WO2010074336A1

WO2010074336A1 - Light-diffusing plate with light-collecting layer

Info

Publication number: WO2010074336A1
Application number: PCT/JP2009/071877
Authority: WO
Inventors: 奥尚規
Original assignee: 住友化学株式会社
Priority date: 2008-12-25
Filing date: 2009-12-24
Publication date: 2010-07-01
Also published as: TW201040586A; JP2010152033A

Abstract

Disclosed is a light-diffusing plate comprised of a light-collecting sheet (41) and a light-diffusing substrate (31), wherein the light-collecting sheet (41) has a condenser lens formation surface and a condenser lens non-formation surface; one surface of said light-diffusing substrate (31) is formed into a corrugated surface (34) where multiple convex parts (32) are formed while forming concave parts (33) between adjacent convex parts (32); the convex part (32) is formed into a quasi-rectangular shape comprising a pair of long sides and a pair of short sides when viewed in a plan view, wherein the long side is 0.8‑2.5mm in length, and the short side is 50‑500µm in length, the light-diffusing substrate (31) and the light-collecting sheet (41) are stacked and integrated by joining the convex parts (32) on the corrugated surface of the light-diffusing substrate (31) and the condenser lens non-formation surface of the light-collecting sheet (41) via an adhesive layer (40); and an air layer (42) is formed between the adhesive layer (40) and the concave parts (33) on the corrugated surface of the light-diffusing substrate (31).

Description

Light diffusion plate with condensing layer

The present invention relates to a light diffusing plate that is prevented from being scratched and has high luminance in the front direction, and also relates to a high-quality surface light source device and liquid crystal display device that have high luminance in the front direction.
In this specification and claims, the term “the center of gravity of the protrusion” means an intersection (intersection) of a pair of diagonal lines of a substantially rectangular shape on the bottom surface of the protrusion that is substantially rectangular in plan view. To do.

As a liquid crystal display device, for example, a configuration in which a surface light source device is disposed as a backlight on the back side of a liquid crystal panel (image display unit) including a liquid crystal cell is known. As the surface light source device for the backlight, a plurality of light sources are arranged in a lamp box (housing), and a light diffusion plate is arranged on the front side of these light sources, and further sufficient luminance is ensured in the front direction. A surface light source device having a configuration in which a lenticular lens as a light condensing sheet is arranged on the front side of a light diffusion plate is known. For example, Japanese Patent No. 3123006 (Patent Document 1) describes a surface light source device having such a configuration.
However, in the surface light source device according to the above configuration, since the light collecting sheet is simply superimposed on the front side of the light diffusing plate, the light diffusing plate and the light collecting sheet are rubbed against each other and easily damaged. There was a problem.
A surface light source device having a configuration in which a lenticular lens is disposed on the front side of a light diffusing plate via an adhesive layer is known as a device that can prevent scratching due to such rubbing (Japanese Patent Laid-Open No. 2006-208930). No. (Patent Document 2)). According to this configuration, since the light diffusing plate and the light condensing sheet are bonded via the pressure-sensitive adhesive layer, the light diffusing plate and the light condensing sheet do not rub against each other, and the occurrence of scratches can be prevented.

However, the latter surface light source device is not always sufficiently improved in luminance in the front direction.
It is an object of the present invention to provide a light diffusing plate that is prevented from being scratched and has high luminance in the front direction, and a high-quality surface light source device and liquid crystal display device that have high luminance in the front direction.
In order to achieve the above object, the present invention provides the following means.
[1] A light diffusing plate comprising a light collecting sheet and a light diffusing substrate,
The condensing sheet has a condensing lens forming surface and a condensing lens non-forming surface,
One surface of the light diffusing substrate is a concavo-convex shape surface in which a plurality of protrusions are formed and a recess is provided between adjacent protrusions,
The protrusion has a substantially rectangular shape having a pair of long sides and a pair of short sides in plan view, and the length of the long side on the bottom surface of the protrusion is 0.8 mm to 2.5 mm. The length of the short side at the bottom of the substrate is 50 μm to 500 μm,
The light diffusing substrate and the light condensing sheet are formed by bonding a projection on the uneven surface of the light diffusing substrate and a light condensing lens non-forming surface of the light condensing sheet via an adhesive layer. Are laminated and integrated, and a light diffusing plate in which an air layer is formed between the pressure-sensitive adhesive layer and the concave portion of the concavo-convex shape surface of the light diffusing substrate.
[2] The light diffusing plate according to [1], wherein the plurality of protrusions are substantially parallel to each other in the length direction.
[3] The light diffusing plate according to [2], wherein the protrusions adjacent in the long side direction are spaced apart from each other at a constant interval, and the protrusions adjacent in the short side direction are spaced apart from each other at a constant interval.
[4] When the distance between the centroids of the protrusions adjacent to each other in the long side direction is U, the barycentric position of the protrusions in the protrusion group forming a line in the long side direction is the short side with respect to the protrusion group. 4. The preceding item 3, wherein a distance of U / 2.2 to U / 1.8 is separated in the long side direction from the position of the center of gravity of the closest protrusion among the plurality of protrusions constituting the adjacent protrusion group adjacent in the direction. Light diffusing plate.
[5] When the distance between the centers of gravity of the protrusions adjacent in the long side direction is U, and the length of the long side on the bottom surface of the protrusion is T,
1.3 ≦ U / T ≦ 2.2
Is established,
When the distance between the centers of gravity of the protrusions adjacent to each other in the short side direction is F and the length of the short side on the bottom surface of the protrusion is L, F is 400 μm or more and 5.0 mm or less,
8.0 ≦ F / L
5. The light diffusing plate according to 3 or 4 above, wherein
[6] The light diffusing plate according to any one of 1 to 5 above and a plurality of light sources arranged on the back side of the light diffusing plate, so that the light condensing sheet is on the front side. A surface light source device in which the light diffusion plate is disposed.
[7] The light diffusing plate according to any one of 1 to 5 above, a plurality of light sources arranged on the back side of the light diffusing plate, a liquid crystal panel arranged on the front side of the light diffusing plate, A liquid crystal display device in which the light diffusing plate is arranged so that the light condensing sheet is on the front side.
In the invention of [1], the projections of the concavo-convex shape surface of the light diffusing substrate and the surface on which the light condensing lens of the light condensing sheet is not formed are bonded via the adhesive layer. The substrate and the light collecting sheet do not rub against each other, and the occurrence of scratches on the light diffusing plate is prevented. Moreover, since an air layer exists between the pressure-sensitive adhesive layer and the concave portion of the concavo-convex shape surface of the light diffusing substrate, high brightness is obtained in the front direction. Further, the plurality of protrusions formed on the surface of the light diffusing substrate have a long side length of 0.8 mm to 2.5 mm and a short side length of 50 μm to 500 μm in plan view. Because of the rectangular shape, it is possible to avoid the influence of these protrusions on the optical function of the light diffusing plate and the image quality of the display image. Furthermore, the air layer can be formed by simply laminating the light diffusing substrate having the specific uneven surface on one side and the light condensing sheet via an adhesive layer. Since the protrusion serves as a spacer to secure an air layer, it is excellent in productivity.
In the invention of [2], since the plurality of protrusions are substantially parallel to each other in the length direction, sufficient bonding strength can be secured in the length direction of the protrusion, and along the length direction of the protrusion. Thus, it is difficult to separate the light diffusing substrate and the light collecting sheet.
In the invention of [3], the protrusions adjacent in the long side direction are spaced apart from each other at a constant interval, and the protrusions adjacent in the short side direction are spaced apart from each other at a constant interval. It is possible to more avoid the influence of these protrusions on the function and the display image quality.
In the invention of [4], when the distance between the centroids of the projections adjacent in the long side direction is U, the barycentric position of the projections in the projection group forming a line in the long side direction is the projection group. On the other hand, a distance of U / 2.2 to U / 1.8 is separated in the long side direction from the barycentric position of the closest protruding part among the plurality of protruding parts constituting the adjacent protruding part group adjacent in the short side direction. Therefore, even if the interval between the protrusions adjacent to each other in the long side direction or the interval between the protrusions adjacent to each other in the short side direction is large, Is prevented from coming into contact with or in close proximity to the concave portion of the concavo-convex shape surface of the light diffusing substrate, and thereby a sufficient air layer is secured, so that the luminance in the front direction can be further improved.
In the invention of [5], when the distance between the centers of gravity of the protrusions adjacent in the long side direction is U and the length of the long side on the bottom surface of the protrusion is T, 1.3 ≦ U / T ≦ 2. Since the relational expression 2 is established, it is possible to prevent the light collecting sheet from being bent and coming into contact with or coming close to the concave portion of the uneven surface of the light diffusing substrate. Since the layer is secured, the luminance in the front direction can be further improved, the distance between the centers of gravity of the protrusions adjacent in the short side direction is F, and the length of the short side on the bottom surface of the protrusion is L. In this case, F is 400 μm or more and 5.0 mm or less, and the relational expression of 8.0 ≦ F / L is established, so that it is formed between the pressure-sensitive adhesive layer and the concave portion of the concavo-convex shape surface of the light diffusing substrate. Air gaps can be widened in the short side direction to transmit light with higher transmittance. Since it is possible to, it can be increased more brightness in the front direction.
In the invention of [6], a surface light source device is provided in which the light diffusing plate is prevented from being damaged and high-quality light with high brightness in the front direction can be obtained.
In the invention of [7], a liquid crystal display device is provided in which the light diffusing plate is prevented from being damaged and a high-quality image with high brightness in the front direction can be obtained.

FIG. 1 is a schematic view showing an embodiment of a liquid crystal display device according to the present invention.
FIG. 2 is a cross-sectional view showing an embodiment of a light diffusing plate according to the present invention.
FIG. 3 is a cross-sectional view showing a light diffusing substrate.
FIG. 4 is a plan view showing an example of the arrangement of the protrusions on the light diffusing substrate.
FIG. 5 is a plan view showing an arrangement mode of protrusions (projections) in the light diffusing substrates of Comparative Examples 2 and 3. FIG.

An embodiment of a liquid crystal display device according to the present invention is shown in FIG. In FIG. 1, (30) is a liquid crystal display device, (11) is a liquid crystal cell, (12) and (13) are polarizing plates, and (1) is a surface light source device (backlight). Polarizing plates (12) and (13) are respectively arranged on the upper and lower sides of the liquid crystal cell (11), and a liquid crystal panel (20) as an image display unit is constituted by these constituent members (11), (12) and (13). Yes. In addition, as the liquid crystal cell (11), those capable of displaying a color image are preferably used.
The said surface light source device (1) is arrange | positioned at the lower surface side (back side) of the polarizing plate (13) below the said liquid crystal panel (20). That is, this liquid crystal display device (30) is a direct liquid crystal display device.
The surface light source device (1) is a thin box-shaped lamp box (5) having a rectangular shape in plan view and having an upper surface side (front surface side) opened, and the lamp box (5) spaced apart from each other. And a light diffusion plate (3) disposed on the upper side (front side) of the plurality of light sources (2). The said light diffusing plate (3) is mounted and fixed with respect to the said lamp box (5) so that the open surface may be block | closed. A light reflecting layer (not shown) is provided on the inner surface of the lamp box (5). In the present embodiment, a linear light source such as a cold cathode ray tube is used as the light source (2).
As shown in FIG. 2, the light diffusing plate (3) includes a light diffusing substrate (31), a light collecting sheet (41), and an adhesive layer (40) arranged in parallel to each other. The light diffusing substrate (31) has a large number of protrusions (32) formed on the surface, and a recess (a flat portion in this embodiment) between adjacent protrusions (32) (33). ) Is provided on one side (see FIG. 3). The projection (32) of the uneven surface (34) of the light diffusing substrate (31) and the non-condensing lens forming surface (on the side where the condensing lens is not formed) of the condensing sheet (41). Surface) is bonded via the pressure-sensitive adhesive layer (40), whereby the pressure-sensitive adhesive layer (40) and the concave-convex surface (34) of the light-diffusing substrate (31) are recessed (33). The light diffusing substrate (31) and the light condensing sheet (41) are laminated and integrated in a state where the air layer (42) is present (see FIG. 2). In addition, the said adhesive layer (40) is laminated | stacked on the substantially whole surface of the single side | surface of the said condensing sheet | seat (41) without gap.
The protrusion (32) has a substantially rectangular shape having a pair of long sides (35) and (35) and a pair of short sides (36) and (36) in plan view (see FIG. 4). The long side length (T) of the bottom surface (surface connected to the light diffusing substrate) of the projection (32) is set to 0.8 mm to 2.5 mm, and the bottom surface (light diffusion of the projection (32)). The length (L) of the short side of the surface connected to the conductive substrate is set to 50 μm to 500 μm.
As shown in FIG. 4, these multiple protrusions (32) are arranged in a scattered state over the whole in a plan view. A large number of protrusions (32) are arranged in a zigzag shape in plan view. In the present embodiment, the protrusions (32) adjacent in the long side direction are spaced apart from each other at a constant interval, and the protrusions (32) adjacent in the short side direction are spaced apart from each other at a constant interval. (See FIG. 4). The constant separation interval in the long side direction and the constant separation interval in the short side direction may be different or the same.
In the present embodiment, the projecting portion (32) has a substantially semicircular cross section (see FIGS. 2 and 3). That is, in the present embodiment, the protrusion (32) is a cylindrical lens-shaped protrusion (substantially semi-cylindrical protrusion), and the plurality of cylindrical lens-shaped protrusions (32) are: They are arranged so as to be substantially parallel to each other in the length direction (axial direction) (see FIG. 4). The cylindrical lens shape means that a substantially cylindrical body is cut by a plane parallel to the axial direction (length direction) (a plane including the axis or a plane not including the axis). The shape corresponding to any one of the members is meant.
In the present embodiment, the cylindrical lens-shaped protrusion (32) is a protrusion having a semi-cylindrical shape, that is, any one of the cylindrical bodies cut into two equally on a plane including the axis thereof. It is a protrusion part provided with the shape equivalent to one member (semi-cylindrical body). The flat surface (cut surface) of the protrusion (32) having a semi-cylindrical shape is connected to the surface of the light diffusing substrate (31) (see FIGS. 2 and 3). It arrange | positions so that the circular arc surface of the protrusion part (32) which consists of the said semi-cylindrical shape may protrude toward the said condensing sheet | seat (41) side (refer FIG. 2).
In this embodiment, a linear light source is used as the light source (2), and the length direction of the linear light source (2) and the cylindrical lens-shaped protrusion (32) of the light diffusing substrate (31). ) In the length direction (long side direction). Further, the length direction (long side direction) of the cylindrical lens-shaped protrusion (32) is arranged so as to substantially coincide with the longitudinal direction of the light diffusion plate (3).
In the liquid crystal display device (30), the light diffusing plate (3) is disposed such that the light condensing sheet (41) is on the front side (the liquid crystal panel (20) side) (see FIG. 1). . That is, in other words, in the liquid crystal display device (30), the light diffusing plate (3) is disposed such that the light diffusing substrate (31) is on the back side (light source (2) side). (See FIG. 1).
In the light diffusing plate (3) according to the above configuration, the projections (32) of the concavo-convex shape surface (34) of the light diffusing substrate (31) and the condensing lens non-forming surface of the light condensing sheet (41) are adhered. Since it is joined via the agent layer (40), the light diffusing substrate (31) and the light condensing sheet (41) do not rub against each other, and the light diffusing plate (3) is prevented from being damaged. Yes. Moreover, the light diffusing plate (3) according to the above configuration has an air layer between the pressure-sensitive adhesive layer (40) and the concave portion (flat portion) (33) of the uneven surface (34) of the light diffusing substrate (31). (42) exists, the front light source device (1) can be illuminated with high luminance in the front direction (normal direction) (Q), and the front direction (normal line) in the liquid crystal display device (30). An image can be displayed with high brightness in the direction (Q). Furthermore, the projection (32) having a substantially rectangular shape with a long side length (T) of 0.8 mm to 2.5 mm and a short side length (L) of 50 μm to 500 μm in plan view is light diffusive. Since it is formed on the surface of the substrate (31), it is possible to avoid an adverse effect of the projection (32) on the optical function of the light diffusing plate (3) and display an image with high quality image quality. .
In the present invention, the length (T) of the long side of the bottom surface of the protrusion (32) is 0.8 mm to 2.5 mm. If the length (T) is short, there is a problem in the moldability of the protrusion (32), and if it is long, the protrusion (32) is visually recognized through the liquid crystal panel and the image quality is deteriorated.
The length (L) of the short side of the bottom surface of the protrusion (32) is 50 to 500 μm. If the length (L) is short, it is difficult to produce a shape with high accuracy, and if the length (L) is long, the shape of the protrusion (32) may be visually recognized like a streak.
In the present invention, when the distance between the centers of gravity (G) of the protrusions (32) adjacent in the long side direction is U, the position of the center of gravity of the protrusions (32) in the protrusion group forming a line in the long side direction ( G1) is U in the long side direction with respect to the gravity center position (G2) of the closest protrusion part (32) among the plurality of protrusion parts constituting the adjacent protrusion part group adjacent to the protrusion part group in the short side direction. A distance of /2.2 to U / 1.8 is preferable (see FIG. 4). That is, in FIG. 4, it is preferable that the relational expression of K = U / 2.2 to U / 1.8 is established. When this configuration is adopted, even if the interval between the projections (32) adjacent in the long side direction and the interval between the projections (32) adjacent in the short side direction are large, the light collecting sheet (41) is bent and the light condensing sheet (41) is prevented from coming into contact with or in close proximity to the concave portion (33) of the concavo-convex shape surface (34) of the light diffusing substrate (31). Since the layer (42) is secured, the luminance in the front direction can be further improved.
Further, when the distance between the centers of gravity (G) of the protrusions (32) adjacent in the long side direction is U, and the length of the long side (35) on the bottom surface of the protrusion (32) is T,
1.3 ≦ U / T ≦ 2.2
It is preferable that the relational expression is established (see FIG. 4). When this configuration is adopted, a sufficient air layer (42) can be secured when 1.3 ≦ U / T, and the light condensing sheet (41) when U / T ≦ 2.2. Can be prevented.
Further, when the distance between the centers of gravity (G) of the protrusions (32) adjacent in the short side direction is F and the length of the short side (36) on the bottom surface of the protrusion (32) is L,
400μm ≦ F ≦ 5.0mm
8.0 ≦ F / L
It is preferable that the relational expression between the two is established (see FIG. 4). When this configuration is adopted, the air layer (42) formed between the pressure-sensitive adhesive layer (40) and the concave portion (33) of the uneven surface (34) of the light diffusing substrate (31) Since the light can be widened in the short side direction and light can be transmitted with higher transmittance, the luminance in the front direction can be further increased.
That is, when F is 400 μm or more, an air layer (42) is sufficiently formed between the pressure-sensitive adhesive layer (40) and the concave portion (33) of the uneven surface (34) of the light diffusing substrate (31). In addition, the light condensing sheet (41) bends and the light condensing sheet (41) has an uneven surface (34) of the light diffusing substrate (31). Can be prevented from coming into contact with or close to the recess (33). Further, since the relational expression of 8.0 ≦ F / L is established, the air space (42) can be widened in the short side direction, and light can be transmitted with higher transmittance. The luminance in the front direction can be further increased.
In the present invention, any material can be used as the light diffusing substrate (31) as long as it can diffuse transmitted light. Among them, light diffusing particles (light diffusing agent) are dispersed in a transparent material. The plate is preferably used.
The light diffusing substrate (31) is not particularly limited. For example, the light diffusing substrate (31) is composed of a single layer plate made of a transparent resin, one or more other types made of a different transparent resin on at least one surface of a base layer made of a transparent resin. A laminated plate in which layers are laminated is used.
Although it does not specifically limit as a transparent material which comprises the said light diffusable board | substrate (31), For example, transparent resin, inorganic glass, etc. are mentioned. As the transparent resin, a transparent thermoplastic resin is suitably used because it is easy to mold. The transparent thermoplastic resin is not particularly limited. For example, polycarbonate resin, ABS resin (acrylonitrile-butadiene-styrene copolymer resin), methacrylic resin, MS resin (methyl methacrylate-styrene copolymer resin). ), Styrene resin, AS resin (acrylonitrile-styrene copolymer resin), polyethylene terephthalate, olefin resin (polyethylene, polypropylene, cyclic polyolefin, cyclic olefin copolymer, etc.) and the like.
The light diffusing particles are particles that are incompatible with the transparent material constituting the light diffusing substrate (31) and have a refractive index different from that of the transparent resin and can diffuse transmitted light. Anything can be used without particular limitation. For example, inorganic particles such as silica particles, calcium carbonate particles, barium sulfate particles, titanium oxide particles, aluminum hydroxide particles, inorganic glass particles, mica particles, talc particles, white carbon particles, magnesium oxide particles, and zinc oxide particles. Alternatively, organic particles such as methacrylic crosslinked resin particles, methacrylic high molecular weight resin particles, styrene crosslinked resin particles, styrene high molecular weight resin particles, and siloxane polymer particles may be used. As the light diffusing particles, one kind of those exemplified above may be used, or two or more kinds thereof may be mixed and used.
As the light diffusing particles, those having a volume average particle diameter of 0.1 μm to 50 μm are usually used. The volume average particle size (D ₅₀ ) is determined by measuring the particle size and volume of all particles, integrating the volume sequentially from the smallest particle size, and the integrated volume is 50% of the total volume of all particles. The particle diameter of the resulting particles.
The amount of the light diffusing particles used varies depending on the intended degree of diffusion of transmitted light, but the content of the light diffusing particles is usually 0.01 parts by mass to 20 parts by mass with respect to 100 parts by mass of the transparent material. is there. The content of the light diffusing particles with respect to 100 parts by mass of the transparent material is preferably 0.1 to 10 parts by mass.
From the viewpoint of light diffusibility, the absolute value of the difference between the refractive index of the transparent material and the refractive index of the light diffusing particles is preferably 0.02 or more, and the absolute value is 0.13 or less. From the viewpoint of sex. That is, the absolute value of the difference between the refractive index of the transparent material and the refractive index of the light diffusing particles is preferably in the range of 0.02 to 0.13.
The light diffusing substrate (31) may contain various additives such as an ultraviolet absorber, a heat stabilizer, an antioxidant, a weathering agent, a light stabilizer, a fluorescent brightener, and a processing stabilizer. .
The thickness (N) of the light diffusing substrate (31) is usually 0.1 mm to 10 mm.
The cross-sectional shape of the projecting portion (32) is not particularly limited. For example, in addition to a substantially semicircular shape, a substantially semi-elliptical shape, a flat curved line shape, a substantially rectangular shape, a substantially triangular shape, etc. Examples include polygonal shapes.
In the above-described embodiment, the projecting portion (32) has a semicircular cross-sectional shape, and is formed in a cross-sectional shape that is symmetrical with respect to the normal line (perpendicular to the horizontal plane) passing through the center of the circle. However, it is not particularly limited to such a configuration, and the right and left may be formed in a non-axisymmetric cross-sectional shape. For example, the left and right arcs may have a non-linearly symmetric cross-sectional shape in which the left arc swells more to the front side than the right arc. Further, when a triangular shape is employed as the cross-sectional shape of the protrusion (32), it may be an isosceles triangular shape that is symmetrical to the left and right lines, or may be a triangular shape that is asymmetrical to the left and right.
A method for forming the protrusion (32) is not particularly limited, and examples thereof include a thermal transfer method using a mold, an injection molding method, a cutting method, a profile extrusion molding method, and a melt extrusion transfer molding method using an engraving roll. Can be mentioned.
The height (H) of the protrusion (32) is preferably 10 μm to 500 μm (see FIG. 3). When the height (H) is 10 μm or more, a sufficient spacer function can be obtained to sufficiently secure the air layer (42), and when the height (H) is 500 μm or less, the projection (32) can be molded. It will be easy.
The light condensing sheet (41) is not particularly limited. For example, a sheet in which a fine light condensing lens such as a fine prism lens, a fine convex lens, or a lenticular lens is formed over the entire surface of one side. Is mentioned. The transmitted light transmitted while diffusing the light diffusing substrate (31) is condensed in the normal direction (Q) of the light diffusing plate (3) by the condensing sheet (41). This condensing sheet (41) is laminated with the light diffusing substrate (31) with the surface opposite to the side on which the condensing lens is formed (the condensing lens non-forming surface) as an overlapping surface. They are integrated (see FIG. 2).
The material of the light condensing sheet (41) is not particularly limited. For example, polycarbonate resin, ABS resin (acrylonitrile-butadiene-styrene copolymer resin), methacrylic resin, methyl methacrylate-styrene copolymer Examples thereof include polymer resins, polystyrene resins, AS resins (acrylonitrile-styrene copolymer resins), polyolefin resins (polyethylene resins, polypropylene resins, etc.). Although it does not specifically limit as a commercial item of the said condensing sheet | seat (41), For example, Sumitomo 3M "BEF" (brand name) (30-micrometer-thick acrylic type on a 125-micrometer-thick polyester film) A resin layer is formed, and V-grooves having a depth (D) of 25 μm and a groove bottom opening angle of 90 degrees are formed on the surface of the acrylic resin layer at a pitch interval (P) of 50 μm, see FIG. ), “Estina” (trade name) manufactured by Sekisui Film Co., Ltd., and the like.
The light condensing sheet (41) may contain various additives such as an ultraviolet absorber, a heat stabilizer, an antioxidant, a weathering agent, a light stabilizer, a fluorescent brightener, and a processing stabilizer. .
The thickness (C) of the light collecting sheet (41) is preferably 10 μm or more from the viewpoint of securing the bonding strength. In addition, the thickness (C) of the light condensing sheet (41) is determined from the viewpoint of preventing bending, that is, the pressure-sensitive adhesive layer (40) is formed on the concave portion (34) of the concave and convex surface (34) of the light diffusing substrate (31). It is particularly preferably 30 μm or more from the viewpoint of preventing contact with 33) (see FIG. 2). From the viewpoint of cost reduction and thickness reduction of the light diffusion plate to be obtained, the thickness (C) of the light condensing sheet (41) is preferably 500 μm or less.
Although it does not specifically limit as a raw material of the said adhesive layer (40), For example, an acrylic adhesive, a urethane type adhesive, a polyether-type adhesive, a silicone type adhesive etc. are mentioned. Among these, it is preferable to use a colorless and transparent pressure-sensitive adhesive because a higher-quality display image can be formed. As the pressure-sensitive adhesive layer (40), a pressure-sensitive adhesive is usually used. In addition, the refractive index of this adhesive is not specifically limited.
The thickness (M) of the pressure-sensitive adhesive layer (40) is preferably 10 μm to 30 μm (see FIG. 2). When the thickness (M) is 10 μm or more, sufficient bonding strength can be secured, and when the thickness (M) is 30 μm or less, the pressure-sensitive adhesive layer (40) is formed in the concave portion (33) of the light diffusing substrate (31). ) Can be prevented from coming into contact with each other, and a sufficient amount of air space (42) can be secured. In particular, the thickness (M) of the pressure-sensitive adhesive layer (40) is particularly preferably set in the range of 5 μm to 25 μm.
The thickness (E) of the air layer (42) is usually 1 μm to 400 μm, and the preferred thickness (E) is 50 μm to 350 μm (see FIG. 2).
The light diffusing plate (3) of this invention is manufactured as follows, for example. A pressure-sensitive adhesive layer (40) is laminated on one side of the light-collecting sheet (41) by laminating a double-sided pressure-sensitive adhesive film on the surface of the light-collecting sheet (41) where the light-collecting lens is not formed. A light collecting sheet is obtained. You may laminate | stack an adhesive layer (40) on the single side | surface of the said condensing sheet | seat (41) by apply | coating an adhesive to the condensing lens non-formation surface of the said condensing sheet | seat (41). On the other hand, a light diffusing substrate (31) having a concavo-convex surface (34) in which a plurality of protrusions (32) are formed on one side and a recess (33) is provided between adjacent protrusions (32). ) (See FIG. 3). The light diffusing substrate (31) and the light condensing sheet with adhesive (41) are overlapped so that the pressure-sensitive adhesive layer (40) is in contact with the uneven surface (34) of the light diffusing substrate (31). Clamp (press). Thereby, the projection part (32) of the light diffusable substrate (31) and the light condensing lens non-formation surface of the light condensing sheet (41) are joined via the pressure-sensitive adhesive layer (40). A plate (3) is obtained.
In addition, the said manufacturing method is only what showed the example, and the light diffusing plate (3) of this invention is not limited to what was manufactured with such a manufacturing method.
The thickness (S) of the light diffusion plate (3) of the present invention is not particularly limited, but is preferably 1 mm to 5 mm (see FIG. 2). The size (area) of the light diffusing plate (3) of the present invention is not particularly limited. For example, depending on the size of the target surface light source device (1) or liquid crystal display device (30). Although appropriately set, it is usually designed in a size of 20 cm × 30 cm to 150 cm × 200 cm.
In the surface light source device (1) and the liquid crystal display device (30) of the present invention, the light source (2) is not particularly limited. For example, a linear light source such as a fluorescent tube, a halogen lamp, or a tungsten lamp is used. In addition, a point light source such as a light emitting diode (LED) is used.
The light diffusing plate (3), the surface light source device (1), and the liquid crystal display device (30) according to the present invention are not particularly limited to those of the above-described embodiment, and the spirit is within the scope of the claims. Any design changes are allowed as long as they do not deviate from.

Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.
<Raw materials>
(Light diffusing substrate material)
Transparent resin A: Styrene resin (Toyo Styrene “HRM40”, refractive index 1.59)
Transparent resin B: MS resin (“MS200NT” manufactured by Nippon Steel Chemical Co., Ltd., refractive index 1.57, styrene / methyl methacrylate = 80 parts by mass / 20 parts by mass)
Light diffusing agent A: PMMA crosslinked particles (“SUMIPEX XC1A” manufactured by Sumitomo Chemical Co., Ltd., refractive index 1.49, volume average particle diameter 35 μm)
Light diffusing agent B: crosslinked siloxane-based polymer particles (“Torefill DY33-719” manufactured by Toray Dow Corning Co., Ltd., refractive index 1.42, volume average particle diameter 2 μm).
(Preparation of light diffusing agent master batch A)
52.0 parts by mass of the transparent resin A, 40.0 parts by mass of the light diffusing agent A, 4.0 parts by mass of the light diffusing agent B, and 2.0 of Sumisorb 200 (manufactured by Sumitomo Chemical Co., Ltd.) which is an ultraviolet absorber. After mass blending 2.0 parts by mass of Sumrizer GP (manufactured by Sumitomo Chemical Co., Ltd.), which is a heat stabilizer, this blend is put into a hopper of a 65 mm twin screw extruder, and melt-mixed in a cylinder. The pellet-shaped light diffusing agent masterbatch A was obtained by extruding into a strand and cutting. Extrusion was performed by setting the temperature in the cylinder so that the temperature gradually decreased from the lower part of the hopper (200 ° C.) to the vicinity of the extrusion die (250 ° C.) toward the downstream.
(Preparation of light diffusing agent master batch B)
78.8 parts by mass of the transparent resin B, 20.0 parts by mass of the light diffusing agent A, 1.0 part by mass of LA-31 (manufactured by Asahi Denka Kogyo Co., Ltd.) which is an ultraviolet absorber, and a smilizer which is a heat stabilizer After 0.2 parts by mass of GP (manufactured by Sumitomo Chemical Co., Ltd.) was dry blended, this blended product was put into a hopper of a 65 mm twin screw extruder, melted and mixed in a cylinder, and then extruded into strands and cut. A pellet-like light diffusing agent master batch B was obtained. Extrusion was performed by setting the temperature in the cylinder so that the temperature gradually decreased from the lower part of the hopper (200 ° C.) to the vicinity of the extrusion die (250 ° C.) toward the downstream.
(Condensable sheet A)
Thickness (C) made of transparent PET (polyethylene terephthalate) resin in which V-grooves with a depth (D) of 11.5 μm and a groove bottom opening angle of 90 degrees formed on one side with a pitch interval (P) of 23.0 μm A 60 μm film was used.
<Example 1>
After 97.0 parts by mass of transparent resin A and 5.0 parts by mass of light diffusing agent masterbatch A are dry blended, they are melt-kneaded with a first extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block did. On the other hand, the light diffusing agent master batch B was melt-kneaded by a second extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block.
The resin supplied from the first extruder to the feed block becomes an intermediate layer (base layer), and the resin supplied from the second extruder to the feed block becomes a surface layer (both sides). Co-extrusion molding from a manifold die and clamping and cooling with a polishing roll make a light diffusibility consisting of a 2.0 mm thick three-layer laminate (intermediate layer 1.9 mm, surface layer 0.05 mm × 2) A substrate (31) was produced.
Next, on the entire surface of one side of the obtained light diffusing substrate (31), a cylindrical lens-shaped protrusion (the cross-sectional shape is approximately the same) using a heat press (Shindo ASF hydraulic press, manufactured by Shindo Metal Industry Co., Ltd.). A plurality of semi-cylindrical protrusions) (32) were formed in a projecting manner as shown in FIG. 4 to obtain a light diffusing substrate (31) having a thickness (N) of 2.0 mm (FIG. 3, 4). Note that a number of short concave grooves corresponding to the protrusions are formed on the lower surface (press surface) of the metal mold on the upper side of the hot press machine. Moreover, in the heat press by the said hot press machine, pressurization was performed for about 3 minutes in the state which set the upper surface side temperature of the hot press machine to 160 degreeC, and set the lower surface side temperature to 70 degreeC.
In the uneven surface (34) of the light diffusing substrate (31) thus obtained, the height (H) of the protrusion (32) is 150 μm, and the length (T) of the long side of the protrusion (32) is 800 μm. The distance between the center of gravity (U) between the protrusions adjacent in the long side direction is 1200 μm, the length (L) of the short side of the protrusion (32) is 389 μm, and the distance between the center of gravity between the protrusions adjacent in the short side direction (F) is designed to be 1650 μm and the shift distance (K) is 600 μm (see FIG. 4).
On the other hand, by sticking a double-sided adhesive film to the non-condensing lens forming surface (smooth surface) of the condensing sheet A (41), a thickness (M) of 20 μm is formed on one side of the condensing sheet A (41). The pressure-sensitive adhesive layer (40) was laminated to obtain a light condensing sheet with pressure-sensitive adhesive.
The light diffusing substrate (31) and the pressure-sensitive condensing sheet (41) were overlapped so that the pressure-sensitive adhesive layer (40) was in contact with the uneven surface (34) of the light diffusing substrate (31). Thereafter, a light diffusing plate (3) having a cross-sectional shape shown in FIG.
In this light diffusing plate (3) with a condensing layer, as shown in FIG. 2, the thickness (between the adhesive layer (40) and the concave portion (flat portion) (33) of the light diffusing substrate (31) ( E) An air layer (42) of 130 μm could be formed.
<Comparative Example 1>
A light diffusing plate was produced in the same manner as in Example 1 except that the protrusion (32) was not formed on the light diffusing substrate obtained by coextrusion molding using a hot press. In this light diffusing plate, the light diffusing substrate and the light collecting sheet A are bonded together by the adhesive layer, and there is no air layer between the light diffusing substrate and the light collecting sheet A. The arithmetic average roughness Ra of the surface (superimposed surface) of the light diffusing substrate obtained by coextrusion molding is 4.78 μm, and the ten-point average roughness Rz of the surface irregularities is 28.61 μm. The average interval Rsm of the unevenness was 148 μm.
<Comparative example 2>
Extending continuously from one end side to the other end side along the longitudinal direction of the substrate obtained by changing the shape of the groove on the lower surface (press surface) of the metal mold on the upper side of the hot press machine (length 70 mm) The light diffusing substrate (31) in which a number of cylindrical lens-shaped protrusions (protrusions) (see FIG. 5) are formed in a projecting manner in a parallel manner is used in the same manner as in Example 1. A diffusion plate was produced.
The height (H) of the ridge is 150 μm, the length (L) of the short side of the ridge is 300 μm, and the distance between the centers of gravity (F) between the ridges adjacent in the short side direction is 2250 μm. It was.
<Comparative Example 3>
Extending continuously from one end side to the other end side along the longitudinal direction of the substrate obtained by changing the shape of the groove on the lower surface (press surface) of the metal mold on the upper side of the hot press machine (length 70 mm) (Ii) Except for using a light diffusing substrate (31) in which a large number of cylindrical lens-shaped protrusions (protrusions) (see FIG. 5) are formed in a projecting manner in parallel, they are collected in the same manner as in Example 1. A light diffusion plate with a light layer was prepared.
The height (H) of the ridges was 150 μm, the length (L) of the short sides of the ridges was 300 μm, and the distance between the centers of gravity (F) between the ridges adjacent in the short side direction was 3250 μm. It was.
Each light diffusion plate produced as described above was evaluated according to the following evaluation method. These results are shown in Table 1.

<Evaluation method of average brightness and brightness uniformity>
After removing the liquid crystal panel, various optical films, and the light diffusing plate from the commercially available 20-inch type liquid crystal television, the edge frame of the lamp box (in which a plurality of fluorescent tubes are arranged apart from each other) The light diffusing plate (Example product / Comparative product) produced above was placed and fixed in a state where it was in contact with the front surface, thereby closing the open surface of the lamp box. The luminance was measured using a luminance meter (“Eye Scale-3WS” manufactured by I-System Co., Ltd.) with the light diffusing plate set. When the minimum luminance value is “C1” and the maximum luminance value is “C2”,
Brightness uniformity (%) = (C1 / C2) × 100
The value obtained by the above formula was defined as the luminance uniformity (%).
The luminance measurement was performed as follows. A liquid crystal television is placed on the floor in a dark room of constant temperature and humidity (temperature 25.0 ° C, humidity 50.0%) with the front side facing up (the back is in contact with the floor). The camera was placed face down on the upper position of the LCD TV so that the entire front surface of the TV was captured. At this time, the distance from the front surface of the liquid crystal television to the camera is set to 65.0 cm, the measurement conditions of the luminance meter are set to SPEED: 1/500, GAIN: 5, aperture: 16, and the central portion of the front surface of the liquid crystal television is set. The luminance at each measurement spot (2601 places) is measured by designating a range of 60 mm × 60 mm centering on the measurement spot, and the average value of these luminances is set as the average luminance (cd / m ² ). The luminance uniformity (%) was obtained from the minimum luminance value and the maximum luminance value among the measured values.
As is apparent from Table 1, the surface light source device configured using the light diffusion plate of Example 1 of the present invention has high luminance in the front direction (normal direction) and excellent luminance uniformity. It was. Further, in the light diffusing plate of Example 1, the light diffusing substrate and the light condensing sheet are bonded via the adhesive layer, so that the light diffusing substrate and the light condensing sheet do not rub against each other, The light diffusing plate is not rubbed.
In contrast, in the surface light source device configured using the light diffusing plate of Comparative Example 1, there is no air layer between the light diffusing substrate and the light collecting sheet due to the entire adhesion of the pressure-sensitive adhesive. In (normal direction), the luminance was remarkably low.
Moreover, in the surface light source device comprised using the light diffusing plate of the comparative example 2 or the comparative example 3, the brightness | luminance was not obtained in the front direction (normal line direction).

The light diffusing plate of the present invention is suitably used as a light diffusing plate for a surface light source device, but is not particularly limited to such applications. The surface light source device of the present invention is preferably used as a backlight for a liquid crystal display device, but is not particularly limited to such applications.

DESCRIPTION OF SYMBOLS 1 ... Surface light source device 2 ... Light source 3 ... Light diffusing plate 20 ... Liquid crystal panel 30 ... Liquid crystal display device 31 ... Light diffusable board | substrate 32 ... Projection part 33 ... Concave-shaped surface 35 ... Long side 36 ... Short side 40 ... Adhesive layer 41 ... Light condensing sheet 42 ... Air layer G ... Center of gravity T of projection part ... Length L of the long side at the bottom surface of the projection part ... Length U of the short side at the bottom surface of the projection part ... Adjacent to the long side direction Distance between center of gravity F of matching protrusions ... Distance between center of gravity K of protrusions adjacent in the short side direction ... Displacement distance (long side direction)

Claims

A light diffusing plate comprising a light collecting sheet and a light diffusing substrate,
The condensing sheet has a condensing lens forming surface and a condensing lens non-forming surface,
One surface of the light diffusing substrate is a concavo-convex shape surface in which a plurality of protrusions are formed and a recess is provided between adjacent protrusions,
The protrusion has a substantially rectangular shape having a pair of long sides and a pair of short sides in plan view, and the length of the long side on the bottom surface of the protrusion is 0.8 mm to 2.5 mm. The length of the short side at the bottom of the substrate is 50 μm to 500 μm,
The light diffusing substrate and the light condensing sheet are bonded to each other by bonding the projections on the concavo-convex shape surface of the light diffusing substrate and the condensing lens non-forming surface of the light condensing sheet via an adhesive layer. Are laminated and integrated, and a light diffusion plate in which an air layer is formed between the pressure-sensitive adhesive layer and the concave portion of the concave-convex shape surface of the light-diffusing substrate.
The light diffusing plate according to claim 1, wherein the plurality of protrusions are substantially parallel to each other in the length direction.
The light diffusing plate according to claim 2, wherein the protrusions adjacent in the long side direction are spaced apart from each other at a constant interval, and the protrusions adjacent in the short side direction are spaced apart from each other at a constant interval.
When the distance between the centers of gravity of the protrusions adjacent in the long side direction is U,
The position of the center of gravity of the protrusion in the protrusion group that forms a line in the long side direction is the center of gravity of the closest protrusion among the plurality of protrusions constituting the adjacent protrusion group adjacent to the protrusion group in the short side direction. The light diffusing plate according to claim 3, wherein the light diffusing plate is separated from the position by a distance of U / 2.2 to U / 1.8 in the long side direction.
When the distance between the centers of gravity of the protrusions adjacent to each other in the long side direction is U, and the length of the long side on the bottom surface of the protrusion is T,
1.3 ≦ U / T ≦ 2.2
Is established,
When the distance between the centers of gravity of the protrusions adjacent to each other in the short side direction is F and the length of the short side on the bottom surface of the protrusion is L, F is 400 μm or more and 5.0 mm or less,
8.0 ≦ F / L
The light diffusing plate according to claim 3 or 4, wherein the following relational expression is satisfied.
A light diffusing plate according to any one of claims 1 to 5 and a plurality of light sources arranged on a back side of the light diffusing plate, wherein the light condensing sheet is on the front side. A surface light source device in which a diffusion plate is disposed.
6. A light diffusing plate according to claim 1, a plurality of light sources arranged on the back side of the light diffusing plate, and a liquid crystal panel arranged on the front side of the light diffusing plate. The liquid crystal display device in which the light diffusing plate is arranged so that the light-collecting sheet is on the front side.