JP3485612B2 - Light diffusion film - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing film. Specifically, the present invention comprises laminating a transparent layer (2) on one surface of a transparent resin film (1), and laminating a transparent resin layer (3) on another surface of the transparent resin film (1); Further, the present invention relates to a light diffusion film having a light diffusion layer (4) made of a resin containing plastic beads laminated on the upper surface thereof. The light diffusion film of the present invention has low light reflection and absorption, and has high light transmittance and light diffusion efficiency. Therefore, it is suitable for use in a word processor, a personal computer, a liquid crystal display device such as a liquid crystal television, a projector type display, and the like. 2. Description of the Related Art In recent years, liquid crystal display devices have been used in various fields due to their features of being thin and power-saving, and in particular, have been widely used in the electronic industry such as word processors, personal computers, and televisions. In this liquid crystal display device, there are a liquid crystal display device in which a light source is disposed behind a liquid crystal portion and a liquid crystal display device in which a light source is disposed on a side surface of a light guide plate as shown in FIG. In order to take advantage of the characteristics of the thin shape, those arranged on the side surface have been frequently used. Since the brightness decreases as the distance from the light source increases, a light diffusion film is used in front of the backlight to obtain a uniform screen display. The light diffusion film must have high light transmittance and high diffusion efficiency in order to efficiently use light emitted from the light source and obtain a uniform and bright screen. In recent years, liquid crystal display devices have tended to be colored and have large screens. In order to supply a large amount of light uniformly to the liquid crystal portion, a light diffusion film having high light transmittance and high diffusion efficiency has been required. ing. Conventionally, a light diffusion film having fine irregularities on its surface, or a light diffusion film having a light diffusing substance on its surface or inside has been devised. JP-A-3-85586 proposes a plastic film having a large number of conical projections on the surface as an example of providing the surface with irregularities. When the light source is placed directly behind the liquid crystal part, uniform bright light can be obtained by using this diffusion film. However, when the light source is placed beside the light guide plate, when light enters the conical protrusion from the lateral direction, both the light transmittance and the light diffusion efficiency deteriorate, so that a bright uniform screen cannot be obtained. Examples of the light-scattering substance provided therein include a light-diffusing resin composition comprising a polycarbonate resin and titanium oxide-containing fine particles of styrene-cyclohexylmaleimide cross-linked as described in JP-A-4-161448.
And a resin film in which silicon spherical particles are dispersed as described in JP-A-1-172801. However, titanium oxide-containing styrene-cyclohexylmaleimide crosslinked fine particles have high concealing properties, and silicon spherical particles themselves reflect light, so that
In both cases, the light diffusion efficiency is high, but the light transmission efficiency is low. However, when incorporated in a liquid crystal display device, a bright screen cannot be obtained. As a result, both were insufficient to respond to such a request. SUMMARY OF THE INVENTION An object of the present invention is to solve these problems, to greatly improve the light transmittance as compared with a conventional light diffusion film, and to increase the light diffusion efficiency. An object of the present invention is to provide an excellent light-diffusing film capable of obtaining a high brightness and uniform screen when incorporated in a liquid crystal display device. Means for Solving the Problems As a result of intensive studies, the present inventors have laminated a transparent layer (2) made of an inorganic substance or an organic substance on one surface of a transparent resin film (1). If the transparent resin layer (3) is laminated on the other surface of the transparent resin film (1), especially when the light refractive index of the transparent layer (2) is smaller than the transparent resin film (1), the transparent resin film (1) ), The light transmittance was found to be much higher than in the case of only the laminate of the transparent resin (3). Further, by further laminating a light diffusion layer (4) composed of a mixed layer of plastic beads and a transparent resin, both the light diffusion efficiency and the light transmittance become extremely high, and the synergistic effect of each layer results in a liquid crystal display device. The present invention was found to be an excellent light-diffusing film capable of obtaining a high-intensity and uniform screen when incorporated in the present invention, and completed the present invention. That is, the gist of the present invention is that a transparent layer (2) is laminated on one surface of a transparent resin film (1), and a transparent resin layer (3) is formed on another surface of the transparent resin film (1). was laminated, further light diffusing fill light diffusing layer (4) laminated comprising a mixed layer of plastic beads and a transparent resin on the upper surface
And the light refractive index n 2 of the transparent layer (2) is
Smaller than the optical refractive index n 1 of the fat film (1), a transparent resin
Light refraction index of layer (3) and light refraction of transparent resin film (1)
The rate is expressed by the following equation (1) [ Equation 2] ( Where n 1 is the light refractive index of the transparent resin film (1)
N 3 indicates the light refractive index of the transparent resin layer (3)).
It is a light diffusion film characterized by the following. The transparent resin film used in the present invention (1)
Examples thereof include homopolymers such as polyethylene terephthalate, polyether sulfone, polyester, poly (meth) acrylate, polymethyl methacrylate, polycarbonate, polyamide, and polyvinyl chloride, or monomers of these resins and copolymerizable monomers. A film made of a copolymer or the like can be mentioned, and can be appropriately selected and used. The thickness of the transparent resin film (1) is not particularly limited, but is preferably 20 to 500 μm from the viewpoint of handling properties. The transparent layer (2) includes a transparent inorganic layer and an organic layer. Examples of the transparent inorganic layer include silicon oxide and calcium fluoride when polyethylene terephthalate is used for the transparent resin film (1).
The method for laminating these inorganic layers is not particularly limited, but includes a vacuum deposition method, a sputtering method, an ion plating method, an ion beam assisted deposition method, a vacuum processing method such as an ion cluster beam method, or a reverse roll coater method, Known methods such as a gravure coater method, a bar coater method, a die coater method, a comma coater method, and a coating method such as a spray method are exemplified. The thickness of the transparent inorganic layer depends on the inorganic substance used, but is not particularly limited as long as it is transparent and has good handleability. For example, in the case of calcium fluoride, it is preferably about 150 μm, which is １ ／ of the wavelength of light. As the organic layer used for the transparent layer (2), for example, when polyethylene terephthalate is used as the transparent resin film (1), an organic silicon compound such as alkyl silicon, alkyl silane, siloxane, etc. Acrylates such as ethyl acrylate, methacrylate resins, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl acetate,
A transparent resin such as silicon is used. The method for forming the transparent layer (2) is not particularly limited. When a liquid material is applied, for example, a reverse roll coater method, a gravure coater method, a bar coater method, a die coater method, a comma coater method, a sprayer Coating methods such as
Known coating methods can be used. The thickness of the transparent organic layer is not particularly limited, but is preferably 1 to 50 μm in terms of productivity and handling. As the transparent resin used for the transparent resin layer (3), for example, when polyethylene terephthalate is used as the transparent resin film (1), acrylate such as polybutyl acrylate and polyethyl acrylate, methacrylate resin, polypropylene, polystyrene, polyvinyl Resins such as alcohol and polyvinyl acetate are exemplified. The method for forming the transparent resin layer (3) is not particularly limited, but when a liquid resin is applied, for example, a reverse roll coater method, a gravure coater method, a bar coater method, a die coater method, a comma coater method, or the like. Or a known coating method such as a spray coating method. The thickness of the transparent resin layer (3) is not particularly limited, but may be 1 to 5 in terms of productivity and handling.
0 μm is preferred. It is preferable that the light refractive index n ₂ of the transparent layer (2) is smaller than the light refractive index n _{1 of the} transparent resin film (1). Further, the light refractive index n of the transparent resin film (1)
The relationship between ₁ and the light refractive index n ₃ of the transparent resin layer (3) is | n ₁
−n ₃ | ≦ 0.25, preferably | n ₁ −n
More preferably, ₃ | ≦ 0.22. When the light refractive index of the transparent layer (2) is smaller than the light refractive index of the transparent resin film (1), and the light refractive indices of the transparent resin layer (3) and the transparent resin film (1) satisfy the above formula, air Interface between layer and transparent layer (2), interface between transparent layer (2) and transparent resin film (1), interface between transparent resin film (1) and transparent resin layer (3), transparent resin layer (3) and plastic beads Since the scattering and reflection of light at the interface of the mixed layer (4) of the transparent resin and the transparent resin are reduced, the light transmittance is remarkably improved by forming a plurality of these layers. Films usually used as a base material of a light diffusion film, such as polyethylene terephthalate, have a light refraction index of about 1.6 compared to air, so that reflection at the interface with the air layer is very large, The presence of the transparent layer (2) is very effective in improving the light transmittance. If the light transmittance can be increased by as much as 1%, it becomes considerably brighter when incorporated in a liquid crystal display device, so that a light diffusion film capable of obtaining a screen with high luminance can be obtained. Examples of the plastic beads include beads made of homopolymers such as polypropylene, polyvinylidene chloride, polyacrylonitrile, and polymethyl methacrylate, or copolymers of monomers of these resins with copolymerizable monomers. Any of these can be appropriately selected and used. The average particle size of the plastic beads is preferably 5 to 50 μm, and 10 to 3 μm.
0 μm is more preferred. When the average particle size of the plastic beads is in the above range, light scattering by the plastic beads is effectively performed, so that the layer has a high light diffusing ability. Examples of the resin mixed with the plastic beads include, for example, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, acrylic resin, polyester resin, styrene resin, alkyd resin, amino resin, polyurethane resin, epoxy resin, and the like. Can be selected and used. Also, the transparent layer used above,
It may be the same as the resin of the transparent resin layer. The shape of the resin is preferably an emulsion type, a dispersion type, a solvent type or the like, but any type can be used as long as it can be applied. Examples of the method for forming the light diffusion layer (4) made of a mixture of a resin and plastic beads include known coating methods such as a reverse roll coater method, a gravure coater method, a bar coater method, a die coater method, and a comma coater method. . The thickness of the light diffusion layer (4) is preferably larger than the average particle size of the plastic beads and smaller than twice the average particle size of the plastic beads. When the thickness is in this range, a coating film in which plastic beads are densely arranged in one layer can be obtained, and a light diffusion film having good light transmittance and high light diffusion can be obtained. Hereinafter, the present invention will be described in detail with reference to examples. In addition, the measured value in an Example was based on the following method. Light refraction index Abbe refractometer (4T manufactured by Atago Co., Ltd.)
Was measured using a sodium light source. The light refractive index of the transparent resin film was measured by itself, and the light refractive index of the transparent layer and the transparent resin layer was determined by measuring the light refractive index of the coated surface after coating on the polyethylene terephthalate film. It was placed at the position of the light diffusion film of a backlight device of a brightness light guide plate type (manufactured by NEC Corporation), and the brightness on the light guide plate was measured using a brightness meter LS-110 (manufactured by Minolta Camera Co., Ltd.). . Light transmittance and haze (HAZE ) were measured using NDH-300A (manufactured by Nippon Denshoku Co., Ltd.). Example 1 Silicone oil emulsion (Dow Corning Toray)
SH7028 manufactured by Silicone Co., Ltd .: light refractive index 1.4
1) was converted to a 100 μm-thick polyethylene terephthalate film (Emblet T-100 manufactured by Unitika Ltd.):
One side of the transparent resin film (1) having a light refractive index of 1.66) was applied by a Mayer bar coating method and dried at 120 ° C. for 5 minutes to obtain a transparent layer (2) having a thickness of 1 μm. Solid content 4
0% aqueous dispersion type acrylic emulsion (Mitsui Toatsu Chemical Co., Ltd., Turtac BH-3: light refractive index 1.53)
Was applied to the surface of the polyethylene terephthalate film opposite to the transparent layer by a Meyer bar coating method and dried at 120 ° C. for 2 minutes to obtain a transparent resin layer (3) having a thickness of 20 μm. On this transparent resin layer, 90% by weight of polymethyl methacrylate beads in dry matter (manufactured by Sekisui Chemical Co., Ltd.)
MBX-20) and an aqueous solution of polyvinyl alcohol (Gohsenol KH-17, manufactured by Nippon Synthetic Chemical Co., Ltd.) was applied by a reverse coating method, and dried at 120 ° C. for 2 minutes.
A light diffusion layer (4) having a thickness of 20 μm was obtained. The luminance, light transmittance, and haze of the light diffusion film obtained as described above were measured. Table 1 shows the results. Example 2 Light diffusion was performed in the same manner as in Example 1 except that the transparent resin film (1) used was a polycarbonate film having a thickness of 100 μm (manufactured by Teijin Limited, Panlite: light refractive index: 1.59). A film was obtained. Table 1 shows the measurement results of the brightness, light transmittance, and haze of the light diffusion film. Example 3 One side of a 100 μm thick polyethylene terephthalate film used in Example 1 with an aqueous solution of polyvinyl alcohol (Gosenol KH-17, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., light refractive index: 1.51) was used. And dried at 120 ° C. for 2 minutes to obtain a light diffusion film in the same manner as in Example 1, except that a transparent layer (2) having a film thickness of 10 μm was obtained. Table 1 shows the results of measuring the luminance, light transmittance and haze of this light diffusion film in the same manner as in Example 1.
Shown in Example 4 A transparent layer (2) of a 100 μm-thick polyethylene terephthalate film used in Example 1 with an ethanol solution of polyvinyl acetate having a solid content of 45% (produced by Wako Pure Chemical Industries, Ltd .; light refractive index: 1.47) ) Is applied by the Meyer bar coating method and dried at 120 ° C. for 2 minutes to form a film having a thickness of 20 μm.
A light diffusing film was obtained in the same manner as in Example 1 except that m of the transparent resin layer (3) was obtained. Table 1 shows the results of measuring the luminance, light transmittance, and haze of this light diffusion film in the same manner as in Example 1. Comparative Example 1 A water-dispersed acrylic emulsion was applied to one side of a 100 μm-thick polyethylene terephthalate film in the same manner as in Example 1 by a Meyer bar coating method.
After drying at 0 ° C. for 2 minutes, a transparent resin layer (3) having a thickness of 20 μm was obtained. An aqueous solution of polyvinyl alcohol containing 90% by weight of polymethyl methacrylate beads in a dry matter was applied on the transparent resin layer by a reverse coating method.
After drying at 20 ° C. for 2 minutes, a light diffusion layer (4) having a thickness of 20 μm
Got. The luminance, light transmittance, and haze of the light diffusion film obtained as described above were measured. Table 1 shows the results. Comparative Example 2 A silicone oil emulsion was prepared in the same manner as in Example 1.
One side of a 100 μm-thick polyethylene terephthalate film is applied by a Mayer bar coating method,
For 5 minutes to obtain a transparent layer (2) having a thickness of 1 μm.
On this transparent resin layer, a polyvinyl alcohol aqueous solution containing 90% by weight of polymethyl methacrylate beads in a dry matter is applied by a reverse coating method, and dried at 120 ° C. for 2 minutes to form a 20 μm-thick light diffusion layer (4). Obtained. The luminance, light transmittance, and haze of the light diffusion film obtained as described above were measured. Table 1 shows the results. Comparative Example 3 An aqueous polyvinyl alcohol solution containing 90% by weight of polymethyl methacrylate beads in a dry matter was applied to one surface of the polyethylene terephthalate film used in Example 1 by a reverse coating method, and dried at 120 ° C. for 2 minutes. Thus, a light diffusion layer (4) having a thickness of 20 μm was obtained. The luminance, light transmittance, and haze of the light diffusion film obtained as described above were measured. Table 1 shows the results. Comparative Example 4 100 parts by weight of N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd.) and polyether sulfone powder (BASF, Inc.) were used on one side of the 100 μm thick polycarbonate film used in Example 2. ), ULTRAS
ONE2010: light refractive index 1.65) A solution in which 30 parts by weight was dissolved was applied to a thickness of 10 μm by a die coater method, and dried at 130 ° C. for 20 minutes to obtain a transparent layer.
A light diffusion film was obtained in the same manner as in Example 2. Table 1 shows the results of measuring the luminance, light transmittance, and haze of the obtained light diffusion film. Comparative Example 5 Chlorotrifluoroethylene having a solid content of 30% (produced by Daikin Industries, Ltd., having a light refractive index of 1.38) was formed on the opposite side of the transparent layer of the polyethylene terephthalate film having a thickness of 100 μm used in Example 1. ) Aqueous dispersion solution was applied by a Meyer bar coating method,
A light-diffusing film was obtained in the same manner as in Example 1, except that the transparent resin layer was obtained by drying for a minute. Table 1 shows the results of measuring the luminance, light transmittance, and haze of the obtained light diffusion film. [Table 1] The numbers in parentheses below the resin names of the transparent resin film (1), the transparent layer (2), and the transparent resin layer (3) all represent the light refractive index. * 1: PET: polyethylene terephthalate PC: polycarbonate * 2: silicone: silicone oil emulsion PVA: polyvinyl alcohol PES: polyether sulfone * 3: acrylic: acrylic emulsion PVAc: polyvinyl acetate The light-diffusing film of the present invention is a light-diffusing film having less light reflection and absorption, higher light-diffusing efficiency and higher light transmittance than conventional light-diffusing films, and is uniform when used in a backlight of a liquid crystal display device or the like. Thus, a backlight with which a high-luminance screen is obtained can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of one embodiment of the light diffusion film of the present invention. FIG. 2 is a schematic view of an example of a backlight for a liquid crystal display device in which a light source unit is placed beside a transparent light guide plate. [Description of Signs] (1) Transparent resin film (2) Transparent layer (3) Transparent resin layer (4) Light diffusion layer (5) Light source section (6) Light reflecting plate for lamp house (7) Light guide plate (8) Diffusion film (9) Light reflection film for backlight

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masato Koyama 2-1-1 Tango-dori, Minami-ku, Nagoya-shi, Aichi Pref. No. 1 Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Yoshihiro Sakai 2-1-1 Tango-dori, Minami-ku, Nagoya-shi, Aichi Prefecture Mitsui Toatsu Chemical Co., Ltd. (56) References JP-A 1-292064 (JP, A JP-A-7-27904 (JP, A) JP-A-50-96226 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/02 G02F 1/1335

Claims (1)

(57) [Claim 1] A transparent layer (2) is laminated on one surface of a transparent resin film (1), and a transparent resin is formed on another surface of the transparent resin film (1). A light diffusion film in which a layer (3) is laminated and a light diffusion layer (4) composed of a mixed layer of plastic beads and a transparent resin is further laminated on the upper surface thereof;
The light refractive index n 2 of (2) is the light bending of the transparent resin film (1).
The refractive index is smaller than the refractive index n 1 ,
The light refractive index of the bright resin film (1) is expressed by the following equation (1).
[Equation 1] [Equation 1] ( Where n 1 is the light refractive index of the transparent resin film (1)
N 3 indicates the light refractive index of the transparent resin layer (3)).
A light diffusion film characterized by being useful .