JP2000066013A - Light reflection optical sheet and surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to enhance the utilization efficiency of light and reflected light luminance, to make the reflecting light even and to remove the unevenness of the luminance by arraying a plurality of unit prisms or unit lenses on the front surface of a reflective base material. SOLUTION: Prism surfaces are formed on the light reflection optical sheet 10 by arraying a plurality of the unit prisms 14 having a triangular prism shape on one surface of the reflective base material 12 in an adjacent one-dimensional direction in such a manner that the ridge lines thereof are paralleled. The reflective base material 12 is integrally formed of the same material as the material of the unit prisms 14 (a) or is composed as another member (b). A sheet having microcells in a resin is used as the reflective base material 12 and more particularly, a foamed polyester resin sheet is adequately used. The unit prisms may be formed at a pitch in a range of, for example, 5 to 200 μm and a height of 5 to 150 μm. The material which is the material different from the reflective base material 12 and forms the unit prisms 14 is composed of an oligomer or prepolymer and an ionization radiation curing type resin contg. a relatively large amt. of a reactive diluent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-reflecting optical sheet suitable for use in a surface light source device used for illuminating a translucent display such as a transmissive liquid crystal display device or an advertising board from the back, and a light-reflecting optical sheet suitable for the same. The present invention relates to a surface light source device using a reflection optical sheet.

[0002]

2. Description of the Related Art In recent years, in a liquid crystal display device, according to the necessity of low power consumption, thinning and lightening, a surface light source device for illuminating the liquid crystal display device from the back has naturally been required to be thin and light. In addition, the light from the light source is effectively used to reduce the power consumption, and the power consumption of the light source is reduced.

As a surface light source device used for a transmission type liquid crystal display device or the like, an edge light type and a direct type are known.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-207, light from a light-emitting surface, which is one surface of the light guide, is usually incident on one side end surface of a plate-like light guide made of a transparent acrylic resin or the like. By guiding, the light is incident on the back surface of the liquid crystal panel or the like, and a light reflection sheet is provided on the surface on the opposite side to the light exit surface of the light guide,
The light use efficiency is improved.

A direct type surface light source device is disclosed in Japanese Utility Model Laid-Open No. 2-3300.
As disclosed in Japanese Patent Laid-Open No. 1 (1993) -1995, the light source light is normally reflected by a light reflection sheet in the direction of a liquid crystal panel or the like, and the light is incident on the back surface of the liquid crystal panel or the like. A light diffusion sheet is arranged on the side or the exit surface side so that the shape of the light source cannot be identified by human eyes.

[0005]

The light reflecting sheet generally has a smooth surface and is made of a foamed polyester resin sheet, particularly a finely foamed polyester resin sheet as disclosed in JP-A-9-801117. In addition, a sheet having a function of shielding light, such as a resin sheet mixed with a white pigment, a metal sheet such as aluminum, or a metal-deposited resin sheet on which a metal such as silver, aluminum, chromium, gold, or copper is deposited is used. .

A foamed polyester resin sheet or a resin sheet mixed with a white pigment has a problem in that light utilization efficiency is low because of its low reflectance.

A metal sheet or a metal-deposited sheet has a high reflectivity but is a regular reflection, and the light does not emit in the front direction of the display, so that the light cannot be effectively used. Easy to be maintained,
There is also a problem that in-plane luminance unevenness occurs. If the light is made uniform by using a strong diffusion film in order to eliminate the uneven brightness, there is a problem that the brightness is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a light reflecting optical sheet which has high light utilization efficiency, high reflected light luminance, and uniform reflected light without luminance unevenness. It is an object of the present invention to provide a surface light source device that uses a light reflecting optical sheet and has high luminance of emitted light and has no luminance unevenness.

[0009]

According to the present invention, there is provided a light-reflecting optical sheet comprising a reflective substrate containing fine bubbles, wherein a unit prism or a unit lens is provided on the surface of the reflective substrate. The above object is achieved by a light reflecting optical sheet characterized in that a plurality of are arranged.

The reflective substrate and the unit prism or the unit lens may be integrally formed.

The unit prism or the unit lens may be formed on the reflective substrate.

According to a fourth aspect of the present invention, on the reflective substrate,
An adhesive layer, the unit prism or the unit lens may be formed.

According to a fifth aspect of the present invention, the average bubble diameter of the fine bubbles of the reflective substrate may be 50 μm or less.

According to the invention relating to a surface light source device, a sheet-like body made of a transparent material is provided, wherein the light introduced from at least one side end surface is a light emitting surface as one surface. A light guide adapted to be emitted from the light guide, a light source for causing light to enter the interior from at least the one side surface of the light guide, and so as to cover at least a surface of the light guide opposite to the light emitting surface. The light reflecting optical sheet according to any one of claims 1 to 5, wherein the unit reflects the light emitted from the light guide and reflects the light toward the light guide, and a unit prism or a unit lens on the surface of the transparent substrate. The above object is achieved by a surface light source device having a plurality of prism sheets.

As in claim 7, the light reflecting optical sheet has a surface of the light guide opposite to the light emitting surface, all the side surfaces of the light guide other than the side facing the light source, and the light source. May be a surface light source device arranged so as to cover the light source.

Further, according to the present invention, there is provided a light diffusion sheet, a light source for irradiating the light diffusion sheet with light,
6. The light-reflecting optical sheet according to claim 1, wherein the light-reflecting sheet is disposed on a side opposite to the light-diffusing sheet, and reflects light from the light source toward the light-diffusing sheet. And a prism sheet in which a plurality of unit prisms or unit lenses are arranged on the surface of a transparent base material arranged so that light is incident thereon.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIGS. 1A and 1B,
The light reflecting optical sheet 10 according to the present invention includes
The prism surface is formed by arranging a large number of unit prisms 14 having a triangular prism shape on one surface (the upper surface in FIG. 1) in adjacent one-dimensional directions so that the ridge lines thereof are parallel.

The light reflecting optical sheet 1 shown in FIG.
Numeral 0 indicates that the reflective base material 12 and the unit prism 14 are integrally formed of the same material, and the light reflecting optical sheet 10 shown in FIG. Is formed as a separate member, for example, by forming and curing an ionizing radiation-curable resin on a reflective substrate made of a foamed polyester resin sheet and arranging a number of unit prisms.

As the reflective substrate 12 constituting the light reflecting optical sheet 10 as shown in FIG.
As disclosed in the gazette, polyester, polycarbonate, polystyrene, polypropylene, polyethylene,
A sheet having fine bubbles in a resin such as polymethyl methacrylate, polyurethane, polyamide, polyimide, polyvinyl chloride, polymethyl pentene, polyvinyl acetal, and cellulose triacetate is used, and a foamed polyester resin sheet is particularly preferably used. .

The fine bubbles preferably have an average bubble diameter of 50 μm or less, more preferably 30 μm or less, and most preferably 20 μm or less.
This is because, when the light reflecting optical sheet 10 is used, when the average bubble diameter of the fine bubbles exceeds 50 μm, the light reflectance decreases, and the original brightness improving effect of the light reflecting optical sheet as described above significantly decreases. This is because When the average bubble diameter is smaller than the wavelength of visible light, incident light is transmitted, so that the light reflection effect is significantly reduced. When the average diameter of the fine bubbles is 50 μm or less, the reflective substrate also has characteristics such as high strength against heat and impact and high processability of the sheet.

As a method for manufacturing the light-reflecting optical sheet 10 shown in FIG. 1A, a sheet having fine bubbles similar to the material forming the reflective base material 12 is used, and the surface shown in FIG. The unit prism 14 constituting the light reflecting optical sheet 10 as shown in FIG. 1) may be formed by, for example, hot pressing a thermoplastic resin as disclosed in Japanese Patent Application Laid-Open No. 56-157310,
It can be formed and manufactured by injection molding, casting of a curable resin by ultraviolet light or heat, or the like.

The unit prism has a pitch of 5 μm to 20 μm.
It can be formed in a range of 0 μm and a height in a range of 5 μm to 150 μm. The pitch and height of the prism need to be sufficiently larger than the wavelength of light, and fine enough to allow visual recognition and display is not impaired. Further, as the sheet having fine bubbles, a sheet having a thickness equal to or larger than the height of the unit prism can be used.

Further, as a material for forming the unit prism 14 constituting the light reflecting optical sheet 10 as shown in FIG. 1B, a (meth) acrylate of a polyfunctional compound such as a polyhydric alcohol (hereinafter referred to as “methacrylate”) is used. Acrylate and methacrylate are referred to as (meth) acrylate), and an ionizing radiation-curable resin containing a relatively large amount of a reactive diluent.
Examples of the diluent include monofunctional monomers such as ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, vinyltoluene, and N-vinylpyrrolidone, and polyfunctional monomers such as trimethylolpropane tri (meth) acrylate and hexanediol. (Meth) acrylate, tripropylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6 hexanediol di (meth) acrylate, neo Examples include pentyl glycol di (meth) acrylate.

Further, when the above-mentioned ionizing radiation-curable resin is used as an ultraviolet-curable resin, among these, acetophenones, benzophenones, Michler benzoyl benzoate, α-amyloxime ester, Thioxanthones and n- as photosensitizers
Butylamine, triethylamine, tri-n-butylphosphine and the like are mixed and used.

The above ionizing radiation-curable resin may contain the following reactive organosilicon compound. RmS
i (OR ') n, where R and R'
Represents an alkyl group having 1 to 10 carbon atoms, m + n = 4, and m and n are each an integer. More specifically, tetramethoxysilane, tetraethoxysilane,
Tetra-iso-propoxysilane, tetra-n-propoxysilane, tetra-n-butoxysilane, tetra-
sec-butoxysilane, tetra-tert-butoxysilane, tetrapentaethoxysilane, tetrapenta-
iso-propoxysilane, tetrapenta-n-propoxysilane, tetrapenta-n-butoxysilane, tetrapenta-sec-butoxysilane, tetrapenta-t
ert-butoxysilane, methyltrimethoxysilane,
Examples include dimethylmethoxysilane, dimethylethoxysilane, methyltripropoxysilane, methyltributoxysilane, dimethyldimethoxysilane, dimethylpropoxysilane, dimethylbutoxysilane, methyldimethoxysilane, methyldiethoxysilane, and hexyltrimethoxysilane.

As shown in FIG. 2, a method of manufacturing the light reflecting optical sheet 10 shown in FIG. 1B is as follows. As shown in FIG.
Is filled with an ionizing radiation-curable resin liquid, a reflective substrate 12 is superimposed on the resin solution, and ionizing radiation such as an ultraviolet ray or an electron beam is directly irradiated from the reflective substrate sheet side to cure the ionizing radiation. The mold resin liquid is cured, and thereafter, the reflective base material is peeled off from the roll intaglio together with the cured resin, so that the cured ionizing radiation-curable resin liquid forms a unit prism layer 16 having a lens array having a desired shape. It can be manufactured by forming on a reflective substrate. If desired, a primer layer for strengthening the adhesion may be provided on the reflective substrate.

The unit prism pitch is 5 μm to 20 μm.
It can be formed in a range of 0 μm and a height in a range of 5 μm to 150 μm. The pitch and height of the prism need to be sufficiently larger than the wavelength of light, and fine enough to allow visual recognition and display is not impaired. Further, as the sheet having fine bubbles, a sheet having a thickness of 5 μm or more can be used.

The unit prism 14 can be formed using not only the above-described reaction-curable resin but also a thermoplastic resin. For example, acrylic resins such as methyl methacrylate and ethyl methacrylate, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polycarbonates, polyhydrocarbons such as polystyrene, polypropylene, and polymethylpentene; 6,6 nylon; It can be selected from thermoplastic resins such as polyamides such as nylon, saponified ethylene / vinyl acetate copolymer, polyimide, polysulfone, polyvinyl chloride, and acetylcellulose.

The method for producing the light-reflecting optical sheet 10 using a thermoplastic resin is as follows: a resin composition in which additives such as a heat stabilizer and a light stabilizer are appropriately added to a thermoplastic resin is used as a reflection base material. It is manufactured by extrusion coating on a heated and molten state and shaping it into a lens shape with a cooling roll, or by extrusion coating and cooling the resin composition, and then reheating and melting to shape it. be able to. If desired, a primer layer for strengthening the adhesion may be provided on the reflective substrate.

As shown in FIG. 2, the reflective optical sheet 10 has a prism surface in which a plurality of triangular prism unit prisms are arranged in parallel (FIG. 2A).
However, the present invention is not limited to this, and FIG. 2 (B) shows a pyramidal shape, (C) a semi-cylindrical shape, (D) an inverted semi-cylindrical shape, and (E) a semi-spherical shape. can do. Although not shown, a unit prism having a semi-cylindrical shape, a unit prism having a sine-curved upper part (peak) and a lower part (valley) in cross section, and a sine-curved upper part (peak) and lower part (valley) in cross section A unit prism having a V-shaped section, a unit prism having a trapezoidal cross section, and a unit prism having a columnar shape may be arranged adjacently so that their axes are parallel to the one-dimensional direction.

Further, the cross section of the unit prism is not limited to a semicircle or a sine curve, but may be a caroid, a rankin egg, a cycloid, a limbolute straight line, or a polygon other than a triangle.

Furthermore, for example, an optical sheet having a so-called fly-eye lens or the like in which hemispherical unit prisms each independently protruding are arranged in a two-dimensional direction may be used.
The unit prism may have a pyramid shape.

As shown in FIGS. 1A and 1B,
The light reflecting optical sheet 10 according to the present invention includes
The prism surface is formed by arranging a large number of unit prisms 14 each having a triangular prism shape on one surface (the upper surface in FIGS. 1 and 2) in adjacent one-dimensional directions so that the ridge lines thereof are parallel to each other. Although it is not clear, it is possible to obtain a light reflecting optical sheet having a higher reflected light luminance and a higher uniformity of the reflected light and having no luminance unevenness with respect to the light reflecting sheet including only the reflective substrate.

Next, an edge light type surface light source device 35 according to an embodiment of the present invention will be described with reference to FIG.

The surface light source device 35 includes the diffusion pattern 23
Light guide plate 22 provided on the surface facing the prism sheet surface 6
A light source 21 disposed on a side surface of the light guide plate 22; a light reflection optical sheet 10 covering at least the light guide plate 22; and a prism disposed above a surface of the light guide plate 22 opposite to the surface facing the light reflection optical sheet 10. It consists of a sheet 26.

Between the light guide plate 22 and the prism sheet 26,
A light diffusion sheet 25 can be provided as needed.

In this embodiment, the light reflecting optical sheet 1
0 encloses the light source 21 and the opposite side of the light guide 21 of the light guide plate 22 except for the surface of the light guide plate 22 facing the prism sheet.
May be installed so as to cover the surface of the light guide plate 22 opposite to the surface facing the prism sheet.

The light from the light source 21 is transmitted to the light guide plate 22.
Is introduced from the left side end of the light guide plate, and is emitted from the light emission surface above the light guide plate, so as to cover the light source 21 and the surface and the side end surface opposite to the light emission surface in the light guide plate. It is arranged so that light emitted from these surfaces is reflected by the light reflecting optical sheet 10 in the direction of the light guide, and light emitted from the upper light emitting surface of the light guide plate is transmitted from the lower surface of the prism sheet 26. The incident light is emitted from the upper surface.

Next, a direct type surface light source device 40 according to an embodiment of the present invention will be described with reference to FIG.

The surface light source device 40 includes a prism sheet 2
6, a light diffusing sheet 25 is arranged, and light from a light source 48 is reflected by the light reflecting optical sheet 10 in which the light reflecting optical sheet is formed in a concave shape. Light is emitted from 25 to a prism sheet 26. The shape of the light reflecting optical sheet 10 may be any as long as it can uniformly reflect the light from the light source 48 as approximately parallel rays, and a shape such as a concave arc, a parabolic column, a hyperbolic column, or an elliptical column is selected. You.

Each of the surface light source devices 35 and 40 has one
Although a single lens film is used, the present invention is not limited to this, and two or three or more lens films may be used. In this case, the direction of the ridge line of the lens film may be orthogonal, parallel, or at any angle.

In each of the surface light source devices 35 and 40, the unit lens surface of the lens film is arranged in the light emitting direction. However, the present invention is not limited to this. It may be arranged toward.

Since the surface light source devices 35 and 40 both use the light reflecting optical sheet, reflected light from the light reflecting optical sheet having high luminance, high uniformity and no luminance unevenness can be obtained. Therefore, the emitted light from the surface light source device can have high brightness, and can be obtained with high uniformity and no uneven brightness.

Next, an embodiment of the present invention will be described.

[0046]

[Example 1] Ultrafine P manufactured by Furukawa Electric Co., Ltd.
ET foam sheet MCPET (product name, thickness 1 mm, average cell diameter 20 μm or less) is used as a reflective substrate, and at a pitch of 50 μm, a unit prism shape cross section is an isosceles triangular prism with a vertex angle of 97 °, and ridge lines are mutually formed. Using a parallel mold, mold temperature 150 ° C, pressure 10kg / c
The light reflecting optical sheet was produced by performing hot pressing under the condition of m2 and transferring the prism shape to the surface of the reflective substrate.

The obtained light reflecting optical sheet was assembled into a direct type surface light source device, and the brightness and appearance were evaluated. The luminance is the luminance in the normal direction on the diffusion sheet of the surface light source as B.
It was measured using an M-7 (luminance meter, manufactured by Topcon), and the results were shown by numerical values based on values relative to Comparative Examples. The appearance was visually observed to confirm how much the image of the linear light source was visible. The results are shown in Table 1.

Example 2 Expanded PET film E manufactured by Toray
60 (product name, thickness 125 μm, average bubble diameter 30 μm or less), apply a transparent adhesive layer to about 1 μm,
An ultraviolet curable resin mainly composed of an epoxy acrylate prepolymer for forming a unit prism pattern is applied thereon, and after the resin coating film is cured, the mold is released to form a unit prism shape at a pitch of 50 μm. Light reflecting optical sheets having a cross-section of an isosceles triangular prism with an apex angle of 97 ° and a shape arranged adjacent to each other such that ridges are parallel to each other were produced.

The obtained light-reflecting optical sheet was assembled in a direct-type surface light source device, and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1] An evaluation in the case where a commonly used resin sheet reflector was incorporated in a direct-type surface light source device was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Comparative Example 2] An evaluation of a case where a commonly used metal sheet reflector was incorporated in a direct-type surface light source device was performed in the same manner as in Example 1, and the results are shown in Table 1.

[0052]

[Table 1]

[0053]

Since the present invention is constructed as described above, a light reflecting optical sheet having a high light use efficiency and a high reflected light luminance and having uniform reflected light and no uneven luminance can be obtained. The surface light source device using the optical sheet has an excellent effect that the emitted light is uniform, there is no luminance unevenness, the light use efficiency is high, and the emitted light luminance is high.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view showing a part of a light reflecting optical sheet having a prism surface according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a prism shape in the light reflecting optical sheet of the present invention.

FIG. 3 is a sectional view showing an apparatus for manufacturing a light reflecting optical sheet of the present invention.

FIG. 4 is a sectional view showing a main part of a surface light source device using a light reflecting optical sheet having a prism surface according to an example of an embodiment of the present invention.

FIG. 5 is a perspective view showing a second example of the embodiment of the surface light source device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Light reflection optical sheet 21, 48 ... Light source 25 ... Light diffusion sheet 26 ... Prism sheet 35, 40 ... Surface light source device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 6/00 331 G02B 6/00 331 G02F 1/1335 530 G02F 1/1335 530

Claims (8)

[Claims] 1. A light reflecting optical sheet comprising a reflective substrate containing fine bubbles, wherein a plurality of unit prisms or unit lenses are arranged on the surface of the reflective substrate. 2. A light reflecting optical sheet according to claim 1, wherein said reflective substrate and said unit prism or unit lens are integrally formed. 3. The light reflecting optical sheet according to claim 1, wherein the unit prism or the unit lens is formed on the reflective substrate. 4. The method according to claim 3, wherein:
A light reflecting optical sheet comprising an adhesive layer, the unit prism or the unit lens formed thereon. 5. The light-reflecting optical sheet according to claim 1, wherein the average diameter of the fine bubbles of the reflective substrate is 50 μm or less. 6. A light guide which is a sheet made of a transparent material, wherein light introduced from at least one end face is emitted from a light emission surface which is one surface, and the light guide. A light source for causing light to enter the interior from at least the one side surface; and a light guide that is disposed to cover at least a surface of the light guide opposite to the light emission surface and reflects light emitted from the light guide. A surface light source device comprising: the light reflecting optical sheet according to any one of claims 1 to 5 that reflects light toward a light body; and a prism sheet in which a plurality of unit prisms or unit lenses are arranged on a surface of a transparent substrate. 7. The light guide according to claim 6, wherein the light reflecting optical sheet is a surface of the light guide opposite to the light emitting surface, all the sides of the light guide other than the side facing the light source, and the light source. A surface light source device arranged so as to cover the light source. 8. A light diffusing sheet, a light source for irradiating the light diffusing sheet with light, and a light source disposed on a side of the light source opposite to the light diffusing sheet, for reflecting light from the light source toward the light diffusing sheet. Item 1; a light reflecting optical sheet according to any one of Items 1 to 5; and a prism sheet in which a plurality of unit prisms or unit lenses are arranged on a surface of a transparent substrate arranged so that light emitted from the light diffusion sheet is incident thereon. A surface light source device comprising: