JP2006098899A - Light diffusion sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet excellent in processing aptitude by giving stable antistatic ability to the light diffusion sheet incorporated into a back light unit for a liquid crystal display while maintaining characteristics of the light diffusion sheet of uniformity and high transmission light amount. <P>SOLUTION: The light diffusion sheet 1 has a base material sheet 4 and a light diffusion layer 2 laminated at least on one side of the base material sheet 4. Further between the base material sheet 4 and the light diffusion layer 2, an antistatic layer 3 which acts toward electrification at a surface of the light diffusion sheet 1 so as to negate electric line of force, that is based on electrified charge and goes to the outside of the light diffusion sheet 1, is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light diffusing sheet suitable for a backlight unit of a liquid crystal display device and the like, and in particular, processing by suppressing static electricity accumulation on the surface of the light diffusing film and eliminating electrostatic attraction such as dust and cutting waste during processing. The present invention relates to a light diffusion sheet with improved suitability.

  Generally, a liquid crystal display device is equipped with a backlight unit that illuminates a liquid crystal panel from the back side. Taking a direct type backlight unit as an example, it is often provided with a rod-shaped cold cathode tube lamp, a light diffusion plate, a light diffusion sheet, and a prism sheet in that order on the surface side of the lamp. There are also backlight units with multiple prism sheets or light diffusing sheets to increase the front luminance value, backlight units with semi-transparent reflective sheets to improve outdoor visibility, etc. is there.

  The function of the backlight unit will be described. Light rays incident on the light diffusion plate from the cold cathode tube lamp are diffused by the light diffusion material dispersed in the light diffusion plate and emitted from the surface of the light diffusion plate. Light rays emitted from the light diffusing plate enter the light diffusing sheet, are diffused and collected, and are emitted from the surface of the light diffusing sheet. The light beam emitted from the light diffusion sheet enters the prism sheet, is further condensed on the surface of the prism sheet, and is emitted as a light beam having a distribution showing a luminance value peak in a substantially frontal direction. In this way, the light beam emitted from the cold cathode tube lamp is diffused and collected to illuminate the entire surface of the liquid crystal panel disposed on the backlight unit.

  The light diffusing sheet installed in the backlight unit is very easily charged with static electricity. When static electricity accumulates, it tends to attract dust, etc., impairs optical characteristics, and causes inconvenience in stacking with prism sheets, etc. There is an influence. In particular, in order to arrange the light diffusing sheet in the backlight unit, it is necessary to punch it into a predetermined shape in advance. However, there is a problem that the scraps generated at that time are easily electrostatically attracted to the light diffusing sheet. It has become. It is difficult to remove the electrostatically adhering swarf and the like, and it takes a lot of time and effort to remove it carefully so as not to damage the sheet surface. Therefore, in general, an antistatic treatment in which a cationic surfactant or the like is added to the binder or an antistatic agent is sprayed on the surface of the light diffusion sheet is performed.

In addition, in order to arrange the light diffusion sheet in the backlight unit, it is necessary to punch it into a predetermined shape in advance, and the chips generated at that time are easily attracted to the light diffusion sheet. It is difficult to remove the cut scraps and the like, and it takes a lot of labor and time to remove carefully so as not to damage the sheet surface.
Furthermore, in order to protect the surface of the light diffusion sheet, a method may be used in which a slightly adhesive film is attached to both surfaces of the light diffusion sheet, and the slightly adhesive sheet is peeled off immediately before being disposed on the backlight unit. . However, there is a case where dust or the like adheres to the surface of the light diffusion sheet due to the peeling electrification generated when the fine adhesive sheet is peeled off, and it is an effective solution to remove them carefully so as not to damage the sheet surface. Is not reached.

  In order to solve these problems, a surfactant-based antistatic agent is added to the binder of the light diffusion sheet, or an antistatic agent is sprayed on the surface of the light diffusion sheet. Although the antistatic ability is imparted to the light diffusion sheet by blending such an antistatic agent, the added antistatic agent is difficult to be uniformly mixed in the binder, and the effect is manifested by bleeding out of the antistatic agent. Uniform antistatic ability is difficult to obtain. In addition, by bleeding out, defects due to surface contamination are likely to occur during work, and the light collecting characteristics may be impaired. When the surface of the light diffusing sheet is wiped away, the antistatic effect is often lost. Furthermore, there is a problem that the antistatic effect is easily influenced by the environment such as temperature and humidity, the antistatic ability is likely to deteriorate with time, and the stable antistatic effect is not sustained.

  In particular, in a light diffusing layer in which a light diffusing material is dispersed, a crosslinking binder is preferred in order to make it easier to impart scratch resistance to the coating film and to obtain adhesion to the base sheet. May interfere. Because of such circumstances, when the antistatic treatment of the light diffusion sheet is performed, it is common to apply only to the backcoat layer.

On the other hand, in the packaging field, a film in which an adhesive primer having antistatic properties is laminated between layers is known as an antistatic film (see, for example, Reference 1). However, when this laminate film is used as a substrate for a light diffusing sheet and a light diffusing layer is formed on the substrate, the layer thickness from the adhesive primer having anti-electrostatic induction properties to the surface of the light diffusing layer is increased. Therefore, there is a disadvantage that it is difficult to obtain a sufficient surface antistatic ability.
JP-A-7-252456 (Page 1-5)

An object of the present invention is to provide a stable antistatic ability to a light diffusion sheet incorporated in a backlight unit for a liquid crystal display device while maintaining the characteristics of a light diffusion sheet that is uniform and has a high amount of transmitted light. Therefore, it is an object of the present invention to provide a light diffusion sheet having high quality and excellent processability.

  In order to solve the above problems, the present invention provides a light diffusion sheet incorporated in a backlight unit for a liquid crystal display device, comprising: a base material sheet; and a light diffusion layer laminated on at least one side of the base material sheet. Between the base sheet and the light diffusion layer, with respect to the charge on the surface of the light diffusion sheet, electric lines of force directed to the outside of the light diffusion sheet based on the charged charges, dielectric polarization and / or Provided is a light diffusing sheet comprising an antistatic layer that acts to counteract electrostatic induction.

  The light diffusing sheet of the present invention cancels electric lines of force based on the charged charges by dielectric polarization and / or electrostatic induction with respect to the charge on the surface of the light diffusing sheet between the base sheet and the light diffusing layer. Since the antistatic layer acting as described above is provided, the antistatic ability is not deteriorated with time, and the antistatic ability that is semipermanently hardly influenced by the environment such as temperature and humidity can be exhibited. In addition, even if the dust on the surface of the light diffusing sheet is wiped off, the antistatic ability does not deteriorate, and contamination and bleeding due to bleed-out such as an antistatic agent can be avoided, adversely affecting the light diffusing performance. Nor. Furthermore, since the antistatic layer is formed between the base sheet and the light diffusion layer, the distance from the antistatic layer to the surface of the light diffusion layer can be shortened, and the function of the antistatic layer is effectively exhibited. . As a result, it is possible to provide a light diffusion sheet having excellent antistatic ability and excellent processability.

In the light diffusion sheet of the present invention, it is preferable that a back coat layer having a sticking prevention function is provided on the surface opposite to the light diffusion layer forming surface of the transparent substrate sheet.
Further, in order for the light diffusion sheet to have an excellent antistatic function, it is preferable that the backcoat layer is also subjected to an antistatic treatment, and an antistatic layer is provided between the transparent substrate sheet and the backcoat layer. It is preferable that Alternatively, the back coat layer may contain an antistatic agent.
The light diffusion sheet of the present invention is preferably a light diffusion sheet in which the antistatic layer is a crosslinkable acrylic copolymer having at least a carboxyl group and a quaternary ammonium base in the side chain.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing a light diffusion sheet in another embodiment different from the light diffusion sheet of FIG. . FIG. 3 is a schematic cross-sectional view showing a conventional light diffusion sheet for comparison with the light diffusion sheet of the present invention.

  The light diffusing sheet 1 in FIG. 1 has a base sheet 4, an antistatic layer 3 and a light diffusing layer 2 laminated in this order on one side of the base sheet 4, and on the side where the light diffusing layer 2 is not formed. The back coat layer 5 is laminated. FIG. 2 shows a configuration in which an antistatic layer 3 is provided between the back coat layer 5 and the base sheet 4 of FIG.

  The base sheet 4 is formed of a colorless and transparent synthetic resin, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic, polycarbonate, polystyrene, and polyolefin. Among these, polyethylene terephthalate is preferably used from the viewpoint of weather resistance and processability.

  The base sheet 4 may be subjected to an easy adhesion treatment in order to improve the adhesion with the antistatic layer 3 or the back coat layer 5 to be laminated. As the easy adhesion treatment, for example, a corona treatment or an easy adhesion layer (not shown) is generally applied and formed on one side or both sides of the base sheet.

  The thickness of the base sheet 4 is 35 μm or more and 300 μm or less, preferably 35 μm or more and 250 μm or less. When the thickness of the base sheet 4 is less than 35 μm, curling is likely to occur after the light diffusion layer 2 is formed, and when the thickness exceeds 300 μm, the optical characteristics may be deteriorated. As a result, the inconvenience arises in that the thickness of the film increases and the transmittance of the total light amount decreases.

  The light diffusion layer 2 includes a binder 8 and a light diffusion material 6 dispersed in the binder 8. With the light diffusing material 6 dispersed in this manner, the light beam transmitted through the light diffusing layer 2 from the back side to the front side can be diffused almost uniformly. Further, by projecting the upper end portion of the light diffusing material 6 from the binder 8, it is possible to have a light diffusing effect and a light collecting effect. The thickness of the light diffusing layer 4 varies depending on the size of the light diffusing material 6, but is preferably about 5 μm to 50 μm, for example, and most preferably 10 μm to 40 μm. When the thickness is less than 5 μm, it is difficult to obtain a sufficient light diffusion effect. When the thickness exceeds 50 μm, it is difficult to obtain the antistatic effect on the surface of the light diffusion sheet by the antistatic layer 3 and the light beam of the backlight light source. There is a disadvantage that it is easy to prevent transmission. Here, the film thickness is not defined by the height to the top of the protruding light diffusing material 6, but by the film thickness of the binder holding the light diffusing material.

  The synthetic resin used for the binder 8 is preferably colorless and transparent, and examples thereof include acrylic resins, polyurethane resins, and polyester resins. In addition, the binder 8 may be blended with various additives in order to impart various characteristics desirable for the light diffusion sheet. Examples of such additives include ultraviolet light inhibitors, antioxidants, plasticizers, and stabilization. Agents, deterioration inhibitors, dispersants and the like.

  The shape of the light diffusing material 6 is not particularly limited, and examples thereof include a spherical shape, a hemispherical shape, a needle shape, a spindle shape, and a scale shape. Among these, spherical resin beads having excellent light diffusibility and light collecting properties are used. preferable.

  Examples of the resin beads include acrylic, styrene, silicone, urethane, acrylurethane, benzoguanamine, and polyethylene resin beads.

  The particle size of the light diffusing material 6 is preferably an average particle size of 1 μm or more and 30 μm or less, and particularly preferably an average particle size of 1 μm or more and 20 μm or less. Moreover, you may adjust the optical characteristic and the smoothness of a coating film in a desired numerical range by mixing the light-diffusion material 6 from which an average particle diameter differs. When the average particle diameter of the light diffusing material 6 is less than 1 μm, the surface of the light diffusing layer 2 formed by the light diffusing material 6 is easily adjusted to be smooth, but it is difficult to satisfy a good haze value necessary as a light diffusing sheet. Thus, if the average particle size of the light diffusing material 6 exceeds 30 μm, the thickness of the light diffusing sheet 1 increases and it becomes difficult to obtain uniform optical characteristics.

  As a compounding quantity of the light-diffusion material 6, 10 mass parts or more and 400 mass parts or less are preferable with respect to 100 mass parts of resin solid content in the binder 8, 30 mass parts or more and 300 mass parts or less are more preferable, 90 masses More preferably, it is at least 250 parts by weight. If the blending amount of the light diffusing material 6 is less than 10 parts by mass, the light diffusing property becomes insufficient. On the other hand, if the blending amount of the light diffusing material 6 exceeds 400 parts by mass, the light transmittance is reduced. This is because it tends to decrease and the light diffusing material 6 is easily detached from the binder.

  The antistatic layer 3 is a functional layer that acts to cancel the lines of electric force based on the charged charges by dielectric polarization and / or electrostatic polarization with respect to the charge on the surface of the light diffusion sheet 1. As a material used as the antistatic layer 3, a copolymer of monomers having the following functional groups is preferable. (1) Monomers having a carboxyl group such as acrylic acid (including meta), acryloyloxyethyl succinic acid, phthalic acid, hexahydrophthalic acid (including meta). (2) A monomer having a quaternary ammonium base such as quaternary dimethylaminoethyl acrylate (including anions such as chloride, sulfate, sulfonate, and alkyl sulfonate as a counter ion). (3) Monomers having a hydroxyl group such as glycerin diglycidyl ether, trimethylolpropane triaziridinyl ether, trimethylolpropane triglycidyl ether. In addition, monomers such as alkyl acrylate (including meta), styrene, vinyl acetate, and vinyl halide can be copolymerized as necessary. Moreover, an amine-type hardener, an epoxy-type hardener, etc. can be mix | blended as needed.

  The film thickness of the antistatic layer 3 is not particularly limited as long as sufficient antistatic ability can be obtained, but is preferably 0.1 μm or more and 3 μm or less, more preferably 0.3 μm or more and 2 μm or less.

  In general, the light diffusing sheet 1 is very easily charged, and is easily charged by frictional charging that occurs at the time of punching or handling, or peeling charging that occurs when the surface protective film that has been subjected to adhesive processing is peeled off. Taking as an example the case where a crosslinkable acrylic copolymer having a carboxyl group and a quaternary ammonium base in at least the side chain is used as the antistatic layer 3, the antistatic layer 3 of the antistatic layer 3 is generated by electric lines of force generated by these static electricity. The quaternary ammonium salt type acrylic resin is polarized and a dipole moment is induced. The generation of this dipole moment is a result of the distribution of electrons of the quaternary ammonium base deviating in the direction of the electric field lines or the relative position between the ions fluctuating. Due to the high dielectric constant of the resin, the direction of the electric lines of force based on this dipole moment effectively cancels the electric lines of force due to static electricity on the surface of the light diffusing sheet 1, and as a result, the surface of the light diffusing sheet 1. The electric lines of force on the surface of the light diffusion sheet 1 can be reduced in spite of the occurrence of static electricity. Furthermore, since the quaternary ammonium salt acrylic resin has high conductivity, electrons and ions move by electrostatic polarization so as to cancel the electric field in the antistatic layer, and the dipole moment is relaxed in a short time. In the antistatic layer, the electric charge lines of the charged charge toward the outside of the sheet are canceled.

  The crosslinkable acrylic copolymer having a carboxyl group and a quaternary ammonium base in the side chain exemplified here has a particularly large effect of reducing electric lines of force due to the dielectric polarizability and conductivity of the quaternary ammonium base. Furthermore, since it has sufficient transmittance in the wavelength region used in the liquid crystal display device, the characteristics of the light diffusion sheet are not impaired. And a carboxyl group has the effect which improves a crosslinking property, and a hydroxyl group has the effect which reacts with the functional group in a hardening | curing agent and improves the adhesiveness with the base material sheet 4 and the light-diffusion layer 2. FIG. Specifically, Bondip PA (manufactured by Konishi Co., Ltd.) has particularly preferable characteristics.

  Due to these effects, the antistatic layer 3 has sufficient physical properties and can prevent electrostatic adsorption such as dust and scraps on the surface of the light diffusion sheet 1. Accordingly, it is possible to prevent dust from adhering during handling of the light diffusion sheet 1, scrap from adhering to the punching process, or dust from adhering to the surface protective adhesive sheet, and to prevent problems caused by electrostatic adsorption when the backlight is incorporated.

  When the back coat layer 5 is provided, it is preferable that the binder 9 and the anti-sticking material 7 are dispersed in the binder 9. By providing the back coat layer 5, it is possible to prevent the light diffusion sheet 1 from being in close contact with the surface of the member disposed below it and causing moire-like optical defects due to light interference (sticking). Furthermore, the scratch resistance of the backcoat layer 5 can be enhanced by the anti-sticking material.

  The binder 9 is not particularly limited as long as it is a highly transparent binder that has excellent adhesion to the base material sheet 4, and may be the same as the binder 8 of the light diffusion layer 2. . Various additives may be blended in the binder 9, and examples thereof include an ultraviolet ray inhibitor, an antioxidant, a plasticizer, a stabilizer, a deterioration inhibitor, and a dispersant.

  The sticking prevention material 7 can be used without particular limitation as long as it does not significantly impair the optical properties of the light diffusion sheet 1, and the same material as the light diffusion material 6 of the light diffusion layer 2 can be used. .

  The thickness of the back coat layer 5 (not the height to the top of the anti-sticking material 7 but the thickness of the binder 9 coating film holding the anti-sticking material) is not particularly limited, but the anti-sticking material 7 is removed from the binder. A thickness that does not separate is necessary, and is preferably about 0.5 μm or more and 10 μm or less.

  The average particle size of the anti-sticking material 7 may be any particle size that can prevent the moire-like optical defects, and is preferably 3 μm or more and 15 μm or less. If the average particle size is less than 3 μm, it becomes difficult to obtain an anti-sticking effect. If the average particle size exceeds 15 μm, the optical properties may be deteriorated, and the thickness of the backlight unit also increases. It is.

  The compounding amount of the anti-sticking material 7 is an amount that does not inhibit the optical properties of the light diffusing sheet 1 and provides an anti-sticking effect, and is 0.1 parts by mass or more with respect to 100 parts by mass of the resin solid content in the binder 9 The amount is preferably 10 parts by mass or less, more preferably 0.5 parts by mass or more and 5 parts by mass or less. The anti-sticking material 7 is dispersed in the binder 9 to form a coating film, and many of the anti-sticking materials 7 have their upper ends protruding from the binder 9 to some extent. Therefore, when this light diffusing sheet 1 is laminated on the light guide plate or the light diffusing plate, or when two or more light diffusing sheets 1 are laminated, the upper end of the protruding anti-sticking material 7 is the light guide plate, light diffusing It is possible to prevent the back coat layer 5 of the light diffusion sheet 1 from coming into contact with the surface of the light guide plate, the light diffusion plate or the light diffusion layer 2 by contacting the plate or the surface of the light diffusion layer 2. As a result, sticking between the light diffusion sheet 1 and the light guide plate, the light diffusion plate, or the light diffusion sheets 1 is prevented, and uneven brightness on the screen of the liquid crystal display device is suppressed.

  Moreover, it is preferable to provide the antistatic performance to the backcoat layer 5 by providing the antistatic layer 3 between the base sheet 4 and the backcoat layer 5. Alternatively, instead of the antistatic layer 3, an antistatic effect can be imparted by adding an antistatic agent such as a surfactant to the binder 9 of the backcoat layer 5 within a range that does not affect the optical characteristics.

  As the antistatic agent, a general commercial product can be used. For example, anionic, cationic, nonionic surfactants are preferable, and quaternary ammonium salt type cationic agents are particularly preferable.

  The light diffusing sheet of the present invention is not limited to the above embodiment. For example, an adhesive layer is provided instead of the back coat layer 5 so that the light diffusing sheet can be directly integrated with the light guide plate. Configuration is also possible.

  Examples of the present invention will be described below, but the present invention is not limited thereto. “Parts” and “%” are based on parts by mass unless otherwise noted.

Example 1
The antistatic layer coating material a was applied and dried on one surface of a substrate sheet 4 made of polyethylene terephthalate having a thickness of 100 μm, and the antistatic layer 3 having a thickness of about 1 μm was laminated. Next, the light diffusion layer 2 having a thickness of about 25 μm was laminated by applying and drying the light diffusion layer coating material b on the antistatic layer 3. Then, on the other surface of the base sheet 4, the back coat layer coating d in which the anti-sticking material 7 is dispersed is applied and dried, and the back coat layer 5 having a thickness of about 2 μm is laminated, and the light diffusion shown in FIG. Sheet 1 was produced.

<Antistatic layer coating material a>
BODEIP PA-200 main agent (manufactured by Konishi Co., Ltd.) 100 parts BODEIP PA-200 curing agent (manufactured by Konishi Co., Ltd.) 100 parts isopropyl alcohol 200 parts water 150 parts

<Light diffusion layer coating material b>
Isocyanate curable acrylic resin (Acridic: solid content 50%, OH value 25%, manufactured by Dainippon Ink & Chemicals, Inc.) 50 parts curing agent (Coronate HL: solid content 75%, manufactured by Nippon Polyurethane Industry Co., Ltd.) 10 parts light Diffuser (030 (F), acrylic beads, average particle size 20 μm, manufactured by Dainichi Seika Co., Ltd.) 65 parts Toluene 200 parts Cyclohexanone 10 parts

<Backcoat layer coating material d>
Acrylic resin (Acridic: 45% solids manufactured by Dainippon Ink & Chemicals, Inc.)
45 parts anti-sticking material (MR-10G, acrylic beads, average particle size 9 μm, manufactured by Soken Chemical Co., Ltd.) 0.2 parts antistatic agent (Katiogen ES-L-9, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 1.1 Part toluene 180 parts cyclohexanone 15 parts

(Example 2)
An antistatic layer coating c was applied and dried on one surface of a substrate sheet 4 made of polyethylene terephthalate having a thickness of 100 μm, and an antistatic layer 3 having a thickness of about 1 μm was laminated. Next, the light diffusion layer 2 having a thickness of about 25 μm was laminated by applying and drying the light diffusion layer coating material b on the antistatic layer 3. Then, the antistatic layer coating c was applied to the other surface of the base sheet 4 and dried to laminate the antistatic layer 3 having a thickness of about 1 μm. Next, the backcoat layer coating material f in which the antisticking material 7 was dispersed was applied and dried, and the backcoat layer 5 having a thickness of about 2 μm was laminated to produce the light diffusion sheet 1 of FIG.

<Coating c for antistatic layer>
BODEIP PA-100 main agent (manufactured by Konishi Co., Ltd.) 100 parts BODEIP PA-100 curing agent (manufactured by Konishi Co., Ltd.) 100 parts isopropyl alcohol 200 parts water 150 parts

<Backcoat layer paint f>
Isocyanate curable acrylic resin (Acridic: solid content 50%, OH value 25%, manufactured by Dainippon Ink & Chemicals, Inc.) 50 parts curing agent (Coronate HL: solid content 75%, manufactured by Nippon Polyurethane Industry Co., Ltd.) 10 parts sticking Prevention material (MR-10G, acrylic beads, average particle size 9 μm, manufactured by Soken Chemical Co., Ltd.) 0.3 parts Toluene 300 parts Cyclohexanone 15 parts

(Example 3)
The antistatic layer coating material c was applied and dried on one surface of a substrate sheet 4 made of polyethylene terephthalate having a thickness of 38 μm, and the antistatic layer 3 having a thickness of about 1 μm was laminated. Next, the light diffusion layer 2 having a thickness of about 10 μm was laminated by applying and drying the light diffusion layer coating material e on the antistatic layer 3. Then, the antistatic layer coating c was applied to the other surface of the base sheet 4 and dried to laminate the antistatic layer 3 having a thickness of about 1 μm. Next, the backcoat layer coating material f in which the antisticking material 7 was dispersed was applied and dried, and the backcoat layer 5 having a thickness of about 2 μm was laminated to produce the light diffusion sheet 1 of FIG.

<Light diffusion layer paint e>
Isocyanate curable acrylic resin (Acridic: solid content 50%, OH value 25%, manufactured by Dainippon Ink & Chemicals, Inc.) 35 parts curing agent (Coronate HL: solid content 75%, manufactured by Nippon Polyurethane Industry Co., Ltd.) 9 parts light Diffusing material (KMP-590, silicon beads, average particle size 2 μm, manufactured by Shin-Etsu Silicone Co., Ltd.) 3 parts Toluene 2 parts Cyclohexanone 5 parts

Example 4
An antistatic layer coating c was applied and dried on one surface of a base sheet 4 made of polyethylene terephthalate having a thickness of 38 μm, and an antistatic layer 3 having a thickness of about 2 μm was laminated. Next, the light diffusion layer 2 having a thickness of about 10 μm was laminated by applying and drying the light diffusion layer coating material e on the antistatic layer 3. Then, the antistatic layer coating material c was applied to the other surface of the base sheet 4 and dried to laminate the antistatic layer 3 having a thickness of about 2 μm. Next, the backcoat layer coating material f in which the antisticking material 7 was dispersed was applied and dried, and the backcoat layer 5 having a thickness of about 2 μm was laminated to produce the light diffusion sheet 1 of FIG.

(Comparative Example 1)
The light diffusion layer 2 having a thickness of about 25 μm was laminated on one surface of the base sheet 4 made of polyethylene terephthalate having a thickness of 100 μm by applying and drying the coating material b for the light diffusion layer. Then, on the other surface of the base sheet 4, the backcoat layer coating material f in which the anti-sticking material 7 is dispersed is applied and dried, and the backcoat layer 5 having a thickness of about 2 μm is laminated, and the light diffusion shown in FIG. Sheet 1 was produced.

(Comparative Example 2)
The light diffusion layer 2 having a thickness of about 10 μm was laminated on one surface of the base sheet 4 made of polyethylene terephthalate having a thickness of 38 μm by applying and drying the coating material e for the light diffusion layer. Then, on the other surface of the base sheet 4, the backcoat layer coating material f in which the anti-sticking material 7 is dispersed is applied and dried, and the backcoat layer 5 having a thickness of about 2 μm is laminated, and the light diffusion shown in FIG. Sheet 1 was produced.

(Comparative Example 3)
The light diffusion layer 2 having a thickness of about 25 μm was laminated on one surface of the base sheet 4 made of polyethylene terephthalate having a thickness of 100 μm by applying and drying the coating material g for the light diffusion layer. Then, on the other surface of the base sheet 4, the backcoat layer coating material f in which the anti-sticking material 7 is dispersed is applied and dried, and the backcoat layer 5 having a thickness of about 2 μm is laminated, and the light diffusion shown in FIG. Sheet 1 was produced.

<Light diffusion layer paint g>
Isocyanate curable acrylic resin (Acridic: solid content 50%, OH value 25%, manufactured by Dainippon Ink & Chemicals, Inc.) 50 parts curing agent (Coronate HL: solid content 75%, manufactured by Nippon Polyurethane Industry Co., Ltd.) 10 parts light Diffusion material (030 (F), acrylic beads, average particle size 20 μm, manufactured by Dainichi Seika Co., Ltd.) 65 parts Antistatic agent (Katiogen ES-L-9, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 1.3 parts Toluene 200 Part cyclohexanone 10 parts

[
(Comparative Example 4)
An antistatic layer coating c is applied and dried on one surface of a substrate sheet made of polyethylene terephthalate having a thickness of 38 μm, and the antistatic layer 3 having a thickness of about 1 μm is laminated. A substrate sheet made of polyethylene terephthalate having a thickness of 38 μm was laminated to obtain a substrate sheet 4 having a thickness of 80 μm. And the light-diffusion layer 2 about 10 micrometers thick was laminated | stacked by apply | coating and drying the coating material e for light-diffusion layers on one surface of the base material sheet 4. FIG. Next, the back coating layer 5 in which the anti-sticking material 7 is dispersed is applied to the other surface of the base sheet 4 and dried to laminate the back coating layer 5 having a thickness of about 2 μm. Produced.
The configurations of the light diffusion sheets of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in Table 1.

  Antistatic property evaluation was performed about the light-diffusion sheet 1 of Examples 1-4 and Comparative Examples 1-4 obtained as mentioned above. Furthermore, the total light transmittance and haze were also evaluated.

[Evaluation of antistatic properties]
In accordance with JIS L1094, the surface of the light diffusion sheet or the backcoat layer is charged with a + 10kV corona discharge field using a static Honestometer (manufactured by Sicid Electric Co., Ltd.) in a 20 ° C / 40% RH environment. The amount of electrostatic charge and the time until the charged voltage was halved (half-life) were measured. It was judged that the smaller the electrostatic charge amount and the more the charged voltage attenuated in a short time, the better the antistatic ability. The results are shown in Table 2.

[Total light transmittance and haze measurement]
Using a haze meter (NDH2000, Nippon Denshoku Industries Co., Ltd.), the total light transmittance (based on JIS K7361) and haze (based on JIS K7136) were measured. The results are shown in Table 2.

  From the results in Table 2, the light diffusing sheet 1 of Example 1 was provided with the antistatic layer 3 only on the light diffusing layer side, and the surface of the light diffusing layer was very difficult to be charged, and exhibited excellent charge attenuation characteristics. The surface of the backcoat layer to which the surfactant was added showed good charge decay characteristics although it was easily charged. Since the light diffusing sheets 1 of Examples 2 to 4 were provided with the antistatic layers 3 on both sides, both surfaces of the light diffusing sheet 1 were very difficult to be charged and exhibited excellent charge attenuation characteristics. From these results, it can be seen that the light diffusion sheets 1 of Examples 1 to 4 have excellent antistatic ability.

  On the other hand, since the light diffusing sheets 1 of Comparative Examples 1 and 2 do not include the antistatic layer 3, both surfaces of the light diffusing sheet 1 are very easily charged, and are difficult to attenuate once charged. It was a thing. In the light diffusion sheet 1 of Comparative Example 3, a surfactant was added to the light diffusion layer without providing the antistatic layer 3. However, the diffusion layer surface is easily charged, hardly attenuates once charged, and has extremely poor antistatic ability. As the light diffusion sheet 1 of Comparative Example 4, the base sheet 4 laminated with the antistatic layer 3 was used. However, both surfaces of the light diffusion sheet 1 are very easy to be charged and are not easily attenuated once charged. It was inferior to. Moreover, as a result of the total light transmittance and haze measurement, the light diffusing sheets 1 of Examples 1 to 4 exhibited the same total light transmittance and haze as the light diffusing sheets 1 of Comparative Examples 1 to 4.

Sectional drawing which shows one Example of the light-diffusion sheet of this invention. Sectional drawing which shows one Example of the light-diffusion sheet of this invention. Sectional drawing which shows one Example of the conventional light-diffusion sheet.

Explanation of symbols

1: Light diffusing sheet 2: Light diffusing layer 3: Antistatic layer 4: Base sheet 5: Backcoat layer 6: Light diffusing material 7: Anti-sticking material 8, 9: Binder

Claims (5)

A light diffusion sheet incorporated in a backlight unit for a liquid crystal display device, comprising: a base sheet; and a light diffusion layer laminated on at least one side of the base sheet; the base sheet and the light diffusion A charge acting between the layers to cancel the electric lines of force directed to the outside of the light diffusion sheet based on the charged charge by dielectric polarization and / or electrostatic induction with respect to the charge on the surface of the light diffusion sheet. A light diffusion sheet characterized by comprising a prevention layer. The light-diffusion sheet of Claim 1 provided with the backcoat layer which has a sticking prevention function in the surface opposite to the light-diffusion layer formation surface of a transparent base material sheet. The light diffusion sheet according to claim 2, wherein the back coat layer contains an antistatic agent. The light-diffusion sheet of Claim 2 provided with the said antistatic layer between the transparent base material sheet and the backcoat layer. The light diffusion sheet according to any one of claims 1 to 4, wherein the antistatic layer is a crosslinkable acrylic copolymer having a carboxyl group and a quaternary ammonium base at least in a side chain.

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