JP2006309248A - Lens sheet, surface light source element using the same and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prism sheet excellent in abrasion resistance without drastically degrading the brightness as a surface light source element. <P>SOLUTION: In the prism sheet formed by arranging a large number of prism arrays of approximate triangle shape in parallel on at least one side surface, flat parts having width of 5 μm or less are formed on top ends of the prism arrays. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device used as a display for notebook computers, portable liquid crystal televisions, etc., a surface light source element used therefor, and a prism sheet, and more particularly, a prism sheet with improved scratch resistance. The present invention also relates to a surface light source element and a liquid crystal display device using the same.

  In recent years, color liquid crystal display devices have been widely used in various fields such as portable notebook personal computers, desktop personal computer liquid crystal monitors, portable liquid crystal televisions, and video integrated liquid crystal televisions. This liquid crystal element itself does not emit light, but acts as a shutter for transmitted light. In order to improve the visibility of a liquid crystal display device, light is emitted from the back of a liquid crystal element (liquid crystal panel) called a backlight. Generally, a surface light source element that hits is used.

  Such a backlight is composed of a fluorescent tube, a light guide, a reflection sheet, a prism sheet, and the like as described in, for example, Japanese Patent Laid-Open No. 2-84618 and Japanese Utility Model Laid-Open No. 3-69184. Among these, the prism sheet is arranged on the light exit surface of the light guide to improve the optical efficiency of the backlight and improve the brightness. For example, the prism pitch is formed on one surface of the translucent sheet. This is a lens sheet in which prism rows each having an isosceles triangle shape with a cross section of 50 μm and a prism apex angle of 60 ° to 100 ° are formed in parallel.

  The prism sheet is formed by continuously forming such a very fine prism row, and since the tip of the prism row is sharp, it is scratched during handling and the tip of the prism row due to vibration during use. There was a problem of generation of optical defects due to scratches or the like. The scratches on the prism row are resistant even when the prism sheet is placed so that the prism row forming surface is opposite to the light exit surface of the light guide, as described in Japanese Utility Model Laid-Open No. 3-69184. Although scratching is required, the case where the prism sheet is placed so that the prism row forming surface is on the light emitting surface side of the light guide, as described in JP-A-2-84618, There is a strong demand for scratch resistance against contact between the light guide and the prism row.

  As a method for improving the scratch resistance of such a prism sheet, a method for improving the scratch resistance of the resin forming the prism row has been proposed as described in JP-A-9-143153. From the relationship with the optical properties of the prism sheet, the scratch resistance cannot be sufficiently improved. Japanese Patent Application Laid-Open No. 11-305011 proposes a method for improving the scratch resistance by making the apex of the prism row into an arc shape having a radius of 10 to 25 μm. However, the luminance of the surface light source element is reduced. However, the original effect of using the prism sheet is greatly impaired.

  Accordingly, an object of the present invention is to improve the scratch resistance of a prism sheet without causing a significant decrease in luminance as a surface light source element.

  In view of the problems of the prior art described above, the inventors have transformed the shape of the prism top of the prism row of the prism sheet into a minute specific shape without causing a significant decrease in luminance as a surface light source element. The inventors have found that the scratch resistance of the prism sheet is improved and have reached the present invention.

  That is, the prism sheet of the present invention is a prism sheet in which a large number of substantially triangular prism rows are formed in parallel on at least one surface, and a flat portion having a width of 5 μm or less is formed at the tip of the prism row. It is characterized by being. The surface light source element of the present invention includes a light source, a light guide having at least one light incident surface facing the light source, and a light output surface substantially orthogonal thereto, and a light output surface side of the light guide. It consists of the above-described prism sheets placed thereon. Furthermore, the liquid crystal display device of the present invention is characterized in that the liquid crystal display element is arranged on the prism sheet of such a surface light source element.

  In the present invention, the top of the prism row of the prism sheet is formed into an arc shape having a radius of curvature of 5 μm or less or a flat part having a width of 5 μm or less, whereby a prism sheet having excellent scratch resistance can be provided. There can be provided a surface light source element and a liquid crystal display device capable of obtaining a high-quality image without causing defects due to scratches during assembly or use in the element and without causing a significant decrease in luminance as a surface light source element. Is.

  As shown in FIG. 1 or FIG. 2, the prism sheet of the present invention is a prism sheet in which a large number of prism rows 2 having a substantially triangular cross section are formed in parallel on at least one surface. 3 (hereinafter, referred to as a prism top) has a minute specific shape. In FIG. 1, the prism top 3 of the prism sheet has an arc shape with a radius of curvature of 5 μm or less. In FIG. 2, a flat portion with a width of 5 μm or less is formed on the prism top 3 of the prism sheet. Thus, by making the top part 3 of the prism row 2 of the prism sheet have a minute specific shape, it is possible to minimize the decrease in luminance as a surface light source element and improve the scratch resistance of the prism sheet. be able to.

  In the lens sheet of the present invention, when the arc shape of the prism top 3 becomes an arc shape exceeding the radius of curvature of 5 μm as shown in FIG. 1, there is a tendency that the luminance decreases as a surface light source element. Is 4 μm or less, more preferably 3 μm or less, more preferably 2 μm or less. The arc-shaped curvature radius is preferably 1 μm or more, more preferably 1.5 μm or more, from the viewpoint of scratch resistance of the prism sheet. On the other hand, if the width of the flat portion formed on the prism top 3 exceeds 5 μm as shown in FIG. 2, the decrease in luminance as a surface light source element tends to increase, preferably 4 μm or less, more preferably The range is 3 μm or less, more preferably 2 μm or less. The width of the flat portion is preferably 1 μm or more, more preferably 1.5 μm or more, from the viewpoint of scratch resistance of the prism sheet. Thus, by making the arc shape a radius of curvature of 5 μm or less or the width of the flat portion of 5 μm or less, the luminance of the surface light source element is reduced to about 10% or less, and the prism does not cause a significant luminance reduction. The scratch resistance of the sheet can be significantly improved.

  Such a shape of the prism top 3 can be given by a method such as cutting and polishing the prism row 2 of the prism sheet, but it is efficient to give it beforehand to a lens mold used for molding the prism sheet. Is. That is, cutting is performed using a cutting tool suitable for a target prism shape (a circular arc shape at the tip or a flat shape) when a prism pattern is formed on a lens mold.

  In the prism sheet of the present invention, the pitch of the prism rows 2 is preferably 20 to 100 μm, and more preferably 20 to 80 μm. This is because when the pitch of the prism rows 2 is less than 20 μm, the luminance as the surface light source element tends to decrease, and when it exceeds 100 μm, the generation of moire between the pixels of the liquid crystal elements and the prism rows 2 is remarkable. It is because it tends to become. The apex angle of the prism row 2 of the present invention is preferably in the range of 50 to 150 °. Generally, when a prism sheet is mounted and used as a surface light source element so that the prism array forming surface is in the direction opposite to the light emitting surface of the light guide, the apex angle is in the range of 80 to 100 °. Preferably, it is in the range of 90 to 100 °. On the other hand, when the prism sheet is mounted and used as a surface light source element such that the prism row forming surface is on the light emitting surface side of the light guide, it is preferably in the range of about 50 to 75 °. Preferably it is the range of 55-70 degrees. In the present invention, the apex angle of the prism array 2 refers to the angle of the intersection obtained by extending the two prism surfaces constituting one prism array. Furthermore, in the present invention, the refractive index of the prism array 2 is such that when the prism sheet is mounted and used as a surface light source element, the prism array formation surface is opposite to the light exit surface of the light guide. In order to improve the luminance of the surface light source element, a relatively high refractive index is preferable, the refractive index is preferably 1.55 or more, and more preferably 1.7 or more.

  The prism sheet of this invention can be comprised from a synthetic resin with a high light transmittance. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, and vinyl chloride resins. In particular, methacrylic resins are optimal because of their high light transmittance, heat resistance, mechanical properties, and molding processability. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and preferably has a methyl methacrylate content of 80% by weight or more. When forming the prism row 2 on the prism sheet, the transparent synthetic resin plate may be formed by hot pressing using a mold member having a desired surface structure, or the prism sheet may be formed by extrusion molding or injection molding. When manufacturing, you may give shape simultaneously. Further, the shape may be transferred by a lens mold using heat or photo-curing resin. Among them, since it is excellent in productivity, transferability of the prism pattern, and the like, the prism array 2 is formed by using an active energy ray-curable composition on at least one surface of the translucent substrate 1 as shown in FIGS. Is preferably formed.

  The translucent substrate 1 constituting the prism sheet of the present invention is not particularly limited as long as it is a sheet or film-like material that transmits active energy rays such as ultraviolet rays and electron beams, and a flexible glass plate or the like is used. However, transparent resin sheets and films such as polyester resins, acrylic resins, polycarbonate resins, vinyl chloride resins, and polymethacrylimide resins are preferable. In particular, it is made of polymethyl methacrylate having a refractive index lower than that of the prism array 2 and having a low surface reflectance, a mixture of polymethyl acrylate and polyvinylidene fluoride resin, a polycarbonate resin, a polyester resin such as polyethylene terephthalate. Those are preferred. The thickness of the translucent substrate 1 varies depending on its use, and the one in the range of 50 to 500 μm is used. However, in order to facilitate handling, the thickness is preferably 70 μm or more. The thing of 200 micrometers or less is preferable. In addition, in order to improve the adhesiveness of the prism row | line | column 2 comprised from an active energy ray curable composition, and the translucent base material 1, the surface of the translucent base material 1 is anchor coat treatment etc. What performed the adhesive improvement process is preferable.

  The active energy ray-curable composition for forming the prism row 2 of the prism sheet is not particularly limited as long as it can be cured with active energy rays such as ultraviolet rays and electron beams. ) Acrylate, epoxy (meth) acrylate, urethane (meth) acrylate, and the like. Of these, (meth) acrylate-based ones are particularly preferred from the viewpoint of optical properties and the like. In particular, in terms of handleability and curability, polyvalent acrylate and / or polyvalent methacrylate (hereinafter referred to as polyvalent (meth) acrylate), monoacrylate and / or monomethacrylate (hereinafter referred to as mono (meth) acrylate) And the main component is a photopolymerization initiator by active energy rays. Typical polyvalent (meth) acrylates include polyol poly (meth) acrylate, polyester poly (meth) acrylate, epoxy poly (meth) acrylate, urethane poly (meth) acrylate, and the like. These are used alone or as a mixture of two or more. Examples of mono (meth) acrylates include mono (meth) acrylates of monoalcohols and mono (meth) acrylates of polyols.

  In the prism sheet of the present invention, when a prism sheet is produced using an active energy ray-curable composition, for example, an active energy ray-curable composition liquid is injected into a lens mold in which a predetermined prism pattern is formed, The translucent substrate 1 is overlaid. Next, a method of obtaining a lens sheet by irradiating active energy rays such as ultraviolet rays and electron beams through the translucent substrate 1, polymerizing and curing the active energy ray-curable composition liquid, and peeling from the lens mold. .

  Next, the surface light source element of the present invention will be described with reference to FIG. As shown in FIG. 3, the surface light source element of the present invention has a light source 6 such as a fluorescent lamp disposed at one end of a light guide 5 made of a transparent resin or the like, A reflection layer 7 such as a reflection film is disposed on the opposite surface, and the prism sheet 4 is placed on the light emitting surface of the light guide 5. Moreover, you may mount a diffusion sheet on the light-projection surface of the light guide 5, or on the prism sheet 4 as needed. The light guide 5 may have a plate shape, a wedge shape, a hull shape as long as at least one side surface facing the light source 6 is a light incident surface and a surface substantially perpendicular to the light incident surface is a light emission surface. Can be used in various shapes such as a synthetic resin having a high light transmittance. In order to effectively introduce light from the light source 6 to the light guide 5, it is preferable that the light incident surfaces of the light source 6 and the light guide 5 are covered with a case or film coated with a reflective agent on the inside. Further, the prism sheet 4 can be mounted on the light emitting surface of the light guide 5 by superimposing two or three or more lens sheets. Although the light source 6 should just be arrange | positioned at the at least 1 edge part of the light guide 5, a some light source can also be arrange | positioned as needed.

  As the synthetic resin constituting the light guide 5, various highly transparent synthetic resins such as methacrylic resin, acrylic resin, polycarbonate resin, and vinyl chloride resin are used. It can be manufactured by the molding method. In particular, a methacrylic resin is excellent as a light transmittance, heat resistance, mechanical properties, and molding processability, and is optimal as a light guide material. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and the methyl methacrylate is preferably 80% by weight or more.

  In the surface light source element of the present invention, the prism sheet 4 placed on the light emitting surface of the light guide 5 is appropriately selected according to the emitted light characteristics of the light guide 3 to be used. be able to. For example, when the light guide 5 having a lens surface or a satin surface formed on the light exit surface or the back surface is used, the emitted light emitted from the light guide 5 has a strong directivity greatly inclined from the normal direction. Therefore, it is preferable to arrange the prism sheet 4 so that the prism row forming surface is on the light emitting surface side of the light guide 5 as shown in FIG. The prism sheet 4 of the present invention is particularly suitable as the prism sheet 4 used for such a surface light source element.

  The liquid crystal display device of the present invention uses the surface light source element having the above-described configuration as a backlight, and places the liquid crystal display element on the lens sheet 4 of such a surface light source element. The liquid crystal display element is not particularly limited, and any of an active matrix driving TFT liquid crystal display element and a simple matrix driving STN liquid crystal display element can be used. Further, in the TFT type liquid crystal display element, various active elements such as the element and polysilicon, amorphous silicon, metal insulator metal and the like can be used.

  Hereinafter, the present invention will be described specifically by way of examples.

Reference example 1
A diamond tool (manufactured by Tokyo Diamond Tool Mfg. Co., Ltd.) having an arc shape with a radius of curvature of 2 μm at the tip having an apex angle of 65 ° was prepared. Next, on the surface of three kinds of JIS brass of 3 mm thickness and 300 mm × 400 mm, the prism rows are cut at a pitch of 50 μm using the above diamond tool, and then a prism pattern is formed. A mold was prepared. One end of a lens mold in which an appropriate amount of an acrylic UV curable monomer mixture is injected into this lens mold prism pattern, and a polyethylene terephthalate film (PET film, A4300 manufactured by Toyobo Co., Ltd.) having a thickness of 125 μm is injected into the UV curable monomer mixture. From this, the ultraviolet curable monomer mixture liquid was gradually overlapped in the direction of the other end while being pressurized with a roll, and the injected ultraviolet curable monomer mixture was spread over the entire lens mold. Thereafter, the ultraviolet curable monomer mixture was polymerized and cured by irradiating with ultraviolet rays for 45 seconds using three 6.4 kW ultraviolet lamps (manufactured by Western Quartz) with an irradiation intensity of 80 W / cm disposed above the PET film. The prism sheet was peeled from the lens mold to obtain a prism sheet in which a large number of prism rows having an arc shape with a radius of curvature of 2 μm, an apex angle of 65 °, and a refractive index of 1.59 were formed in parallel on one surface of the PET film. . The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was not easily scratched and was excellent in scratch resistance.

On the other hand, blasting is performed at a spraying pressure of 4 kg / cm ² from a distance of 10 cm using glass beads having a particle size of 125 to 149 μm (FGB-120 manufactured by Fuji Seisakusho Co., Ltd.), and the other surface is roughened. An acrylic resin (Acrypet VH5 # 000 manufactured by Mitsubishi Rayon Co., Ltd.) was injection-molded using a mold having a mirror surface to obtain a light guide having a thickness of 3 mm, 243 mm × 194 mm.

  Adhering and pasting silver-deposited PET film on the two short end faces and the other end face of the obtained light guide, tape the silver-deposited PET film on the back surface facing the roughened light exit surface The reflection surface was formed by stopping. A PET film on which a 2 mm diameter straight cold cathode tube (NMBSM2BWE253W manufactured by Harrison Co., Ltd.) is silver-wrapped is wound around the remaining end face of the light guide, and the prism is placed on the light exit surface of the light guide. The surface light source element having the structure shown in FIG. 3 is placed by placing the sheet so that the prism row is substantially parallel to the light incident surface of the light guide and the prism row forming surface faces the light exit surface side of the light guide. Assembled. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

  A direct current power source was connected to the cold cathode tube of the obtained surface light source element via an inverter (CXA-M10L manufactured by TDK), and DC12V was applied to light it, and the luminance in the normal direction was measured with a luminance meter. The measurement results are shown in Table 1 as relative values when the luminance of Comparative Example 1 is 100. Compared with Comparative Example 1, the decrease in luminance was about 3%. Further, using the obtained surface light source element, a sweep durability test with a vibration frequency of 10 to 500 Hz was performed as a sinusoidal vibration test with an acceleration amplitude of 0.5 G and a sweep cycle number of 10 cycles. After completion of the test, the cold cathode tube was turned on and the presence or absence of defects in the surface light source element was confirmed visually, but no defects were confirmed. The results of the vibration test are shown in Table 1 as “◯” when no defect was confirmed and “X” when a defect was confirmed.

Reference example 2
A prism sheet was obtained in the same manner as in Reference Example 1 except that the arc shape of the tip of the diamond tool was changed to a radius of 4 μm. The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was not easily scratched and was excellent in scratch resistance. Further, using this prism sheet, a surface light source element was assembled in the same manner as in Reference Example 1. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

  The results of measuring the normal luminance using the obtained surface light source element in the same manner as in Reference Example 1 are shown in Table 1 as relative values when the luminance of Comparative Example 1 is 100. Compared with Comparative Example 1, the decrease in luminance was 9%. Further, a vibration test was performed in the same manner as in Reference Example 1, and the results are shown in Table 1.

Example 1
A prism sheet was obtained in the same manner as in Reference Example 1 except that a flat shape having a width of 2 μm was given to the tip of the diamond tool. The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was not easily scratched and was excellent in scratch resistance. Further, using this prism sheet, a surface light source element was assembled in the same manner as in Reference Example 1. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

  The results of measuring the normal luminance using the obtained surface light source element in the same manner as in Reference Example 1 are shown in Table 1 as relative values when the luminance of Comparative Example 1 is 100. Compared with Comparative Example 1, the decrease in luminance was 5%. Further, a vibration test was performed in the same manner as in Reference Example 1, and the results are shown in Table 1.

Example 2
A prism sheet was obtained in the same manner as in Reference Example 1 except that a flat shape having a width of 4 μm was given to the tip of the diamond tool. The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was not easily scratched and was excellent in scratch resistance. Further, using this prism sheet, a surface light source element was assembled in the same manner as in Reference Example 1. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

  The results of measuring the normal luminance using the obtained surface light source element in the same manner as in Reference Example 1 are shown in Table 1 as relative values when the luminance of Comparative Example 1 is 100. Compared with Comparative Example 1, the decrease in luminance was 10%. Further, a vibration test was performed in the same manner as in Reference Example 1, and the results are shown in Table 1.

Comparative Example 1
A prism sheet was obtained in the same manner as in Reference Example 1 except that a diamond-bide with a sharp tip was used. The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was easily scratched and inferior in scratch resistance. Further, using this prism sheet, a surface light source element was assembled in the same manner as in Reference Example 1. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

  Using the obtained surface light source element, the normal luminance was measured in the same manner as in Reference Example 1, and this luminance was set to the standard value 100. Further, a vibration test was performed in the same manner as in Reference Example 1, and the results are shown in Table 1. After completion of the vibration test, the fluorescent tube was turned on to check for the presence or absence of defects in the surface light source element. As a result, an area that appeared white was generated in a part of the bar light source element. When the defective part was observed with the electron microscope, the top part of the prism row of the prism sheet was partially lost.

Comparative Example 2
A prism sheet was obtained in the same manner as in Reference Example 1 except that the arc shape of the tip of the diamond tool was changed to a radius of 8 μm. The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was not easily scratched and was excellent in scratch resistance. Further, using this prism sheet, a surface light source element was assembled in the same manner as in Reference Example 1. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

  The results of measuring the normal luminance using the obtained surface light source element in the same manner as in Reference Example 1 are shown in Table 1 as relative values when the luminance of Comparative Example 1 is 100. Compared with Comparative Example 1, the decrease in luminance was 25%. Further, a vibration test was performed in the same manner as in Reference Example 1, and the results are shown in Table 1.

Comparative Example 3
A prism sheet was obtained in the same manner as in Reference Example 1 except that a flat shape having a width of 8 μm was added to the tip of the diamond tool. The prism array forming surface of the obtained prism sheet was scratched with a nail to confirm the degree of scratching, but it was not easily scratched and was excellent in scratch resistance. Further, using this prism sheet, a surface light source element was assembled in the same manner as in Reference Example 1. Although the presence or absence of defects or the like in the state where the obtained surface light source element and liquid crystal display element were placed was confirmed visually, no defects were particularly visually recognized.

The results of measuring the normal luminance using the obtained surface light source element in the same manner as in Reference Example 1 are shown in Table 1 as relative values when the luminance of Comparative Example 1 is 100. Compared with Comparative Example 1, the decrease in luminance was 21%. Further, a vibration test was performed in the same manner as in Reference Example 1, and the results are shown in Table 1.

It is a typical fragmentary sectional view showing one embodiment of a prism sheet of the present invention. It is a typical fragmentary sectional view showing one embodiment of a prism sheet of the present invention. It is the schematic which shows the surface light source element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Translucent base material 2 Prism row | line | column 3 Prism top part 4 Prism sheet 5 Light guide 6 Light source 7 Reflective layer

Claims (5)

A prism sheet in which a large number of prism rows having a substantially triangular cross section are formed in parallel on at least one surface, wherein a flat portion having a width of 5 μm or less is formed at the tip of the prism row. The prism sheet according to claim 1, wherein a prism row is formed of an active energy ray-curable composition on at least one surface of the translucent substrate. The light source having a light source, at least one light incident surface facing the light source, and a light emitting surface substantially orthogonal thereto, and mounted on the light emitting surface side of the light guide. A surface light source element comprising the prism sheet described above. The surface light source element according to claim 3, wherein the prism sheet is placed so that a prism row forming surface thereof is on a light emitting surface side of the light guide. 5. A liquid crystal display device comprising a liquid crystal display element disposed on a prism sheet of the surface light source element according to claim 3.

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