JP2772775B2 - Light diffusion sheet, edge light type surface light source using the same, and liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transflective reflector for illuminating light used on the back of a non-light-emitting display device such as a liquid crystal display device, a non-light-emitting display device such as a liquid crystal display device, an advertising signboard, The present invention relates to a light diffusion sheet useful for a surface light source used as a back light source such as a display panel, a projection screen, and the like.

[0002]

2. Description of the Related Art A light-diffusing sheet (also referred to as a semi-transmissive reflector) which is semi-transmissive and has a diffusing effect on both transmitted light and reflected light has been conventionally used exclusively. It is arranged as a reflector for external light and a diffused transmission plate for light from the rear light source on the back of the liquid crystal display (LCD), and the LCD can be of a reflective type (light from sunlight or room light) or a transmissive type (light from the rear light source). ) Has been used as an element for enabling both types of switching.

As such a light diffusion sheet, an inorganic fine powder such as calcium carbonate and barium sulfate (having a particle size of 0.01 to 100 μm) is contained in an adhesive layer of a polarizing plate having a plurality of layers.
m) (see JP-A-59-50412), a light-diffusing agent comprising fine powder of titanium oxide, calcium carbonate, silica, etc. on a light-transmitting plastic film sandwiching a polarizer from both sides. Transflective polarizing plate coated with a light-diffusing film (see JP-A-61-260202), and transflective reflective film made of expanded polypropylene or a polyester film having an embossed surface (JP-A-62-226124). And the like are known.

[0004]

However, none of the above-mentioned conventional light diffusing sheets have both a diffuse reflectance and a diffuse transmittance of light. That is, the higher the reflectance, the lower the transmittance, and the lower the reflectance, the higher the transmittance. In addition, in each case, a part of unnecessary light (stray light) obliquely incident is reflected toward the vicinity of the normal direction of the surface (observation direction), so that there is a problem that image contrast is reduced.

Therefore, a coating film or an adhesive layer in which scale-like foils of titanium dioxide-coated mica are dispersed as a light-diffusing material has been studied. However, these materials have higher reflectivity and transmittance than those described above. However, it is still insufficient for practical use, and there is the same problem as described above regarding the reduction in contrast due to oblique incident light.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and it is an object of the present invention to provide a light diffusion device that has high efficiency for both reflected light and transmitted light, and has little contrast reduction due to obliquely incident light. An object of the present invention is to provide a sheet and an edge light type surface light source and a liquid crystal display device using the sheet.

[0007]

In order to achieve the above object, the light diffusing sheet according to claim 1 uses a light-reflective flaky foil piece as a light diffusing material, and this light diffusing material is provided in a transparent resin layer. Was divided into two layers to constitute a light diffusion layer. In the first light diffusion layer on the side opposite to the observer side (referred to as the back side), the orientation direction of the bottom surface of the foil piece has a distribution having a peak in a direction parallel to the front and back sides of the transparent resin layer. In the second light diffusion layer on the side (referred to as the front surface), the orientation distribution of the bottom surface of the foil piece is smaller in the proportion of the foil piece parallel to the front and back surfaces of the transparent resin layer than in the first light diffusion layer. The distribution was such that the percentage of foil pieces in the direction perpendicular to the direction (normal direction of the light diffusion sheet) was large.

In the light diffusion sheet according to the first aspect of the present invention, as shown in FIG. 1, near the normal direction effective for observation (usually, the normal 30 to 60 °), a part of the light rays incident on the second light diffusion layer 20, for example, L _6, is reflected by the foil piece 21 b whose bottom surface faces obliquely and is out of the effective angle for observation. although to or departing decays mostly directly as L ₁ and L _3, or the first light diffusing layer is reflected by Hakuhen 21a with oriented bottom in the normal direction as L ₂ Reaches up to 10. Then, the bottom surface in the first light diffusion layer 10 is specularly reflected by a foil piece 11 oriented in a direction parallel to the front and back surfaces of the light reflection sheet, and is directly reflected as L ₁ or L ₃ or as L ₂ . 2 foil pieces 21a oriented in the normal direction in the light diffusion layer 20
And reflected light is output to the observer side (surface) as reflected light. Further, at this time, the emission angle distribution of the reflected light is concentrated in a predetermined range by the reflection on the foil piece 21a oriented in the normal direction. Therefore, the ratio of the reflected light that is effectively used is increased, and a high reflectance is obtained. Further, the stray light L ₄ from an oblique direction shifted from the effective angle to the observation (viewing angle and designation) is to either attenuated multiple reflection in the foil piece 21a oriented in the normal direction deviates outside the viewing angle . Therefore, it is possible to prevent the stray light from entering the viewing angle and lowering the image contrast.

On the other hand, looking at the case where the diffused light from the back surface incident, as shown in FIG. 2, the incident light beam is often oblique incident light component, large light generally incident angle bottom light as L ₇ While being multiply-reflected by the foil pieces 11 parallel to the front and back surfaces of the reflection sheet, they pass through the first light diffusion layer 10 and enter the second light diffusion layer 20. Then, the light is multiple-reflected by the foil piece 21a oriented in the normal direction, and is emitted while the emission angle distribution is concentrated. Moreover, some small light of some particularly incident angle is reflected by the Hakuhen 11 as L _8, would also be present not emitted from the light diffusion sheet surface. Alternatively, the foil strips 21b, the bottom surface of the second light diffusion layer 20 are oriented obliquely as L ₉
Some of them deviate outside the viewing angle or attenuate, but these are only a part. Therefore, there are many light rays emitted from the back side to the front side, and the transmittance is kept high. Moreover, since the emitted light is concentrated within the viewing angle, the utilization of the transmitted light is high. That is, it becomes bright even with a small amount of light.

[0010] When the reflectance and the transmittance are compared,
Generally, the reflectance is higher. This is shown in FIGS. 1 and 2
It is intuitively clear when comparing the number of multiple reflections of the reflected light and the transmitted light by the foil piece in the above.

In the case where reflected light is used in applications such as a transflective light diffusion plate on the back surface of an LCD, the utilization factor is as high as possible because limited uncontrollable light existing in the surrounding environment is used as it is. It is necessary. On the other hand, in the case of using transmitted light, light from a pre-designed light source can be efficiently input to the light diffusion sheet under certain conditions. Even if it is low, it can be compensated by the design of the light source. Therefore, it can be said that the characteristics of the light diffusion sheet of the present invention, in which the reflectance is relatively higher than the transmittance, are preferable in practice.

Here, the direction in which the bottom surface of the foil piece is oriented is defined as the inclination direction of the surface in a three-dimensional space. Specifically, as shown in FIG. 3, an orthogonal coordinate system (xyz) is set so that a plane parallel to the front surface or the back surface of the light diffusion layer (light diffusion sheet) to be used as a reference is set to the xy plane. Let the equation be Φ (x, y, z). Although the bottom surface exists on both the front and back surfaces of the foil piece, when the foil piece is thin and the bottom surface is almost perfect, both the front and back surfaces may be considered to be parallel. The bottom is also the same. Therefore, in the following description, it is assumed that Φ is the front bottom surface in FIG. The orientation direction is defined by the gradient vector gradΦ = (∂Φ / ∂x, ∂Φ / ∂y, ∂Φ / ∂z) of the bottom surface. As is well known in the general theory of potential, when water is poured onto the front and bottom surfaces of a foil piece in a gravitational field, the direction in which water flows down is the gradΦ vector direction. Since the orientation direction of the foil pieces differs depending on the individual foil pieces, a large number of flake-like foil pieces dispersed in the light diffusion layer have a distribution with respect to the azimuth (θ, φ) in the three-dimensional space. Therefore, the orientation state of the foil pieces is determined by the grad of the orientation direction of each foil piece.
Is represented by a probability density function f (θ, φ) in the three-dimensional space of Φ. Here, f (θ, φ) is expressed in polar coordinates (spherical coordinates). The relationship between the rectangular coordinates and the polar coordinates is as shown in FIGS.

The γ coordinates of the three-dimensional polar coordinates (γ, θ, φ) are applied to the probability density distribution in the azimuth (θ, φ) direction, and f
FIG. 5 is a plot of the curved surface of (θ, φ) in the original rectangular coordinates (the xy plane is parallel to the front and back surfaces of the light diffusion layer). The distribution of the orientation direction of the foil pieces can be grasped in the form of the curved surface f (θ, φ). Note that FIG. 5A shows the foil piece orientation distribution of the first light diffusion layer, and FIG. 5B shows the foil piece orientation distribution of the second light diffusion layer. That is, as shown in FIG. 5A, the distribution of the orientation of the foil pieces in the first light diffusion layer has a peak in the xy plane, that is, in the direction of the front and back surfaces of the light diffusion layer, and The foil pieces in the light diffusion layer have a smaller distribution (probability density) in the xy plane than the first light diffusion layer as shown in FIG. The distribution of foil piece orientation in the line direction is more.

A surface f (θ, θ,
In (φ), the peak directions of the first light diffusion layer and the second light diffusion layer do not necessarily need to be orthogonal to each other. It is sufficient that the probability density in the xy plane direction of the second light diffusion layer is relatively lower between the two light diffusion layers. Also, FIG.
(Θ, φ) schematically shows a representative example, and does not necessarily have to be a spheroid. Further, the distribution in the xy plane is asymmetric (b ₁ > a) as shown in FIG.
₁ ) or symmetric (b ₂ ) as shown in FIG.
= A ₂ ).

In order to achieve the same object, a light diffusion sheet according to a second aspect of the present invention further comprises a light diffusion layer provided on the back surface of the first light diffusion layer. A layer that diffuses and transmits transmitted light isotropically or substantially isotropically is used as the layer. In the light diffusion sheet according to the first aspect, if the incident light from the back surface is a parallel light flux composed only of light rays (incident angle ≒ 0) close to the light diffusion sheet in a vertical direction, almost all the light rays are the second light rays as shown in FIG. Foil piece 11 in one light diffusion layer 10
And the transmitted light becomes unusable. However, in the light diffusion sheet of claim 2, the first light diffusion layer 10
Even if a parallel light beam is incident on the back surface (light source side) of FIG. 2, the light is converted into diffused light by the third light diffusion layer 30 as shown in FIG. can get.

[0016]

8 (a) and 8 (b) are cross-sectional views each showing a light diffusion sheet as an embodiment of the present invention.

As shown, the light diffusion sheets A and B are the first
Light diffusion layer 10 and second light diffusion layer 2 laminated thereon
It consists of 0. The first light diffusion layer 10 includes a transparent resin layer 12
Light-reflective scale-like foil pieces 11 are dispersed therein, and the probability density function of the orientation angle distribution on the bottom surface of the foil pieces 11 has a peak in a direction parallel to the front and back surfaces of the transparent resin layer 12. Further, the second light diffusion layer 20 is formed by dispersing light-reflective flaky foil pieces 21 in a transparent resin layer 22 laminated on the first light diffusion layer. The value of the probability density function of the orientation angle distribution in the direction parallel to the front and back surfaces of the transparent resin layer 22 is smaller than that of the foil piece 11 in the first light diffusion layer 10. The peak of the foil piece orientation distribution is sharper in the light diffusion sheet A than in the light diffusion sheet B.

As the transparent resins 12 and 22, basically, any resin can be used as long as it can form a solid film with the scale-like foil pieces 11 and 21 dispersed therein and has sufficiently high transparency. You may. For example, acrylic resins such as polymethyl (meth) acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate, and methyl (meth) acrylate / butyl (meth) acrylate copolymer (where (meth) acryl is acrylic or methacryl) ), Styrene resins such as polystyrene and styrene / acrylonitrile copolymer, thermoplastic polyesters such as polyethylene terephthalate and polybutylene terephthalate, and thermoplastic resins such as polycarbonate and vinyl chloride / vinyl acetate copolymer. Further, a so-called “ionizing radiation” obtained by crosslinking and curing a prepolymer or a monomer having one or more ethylenically unsaturated groups, cationically polymerizable unsaturated groups or thiol groups in the molecule with ionizing radiation such as ultraviolet rays or electron beams. Curable resins "can also be used. Examples of the prepolymer having an ethylenically unsaturated group include prepolymers such as urethane (meth) acrylate, polyester (meth) acrylate, and epoxy (meth) acrylate;
Examples of the monomer having an ethylenically unsaturated group include trimethylolpropane tri (meth) acrylate and dipentaerythritol hexa (meth) acrylate. Examples of the prepolymer or monomer having a cationically polymerizable unsaturated group include a prepolymer or monomer of an epoxy compound. Also, urethane resin, thermosetting acrylic resin,
Thermosetting resins such as thermosetting epoxy resins and thermosetting polyesters can also be used. These resins are used alone or in combination of two or more.

The scaly foil pieces 11 and 21 are made of a material having light reflectivity. This substance includes transparent resin 1
Having a refractive index different from that of the transparent resin
Select a substance that can reflect light at the interface with 2. The versatility for various transparent resins 12 and 22 is as follows.
Mica, titanium dioxide coated mica, iron oxide coated mica, bismuth oxychloride, calcium carbonate (such as calcite), barium sulfate, pearl shell, glass, aluminum, tin, brass, gold,
There are silver, a metal-deposited resin on the surface, and the like. The shape of the foil piece may be any of a flat circular column, a triangular column, a quadrangular column, a polygonal column such as a hexagonal column, various irregular shapes, a leaf shape, a fish scale shape, and the like, and generally includes a side surface and a bottom surface. Natural crystal forms or cleavage forms may be used, or artificially formed into predetermined shapes.

The grain size of the foil pieces 11 and 21 is 1 to 20 (evaluated by the diameter of the circumscribed circle, the longest diagonal length, etc.).
It is preferably 0 μm. More preferably, 10-1
50 μm. If it is too small, the reflectivity of light, the oblique ray blocking effect, and the convergence of emitted light are reduced. Conversely, if it is too large, bright spots are conspicuous, and the uniformity of emitted light decreases. The relative grain size of the foil pieces may be the same for the first and second light diffusion layers, or may be small for the first light diffusion layer 10 and large for the second light diffusion layer 20. It is preferable in terms of compatibility between high transmittance and high reflectivity, shielding of oblique rays, and convergence of emitted rays. As the ratio, (particle diameter of foil piece in second light diffusion layer) / (particle diameter of foil piece in first light diffusion layer) =
1 to 5 are preferred. Further, the amount added to the transparent resins 12 and 22 is preferably 0.1 to 70% by weight. Addition amount is 1st
It is preferable that the amount of the second light diffusion layer is the same as that of the second light diffusion layer, or the amount of the second light diffusion layer is smaller than that of the first light diffusion layer.

More specifically, the first light diffusion layer 10 has a thickness of 1 to 15 μm, and a particle size of the foil piece 12 to be added is 1 to 70 μm.
m, the amount of addition is 5 to 70% by weight, and the second light diffusion layer 20 has a thickness of 10 to 500 μm, a particle size of the foil piece to be added of 10 to 200 μm, and an addition amount of 0.1 to 70%. % By weight. In the case where the foil pieces in the first light diffusion layer are oriented in a direction parallel to the layers and the thickness is increased, the first light is diffused by stacking thin layers having a reduced thickness. It is preferable to form a diffusion layer.

The first and second light diffusion layers are formed by coating,
It is performed by a known method such as a casting method, a calender method, and an extrusion method. As a method of laminating another light diffusion layer on one light diffusion layer, there are known methods such as heat fusion, coating, and melt extrusion coating.

When the light diffusion layer is formed by coating, the orientation angle distribution of the foil pieces can be controlled by the coating conditions. Using a coating liquid obtained by dispersing foil pieces in a transparent resin liquid, a coating method in which a shear stress is applied between a substrate to be coated and a coating head, for example, gravure roll coating, roll coating, knife coating , Comma coat, wire bar coat and the like. When the first light diffusion layer is formed, the thickness of the coating film is made relatively small as compared with the particle size of the foil piece. Then, as shown in FIG. 9A, the coating head 31 and the base material 32
The foil piece 33 is forcibly parallel to the front and back surfaces of the transparent resin liquid 34 by direct contact with the coating head 31 or by shearing stress based on the velocity gradient of the transparent resin liquid 34. It is oriented by receiving a couple [F] in the direction ([F] indicates a vector amount). In particular, (foil piece thickness) <(coating film thickness) <
(Grain size) is preferred. In the case where the second light diffusion layer is formed, the thickness of the coating film is relatively large as compared with the particle size of the foil piece. Then, as shown in FIG. 9B, a couple [F]
In the case where the bottom surface is oriented parallel to the front and back surfaces of the coating film, only some of the foil pieces 33 near the front surface, and the other (the one closer to the base material 32) foil piece 33 is less affected by shear stress. No orientation remains. Also, once oriented foil piece 3 near the surface
In No. 3, since the orientation is easily disturbed by convection in the coating film, etc., the non-orientation becomes strong. That is, the ratio of the foil pieces 33 whose bottom faces are oriented in the normal direction of the coating film is higher than that in the case of FIG. When a coating method such as spray coating that does not generate a velocity gradient and shear stress in the thickness direction of the coating film is used, non-orientation is further enhanced. In particular, it is preferable that (coating film thickness)> (foil piece particle size).

To obtain a second light diffusion layer in which the bottom surface of the foil piece is oriented at a higher ratio in the normal direction of the coating film, as shown in FIG. 10, a foil piece 41 made of a magnetic material (for example, Using ferric oxide (α-type or γ-type), barium ferrite, permalloy, ALNICO, iron, cobalt, nickel, etc., the magnetic field [H] in the normal direction by the magnet 43 while the transparent resin 42 is in an uncured state. To apply. If the axis of easy magnetization of the magnetic material foil piece 41 is selected within the bottom face, the foil piece 41 is oriented with the bottom face aligned at a high ratio in the normal direction due to the couple [F] received in the magnetic field. The magnetic field may be formed using either a permanent magnet or an electromagnet.

In order to form the light diffusion layer by a stretching method, a foil piece is dispersed in a transparent resin layer to form a solid film, and then the transparent resin layer is stretched uniaxially or biaxially to form an inner foil piece. Are oriented in the stretching direction.

FIG. 11 shows the optical behavior when the foil pieces are randomly oriented (non-oriented) in the light diffusion layer.
FIG. 11A shows a case where incident light is applied from the front side,
Light reaching the back surface as rays L ₁₂ and L ₁₃ are, will be flowed through it, there is no chance of reflection to the surface. On the other hand, come reflected on the surface is the case, such as L ₁₄ and L _15, what is the attenuation is large, which multiply reflected in a number of the foil strips as these L _14, also the reflection angle increases, There are many things outside the viewing angle. The L ₁₅ is the attenuation for the single reflection is small but the greater the larger the reflection angle as shown in stochastic. Therefore, the amount of reflected light that returns within the normal viewing angle of the observer is smaller than that of the second light diffusion layer 20 shown in FIG. Further, the oblique incident light entering from the surface is present some others are reflected into the field of view angle as L ₁₆ (of course, L ₄ in FIG. 1
Although there are some that are removed from within the viewing angle, such as Therefore, the effect of blocking obliquely incident light is lower than that in FIG. FIG. 11 (b) is a case containing the incident light from the rear surface (diffused light), because the orientation of the foil strip is random, L ₁₈ and L
₁₉ some of which transmit as diffused light to the surface as it is small, the greater the light would rather go back to the incident side as L _17. Since the light transmitted to the surface side is also the number of times of multiple reflections as L _19, often attenuated in comparison with FIG. Therefore, the amount of transmitted light is smaller than that of the first light diffusion layer 10 shown in FIG.

FIG. 12 shows the optical behavior when only the first light diffusion layer is used. FIG. 12A shows incident light from the surface. The incident light in the normal direction near the viewing angle, since the majority of light coming back after being reflected in the visual field angle as L ₂₀ and L _21, the reflectivity as in FIG high. Further, the oblique incident light is also intended to be reflected in the viewing angle as the field of view outside of those that are excluded from the angle, L ₂₂ as L _23, the blocking effect is lower than in Figure 1. FIG. 12B shows incident light from the back surface. Most light rays are reflected by the same principle as that of FIG. Therefore, the transmittance is low.

FIG. 13 shows the optical behavior when only the second light diffusion layer is used. FIG. 13A shows incident light from the surface. Most light is transmitted as L ₂₈ , and the transmitted light is no longer reflected by anything. Therefore, the reflectance is low. The obliquely incident light is reflected out of the viewing angle and removed as indicated by L ₂₉ , and its blocking effect is large. FIG.
(B) is a case of the incident light from the back surface. Ray of majority as L ₂₉ is transmitted while being slightly diffused. Therefore, the transmittance is high as in FIG.

When a third light diffusion layer is provided on the back surface of the first light diffusion layer in the light diffusion sheets A and B shown in FIG. 8, a conventional ordinary light diffusion transmission sheet is used as the light diffusion layer. I just need. For example, polyethylene terephthalate,
A resin sheet made of acrylic, polycarbonate, or the like is provided with light diffusion transmittance by sandblasting, embossing, kneading light diffusing agent particles such as silica, or the like. The thickness may be about 10 to 1000 μm, and the haze may be about 70 to 90.

The light diffusion sheets A and B shown in FIG. 8 are laminated on the surface of various surface light sources so that the second light diffusion layer 20 faces the observer and the first light diffusion layer 10 faces the light source. Thus, when the surface light source is turned on when the surroundings are dark, it is possible to output diffused light having a uniform distribution within an appropriate viewing angle due to the characteristics of the light diffusion sheet. In addition, when the surface light source is turned off when the surroundings are bright, the light within a predetermined viewing angle among the external light such as sunlight and electric light is reflected within the viewing angle with a high reflectance. Looks bright. Therefore, a bright surface can be obtained in both a bright place and a dark place, and the power supply can be consumed only when necessary (only in the bright place), so that the energy efficiency is good.

As the surface light source, a direct light type as shown in FIG. 14, an edge light type as shown in FIG.
Any of the electroluminescent materials (EL) shown in FIG.

In the direct type surface light source shown in FIG. 14, a light emitting diode (LED), an incandescent light bulb or the like is used as the point light source 52, or a fluorescent lamp or the like is used as a line light source instead of the point light source.
The inner surface of the housing 53 (housing) is finished with a reflective surface 53a having a high reflectance by a metal mirror surface, white paint, or the like. In the structure shown in the figure, it is preferable to use the third light diffusion layer 30 because the light diffusion property of the light source itself is insufficient.

In the edge light type surface light source shown in FIG. 15, the light source 61 may be a point light source in addition to the line light source as shown in FIG. For the light guide 62 made of a translucent flat plate, a resin such as ceramics such as glass, acrylic, or polycarbonate is used. In addition to the rectangular parallelepiped as shown, the shape may be a known shape such as a wedge-shaped cross section whose thickness becomes thinner as it goes away from the light source 61. The light reflection layer on the back surface of the light guide 62 usually has a diffuse reflection layer 63 in a partial pattern such as dots (circles and polygons) and stripes as shown in the figure, and a mirror reflection layer 64 on the back surface. By increasing the coverage area ratio of the diffuse reflection layer 63 as the distance from the light source 61 increases, the luminance distribution in the output surface can be made constant regardless of the distance from the light source 61. A reflecting mirror 65 made of a metal plate or the like is provided around the line (or point) light source 61 so that light from the light source can be efficiently input into the light guide plate 62 from the side end surface of the light guide 62. The light source 61 may be provided on only one, two, three or four end faces of the light guide 62 as shown in the figure. The light diffusion sheet has a structure in which the first light diffusion layer 10 has the light guide 6.
Place it so that it faces two sides. Further, in order to increase the diffusion angle of the output light or to further increase the invisibility of the light diffusion reflective pattern, a third light diffusion layer is further provided between the first light diffusion layer 10 and the light guide 62. May be inserted.

As a method of forming the first light diffusion layer and the second light diffusion layer, or the first, second, and third light diffusion layers on the light guide 62, a method of simply forming the first light diffusion layer and the second light diffusion layer on the surface of the light guide 62. A method for mounting these light diffusion layers, a method for thermally fusing these light diffusion layers to the surface of the light guide 62 by hot pressing, co-extrusion molding, or the like, and a method for disposing these light diffusion layers on the surface of the light guide 62 are known. Or a method using the light diffusion sheet itself of FIG. 6, FIG. 7, or FIG. 8 as a light guide (in this case, the first or third light Light source light from the diffusion layer).

The light diffusing sheet of the present invention is preferably laminated on the back surface of a liquid crystal display (LCD) so that the second light diffusing layer is located. In a light place, ambient light is reflected by the light diffusion sheet on the back of the LCD, and by using the reflected light, a sufficiently bright image can be observed even when the back light source is turned off. Further, whitening of an image and lowering of contrast due to obliquely incident light can be suppressed. On the other hand, in a dark place, by turning on the back light source, a bright image can be observed, and the viewing angle becomes appropriate. As the LCD, various types such as a TN type and an STN type can be used. Adhesion to the LCD uses heat fusion, adhesion with an adhesive or an adhesive, or the like. Usually, it is often bonded to the back polarizing plate of the LCD, but the back light source, the transparent electrode plate,
Alternatively, it may be adhered to a protective film of a polarizing plate. Also, LC
D, ECD (Electrochromic Display)
The light diffusion sheet of the present invention can be applied to the back surface of a display device of a non-light-emitting type in which transmitted light is modulated to form an image.

An electroluminescent (E) as a surface light source shown in FIG.
As L) 71, various commonly used materials are used.
The phosphor layer is interposed between the front and back electrodes, at least on the front side of which is a transparent electrode, and the entire EL element is sealed with a protective layer for preventing moisture and the like, if necessary. A DC or AC voltage (electric field) is applied between the front and back electrodes to cause the phosphor to emit light to form a surface light source. As a phosphor, ZnS, SrS, SeS, or the like is used as a base material, and Cu, Mn, Ce, Eu, Sm, Tb
A material doped with F ₃ , PrF ₃ , Cl, or the like as an activator (emission center) is used. The phosphor is applied as a powder dispersed in a binder of a dielectric material such as acrylic or polyvinylcarbazole as a powder, or the phosphor itself is formed into a thin film by sputtering, vapor deposition, CVD, or the like to form a phosphor layer. As the transparent electrode, an electrode in which a transparent conductive layer made of tin oxide, indium oxide, ITO or the like and a light-reflective conductive layer made of Al, Ag or the like are formed on the phosphor side of a transparent plate made of glass, resin, or the like is used.

FIG. 17 shows a lens arrangement sheet 81 in which minute lenses (or prisms) are arranged in a one-dimensional or two-dimensional direction, in which the light diffusion sheet of the present invention is laminated on the non-lens surface. It is. By placing this sheet on the surface of a surface light source such as an edge light type, a direct type, or an EL, the light distribution of output light can be achieved by the action of the lens array sheet 81 as compared with the surface light source having the configuration shown in FIGS. The characteristics are modulated in various ways to obtain desired light distribution characteristics depending on the application. That is,
The viewing angle can be widened or narrowed, and the peak direction of the light distribution characteristics can be changed to an arbitrary angle with the normal to the light exit surface. In addition, it can also be used as a transmissive / reflective projection screen. As the lens or prism array, in addition to the triangular prism prism linear array of FIG.
A so-called linear (1) in which a large number of columnar unit lenses such as a circular (or elliptical) column lenticular lens and a linear Fresnel lens are arranged so that their ridge directions are parallel to each other.
Various types such as a so-called two-dimensional array in which unit lenses such as a fly-eye lens or a unit lens such as a fly-eye lens are arranged in a two-dimensional direction (front-back, left-right) in a plane, or an annular Fresnel lens are selected according to the application. .

The light diffusion sheet of the present invention is also used as a projection film. Also, the configuration as shown in FIG. 17 is used as a projection screen. That is, the projection light enters from the first (or third) light diffusion layer side and is observed from the second light diffusion layer (or lens array sheet) side, so that it can be used as a transmission type projection screen. Also, if projection light enters from the second light diffusion layer (or lens array sheet) side and is observed from the same side, it can be used as a reflection type projection screen. That is, the same projection screen can be used for both the reflection type and the transmission type, and in each case, the projection screen is excellent in both a bright image (screen), an appropriate viewing angle, and a performance of preventing a decrease in contrast against oblique incident light. .

The light diffusion sheet of the present invention may be in the form of a transfer sheet or a pressure-sensitive adhesive sheet for convenient application to various members. The transfer sheet has a configuration in which the transfer sheet is laminated on a flexible support sheet (for example, biaxially stretched PET) in a releasable manner, and an adhesive layer is formed on the light diffusion sheet. The adhesive layer of the transfer sheet is brought into contact with the surface of the substrate on which the light diffusion sheet is to be formed, and the adhesive force is exerted by heating, pressurizing, etc. The light diffusion sheet of the present invention can be laminated. Examples of adhesives include various known heat-sensitive adhesives (thermoplastic resins such as vinyl acetate) and adhesives (acrylic, rubber, etc.)
May be used. The pressure-sensitive adhesive sheet has a configuration in which a pressure-sensitive adhesive layer is provided on the light diffusion sheet directly or without a transparent base sheet (for example, biaxially stretched PET). If necessary, a known release sheet (paper) may be temporarily bonded on the pressure-sensitive adhesive layer.

[0040]

EXAMPLES Hereinafter, examples will be described together with comparative examples.

Table 1 shows the light diffusion sheet (Example, Comparative Example 1,
The layer structure of 2) and the measurement results of various evaluations for each are shown in FIG. The light diffusion sheet provided with the third light diffusion layer is described as an example. In the case of the configuration including only the first and second light diffusion layers, the incident light from the back surface is used by making the same diffused light as the transmitted light of the third light diffusion layer incident thereon, so that the It is obvious that the characteristics are substantially the same as those of the light diffusion sheet of the embodiment, so that the description is omitted, and the light diffusion sheet including the first and second light diffusion layers is also represented in the embodiment of Table 1.

[0042]

[Table 1]

The evaluation items in Table 1 are as follows:
It is like (3).

(1) Transmittance for incident light from the back surface (third light diffusion layer side) “Tt” is the total light transmittance (%), and “Td” is the diffuse transmittance (%). It represents the brightness of light, and the larger the value, the brighter the light. "Haze" indicates the degree of cloudiness of the layer. The greater this value, the higher the uniformity of transmitted light (uniformity in the output plane and uniformity with respect to the angle in the viewing angle). Also, the pattern of the light source on the back surface is difficult to see. These Tt, Td, and haze are all JIS-K-
7105 ".

(2) Reflectance for incident light from the surface (the second light diffusion layer side) "Rt" is the total light reflectance (%), and the larger this value is, the brighter the reflected light is. This was also measured based on "JIS-K-7105".

(3) Reflectivity for obliquely incident light on the surface “G ₆₀ ” is specular glossiness for incident light at 60 °, which corresponds to whitening of the surface and reduction in contrast due to reflection of obliquely incident light. The smaller this value is, the better the oblique incident light blocking and antireflection performance is. This is "JIS-Z-874
1 ".

The structure of each light diffusion layer in Table 1 is as follows (1) to (3).

(1) Third light diffusion layer "Lumirror X42" (50 μm thick) manufactured by Toray was used. This is a light diffusion transmission sheet obtained by kneading a light diffusion agent into biaxially stretched PET, and its optical property is Tt = 5.
5.7%, Td = 51.6%, haze = 92.3, G ₆₀
= 23.2.

(2) First light diffusing layer On the third light diffusing layer, an ink in which light reflecting foil pieces were dispersed was printed by gravure printing. In particular,
A gravure plate having a cell shape of a tortoiseshell shape, a screen ruling of 127 lines / inch and a plate depth of 50 μm was used. Five 2.6 μm-thick layers were overprinted using an ink having the following composition. Thus, a light diffusion layer having a total thickness (when dried) of 13 μm was obtained. In the first light diffusion layer, almost all the foil pieces were oriented in a direction parallel to the front and back surfaces of the layer (approximately like the first light diffusion layer 10 shown in FIG. 8B).

[Ink composition] Pigment: scale-like foil of titanium dioxide-coated mica (particle size (diameter of circumscribed sphere) distribution is 10 to 130 µm). The added amount is (pigment) / (binder + pigment) = 0.62 (weight ratio) Binder (transparent resin): mixture of vinyl chloride / vinyl acetate copolymer, polyol, diisocyanate Diluent solvent: methyl ethyl ketone / toluene = 1/1
(Weight ratio)

(3) Second Light Diffusion Layer On the first (or third) light diffusion layer, an ink in which light reflecting foil pieces were dispersed was applied using a comma coater. Specifically, a layer having a thickness of 15 μm (when dried) was obtained by one coating using the ink having the same composition as described above. In this second light diffusion layer, the foil pieces were distributed substantially uniformly in all directions (generally, the second diffusion layer 20 shown in FIG. 8B).
Like).

As can be seen from Table 1, in the light diffusion sheet comprising only the third and first light diffusion layers (Comparative Example 1), the reflectance for the light incident on the front is high, but the transmittance for the light incident on the back is low. Also, reflection of obliquely incident light is not suppressed. Further, in the light diffusion sheet (Comparative Example 2) including only the third and second light diffusion layers, the transmittance for the light incident on the back surface increases, but the reflectance for the light incident on the front surface decreases instead. However, reflection of the obliquely incident light is suppressed.
On the other hand, in the light diffusion sheet of the example, both the transmittance of the rear incident light and the reflectivity of the front incident light are high, and the reflectivity of the oblique incident light is also low. In addition, haze is 9
Since it is as high as 3.3, the uniformity of transmitted light is good and the pattern of the light source on the back surface is not conspicuous.

[0053]

Since the present invention is configured as described above, the following effects can be obtained.

In the light diffusing sheet according to the first aspect, a high diffuse reflectance and a high diffuse transmittance, which were conventionally incompatible, are compatible, and the reflectance is relatively higher than the transmittance. Moreover, the ratio of obliquely incident light (stray light) entering from outside the viewing angle to be reflected within the viewing angle becomes extremely small. Therefore, the entire image is not whitened or the contrast is not reduced.

In the light diffusion sheet according to the second aspect, when the incident light from the back surface is a parallel light beam, a sufficiently high diffusion transmittance can be obtained.

According to the edge light type surface light source according to the third aspect, when light is emitted from the light source, it is possible to obtain output light having high efficiency, high brightness and an appropriate viewing angle. When the light source is turned off, the output surface of the light source functions as a reflection surface having a high diffuse reflectance. Moreover, the reflectance of the obliquely incident light in the viewing angle direction is extremely low. Therefore, by using this light source as a back light source for various non-light emitting display devices, advertising signs, etc., in a bright place, reflected light of surrounding light can be efficiently used, and a bright image can be observed without power consumption of the light source. . In a dark place, a bright image can be observed by turning on the back light source, and the power can be used efficiently. That is,
Both natural light and artificial light can be effectively utilized by appropriate switching. In addition, the decrease in contrast and whitening of the image due to obliquely incident light are inconspicuous.

A liquid crystal display (LCD) according to claim 4.
According to the method, in a bright place, ambient light is reflected by the light diffusion sheet on the rear surface of the LCD, and by using the reflected light, a sufficiently bright image can be observed even when the rear light source is turned off. Further, whitening of an image and lowering of contrast due to obliquely incident light can be suppressed. On the other hand, in a dark place, by turning on the back light source, a bright image can be observed, and the viewing angle becomes appropriate.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an optical behavior with respect to incident light from the surface of a light diffusion sheet including first and second light diffusion layers.

FIG. 2 is an explanatory diagram showing an optical behavior with respect to diffused light from the back surface.

FIG. 3 is an explanatory diagram of an orthogonal coordinate system used to define an orientation direction of a bottom surface of a foil piece.

FIG. 4 is an explanatory diagram of polar coordinates.

FIG. 5 is orthogonal coordinates showing a curved surface on which the foil piece orientation distribution of the light diffusion layer is plotted.

FIG. 6 is an explanatory diagram showing an optical behavior when incident light from the back surface is a parallel light beam.

FIG. 7 is an explanatory diagram illustrating an optical behavior when incident light from the back surface is a parallel light beam when a third light diffusion layer is provided.

FIG. 8 is a sectional view showing a light diffusion sheet as an embodiment of the present invention.

FIG. 9 is a cross-sectional view showing how a light diffusion layer is formed by coating.

FIG. 10 is a cross-sectional view showing how a foil piece in a transparent resin layer is oriented when a foil piece made of a magnetic material is used.

FIG. 11 is an explanatory diagram showing an optical behavior when the foil pieces are randomly oriented in the light diffusion layer.

FIG. 12 is an explanatory diagram showing an optical behavior in a case where only the first light diffusion layer is provided.

FIG. 13 is an explanatory diagram showing an optical behavior in a case where only a second light diffusion layer is used.

FIG. 14 is a sectional view showing a direct-type surface light source.

FIG. 15 is a perspective view showing a part of an edge light type surface light source.

FIG. 16 is a sectional view showing a surface light source using an electroluminescent body.

FIG. 17 is a perspective view showing a lens array sheet provided with a light diffusion sheet.

[Explanation of symbols]

 Reference Signs List 10 first light diffusion layer 11 foil piece 12 transparent resin 20 second light diffusion layer 21 foil piece 22 transparent resin 30 third light diffusion layer

Claims (4)

(57) [Claims] 1. A method in which light-reflective scale-like foil pieces are dispersed in a transparent resin layer, and a probability density function of an orientation angle distribution on a bottom surface of the foil pieces is parallel to the front and back surfaces of the transparent resin layer. A first light-diffusing layer having a peak, and a light-reflective flaky foil piece dispersed in a transparent resin layer laminated on the first light-diffusion layer, and a bottom surface of the foil piece. A second light diffusion layer in which the probability density function of the orientation angle distribution has a smaller value in the direction parallel to the front and back surfaces of the transparent resin layer than the foil pieces in the first light diffusion layer. Light diffusion sheet. 2. A light diffusion sheet according to claim 1, wherein a third light diffusion layer for diffusing and transmitting light isotropically or substantially isotropically is laminated on the back surface of the first light diffusion layer. A light-diffusing sheet, comprising: 3. A light guide made of a light-transmitting flat plate, a light reflection layer provided on a back surface of the light guide, and a light guide provided adjacent to at least one of side end surfaces of the light guide. And a light source or a point light source provided on the surface of the light guide, wherein the first light diffusion layer is stacked in a direction in contact with the light guide. An edge light type surface light source characterized in that: 4. A liquid crystal display device comprising the light diffusion sheet according to claim 1 or 2 laminated on the back surface of a liquid crystal display panel such that the second light diffusion layer faces the light diffusion sheet.