of the film, continuous sheet extrusion molding equipped with a surface shape transfer die is preferable. As an example of the sheet extrusion molding, the following continuous sheet extrusion molding method can be given, that is, it has an extrusion step of supplying a resin in a heated and molten state to a feed block and continuously extruding from a die to form a sheet. The squeezing step in which the resin sheet is sandwiched between a pressure roller and a cooling roller, and a conveying step in which the resin sheet is brought into close contact with the cooling roller after the squeezing step. The surface of the cooling roller is equipped with a transfer mold, and by changing the shape of the transfer mold, it is possible to transfer any irregularities on the sheet surface. In addition, the edge-emitting light guide plate of the present invention has a concave-convex shape on the front surface (light-emitting surface), but is subjected to reflection processing to diffuse light on the back surface. As the reflection processing, for example, in addition to screen printing and inkjet printing, a method of providing unevenness of a dot shape by laser irradiation has also been proposed, and the printing of the dot pattern can use ink having fine particles that diffuse light.

2. Edge-emitting cotton light source unit The edge emission type (side-light type) surface light source unit of the present invention is an edge emission type surface light source unit having an edge emission type light guide plate and a light source that supplies light to the end surface of the light guide plate. The edge-emitting surface light source unit of the present invention is preferably used as a surface light source device for a liquid crystal display device. [Example]

Hereinafter, the present invention will be explained in more detail with examples. In addition, these Examples are all exemplifications, and do not limit the content of the present invention.

(Manufacturing of styrene resin PS-1～PS-3) The first reactor and the second reactor as a complete mixing type stirred tank and the third reactor as a plug flow reactor with a static mixer were connected in series to form a polymerization step, which was carried out under the conditions shown in Table 1. Manufacture of styrene resin. The capacity of each reactor is 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. Using the raw material composition described in Table 1, a raw material solution was prepared, and the raw material solution was continuously supplied to the first reactor at the flow rate described in Table 1. The polymerization initiator was added to the raw material solution at the addition concentration (concentration relative to the mass standard of the raw material styrene) described in Table 1 at the inlet of the first reactor, and uniformly mixed. The polymerization initiators described in Table 1 are as follows: Polymerization initiator-1: 2,2-bis(4,4-tert-butylperoxycyclohexyl) propane (per TETR A manufactured by NOF Corporation) polymerization initiator-2: 1,1-bis(tert-butyl) (Peroxy) cyclohexane (perhexa C manufactured by NOF Corporation is used) In addition, in the third reactor, a temperature gradient was applied along the direction of flow, and the middle part and the outlet part were adjusted to the temperatures in Table 1. Next, the polymer-containing solution continuously taken out from the third reactor was introduced into a two-stage series-connected vacuum devolatilizer equipped with a preheater, and the temperature of the preheater was adjusted to the resin temperature described in Table 1, and The pressure was adjusted to the pressure described in Table 1 to separate unreacted styrene and ethylbenzene, and then extruded into a pellet form from a porous die. The pellets were cooled and cut using a cold cutting method to form pellets. The melt mass flow rate (MFR) is measured in accordance with JIS K 7210 at a temperature of 200°C and a load of 49N, and the Vicat softening temperature is measured in accordance with JIS K 7206 at a heating rate of 50°C/hr and a test load of 50N. The weight average molecular weight (Mw), Z average molecular weight (Mz), and number average molecular weight (Mn) were measured under the following conditions using gel permeation chromatography (GPC). GPC model: Shodex GPC-101 manufactured by Showa Denko Co., Ltd. Column: PLgel 10μm MIXED-B manufactured by Polymer Laboratories Mobile phase: tetrahydrofuran Sample concentration: 0.2% by mass Temperature: oven 40℃, injection port 35℃, detector 35℃ Detector: Differential Refractometer The molecular weight was calculated from the elution curve of monodisperse polystyrene at each elution time, and it was calculated as the molecular weight in terms of polystyrene.

[Table 1]

[Examples 1-19, Comparative Examples 1-7] <Preparation of resin composition> Using the content shown in Table 2 and Table 3, use a screw diameter of 40mm for styrene resin PS-1, PS-2, PS-3, phosphorus antioxidant (A) and/or phenol antioxidant (B) A single-screw extruder melted and kneaded at a barrel temperature of 230°C and a screw rotation speed of 100 rpm to obtain pellets.

In addition, the phosphorus antioxidant (A) and phenolic antioxidant (B) in Table 2 and Table 3 are as follows, respectively.

(Phosphorus antioxidant (A)) HP-10: 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus (ADK STAB HP-10 manufactured by ADEKA Co., Ltd.) ) 168: Tris(2,4-di-tert-butylphenyl) phosphite (Irgafos 168 manufactured by BASF Japan Co., Ltd.) PEP-36: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro (5.5 ]Undecane (ADK STAB PEP-36 manufactured by ADEKA Co., Ltd.) P-EPQ: Tetra(2,4-di-tert-butylphenyl) [1,1 biphenyl]-4,4-diyl diphosphonite (Hostanox P-EPQ manufactured by Clariant Co. Ltd.) 38: Bis(2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite, (Irgafos 38 manufactured by BASF Japan Co., Ltd.)

(Phenolic antioxidant (B)) GP: 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f] 〔1,3,2〕Dioxaphos (Sumilizer GP manufactured by Sumitomo Chemical Co., Ltd.) 1076: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox 1076 manufactured by BASF Japan Co., Ltd.) 245: Ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] (Irganox 245 manufactured by BASF Japan Co., Ltd.) 1010: pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] ester (Irganox 1010 manufactured by BASF Japan Co., Ltd.) AO80: 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2, 4,8,10-Tetraoxaspiro[5.5]undecane (ADK STAB AO-80 manufactured by ADEKA Co., Ltd.)

<Evaluation of optical properties of resin composition> Using the obtained pellets, injection molding was performed at a cylinder temperature of 230°C and a mold temperature of 50°C to form a plate-shaped molded product with a thickness of 127×127×3 mm. In order to evaluate the long-term durability, the obtained molded article was stored in an oven at 80°C for 1,000 hours. In order to evaluate the optical properties of the initial molded product before storage (initial sample) and the molded product after storage (sample after long-term durability test), a test piece with a thickness of 115×85×3mm was cut out from the plate-shaped molded product and polished. Polishing polishes the end surface to produce a plate-shaped molded product having a mirror surface on the end surface. For the polished plate-shaped molded product, use the UV-Visible Spectrophotometer V-670 manufactured by JASCO Corporation to measure the optical path length of 115mm and the wavelength of 350nm～800nm in incident light with a size of 20×1.6mm and a diffusion angle of 0° For the spectral transmittance below, the YI value of the 2° field of view of the C light source was calculated in accordance with JIS K7105. The total light transmittance shown in Table 2 and Table 3 represents the average transmittance with a length of 380 nm to 780 nm.

＜Manufacture of light guide plate＞ As shown in Figure 3, the obtained pellets were supplied to a single-screw extruder 5 with a screw diameter of 120mm and L/D=32, and the barrel temperature was set to 150-230°C. After melting and kneading, it was passed through a gear pump 7 , At a resin temperature of 260°C, it was ejected from a T-die 9 with a width of 1500 mm, and the sheet was extruded. Next, the extruded sheet is sandwiched between the pressure contact roller 11 (mirror surface cooling roller) and the first cooling roller 13 (mirror surface cooling roller), and after being transported in a state wound around the first cooling roller 13, it is further sandwiched Between the first cooling roller 13 and the second cooling roller 15 (transfer mold mounting roller), after the uneven shape is transferred to the single side of the resin sheet, the resin sheet peeled from the second cooling roller 15 is used for the drawing roller 17 The traction speed is 5.2m/min for traction. It should be noted that the pressure contact roller 11, the first cooling roller 13 and the second cooling roller 15 are chrome-plated, and the temperature of each roller is set as the pressure contact roller 11/first cooling roller 13/second cooling roller 15=80°C/ 85°C/90°C. Then, by changing the shape of the transfer mold attached to the second cooling roll 15, a resin sheet having the surface convex shape shown in Table 2 and Table 3 was obtained.

It should be noted that "shape", "height P", "pitch P", and "H/P" in Table 2 and Table 3 are the values defined above, respectively, and "Lenti" means "Lenticular" ".

＜Evaluation of moldability and strength of light guide plate＞ The extrusion stability (lipid accumulation), roll transferability, roll releasability, and the strength of the light guide plate produced by the light guide plates of Table 2 and Table 3 were evaluated as follows.

(Extrusion stability (lipid accumulation)) The resin temperature of the die was adjusted to 300°C, and the occurrence of grease accumulation in the orifice near the die was evaluated based on the following criteria. ○: No fat accumulation in the orifice was observed after 30 minutes from the start of sheet extrusion. △: Fat accumulation in the orifice is observed 10 to 30 minutes after the start of sheet extrusion. ×: Fat accumulation in the orifice was observed within 10 minutes after the start of sheet extrusion. It should be noted that "orifice grease" is a brown or black resin deterioration produced around the exit nozzle of the die. It usually increases with the increase in the amount of extrusion. If it exceeds the specified amount, it will detach from the nozzle and adhere to it. On the surface of the film.

(Roller transferability) The roller transfer rate T was obtained by the following formula, the roller transfer rate T was 95% or more evaluated as ○, 85 to 95% was evaluated as Δ, and 85% or less was evaluated as ×, and thus the roller transferability was evaluated. Roller transfer rate T (%) = the height of the convex part of the resin sheet H/the depth of the groove part of the transfer mold H´×100'

(Roll releasability) The resin temperature of the die was adjusted to 270°C and 290°C, and after continuous extrusion was performed at each temperature for 30 minutes, the appearance of a single surface was observed. The case where there is no change in appearance at 290°C is set as ○, and the case where surface roughness and whitening occur on a single surface at 290°C and there is no change in appearance at 280°C is set as △, and the surface roughness occurs on the sheet surface at 280°C. The case of whitening is set as ×, and the roll release properties are evaluated in this way.

(strength) A test piece of 200 mm×200 mm was cut out from the obtained resin sheet, and a ball weighing 16.6 g was used to measure the 50% breaking height in accordance with JIS K-7211. The case where the 50% fracture height is 50 cm or more is defined as ○, the case of 30 to 50 cm is defined as △, and the case of 30 cm or less is defined as ×, and the strength of the light guide plate is measured in this way.

[Table 2]

[table 3]

1: Light guide plate 3A: Convex part (convex lens shape) 3B: Convex (prismatic) 5: Single shaft extruder 7: Gear pump 9: T-die head 11: crimping roller 13: The first cooling roll 15: The second cooling roll 17: Traction roller

Fig. 1 is a perspective view showing the outline of the light guide plate of the present invention. Fig. 1A is a perspective view when the convex portion is in the shape of a convex lens. Fig. 1B is a perspective view when the convex portion is prismatic. Fig. 2 is a cross-sectional view of the light guide plate of the present invention. Fig. 2A is a cross-sectional view when the convex portion is in the shape of a convex lens. Fig. 2B is a cross-sectional view when the convex portion has a prismatic shape. Fig. 3 is a schematic diagram showing an example of a method of manufacturing the light guide plate of the present invention.

Claims (8)

An edge-emitting light guide plate, which contains a styrene resin composition, Having a plurality of convex lens-shaped and/or prismatic convex portions on the surface of the light guide plate, The thickness T of the light guide plate is 1.0-3.0 mm, The styrene-based resin composition contains a styrene-based resin, a phosphorus-based antioxidant (A) and/or a phenol-based antioxidant (B), And satisfy at least one of the following (1) and (2), (1) The height H of the convex part is 10～500μm (2) The pitch P of the convex portions is 30 to 800 μm. The edge-emitting light guide plate according to claim 1, wherein the height H of the convex portion is 10 to 500 μm, and the pitch P of the convex portion is 30 to 800 μm. The edge-emitting light guide plate according to claim 1 or 2, wherein: With respect to 100 parts by mass of the styrene-based resin composition, 0.001 to 0.5 parts by mass of the phosphorus-based antioxidant (A) and 0.001 to 0.5 parts by mass of the phenol-based antioxidant (B) are contained. The edge-emitting light guide plate according to claim 1 or 2, wherein: The phosphorus antioxidant (A) is selected from 2,2'-methylene bis(4,6-di-tert-butyl-1-phenyloxy) (2-ethylhexyloxy) phosphorus, tri (2,4-di-tert-butylphenyl) phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxy Hetero-3,9-diphosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1biphenyl]-4,4-diyldiphosphonite At least one of esters and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite. The edge-emitting light guide plate according to claim 1 or 2, wherein: The phenolic antioxidant (B) is selected from 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetratert Butyl dibenzo[d,f][1,3,2]dioxin, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate , Ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyl) Phenyl) propionate], 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethyl At least one of ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane. The edge-emitting light guide plate according to claim 1 or 2, wherein: The weight average molecular weight (Mw) of the styrene-based resin is 200,000 to 400,000, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.0 to 3.0. The edge-emitting light guide plate according to claim 1 or 2, wherein: The styrene-based resin composition has an initial optical path length of 115 mm and an average transmittance of 80% or more at a wavelength of 380 to 780 nm. An edge-emitting surface light source unit comprising the edge-emitting light guide plate according to any one of claims 1 to 7 and a light source that supplies light to the end surface of the edge-emitting light guide plate.

Images