Anisotropic light-diffusing adhesive layer and display device having an anisotropic light-diffusing adhesive layer

Abstract

[The technical problem to be solved] The objective of this invention is to provide an anisotropic light-diffusing adhesive layer with excellent viewing angle magnification. Technical means to solve the problem The solution of the present invention is an anisotropic light-diffusing adhesive layer containing an adhesive and needle-shaped fillers. The needle-shaped fillers are aligned and dispersed in one direction within the anisotropic light-diffusing adhesive layer. When the anisotropic light-diffusing adhesive layer is deposited between two polarizing plates with absorption axes 90° apart, such that the absorption axis of one polarizing plate is parallel to the alignment axis of the needle-shaped fillers, the degree of alignment shown as [(total transmittance emitted from another polarizing plate having an absorption axis that is not parallel to the alignment direction of the needle-shaped fillers in the anisotropic light-diffusing adhesive layer) / (weight ratio of needle-shaped fillers in the anisotropic light-diffusing adhesive layer)] is 30% or less.

Description

[Technical Field]

[0001] The present invention relates to an anisotropic light-diffusing adhesive layer and a display device having an anisotropic light-diffusing adhesive layer. [Previous Technology]

[0002] In recent years, anisotropic light diffusion elements have been proposed for light diffusion elements used in liquid crystal display devices, in which the transmitted light is not isotropic but deflected in a specific direction and diffuses.

[0002] For example, Patent Document 1 discloses an anisotropic light-diffusing adhesive laminate, which contains at least one adhesive layer containing needle-like fillers dispersed in an adhesive in a manner that is roughly aligned in the same direction, and the adhesive layer has two or more layers. According to this anisotropic light-diffusing adhesive laminate, when a straight light is incident perpendicularly on the anisotropic light-diffusing adhesive laminate, the projected image of the transmitted light will become an elliptical shape extending in a direction orthogonal to the long axis of the needle-like fillers.

[0002] [Previous Technical Documents]

[0002] [Patent Documents]

[0003] Patent Document 1: Japanese Patent Application Publication No. 2004-258105.

[0004] The aforementioned anisotropic light-diffusing adhesive laminate can have both anisotropic light-diffusing and adhesive functions, and is therefore a usable technology.

[0005] However, with the diversification of applications of liquid crystal display devices, there is a demand for anisotropic light diffusion elements that further enhance the viewing angle magnification effect.

[0006] Therefore, the objective of the present invention is to provide an anisotropic light-diffusing adhesive layer with excellent viewing angle magnification.

[0007] Through in-depth research, the inventors discovered that the above-mentioned problems can be solved by making the anisotropic light-diffusing adhesive layer satisfy specific physical properties, thereby completing the present invention.

[0008] This invention relates to an anisotropic light-diffusing adhesive layer, which contains an adhesive and needle-like fillers.

[0008] The aforementioned needle-shaped filler is aligned and dispersed in one direction within the aforementioned anisotropic light-diffusing adhesive layer.

[0008] When the aforementioned anisotropic light-diffusing adhesive layer is deposited between two polarizing plates whose absorption axes differ from each other by 90°, with the absorption axis of one polarizing plate parallel to the alignment axis of the aforementioned needle-shaped filler, the alignment degree shown in the following formula (1) is 30% or less.

[0008] Orientation degree = (total transmittance emitted from another polarizing plate having an absorption axis that is not parallel to the orientation direction of the needle-like filler in the anisotropic light-diffusing adhesive layer) / (content ratio of needle-like filler in the anisotropic light-diffusing adhesive layer)...(1)

[0009] Preferably, the short diameter of the aforementioned needle-shaped filler is 0.1 μm to 20 μm and the long diameter is 2 μm to 5000 μm.

[0009] Preferably, the aforementioned adhesive is an adhesive made of acrylic resin, wherein the aforementioned acrylic resin is composed of a copolymer containing (meth)acrylate monomers having aromatic rings.

[0009] Preferably, the absolute value of the difference between the refractive index of the aforementioned needle-shaped filler in the long axis direction and the refractive index of the aforementioned acrylic resin is 0.07 or less.

[0009] Preferably, the weight average molecular weight of the aforementioned adhesive is 200,000 to 1,000,000.

[0009] The thickness of the anisotropic light-diffusing adhesive layer is preferably 5 μm to 100 μm.

[0010] Furthermore, the present invention is a display device in which the aforementioned anisotropic light-diffusing adhesive layer is deposited on a polarizing plate of a liquid crystal display device in such a way that the alignment axis of the needle-shaped filler in the aforementioned anisotropic light-diffusing adhesive layer is parallel to the absorption axis of the aforementioned upper polarizing plate.

[0011] According to the present invention, an anisotropic light-diffusing adhesive layer with excellent viewing angle magnification can be provided. [Simplified Explanation of the Diagram]

[0012] Figure 1 is a graph showing the relationship between the contrast of the front and the 60° direction in an embodiment of the present invention.

Implementation Method

[0013] The anisotropic light-diffusing adhesive layer of the present invention will be specifically described below, but the present invention is not limited to the following description. Furthermore, the present invention is not only anisotropic light-diffusing adhesive layer, but also an adhesive coating for obtaining anisotropic light-diffusing adhesive layer, a display device applying the anisotropic light-diffusing adhesive layer, or a manufacturing method thereof. Furthermore, the present invention can also be a laminate containing the anisotropic light-diffusing adhesive layer of the present invention and other specific layers (substrate or other adhesive layers).

[0014] In the following description, when an upper limit value and a lower limit value are individually recorded, they shall be regarded as all combinations of the upper limit value and the lower limit value recorded in this specification.

[0015] In the following description, the anisotropic light-diffusing adhesive layer is sometimes referred to simply as the "adhesive layer".

[0016] <<<Composition of Anisotropic Light-Diffusing Adhesive Layer>>>

[0016] The anisotropic light-diffusing adhesive layer contains an adhesive and needle-like fillers. Furthermore, the anisotropic light-diffusing adhesive layer may contain other components.

[0017] <<Ingredients>>

[0017] <Adhesive>

[0017] There are no particular limitations on the adhesive. However, when used in liquid crystal display devices, it is preferable to meet the following necessary conditions: (a) high optical transparency; (b) a refractive index close to that of the adjacent substrate (e.g., a TAC film, which is a protective film for a polarizing plate) during lamination; (c) proven high reliability as an adhesive for polarizing elements; and (d) low cost. Examples of adhesives that meet these necessary conditions include adhesives made of acrylic resin (acrylic resin-containing adhesives / acrylic adhesives).

[0018] The main components of acrylic adhesives may include homopolymers or copolymers of acrylic acid monomers such as acrylic acid and its esters, methacrylic acid and its esters, acrylamide, and acrylonitrile, or copolymers of at least one of the acrylic acid monomers with vinyl acetate, maleic anhydride, styrene, etc.

[0018] Also, monomers with aromatic rings may be used.

[0019] For example, acrylic adhesives are preferably copolymers composed of monomers such as ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, and monomers with aromatic rings such as 2-phenoxyethyl acrylate. Furthermore, the monomers are preferably monomers containing functional groups, such as acrylic acid, methacrylic acid, itconic acid, maleic anhydride, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, hydroxymethylacrylamide, and glycidyl methacrylate.

[0020] Furthermore, acrylic adhesives can also be made by adding photopolymerization initiators to oligomers with acrylamide groups at the ends or side chains and acrylic monomers, and then making the coating layer adhesive by irradiation with ultraviolet light after being coated on a substrate.

[0021] The weight-average molecular weight (Mw) of the adhesive is not particularly limited within a range that does not impede the effects of the present invention; for example, it is preferably between 200,000 and 1,000,000. By achieving a weight-average molecular weight within this range, an adhesive with good hardness and resistance to peeling can be obtained. The weight-average molecular weight can be determined using known methods, such as by the method according to JIS K 7252-1:2008 "Determination of the average molecular weight and molecular weight distribution of polymers by plastic-size exclusion chromatography".

[0022] The refractive index of the adhesive is preferably 1.48 to 1.58. The refractive index of the adhesive can be determined by method A as described in JIS K-7142 (1996).

[0023] The glass transition temperature (Tg) of the adhesive is preferably -50°C to -10°C, and more preferably -40°C to -30°C. By maintaining the Tg within this range, the adhesive can achieve higher hardness and improve adhesion to the polarizer surface of the display device. This results in an adhesive that is less prone to swelling or peeling. The Tg can be determined using known methods, such as the method according to JIS K 7121-1987 "Method for Determining the Glass Transition Temperature of Plastics".

[0024] (Cross-linking agent)

[0024] The adhesive of the present invention can be further cross-linked using a cross-linking agent to adjust the gel fraction appropriately. The cross-linking agent is not particularly limited as long as it does not hinder the effect of the present invention; for example, isocyanate-based cross-linking agents, aziridine-based cross-linking agents, epoxy-based cross-linking agents, metal chelate-type cross-linking agents, etc., can be used. These can be used alone or in combination. Among these, isocyanate-based cross-linking agents have suitable reactivity, which is preferred from a production point of view.

[0025] Isocyanate-based crosslinking agents are not particularly limited to any extent that they do not impede the effects of the present invention. Examples include aromatic polyisocyanates such as toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), naphthalene diisocyanate, xylene diisocyanate, and polymeric polyisocyanate (crude MDI); aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanate, and dicyclohexane diisocyanate; alicyclic polyisocyanates such as cyclohexane 1,4-diisocyanate, isophorone diisocyanate (IPDI), hydrogenated xylene diisocyanate, hydrogenated bis(isocyanoxyphenyl)methane, and dicycloheptane triisocyanate; triisocyanate compounds; biuret-type compounds; and modified forms of these compounds. These can be used alone or in combination or in plurality of combinations.

[0026] <Needle-shaped packing>

[0026] (Material)

[0026] The needle-shaped filler is not particularly limited as long as it is a filler with a high aspect ratio that presents a needle shape (including fibrous shape). When the anisotropic light-diffusing adhesive layer of the present invention is used in liquid crystal display devices, etc., it is preferable to be colorless or white in order to prevent the coloration of transmitted light.

[0027] Specifically, needle-like or fibrous materials composed of metal oxides such as titanium dioxide, zirconium oxide, and zinc oxide, as well as metal compounds such as gibbsite, aluminum borate, calcium silicate, alkaline magnesium sulfate, calcium carbonate, and potassium titanate, glass, and synthetic resins are suitable.

[0028] In order to improve the effect of the present invention, the needle-shaped filler is preferably calcium carbonate.

[0029] (shape)

[0029] The short diameter of the needle-shaped filler is preferably 0.1 μm to 20 μm, more preferably 0.3 μm to 5 μm, and even more preferably 0.5 μm to 1 μm.

[0030] The long diameter of the needle-shaped packing is preferably 2 μm to 5000 μm, more preferably 10 μm to 300 μm.

[0031] By making the short diameter and long diameter of the needle-shaped filler within this range, the light diffusion formed by the needle-shaped filler in the anisotropic light diffusion layer can be optimized, thereby improving the viewing angle magnification effect of the anisotropic light diffusion adhesive layer.

[0032] The aspect ratio (major diameter / minor diameter) of the needle-shaped filler is preferably 10 to 60, more preferably 20 to 60, and even more preferably 30 to 60. By making the aspect ratio of the needle-shaped filler within this range, the light diffusion formed by the needle-shaped filler in the anisotropic light diffusion layer can be optimized, thereby improving the viewing angle magnification effect of the anisotropic light diffusion adhesive layer.

[0033] The refractive index of the needle-shaped filler along its long axis is preferably 1.48 to 1.58.

[0033] Furthermore, the absolute value of the difference between the refractive index of the needle-shaped filler in the long axis direction and the refractive index of the adhesive is preferably 0.07 or less, more preferably 0.05 or less, and even more preferably 0.03 or less.

[0033] The refractive index of the needle-shaped filler in the short axis direction is preferably 1.60 to 1.70.

[0033] Furthermore, the absolute value of the difference between the refractive index of the needle-shaped filler in the short axis direction and the refractive index of the adhesive is preferably 0.1 to 0.2, more preferably 0.15 to 0.2.

[0033] By making the difference between the refractive index of the needle-shaped filler in the short or long axis direction and the refractive index of the adhesive within this range, the light diffusion formed by the needle-shaped filler in the anisotropic light diffusion layer can be optimized, thereby improving the viewing angle magnification effect of the anisotropic light diffusion adhesive layer.

[0034] (Content)

[0034] When the total solids of the coating are 100, the content of needle-like filler is preferably 1 part by weight to 50 parts by weight, more preferably 15 parts by weight to 40 parts by weight, and even more preferably 15 parts by weight to 30 parts by weight. By keeping the content of needle-like filler within this range, the light diffusion formed by the needle-like filler in the anisotropic light diffusion layer can be optimized, thereby improving the viewing angle magnification effect of the anisotropic light diffusion adhesive layer.

[0035] <Other Ingredients>

[0035] The anisotropic light-diffusing adhesive layer of the present invention may contain other components. These other components are not particularly limited as long as they do not impede the effects of the present invention. For example, they may contain various additives commonly found in the field of adhesive compositions, such as coupling agents, leveling agents, crosslinking aids, plasticizers, softeners, fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and surfactants. Such additives can be used in accordance with conventional methods and are not characteristic of the present invention; therefore, detailed descriptions are omitted.

[0036] <<<Structure / Properties of Anisotropic Light-Diffusing Adhesive Layers>>>

[0036] <<Orientation of Needle-shaped Packings>>

[0036] The needle-shaped filler is preferably oriented and dispersed in one direction within the adhesive layer.

[0037] In this invention, when an anisotropic light-diffusing adhesive layer is deposited between two polarizing plates with absorption axes 90° apart, such that the absorption axis of one polarizing plate is parallel to the alignment axis of the needle-shaped filler in the anisotropic light-diffusing adhesive layer, the ratio of (total transmittance emitted from another polarizing plate having an absorption axis that is not parallel to the alignment direction of the needle-shaped filler in the anisotropic light-diffusing adhesive layer) to (the ratio of needle-shaped filler content in the anisotropic light-diffusing adhesive layer) is called the "degree of alignment" which is an indicator of alignment.

[0038] At this point, the smaller the alignment degree, the smaller the influence of the anisotropic light-diffusing adhesive layer on the 90° relationship between the transmission axes of the two polarizing plates (crossed polarizers), which means that the alignment of the needle-like filler is good. The alignment degree should be below 30%, but it is preferable to have a smaller alignment degree, preferably below 25%, and even more preferably below 15%. By keeping the alignment degree within this range, the light diffusion formed by the needle-like filler in the anisotropic light-diffusing layer can be optimized, thereby improving the viewing angle magnification effect of the anisotropic light-diffusing adhesive layer. The lower limit of the alignment degree is preferably 10%.

[0039] The total transmittance (specific total transmittance) of the anisotropic light-diffusing adhesive layer is determined by depositing the anisotropic light-diffusing adhesive layer between two polarizing plates belonging to a crossed polarizer. The polarizing plate is arranged such that its absorption axis, perpendicular to the transmission axis, is parallel to the alignment direction of the needle-like filler in the anisotropic light-diffusing adhesive layer, and the transmittance is measured according to the method in JIS K 7361. Light irradiated from the light source travels from one polarizing plate side, and the transmittance is obtained by measuring the transmittance of the other polarizing plate (the polarizing plate whose absorption axis is not parallel to the alignment direction of the needle-like filler in the anisotropic light-diffusing adhesive layer).

[0040] The specific total light transmittance is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less.

[0041] A specific total transmittance can be adjusted by the orientation of the filler, the viscosity of the coating, the coating thickness, the coating speed, and the type of resin and needle filler in the adhesive.

[0042] <<Thickness>>

[0042] The thickness of the anisotropic light-diffusing adhesive layer is preferably 5 μm to 100 μm. By making the thickness of the anisotropic light-diffusing adhesive layer within this range, the light diffusion formed by the needle-like filler in the anisotropic light-diffusing layer can be optimized, thereby improving the viewing angle magnification effect of the anisotropic light-diffusing adhesive layer.

[0043] <<<Method for manufacturing anisotropic light-diffusing adhesive layer>>>

[0043] The following presents an example of a method for manufacturing an anisotropic light-diffusing adhesive layer.

[0044] First, a solution containing the components constituting the above-mentioned anisotropic light-diffusing adhesive layer and, if necessary, further containing volatile solvents is stirred to prepare a coating.

[0044] Next, the coating is applied to a substrate such as a release film or various optical elements, and the solvent is removed by drying to form a composition. A release film or various optical elements are then laminated onto the composition. Further, as needed, the composition is cured at room temperature or at a temperature of about 30°C to 60°C for about 1 day to 2 weeks in order to harden or stabilize it, thereby creating an anisotropic light-diffusing adhesive layer.

[0045] When coating a paint containing needle-like fillers, the needle-like fillers are oriented so that their long axis is almost along the coating direction by applying shear force to the paint containing needle-like fillers. Therefore, an anisotropic light-diffusing adhesive layer in which the needle-like fillers are oriented and dispersed in approximately the same direction can be produced. Furthermore, the degree of orientation of the needle-like fillers can be adjusted by the size of the needle-like fillers, the viscosity of the paint containing the needle-like fillers, the coating method, the coating speed, etc. Furthermore, the film thickness of the formed anisotropic light-diffusing adhesive layer can be adjusted by the amount of solvent in the paint, etc.

[0046] <<<Applications>>>

[0046] The anisotropic light diffusion adhesive layer can be used for bonding optical functional layers such as hard coatings to the surface of the viewing side polarizer (upper polarizer) of a display device.

[0047] As an example, when the display device is a liquid crystal display device, a display device is formed on a polarizing plate (which becomes the viewing side) of the liquid crystal display device in such a way that the absorption axis of the upper polarizing plate is parallel to the alignment direction of the needle-shaped filler of the anisotropic light diffusion adhesive layer, thereby obtaining a display device with excellent viewing angle magnification effect.

[0048] The method of applying an anisotropic light-diffusing adhesive layer to a component that is to be adhered to may be a method of directly forming an anisotropic light-diffusing adhesive layer on the component; or a method of forming an anisotropic light-diffusing adhesive layer in a sheet form on a release substrate (e.g., a film), adhering the anisotropic light-diffusing adhesive layer on the release substrate to the component, and then peeling off the release substrate.

[0048] (Example)

[0049] The present invention will be further described in detail below by way of examples, etc., but the scope of the present invention is not limited to these examples, etc.

[0050] <<Fabrication of Anisotropic Light-Diffusing Adhesive Layer>>

[0050] <Example 1>

[0050] 100 parts by weight of the solids of acrylic resin 1 (solids concentration of 40%, weight average molecular weight of 700,000, solvent of ethyl acetate), which is composed of a copolymer of (meth)acrylate monomers containing aromatic rings, 15 parts by weight of calcium carbonate whiskers (major diameter of 10 μm to 30 μm, minor diameter of 0.5 μm to 1.0 μm, refractive index in the major axis direction of 1.49) as needle-like filler, and 0.275 parts by weight of hexamethylene diisocyanate as a crosslinking agent are mixed, diluted with ethyl acetate, and stirred for 60 minutes to prepare coating 1 with a viscosity of 3010 mPa·s. At this time, the absolute value of the difference in refractive index in the major axis direction between the acrylic resin and the needle-like filler is 0.03.

[0050] Next, coating 1 is applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 1. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, is then laminated onto composition 1 and cured at room temperature for 1 week to obtain the anisotropic light-diffusing adhesive layer 1 of Example 1, which has an anisotropic light-diffusing adhesive layer 1 sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 1 is 15 μm.

[0051] <Example 2>

[0051] The ethyl acetate dilution amount and stirring time of the coating material were changed so that the coating viscosity was 1500 mPa·s. Otherwise, the coating 2 with a viscosity of 1530 mPa·s was prepared by the same method as the preparation of the anisotropic light-diffusing adhesive layer 1 with two films. At this time, the absolute value of the difference in refractive index between the acrylic resin and the needle-like filler in the long axis direction was 0.03.

[0051] Next, the coating 2 is applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 2. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, is then laminated onto composition 2 and cured at room temperature for 1 week to obtain the anisotropic light-diffusing adhesive layer 2 of Example 2, which has an anisotropic light-diffusing adhesive layer 2 sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 2 is 15 μm.

[0052] <Example 3>

[0052] 100 parts by weight of the solids of acrylic resin 2 (solids concentration of 40%, weight average molecular weight of 600,000, solvent of ethyl acetate), composed of a copolymer of (meth)acrylate monomers containing aromatic rings, 20 parts by weight of calcium carbonate whiskers (major diameter of 10 μm to 30 μm, minor diameter of 0.5 μm to 1.0 μm, refractive index in the major axis direction of 1.49) as needle-like filler, and 0.125 parts by weight of hexamethylene diisocyanate as a crosslinking agent were mixed, diluted with ethyl acetate, and stirred for 60 minutes to prepare a coating 3 with a viscosity of 3040 mPa·s. At this time, the absolute value of the difference in refractive index in the major axis direction between the acrylic resin and the needle-like filler is 0.

[0052] Next, the coating 3 is applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 3. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, is then laminated onto composition 3 and cured at room temperature for 1 week to obtain the anisotropic light-diffusing adhesive layer 3 of Example 3, which has an anisotropic light-diffusing adhesive layer 3 sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 3 is 15 μm.

[0053] <Example 4>

[0053] The ethyl acetate dilution amount and stirring time of the coating material were changed so that the coating viscosity was 1500 mPa·s. Otherwise, the coating 4 with a viscosity of 1490 mPa·s was prepared by the same method as the preparation of the anisotropic light-diffusing adhesive layer 3 with two films. At this time, the absolute value of the difference in refractive index between the acrylic resin and the needle-like filler in the long axis direction is 0.

[0053] Next, the coating 4 is applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 4. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, is then laminated onto composition 4 and cured at room temperature for 1 week to obtain the anisotropic light-diffusing adhesive layer 4 of Example 4, which has an anisotropic light-diffusing adhesive layer 4 sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 4 is 15 μm.

[0054] <Example 5>

[0054] 100 parts by weight of the solids of acrylic resin 3 (solids concentration of 40%, weight average molecular weight of 800,000, solvent of ethyl acetate), composed of a copolymer of (meth)acrylate monomers containing aromatic rings, 25 parts by weight of calcium carbonate whiskers (major diameter of 10 μm to 30 μm, minor diameter of 0.5 μm to 1.0 μm, refractive index in the major axis direction of 1.49) as needle-like filler, and 0.7 parts by weight of hexamethylene diisocyanate as a crosslinking agent were mixed, diluted with ethyl acetate, and stirred for 60 minutes to prepare a coating 5 with a viscosity of 2950 mPa·s. At this time, the absolute value of the difference in refractive index in the major axis direction between the acrylic resin and the needle-like filler is 0.04.

[0054] Next, the coating 5 is applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 5. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, is then laminated onto composition 5 and cured at room temperature for 1 week to obtain the anisotropic light-diffusing adhesive layer 5 of Example 5, which has an anisotropic light-diffusing adhesive layer 5 sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 5 is 15 μm.

[0055] <Example 6>

[0055] The ethyl acetate dilution amount and stirring time of the coating material were changed so that the coating viscosity was 1500 mPa·s. Otherwise, the coating 6 with a viscosity of 1510 mPa·s was produced by the same method as the preparation of the anisotropic light-diffusing adhesive layer 5 with two films. At this time, the absolute value of the difference in refractive index between the acrylic resin and the needle-like filler in the long axis direction was 0.04.

[0055] Next, the coating 6 is applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 6. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, is then laminated onto composition 6 and cured at room temperature for 1 week to obtain the anisotropic light-diffusing adhesive layer 6 of Example 6, which has an anisotropic light-diffusing adhesive layer 6 sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 6 is 15 μm.

[0056] <Comparative Example 1>

[0056] The ethyl acetate dilution amount and stirring time of the coating material were changed so that the coating viscosity was 800 mPa·s. Otherwise, the coating 7 with a viscosity of 790 mPa·s was prepared by the same method as the preparation of the anisotropic light-diffusing adhesive layer 1 with two films. At this time, the absolute value of the difference in refractive index between the acrylic resin and the needle-like filler in the long axis direction was 0.03.

[0056] Next, the coating 7 was applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 7. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, was then laminated onto composition 7 and cured at room temperature for 1 week to obtain an anisotropic light-diffusing adhesive layer 7 with two films attached, similar to Comparative Example 1, where an anisotropic light-diffusing adhesive layer 7 is sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 7 is 15 μm.

[0057] <Comparative Example 2>

[0057] The ethyl acetate dilution amount and stirring time of the coating material were changed so that the coating viscosity was 800 mPa·s. Otherwise, the coating 8 with a viscosity of 805 mPa·s was produced by the same method as the preparation of the anisotropic light-diffusing adhesive layer 3 with two films. At this time, the absolute value of the difference in refractive index between the acrylic resin and the needle-like filler in the long axis direction is 0.

[0057] Next, the coating 8 was applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 8. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, was then laminated onto composition 8 and cured at room temperature for 1 week to obtain an anisotropic light-diffusing adhesive layer 8 with two films attached, as in Comparative Example 2, where an anisotropic light-diffusing adhesive layer 8 is sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 8 is 15 μm.

[0058] <Comparative Example 3>

[0058] The ethyl acetate dilution amount and stirring time of the coating material were changed so that the coating viscosity was 3000 mPa·s. Otherwise, the coating 9 with a viscosity of 3010 mPa·s was produced by the same method as the preparation of the anisotropic light-diffusing adhesive layer 5 with two films. At this time, the absolute value of the difference in refractive index between the acrylic resin and the needle-like filler in the long axis direction was 0.04.

[0058] Next, the coating 9 was applied to a 38 μm thick release PET film using a coater, and then dried at 80°C for 2 minutes to form composition 9. A 38 μm thick release PET film, which is easier to peel off than the coated release PET film, was then laminated onto composition 9 and cured at room temperature for 1 week to obtain an anisotropic light-diffusing adhesive layer 9 with two films attached, as in Comparative Example 3, where an anisotropic light-diffusing adhesive layer 9 is sandwiched between a pair of release PET films. Furthermore, the thickness of the anisotropic light-diffusing adhesive layer 9 is 15 μm.

[0059] <<Evaluation>>

[0059] The following evaluation was performed on the anisotropic light-diffusing adhesive layers with two films obtained in Examples 1 to 6 and Comparative Examples 1 to 3 above.

[0060] <Evaluating alignment by measuring alignment degree>

[0060] Between two polarizing plates (composed of crossed polarizers) with absorption axes 90° apart, the absorption axis of one polarizing plate is parallel to the alignment direction of the needle-shaped filler of the anisotropic light diffusion adhesive layer. The two films of the anisotropic light diffusion adhesive layer with two films in the examples and comparative examples are peeled off and laminated.

[0060] Next, the total transmittance was measured using a haze meter (NDH7000 manufactured by Nippon Denshoku Kogyo Co., Ltd.) according to JIS K 7361. At this time, the light irradiated from the light source was side-irradiated from a polarizer whose absorption axis was parallel to the alignment direction of the needle-like filler of the anisotropic light-diffusing adhesive layer, and the total transmittance was measured from the side of the other polarizer (a polarizer whose absorption axis was not parallel to the alignment direction of the needle-like filler of the anisotropic light-diffusing adhesive layer).

[0060] Calculate the total transmittance / (the ratio of needle-like fillers in the anisotropic light-diffusing adhesive layer) from the obtained total transmittance, and use this value as the alignment degree.

[0060] Furthermore, the smaller the alignment value, the better the alignment evaluation of the needle packing.

[0061] <Evaluating viewing angle characteristics by measuring contrast at the front and 60° angles>

[0061] After peeling off the release PET film, which is easier to peel off from the anisotropic light-diffusing adhesive layer with two films in the examples and comparative examples, a TAC film is laminated. Then, after peeling off the release PET film on the opposite side that is laminated with the TAC film, the anisotropic light-diffusing adhesive layer with the TAC film is deposited on the surface of the VA-type liquid crystal display in such a way that the absorption axis of the polarizer (viewing side) of the liquid crystal display is parallel to the alignment direction of the needle-like filler of the anisotropic light-diffusing adhesive layer.

[0061] The brightness of the white display and the brightness of the black display were measured from the viewing side of the liquid crystal display with an anisotropic light-diffusing adhesive layer using a brightness viewing angle meter (CONOMETER 80 manufactured by TEMIncorporated) in the range of -80° to 80° in the orthogonal direction of the alignment direction of the needle filler.

[0061] The contrast ratio (white brightness / black brightness) was calculated from the measured values ​​of white brightness and black brightness at various angles. The frontal contrast ratio was (0° contrast ratio) / (0° contrast ratio of the anisotropic light-diffusing adhesive layer without TAC film), and the 60° contrast ratio was (60° contrast ratio) / (0° contrast ratio). The relationship between the contrast ratios in each direction was plotted with the 60° contrast ratio as the X-axis and the frontal contrast ratio as the Y-axis, and is shown in Figure 1.

[0061] Furthermore, the determination of viewing angle characteristics in Figure 1 takes into account the balance of contrast in each direction. When the contrast (X) value in the 60° direction is "X>15" and the contrast (Y) value in the front direction is "Y>-2.67X+110", it is evaluated as "○". When the contrast (X) value in the 60° direction is "X>15" and the contrast (Y) value in the front direction is "Y≦-2.67X+110", it is determined as "×".

[0062] <Evaluating Reflectance Characteristics by Reflectivity Measurement>

[0062] After peeling off the release PET film, which is easier to peel off from the anisotropic light-diffusing adhesive layer with two films in the examples and comparative examples, it is laminated onto the TAC side of the LR-TAC film made according to Example 1 of Japanese Patent No. 663471. Next, after peeling off the release PET film on the opposite side of the LR-TAC film lamination, the anisotropic light-diffusing adhesive layer with the LR-TAC film is laminated onto the adhesive side of the black PET film with adhesive (manufactured by Tomoewa Paper Co., Ltd., "clearly appear"). The reflectance is measured by SCI method using a spectrophotometer (manufactured by KONICA MINOLTA Co., Ltd., according to JIS Z 8722, from the LR-TAC film side of the anisotropic light-diffusing adhesive layer with the LR-TAC film and the black PET film with adhesive, and the value is used as an indicator of reflectance characteristics.

[0063] The above evaluation results are summarized in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, the anisotropic light-diffusing adhesive layer of the present invention has excellent viewing angle characteristics.

[0065] In contrast, the anisotropic light-diffusing adhesive layer of the comparative example has poor alignment of its needle-like filler, resulting in poorer viewing angle characteristics.

[0066] As can be seen from the evaluation results of the embodiments, the anisotropic light diffusion adhesive layer of the present invention is an anisotropic light diffusion adhesive layer with excellent viewing angle magnification.

[0067] The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described forms. That is, the technical scope of the present invention also includes other forms or various modifications that can be deduced by those skilled in the art from the scope of the invention described in the claims.

Claims

1. An anisotropic light-diffusing adhesive layer comprising an adhesive and needle-like fillers, wherein the needle-like fillers are aligned and dispersed in one direction within the anisotropic light-diffusing adhesive layer, and the anisotropic light-diffusing adhesive layer is deposited between two polarizing plates whose absorption axes differ from each other by 90°, such that the absorption axis of one polarizing plate is parallel to the alignment axis of the needle-like fillers, and the alignment degree shown in the following formula (1) is 30% or less, alignment degree = (total transmittance emitted from another polarizing plate having an absorption axis that is not parallel to the alignment direction of the needle-like fillers in the anisotropic light-diffusing adhesive layer) / (weight ratio of the needle-like fillers in the anisotropic light-diffusing adhesive layer)...(1).

2. The anisotropic light-diffusing adhesive layer as described in claim 1, wherein the aforementioned needle-like filler has a short diameter of 0.1 μm to 20 μm and a long diameter of 2 μm to 5000 μm.

3. The anisotropic light-diffusing adhesive layer as described in claim 1 or 2, wherein the adhesive is an adhesive made of acrylic resin, and the acrylic resin is composed of a copolymer containing a (meth)acrylate monomer having an aromatic ring.

4. The anisotropic light-diffusing adhesive layer as described in claim 1 or 2, wherein the absolute value of the difference between the refractive index of the aforementioned needle-shaped filler in the long axis direction and the refractive index of the aforementioned acrylic resin is 0.07 or less.

5. An anisotropic light-diffusing adhesive layer as described in claim 1 or 2, wherein the weight-average molecular weight of the aforementioned adhesive is between 200,000 and 1,000,000.

6. An anisotropic light-diffusing adhesive layer as described in claim 1 or 2, wherein the film thickness is from 5 μm to 100 μm.

7. A display device comprising depositing an anisotropic light-diffusing adhesive layer as described in any one of claims 1 to 6 on a polarizing plate of a liquid crystal display device, wherein the alignment axis of the needle-like filler in the anisotropic light-diffusing adhesive layer is parallel to the absorption axis of the upper polarizing plate.

Images