JP3703133B2 - Light diffusing sheet and optical element - Google Patents

Description

表１に示す通り、実施例の光拡散性シートは、ギラツキ防止効果、白ぼけ防止効果のいずれにも優れておりバランスがよい。一方、比較例の光拡散性シートは、ギラツキ防止効果、白ぼけ防止効果の両者の少なくとも一方を満足していない。なお、蛍光灯下における写り込み（防眩性）はいずれも良好であった。
【図面の簡単な説明】
【図１】全ヘイズ値の測定に供する光拡散性シートの断面図の一例である。
【図２】内部ヘイズ値の測定に供する光拡散性シートの断面図の一例である。
【図３】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
５：粘着剤層付透明シート[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. In addition, improvement of the glare is also demanded from the viewpoint of ergonomics such as easy eye fatigue.
[0004]
In order to improve the glare phenomenon, for example, a method has been proposed in which a large number of fine concavo-convex structures are continuously formed by means such as dispersing a large amount of fine particles in a resin film layer. According to this method, the antiglare effect is also increased. However, in this method, the surface reflection of external light occurs along with the improvement of glare, and a phenomenon called so-called white blur occurs, which causes the display screen to become whitish. In particular, white blurring appears remarkably during black display, causing problems such as a decrease in contrast of the screen display.
[0005]
For this reason, in the design of a light diffusive sheet used in a high-definition LCD, the surface diffusivity is controlled in order to achieve an anti-glare effect and an anti-blurring effect. For example, Japanese Patent Application Laid-Open No. 11-305010 describes that the surface haze value of a light diffusing sheet is 7 to 20% and the internal haze value is 1 to 15%. However, the light diffusive sheet having the internal haze value cannot exhibit a sufficient glare prevention effect. In addition, it is also described that the light diffusive sheet increases surface blur when the sum of the surface haze value and the internal haze value exceeds 30, and the surface haze value and the internal haze value are adjusted in the range. Even so, it has been difficult to provide an excellent antiglare effect and white blur prevention effect.
[0006]
[Problems to be solved by the invention]
The present invention is a light diffusive sheet that suppresses glare of the screen while maintaining anti-glare properties even when applied to a high-definition LCD, and has almost no white blur, and the light diffusable sheet. It aims at providing the optical element provided with.
[0007]
[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.
[0008]
That is, the present invention provides a light diffusing sheet in which a light diffusing layer composed of a resin film layer having a fine unevenness on the surface is formed on at least one surface of a transparent substrate. the following ratio of the internal haze value (internal haze value / total haze value) a 0.5 to 0.8, and Ri der total haze value is less than 50% 35%, the internal haze is 20-40% light diffusing sheet, characterized in der Rukoto relates.
Total haze value: haze value of the light diffusing sheet.
Internal haze value: A value obtained by subtracting 11% of the haze value from the haze value of a state in which a transparent sheet with an adhesive having a haze value of 11% is bonded to the surface of the fine concavo-convex shape of the light diffusing sheet.
[0009]
The light diffusing sheet of the present invention has a total haze value of 35% or more and 50% or less and a ratio (internal haze value / total haze value) of 0.5 or more and less than 1, thereby preventing glare and blurring. The light diffusing sheet has a good balance of prevention effects.
[0010]
If the total haze value is less than 35%, glare in the case of high definition cannot be suppressed. The total haze value is preferably 38% or more. On the other hand, when the total haze value increases, the transmittance decreases, and therefore the total haze value is preferably 42% or less.
[0011]
Further, when the ratio (internal haze value / total haze value) is less than 0.5, the ratio of the internal haze value is small and the glare in the case of high definition cannot be suppressed. The ratio (internal haze value / total haze value) is preferably 0.6 or more. On the other hand, when the ratio (internal haze value / total haze value) increases, the effect of preventing white blurring decreases, so the ratio (internal haze value / total haze value) is preferably 0.8 or less. The internal haze value is not particularly limited as long as it satisfies the above ratio in relation to the total haze value, but is generally about 20 to 40%, preferably 20 to 30%.
[0012]
In addition, as shown in FIG. 1, the total haze value is a haze value of a light diffusive sheet in which a light diffusing layer 4 composed of a resin film layer 2 having a fine concavo-convex shape is provided on at least one surface of a transparent substrate 1. It is. The internal haze value is 11 based on the haze value measured for the state in which the transparent sheet 5 with a pressure-sensitive adhesive layer (haze value 11%) is bonded to the fine uneven surface of the light diffusing sheet shown in FIG. It is the value which subtracted%. The type of the adhesive 5b and the transparent sheet 5a is not limited as long as the haze value of the adhesive-attached transparent sheet is 11%.
[0013]
In the light diffusing sheet, it is preferable that the resin film layer contains fine particles, and the uneven surface shape of the resin film layer is formed of fine particles. The fine particles contained in the resin film layer are preferably organic fine particles. Furthermore, it is preferable that the resin film layer is formed of an ultraviolet curable resin.
[0014]
By using fine particles, a resin film layer having a surface irregularity shape can be realized easily and reliably, and the adjustment of the haze value is easy. 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.
[0015]
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.
[0016]
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.
[0017]
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.
[0018]
The light diffusing sheet of the present invention can be used for various applications, for example, an optical element.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG.
FIG. 3 shows a light diffusing sheet in which a light diffusing layer 4 comprising 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. 3, 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.
[0020]
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.
[0021]
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.
[0022]
As long as the resin film layer 2 having a fine concavo-convex structure surface is formed on the transparent substrate 1, the formation method is not particularly limited, and an appropriate method can be adopted. For example, the surface of the film used for forming the resin film layer 2 is previously roughened by an appropriate method such as sand blasting, embossing roll, chemical etching, etc. A method of forming the surface of the material itself for forming the resin film layer 2 in a fine concavo-convex structure is exemplified. Further, there is a method in which a resin film layer is separately applied on the resin film layer 2 and a fine concavo-convex structure is imparted to the surface of the resin film layer by a transfer method using a mold or the like. Further, as shown in FIG. 3, there is a method in which fine concavo-convex structure is given by dispersing fine particles 3 in the resin film layer 2. These fine concavo-convex structure forming methods may be formed as a layer in which two or more methods are combined to combine the fine concavo-convex structure surfaces in different states. Among the methods for forming the resin film layer 2, a method of providing the resin film layer 2 containing the fine particles 3 in a dispersed manner is preferable from the viewpoint of the formability of the surface of the fine concavo-convex structure.
[0023]
Hereinafter, a method for providing the resin film layer 2 by dispersing the fine particles 3 will be described. As the resin for forming the resin film layer 2, fine particles 3 can be dispersed, and a resin having sufficient strength and transparency as a film after the resin film layer is formed can be used without particular limitation. 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.
[0024]
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.
[0025]
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.
[0026]
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 is 1 to 10 μm, preferably 2 to 5 μm.
[0027]
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.
[0028]
In order to set the haze value of the surface of the formed light diffusion layer 4 within the above range, the average particle diameter and the ratio of the fine particles 3 contained in the coating liquid and the thickness of the resin film layer 2 are appropriately adjusted.
[0029]
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 4 to 8 μm.
[0030]
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.
[0031]
Also, an optical element can be bonded to the transparent substrate 1 of the light diffusing sheet of FIG. 3 (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.
[0032]
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.
[0033]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0034]
Example 1
12 parts of polystyrene particles having an average particle diameter of 3.5 μm, 5 parts of benzophenone photopolymerization initiator, 2.5 parts of thixotropic agent (mica) with respect to 100 parts of acrylic urethane ultraviolet curable resin (urethane acrylate monomer) A coating solution of 40% by weight solid content mixed with a toluene solvent is applied onto a triacetyl cellulose film (thickness 80 μm), dried at 120 ° C. for 5 minutes, and then cured by ultraviolet irradiation to form a coating film. A light diffusing sheet having a resin film layer on the surface of a fine concavo-convex structure having a thickness of 7 μm was prepared.
[0035]
Example 2
In Example 1, a light diffusable sheet was produced in the same manner as in Example 1 except that the film thickness of the coating film formed on the triacetylcellulose film was changed to 6 μm.
[0036]
Example 3
In Example 1, a light diffusable sheet was produced in the same manner as in Example 1 except that the film thickness of the coating film formed on the triacetyl cellulose film was changed to 5 μm.
[0037]
Example 4
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.
[0038]
Comparative Example 1
In Example 1, a light diffusable sheet was produced in the same manner as in Example 1 except that the film thickness of the coating film formed on the triacetyl cellulose film was 3 μm.
[0039]
Comparative Example 2
In Example 1, the amount of polystyrene particles used was changed to 4 parts by weight, and a coating solution similar to that used in Example 1 was used except that a thixotropic agent was not used. A light diffusing sheet was produced in the same manner as in Example 1 except that the film thickness was 1 μm.
[0040]
Comparative Example 3
In Example 1, the amount of polystyrene particles used was changed to 8 parts by weight, and the same coating solution as in Example 1 was used except that no thixotropic agent was used. A light diffusing sheet was produced in the same manner as in Example 1 except that the film thickness was 1 μm.
[0041]
Comparative Example 4
In Example 1, the amount of polystyrene particles used was changed to 8 parts by weight, and the same coating solution as in Example 1 was used except that no thixotropic agent was used. A light diffusing sheet was produced in the same manner as in Example 1 except that the film thickness was 3 μm.
[0042]
The total haze value and the internal haze value of the light diffusing sheets obtained in Examples and Comparative Examples were measured, and the ratio (internal haze value / total haze value) was determined. In addition, the haze value of Example 4 is a value when the low refractive index layer is not provided. Further, the resulting light diffusive sheet was evaluated for glare and white blur. The results are shown in Table 1.
[0043]
(All haze values)
The haze value of the light diffusing sheet was measured according to JIS-K7105 using a haze meter manufactured by Suga Test Instruments Co., Ltd.
[0044]
(Internal haze value)
A haze value was measured on a surface of a fine concavo-convex shape of a light diffusive sheet with a pressure-sensitive adhesive polyethylene terephthalate film (haze value 11%) coated with an acrylic pressure-sensitive adhesive on one side. A value obtained by subtracting 11% from the value was defined as an internal haze value. The measurement of the haze value and the internal haze of the polyethylene terephthalate film with an adhesive is the same method as the measurement of the total haze value.
[0045]
(Glitter)
A sample obtained by adhering a light diffusing sheet to a polarizing plate (185 μm) that had not been surface-treated was bonded to a glass plate having a thickness of 1.1 mm. This sample was set on a lattice pattern placed on a backlight. A lattice pattern having an opening of 90 μm × 20 μm, a vertical line width of 20 μm, and a horizontal line width of 40 μm was used. The distance from the lattice pattern to the light diffusion layer was fixed at 1.3 mm, and the distance from the backlight to the lattice pattern was fixed at 1.5 mm. The glare state at that time was visually evaluated according to the following criteria.
[0046]
○: There is almost no glare.
Δ: A level where there is glare but there is no problem in practical use.
X: A level in which glare is severely problematic in practical use.
[0047]
(White blur)
A black tape was attached to the glass surface of the sample subjected to the glare evaluation, and evaluated under the following criteria visually from the direction of 30 ° from the vertical direction of the polarizing plate and 180 ° azimuth with respect to incident light under a fluorescent lamp. .
[0048]
○: There is almost no white blur.
Δ: A level at which there is white blur but there is no problem in practical use.
X: Level at which there is white blur and there is a problem in practical use.
[0049]
[Table 1]

As shown in Table 1, the light diffusing sheets of the examples are excellent in both the glare prevention effect and the white blurring prevention effect, and are well balanced. On the other hand, the light diffusing sheet of the comparative example does not satisfy at least one of the glare prevention effect and the white blur prevention effect. In addition, the reflection (antiglare property) under a fluorescent lamp was good.
[Brief description of the drawings]
FIG. 1 is an example of a cross-sectional view of a light diffusive sheet used for measurement of a total haze value.
FIG. 2 is an example of a cross-sectional view of a light diffusing sheet used for measuring an internal haze value.
FIG. 3 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 5: Transparent sheet with adhesive layer

Claims (7)

In a light diffusing sheet in which a light diffusing layer composed of a resin film layer having a fine concavo-convex shape is formed on at least one surface of a transparent substrate, the ratio of the following total haze value and the following internal haze value of the light diffusing sheet a is (internal haze value / total haze value) of 0.5 to 0.8, and the total haze value Ri der 50% 35% or more, wherein 20-40% der Rukoto internal haze A light diffusing sheet.
Total haze value: haze value of the light diffusing sheet.
Internal haze value: A value obtained by subtracting 11% of the haze value from the haze value of a state in which a transparent sheet with an adhesive having a haze value of 11% is bonded to the surface of the fine concavo-convex shape of the light diffusing sheet.   2. The light diffusing sheet according to claim 1, wherein the resin film layer contains fine particles, and the surface irregularity shape of the resin film layer is formed of fine particles.   The light diffusing sheet according to claim 2, wherein the fine particles are organic fine particles.   The light diffusive sheet according to claim 1, wherein the resin film layer is formed of an ultraviolet curable resin.   The light-diffusing sheet according to any one of claims 1 to 4, wherein the resin film layer has a thickness of 4 to 8 µm.   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 5. A light diffusing sheet.   An optical element, wherein the light diffusing sheet according to claim 1 is provided on one side or both sides of the optical element.

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