WO2010010840A1

WO2010010840A1 - Photodiffusion plate, photodiffusion plate manufacturing method, surface illuminant device, and display device

Info

Publication number: WO2010010840A1
Application number: PCT/JP2009/062891
Authority: WO
Inventors: 啓介塚田
Original assignee: 日本ゼオン株式会社
Priority date: 2008-07-22
Filing date: 2009-07-16
Publication date: 2010-01-28
Also published as: JPWO2010010840A1

Abstract

Provided is a photodiffusion plate comprising a light incident surface, on which a light is incident, and a light-emitting surface formed on the surface opposite to the light incident surface for diffusing and emitting the light incident on the light incident surface, wherein at least one of the light incident surface and the light-emitting surface includes recess-projection regions having a plurality of repetition units, wherein each of the repetition units includes at least one recess-projection structure having at least two surfaces, wherein at least two of the surfaces in the repetition units are rough, wherein the ratio of the rough surfaces to the surface of the entire region having the repetition units in each of the recess-projection regions is 50 % or less, and wherein at least one of the surfaces facing a rough surface in the repetition units is also rough. Further provided are a surface illuminant device and a display device having the photodiffusion plate.

Description

Light diffusing plate, light diffusing plate manufacturing method, surface light source device, and display device

The present invention relates to a light diffusing plate, a manufacturing method thereof, and a surface light source device and a display device including the light diffusing plate.

In a display device such as a liquid crystal display device, a backlight device such as a direct-type backlight device having a reflector, a plurality of light sources, and a light diffusing plate may be used. In such a direct type backlight device, a cross-sectional polygon extending parallel to the longitudinal direction of the light source is provided on the surface of the light diffusing plate for the purpose of making the luminance uniform on the exit surface of the light diffusing plate (increasing the luminance uniformity). It has been practiced to provide a prism array in which a plurality of linear prisms are arranged (Japanese Patent Laid-Open No. 2006-066074). Such a light diffusing plate can be obtained, for example, by forming a concavo-convex structure corresponding to the prism row on the cavity surface of a mold part and performing injection molding using the mold part. However, when a light diffusing plate having such a linear prism is molded by injection molding, depending on the resin used, the molded light diffusing plate is attached to a mold part, making it difficult to release the light diffusing plate. There was a case. For this reason, the molding operation is not always efficient.

On the other hand, in Japanese Patent Application Laid-Open No. 2001-287227, in order to improve the releasability of a molded product due to the close contact between the mold and the molded product, the surface of the mold has a ten-point average roughness. It is disclosed that the rough surface has a thickness Rz of 0.2 to 3.0 μm.

In order to efficiently perform the injection molding of the light diffusing plate, it is conceivable to roughen the surface of the concavo-convex structure corresponding to the prism row by using the technique disclosed in Japanese Patent Application Laid-Open No. 2001-287227. . However, simply applying this technique can improve the mold releasability of the molded product, but there are cases where the optical performance such as luminance uniformity cannot be sufficiently exhibited. For this reason, development of mold parts having sufficient optical performance and excellent releasability is desired.
The above problem is not limited to the light diffusion plate for a direct backlight device used in a display device such as a liquid crystal display device, but also a light diffusion plate for a lighting device, a direct light backlight used for an advertisement or a signboard. The same applies to the light diffusion plate for the light device.

An object of the present invention is to provide a light diffusing plate that can provide a surface light source device and a display device having high luminance and high luminance uniformity and can be efficiently manufactured, and a method for manufacturing the same.

A further object of the present invention is to provide a surface light source device and a display device that have high luminance and luminance uniformity and can be efficiently manufactured.

As a result of intensive studies to solve this problem, the present inventor has found that the above problem can be solved by making the uneven structure of the light diffusion plate specific, and has completed the present invention.
Thus, the present invention includes the following.

[1] A light diffusing plate comprising a light incident surface on which light is incident and a light emitting surface that is formed on a surface opposite to the light incident surface and diffuses and emits light incident from the light incident surface. There,
At least one of the light incident surface and the light emitting surface has an uneven region having a plurality of repeating units,
Each of the plurality of repeating units has one or more concavo-convex structures having two or more faces,
Two or more of all the surfaces included in the repeating unit are rough surfaces,
In each of the uneven regions, the ratio of the area of the rough surface to the area of the surface of the entire region where the repeating unit is formed is 50% or less,
A light diffusing plate in which at least one of a plurality of surfaces facing each other with respect to an arbitrary rough surface in the repeating unit is a rough surface.
[2] The light diffusion plate, wherein the concavo-convex structure is a linear prism having a polygonal cross section.
[3] The light diffusing plate, wherein the uneven structure is a polygonal pyramid or an inverted shape thereof.
[4] The light diffusing plate, wherein a difference in maximum center line average roughness of the facing rough surfaces is within 1.0 μm.
[5] A method for producing the light diffusing plate,
Manufacturing comprising: cutting a mold material using a cutting tool to prepare a mold including a surface corresponding to the uneven region; and molding a resin material using the mold Method.
[6] Of the surface corresponding to the uneven region in the mold, the cutting tool that cuts the surface corresponding to the rough surface is a cutting tool including single crystal diamond or single crystal boron nitride, and the mold The manufacturing method according to claim 1, wherein the cutting surface is a cutting tool processed prior to cutting of the material.
[7] A surface light source device comprising a light source and the light diffusing plate or the light diffusing plate manufactured by the manufacturing method.
[8] A display device comprising an object to be illuminated and the surface light source device.

Since the light diffusion plate of the present invention has a concavo-convex structure that can increase luminance and luminance uniformity and is easy to release, the surface light source device and display device of the present invention provided with the light diffusion plate have luminance and luminance uniformity. High and efficient production. Moreover, in the manufacturing method of the light diffusing plate of this invention, the said light diffusing plate of this invention can be manufactured efficiently. Further, since the rough surfaces are in a relationship facing each other, there is an effect that the luminance unevenness due to the observation direction can be reduced.

FIG. 1 is a perspective view schematically showing a light diffusing plate and a surface light source device according to an embodiment of the present invention. FIG. 2 is an enlarged plan view showing a light emission surface of the light diffusion plate shown in FIG. FIG. 3 is an enlarged perspective view showing a part of the light diffusing plate shown in FIG. FIG. 4 is a longitudinal sectional view in which a part of the light diffusing plate shown in FIG. 3 is further cut by a plane along the line 3a. FIG. 5 is a partial plan view schematically showing the main surface of the light diffusing plate shown in FIG. FIG. 6 is a partial plan view showing an outline of the main surface of the light diffusing plate in Comparative Example 3. FIG. 7 is a partial plan view showing an outline of the main surface of the light diffusing plate in Comparative Example 1. FIG. 8 is a schematic view showing an example of the edge tip of the rough surface forming tool. FIG. 9 is an enlarged view showing the cutting portion 813 of the cutting tool shown in FIG. FIG. 10 is a perspective view schematically showing a surface light source device according to another embodiment of the present invention. FIG. 11 is a cross-sectional view of the surface light source device shown in FIG. 10 cut along a cross section perpendicular to the longitudinal direction of the linear light source 1011. FIG. 12 is a plan view schematically showing the arrangement of point light sources in the surface light source device shown in FIG. 13 is an enlarged perspective view showing a part of the light diffusion plate shown in FIG. FIG. 14 is a plan view of the concavo-convex structure shown in FIG. 13 observed from above. FIG. 15 is an enlarged perspective view showing the light emitting surface of the light diffusing plate shown in FIG.

In the following, the present invention will be described in detail with reference to the drawings.
(Light Diffusing Plate and Surface Light Source Device: First Embodiment)
FIG. 1 is a perspective view schematically showing a surface light source device 100 including a light diffusing plate 101 according to the first embodiment of the present invention.
The surface light source device of the present invention includes a light source, a reflecting plate that reflects light from the light source, direct light from the light source and reflected light from the reflecting plate from a light incident surface, and diffuses from the light emitting surface. And a light diffusing plate to be irradiated. In the first embodiment shown in FIG. 1, the surface light source device 100 includes a reflecting plate 121, a point light source 111 provided on the reflecting surface 121 </ b> A of the reflecting plate 121, and an upper portion of the reflecting plate 121 and the point light source 111. And a light diffusing plate 101 that is spaced apart on the side.

In this specification, unless otherwise specified, the “up” and “down” directions mean “up” and “down” in a state where the surface light source device is placed so that its light emission surface is horizontally upward. ”Direction, which corresponds to the upward and downward directions in the drawings of FIGS. 1 and 10.

(a reflector)
As a material of the reflector, a resin colored in white or silver, a metal, or the like can be used, and a resin is preferable from the viewpoint of weight reduction. The color of the reflector is preferably white from the viewpoint of improving the luminance uniformity, but white and silver may be mixed in order to highly balance the luminance and the luminance uniformity.

(light source)
The light source used in the present invention may be a point light source shown in FIG. 1 or a linear light source shown in other embodiments described later. As such a point light source, a light source such as an LED can be used. Some LEDs emit various colors such as white, red (R), green (G), and blue (B). In this embodiment, the color balance is adjusted such that (1) only white LEDs are used as point light sources, (2) RGB three primary colors are combined, and (3) RGB three primary colors are combined with an intermediate color or white. It can be appropriately selected and used in consideration. In the combination of the three primary colors of RGB ((2) and (3)), (A) at least one red LED, green LED and blue LED are arranged close to each other, and each color is mixed to emit white light. And (B) a red LED, a green LED, and a blue LED appropriately disposed. In the case of (A), a combination of LEDs arranged close to each other is regarded as one point light source. As shown in FIG. 12, the arrangement of the point light sources on the reflecting plate is such that the reflecting surface 121A on the reflecting plate 121 is arranged in a direction along the longitudinal direction and the short direction of the light emitting surface of the surface light source device 100. It can be arranged. In this case, the

intervals

113W and 113L of the point light sources can be set to 10 to 200 mm.

(Light diffusion plate: material)
In the present invention, as the material constituting the light diffusing plate, glass, a mixture of two or more kinds of resins that are difficult to mix, a material in which a light diffusing agent is dispersed in a transparent resin, and one kind of transparent resin are used. it can. Among these, a resin is preferable because it is lightweight and easy to mold, and one kind of transparent resin is preferable from the viewpoint that luminance can be easily improved, and adjustment of total light transmittance and haze is easy. From the viewpoint, a transparent resin in which a light diffusing agent is dispersed is preferable.

The transparent resin is a resin having a total light transmittance of 70% or more measured with a 2 mm-thick plate smooth on both sides based on JIS K7361-1, for example, polyethylene, propylene-ethylene copolymer, Polypropylene, polystyrene, polymethylpentene-1, copolymer of aromatic vinyl monomer and (meth) acrylic acid alkyl ester having lower alkyl group, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, terephthalic acid-ethylene Examples include glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, and resin having an alicyclic structure. In addition, (meth) acrylic acid is acrylic acid and methacrylic acid.

The light diffusing agent is a particle having a property of diffusing light, and can be roughly classified into an inorganic filler and an organic filler. Examples of the inorganic filler include silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, and a mixture thereof. Examples of the organic filler include acrylic resin, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, and benzoguanamine resin. Among these, as the organic filler, fine particles composed of polystyrene resin, polysiloxane resin, and cross-linked products thereof are preferable in terms of high dispersibility, high heat resistance, and no coloration (yellowing) during molding. Among these, fine particles made of a cross-linked product of polysiloxane resin are more preferable from the viewpoint of more excellent heat resistance.

The proportion of the light diffusing agent dispersed in the transparent resin can be appropriately selected according to the thickness of the light diffusing plate, the interval between the linear light sources, and the like. Usually, the total light transmittance of the dispersion is 60% to 98%. It is preferable to adjust the content of the light diffusing agent so as to be, and it is more preferable to adjust the content of the light diffusing agent to be 65% to 95%. By setting the total light transmittance within the above preferable range, the luminance and the luminance uniformity can be further improved.

The total light transmittance is a value measured with a 2 mm-thick plate smooth on both sides based on JIS K7361-1, and the haze is a value measured on a 2 mm-thick plate smooth on both sides with JIS K7136. .

(Light diffusion plate: outline)
In the present invention, the light diffusing plate is formed on a light incident surface on which light is incident and a surface opposite to the light incident surface, and diffuses and emits light incident from the light incident surface; And at least one of the light incident surface and the light emitting surface has an uneven region having a plurality of repeating units, and each of the plurality of repeating units has an uneven structure having two or more surfaces. 1 or more. In the present invention, the concavo-convex structure means a concave structure and / or a convex structure unless otherwise specified.
Here, in the present invention, for example, when the relative position of the rough surface described later is different in the repeating unit, it does not correspond to the repeating unit, and its outer shape including the relative position of the rough surface is the same. If equal, it corresponds to a repeating unit.

The light diffusing plate 101 in the first embodiment shown in FIG. 1 has a plate-like structure having a light incident surface and a light emitting surface as main surfaces, and has an uneven region on the entire surface of the light emitting surface. . In the present invention, the concavo-convex region may be provided on the entire surface of the light incident surface or the light output surface, but is provided in a part of the region such as 50% or more of the effective area (the area where light is actually emitted). May be.

The uneven structure on the light exit surface of the light diffusion plate 101 will be described in more detail with reference to FIG. FIG. 2 is an enlarged plan view showing a light emitting surface of the light diffusion plate 101 shown in FIG. As shown in FIG. 2, the concavo-convex structures 311 are arranged on the light emitting surface of the light diffusing plate 101 without any gaps.

The concavo-convex structure 311 is a concave structure in which the quadrangular pyramid is inverted (the shape of the contour of the dent defined is a quadrangular pyramid shape with an apex downward (inverted pyramid shape)). The base extends in the direction of a line 211 and a line 212 orthogonal thereto, and the line 212 forms an angle θ2 with the edge 212 of the light diffusing plate. As shown in FIG. 1, when the point light sources 111 are arranged along the longitudinal direction and the short direction of the light emitting surface of the surface light source device, a preferable range of θ2 is 5 to 45 °, more preferably 5 °. -40 °, more preferably 10-40 °. By setting the angle θ2 between the arrangement direction of the point light sources and the line 212 to the above angle, the region surrounded by the four point light sources that becomes the darkest when there is no uneven structure can be brightened. The brightness uniformity of the surface can be further increased.

The structure of the concavo-convex structure 311 will be described in more detail with reference to FIGS. 3 is an enlarged perspective view of the light diffusing plate 101 of FIG. 2, in which a portion 101R obtained by cutting out a 5 × 5 area of the concavo-convex structure 311 is illustrated, and FIG. 4 further illustrates the portion 101R. It is the longitudinal cross-sectional view cut | disconnected by the surface along 3a. As shown in FIGS. 3 and 4, each of the concavo-convex structures 311 is a concave structure having four surfaces 311A to 311D and having a shape in which a regular square pyramid is inverted. The bases of the regular square pyramids are aligned in the direction along the

lines

211 and 212, and the apex 311P of the regular square pyramid is located at the bottom of the concave structure. The length 311S of one side of the square at the bottom of the regular square pyramid is usually 30 to 500 μm, preferably 35 to 300 μm, more preferably 40 to 200 μm. When the length of one side 311S is smaller than the above numerical range, for example, when the concave and convex structure of the mold is transferred to form the concave and convex structure of the present invention, the concave and convex structure is difficult to transfer, or the luminance uniformity decreases due to the diffraction phenomenon. In addition, when the length 311S of one side is larger than the above numerical range, the uneven structure can be visually recognized, resulting in uneven brightness, and the displayed image does not look normal. The problem can arise. For this reason, by setting the length 311S of one side of the regular quadrangular pyramid to satisfy the above numerical range, there is an advantage that the luminance uniformity can be improved without causing the above problem. The apex angle θ311 of the regular quadrangular pyramid is usually 40 to 170 °, preferably 50 to 165 °, more preferably 60 to 160 °. When the apex angle θ311 is smaller than the above numerical range, for example, when the concave / convex structure of the present invention is formed by transferring the concave / convex structure of the mold, it is difficult to transfer the concave / convex structure, so that the shape cannot be formed as designed. If the apex angle θ311 is larger than the above numerical range, light perpendicularly incident on the light diffusion plate is likely to be transmitted, and as a result, the linear light source Since the portion directly above the screen becomes bright, there may be a problem that the luminance uniformity decreases. For this reason, there exists an advantage which can improve a brightness | luminance uniformity by setting the vertex angle (theta) 311 of a regular quadrangular pyramid to satisfy | fill the said numerical range.

In the present invention, two or more of all the surfaces included in the repeating unit are rough surfaces. The rough surface may have a maximum value Ra (max) of centerline average roughness Ra measured in various directions parallel to the rough surface that is greater than or equal to a predetermined value. Specifically, the rough surface can be a surface having Ra (max) of 0.05 μm or more and less than 3.0 μm, preferably 0.10 μm or more and less than 2.0 μm.
Specifically, the rough surface having such roughness can be formed by providing fine irregularities such as dots or streaks on a smooth surface. Such fine irregularities may be evenly provided on the entire rough surface, but may not be evenly provided on the entire rough surface, and have fine irregularities on one surface. The part and the smooth part may be mixed. Specifically, for example, a rough surface provided with periodically fine irregularities based on the cutting shape of a cutting tool having a periodic notch on the edge, such as a rough surface in Example 7 described later. There may be.
On the other hand, the surface other than the rough surface can be a smooth surface, and the smooth surface can be a surface having a Ra (max) of less than 0.05 μm.
The centerline average roughness Ra can be obtained based on JIS B0601.
By providing a rough surface having such a fine roughness, it is possible to increase the releasability at the time of molding and to scatter visible light within a desired range.

Furthermore, in this invention, the ratio of the area of a rough surface with respect to the area of the said surface of the whole area | region in which the said repeating unit was formed in each uneven | corrugated area | region is 50% or less. For example, in the case where an uneven area is provided on the light emitting surface, this requirement is satisfied when the ratio of the surface processed as a rough surface to the entire uneven area on the light emitting surface is 50% or less.
For example, in the case where uneven areas are provided on both the light incident surface and the light exit surface, the ratio of the rough surface to the entire uneven area on the light incident surface is 50% or less, and the unevenness on the light exit surface. This requirement is satisfied when the ratio of the rough surface to the entire region is 50% or less.
In the present invention, by having the rough surface at such a specific ratio, the luminance uniformity is increased, the variation of the luminance uniformity due to the difference in the observation direction is reduced, and the releasability when manufacturing the light diffusion plate Can be improved.

In the present invention, the rough surface on the light diffusing plate may have a form having anisotropy in the roughness. Specifically, Ra (max) and the minimum value Ra (min) of the center line average roughness are Ra (max)> Ra (min), preferably Ra (max)> 2 × Ra (min), More preferably, the relationship Ra (max)> 3 × Ra (min) may be satisfied.
Further, the direction in which the roughness of the rough surface is maximized may be a direction that intersects the main surface of the light diffusion plate. By setting it as such a form, a brightness | luminance uniformity can be raised and manufacture of a light diffusing plate and a mold component can be made easy. The specific example of such a form is explained in full detail later together with the manufacturing method of a light diffusing plate.

Furthermore, in the present invention, at least one of the plurality of surfaces facing each other with respect to an arbitrary rough surface in the repeating unit is also a rough surface. In the present invention, the “faced relationship” between the surface (i) having the concavo-convex structure and the other surface (ii) means that any of the following requirements (a) to (c) is satisfied:
(A) A line (iii) parallel to both the surface (i) and the main surface of the light diffusing plate is also parallel to the surface (ii).
(B) There is a portion where the surface (i) and the surface (ii) overlap when viewed from the direction of the line (iv) parallel to the main surface of the light diffusion plate and orthogonal to the line (iii).
(C) With respect to the main surface of the light diffusing plate, the direction in which the surface (i) is inclined and the direction in which the surface (ii) is inclined are opposite to each other.

The requirements (a) to (c) will be described using the uneven structure shown in FIG. 15 as an example. FIG. 15 illustrates the concave structures 311-1, 311-2, and 311-3, which are provided as three concave-convex structures on the main surface of the light emitting surface and have a shape in which regular square pyramids are inverted.

First, since these concave structures are all provided on the main surface of the light emitting surface, their bases (211-1 to 211-4, etc.) are all parallel to the main surface. A line 211-2 which is the base of the surface 311A-2 is a line parallel to both the light emitting surface and the surface 311A-2. Therefore, the surfaces 311A-1, 311C-1, 311C-2, 311A-3, and 311C-3 each having a base parallel to the line 211-2 satisfy the requirement (A) with respect to the surface 311A-2. It is a surface to fill.

Furthermore, the direction of the line parallel to the light emitting surface and perpendicular to the line 211-2 is the left-right direction in FIG. Since the square weights 311-1 to 311-3 are all regular square weights, the surfaces 311A-1, 311C-1, 311C-2, 311A-3, and 311C-3 are all viewed from the left-right direction in FIG. Since they overlap with the surface 311A-2 when viewed, they both satisfy the requirement (b) with respect to the surface 311A-2. In the requirement (b), the ratio of the overlapping portion to the entire surface (i) is preferably 5 to 100%. From the requirement (b), for example, the surfaces 311B-1 and 311D-1 can be opposed surfaces, but the surfaces 311B-1 and 311D-2 cannot be opposed surfaces.

Further, the direction in which the surface 311A-2 is inclined with respect to the light emitting surface is the same as the surface 311A-1 and the surface 311A-3, and is opposite to the surface 311C-1, the surface 311C-2, and the surface 311C-3. The direction of the direction. Accordingly, the surface 311C-1, the surface 311C-2, and the surface 311C-3 satisfy the requirement (c) with respect to the surface 311A-2, while the surface 311A-1 and the surface 311A-3 become the surface 311A-2. On the other hand, it does not meet requirement (c).

From the above, when the concave structures 311-1, 311-2 and 311-3 constitute one repeating unit, for example, one or more of 311A-1, 311A-2 and 311A-3, 311C- When one or more of 1, 311C-2 and 311C-3 is a rough surface, at least one of the plurality of surfaces facing the rough surface in the repeat unit is also a rough surface. .

For example, the surfaces 311C-1 and 311A-3 may be spaced apart from each other in the repeating unit. However, it is more preferable that the facing rough surfaces are arranged in contact with each other. It is preferable because it is easy to manufacture with a rough surface forming tool. For example, an arrangement in which the surfaces 311C-1 and 311A-2 that are in contact with the side 211-2 are rough surfaces facing each other is preferable.

In relation to requirement (c), the maximum centerline average roughness of surface (i) (the maximum of the centerline average roughness of surface (i) with the line parallel to surface (i) as the centerline) And the maximum center line average roughness of the surface (ii) facing the surface (i) is preferably within 1.0 μm, more preferably within 0.5 μm, and 0.3 μm More preferably, it is within. By setting the difference of the maximum center line average roughness within such a range, the difference in luminance unevenness depending on the observation direction can be reduced, and the releasability in manufacturing the light diffusion plate can be improved.

Further, the angle formed by the surface (i) and the main surface of the light diffusing plate is θ (i) ° (where 0 <θ (i) <90), and the angle formed by the surface (ii) and the main surface of the light diffusing plate. Is θ (ii) ° (where 0 <θ (ii) <90), the difference between θ (i) and θ (ii) is preferably smaller. Specifically, | θ (i) −θ ( ii) | ≦ 60 ° is preferable, | θ (i) −θ (ii) | ≦ 50 ° is more preferable, and | θ (i) −θ (ii) | ≦ 40 ° is satisfied. Is more preferable.

In the definition of the shape of the light diffusion plate in the present invention, the fact that the plane and the line are parallel may include, for example, an error of ± 10 °.

FIG. 5 shows an example of the rough surface arrangement in which the rough surface having a repeating unit and the surface opposite to the rough surface are rough surfaces in the uneven region. FIG. 5 is a partial plan view schematically showing the main surface of the light diffusing plate. This surface is composed of four surfaces 311A to 311D, and has a concavo-convex structure having a shape in which a regular square pyramid is inverted, The concavo-convex structure is arranged without a gap to form the concavo-convex region. This uneven | corrugated area | region is comprised by the repetition of the repeating unit 311R which consists of two uneven structures. In this repeating unit, the surface 311C having a certain concavo-convex structure and the opposing surface in the adjacent concavo-convex structure are rough surfaces. Since two surfaces out of eight surfaces having the same area in one repeating unit are rough surfaces, the ratio of the rough surface in the uneven region is 25%.

As shown in FIG. 5, the rough surface of the concavo-convex region is arranged so that a surface along a part of the lines 211-1 to 211-9 constituting the bottom of the surface of the concavo-convex structure is a rough surface. This is particularly preferable because a stamper for manufacturing a light diffusing plate can be easily formed using a smooth surface and rough surface forming tool, which will be described later.

The height (depth) of the concavo-convex structure in the concavo-convex area is not particularly limited, but the maximum center line average roughness with a plane parallel to the main surface of the light diffusing plate as the center line is within a range of 1 to 1000 μm. The thickness is preferably 3 to 200 μm.

The thickness of the light diffusing plate is preferably 0.4 mm to 5 mm, and more preferably 0.8 mm to 4 mm. By setting the thickness of the light diffusing plate within the above preferable range, it is possible to suppress bending due to its own weight and to facilitate the molding.

(Method for manufacturing light diffusion plate)
In the present invention, the manufacture of the light diffusing plate includes a step of cutting a mold material using a cutting tool to prepare a mold including a surface corresponding to the uneven area, and a resin material using the mold. It can be manufactured by a method including a molding step.

(Manufacturing method of light diffusion plate: mold preparation process)
In the step of preparing the mold, the mold material for molding the portion of the surface corresponding to the uneven area in the mold can be a mold itself and / or a stamper disposed on the main surface of the mold. . From the viewpoint of ease of processing and the ease of replacement when the fine concavo-convex structure of the mold is damaged due to the use of a mold, the surface portion corresponding to the concavo-convex region is preferably formed on a stamper.

A description will be given by taking as an example the formation of a stamper for obtaining a concavo-convex structure in which the shapes of the inverted square pyramids of the light diffusion plate of the first embodiment of the present application shown in FIGS. 1 to 5 are arranged.

First, a nickel-phosphorous electroless plating layer having a thickness of, for example, about 100 μm is applied to the entire surface of a metal rectangular plate. Next, a fine machining tool provided with a cutting tool having a triangular cutting portion whose apex angle is a predetermined angle (the same angle as the apex angle θ311 of the concave structure shown in FIG. 4) on the surface of the plating layer. Using a machine (for example, nanogruber AMG71P, manufactured by Fujikoshi Co., Ltd.), by cutting at a predetermined pitch in a direction parallel to the stamper surface and corresponding to the line 211 on the light diffusion plate shown in FIG. A plurality of grooves are formed. Further, by cutting at a predetermined pitch in a direction corresponding to the line 212 shown in FIG. 2, a groove having a triangular cross section is dug in two directions orthogonal to each other, and as a result, the concavo-convex structure shown in FIGS. 3 and 4 is inverted. It is possible to obtain a structure in which the square pyramids are arranged without gaps.
Here, in the machining of the grooves corresponding to the surfaces along the lines 211-1, 211-3, 211-5, 211-7, 211-9,... On the light diffusion plate shown in FIG. 5 by cutting using a rough surface forming tool with a rough surface, while cutting with a smooth surface forming tool with the cutting surface as a smooth surface in the machining of the grooves in other parts. A stamper corresponding to the arrangement of the rough surface on the light diffusing plate shown in FIG. As the smooth surface forming tool, a single crystal diamond tool or a single crystal boron nitride tool can be preferably used.

An example of a rough surface forming tool will be described with reference to FIGS. FIG. 8 is a schematic view showing an example of the edge tip of the rough surface forming tool. In FIG. 8, a processing portion 813 is periodically provided in a part of each of the

edges

801 and 802 of the cutting portion of the rough surface forming bit 800. FIG. 9 is an enlarged view of such a processing portion 813. As shown in FIG. 9, the processed portion 813 is provided with a plurality of cutout portions having an apex angle θ823 and having a length indicated by an arrow 823A. The shape of the notch is a shape that usually does not cause an undercut portion so that the mold release is not hindered when the molded product is released from the stamper. Such a notch can be formed using a high energy beam processing apparatus such as a focused ion beam (FIB) apparatus (for example, manufactured by Hitachi High-Technology Corporation). By having such a machined portion, fine streaky irregularities based on the shape of the notch are formed on the stamper surface cut by the rough surface forming tool 800, and as a result, the surface is roughened. It becomes. The smooth surface forming tool may be processed into the above-described embodiment. Since fine processing can be performed particularly efficiently, it is particularly preferable to use a tool obtained by processing a bite containing single crystal diamond or single crystal boron nitride.

As the rough surface forming tool, a tool having at least one of sintered diamond, sintered boron nitride, cemented carbide, steel added with a rare earth metal, and ceramics can be used as the material for forming the rough surface. . As the cemented carbide, an alloy obtained by sintering metal carbide powder can be used. Examples of rare earth metals that can be added to the steel include cobalt, vanadium, and molybdenum. A bit made of sintered diamond, sintered boron nitride, or sintered metal can be used as a rough surface forming bit without being processed, and may be processed with a high energy beam as described above.

(Manufacturing method of light diffusion plate: molding of resin material)
Subsequently, the light diffusing plate of the present invention can be obtained by molding a resin material using the stamper obtained as described above. The molding method is not particularly limited as long as it is a molding method using the stamper, and a molding method such as injection molding or extrusion molding can be adopted. In particular, injection molding is preferable because the molding can be performed efficiently.

Specifically, by arranging the stamper obtained as described above so that the formed concavo-convex structure becomes the cavity surface of the injection mold, the light diffusing plate is formed by injection molding using the resin. Obtainable.

(Rough surface of the obtained molded product)
In the rough surface on the light diffusing plate obtained by the method for manufacturing a light diffusing plate described above, anisotropy occurs in the roughness. That is, since the light diffusing plate was obtained by molding using a stamper in which streaky fine irregularities based on the shape of the notch portion of the rough surface forming bit were formed, the rough surface of the light diffusing plate had its The center line average roughness Ra is minimum in the cutting direction of the cutting tool and is maximum in a direction perpendicular to the cutting direction of the cutting tool.

This will be described with reference to FIG. 13 and FIG. FIG. 13 is an enlarged view of one of the concavo-convex structure in which the regular square pyramid formed on the light emitting surface of the light diffusion plate 101 of the first embodiment shown in FIG. 14 is a perspective view, and FIG. 14 is a plan view of the concavo-convex structure shown in FIG. 13 observed from above. Here, in the case where 311A of the surfaces 311A to 311D is a rough surface, as described above, the cutting is performed by moving the rough surface forming tool parallel to the stamper surface, thereby performing streaking on the surface 311A. These fine irregularities are provided in a direction parallel to the main surface of the light diffusion plate in the surface 311A, which is indicated by an arrow A1401. As a result, the direction in which Ra is maximum is the A1402 direction orthogonal to the arrow A1401. The surface 311A is a surface that is non-parallel to the main surface of the light diffusing plate, and among the lines in the surface 311A, the line parallel to the main surface of the light diffusing plate is only the line in the A1401 direction. The direction is a direction intersecting with the main surface of the light diffusion plate. Such a direction in which the roughness of the rough surface is the maximum is a direction intersecting with the main surface, which is preferable because it is easy to mold and the brightness uniformity can be in a desired state.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 10 is a perspective view schematically showing a surface light source device 1000 including a light diffusing plate 1001 according to the second embodiment of the present invention. FIG. 11 shows the surface light source device 1000 shown in FIG. It is sectional drawing cut | disconnected by the plane perpendicular | vertical to the longitudinal direction of the light source 1011. FIG.

The surface light source device 1000 includes a plurality of linear light sources 1011 arranged in parallel, a reflective plate 1021 that reflects light from the linear light source 1011, and diffuses and emits light incident from the linear light source 1011 and the reflective plate 1021. A light diffusing plate 1001 to be used. As the linear light source used in the present invention, a cathode tube such as a cold cathode tube and a hot cathode tube, an external electrode fluorescent tube (EEFL), a xenon lamp, a xenon mercury lamp, and a light emitting diode (LED) are linearly arranged. A combination of an LED and a light guide can be used. In this embodiment, a straight tube is used as the linear light source, but a substantially U-shaped tube in which two substantially parallel tubes are connected by a single linear or semicircular tube, An approximately N-shaped tube in which three parallel tubes are connected by two linear or semicircular tubes, and an approximately N-shaped tube in which approximately four parallel tubes are connected by three linear or semicircular tubes A W-shaped tube can be listed. Further, as the reflector, the same one as in the first embodiment described above can be used.

As shown in FIG. 11, the light diffusing plate 1001 in the second embodiment has a light incident surface 1001A and a light emitting surface 1001B, and the light incident surface 1001A is a smooth surface, while the light emitting surface 1001B is uneven. As a structure, it has a convex linear prism 1311 having a triangular cross section and two surfaces each. A plurality of linear prisms 1311 are arranged in parallel to form an uneven region on the entire surface of the light emitting surface 1001B. The linear prism 1311 extends in a direction parallel to the longitudinal direction of the linear light source 1011 so that the bright line based on the shape of the linear prism is concealed when observed from the light exit surface, and the luminance uniformity is improved. It is configured to

Here, for example, two surfaces of one of the three linear prisms 1311 have a rough surface, and the three linear prisms can be used as one repeating unit. In such a repeating unit, there are three linear prisms having a concavo-convex structure having two surfaces, two of the six surfaces are rough surfaces, and the ratio of the rough surfaces is 33.3%. . Further, the two surfaces of one linear prism satisfy the requirements (A) to (C), and thus are opposed surfaces.

For example, a method of manufacturing a light diffusing plate having a prism array composed of a plurality of linear prisms such as the light diffusing plate 1001 is prepared by using a stamper having a shape corresponding to the light emitting surface 1001B. The light diffusing plate can be manufactured in the same manner as in the first embodiment described above. In such a stamper, in the preparation of the stamper used in the manufacture of the light diffusing plate of the first embodiment described above, the direction of digging the groove is changed to two directions orthogonal to each other, and in addition, It can be prepared by cutting using a smooth surface forming bit and a rough surface forming bit according to the number of linear prisms having a desired rough surface.

(Other embodiments)
In the present invention, the concavo-convex structure provided on the light diffusing plate is other than the concave structure of the structure in which the regular square pyramid illustrated in the first embodiment is inverted and the convex structure of the linear prism illustrated in the second embodiment. Can be of various forms.

For example, the repeating unit may have a plurality of differently shaped uneven structures. More specifically, the repeating unit may be composed of a plurality of types of quadrangular pyramidal concavo-convex structures having different apex angles, or may be composed of a plurality of types of prismatic concavo-convex structures having different apex angles. Good. In addition, the concavo-convex structure may be a truncated pyramid shape obtained by cutting and flattening the top of a pyramid, or a linear prism having a cross section other than a triangle such as a pentagon or a heptagon.

Further, the direction in which the Ra of the rough surface is maximized is not necessarily limited to the arrow A1402 (FIG. 13) direction shown in the first embodiment, and the maximum centerline average roughness direction may be set to any other direction depending on the manufacturing method. It can be a direction. For example, as in Example 8 described later, by cutting the stamper while vibrating the cutting tool, the direction in which the Ra of the rough surface is maximized can be set to a direction other than the arrow A1402. However, from the viewpoint of efficient manufacturing, fine uneven lines are provided in the cutting direction of the cutting tool, and the direction in which the Ra of the rough surface is minimum is parallel to the main surface of the light diffusion plate, and the direction in which the maximum is the maximum It is preferable that the direction is perpendicular to the rough surface.

In the present invention, the concavo-convex structure group in which predetermined repeating units are periodically arranged may be formed only on the light emitting surface as in the above embodiments, but is not limited thereto, and only the light incident surface. The concavo-convex structure group may be formed on both the light incident surface and the light emitting surface. Further, the predetermined repeating unit may be periodically arranged on a part of the light incident surface and / or the light emitting surface instead of the entire surface.

Applications of the surface light source device of the present invention include backlights such as liquid crystal display devices, illumination devices for illuminating indoor and outdoor environments, and backlight devices such as advertisements and signboards.

(Display device)
The display device of the present invention includes an object to be illuminated and the surface light source device of the present invention. Specifically, in addition to the surface light source device, a liquid crystal display device having liquid crystal cells of various display modes as an object to be illuminated and emitting light emitted from the surface light source device from the display surface through the liquid crystal cell. Can do. The display device of the present invention includes, for example, twisted nematic (TN) mode, super twisted nematic (STN) mode, hybrid alignment nematic (HAN) mode, vertical alignment (VA) mode, multi-domain vertical alignment (MVA) mode, in-plane switching. A liquid crystal display device with a display mode such as an (IPS) mode or an optically compensated birefringence (OCB) mode can be obtained.

In addition to the liquid crystal cell, the display device of the present invention includes a translucent plate-like member on which characters, colors, figures, and the like are drawn, which can be used as an object to be illuminated, such as an advertisement or a signboard. it can.

The light diffusing plate, the manufacturing method thereof, the surface light source device, and the display device of the present invention are not limited to the above-described embodiments, and can be modified within the scope of the claims of the present application and within the equivalent scope thereof. Moreover, other arbitrary components can be further included. For example, in the surface light source device according to each of the embodiments, an optical member for further improving luminance and luminance uniformity may be appropriately arranged. Examples of such an optical member include a diffusion sheet and a prism sheet. These optical members can be provided on the light exit surface side of the light diffusion plate, for example. In addition, a housing for forming the surface light source device, a power supply device, and the like can be provided as appropriate. In addition, the surface light source device of the present invention can be suitably used for a method of controlling turning on and off of the light source according to the brightness in the screen of the display device.

Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example. In the following, “parts” and “%” relating to the amount ratio of components are based on parts by weight unless otherwise specified.

<Example 1>
A surface light source device 100 having a light diffusing plate 101 having a square pyramid inverted concavo-convex shape schematically shown in FIG. 1 was manufactured and evaluated.

(1-1: Preparation of stamper)
Nickel-phosphorous electroless plating with a thickness of 100 μm was applied to the entire surface of a rectangular plate made of stainless steel SUS430 having dimensions of 170 mm × 170 mm and a thickness of 2 mm. Next, a single crystal diamond tool (trade name “New Divide”, manufactured by Allied Materials) is used for the smooth surface forming tool, and a sintered diamond tool (product name “PCD”, manufactured by Allied Material) is used for the tool for forming the rough surface. The cross section isosceles with a width of 70 μm, a height of 35 μm, a pitch of 70 μm, and an apex angle of 90 ° along the direction that makes an angle of 30 ° and 120 ° with the short side of the plate relative to the nickel-phosphorous electroless plating surface A plurality of triangular linear portions were cut to form a concavo-convex structure in which quadrangular pyramidal projections were arranged without gaps, and a stamper was obtained. A part of the four slopes of the quadrangular pyramid-shaped protrusions was formed with a rough surface forming tool to make a rough surface.

(1-2: Preparation of light diffusion plate pellets)
99.85 parts of a resin having an alicyclic structure (Zeon Corporation, ZEONOR 1060R, water absorption 0.01%), which is a transparent resin, and a crosslinked product of a polysiloxane polymer having an average particle diameter of 2 μm as a light diffusing agent Then, 0.15 part of the resulting fine particles were mixed, kneaded with a twin-screw extruder, extruded into a strand, and cut with a pelletizer to produce a light diffusion plate pellet. Using this light diffusion plate pellet as a raw material, an injection molding machine (clamping force 1000 kN) was used to mold a 100 mm × 50 mm test plate with a smooth thickness of 2 mm on both sides. The total light transmittance and haze of this test plate were measured using an integrating sphere type color difference turbidimeter based on JIS K7361-1 and JIS K7136. The test plate had a total light transmittance of 92% and a haze of 93%.

(1-3: Molding of light diffusion plate)
A mold was prepared, and the stamper obtained in (1-1) was attached to one mold constituting the mold, and the cavity surface of the other mold was a smooth surface. Using an injection molding machine having such a mold (clamping force 4,410 kN), the conditions for a cylinder temperature of 280 ° C. and a mold temperature of 85 ° C. using the light diffusion plate pellet obtained in (1-2) as a raw material A light diffusion plate was formed below. In the molding of 100 shots, the number of times the light diffusing plate was adhered to the stamper was measured to evaluate the mold release property. The result was 0 times.

The obtained light diffusing plate 101 has a rectangular shape with a thickness of 2 mm and 150 mm × 150 mm to which the uneven structure of the stamper is transferred, and one surface thereof has an inverted quadrangular pyramid shape shown in FIGS. A concave-convex structure was formed in which the concave structures were arranged without gaps. The

base directions

211 and 212 of the quadrangular weight are orthogonal to each other, and the angle θ2 formed by the base direction 212 and the side 213 of the light diffusion plate 101 is 30 °. The apex angle θ311 of the depression of the square pyramid was 90 °, the bottom surface was square, and the length of the base 311 was 70 μm.

Each of the quadrangular pyramid-shaped depressions has four inclined surfaces 311A to 311D, and a part of them has a rough surface corresponding to the rough surface of the stamper formed by the rough surface forming tool.
The arrangement of the rough surface will be described with reference to FIG. As shown in FIG. 5, the surface of the stamper corresponding to the surface along a part of the lines 211-1, 211-2, 211-3,. Was formed with a rough surface forming tool, so that the rough surface appeared periodically. Although FIG. 5 shows an example in which every other rough surface is formed, in this embodiment, the rough surface is formed in one of 25, and as a result, the ratio of the rough surface in the uneven region is as follows. 2%.

The rough surface on the slope of the quadrangular pyramid-shaped depression is formed by traces of the movement of the cutting tool in the direction of arrow A1401 parallel to the bottom side 211 of the quadrangular pyramid, as shown in FIGS. In the direction of an arrow A1402, the centerline average roughness Ra is maximized, and in the direction of the arrow A1401, the centerline average roughness Ra is minimized. Table 1 shows the results of measuring the maximum center line average roughness Ra (max) and the minimum center line average roughness Ra (min) on a rough surface using NewView 600 manufactured by ZYGO.

(1-4: Manufacturing and evaluation of surface light source device)
A reflective sheet (RF188, manufactured by Tsujiden Co., Ltd.) is attached to the inner surface of a milky white plastic case having an inner dimension of 150 mm, a short side of 150 mm, and a depth of 20 mm to form a reflector. On the reflector, LED ( 36 high-brightness chip LEDs “1306L” manufactured by Stanley) were arranged in the arrangement shown in FIG. The LED spacings 113W and 113L were 25 mm. A wiring for energization was connected to each LED.

Next, the light diffusing plate obtained in (1-3) was placed so that the surface having the concavo-convex structure was opposite to the light source (light emitting surface side), and placed on the plastic case. The distance between the reflector on the bottom of the case and the light incident surface of the light diffusing plate was 20 mm. Furthermore, a diffusion sheet (“188GM3”, manufactured by Kimoto), a prism sheet (“BEFIII”, manufactured by Sumitomo 3M), and a diffusion sheet (“188GM3”, manufactured by Kimoto) are installed in this order on the light diffusion plate. did. The prism array direction of the prism sheet was parallel to the LED array direction. Thus, a surface light source device 100 having a plurality of light sources 111, a reflecting plate 121, and a light diffusing plate 101 as schematically shown in FIG.

Next, a current of (R / G / B) = 20/20/20 mA is applied to each of the obtained surface light source LEDs to light them, and the light emission surface is measured using a two-dimensional color distribution measuring device. The luminance of 100 points in the front direction is measured at equal intervals on a line that is equidistant (75 mm) from both short sides, and the luminance average value La and luminance unevenness Lu are calculated according to the following

equations

1 and 2. Obtained. At this time, the luminance average value was 3240 cd / m ² and the luminance unevenness was 0.4%.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average of maximum brightness values directly above a plurality of or a plurality of cold-cathode tubes or LEDs L2: Average of minimum values sandwiched between maximum values Note that brightness unevenness is an indicator of brightness uniformity. If the brightness unevenness is bad, the numerical value becomes large.

Furthermore, the light emission surface of the surface light source device was observed from a plurality of directions inclined from the front direction. As a result of observation from a plurality of directions of 45 ° polar angles (angles relative to the normal direction of the light exit surface), no difference in luminance unevenness depending on the observation direction was observed.

<Example 2>
A surface light source device was manufactured in the same manner as in Example 1, except that the arrangement of the rough surface on the light exit surface of the light diffusing plate was changed as described below.
In the first embodiment, the rough surface is arranged such that the surface along one of 25 lines out of the one-way lines 211-1, 211-2, 211-3,. In this example, as shown in FIG. 5, every other rough surface was formed, and as a result, the ratio of the rough surface in the uneven region was 25%.
The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Example 3>
A surface light source device 1000 having a light diffusing plate 1001 having a concavo-convex shape of a linear prism schematically shown in FIGS. 10 and 11 was manufactured and evaluated.

(3-1: Preparation of stamper)
Nickel-phosphorous electroless plating with a thickness of 100 μm was applied to the entire surface of a rectangular plate made of stainless steel SUS430 having a long side of 720 mm × a short side of 420 mm and a thickness of 2 mm. Next, using a tool for forming a smooth surface (trade name “New Divide”, manufactured by Allied Materials) and a tool for forming a rough surface (trade name “PCD”, manufactured by Allied Materials), the nickel-phosphorous electroless plating surface was applied. On the other hand, along the direction parallel to the long side, a plurality of linear parts having an isosceles triangular section with a width of 70 μm, a height of 29.4 μm, a pitch of 70 μm, and an apex angle of 100 ° are cut to obtain a linear prism. A concavo-convex structure having a shape arranged without gaps was formed to obtain a stamper. A part of the surface of the linear prism was formed with a rough surface forming tool to obtain a rough surface.

(3-2: Preparation of light diffusion plate pellets)
99.7 parts of a resin having an alicyclic structure (Zeon Corporation, ZEONOR 1060R, water absorption 0.01%), which is a transparent resin, and a crosslinked product of a polysiloxane polymer having an average particle diameter of 2 μm as a light diffusing agent The resulting fine particles (0.3 parts) were mixed, kneaded with a twin-screw extruder, extruded into a strand shape, and cut with a pelletizer to produce a light diffusion plate pellet. Using this light diffusion plate pellet as a raw material, a 100 mm × 50 mm test plate having a smooth thickness of 2 mm on both sides was formed using an injection molding machine (clamping force 1000 kN). The total light transmittance and haze of this test plate were measured using an integrating sphere type color difference turbidimeter based on JIS K7361-1 and JIS K7136. The test plate had a total light transmittance of 86% and a haze of 99%.

(3-3: Molding of light diffusion plate)
A mold was prepared, and the stamper obtained in (3-1) was attached to one mold constituting the mold, and the cavity surface of the other mold was a smooth surface. Using an injection molding machine having such a mold (clamping force 4,410 kN), the conditions for a cylinder temperature of 280 ° C. and a mold temperature of 85 ° C. using the light diffusion plate pellet obtained in (3-2) as a raw material A light diffusion plate was formed below. In the molding of 100 shots, the number of times the light diffusing plate was attached to the stamper was measured to evaluate the releasability. The result was 0 times.

The obtained light diffusing plate 1001 has a rectangular shape with a thickness of 2 mm, a long side of 700 mm and a short side of 400 mm, to which the concavo-convex structure of the stamper is transferred, and one surface thereof is along a direction parallel to the long side. A concavo-convex structure having a shape in which linear prisms having an isosceles triangular shape with a width of 70 μm, a height of 29.4 μm, a pitch of 70 μm, and an apex angle of 100 ° are arranged without gaps was formed. The surface on the stamper corresponding to a part of the linear prisms was formed with a rough surface forming tool so that the rough surface appeared periodically. A rough surface was formed on one of the 50 linear prisms. As a result, the ratio of the rough surface in the uneven region was 2%.

The rough surface on the inclined surface of the linear prism is formed by traces of the movement of the cutting tool parallel to the extending direction of the linear prism. Therefore, the center line average roughness Ra is maximized in the direction orthogonal to the linear prism. In the direction parallel to the extending direction, the center line average roughness Ra was minimized.

(3-4: Manufacturing and evaluation of surface light source device)
A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) was attached to the inner surface of a milky white plastic case having an inner length of 700 mm, a short side of 400 mm, and a depth of 20 mm to obtain a reflector. 10 cold cathode fluorescent lamps having a diameter of 3.0 mm and a length of 32 inches (81.3 cm), the longitudinal direction is parallel to the long side direction of the case, and the distance 1131 (FIG. 11) between the tube center line and the case bottom is 5 mm. It was fixed in the case. The distance 1141 between the centers of adjacent cold-cathode tubes was 40 mm. Each cold cathode tube was connected to a wiring for energization.

Next, the light diffusing plate obtained in (3-3) was placed so that the surface having the concavo-convex structure was opposite to the light source (light emitting surface side), and placed on the plastic case. The distance 1132 between the reflecting plate on the bottom of the case and the light incident surface of the light diffusing plate was 20 mm. Furthermore, a diffusion sheet (“188GM3”, manufactured by Kimoto), a prism sheet (“BEFIII”, manufactured by Sumitomo 3M), and a diffusion sheet (“188GM3”, manufactured by Kimoto) are installed in this order on the light diffusion plate. did. The prism array direction of the prism sheet was parallel to the cold cathode tube array direction. Thus, a surface light source device 1000 having a plurality of linear light sources 1011, a reflecting plate 1021, and a light diffusing plate 1001 as schematically shown in FIG. 10 was produced.

Next, a current of a tube current of 5 mA is applied to each of the obtained cold-cathode tubes of the surface light source to light it, and from both short sides on the light emission surface using a two-dimensional color distribution measuring device. The luminance in the front direction at 100 points was measured at equal intervals on a line at the equidistant (350 mm) position, and the luminance average value La and luminance unevenness Lu were obtained according to Equation 1 and Equation 2 above. At this time, the luminance average value was 6250 cd / m ² and the luminance unevenness was 0.7%.

<Example 4>
A surface light source device was manufactured in the same manner as in Example 3 except that the arrangement of the rough surface on the light exit surface of the light diffusing plate was changed as described below.
In Example 3, a rough surface was formed on one of the 50 linear prisms, but in this example, a rough surface was formed on one of the three, and as a result, the ratio of the rough surface in the uneven region. Was 33%.
The obtained surface light source device was evaluated in the same manner as in Example 3, and the results are shown in Table 1.

<Example 5>
A surface light source device was manufactured in the same manner as in Example 3 except that the procedure was changed as follows.

In (3-1), the concavo-convex structure of the stamper was changed, and a stamper for the concavo-convex structure on the light incident surface side was separately produced.
In (3-2), the ratio of resin and fine particles was changed to 99.9 parts and 0.10 parts, respectively. The total light transmittance of the test plate was 94%, and the haze was 89%.
In (3-3), a stamper was also attached to the surface on the light incident surface side of the mold to perform molding. The obtained light diffusing plate has a rectangular shape with a thickness of 2 mm, a long side of 700 mm and a short side of 400 mm, to which the concavo-convex structure of the stamper is transferred, and the light emitting surface side has a surface parallel to the long side. A concavo-convex structure having a shape in which linear prisms having an isosceles triangular section with a width of 70 μm, a pitch of 70 μm, and an apex angle of 110 ° are arranged without gaps. The surface of the stamper corresponding to a part of the linear prisms is formed with a rough surface forming tool so that the rough surface appears periodically. A rough surface was formed on one of the 50 linear prisms. As a result, the ratio of the rough surface in the uneven region was 2%. On the other hand, on the light incident surface side, a concavo-convex structure in which linear prisms having an isosceles triangular shape with a width of 70 μm, a pitch of 70 μm, and an apex angle of 140 ° are arranged without gaps along a direction parallel to the long side. Was formed. The surfaces of the linear prisms on the light incident surface side were all smooth surfaces.

In (3-4), the case was changed to a depth of 9 mm. The cold cathode tube was changed to 3.4 mm in diameter, the number was changed to 14, the distance between the tube center line and the case bottom was 2.5 mm, and the distance between the centers of adjacent cold cathode tubes was 28 mm. . The distance between the reflector on the bottom of the case and the light incident surface of the light diffusing plate was 9 mm.

The obtained surface light source device was evaluated in the same manner as in Example 3, and the results are shown in Table 1.

<Example 6>
The roughness of the rough surface is the same as in Example 1 except that “PCBN” (trade name, manufactured by Nagoya Diamond Co., Ltd.) is used instead of “PCD” manufactured by Allied Materials as the rough surface forming tool. A surface light source device identical to that of Example 1 was manufactured except for the difference.
The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Example 7>
Example 1 except that instead of “PCD” manufactured by Allied Materials, the cutting part of “New Debite” was subjected to the processing shown in FIGS. 8 and 9 as the rough surface forming tool. The same surface light source device as that of Example 1 was manufactured except that the roughness of the rough surface was different.

As shown in FIG. 8, a processing portion 813 was periodically provided on a part of each of the

edges

801 and 802 of the cutting portion of the cutting tool 800. The length 821 of the non-machined part 811 from the tip 800P to the first machined part was 4.6 μm, and four machined parts 813 were provided in the subsequent area of 36.5 μm (arrow 822). The length 823 of the processed part 813 was 4.0 μm, and the length 824 of the non-processed part 814 between the processed parts 813 was also 4.0 μm. As shown in FIG. 9, two notches were formed in the processed portion 823. The notch width 823A was 2.0 μm and the notch apex angle θ 823 was 90 °. Formation of such a notch was performed using a focused ion beam (FIB) apparatus (manufactured by Hitachi High-Technology Corporation).

The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Example 8>
The same rough surface forming tool as that used for forming a smooth surface (trade name “New Debite”, manufactured by Allied Materials) is used. When forming the rough surface of the stamper, the tool is moved up and down (perpendicular to the main surface of the stamper). The surface is the same as that of Example 1 except that the cutting surface is roughened by performing cutting while oscillating 0.4 μm in the direction), except that the rough surface is operated in the same manner as in Example 1. A light source device was manufactured.

The rough surface on the slope of the quadrangular pyramid-shaped depression has the maximum centerline average roughness Ra in the direction of arrow A1401, which is the direction parallel to the base 211 of the quadrangular pyramid shown in FIGS. 13 and 14, and the arrow A1402 In this direction, the center line average roughness Ra was minimized. Table 1 shows the results of measuring the maximum center line average roughness Ra (max) and the minimum center line average roughness Ra (min) on a rough surface using NewView 600 manufactured by ZYGO.

Further, the obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Comparative Example 1>
A surface light source device was manufactured in the same manner as in Example 1, except that the arrangement of the rough surface on the light exit surface of the light diffusing plate was changed as described below.
In the first embodiment, the rough surface is arranged in one of 25 lines out of the unidirectional lines 211-1, 211-2, 211-3,... Corresponding to the base of the quadrangular pyramid as shown in FIG. In this comparative example, as shown in FIG. 7, 311A and 311D out of the four surfaces 311A to 311D of the quadrangular pyramid-shaped depressions are made rough as shown in FIG. As a result, the ratio of the rough surface in the uneven region was 50%.
In order to obtain such a light diffusing plate, in this comparative example, a notch was provided only on one side of the cutting part of “New Divite” manufactured by Allied Materials as a cutting tool. That is, in the bite shown in FIG. 8, a notch is provided only at the edge 801, and the edge 802 is left in a smooth state. By cutting with this, the above light diffusion plate is formed. A stamper was produced.

The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative example 2>
A surface light source device was manufactured in the same manner as in Example 1 except that the light exit surface of the light diffusion plate was not provided with a rough surface and the concavo-convex structure was entirely composed of a smooth surface.
The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative Example 3>
A surface light source device was manufactured in the same manner as in Example 1 except that the arrangement of the rough surface of the light exit surface of the light diffusing plate was changed as described below.
In the first embodiment, as shown in FIG. 5, the rough surface is arranged along one of 25 lines in one-way lines 211-1, 211-2, 211-3,... Corresponding to the base of the quadrangular pyramid. In this embodiment, as shown in FIG. 6, the surfaces along all the lines in the one-way lines 211-1, 211-2, 211-3,. In the lines 212-1, 212-2, 212-3,... Orthogonal to these lines, the surface along one of the two lines is a rough surface, and as a result, the ratio of the rough surface to the uneven region is 75%.
The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative example 4>
A surface light source device was manufactured in the same manner as in Example 1 except that the rough surface of the light exit surface of the light diffusing plate was arranged in the entire uneven region and the ratio of the rough surface in the uneven region was 100%. .
The obtained surface light source device was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

<Comparative Example 5>
A surface light source device was manufactured in the same manner as in Example 3 except that the light exit surface of the light diffusion plate was not provided with a rough surface and the concavo-convex structure was entirely composed of a smooth surface.
The obtained surface light source device was evaluated in the same manner as in Example 3, and the results are shown in Table 2.

<Comparative Example 6>
A surface light source device was manufactured in the same manner as in Example 3 except that the arrangement of the rough surface of the light exit surface of the light diffusing plate was changed as described below.
In Example 3, a rough surface was formed on one of the 50 linear prisms, but in this comparative example, a rough surface was formed on two of the three, and as a result, the ratio of the rough surface in the uneven region. Was 67%.
The obtained surface light source device was evaluated in the same manner as in Example 3, and the results are shown in Table 2.

<Comparative Example 7>
A surface light source device was manufactured in the same manner as in Example 3 except that the rough surface of the light exit surface of the light diffusing plate was arranged in the entire uneven region and the ratio of the rough surface in the uneven region was 100%. .
The obtained surface light source device was evaluated in the same manner as in Example 3, and the results are shown in Table 2.

Tables 1 and 2 show the results of Examples 1 to 8 and Comparative Examples 1 to 7. In all the examples and comparative examples, Ra (max) of a surface formed as a smooth surface instead of a rough surface among the surfaces of the concavo-convex structure was 30 nm or less.

As is apparent from the results of Tables 1 and 2, the surface light source devices of the examples in which the rough surface of the light diffusing plate is within the specified range of the present invention are arranged so that the rough surfaces do not face each other. Compared to Comparative Example 1, the difference in luminance unevenness depending on the observation direction is small, the releasability is remarkably superior to Comparative Examples 2 and 5 that do not have a rough surface, and the ratio of the rough surface is that of the present invention. Compared with Comparative Examples 3, 4, 6 and 7 which are outside the specified range, the luminance unevenness was very small.

100, 1000 Surface

light source device

101, 1001

Light diffusing plate

111, 1011

Light source

121, 1021 Reflecting plate 311 Concavity and convexity 311A to 311D Surface 311P Concavity and convexity vertex 800

bytes

801, 802 Edge 813 Processing portion 1311 Linear prism

Claims

A light diffusing plate comprising a light incident surface on which light is incident and a light exit surface that is formed on a surface opposite to the light incident surface and diffuses and emits light incident from the light incident surface;
At least one of the light incident surface and the light emitting surface has an uneven region having a plurality of repeating units,
Each of the plurality of repeating units has one or more concavo-convex structures having two or more faces,
Two or more of all the surfaces included in the repeating unit are rough surfaces,
In each of the uneven regions, the ratio of the area of the rough surface to the area of the surface of the entire region where the repeating unit is formed is 50% or less,
A light diffusing plate in which at least one of a plurality of surfaces facing each other with respect to an arbitrary rough surface in the repeating unit is a rough surface.
The light diffusing plate according to claim 1,
The light diffusing plate is characterized in that the uneven structure is a linear prism having a polygonal cross section.
The light diffusing plate according to claim 1,
The light diffusing plate is characterized in that the uneven structure is a polygonal pyramid or its inverted shape.
The light diffusing plate according to claim 1,
The difference in maximum center line average roughness of the facing rough surfaces is within 1.0 μm.
It is a manufacturing method of the light diffusing plate according to claim 1,
Manufacturing comprising: cutting a mold material using a cutting tool to prepare a mold including a surface corresponding to the uneven region; and molding a resin material using the mold Method.
It is a manufacturing method of the light diffusing plate according to claim 5,
Of the surfaces corresponding to the concavo-convex region in the mold, the cutting tool that cuts the surface corresponding to the rough surface is a cutting tool including single crystal diamond or single crystal boron nitride, and cutting of the mold material A manufacturing method characterized in that a cutting surface of the cutting surface is processed prior to processing.
A surface light source device comprising a light source and the light diffusing plate according to claim 1.
A display device comprising an object to be illuminated and the surface light source device according to claim 7.