JP2006162846A - Diffusion plate for direct type backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion plate for direct type liquid crystal backlight capable of selecting total light beam transmittance and haze value on the user side. <P>SOLUTION: The diffusion plate for direct type liquid crystal backlight comprises a glass substrate and a diffusion layer formed on the substrate surface, wherein the diffusion layer is formed by using a composition including spherical beads of average particle size 5μm to 40μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diffusion plate used by being incorporated in a direct type backlight of a liquid crystal display device.

  In recent years, an increase in the size of a backlight has been required due to an increase in the screen size of a liquid crystal display device such as a liquid crystal television. The backlight is roughly classified into a sidelight type and a direct type, but the latter type is often used for large backlights. The direct type is configured by arranging a light emitter, for example, a plurality of lamps (cold cathode fluorescent lamps) behind the diffuser plate. This lamp can be used, and it is easy to obtain high brightness even when the lamp is enlarged. In addition, the direct type is suitable for increasing the size of the high brightness because the inside of the apparatus has a hollow structure and is light even if the size is increased.

However, in the conventional direct type backlight, when the luminance is increased and the thickness is further reduced, it is difficult to maintain a good light emission quality. That is, the direct type backlight has a structure in which a lamp is arranged behind the diffuser plate, so that the device is thicker than the sidelight type backlight, and it is originally difficult to reduce the thickness. .
In addition, if the distance between the diffuser and the lamp is reduced to reduce the thickness, the lamp image on the light emitting surface of the diffuser (the brightness near the lamp on the diffuser is high and the brightness between the lamps is low) ) Occurs strongly, and it becomes difficult to erase the lamp image, and the luminous quality is lowered. That is, in the direct type backlight, when the thickness is reduced, the light emission quality is lowered.

Furthermore, when the direct-type backlight is to be enlarged to ensure high brightness, the display surface is large, so that it is necessary to use a large number of lamps, and heat generation from the lamps or the like increases. In the conventional direct type backlight, since the diffusion plate is made of a synthetic resin such as an acrylic resin or a polycarbonate resin, the diffusion plate is easily warped, yellowed, or thermally deformed due to the influence of heat generation. When warping or the like occurs in the diffusion plate, the light emission quality is lowered, and the life of the diffusion plate is shortened.
As described above, in a direct type backlight using a resin-made diffusion plate, it is necessary to increase the distance between the lamp and the diffusion plate in order to avoid the influence of deterioration in light emission quality and heat generation. Increasing the distance between the lamp and the diffusion plate increases the thickness of the device, which is contrary to the reduction in thickness. In addition, the brightness of the backlight also decreases.
Moreover, since the diffusion plate made of synthetic resin is warped due to moisture absorption, the diffusion plate is warped even when the distance between the lamp and the diffusion plate is increased and the influence of heat generated by the lamp is fully considered. As a result, the light emission quality is lowered, and the life may be shortened.

  In order to solve such a problem, a direct type backlight using a heat-resistant glass diffusion plate instead of a synthetic resin as a diffusion plate is disclosed. In the liquid crystal display device described in Patent Document 1, a plate glass coated with a light diffusing agent is used as a diffusion plate of a backlight unit. However, in Patent Document 1, regarding the light diffusing agent, the component is an organic or inorganic coating agent, and it is described that a pigment may be mixed therein, but a specific aspect of the light diffusing agent is described below. Not shown at all. Further, it is described that the light diffusing agent may be applied to the plate glass at a high temperature, but no specific means for applying or applying the light diffusing agent to the plate glass is shown. Furthermore, it is described that the light diffusing agent to be applied is a material having a low transmittance and prevents the light transmittance of the diffusion plate from becoming excessively high. No numerical values are given at all. That is, Patent Document 1 does not show the light transmittance and haze rate of the light diffusion plate, which are important parameters for the light emission quality of the backlight.

Patent Document 2 discloses a direct type backlight using a glass diffusion plate having a haze value of 95% or more and a transmittance of 10% to 60%. This direct type backlight is said to be capable of increasing the brightness, increasing the size, and reducing the thickness while maintaining good light emission quality.
However, the direct type backlight described in Patent Document 2 uses a glass diffuser plate with high haze (haze in the present application) and low transmittance, while maintaining uniformity in luminance (light emission quality), Since the high brightness is ensured by reducing the distance between the diffusion plate and the lamp and reducing the lamp pitch, it is not preferable in terms of the effective utilization rate of light from the lamp. Low power consumption is important as a required characteristic for electrical equipment. Even in direct type backlights used in liquid crystal display devices, the effective utilization rate of light from the lamp is increased to reduce power consumption. It is preferable to do.
Furthermore, in the direct type backlight of Patent Document 2, since a glass plate having a predetermined haze value and transmittance is molded, many manufacturing processes and a lot of work are required, and a desired haze value and transmission are desired on the user side. The rate could not be selected.

Patent Document 3 discloses a plate-like diffusion in which an optical sheet having a total light transmittance of about 70% ± 10% and a haze value (haze in the present application) of 80% or more is laminated on a transparent resin or transparent glass transparent plate. A backlight device using the means is disclosed. In the backlight device of Patent Document 3, a plate-like diffusing unit having a desired haze value can be selected on the user side by using an optical sheet and a transparent plate, and a device capable of freely controlling the total light transmittance is obtained. At the same time, it is said that a backlight device capable of reducing pin unevenness can be obtained.
However, in the backlight device of Patent Document 3, a transparent sheet made of synthetic resin such as polyethylene terephthalate, acrylic, polycarbonate, and cycloolefin polymer is used. There are concerns about the effect and the effect of moisture absorption of the transparent sheet. Further, since the transparent sheet made of synthetic resin is laminated on the plate-like diffusion means, the transparent sheet may be peeled off due to heat generated by a lamp or the like.
Furthermore, by laminating an optical sheet made of synthetic resin, the thickness of the plate-like diffusion means increases. In Patent Document 3, an optical sheet made of PET having a thickness of 125 μm is illustrated as a specific example of the optical sheet. When an optical sheet having such a thickness is used, the equipment that has been conventionally used for a diffusion plate made of a synthetic resin cannot be used as it is, and the equipment needs to be modified.

  Furthermore, in the backlight device of Patent Document 3, the total light transmittance and haze value of the plate-like diffusing means are adjusted by the total light transmittance and haze value of the optical sheet. Compared with the direct type backlight of Patent Document 2 that needs to mold a glass plate having a high rate, the range of choices on the user side has expanded, but since it depends on the optical sheet to be used, The total light transmittance and haze value cannot be freely selected on the user side.

Japanese Patent Laid-Open No. 4-350821 Japanese Patent Laid-Open No. 2004-127643 Japanese Patent Laid-Open No. 2004-219838

  In order to solve the above-described problems in the prior art, an object of the present invention is to provide a diffusing plate for a direct type liquid crystal backlight capable of selecting a total light transmittance and a haze ratio on the user side.

In order to achieve the above object, the present invention is a diffusion plate for a direct liquid crystal backlight comprising a glass substrate and a diffusion layer formed on the substrate surface,
The diffusion layer is formed using a composition including spherical beads having an average particle diameter of 5 μm to 40 μm, and is a direct type liquid crystal backlight diffusion plate (hereinafter simply referred to as “diffusion for backlight of the present invention”). Board ").
In the present specification, the term “direct backlight” includes a wide variety of backlights including a light emitter disposed behind the diffusion plate. Therefore, the present invention is not limited to a configuration in which a plurality of lamps are arranged, and one surface light emitter may be arranged behind the diffusion plate.

  In the backlight diffusion plate of the present invention, the diffusion layer is preferably formed by screen-printing the composition on the surface of the substrate.

  In the backlight diffusion plate of the present invention, the spherical beads are contained in the composition in an amount of 15 to 35% by mass, and the thickness of the diffusion layer is preferably 5 to 100 μm.

  In the backlight diffusion plate of the present invention, the composition may further contain a white pigment or a colorant.

The backlight diffusion plate of the present invention has a diffusion layer formed using a composition containing spherical beads having an average particle diameter of 5 μm to 40 μm, thereby having a high total light transmittance and a high haze ratio. Can be obtained. If a diffusion layer having a thickness of 5 to 100 μm is formed using a composition containing 15 to 35% by mass of spherical beads having the above average particle diameter, a diffusion plate having a particularly high total light transmittance and a high haze ratio can be obtained. Can do.
In addition, the haze ratio of the diffusion plate can be adjusted by changing the average particle diameter of spherical beads in the composition, the content or the thickness of the diffusion layer formed, the total light transmittance of the diffusion plate is Since it can be adjusted by adding a white pigment or a colorant, a diffusion plate having desired total light transmittance and haze ratio can be obtained. Therefore, the total light transmittance and haze ratio of the diffusion plate can be selected on the user side. For this reason, it is not necessary to prepare many different compositions in order to produce a diffuser plate having different total light transmittance and haze ratio, and the backlight diffuser plate of the present invention is excellent in economic efficiency.

  A diffusion layer having a desired thickness can be easily obtained by screen-printing the composition on the substrate surface to form a diffusion layer. The thickness of the diffusion layer can be adjusted by changing screen printing conditions, or can be adjusted by simply changing the number of printings. When adjusting the thickness of the diffusion layer according to the number of printings, it is not necessary to change the setting conditions of the equipment used. Therefore, the backlight diffusion plate of the present invention is excellent in productivity.

  Since the backlight diffusion plate of the present invention uses a glass substrate, it does not cause warpage, yellowing, or thermal deformation due to the influence of heat generated by a lamp or the like, unlike a synthetic resin diffusion plate. Also, no warpage occurs due to moisture absorption. Therefore, even when the lamp and the diffusing plate are arranged close to each other, the light emission quality of the backlight is not deteriorated, and the lifetime of the backlight is not shortened. Therefore, the backlight diffusion plate of the present invention is suitable for increasing the brightness and size of the backlight.

  The backlight diffusion plate of the present invention having a high total light transmittance and a high haze ratio is excellent in the effective utilization rate of light from the lamp. By using a backlight diffuser plate with excellent effective utilization of light from this lamp, it is possible to reduce the number of lamps necessary to obtain the same brightness without lowering the light emission quality of the backlight, In a backlight using a surface emitting type body, a light emitting body with lower illuminance can be used. And it contributes to reduction of the power consumption of a backlight and a liquid crystal display device using the same.

The backlight diffusion plate of the present invention exhibits a light diffusing effect due to the diffusion layer containing spherical beads, so that a desired light diffusing effect can be obtained compared to a conventional diffusion plate using a synthetic resin diffusion sheet. The required diffusion layer thickness is small. Therefore, the thickness of the diffusion plate can be reduced.
Further, in the backlight diffusion plate of the present invention, if the above composition is screen-printed on the surface of the substrate to form a diffusion layer, a lamp or the like like a conventional diffusion plate laminating a diffusion sheet made of synthetic resin There is no possibility that the diffusion sheet is peeled off due to the heat generated from the substrate.

  The backlight diffusion plate of the present invention comprises a glass substrate and a diffusion layer formed on the surface of the substrate. The diffusion layer is formed using a composition containing spherical beads having an average particle diameter of 5 μm to 40 μm. Specific methods for forming the diffusion layer include, for example, a method of coating the composition on the surface of the substrate using a coating method or a dipping method, or a method of screen printing the composition on the surface of the substrate. It is done. Among these, a diffusion layer having a desired film thickness and a uniform film thickness can be easily obtained, and the formed diffusion layer is not likely to be peeled off due to heat generated by a lamp or the like. Therefore, it is preferable to form a diffusion layer by screen-printing the composition on the substrate surface.

  In the backlight diffusion plate of the present invention, the glass substrate may be a normal plate glass such as non-colored transparent soda-lime-based, borosilicate-based, or lithium alumina silicate-based. However, in the backlight diffusion plate of the present invention, the glass substrate preferably has a high visible light transmittance because the diffusion layer formed on the substrate surface exhibits a light diffusion effect. Specifically, the visible light transmittance is preferably 90% or more.

  The thickness of the substrate may be in a general range as the thickness of the backlight diffusion plate. Specifically, for example, the nominal value may be 1.0 mm to 3.0 mm. However, in the backlight substrate of the present invention, the diffusion layer formed on the surface of the substrate exhibits a light diffusion effect, so that the thickness of the substrate is sufficient as long as the properties required for the diffusion plate, such as mechanical strength, can be satisfied. It may be reduced. A glass substrate has a higher specific gravity than a synthetic resin diffusion plate, and thus becomes heavier when the same dimensions are used. However, an increase in weight can be reduced by reducing the thickness of the substrate.

  The dimensions of the substrate are determined by the backlight used and thus the liquid crystal display device used. Specifically, the dimensions correspond to various liquid crystal display devices such as a 10-inch type, a 17-inch type, a 20-inch type, a 30-inch type, and a 50-inch type.

  The composition used for forming the diffusion layer is mainly composed of spherical beads having an average particle diameter of 5 to 40 μm and a resin component forming a matrix of the diffusion layer.

  In the present invention, the resin component forming the matrix of the diffusion layer is preferably a thermosetting resin excellent in light transmittance, specifically, total light transmittance. Specific examples of such resin materials include (meth) acrylic acid esters of N-alkylamino alcohols, polyethylene glycol (meth) acrylic acid esters, N-alkyl (meth) acrylic acid amides, and vinyl ethers of polyhydric alcohols. 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, vinyl caprolactam, 2-ethylhexyl acrylate, etc., and the composition may contain only one of these resin materials. Or two or more of them may be contained.

The spherical beads contained in the composition are preferably those having a narrow particle size distribution, and glass beads or resin beads such as acrylic resin, silicon resin, urethane resin, urea resin, nylon, polyolefin, and fluorine resin can be used. . The composition may contain only 1 type of these beads, or may contain 2 or more types. As the physical properties of the beads, those having a high refractive index are preferable.
In the present invention, spherical beads having an average particle diameter of 5 μm to 40 μm are used. The spherical beads preferably have an average particle diameter of 20 μm to 30 μm. When the average particle diameter of the spherical beads is less than 5 μm or more than 40 μm, the formed diffusion layer cannot exhibit a sufficient light diffusion effect.

  In the present invention, the spherical beads are preferably contained in the composition at 15 to 35% by mass. If the content of the spherical beads in the composition is in the above range, the coating property is excellent when coating or screen printing on the surface of the substrate, and the spherical beads are sufficiently present in the diffusion layer. Excellent light diffusion effect.

  In the present invention, the composition may contain components other than the resin component forming the matrix of the spherical beads and the diffusion layer. Specific examples of other components that can be contained in the composition include white pigments typified by titanium pigments, colorants, reinforcing agents, and leveling agents. These other components can be contained in a range that does not adversely affect the light diffusion effect of the diffusion layer. The white pigment and the colorant can be used for the purpose of adjusting the total light transmittance of the diffusion plate, as will be described in detail later. In addition, you may make the composition contain the desired solvent according to the resin component.

A preferred method for producing the backlight diffusion plate of the present invention will be described below. However, the manufacturing method of the backlight diffusion plate of the present invention is not limited to this.
A composition prepared in advance so that the average particle diameter and content of the spherical beads have desired values is screen-printed on the surface of the glass substrate so as to have a desired thickness. The thickness of the composition on the substrate surface can be adjusted by the solid content concentration in the composition, the mesh number, the emulsion thickness, the squeegee pressure, the number of printings, and the like.
Then, in order to volatilize the solvent in the composition and heat cure the resin component in the composition, the diffusion layer is formed by heating the glass substrate. The heating temperature and the heating time are appropriately selected according to the type of resin component contained in the composition and the coating amount of the composition. For example, in the examples described later, heating was performed at 250 ° C. for 3 minutes in the atmosphere.
The diffusion layer may be formed only on one side of the substrate, or may be formed on both sides of the substrate. However, in order to prevent the resin component forming the matrix of the diffusion layer from being affected by heat generated from a lamp or the like, the diffusion layer is attached to only one side of the base material, more specifically, to the backlight. At this time, it is preferable to form on the surface of the base material on the side away from the lamp (surface opposite to the lamp).

The diffusion layer formed by the above procedure preferably has a thickness of 5 μm to 100 μm, more preferably 10 μm to 80 μm. In addition, when the unevenness | corrugation exists in the surface of a diffusion layer, the average value of the thickness of a diffusion layer is said range. When the thickness of the diffusion layer is less than 5 μm, the diffusion layer cannot sufficiently exhibit the light diffusion effect. On the other hand, even if the thickness of the diffusion layer is larger than 100 μm, the contribution to the light diffusion effect is no longer significant, which is not preferable from the viewpoint of economy. If the thickness of the diffusion layer exceeds 100 μm, the diffusion layer having the resin component as a matrix may be adversely affected by heat generation or moisture absorption from a lamp or the like. Furthermore, when the thickness of the diffusion layer exceeds 100 μm, the total light transmittance of the diffusion plate is lowered.
In addition, when forming a diffusion layer on both surfaces of a base material, it forms so that the thickness of each diffusion layer may become the said range.

  In the diffusion plate of the present invention, a diffusion plate having a high total light transmittance and a high haze ratio is obtained by having a diffusion layer formed using a composition containing spherical beads having an average particle size of 5 μm to 40 μm. Can do. If a diffusion layer having a thickness of 5 to 100 μm is formed using a composition containing spherical beads having an average particle diameter of 15 to 35% by mass, a diffusion plate having a particularly high total light transmittance and a high haze ratio is obtained. be able to.

The total light transmittance of the diffusing plate can be adjusted by adding a white pigment or a colorant. For this reason, the total light transmittance can be appropriately adjusted according to the light emission quality required for the diffusion plate and the luminance while keeping the diffusion plate at a high haze ratio. In addition, the diffuser plate of the present invention has a total light transmittance of 80% to 95% as defined in JIS-K7361-1 (1997) with respect to those prepared without adding a white pigment and a colorant to the composition. It is preferably 90% to 95%. Moreover, it is preferable that the C light source haze rate measured using the haze meter of the diffusion plate of this invention is 90% or more and less than 100%, More preferably, it is 94% or more and less than 100%.
On the other hand, the haze ratio of the diffusion plate can be adjusted by changing the average particle diameter of spherical beads in the composition, the content, or the thickness of the diffusion layer to be formed.

  As described above, according to the present invention, a diffuser plate having a high total light transmittance and a high haze ratio can be obtained, and the diffuser plate can be kept at a high haze ratio by including a white pigment or a colorant in the composition. However, only the total light transmittance can be largely adjusted, and a diffuser plate having a total light transmittance of 50% to 80% and a C light source haze ratio of 90% to less than 100% can be obtained. For example, by adding a white pigment or colorant to the composition, the C light source haze ratio is maintained at 90% or more so that the total light transmittance and haze ratio are the same as those of a conventional synthetic resin diffusion plate. However, by making the total light transmittance as low as about 50% to 60%, it can be used as a substitute for a conventional synthetic resin diffusion plate.

  On the other hand, when the composition does not contain a white pigment and a colorant, a diffusion plate having a high total light transmittance and a high haze ratio can be obtained. Specifically, the total light transmittance is 90% or more, and the C light source haze is obtained. A diffusion plate having a rate of 90% or more can also be obtained. Such a diffusing plate can increase the light utilization rate from the lamp while sufficiently exhibiting the light diffusing effect. When such a diffuser plate is used, the number of lamps used in the backlight can be reduced without impairing the light emission quality and brightness of the backlight. In the case of a backlight using a surface light emitter, It is considered that a light emitter with lower illuminance can be used. As a result, the power consumption of the backlight and the fluorescent display device using the backlight can be reduced.

The diffusion plate of the present invention will be further described below with reference to examples.
Example 1
A glass substrate was prepared by cutting a plate glass (made of soda-lime glass) having a thickness of 2 mm into a size of 30 cm square. After chamfering the substrate, hot water brush cleaning and air knife drying were performed. Subsequently, a composition comprising the following components was screen-printed on the substrate surface.
Composition Spherical beads: 17.5 g of urethane resin beads having an average particle diameter of 5 [mu] m
(20% by mass in 100% by mass of the composition)
Vinyl caprolactam 22.0g
Tripropylene glycol diacrylate 22.0g
Bifunctional urethane oligomer (leveling agent) 30.0 g
Auxiliary agent (silicon oil, etc.) 5.0g
Screen printing was performed under the following conditions.
Screen board: Mesh Bancho # 200
Bias angle: 25 degrees Emulsion thickness: 3 μm
Number of printing: 2 times Thereafter, a drying layer having a thickness of 20 μm was formed on the substrate surface by drying in the atmosphere at 250 ° C. for 3 minutes.

(Example 2)
Except for the use of the following composition, the reaction was carried out under the same conditions as in Example 1 to form a diffusion layer having a thickness of 20 μm on the substrate surface.
Composition Spherical beads: 25 g of urethane resin beads having an average particle diameter of 5 [mu] m
(20% by mass in 100% by mass of the composition)
Vinyl caprolactam 15.0g
Tripropylene glycol diacrylate 22.0g
Bifunctional urethane oligomer (leveling agent) 30.0 g
Titanium pigment (white pigment) 20.0g
Auxiliary agent (silicon oil, etc.) 5.0g

(Example 3)
The diffusion layer having a thickness of 12 μm was formed on the surface of the base material except that the number of times of printing was changed to 1 under the same conditions as in Example 2.

Measurement of total light transmittance and haze ratio About the diffusers obtained in Examples 1 to 3, the C light source haze ratio and total light transmittance were measured using a haze meter (HGM-2DP, Suga Test Instruments Co., Ltd.). A C light source was used as the light source, and light was applied to the surface of the base material on which the diffusion layer was not formed.

The measurement results of the total light transmittance and the C light source haze ratio were as follows. As a comparative example, a conventional synthetic resin diffusion plate (Panlite (registered trademark) ML-1102 (QF1231) (manufactured by Teijin Chemicals Ltd.), polycarbonate resin, thickness 2 mm) catalog value (flat panel display) Recommended material catalog (issued in June 2004) is shown.

  In Example 1 using the composition containing no white pigment, a diffusion plate having a high total light transmittance and a high C light source haze ratio was obtained. Example 2 is an example in which a titanium pigment that is a white pigment is added to the composition of Example 1, and the total light transmittance is greatly adjusted from 90% to 68% while keeping the C light source haze rate high. I was able to. Example 3 is an example in which the film thickness of the diffusion layer was changed by setting the number of printings of the composition of Example 2 to one, and the total light transmittance and the C light source haze ratio were adjusted. As apparent from Examples 1 to 3, according to the diffusion plate of the present invention, the total light transmittance and C light source haze ratio of the diffusion plate can be selected in a wide range on the user side.

The diffusing plates of Examples 1 and 3 are promising as diffusing plates excellent in the effective utilization rate of light from the lamp because they have a higher total light transmittance than the diffusing plate of the comparative example. Since the diffuser plate of Example 1 has a higher total light transmittance and a C light source haze ratio than the conventional diffuser plate, the number of lamps used for the backlight can be reduced without impairing the light emission quality and brightness of the backlight. It can be reduced. The diffuser plate of Example 3 has a C light source haze ratio close to that of the conventional diffuser plate. However, since the total light transmittance is high, the luminance of the backlight when used in a backlight using a surface light emitter is high. It is considered that a light emitter with lower illuminance can be used without impairing the brightness. When the diffusion plates of Examples 1 and 3 are used, the power consumption of the backlight and further the fluorescent display device using the backlight is reduced by reducing the number of lamps or using a light emitter with lower illuminance. I think it can be done.
On the other hand, since the diffuser plate of Example 2 has a total light transmittance close to that of the conventional diffuser plate, it can be used as an alternative to the conventional diffuser plate. Moreover, since the C light source haze ratio is higher than that of the conventional diffusion plate, the light scattering property (uniformity) is excellent.

Claims (4)

A diffusion plate for a direct type liquid crystal backlight having a glass substrate and a diffusion layer formed on the surface of the substrate,
The diffusion layer for a direct type liquid crystal backlight, wherein the diffusion layer is formed using a composition containing spherical beads having an average particle diameter of 5 μm to 40 μm.   The said diffusion layer is a diffusion plate for direct type | mold liquid crystal backlights of Claim 1 formed by screen-printing the said composition on the said base material surface. The spherical beads are contained in the composition at 15 to 35% by mass,
The diffusion plate for a direct type liquid crystal backlight according to claim 1, wherein the diffusion layer has a thickness of 5 to 100 μm.   The diffusion plate for a direct type liquid crystal backlight according to any one of claims 1 to 3, wherein the composition further contains a white pigment or a colorant.