JP3948625B2 - Surface light source using lens sheet - Google Patents

Description

  The present invention relates to a surface light source using a lens sheet, and is useful for backlights of display devices such as liquid crystal display devices, lighting advertisements, traffic signs, and the like.

As a surface light source for backlight of liquid crystal display (LCD),
(1) An edge light type using a light-transmitting flat plate as shown in FIG. 1 is known. In such a surface light source, light is incident from both or one of the side end surfaces of a light guide made of a transparent parallel plate, and light is propagated uniformly throughout the light guide plate using total reflection inside the translucent plate. A part of the propagated light is diffused and reflected below the critical angle by the light scattering and reflecting plate on the back surface of the light guide, and diffused light is emitted from the surface of the light guide plate (Japanese Utility Model Laid-Open No. 55-162201).

  (2) A lens sheet having a projection on one surface as shown in FIG. 2 and a smooth surface on the other surface is overlaid on the light guide plate surface of the surface light source of (1) with the projection surface facing upward. The diffused radiation can be uniformly and isotropically diffused within a desired angle range by utilizing the light focusing action of the lens (Actual Hei 4-107201). When this lens sheet is used in combination with a matte transparent diffuser (matte transparent sheet), the light of the light source is more than that using only the matte transparent diffuser (US Pat. No. 4,729,067). It was possible to intensively distribute energy within a desired limited angular range, and to obtain diffused light with high uniformity and isotropicity within that angular range.

  However, in the conventional technique (1) described above, the emission light is relatively sharp with a peak at an angle of 60 degrees with respect to the normal direction of the light guide surface only by providing a light scattering plate on the back surface of the light guide. It will be distributed, and the luminance in the normal direction that requires the most light will be insufficient, and light energy will be dissipated in the oblique lateral direction where there is little demand. Further, in the conventional technique (2), when a lens sheet is laminated on the light emitting surface of the light guide, and a lenticular lens in which a large number of triangular prism prism unit lens portions are arranged in parallel is used as the lens sheet. The ratio of light energy emitted within an angle of 30 ° to 60 ° centering on the normal direction of the light emitting surface is high, but contrary to expectation, it is high from 2 to 4 cm from the light guide plate side end. Although it is a brightness | luminance, a brightness | luminance will fall gradually if it goes away more, and it will become conspicuously dark in the edge part on the opposite side to a light source.

To improve the ratio,
(3) As disclosed in JP-A-1-245220, the light scattering layer on the back surface of the light guide has a pattern such as a halftone dot, and the area of the pattern decreases as it approaches the light source and increases as it moves away from the light source. An attempt to correct and equalize the luminance distribution in the optical plate.

(4) An attempt to correct and equalize the luminance distribution in the surface of the light guide plate by disposing light sources at two or more locations on the side edge of the light guide plate as disclosed in JP-A-3-9306.
However, in all cases, it is difficult to make the luminance completely uniform. In (3), the light scattering layer is conspicuous from the light emitting surface side. In (4), the light source There was a drawback that both space and power consumption were more than doubled.

  An object of the present invention is to solve the above-mentioned problems and provide a surface light source using a lens sheet for use in a backlight of a liquid crystal display device, without increasing power consumption or heat generation. It is to obtain uniform and high luminance light emission only within a desired angle range, and to obtain surface light emission with no variation in luminance depending on the location within the surface.

In order to achieve the above object, a surface light source of the present invention includes a light guide made of a light-transmitting flat plate, a light source unit provided adjacent to one or both of the side end faces of the light guide, and the light guide. A light reflecting layer on the back surface of the light body, a lens sheet disposed on the light emitting surface of the light guide body, and a light isotropic diffusive sheet disposed between the light guide body and the lens sheet. A surface light source comprising:
The surface of the light guide is a smooth plane having a surface roughness equal to or less than the wavelength of the light source light,
On the surface of the light isotropic diffusive sheet, a gap forming protrusion group having a height of 100 μm or less and a light source light wavelength is formed, and
The projection group is characterized in that a gap having a wavelength longer than that of the light source light is formed at least partially between the surface of the light guide and the light isotropic diffusive sheet.

  In the above surface light source, the lens sheet is formed by forming a lens group including a convex portion or a concave portion on one surface and laminating the lens group toward the side opposite to the light guide.

  Because of the group of protrusions on the surface of the light isotropic diffusive sheet used in the surface light source of the present invention, when placed on the smooth plane of the light guide plate of the edge light type surface light source, A gap having a wavelength longer than that of the light source light can be reliably formed.

  Therefore, even if a lens sheet is placed, uniform distribution of light source light to the entire light guide plate due to total light reflection on the surface of the light guide plate is not hindered.

  Further, since the edge light type surface light source of the present invention uses a lens sheet, the lens can obtain a uniform luminance within a desired angle range, and the luminance is not concentrated only in the vicinity of the light source. A uniform luminance distribution can be obtained.

  The lens sheet 4 of the present invention includes a columnar lens group (bent lenticular lens in a broad sense) in which columnar unit lenses 42 are arranged adjacent to each other with their long axis (ridgeline) directions in parallel as shown in FIG. As shown in FIG. 14, an eyelid lens in which a large number of unit lenses 42 having an independent hemispherical periphery are arranged in a two-dimensional direction is used.

  The cross-sectional shape of the unit lens is a continuous and smooth curve such as a circle, ellipse, cardioid, Rankine oval, cycloid, or involute curve as shown in FIGS. 12 and 14, or a triangle as shown in FIG. A part or the whole of a polygon such as a square, a hexagon, or the like is used.

  These unit lenses may be convex lenses as shown in FIG. 12 or concave lenses as shown in FIG. Among these, preferred are design, ease of manufacture, light collection, light diffusion characteristics (half-value angle, small sidelobe light (brightness peak that can be formed in an oblique direction), isotropic half-angle angle brightness, It is a cylinder or an elliptical column in terms of brightness in the normal direction). In particular, an ellipse having a long axis in the normal direction of the surface light source is preferable because of high luminance. The range of long axis / short axis = 1.56 to 1.27 is particularly good.

  These lens sheets can be used in a single-sheet configuration, but in order to control the light diffusion angle in two directions (vertical and horizontal directions) using a columnar lens, two lens sheets are used as shown in FIG. The layers may be laminated so that their long axes are orthogonal to each other. In this case, the orientation of the lens surfaces is the same as shown in FIG. 15 because the light transmission is the highest and the best, but of course the lenses of the lens sheet face each other (two lens surfaces are facing each other). Between the lens sheets). Further, the lens sheet may be obtained by integrally molding a translucent substrate as shown in FIG. 6, or a unit lens 42 is formed on a translucent flat plate (or sheet) 44 as shown in FIG. Things can be used.

  The lens sheet 4 is formed from a translucent substrate. Here, as the translucent base material, acrylic acid ester such as polymethyl methacrylate, polymethyl acrylate or the like, or homopolymer or copolymer of methacrylic ester, polyethylene terephthalate, polyester such as polybutylene terephthalate, polycarbonate, polystyrene , Thermoplastic resins such as polymethylpentene, or polyfunctional urethane acrylates such as polyacrylates such as urethane acrylates and polyester acrylates, transparent resins such as unsaturated polyesters, transparent glass, transparent ceramics, and the like that are crosslinked with infrared rays or electron beams .

  When this translucent base material is used as a lens sheet, the total thickness is usually about 20 to 1000 μm.

  As a method for forming the lens shape, for example, a known heat press method (described in JP-A-56-157310), an ultraviolet curable thermoplastic resin film is embossed with a roll emboss plate, and then irradiated with ultraviolet rays. Then, the film is cured (described in JP-A-61-156273), an ultraviolet or electron beam curable resin liquid is applied on a roll intaglio engraved with a lens shape, filled in the concave portion, and then passed through the resin liquid. Then, the resin cured by irradiating UV or electron beam with the transparent base film coated on the roll intaglio and the base film adhered thereto are released from the roll intaglio, and the lens shape of the roll intaglio is cured resin layer. And the like (JP-A-3-2233883, US Pat. No. 4,576,850, etc.) and the like are used.

  The translucency required for the translucent substrate must be selected so that it can transmit diffused light to the minimum to the extent that it does not hinder the use of each application. May be colored transparent or matte translucent.

Here, matte transparency refers to the property of transmitting and transmitting transmitted light almost uniformly and isotropically in all directions within a half solid angle, and is used synonymously with light isotropic diffusibility. In other words, annihilation transparency is the transmitted light intensity when a parallel light beam is incident from the back surface (incident angle i = 0 °), where θ is the angle formed with the normal direction of the surface of the transparent substrate. angular distribution I ⁰ (theta) is cos distribution ^{[I 0 (θ) = I 0} mp cosθ, -90 ° ≦ θ ≦ 90 °, θ is the angle between the normal line N, I ⁰ _mp is the normal direction Transmitted light intensity] or similar distribution. The definition of I ⁱ (θ) will be described later.

  The projection group 41 whose height to be 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 is directly formed on the back surface of the integrally molded lens sheet 4 by hot embossing, sandblasting, or the like as shown in FIG. Alternatively, it is possible to form a translucent material layer having protrusions on the flat back surface of the lens sheet 4 as shown in FIG. Specifically, a method of applying a coating material in which transparent fine particles such as calcium carbonate, silica, acrylic resin, etc. are dispersed in a transparent binder to reveal irregularities of the fine particles on the surface of the coating film, or the above-mentioned JP-A For example, a method of forming ultraviolet or electron beam curable resin liquid on a roll intaglio disclosed in Japanese Patent No. 3-223883 and US Pat.

  The purpose of the protrusion 41 is to form at least partially a gap 9 (dimension ΔX) that is equal to or greater 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. As will be described later, when the gap ΔX is less than the wavelength of the light source light, the total reflection of light on the smooth plane 10 of the light guide plate 1 does not occur sufficiently, and when it exceeds 100 μm, the uneven shape of the protrusion becomes noticeable.

  If this purpose is achieved, the projection 41 may have any irregular shape, but the most preferable attitude is to obtain a uniform luminance distribution within a desired diffusion angle and a uniform luminance distribution within the light source light. FIG. 5, FIG. 6, FIG. 9, and FIG. 10 are obtained by forming a random uneven shape (for example, grained pattern, satin pattern, etc.) on the entire back surface of the lens sheet 4.

  In this case, as shown in FIG. 5, the light L1, L2S and the like incident from the back surface of the lens sheet 4 is diffused isotropically because the projection group 41 also acts as a light diffusion layer. A uniform angular distribution can be obtained without interposing a matte transparent sheet, and a dot-like pattern is not noticeable.

  Of course, as shown in FIG. 4, a light isotropic diffusive sheet 8 having a matte transparency and a projection group 41 having a surface wavelength of 100 μm or less is interposed between the lens sheet 4 and the smooth plane 10 of the light guide plate. It can also intervene. However, in this case, there are a plurality of interfaces through which light diffuses (smooth plane 10 / projection group 41, light isotropic diffusive sheet 8 / back surface of lens sheet 4, and light isotropic diffusibility if a matting agent is contained. Therefore, the loss of effective light energy in the vicinity of the normal direction increases.

  Further, as shown in FIG. 11, the projection group 41 may be a pattern in which dotted patterns such as halftone dots are distributed in a plane. However, since the pattern 41 is conspicuous in this way, it is necessary to devise such as dispersing the matting agent in the lens sheet 4.

  The surface light source of the present invention has a configuration shown in the sectional view of FIG. 5 and the perspective view of FIG. The light guide plate 1, a linear or point light source 3 installed adjacent to at least one of its side edges, the light reflection layer 2 on the back surface of the light guide plate, and the light reflection layer on the opposite side of the light reflection plate The lens sheet 4 is a minimum configuration. Usually, these are also accompanied by a housing (not shown), a power source (not shown), etc., which house the entire light source light reflecting mirror 5 and have a light emitting surface as a window.

  The opposite surface 10 of the light reflection 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 finished to be 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 to 0.8 μm, so the surface roughness is 0.4 μm or less.

  As a method for raising the roughness to such a level, known methods such as hot pressing with a mirror plate, injection molding using a specular shape, casting (casting) molding, precision polishing performed by optical lens, etc. Etc. may be used.

  The material of the light guide plate 1 is selected from the same translucent materials as those 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 line light source such as a fluorescent lamp is preferable for obtaining 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 of the light guide plate as shown in the drawing, and the side end of the light guide plate 1 is partly cut out and partly or entirely embedded in the light guide plate. Things are also possible.

  The light source 3 can also be installed at the other side end of the light guide plate 1 from the viewpoint of improving the uniformity in the surface of high luminance and luminance.

  As the light source light reflecting mirror 5, a publicly known one, for example, a metal vapor-deposited material on the inner surface of a parabolic column, a hyperbolic column, an elliptic column or the like is used.

The lens sheet 4 is laminated on the smooth plane 10 of the light guide plate. At this time, as shown in FIG. 5, the lens sheet 4 and the light guide plate 1 are mounted by placing the lens surface of the lens sheet 4 on the outside (opposite surface of the plane 10) and the projection group 41 facing the inside (plane 10 side). A gap 9 having a wavelength λ or more of the light source light is formed at least partially between the smooth surface 10 and the flat surface 10. The area ratio R of the void portion 9, that is,
R = (Area of the portion having a gap of wavelength λ or more / total surface area of the light guide plate) × 100%
Is determined by the required in-plane luminance uniformity, light energy utilization efficiency, light guide plate dimensions, etc., but usually the ratio R needs to be 80% or more, more preferably 90% or more. .

  The reason for this is that, as a result of the experiment, as shown in FIG. 3, when the smooth light guide plate surface 10 whose surface roughness is equal to or less than the wavelength of light and the surface 41 of the lens sheet are brought into close contact, the input from the line light source 3 It has been found that most of the light is emitted without being totally reflected at a distance y from the side end on the light source side, and the brightness is suddenly lowered and darkened at a distance farther than y.

And it turned out that it is the ratio with respect to the full length Y of the light propagation direction of the length y of a light-emitting part, and the light-guide plate, (y / Y) * 100 = 10-20%. Therefore, in order to evenly distribute the amount of light energy incident on the light guide plate plane 10 from the light source to the entire length Y, 10 to 20% of the incident light on the plane 10 is transmitted and the remaining 90 to 80%. Must be totally reflected. In general,
(Total reflected light amount / transmitted light amount) = (Area of a portion having a gap of wavelength λ or more / total surface area of light guide plate) = R
From the above, it was found that R needs 80 to 90% or more.

  As a method of forming a gap longer than the wavelength of the light guide between the lens sheet 4 and the light guide plate 1, the lens sheet 4 is placed with the lens surface 42 and the projection group 41 being reversed with respect to FIG. 5. (Not shown).

  However, in this case, since the light once focused within the desired angle on the lens surface 42 diverges isotropically again, the light diffusion angle is 30 degrees or more about the normal that is the optimum value. It is difficult to control within 60 degrees.

The light reflecting layer 2 is a layer having the ability to diffusely reflect light and can be configured as follows.
(1) On one side of the light guide plate layer, a white layer in which a powder of high concealment and high whiteness, for example, a powder of titanium dioxide, aluminum or the like is dispersed is formed by painting or the like.
(2) The metal thin film layer is formed by plating or vapor-depositing a metal such as aluminum, chromium, silver, etc. on the uneven pattern surface of the light guide plate on which the matte fine unevenness is formed by sand bright processing, embossing, etc. Form.
(3) A metal thin film layer is formed on a white layer which has low concealability and is simply formed by applying a matte surface.
(4) It may be formed in a halftone dot white layer, and the area ratio may be increased as the distance from the light source is increased to correct the attenuation of the light amount of the light source.

  The configuration when the surface light source 100 of the present invention is used as a backlight (back light source) of a transmissive display device such as a transmissive LCD is as shown in FIG. That is, the transmissive display device 6 may be laminated on the lens surface of the lens sheet of the surface light source 100 of the present invention (the side where the unit lens 42 is present).

  The diffusion angle is effective for evaluating the light distribution state of the surface light source.

As the diffusion angle, for example, the half-value angle θ _H is used. This is when the transmitted light intensity (or intensity) is a decreasing function I of an angle theta from the normal of the light emitting surface (theta), as _{I (θ H) = I (} 0) / 2 to become angle theta _H Defined.

  Next, the operation of the present invention will be described.

  As shown in FIG. 1, the working mechanism of the edge light type surface light source is L1 which is incident near the light source among the light rays incident on the light guide plate 1 from the light source 3 and directly incident on the smooth plane 10 of the light guide plate. The angle formed with the normal line is small and less than the critical angle, and therefore, a percentage of the incident light quantity is emitted as transmitted light L1T. Thereby, emitted light near the light source is formed. On the other hand, the light beam L2 that directly enters the light source 3 relatively far away has a large incident angle and is greater than the critical angle. Therefore, the light beam L2 is not emitted to the outside but is sent to the far end as total reflected light L2R. The light diffuse reflection layer 2 on the back surface becomes diffuse (random) reflected light L2S and travels in all directions, and some of these are incident on the surface 10 at less than the critical angle, and another part of the light is emitted light. As a result, emitted light at a position away from the light source is formed.

  Here, FIG. 3 shows a state in which the smooth surface of the lens sheet 4 whose non-lens surface is a smooth plane is laminated on the smooth plane 10 of the light guide plate 1 in a direction in contact with the surface 10. The refractive indexes of light-transmitting materials that are usually used are all about 1.5, and the difference between them is not large. Therefore, the lens sheet 4 and the light guide plate 1 are optically almost integrated as shown in FIG. Then, since the surface of the unit lens 42 of the lens sheet 4 has an inclination with respect to the smooth plane 10, most of the light rays incident on the light guide plate in the vicinity of the light source, for example, L1, L2, and L3 are incident at less than a critical angle. A few percent of the soot is emitted, and most of the reflected light is returned to the light source direction and is not propagated far away.

  Of course, there is also a light ray that directly enters the lens surface far from the light source and becomes emission light, for example, L4 in FIG. 3, but the amount thereof is smaller than that in FIG.

  Therefore, as described above, the emitted light from the surface light is mostly concentrated at 10 to 20% of the total area of the light guide plate near the light source.

  On the other hand, in the present invention, as shown in FIG. 5, a projection group 41 is formed on the non-lens surface side of the lens sheet 4, thereby at least partially between the smooth plane 10 of the light guide plate and the lens sheet 4. 9 is formed.

  In this gap portion 9, the light guide plate 1 having a refractive index of about 1.5 and an air layer (or a vacuum layer) having a refractive index of about 1.0 are generally adjacent to each other with the plane 10 as an interface. Total light reflection occurs. Therefore, in the region near the light source, the emitted light is obtained by the light beam L1T that is incident on and transmitted through the plane 10 at a angle less than the critical angle. In the region far from the light source, the light on the back surface is totally reflected at the interface of the gap 9. Of the light rays diffusely reflected by the diffuse reflection layer 2, emitted light is obtained by the component L <b> 2 </ b> T that is less than the critical angle.

  Of course, in L2T, part of the light incident on the region where the projection group 41 and the flat surface 10 are in contact is not totally reflected but is transmitted as it is to become emitted light. As described above, when the area ratio R of the gap is 80 to 90% or more, the entire surface has a substantially uniform luminance distribution.

  Here, the total reflection on the surface 10 is ensured by setting the height of the protrusions (that is, the gap interval) to be equal to or longer than one wavelength of the light source light.

  The reason for this is that, as shown in FIG. 16, when the light beam L1 incident on the smoothing plane 10 of the light guide plate from the inside of the light guide plate is totally reflected and becomes reflected light L1R, strictly speaking, the electromagnetic field of light is completely air (or vacuum). ) The electromagnetic field L1V transmitted through the interface 10 is partially present due to the tunnel effect. However, this electromagnetic field L1V attenuates exponentially, and the amplitude becomes zero on the order of the wavelength of light.

  Therefore, if the gap 9 continues for a sufficiently large distance compared to the wavelength of light, the light beam L1 does not enter the gap portion 9 at all.

  However, as shown in FIG. 17, when the lens sheet 4 having substantially the same refractive index as that of the light guide plate 1 approaches the light guide plate surface 10 to a distance ΔX that is less than the wavelength λ of light (ΔX <λ), it is completely attenuated. Otherwise, the electromagnetic field L1V that has entered the lens sheet 4 again becomes a traveling wave L1T, that is, the transmitted light L1T is generated.

  In the present invention, since the projection 41 is formed on the back surface of the lens sheet 4, there is no area having a gap 9 and no gap between the light guide plate 1 and the lens sheet 4 as shown in FIG. A region where both of them are optically integrated (or less than the wavelength of light even if there is a void) can be formed.

  Among these, the total reflection of the incident light occurs in the gap portion, and the incident light is transmitted in the portion without the gap. As described above, the ratio of the amount of light totally reflected on the surface 10 is determined by the ratio of the gap area to the light guide plate area.

[Example 1]
(Lens formation process)
Using the apparatus as shown in FIG. 19, it was manufactured by the following process.
(1) A colorless and transparent biaxially stretched polyethylene terephthalate base film winding roll 11 having a thickness of 100 μm was prepared.
(2) A roll-shaped concave plate 14 provided with an elliptical lenticular lens-shaped inverted mold (same shape and reverse concave and convex) 15 is prepared on the surface of a metal cylinder, and the T-die is rotated while rotating this around the central axis. The ultraviolet curable resin liquid 16 was supplied from the mold nozzle 21 to the plate surface, and the reverse surface of the lens was filled and coated.
(3) Next, the base film 12 is unwound from the take-up roll 11 at a speed synchronized with the rotational peripheral speed of the roll-shaped intaglio 14, and the base film is placed on the roll intaglio with the press roll 13. In the state where the film was laminated, ultraviolet rays from mercury bottles 23 and 23 were irradiated from the side of the base film, and the resin liquid was cross-linked and cured in the reverse mold and simultaneously adhered to the base film.
(4) Next, the base film traveling using the peeling roll 18 was peeled off together with the cured resin having the lens shape 19 adhered thereto to obtain an elliptical lenticular lens sheet 20. The lens sheet was wound up as it was.

By the way;
(Lens shape); as shown in FIG.
Unit lens shape: elliptic cylinder (Long axis is in the normal direction of the lens sheet.)
Long axis length 2b = 204 μm
Short axis length 2a = 150μm
Long axis length / short axis length = 2b / 2a = 1.36
Repetition period of lens unit p = 130 μm
UV curable resin liquid;
The main component is a polyfunctional polyester acrylate oligomer photoinitiator.
(Molding process of back projection group)
(1) A roll-shaped intaglio was prepared in which a reverse surface of a satin-like microprojection group was provided on the surface of a metal cylinder. (2) Next, the lens sheet produced in the lens molding process was unwound from the winding roll, and the lens molding process. Using the same apparatus and resin liquid, a satin-like microprojection group made of an ultraviolet curable resin cured product was formed on the back surface of the lens sheet.

  (3) Thus, the lens sheet of the present invention as shown in FIG. 20 was obtained.

By the way,
(Microprojection group)
Total coating thickness = 2.0μm
Surface roughness (JIS-B-0601 ten-point average roughness) Rz = 0.8 μm
[Example 2]
Using the elliptical lens sheet manufactured in Example 1, an edge light type surface light source having a configuration as shown in FIG. 7 was obtained.
(Light guide plate);
Material: Polymethylmethacrylate polymer resin Shape: rectangular parallelepiped. 4mm thickness
Surface: Centerline average roughness was finished to a smoothness of less than Rz = 0.1 μm over the entire surface.

    Back side: Matte transparent ink was printed on the back side of the light guide plate in the form of a circular dot, and the back side was covered with a specular reflective film in which aluminum was vacuum-deposited on a polyethylene terephthalate film.

          The halftone dots were formed by silk screen printing using a fine silica powder dispersed in an acrylic resin binder.

          The halftone dots were arranged in the vertical and horizontal directions with a repetition period of 5 mm.

The diameter of the halftone dot was 0.1 mm near the light source, increased in proportion to the distance from the light source, and 2 mm at the end opposite to the light source.
(light source)
A white fluorescent lamp was placed at one end of the light guide plate as a line light source. A metallic reflector was placed on the opposite side of the light guide plate.

  The performance of the surface light source with the above configuration is as follows.

Half-value angle = 36 degrees
Normal direction luminance (light guide plate center) = 2028 cd / m ²
Distribution in the light emission surface of normal direction luminance; within + -5%. Visually almost uniform [Comparative example]
In Example 2, a lens sheet that does not form a rear projection group was used. The back surface was the substrate film surface itself, and the surface had a ten-point average roughness Rz of a flat bone plane of less than 0.1 μm.

  Others were the same as in Example 2.

  The performance of the surface light source having the above configuration is that the luminance in the normal direction of the light emission surface is high near the end on the light source side, but rapidly decreases with the distance from the light source, and is visually dark at a position 2 cm from the light source. The brightness has fallen as much as I felt.

Sectional drawing of the edge light type surface light source of a prior art. When there is no lens sheet. The perspective view of the edge light type surface light source of a prior art. When a lens sheet with a flat back surface is used. Sectional drawing of FIG. Sectional drawing of the Example of the edge light type surface light source of this invention. When the projection group is formed as a separate layer. Sectional drawing of another Example of the edge light type surface light source of this invention. When the projection group is formed directly on the back surface of the lens sheet. The perspective view of the Example of the lens sheet of this invention. When a projection group is formed directly on the back surface using a triangular prism type lenticular lens. The lens sheet is a single layer. The perspective view of the Example of the edge light type surface light source of this invention. The perspective view at the time of using the edge light type surface light source of this invention as a back light source of a liquid crystal display device. The perspective view of another Example of the lens sheet of this invention. When the projection group on the back is formed as a separate layer with a triangular prism type lenticular lens. The perspective view of another Example of the lens sheet of this invention. When a lens sheet is formed on a transparent substrate sheet. Sectional drawing of another Example of the lens sheet of this invention. When the projection group is partially formed. The perspective view of another Example of the lens sheet of this invention. (Convex lens type) In the case of a cylindrical lenticular lens. The perspective view of another Example of the lens sheet of this invention. For concave lens type cylindrical lenticular lens. The perspective view of another Example of the lens sheet of this invention. For acupuncture eye lenses. The perspective view of another Example of the lens sheet of this invention. When two cylindrical lenticular lenses are stacked so that their axes are orthogonal. Sectional drawing which shows the behavior of the light ray which progresses toward the exterior from the inside of a light-guide plate. Sectional drawing which shows that the light which oozed out from the light-guide plate by the tunnel effect, or it becomes a traveling wave again in a lens sheet | seat. Sectional drawing which shows that the light ray which progresses toward the exterior from a light-guide plate is partially reflected totally and it permeate | transmits in the lens sheet of this invention. Sectional drawing which shows an example of the manufacturing method of this invention. This corresponds to Example 1. Sectional drawing which shows an example of the lens sheet of this invention. This corresponds to Example 1. Ellipsoidal lenticular lens.

Explanation of symbols

1 Light guide plate 2 Light reflection layer
3 Light source (unit)
4 Lens sheet 5 Reflecting mirror 6 Transmission type display device 7 such as a liquid crystal display device Smooth flat surface 8 on the back of the lens sheet 8 Light isotropic diffusive sheet 9 Air gap 10 Smooth flat surface on the surface of the light guide plate.
DESCRIPTION OF SYMBOLS 11 Winding roll 12 Base film 13 Press roll 14 Roll-shaped intaglio 15 Lens-shaped reverse mold 16 UV curable resin liquid 17 Uncured resin liquid 18 in lens reverse mold 18 Release roll 19 Lens shape (lens unit)
20 Lens sheet 21 T-die nozzle 22 Liquid reservoir 23 Mercury bottle 41 Projection (group) of lens sheet
42 Lens unit 43 Transparent layer 44 having projection group Transparent substrate layer 100 Surface light source 200 Display device

Claims (2)

A light guide made of a translucent flat plate, a light source unit provided adjacent to one or both of the side end faces of the light guide, a light reflecting layer on the back of the light guide, and a surface of the light guide A surface light source composed of a lens sheet disposed on a light emitting surface, and a light isotropic diffusive sheet disposed between the light guide and the lens sheet,
The surface of the light guide is a smooth plane having a surface roughness equal to or less than the wavelength of the light source light,
On the surface of the light isotropic diffusive sheet, a gap forming protrusion group having a height of 100 μm or less and a light source light wavelength is formed, and
The surface light source characterized in that the projection group is formed at least partially with a gap having a wavelength longer than the wavelength of the light source light between the light guide surface and the light isotropic diffusive sheet. 2. The surface light source according to claim 1 , wherein the lens sheet is formed by forming a lens group including a convex portion or a concave portion on one surface, and laminating the lens group toward a side opposite to the light guide. Surface light source characterized by being made.

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