JP2009003050A - Light-diffusing plate and direct backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-diffusing plate which is superior in light anisotropically diffusing effect and has high luminance, and to provide a direct backlight device that uses the same. <P>SOLUTION: The light-diffusing plate has a line-shaped irregularity pattern on one surface, has total light transmissivity of 75 to 95%; and when light is made incident from another surface at an incidence angle of 0°, emission intensity distribution of light emitted from one surface satisfies the conditions (1), (2): (1) an emission angle where emission intensity is 50% of that at emission angle 0° is in a range of 20° and 25°, with regard to the emission intensity distribution, in a plane which is perpendicular to a longitudinal direction of the line-shaped irregularity pattern; and (2) an emission angle where emission intensity is 50% of that at emission angle 0° is in a range of 0.5° and 19° with regard to emission intensity distribution, in a plane which is in parallel with the longitudinal direction of the line-shaped irregularity pattern. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light diffusing plate suitable for various display devices, particularly a direct backlight device of a liquid crystal display device, and a direct backlight device using the same.

  Liquid crystal display devices are used in various applications such as notebook computers and mobile phone devices, televisions, monitors, car navigation systems, and the like. The liquid crystal display device incorporates a backlight device serving as a light source, and is configured to display light by controlling light beams from the backlight device through a liquid crystal cell. The characteristic required for this backlight device is not only as a light source for emitting light, but also to make the entire screen shine brightly and uniformly.

  The structure of the backlight device can be roughly divided into two. One is a system called a sidelight type backlight. This is a method mainly used for, for example, a notebook personal computer or the like that is required to be thin and small, but is characterized by using a light guide plate as a basic configuration. In the case of a sidelight-type backlight, a fluorescent tube is installed on the side surface of the light guide plate, light is incident on the light guide plate from the side surface, and light is propagated throughout the surface while totally reflecting inside the light guide plate. A part of the light is removed from the total reflection condition by diffusing dots or the like applied to the back surface of the light, and the light is collected from the front surface of the light guide plate, thereby functioning as a backlight, that is, a surface light source. In the case of a sidelight type backlight, in addition to these configurations, a reflection film that functions to reflect and reuse light leaking from the back surface of the light guide plate, and a diffusion sheet that equalizes light emitted from the front surface of the light guide plate Many kinds of optical films are used, such as a light collecting sheet represented by a prism sheet for improving the front luminance and a luminance improving sheet for improving the luminance on the liquid crystal panel.

Another method is a method called a direct type backlight. This is a system that is preferably used for television applications that require large size and high brightness, but the basic structure is characterized by a structure in which fluorescent tubes are arranged directly behind the screen without using a light guide plate. By arranging a plurality of linear or partially linear fluorescent tubes in parallel at the back of the screen, it is possible to cope with a large screen and to secure sufficient brightness. However, uneven brightness (brightness unevenness) occurs in the screen due to the fluorescent tube installed at the back of the screen, which is also a feature. That is, the portion directly above the fluorescent tubes arranged in a row is bright and the space between adjacent fluorescent tubes is dark (tube unevenness). For this reason, in the direct type backlight, in order to eliminate this tube unevenness, a light diffusing plate (milky white plate) having extremely strong light diffusibility is installed on the upper side of the fluorescent tube to make the screen uniform (patent) Reference 1). The light diffusing plate is a light diffusing plate made of an acrylic resin or a polycarbonate resin in which fine particles are dispersed. This light diffusing plate eliminates tube unevenness and makes the screen uniform, but because it diffuses strongly, the total light transmittance is low and the light utilization efficiency deteriorates. As a result, the required front brightness is insufficient. Therefore, a diffusion sheet that exhibits a light collecting effect in the front direction is installed on the light diffusion plate while diffusing light isotropically. This diffusion sheet is a sheet called a bead sheet in which a diffusion layer containing fine particles such as organic cross-linked particles is formed on a base material sheet. Unlike a light diffusion plate, this diffusion film is an optical film that exhibits a certain degree of directivity in the front direction. It is. Besides these, the reflective film that reflects the light emitted backward from the fluorescent tube, the light collecting sheet represented by the prism sheet for improving the light collecting property, and the lack of brightness on the liquid crystal panel In addition, a brightness enhancement sheet for improving the brightness on the liquid crystal panel is incorporated.
JP 2004-29091 A

  In a direct type backlight device, it is necessary to eliminate luminance unevenness derived from the fluorescent tube at the back of the screen and to make the screen uniform and increase the luminance at the same time. Usually, as a direct type backlight device, as described above, a light diffusing plate having extremely strong light diffusibility is installed, and this plate-like member eliminates tube unevenness and increases the uniformity of the screen. In the case of a light diffusing plate that emphasizes uniformity, the total light transmittance is low and the light utilization efficiency is poor, so high brightness cannot be achieved. In the case of a light diffusing plate that emphasizes brightness, the total light transmittance is high. There is a contradictory phenomenon that the degree of uniformity cannot be increased due to a decrease in light diffusivity. Of course, it is obvious that the degree of uniformity is further inferior only with the conventionally used bead sheet, condensing sheet, and brightness enhancement sheet.

  In addition, conventionally used brightness enhancement sheets are generally composed of a thin synthetic resin film having a thickness of less than 500 μm, and are prone to thermal deformation such as deflection and are vulnerable to heat. When applied to backlights and devices for large screens, especially those that exceed 20 inches, it is necessary to increase the thickness to increase the heat capacity, but the cost increases as the thickness increases. Cause up.

  Therefore, in view of the background of the prior art, the present invention is to provide a light diffusing plate that is excellent in the anisotropic diffusion effect of light and has high luminance, and a direct type backlight device using the same. That is, in the present invention, an efficient diffusion effect is exhibited by combining the light diffusing plate with the light diffusing plate, thereby efficiently eliminating the tube unevenness derived from the fluorescent tube, and there is no brightness enhancement sheet. However, there is an effect that the screen uniformity and high luminance characteristics can be expressed without moiré on the liquid crystal panel.

The present invention employs the following means in order to solve such problems. That is, the light diffusing plate of the present invention has a line-shaped uneven pattern on one surface, the total light transmittance is 75 to 95%, and light is incident at an incident angle of 0 ° from the other surface. The light diffusing plate satisfies the following conditions (1) and (2) in the emission intensity distribution of light emitted from one surface.
(1) With respect to the emission intensity distribution in a plane perpendicular to the longitudinal direction of the line-shaped uneven pattern, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 20 to 25 °. .
(2) With respect to the emission intensity distribution in the plane parallel to the longitudinal direction of the line-shaped uneven pattern, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 0.5 to 19 °. It is.

  In the direct type backlight device of the present invention, a plurality of linear light sources, the light diffusing plate, and the light collecting sheet are arranged in this order, and a surface that does not have the linear concavo-convex pattern of light diffusion is a line. This is a direct type backlight device that is directed to the light source side and is arranged so that the longitudinal direction of the line-shaped uneven pattern and the linear portion of the line light source are parallel to each other.

  According to the present invention, it is possible to provide a direct-type backlight device having an anisotropic diffusion effect of light and having high luminance characteristics by disposing a light collecting sheet on such a light diffusing plate. By incorporating the device into the apparatus, both high screen uniformity and high luminance characteristics can be achieved without moire even when the luminance enhancing sheet is not disposed.

As a result of intensive studies on the above-mentioned problem, that is, a direct type backlight device having an anisotropic diffusion effect of light and having high luminance characteristics, the present invention has a line-shaped uneven pattern on the A surface and has a total light transmittance. It is a light diffusing plate that is 75 to 95% and that the light intensity emitted from the A surface when the light beam is incident from the B surface at an incident angle of 0 ° satisfies the following conditions (1) and (2). .
(1) With respect to the emission intensity distribution in a plane perpendicular to the longitudinal direction of the line-shaped uneven pattern, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 20 to 25 °. .
(2) With respect to the emission intensity distribution in the plane parallel to the longitudinal direction of the line-shaped uneven pattern, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 0.5 to 19 °. It is.

  The light diffusing plate of the present invention has a configuration in which a line-shaped uneven pattern is formed on the A surface. The anisotropic diffusivity is expressed by the line-shaped uneven pattern on the A surface. When the light diffusion plate of the present invention is incorporated in a direct type backlight device, the longitudinal direction of the line-shaped uneven pattern formed on the A surface of the light diffusion plate and the direction parallel to the linear portion of the light source are parallel to each other. It installs so that it may become. The direction perpendicular to the longitudinal direction of the line-shaped concavo-convex pattern is the direction in which the diffusion plate exhibits the strongest diffusivity, so that the anisotropic diffusion property of the light diffusion plate is maximized and the fluorescent tube image can be seen through. It is possible to efficiently eliminate luminance unevenness.

  When the light diffusing plate of the present invention is mounted on a direct type backlight device, a direction having a strong diffusivity (longitudinal direction) can be provided by setting the direction parallel to the linear portion of the light source and the longitudinal direction of the line-shaped uneven pattern in parallel. The direction of the light source diffuses the image of the light source to improve the uniformity. Therefore, if the diffusibility in this direction is insufficient, the light source image is seen through, resulting in poor uniformity. That is, in the light diffusing plate of the present invention, when a light beam is incident on the B surface at an incident angle of 0 °, the emission intensity distribution of the light beam emitted from the A surface is perpendicular to the longitudinal direction of the line-shaped uneven pattern on the A surface. In such a plane, it is necessary that the emission angle at which the intensity is 50% of the emission intensity at the emission angle of 0 ° satisfies the range of 20 ° to 25 °. If the emission angle is less than 20 °, the diffusivity is insufficient, and thus uneven brightness appears. On the other hand, when the emission angle exceeds 25 °, the diffusibility is sufficient and preferable in terms of uniformity, but the light in the front direction is lowered by excessively diffusing light rays.

  The light diffusing plate of the present invention is such that when a light beam is incident on the B surface at an incident angle of 0 °, the intensity distribution of the light beam emitted from the A surface is perpendicular to the diffusing plate surface and the line-shaped irregularities on the A surface. In the plane parallel to the longitudinal direction of the pattern, when the emission angle that is 50% of the emission intensity at the emission angle of 0 ° satisfies the range of 0.5 to 19 °, It is possible to reduce the diffusion and achieve a bright backlight. When the light diffusing plate of the present invention is mounted on a direct type backlight device, this direction corresponds to a direction parallel to the linear portion of the light source, so that strong diffusibility is not required. That is, by satisfying the above range and giving a fine diffusion effect while suppressing diffusion in an unnecessary direction as much as possible, it is possible to contribute to improvement in luminance while preventing unevenness such as interference fringes. When the emission angle is less than 0.5 °, the regularity of the line-shaped uneven pattern on the A surface is high, and unevenness such as interference fringes appears. On the other hand, when the emission angle exceeds 19 °, the anisotropic diffusibility of the sheet due to the A-line line uneven pattern is insufficient, and an efficient diffusion effect cannot be obtained.

  In addition, the light diffusing plate of the present invention is configured by laminating at least a support plate, an intermediate layer, and a diffusing layer in this order, and a line-shaped uneven pattern is formed on the surface of the diffusing layer opposite to the intermediate layer side. Preferably it is formed. This configuration is preferable in terms of the ease of processing the line-shaped uneven pattern and the reduction of members constituting the direct type backlight device.

  The role of the support plate according to the present invention includes supporting various optical sheets installed on the side opposite to the light source side and preventing deformation due to heat generated from the light source. As the material for the support plate, glass, a mixture of two or more kinds of resins that are difficult to mix, a resin composition containing a transparent resin and a light diffusing agent, and the like are preferable from the viewpoint of supporting various optical sheets and a heat insulating effect from a light source. Among these, a resin composition containing a transparent resin and a light diffusing agent is lighter and more preferably used from the viewpoint of production cost.

  Although the thickness of the support plate concerning this invention is not specifically limited, 500 micrometers or more are preferable from the point of the heat insulation effect from the support of a various optical sheet, or a light source.

  The role of the diffusion layer according to the present invention includes ease of processing a line-shaped uneven pattern and its retention. As the material for the diffusion layer, a substantially transparent base material, a single layer body containing particles inside, or a base material made of a laminate having at least a layer containing particles inside is preferably used. Axis-stretched polyethylene terephthalate, polyethylene-2,6-naphthalate, a copolymer with other components based on these, or a polyester resin such as a mixture is more preferably used from the viewpoint of ease of pattern processing.

  However, it is not preferable that both the support plate and the diffusion layer are made of a transparent material because the total light transmittance described later increases and a diffusion effect cannot be obtained. Accordingly, it is preferable that either the support plate or the diffusion layer is not transparent.

  The role of the intermediate layer according to the present invention is to bond the support and the diffusion layer without entrapment of the air layer. By simply laminating the support plate and the diffusion layer directly without using the intermediate layer, the total light transmittance of the light diffusion plate is lowered, and the maximum luminance required for the liquid crystal panel cannot be obtained. The reason for this is not clear, but there is a part containing air at the interface between the support plate and the diffusion layer due to minute irregularities on the surface of the support plate and the diffusion layer, and the total light transmittance is reduced due to the influence of the air. It is estimated. Therefore, it is presumed that by providing an intermediate layer between the support plate and the diffusion layer, air can be eliminated by filling the minute irregularities with the intermediate layer. As the material for the intermediate layer, adhesives such as acrylic copolymers, epoxy copolymers, polyester copolymers, and fillers such as thermoplastic and thermosetting resins are preferably used. Even if it does not limit, what is necessary is just a material which is flexible to the extent that the above-mentioned minute unevenness can be filled.

  Moreover, as another structure of the light diffusing plate of this invention, what is comprised at least by the support plate and the line-shaped uneven | corrugated pattern was formed in one surface of a support plate is used preferably. With this configuration, since there is no interface between the support plate and the diffusion layer as described above, the problem of a decrease in total light transmittance due to the air portion is eliminated.

  Further, the light diffusion plate of the present invention needs to have a total light transmittance of 75 to 95%. By setting the total light transmittance, it is possible to reduce luminance unevenness through which the fluorescent tube image can be seen while maintaining the luminance. If the total light transmittance is greater than 95%, the unevenness of brightness appears remarkably because the diffusibility is insufficient. Further, when the total light transmittance is less than 75%, the diffusibility is sufficient and preferable in terms of uniformity, but the light is diffused too much and the brightness in the front direction is lowered. This total light transmittance is a value measured based on JIS K7361-1 (1997).

  Furthermore, the light diffusing plate of the present invention preferably has a haze of 95% or more. By setting this haze, it is possible to reduce luminance unevenness through which the fluorescent tube image can be seen while maintaining the luminance. When the haze is less than 95%, the diffusibility is sufficient and preferable from the viewpoint of uniformity, but the light in the front direction is lowered due to excessive diffusion of light rays. This haze is a value measured based on JIS K7136 (2000).

  Therefore, when the light diffusing plate of the present invention is incorporated in a direct type backlight device having a configuration to be described later, the linear light source image is diffused by the effect of anisotropic diffusion and the screen uniformity is improved. However, due to the anisotropic diffusion effect of the light diffusing plate, the total light transmittance is low and the light utilization efficiency is lowered, so that the front luminance required when installing the liquid crystal panel becomes insufficient. Therefore, in the direct type backlight device using the diffusing plate of the present invention, a condensing sheet is installed on the side opposite to the light source side of the light diffusing plate in order to condense the light diffused by the light diffusing plate again.

  Such a condensing sheet is characterized in that it has a concave or convex shape on the surface made of a light transmissive material and arranged one-dimensionally or two-dimensionally. When the concave or convex arrangement is a one-dimensional light collecting sheet, the concave or convex arrangement is two-dimensional by arranging the concave or convex arrangement direction so as to be parallel to the linear portion of the light source. In the case of the light condensing sheet, a direct-type backlight device having high uniformity and high brightness without moire by arranging so that one of the concave or convex arrangement directions is parallel to the linear portion of the light source Is obtained. A condensing sheet having a concave or convex lens shape arranged in a one-dimensional manner is preferably used from the viewpoint of ease of uneven processing.

  In addition, the liquid crystal backlight device of the present invention satisfies the required luminance on the liquid crystal panel only with the light diffusion plate of the present invention and the light collecting sheet, so there is no practical problem even if a luminance enhancing sheet is not provided. . Of course, a brightness enhancement sheet may be further provided, but it is preferable not to provide the brightness enhancement sheet from the viewpoint of cost reduction.

  The pattern formed on the A surface of the light diffusing plate of the present invention is a line-shaped concavo-convex pattern in which the longitudinal direction is substantially aligned in one direction. In FIG. 1, the surface shape of the A surface of the light diffusing plate of this invention is illustrated. FIG. 1A shows a pattern on the light diffusion plate surface, and FIG. 1B shows a light diffusion plate cross-sectional pattern in a cross section perpendicular to the longitudinal direction of the line-shaped uneven pattern.

  The light diffusion plate surface pattern of the A surface of the light diffusion plate of the present invention is characterized in that each unevenness extends in one direction (line shape) as illustrated in FIG. To do. Furthermore, it is the surface where the longitudinal direction of each line-shaped unevenness | corrugation was spread in substantially one direction. The light diffusing plate of the present invention has an anisotropic diffusivity that is strong in a direction perpendicular to the longitudinal direction and weakly diffused in a parallel direction by forming the longitudinal direction of the line-shaped unevenness substantially in one direction. It comes to express. In addition, it is preferable that the line-shaped unevenness is spread on the light diffusing plate without a gap, that is, without a flat portion. This is preferable because the diffusibility is improved.

  The diffuser plate cross-sectional pattern (the pattern observed in the cross section perpendicular to the longitudinal direction of the line-shaped uneven pattern) on the A surface of the light diffusing plate of the present invention is a curved pattern in which curves such as arcs are connected. Preferable examples include a smoothly connected pattern, a pattern in which semicircular (or its inverted shape) curves are connected, such as a lenticular lens, and a pattern in which these are combined.

  With respect to the regularity of the diffusion plate surface pattern on the A side and the diffusion plate cross-sectional pattern of the light diffusion plate of the present invention, the shape and size are less than the regular pattern in which the same shape and the same size are repeated. It is important to make a random pattern in which different shapes are arranged in a rule. The random pattern prevents light interference fringes and moire patterns, makes defects less noticeable, and improves the uniformity when mounted on the backlight unit. That is, as illustrated in FIG. 1A, the vertical and horizontal lengths of the line shapes extending in one direction in each pattern on the diffusion plate surface are preferably irregular. Further, as illustrated in FIG. 1B, even in the diffusion plate cross-sectional pattern, it is preferable that each shape is not the same, but irregular shapes are linked and the arrangement pitch is random.

  In the pattern on the diffusion plate surface of the A surface of the light diffusion plate of the present invention, it is preferable that the length in the longitudinal direction of the line pattern is longer than the length in the minor axis direction. When the length in the longitudinal direction is long, anisotropic diffusibility can be improved. The ratio of the length in the longitudinal direction to the length in the minor axis direction (length in the longitudinal direction / length in the minor axis direction) of the line pattern is preferably 10 or more.

  The light source of the direct type backlight device of the present invention may be a linear light source or a shape having a linear portion (U-shaped tube, W-shaped tube, etc.), or a device that can observe light and darkness in a straight line shape. Although not particularly limited, for example, a fluorescent tube is preferably used. It is also a preferable aspect that the arrangement pitch of the light sources is unequal within the backlight unit plane. For example, when it is desired to brighten the central portion of the backlight, this can be achieved by shortening the light source array pitch at the central portion of the screen. Moreover, since it becomes dark near the frame of the casing at the edge of the screen, it can be brightened by shortening the arrangement pitch here. As described above, for the purpose of adjusting the brightness in the screen, it is preferable that the effect is exhibited by making the arrangement pitch of the light sources unequal.

  Moreover, it is usually preferable to install a reflecting member such as a light reflecting film on the lower side of these light sources (in the direction opposite to the screen). By this reflecting member, the light beam directly emitted from the light source or the light beam returned from the upper member is reflected to the screen side, so that the light use efficiency can be increased and the luminance can be improved.

  Below, the measuring method and evaluation method of each Example and a comparative example are demonstrated. In each of the following measurements, each sample was evaluated with an average value of values obtained by performing the measurement three times. In addition, the surface in which the linear uneven | corrugated pattern of the light diffusing plate was formed is set to A surface, and the other surface is set to B surface.

(Measurement and evaluation method)
A. Output intensity distribution The output intensity distribution of the light diffusing plate was measured using a variable angle photometer GP-200 manufactured by Murakami Color Research Laboratory. The light diffusing plate was set on the sample stage so that light rays were incident from the B surface, and the intensity distribution of the emitted light emitted from the A surface was measured.
The intensity of the emitted light emitted from the A surface when a light beam is incident on the B surface of the diffusion plate at an incident angle of 0 ° (normal direction), in a plane perpendicular to the longitudinal direction of the line-shaped uneven pattern on the A surface, and Each measurement was performed in 0.1 ° increments in the range of the emission angle of −90 ° to 90 ° in a plane perpendicular to the diffusion plate surface and parallel to the longitudinal direction of the line-shaped uneven pattern. From the obtained emission intensity distribution, the emission angle on the plus side, which is 50% of the emission intensity at the emission angle of 0 °, was read in each direction. Further, the emission angle is an acute angle formed by the normal direction of the emission surface and the optical axis of the emitted light, and one direction is positive with respect to the normal direction and the other direction is negative. The measurement conditions are as follows.
・ Light source: halogen lamp 12V50W
・ Light source side filter: Light quantity adjustment filter with average transmittance of 1% ・ Flux aperture: Setting 3 (φ 11 mm)
・ Light receiving aperture: Setting 6 (φ approx. 13 mm)
・ Sample stage: Standard specimen stage with tilt for reflection and transmission (no tilt is used)
・ Measurement mode: Transmission.

B. Total light transmittance, haze Nippon Denshoku Industries Co., Ltd. product, turbidimeter (cloudiness meter) NDH-2000 was used, the total light transmittance was based on JIS K7361-1 (1997), and haze was JIS K7136. (2000). The sample was cut into an 8 cm square and set and measured so that light was incident from the B surface of the light diffusion plate.

C. Luminance, luminance unevenness (uniformity)
A 15-inch evaluation (330 mm × 250 mm: diagonal 400 mm) direct type backlight (housing, reflection film, fluorescent tube portion, light diffusion plate of the present invention) was turned on at 12 V, and after 1 hour, A prism sheet is installed on the upper side of the light diffusing plate, and brightness and brightness unevenness in the front direction on the brightness measurement line shown in FIG. 3 using a brightness unevenness analysis device Eye-Scale3 manufactured by I-System Co., Ltd. (Uniformity) was measured.
The light diffusing plate was installed such that the B surface was directed to the light source side, and the longitudinal direction of the line-shaped uneven pattern on the A surface was parallel to the direction parallel to the linear portion of the fluorescent tube.
The luminance was evaluated as the maximum value of the measurement position. The luminance unevenness is expressed by the following equation, where Cmax is the latest luminance maximum value from the central luminance measurement position 7 shown in FIG. 3, Cmin is the latest luminance minimum value, and Cave is the average luminance value on the luminance measurement line 8. Calculated.
・ Luminance unevenness (uniformity) (%) = 100 × (Cmax−Cmin) ÷ Cave
The backlight configuration for evaluation was as follows.
(Fluorescent tube)
Diameter: 3mm
Number: 8 Adjacent spacing (pitch): 28 mm (= 2p)
Distance between tube center and reflector (lower side): 5mm
Distance between tube center and light diffusion plate (upper side) 10mm (= h)
θ: 51.3 ° (tan θ = p / h = 1.25)
(Reflective film)
Lumirror (registered trademark) 188E60L manufactured by Toray Industries, Inc.

D. Moire evaluation Turn on the evaluation backlight in the dark room, and place the light diffuser plate and prism sheet (BEFII, manufactured by Sumitomo 3M Co.) in this order on the light source side. Confirmed. The prism sheet had a line-shaped uneven pattern on the surface opposite to the light source, and was installed so that the longitudinal direction of the line-shaped uneven pattern was parallel to the direction parallel to the linear portion of the fluorescent tube. The evaluation result is described as ◯: no moire and x: moire. All of the above measurements were performed at room temperature of 23 ° C. and humidity of 65%.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

(Example 1)
One side of a 188 μm transparent polyethylene terephthalate (PET) base material was coated with coating agent 1 to form a coating film with a thickness of 30 μm (hereinafter, the side coated with coating agent 1 is the a side, and the other side is b side).
(Coating 1)
Adeka optomer KRM-2199 (Asahi Denka Kogyo Co., Ltd.) 10 parts by mass Aron Oxetane OXT-221 (Toagosei Co., Ltd.) 1 part by mass Adeka optomer SP170 (Asahi Denka Kogyo Co., Ltd.) 0.25 Parts by mass.

A mold with a line-shaped uneven shape is pressed against the a-side of the base material coated with the coating 1 and irradiated with 1 J / m ² from the b-side of the base with an ultra-high pressure mercury lamp. After curing, the mold was released to obtain a diffusion sheet 1 as a diffusion layer. The line-shaped uneven pattern on the surface a of the obtained diffusion sheet has a pitch p of about 3 to 8 μm and a height h of about 0.6 to 6 μm, as shown in FIG. The on-surface pattern was a shape as illustrated in FIG. 1 (a). The ratio of the length L in the longitudinal direction and the length S in the short axis direction (longitudinal length L / short axis direction length S) of the surface pattern was 20 or more.

  Adhesive (acrylic resin) as an intermediate layer so that the b-side faces the milky white plate ("Kuralex" manufactured by Nippon Resin Kogyo Co., Ltd., DR-IIIC-E DR-90C). System adhesive "Cooponyl" N2233 manufactured by Nippon Synthetic Chemical Co., Ltd.) to produce a light diffusion plate.

Next, the light diffusion plate and the prism sheet (Sumitomo 3M, BEFII) were stacked in this order on the evaluation backlight from the light source side, and the luminance and luminance unevenness were measured. Moreover, the presence or absence of moire was confirmed visually. Further, the prism sheet had a line-shaped uneven pattern on the surface opposite to the light source, and was installed so that the longitudinal direction of the line-shaped uneven pattern was parallel to the direction parallel to the linear portion of the fluorescent tube. The evaluation results are shown in Table 1.
It has been found that this direct type backlight device equipped with the light diffusion plate of the present invention exhibits high brightness and excellent screen uniformity without moire.

(Comparative Example 1)
In Example 1, a light diffusion plate was produced in the same manner as in Example 1 except that a prism sheet (manufactured by Sumitomo 3M, RBEF) was used instead of the diffusion sheet 1. The evaluation results are shown in Table 1.
This direct type backlight device equipped with the light diffusing plate has a low total light transmittance and an emission angle at which the intensity is 50% is larger than 25 °. However, light interference occurs due to the influence of moire. Compared with, the maximum brightness is increased. However, it was found that the screen uniformity deteriorated compared to Example 1 due to the influence of moire.

(Comparative Example 2)
In Example 1, a light diffusion plate was prepared in the same manner as in Example 1 except that a diffusion sheet 2 (manufactured by Kimoto, GM2) was used instead of the diffusion sheet 1. The evaluation results are shown in Table 1.
In this direct type backlight device equipped with the light diffusing plate, moire cannot be confirmed, but the total light transmittance is 75% or less, and the emission angle at which the intensity is 50% is larger than 19 °. It was found that the brightness was reduced compared to.

(Comparative Example 3)
In Example 1, luminance and luminance unevenness were measured in the same manner as in Example 1 except that the diffusion sheet 1 and the milky white plate were stacked without being bonded with an adhesive. The evaluation results are shown in Table 1.
This direct type backlight device equipped with the above-described configuration has no screen moire and excellent screen uniformity, but the total light transmittance is 75% or less, so that the luminance is reduced as compared with Example 1. I found out that

(Comparative Example 4)
In Example 1, luminance and luminance unevenness were measured in the same manner as in Example 1 except that a milky white plate was disposed instead of the light diffusing plate. The evaluation results are shown in Table 1.
In this direct type backlight device equipped with the above configuration, moire is not confirmed, but the emission angle at which the intensity is 50% is smaller than 20 ° and the total light transmittance is 75% or less. As a result, the screen uniformity deteriorated and the luminance decreased.

  According to the present invention, it is possible to provide a direct-type backlight device having an anisotropic diffusion effect of light and having high luminance characteristics by disposing a light collecting sheet on such a light diffusing plate. By incorporating the device into the apparatus, both high screen uniformity and high luminance characteristics can be achieved without moire even when the luminance enhancing sheet is not disposed.

It is a figure which shows typically the surface shape of the light diffusing plate of this invention. It is a figure which shows typically the preferable base-material structure of the light diffusing plate of this invention. It is a figure which shows typically the backlight for evaluation used for the brightness | luminance measurement of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusing plate of this invention 2 Diffusion layer 3 Intermediate | middle layer 4 Support plate 5 Backlight for evaluation 6 Fluorescent tube 7 Center luminance measurement position (black circle part)
8 Luminance measurement line (bold dotted line)
h Height of line-shaped uneven pattern p Pitch of line-shaped uneven pattern L Length of line-shaped uneven pattern S Length of short-axis direction of line-shaped uneven pattern

Claims (4)

It has a line-shaped uneven pattern on one surface, has a total light transmittance of 75 to 95%, and emits light from one surface when the light is incident at an incident angle of 0 ° from the other surface. A light diffusion plate whose distribution satisfies the following conditions (1) and (2).
(1) Regarding the emission intensity distribution in a plane perpendicular to the longitudinal direction of the line-shaped uneven pattern, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 20 to 25 °.
(2) With respect to the emission intensity distribution in a plane parallel to the longitudinal direction of the line-shaped uneven pattern, the emission angle that is 50% of the emission intensity at the emission angle of 0 ° is in the range of 0.5 to 19 °. is there.   2. The light diffusing plate according to claim 1, wherein at least a support plate, an intermediate layer, and a diffusion layer are laminated in this order, and the line-shaped uneven pattern is formed on the surface of the diffusion layer opposite to the intermediate layer side. .   The light diffusing plate according to claim 1, wherein the light diffusing plate is constituted by at least a supporting plate, and the line-shaped uneven pattern is formed on one surface of the supporting plate.   A plurality of linear light sources, the light diffusing plate according to any one of claims 1 to 3 and a light collecting sheet are arranged in this order, and the surface of the light diffusing plate that does not have the line-shaped uneven pattern is linear. A direct-type backlight device that is directed toward the light source and is arranged so that the longitudinal direction of the line-shaped uneven pattern and the linear portion of the linear light source are parallel to each other.

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