JPH1138207A - Optical sheet, surface light source device, and transmission type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-luminance optical sheet of a thin type which suppresses the generation of interference fringes and has the excellent intra- surface luminance uniformity by arranging a light transmittance adjusting sheet on the rear surface side of a lens sheet in superposition on the lens sheet. SOLUTION: The optical sheet 20 comprises the lens sheet 22 and the light transmittance adjusting sheet 24 arranged along the rear surface side thereof. The lens sheet 22 is formed of a translucent material. Many pieces of unit lenses 26 consisting of prisms of a triangular prism shape are arrayed one- dimensionally on the front surface of the lens sheet in such a manner that the ridge lines 26A of the respective unit lenses 26 are parallel with each other. A light diffusion layer 28 is formed on the rear surface side of the lens sheet 22. The light transmittance adjusting sheet 24 consists of a translucent base material and is constituted by providing the front surface thereof with a light transmittance adjusting function to change the light transmittance within the plane. As a result, the generation of the interference fringe is suppressed, and the optical sheet of high-luminance and thin type excellent in intra-surface luminance uniformity can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sheet for obtaining a more uniform surface light emitting state when a translucent display such as a transmissive liquid crystal display device or an advertising board is illuminated from the back. The present invention relates to a surface light source device using a sheet and a transmission type display device.

[0002]

2. Description of the Related Art In a transmissive display device, for example, a transmissive liquid crystal display device used as a display of a personal computer, in recent years, lower power consumption, lighter weight, and higher luminance have been further demanded. As one of the means,
2. Description of the Related Art A surface light source device that effectively uses light from a light source without waste has been proposed.

[0003] For example, Japanese Patent Application Laid-Open No. 5-127159,
As disclosed in Japanese Utility Model Laid-Open Publication No. 3-69184, there is a lens sheet or the like that condenses light from a surface light source in a specific direction (in many cases, a normal direction of a light exit surface).

As such a lens sheet, for example, as shown in FIG. 10A, a prism having a triangular prism shape is used as a unit lens 1 and this is used as a ridge line 1 of each unit lens 1.
There is a large number of lens sheets 2 arranged in a one-dimensional direction such that the directions A are parallel to each other.

As shown in FIG. 10B, a large number of unit lenses 3 each having a convex shape in cross section are arranged in a one-dimensional direction such that the ridge lines of the unit lenses 3 are parallel to each other. There is a lens sheet 4 formed by the following method.

Further, as shown in FIG. 10C, a large number of unit lenses 5 having a corrugated cross section are arranged in a one-dimensional direction so that the ridge lines of each unit lens 5 are parallel to each other. There is a lens sheet 6.

As the surface light source device using the lens sheet as described above, there are an edge light type surface light source device 7 as shown in FIG. 11 and a direct type surface light source device 8 as shown in FIG. .

The edge light type surface light source device 7 includes a light guide 9 made of a plate material such as a transparent acrylic resin.
A, a linear light source 10 is disposed on the light guide 9, and the light from the light source 10 that has entered the light guide 9 from the one end surface 9 </ b> A is applied to the surface of the light guide 9 by a light diffusing action to cause the light to travel in the traveling direction. Are excluded from the condition of total reflection inside the light guide 9, and the light is emitted from the light exit surface 9 </ b> B of the light guide 9.

The lens sheet 2, 4, or 6 is usually
The light guide 9 is arranged along the light exit surface 9B.

The edge light type surface light source device 7 as described above
In order to make the luminance distribution in the light exit surface 9B of the light guide 9 more uniform, for example,
As disclosed in Japanese Patent Application Laid-Open No. 9-209, the light diffusion effect applied to the surface of the light guide 9 is adjusted.

The direct type surface light source device 8 includes a light source 11.
Is reflected in the direction of the light emitting surface 13 by the reflector 12 disposed so as to surround the light, and at this time, for example, as disclosed in Japanese Patent Publication No. 59-8809, In order to make the luminance distribution in the light exit surface 13 more uniform, an optical sheet 14 having a light transmittance adjusting function may be used.

[0012]

As described above, in order to meet the demands for low power consumption, light weight, and high brightness and to increase the size of the surface light source device as described above, it is necessary to reduce the size of the device as much as possible. It is necessary to increase the light emitting area while keeping the thickness small, but in this case, it becomes difficult to distribute light from the light source evenly to every corner of the light exit surface, and as a result, the There is a problem that luminance uniformity is deteriorated.

On the other hand, it is conceivable to arrange the light transmittance adjusting sheet on the light emitting surface of the surface light source device. In the case of a surface light source device using a lens sheet for the light emitting surface, the lens sheet and the light transmittance are adjusted. There is a problem that an interference fringe is generated due to a slight change in the optical distance with the adjustment sheet.

The present invention has been made in view of the above-mentioned conventional problems, and suppresses the occurrence of interference fringes.
Combination of a lens sheet and a light transmittance adjusting sheet to provide an optical sheet having high luminance, thinness, and excellent in-plane luminance uniformity, and a surface light source device and a transmission type display device using the optical sheet. With the goal.

[0015]

According to the present invention, there is provided a lens sheet having a plurality of unit lenses formed on the surface of a light-transmitting material and a light diffusion layer formed on the back surface, and a lens sheet formed on the surface of a light-transmitting substrate. The above-mentioned object is achieved by a light transmittance adjusting sheet having a light transmittance adjusting function of changing the light transmittance within the lens sheet, and the light transmittance adjusting sheet disposed on the back side of the lens sheet so as to overlap with the lens sheet. .

In another aspect of the present invention, a plurality of unit lenses are formed on the surface of a light-transmitting material, and the light transmittance in the plane is changed on the back surface of the lens sheet having a light diffusion layer formed on the back surface. The above object is achieved by an optical sheet comprising a light transmittance adjusting layer having a light transmittance adjusting function.

The invention relating to a surface light source device comprises at least a light guide, a light source, and the optical sheet according to claim 1 or 2, wherein the light guide receives light incident from one side end face of the light guide. The light source is arranged to emit light from a light emitting surface that is a surface, the light source is arranged to emit light to the one end surface of the light guide, and the optical sheet has a light transmittance adjusting function. The above object is achieved by a surface light source device characterized in that the surface light source device is arranged to face a light emitting surface of the light guide.

According to another aspect of the present invention, there is provided a surface light source device including at least a light source, a reflector, and an optical sheet according to claim 1 or 2, wherein the light source has a function of adjusting the light transmittance of the optical sheet. Disposed on the side, the reflection plate, between the light source, by the surface light source device characterized by being arranged to reflect light from the light source on the opposite side to the optical sheet in the direction of the optical sheet, The above object is achieved.

Further, the invention relating to a transmissive display device is a transmissive display for displaying an image by irradiating an image with illumination light from the back, and a back light source disposed on the back side of the transmissive display. The above object is achieved by a transmissive display device having the surface light source device of (3) or (4).

In the present invention, an optical sheet is formed by combining a lens sheet provided with a light diffusion layer on the rear surface side and a light transmittance adjusting sheet, thereby suppressing the occurrence of interference fringes.
The brightness is high, the thickness is low, and the in-plane brightness uniformity is improved.

In particular, by providing the light diffusing surface directly on the surface of the lens sheet opposite to the unit lens, interference fringes generated between the lens sheet and the light transmittance adjusting sheet are suppressed.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, an optical sheet 20 according to a first embodiment of the present invention includes a lens sheet 22.
And light transmittance adjusting sheet 2 arranged along the back side
And 4.

The lens sheet 22 is formed of a translucent material, and on its surface (upper side in FIG. 1), a large number of unit lenses 26 composed of triangular prisms (ridge lines 26A of each unit lens 26 are mutually connected). The light diffusion layers 28 are formed on the rear surface of the lens sheet 22 so as to be parallel to each other in a one-dimensional direction.

The light transmittance adjusting sheet 24 is made of a light-transmitting base material, and has a surface provided with a light transmittance adjusting function of changing the light transmittance in the plane (details will be described later). I have.

The light-transmitting material forming the lens sheet 22 is a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, an acrylic resin such as polymethyl methacrylate, a thermoplastic resin such as a polycarbonate resin, a polystyrene resin or a polymethyl pentene resin. Or a resin obtained by curing an ionizing radiation-curable resin composed of oligomers such as polyester acrylate, urethane acrylate, epoxy acrylate and / or monomers such as acrylates with ionizing radiation such as ultraviolet rays or electron beams, and It is selected from resins having good properties.

Such resins usually have a refractive index of 1.4 to 1.4.
It is about 1.6. In addition, glass, ceramics, etc. with good translucency other than resin may be used.

Next, the light diffusion layer 28 formed directly on the back surface of the lens sheet 22 will be described.

As shown in FIG. 2, the light-diffusing layer 28 is formed by spraying a coating material in which light-transmitting fine particles 28A are dispersed in a light-transmitting binder 28 on the back surface of the lens sheet 22 by spray coating or roll coating. It is formed by a method such as coating with a coat or the like to make fine particles have irregularities on the surface of the coating film.

Here, as the light-transmitting fine particles 28A, polymethyl methacrylate (acryl) beads, polybutyl methacrylate beads having a diameter of 1 to 10 μm,
Polycarbonate beads, polyurethane beads, calcium carbonate beads, silica beads and the like are used.

As described above, the reason why the diameter of the translucent beads 28A is set to 1 μm or more is that if the diameter is smaller than this, the wavelength becomes too close to the wavelength of visible light, and the color is seen. This is because it is difficult to mass-produce small translucent beads and to disperse them in a binder.

The reason why the diameter of the light-transmitting beads is set to 10 μm or less is that when the diameter is larger than this, the light from the surface light source is condensed in a specific direction (in many cases, the normal direction of the light exit surface). This is because the action to be performed is extremely reduced.

Since the diameter of the light-transmitting beads 28A always varies when the light-transmitting beads 28A are manufactured, the diameter of the light-transmitting beads 28A is the average value of the diameter of the light-transmitting beads of 1 μm or more. Say

As the light-transmitting binder 28B in which the light-transmitting beads 28A are to be dispersed, there are acrylic, polystyrene, polyester, vinyl polymer, and the like. In particular, a transparent resin such as a polyester resin or an acrylic resin is used. Conveniently, the ratio of the refractive index of the light-transmitting beads 28A to the refractive index of the binder resin is preferably in the range of 0.9 to 1.1. Is 2-15 of the binder resin content.
% Is preferred.

The reason that the refractive index ratio is set to 0.9 to 1.1 is that if the refractive index ratio is out of this range, the interface between the light-transmitting beads and the coating layer of the binder resin in contact therewith. The light diffusion effect of the coating layer itself increases, and the brightness improvement effect of condensing light from the surface light source, which is the purpose of using the lens sheet, in a specific direction as described above is significantly reduced. It is because.

Also, a binder resin and light-transmitting beads 28
The thickness of the coating layer made of A is preferably 1 to 20 μm.

When the thickness of the coating layer is less than 1 μm, it is difficult to completely fix the light-transmitting beads 28 A to the light-transmitting substrate 23. The effect of condensing the light from the surface light source, which is the purpose of using the sheet, in a specific direction to improve the brightness is significantly reduced.

The total thickness of the lens sheet 22 is usually 20
About 1000 μm.

Next, the configuration of the light transmittance adjusting sheet 24 will be described.

The light transmittance adjusting sheet 24 is provided with a light transmittance adjusting function on the surface of a light transmissive substrate, and the light transmissive substrate is made of polyester such as polyethylene terephthalate and polybutylene terephthalate. Resin, acrylic resin such as polymethyl methacrylate, thermoplastic resin such as polycarbonate resin, polystyrene resin, polymethylpentene resin, or oligomer such as polyester acrylate, urethane acrylate, epoxy acrylate and / or monomer such as acrylate The resin is a resin or the like obtained by curing the ionizing radiation-curable resin with ionizing radiation such as an ultraviolet ray or an electron beam, and is selected from resins having good translucency. Such a resin usually has a refractive index of about 1.4 to 1.6. In addition, glass, ceramics, and the like may be used as long as they have translucency other than the above resins.

Means for imparting a light transmittance adjusting function of changing the light transmittance in the plane to the surface of the light-transmitting substrate as described above include, for example, JP-B-59-8809 and JP-A-5-88509.
As disclosed in JP-A-5-15126 and JP-A-59-22493, a transparent member is provided with a reflection surface having a reflection distribution characteristic so that the light transmittance can be adjusted.

In this case, the reflection distribution characteristic is generally such that the reflectance increases as the distance from the light source decreases.

The optical sheet 20 shown in FIG. 1 has a light transmittance adjusting sheet 24 provided separately from the lens sheet 22, but the present invention is not limited to this. The light transmittance adjusting means may be provided directly on the back surface of the light emitting element.

For example, in the optical sheet 30 as shown in FIG. 3, a light transmittance adjusting layer is directly applied to the back surface of the lens sheet 32 by the light transmittance adjusting means as applied to the surface of the light transmittance adjusting sheet 24 described above. 34 may be formed.

In this case, loss due to surface reflection is eliminated, which is preferable. The light transmittance adjusting layer 34 may be provided on both or one of the outside and the inside of the light diffusion layer 28 provided on the lens sheet 32.

The optical sheet 2 shown in FIGS. 1 and 3
The lens sheets 22 and 32 at 0 and 30 each have a unit lens 26 having a triangular prism shape, but the present invention is not limited to this.
A cylindrical lens-shaped unit lens 26 as shown in FIG.
Sheet 20 including a lens sheet 22A provided with A
A, an optical sheet 2 including a lens sheet 22B provided with a unit lens 26B having a sectional wave shape as shown in FIG.
0B.

In the case of a lens sheet on which the light transmittance adjusting layer 34 is directly formed, an optical sheet 32 having a cylindrical lens-shaped unit lens 26A as shown in FIG.
A or an optical sheet 32B having a corrugated unit lens 26B may be used.

In addition to the case where the unit lenses are formed in parallel in a one-dimensional direction, for example, as shown in FIG. 6, a fly-eye lens in which hemispherical unit lenses are arranged in a two-dimensional direction is used. A lens sheet 33 formed with the unit lens 26C may be included.

Further, the cross-sectional shape of the unit lens as described above may be triangular prism shape, cylindrical lens shape, corrugated shape, circular shape, caroid, Rankine's egg shape, cycloid, sine wave shape, involute curve or the like. May be used as a continuous smooth curve, or a part or the whole of a polygon. In addition, as a unit lens arranged in a two-dimensional direction,
Besides a hemisphere, a conical lens, a pyramid lens, or the like may be used.

Here, the method of manufacturing the lens sheet is as follows.
In order to obtain a lens sheet having a single-layer structure (an intermediate sheet before coating the light diffusion layer 28) as shown in FIG. 1, for example, a heat-superplastic lens disclosed in JP-A-56-157310 is used. The method may be a hot pressing method or an injection molding method of a resin, or a casting method of a curable resin by ultraviolet rays or heat.

Further, as a method for producing an intermediate sheet having a multilayer structure, for example, as disclosed in JP-A-5-1699015, a roll intaglio having a female mold corresponding to a desired lens arrangement shape is irradiated with ionizing radiation. A curable resin liquid is filled, and the above-mentioned translucent substrate sheet is overlaid thereon, and then irradiated with ionizing radiation such as ultraviolet rays and electron beams from the transparent substrate sheet side as it is (roll intaglio is made of glass or the like). If it is transparent, it can also be irradiated from the roll intaglio side), the ionizing radiation-curable resin liquid is cured, and then the transparent base sheet is peeled off from the roll intaglio together with the cured resin, so that the cured ionizing radiation-curable resin liquid Is formed on the transparent substrate sheet in a desired male lens arrangement.

Next, an edge light type surface light source device 40 according to the present invention as shown in FIG. 7 will be described.

This edge light type surface light source device 40
A light guide 42, a light source 44, and the high-priced sheet 20 or 30 are included. The light source 44 is a linear light source along one end surface 42A of the light guide 42, and the light is emitted from the one side. The light guide 42 is configured to enter the light guide 42 from the end surface 42A and to emit light from the light emission surface 42B that is one surface of the light guide 42, and the optical sheet 20 or 30 is disposed along the light emission surface 42B. ing.

Reference numeral 42C in the figure denotes a light reflecting surface formed so as to cover the surface opposite to the light emitting surface 42B and the side end surface opposite to the one end surface 42A.

Next, the direct type surface light source device 46 shown in FIG. 8 will be described.

The direct type surface light source device 46 includes a light source 4
8, the reflection plate 50 and the optical sheet 20 or 30.

The light source 48 is disposed on the optical sheet 20 or 30 on the side having a light transmittance adjusting function, and the reflection plate 50 is disposed between the light source 48 and the opposite side to the optical sheet 20 or 30. The light from the light source 48 is
Or, it is arranged to reflect in 30 directions.

Next, the transmission type display device 52 according to the present invention shown in FIG. 9 will be described.

The transmissive display device 52 illuminates and displays an image with illumination light from the back, for example, a transmissive display 54 composed of a liquid crystal display panel, and is disposed on the back side of the transmissive display. And the edge light type surface light source device 40 as a back light source. The direct-type surface light source device 46 may be used as the back light source.

The optical sheet 20 or 30 in FIGS. 7, 8 and 9 is, of course, any of the optical sheets 22A, 22B, 32A, 32B and 33 (lens sheet) shown in FIGS. Alternatively, the optical sheet may have another shape.

The light sources 44 and 48 are preferably linear light sources such as fluorescent lamps in order to obtain uniform brightness in the plane direction, but may be point light sources such as incandescent lamps.

In the optical sheets 20 and 30 as described above, the light transmittance adjusting sheet 24 or the light transmittance adjusting layer 34 ensures that the light entering the lens sheet has a uniform brightness in the plane direction. Accordingly, even if the area of the optical sheet, the edge light type surface light source device 40, the direct type surface light source device 46, or the transmissive display body 54 is increased, the thickness or the like is not greatly increased. Brightness can be obtained.

[0063]

EXAMPLES Next, examples of the optical sheet of the present invention will be described.

In this embodiment, a transparent adhesive layer of about 1 μm was formed on a transparent biaxially stretched PET (polyethylene terephthalate) film (125 μm thick) as a light-transmitting substrate.
And a UV curable resin mainly composed of a prepolymer of epoxy acrylate for forming a unit lens pattern is applied thereon, and the resin coating is cured (solidified). By releasing the mold, a lens sheet in which isosceles triangular columnar unit lenses having a pitch of 50 μm and an apex angle of 85 ° were arranged adjacently so that each ridge line was parallel.

A light diffusing layer was formed on the side of the lens sheet opposite to the lens forming surface by microhill-shaped projections in the following manner.

[Composition] A cross-linked acrylic resin having an average particle size of 5 μm was used for the translucent beads, and a polyester resin was used for the binder.

[Manufacturing process] An ink containing the light-transmitting beads at a concentration of 8% of the binder resin was diluted with a solvent of MEK: toluene = 1: 1, and the viscosity was measured with a Zahn cup viscometer # 3. Seconds. This ink was applied to the non-lens surface (back surface) of the translucent substrate by a slit reverse coating method, and then the solvent was dried to solidify a coating film as a light diffusion layer.

This coating film has a thickness of 10 according to JIS B0601.
The fine hill-shaped projections having a point average roughness Rz = 3 μm have an average interval d =
It was 30 μm and formed in a random arrangement.

Separately, a transparent biaxially stretched PET film is used for a sheet having a light transmittance adjusting function so that a portion having a higher in-plane luminance has a larger reflection pattern area per unit area. Created.

[0070]

As described above, the present invention has an excellent effect that the light transmittance to the lens sheet becomes uniform in the plane direction and uniform brightness can be obtained in the plane direction.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a part of an optical sheet according to an example of an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a lens sheet constituting a part of the optical sheet of FIG. 1;

FIG. 3 is a perspective view showing a part of a second example of the embodiment of the optical sheet.

FIG. 4 is a perspective view showing a third example and a fourth example of the embodiment of the optical sheet similar to FIG. 1;

FIG. 5 is a perspective view showing a fifth example and a sixth example of the embodiment of the optical sheet similar to FIG. 2;

FIG. 6 is a perspective view showing a seventh example of the embodiment of the optical sheet.

FIG. 7 is a sectional view showing an example of an embodiment of a surface light source device according to the present invention.

FIG. 8 is a perspective view partially showing a second example of the embodiment of the surface light source device according to the present invention;

FIG. 9 is a sectional view showing an example of an embodiment of a transmission type display device according to the present invention.

FIG. 10 is a perspective view showing the shape of a conventional lens sheet.

FIG. 11 is a sectional view showing a conventional surface light source device.

FIG. 12 is a sectional view showing another conventional surface light source device.

[Explanation of symbols]

20, 20A, 20B, 30, 32A, 32B: Optical sheet 22, 32, 33: Lens sheet 24: Light transmittance adjusting sheet 26, 26A, 26B, 26C: Unit lens 28: Light diffusing layer 34: Light transmittance adjusting Layer 40: Edge light type surface light source device 42: Light guide 42A: One side end surface 42B: Light emitting surface 44, 48 ... Light source 46: Direct type surface light source device 50: Reflector plate 52: Transmission type display device 54: Transmission type Display body

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G09F 9/00 336 G09F 9/00 336E

Claims (5)

[Claims] A plurality of unit lenses are provided on a surface of a translucent material,
A lens sheet in which a light diffusion layer is formed on the back surface, and a light transmittance adjusting function for changing the in-plane light transmittance on the surface of the light-transmissive base material; An optical sheet comprising: a light transmittance adjusting sheet disposed on the sheet; 2. A plurality of unit lenses on a surface of a translucent material,
An optical sheet, wherein a light transmittance adjusting layer having a light transmittance adjusting function of changing light transmittance in a surface is formed on the back surface of the lens sheet having a light diffusion layer formed on the back surface. . 3. A light guide, a light source, and at least a light source.
Or wherein the light guide is configured to emit light incident from one end face of the light guide from a light emission surface which is one surface, and the light source is a light guide of the light guide. A surface, which is arranged so as to emit light to the one side end surface, wherein the optical sheet is arranged such that a side having the light transmittance adjusting function is directed toward a light emitting surface of the light guide. Light source device. 4. A light source, a reflector, and at least a light source.
Or comprising two optical sheets, the light source is disposed on a side having a light transmittance adjustment function of the optical sheet,
The surface light source device, wherein the reflection plate is disposed between the light source and the opposite side of the optical sheet so as to reflect light from the light source toward the optical sheet. 5. A transmissive display for irradiating and displaying an image with illumination light from the back, and a surface light source device according to claim 3 or 4 as a back light source disposed on the back side of the transmissive display. , A transmission type display device comprising: