JPH06301035A - Plane light source, display device using the same and lens sheet used for the same - Google Patents

Abstract

PURPOSE:To provide a screen having high brightness, adequate visual field angle and a uniform intra-surface brightness distribution and to provide the plane light source for this purpose with the transmission type display device of a liquid crystal, etc. CONSTITUTION:The lenticular lens sheet 4 of the edge light type plane light source consisting of a light transmission plate 1, a light diffusion reflection layer 2 on the rear surface of this light transmission plate 1, a wire-shaped light source 3 on the flank of the light transmission plate 1 and the lens sheet 4 on the surface of the light transmission plate 1 consists of a sheet formed by arranging many unit lenses of an elliptic column or hyperbolic column shape by paralleling their ridge lines. The major axis of the ellipse or hyperbola faces the normal direction of the plane light source. A more preferable embodiment is a lens sheet formed by including a spacing 9 of the wavelength of light or above between the rear surface of the lens sheet 4 and the front surface of the light transmission plate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source, and a backlight for a transmissive display device such as a liquid crystal display device,
It is useful for lighting advertisements, traffic signs, etc. The present invention also discloses a transmissive display device such as a liquid crystal display device using the surface light source as a back light source.

[0002]

2. Description of the Related Art As a surface light source for a backlight of a liquid crystal display device (LCD), an edge light type one using a transparent flat plate as a light guide as shown in FIG. 7 is known. In such a surface light source, light is made incident from both or one of the side end surfaces of the light guide body made of a transparent parallel plate, and the light is propagated uniformly throughout the light guide plate by utilizing the total internal reflection of the transparent plate. A part of the propagated light is made into a diffuse reflection light having a critical angle less than a critical angle by a light scattering reflection plate on the back surface of the light guide, and the diffuse light is emitted from the surface of the light guide plate. (Actual development 55
-162201). As shown in FIG. 6, a lens sheet having a triangular prism type lenticular lens projection on one surface and a smooth surface on the other surface is stacked on the light guide plate surface of the surface light source with the projection surface facing upward. By utilizing the light focusing effect of the lens, the diffused radiation can be uniformly and isotropically diffused within a desired angular range (actual 4-107201). When this lens sheet is used in combination with a matte transparent diffusion plate (matte transparent sheet), the light energy of the light source is higher than that using only the matte transparent diffusion plate (US Pat. No. 4,729,067). Focused distribution within the desired limited angle range,
In addition, it was possible to obtain diffused light with high uniform isotropicity within the angle range.

[0003]

However, in the above-mentioned conventional technique, if only the light-scattering plate is provided on the back surface of the light guide, the emitted light is 60 degrees with respect to the direction normal to the surface of the light guide. The distribution has a relatively sharp distribution with the angle at the peak, the brightness in the normal direction, which requires the most light, is insufficient, and the light energy is dissipated in the oblique lateral direction where there is little acceptance. In the prior art, the triangular prism type lenticular lens sheet on the light emitting surface of the light guide refracts and focuses the emitted light, so that the normal direction of the light emitting surface has a peak at 30 ° to 6 °.
Although the ratio of the light energy emitted within the angle of 0 ° becomes high, on the other hand, as shown in FIG. 17, the peak (side lobe) of the emitted light also occurs in the direction (oblique direction) away from the normal direction. was there. For this reason, there remains loss light that does not contribute to the observer. Further, this side lobe is also inconvenient because it radiates unnecessary noise light to the surroundings. Further, contrary to the expectation about the brightness distribution in the emission surface, the brightness is high from 2 to 4 cm from the end portion on the light guide plate side,
It was found that when the distance from the light source is further increased, the brightness gradually decreases, and there is a problem that the end portion on the side opposite to the light source becomes noticeably dark.

In order to improve these drawbacks, as in Japanese Patent Laid-Open No. 1-245220, the light-scattering layer on the back surface of the light guide has a pattern of halftone dots or the like, and the area of the pattern is small as it approaches the light source. Attempt to correct and uniformize the brightness distribution within the light guide plate surface by increasing the distance from the light source. As in Japanese Patent Laid-Open No. 3-9306, light sources are arranged at two or more positions on the side edge of the light guide plate to correct the luminance distribution in the plane of the light guide plate.
Attempt to homogenize. However, in both cases, it is difficult to completely uniformize the brightness, and there is a drawback that halftone dots are conspicuous in the light scattering layer from the light emitting surface side. It had the drawback of being more than doubled.

An object of the present invention is to solve the above-mentioned problems and to provide a lens sheet for use as a backlight of a liquid crystal display device and a surface light source using the lens sheet. The object is to obtain uniform surface light emission with high brightness only within a desired angle range without increasing the amount of heat generation, and to obtain surface light emission without variation in brightness depending on the position in the surface.

[0006]

In order to achieve the above object, the present invention provides

1. A light guide body comprising a transparent flat plate or a rectangular parallelepiped cavity, a line light source or a point light source provided adjacent to at least one side end surface of the light guide body, and a back surface of the light guide body. A surface light source comprising a light reflecting layer and a concave or convex lenticular lens sheet laminated on the light emitting surface of the light guide surface, the lens sheet comprising elliptic cylinder unit lenses whose ridge line directions are parallel to each other. Are arranged in a large number of planes so that
The major axis of the elliptic cylinder unit lens is oriented in the direction normal to the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≦ long axis / minor axis ≦ 0.9 ×
A surface light source characterized by having n / (n ² −1) ^1/2 .

2. A light guide body comprising a light-transmissive flat plate or a rectangular parallelepiped cavity, a line light source or a point light source provided adjacent to at least one side end face of the light guide body, and a back surface of the light guide body. A surface light source comprising a light reflection layer and a concave or convex lenticular lens sheet laminated on the light emitting surface of the light guide surface, the lens sheet comprising hyperbolic column unit lenses whose ridge directions are parallel to each other. Are arranged in a plurality of planes so that the long axis direction of the hyperbolic pillar unit lens is oriented in the normal direction of the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≤ Asymptotic slope ≤ 0.9
A surface light source characterized by being × n / (n ² −1) ^1/2 .

3. The light guide is made of a light-transmissive flat plate having a smooth surface whose surface roughness is equal to or less than the wavelength of the light from the light source, and the lenticular lens sheet is provided on the surface opposite to the lens surface where the surface roughness is the wavelength of the light from the light source. It has the above-mentioned minute unevenness and is laminated with the minute uneven surface facing the smooth surface side of the light guide, and at least part of the gap between the light guide and the lens sheet is longer than the wavelength of the source light. The surface light source according to claim 1, wherein the surface light source has the following characteristics.

4. The light guide is made of a translucent flat plate having a smooth surface whose surface roughness is equal to or less than the wavelength of the light from the light source, and a light diffusion layer is provided between the back surface of the lenticular lens sheet and the light guide surface. It has been inserted, and the surface roughness and the back surface of the light diffusing layer have minute irregularities with a wavelength of the light of the light source or more, and as a result, voids having the wavelength of the light of the light source or more are formed at least partially. The surface light source according to claim 1, wherein the interface is provided at two locations, that is, an interface between the light guide surface and the light diffusion layer and an interface between the light diffusion layer and the back surface of the lens sheet.

5. A lamp house having at least one line light source or point light source, a lamp house which covers a lower surface and a side surface of the light source and has a window opened on an upper surface of the light source, and an inner surface on the light source side serving as a light reflecting surface, and the window. A surface light source comprising a concave or convex lenticular lens for covering a portion, the lens sheet comprising elliptic cylinder unit lenses arranged in a plurality of planes such that their ridge directions are parallel to each other. In the pillar unit lens, the major axis direction is oriented in the direction normal to the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≦ long axis / minor axis ≦ 0.9 ×
A surface light source characterized by having n / (n ² −1) ^1/2 .

6. A lamp house having at least one line light source or point light source, a lamp house which covers a lower surface and a side surface of the light source and has a window opened on an upper surface of the light source, and an inner surface on the light source side serving as a light reflecting surface, and the window. A concave or convex lenticular lens that covers a portion, and the lens sheet, wherein the lens sheet is formed by arranging hyperbolic pillar unit lenses in a plurality of planes such that their ridge directions are parallel to each other. In the pillar unit lens, the long axis direction is oriented in the direction normal to the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≦ asymptote slope ≦ 0.9
A surface light source characterized by being × n / (n ² −1) ^1/2 .

7. A display device, wherein a transmissive display element is laminated on a light emitting surface of the surface light source according to any one of claims 1 to 6.

The lens sheet 4 of the present invention is an elliptic cylinder lenticular lens or a hyperbolic cylinder lenticular lens. First, an elliptic cylinder lenticular lens will be described as an example. That is, as shown in FIG. 3A, it is a columnar lens group (so-called lenticular lens) in which convex unit lenses 42 having an elliptic columnar shape are arranged adjacent to each other with their ridge directions parallel.
The major axis direction of the ellipse faces the normal direction of the lens sheet 4. As the flatness of the ellipse, the ellipse equation is expressed as X ² / a ² + Y ² / b ² = 1 equation (1) where a is the minor axis length, b is the major axis length, and a <b ,
The major axis / minor axis = b / a = is 1.1 × n / (n ² −1) ^1/2 ≦ b / a ≦ 0.9 × n / (n ² −1) ^1/2 −−− --It is preferable to use the formula (2). The reason for designing the ellipse in this way is to eliminate the spherical aberration of the lenticular lens and to minimize the loss during focusing. That is, FIG.
5A and 5A, when a true cylindrical lenticular lens is used, even if the emitted light is focused within a predetermined diffusion angle θ by utilizing the focusing function of the lens, it is actually focused on the focal point F. The focused light is only the paraxial ray LN near the center of the lens, and the other rays LF defocus and become dissipated light (so-called spherical aberration). At this time, the light beam LF defocused
Will be dissipated from within each predetermined θ, resulting in light loss and unnecessary noise light.

The geometrical optical condition for minimizing the spherical aberration of the lenticular lens is between the flatness e of the ellipse of the cross section (main cutting plane) orthogonal to the ridge of the lenticular lens and the refractive index n of the lens material. , N = 1 / e Equation (3) should be satisfied. The flatness e can be written as e ² = (b ² −a ² ) / b ² formula (4) using the length 2b of the major axis and the length 2a of the minor axis of the ellipse. Therefore, from the formulas (1) and (2), the major axis / minor axis = 2b / 2a = b / a = n / (n ² −1) ^1/2 formula (5) If the substance of 1.5 is used, the spherical aberration disappears from the formula (5) when the major axis / minor axis = 1.34. However, in reality, a part of the light rays whose direction is deviated due to light diffusion and refraction due to the light diffusion / reflection layer 2 on the back surface of the light guide plate, the light diffusion layer 8 between the light guide plate and the lens sheet, etc. The light energy deviating from the angle θ is not zero, but can be minimized.

Even if it deviates from the expression (5) to some extent, it is possible to obtain characteristics close to those of the expression (5) while the difference is small. However, if it deviates from the expression (5) more than a certain degree, the peak of the angular distribution of luminance becomes a flat mountain centered in the normal direction of the light emitting surface due to spherical aberration, and side lobes are formed at both ends of the flat top. (Side peak) is made. It becomes unsuitable for the purpose of the present invention. As a result of the examination, if it is within + -20% of the formula (5), side lobes do not occur, and good light energy utilization efficiency, sharp diffusion angle, and
It was found that a high normal direction luminance can be obtained. However, from the practical viewpoint, it is preferable that the flatness ratio is within + -10% of the formula (5).

This unit lens is shown in FIGS. 3 (A) and 3 (C).
A convex lens as shown in FIG. 3B or a concave lens as shown in FIGS. 3B and 3D may be used.

The behavior of light rays of the elliptic cylinder unit lens is as follows:
This is as shown in FIGS. 5B and 5B. A ray incident parallel to the optical axis does not cause spherical aberration and has a focal point F.
And then diverge at a predetermined diffusion angle θ. With respect to the divergence angle θ, spherical aberration can be neglected, and a light ray largely deviated from the normal line of the light guide plate is fed back into the light guide plate due to total reflection between the smooth surface 10 of the light guide plate and the lens sheet 4. If light rays in the vicinity of the normal direction of the light guide plate, that is, light rays substantially parallel to the optical axis mainly enter the lens due to the diffuse reflection of the light reflection layer on the back surface of the light plate, roughly, θ = 2ta
n ⁻¹ (p / 2f) Expression (6) is obtained. However, p is the repeating period of the unit lens, and f is the focal length. As can be seen from the comparison between FIG. 4 and FIG. 5, the focusable position varies depending on the concave lens and the convex lens. That is, in the case of a convex lens as shown in FIG. 4B, the image formation becomes a real image and the focus can be on the outside of the lens (on the other side). See also FIG.
In the case of the concave lens as in (B), the image is formed as a virtual image and the focus can be inside the lens (front side). However, in any case, in the case of the use of the present invention, the focal length is set sufficiently smaller than the distance from the lens surface (that is, the surface of the surface light source) to the observer (usually 10 mm or less). There is no big difference between the concave and convex lenses.

In the above description, the elliptic cylinder type lenticular lens is exclusively described, but the unit lens cross section is expressed by the formula (6), X ² / a ² -Y ² / b ² = 1 formula (6) (however, here Where b / a is the slope of the asymptote, and a <
Similar effects can be expected even with a hyperbolic columnar lenticular lens represented by b,). The optimum ranges of a and b are the same as in the case of an elliptic cylinder.

Although these lens sheets can be used as a single sheet, in order to control the light diffusion angle in the X, Y2 directions (vertical direction, horizontal direction, etc.) by using a columnar lens, as shown in FIG. The lens sheets may be laminated so that their major axes are orthogonal to each other. In this case, the lens surfaces should be oriented in the same direction as shown in FIG. 6 because of the high transmittance of the components of light rays coming from the light reflecting layer 2 which are relatively close to the normal direction, It is the best in terms of balance with the high feedback rate of the light beam inclined from the normal direction to the light guide plate, but of course the lenses of each lens sheet face each other (the lens surface is sandwiched between two lens sheets). Can be laminated. Also, the lens sheet is shown in FIGS.
It may be obtained by integrally molding a translucent substrate as shown in Fig. 3, or as shown in Figs. 3 (B) and 3 (D), a translucent flat plate (or sheet) 4
The unit lens 42 may be formed on the surface 4.

The lens sheet 4 is formed of a transparent base material. Here, as the translucent base material, a homopolymer or a copolymer of acrylic acid ester or methacrylic acid ester such as polymethyl methacrylate, polymethyl acrylate, and the like,
Polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonates, polystyrenes, thermoplastic resins such as polymethylpentene, or transparent resins such as polyfunctional urethane acrylates, polyester acrylates and other acrylates, unsaturated polyesters crosslinked by ultraviolet rays or electron beams. , Transparent glass, transparent ceramics, etc. are used.

When used as a lens sheet, this translucent substrate usually has a total thickness of about 20 to 1000 μm.

As a method for forming a lens shape, for example, a publicly known hot pressing method (described in JP-A-56-157310), an emulsifying process using a roll embossing plate on an ultraviolet-curable thermoplastic resin film, A method of irradiating ultraviolet rays to cure the film (JP-A-61-61
No. 156273), an ultraviolet or electron beam curable resin liquid is applied on a roll intaglio engraved with a lens shape and filled in the recess, and then the roll intaglio is still coated with the transparent base film through the resin liquid. A method in which a resin cured by irradiation with ultraviolet rays or an electron beam and a base film adhered to the resin are released from a roll intaglio, and the lens shape of the roll intaglio is applied to a cured resin layer (JP-A-3-223883, US Pat. No. 4,576,850) and the like are used. In the case of the method, the ultraviolet ray or electron beam curable resin has relatively flexibility and flexibility in order to prevent the occurrence of cracks and the like during processing because of the convenience of winding and processing the molded lens sheet. Select one.

The translucency required for the translucent base material must be selected so that diffused light can be sufficiently transmitted to the extent that it does not hinder the use of each application, and colorless and transparent is most preferable. Depending on the application, it may be colored transparent or matt translucent.
Here, the matte transparent has a property of diffusing and transmitting the transmitted light almost uniformly and isotropically in all directions within a semi-solid angle, and is synonymous with light isotropic diffusivity. That is, the term "matte transparent" means that when a parallel light flux is incident from the rear surface (incident angle i
= 0 °), the angular distribution I ⁰ (θ) of the transmitted light intensity is c
os distribution I ⁰ (θ) = I ⁰ _mp cos θ, −90 ° ≦ θ ≦ 90 ° Formula (8) θ is the angle formed by the normal line N, I ⁰ _mp is the transmitted light intensity in the normal direction or similar to it. It is said to be distributed. Note that I ⁱ
The definition of (θ) will be described later.

It is preferable to provide minute irregularities (a group of minute protrusions) on the back surface of the lens sheet (the surface opposite to the lens surface). The reason is different between the so-called edge light type surface light source as in claims 1 to 4 and the so-called direct type surface light source as in claims 5 to 6. In the case of the edge light type, as will be described later, it is for uniforming the luminance distribution in the light emitting surface, while in the case of the direct type, the purpose is to make the angular distribution of luminance within a predetermined light diffusion angle uniform. (In this case, just the light diffusion effect). Minute irregularities 4 whose height formed on the back surface of the lens sheet is not less than the wavelength of the light source light and not more than 100 μm
No. 1 can be directly formed on the back surface of the integrally molded lens sheet 4 as shown in FIG. 14 by embossing by heat pressing, sandblasting, etc., or else on the flat back surface of the lens sheet 4 as shown in FIG. It is also possible to form a light-transmitting material layer having protrusions. Specifically, a method in which transparent fine particles of calcium carbonate, silica, acrylic resin, or the like are dispersed in a transparent binder to coat the surface of the coating film to form irregularities of the fine particles, or the method described in JP A method of molding an ultraviolet or electron beam curable resin liquid on a roll intaglio disclosed in, for example, US Pat. No. 3,223,883, U.S. Pat.

The projection 41 is intended to at least partially form a gap 9 (dimension ΔX) equal to or longer than the wavelength of the light source light between the smooth surface 10 of the light guide plate 1 and the lens sheet 4 as shown in FIG. Is. As will be described later, when the gap ΔX is less than the wavelength of the light from the light source, total reflection of light on the smooth flat surface 10 of the light guide plate 1 does not sufficiently occur, and when it exceeds 100 μm, the uneven shape of the protrusions becomes conspicuous, which is inconvenient.

The projection 41 may have any uneven shape as long as this purpose is achieved, but from the viewpoint of obtaining a uniform brightness angular distribution within a desired diffusion angle and a uniform brightness distribution within a light source surface, In the best mode, as shown in FIGS. 3C and 3D, a random uneven shape (for example, a grain pattern, a satin pattern, etc.) is formed on the entire back surface of the lens sheet 4. In this way, as shown in FIG. 11, the light L1, L2S, etc. incident from the back surface of the lens sheet 4 is isotropically diffused by the projection group 41 also acting as a light diffusion layer. A uniform angle distribution can be obtained without interposing a matte transparent sheet, and a dot pattern is not conspicuous, which is good.

In addition to this, of course, as shown in FIG. 10, a light isotropic diffusive sheet 8 having a matt transparency and a group of protrusions 41 having a surface wavelength of 100 μm or less, a lens sheet 4 and a smooth surface 10 of the light guide plate. You can also intervene between. However, in this case, since there are a plurality of interfaces for diffusing light (smooth flat surface 10 light isotropic diffusing sheet 8 /, light isotropic diffusing sheet 8 / rear surface of lens sheet 4), it is effective to move in the vicinity of the normal direction. The transmittance of light energy is maximized, and the reflectance of light energy that is wasted as a light source far from the normal direction (oblique to the tangential direction of the light emission surface) is also maximized (this reflected light is As you can see, the light reflection layer 2 in another place
Sent to and reused there. ) The light energy utilization efficiency is maximized, and at the same time, the brightness distribution in the entire light emission surface is also most uniform.

Further, as shown in FIG. 14, the minute concavo-convex pattern 41 may be a pattern in which dot-like patterns such as halftone dots are arranged in a plane in a distributed manner. However, in this case, the pattern 41 is conspicuous, and it is necessary to devise a method of dispersing the matting agent in the lens sheet 4.

The surface light source of the present invention has a structure shown in the sectional views of FIGS. 10 and 11 and the perspective views of FIGS. The light guide plate 1, the linear or point light source 3 installed adjacent to at least one of the side end portions thereof, the light reflection layer 2 on the back surface of the light guide plate, and the surface opposite to the light reflection layer of the light guide plate. The lens sheet 4 has a minimum configuration. Usually, the light source light reflecting mirror 5, the entire housing, a housing (not shown) having a light emitting surface as a window, a power source (not shown), etc. are also attached to these.

The opposite surface 10 of the light-reflecting layer of the light guide plate 1 is a flat surface, and the surface roughness (measured by the ten-point average roughness Rz of JIS-B-0601) is equal to or less than the wavelength of the light source light. . Usually, the light source is visible light, and its wavelength is 0.4 ~
Since it is 0.8 μm, the surface roughness is 0.4 μm or less. Known methods for finishing to this degree of roughness, such as heat pressing with a mirror surface plate, injection molding using a mirror surface shape, casting (casting) molding, precision polishing performed with optical lenses, etc. Should be used.

The material of the light guide plate 1 is selected from the same translucent materials as the material of the lens sheet. Usually, acrylic or polycarbonate resin is used. The thickness of the light guide plate is usually about 1 to 10 mm.

As the light source 3, a linear light source such as a fluorescent lamp is preferable in order to obtain uniform brightness over the entire surface, but a point light source such as an incandescent lamp can also be used. The light source 3 is provided outside the side end portion of the light guide plate as shown in the figure, and the side end portion of the light guide plate 1 is partially cut away so that a part or the whole is embedded in the light guide plate. Things are possible. The light source 3 can also be installed at the other side end of the light guide plate 1 from the viewpoint of high brightness and uniformity of brightness in the plane. As the light source light reflecting mirror 5, a well-known one is used, for example, a plate having a shape of a parabolic column, a hyperbolic column, an elliptic column, or the like, on the inner surface of which metal vapor deposition is performed.

In the case of an edge light type surface light source, the lens sheet 4 is laminated on the smooth flat surface 10 of the light guide plate.
At that time, as shown in FIGS. 10 and 11, the lens surface of the lens sheet 4 is placed on the outside (opposite surface of the flat surface 10) so that the minute irregularities 41 face inward (on the flat surface 10 side). At least a part of the gap 9 having a wavelength λ of the light of the light source or more is formed between the light guide plate 1 and the smooth surface 10. The area ratio R of the void portion 9, that is, R = (area of the void portion having a wavelength of λ or more / total surface area of the light guide plate) × 100% is the required uniformity of brightness in the plane and the utilization efficiency of light energy. Although it is determined by the dimensions of the light guide plate, the ratio R is usually required to be 80% or more, and more preferably 90% or more.

The reason for this is that as a result of the experiment, when the surface 10 of the lens sheet and the surface 10 of the light guide plate, both of which have a surface roughness equal to or less than the wavelength of light as shown in FIG. It has been found that most of the input light from Eq. 1 is emitted from the side end on the light source side at a distance y without being totally reflected, and the brightness is sharply reduced and dark at a position far from y. The ratio of the length y of the light emitting portion to the total length Y of the light guide plate in the light propagation direction, (y / Y) × 100 = 10 to 20%
It turned out to be Therefore, from the light source to the light guide plate plane 10
In order to evenly distribute the amount of light energy incident on the total length Y, it is necessary to transmit 10% to 20% of the incident light on the plane 10 and totally reflect the remaining 90% to 80%.
Generally, (amount of transmitted light / amount of total reflected light) = (area of void portion having wavelength λ or more / total surface area of light guide plate) = R Since it is approximated by the formula (9), R is required to be 80 to 90% or more. It turned out that

As a method of forming an air gap having a wavelength equal to or longer than the light source light between the lens sheet 4 and the light guide plate 1, the lens sheet 4 is arranged such that the lens surface 42 and the projection group 41 are oriented as shown in FIG.
0, it is also possible to invert it from FIG. 11 (not shown). However, in this case, the light once focused within the desired angle on the lens surface 42 diverges in a eastern fashion again,
30 degrees to 6 around the normal, which is the optimum value for the light diffusion angle
It is difficult to control within 0 degrees.

The light reflecting layer 2 is a layer having a property of diffusing and reflecting light, and can be constructed as follows. On one surface of the light guide plate layer, a white layer in which a pigment having high hiding property and high whiteness, for example, powder of titanium dioxide, aluminum or the like is dispersed is formed by coating or the like. A metal thin film layer is formed by further plating or vapor-depositing a metal such as aluminum, chromium, or silver on the uneven surface of the light guide plate on which matte fine unevenness has been formed by sandbright processing, embossing, or the like. A metal thin film layer is formed on a white layer which has a low hiding property and is formed by simply coating a matte surface. It may be formed in a white dot-like layer and the area ratio may be increased as the distance from the light source increases so as to correct the attenuation of the light amount of the light source.

The structure of the surface light source 100 of the present invention used as a backlight (rear surface light source) of a transmissive display device such as a transmissive LCD is as shown in FIGS. That is, the display device of the present invention is obtained by stacking the transmissive display device 6 on the lens surface (the side where the unit lens 42 is located) of the lens sheet of the surface light source 100 of the present invention.

The diffusion angle is effective for evaluating the light distribution of the surface light source. A half value angle θ _H is used as the diffusion angle, for example. When the transmitted light brightness (or intensity) is defined as a decreasing function I (θ) of the angle θ from the normal line of the light emitting surface,
It is defined as an angle θ _{H such that} I (θ _H ) = I (θ) / 2.

[0033]

The elliptic cylinder lenticular lens according to the first and fifth aspects does not cause spherical aberration geometrically as described above. That is, the true cylindrical unit lens has spherical aberration as shown in FIGS. 4 (A) and 5 (A), and the incident light ray L2 distant from the optical axis.
Is not focused on the focal point, and as a result, a part of the light deviates from the range of the predetermined diffusion angle θ and is wasted. On the other hand, the elliptic cylinder unit lenses of FIGS. 4 (B) and 5 (B) used in the present invention are designed so that spherical aberration does not occur or that it can be ignored as described above. Therefore, the incident light parallel to the optical axis is refracted by the lens lens 4 and then converges to one focal point, and then diverges at that point, so that the emitted light has a desired diffusion angle θ (equation (6)). The light is condensed at an angle close to, and is effectively used. In the case of a concave lens, the focus position is the difference between the entire position and the rear of the lens as compared with the convex lens as described above. Therefore, for an observer who is far away from the focal length of the lens sheet 4, the same action as the convex lens is performed.

Also in the case of a hyperbolic lenticular lens,
This is similar to the case of the elliptic cylinder lenticular lens.

Next, the void 9 in the edge light type surface light source will be described. As shown in FIG. 7, the action mechanism of the edge light type surface light source is that, among the light rays that are incident on the light guide plate 1 from the light source 3 and are directly incident on the smooth flat surface 10 of the light guide plate, L1 that is incident near the light source is the incident angle (the surface 10 Since the angle formed by the normal line of 1) is small and less than the critical angle, some of the incident light amount is emitted as transmitted light L1T. Thereby, emitted light near the light source is formed. On the other hand, the light ray L2 that is directly incident on a relatively distant place from the light source 3 has a large incident angle and is equal to or greater than the critical angle. Diffuse (random) reflected light L2S is propagated in all directions in the light diffusive reflection layer 2 on the back surface. Some of these incident on the surface 10 at less than the critical angle, and some more of it becomes emitted light. This forms the emitted light at a distance from the light source.

Here, on the smooth flat surface 10 of the light guide plate 1,
FIGS. 8 and 9 show a state in which the smooth surface of the lens sheet 4 whose non-lens surface is a smooth flat surface is laminated so as to contact the surface 10. The refractive indexes of the translucent materials that are normally used are all around 1.5, and the mutual differences are not large. Therefore, to some extent, as shown in FIG. 9, the lens sheet 4 and the light guide plate 1 are optically almost integrated. Then,
The surface of the unit lens 42 of the lens sheet 4 is a smooth flat surface 10.
Since most of the light rays that enter the light guide plate near the light source, such as L1, L2, and L3, are incident at less than the critical angle, some of them are emitted and the reflected light is mostly reflected. Is returned to the light source and does not propagate far away. Of course, there is also a ray of light that is emitted from the light source directly to the lens surface far away and becomes emitted light, for example, L4 in FIG. 9, but the amount thereof is smaller than in the case of FIG. Therefore, as described above, the light emitted from the surface light source is 10 to 2 of the total area of the light guide plate near the light source side.
Most of it will be concentrated at 0%.

On the other hand, in the present invention, as shown in FIGS. 10 and 11, the projection group 41 is formed on the non-lens surface side of the lens sheet 4, whereby the smooth flat surface 10 of the light guide plate and the lens sheet 4 are formed.
An air gap 9 is formed at least partially between and. In this space 9, since the light guide plate 1 having a refractive index of about 1.5 and the air layer (or vacuum layer) having a refractive index of about 1.0 are adjacent to each other with the plane 10 as an interface, the same as in the case of FIG. Total internal reflection occurs. Therefore, in the region near the light source, the emitted light is obtained by the light ray L1T which is incident on the plane 10 at less than the critical angle and is transmitted, and in the region away from the light source, the light on the back surface is totally reflected at the interface of the void 9. Emitted light is obtained by the component L2T of the light rays diffusely reflected by the diffuse reflection layer 2 and having a smaller angle than the critical angle.

Of course, in the L2T, a part of the fine unevenness 4
Light incident on a region where 1 and the flat surface 10 are in contact with each other is not totally reflected but is transmitted as it is and becomes emitted light. As described above, when the area ratio R of the voids is 80 to 90% or more, the luminance distribution is uniform over the entire surface.

Here, the height of the minute irregularities 41 (that is, the space between the voids) is set to be equal to or more than one wavelength of the light source light.
Total reflection on the surface 10 is ensured. The reason is that, as shown in FIG. 12, when the light ray L1 incident on the smooth plane 10 of the light guide plate from the inside of the light guide plate is totally reflected to become the reflected light L1R, strictly speaking, the electromagnetic field of the light is completely air (or vacuum). )
9 does not exist, but there is an electromagnetic field L1V that has partially passed through the interface 10 due to the tunnel effect. However, this electromagnetic field L1V is attenuated exponentially, and its amplitude becomes 0 on the order of the wavelength of light. Therefore, if the void 9 continues for a distance sufficiently larger than the wavelength of light, the light ray L1 practically does not enter the void 9.

However, as shown in FIG. 13, when the lens sheet 4 having substantially the same refractive index as the light guide plate 1 approaches the surface 10 of the light guide plate up to a distance ΔX less than the wavelength λ of light (ΔX <
λ), the electromagnetic field L1V entering the lens sheet 4 without being completely attenuated becomes the traveling wave L1T again, that is, the transmitted light L1T is generated.

In the present invention, since the minute irregularities 4 are formed on the back surface of the lens sheet 4, as shown in FIG. 14, a region having a space 9 between the light guide plate 1 and the lens sheet 4 is formed. There can be a region where there is no void and both are optically integrated (or less than the wavelength of light even if there is a void). Of these, the incident light is totally reflected in the void portion, and the incident light is transmitted in the portion without the void. As described above, the ratio of the amount of light totally reflected by the surface 10 is determined by the ratio of the area of the void portion to the total area of the light guide plate.

[0042]

Since the surface light source of claim 1, claim 2, claim 5, and claim 6 does not have spherical aberration, the light emitted from the light guide plate is almost converged within a predetermined diffusion angle. Light energy which is wasted from the oblique to tangential directions of the surface light source can also be used as illumination light effective for observation. Therefore, the energy utilization efficiency is high, the brightness is high, and no noise light is emitted to the side surface of the surface light source. Since the surface light source according to claim 3 or 4 has fine irregularities on the back surface (the surface opposite to the lens surface) of the lens sheet 4, the light source light can be reliably provided between the light guide plate of the edge light type surface light source and the lens sheet. It is possible to form voids having a wavelength longer than Therefore, even if the lens sheet is placed, the uniform distribution of the light source light throughout the light guide plate due to the total reflection of light on the surface of the light guide plate is not hindered, and the luminance distribution on the light emission surface is uniform.

Since the display device of claim 7 uses the surface light source of claims 1 to 6, it has high energy utilization efficiency such as electric power, high brightness, an appropriate viewing angle, and a front surface. It is possible to obtain a display with uniform brightness.

[0044]

Example 1 (Lens Molding Step) Using a device as shown in FIG. 15, the lens was manufactured by the following steps. A winding roll 11 of a transparent and colorless biaxially stretched polyethylene terephthalate base film having a thickness of 100 μm was prepared. A roll-shaped intaglio 14 is prepared by engraving an elliptic cylinder lenticular lens-shaped reverse type (the same shape but the concavities and convexities are opposite) 15 on the surface of a metal cylinder, and while rotating this around the central axis, T
The UV curable resin liquid 16 was supplied to the plate surface from the die nozzle 21 to fill and coat the reverse concave and convex surface of the lens. Next, the base film 12 is unwound from the winding roll 11 at a speed that is synchronized with the rotational peripheral speed of the roll-shaped intaglio plate 14, and the base film is pressed onto the roll intaglio plate by the pressing roll 13 with the resin liquid interposed therebetween. Then, ultraviolet rays from the mercury lamps 23, 23 were irradiated from the side of the base material film in this state, and the resin solution was cross-linked and cured in the reverse mold and simultaneously adhered to the base material film. Next, the base film running using the peeling roll 18 was peeled off together with the cured resin having the lens shape 19 adhered thereto, thus obtaining the elliptic cylinder lenticular lens sheet 20. By the way, lens shape ; as shown in FIG. 3 (A), unit lens shape; convex elliptic cylinder (long axis oriented in the normal direction of the lens sheet), major axis length 2b = 204 μm, minor axis length 2a = 150 μm Long axis length / Short axis length = 2b / 2a = 1.36-Repeating cycle of lens unit p = 130 μm UV curable resin liquid; -Polyfunctional polyester acrylate oligomer-Photoreaction initiator as a main component.

(Process of forming matte layer having fine irregularities) A roll-shaped intaglio was prepared by engraving a reverse mold of fine irregularities (projections) obtained by sandblasting on the surface of a metal cylinder. Then, a colorless and transparent biaxially stretched polyethylene terephthalate base film having a thickness of 50 μm is unwound from a winding roll, and the same apparatus and resin solution as those used in the lens forming step are used to form an ultraviolet ray curable resin on the back surface of the lens sheet. Matte transparent fine irregularities made of a resin cured product were molded. Thus, the light diffusion layer specified in the present invention was obtained. By the way, minute irregularities -Haze value = 88.8-Surface gloss (JIS-Z-8741) = 11.1-Surface roughness (10-point average roughness of JIS-B-0601) R
z = 38.4 μm Surface roughness (center line average roughness of JIS-B-0601)
Ra = 7.3 μm

[0046]

Example 2 The elliptic cylinder lens sheet produced in Example 1 was overlaid on the light guide plate through the light diffusion layer produced in Example 1 to obtain an edge light type surface light source having the constitution 100 in FIG. . Light guide plate : -Material: Polymethylmethacrylate polymer resin-Shape: Rectangular solid. Thickness 4 mm ・ Surface; 10-point average roughness Rz = 0.1 μm on the entire surface
Finished to less than smoothness. -Back surface: Matte transparent ink was printed on the back surface of the light guide plate in a circular halftone dot pattern, and a specular reflective film obtained by vacuum-depositing aluminum on a polyethylene terephthalate film was placed on the back surface. The halftone dots were formed by silk screen printing using fine silica powder dispersed in an acrylic resin binder. The halftone dots were arranged in a vertical and horizontal direction with a repeating cycle of 5 mm. The diameter of the halftone dot is 0.1 mm near the light source, and it is increased in proportion to the distance from the light source.
It was set to 2 mm at the end opposite to the light source. A white fluorescent lamp was arranged at one end of the light guide plate as a light source line light source.
A metallic reflecting mirror was placed on the side opposite to the light guide plate. The performance of the surface light source with the above configuration is as follows. -The angular distribution of brightness is as shown in Fig. 16.・ Half-value angle = 36 degrees ・ Brightness in normal direction (center of light guide plate) = 2028 cd / m ²・ Distribution of brightness in normal direction in light emitting surface: within + -15%.
Almost visually uniform ・ No side lobes are generated.

[0037]

Comparative Example 1 The following triangular prism prism type lenticular lens was used in place of the convex elliptic cylinder lenticular lens of the lens sheet in Example 2. -Cross-sectional shape: right-angled isosceles triangle. The 90-degree apex angle is oriented in the direction normal to the surface light source.・ Repeat cycle of unit lens (length of one side) = 100μ
m The material, layer configuration, and manufacturing method are the same as those of the convex elliptic cylinder lenticular lens of the first embodiment. The performance of the surface light source with the above configuration is as follows. -The angular distribution of brightness is as shown in Fig. 17. · Half-value angle = 34 degrees, the normal direction brightness (light guide plate central portion) = 2074cd / m ² · normal direction brightness distribution in the light emitting surface of; + - 15% or less.
Almost visually uniform ・ Side lobes occur. (Peak in + -75 degree direction from the normal) Sidelobe peak brightness / normal brightness = 26%

Comparative Example 2 In Example 2, the light diffusion layer prepared in Example 1 was used instead of the lens sheet. That is, two light diffusion layers were stacked and placed. Others were the same as in Example 2.
The performance of the surface light source having the above configuration is as follows: The angular distribution of luminance is as shown in FIG.・ Half-value angle = 38 degrees (However, outside the half-value angle, it is not attenuated abruptly and a certain amount of emitted light is distributed.) ・ Normal direction luminance (center of light guide plate) = 1491 cd / m ²・ Normal line Distribution of directional luminance within the light emitting surface; within + -15%.
Almost visually uniform ・ No side lobes are generated.

Comparative Example 3 In Example 2, a convex elliptic cylinder lenticular lens having the following shape was used. -Unit lens shape: convex elliptic cylinder (the short axis is oriented in the normal direction of the lens sheet) -Long axis length 2b = 150 μm- Short axis length 2a = 204 μm-Long axis length / short axis length = 2b / 2a = 0 .74 Repetition cycle of lens unit p = 177 μm Others were the same as in Example 2. The performance of the surface light source having the above configuration is as follows: The angular distribution of brightness is as shown in FIG. · Half-value angle = 42 deg, the normal direction brightness (light guide plate central portion) = 1738cd / m ² · normal direction brightness distribution in the light emitting surface of; + - 5% or less. Almost visually uniform ・ Side lobes occur. (Brightness peak exists in the direction + -75 degrees away from the normal direction) Sidelobe peak brightness / normal direction brightness = 37%

[Comparative Example 4] In Example 2, an article having no matte layer on the back surface of the lens sheet was used. The back surface of the lens sheet is the surface of the base film itself, and the ten-point average roughness Rz of the surface is a smooth flat surface of less than 0.1 μm. Others were the same as in Example 2. Regarding the performance of the surface light source configured as described above, although the brightness in the normal direction of the light emitting surface is high near the end on the light source side, the brightness decreases sharply with the distance from the light source.
At a position of cm, the brightness was lowered to such an extent that it was visually dark.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of an edge light type surface light source of the present invention and a transmissive display device using the same.

FIG. 2 is a perspective view of an example of a direct type surface light source of the present invention and a transmissive display device using the same.

FIG. 3 is a perspective view of an embodiment of a lens sheet of the present invention. For an elliptic cylinder lenticular lens. (A) and (C) are convex lenses, and (B) and (D) are concave lenses.

FIG. 4 is a diagram illustrating behavior of light rays on a lens sheet, particularly spherical aberration, with a unit lens. (A) shows a case of a convex true cylindrical lens, and (B) shows a case of a convex elliptic cylinder lens of the present invention.

FIG. 5 is a diagram illustrating behavior of light rays on a lens sheet, particularly spherical aberration, with a unit lens. (A) shows a case of a concave true cylindrical lens, and (B) shows a case of a concave elliptic cylinder lens of the present invention.

FIG. 6 is a perspective view of another embodiment of the lens sheet of the present invention.
When two elliptic cylinder type lenticular lenses are laminated so that their axes are perpendicular to each other.

FIG. 7 is a cross-sectional view of a conventional edge light type surface light source. When there is no lens sheet on the light guide plate.

FIG. 8 is a perspective view of a conventional edge light type surface light source. When the lens sheet is closely attached to the light guide plate without leaving a gap between them.

FIG. 9 is an enlarged sectional view of FIG. It shows that the interface between the lens sheet and the light guide plate is optically eliminated and integrated.

FIG. 10 is a sectional view of an embodiment of an edge light type surface light source of the present invention. An example in which a light diffusion layer having fine irregularities on both sides is inserted at the interface between the light guide plate and the lens sheet to form voids at two locations (two layers).

FIG. 11 is a sectional view of another embodiment of the edge light type surface light source of the present invention. An example in which minute concaves and convexes are directly formed on the back surface of the lens sheet to have only one layer of voids.

FIG. 12 is a cross-sectional view showing the behavior of light rays that are totally reflected by a smooth flat surface of the light guide plate. The electromagnetic field seeps out in the air due to the tunnel effect.

FIG. 13 is a cross-sectional view showing that a light beam oozing out from the light guide plate due to a tunnel effect becomes a traveling wave again in the lens sheet.

FIG. 14 is a cross-sectional view showing that in the lens sheet of the present invention, a light ray traveling from the light guide plate to the outside is partially totally reflected and partially transmitted.

FIG. 15 is a cross-sectional view showing an example of the manufacturing method of the present invention. This corresponds to [Example 1].

FIG. 16 is a characteristic of the edge light type surface light source according to the second embodiment of the present invention. 9 illustrates an angular distribution of emission light luminance when a convex elliptic cylinder lenticular lens whose long axis is oriented in the normal direction is used.

FIG. 17 is a characteristic of the edge light type surface light source of [Comparative example 2]. The angle distribution of emission light brightness when a triangular prism lenticular lens is used is shown in the figure.

FIG. 18 shows the characteristics of the edge light type surface light source of [Comparative Example 3]. The angle distribution of the emission light brightness when a convex elliptic cylinder lenticular lens whose short axis faces the normal direction is used is shown.

FIG. 19 shows the characteristics of the edge light type surface light source of [Comparative Example 3]. When two light diffusion layers (films) are laminated on the light guide plate. 9 illustrates the angular distribution of emitted light brightness.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Light reflection layer 3 Light source (unit) 4 Lens sheet 5 Reflecting mirror 6 Transmissive display device such as liquid crystal display device 7 Smooth flat surface of lens sheet back surface 8 Light isotropic diffusive sheet (light diffusion layer) 9 Void 10 A smooth flat surface of the light guide plate. 11 Winding Roll 12 Base Film 13 Pressing Roll 14 Roll Intaglio 15 Lens Shape Reverse Type 16 UV Curable Resin Liquid 17 Uncured Resin Liquid in Lens Reverse Mold 18 Peeling Roll 19 Lens Shape (Lens Unit) 20 Lens Sheet 21 T-die type nozzle 22 Liquid pool 23 Mercury lamp 41 Lens sheet projections (group) 42 Lens unit 43 Transparent layer having projection groups 44 Transparent base material layer 100 Surface light source 200 Display device F Focus L1 Direct incidence on a nearby lens surface from a light source And then the light rays that pass through. Light rays that are directly incident on and transmitted through the lens surface in the vicinity from the L2 light source. A light ray that is directly incident on and transmitted through the lens surface in the vicinity from the L3 light source. Light rays that are directly incident on the lens surface at a distance from the L4 light source and are transmitted therethrough. LN paraxial ray. LF Rays off paraxial. Light reflected on the smooth flat surface 10 of the L1R light guide plate. Light reflected on the smooth flat surface 10 of the L2R light guide plate. Transmitted light on the smooth flat surface 10 of the L1T light guide plate. Transmitted light on the smooth flat surface 10 of the L2T light guide plate. Diffuse reflected light from the light reflecting layer 2 on the back surface of the L1S light guide plate. Diffuse reflected light from the light reflecting layer 2 on the back surface of the L2S light guide plate.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 26, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Surface light source , display device using the same, and
Lens sheet used for them

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source, and a backlight for a transmissive display device such as a liquid crystal display device,
It is useful for lighting advertisements, traffic signs, etc. The present invention also discloses a transmissive display device such as a liquid crystal display device using the surface light source as a back light source.

[0002]

2. Description of the Related Art As a surface light source for a backlight of a liquid crystal display device (LCD), an edge light type one using a transparent flat plate as a light guide as shown in FIG. 7 is known. In such a surface light source, light is made incident from both or one of the side end surfaces of the light guide body made of a transparent parallel plate, and the light is propagated uniformly throughout the light guide plate by utilizing the total internal reflection of the transparent plate. A part of the propagated light is made into a diffuse reflection light having a critical angle less than a critical angle by a light scattering reflection plate on the back surface of the light guide, and the diffuse light is emitted from the surface of the light guide plate. (Actual development 55
-162201). As shown in FIG. 6, a lens sheet having a triangular prism type lenticular lens projection on one surface and a smooth surface on the other surface is stacked on the light guide plate surface of the surface light source with the projection surface facing upward. By utilizing the light focusing effect of the lens, the diffused radiation can be uniformly and isotropically diffused within a desired angular range (actual 4-107201). When this lens sheet is used in combination with a matte transparent diffusion plate (matte transparent sheet), the light energy of the light source is higher than that using only the matte transparent diffusion plate (US Pat. No. 4,729,067). Focused distribution within the desired limited angle range,
In addition, it was possible to obtain diffused light with high uniform isotropicity within the angle range.

[0003]

However, in the above-mentioned conventional technique, if only the light-scattering plate is provided on the back surface of the light guide, the emitted light is 60 degrees with respect to the direction normal to the surface of the light guide. The distribution has a relatively sharp distribution with the angle at the peak, the brightness in the normal direction, which requires the most light, is insufficient, and the light energy is dissipated in the oblique lateral direction where there is little acceptance. In the prior art, the triangular prism type lenticular lens sheet on the light emitting surface of the light guide refracts and focuses the emitted light, so that the normal direction of the light emitting surface has a peak at 30 ° to 6 °.
Although the ratio of the light energy emitted within the angle of 0 ° becomes high, on the other hand, as shown in FIG. 17, the peak (side lobe) of the emitted light also occurs in the direction (oblique direction) away from the normal direction. was there. For this reason, there remains loss light that does not contribute to the observer. Further, this side lobe is also inconvenient because it radiates unnecessary noise light to the surroundings. Further, contrary to the expectation about the brightness distribution in the emission surface, the brightness is high from 2 to 4 cm from the end portion on the light guide plate side,
It was found that when the distance from the light source is further increased, the brightness gradually decreases, and there is a problem that the end portion on the side opposite to the light source becomes noticeably dark.

In order to improve these drawbacks, as in Japanese Patent Laid-Open No. 1-245220, the light-scattering layer on the back surface of the light guide has a pattern of halftone dots or the like, and the area of the pattern is small as it approaches the light source. Attempt to correct and uniformize the brightness distribution within the light guide plate surface by increasing the distance from the light source. As in Japanese Patent Laid-Open No. 3-9306, light sources are arranged at two or more positions on the side edge of the light guide plate to correct the luminance distribution in the plane of the light guide plate.
Attempt to homogenize. However, in both cases, it is difficult to completely uniformize the brightness, and there is a drawback that halftone dots are conspicuous in the light scattering layer from the light emitting surface side. It had the drawback of being more than doubled.

An object of the present invention is to solve the above-mentioned problems and to provide a lens sheet for use as a backlight of a liquid crystal display device and a surface light source using the lens sheet. The object is to obtain uniform surface light emission with high brightness only within a desired angle range without increasing the amount of heat generation, and to obtain surface light emission without variation in brightness depending on the position in the surface.

[0006]

In order to achieve the above object, the present invention provides

The lens sheet 4 of the present invention is an elliptic cylinder lenticular lens or a hyperbolic cylinder lenticular lens. First, an elliptic cylinder lenticular lens will be described as an example. That is, as shown in FIG. 3A, it is a columnar lens group (so-called lenticular lens) in which convex unit lenses 42 having an elliptic columnar shape are arranged adjacent to each other with their ridge directions parallel.
The major axis direction of the ellipse faces the normal direction of the lens sheet 4. As the flatness of the ellipse, the ellipse formula is expressed as follows: X ² / a ² + Y ² / b ² = 1 (1) where a is the short axis length, b is the long axis length, and a <b ,
The major axis / minor axis = b / a = is 1.1 × n / (n ² −1) ^1/2 ≧ b / a ≧ 0 . 9 × n / (n ² −1) ^1/2 −−−− Formula (2) is preferable. The reason for designing the ellipse in this way is to eliminate the spherical aberration of the lenticular lens and to minimize the loss during focusing. That is, FIG.
5A and 5A, when a true cylindrical lenticular lens is used, even if the emitted light is focused within a predetermined diffusion angle θ by utilizing the focusing function of the lens, it is actually focused on the focal point F. The focused light is only the paraxial ray LN near the center of the lens, and the other rays LF defocus and become dissipated light (so-called spherical aberration). At this time, the light beam LF defocused
Will be dissipated from within each predetermined θ, resulting in light loss and unnecessary noise light.

The geometrical optical condition for minimizing the spherical aberration of the lenticular lens is between the flatness e of the ellipse of the cross section (main cutting plane) orthogonal to the ridge of the lenticular lens and the refractive index n of the lens material. , N = 1 / e Equation (3) should be satisfied. The flatness e can be written as e ² = (b ² −a ² ) / b ² formula (4) using the length 2b of the major axis and the length 2a of the minor axis of the ellipse. Therefore, from the formulas (1) and (2), the major axis / minor axis = 2b / 2a = b / a = n / (n ² −1) ^1/2 formula (5) For example, with an acrylic resin, the refractive index = If the substance of 1.5 is used, the spherical aberration disappears from the formula (5) when the major axis / minor axis = 1.34. However, in reality, a part of the light rays whose direction is deviated due to light diffusion and refraction due to the light diffusion / reflection layer 2 on the back surface of the light guide plate, the light diffusion layer 8 between the light guide plate and the lens sheet, etc. The light energy deviating from the angle θ is not zero, but can be minimized.

Even if it deviates from the expression (5) to some extent, it is possible to obtain characteristics close to those of the expression (5) while the difference is small. However, if it deviates from the expression (5) more than a certain degree, the peak of the angular distribution of luminance becomes a flat mountain centered in the normal direction of the light emitting surface due to spherical aberration, and side lobes are formed at both ends of the flat top. (Side peak) is made. It becomes unsuitable for the purpose of the present invention. As a result of the examination, if it is within + -20% of the formula (5), side lobes do not occur, and good light energy utilization efficiency, sharp diffusion angle, and
It was found that a high normal direction luminance can be obtained. However, from the practical viewpoint, it is preferable that the flatness ratio is within + -10% of the formula (5).

This unit lens is shown in FIGS. 3 (A) and 3 (C).
A convex lens as shown in FIG. 3B or a concave lens as shown in FIGS. 3B and 3D may be used.

The behavior of light rays of the elliptic cylinder unit lens is as follows:
This is as shown in FIGS. 5B and 5B. A ray incident parallel to the optical axis does not cause spherical aberration and has a focal point F.
And then diverge at a predetermined diffusion angle θ. With respect to the divergence angle θ, spherical aberration can be neglected, and a light ray largely deviated from the normal line of the light guide plate is fed back into the light guide plate due to total reflection between the smooth surface 10 of the light guide plate and the lens sheet 4. If light rays in the vicinity of the normal direction of the light guide plate, that is, light rays substantially parallel to the optical axis mainly enter the lens due to the diffuse reflection of the light reflection layer on the back surface of the light plate, roughly, θ = 2ta
n ⁻¹ (p / 2f) Expression (6) is obtained. However, p is the repeating period of the unit lens, and f is the focal length. As can be seen from the comparison between FIG. 4 and FIG. 5, the focusable position varies depending on the concave lens and the convex lens. That is, in the case of a convex lens as shown in FIG. 4B, the image formation becomes a real image and the focus can be on the outside of the lens (on the other side). See also FIG.
In the case of the concave lens as in (B), the image is formed as a virtual image and the focus can be inside the lens (front side). However, in any case, in the case of the use of the present invention, the focal length is set sufficiently smaller than the distance from the lens surface (that is, the surface of the surface light source) to the observer (usually 10 mm or less). There is no big difference between the concave and convex lenses.

In the above description, the elliptic cylinder type lenticular lens was exclusively described, but the unit lens cross section is expressed by the formula (6), X ² / a ² -Y ² / b ² = 1 formula (6) (where Where b / a is the slope of the asymptote, and a <
Similar effects can be expected even with a hyperbolic columnar lenticular lens represented by b,). The optimum ranges of a and b are the same as in the case of an elliptic cylinder.

Although these lens sheets can be used as a single sheet, in order to control the light diffusion angle in the X, Y2 directions (vertical direction, horizontal direction, etc.) by using a columnar lens, as shown in FIG. The lens sheets may be laminated so that their major axes are orthogonal to each other. In this case, the lens surfaces should be oriented in the same direction as shown in FIG. 6 because of the high transmittance of the components of light rays coming from the light reflecting layer 2 which are relatively close to the normal direction, It is the best in terms of balance with the high feedback rate of the light beam inclined from the normal direction to the light guide plate, but of course the lenses of each lens sheet face each other (the lens surface is sandwiched between two lens sheets). Can be laminated. Also, the lens sheet is shown in FIGS.
It may be obtained by integrally molding a translucent substrate as shown in Fig. 3, or as shown in Figs. 3 (B) and 3 (D), a translucent flat plate (or sheet) 4
The unit lens 42 may be formed on the surface 4.

The lens sheet 4 is formed of a transparent base material. Here, as the translucent base material, a homopolymer or a copolymer of acrylic acid ester or methacrylic acid ester such as polymethyl methacrylate, polymethyl acrylate, and the like,
Polyesters such as polyethylene terephthalate and polybutylene terephthalate, thermoplastic resins such as polycarbonate, polystyrene and polymethylpentene, or transparent resins such as polyfunctional urethane acrylates, polyester acrylates and other acrylates, unsaturated polyesters cross-linked by ultraviolet rays or electron beams. , Transparent glass, transparent ceramics, etc. are used.

When used as a lens sheet, this translucent substrate usually has a total thickness of about 20 to 1000 μm.

As a method for forming a lens shape, for example, a publicly known hot pressing method (described in JP-A-56-157310), an emulsifying process using a roll embossing plate on an ultraviolet-curable thermoplastic resin film, A method of irradiating ultraviolet rays to cure the film (JP-A-61-61
No. 156273), an ultraviolet or electron beam curable resin liquid is applied on a roll intaglio engraved with a lens shape and filled in the recess, and then the roll intaglio is still coated with the transparent base film through the resin liquid. A method in which a resin cured by irradiation with ultraviolet rays or an electron beam and a substrate film adhered to the resin are released from the roll intaglio, and the lens shape of the roll intaglio is imprinted on the cured resin layer (JP-A-3-223883, US Pat. No. 4,576,850) and the like are used. In the case of the method, the ultraviolet ray or electron beam curable resin is relatively flexible and flexible in order to prevent the occurrence of cracks during processing, for the convenience of winding and processing the molded lens sheet. Is selected.

The translucency required for the translucent base material must be selected so that diffused light can be sufficiently transmitted to the extent that it does not hinder the use of each application, and colorless and transparent is most preferable. Depending on the application, it may be colored transparent or matt translucent.
Here, the matte transparent has a property of diffusing and transmitting the transmitted light almost uniformly and isotropically in all directions within a semi-solid angle, and is synonymous with light isotropic diffusivity. That is, the term "matte transparent" means that when a parallel light flux is incident from the rear surface (incident angle i
= 0 °), the angular distribution I ^o (θ) of the transmitted light intensity is c
os distribution I ^o (θ) = I ^o _mp cos θ, −90 ° ≦ θ ≦ 90 ° Equation (8) θ is the angle formed by the normal line N, I ^o _mp is the transmitted light intensity in the normal direction or is similar thereto. It is said to be distributed. Note that I
The definition of ⁱ (θ) will be described later.

It is preferable to provide minute irregularities (a group of minute protrusions) on the back surface of the lens sheet (the surface opposite to the lens surface). The reason is different between the so-called edge light type surface light source as in claims 1 to 4 and the so-called direct type surface light source as in claims 5 to 6. In the case of the edge light type, as will be described later, it is for uniforming the luminance distribution in the light emitting surface, while in the case of the direct type, the purpose is to make the angular distribution of luminance within a predetermined light diffusion angle uniform. (In this case, just the light diffusion effect). Minute irregularities 4 whose height formed on the back surface of the lens sheet is not less than the wavelength of the light source light and not more than 100 μm
No. 1 can be directly formed on the back surface of the integrally molded lens sheet 4 as shown in FIG. 14 by embossing by heat pressing, sandblasting, etc., or else on the flat back surface of the lens sheet 4 as shown in FIG. It is also possible to form a light-transmitting material layer having protrusions. Specifically, a method in which transparent fine particles of calcium carbonate, silica, acrylic resin, or the like are dispersed in a transparent binder to coat the surface of the coating film to form irregularities of the fine particles, or the method described in JP A method of molding an ultraviolet or electron beam curable resin liquid on a roll intaglio plate disclosed in, for example, US Pat. No. 3,223,883, US Pat.

The projection 41 is intended to at least partially form a gap 9 (dimension ΔX) equal to or longer than the wavelength of the light source light between the smooth surface 10 of the light guide plate 1 and the lens sheet 4 as shown in FIG. Is. As will be described later, when the gap ΔX is less than the wavelength of the light from the light source, total reflection of light on the smooth flat surface 10 of the light guide plate 1 does not sufficiently occur, and when it exceeds 100 μm, the uneven shape of the protrusions becomes conspicuous, which is inconvenient.

The projection 41 may have any uneven shape as long as this purpose is achieved, but from the viewpoint of obtaining a uniform brightness angular distribution within a desired diffusion angle and a uniform brightness distribution within a light source surface, In the best mode, as shown in FIGS. 3C and 3D, a random uneven shape (for example, a grain pattern, a satin pattern, etc.) is formed on the entire back surface of the lens sheet 4. In this way, as shown in FIG. 11, the light L1, L2S, etc. incident from the back surface of the lens sheet 4 is isotropically diffused by the projection group 41 also acting as a light diffusion layer. A uniform angle distribution can be obtained without interposing a matte transparent sheet, and a dot pattern is not conspicuous, which is good.

In addition to this, of course, as shown in FIG. 10, a light isotropic diffusive sheet 8 having a matt transparency and a group of protrusions 41 having a surface wavelength of 100 μm or less, a lens sheet 4 and a smooth surface 10 of the light guide plate. You can also intervene between. However, in this case, since there are a plurality of interfaces for diffusing light (smooth flat surface 10 light isotropic diffusing sheet 8 /, light isotropic diffusing sheet 8 / rear surface of lens sheet 4), it is effective to move in the vicinity of the normal direction. The transmittance of light energy is maximized, and the reflectance of light energy that is wasted as a light source far from the normal direction (oblique to the tangential direction of the light emission surface) is also maximized (this reflected light is As you can see, the light reflection layer 2 in another place
Sent to and reused there. ) The light energy utilization efficiency is maximized, and at the same time, the brightness distribution in the entire light emission surface is also most uniform.

Further, as shown in FIG. 14, the minute concavo-convex pattern 41 may be a pattern in which dot-like patterns such as halftone dots are arranged in a plane in a distributed manner. However, in this case, the pattern 41 is conspicuous, and it is necessary to devise a method of dispersing the matting agent in the lens sheet 4.

The surface light source of the present invention has a structure shown in the sectional views of FIGS. 10 and 11 and the perspective views of FIGS. The light guide plate 1, the linear or point light source 3 installed adjacent to at least one of the side end portions thereof, the light reflection layer 2 on the back surface of the light guide plate, and the surface opposite to the light reflection layer of the light guide plate. The lens sheet 4 has a minimum configuration. Usually, the light source light reflecting mirror 5, the entire housing, a housing (not shown) having a light emitting surface as a window, a power source (not shown), etc. are also attached to these.

The opposite surface 10 of the light reflecting layer of the light guide plate 1 is a flat surface, and the surface roughness (measured by the ten-point average roughness R _{z of} JIS-B-0601) is not more than the wavelength of the light source. Finish. Usually, the light source is visible light, and its wavelength is 0.4 ~
Since it is 0.8 μm, the surface roughness is 0.4 μm or less. Known methods for finishing to this degree of roughness, such as heat pressing with a mirror surface plate, injection molding using a mirror surface shape, casting (casting) molding, precision polishing performed with optical lenses, etc. Should be used.

The material of the light guide plate 1 is selected from the same translucent materials as the material of the lens sheet. Usually, acrylic or polycarbonate resin is used. The thickness of the light guide plate is usually about 1 to 10 mm.

As the light source 3, a linear light source such as a fluorescent lamp is preferable in order to obtain uniform brightness over the entire surface, but a point light source such as an incandescent lamp can also be used. The light source 3 is provided outside the side end portion of the light guide plate as shown in the figure, and the side end portion of the light guide plate 1 is partially cut away so that a part or the whole is embedded in the light guide plate. Things are possible. The light source 3 can also be installed at the other side end of the light guide plate 1 from the viewpoint of high brightness and uniformity of brightness in the plane. As the light source light reflecting mirror 5, a well-known one is used, for example, a plate having a shape of a parabolic column, a hyperbolic column, an elliptic column, or the like, on the inner surface of which metal vapor deposition is performed.

In the case of an edge light type surface light source, the lens sheet 4 is laminated on the smooth flat surface 10 of the light guide plate.
At that time, as shown in FIGS. 10 and 11, the lens surface of the lens sheet 4 is placed on the outside (opposite surface of the flat surface 10) so that the minute irregularities 41 face inward (on the flat surface 10 side). At least a part of the gap 9 having a wavelength λ of the light of the light source or more is formed between the light guide plate 1 and the smooth surface 10. The area ratio R of the void portion 9, that is, R = (area of the void portion having a wavelength of λ or more / total surface area of the light guide plate) × 100% is the required uniformity of brightness in the plane and the utilization efficiency of light energy. Although it is determined by the dimensions of the light guide plate, the ratio R is usually required to be 80% or more, and more preferably 90% or more.

The reason for this is that as a result of the experiment, when the surface 10 of the lens sheet and the surface 10 of the light guide plate, both of which have a surface roughness equal to or less than the wavelength of light as shown in FIG. It has been found that most of the input light from Eq. 1 is emitted from the side end on the light source side at a distance y without being totally reflected, and the brightness is sharply reduced and dark at a position far from y. The ratio of the length y of the light emitting portion to the total length Y of the light guide plate in the light propagation direction, (y / Y) × 100 = 10 to 20%
It turned out to be Therefore, from the light source to the light guide plate plane 10
In order to evenly distribute the amount of light energy incident on the total length Y, it is necessary to transmit 10% to 20% of the incident light on the plane 10 and totally reflect the remaining 90% to 80%.
Generally, (amount of transmitted light / amount of total reflected light) = (area of void portion having wavelength λ or more / total surface area of light guide plate) = R Since it is approximated by the formula (9), R is required to be 80 to 90% or more. It turned out that

As a method of forming an air gap having a wavelength equal to or longer than the light source light between the lens sheet 4 and the light guide plate 1, the lens sheet 4 is arranged such that the lens surface 42 and the projection group 41 are oriented as shown in FIG.
0, it is also possible to invert it from FIG. 11 (not shown). However, in this case, the light once focused within the desired angle on the lens surface 42 diverges in a eastern fashion again,
30 degrees to 6 around the normal, which is the optimum value for the light diffusion angle
It is difficult to control within 0 degrees.

The light reflecting layer 2 is a layer having a property of diffusing and reflecting light, and can be constructed as follows. On one surface of the light guide plate layer, a white layer in which a pigment having high hiding property and high whiteness, for example, powder of titanium dioxide, aluminum or the like is dispersed is formed by coating or the like. A metal thin film layer is formed by further plating or vapor-depositing a metal such as aluminum, chromium, or silver on the uneven surface of the light guide plate on which matte fine unevenness has been formed by sandbright processing, embossing, or the like. A metal thin film layer is formed on a white layer which has a low hiding property and is formed by simply coating a matte surface. It may be formed in a white dot-like layer and the area ratio may be increased as the distance from the light source increases so as to correct the attenuation of the light amount of the light source.

The structure of the surface light source 100 of the present invention used as a backlight (rear surface light source) of a transmissive display device such as a transmissive LCD is as shown in FIGS. That is, the display device of the present invention is obtained by stacking the transmissive display device 6 on the lens surface (the side where the unit lens 42 is located) of the lens sheet of the surface light source 100 of the present invention.

The diffusion angle is effective for evaluating the light distribution of the surface light source. A half value angle θ _H is used as the diffusion angle, for example. When the transmitted light brightness (or intensity) is defined as a decreasing function I (θ) of the angle θ from the normal line of the light emitting surface,
It is defined as an angle θ _{H such that} I (θ _H ) = I (θ) / 2.

[0033]

The elliptic cylinder lenticular lens according to the first and fifth aspects does not cause spherical aberration geometrically as described above. That is, the true cylindrical unit lens has spherical aberration as shown in FIGS. 4 (A) and 5 (A), and the incident light ray L2 distant from the optical axis.
Is not focused on the focal point, and as a result, a part of the light deviates from the range of the predetermined diffusion angle θ and is wasted. On the other hand, the elliptic cylinder unit lenses of FIGS. 4 (B) and 5 (B) used in the present invention are designed so that spherical aberration does not occur or that it can be ignored as described above. Therefore, the incident light parallel to the optical axis is refracted by the lens lens 4 and then converges to one focal point, and then diverges at that point, so that the emitted light has a desired diffusion angle θ (equation (6)). The light is condensed at an angle close to, and is effectively used. In the case of a concave lens, the focus position is the difference between the entire position and the rear of the lens as compared with the convex lens as described above. Therefore, for an observer who is far away from the focal length of the lens sheet 4, the same action as the convex lens is performed.

Also in the case of a hyperbolic lenticular lens,
This is similar to the case of the elliptic cylinder lenticular lens.

Next, the void 9 in the edge light type surface light source will be described. As shown in FIG. 7, the action mechanism of the edge light type surface light source is that, among the light rays that are incident on the light guide plate 1 from the light source 3 and are directly incident on the smooth flat surface 10 of the light guide plate, L1 that is incident in the vicinity of the light source is the incident angle (the surface 10 Since the angle formed by the normal line of 1) is small and less than the critical angle, some of the incident light amount is emitted as transmitted light L1T. Thereby, emitted light near the light source is formed. On the other hand, the light ray L2 that is directly incident on a relatively distant place from the light source 3 has a large incident angle and is equal to or greater than the critical angle. Diffuse (random) reflected light L2S is propagated in all directions in the light diffusive reflection layer 2 on the back surface. Some of these incident on the surface 10 at less than the critical angle, and some more of it becomes emitted light. This forms the emitted light at a distance from the light source.

Here, on the smooth flat surface 10 of the light guide plate 1,
FIGS. 8 and 9 show a state in which the smooth surface of the lens sheet 4 whose non-lens surface is a smooth flat surface is laminated so as to contact the surface 10. The refractive indexes of the translucent materials that are normally used are all around 1.5, and the mutual differences are not large. Therefore, to some extent, as shown in FIG. 9, the lens sheet 4 and the light guide plate 1 are optically almost integrated. Then,
The surface of the unit lens 42 of the lens sheet 4 is a smooth flat surface 10.
Since most of the light rays that enter the light guide plate near the light source, such as L1, L2, and L3, are incident at less than the critical angle, some of them are emitted and the reflected light is mostly reflected. Is returned to the light source and does not propagate far away. Of course, there is also a ray of light that is emitted from the light source directly to the lens surface far away and becomes emitted light, for example, L4 in FIG. 9, but the amount thereof is smaller than in the case of FIG. Therefore, as described above, the light emitted from the surface light source is 10 to 2 of the total area of the light guide plate near the light source side.
Most of it will be concentrated at 0%.

On the other hand, in the present invention, as shown in FIGS. 10 and 11, the projection group 41 is formed on the non-lens surface side of the lens sheet 4, whereby the smooth flat surface 10 of the light guide plate and the lens sheet 4 are formed.
An air gap 9 is formed at least partially between and. In this space 9, since the light guide plate 1 having a refractive index of about 1.5 and the air layer (or vacuum layer) having a refractive index of about 1.0 are adjacent to each other with the plane 10 as an interface, the same as in the case of FIG. Total internal reflection occurs. Therefore, in the region near the light source, the emitted light is obtained by the light ray L1T which is incident on the plane 10 at less than the critical angle and is transmitted, and in the region away from the light source, the light on the back surface is totally reflected at the interface of the void 9. Emitted light is obtained by the component L2T of the light rays diffusely reflected by the diffuse reflection layer 2 and having a smaller angle than the critical angle.

Of course, in the L2T, a part of the fine unevenness 4
Light incident on a region where 1 and the flat surface 10 are in contact with each other is not totally reflected but is transmitted as it is and becomes emitted light. As described above, when the area ratio R of the voids is 80 to 90% or more, the luminance distribution is almost uniform over the entire surface.

Here, the height of the minute irregularities 41 (that is, the space between the voids) is set to be equal to or more than one wavelength of the light source light.
Total reflection on the surface 10 is ensured. The reason is that, as shown in FIG. 12, when the light ray L1 incident on the smooth plane 10 of the light guide plate from the inside of the light guide plate is totally reflected to become the reflected light L1R, strictly speaking, the electromagnetic field of the light is completely air (or vacuum). )
9 does not exist, but there is an electromagnetic field L1V that has partially passed through the interface 10 due to the tunnel effect. However, this electromagnetic field L1V is attenuated exponentially, and its amplitude becomes 0 on the order of the wavelength of light. Therefore, if the void 9 continues for a distance sufficiently larger than the wavelength of light, the light ray L1 practically does not enter the void 9.

However, as shown in FIG. 13, when the lens sheet 4 having substantially the same refractive index as the light guide plate 1 approaches the surface 10 of the light guide plate up to a distance ΔX less than the wavelength λ of light (ΔX <
λ), the electromagnetic field L1V entering the lens sheet 4 without being completely attenuated becomes the traveling wave L1T again, that is, the transmitted light L1T is generated.

In the present invention, since the minute irregularities 4 are formed on the back surface of the lens sheet 4, as shown in FIG. 14, a region having a space 9 between the light guide plate 1 and the lens sheet 4 is formed. There can be a region where there is no void and both are optically integrated (or less than the wavelength of light even if there is a void). Of these, the incident light is totally reflected in the void portion, and the incident light is transmitted in the portion without the void. As described above, the ratio of the amount of light totally reflected by the surface 10 is determined by the ratio of the area of the void portion to the total area of the light guide plate.

[0042]

Since the surface light source of claim 1, claim 2, claim 5, and claim 6 does not have spherical aberration, the light emitted from the light guide plate is almost converged within a predetermined diffusion angle. Light energy which is wasted from the oblique to tangential directions of the surface light source can also be used as illumination light effective for observation. Therefore, the energy utilization efficiency is high, the brightness is high, and no noise light is emitted to the side surface of the surface light source. Since the surface light source according to claim 3 or 4 has fine irregularities on the back surface (the surface opposite to the lens surface) of the lens sheet 4, the light source light can be reliably provided between the light guide plate of the edge light type surface light source and the lens sheet. It is possible to form voids having a wavelength longer than Therefore, even if the lens sheet is placed, the uniform distribution of the light source light throughout the light guide plate due to the total reflection of light on the surface of the light guide plate is not hindered, and the luminance distribution on the light emission surface is uniform.

Since the display device of claim 7 uses the surface light source of claims 1 to 6, it has high energy utilization efficiency such as electric power, high brightness, an appropriate viewing angle, and a front surface. It is possible to obtain a display with uniform brightness.

[0044]

Example 1 (Lens Molding Step) Using a device as shown in FIG. 15, the lens was manufactured by the following steps. A winding roll 11 of a transparent and colorless biaxially stretched polyethylene terephthalate base film having a thickness of 100 μm was prepared. A roll-shaped intaglio 14 is prepared by engraving an elliptic cylinder lenticular lens-shaped reverse type (the same shape but the concavities and convexities are opposite) 15 on the surface of a metal cylinder, and while rotating this around the central axis, T
The UV curable resin liquid 16 was supplied to the plate surface from the die nozzle 21 to fill and coat the reverse concave and convex surface of the lens. Next, the base film 12 is unwound from the winding roll 11 at a speed that is synchronized with the rotational peripheral speed of the roll-shaped intaglio plate 14, and the base film is pressed onto the roll intaglio plate by the pressing roll 13 with the resin liquid interposed therebetween. Then, ultraviolet rays from the mercury lamps 23, 23 were irradiated from the side of the base material film in this state, and the resin solution was cross-linked and cured in the reverse mold and simultaneously adhered to the base material film. Next, the base film running using the peeling roll 18 was peeled off together with the cured resin having the lens shape 19 adhered thereto, thus obtaining the elliptic cylinder lenticular lens sheet 20. By the way, lens shape ; as shown in FIG. 3 (A), unit lens shape; convex elliptic cylinder (long axis oriented in the normal direction of the lens sheet), major axis length 2b = 204 μm, minor axis length 2a = 150 μm Long axis length / Short axis length = 2b / 2a = 1.36-Repeating cycle of lens unit p = 130 μm UV curable resin liquid; -Polyfunctional polyester acrylate oligomer-Photoreaction initiator as a main component.

(Process of forming matte layer having fine irregularities) A roll-shaped intaglio was prepared by engraving a reverse mold of fine irregularities (projections) obtained by sandblasting on the surface of a metal cylinder. Then, a colorless and transparent biaxially stretched polyethylene terephthalate base film having a thickness of 50 μm is unwound from a winding roll, and the same apparatus and resin solution as those used in the lens forming step are used to form an ultraviolet ray curable resin on the back surface of the lens sheet. Matte transparent fine irregularities made of a resin cured product were molded. Thus, the light diffusion layer specified in the present invention was obtained. By the way, minute irregularities -Haze value = 88.8-Surface gloss (JIS-Z-8741) = 11.1-Surface roughness (10-point average roughness of JIS-B-0601) R
z = 38.4 μm Surface roughness (center line average roughness of JIS-B-0601)
Ra = 7.3 μm

[0046]

Example 2 The elliptic cylinder lens sheet produced in Example 1 was overlaid on the light guide plate through the light diffusion layer produced in Example 1 to obtain an edge light type surface light source having the constitution 100 in FIG. . Light guide plate : -Material: Polymethylmethacrylate polymer resin-Shape: Rectangular solid. Thickness 4 mm ・ Surface; 10-point average roughness Rz = 0.1 μm on the entire surface
Finished to less than smoothness. -Back surface: Matte transparent ink was printed on the back surface of the light guide plate in a circular halftone dot pattern, and a specular reflective film obtained by vacuum-depositing aluminum on a polyethylene terephthalate film was placed on the back surface. The halftone dots were formed by silk screen printing using fine silica powder dispersed in an acrylic resin binder. The halftone dots were arranged in a vertical and horizontal direction with a repeating cycle of 5 mm. The diameter of the halftone dot is 0.1 mm near the light source, and it is increased in proportion to the distance from the light source.
It was set to 2 mm at the end opposite to the light source. A white fluorescent lamp was arranged at one end of the light guide plate as a light source line light source.
A metallic reflecting mirror was placed on the side opposite to the light guide plate. The performance of the surface light source with the above configuration is as follows. -The angular distribution of brightness is as shown in Fig. 16. · Half-value angle = 36 degrees, the normal direction brightness (light guide plate central portion) = 2028cd / ^{m 2} · normal direction brightness distribution in the light emitting surface of; + - 15% or less.
Almost visually uniform ・ No side lobes are generated.

[ 47 ]

Comparative Example 1 The following triangular prism prism type lenticular lens was used in place of the convex elliptic cylinder lenticular lens of the lens sheet in Example 2. -Cross-sectional shape: right-angled isosceles triangle. The 90-degree apex angle is oriented in the direction normal to the surface light source.・ Repeat cycle of unit lens (length of one side) = 100μ
m The material, layer configuration, and manufacturing method are the same as those of the convex elliptic cylinder lenticular lens of the first embodiment. The performance of the surface light source with the above configuration is as follows. -The angular distribution of brightness is as shown in Fig. 17. · Half-value angle = 34 degrees, the normal direction brightness (light guide plate central portion) = 2074cd / ^{m 2} · normal direction brightness distribution in the light emitting surface of; + - 15% or less.
Almost visually uniform ・ Side lobes occur. (Peak in + -75 degree direction from the normal) Sidelobe peak brightness / normal brightness = 26%

Comparative Example 2 In Example 2, the light diffusion layer prepared in Example 1 was used instead of the lens sheet. That is, two light diffusion layers were stacked and placed. Others were the same as in Example 2.
The performance of the surface light source having the above configuration is as follows: The angular distribution of luminance is as shown in FIG. -Half-value angle = 38 degrees (However, some amount of emitted light is distributed without being attenuated abruptly even outside the half-value angle.)-Normal direction luminance (center of light guide plate) = 1491 cd / m ² -Normal line Distribution of directional luminance within the light emitting surface; within + -15%.
Almost visually uniform ・ No side lobes are generated.

Comparative Example 3 In Example 2, a convex elliptic cylinder lenticular lens having the following shape was used. -Unit lens shape: convex elliptic cylinder (the short axis is oriented in the normal direction of the lens sheet) -Long axis length 2b = 150 μm- Short axis length 2a = 204 μm-Long axis length / short axis length = 2b / 2a = 0 .74 Repetition cycle of lens unit p = 177 μm Others were the same as in Example 2. The performance of the surface light source having the above configuration is as follows: The angular distribution of brightness is as shown in FIG. · Half-value angle = 42 deg, the normal direction brightness (light guide plate central portion) = 1738cd / ^{m 2} · normal direction brightness distribution in the light emitting surface of; + - 5% or less. Almost visually uniform ・ Side lobes occur. (Brightness peak exists in the direction + -75 degrees away from the normal direction) Sidelobe peak brightness / normal direction brightness = 37%

[Comparative Example 4] In Example 2, an article having no matte layer on the back surface of the lens sheet was used. The back surface of the lens sheet is the surface of the base film itself, and the ten-point average roughness Rz of the surface is a smooth flat surface of less than 0.1 μm. Others were the same as in Example 2. Regarding the performance of the surface light source configured as described above, although the brightness in the normal direction of the light emitting surface is high near the end on the light source side, the brightness decreases sharply with the distance from the light source.
At a position of cm, the brightness was lowered to such an extent that it was visually dark.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of an edge light type surface light source of the present invention and a transmissive display device using the same.

FIG. 2 is a perspective view of an example of a direct type surface light source of the present invention and a transmissive display device using the same.

FIG. 3 is a perspective view of an embodiment of a lens sheet of the present invention. For an elliptic cylinder lenticular lens. (A) and (C) are convex lenses, and (B) and (D) are concave lenses.

FIG. 4 is a diagram illustrating behavior of light rays on a lens sheet, particularly spherical aberration, with a unit lens. (A) shows a case of a convex true cylindrical lens, and (B) shows a case of a convex elliptic cylinder lens of the present invention.

FIG. 5 is a diagram illustrating behavior of light rays on a lens sheet, particularly spherical aberration, with a unit lens. (A) shows a case of a concave true cylindrical lens, and (B) shows a case of a concave elliptic cylinder lens of the present invention.

FIG. 6 is a perspective view of another embodiment of the lens sheet of the present invention.
When two elliptic cylinder type lenticular lenses are laminated so that their axes are perpendicular to each other.

FIG. 7 is a cross-sectional view of a conventional edge light type surface light source. When there is no lens sheet on the light guide plate.

FIG. 8 is a perspective view of a conventional edge light type surface light source. When the lens sheet is closely attached to the light guide plate without leaving a gap between them.

FIG. 9 is an enlarged sectional view of FIG. It shows that the interface between the lens sheet and the light guide plate is optically eliminated and integrated.

FIG. 10 is a sectional view of an embodiment of an edge light type surface light source of the present invention. An example in which a light diffusion layer having fine irregularities on both sides is inserted at the interface between the light guide plate and the lens sheet to form voids at two locations (two layers).

FIG. 11 is a sectional view of another embodiment of the edge light type surface light source of the present invention. An example in which minute concaves and convexes are directly formed on the back surface of the lens sheet to have only one layer of voids.

FIG. 12 is a cross-sectional view showing the behavior of light rays that are totally reflected by a smooth flat surface of the light guide plate. The electromagnetic field seeps out in the air due to the tunnel effect.

FIG. 13 is a cross-sectional view showing that a light beam oozing out from the light guide plate due to a tunnel effect becomes a traveling wave again in the lens sheet.

FIG. 14 is a cross-sectional view showing that in the lens sheet of the present invention, a light ray traveling from the light guide plate to the outside is partially totally reflected and partially transmitted.

FIG. 15 is a cross-sectional view showing an example of the manufacturing method of the present invention. This corresponds to [Example 1].

FIG. 16 is a characteristic of the edge light type surface light source according to the second embodiment of the present invention. 9 illustrates an angular distribution of emission light luminance when a convex elliptic cylinder lenticular lens whose long axis is oriented in the normal direction is used.

FIG. 17 is a characteristic of the edge light type surface light source of [Comparative example 2]. The angle distribution of emission light brightness when a triangular prism lenticular lens is used is shown in the figure.

FIG. 18 shows the characteristics of the edge light type surface light source of [Comparative Example 3]. The angle distribution of the emission light brightness when a convex elliptic cylinder lenticular lens whose short axis faces the normal direction is used is shown.

FIG. 19 shows the characteristics of the edge light type surface light source of [Comparative Example 3]. When two light diffusion layers (films) are laminated on the light guide plate. 9 illustrates the angular distribution of emitted light brightness.

[Explanation of reference numerals] 1 light guide plate 2 light reflecting layer light source (unit) 4 lens sheet 5 reflecting mirror 6 transmissive display device such as liquid crystal display device 7 smooth flat surface on the back surface of lens sheet 8 light isotropic diffusing sheet (light diffusing layer ) 9 Void 10 A smooth flat surface of the light guide plate. 11 Winding Roll 12 Base Film 13 Pressing Roll 14 Roll Intaglio 15 Lens Shape Reverse Type 16 UV Curable Resin Liquid 17 Uncured Resin Liquid in Lens Reverse Mold 18 Peeling Roll 19 Lens Shape (Lens Unit) 20 Lens Sheet 21 T-die type nozzle 22 Liquid pool 23 Mercury lamp 41 Lens sheet projections (group) 42 Lens unit 43 Transparent layer having projection groups 44 Transparent base material layer 100 Surface light source 200 Display device F Focus L1 Direct incidence on a nearby lens surface from a light source And then the light rays that pass through. Light rays that are directly incident on and transmitted through the lens surface in the vicinity from the L2 light source. A light ray that is directly incident on and transmitted through the lens surface in the vicinity from the L3 light source. Light rays that are directly incident on the lens surface at a distance from the L4 light source and are transmitted therethrough. LN paraxial ray. LF Rays off paraxial. Light reflected on the smooth flat surface 10 of the L1R light guide plate. Light reflected on the smooth flat surface 10 of the L2R light guide plate. Transmitted light on the smooth flat surface 10 of the L1T light guide plate. Transmitted light on the smooth flat surface 10 of the L2T light guide plate. Diffuse reflected light from the light reflecting layer 2 on the back surface of the L1S light guide plate. Diffuse reflected light from the light reflecting layer 2 on the back surface of the L2S light guide plate.
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[Procedure amendment]

[Submission date] March 18, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 5]

[Figure 4]

[Figure 6]

[Figure 7]

[Figure 8]

[Fig. 12]

[Figure 9]

[Figure 10]

FIG. 11

[Fig. 13]

FIG. 14

FIG. 15

FIG. 16

FIG. 17

FIG. 18

FIG. 19

Claims (7)

[Claims] 1. A light guide body comprising a transparent flat plate or a rectangular parallelepiped cavity, a line light source or a point light source provided adjacent to at least one side end surface of the light guide body, and a back surface of the light guide body. A surface light source comprising a light reflecting layer and a concave or convex lenticular lens sheet laminated on the light emitting surface of the light guide surface, the lens sheet comprising elliptic cylinder unit lenses whose ridge directions are parallel to each other. Are arranged in a plurality of planes such that the major axis direction of the elliptic cylinder unit lens is in the direction normal to the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≤ major axis / minor axis ≤ 0.9 x
A surface light source characterized by having n / (n ² −1) ^1/2 . 2. A light guide body comprising a light-transmissive flat plate or a rectangular parallelepiped cavity, a line light source or a point light source provided adjacent to at least one side end face of the light guide body, and a back surface of the light guide body. A surface light source comprising a light reflecting layer and a concave or convex lenticular lens sheet laminated on the light emitting surface of the light guide surface, wherein the lens sheet comprises hyperbolic column unit lenses whose ridge directions are parallel to each other. Are arranged in a plurality of planes so that the long axis direction of the hyperbolic pillar unit lens is oriented in the normal direction of the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≤ Asymptotic slope ≤ 0.9
A surface light source characterized by being × n / (n ² −1) ^1/2 . 3. The light guide is made of a light-transmissive flat plate having a smooth surface whose surface roughness is equal to or less than the wavelength of the light from the light source, and the lenticular lens sheet is provided on the surface opposite to the lens surface where the surface roughness is the wavelength of the light from the light source. It has the above-mentioned minute unevenness and is laminated with the minute uneven surface facing the smooth surface side of the light guide, and at least part of the gap between the light guide and the lens sheet is longer than the wavelength of the source light. The surface light source according to claim 1, wherein the surface light source has the following characteristics. 4. The light guide is made of a translucent flat plate having a smooth surface whose surface roughness is equal to or less than the wavelength of the light from the light source, and a light diffusion layer is provided between the back surface of the lenticular lens sheet and the light guide surface. It has been inserted, and the surface roughness and the back surface of the light diffusing layer have minute irregularities with a wavelength of the light of the light source or more, and as a result, voids having the wavelength of the light of the light source or more are formed at least partially. The surface light source according to claim 1, wherein the interface is provided at two locations, that is, an interface between the light guide surface and the light diffusion layer and an interface between the light diffusion layer and the back surface of the lens sheet. 5. A lamp house having at least one line light source or point light source, a lamp house which covers a lower surface and a side surface of the light source and has a window opened on an upper surface of the light source, and an inner surface on the light source side serving as a light reflecting surface, and the window. A surface light source composed of a concave or convex lenticular lens covering a portion, wherein the lens sheet is formed by arranging elliptic cylinder unit lenses in a plurality of planes such that their ridge directions are parallel to each other. In the pillar unit lens, the major axis direction is oriented in the direction normal to the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≦ long axis / minor axis ≦ 0.9 ×
A surface light source characterized by having n / (n ² −1) ^1/2 . 6. A lamp house having at least one line light source or point light source, a lamp house which covers a lower surface and a side surface of the light source and has a window opened on an upper surface of the light source, and an inner surface on the light source side serving as a light reflecting surface, and the window. A surface light source comprising a concave or convex lenticular lens covering a portion, wherein the lens sheet is formed by arranging hyperbolic column unit lenses in a plurality of planes such that their ridge directions are parallel to each other. In the pillar unit lens, the long axis direction is oriented in the direction normal to the light emitting surface, and 1.1 × n / (n ² −1) ^1/2 ≦ asymptote slope ≦ 0.9
A surface light source characterized by being × n / (n ² −1) ^1/2 . 7. A display device, wherein a transmissive display element is laminated on a light emitting surface of the surface light source according to any one of claims 1 to 6.