JP2003270447A - Light guide body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-luminance light guide plate having integrated light diffusing functions suitable for a display device used for office automation equipment such as a personal computer and a word processor, various monitors which display image signals, e.g. a panel monitor, a television monitor, etc., a display device used for an indoor- or outdoor-space illumination device, a signboard, etc. <P>SOLUTION: The light guide body is characterized in that at least one side end surface of an edge write type transparent thermoplastic resin substrate having a light source arranged on at least one or more side end surfaces of a surface light source device transparent substrate is a light incidence surface and one surface crossing the light incidence surface at right angles is a light projection surface; and many convex lens arrays which are mutually connected at right angles to the light incidence surface and extend are formed on at least one of the light projection surface and its reverse surface and the section of the unit convex lens shapes parallel to the light incidence surface is of 0.6 to 2.0 in the ratio of a radius of curvature and the convex lens array pitch. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide for an edge light type surface light source device used for back lighting of a liquid crystal display device.

[0002]

2. Description of the Related Art Transparent thermoplastic resins, especially methacrylic resins, have been used for many lighting applications because of their excellent light transmission and mechanical properties. In recent years, however, they have been equipped with lighting lamps. It has come to be used as a light guide for a surface light source device such as a liquid crystal display. As a method of this surface light source device, there are usually used two types, that is, a so-called direct type in which a light guide is sandwiched between a light source and a liquid crystal unit, and an edge light method in which a light source is provided on a side end surface of the light guide, At present, the edge light method, which enables thinness, is the mainstream.
The edge light system of this surface light source device is, for example, a transparent thermoplastic resin substrate having a rectangular cross section made of a highly transparent material such as methacrylic resin, and a fluorescent tube, which is a linear light source, is provided on the side end surface of the transparent thermoplastic resin substrate. The fluorescent lamp is disposed so as to substantially contact the side end surface of the substrate, and the outer peripheral surface of the fluorescent tube and a portion other than the surface facing the side end surface are covered with a reflector on which aluminum, silver or the like is deposited. A reflective material such as a reflective tape is added to the side end surfaces other than the fluorescent tubes.

On the back surface of the light emitting surface of the transparent thermoplastic resin substrate, a white or milky white ink is usually used for screen printing so that the density of the light source changes from the one end surface side away from the light source. A light guide is provided with a printed light scattering pattern. Further, a reflection sheet is arranged behind the light scattering pattern. Further, a diffusion film, a light collecting film, etc. are arranged on the light emitting surface of the light guide.

Regarding the behavior of light rays in the edge light system of the surface light source device configured as described above, since the light rays emitted from the fluorescent tube are reflected by the reflector, most of them reach the side end surface of the light guide, Enter the inside of the light guide. Of these rays, only the rays that hit the light-scattering pattern printed on the back surface of the light guide are scattered, and the scattered rays and scattering patterns that reach the surface of the transparent thermoplastic resin substrate pass through to the back surface. Two light rays, which are reflected by the reflection sheet and directed toward the surface of the transparent resin substrate, are transmitted through the diffusion film and are emitted to the surface. A light ray that does not strike the light scattering pattern applied to the back surface of the light guide and a ray that hits the surface of the transparent resin substrate immediately from the fluorescent tube repeats total internal reflection and propagates until reaching the light scattering pattern. Since the density distribution is given to the light scattering pattern according to the distance from the light source so that the emitted light has a uniform emission intensity on the entire screen, it is possible to realize a relatively uniform luminance distribution in the light emitting surface. Has become.

By the way, the function of the diffusion film provided on the front surface of the transparent surface light source device is to remove the so-called dot image in which only the light scattering pattern printed on the back surface of the light guide appears to be shining, and It is used as a member for realizing uniform light emission, and has a function of diffusing light rays. The structure of this diffusion film is, for example, to provide a transparent resin layer in which true spherical particles of polystyrene resin are mixed and dispersed in methacrylic resin or the like as a diffusion member on a transparent support. By adding it as a diffusion film that is an optical member as described above, it becomes possible to obtain the desired characteristics, but as the number of constituent members increases, the interface between the air layer and the member increases. As a result, there are problems such as an increase in surface reflectance and a decrease in brightness, and an increase in the number of parts in the assembly process complicates the assembly operation.
Foreign matter is easily mixed between the light guide plates, and the mixed foreign matter causes defects such as bright spots, which causes a reduction in product yield.

For this reason, there have been disclosed a plurality of technologies for integrating the function of a diffusion film into a light guide used in a surface light source device such as a liquid crystal display and simplifying a complicated assembling process. For example, Japanese Patent Application No. 2-228907 discloses a technique of attaching a light guide containing a diffusion material having a transmittance of 40 to 70% to a methacrylic resin plate, and also Japanese Patent Application No. 5-1.
10630 discloses a technique in which a plate or film having a light diffusing property is used and is integrated with a base resin plate by a bonding method or a casting method, and Japanese Patent Application No. 6-1495.
Japanese Laid-Open Patent Publication No. 25-25 discloses a technique in which the light emitting surface of the light guide body is roughened by sandblasting and integrated.

[0007]

However, in a surface light source device in a light guide in which the functions of these diffusion films are integrated, a light diffusing layer containing light diffusing fine particles is provided on the light emitting surface, or a rough surface is provided. The behavior of the light rays on the converted surface is that among the light rays emitted from the fluorescent tube that is the light source, the light rays that reach the light exit surface side of the light guide enter the light diffusing layer and are diffused by the light diffusing fine particles. Alternatively, the light rays that have reached the rough surface are emitted to the outside from the surface of the surface light source device over a critical angle, so that the light rays that are totally reflected on the light emission surface and propagate to the inside are reduced. Furthermore, since the light rays striking the light scattering pattern on the back surface are scattered and emitted from the light exit surface, the amount of light rays reaching the front and back surfaces increases in the vicinity of the fluorescent tube of the light guide. As the brightness increases and the distance from the fluorescent tube increases, the amount of emitted light decreases, so that the brightness of the screen gradually decreases.

As described above, when the surface light source device is constructed by using the light guide body integrated with the function of the diffusion film formed by providing the light diffusion surface with the light diffusion layer containing the light diffusion fine particles or roughening the surface, Since the brightness distribution on the light source side is higher than the brightness distribution in the central part on the light exit surface and the balance is lost, it is extremely difficult to realize a uniform surface light source over the entire light exit surface. is there. The present invention eliminates the so-called dot image in which only the light scattering pattern, which is the function of the diffusion film, looks bright, has high brightness, and provides a light guide having excellent uniformity of brightness distribution on the light emitting surface. It is an object of the present invention to achieve simplification of the assembly process and reduction of defects, and to easily and stably manufacture the sheet used for the light guide.

[0009]

In order to solve the above-mentioned problems, the present inventors have made earnest studies, that is, the present invention is as follows. Surface light source device At least one side end surface of an edge light type transparent thermoplastic resin substrate in which a light source is disposed on at least one side end surface of a transparent substrate is a light incident surface, and one surface orthogonal to the light incident surface. In a light guide body having a light emitting surface as a light emitting surface, on at least one surface of the light emitting surface and the back surface thereof, a large number of convex lens rows that are connected and extend in a direction orthogonal to the light incident surface are formed, and the unit convex lens shape is A light guide body, wherein a cross section parallel to the light incident surface is composed of a large number of convex lens rows having a curvature radius and a convex lens row pitch ratio of 0.6 to 2.0. 2. 2. The light guide according to the above 1, wherein the transparent thermoplastic resin substrate contains light diffusing fine particles. 3. The fine particles are aluminum trioxide having an average particle diameter of 1.0 μm or less, and the content thereof is 1 to 200 pp.
3. The light guide according to claim 2, wherein m is m. The present invention will be described in detail below.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION At least one light guide according to the present invention is provided.
One side end surface is the light incident surface, and it is orthogonal to this light incident surface 1
It is composed of a transparent thermoplastic resin substrate having one surface as a light emitting surface. In such a light guide, a light ray incident on the light guide propagates in the light guide by repeating total reflection on the surface of the light guide with a distribution of light within a critical angle. Of these rays, only the rays that hit the light scattering pattern printed on the back surface of the light guide are scattered, and the scattered rays and the scattering pattern that reach the surface of the transparent thermoplastic resin substrate pass through and escape to the back surface. Two light rays, which are reflected by the reflection sheet and reflected toward the surface of the transparent resin substrate, are emitted to the surface. The density distribution is given to the light scattering pattern according to the distance from the light source so that the emitted light has a uniform emission intensity on the entire screen. ing.

In the present invention, the uniformity (ΔB) represented by the following equation (1) is used as a measure of the uniformity of the luminance distribution.
Was used to perform measurement evaluation and examination on the uniformity of the brightness distribution of the light guide. The uniformity (ΔB) is obtained by the following equation (1) when the measured brightness values for the measurement points P _{0 to} P ₆ shown in FIG. 4 are B _{0 to} B ₆ . ΔB _i = B _i / B ₀ × 100% (i = 1 to 6) (1) B ₀ : Luminance uniformity in edge light type surface light source device used for liquid crystal display with light guide center. Is required, but it is also required that the light guide center brightness (B ₀ ) is higher than the light incident surface side brightness (B _{1 to 6} ) at each of the brightness measurement points.

As a result, regarding the uniformity (ΔB _i ), if the light emitting surface of the light guide has a ridge line of the convex lens in the direction parallel to the rough surface portion or the light incident surface, the ridge line of the rough surface portion or the convex lens is reached. Rays exceeding the critical angle with respect to the rough surface portion or the ridgeline of the convex lens of the light are refracted and emitted to the outside of the light guide,
Light rays within the critical angle are reflected, but the light rays reflected by the rough surface portion or the convex lens ridge line have a large incident angle on the opposite surface, and the light rays within the critical angle on the opposite surface are small, resulting in light incident light. Most of the light rays entering from the surface radiate on the light incident light surface side, and the brightness (B _{1 to 6} ) on the light incident surface side is higher than the light guide center brightness (B ₀ ). Degree (Δ
B _i ) becomes 100% or more, and the uniformity of the luminance distribution on the light emitting light surface becomes poor. Therefore, in this convex lens shape, the ridgeline of the convex lens needs to be formed in the direction orthogonal to the incident light surface of the light guide body, and in this direction, the light rays coming from the original incident light surface of the light guide body are guided in the traveling direction. The degree of uniformity (ΔB _i ) at each measurement point can be set to 100% or less without hindering the above function.

The function of the diffusion film is to remove the so-called dot image in which only the light-scattering pattern screen-printed on the back surface of the light guide body appears to be bright. In order to impart the function of the light diffusion film to the light guide without impairing the uniformity of the luminance distribution on the light exit surface, the shape of the convex lens array formed in the light guide will be described with reference to FIG. At least one surface of the light emitting surface of the light guide and its back surface,
A large number of convex lens rows whose unit convex lens shape has a ratio of the radius of curvature (R) to the convex lens row pitch (P) of 0.6 to 2.0 are formed so as to extend in the direction perpendicular to the light incident surface of the light guide. It is necessary.

This is because when the ratio of the radius of curvature (R) to the convex lens array pitch (P) is less than 0.6, the surface area difference between the front and back surfaces of the light guide is large and the light guide warps due to environmental temperature and humidity. Becomes larger and the liquid crystal unit is pushed up even if the direction of warpage is uneven, which is not preferable because it affects the liquid crystal screen display. On the contrary, when the ratio of the radius of curvature (R) and the convex lens array pitch (P) exceeds 2.0, the focal length of the convex lens becomes long, so that the light scattering pattern is visually observed.
The light condensing effect of this convex lens is almost eliminated. The ratio of the radius of curvature (R) to the convex lens array pitch (P) is preferably in the range of 0.6 to 1.75, and more preferably 0.75 to 1.50. The height (H) of the peaks and valleys of the convex lens array formed on the surface of the light guide is appropriately selected as long as the ratio of the radius of curvature (R) and the convex lens array pitch (P) is within the above range, but usually 2 μm to It is preferably within the range of 1 mm.

Examples of the transparent thermoplastic resin constituting the light guide of the present invention include methacrylic resin, polycarbonate resin, styrene resin, cyclic olefin resin, and amorphous polyester. Especially preferred is methacrylic resin. The methacrylic resin can be obtained by copolymerizing 70% by weight or more of methyl methacrylate or ethyl methacrylate with a monomer having a copolymerizability therewith. Examples of the monomer copolymerizable with these include methacrylic acid esters such as butyl methacrylate, ethyl methacrylate, methyl methacrylate, propyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, 2-ethylhexyl methacrylate, and acrylic acid. Methyl, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, acrylic acid 2
Examples thereof include acrylic acid esters such as ethylhexyl and unsaturated acids such as methacrylic acid and acrylic acid, but the invention is not limited thereto and the manufacturing method is not limited at all.

Further, heat-resistant methacrylic resin, low hygroscopic methacrylic resin, impact-resistant methacrylic resin and the like are included.
The impact-resistant methacrylic resin is, for example, a methacrylic resin blended with a rubber elastic body, and the rubber elastic body is disclosed in JP-A-53-58554 and JP-A-55-949.
No. 17 and No. 61-32346, etc. As the polycarbonate resin, a polymer derived from a dihydric phenol compound represented by bisphenol A is used. Polycarbonate resin manufacturing method,
It is not particularly limited, and those manufactured by a well-known and commonly used method such as a phosgene method, a transesterification method, or a solid phase polymerization method can be used.

The cyclic olefin resin is a polymer containing a cyclic olefin skeleton in the polymer chain or a copolymer containing them, such as norbornene or cyclohexadiene, and belongs to an amorphous thermoplastic resin. The manufacturing method is not particularly limited. For example, as a cyclic olefin resin containing norbornene as a main component, Japanese Patent Laid-Open No.
-168708, JP-A-62-252406, JP-A-2-133413, JP-A-63-14.
Resins described in Japanese Patent No. 5324, Japanese Patent Laid-Open No. 63-264626, Japanese Patent Laid-Open No. 1-240517, Japanese Patent Publication No. 57-8815 can be used. Moreover, you may add a soft polymer as needed.

For example, an olefin-based soft polymer composed of α-olefin, an isobutylene-based soft polymer composed of isobutylene, a diene-based soft polymer composed of a conjugated diene such as butadiene and isoprene, a cyclic olefin composed of a cyclic olefin such as norbornene and cyclopentene. Olefin-based soft polymer, organic polysiloxane-based soft polymer, α, β-
Examples thereof include soft polymers composed of unsaturated acids and their derivatives, soft polymers composed of unsaturated alcohols and amines or their acyl derivatives or acetals, polymers of epoxy compounds, and fluororubbers.

The styrene resin is a homopolymer or copolymer containing styrene as an essential component, or a polymer blend obtained from these polymers and other resins. Particularly, polystyrene, 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 having rubber distributed in the styrene resin phase can also be preferably used. As the method for producing the styrene-based resin, those produced by a well-known and commonly used method can be used.

The amorphous polyester is an aliphatic glycol such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol or hexamethylene glycol, an alicyclic glycol such as cyclohexanedimethanol, bisphenol, 1, Aromatic dihydroxy compounds such as 3-bis (2-hydroxyethoxy) benzene and 1,4-bis (hydroxyethoxy) benzene, or dihydroxy compound units selected from two or more of these, terephthalic acid, isophthalic acid,
Aromatic dicarboxylic acids such as 2,6-naphthalene dicarboxylic acid, aliphatic carboxylic acids such as oxalic acid, adipic acid, sebacic acid, succinic acid, undecadicarboxylic acid, and alicyclic dicarboxylic acids such as hexahydroterephthalic acid, or It is an amorphous resin among polyesters formed from a dicarboxylic acid unit selected from two or more of these.

As the method for producing the amorphous polyester, those produced by a well-known and commonly used method can be used. A commercially available product that can be easily obtained as the amorphous polyester is KODA which is a product of Eastman Kodak Company.
There are R PETG, PCTA, and the like. Further, the light guide of the present invention suppresses coloring due to ultraviolet rays generated from the fluorescent tubes arranged along the side end face, and particularly in the color light source device, even if the color tone on the monitor screen is used for a long time. An ultraviolet absorber can be added to the transparent thermoplastic resin substrate, if necessary, for the purpose of always exhibiting a constant color tone, suppressing the occurrence of color unevenness, and further suppressing the decrease in brightness. .

As the ultraviolet absorber, for example, 2- (5
-Methyl-2hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α'dimethylbenzyl) phenyl] benzotriazole, 2-
(3,5-di-t-amyl-2-hydroxyphenyl)
Benzotriazole-based UV absorbers such as benzotriazole, benzophenone-based UV absorbers such as 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone Absorber, salicylic acid-based UV absorber such as phenyl salicylate, 4-t-butylphenyl salicylate, and one or more UV absorbers selected from these are 30 to 2000 ppm relative to the transparent thermoplastic resin substrate. , Preferably 80
It can be added at a concentration of ~ 500 ppm.

Further, for example, a glycerin fatty acid ester such as glycerin monostearate, a higher alcohol such as stearyl alcohol, a higher fatty acid such as stearic acid may be added as a release agent to the light guide of the present invention, and phenol may be added. It is possible to add an antioxidant such as a system-based, thiether-based, or phosphite-based agent, in which case it is used within a range that does not impair the object of the present invention, and it is usually preferable to use it at a concentration of 5000 ppm or less. . As the light diffusing fine particles dispersed in the transparent thermoplastic resin substrate in the present invention, for example, barium sulfate, calcium carbonate, aluminum trioxide, titanium dioxide, silicon dioxide,
Inorganic fine particles such as glass beads, styrene cross-linked beads, M
Examples include organic fine particles such as S-crosslinked beads and siloxane-based crosslinked beads. Further, hollow crosslinked fine particles made of highly transparent resin material such as methacrylic resin, polycarbonate resin, MS resin, cyclic olefin resin and hollow fine particles made of glass can also be used.

The light-diffusing fine particles dispersed in the transparent thermoplastic resin substrate are preferably aluminum trioxide. The aluminum trioxide has an average particle size of 1.0 μm or less. When the average particle diameter exceeds 1.0 μm, when the traveling direction of the light rays entering from the fluorescent tube arranged along the side end surface is converted to a direction closer to the vertical direction with respect to the light exit surface of the light guide, Light loss occurs due to reflection and the like, and the incident light beam cannot be efficiently scattered to the light emission surface side, which makes it difficult to obtain the target brightness, which is not preferable. As the shape of aluminum trioxide, a spherical shape, a spherical shape, a scale shape, a cubic shape, an amorphous shape or the like can be preferably used.

Further, in the transparent thermoplastic resin substrate used for the light guide of the present invention, the compounding amount of aluminum trioxide which can be preferably used as the light diffusion fine particles to be dispersed is 1 to 200 ppm with respect to the transparent thermoplastic resin. Is desirable. Mixing ratio of aluminum trioxide is 1ppm
If it is less than 2, there is almost no effect of improving the scattering property, and conversely 2
When it exceeds 00 ppm, for example, in a large-sized liquid crystal display device of 15 inches or more, the light rays emitted from the fluorescent tubes arranged along the side end face are perpendicular to the light emitting surface in the vicinity of the fluorescent tubes of the light guide. The rate of conversion toward the direction becomes too large, and even if a light scattering pattern for correcting scattered light is applied to the side opposite to the light emitting surface of the light guide, the brightness distribution of the light emitting surface is properly balanced. Is difficult to do, which is not preferable.

The processing method for forming a large number of convex lens rows having a specific radius of curvature (R) and convex lens row pitch (P) on the surface of the light guide according to the present invention is not particularly limited. However, for example, using a mold having a convex lens pattern formed by chemical etching, bead cutting, laser processing, or the like, hot pressing a transparent substrate,
A method of applying active energy ray curable resin on a transparent substrate and subjecting it to shape hardening by irradiation of active energy ray to transfer a convex lens pattern, a method of forming by injection molding, a method of etching a light guide, cutting a bite, laser processing Examples of the method include a method of directly processing by, etc., but there is preferably an extrusion molding method capable of stable mass production using an embossing roll having a convex lens array shape, and more preferably a multilayer extrusion molding method. Is.

In this multi-layer extrusion molding method (a schematic view of the multi-layer extrusion molding machine is shown in FIG. 2), it is preferable to use a transparent thermoplastic resin having a difference in viscosity between the outer layer 3 and the base material layer 2, that is, A convex lens array shape is formed on a transparent thermoplastic resin having a low viscosity in the outer layer by an embossing roll 5, and the base material layer 2 made of a transparent thermoplastic resin having a viscosity higher than that of the transparent thermoplastic resin of the outer layer 3 serves as a core to form the entire molten sheet. Come to support. That is, the molten sheet, which has been easily processed into the convex lens array shape, is sent out between the embossing roll 5 and the polishing roll 6, and the embossing roll 5 gives the convex lens array shape.

The transparent thermoplastic resin forming the outer layer 3 may be a transparent thermoplastic resin different from that of the base material layer 2 as long as the viscosity of the transparent thermoplastic resin of the base material layer 2 is small. The thickness of the outer layer 3 constituting the convex lens array is appropriately selected depending on its application and plate thickness, but is usually 10 μm.
It is preferably in the range of ˜500 μm. Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. (Measurement of Convex Lens Shape) A cross-sectional shape orthogonal to the convex lens shape array was measured with a universal projector (magnification: 200 times).

(Measurement Method of Average Particle Size) Regarding the average particle size of the fine particles, a photograph is taken with a transmission electron microscope, the major axis and the minor axis of the obtained particle image are measured, and the average value thereof is used as the fine particle 1 As the individual particle diameter, the average value of the particle diameters of 30 fine particles was taken as the average particle diameter. (Preparation of methacrylic resin composition 1) Methacrylic resin pellets (Delpet LP-1, MFR 1.0 g / 10 mi
n, manufactured by Asahi Kasei Co., Ltd., aluminum trioxide (average particle size: 0.45 μm) so that the concentration becomes 20 ppm.
・ Nippon Light Metal Co., Ltd.) xylene: methanol = 3:
Using an ultrasonic cleaner in the mixed organic solvent of 1, disperse for 30 minutes at an oscillation frequency of 38 KHz, after confirming uniform dispersion, sprinkle it evenly on the methacrylic resin pellets, then blend it for 1 minute at 1400 rpm with a Henschel mixer. did. This operation is repeated until the required amount of the mixed pellets is obtained, and the obtained mixed pellets are heated to 100 T with a twin-screw extruder.
It was extruded while being devolatilized under reduced pressure to an orr to obtain a methacrylic resin composition having a concentration of 12 ppm. Hereinafter, this is referred to as raw material pellet A.

[0030]

Example 1 (Production of Light Guide) Convex Lens Curvature Radius 100
μm and a convex lens array pitch of 100 μm were used for methacrylic resin pellets (Delpet LP-1,
MFR 1.0g / 10min, Asahi Kasei Co., Ltd. 30m
mφ, L / D = 24 Using a single layer T die using an extruder,
The lip opening and the clearance between the embossing roll and the polishing roll were adjusted so that the plate thickness was 5.0 mm, and the temperature of the extruder and the single layer T-die was 250 to 260 ° C. In this way, an extruded plate having a width of about 320 mm could be produced, and the total thickness of the extruded plate was 5.0 mm. Then, from the obtained extruded plate, the convex lens array was perpendicular to the length direction. A plate having a width of 235 mm and a length of 307 mm was cut out using a circular saw. Then, the cut surface of the cut plate is polished by using a precision polishing machine (PLA-BEAUTY: manufactured by Megarotechnica Co., Ltd.), further buffed, and finished into a mirror surface to obtain a 15-inch size light guide. It was A printing screen with a 15-inch dot gradation is applied to the obtained light guide, and Matt Medium SR931 (manufactured by Mino Group) is used as the ink.
A light scattering pattern was formed on the back surface of the light guide by screen printing.

(Measurement of Luminance of Light Guide) According to the light source device shown in FIG. 3, a cold cathode tube of 4 mmφ (manufactured by Harrison Electric Co., Ltd.) was installed as a light source on both end surfaces of the surface light emitter on the side of 307 mm in length and reflected. Ray White 75 (made by Kimoto) is used as the sheet, and BE is used as the prism sheet 10 on the upper part of the light guide 8.
Two FIIs (made by Sumitomo 3M) were placed so that the prism rows are orthogonal to each other (the lower side of the prism sheet is an arrangement in which the prism rows are orthogonal to the cold cathode tubes, and the upper side is to the cold cathode tubes). And the prism rows are parallel). A voltage of 12 V was applied to the cold cathode tube from a DC voltage stabilizer for 20 minutes, and after lighting for 20 minutes, a luminance meter (CA-1000: made by Minolta) installed at a position 1 m away from the light emitting surface was used to measure the entire light emitting surface vertically 9 ×. Width 9) = 81 The brightness of each of the divided measurement points was measured. Then, the average value (B _ave ) was calculated from the obtained measured luminances.

(Uniformity of the light guide) When the brightness measurement values for the measurement points P _{0 to} P ₆ shown in FIG. 4 at the division points obtained by the brightness measurement of the light guide are B _{0 to} B ₆ , each measurement The degree of uniformity of points (ΔB _i ) is calculated by the following equation (1). ΔB _i = B _i / B ₀ × 100% (i = 1 to 6) (1) (Observation of dot image) From the light emission surface side with the cold cathode tube turned on when evaluating the brightness of the light guide. The presence or absence of a dot image of the printed light scattering pattern was visually observed.

[0033]

Example 2 A light guide was produced in the same procedure as in Example 1 except that an embossing roll having a convex lens curvature radius of 175 μm and a convex lens row pitch of 100 μm was used, and the obtained light guide was obtained in the same manner as in Example 1. The average value of brightness and the uniformity were calculated by the procedure, and the presence or absence of the dot image was visually observed by the same method as in Example 1 when measuring the brightness.

[0034]

[Example 3] Example 1 except that the raw material pellet A was used
A light guide was prepared in the same procedure as in Example 1, and the obtained light guide was calculated in the same manner as in Example 1 to calculate the average value of luminance and the uniformity, and at the time of measuring the brightness, the same method as in Example 1 was used. The presence or absence of the dot image was visually observed.

[0035]

[Comparative Example 1] A light guide was prepared in the same manner as in Example 1 except that the embossing roll was changed to a polishing roll, and the brightness was measured and the printed light scattering pattern image was visually observed. Diffusion film D121 made by Tsujiden Co., Ltd. is placed on the prism sheet BEFII (Sumitomo 3M).
Except that two prisms are mounted so that the prism rows are perpendicular to each other,
The average value of luminance and the uniformity were calculated in the same procedure as in Example 1, and the presence or absence of a dot image was visually observed by the same method as in Example 1 when measuring the luminance.

[0036]

Comparative Example 2 A light guide was prepared in the same manner as in Example 1 except that an embossing roll having a convex lens curvature radius of 250 μm and a convex lens row pitch of 100 μm was used, and the obtained light guide was manufactured in the same procedure as in Example 1. The average value of brightness and the uniformity were calculated, and the presence or absence of a dot image was visually observed in the same manner as in Example 1 when measuring the brightness.

[0037]

COMPARATIVE EXAMPLE 3 An extruded plate manufactured in the same manner as in Example 2 was 235 m wide so that the convex lens rows were parallel to the length direction.
A plate having a size of m and a length of 307 mm was cut out using a circular saw. Then, the cut surface of the cut plate is polished using a precision polishing machine (PLA-BEAUTY: manufactured by Megaro Technica Co., Ltd.), and further buffed to give a mirror-like finish.
A 15-inch size light guide was obtained. A light-scattering pattern was formed on the back surface of the light guide by screen printing using a 15-inch dot gradation printing screen on this light guide and using Matt Medium SR931 (manufactured by Mino Group) as the ink. The average value of brightness and the uniformity of the obtained light guide were calculated in the same procedure as in Example 1, and the presence or absence of a dot image was visually observed by the same method as in Example 1 when measuring the brightness. The results of Examples and Comparative Examples are
It shows in Table 1.

[0038]

[Table 1]

[0039]

INDUSTRIAL APPLICABILITY The present invention is suitable for various monitors for displaying image signals, such as display devices used for panel monitors, television monitors, etc., and display devices used for indoor and outdoor space lighting devices, signboards, etc. To remove the so-called dot image in which only the light-scattering pattern, which is the function of the film, looks bright, has high brightness, and provides a light guide having excellent uniformity of brightness distribution on the light exit surface,
It is possible to simplify the assembly process and reduce defects, and to easily and stably manufacture the sheet used for the light guide.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a convex lens array formed in a light guide according to the present invention.

FIG. 2 is an explanatory view showing an embodiment of a method for manufacturing a light guide according to the present invention.

FIG. 3 shows an example of a luminance measuring method in an edge light type liquid crystal surface light source device using the light guide according to the present invention.

FIG. 4 is an explanatory diagram showing divided measurement points and luminance measurement calculation points when measuring the luminance of the light guide according to the present invention.

[Explanation of symbols]

1: T die 2: Base material layer 3: Outer layer 4: Extruded plate 5: Embossing roll 6: Polishing roll 7: Light source (cold cathode tube) 8: Lamphouse 9: Light guide 10: Reflective sheet 11: Prism sheet

Claims (3)

[Claims] 1. A surface light source device transparent substrate, at least one side end surface of an edge light type transparent thermoplastic resin substrate in which a light source is disposed on at least one side end surface is a light incident surface, and this light incident surface is In a light guide body having one light emitting surface that is orthogonal to each other, at least one surface of the light emitting surface and the back surface thereof is provided with a plurality of convex lens rows that are connected and extend in a direction perpendicular to the light incident surface. A light guide characterized in that a cross section whose unit convex lens shape is parallel to the light incident surface is composed of a plurality of convex lens rows having a curvature radius and a convex lens row pitch ratio of 0.6 to 2.0. . 2. The light guide according to claim 1, wherein the transparent thermoplastic resin substrate contains light diffusing fine particles. 3. The fine particles are aluminum trioxide having an average particle diameter of 1.0 μm or less, and the content thereof is 1 to 2.
It is 00 ppm, The light guide of Claim 2 characterized by the above-mentioned.