JP2008224779A - Light diffusion sheet and light source unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet with which the shape of a light source does not appear and which shows high luminance when it is arranged in the light source unit. <P>SOLUTION: The light diffusion sheet 1 is characterized in that it is constituted by forming fine structure comprising mountain-like parts 11 aligned and extended in a specific direction and a groove-like part 12 formed between the mountain-like parts 11. The light source unit is equipped with the light source 221 and the light diffusion sheet 222 arranged on the light source 221 and makes light from the light source 221 incident on a liquid crystal panel 21 via the light diffusion sheet 222. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light diffusion sheet and a method for manufacturing the same, and more particularly to a light diffusion sheet used for a light source unit such as a backlight of a liquid crystal display device and a light source unit using the same.

In a transmissive or transflective liquid crystal display device, a backlight is provided as a light source unit that illuminates a liquid crystal panel. This backlight is configured to allow light emitted from a linear light source such as a cold cathode tube to enter a liquid crystal panel via a light guide plate or a light diffusion sheet (Patent Document 1). As the light diffusion sheet, there are those in which a diffusing agent is dispersed in a base sheet, and those in which a wrench shape or a lens shape is formed on the base sheet.
JP 2006-39503 A

  Light diffusing sheets in which a diffusing agent is dispersed in a base sheet can be produced in large quantities at low cost by extrusion molding. The brightness is remarkably lowered, the extrudability is also lowered, and the yield is lowered. On the other hand, if the amount of the diffusing agent is reduced in order to increase the front luminance, the shape of the light source (lamp image) appears when it is used in a display device and cannot be put into practical use.

  On the other hand, a light diffusing sheet with a wrench shape or lens shape on a base sheet sheet improves brightness due to the light collecting effect of the shape, but it displays a strong lamp image at a certain viewing angle. When used in an apparatus, a light diffusion sheet using the diffusing agent must be used in combination. When a light diffusion sheet using a diffusing agent is used in this way, improvement in front luminance that can be expected alone is hindered, resulting in a decrease in luminance.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a light diffusing sheet that does not show the shape of a light source (lamp image) and exhibits high luminance when disposed in a light source unit. .

  The light diffusing sheet of the present invention has a fine shape composed of a mountain-shaped portion extending in a specific direction on the surface of the base sheet, and a groove-shaped portion formed between the mountain-shaped portions. Is formed.

In the light diffusion sheet of the present invention, when the fine shape in an arbitrary cross section along the direction orthogonal to the specific direction is subjected to frequency analysis, the wavelength characteristics include at least two frequency components, and the fine shape is formed. It is preferable that the position factor X in the specific direction on the surface and the position factor Y in the direction orthogonal to the specific direction are represented by the following formula (1).
Where 2 ≦ n ≦ 10 Formula (1)

In the light diffusion sheet of the present invention, λ _i in the formula (1) is preferably 0.50 μm to 100 μm.

In the light diffusion sheet of the present invention, a _i in the formula (1) is preferably 0.5 μm to 10 μm.

In the light diffusion sheet of the present invention, a _i / λ _i is preferably 0.02 to 2.0.

  In the light diffusing sheet of the present invention, the fine shape composed of the mountain-shaped portion formed on the base sheet and the groove-shaped portion formed between the mountain-shaped portions is a molded product of a thermoplastic resin. Preferably there is.

  In the light diffusing sheet of the present invention, the fine shape composed of the mountain-shaped portion formed on the base sheet and the groove-shaped portion formed between the mountain-shaped portions is a cured product of a photocurable resin. It is preferable that

  In the light diffusing sheet of the present invention, the fine shape is a stamper using an original plate having a pattern corresponding to the fine shape provided by exposing and hardening a photocurable resin using light interference exposure. Preferably, the pattern is formed by transferring and shaping the pattern.

  In the light diffusion sheet of the present invention, it is preferable that the base sheet has a thickness of 10 μm to 1000 μm.

  The light source unit of the present invention includes a light source and the light diffusion sheet according to any one of claims 1 to 9 disposed on the light source, and transmits light from the light source to the light diffusion sheet. It is made to enter into a to-be-illuminated body via.

  The light diffusing sheet of the present invention has a fine shape composed of a mountain-shaped portion that is oriented and extends in a specific direction on the surface of the base sheet, and a groove-shaped portion formed between the mountain-shaped portions. Therefore, when arranged in the light source unit, the shape of the light source does not appear, and high brightness can be exhibited.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1A and 1B are schematic views showing the surface layer region of the light diffusion sheet according to the embodiment of the present invention. FIG. 1 schematically illustrates the surface region of the light diffusing sheet, and is not limited to this. As shown to Fig.1 (a), the light-diffusion sheet 1 which concerns on this invention has a fine shape formed in the surface layer area | region of a base material sheet. This fine shape is composed of a mountain-shaped portion 11 oriented and extending in a specific direction, and a groove-shaped portion 12 formed between the mountain-shaped portions 11.

  The height of the mountain-shaped portion 11, that is, the distance from the top of the mountain-shaped portion 11 to the bottom of the groove-shaped portion 12 is preferably 0.5 μm to 10.0 μm in view of mold transfer properties and the like. In addition, the distance (pitch) between the top portions of the mountain-shaped portions 11 is preferably 0.5 μm to 100 μm in consideration of light diffusibility and the like. Note that the shape of the tip of the mountain-shaped portion 11 is preferably a spherical shape or a spheroid shape in consideration of light transmittance and the like.

  As shown in FIGS. 1A and 1B, the height and shape of each mountain-shaped portion 11 are random. Here, “random” means that there is substantially no regularity with respect to the height and shape of the mountain-shaped portion 11 in an arbitrary region of the light diffusion sheet. Therefore, even if the height and shape of the mountain-shaped portion 11 have regularity in a minute region in an arbitrary region, the height and shape of the mountain-shaped portion 11 does not have regularity in the entire arbitrary region here. It is included in “random”.

In addition, “random” is a frequency analysis of a fine shape in an arbitrary cross section along a direction (orthogonal direction) orthogonal to a specific direction (direction in which the mountain-shaped portion 11 extends as a whole: orientation direction) The wavelength characteristic includes at least two frequency components, and the position factor X in the orientation direction and the position factor Y in the orthogonal direction on the surface where the fine shape of the light diffusion sheet is formed are expressed by the following formula (1). Means.
Where 2 ≦ n ≦ 10 Formula (1)

In the above formula (1), λ _i is preferably 0.50 μm to 100 μm in consideration of light diffusibility and the like. In the above formula (1), _ai is preferably 0.5 μm to 10 μm in view of mold transferability and the like. Furthermore, when light condensing property is taken into consideration, a _i / λ _i is preferably 0.02 to 2.0.

  Thus, the light diffusing sheet 1 having a fine shape composed of the mountain-shaped portions 11 oriented and extending in a specific direction and the groove-shaped portions 12 formed between the mountain-shaped portions 11 in the surface layer region. Due to its fine shape, it can improve the luminance by exhibiting the light collecting function seen in the wrench shape and the lens shape. Further, by having a plurality of frequency components (wavelength components) in the cross-sectional shape, the shape has randomness and appropriate light diffusibility is exhibited. At this time, it is considered that the lamp image can be prevented from appearing because the shape includes even very fine wavelength components. In such a configuration, since a diffusing agent is not used, it is advantageous in terms of raw material costs. Moreover, you may use a small amount of diffusing agents together as needed.

  The base material sheet of the light diffusion sheet 1 may be a molded product of a thermoplastic resin or a cured product of a photocurable resin. Examples of the thermoplastic resin include polystyrene, polymethyl methacrylate, polycarbonate, and cycloolefin polymer. At this time, there are no particular limitations on the molding method and molding conditions. Moreover, when using photocurable resin, the sheet | seat comprised by polystyrene, polymethylmethacrylate, a polycarbonate, a cycloolefin polymer, a polyethylene terephthalate, a triacetyl cellulose etc. can be mentioned. At this time, in order to form a fine shape composed of a mountain-shaped portion and a groove-shaped portion formed between the mountain-shaped portions, the photocurable resin used is urethane acrylate, epoxy acrylate, polyester acrylate, Acrylate resins such as are preferred. There are no particular restrictions on the curing conditions.

  The thickness of the base sheet (thickness including the surface layer region) is preferably 10 μm to 1000 μm.

  When the fine shape is formed on the base sheet, first, a photocurable resin is exposed and solidified by using an optical interference exposure method to prepare an original having a pattern corresponding to the fine shape. Then, a stamper is prepared from the original plate, and the pattern is transferred and formed on the base sheet using the stamper. As a method of transfer shaping, a nanoimprint technique that has been rapidly developed in recent years can be used. For example, methods such as press molding using a thermoplastic resin, roll molding using a roll stamper, and injection molding with a stamper inserted in a mold can be used. Also, when using a photocurable resin, a method of applying a photocurable resin to a base material, transferring it to a stamper and curing it, applying a photocurable resin to a stamper, transferring it to the base material, and curing it A method or the like can be used.

  Here, the optical interference exposure method is a method of performing exposure using interference fringes formed by irradiating a laser beam having a specific wavelength from two directions of an angle θ. Lasers that can be used for optical interference exposure are limited to TEM00 mode lasers. Examples of the ultraviolet laser capable of laser oscillation in the TEM00 mode include an argon laser (wavelengths 364 nm, 351 nm, and 333 nm) and a fourth harmonic wave (wavelength 266 nm) of a YAG laser. Note that the wavelength of the laser light used for the optical interference exposure is appropriately set according to the interval between the fine ridges 11 to be formed. Further, a light diffusing material or the like may be inserted into one or both optical paths in order to provide randomness.

  The light diffusion sheet having the above-described configuration is disposed in a light source unit of a liquid crystal display device that is an illuminated body. FIG. 2 is a view showing a liquid crystal display device using the light diffusion sheet according to the embodiment of the present invention. The liquid crystal display device shown in FIG. 2 mainly includes a liquid crystal panel 21 and a light source unit 22 that makes light incident on the liquid crystal panel 21. The liquid crystal panel 21 includes a pair of glass substrates 211 and 213 and a liquid crystal layer 212 sandwiched between the glass substrates 211 and 213. The light source unit 22 includes a light source 221 such as a cold cathode tube, and a light diffusion sheet 222 according to the present invention disposed between the light source 221 and the liquid crystal panel 21. In such a liquid crystal display device, the light from the light source 221 passes through the light diffusion sheet 222 and enters the liquid crystal panel 21.

  Since this liquid crystal display device uses the light diffusion sheet according to the present invention, it is possible to perform screen display without revealing the lamp image of the light source in a state having sufficient luminance. In the liquid crystal panel 21, description of various optical elements such as a polarizing plate protective film, a retardation film, a diffusion plate, an alignment film, a transparent electrode, and a color filter that are normally used is omitted.

Next, examples performed for clarifying the effects of the present invention will be described.
・ Production of stamper A photosensitive resist is coated on a flat plate such as a glass substrate as a base material, and as described above, it is irradiated with a laser beam consisting of two beams and cured by exposure, so that a fine shape due to light interference can be obtained. After the pattern is formed and unnecessary portions are cleaned, electroforming is performed with nickel or the like to obtain a metal master stamper. As a base material, a roll-shaped stamper may be produced by exposing in the same manner using a roll instead of a flat plate.

  Using the obtained flat metal master, for example, a 0.5 mm-thick cycloolefin polymer (Arton, manufactured by Nippon Synthetic Rubber) sheet is used to form a fine pattern using the metal master stamper produced as described above. Thermally transferred. In thermal transfer, a metal master stamper is brought into contact with the sheet, heated and pressurized at a temperature of 180 ° C. and a pressure of 15 MPa for 10 minutes, and then cooled to room temperature to obtain a resin master stamper. The transfer method for obtaining the resin master stamper is not limited to the thermal transfer, and nanoimprint techniques such as transfer using a photosensitive resin can also be used. Next, the resin master stamper is electroformed with nickel or the like to obtain a metal mother stamper (hereinafter abbreviated as a stamper). If a resin master stamper equivalent is available as a commercial product or a sample, this may be used as a resin master stamper and electrocasted as a stamper.

(Example 1)
A LSD9535 sheet manufactured by Luminit (California, USA) having a fine pattern formed on the surface was used as a resin master stamper, and this was subjected to electroforming treatment to obtain a stamper. Next, the fine pattern was thermally transferred onto a 0.5 mm thick sheet of cycloolefin polymer (Arton, manufactured by Nippon Synthetic Rubber) using the stamper produced as described above. The thermal transfer was performed by bringing a stamper into contact with the sheet, heating and pressing at a temperature of 180 ° C. and a pressure of 15 MPa for 10 minutes, and then cooling to room temperature. In this way, a cycloolefin polymer sheet (Example 1) having a fine pattern was formed. When the surface layer region of this cycloolefin polymer sheet was viewed with a scanning electron microscope (SEM: S-4700, manufactured by Hitachi, Ltd.), as shown in FIG. 4, a mountain-shaped portion extending in a specific direction and extending, It had the fine shape comprised from the groove-shaped part formed between these mountain-shaped parts.

-Quantification approximation of cross-sectional shape When the obtained cycloolefin polymer sheet was cut out and the cross-sectional shape (the cross-sectional shape along the direction orthogonal to the orientation direction of the mountain-shaped portion) was observed by SEM, the shape shown in FIG. there were. The obtained cross-sectional image was binarized, a cross-sectional waveform was extracted, and this was subjected to a fast Fourier transform process to obtain main frequency components included. From the obtained frequency component, an approximate expression using a Fourier series was created and defined as a parameter having an optical role. FIG. 6 shows an approximate cross section calculated based on such frequency analysis. The approximate equations and parameters used here are as follows.
(Approximation formula)
A1 * sin (2πx / λ1) + A2 * sin (2πx / λ2) + A3 * sin (2πx / λ3)
(Parameter)
A1 = 3.0, λ1 = 5.8
A2 = 1.0, λ2 = 7.1
A3 = 1.0, λ3 = 11.6
FIG. 7 shows the cross-sectional wavelength characteristics obtained in this way. As can be seen from FIG. 7, the wavelength characteristics included at least two frequency components.

-Diffusion function evaluation About the obtained cycloolefin polymer sheet, front luminance measurement and lamp image evaluation were performed. The front luminance and the lamp image were evaluated by measuring with a two-dimensional color luminance meter CA-2000 manufactured by Konica Minolta by arranging a light diffusion sheet on the backlight of the liquid crystal television LC26BD1 manufactured by Sharp Corporation. The angle dependency of the transmitted light of the front incident light, that is, the diffuse transmittance was evaluated by a variable angle high-speed spectrophotometer GSP-2 manufactured by Murakami Color Research Laboratory. The result of front luminance is shown in FIG. As can be seen from FIG. 12, the front brightness was high and the lamp image was not confirmed. Moreover, the measurement result of diffuse permeability is shown in FIG. As can be seen from FIG. 11, the diffusibility and the front transmitted light were distributed in a well-balanced manner. In addition, as a comparison between diffusibility and front luminance, measured values (Comparative Example 1) of a commercially available diffusion plate (a diffusion plate mounted on a Sony liquid crystal television BRAVIA LC32BD1) were employed.

(Example 2)
An LSD7535 sheet manufactured by Luminit (Luminit LLC, California, USA) having a fine pattern formed on the surface was used as a resin master, and this was subjected to electroforming to obtain a stamper. Using this stamper, a fine pattern was thermally transferred in the same manner as in Example 1. In this way, a cycloolefin polymer sheet (Example 2) having a fine pattern was formed.

-Quantification approximation of a cross-sectional shape A cycloolefin polymer sheet was cut out, and a cross-sectional shape (a cross-sectional shape along a direction orthogonal to the orientation direction of the mountain-shaped portion) was observed by SEM. The obtained cross-sectional image was binarized, a cross-sectional waveform was extracted, and this was subjected to a fast Fourier transform process to obtain main frequency components included. From the obtained frequency component, an approximate expression using a Fourier series was created and defined as a parameter having an optical role. FIG. 9 shows an approximate cross section calculated based on such frequency analysis. The approximate equations and parameters used here are as follows.
(Approximation formula)
A1 * sin (2πx / λ1) + A2 * sin (2πx / λ2) + A3 * sin (2πx / λ3) + A4 * sin (2πx / λ4) + A5 * sin (2πx / λ5)
(Parameter)
A1 = 3.0, λ1 = 3.5
A2 = 2.0, λ2 = 6.4
A3 = 2.0, λ3 = 8.5
A4 = 1.0, λ4 = 14.2
A5 = 1.0, λ5 = 18.3
The cross-sectional wavelength characteristics obtained in this way are shown in FIG. As can be seen from FIG. 10, the wavelength characteristics included at least two frequency components.

-Evaluation of diffusion function The front luminosity measurement and the lamp image of the cycloolefin polymer sheet were evaluated. The front luminance and the lamp image were evaluated by measuring with a two-dimensional color luminance meter CA-2000 manufactured by Konica Minolta by arranging a light diffusion sheet on the backlight of the liquid crystal television LC26BD1 manufactured by Sharp Corporation. The diffuse permeability was evaluated by a variable angle high-speed spectrophotometer GSP-2 manufactured by Murakami Color Research Laboratory. The result of front luminance is shown in FIG. As can be seen from FIG. 12, the front brightness was high and the lamp image was not confirmed. Moreover, the measurement result of diffuse permeability is shown in FIG. As can be seen from FIG. 11, the diffusibility and the front transmitted light were distributed in a well-balanced manner. In addition, as a comparison between diffusibility and front luminance, measured values (Comparative Example 1) of a commercially available diffusion plate (a diffusion plate mounted on a Sony liquid crystal television BRAVIA LC32BD1) were employed.

  As described above, according to the light diffusing sheet of the present invention, when arranged in the light source unit, the shape of the light source does not appear, and high brightness can be exhibited.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, the dimensions, materials, and the like in the above-described embodiment are illustrative, and can be changed as appropriate. For example, as shown in FIG. 3, it is considered that the same effect can be obtained when the shape formed of the approximate cross section calculated based on the parameters estimated from Examples 1 and 2 is produced by the interference exposure method. Such a shape is also included in the scope of the present invention. In the above embodiment, the case where the present invention is applied to a light source unit of a liquid crystal television has been described. However, the present invention can be similarly applied to a case where the present invention is used for a light source unit of a device other than a liquid crystal television. In addition, various modifications can be made without departing from the scope of the present invention.

The present invention can be applied to a light source unit of a display device such as a liquid crystal display device.

(A), (b) is the schematic which shows the part for surface layer area | region of the light-diffusion sheet which concerns on embodiment of this invention. It is a figure which shows the liquid crystal display device using the light-diffusion sheet which concerns on embodiment of this invention. It is a figure which shows the approximate cross section calculated based on the parameter estimated from Example 1,2. 2 is a scanning electron micrograph showing the surface layer region of the light diffusion sheet of Example 1. FIG. 2 is a scanning electron micrograph showing a cross section of a surface layer region of the light diffusion sheet of Example 1. FIG. It is a figure which shows the approximate cross section calculated based on the frequency analysis about the light-diffusion sheet | seat of Example 1. FIG. It is a figure which shows the cross-sectional shape wavelength characteristic about the light-diffusion sheet of Example 1. FIG. 3 is a scanning electron micrograph showing a cross section of a surface layer region of a light diffusion sheet of Example 2. FIG. It is a figure which shows the approximate cross section calculated based on the frequency analysis about the light-diffusion sheet | seat of Example 2. FIG. It is a figure which shows the cross-sectional shape wavelength characteristic about the light-diffusion sheet of Example 2. FIG. It is a figure which shows the diffuse permeability of the light-diffusion sheet of Example 1,2. It is a figure which shows the front luminance of the light-diffusion sheet | seat of Example 1,2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusion sheet 11 Mountain part 12 Groove part 21 Liquid crystal panel 22 Light source unit 211,212 Glass substrate 213 Liquid crystal layer 221 Light source

Claims (10)

  On the surface of the base sheet, a fine shape composed of a mountain-shaped portion extending in a specific direction and a groove-shaped portion formed between the mountain-shaped portions is formed. A light diffusion sheet. When the fine shape in an arbitrary cross section along the direction orthogonal to the specific direction is subjected to frequency analysis, the wavelength characteristic includes at least two frequency components, and the position factor X in the specific direction on the surface on which the fine shape is formed The light diffusion sheet according to claim 1, wherein a position factor Y in a direction orthogonal to the specific direction is represented by the following formula (1).
Where 2 ≦ n ≦ 10 Formula (1) The light diffusion sheet according to claim 2, wherein λ _i in the formula (1) is 0.50 μm to 100 μm. The light diffusion sheet according to claim 2 or 3, wherein a _i in the formula (1) is 0.5 µm to 10 µm. The light diffusion sheet according to claim 2, wherein a _i / λ _i is 0.02 to 2.0.   2. The fine shape composed of a mountain-shaped portion formed on the base sheet and a groove-shaped portion formed between the mountain-shaped portions is a molded product of a thermoplastic resin. The light diffusion sheet according to claim 5.   The fine shape composed of a mountain-shaped portion formed on the base sheet and a groove-shaped portion formed between the mountain-shaped portions is a cured product of a photocurable resin. The light diffusion sheet according to any one of claims 1 to 5.   The fine shape is formed by transferring and shaping the pattern onto the base sheet with a stamper using an original plate having a pattern corresponding to the fine shape provided by light-curing a photocurable resin using light interference exposure. The light diffusing sheet according to claim 1, wherein the light diffusing sheet is formed by:   The thickness of the said base material sheet is 10 micrometers-1000 micrometers, The light-diffusion sheet in any one of Claims 1-8 characterized by the above-mentioned.   A light source and a light diffusion sheet according to any one of claims 1 to 9 disposed on the light source, wherein light from the light source is directed to an illuminated body via the light diffusion sheet. A light source unit characterized by being incident.