JPWO2009078055A1 - Direct type backlight and liquid crystal television incorporating the backlight - Google Patents

Abstract

A light diffusing lens sheet having a lens surface and a concavo-convex array structure surface, wherein the lens surface has a substantially triangular prism portion made of a transparent polymer material so that the major axes of the triangular prisms are substantially parallel to each other. The concave / convex array structure in which the height difference A is 2 μm to 30 μm, the period B is 50 μm to 1000 μm, and the B / A is in the range of 10 to 50 is formed on the surface of the concave / convex array structure. It is characterized by being provided with a swing angle of 5 to 30 degrees with respect to the major axis. The light diffusing lens sheet of the present invention has high light utilization efficiency, makes it easy to see the screen from the front, makes it difficult to see the location of the light source, and suppresses the generation of interference fringes, and emits uniform light from the entire emission surface. In addition, since the number of backlight components can be reduced, the manufacturing cost is reduced and the productivity is improved.

Description

  The present invention relates to a light diffusing lens sheet for a liquid crystal display device. More specifically, the present invention relates to light with high light utilization efficiency and capable of obtaining uniform and high-quality light from a direct type backlight using a linear light source. The present invention relates to a diffusive lens sheet, a direct type backlight using the sheet, and a liquid crystal television incorporating the backlight.

The backlight of the liquid crystal display device includes an edge light type in which a light source is arranged on an end face of a light guide plate, and a direct type backlight in which a plurality of light sources are arranged and a light diffusion plate is arranged thereon. In recent years, with the increase in the size of display devices, there has been a demand for a planar direct-type backlight capable of obtaining uniform light with high light use efficiency.
As a light source for a direct type backlight, a linear cathode ray tube is mainly used. However, when a linear light source is used in parallel as a backlight, a difference in brightness is likely to occur depending on the location. A difference in brightness is likely to occur between the top and the intermediate portion between the light sources. Therefore, in order to make the light from these light sources uniform, the light source is usually a planar light source through a light diffusing plate which is a plate-like translucent plate having a diffusing function. However, if light is diffused and homogenized to such an extent that the location of the light source cannot be seen with this light diffusing plate, the light utilization efficiency will be poor, that is, the amount of light transmission will be reduced and the screen will be darkened. If you try to improve, the light source behind you will see through, making it difficult to see the screen.

  Therefore, in order to improve the light utilization efficiency and make the light source arrangement location invisible, it is also possible to use a light diffusion sheet having a diffusion surface formed on the surface on a translucent light diffusion plate. Has been done. However, in order to ensure light transmittance and prevent the location of the light source from being visible, the translucency of the translucent light diffusing plate is adjusted, and two or three diffusion sheets are installed on it. Therefore, there is a problem that the number of parts increases and the manufacturing cost increases.

  On the other hand, in a direct type backlight, a prism sheet having a prism structure on the surface is placed on the light diffusing plate, thereby condensing the emitted light in the normal direction of the light diffusing plate. Yes. However, this is not sufficient for the effect of making it impossible to visually recognize the location of the light source. In addition, glare is likely to occur particularly when light is emitted in a specific direction. This glare is generally likely to occur when lenses are installed to collect emitted light. Therefore, a diffusion sheet having a diffusion surface on the surface must be installed on the top or bottom of the prism sheet, and more often on both the top and bottom.

  In order to enhance the diffusibility of the emitted light by the prism sheet, the back surface is coated using light diffusing particles (see Patent Document 1), the layer provided with the prism-shaped portion and the layer kneaded with the light diffusing agent, A multilayer film (see Patent Document 2), a method of incorporating light diffusing particles in the prism mechanism (see Patent Document 3), and the like have been proposed. However, both of these include the problem that the effect of making the direct light source invisible and the light diffusion and light collecting functions of the prism cannot be compatible. That is, if there are few light diffusion particles etc., a light source will be visible from a screen, and if there are many, a condensing function will fall.

On the other hand, there is an attempt to obtain light diffusibility by a concave / convex mechanism of a transparent resin in an illumination device of a direct type light source, a method of providing a prism plate between a light source and an object to be illuminated (see Patent Document 4), There is also a proposal of a prism array (see Patent Document 6) having a specific apex angle related to the positional relationship with a linear light source, such as a light diffusing plate (see Patent Document 5) provided with a number of strips having inclined surfaces. is there. However, even with this method, the effect of eliminating the difference in brightness and darkness is not sufficient, and interference fringes may be generated, so that uniform light cannot be obtained after all.
Japanese Patent Laid-Open No. 10-300908 JP-A-8-313708 JP-A-10-68804 JP-A-5-333333 JP-A-8-297202 JP 2006-195276 A

  In view of such circumstances, the present invention solves the above-described conventional problems, has high light use efficiency, collects light in the normal direction of the display surface, suppresses the occurrence of glare, makes the screen easy to see from the front, and linear A uniform surface light source can be obtained by substantially eliminating the light and dark difference resulting from the use of the light source, making it difficult to see the location of the light source and suppressing the occurrence of interference fringes between optical members, and the number of backlight components An object of the present invention is to provide a light diffusing lens sheet that can be reduced, a direct-type backlight using the sheet, and a liquid crystal television incorporating the backlight.

The present invention has been made to achieve the above object, and the invention according to claim 1 of the present invention is characterized in that a prism portion of a substantially triangular prism made of a transparent polymer material on one side has a length of the triangular prism. A large number are arranged at a constant period so that the axes are almost parallel to each other,
On the other surface, an uneven row structure in which the height difference A is 2 μm to 30 μm, the period B is 50 μm to 1000 μm, and the B / A is in the range of 10 to 50 is 5 degrees to 30 degrees with respect to the major axis of the prism portion. The light diffusing lens sheet is characterized by being provided with a swing angle of

  The invention according to claim 2 of the present invention includes the light diffusing lens sheet according to claim 1, wherein the arrangement period of the prism portions is 10 μm to 500 μm.

  The invention according to claim 3 of the present invention comprises the light diffusing lens sheet according to claim 1 or 2, wherein the thickness is 50 μm to 500 μm.

  The invention according to claim 4 of the present invention is used for a direct-type backlight comprising a plurality of linear light sources arranged in parallel, and the light diffusibility according to any one of claims 1 to 3. The content is a lens sheet.

  The invention according to claim 5 of the present invention is arranged such that the direction of the major axis of the prism portion of the light diffusing lens sheet according to any one of claims 1 to 4 substantially coincides with the direction of the linear light source. The content is a direct type backlight characterized by the above.

  The invention according to claim 6 of the present invention is characterized in that the direct type backlight according to claim 5 is incorporated so that the major axis direction of the prism portion coincides with the longitudinal direction of the display surface of the liquid crystal television. Includes LCD TV.

The light diffusing lens sheet of the present invention has a lens surface on which triangular prisms are arranged on one surface, and has a specific height difference A and period B on both surfaces, and a ratio B / A between the two. Since it is a light diffusing lens sheet having a diffusing surface composed of an uneven row structure, the lens surface is placed on the light diffusing plate of a direct type backlight using a linear light source so that the lens surface is on the light exit side. Providing a backlight for a liquid crystal display device that provides the highest brightness in the normal direction of the backlight and improves the light utilization efficiency, eliminates the difference in brightness due to the location of the light source, and does not cause glare. Can do.
Furthermore, since the concave and convex array structure is provided with a specific swing angle with respect to the major axis of the prism portion, a surface light source that emits uniform light without generating interference fringes can be obtained.
This light diffusing lens sheet can provide a suitable surface light source even when used in a direct type backlight composed of a plurality of linear light sources arranged in parallel, and is particularly used for a liquid crystal television. It is suitable as a light diffusing lens sheet for a direct type backlight.
In addition, if the major axis direction of the prism portion is arranged so as to substantially coincide with the direction of the linear light source, an appropriate amount of light is emitted in the front and left and right directions of the screen while limiting the light emitted in the vertical direction. The backlight provided with the light diffusing lens sheet of the present invention is more suitable for a liquid crystal television.

It is a schematic explanatory drawing which shows the relationship between the prism surface of the light diffusable lens sheet of this invention, and an uneven | corrugated row | line | column structure surface. It is AA sectional view taken on the prism side of the light diffusing lens sheet of the present invention. It is BB sectional drawing of the uneven | corrugated row | line | column structure surface side of the light diffusable lens sheet | seat of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusing lens sheet 2 Lens surface 3 Prism part 4 Diffusion surface 4a Concave and convex row structure 5 Concave strip row 6 Convex strip row L1 A line parallel to the major axis direction of the prism portion L2 Parallel to the major axis direction of the convex and concave row Line C Prism unit arrangement period A Height difference of uneven rows B Period of uneven rows b1 Convex row width b2 Convex row width α Swing angle

As described above, installing a prism sheet on the light diffusing plate of the direct type backlight has the effect of condensing the emitted light in the normal direction of the light diffusing plate, but there is a difference in brightness between the location of the light source and its gap. Therefore, uniform light cannot be obtained.
Therefore, when various light diffusion methods were examined on the opposite surface of the lens surface of the prism structure, a specific uneven row structure was provided on the opposite side of the lens surface, and the major axis direction of the row was defined as the length of the linear light source. It has been found that, when substantially matched with the axial direction, it is very effective in eliminating the above-described difference in brightness, but interference fringes are generated at the same time, and a uniform surface light source cannot be obtained after all.
As a result of further diligent research, it was found that the interference fringes were caused by the fact that the concave / convex array direction and the major axis direction of the prism portion were matched. By providing a swing angle of 5 to 30 degrees between the long axis directions of the row, the generation of interference fringes can be prevented, the brightness in the normal direction is sufficient, and the difference in brightness of the light source is eliminated. The present invention has been found that a uniform surface light source can be obtained.

  The light diffusing lens sheet of the present invention is provided with a prism portion (hereinafter referred to as a lens surface) on one surface and an uneven row structure (hereinafter referred to as a diffusion surface) on the other surface. Here, as shown in FIG. 1, the major axis direction L2 of the concavo-convex array structure 4a of the diffusion surface 4 is provided with a swing angle α with respect to the major axis direction L1 of the prism portion 3 of the lens surface 2. In FIG. 1, the prism portion 3 is indicated by a solid line, and the uneven row structure 4 a is indicated by a broken line.

As shown in FIGS. 1 and 2, prism portions 3 each having a prism-shaped unit substantially formed of a triangular prism are arranged on the lens surface 2 at a constant period C so as to be substantially parallel to each other.
The prism portion 3 can be selected from a shape having a triangular prism cross section shape that easily exhibits a light condensing capability and a vertex angle of 60 degrees to 120 degrees. Preferably, it is in the range of 70 degrees to 110 degrees. The shape of the triangle is not particularly limited and may be either an equal side or an unequal side, but isosceles triangle is preferable in terms of improving the light collecting performance in the normal direction of the diffusion sheet, and therefore adjacent to the bottom side relative to the apex angle. Then, it is preferable that adjacent isosceles triangles are sequentially arranged and arranged such that apex angle columns are long axes and are substantially parallel to each other. In this case, the top and bottom angles of the triangular prism may have curvature as long as the light collecting ability is not significantly reduced.
As for the arrangement period C of the prism portion 3, a range of 10 μm to 500 μm is preferable because it increases the homogeneity of the emitted light, and more preferably a range of 30 μm to 200 μm.

As shown in FIGS. 1 and 3, the diffusing surface 4 is provided with a concavo-convex array structure 4 a for eliminating the light / dark difference due to the location of the linear light source and for eliminating the glare caused by the emission of light in a specific direction. The height difference A of the concave / convex array structure 4a is 2 μm to 30 μm. If the height difference A is less than 2 μm, there will be no effect of eliminating the difference in brightness and glare, and if it is greater than 30 μm, it will require not only high processing technology to provide an uneven row structure on the back surface of the prism sheet, but also increase the cost. , Productivity decreases.
A period B of the uneven row structure is 50 μm to 1000 μm, preferably 50 μm to 500 μm. If the period B is smaller than 50 μm, the light condensing ability of the prism is lowered, and if it is larger than 1000 μm, the number of the concavo-convex rows is reduced, so that interference with the prism is reduced. As a result, the difference in brightness is increased and the appearance is deteriorated.
The ratio B / A of the period B to the height difference A is adjusted to a range of 10-50. If this ratio is less than 10, the number of the concave and convex lines increases, so that the front luminance is lowered. On the other hand, if it exceeds 50, the number of the concave and convex lines decreases, and as a result, the interference with the prism is reduced and the difference in brightness is large. And the appearance is poor.

The cross-sectional shapes of the concave row 5 and the convex row 6 in the concave / convex row structure 4a are not particularly limited, and examples thereof include a rectangular quadrangle and a trapezoid having a slope.
Moreover, the ratio (b1 / b2) of the width of the row of ridges 5 and the row of ridges 6 is not particularly limited, and can be adopted even in a structure in which thin rows of ridges and rows of ridges are provided for each specific period described above. However, when the ratio is preferably 1: 4 to 4: 1, more preferably 1: 2 to 2: 1, and most preferably about 1: 1, the effect of eliminating the light / dark difference is remarkable and the effect of suppressing the glare is also remarkable.
The concave and convex rows constituting the concave / convex row structure 4a do not have to be linear, but may be curved or wavy. In each portion of the concave / convex row structure, the prism portion It is necessary that the deflection angle is 5 to 30 degrees with respect to the major axis of 3.

  As shown in FIG. 1, the uneven row structure 4 a is provided with a swing angle α of 5 degrees to 30 degrees with respect to the major axis of the prism portion 3. In other words, the line parallel to the direction of the concavo-convex row structure 4a and the line parallel to the major axis direction of the prism portion 3 intersect at an angle of 5 degrees to 30 degrees. Thereby, the generation of interference fringes is eliminated, the prism condensing function is increased, and the brightness in the normal direction is also increased. Here, when the swing angle is smaller than 5 degrees, interference fringes are likely to occur. On the other hand, when the swing angle is larger than 30 degrees, the effect of eliminating the light / dark difference cannot be obtained, and glare occurs.

The material of the light diffusing lens sheet is not particularly limited as long as it is a transparent polymer material, and can be selected from ordinary optical transparent resins. Specific examples thereof include acrylic resins, polycarbonate, polystyrene, polyvinyl chloride, polypropylene, polymethylpentene and other polyolefins, cyclic polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and other polyester resins, polyamide resins, poly Examples include arylate and polyimide. Further, in addition to the thermoplastic resin, a curable resin that is cured by ionizing radiation such as an acrylic resin can also be used.
There are a method using a thermoplastic resin and a method using a curable resin as a method of forming a prism portion on the lens surface of a light diffusing lens sheet and forming an uneven row structure on the diffusion surface. In the case of a thermoplastic resin, a normal forming method is possible, and a method of injection molding into a desired mold, or a method of compression-molding a sheet-like material with a mold is possible.
In extrusion molding, the material extruded into a sheet is embossed under heating, pressed against a mold roll during melt extrusion, or released in advance as described in Japanese Patent No. 2925069. The mold can be formed by transferring the mold while sandwiching the mold sheet. And when forming simultaneously, one side can also be shape | molded by a mold release sheet, and the other side can also be shape | molded by a metal mold | die roll.
Further, in the case of curable resin, in the case of using ionizing radiation, it is usual to use an ultraviolet curable resin. In general, after applying a curable resin on a transparent support, it is molded by irradiating ultraviolet rays in a mold.
The prism portion of the lens surface and the concave / convex array structure of the diffusing surface may be formed separately and bonded together, or may be integrally formed at the same time.

Hereinafter, a method for using the light diffusing lens sheet of the present invention will be described.
Usually, a direct type backlight has a linear light source composed of a plurality of cold cathode ray tubes arranged in parallel, a light diffusing plate having a thickness of 2 mm to 4 mm is installed on the display surface side, and a light reflecting plate is installed on the opposite side. The light diffusing lens sheet of the present invention is installed on the light diffusing plate with the lens surface facing the light exit side.
The installation direction is not particularly limited as long as the major axis direction of the prism portion is substantially lateral, and for example, the major axis direction of the linear light source and the major axis direction of the concavo-convex rows of the diffusion surface are aligned with each other. Alternatively, the major axis direction of the prism portion may be set so as to coincide with the major axis of the linear light source, and further, it may be installed at an intermediate position. It is preferable that the light beam is arranged so as to be substantially coincident with the direction of the shaped light beam because the emitted light is easily condensed in the normal direction of the light diffusing lens sheet.

  In the case of a liquid crystal television, the display surface is generally horizontally long. It is important that viewing is easy from the left and right diagonal directions of the display surface, and viewing from the top and bottom directions is not so important. Therefore, in order to ensure the brightness in the front direction, the left-right direction, and the left-right oblique direction of the display surface, it is preferable to adjust the emission by concentrating light in the vertical direction that is not important in the front direction.

Here, the lens sheet in which the prism portions are arranged so that the major axes are substantially parallel to each other has different emission luminances in the major axis direction and the vertical direction perpendicular thereto, and the light diffused in the vertical direction by the prism sheet. Is known to be focused in the front direction.
Therefore, if the linear light source of the backlight of the liquid crystal television is installed in the longitudinal direction of the liquid crystal screen, the major axis direction of the prism portion and the major axis direction of the concavo-convex array structure are also directed toward the longitudinal direction of the liquid crystal screen. It is a good idea to install a diffusive lens sheet. Thereby, the slightly unnecessary upward and downward emission is limited, and the brightness in the front direction and the brightness in the oblique direction on the left and right of the display surface can be secured, and a homogeneous and mild light source can be obtained. Furthermore, if necessary, a normal light diffusion sheet may be further installed. When this light diffusing sheet is used in combination with a prism sheet, the lower diffusing sheet and the upper diffusing sheet are commercially available with the prism sheet as the center.

  The thickness of the light diffusing lens sheet of the present invention is arbitrary, but from the viewpoint of handling at the time of assembling the liquid crystal television, it is usually preferably from 50 μm to 500 μm, and from the viewpoint of continuous production, preferably from 200 μm to 400 μm.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1
(Manufacture of light diffusing lens sheet)
Polycarbonate transparent resin “Panlite L-1225Y” (manufactured by Teijin Kasei Co., Ltd.) is extruded from a die at a melt extrusion resin temperature of 295 ° C. into a sheet shape, and the extruded sheet-shaped molten resin is pre-shaped with a prism shape. Described in Japanese Patent No. 2925069, which is sandwiched between the formed release sheet and a cooling roll provided with a concavo-convex array structure on the surface thereof with a swing angle of 20 degrees with respect to the major axis direction of the prism portion. The lens sheet was manufactured by the method of.
The releasable sheet has a triangular prism shape having an isosceles triangle in which the cross-sectional triangle is an apex angle of 100 degrees and the base angle is 40 degrees so that the long axes are adjacent to each other with a period of 50 μm and the major axes are parallel to each other. An array was used. Moreover, the uneven | corrugated row | line | column structure of the said cooling roll arrange | positions the uneven | corrugated row | line | column with a planar view linear form with the period of 60 micrometers, the unevenness | corrugation height difference A is 2 micrometers, and the period B is 60 micrometers (concave line and convex line). Each of which has a width of 30 μm), and the cross-sectional shape of the ridges is a trapezoidal shape having a lower base of 30 μm and an upper base of 24 μm. The ratio B / A of the period B to the height difference A is 30.
The thickness of the obtained sheet was 240 μm. The optical properties of the obtained light diffusing lens sheet were measured and determined by the following method. The measurement / judgment results are shown in Table 1.

(Measurement / judgment method of optical characteristics)
The brightness difference of the light diffusing lens sheet can be measured by measuring the luminance of each part of the backlight by reducing the light receiving surface of the luminance meter and calculating the difference. However, the quality of the surface light source must be judged by the naked eye.
Further, the quality of the backlight is characterized by the presence or absence of light rays that are strongly emitted in a specific direction, which can be determined by the naked eye as glare.
Therefore, the optical characteristics were evaluated by measurement with a luminance meter and determination with the naked eye.

Backlight Configuration A backlight for a 32-inch television having a length of 400 mm and a width of 705 mm, in which 16 linear cathode ray tubes are arranged at equal intervals in the horizontal direction, is turned on. A light reflector is placed under the linear light source in the backlight cavity, and a 2 mm thick light diffuser “Opt Max” (manufactured by Sumitomo Bakelite Co., Ltd.) is installed on the light diffuser. A diffusive lens sheet was installed. The light diffusing lens sheet was installed such that the lens surface was the exit surface side and the major axis direction of the prism portion was matched with the major axis direction of the cathode ray tube.

Luminance measurement Installed light diffusing lens sheet at a distance of 500 mm above the surface on which the light diffusing lens sheet was installed, using a luminance meter Minolta CA-1500 (manufactured by Konica Minolta Co., Ltd.) as a measurement area of 4.8 cm ^2. The brightness of the center point of was measured.

Judgment of appearance quality of backlight emission:
Glare:
The glare that enters the viewer's eyes directly from each direction due to reflection, refraction, etc. from the light source is visually determined according to the following criteria.
○: Glittering is not visible and the light is exiting gently.
○ △: Slight glare is seen only in one specific direction.
Δ: Slight glare is seen, but it disappears after passing through the liquid crystal panel.
X: Glitter is visible and may be visible after passing through the liquid crystal panel.

Difference in brightness between the line light source and the middle part:
The light / dark difference between the line light source and the intermediate portion thereof is visually determined according to the following criteria.
○: No difference in brightness is recognized.
○ △: Close to ○, with very slight difference in brightness.
Δ: A slight difference in brightness is recognized.
Δ ×: Close to ×, and the difference in brightness is clearly recognized.
X: A contrast difference is clearly recognized.

Brightness / darkness difference between the linear light source and its middle part:
A luminance meter Topcon BM-5A (manufactured by Topcon Co., Ltd.) was narrowed down to a measurement area of 0.2 cm ² by the same method as the luminance measurement described above, approached up to 300 mm above the backlight, and immediately above the two cold cathode tubes. The luminance with the intermediate point was measured, and the luminance difference was calculated to obtain an average value.

Example 2
Implemented except that the period B of the concave / convex row structure of the cooling roll was changed to a trapezoidal shape of 100 μm (the width of the concave row and the convex row is 50 μm, and the cross-sectional shape of the convex row is the bottom 50 μm and the upper bottom 30 μm). A light diffusing lens sheet was prepared in the same manner as in Example 1, and its optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.

Example 3
A light diffusing lens sheet was prepared in the same manner as in Example 2 except that the height difference of the concavo-convex row structure of the cooling roll was changed to 10 μm, and its optical characteristics were measured and determined. The measurement / judgment results are shown in Table 1.

Example 4
The period B of the concave and convex row structure of the cooling roll is changed to a trapezoidal shape of 500 μm (the width of the concave row is 450 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is 50 μm at the bottom and 30 μm at the top). A light diffusing lens sheet was produced in the same manner as in Example 3 except that the optical characteristics were measured and determined. The measurement / judgment results are shown in Table 1.

Example 5
The height difference A of the concave / convex row structure of the cooling roll is 15 μm, and the period B is 250 μm (the width of the concave row is 200 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is 50 μm at the bottom, and 30 μm at the top) A light diffusing lens sheet was produced in the same manner as in Example 1 except that the trapezoidal shape was changed, and its optical characteristics were measured and determined. The measurement / judgment results are shown in Table 1.

Example 6
The height difference A of the concavo-convex row structure of the cooling roll is 30 μm, and the period B is 900 μm (the width of the concave row is 850 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is the bottom 50 μm, the top bottom 30 μm) A light diffusing lens sheet was produced in the same manner as in Example 1 except that the trapezoidal shape was changed, and its optical characteristics were measured and determined. The measurement / judgment results are shown in Table 1.

Examples 7-9
A light diffusing lens sheet was produced in the same manner as in Example 4 except that the swing angle of the concave and convex row structure of the cooling roll was changed to 5 degrees, 10 degrees, and 30 degrees, and its optical characteristics were measured and determined. The measurement / judgment results are shown in Table 1.

Comparative Example 1
Optical characteristics were measured and determined in the same manner as in Example 1 except that two commercially available light diffusion sheets BS300 (manufactured by Eiwa Co., Ltd.) were installed on the backlight light diffusion plate instead of the light diffusing lens sheet. . The measurement / judgment results are shown in Table 1.

Comparative Example 2
Optical properties were measured in the same manner as in Example 1 except that three commercially available light diffusion sheets BS702 (manufactured by Keiwa Co., Ltd.) were stacked in place of the light diffusing lens sheet and placed on the light diffusion plate of the backlight. Judged. The measurement / judgment results are shown in Table 1.

Comparative Example 3
A sheet was produced in the same manner as in Example 4 except that the swing angle of the concavo-convex row structure of the cooling roll was changed to 0 degree, and the optical characteristics of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.

Comparative Example 4
Implemented except that the period B of the concave / convex row structure of the cooling roll was changed to a trapezoidal shape of 30 μm (the width of the concave row and the convex row is 15 μm, and the cross-sectional shape of the convex row is the bottom 15 μm and the top 10 μm). A sheet was produced in the same manner as in Example 3, and the optical properties of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.

Comparative Example 5
The height difference A of the concave / convex row structure of the cooling roll is 4 μm, and the period B is 300 μm (the width of the concave row is 250 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is the bottom 50 μm, the top bottom 30 μm) A sheet was produced in the same manner as in Example 1 except that the trapezoidal shape was changed, and the optical characteristics of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.

Comparative Example 6
An optical sheet was produced in the same manner as in Example 4 except that the swing angle of the concavo-convex row structure of the cooling roll was changed to 45 degrees, and the optical characteristics of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.

Comparative Example 7
The optical characteristics were measured and determined in the same manner as in Example 1 except that the light diffusing lens sheet was not used. The measurement / judgment results are shown in Table 1.

As is clear from the examples and comparative examples in Table 1 above, the brightness difference between light and dark is large only with a normal light diffusion plate with a thickness of 2 mm, and the light and dark difference between the linear light source and its gap is clearly recognized by the naked eye. The luminance is also low (see Comparative Example 7). When two or more commercially available diffusion sheets are stacked on this, a difference in brightness is hardly recognized with the naked eye, but the number of parts increases, manufacturing costs increase, and productivity decreases (see Comparative Examples 1 and 2). .
On the other hand, by providing an uneven row structure on the opposite side of the lens surface, the light / dark difference of the light source is almost eliminated.
Further, the value of the period B (B / A) with respect to the height difference A is important. If this value is less than 10, the luminance decreases (see Comparative Example 4), whereas if it exceeds 50, the glare increases (Comparative Example). 5). Further, when the direction of the projections and depressions coincides with the direction of the prism portion (the swing angle is 0 degree), interference fringes appear (see Comparative Example 3). On the other hand, when the swing angle is too large, the glare becomes remarkable (Comparative Example 6). See).
As a result of the above, by providing an appropriate uneven row structure on the opposite surface of the lens surface at an appropriate swing angle, even a single light diffusing lens sheet can sufficiently improve the quality of the backlight, resulting in a decrease in luminance. (See Examples 1 to 9).

  As described above, the light diffusing lens sheet of the present invention has a specific elevation difference and period unevenness with a specific swing angle with respect to the major axis direction of the prism portion on the opposite side of the lens surface having the prism portion. By providing a row structure, it is possible to greatly improve the quality by eliminating the light and darkness and glare between the light source and the light source of the direct type backlight with a linear light source, and to increase the front brightness. Since the number of parts of the backlight can be reduced, it is useful as a light diffusion sheet for a liquid crystal display device.

[Document Name] Description
[Title of the Invention] straightLower backlight, and liquid crystal television incorporating the backlight
【Technical field】
  [0001]
  The present invention relates to a liquid crystal display device.Direct type backlightMore specifically, the use efficiency of light is high and a linear light source is used.TheUniform and high-quality light can be obtainedDirect type backlight,And a liquid crystal television incorporating the backlight.
[Background]
  [0002]
  The backlight of the liquid crystal display device includes an edge light type in which a light source is arranged on an end face of a light guide plate, and a direct type backlight in which a plurality of light sources are arranged and a light diffusion plate is arranged thereon. In recent years, with the increase in the size of display devices, there has been a demand for a planar direct-type backlight capable of obtaining uniform light with high light use efficiency.
  As a light source for a direct type backlight, a linear cathode ray tube is mainly used. However, when a linear light source is used in parallel as a backlight, a difference in brightness is likely to occur depending on the location. A difference in brightness is likely to occur between the top and the intermediate portion between the light sources. Therefore, in order to make the light from these light sources uniform, the light source is usually a planar light source through a light diffusing plate which is a plate-like translucent plate having a diffusing function. However, if light is diffused and homogenized to such an extent that the location of the light source cannot be seen with this light diffusing plate, the light utilization efficiency will be poor, that is, the amount of light transmission will be reduced and the screen will be darkened. If you try to improve, the light source behind you will see through, making it difficult to see the screen.
  [0003]
  Therefore, in order to improve the light utilization efficiency and make the light source arrangement location invisible, it is also possible to use a light diffusion sheet having a diffusion surface formed on the surface on a translucent light diffusion plate. Has been done. However, in order to ensure light transmittance and prevent the location of the light source from being visible, the translucency of the translucent light diffusing plate is adjusted, and two or three diffusion sheets are installed on it. Therefore, there is a problem that the number of parts increases and the manufacturing cost increases.
  [0004]
  On the other hand, in a direct type backlight, a prism sheet having a prism structure on the surface is placed on the light diffusing plate, thereby condensing the emitted light in the normal direction of the light diffusing plate. Yes. However, this is not sufficient for the effect of making it impossible to visually recognize the location of the light source. In addition, glare is likely to occur particularly when light is emitted in a specific direction. This glare is generally likely to occur when lenses are installed to collect emitted light. Therefore, a diffusion sheet having a diffusion surface on the surface must be installed on the top or bottom of the prism sheet, and more often on both the top and bottom.
  [0005]
  In order to enhance the diffusibility of the emitted light by the prism sheet, the back surface is coated using light diffusing particles (see Patent Document 1), the layer provided with the prism-shaped portion and the layer kneaded with the light diffusing agent, A multilayer film (see Patent Document 2), a method of incorporating light diffusing particles in the prism mechanism (see Patent Document 3), and the like have been proposed. However, both of these include the problem that the effect of making the direct light source invisible and the light diffusion and light collecting functions of the prism cannot be compatible. That is, if there are few light diffusion particles etc., a light source will be visible from a screen, and if there are many, a condensing function will fall.
  [0006]
  On the other hand, there is an attempt to obtain light diffusibility by a concave / convex mechanism of a transparent resin in an illumination device of a direct type light source, a method of providing a prism plate between a light source and an object to be illuminated (see Patent Document 4), There is also a proposal of a prism array (see Patent Document 6) having a specific apex angle related to the positional relationship with a linear light source, such as a light diffusing plate (see Patent Document 5) provided with a number of strips having inclined surfaces. is there. However, even with this method, the effect of eliminating the difference in brightness and darkness is not sufficient, and interference fringes may be generated, so that uniform light cannot be obtained after all.
  [Patent Document 1] Japanese Patent Laid-Open No. 10-300908
  [Patent Document 2] JP-A-8-313708
  [Patent Document 3] Japanese Patent Laid-Open No. 10-68804
  [Patent Document 4] Japanese Patent Laid-Open No. 5-333333
  [Patent Document 5] JP-A-8-297202
  [Patent Document 6] Japanese Patent Laid-Open No. 2006-195276
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
  [0007]
  In view of such circumstances, the present invention solves the above-described conventional problems, has high light use efficiency, collects light in the normal direction of the display surface, suppresses the occurrence of glare, makes the screen easy to see from the front, and linear A uniform surface light source can be obtained by substantially eliminating the light and dark difference resulting from the use of the light source, making it difficult to see the location of the light source, and suppressing the occurrence of interference fringes between optical members.RuIt is an object of the present invention to provide a direct type backlight and a liquid crystal television incorporating the backlight.
[Means for Solving the Problems]
  [0008]
  The present invention was made to achieve the above object, and the invention according to claim 1 of the present invention isA direct type backlight composed of a plurality of linear light sources arranged in parallel,
  A plurality of substantially triangular prism portions made of a transparent polymer material on one side are arranged in a constant cycle so that the major axes of the triangular prisms are substantially parallel to each other,
  On the other surface, an uneven row structure in which the height difference A is 2 μm to 30 μm, the period B is 50 μm to 1000 μm, and the B / A is in the range of 10 to 50 is 5 degrees to 30 degrees with respect to the major axis of the prism portion. With a swing angle ofHaveLight diffusing lens sheetBut
  A direct-type backlight characterized in that the prism portion is disposed on the light emitting side.Is the content.
  [0009]
  The invention according to claim 2 of the present invention is characterized in that the arrangement period of the prism portions is 10 μm to 500 μm.Direct type backlightIs the content.
  [0010]
  The invention according to claim 3 of the present invention is characterized in that the thickness is 50 μm to 500 μm.Direct type backlightIs the content.
  [0011]
  Claims of the invention4The invention related to,lightThe long axis direction of the prism portion of the diffusive lens sheet is arranged so as to substantially coincide with the direction of the linear light source.The method according to any one of claims 1 to 3.The content is a direct type backlight.
  [0012]
  Claims of the invention5The invention relating toIn any one of 1-4The liquid crystal television is characterized in that the direct type backlight described above is incorporated so that the major axis direction of the prism portion coincides with the longitudinal direction of the display surface of the liquid crystal television.
【The invention's effect】
  [0013]
  Of the present inventionDirect type backlightHas a lens surface in which triangular prisms are arranged on one surface, and a diffusing surface composed of an uneven row structure having a specific height difference A and period B and a ratio B / A between them on the other surface. Light diffusing lens sheet havingTheBy providing a lens surface on the light diffusing plate of a direct type backlight using a linear light source so that it is on the light exit side, the brightness in the normal direction of the backlight is maximized and the light utilization efficiency is improved. It becomes higher, and the light / dark difference due to the location of the light source is eliminated and no glare occurs..
  Furthermore, since the concave and convex array structure is provided with a specific swing angle with respect to the major axis of the prism portion, a surface light source that emits uniform light without generating interference fringes can be obtained.
  In addition, thisDirect type backlightIs a plurality of linear light sources arranged in parallelDespite being usedIt is possible to provide a suitable surface light source, and particularly a direct type backlight used for an LCD TV.AndIt is preferable.
  Also,The above light diffusing lens sheetIf the major axis direction of the prism portion is arranged so as to substantially coincide with the direction of the linear light source, an appropriate amount of light is emitted in the front and left and right directions of the screen while limiting the light emitted in the vertical direction.Direct type like thisThe backlight is more suitable for a liquid crystal television.
BEST MODE FOR CARRYING OUT THE INVENTION
  [0014]
  As mentioned above,Prism sheet was installed on the light diffusion plateDirect type backlightThenAlthough there is an effect of condensing outgoing light in the normal direction of the light diffusion plate, uniform light cannot be obtained because there is a difference in brightness between the location of the light source and its gap.
  Therefore, when various light diffusion methods were examined on the opposite surface of the lens surface of the prism structure, a specific uneven row structure was provided on the opposite side of the lens surface, and the major axis direction of the row was defined as the length of the linear light source. It has been found that, when substantially matched with the axial direction, it is very effective in eliminating the above-described difference in brightness, but interference fringes are generated at the same time, and a uniform surface light source cannot be obtained after all.
  As a result of further diligent research, it was found that the interference fringes were caused by the fact that the concave / convex array direction and the major axis direction of the prism portion were matched. By providing a swing angle of 5 to 30 degrees between the long axis directions of the row, the generation of interference fringes can be prevented, the brightness in the normal direction is sufficient, and the difference in brightness of the light source is eliminated. The present invention has been found that a uniform surface light source can be obtained.
  [0015]
  The present inventionUsed inThe light diffusing lens sheet is provided with a prism portion (hereinafter referred to as a lens surface) on one surface and an uneven row structure (hereinafter referred to as a diffusion surface) on the other surface. Here, as shown in FIG. 1, the major axis direction L2 of the concavo-convex array structure 4a of the diffusion surface 4 is provided with a swing angle α with respect to the major axis direction L1 of the prism portion 3 of the lens surface 2. In FIG. 1, the prism portion 3 is indicated by a solid line, and the uneven row structure 4 a is indicated by a broken line.
  [0016]
  As shown in FIGS. 1 and 2, prism portions 3 each having a prism-shaped unit substantially formed of a triangular prism are arranged on the lens surface 2 at a constant period C so as to be substantially parallel to each other.
  The prism portion 3 can be selected from a shape having a triangular prism cross section shape that easily exhibits a light condensing capability and a vertex angle of 60 degrees to 120 degrees. Preferably, it is in the range of 70 degrees to 110 degrees. The shape of the triangle is not particularly limited and may be either an equal side or an unequal side, but isosceles triangle is preferable in terms of improving the light collecting performance in the normal direction of the diffusion sheet, and therefore adjacent to the bottom side relative to the apex angle. Then, it is preferable that adjacent isosceles triangles are sequentially arranged and arranged such that apex angle columns are long axes and are substantially parallel to each other. In this case, the top and bottom angles of the triangular prism may have curvature as long as the light collecting ability is not significantly reduced.
  As for the arrangement period C of the prism portion 3, a range of 10 μm to 500 μm is preferable because it increases the homogeneity of the emitted light, and more preferably a range of 30 μm to 200 μm.
  [0017]
  As shown in FIGS. 1 and 3, the diffusing surface 4 is provided with a concavo-convex array structure 4 a for eliminating the light / dark difference due to the location of the linear light source and for eliminating the glare caused by the emission of light in a specific direction. The height difference A of the concave / convex array structure 4a is 2 μm to 30 μm. If the height difference A is less than 2 μm, there will be no effect of eliminating the difference in brightness and glare, and if it is greater than 30 μm, it will require not only high processing technology to provide an uneven row structure on the back surface of the prism sheet, but also increase the cost. , Productivity decreases.
  A period B of the uneven row structure is 50 μm to 1000 μm, preferably 50 μm to 500 μm. If the period B is smaller than 50 μm, the light condensing ability of the prism is lowered, and if it is larger than 1000 μm, the number of the concavo-convex rows is reduced, so that the interference with the prism is reduced.
  The ratio B / A of the period B to the height difference A is adjusted to a range of 10-50. If this ratio is less than 10, the number of the concave and convex lines increases, so that the front luminance is lowered. On the other hand, if it exceeds 50, the number of the concave and convex lines decreases, and as a result, the interference with the prism is reduced and the difference in brightness is large. And the appearance is poor.
  [0018]
  The cross-sectional shapes of the concave row 5 and the convex row 6 in the concave / convex row structure 4a are not particularly limited, and examples thereof include a rectangular quadrangle and a trapezoid having a slope.
  Moreover, the ratio (b1 / b2) of the width of the row of ridges 5 and the row of ridges 6 is not particularly limited, and can be adopted even in a structure in which thin rows of ridges and rows of ridges are provided for each specific period described above. However, when the ratio is preferably 1: 4 to 4: 1, more preferably 1: 2 to 2: 1, and most preferably about 1: 1, the effect of eliminating the light / dark difference is remarkable and the effect of suppressing the glare is also remarkable.
  The concave and convex rows constituting the concave / convex row structure 4a do not have to be linear, but may be curved or wavy. In each portion of the concave / convex row structure, the prism portion It is necessary that the deflection angle is 5 to 30 degrees with respect to the major axis of 3.
  [0019]
  As shown in FIG. 1, the uneven row structure 4 a is provided with a swing angle α of 5 degrees to 30 degrees with respect to the major axis of the prism portion 3. In other words, the line parallel to the direction of the concavo-convex row structure 4a and the line parallel to the major axis direction of the prism portion 3 intersect at an angle of 5 degrees to 30 degrees. Thereby, the generation of interference fringes is eliminated, the prism condensing function is increased, and the brightness in the normal direction is also increased. Here, when the swing angle is smaller than 5 degrees, interference fringes are likely to occur. On the other hand, when the swing angle is larger than 30 degrees, the effect of eliminating the light / dark difference cannot be obtained, and glare occurs.
  [0020]
  The material of the light diffusing lens sheet is not particularly limited as long as it is a transparent polymer material, and can be selected from ordinary optical transparent resins. Specific examples thereof include polyolefins such as acrylic resin, polycarbonate, polystyrene, polyvinyl chloride, polypropylene, and polymethylpentene, cyclic polyolefin, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyamide resins, poly Examples include arylate and polyimide. Further, in addition to the thermoplastic resin, a curable resin that is cured by ionizing radiation such as an acrylic resin can also be used.
  There are a method using a thermoplastic resin and a method using a curable resin as a method of forming a prism portion on the lens surface of a light diffusing lens sheet and forming an uneven row structure on the diffusion surface. In the case of a thermoplastic resin, a normal forming method is possible, and a method of injection molding into a desired mold, or a method of compression-molding a sheet-like material with a mold is possible.
  In extrusion molding, the material extruded into a sheet is embossed under heating, pressed against a mold roll during melt extrusion, or released in advance as described in Japanese Patent No. 2925069. The mold can be formed by transferring the mold while sandwiching the mold sheet. And when forming simultaneously, one side can also be shape | molded by a mold release sheet, and the other side can also be shape | molded by a metal mold | die roll.
  Further, in the case of curable resin, in the case of using ionizing radiation, it is usual to use an ultraviolet curable resin. In general, after applying a curable resin on a transparent support, it is molded by irradiating ultraviolet rays in a mold.
  The prism portion of the lens surface and the concave / convex array structure of the diffusing surface may be formed separately and bonded together, or may be integrally formed at the same time.
  [0021]
  Less than,lightDiffuse lens sheetInstallationA method will be described.
  Usually, a direct type backlight has a linear light source composed of a plurality of cold cathode ray tubes arranged in parallel, a light diffusing plate having a thickness of 2 mm to 4 mm is installed on the display surface side, and a light reflecting plate is installed on the opposite side. It is formed by installing,thisThe light diffusing lens sheet is placed on the light diffusing plate with the lens surface facing the light exit side.
  The installation direction is not particularly limited as long as the major axis direction of the prism portion is substantially lateral, and for example, the major axis direction of the linear light source and the major axis direction of the concavo-convex rows of the diffusion surface are aligned with each other. Alternatively, the major axis direction of the prism portion may be set so as to coincide with the major axis of the linear light source, and further, it may be installed at an intermediate position. It is preferable that the light beam is arranged so as to be substantially coincident with the direction of the shaped light beam because the emitted light is easily condensed in the normal direction of the light diffusing lens sheet.
  [0022]
  In the case of a liquid crystal television, the display surface is generally horizontally long. It is important that viewing is easy from the left and right diagonal directions of the display surface, and viewing from the top and bottom directions is not so important. Therefore, in order to ensure the brightness in the front direction, the left-right direction, and the left-right oblique direction of the display surface, it is preferable to adjust the emission by concentrating light in the vertical direction that is not important in the front direction.
  [0023]
  Here, the lens sheet in which the prism portions are arranged so that the major axes are substantially parallel to each other has different emission luminances in the major axis direction and the vertical direction perpendicular thereto, and the light diffused in the vertical direction by the prism sheet. Is known to be focused in the front direction.
  Therefore, if the linear light source of the backlight of the liquid crystal television is installed in the longitudinal direction of the liquid crystal screen, the major axis direction of the prism portion and the major axis direction of the concavo-convex array structure are also directed toward the longitudinal direction of the liquid crystal screen. It is a good idea to install a diffusive lens sheet. Thereby, the slightly unnecessary upward and downward emission is limited, and the brightness in the front direction and the brightness in the oblique direction on the left and right of the display surface can be secured, and a homogeneous and mild light source can be obtained. Furthermore, if necessary, a normal light diffusion sheet may be further installed. When this light diffusing sheet is used in combination with a prism sheet, the lower diffusing sheet and the upper diffusing sheet are commercially available with the prism sheet as the center.
  [0024]
  The present inventionUsed inThe thickness of the light diffusing lens sheet is arbitrary, but from the viewpoint of handling at the time of assembling the liquid crystal television, it is usually preferably from 50 μm to 500 μm, and from the viewpoint of continuous production, preferably from 200 μm to 400 μm.
【Example】
  [0025]
  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
  [0026]
Example 1
(Manufacture of light diffusing lens sheet)
  Polycarbonate transparent resin “Panlite L-1225Y” (manufactured by Teijin Kasei Co., Ltd.) is extruded into a sheet form from a die at a resin temperature of melt extrusion of 295 ° C., and the extruded sheet-shaped molten resin is pre-shaped with a prism shape. Described in Japanese Patent No. 2925069, which is sandwiched between the formed release sheet and a cooling roll provided with a concavo-convex array structure on the surface thereof with a swing angle of 20 degrees with respect to the major axis direction of the prism portion. The lens sheet was manufactured by the method of.
  The releasable sheet has a triangular prism shape in which a triangle of a cross section is an isosceles triangle having an apex angle of 100 degrees and an angle with the base of 40 degrees so that the long axes are adjacent to each other with a period of 50 μm and the major axes are parallel to each other. An array was used. Moreover, the uneven | corrugated row | line | column structure of the said cooling roll arrange | positions the uneven | corrugated row | line | column with a planar view linear form with the period of 60 micrometers, the unevenness | corrugation height difference A is 2 micrometers, and the period B is 60 micrometers (concave line and convex line) Each of which has a width of 30 μm), and the cross-sectional shape of the ridges is a trapezoidal shape having a lower base of 30 μm and an upper base of 24 μm. The ratio B / A of the period B to the height difference A is 30.
  The thickness of the obtained sheet was 240 μm. Obtained light diffusing lens sheetThe direct type backlight obtained by installing the above on the following backlightThe optical characteristics of were measured and judged by the following method. The measurement / judgment results are shown in Table 1.
  [0027]
(Measurement / judgment method of optical characteristics)
  Direct type backlightThe brightness difference can be measured by reducing the light receiving surface of the luminance meter, measuring the luminance of each part of the backlight, and calculating the difference. However, the quality of the surface light source must be judged by the naked eye.
  Further, the quality of the backlight is characterized by the presence or absence of light rays that are strongly emitted in a specific direction, which can be determined by the naked eye as glare.
  Therefore, the optical characteristics were evaluated by measurement with a luminance meter and determination with the naked eye.
  [0028]
Backlight configuration
  A backlight for a 32-inch television having a length of 400 mm and a width of 705 mm, in which 16 linear cathode ray tubes are arranged at equal intervals in the horizontal direction, is turned on. A light reflector is placed under the linear light source in the backlight cavity, and a 2 mm thick light diffuser “Opt Max” (manufactured by Sumitomo Bakelite Co., Ltd.) is installed on the light diffuser. A diffusive lens sheet was installed. The light diffusing lens sheet was installed such that the lens surface was the exit surface side and the major axis direction of the prism portion was matched with the major axis direction of the cathode ray tube.
  [0029]
Luminance measurement
  Measurement area 4.8 cm by luminance meter Minolta CA-1500 (manufactured by Konica Minolta Co., Ltd.) at a distance of 500 mm above the surface where the light diffusing lens sheet is installed.²As a result, the luminance at the center point of the installed light diffusing lens sheet was measured.
  [0030]
Judgment of appearance quality of backlight emission:
  Glare:
  The glare that enters the viewer's eyes directly from each direction due to reflection, refraction, etc. from the light source is visually determined according to the following criteria.
  ○: Glittering is not visible and the light is exiting gently.
  ○ △: Slight glare is seen only in one specific direction.
  Δ: Slight glare is seen, but it disappears after passing through the liquid crystal panel.
  X: Glitter is visible and may be visible after passing through the liquid crystal panel.
  [0031]
  Difference in brightness between the line light source and the middle part:
  The light / dark difference between the line light source and the intermediate portion thereof is visually determined according to the following criteria.
  ○: No difference in brightness is recognized.
  ○ △: Close to ○, with very slight difference in brightness.
  Δ: A slight difference in brightness is recognized.
  Δ ×: Close to ×, and the difference in brightness is clearly recognized.
  X: A contrast difference is clearly recognized.
  [0032]
  Brightness / darkness difference between the linear light source and its middle part:
  Luminance meter TOPCON BM-5A (manufactured by Topcon Co., Ltd.) was measured in the same manner as the luminance measurement described above.²The brightness was measured by approaching the backlight to 300 mm above the backlight and measuring the brightness between two cold cathode fluorescent lamps directly above and the midpoint thereof, and the brightness difference was calculated to obtain an average value.
  [0033]
Example 2
  Implemented except that the period B of the concave / convex row structure of the cooling roll was changed to a trapezoidal shape of 100 μm (the width of the concave row and the convex row is 50 μm, and the cross-sectional shape of the convex row is the bottom 50 μm and the upper bottom 30 μm). Create a light diffusing lens sheet as in Example 1.The direct type backlight obtained by installing this on the above backlightThe optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.
  [0034]
Example 3
  Except having changed the height difference of the uneven | corrugated row structure of a cooling roll to 10 micrometers, it carried out similarly to Example 2, and changed it.Direct type backlightThe optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.
  [0035]
Example 4
  The period B of the concave and convex row structure of the cooling roll is changed to a trapezoidal shape of 500 μm (the width of the concave row is 450 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is 50 μm at the bottom and 30 μm at the top). Except that manufactured in the same manner as Example 3,Direct type backlightWas manufactured, and its optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.
  [0036]
Example 5
  The height difference A of the concave / convex row structure of the cooling roll is 15 μm, and the period B is 250 μm (the width of the concave row is 200 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is 50 μm at the bottom, and 30 μm at the top) Except for the trapezoidal shape, the same as in Example 1Direct type backlightWas manufactured, and its optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.
  [0037]
Example 6
  The height difference A of the concavo-convex row structure of the cooling roll is 30 μm, and the period B is 900 μm (the width of the concave row is 850 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is the bottom 50 μm, the top bottom 30 μm) Except for the trapezoidal shape, the same as in Example 1Direct type backlightWas manufactured, and its optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.
  [0038]
Examples 7-9
  Except for changing the swing angle of the concavo-convex row structure of the cooling roll to 5 degrees, 10 degrees, and 30 degrees, the same as in Example 4Direct type backlightWas manufactured, and its optical characteristics were measured and judged. The measurement / judgment results are shown in Table 1.
  [0039]
Comparative Example 1
  Optical characteristics were measured and determined in the same manner as in Example 1 except that two commercially available light diffusion sheets BS300 (manufactured by Eiwa Co., Ltd.) were installed on the backlight light diffusion plate instead of the light diffusing lens sheet. . The measurement / judgment results are shown in Table 1.
  [0040]
Comparative Example 2
  Optical properties were measured in the same manner as in Example 1 except that three commercially available light diffusion sheets BS702 (manufactured by Keiwa Co., Ltd.) were stacked in place of the light diffusing lens sheet and placed on the light diffusion plate of the backlight. Judged. The measurement / judgment results are shown in Table 1.
  [0041]
Comparative Example 3
  A sheet was produced in the same manner as in Example 4 except that the swing angle of the concavo-convex row structure of the cooling roll was changed to 0 degree, and the optical characteristics of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.
  [0042]
Comparative Example 4
  Implemented except that the period B of the concave / convex row structure of the cooling roll was changed to a trapezoidal shape of 30 μm (the width of the concave row and the convex row is 15 μm, and the cross-sectional shape of the convex row is the bottom 15 μm and the top 10 μm). A sheet was produced in the same manner as in Example 3, and the optical properties of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.
  [0043]
Comparative Example 5
  The height difference A of the concave / convex row structure of the cooling roll is 4 μm, and the period B is 300 μm (the width of the concave row is 250 μm, the width of the convex row is 50 μm, the cross-sectional shape of the convex row is the bottom 50 μm, the top bottom 30 μm) A sheet was produced in the same manner as in Example 1 except that the trapezoidal shape was changed, and the optical characteristics of the obtained sheet were measured and determined. The measurement / judgment results are shown in Table 1.
  [0044]
Comparative Example 6
  Optical sheet in the same manner as in Example 4 except that the swing angle of the concave and convex row structure of the cooling roll was changed to 45 degrees.And install it on the above backlight, direct type backlightManufactured and obtainedDirect type backlightThe optical properties of were measured and judged. The measurement / judgment results are shown in Table 1.
  [0045]
Comparative Example 7
  The optical characteristics were measured and determined in the same manner as in Example 1 except that the light diffusing lens sheet was not used. The measurement / judgment results are shown in Table 1.
  [0046]
[Table 1]
  [0047]
  As is clear from the examples and comparative examples in Table 1 above, the brightness difference between light and dark is large only with a normal light diffusion plate with a thickness of 2 mm, and the light and dark difference between the linear light source and its gap is clearly recognized by the naked eye. The luminance is also low (see Comparative Example 7). When two or more commercially available diffusion sheets are stacked on this, a difference in brightness is hardly recognized with the naked eye, but the number of parts increases, manufacturing costs increase, and productivity decreases (see Comparative Examples 1 and 2). .
  On the other hand, by providing an uneven row structure on the opposite side of the lens surface, the light / dark difference of the light source is almost eliminated.
  Further, the value of the period B (B / A) with respect to the height difference A is important. If this value is less than 10, the luminance decreases (see Comparative Example 4), whereas if it exceeds 50, the glare increases (Comparative Example). 5). Further, when the direction of the projections and depressions coincides with the direction of the prism portion (the swing angle is 0 degree), interference fringes appear (see Comparative Example 3). On the other hand, when the swing angle is too large, the glare becomes remarkable (Comparative Example 6). See).
  As a result of the above, by providing an appropriate uneven row structure on the opposite surface of the lens surface at an appropriate swing angle, even a single light diffusing lens sheet can sufficiently improve the quality of the backlight, resulting in a decrease in luminance. (See Examples 1 to 9).
[Industrial applicability]
  [0048]
  As mentioned above, the present inventionDirect type backlightIsLight diffusing lens sheetDirectly below the linear light source by providing a concave and convex array structure with a specific height difference and period on the opposite side of the lens surface having the prism part with a specific swing angle with respect to the major axis direction of the prism part Eliminates the brightness and glare between the light source and the light source of the mold backlight, greatly improving the quality, increasing the brightness of the front, and reducing the number of parts of the backlight.Direct type backlightUseful as.
[Brief description of the drawings]
  [0049]
    FIG. 1 shows the present invention.Used inIt is a schematic explanatory drawing which shows the relationship between the prism surface of a light diffusable lens sheet, and an uneven | corrugated row | line | column structure surface.
    FIG. 2 shows the present invention.Used inIt is AA sectional view taken on the side of the prism surface of the light diffusing lens sheet.
    FIG. 3 shows the present invention.Used inIt is BB sectional drawing of the uneven | corrugated row | line | column structure surface side of a light diffusable lens sheet.
[Explanation of symbols]
  [0050]
  1 Light diffusing lens sheet
  2 Lens surface
  3 Prism section
  4 Diffusion surface
  4a Uneven row structure
  5 concave line
  6 ridges
  L1 Line parallel to the long axis direction of the prism
  L2 Line parallel to major axis direction
  C Prism unit arrangement period
  A Difference in height of uneven rows
  B Period of the irregular row
  b1 Width of concave row
  b2 Width of ridge row
  α Swing angle

Claims (6)

A plurality of substantially triangular prism portions made of a transparent polymer material on one side are arranged in a constant cycle so that the major axes of the triangular prisms are substantially parallel to each other,
On the other surface, an uneven row structure in which the height difference A is 2 μm to 30 μm, the period B is 50 μm to 1000 μm, and the B / A is in the range of 10 to 50 is 5 degrees to 30 degrees with respect to the major axis of the prism portion. A light diffusing lens sheet characterized by being provided with a swing angle of   The light diffusing lens sheet according to claim 1, wherein the arrangement period of the prism portions is 10 μm to 500 μm.   The light diffusing lens sheet according to claim 1, wherein the thickness is 50 μm to 500 μm.   4. The light diffusing lens sheet according to claim 1, wherein the light diffusing lens sheet is used for a direct type backlight including a plurality of linear light sources arranged in parallel. 5.   5. A direct type backlight comprising: a prism portion of the light diffusing lens sheet according to claim 1, which is arranged so that a major axis direction of the prism portion substantially coincides with a linear light source direction.   6. A liquid crystal television, wherein the direct type backlight according to claim 5 is incorporated so that the major axis direction of the prism portion coincides with the longitudinal direction of the display surface of the liquid crystal television.

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