JP2010020988A - Backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit capable of dispersing light from a light source to obtain uniform surface light emission even when a light diffusing body having a pattern print layer formed by printing is deformed by heat from the light source. <P>SOLUTION: The backlight unit 1 comprises a housing 10 having an opening part 10a, the light diffusing body 20 formed by sealing the opening part 10a of the housing 10, the light source 30 housed in the housing 10, and a light source fixing member 40 vertically disposed on a surface 20a on a housing 10 side of the light diffusing body 20 and holding the light source 30 at a tip end. A linear light transmittance in a planar direction of the light diffusing body 20 is lower in a part adjacent to the light source fixing member 40 than in a part apart from the light source fixing member 40. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a backlight unit used in, for example, a liquid crystal display device.

As a lighting device of a liquid crystal display device, a backlight unit including a housing having an opening, a light diffuser provided by closing the opening of the housing, and a light source accommodated in the housing may be used.
Among the backlight units, those directly under the light source tend to be bright directly above the light source and relatively dark between the light sources. If this is left as it is, in-plane luminance unevenness occurs. For this reason, a pattern printing layer is provided in which the area, size, or density to be printed is changed between the light source and the light source, and the diffusion effect becomes higher immediately above the light source, and the diffusion effect gradually decreases between the light sources. The light diffuser made to become is devised to diffuse and uniformize the light from the light source. However, in the conventional backlight unit, the light diffuser may be deformed such as stretching or warping due to the heat generated together with the light from the light source. When the light diffuser is deformed, the positional relationship between the light source and the portion having a high diffusion effect is shifted, so that uniform surface light emission cannot be obtained.
In recent years, liquid crystal display devices have been made thinner, and the distance between the light source and the light diffuser has become shorter. Therefore, the problem of the position shift of the light diffuser due to the heat of the light source is more likely to occur.
As a countermeasure against deformation of the light diffuser, in Patent Document 1, a spacer pin is attached to the lamp house, and when the light diffuser extends and bends due to change over time, the tip of the spacer pin is brought into contact with the light diffuser, A method for restricting the light diffuser so as not to bend has been proposed.
Further, Patent Document 2 proposes a method for preventing the positional correspondence between the print pattern and the light source from being shifted due to temperature fluctuation by forming a positioning hole portion on the film that matches the positioning pin attached to the light source fixing plate. Has been.
JP-A-10-326517 Japanese Patent Laid-Open No. 6-301034

However, the methods described in Patent Document 1 and Patent Document 2 do not sufficiently prevent deformation of the light diffuser due to heat, and thus cannot always obtain uniform surface light emission.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a backlight unit capable of obtaining uniform surface light emission even when a light diffuser is deformed by heat from a light source.

The present invention includes the following modes.
(1) A housing having an opening, a light diffuser provided by closing the opening of the housing, a light source accommodated in the housing, and a housing-side surface of the light diffuser. A light source fixing member that grips the light source, and the light diffuser is provided with a pattern printing unit, and the linear light transmittance in the surface direction is close to the light source fixing member. The backlight unit is characterized by being lower than the part away from the unit.
(2) The backlight unit according to (1), wherein the light source fixing member has light diffusibility.

  According to the backlight unit of the present invention, even surface light emission can be obtained even when the light diffuser is deformed by heat from the light source.

<First embodiment>
An embodiment of the backlight unit of the present invention will be described.
FIG. 1 shows a backlight unit of the present embodiment. The backlight 1 according to the present embodiment includes a housing 10 having an opening 10a, a light diffuser 20 provided by closing the opening 10a of the housing 10, and light sources 30, 30,. And a light source fixing member 40 suspended from a surface 20a of the light diffuser 20 on the housing 10 side, and a prism sheet 50 provided on a surface 20b of the light diffuser 20 opposite to the housing 10.

(housing)
The housing 10 in the present embodiment has a substantially square frustum shape, and the bottom surface on the side with the larger area is the opening 10a. The housing 10 has a substantially square frustum-shaped base body 11 having an opening 10a and a reflection layer 12 provided on the surface of the base body 11 on the light diffuser 20 side, and diffuses light from the light source 30. Reflected to the body 20 side.

(light source)
The light sources 30, 30,... In the present embodiment are cold cathode tubes. Each light source 30, 30,... Extends in a direction orthogonal to the paper surface of FIG.

(Light diffuser)
The light diffuser 20 in the present embodiment is a substantially rectangular flat plate or film, and the periphery thereof is fixed to the housing 10 at the outer edge 10c of the opening 10a. As shown in FIG. 2C, the light diffuser 20 is provided with a pattern printing unit 21 on a base material 22.
Hereinafter, for convenience of explanation, in the light diffuser 20, a region having a high linear light transmittance is referred to as a high transmittance region, and a region having a low linear light transmittance is referred to as a low transmittance region. However, there is no need for a clear boundary between the high transmittance region and the low transmittance region.
From the haze meter measurement, it was found that the diffuse light transmittance is high in the portion where the linear light transmittance is low, and the diffuse light transmittance is low in the portion where the linear light transmittance is high. ing.
The linear light transmittance may be measured by any optical device, but for easy measurement, it is preferable to use a haze meter based on JIS-K7105.
In the present embodiment, as shown in FIGS. 1 and 2, the upper side of the light source fixing member 40 in the drawing (the portion close to the light source fixing member 40) is the low transmittance region 20 c, and each of the light source fixing members 40, 40 is The upper side in the figure (the part away from the light source fixing member 40) is the high transmittance region 20d. Each of the low transmittance region 20c and the high transmittance region 20d extends in parallel to the light source 30 in a direction perpendicular to the paper surface of FIGS.

The shape of the printed portion of pattern printing is not particularly limited. For example, the upper surface may be a dot having a circular shape, a triangular shape, a quadrangular shape, an elliptical shape, or a belt shape. Among these shapes, a dot having a circular upper surface is preferable because it is versatile. When the shape of the printing part is a dot whose upper surface is circular, the diameter is preferably 5 μm to 100 μm. If the diameter of the dots is 5 μm or more, the light diffusibility can be further increased. If the diameter is 100 μm or less, the dots are sufficiently small, so that the patterns are not visually recognized as dots and have no graininess.
The predetermined pattern is appropriately set according to the light diffusibility required for the light diffuser 20. The printed layer printed in a predetermined pattern diffuses light from the light source and efficiently improves the luminance uniformity. As a result, when the intensity distribution of the light that has passed through the optical sheet is measured, the luminance is uniform.

As a pattern of this embodiment, for example, a low transmittance region is formed such that the area ratio of dots per unit area immediately above the light source is increased, and the dot density is gradually reduced or the dot density is gradually increased as the distance from the light source increases. The high transmittance region is formed by adjusting the diameter to decrease. In particular, when a method for adjusting the diameter of dots is used, the method of so-called halftone dots can be used based on the concept of halftone or gray scale, which is convenient.
Another method for adjusting the uniformity is density gradation in which a solid print layer is provided and the thickness of the print layer is adjusted. That is, the low transmittance region is formed so that the thickness of the printing layer immediately above the light source is increased, and the high transmittance region is formed by gradually decreasing the thickness of the printing layer as the distance from the light source increases. To equalize the light that has passed through the light diffuser.

The thickness of the printing layer of the pattern printing unit 21 is preferably 0.5 μm to 100 μm. If the thickness of the printing layer 21 is 0.5 μm or more, the light diffusibility can be further increased and the linear light transmittance can be decreased. If it is 100 micrometers or less, peeling from the base material 22 of a printing layer can be suppressed.

As the substrate 22, a plate or film made of a transparent resin is used. Examples of the transparent resin that forms the substrate 22 include, but are not limited to, polyethylene terephthalate, polyethylene naphthalate, triacetate cellulose, polyethylene, polypropylene, polystyrene, polycarbonate, acrylic resin, and the like. In addition, the transparent base material may contain a colorant as long as it transmits visible light, or may contain light diffusing particles and have light diffusibility.
The surface of the substrate 22 on the side opposite to the pattern printing unit 21 may be flat, or an uneven pattern may be formed. When the concavo-convex pattern is formed, it is more preferable because light is diffused even in the concavo-convex portion.
The pattern printing unit 21 in the present embodiment is formed so that the linear light transmittance changes corresponding to the light source.

(Light source fixing member)
The light source fixing member 40 in the present embodiment is suspended by an adhesive 60 on a surface 20 a on the housing 10 side opposite to the low transmittance region 20 c in the light diffuser 20.
The light source fixing member 40 in the present embodiment is a long member extending in the longitudinal direction of the light source and having a bowl shape as shown in FIG. The light source 30 is held. Further, the light diffuser 20 is attached to the end surface 42 a of the connection portion 42 extending from the peripheral surface of the light source gripping portion 41.
The light source fixing member 40 is disposed so as to extend in a direction orthogonal to the paper surface of FIG.
As the material of the light source fixing member 40, the same transparent resin as that of the base material 22 of the light diffuser 20 can be used. Especially, what has the heat resistance with respect to the heat | fever of the light source 30 is preferable, and what has flexibility is preferable. Specific examples of the heat-resistant and flexible transparent resin include polyethylene terephthalate, polycarbonate, polyimide, and a methyl methacrylate-styrene copolymer.

(adhesive)
An adhesive 60 is applied to the end surface 42 a of the connection portion 42 of the light source fixing member 40.
The adhesive 60 in the present embodiment is capable of bonding the material constituting the base material 22 and the material constituting the light source fixing member 40, for example, constituting the material constituting the base material 22 and the light source fixing member 40. Resins having a solubility parameter SP equivalent to the material to be used. Here, the solubility parameter is a scale representing the intermolecular force of substances, and substances having similar solubility parameters have high compatibility.
Specific examples of the adhesive 60 include epoxy resin, polyvinyl chloride, polyvinyl acetate, and polyvinylidene chloride.

(Prism sheet)
The backlight unit 1 of this embodiment further includes a prism sheet 50.
The prism sheet 50 is for aligning the traveling direction of the light emitted from the light diffuser 20 in the direction perpendicular to the surface. Specific examples of the prism sheet 50 include a resin sheet having a regular number of conical or pyramidal protrusions on one surface.

(Backlight unit manufacturing method)
An example of the manufacturing method of the backlight unit 1 will be described below.
In this production example, first, a pattern printing unit is provided on one surface of the base material 22.
Examples of the printing method include offset printing, flexographic printing, gravure printing, screen printing, and ink jet printing.
As the color of the ink used for the above printing, white ink, black ink, gray ink, and the like are possible, but since white ink has little loss of light and is suitable for improving the brightness of diffused light, it can be used. preferable.
The white pigment ink composition contains a solvent, a white pigment, a dispersant, and a resin as a fixing agent on the surface of the object as basic components. Examples of white pigments in the ink composition include titanium oxide (TiO ₂ , titanium white), silica (SiO ₂ ), calcium carbonate, talc, clay, aluminum silicate, basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , silver White), zinc oxide (ZnO, zinc white), strontium titanate (SrTiO ₃ , titanium strontium white), barium sulfate and the like can be used alone or in a mixed system.
Titanium oxide in particular has a low specific gravity compared to other inorganic white pigments, and thus has dispersion stability, a large refractive index, excellent optical diffusivity, and is chemically and physically stable. For this reason, since the hiding power and optical diffusibility as a pigment are large, it is preferable to use titanium oxide as a main component as the inorganic white pigment used in the present invention. The white pigment can be mixed for the purpose of adjusting the color of the diffused light.
The mixing ratio of the white pigment is preferably 30% by mass to 60% by mass with respect to the entire ink composition. A white pigment other than titanium oxide is generally used in an amount of up to about 30% of the entire pigment for the purpose of dispersion aid, if necessary.

As resins in the ink composition, ketone resin, sulfoamide resin, maleic acid resin, ester gum, xylene resin, alkyd resin, rosin, polyvinylpyrrolidone, polyvinyl butyral, acrylic resin, melamine resin, cellulose resin, vinyl resin, phenol resin An ester resin can be used, and among them, an acrylic resin can be preferably used.
The organic solvent in the ink composition is used for the purpose of dissolving the resin and adjusting the viscosity, and is an aromatic hydrocarbon solvent such as toluene, xylene, ethylbenzene, n-hexane, n-heptane, isoheptane, n-octane. In addition, aliphatic hydrocarbon solvents such as isooctane, cycloparaffin solvents such as methylcyclohexane and ethylcyclohexane, and the like can be used alone or in the form of a mixture. The amount of the organic solvent used is about 30% by mass to 60% by mass with respect to the entire ink composition.
It is also possible to print with black ink or gray ink. For example, an ink set containing carbon black as the black ink and a mixture of the above white ink and metal particles as the gray ink can be used.

Next, the adhesive 60 is applied to the end surface 42a of the light source fixing member 40, and the light source fixing member 40 is applied to the surface 20a on the housing 10 side of the low transmittance region 20c of the light diffuser 20 by the adhesive 60 applied to the end surface 42a. Install and hang. Further, the light source 30 is attached and fixed to the light source gripping portion 41 of the light source fixing member 40.
Next, it arrange | positions so that the opening part 10a of the housing 10 of the light-diffusion body 20 may be plugged up. At that time, an appropriate adhesive is interposed between the periphery of the surface 20a of the light diffuser 20 on the housing 10 side and the outer edge 10c of the opening 10a. Thereby, the light diffuser 20 is fixed and the backlight unit 1 is obtained.

In the backlight unit 1 described above, the light source 30 is gripped by the light source fixing member 40 suspended from the surface 20a on the housing 10 side of the low transmittance region 20c of the light diffuser 20.
In other words, the light diffuser 20 has a high light diffusibility at a portion close to the light source 30. Thereby, it can suppress that emitted light becomes too strong just above the light source 30. FIG. Further, the light diffused in the low transmittance region 20c can be emitted from a portion away from the light source 30 where the emitted light is likely to be weak after being reflected directly or by the reflective layer 12 or the like. That is, the emitted light can be made uniform in the surface direction.
In the backlight unit 1, since the light source 30 is held by the light source fixing member 40 attached to the light diffuser 20, even if the light diffuser 20 is heated and extended by the heat of the light source 30, the light source 30. Moves in synchronization with the extension of the light diffuser 20. Therefore, in the light diffuser 20, the light diffusibility in the surface direction is always higher in the part close to the light source fixing member 40 than in the part away from the light source fixing member 40.
Therefore, according to the backlight unit 1 of the present embodiment, even when the light diffuser 20 is deformed by the heat of the light source 30, the light from the light source 30 can be diffused so that uniform surface emission can be obtained.

<Second Embodiment>
A second embodiment of the backlight unit of the present invention will be described.
FIG. 4 shows the backlight unit of the present embodiment. The backlight unit 2 of the present embodiment includes a housing 10 having an opening, a light diffuser 20 provided by closing the opening of the housing 10, and light sources 30, 30,. A light source fixing member 80 suspended from a surface 20a of the light diffuser 20 on the housing 10 side and a prism sheet 50 provided on a surface 20b of the light diffuser 20 opposite to the housing 10 are provided.
The housing 10, the light diffuser 20, the light source 30, the prism sheet 50, and the adhesive 60 in the present embodiment are the housing 10, the light diffuser 20, the light source 30, the prism sheet 50, and the adhesive in the first embodiment. Since this is the same as 60, description thereof will be omitted.

(Light source fixing member)
The light source fixing member 80 in the present embodiment is suspended by an adhesive 60 on the surface 20a of the light diffuser 20 on the housing 10 side as in the first embodiment.
As shown in FIG. 5, the light source fixing member 80 is made of a material containing light scattering particles 80b, 80b,... In a transparent resin matrix 80a, and has light diffusibility.
Here, as the transparent resin matrix 80a forming the light source fixing member 80, the same transparent resin as the material of the base material 22 of the light diffuser 20 in the first embodiment can be used.
As the light scattering particles 80b, for example, acrylic, styrene-acrylic, polyethylene organic crosslinked polymer beads, silicon beads, hollow particles, or the like are used.

(Backlight manufacturing method)
An example of the manufacturing method of the backlight unit 2 will be described below.
In this production example, first, a pattern printing portion is formed on one surface of the base material 22. At that time, the linear light transmittance in the surface direction is printed so that the portion close to the light source fixing member 80 is lower than the portion away from the light source fixing member 80 to obtain the light diffuser 20.
Next, the adhesive 60 is applied to the end surface 82 a of the light source fixing member 80, and the light source fixing member 80 is attached to the surface 20 a of the light diffuser 20 on the housing 10 side by the adhesive 60 applied to the end surface 82 a and is suspended. Further, the light source 30 is attached and fixed to the light source gripping portion 81 of the light source fixing member 80.
Next, the light diffuser 20 is disposed so as to close the opening 10 a of the housing 10. At that time, an appropriate adhesive is interposed between the periphery of the surface 20a of the light diffuser 20 on the housing 10 side and the outer edge 10c of the opening 10a. Thereby, the light diffuser 20 is fixed and the backlight unit 2 is obtained.

In the backlight unit 2 described above, the light source 30 is gripped by the light diffusing light source fixing member 80 suspended from the surface 20a on the housing 10 side of the low transmittance region 20c of the light diffuser 20. Therefore, light traveling in a substantially vertical direction toward the surface 20 a of the light diffuser 20 on the housing 10 side can be diffused by the low transmittance region 20 c of the light diffuser 20 and the light source fixing member 80. Thereby, it can suppress that emitted light becomes too strong just above the light source 30. FIG. Further, the light diffused by the low transmittance region 20c and the light source fixing member 80 can be emitted from a portion away from the light source 30 where the emitted light is likely to be weakened directly or after being reflected by the reflective layer 12 or the like. That is, the emitted light can be made uniform in the surface direction.
Even in the backlight unit 2, even if the light diffuser 20 is heated and stretched by the heat of the light source 30, the positional relationship between the light source 30 and the light source fixing member 80 does not change. Can be maintained.
Therefore, according to the backlight unit 2 of this embodiment, even when the light diffuser 20 is deformed by heat from the light source 30, uniform surface light emission can be obtained.

<Other embodiments>
In addition, this invention is not limited to the said embodiment.
For example, in the present invention, the light diffuser 20 may be a single layer or three or more layers.
As what the light diffuser 20 is comprised by three or more layers, what replaced the base material 22 in the light diffuser 20 with the base material comprised from the several layer is mentioned, for example. Here, in the base material composed of a plurality of layers, all the layers may be transparent, only some of the layers may have light diffusibility, or all the layers may be light diffusing. You may have sex.
The light source fixing members 40 and 80 are suspended from the light diffuser 20 by the adhesive 60 applied to the end faces 42a and 82a. However, the end faces 42a and 82a are coated with an adhesive. 82a may be inserted into a recess provided in advance in the light diffuser 20 and suspended.

In the first and second embodiments, a light source fixing member having an annular light source gripping portion can be used instead of the bowl-shaped light source fixing members 40 and 80.
In the backlight unit of the present invention, a point light source such as a light emitting diode (LED) may be used as the light source 30. In the case of a point light source, the low transmittance regions 20c in the first and second embodiments are also arranged in a dot shape according to the position of each point light source.
In the backlight unit of the present invention, a viewing angle improving film may be provided on the surface of the prism sheet 50 opposite to the light diffuser 20 side.
Further, the backlight unit of the present invention may not have the prism sheet 50. If the prism sheet 50 is not provided, a diffusion film may be further disposed instead.

It is sectional drawing which shows 1st embodiment of the backlight unit of this invention. (A) It is a schematic diagram of the printing pattern in the case of equalizing a brightness | luminance with the density of a dot. (B) It is a schematic diagram of the density | concentration gradation in the case of equalizing a brightness | luminance with the thickness of an ink layer. (C) It is a cross-sectional schematic diagram which shows a part of light diffuser which comprises the backlight unit shown in FIG. It is a perspective view of the light source fixing member which comprises the backlight unit shown in FIG. It is sectional drawing which shows 2nd embodiment of the backlight unit of this invention. It is a cross-sectional schematic diagram which shows the light source fixing member which comprises the backlight unit shown in FIG.

Explanation of symbols

Backlight unit 10 Housing 11 Base 12 Reflective layer 20 Light diffuser 20c Low transmittance region 20d High transmittance region 21 Pattern printing unit 22 Base material 30 Light source 50 Prism sheet 40, 70 Light source fixing member 60 Adhesive 80a Light source fixing member matrix 80b Light-scattering particle 41 Light source gripping part 42, 82 Connection part 42a, 82a End face

Claims (2)

A housing having an opening; a light diffuser provided to close the opening of the housing; a light source accommodated in the housing; and a light source disposed on the housing side surface of the light diffuser. The light diffuser is provided with a pattern printing unit, and a portion close to the light source fixing member is separated from the light source fixing member with respect to the linear light transmittance in the surface direction. Backlight unit characterized by being lower than the part. The backlight unit according to claim 1, wherein the light source fixing member has light diffusibility.

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