JP3698978B2 - Light diffusing sheet and optical element - Google Patents

Description

【図面の簡単な説明】
【図１】本発明の光拡散性シートの断面図の一例である。
【符号の説明】
１：透明基板
２：樹脂層
３：微粒子
４：光拡散層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light diffusing sheet used for suppressing a decrease in screen visibility in a liquid crystal display (LCD), EL, PDP, and the like, and an optical element provided with the light diffusing sheet.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image display device such as an LCD is hindered in visibility of an image due to reflection of indoor lighting such as a fluorescent lamp, sunlight from a window, and an operator's shadow on a display device surface. Therefore, on the display surface, in order to improve the visibility of the image, the surface reflection light is diffused, regular reflection of external light is suppressed, and reflection of the external environment can be prevented (having anti-glare property) A light diffusion layer having a concavo-convex structure is provided. As a method for forming the light diffusion layer, a method in which a resin film layer is formed by coating a resin in which fine particles are dispersed has become the mainstream because the structure can be easily refined and the productivity is good.
[0003]
However, in the case of a high-definition (for example, 100 ppi or more) LCD, when the light diffusion layer is mounted, glare (brightness intensity) that is thought to be caused by the fine uneven structure formed by the particles protruding on the surface of the light diffusion layer ) Occurs on the LCD surface, and there is a problem that visibility is lowered.
[0004]
In order to improve this glare phenomenon, if the surface of the fine concavo-convex structure is controlled, there will be a problem that the screen display contrast will be reduced due to so-called white blurring due to the surface scattering due to the improvement of glare and the image of the transmission image. There arises a problem that the sharpness is deteriorated. For example, Japanese Patent Application Laid-Open No. 11-326608 discloses a technique capable of preventing glare by setting the light diffusive sheet to a haze of 10% or more and less than 40% and an image sharpness of 50 or more. . However, this technology only has an anti-glare effect at 12.1 inch XGA (106 ppi), and if the panel has a higher definition and is 200 ppi or more (for example, 6 inch, XGA; 210 ppi), The glare problem has not been resolved.
[0005]
[Problems to be solved by the invention]
Even when applied to a high-definition LCD, the present invention suppresses the glare phenomenon of the screen while maintaining the antiglare property, and hardly has white blur and has a light diffusing layer with good image clarity. It is an object of the present invention to provide a diffusive sheet and further an optical element provided with the light diffusive sheet.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by a light diffusing sheet having the following characteristics, and have completed the present invention.
[0007]
That is, according to the present invention, a light diffusion layer comprising a resin film layer containing fine particles on the surface and having a fine concavo-convex shape formed on the surface is formed on at least one surface of a transparent substrate. In the light diffusing sheet, the average particle diameter of the fine particles is 2 to 10 μm, the haze value of the light diffusing sheet is 40% or more and 60% or less , and an optical comb having a width of 0.5 mm in JISK7105. It is related with the light diffusable sheet | seat characterized by the image clarity measured being 35-60 .
[0008]
The light diffusive sheet of the present invention has a haze value of 40% or more and an image definition of 35 or more, thereby suppressing glare and white blurring and ensuring image clarity. If the haze value is less than 40%, glare in the case of high definition cannot be suppressed. The haze value is preferably 40% or more. On the other hand, when the haze value is increased, the transmittance is decreased. Therefore, the haze value is preferably 60% or less. The haze value is particularly preferably 40 to 50%. Further, if the image clarity is less than 35, the transmitted image is blurred, so that the meaning is reduced when a high-definition LCD is used. The image clarity is preferably 40 or more, particularly preferably in the range of 40 to 60.
[0009]
In the light diffusing sheet, the fine particles contained in the resin film layer are preferably organic fine particles. The resin film layer is preferably formed of an ultraviolet curable resin. Furthermore, it is preferable that the resin film layer contains a thixotropic agent.
[0010]
By using fine particles, it is possible to easily and reliably realize a resin film layer having an uneven surface shape, and it is easy to adjust the haze value and image sharpness. In particular, when organic fine particles are used as the fine particles, it is effective for suppressing glare. In addition, the ultraviolet curable resin can efficiently form a resin film layer (light diffusion layer) by a simple processing operation by a curing treatment by ultraviolet irradiation. Furthermore, when the resin film layer is formed, a fine concavo-convex structure can be easily formed by protruding particles on the surface of the resin film layer (light diffusion layer) by containing a thixotropic agent.
[0011]
In the light diffusion sheet according to the present invention, a low refractive index layer having a refractive index lower than that of the resin film layer is provided on the uneven surface of the resin film layer of the light diffusing sheet. Sex sheet.
[0012]
The antireflective function can be imparted by the low refractive index layer, and the blurring of the screen due to the irregular reflection of the image surface of a display or the like can be effectively suppressed.
[0013]
Furthermore, the present invention relates to an optical element, wherein the light diffusing sheet is provided on one side or both sides of the optical element.
[0014]
The light diffusing sheet of the present invention can be used for various applications, for example, an optical element.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a light diffusing sheet in which a light diffusing layer 4 composed of a resin film layer 2 in which fine particles 3 are dispersed is formed on a transparent substrate 1, and the fine particles dispersed in the resin film layer 2. 3 forms an uneven shape on the surface of the light diffusion layer 4. In addition, in FIG. 1, although the case where the resin film layer 2 is one layer is shown, by separately forming a resin film layer containing fine particles between the resin film layer 2 and the transparent substrate 1, The light diffusion layer can also be formed by a plurality of resin film layers.
[0016]
Examples of the transparent substrate 1 include films made of transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Can be given. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, nylon and aromatic polyamides, etc. Examples thereof include films made of transparent polymers such as amide polymers. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Examples thereof include a film made of a transparent polymer such as a polymer, an epoxy-based polymer, and a blend of the aforementioned polymers. In particular, those having a small optical birefringence are preferably used.
[0017]
The thickness of the transparent substrate 1 can be appropriately determined, but is generally about 10 to 500 μm from the viewpoints of workability such as strength and handleability, and thin layer properties. 20-300 micrometers is especially preferable, and 30-200 micrometers is more preferable.
[0018]
The resin film layer 2 having a fine concavo-convex structure surface is formed on the transparent substrate 1 by a method of providing a fine concavo-convex structure by dispersing fine particles 3 in the resin film layer 2 as shown in FIG.
[0019]
The resin for forming the equivalent of the resin film layer 2 can be dispersed in fine particles 3, it has a sufficient strength as a film after the resin film layer formed can be used without particular limitation in a transparent. Examples of the resin include thermosetting resins, thermoplastic resins, ultraviolet curable resins, electron beam curable resins, and two-component mixed resins. An ultraviolet curable resin that can efficiently form a light diffusion layer by a processing operation is preferable.
[0020]
Examples of the ultraviolet curable resin include polyester-based, acrylic-based, urethane-based, amide-based, silicone-based, and epoxy-based resins, and include ultraviolet curable monomers, oligomers, polymers, and the like. The UV curable resin preferably used includes, for example, those having an ultraviolet polymerizable functional group, and in particular, those containing an acrylic monomer or oligomer having 2 or more, particularly 3 to 6 functional groups. . Further, an ultraviolet polymerization initiator is blended in the ultraviolet curable resin.
[0021]
For the ultraviolet curable resin (formation of the resin film layer 2), additives such as a leveling agent, a thixotropic agent, and an antistatic agent can be used. Use of a thixotropic agent is advantageous for the formation of protruding particles on the surface of the fine concavo-convex structure. Examples of the thixotropic agent include silica and mica of 0.1 μm or less. In general, the content of these additives is preferably about 1 to 15 parts by weight with respect to 100 parts by weight of the ultraviolet curable resin.
[0022]
As the fine particles 3, those having transparency such as various metal oxides, glass, and plastic can be used without particular limitation. For example, inorganic fine particles such as silica, alumina, titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, and antimony oxide, polymethyl methacrylate, polystyrene, polyurethane, acrylic-styrene copolymer, Examples thereof include crosslinked or uncrosslinked organic fine particles and silicone fine particles composed of various polymers such as benzoguanamine, melamine, and polycarbonate. These fine particles 3 can be used by appropriately selecting one kind or two or more kinds, but organic fine particles are preferred. The average particle diameter of the fine particles 2 to 10 [mu] m, preferably 2 to 5 [mu] m.
[0023]
The method for forming the resin film layer 2 containing the fine particles 3 is not particularly limited, and an appropriate method can be adopted. For example, a resin film layer in which a resin containing fine particles 3 (for example, an ultraviolet curable resin: a coating solution) is applied on the transparent substrate 1, dried, and cured to exhibit an uneven shape on the surface. 2 is performed. The coating solution is applied by an appropriate method such as phantom, die coater, casting, spin coating, phanten metalling, and gravure.
[0024]
In order to set the haze value and image sharpness of the surface of the formed light diffusion layer 4 within the above ranges, the average particle diameter of the fine particles 3 contained in the coating liquid, the ratio thereof, and the thickness of the resin film layer 2 are appropriately set. adjust.
[0025]
The ratio of the fine particles 3 contained in the coating liquid is not particularly limited, but it is 1 to 20 parts by weight, more preferably 5 to 15 parts by weight with respect to 100 parts by weight of the resin. Is preferable for satisfying. The thickness of the resin film layer 2 is not particularly limited, but is preferably about 1 to 10 μm, particularly 3 to 5 μm.
[0026]
A low refractive index layer having an antireflection function can be provided on the uneven surface of the resin film layer 2 that forms the light diffusion layer 4. The material of the low refractive index layer is not particularly limited as long as it has a refractive index lower than that of the resin film layer 2. For example, a low refractive index material such as fluorine-containing polysiloxane can be used. The thickness of the low refractive index layer is not particularly limited, but is preferably about 0.05 to 0.3 μm, particularly preferably 0.1 to 0.3 μm.
[0027]
Further, an optical element can be bonded to the transparent substrate 1 of the light diffusing sheet of FIG. 1 (not shown). Examples of the optical element include a polarizing plate, a retardation plate, an elliptical polarizing plate, a polarizing plate with optical compensation, and the like, and these can be used as a laminate. The optical element can be bonded through an appropriate adhesive layer having excellent transparency and weather resistance, such as an acrylic, rubber-based, or silicone-based pressure-sensitive adhesive, or a hot-melt adhesive, if necessary.
[0028]
As the polarizing plate, a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer-based partially saponified film, or the like, which is stretched by adsorbing iodine, dye or the like, polyvinyl Examples thereof include polarizing films such as a dehydrated product of alcohol and a dehydrochlorinated product of polyvinyl chloride. Examples of the retardation plate include a uniaxial or biaxially stretched film of a polymer film exemplified for the transparent substrate and a liquid crystal polymer film. The retardation film may be formed as a superposed body of two or more stretched films. The elliptically polarizing plate and the polarizing plate with optical compensation can be formed by laminating a polarizing plate and a retardation plate. The elliptically polarizing plate and the polarizing plate with optical compensation have a light diffusion layer formed on the surface on the polarizing plate side.
[0029]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0030]
Example 1
100 parts by weight of an acrylic UV curable resin (urethane acrylate monomer), 15 parts by weight of polystyrene beads having an average particle size of 3 μm, 3 parts by weight of a thixotropic agent (mica) and a photopolymerization initiator (trade name: Irgacure 907) , Manufactured by Ciba Specialty Chemicals Co., Ltd.) 3 parts by weight was mixed with toluene, and a coating solution adjusted to 50% by weight was applied onto a triacetyl cellulose film (thickness 80 μm) and dried at 120 ° C. for 5 minutes. Thereafter, a light diffusive sheet having a resin film layer on the surface of a fine concavo-convex structure having a thickness of about 5 μm was prepared by curing with ultraviolet irradiation.
[0031]
Example 2
In Example 1, a light-diffusing sheet was produced in the same manner as in Example 1 except that 15 parts by weight of melamine beads having an average particle diameter of 3 μm were used as the fine particles.
[0032]
Example 3
In Example 1, a low refractive index layer having a refractive index lower than the refractive index (1.52) of the resin film layer (LR-202 of Nissan Chemical Co., Ltd. is used as a material) on the uneven surface of the resin film layer. , Refractive index: 1.39) A light diffusing sheet was produced in the same manner as in Example 1 except that 0.1 μm was provided.
[0033]
Comparative Example 1
In Example 1, a light diffusing sheet was produced in the same manner as in Example 1 except that 15 parts by weight of silica beads having an average particle diameter of 3.5 μm were used as the fine particles.
[0034]
Comparative Example 2
In Example 1, a light diffusable sheet was produced in the same manner as in Example 1 except that 1.5 parts by weight of melamine beads having an average particle diameter of 3 μm were used as the fine particles.
[0035]
Comparative Example 3
In Example 1, a light-diffusing sheet was produced in the same manner as in Example 1 except that 20 parts by weight of silicone particles having an average particle diameter of 3 μm were used as the fine particles.
[0036]
The haze value and image sharpness of the light diffusive sheets obtained in Examples and Comparative Examples were measured. In addition, about Example 3, it is a value when the low refractive index layer is not provided. The results are shown in Table 1.
[0037]
(Haze)
According to JIS-K7105, it measured using the haze meter (Tokyo Denshoku Industries model TC-H3DP).
[0038]
(Image clarity)
In accordance with JIS K7105, measurement was performed with an optical comb having a width of 0.5 mm using an image clarity measuring device manufactured by Suga Test Instruments.
[0039]
A mask pattern (pattern corresponding to 6-inch XGA) obtained by adhering a polarizing plate (185 μm) to the light diffusing sheet obtained in the above-mentioned examples and comparative examples, and adhering it to a glass substrate and fixing it on a light table. (210ppi)) The degree of glare (glare) was visually evaluated according to the following criteria. Moreover, a black tape was affixed to the surface opposite to the polarizing plate adhesion surface of the glass substrate, and white blur was visually evaluated according to the following criteria. Moreover, the paper which printed the character on the said glass substrate was set | placed, and the clarity at the time of seeing this character was evaluated by the following references | standards. The evaluation results are shown in Table 1. In addition, the reflection (antiglare property) under a fluorescent lamp was good.
[0040]
For the evaluation of glare, white blur, and clarity, 10 people visually evaluated.
Good: Impressive for each characteristic,
Normal: Does not feel the effect on actual use for each characteristic,
Defect: Judged by feeling the actual use effect on each characteristic,
◎: 9 or more people are good,
○: 5 or more people are good
X: Three or more people evaluated it as bad.
[0041]
[Table 1]

[Brief description of the drawings]
FIG. 1 is an example of a cross-sectional view of a light diffusing sheet of the present invention.
[Explanation of symbols]
1: Transparent substrate 2: Resin layer 3: Fine particles 4: Light diffusion layer

Claims (7)

In a light diffusive sheet, on which at least one surface of a transparent substrate is a resin film layer containing fine particles, and a light diffusion layer comprising a resin film layer having fine irregularities formed on the surface is formed by fine particles. The average particle diameter of the fine particles is 2 to 10 μm, the haze value of the light diffusable sheet is 40% or more and 60% or less , and the image clarity measured with an optical comb having a width of 0.5 mm in JISK7105. A light diffusive sheet, which is 35 to 60 .   2. The light diffusing sheet according to claim 1, wherein the fine particles are organic fine particles.   3. The light diffusing sheet according to claim 1, wherein the resin film layer is formed of an ultraviolet curable resin.   The light diffusable sheet according to claim 1, wherein the resin film layer contains a thixotropic agent.   A low refractive index layer having a refractive index lower than the refractive index of the resin film layer is provided on the uneven surface of the resin film layer of the light diffusing sheet according to any one of claims 1 to 4. A light diffusing sheet.   An optical element, wherein the light diffusive sheet according to claim 1 is provided on one side or both sides of the optical element.   An image display device comprising the light diffusing sheet according to claim 1 or the optical element according to claim 6.

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