JP5200437B2 - Optical sheet for surface light source, surface light source device and display device - Google Patents

Description

  The present invention relates to an optical sheet for a surface light source, a surface light source device, and a display device. More specifically, in an optical sheet having a unit prism, a white spot generated when the top of the unit prism is pressed against a component of the surface light source device. The present invention relates to an optical sheet for a surface light source in which generation is suppressed, a surface light source device having the optical sheet, and a display device having the surface light source device.

  In recent liquid crystal display devices and the like, surface light source devices for illuminating the liquid crystal display devices and the like from the back are required to be thin and light as required for low power consumption, thin and light weight, and light sources The light from the light source is effectively used to reduce the power consumption of the light source. As a surface light source device used for such a liquid crystal display device, an edge light type surface light source device and a direct type surface light source device are known.

  An edge-light type surface light source device usually enters light source light from one end face of a plate-like light guide made of transparent acrylic resin or the like, and a liquid crystal panel or the like from a light exit surface which is one side of the light guide. Light is emitted to the back surface. In this surface light source device, the light utilization efficiency is improved by providing a reflective plate or a reflective film that reflects light on the surface opposite to the light exit surface of the light guide. On the other hand, a direct type surface light source device has a liquid crystal panel and a reflector arranged with a light source sandwiched between them. Usually, the light source light is reflected on the back of the liquid crystal panel by the reflector and used as light. Improves efficiency.

In the edge light type or direct type surface light source device described above, an optical sheet having a prism portion formed by arranging a plurality of unit prisms is disposed on the light output surface of the light guide. As an optical sheet, for example, as shown in Patent Documents 1 and 2, a unit prism having a substantially triangular cross section or a substantially semicircular cross section and having a ridge line (also referred to as a ridge line part) at the top thereof is orthogonal to the ridge line part. One having a plurality of prism portions arranged in a direction has been proposed. The surface light source device is configured such that the ridge line portion of the unit prism is pressed against a sheet member such as a diffusion sheet or a light guide.
JP-A-6-118246 JP 7-234305 A

  However, in the surface light source device configured in the above aspect, when the ridge line portion of the unit prism is pressed against the sheet member or the light guide, there is a contact portion between the tip of the ridge line portion and the sheet member or the light guide. The contact portion becomes a so-called “optical contact portion”. In this optical contact portion, the light from the light source passes through without being refracted by the unit prism, so that the luminance is increased more than the surroundings. Usually, such an optical contact portion does not extend over the entire length of the ridge line, but is generated in a partially intermittent dot shape, so that the light passing through causes display unevenness such as a white spot (white pattern) on the display surface of the display device. . Depending on the degree of such display unevenness, it becomes conspicuous for an observer, and there is a problem that the display performance of the display device is degraded.

  The present invention has been made to solve the above-described problems, and its object is to reduce display unevenness such as white spots (white patterns) on the display surface of a display device to prevent deterioration in display performance. An object of the present invention is to provide an optical sheet for a surface light source. Another object of the present invention is to provide a surface light source device having the surface light source optical sheet and a display device having the surface light source device.

  An optical sheet for a surface light source according to the present invention for solving the above problems is a unit having a translucent substrate and a ridge line at the top with a substantially triangular cross section provided on one surface of the translucent substrate. An optical sheet for a surface light source having a plurality of prisms arranged in a direction orthogonal to the ridgeline, and the top of one unit prism in two to eight rows of the unit prisms It is characterized in that it is formed higher in the range of 0.4 to 10 μm than the top, the top of the unit prism is flat, and the flat width W is in the range of 100 nm to 400 nm.

  According to this invention, since the top of one unit prism is formed higher than the other tops in 2 to 8 rows of the unit prisms, the top of the unit prism hits the sheet member or the light guide, for example. Even when the contact portion is a so-called “optical contact portion” and a white spot (white pattern) or the like is generated on the display surface of the display device, the density of the white spots is 1/2 to 1/1 of the conventional density. 8 As a result, display unevenness based on white spots becomes inconspicuous, and deterioration in display performance can be prevented. In addition, if the top part of a unit prism is made higher in the range of 0.4-10 micrometers than another top part, the high top part provided in one in 2 rows-8 rows may be provided in a fixed period. However, it may be provided irregularly, and in any case, the density of white spots is 1/2 to 1/8 that of the prior art, and display unevenness becomes inconspicuous.

  Also, the top of the unit prism becomes the contact portion and causes white spots, but according to the present invention, the top of the unit prism is flat and the flat width W is in the above range. The range becomes a value smaller than the wavelength of 400 nm to 830 nm of a light source usually used. As a result, the light beam cannot substantially enter the flat portion having a width narrower than the wavelength. Therefore, since the light beam passing through the contact portion that causes the white spot is substantially eliminated, the white spot can be made less noticeable.

  A surface light source device according to a first aspect of the present invention for solving the above-described problem is a light guide made of a light-transmitting material and emitting light introduced from at least one end surface from a light emission surface which is one surface. An optical sheet that is provided on a light emission surface of the light guide and transmits light emitted from the light emission surface; and a light source that causes light to enter inside from at least one end face of the light guide. It is a surface light source device which has this, Comprising: The said optical sheet is an optical sheet for surface light sources concerning the said invention, It is characterized by the above-mentioned.

  A surface light source device according to a second aspect of the present invention for solving the above-described problems includes an optical sheet for a surface light source according to the present invention, a light source that emits light from the back side of the optical sheet, and the light source of the light source. And a reflector that is disposed on the opposite side of the optical sheet and reflects light from the light source toward the optical sheet.

  According to the first and second aspects of the invention, since the optical sheet according to the present invention is used as an optical sheet for a surface light source, there is provided a surface light source device with good display performance in which display unevenness based on white spots is not noticeable. it can.

  The display device of the present invention for solving the above-described problems is a planar light-transmitting display body and the book that is disposed on the back surface of the light-transmitting display body and that irradiates light from the back surface. A surface light source device according to the invention.

  According to this invention, since the surface light source device according to the present invention is used as the light source of the display device, it is possible to provide a liquid crystal display device with good display performance in which display unevenness based on white spots is not noticeable.

  According to the optical sheet for a surface light source of the present invention, the top of the unit prism hits, for example, a sheet member or a light guide constituting the surface light source device, and the contact portion becomes a so-called “optical contact portion” of the display device. Even when white spots (white pattern) or the like are generated on the display surface, the generation density of the white spots is 1/2 to 1/8 of the conventional display, so that the display unevenness based on the white spots becomes inconspicuous, A decrease in display performance can be prevented. Further, the high top provided in one of the 2nd to 8th rows may be provided at a fixed period or may be provided irregularly, and in any case, a white spot The generation density becomes 1/2 to 1/8 of the conventional, and display unevenness becomes inconspicuous.

  Further, according to the optical sheet for surface light source of the present invention, the range of the flat width W at the top of the unit prism is shorter than the wavelength 400 nm to 830 nm of the light source that is usually used. It becomes substantially impossible to enter into the narrow flat part of the. Therefore, since the light beam passing through the contact portion that causes the white spot is substantially eliminated, the white spot can be made less noticeable.

  Therefore, according to the present invention, it is possible to provide an optical sheet for a surface light source that does not cause display unevenness such as a white spot (white pattern) on the display surface of the display device and provides a stable and good display performance. It can be preferably used as an optical sheet for a surface light source for a recent high-quality liquid crystal display device. In addition, it is possible to provide a surface light source device with good display performance, in which display unevenness based on white spots is not conspicuous, and a display device including the surface light source device.

  Hereinafter, an optical sheet for a surface light source, a surface light source device, and a display device of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment.

[Optical sheet for surface light source]
First, an optical sheet for a surface light source (hereinafter also simply referred to as “optical sheet”) will be described. FIG. 1 is a schematic perspective view showing an example of the optical sheet of the present invention. As shown in FIG. 1, the optical sheet 10 of the present invention includes a translucent substrate 12 and a prism portion 16 including a large number of unit prisms 14 provided on one surface S1 of the translucent substrate 12. have. The prism portion 16 has a substantially triangular cross section, and is formed by arranging a large number of unit prisms 14 having ridge lines at the apex 5 in a direction perpendicular to the ridge lines.

(Translucent substrate)
The translucent substrate 12 is a main constituent member of the optical sheet 10 and acts as a substrate of the prism unit 16 described in detail later, and transmits most of the light from the light source to the prism unit 16 side. Act on. The light-transmitting substrate 12 may be any light-transmitting substrate, and a substrate having a transmittance of 85% or more as a single substrate is particularly preferably used. In addition, the transmittance here is a value measured by a light transmittance meter (model: HM-150) manufactured by Murakami Color Research Laboratory Co., Ltd. Although the thickness of the translucent base material 12 is not specifically limited, Usually, it exists in the range of 50-500 micrometers which can be rolled.

  As the translucent substrate 12, resin or glass is used. Examples of the resin include a polyester resin such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, an acrylic resin such as polymethyl methacrylate, a transparent resin composed of a thermoplastic resin such as a polycarbonate resin, a polystyrene resin, and a polymethylpentene resin. Preferred examples of the base material are as follows. As the translucent substrate 12 made of glass, for example, soda glass, borosilicate glass, or the like is used.

  The translucent substrate 12 made of a resin material is preferably produced by extrusion of a single layer or by coextrusion together with a light diffusion layer 18 described later. In addition, the translucent base material 12 may be produced by other methods. The translucent base material 12 produced by extrusion or the translucent base material 12 produced by other methods is usually subjected to stretching treatment. This stretching process may be a biaxial stretching process or a uniaxial stretching process, but usually a biaxial stretching process is preferably applied.

(Prism part)
The prism portion 16 is provided on one surface S1 of the translucent substrate 12, and as shown in FIG. 1, a unit prism 14 having a substantially triangular cross section and having a ridge line at the apex 5 is arranged in a direction orthogonal to the ridge line and It is a prism group formed by arranging a large number of ridgelines so that they are parallel. The period of the unit prism 14 is usually selected in the range of 12.5 μm to 200 μm in order to satisfy the performance required for the surface light source device for the translucent display. FIG. 2 is a cross-sectional view showing an embodiment of a unit prism constituting the optical sheet of the present invention, and FIG. 3 is an enlarged cross-sectional view in the vicinity of the top of the prism portion shown in FIG.

  Hereinafter, the prism portion will be described.

  In the prism portion 16 according to the present invention shown in FIG. 2, the top portions 5 of one unit prism 14 in two to eight rows out of the unit prisms 14 arranged in a direction orthogonal to the ridge line are more than the other top portions 5 ′. Highly formed. When the tops 5 formed higher than the others are separated by 9 rows or more, the optical sheet is within the range of prisms of a commonly used material (as exemplified above) and a period (as above 12.5 to 200 μm). As a result of bending, the top 5 ′ formed by being pulled down comes into contact with other adjacent members, and the effect of the present invention may not be achieved. In addition, the difference H between the top 5 and the other top 5 ′ is that only the high top 5 hits other members (sheet member, light guide plate, etc .; the same shall apply hereinafter) and the low top. 5 ′ is preferably a difference H that does not cause contact with another member or does not become an optical contact portion that generates a white spot even if it is pressed.

  Specifically, the difference H between the high top 5 and the other top 5 ′ is preferably in the range of 0.4 μm to 10 μm. By setting the difference H within this range, the high top portion 5 comes into contact with another member, and the contact portion becomes a so-called “optical contact portion”, and a white spot (white pattern) or the like is generated on the display surface of the display device. Even in such a case, the density of white spots is 1/2 to 1/8 that of the prior art, so that display unevenness based on white spots becomes inconspicuous and display performance deterioration can be prevented. If the difference H is less than 0.4 μm, even if the optical sheet is not bent, the electromagnetic field of light that has exuded out of the prism as an evanescent wave is combined with another adjacent optical member and enters and transmits. In addition, when the optical sheet is bent even a little, the high top 5 is pressed against the other member and at the same time the low top 5 ′ is pressed against the other member to become an optically contacting contact portion. There is also a possibility that display unevenness such as a white spot (white pattern) may occur as in the conventional case. On the other hand, even if the difference H exceeds 10 μm, the display unevenness based on the contact portion does not occur, but the white point prevention effect is saturated, so that it is not necessary to make the altitude difference H so far. In addition, in a unit prism having a period and height of about 12.5 to 200 μm, the height changes by 10 μm or more, and the optical behavior of the prism itself also differs from the design. So rather problems may arise.

  The high top 5 may be provided with a two-row cycle as shown in FIG. 2 (A), may be provided with a four-row cycle as shown in FIG. 2 (B), or an eight-row cycle (not shown). May be provided. In addition, if one top 5 is provided in two to eight rows, the interval between the high tops 5 may be regular, for example, every 2 cycles, every 5 cycles, or every 8 cycles. , May be provided at irregular intervals (on average, the top 5 is one higher in 2 to 8 rows). In any case, the density of white spots is 1/2 to 1/8 that of the prior art, and display unevenness becomes inconspicuous.

  If the difference H between the high top 5 and the other low top (5 ′, 5 ″) is within the above range, the height of the low top (5 ′, 5 ″) is as shown in FIG. It may be constant as shown in FIG. 2B or may not be constant as shown in FIG. The example shown in FIG. 2 (C) shows a mode in which a top 5 ′ having a height H lower than the high top 5 and a top 5 ″ having a difference H ′ lower than the top 5 ′ coexist. At this time, the difference H ′ between the lower top 5 ′ and the lower top 5 ″ is not particularly limited, and may be, for example, about 0.4 μm to 5 μm. In the present invention, the thickness (height h) of the prism portion 16 from the top portion 5 of the prism portion 16 to the surface of the translucent substrate 12 is usually constant and is in the range of about 20 to 100 μm.

  Next, the flat part at the top of the prism part will be described.

  FIG. 3 is an enlarged view of the vicinity of the top of the prism portion 16 shown in FIG. In the unit prisms 14 arranged in a number orthogonal to the ridge line extending in one direction, the tops 5 of the unit prisms 14 are formed to be substantially flat rather than an acute angle. The flat width W of the flat top 5 is in the range of 100 nm to 400 nm. The flat width W in the above range is a value smaller than the wavelength 400 nm to 830 nm of a commonly used light source.

  Since the flat width W of the top portion 5 is equal to or less than the wavelength of the light source used, when the top portion 5 is pressed against another member and becomes a contact portion, the light emitted from the light source is less than the wavelength. However, it is substantially impossible to enter the narrow flat portion. Therefore, the white spot generated by the contact portion becomes inconspicuous. On the other hand, if the flat width W of the top is larger than the wavelength of the light source used, the contact portion where the top 5 is pressed against another member transmits light that should not be transmitted. This may cause white spots and may cause display unevenness. Therefore, in this prism portion 16, the top portion 5 that is pressed against another member to become a contact portion is displayed by setting the flat width W to a value smaller than any of the wavelengths 400 nm to 830 nm of the light source used. White spots that cause unevenness can be made inconspicuous.

  For this reason, as shown in FIG. 2, the prism portion 16 according to the present invention is formed such that the top portion 5 of one unit prism 14 is formed higher than the other top portions 5 ′ in two to eight rows. 5 is pressed against another member to become a contact portion, and a white spot of 1/2 to 1/8 is generated as compared with the case where all unit prisms have the same height, but the flat width of the top 5 is used. Since the wavelength of the light source light is equal to or less than the wavelength of the light source light, the density of white spots, which is 1/2 to 1/8 of the conventional one, can be further prevented and made inconspicuous.

  When such a prism portion 16 according to the present invention is used in the mode of FIGS. 4 and 5 (a mode in which the top portion does not face the light guide 32), as shown in FIG. It is preferable that the angle α of the top portions 5 and 5 ′ (5 ″) is 90 ° or approximately 90 ° (about 85 ° to 105 °). Further, usually, a slope extending from the valley portion between the unit prisms 14 and 14 The base angles β and γ represented by imaginary lines parallel to the surface S1 of the translucent substrate 12 are usually preferably 45 ° or approximately 45 °. 6A and 6B, the prism portion 16 according to the present invention is arranged in the form of an isosceles triangle having a top portion of 90 ° or approximately 90 °. In the case of use in the embodiment, the top portions 5 and 5 '(5 "of the unit prism 14 are used. ) Is preferably in the range of 40 ° to 70 °. Further, the base angles β and γ similar to those described above are preferably in the range of 70 ° to 55 °, and the unit prism 14 is usually in a cross-sectional form made of an isosceles triangle in the range of the apex 40 ° to 70 °. It has become. The unit prisms 14 that are arranged are arranged in parallel in a direction perpendicular to the ridgeline, and the pitch is usually formed at, for example, about 12.5 μm to 200 μm, but the value is not particularly limited.

  Next, the constituent material of the prism portion and the method for forming it will be described.

  The prism part 16 is formed with the resin composition for optical sheets which mix | blended the conventionally well-known compound so that hardened | cured material may show said resin physical property. As such a resin composition for an optical sheet, various types can be exemplified, for example, a homopolymer of (meth) acrylate ester such as poly (meth) acrylate methyl, poly (meth) acrylate butyl, or ( Copolymers of (meth) acrylic acid esters such as methyl (meth) acrylate-butyl (meth) acrylate (herein, “(meth) acrylic acid” means acrylic acid or methacrylic acid) ), Polyesters such as polyethylene terephthalate and polybutylene terephthalate, thermoplastic resins such as polycarbonate, polystyrene and polymethylpentene, or transparent resins such as ionizing radiation curable resins crosslinked with ionizing radiation such as ultraviolet rays or electron beams. It is done. As ionizing radiation curable resins, polyfunctional urethane (meth) acrylates, (meth) acrylate oligomers such as (meth) acrylates such as polyester (meth) acrylate, oligomers such as unsaturated polyester oligomers and epoxy resin oligomers, or Monofunctional monomers such as methyl (meth) acrylate and ethyl (meth) acrylate, hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and (meth) acrylates such as dipentaerythritol hexa (meth) acrylate One or more compounds selected from functional monomers and the like are used. When using ultraviolet rays or visible rays as ionizing radiation, a photoinitiator is added. As the photoinitiator, known photoinitiators such as benzophenone series, benzoin series, thioxanthone series, and aromatic iodonium salts are used.

  Among these, an ionizing radiation curable resin composition composed of epoxy (meth) acrylate, urethane (meth) acrylate, monofunctional monomer, polyfunctional monomer, photoinitiator and the like is preferably used. The blending ratio of the constituent materials of the ionizing radiation curable resin composition is not particularly limited, but preferably, polyfunctional epoxy (meth) acrylate oligomer: 5 to 50 parts by weight, polyfunctional urethane (meth) acrylate oligomer: 5 to 50 Parts by weight, monofunctional monomer: 1-60 parts by weight, polyfunctional monomer: 5-30 parts by weight, photoinitiator: 0.01-10 parts by weight. The number of functional groups per molecule of the polyfunctional monomer or polyfunctional oligomer is about 2 to 8.

  In addition, as a resin composition, the compound (monomer component) containing (meth) acryloyl group and vinyl group other than the said monofunctional monomer and polyfunctional monomer as an arbitrary component can also be used. Moreover, what is generally used as an initiator for optical sheets can also be used as a photoinitiator (photopolymerization initiator). In addition to the above components, the resin composition may contain silicone, antioxidant, polymerization inhibitor, mold release agent, antistatic agent, ultraviolet absorber, light stabilizer, antifoaming agent, solvent, as necessary. Non-reactive acrylic resins, non-reactive urethane resins, non-reactive polyester resins, pigments, dyes, light diffusing agents, and the like can be used in combination.

  The refractive index of the prism portion 16 is preferably 1.555 or more, and the resin composition is adjusted so as to have such a refractive index. The upper limit of the refractive index of the prism portion 16 is not particularly limited, but is preferably 1.600 or less from the viewpoint of cost.

  The prism portion 16 uses the above-described resin composition for an optical sheet, for example, (1) a known hot press method (Japanese Patent Laid-Open No. 56-157310), (2) a roll on an ultraviolet curable thermoplastic resin film. A method of embossing the shape of the unit prism 14 with an emboss plate and then curing the film by irradiating with ultraviolet rays (Japanese Patent Laid-Open No. 61-156273), (3) A rotating roll engraved with the shape of the unit prism 14 After applying the active energy ray-curable resin liquid on the intaglio and filling the concave portions, the active energy rays such as ultraviolet rays or electron beams with the film-shaped translucent substrate 12 covered on the roll intaglio via the resin liquid And then releasing them from the roll intaglio to form the shape of the unit prism 14 of the roll intaglio on the film-like translucent substrate 12 (special feature). Rights 3-223883, U.S. Patent No. 4576850, etc.), and the like.

(Other layers)
The optical sheet 10 can be provided with a light diffusion function. For example, as shown in FIG. 1, the light diffusing function can be provided by providing a light diffusing layer 18 on at least one surface of the translucent substrate 12 or performing a so-called mat treatment. . Since many proposals have been made to provide such a light diffusing function, only the following explanation will be given here, and a detailed explanation will not be given.

  The light diffusing layer 18 illustrated in FIG. 1 is an arbitrary layer that is preferably provided, and may have any function of diffusing light, and is formed on a general light diffusing sheet. For example, a layer in which light diffusing fine particles are dispersed in a translucent resin can be applied. This light diffusion layer 18 may be provided on the other surface S2 of the translucent substrate 12, or between one surface S1 of the translucent substrate 12 and the prism portion 16 (not shown). It may be provided, or may be provided on both of them.

  As the translucent resin material constituting the light diffusion layer 18, a resin material similar to that of the translucent substrate 12, for example, a transparent material such as acrylic, polystyrene, polyester, or vinyl polymer is used. Further, light diffusing fine particles are uniformly dispersed in the light diffusion layer 18. As the light diffusing fine particles, light diffusing fine particles generally used for optical sheets are used. For example, polymethyl methacrylate (acrylic) beads, polybutyl methacrylate beads, polycarbonate beads, polyurethane beads , Calcium carbonate beads, silica beads and the like are used.

  The light diffusion layer 18 can be produced by various methods. For example, a paint in which light diffusing fine particles are dispersed in a translucent binder resin may be formed by spray coating, roll coating, or the like, or a resin material in which light diffusing fine particles are dispersed is prepared. Then, the resin material may be formed by co-extrusion together with the extrusion material of the translucent substrate 12. The thickness of the light diffusion layer 18 is usually in the range of 1 to 20 μm.

  Although not shown, the mat treatment has a light diffusion function by giving a predetermined surface roughness to the surface S2 instead of providing the light diffusion layer 18 on the other surface S2 of the translucent substrate 12, for example. It has been granted. Examples of such means include a method of mechanically roughening the surface by sand blasting or the like, or forming an uneven layer containing particles.

  The optical sheet 10 having the prism portion 16 according to the first and second aspects described above can be used in a single sheet configuration, but in order to control the light diffusion angle in two directions (vertical direction, horizontal direction) The two optical sheets 10 having the prism portion 16 may be laminated so that the ridge lines cross each other. The crossing angle is usually about 15 ° to 90 ° (orthogonal). In this case, it is most preferable that the prism surfaces are oriented in the same direction, so that the light transmittance is the highest, but the prism portion 16 side faces each other, or the prism portion side 16 faces back to back. You may comprise. In the present invention, since the optical sheet 10 as described above is used, even when the top portion 5 of one unit prism 14 is pressed against the other optical sheet by being overlapped in this way, the contact portion is generated. The white spot generated based on the contact portion can be made inconspicuous, or the generation of the white spot can be prevented.

[Surface light source device]
FIG. 4 is a perspective view showing an example of the surface light source device according to the first aspect of the present invention. The surface light source device 30 according to the first aspect of the present invention is a so-called edge light type surface light source device, and guides light introduced from at least one side end surface 32A from a light emitting surface 32B as one surface. A light source 32, a light source 34 for allowing light to enter from at least one side end surface 32A of the light guide 32, and a light emission surface 32B of the light guide 32 are provided via an adhesive layer 31, for example. It has the optical sheet 10 according to the present invention that transmits light emitted from the light emitting surface 32B. In FIG. 4, the single light source 34 is shown as the light source 34. However, the light source 34 may be a two-sided surface light source device (not shown) having both end faces.

  The light guide 32 is a plate-like body made of a translucent material, and is configured to emit light introduced from the left side end surface 32A in FIG. 4 from the upper light emission surface 32B. The light guide 32 is made of a light-transmitting material similar to the material of the optical sheet 10, but is usually made of acrylic or polycarbonate resin. The thickness of the light guide 32 is usually about 1 to 10 mm, and the thickness may be constant over the entire range, or as shown in FIG. 4, it is the thickest at the position of the side end surface 32A on the light source 34 side. The taper shape may be gradually thinned in the opposite direction. In order to emit light from a wide surface (light emission surface 32B), it is preferable that a light scattering function is added to the inside or the surface of the light guide 32.

  The light source 34 causes light to enter the inside from at least one side end face 32 </ b> A of the light guide 32, and is disposed along the side end face 32 </ b> A of the light guide 32. The light source 34 is not limited to a linear light source as shown in FIG. 4, and point light sources such as incandescent light bulbs and LEDs (light emitting diodes) may be arranged in a line along the side end face 32A. . A plurality of small flat fluorescent lamps may be arranged along the side end face 32A.

  On the light emission surface 32B of the light guide 32, the above-described optical sheet 10 according to the present invention is provided, for example, via a light diffusion sheet. The optical sheet 10 is provided so that the opposite surface of the prism portion 16 becomes the light emission surface 32 </ b> B of the light guide 32. The details of the optical sheet 10 have already been described and will not be described here.

  As shown in FIG. 4, the reflector 36 is provided on a surface opposite to the light emitting surface 32 </ b> B of the light guide 32 and is provided on a side end surface other than the left side end surface 32 </ b> A and emits from these surfaces. This is for reflecting light back into the light guide 32. As the reflector 36, a thin metal plate deposited with aluminum or the like, or white foamed PET (polyethylene terephthalate) is used.

  FIG. 5 is a perspective view showing an example of a surface light source device according to the second aspect of the present invention. The surface light source device 40 according to the second aspect of the present invention is a direct-type surface light source device that irradiates light from the optical sheet 10 according to the present invention and the opposite surface of the optical sheet 10 on the prism portion 16 side. The light source 34 has a concave reflector 44 that is disposed on the opposite side of the optical sheet as viewed from the light source 34 and reflects the light from the light source 34 toward the optical sheet 10. The details of the optical sheet 10 have already been described and will not be described here.

  The light from the light source 34 is transmitted through the optical sheet 10 toward the light emitting surface 42 on the optical sheet 10 side, and the light transmitted through the optical sheet 10 toward the light emitting surface 42 after being reflected by the reflector 44. is there.

  The reflector 44 is formed by depositing aluminum or the like on a thin metal plate, white foamed PET (polyethylene terephthalate), or the like, as in the surface light source device according to the first aspect. The shape of the reflector 44 is not particularly limited as long as the light from the light source 34 can be uniformly reflected as a parallel ray, and a shape such as a concave arc shape, a parabolic column shape, a hyperbolic column shape, an elliptic column shape, or the like is selected.

  FIG. 6 is a perspective sectional view showing another example of the surface light source device according to the first and second aspects of the present invention, and FIG. 6A is another example of the edge light type surface light source device according to the first aspect. (B) has shown another example of the direct type surface light source device which concerns on a 2nd aspect. The surface light source device 30 ′ shown in FIG. 6A differs from the surface light source device 30 shown in FIG. 4 in the direction of the prism portion 16 constituting the optical sheet 10, and the prism portion 16 is a light source 34. Alternatively, it may be provided on the side from which light is emitted toward the optical sheet 10, that is, on the light emission surface 32 </ b> B side of the light guide 32. Further, the surface light source device 40 ′ shown in FIG. 6B is different from the surface light source device 40 in FIG. 5 described above in the direction of the prism portion 16 constituting the optical sheet 10 and constitutes the optical sheet 10. The prism unit 16 may be provided on the side from which light is emitted from the light source 34 toward the optical sheet 10, that is, on the light emission surface 42 side on the optical sheet 10 side.

  In the surface light source device shown in FIGS. 4 to 6, a linear light source, a light source arranged in a line in one direction, or the like is used, but the extending direction of the light source and the optical sheet 10 according to the present invention are used. Usually, the unit prism is arranged so as to be parallel to the direction in which the ridgeline of the unit prism extends, as shown in FIGS. Examples of the non-parallel case include a case where the light source extending direction and the unit prism ridge line extending direction are orthogonal to each other, and a case where the light source is arranged so as to cross at an arbitrary angle.

  As described above, since the surface light source device of the present invention employs the optical sheet 10 described above, even if the top 5 of the unit prism 14 is pressed against the light guides 32 and 42 and becomes a contact portion, white Dots and the like can be made inconspicuous, and display unevenness can be reduced.

[Display device]
FIG. 7 is a schematic perspective view showing an example of a liquid crystal display device which is a representative example of the translucent display device of the present invention. A liquid crystal display device 50 shown in FIG. 7 includes a liquid crystal panel 52 which is a flat light-transmitting display, and the edge light of the present invention which is disposed on the back surface of the liquid crystal panel 52 and irradiates the liquid crystal panel 52 from the back surface. And a surface light source device 30 (see FIG. 4). Similarly, the liquid crystal display device 60 shown in FIG. 8 is also a liquid crystal panel 62 that is a planar light-transmitting display, and the book that is arranged on the back surface of the liquid crystal panel 62 and that irradiates the liquid crystal panel 62 with light from the back surface. And a direct-type surface light source device 40 (see FIG. 5) according to the invention. The liquid crystal display devices 50 and 60 are transmissive liquid crystal display devices including backlight surface light source devices 30 and 40, and each pixel forming a liquid crystal screen is illuminated from the back side by light emitted from the surface light source devices 30 and 40. Is configured to do. In addition, as the surface light source device, the surface light source devices 30 ′ and 40 ′ having the modes shown in FIGS. 6A and 6B may be applied.

  The liquid crystal display devices 50 and 60 have the surface light source devices 30 and 40 according to the present invention as constituent members, but the surface light source devices 30 and 40 are optical sheets that reduce the display unevenness by making the white spots and the like inconspicuous. 10 is provided. As a result, the liquid crystal display devices 50 and 60 can reduce display unevenness and form a good image.

  Next, the present invention will be described in more detail with reference to examples and comparative examples.

Example 1
A polyethylene terephthalate (hereinafter referred to as “PET”) resin having a refractive index of 1.56 is used as an extrusion resin for forming a translucent substrate, and the extruded material is put into an extrusion apparatus so that the thickness after extrusion is 180 μm. After that, the base sheet 71 was produced by subjecting the obtained sheet to stretching in the longitudinal direction and the width direction using a stretching apparatus.

  The base sheet 71 thus manufactured is put into a manufacturing apparatus 70 shown in FIG. 9 to form the prism portion 16 on the surface thereof. First, a winding roll 72 for the base sheet 71 obtained as described above was prepared. On the other hand, a shaping roll 73 in which a triangular unit prism shaping die 76 is formed on the surface of a metal cylinder is prepared, and an ultraviolet curable resin liquid is fed from a T-die nozzle 74 while rotating around the central axis. 80 was supplied to the shaping roll surface and filled in the shaping die 76 of the unit prism. Next, the base sheet 71 is unwound from the winding roll 72 at a speed synchronized with the rotational peripheral speed of the shaping roll 73, and the base sheet 71 is placed on the shaping roll 73 by the pressing roll 81. In this state, ultraviolet rays from the ultraviolet irradiation devices 82 and 82 are irradiated from the substrate sheet 71 side, and the resin liquid 80 is crosslinked and cured in the shaping mold 76 at the same time. The sheet 71 was adhered. Next, the base sheet 71 traveling using the peeling roll 83 was peeled off together with the prism portion 16 adhered thereto, thereby obtaining the optical sheet 10 having the form shown in FIG. 1 in which a plurality of unit prisms each having a triangular cross section were arranged.

  The unit prism of Example 1 has a triangular cross section. Specifically, the unit prism is an isosceles triangle having a pitch of 50 μm and a vertical angle α of the unit prism of 90 ° and base angles β and γ of 45 °. The ridgelines are formed so as to be adjacent to each other so that the ridgelines are parallel to each other. Further, as shown in FIG. 2 (A), a prism portion having a thickness (height h) of 28 μm, in which the top portions 5 of one unit prism 14 in four rows of the unit prisms 14 are 3 μm higher than the other top portions 5 ′. 16 was formed. The prism portion 16 having such a form can be obtained by preparing a shaping mold corresponding to the form of the unit prism. Each of the top portions 5 and 5 ′ is an acute angle portion having a flat width W of 0.1 μm (= 100 nm).

(Example 2)
Thickness (height h) in which the top 5 of one unit prism 14 in four rows of unit prisms 14 is 3 μm higher than the other top 5 ′, and the flat width W of the high top 5 is 0.2 μm. An optical sheet of Example 2 was produced in the same manner as Example 1 except that the 26 μm prism portion 16 was formed.

(Example 3)
Thickness (height h) where the top 5 of one unit prism 14 in two rows of unit prisms 14 is 3 μm higher than the other top 5 ′, and the flat width W of the high top 5 is 0.3 μm. An optical sheet of Example 3 was produced in the same manner as Example 1 except that the 28 μm prism portion 16 was formed.

(Examples 4 to 9)
Optical sheets of Examples 4 to 9 were produced in the same manner as in Example 1 except that the ratio of the high top, the height of the high top, and the flat width of the high top were as shown in Table 1.

(Comparative Examples 1-5)
Optical sheets of Comparative Examples 1 to 5 were produced in the same manner as in Example 1, except that the ratio of the high top, the height of the high top, and the flat width of the high top were as shown in Table 1.

(Evaluation)
About each optical sheet of Examples 1-9 and Comparative Examples 1-5, the presence or absence of the white spot was observed. For observation, a glass having a thickness of 1.0 mm was prepared, the top 5 side of the unit prism 14 of the obtained optical sheet was placed on the glass, and the transparent sheet having a diameter of 1 cm and a weight of 50 g from the PET substrate side of the optical sheet. A cylinder was placed as a load, and a light source was irradiated from the lower side of the glass. At this time, it was observed whether or not a white spot was generated in the load region by the transparent cylinder. The results are shown in Table 1, where “◯” indicates that the white spot is not conspicuous, “×” indicates that the white spot is conspicuous, and “Δ” indicates the middle level.

  From the results in Table 1, the top of one unit prism is formed higher in the range of 0.4 μm to 10 μm than the other tops in 2 to 8 rows of unit prisms, and the top of the unit prism is flat. In Examples 1 to 9 in which the flat width W is in the range of 100 nm to 400 nm, good results with inconspicuous white spots were obtained. On the other hand, in Comparative Examples 1 to 5 not corresponding to the above, white spots were conspicuous.

It is a typical perspective view which shows an example of the optical sheet of this invention. It is sectional drawing which shows embodiment of the unit prism which comprises the optical sheet of this invention. FIG. 3 is an enlarged cross-sectional view in the vicinity of the top of the prism portion shown in FIG. 2. It is a perspective view which shows an example of the surface light source device which concerns on the 1st aspect of this invention. It is a perspective view which shows another example of the surface light source device which concerns on the 2nd aspect of this invention. It is a perspective sectional view showing other examples of the surface light source device concerning the 1st and 2nd modes of the present invention, (A) shows other examples of the surface light source device shown in FIG. 4, and (B) is FIG. Another example of the surface light source device shown in FIG. It is a schematic perspective view which shows an example of the liquid crystal display device as a display apparatus of this invention. It is a schematic perspective view which shows another example of the liquid crystal display device as a display apparatus of this invention. It is a typical block diagram which shows an example of the manufacturing apparatus for forming a prism part on a sheet-like translucent base material.

Explanation of symbols

5, 5 ', 5 "... Top part 10 ... Optical sheet 12 ... Translucent base material 14 ... Unit prism 16 ... Prism part 18 ... Light diffusion layer 30, 30', 40, 40 '... Surface light source device 31 ... Adhesive layer 32 ... Light guide 32A ... Side end face 32B ... Light emission surface 34 ... Light source 36, 44 ... Reflector 50, 60 ... Liquid crystal display device 52, 62 ... Liquid crystal panel S1 ... One surface of translucent substrate S2 ... Transparent The other surface of the optical substrate H: Difference between the high top and the other top W: Flat width of the top of the unit prism

Claims (4)

A translucent substrate, provided on one surface of the light transmitting substrate, have a ridge on the top with triangular cross-section, the unit prisms said top are formed at the same apex angle as the該稜line orthogonal An optical sheet for a surface light source having a plurality of prism portions arranged in a direction to perform,
Among the unit prisms, the top part of one unit prism in 2 to 8 rows is formed higher in the range of 0.4 μm to 10 μm than the other top part, and the top part of the unit prism is flat. The optical sheet for a surface light source, wherein the flat width W is in the range of 100 nm to 400 nm. A light guide made of a translucent material that emits light introduced from at least one end face from a light emitting face that is one side, and light is incident on the inside from at least one end face of the light guide A surface light source device comprising: a light source; and an optical sheet provided on a light emission surface of the light guide and transmitting light emitted from the light emission surface,
The surface light source device, wherein the optical sheet is the surface light source optical sheet according to claim 1. An optical sheet for a surface light source according to claim 1,
A light source that emits light from the back side of the optical sheet;
A surface light source device comprising: a reflector disposed on a side opposite to the optical sheet of the light source and reflecting light from the light source toward the optical sheet.   A planar light-transmitting display body, and a surface light source device according to claim 2, which is disposed on a back surface of the light-transmitting display body and irradiates light from the back surface. A display device.

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