WO2007058060A1

WO2007058060A1 - Light guide plate

Info

Publication number: WO2007058060A1
Application number: PCT/JP2006/321263
Authority: WO
Inventors: Takeo Kuroki; Satoru Hirota
Original assignee: Asahi Kasei Chemicals Corporation
Priority date: 2005-11-17
Filing date: 2006-10-25
Publication date: 2007-05-24
Also published as: TW200730903A; KR100969343B1; JPWO2007058060A1; CN101313175A; CN101313175B; JP5137581B2; KR20080032208A; TWI348562B

Abstract

A light guide plate of a surface light source device of edge-light type in which a light source is disposed on a side surface of the plate. The light guide is formed of a transparent thermoplastic resin containing particles. The front surface of the light guide plate serves as a light output surface, and the back surface of the light guide plate is subjected to a light diffusion processing to have a gradation from the side surface toward the direction far from the light source. The light guide plate is characterized in that the color tone variation (ΔYImax-min) which is the difference between the maximum value (YImax) and the minimum value (YImin) of the yellow index (YI) determined from the tristimulus values (XYZ) in the 25 luminance measurement point on the light output surface is 20 or less.

Description

Specification

Light guide plate

Technical field

[0001] The present invention relates to an office automation device such as a personal computer or a word processor, a liquid crystal display device used for various liquid crystal monitors (for example, a panel monitor or a television monitor) for displaying an image signal, and illumination of indoor and outdoor spaces. The present invention relates to a light source plate suitable for a surface light source display device or a signboard used in the device.

Background art

[0002] Transparent thermoplastic resin, especially methallyl resin, in particular, has been used for many lighting applications because of its excellent light transmission and mechanical properties. It is suitably used as a material for the light guide plate or diffusion plate of the source device. This surface light source device is broadly classified into two types: a so-called direct type in which a diffusion plate is sandwiched between a light source (cold cathode tube) and a liquid crystal unit, and an edge light type in which a light source is arranged on the side end surface of the light guide plate. . Liquid crystal display devices represented by large-sized liquid crystal televisions of 21 inches or larger are mainly under the direct method, whereas edge light systems are used for surface light source devices for liquid crystal televisions of smaller sizes and liquid crystal monitors for personal computers. Is often used.

The mechanism of the edge light type surface light source device is as follows. Light diffusion gradation processing such as dot printing is performed on one side of the light guide plate, and a light source is arranged on the side end surface of the light guide plate. The light incident on the side surface of the plate travels while being totally reflected in the light guide plate, changes its direction by the light diffusion gradation process on the surface of the plate, and the light is emitted from the opposite surface. The edge light system has the feature that the surface light source device can be made thin and compact. However, the number of light sources that can be arranged is limited due to its structure, so that the luminance as a surface light source device is lower than in the direct type. Recently, liquid crystal display devices have been developed that are bright and have good color reproducibility even with the edge-light method, which demands products with higher image quality while being thin and power-saving. In particular, there is a strong demand for the development of surface emitting devices with high brightness and small color unevenness.

[0004] Many techniques have been disclosed to increase the brightness of the light guide plate. For example In the light guide plate, light-scattering plastic fine particles having a refractive index different from that of transparent thermoplastic resin

(Japanese Patent Laid-Open No. 145485: Patent Document 1) and a method for increasing the brightness by dispersing fine particles having a hollow structure (Japanese Patent Laid-Open No. 2000-113708: Patent Document 2) are disclosed. In Patent Document 3 (Japanese Patent Application Laid-Open No. 2004-351649), a light guide plate is prepared by dispersing fine particles in advance in a thermoplastic resin so as to prevent the fine particles from agglomerating during polymerization. A method for increasing the brightness is also disclosed. Furthermore, Patent Document 4 (Japanese Patent Laid-Open No. 2005-181632) discloses a method for increasing the brightness by optimizing the particle size distribution of fine particles.

Patent Document 1: Japanese Patent Laid-Open No. 4 145485

Patent Document 2: JP 2000-113708 A

Patent Document 3: Japanese Patent Laid-Open No. 2004-351649

Patent Document 4: Japanese Unexamined Patent Application Publication No. 2005-181632

Disclosure of the invention

Problems to be solved by the invention

[0006] In these prior arts, the fine particles selected according to the selection criteria for the fine particles are those that contribute to the improvement of the brightness. However, it was impossible to obtain a light guide plate that could satisfy the requirements.

[0007] For example, if the particle diameter of the fine particles is small, blue light having a relatively short wavelength is scattered by the fine particles in the wavelength range of the incident visible light, and the color tone unevenness of the light exit surface increases. Therefore, if the particle size of the particles is increased, the light scattering effect is reduced, and the amount of fine particles added must be increased in order to obtain the desired luminance. Increasing the amount of added fine particles increases the amount of light transmitted through the fine particles, and the fine particles themselves absorb light having a wavelength of visible light. For this reason, the color of the light that has passed through the fine particles changes from that before transmission, resulting in increased color tone unevenness and light output unevenness. This problem is particularly noticeable when titanium dioxide with high brightness is obtained. From such a situation, in Patent Document 4, titanium dioxide can be used, but in the examples, only acid aluminum is cited.

As described above, the conventional technique requires high color reproducibility while having a compact structure. At present, it has not reached the level of providing a light guide plate that has sufficient performance for the products that are available. An object of the present invention is to provide a light guide plate that has high luminance and little color unevenness and light output unevenness.

Means for solving the problem

As a result of intensive studies to solve the above problems, the present inventors have included a predetermined amount of a light guide plate having a color tone unevenness of a certain amount or less, in particular, a specific amount of titanium dioxide fine particles having a specific primary particle size distribution. The light guide plate of the present invention was completed by using the transparent thermoplastic resin composition possessed. The obtained light guide plate efficiently scatters incident light to the exit surface side and suppresses the scattering of blue light with a short wavelength of visible light, thereby improving color unevenness and further emitting light. The present inventors have found that the luminance can be increased, and have completed the present invention.

That is, the present invention has the following configuration.

1. a light guide plate for an edge light type surface light source device, which is made of a transparent thermoplastic resin containing fine particles and has a light source disposed on a side end surface of the plate, and when one side of the plate is used as a light emitting surface, Side end surface force on which the light source is disposed on the back surface Light source force Light diffusion treatment having a dullion is applied in the direction of moving away, and three of 25 luminance measurement points on the light exit surface are applied. The color unevenness (Δ Ylmax-min), which is the difference between the maximum value (Ylmax) and the minimum value (Ylmin) of the yellowness (YI) obtained from the stimulus value (XYZ), is 20 or less. Light plate

2. The fine particles are titanium dioxide fine particles having an average primary particle diameter of 0.2 to 0.3 m, and 0.01 to 20 ppm of titanium dioxide fine particles are contained in the transparent thermoplastic resin composition. 2. The light guide plate according to 1 above, wherein

3. The light guide plate according to 2, wherein the transparent thermoplastic resin composition comprises a transparent thermoplastic resin composition containing 0.01 to 4 ppm of titanium dioxide fine particles in the transparent thermoplastic resin composition.

4. The ratio (D90ZD10) of 90% cumulative average particle size (D90) to 10% cumulative average particle size (D10) in terms of volume of the titanium dioxide fine particles is 5.0 or less. 4. The light guide plate according to any one of 2 and 3 above.

5. At least one of the light emitting surface and the back surface thereof is formed by arranging semicircular circular arcs that are connected and arranged so that the connected circular arcs are substantially perpendicular to the side end surfaces. The cross-sectional shape of each semi-cylinder is such that the ratio (RZP) of the radius of curvature (R) to the pitch (P) of the semi-cylinder is 0.6 to 2.0. A light guide plate according to any one of the above.

6. The light guide plate according to any one of 2 to 5 above, wherein the transparent thermoplastic resin is one selected from a methacrylic resin, a polycarbonate resin, and a cyclic polyolefin resin.

The invention's effect

[0011] The light guide plate of the present invention has a high luminance due to the increased luminous efficiency of incident light with light source power. In addition, light emission unevenness, that is, a phenomenon in which the emitted light in the vicinity of the light source is large and the emitted light in the central portion is not too small is unlikely to occur. Along with this, there is a remarkable effect that the bluish color is strong near the light source and the yellow color is strong in the center, and there is no uneven color tone. Accordingly, it is possible to provide a light guide plate suitable for a display device used for various monitors such as a panel monitor and a television monitor for displaying an image signal, a display device used for a lighting device for indoor and outdoor spaces, a signboard, and the like.

Brief Description of Drawings

FIG. 1 is an explanatory view of a portion where arcs of semicircular cylinders formed on the surface of a light guide plate are connected.

FIG. 2 shows a method for evaluating luminance in an edge light type surface light source device using the light guide plate of the present invention.

FIG. 3 is an explanatory diagram showing measurement points when measuring the luminance of the light guide plate of the present invention.

Explanation of symbols

[0013] A: Light source (cold cathode tube)

B: Lamp house

C: Light guide plate

D: Light reflection sheet

E: Light diffusion sheet

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] Embodiments of the light guide plate according to the present invention will be specifically described below.

<Transparent thermoplastic resin constituting the light guide plate> In the present invention, examples of the transparent thermoplastic resin constituting the light guide plate include a metataryl resin, a polycarbonate resin, a cyclic olefin-based resin, a styrene-based resin, and an amorphous polyester. Preferred are methallyl resin, polycarbonate resin, and cyclic olefin-based resin, and more preferably methacrylic resin.

[0015] The methacrylic resin can be obtained by copolymerizing 70% by weight or more of methyl methacrylate or ethyl acetate and a monomer having copolymerizability with methyl methacrylate or ethyl methacrylate. Monomers that are copolymerizable with these include butyl methacrylate, ethyl methacrylate, methyl methacrylate, propyl methacrylate, cyclohexyl methacrylate, methacrylic acid phenol, and 2-ethylhexyl methacrylate. Methacrylic acid esters, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, acrylic acid phenol, 2-ethyl hexyl acrylate, acrylic acid esters, methacrylic acid, acrylic acid, etc. Of unsaturated acids. Note that the methacrylic resin is not limited to these. Further, the production method is not limited at all.

[0016] As the polycarbonate resin, a polymer derived from a divalent phenol compound represented by bisphenol A is used. The production method of the polycarbonate resin is not particularly limited, and well-known and commonly used methods such as a phosgene method, a transesterification method or a solid phase polymerization method can be mentioned.

[0017] The cyclic olefin fin resin is a polymer having a cyclic olefin skeleton in a polymer chain, such as norbornene cyclohexane, or a copolymer containing these, and belongs to an amorphous thermoplastic resin. The manufacturing method is not particularly limited. For example, as cyclic olefin fin resins mainly composed of norbornene, JP-A-60-168708, JP-A-62-252406, JP-A-2-133413, JP-A-63-145324 The resin described in JP-A-63-264626, JP-A-1-240517, JP-B-57-8815 and the like can be used. Further, if necessary, a soft polymer may be added. For example, an olefin-based soft polymer such as α-olefin linker, an isobutylene-based soft polymer composed of isobutylene, a gen-based soft polymer such as conjugated jean such as butadiene or isoprene, or a cyclic olefin such as norbornene or cyclopentene. A cyclic olefin-based soft polymer, an organic polysiloxane-based soft polymer, a, j8-soft polymer composed of an unsaturated acid and a derivative thereof, an unsaturated alcohol and amine, an acyl derivative thereof, or a soft polymer capable of acetal force, Examples thereof include polymers of epoxy compounds and fluorine rubber.

[0018] The styrene-based resin is a homopolymer or copolymer having styrene as an essential component, or a polymer blend in which such a polymer and other resin and force can be obtained. In particular, polystyrene resin, AS resin which is a copolymer resin of acrylonitrile and styrene, and MS resin which is a copolymer resin of methacrylic acid ester and styrene are preferable. Furthermore, transparent reinforced polystyrene in which rubber is distributed in the styrene-based resin phase can also be preferably used. The method for producing the styrene-based resin is not particularly limited, and those produced by a well-known and commonly used method can be used.

[0019] Amorphous polyester includes ethylene glycol, propylene glycol, 1, 4 butane diol, neopentyl glycol, hexamethylene glycol and other aliphatic glycols, cyclohexane dimethanol and other alicyclic glycols, and bisphenol. Aromatic dihydroxy compounds such as 1,3 bis (2-hydroxyethoxy) benzene, 1,4 bis (hydroxyethoxy) benzene, or two or more dihydroxy compounds selected from these units, and Aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2, 6 naphthalene dicarboxylic acid, aliphatic dicarboxylic acids such as oxalic acid, adipic acid, sebacic acid, succinic acid, undecadicarboxylic acid, hexahydroterephthalic acid, etc. Selected from alicyclic dicarboxylic acids, or two or more of these Among the polyesters units and mosquito ゝ et forming a noncrystalline resin. The method for producing the amorphous polyester is not particularly limited, and those produced by a well-known and commonly used method can be used. Commercially available brands that are readily available as amorphous polyesters include KODA R PETG or PCTA, which are Eastman Kodak products.

[0020] <Fine particles>

As fine particles dispersed in the light guide plate of the present invention, known fine particles such as acid aluminum and titanium dioxide can be used. Of these, titanium dioxide fine particles having an average primary particle diameter in the range of 0.24 m to 0.3 m are preferable. Within this range, the light source to the light guide plate The incident light is scattered by the fine particles, so that a phenomenon in which the emitted light color tone is different between the vicinity of the light source and the central portion of the plate, that is, so-called uneven color tone hardly occurs. In addition, there is little light loss due to back reflection. Furthermore, the light source power can also efficiently scatter incident light to the exit surface side. As a result, it is possible to achieve a good balance between the effect of improving the light emission luminance and the suppression of color unevenness in the exit surface. Titanium diacid titanium has high brightness, so even if the concentration relative to transparent thermoplastic resin is relatively low, there is a feature that high brightness can be obtained, but even if the particle size is too large or too small, the color unevenness becomes severe There is a tendency. If the particle diameter falls outside the above range and becomes less than or equal to 0., the relatively short wavelength, blue, and light are scattered by the fine particles in the visible light wavelength range, resulting in increased color unevenness on the light exit surface. There is a tendency. If the particle size is 0 or more, the light scattering effect may be lowered, and the amount of added fine particles must be increased in order to increase the brightness of the light guide plate. As the number of fine particles increases, the amount of light that passes through the fine particles increases, and the light that has passed through the fine particles changes its color before transmission because the fine particles themselves absorb light of the visible light wavelength. Color unevenness increases.

[0021] Next, the amount of fine particles dispersed in the transparent thermoplastic resin is preferably 0.01 to 20 ppm force S, more preferably 0.75 or more to the weight of the transparent thermoplastic resin. LOppm, more preferably 0.1 to 4ppm. If the amount of fine particles is within the range of 0.01 ppm to 20 ppm, for example, even in a relatively large liquid crystal display device of 15 inches or more, light scattering gradation processing should not be applied to the back surface of the exit surface! / However, the light emitted from the light source has a uniform light output distribution on the entire exit surface where there is no difference between the luminance in the vicinity of the light source and the luminance at the farthest position from the light source. Therefore, even if the light diffusion gradation process for correcting the emitted light is performed on the back surface of the light exiting surface of the light guide plate, the light source power will not be darkened at the farthest part, and the light output distribution on the light emitting surface should be properly balanced. Can do. Furthermore, when the proportion of fine particles is 20 ppm or less, it is possible to suppress the color tone distribution of the outgoing light within the outgoing surface where the change in the color tone near the light source of the light guide plate is small due to scattering.

[0022] The particle size distribution of the fine particles is sharp when the ratio of the 90% cumulative average particle size (D90) to the 10% cumulative average particle size (D10) (D90ZD10) is 5.0 or less in terms of volume. It is preferable that The closer the D90ZD10 is to 1, the sharper the particle size distribution, and each particle size is closer to the average particle size (D50). More preferably 3.5 or less, even more preferably 3.0 or less It is.

[0023] Conversely, when D10 becomes smaller and D90ZD10 becomes larger, the color tone unevenness in the exit surface tends to become larger. In addition, when D90 becomes larger and D90ZD10 becomes larger, the scattering efficiency tends to deteriorate, and the brightness enhancement effect of the fine particles may be reduced. Preferably, it is 3.5 or less, more preferably 3.0 or less. The cumulative average particle size referred to here was obtained from the cumulative distribution in terms of volume. The average particle size at which the cumulative volume was 90% was D90, and the average particle size at which the cumulative volume was 10% was D10.

[0024] It should be noted that the particle size distribution D90ZD10 is 5.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and the average primary particle size is 0.24 / ζ πι to 0.3 m. A light guide plate containing 0.01 to 20 ppm, more preferably 0.05 to: LOppm, and still more preferably 0.1 to 4 ppm of fine particles within the range has the effect of improving luminance, suppressing color tone unevenness, and suppressing light emission unevenness. Especially high.

[0025] The shape of the fine particles is not particularly limited, such as a spherical shape, a spherical shape, a scale shape, a cubic shape, and an indefinite shape. Of these, spherical is preferable.

The crystal structure of titanium diacid-titanium is not particularly limited to forces including, for example, a rutile type and an anatase type.

The light guide plate of the present invention has a light diffusion gradation on the back surface of the exit surface. The light diffusion process is to correct the angle of the light so that a sufficient amount of the light incident on the entrance surface reaches the exit surface. For example, the size gradually increases from the edge of the light guide plate surface to the center, or from one end to the other end (the light source is also directed to the farthest part of the light source).

Add a dot pattern that has a large number of circles, squares, etc., with a gradually increasing number of gradations.

[0027] The shape of the light guide plate of the present invention is basically a plate shape, but may be a shape obtained by shaping the plate surface. By shaping the plate surface, it is possible to remove the so-called dot image in which only the light diffusion gradation appears to shine, and to further increase the light emission luminance of the light guide plate. When the side end surface facing the light source is the light incident surface and the surface substantially orthogonal to the light incident surface is the light exit surface, the shaping process is performed on at least one of the light entrance surface and the back surface of the exit surface. . As the shape of shaping, for example, semicircular arcs are connected, that is, the cross section There is a substantially semi-cylindrical shape in which substantially semi-circular cylinders are connected to each other, and a substantially semi-cylindrical shape with a ridge line extending substantially perpendicular to the light incident surface.

[0028] The substantially semicircular shape of the semi-cylindrical cross section is a part of an arc or an elliptical arc, and preferably the radius of curvature (R) and the semi-cylindrical row pitch (P) shown in Fig. 1 are used. The cross-sectional shape with a ratio force (RZP) in the range of 0.6 to 1.75 is also desirable. More preferably, it is 0.6-1.5, More preferably, it is 0.7-1.3. The heights (H) of the substantially semicircular cylinders are preferably all the same, but the heights may be somewhat different as long as the difference in height is within 20%.

[0029] If the shaping process is formed at least on the back surface of the light emitting surface, a sufficient light emission luminance improving effect can be obtained, but it is more preferable if it is also formed on the light emitting surface.

[0030] The method of shaping the light guide plate is not particularly limited! /, For example, a method of directly covering the light guide plate by etching, cutting by cutting, laser processing, etc .; A method of heat-pressing the surface of the light guide plate using a die or the like having a lens pattern formed by a blade cutting, laser processing, etc., applying an active energy ray-curable resin on the light guide plate and applying the active energy ray Examples thereof include a method of transferring a cylindrical lens array by mold hardening and a method of forming a light guide plate having a semi-cylindrical array by extrusion molding or injection molding. In particular, when extrusion is performed using an embossing roll having a lens array shape, stable mass production is possible.

[0031] <Light guide plate forming method>

As a method for forming the light guide plate of the present invention, a force S for which a known method can be used, for example, the following method may be mentioned. The above-mentioned transparent thermoplastic resin and the resin composition having fine particle force are formed into a sheet molded body by, for example, an extruder or a press molding machine, then cut into a predetermined size, and the cut surface is polished and guided. A light plate is obtained, and if necessary, the cylindrical lens array is shaped and subjected to a light diffusion treatment. There is also a method of molding with an injection molding machine using a shaping mold.

[0032] Examples of a method for obtaining a rosin composition containing fine particles include the following methods.

1. A resin composition is produced by uniformly dispersing fine particles in an organic liquid using, for example, an ultrasonic generator. The organic liquid mentioned here is a general organic liquid or transparent thermoplastic resin. It is not limited at all as long as it is a polymerizable monomer or the like constituting fat, and the light diffusing agent is difficult to dissolve and swell, and can be uniformly dispersed. Depending on the dispersion state of the fine particles, several kinds of organic liquids can be mixed in any proportion. Examples of the general organic liquid include ketones such as acetone and methyl ethyl ketone, aromatics such as xylene and toluene, and alcohols such as methanol and ethanol.

[0033] As the polymerizable monomer, for example, when the transparent thermoplastic resin is a methacrylic resin, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, methacrylate methacrylate Methacrylic acid esters such as 2-ethylhexyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, acrylic acid acrylic acid, 2-ethylhexyl acrylic acid, etc. Examples include acrylic acid esters, unsaturated acids such as methacrylic acid and acrylic acid. When the resin composition is melt-kneaded with an extruder, the mixing ratio between the fine particles and the organic liquid can be arbitrarily determined in consideration of the dispersibility of the fine particles. If it says strongly, it is preferable that microparticles | fine-particles are the range of 0.001-80 mass parts with respect to 100 mass parts of organic liquids. Further, the mixing ratio of the dispersion liquid and the transparent thermoplastic resin can be arbitrarily determined in consideration of the handling property in the mixing extrusion process. In other words, it is preferably in the range of 0.001 to 10 parts by mass with respect to 100 parts by mass of the transparent thermoplastic resin!

[0034] 2. After fine particles are uniformly dispersed in a syrup containing a monomer or a partial polymer constituting a transparent thermoplastic resin, for example, using an ultrasonic generator, and then cast by a known method. Polymerize. The amount ratio between the fine particles and the raw material monomer to disperse them can be arbitrarily determined in terms of dispersibility, charging viscosity, handling properties, and the like. Also, other conditions are not particularly limited, and well-known and customary conditions of the casting method can be applied.

[0035] 3. A master batch pellet containing a high concentration of fine particles in the transparent thermoplastic resin composition is prepared, and diluted to a desired concentration with the transparent thermoplastic resin during molding. As a guide, it is better to disperse the fine particles into a transparent thermoplastic resin composition 5 to 300 times the fine particles to be finally included in the light guide plate to form pellets.

[0036] In the above method, an ultrasonic generator used for dispersing particles is a commercially available A sonic cleaner or an ultrasonic stirrer can be used. For example, an ultrasonic cleaner having an ultrasonic frequency of 28 kHz to: LOOKHz is generally used. The irradiation time by the ultrasonic generator can be arbitrarily set according to the dispersion state of the fine particles, but it is generally preferable to irradiate for 1 minute to 60 minutes.

[0037] In order to melt-knead and mold the resin composition thus obtained, for example, an extruder is generally used. In the case of melt kneading with an extruder, the above-mentioned rosin composition is mixed with a transparent thermoplastic rosin using, for example, a Henschel mixer, a super floater, a tumbler, and other well-known and conventional devices. be able to. Examples of the extruder for melt-kneading the above mixture include a single-screw or twin-screw extruder, but it is preferable to use a twin-screw extruder because it can prevent secondary aggregation of fine particles. In order to remove the volatile component of the organic liquid used for dispersing the fine particles, it is preferable to perform degassing under reduced pressure at the vent port. The pressure at this time should be less than 300 Torr. Furthermore, the temperature of the extruder can be arbitrarily set according to the type of transparent thermoplastic resin used. For example, in the case of metataryl resin, it is around 180-260 ° C.

[0038] <Light diffusion treatment>

In the light guide plate of the present invention, in order to make the emitted light distribution uniform, the light having a gradation is directed to the direction in which the side end surface force and the light source force are disposed away from the rear surface of the light emitting surface. It is necessary to apply diffusion treatment.

Examples of the light diffusion process include a dot or uneven shape that has a gradation pattern that gradually increases in area as the light source is placed, or a dot or uneven shape that is the same size is pitched as the light source power increases. There is a gradation notation that makes the width narrower. In this case, the shape of the dots and irregularities can be round or square, and the size is about 0.1 to 2 Omm.

[0039] The method of the light diffusion treatment is not particularly limited, and the exit surface of the light guide plate is formed by screen printing using a white or translucent ink mixed with titanium oxide, silica, or the like after making a plate-like gradation pattern. There are a method of applying to the back surface of the material and a method of performing press processing and injection molding processing using a mold having a gradation pattern.

[0040] <Color tone unevenness> The light guide plate of the present invention needs to have a color tone unevenness (AYImax-min) of 20 or less. Color tone irregularity refers to the following phenomenon. That is, the light incident on the side end surface of the light guide plate from the light source is scattered by the light diffusion process while repeating total reflection inside the light guide plate, and thus emits light from the exit surface beyond the critical angle. At that time, the blue light on the short wavelength side of the visible light castle is scattered by the transparent thermoplastic resin constituting the light guide plate, fine particles, and other necessary UV absorbers, mold release agents and anti-oxidation agents. Or it appears yellow when absorbed. This uneven color tone tends to increase as the distance on the light exit surface increases with the light source power. The color unevenness (AYImax-min) is obtained as follows.

[0041] First, the light guide plate is set in an edge light type liquid crystal light source evaluation apparatus as shown in FIG. At this time, a cold-cathode tube of 4 mmφ (made by Harrison Electric Co., Ltd.) is used as the light source A in FIG. 2, a light guide plate having a length of 319 mm and a width of 241 mm is used as the light guide plate C, and Ray White 75 (manufactured by Kimoto ) And place two light diffusion sheets E (light diffusion sheet D121 (made by Gidden)) on top of the light guide plate C. Next, an inverter is connected to the cold-cathode tube, a voltage of 12V is applied to the inverter from a DC voltage stabilizer, and the lamp is lit for 30 minutes, and then a luminance meter (BM-7Fast: manufactured by Topcon) located at a distance of lm from the emission surface Measure the tristimulus values (X, Y, Z) at the measurement points obtained together with the brightness. As shown in Fig. 3, the whole emission surface is divided into 25 parts, total 5 parts in length and 5 parts in width, as shown in Fig. 3, and 25 points are measured at the center P1 to P25 of each section. The yellowness (YI) is calculated from the obtained tristimulus values (X, Υ, Z), and the difference between the maximum yellowness (YImax) and minimum yellowness (YImin) at the measurement point (ΔYIMAX—MIN) And

[0042] Yellowness (YI) was calculated using the following equation.

Yellowness (YI) = 100 (1.28X- 1. 06Ζ) / Υ

If the color unevenness is 20 or less, for example, in a liquid crystal monitor, the surface light source device power is excellent in the color reproducibility of light transmitted through the liquid crystal panel. Preferably it is 10 or less, more preferably 8 or less.

[0043] <Addition of UV absorber, etc.>

In addition, an ultraviolet absorber can be added to the light guide plate of the present invention, if necessary, in order to prevent the light guide plate from being colored by the ultraviolet light generated by the light source. Due to the addition of UV absorber, the color light source device can be used even if the monitor is used for a long time. The upper color tone is always constant, and the occurrence of color tone unevenness can be further suppressed. Furthermore, it is possible to suppress a decrease in luminance and an increase in luminance unevenness.

[0044] Examples of the ultraviolet absorber include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2 hydroxy-3,5 bis (α, α, dimethylbenzyl) phenol] base. Benzotriazole UV absorbers such as Nzotriazolole, 2- (3,5 di-aminole-2-hydroxyphenol) benzotriazole, 2-Hydroxy-4-methoxybenzophenone, 2, 2, monodihydroxy 1-Methoxybenzophenone, 2-hydroxy-1 4-n-benzophenone UV absorbers such as oxyoxybenzophenone, salicylate, salicylic acid UV absorbers such as 4-t-butylphenol salicylate These may be used in combination of two or more. The ultraviolet absorber should be added at a concentration of 30 to 2000 ppm, more preferably 80 to 500 ppm, based on the transparent thermoplastic lunar effect. When the amount of the ultraviolet absorber is within this range, a coloring suppression effect is ensured, and a luminance reduction and luminance unevenness suppression effect can also be obtained.

[0045] Further, for example, glycerin fatty acid esters such as glycerin monostearate, higher alcohols such as stearyl alcohol, and higher fatty acids such as stearic acid are added to the light guide plate of the present invention as a mold release agent, or phenol. It is possible to add anti-oxidation agents such as thioether, thioether and phosphite. In that case, it is preferably used at a concentration of 5000 ppm or less, as long as it does not impair the object of the present invention.

Example

[0046] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

The average primary particle diameter of the fine particles was measured by the following method. The fine particles were photographed with a transmission electron microscope, and the major and minor diameters of the obtained particle images were measured.

In order to measure the size of one unit of fine particles in consideration of light scattering and wavelength dependency, the average value of the obtained measurement values is the particle size of one fine particle, and the average of the particle size of 100 fine particles The value was defined as the average primary particle size.

<Measuring method of particle size distribution> An aqueous sodium hexametaphosphate solution was used as a fine particle dispersion medium, and measurement was performed using a “laser diffraction Z scattering type particle size distribution analyzer LA-750” (manufactured by Horiba, Ltd.). The cumulative average particle size was obtained from the cumulative distribution in terms of volume. The average particle size at which the cumulative volume was 90% was D90, and the average particle size at which the cumulative volume was 10% was D10.

[0048] <Measuring method for measuring average luminance of light guide plate>

Evaluation was performed using the edge light type liquid crystal light source device shown in FIG. As a light source A, a cold cathode tube (made by Harrison Electric) with a diameter of 4 mm φ is installed on both end faces of a light guide plate C with a length of 319 mm and a width of 24 lmm, and a light-reflective sheet D with a white length of 318 mm and a width of 240 mm. (Manufactured by Kimoto), two light diffusion sheets E (light diffusion sheet D121; made by Gidden) were placed on top of the light guide plate C.

A luminance meter (BM — 7FastZ viewing angle set to 1 degree) was installed at a position 0.5m away from the light exit surface after connecting the inverter to a cold cathode tube, applying a voltage of 12V from the DC voltage stabilizer to the inverter and lighting it for 30 minutes. Brightness measured at 25 points on the exit surface. As shown in Fig. 3, 25 points were divided into a total of 25 parts, 5 parts in length and 5 parts in width, and the center of each section was used as the measurement point. The average luminance was also calculated for the obtained measured value force.

<0049> <Evaluation method of uneven color tone of light guide plate>

The evaluation was performed in order to see the degree of unevenness in color tone, which is a phenomenon in which the bluish color near the light source is strong and the yellow color is strong in the part away from the light source power when the light source is placed on the light guide plate.

In the above average luminance measurement, the yellowness (YI) is calculated by the following formula using the tristimulus values (X, Y, Z) of each measurement point obtained together with the luminance by the luminance meter, and the maximum of the measurement points is calculated. The difference in yellowness (YImax)-minimum yellowness (YImin) (ΔYIMAX – MIN) was defined as uneven color tone. Formula for calculating yellowness (YI): Yellowness (YI) = 100 (1.28X-1.06Ζ) / Υ

In order to see the balance between the emitted light in the vicinity of the light source and the emitted light at the center, the above-mentioned average luminance measurement was evaluated by visually observing the luminance tolerance of the entire emitting surface. Was calculated from the following equation using the maximum luminance (luminance max) and the minimum luminance (luminance min) among the 25 divided measurement points when measuring the average luminance of the light guide plate. Emission light unevenness = (luminance minZ luminance max) X 100 (%)

[0051] In the calculation of the unevenness of the emitted light, the luminance at the central point of the surface light emitting device at the measurement point P13 shown in Fig. 2 among the 25 divided measurement points is defined as the central luminance (luminance Center), and the central luminance (luminance Center) ) Is the maximum luminance (luminance max), the unevenness of light emission is set to `` None '', and if there is the maximum luminance (luminance max) between the light source side of measurement points P6 to P10 and P16 to P20 and the center of the light guide plate, Unevenness S was “slightly”, and if there was maximum brightness (luminance max) on the light source side of measurement points P1 to P5 and P21 to P25, output unevenness was determined to be “large”.

[0052] <Production of methacrylic resin ex pellet>

Methyl methacrylate 79.9%, methyl acrylate 5.1% by weight, and ethylbenzen 15% by weight are added to a monomer mixture of 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclo 150 ppm hexane and 300 ppm n-octyl mercaptan were added and mixed uniformly. This mixed solution was continuously supplied to a sealed pressure resistant reactor having an internal volume of 10 liters, and polymerized with stirring at an average temperature of 130 ° C. and an average residence time of 2 hours. This resin was continuously sent to a storage tank connected to the reactor, and after removing volatile components under reduced pressure, it was continuously transferred to an extruder in a molten state. Using a feed pump from the side of the extruder, add a predetermined amount of UV absorber (2- (5-methyl-2-hydroxyphenol) benzotriazole) melted by heating at 140 ° C. By extruding the fat composition, methacrylic resin OC pellets were obtained. As a result of analyzing this pellet, the copolymerization ratio was 94.0% by weight of methyl methacrylate, 6.0% by weight of methyl acrylate, and 150 ppm of 2- (5-methyl-2-hydroxyphenyl) benzotriazole. It was what was contained.

[0053] <Preparation of raw material pellet A>

Titanium dioxide (average primary particle size: 0.29 ^ πι) 0.15 g of xylene: methanol = 3: 1 mixed organic liquid in 20 g of ultrasonic cleaning machine (US — 4 manufactured by IUCHI) was used for transmission frequency 3 It was dispersed for 30 minutes at 8 KHz and confirmed to be uniformly dispersed. The dispersion was uniformly sprinkled onto 1.5 kg of methanolic α-pellet and blended at 1400 rpm for 1 minute using a Henschel mixer (Mitsui Miike Kogyo Co., Ltd.). This operation is repeated until the required amount of mixed pellets is obtained, and the obtained mixed pellets are extruded at a temperature of 250 ° C while being devolatilized under reduced pressure using a 30 mm φ twin screw extruder (manufactured by Nakata).メタ Metatari containing lOOppm of titanium A rubber composition was obtained. This is hereinafter referred to as raw material pellet A.

A pellet was prepared in the same manner as in the preparation of the raw material pellet A, except that the average primary particle diameter of titanium dioxide was changed to 0.25 m. The obtained methacrylic resin composition is referred to as raw material pellet B.

A pellet was prepared in the same manner as in the preparation of the raw material pellet A, except that the average primary particle diameter of titanium dioxide was changed to 0.045 μm. The obtained methacrylic resin composition is referred to as raw material pellet C.

In the preparation of the above raw material pellet A, the same procedure was performed except that, instead of titanium dioxide having an average primary particle size of 0.29 m, acid / aluminum having an average primary particle size of 0.5 / zm was used. A pellet was prepared. The obtained pellets contained lOOppm of aluminum oxide. This methacrylic resin composition is designated as raw material pellet D.

In the preparation of the above raw material pellet A, the same procedure was performed except that, instead of titanium dioxide having an average primary particle size of 0.29 m, acid-aluminum having an average primary particle size of 0.27 / zm was used. A pellet was prepared. The obtained pellets contained lOOppm of aluminum oxide. This methacrylic resin composition is referred to as raw material pellet E.

A pellet was prepared in the same manner as in the preparation of the raw material pellet A, except that the average primary particle diameter of titanium dioxide was changed to 0.2 μm. The obtained methacrylic resin composition is designated as raw material pellet F.

A pellet was prepared in the same manner as in the preparation of the raw material pellet A, except that the average primary particle diameter of titanium dioxide was changed to 0.4 μm. The obtained methacrylic resin composition is referred to as raw material pellet G.

<Preparation of raw material pellet H> In the preparation of the above raw material pellet A, the methacrylic resin α pellet was changed to a cyclic olefin fin resin pellet (manufactured by Nippon Zeon: Zeonor 1060R), and the hopper was purged with nitrogen with a 30 mm φ twin screw extruder (manufactured by Nakata), and Pellets were produced in the same manner except that extrusion was performed at 250 ° C while evacuating to lOOTorr. The obtained cyclic olefin fin resin composition is designated as raw material pellet H.

In the preparation of the above raw material pellet A, methacrylic resin α pellet was replaced with polycarbonate resin resin pellet (Teijin Chemicals: Panlite ZL-1250Y), and nitrogen was purged into the hopper with a 30mm φ twin screw extruder (manufactured by Nakata). In addition, pellets were produced in the same manner except that extrusion was performed at 260 ° C. while evacuating to 10 torr. Let the obtained polycarbonate resin composition be the raw material pellet K.

[Example 1]

Raw material pellet A and methacrylic resin ex pellet were uniformly mixed by a tumbler at a mixing weight ratio of 1: 199. The resulting mixed pellets were extruded at a temperature of 250 ° C using a 50mm φ single-screw extruder with a T-die for the sheet, a polishing roll adjusted to 80 ° C, and an extrusion sheet forming machine with a pulling device. Thus, an extruded plate having a width of 400 mm and a thickness of 6 mm and containing 0.5 ppm of titanium dioxide was obtained.

Next, the resulting extruded plate was cut into a size of 241 mm in width and 319 mm in length using a circular saw, and the cut surface of the cut-out plate was cut using a precision polishing machine (PLA—Beauty: manufactured by Megalotech Co., Ltd.) Polished and then puffed to give a mirror finish. Next, using a printing screen with a 15-inch size dot gradation and using matte medium SR9 31Z15 (Mino Group) as ink, screen printing is performed on one side of the light guide plate to obtain a light diffusion layer. It was.

[Example 2]

A light guide plate containing 2. Oppm of titanium dioxide was obtained in the same manner as in Example 1, except that the raw material pellet A was used and the mixing weight ratio with the methacrylic resin ex pellet was changed to 1:49.

[Example 3]

The raw material pellet A was used, and the mixing weight ratio with the methacrylic resin oc pellet was changed to 1: 4. In the same manner as in Example 1, a light guide plate containing 20. Oppm of titanium dioxide was obtained.

[Example 4]

A light guide plate containing 2. Oppm of titanium dioxide was obtained in the same manner as in Example 1 except that the raw material pellet B was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1:49.

[Example 5]

A light guide plate containing 4. Oppm of titanium dioxide was obtained in the same manner as in Example 1 except that the raw material pellet B was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1:24.

[Example 6]

Raw material pellet G and cyclic olefin fin resin pellets (Nippon Zeon: ZENOOR 1060R) were mixed at a mixing weight ratio of 1:49, and the resulting mixed pellets were mixed into the hopper part using the same extrusion sheet molding machine. Extruded plates containing 2. Oppm of titanium dioxide were obtained in the same manner except that extrusion was performed at a temperature of 250 ° C while purging with nitrogen.

[Example 7]

Raw material pellets K and polycarbonate resin pellets (manufactured by Teijin Chemicals: Panlite / L-1250 Y) were mixed at a mixing weight ratio of 1:49 and extruded at a temperature of 260 ° C using the same extrusion sheet molding machine. Except that, an extruded plate containing 2. Oppm of titanium dioxide was obtained in the same manner.

[Example 8]

A light guide plate containing 2. Oppm of acid aluminum was obtained in the same manner as in Example 1 except that the raw material pellet D was used and the mixing weight ratio with the methacrylic resin ex pellet was changed to 1:49.

[Example 9]

The same method as in Example 1 except that one side of the light guide plate was shaped with an embossing roll that was surface-covered with a lathe at a pitch of 100 m using a 1Z2 circular tip with a radius of curvature of 100 m. An extruded plate was obtained. After cutting out using a circular saw with a size of 241 mm in width and 319 mm in length so that the obtained cylindrical force is approximately perpendicular to the light incident surface, the cylindrical lens array is cut out of the cut surface of the cut plate. Polishing, puffing, and screen printing were performed in the same manner as in Example 1 to obtain a light guide plate.

[Example 10] A method similar to that of Example 2 except that one side of the light guide plate was shaped with an embossing roll that was surface-covered with a lathe at a pitch of 100 m using a 1Z2 circular tip with a radius of curvature of 100 m. An extruded plate was obtained. The obtained extruded plate was processed in the same manner as in Example 8 to obtain a light guide plate.

[Example 11]

One side of the light guide plate was shaped with an embossing roll that was surface-coated into a shape in which a cylindrical lens-shaped mountain with a curvature radius of 175 μm cut vertically into 1Z2 was connected at a pitch of 100 μm. Except for the above, an extruded plate was obtained in the same manner as in Example 1. The obtained extruded plate was processed in the same manner as in Example 8 to obtain a light guide plate.

[Example 12]

Example 1 except that a 1Z2 circular tip with a radius of curvature of 100 m was used, and both sides of the light guide plate were shaped using two embossing rolls that were surface-covered with a lathe at a pitch of 100 m. Extruded plates were obtained in the same manner. The obtained extruded plate was processed in the same manner as in Example 8 to obtain a light guide plate.

[Comparative Example 1]

A light guide plate was produced in the same manner as in Example 1 except that no titanium dioxide fine particles were used.

[Comparative Example 2]

A light guide plate containing 100. Oppm of titanium dioxide was obtained in the same manner as in Example 1 except that the mixing weight ratio of the raw material pellet A and methacrylic resin a pellet was changed to 1: 0.

[Comparative Example 3]

A light guide plate containing 2. Oppm of titanium dioxide was obtained in the same manner as in Example 1 except that the raw material pellet C was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1:49.

[Comparative Example 4]

A light guide plate containing 20. Oppm of acid aluminum was obtained in the same manner as in Example 1 except that the raw material pellet D was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1: 4.

[Comparative Example 5]

A light guide plate containing 12.5 ppm of acid aluminum was obtained in the same manner as in Example 1 except that the raw material pellet E was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1: 1.15. It was.

[Comparative Example 6]

A light guide plate containing 2. Oppm of titanium dioxide was obtained in the same manner as in Example 1 except that the raw material pellet F was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1:49.

[Comparative Example 7]

A light guide plate containing 2. Oppm of titanium dioxide was obtained in the same manner as in Example 1 except that the raw material pellet G was used and the mixing weight ratio with the methacrylic resin α pellet was changed to 1:49.

[0056] The light guide plates obtained in Examples 1 to 12 and Comparative Examples 1 to 7 were subjected to the luminance measurement, the color tone unevenness (ΔYImax-min), and the visual evaluation of the emitted light unevenness by the above methods.

[0057] The results are shown in Tables 1 and 2.

[0058] [Table 1]

¾005

[0060] <Brightness measurement and visual evaluation results of color tone unevenness and output light unevenness>

As shown in Table 1, all of the light guide plates of Examples 1 to 11 had excellent performances in terms of average luminance, color tone unevenness, and light emission unevenness. In particular, for a light guide plate for a display device such as a liquid crystal monitor, it is desirable that the color tone unevenness (ΔYImax-min) is about 4 times or less the color tone unevenness in the case where no fine particles are added (Comparative Example 1). All of the light guide plates were 24 or less. In addition, the average luminance was further increased by forming the surface into a shape in which the cylindrical lens-shaped peaks were connected like the light guide plate of Example 8-.

[0061] The light guide plate of Comparative Example 1 had a low average luminance because fine particles were not added.

[0062] In the light guide plate of Comparative Example 2, since there was too much lOOppm of titanium dioxide, unevenness in light emission became significant. At the same time, the uneven color tone was 45.1, which was about 10 times that of Example 1, and the color unevenness was significant.

[0063] Since the light guide plate of Comparative Example 3 had a small average primary particle size of 0.045 μm, both the output light unevenness and the color tone unevenness were strong.

[0064] The light guide plate of Comparative Example 4 had a large average primary particle size of 0.5 μm, and thus the output light unevenness and the color tone unevenness were strong.

In the light guide plate of Comparative Example 5, the average primary particle diameter of aluminum oxide is 0.27 μm, but since the refractive index is lower than that of titanium dioxide, the scattering efficiency is small and the average luminance is low. In addition, it is unsuitable for a light guide plate for a display device such as a liquid crystal monitor with large color unevenness.

[0066] In Comparative Example 6, the average primary particle size was as small as 0.2 m, so that it was unsuitable for a light guide plate for a display device such as a liquid crystal monitor with large color tone unevenness.

[0067] In Comparative Example 7, the average primary particle diameter was as large as 0.4 m, so that the color unevenness was large and the average luminance was low.

Industrial applicability

[0068] The present invention is used in office automation equipment such as personal computers and word processors, display devices used for displaying various image signals, such as panel monitors and television monitors, and lighting devices for indoor and outdoor spaces. A light guide plate suitable for a display device, a signboard or the like is preferably obtained.

Claims

The scope of the claims

[1] A light guide plate for an edge light type surface light source device comprising a transparent thermoplastic resin containing fine particles and having a light source disposed on a side end surface of the plate, wherein one side of the plate is used as a light emitting surface The light source is disposed on the back surface of the light source and is subjected to a light diffusion process having a gradient in a direction in which both the side surface force and the light source force move away from each other, and 25 luminance measurement points on the light emitting surface are provided. Maximum (YImax) and minimum (YImin) of yellowness (YI) obtained from tristimulus values (XYZ)

The light guide plate is characterized in that the color tone unevenness (Δ YImax-min), which is a difference from), is 20 or less.

[2] The fine particles are titanium dioxide fine particles having an average primary particle diameter of 0.2 to 0.3 m, and the fine particles of titanium dioxide in the transparent thermoplastic resin composition are 0.01 to The light guide plate according to claim 1, wherein the light guide plate contains 20 ppm.

[3] The light guide plate according to claim 2, wherein the transparent thermoplastic resin composition comprises a transparent thermoplastic resin composition containing 0.01 to 4 ppm of titanium dioxide fine particles in the transparent thermoplastic resin composition. .

[4] The ratio (D90ZD10) of the 90% cumulative average particle size (D90) to the 10% cumulative average particle size (D10) in terms of volume of the titanium dioxide fine particles is 5.0 or less. Claim 2 or

3. The light guide plate according to any one of the above.

[5] At least one surface of the light emitting surface and the back surface thereof has a shape in which semicircular circular arcs are connected and arranged so that the connected circular arcs are substantially perpendicular to the side end surfaces. The ratio of the radius of curvature (R) to the pitch (P) of the half cylinder (RZP) is 0.6.

The light guide plate according to claim 2, wherein the light guide plate is ˜2.0.

6. The light guide plate according to any one of claims 2 to 5, wherein the transparent thermoplastic resin is a kind selected from a methacrylic resin, a polycarbonate resin, and a cyclic olefin resin.