JPH11142846A - Back light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back light capable of improving luminance while thinning the thickness of a back light system. SOLUTION: This back light is provided with a prism sheet forming a prism string 10A on one face of a resin sheet and smoothing the other face and a scattering light transmission plate 12 obtained by dispersing a transparent dispersing material into transparent resin. A prism string (a vertical angle is 80 to 140 deg.) is formed on one side of the plate 12 in a direction rectangular to a light source 14 arranged on the side face part of the plate 12, the prism string is opposed to the prism string 10A (a vertical angle is 50 to 60 deg. and an angle formed by a normal from the vertical angle and a light source side prism surface is 10 to 30 deg.) of the sheet 10 and these prism strings are arranged so as to be orthogonally crossed to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight, and more particularly, to a backlight suitable for use in a liquid crystal display such as a notebook computer, a word processor, a liquid crystal television, and a car navigation system.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as portable terminals as lightweight and thin display devices. Since a liquid crystal display does not have a self-luminous function, a flat light-emitting body (backlight) is usually used on the back of the liquid crystal. 2. Description of the Related Art In recent years, high definition and colorization of a liquid crystal display have been promoted, and high luminance of a backlight is required. Also, in portable devices, it is necessary to reduce the size of the battery and prolong the pot life, so that low power consumption is desired. From that point, it is necessary to increase the brightness of the backlight. .

Conventionally, as a backlight for a liquid crystal display, light is incident on a transparent light guide plate from a side surface thereof.
A so-called edge light method is known. In this method, light entering from the side surface of the light guide plate is reflected by dots formed on the back surface of the light guide plate, and as a result, light is emitted toward the upper surface of the light guide plate. In addition, a scattering light guide plate in which spherical fine particles are dispersed instead of a transparent light guide plate is also known. In this method, light is emitted toward the upper surface by refracting or reflecting light with the spherical fine particles. I have. In these backlight systems, a prism sheet is called to increase the brightness.
A sheet having a light condensing function is used by overlapping one sheet on the light guide plate with the prism surface facing up.

However, in such a backlight system, there is a limit in improving the luminance, and it is necessary to improve the luminance of the light source in order to improve the luminance. The method of increasing the brightness of the light source has problems such as an increase in the amount of heat generated and a decrease in the life of the battery, and the method of stacking several prism sheets to improve the brightness makes the backlight system thinner. It will be difficult.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight capable of improving luminance while reducing the thickness of the backlight system.

[0006]

An object of the present invention is to provide a prism sheet in which a prism array is formed on one side of a resin sheet and the other side is formed smoothly, and a scattering sheet in which a transparent dispersion material is dispersed in a transparent resin. A light guide plate, a prism array is formed on one surface of the scattering light guide plate in a direction orthogonal to a light source disposed on a side surface of the scattering light guide plate, and the prism array and the prism array of the prism sheet are opposed to each other. And the prism rows are arranged so as to be orthogonal to each other. Prism sheet is the apex angle of each of the cross-sectional shape of the prism rows formed on it is a 50 to 60 degrees, the angle theta ₁ between the normal and the prism surface from the apex angle is 10 to 30 degrees It is preferable that the angle at which the slopes of the cross-sectional shapes of the prism rows formed on the scattering light guide plate intersect is 80 to 14.
Desirably, it is 0 degrees. It is desirable that the scattering light guide plate contains 0.001 to 1.0% by weight of a transparent dispersion material in a transparent resin, and the prism sheet is made of thermosetting polyurethane. In the backlight of the present invention, a resin film is bonded to the smooth surface side of the prism sheet as needed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the backlight according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a preferred embodiment of a backlight according to the present invention, FIG. 2 is an enlarged detailed view of a main part of FIG. 1, and FIG. 3 is an explanatory view showing an aspect of a sectional shape of a prism in FIG. This backlight mainly includes a prism sheet 10, a scattering light guide plate 12, and a light source 14.

The prism sheet 10 is made of a transparent resin sheet, and has a prism array 10A formed on one surface (a surface facing the scattering light guide plate 12) and a smooth surface on the other surface. Further, the prism sheet 10 of the scattering light guide plate 12
The prism row 12A is also formed on the surface facing the.
The prism array 12A has a prism array formed in a direction orthogonal to the light source 14 and has a prism sheet 10A.
Are arranged so as to be orthogonal to the prism row 10A formed in the first row.

In the prism array 10A of the prism sheet 10, the apex angle of each cross-sectional shape (indicated by a in FIG. 2).
There is a 50-60 degrees, the angle between the normal and the prism surface from the apex angle (in FIG. 2, indicated by theta ₁₎ 10 to 30
Degree. That, theta ₁ during vertical angle and FIG an angle between the prism face direction side (light source side) indicated by the arrow. On the other hand, the apex angle at which the slope of each cross-sectional shape of the prism array 12A of the scattering light guide plate 12 orthogonal to the prism array 10A of the prism sheet 10 intersects is 80 to 140 degrees.

[0010] The angles of these apical angles greatly affect the brightness and uniformity of the backlight, and sufficient performance can be expected within the range of these angles. Scattering light guide plate 12
When the angle of intersection of the slopes of the respective cross-sectional shapes in the prism array 12A is less than 80 degrees, the uniformity is in a good direction, but the brightness tends to decrease. On the other hand, when the crossing angle of the slope of each cross-sectional shape in the prism array 12A of the scattering light guide plate 12 exceeds 140 degrees, the brightness tends to be improved, but the uniformity is deteriorated and the balance performance as a backlight is deteriorated. It is difficult to achieve.

The angle of the chief ray emitted from the scattering light guide plate 12 in the present invention is 60 to 80 degrees. When this light ray enters the _first surface of the prism sheet at 90 degrees (perpendicular), loss due to refraction and reflection at the interface is suppressed, which is advantageous in terms of improving luminance. Further, when the material of the prism sheet is changed, it is not necessary to consider a change in the refractive index due to the change, which is convenient in design. Accordingly, the theta ₁ angle is 10 to 30 degrees.場合 If the angle of ₁ is less than 10 degrees,
Since the refraction phenomenon and the reflection development occur at the interface, the brightness is not increased. Theta ₁ angle is the same when it exceeds 30 degrees.

Further, ま た₂ is set to an angle at which the incident light is emitted in the normal direction, so that it becomes 30 to 40 degrees. Therefore, the range of the apex angle is 50 to 60 degrees. Θ The _second angle is the range, since the light exiting from the prism sheet is not suitable for normal direction, it is difficult to improve the front luminance.

The crossing angles of the slopes of the cross-sectional shape of the scattering light guide plate 12 include the modes shown in FIGS. 3 (a), 3 (b) and 3 (c). That is, there is a triangular vertex angle (Θ) as shown in (a), an angle at which the slope intersects when the vertex has a curved surface as shown in (b) and (c).

Further, the prism row 1 of the prism sheet 10
The distance (pitch) between each vertical angle of 0A is 10 to 300 μ
m is preferred. When the pitch is less than 10 μm, the effective flat portion of the prism surface (slope) is reduced in the mold processing, so that the prism effect is reduced. When the pitch is more than 300 μm, bright and dark stripes due to the prism rows of the prism sheet are reduced. It is not preferable because it degrades the quality. Further, the distance (pitch) between the apex angles of the prism rows 12A of the scattering light guide plate 12 is preferably 10 to 300 μm for the same reason as described above.

The thickness (distance from the smooth surface to the top of the prism array) of the prism sheet 10 is preferably 50 to 800 μm. When the thickness is less than 50 μm, the rigidity of the sheet is reduced, so that the assembling property is impaired. On the other hand, 800
If it exceeds μm, the thickness of the system becomes thick, which is not preferable. On the other hand, the thickness (distance from the smooth surface to the top of the prism array) of the scattering light guide plate 12 is preferably 1.0 to 5.0 mm. When the thickness is less than 1.0 μm, the efficiency of incidence from a fluorescent lamp used as a light source decreases. on the other hand,
If it exceeds 5.0 mm, the system becomes heavy and thick, which is not preferable.

There is no particular limitation on the material of the prism sheet 10 in the present invention, and thermosetting polyurethane, acrylic resin, epoxy resin, unsaturated polyester resin, polyethylene terephthalate, polyethylene naphthalate, polymethylpentene-1 resin, polycarbonate resin, It may be manufactured by injection molding a transparent resin such as an ethylene-vinyl acetate copolymer, a vinyl chloride resin, a polystyrene resin, and a polynorbornene resin, and a thermosetting polyurethane,
A liquid resin such as an acrylic resin is coated on a mold in which the prism rows are formed, thermally cured, and then peeled from the mold.

Among these resins, thermosetting polyurethane is particularly preferred. In the case of the thermosetting polyurethane, the prism row 10A is hardly damaged by the elasticity and abrasion resistance characteristics of the thermosetting polyurethane, and the prism row 1A is hardly damaged.
It is possible to prevent a decrease in luminance due to a scratch generated at 0A.

The thermosetting polyurethane can be obtained by reacting a hydroxyl-terminated prepolymer with an isocyanate component under a urethane-forming catalyst. The hydroxyl-terminated prepolymer can be obtained by reacting a polyol component with an equivalent or less of a non-yellowing-modified diisocyanate.

As the polyol component, a mixture of a polyester polyol and a polyester polyol having a hydroxyl value of 30 to 400 or a short-chain diol having a molecular weight of 300 or less can be used. As the polyester polyol having a hydroxyl value of 30 to 400, poly (ε-caprolactone) polyol, poly (alkylene carbonate) polyol, poly (β-methyl-δ-valerolactone) polyol and the like can be used. It is desirable that these polyester polyols have an average of 1.8 or more and less than 3.5 hydroxyl groups per molecule.

The diol having a molecular weight of 300 or less includes ethylene glycol, 1,2-propanediol,
1,3-propanediol, 1,4-butanediol,
1,3-butanediol, neopentyldiol, 1,
6-hexanediol, polyoxyethylene glycol, polyoxypropylene glycol and the like can be used.

On the other hand, non-yellowing diisocyanates include hexamethylene diisocyanate, octamethylene diisocyanate, dodecamethylene diisocyanate,
2,24-trimethylhexamethylene diisocyanate, 3,3′-diisocyanate propyl ether, 3
-Isocyanatemethyl-3,3,5-trimethylcyclohexyl isocyanate, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 4,4-methylenebis (cyclohexyl isocyanate), bis (isocyanatomethyl) cyclohexane, and the like can be used.

By reacting the polyol component with isocyanate in an amount of 0.8 equivalent or less, preferably 0.6 equivalent or less, a hydroxyl-terminated prepolymer can be obtained. A cured urethane product can be obtained by reacting an isocyanate in an amount of 0.8 to 1.3 equivalents to the hydroxyl-terminated prepolymer in the presence of a urethane-forming catalyst.

As the urethanization catalyst, metal compounds such as tin compounds, lead compounds and bismuth compounds can be used. Specific examples include stannous chloride, stannic chloride, tin nitrate, tin sulfate, tetra-n-butyltin, n-butyltin trichloride, trimethyltin hydroxide, di-n-butyltin diacetate, -N-butyltin dilaurate, stannas octoate and the like can be used. The amount of the urethane-forming catalyst used is 1 ppm to 0.1% by weight based on the total amount of the hydroxyl-terminated prepolymer and the isocyanate.

In the resin composition constituting the prism sheet 10 of the present invention, components such as an antioxidant, an ultraviolet absorber, an anti-yellowing agent, and a bluing agent may be added, if necessary, to the properties of the prism sheet. It can be added within the range.

The scattering light guide plate 12 is formed by uniformly dispersing a transparent dispersion material having a different refractive index from that of a matrix made of a transparent resin material. In this case, the refractive index of the transparent resin matrix material ( The difference between n ₁ ) and the refractive index (n ₂ ) of the transparent dispersion material is desirably 0.005 or more.

[0026] When the scattering guide plate 12, the difference in refractive index (n ₁₎ and the refractive index of the transparent dispersion material of the transparent resin matrix material _{(n 2) (n 1 -n} 2) is required luminance,
0.01 or more, when higher brightness is required, the value of 0.
03 or more is desirable. If the difference in refractive index is less than 0.005, sufficient light scattering may not be obtained.

When the transparent dispersion material is dispersed in a matrix made of a transparent resin material such as an acrylic resin or polycarbonate, the transparent dispersion material may be any of an inorganic material, an organic material, and a gas, and the vacuum holes may be dispersed. You may. Examples of the inorganic material include transparent metal oxides such as aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, tin oxide, and zinc oxide, as well as calcium carbonate, basic magnesium carbonate, calcium fluoride, barium sulfate, and quartz crow. , Multi-component glass,
Powders such as sapphire and quartz, fibers, beads and the like can be mentioned.

As organic materials, polyamide, polystyrene, polymethyl methacrylate, polycarbonate,
Polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyvinyl alcohol, polyethylene-polyvinyl alcohol copolymer, polynorbornene, polybutene, fluororesin, silicone resin, polyisoprene rubber, polybutadiene rubber, styrene -Butadiene copolymer, butyl rubber, halogenated butyl rubber, chloroprene rubber, acrylic rubber,
EPDM, acrylonitrile-butadiene rubber, fluorine rubber, silicone rubber, ABS resin, acrylonitrile-
Styrene copolymer resin, acrylonitrile-EPDM-styrene-terpolymer, styrene-methyl methacrylate copolymer, methacrylic resin, epoxy resin, polymethylpentene, allyl diglycol carbonate resin, spirane resin, amorphous polyolefin, polyarylate, Polysulfone, polyallylsulfone, polyetherimide, polyimide, polyethylene terephthalate,
Diallyl phthalate, polyester carbonate, paraffin, polybutene, polyisobutylene and the like. Examples of the gas include air, nitrogen, argon, helium, carbon dioxide and the like.

In addition to the bulk material, a liquid transparent material can be dispersed in a base transparent plastic or elastomer material. Such a liquid transparent dispersion material can be selected from inorganic or organic transparent liquids. For example, silicon-based oil, fluorine oil, liquid paraffin, ethylene glycol, polybutene, polyisobutylene and the like can be used.

The transparent dispersion material means a dispersion having a spherical shape, an elliptical shape, a rod shape, a plate shape or any other irregular shape. The size of the transparent dispersion material (the transmission distance on the incident axis of light) is 0.1 to 50 times, preferably 0.5 to 20 times, and more preferably 2 to 10 times the wavelength of the incident light. Is preferred. When the size is less than 0.1 times the wavelength of the incident light, Rayleigh scattering is dominant, so that the light scattering becomes weak and may be easily affected by the wavelength, and exceeds 50 times the wavelength of the incident light. Then, the aggregation of the transparent dispersion material is likely to occur, so that the light scattering property may decrease. Therefore, the particle size of the transparent dispersion material is 3 to 20 μm.
It is.

The amount of the transparent dispersion material is preferably 0.001 to 1.0% by weight, particularly 0.01 to 0.5% by weight, based on the matrix composed of the transparent resin material. When the amount of the transparent dispersion material is less than 0.001% by weight, a sufficient scattering effect cannot be obtained. On the other hand, 1.0% by weight
Is exceeded, strong scattering occurs in the vicinity of the light source, resulting in high brightness, and in the portion far from the light source, the amount of light reaching the light source decreases, resulting in low brightness and poor uniformity of brightness. When a prism array is formed on the surface of the scattered light guide plate 12, the brightness of the backlight can be improved, and the unevenness of the brightness at the corners of the backlight can be particularly improved, so that a high-quality planar light emitter can be obtained.

The scattered light guide plate 12 made of such a material is gradually thinned as it goes away from the light incident part (the light source 14 side), and the light reflection effect occurring in the scattered light guide plate 12 causes the brightness as a surface light source to be increased. Thus, the front luminance is made uniform by the prism sheet 10. The scattered light guide plate 12 is not limited to the type in which the thickness is gradually reduced from the light incident portion as shown in FIG. 1, but may be a type in which the thickness of the scattered light guide plate 12 is uniform. Examples of the light source include a cold cathode tube, a hot cathode tube, and a semi-hot tube.

Next, referring to FIG. 4, which shows a main configuration of a liquid crystal display device using the backlight configured as described above,
The prism array 10A of the prism sheet 10 is disposed so as to face the prism array 12A surface side of the scattering light guide plate 12,
A liquid crystal panel 16 is disposed on the smooth surface side of the prism sheet 10, and a drive circuit and other components (not shown) are integrally fixed.

FIG. 5 is a sectional view showing another preferred embodiment of the backlight according to the present invention. 5 is different from the backlight shown in FIG. 1 in that a transparent resin film 18 is bonded to a smooth surface of the prism sheet 10, and other components are substantially the same as those shown in FIG. And are represented by the same reference numerals.

The transparent resin film 18 includes acrylic resin, polycarbonate resin, polystyrene resin, vinyl chloride resin, polyethylene terephthalate (P
ET), polyethylene naphthalate (PEN) and the like. Any of these resins can be arbitrarily selected according to properties such as strength and heat resistance required for the prism sheet. The thickness of the transparent resin film 18 varies depending on the required characteristics, but is preferably about 25 to 200 μm.

The prism sheet 10 and the transparent resin film 1
For example, the transparent resin film 18 can be placed in a cavity of an injection molding machine, and a composition product such as a thermosetting urethane can be injected into the cavity.

[0037]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. Example 1 10 μm spherical silicone resin as a transparent dispersion material.
2% by weight was dispersed in an acrylic resin as a transparent resin material to produce a scattering light guide plate by injection molding. The size of the light guide plate is 44 mm in length and 55 mm in width, and the thickness of the incident portion of the light from the cold cathode fluorescent lamp is 3 mm, and the thickness on the side opposite to the incident portion is 0.5 mm. The prism array of the scattering light guide plate is formed in a direction orthogonal to the cold cathode fluorescent lamp, and has a vertical angle of 90 degrees and a pitch of 50 μm. On the other hand, thickness 100
A prism sheet was prepared in which a prism having a triangular cross section made of thermosetting polyurethane was formed on a μm polyethylene terephthalate film. Apex angle 58 ° of the prisms of the prism sheet, theta ₁ is 27 (hence, the angle between the normal and the other parts prism faces is 31 degrees.) Pitch top Kakuma was 50 [mu] m. The scattered light guide plate and the prism sheet were arranged such that the prism forming surface of the prism sheet faced the prism forming surface of the scattered light guide plate, and the respective prism rows of the scattered light guide plate and the prism sheet were orthogonal to each other. The front luminance of the backlight when a current value of 3 mA was applied to the cold cathode fluorescent lamp was 3600 cd / m ² , and it was confirmed that the backlight had good uniformity and improved luminance.

[0038]

As described above, according to the present invention, the brightness can be improved while the thickness of the backlight system is reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a preferred embodiment of a backlight according to the present invention.

FIG. 2 is an enlarged detailed view of a main part of FIG.

FIG. 3 is an explanatory diagram showing an angle at which a slope of a cross-sectional shape of a scattering light guide plate intersects in the present invention.

FIG. 4 is an exploded perspective view of a main configuration of a liquid crystal display device using the backlight of FIG. 1;

FIG. 5 is a sectional view showing another preferred embodiment of the backlight of the present invention.

[Explanation of symbols]

 Reference Signs List 10 prism sheet 12 scattering light guide plate 14 light source 16 liquid crystal panel 18 transparent resin film

Claims (6)

[Claims] 1. A prism sheet having a prism array formed on one side of a resin sheet and a smooth surface on the other side; and a scattering light guide plate in which a transparent dispersion material is dispersed in a transparent resin. A prism array is formed on one surface of the light plate in a direction orthogonal to the light source arranged on the side surface of the scattering light guide plate,
A backlight characterized in that the prism rows and the prism rows of the prism sheet face each other, and these prism rows are arranged so as to be orthogonal to each other. 2. An apex angle of a cross-sectional shape of each of the prism rows formed on the prism sheet is 50 to 60 degrees, and an angle Θ ₁ between a normal from the apex angle and the prism surface is 10 degrees.
The backlight according to claim 1, wherein the angle is from 30 to 30 degrees. 3. The angle of intersection of the slopes of the cross-sectional shape of each of the prism rows formed on the scattered light guide plate is 80-140.
The backlight according to claim 2, wherein the backlight has a degree. 4. The scattering light guide plate according to claim 1, wherein the transparent resin contains 0.001 to 1.0% by weight of a transparent dispersion material. Hack light described. 5. The backlight according to claim 1, wherein the prism sheet is made of a thermosetting polyurethane. 6. The backlight according to claim 1, wherein a resin film is bonded to the smooth surface side of the prism sheet.