JP6732407B2 - Optical laminate, method for manufacturing the same, and image display device using the optical laminate - Google Patents

Description

The present invention relates to an optical layered body, a method for manufacturing the same, and an image display device using the optical layered body.

In recent years, image display devices such as mobile phones, smartphones, tablet personal computers (PCs), car navigation systems, digital signage, and window displays are increasingly used under strong external light. When the image display device is used outdoors as described above, when the viewer wears polarized sunglasses and looks at the image display device, the transmission axis direction of the polarized sunglasses and the emission of the image display device may be different depending on the viewing angle. There is a case where the transmission axis on the side is in a crossed Nicols state, and as a result, the screen becomes black and the displayed image cannot be visually recognized. In order to solve such a problem, there has been proposed a technique of disposing a circularly polarizing plate (a polarizing plate corresponding to polarized sunglasses) on the viewing side surface of the image display device.

By the way, there is an increasing demand for thinner image display devices, and accordingly, there is also an increasing demand for thinner optical members used in the image display devices. However, when attempting to reduce the thickness of the polarizing plate compatible with polarized sunglasses as described above, there is a problem that curling (particularly, curling in a diagonal direction of the polarizing plate) is remarkable.

JP, 2014-16425, A

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide an optical laminated body having a circular polarization function or an elliptically polarization function, which is thin and curls suppressed. To do.

The optical layered body of the present invention comprises a polarizer, a retardation layer arranged on one side of the polarizer, and a protective layer arranged on the other side of the polarizer. The retardation layer has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. In this optical laminate, the difference between the heating dimensional change rate in the first direction and the heating dimensional change rate in the second direction substantially orthogonal to the first direction is 1.0% or less.
In one embodiment, the first direction is a slow axis direction or a fast axis direction of the retardation layer, and the second direction is a fast axis direction or a slow axis direction of the retardation layer. Is.
In one embodiment, the angle formed by the absorption axis of the polarizer and the slow axis of the retardation layer is 35° to 55°.
In one embodiment, the above-mentioned optical layered product is elongate, and the angle between the slow axis of the above-mentioned retardation layer and the elongate direction is 35°-55°.
In one embodiment, the optical layered body further comprises a hard coat layer on the side of the retardation layer opposite to the polarizer.
In one embodiment, the above-mentioned polarizer, the above-mentioned retardation layer, and the above-mentioned protective layer are pasted together by the water system adhesives whose solid content concentration is 6 weight% or less.
According to another aspect of the present invention, an image display device is provided. In this image display device, the optical layered body is provided on the viewing side, and the retardation layer is arranged on the viewing side.

According to an embodiment of the present invention, in an optical laminate having a polarizer, a retardation layer having a circular polarization function or an elliptically polarization function, and a protective layer, a heating dimensional change rate in the first direction and the first direction. By controlling the difference from the heating dimensional change rate in the second direction substantially orthogonal to, it is possible to realize an optical laminated body that is extremely thin and has curl suppressed. In particular, curl suppression in the diagonal direction is remarkable.

1 is a schematic cross-sectional view of an optical layered body according to an embodiment of the present invention. 3 is a graph showing profiles of dimensional change rates in the slow axis direction and the fast axis direction with respect to temperature in Example 1. 7 is a graph showing profiles of dimensional change rates in the slow axis direction and the fast axis direction with respect to temperature in Comparative Example 1. 9 is a graph showing profiles of dimensional change rates in the slow axis direction and the fast axis direction with respect to temperature in Comparative Example 2. 3 is a photograph showing the curled state of the optical layered body of Example 1. 5 is a photograph showing a curled state of the optical layered body of Comparative Example 1. 5 is a photograph showing a curled state of the optical layered body of Comparative Example 2.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)
The definitions of terms and symbols used herein are as follows.
(1) Refractive index (nx, ny, nz)
“Nx” is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), and “ny” is in the surface in the direction orthogonal to the slow axis (that is, the fast axis direction). , And “nz” is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
“Re(λ)” is the in-plane retardation of the film measured with light having a wavelength of λ nm at 23° C. For example, “Re(450)” is the in-plane retardation of the film measured with light having a wavelength of 450 nm at 23° C. Re(λ) is calculated by the formula: Re=(nx−ny)×d when the film thickness is d (nm).
(3) Phase difference in the thickness direction (Rth)
“Rth(λ)” is a retardation in the thickness direction of the film measured with light having a wavelength of 550 nm at 23° C. For example, “Rth(450)” is the retardation in the thickness direction of the film measured with light having a wavelength of 450 nm at 23° C. Rth(λ) is calculated by the formula: Rth=(nx−nz)×d when the film thickness is d(nm).
(4) Nz coefficient The Nz coefficient is calculated by Nz=Rth/Re.
(5) Substantially orthogonal or parallel The expressions “substantially orthogonal” and “substantially orthogonal” include the case where the angle formed by the two directions is 90°±10°, preferably 90°±7°. And more preferably 90°±5°. The expressions "substantially parallel" and "substantially parallel" include the case where the angle formed by the two directions is 0°±10°, preferably 0°±7°, and more preferably 0°±. It is 5°. Further, in the present specification, when simply referred to as “orthogonal” or “parallel”, it may include a substantially orthogonal or substantially parallel state.
(6) Angle When referring to an angle in this specification, the angle includes an angle in both clockwise and counterclockwise directions unless otherwise specified.
(7) Long shape "Long shape" means an elongated shape having a length sufficiently longer than the width, and for example, a length having a length 10 times or more, preferably 20 times or more the width. Including shape.

A. Overall Structure of Optical Laminate FIG. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. The optical layered body 100 of the present embodiment includes a polarizer 10, a retardation layer 20 arranged on one side of the polarizer 10, and a protective layer 30 arranged on the other side of the polarizer 10. Prepare The retardation layer 20 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. Therefore, the optical layered body 100 may typically be a circular polarization plate or an elliptically polarization plate. The optical laminate 100 is typically arranged on the viewing side of the image display device. In this case, the retardation layer 20 is arranged so as to be on the viewing side. With the above configuration, excellent visibility can be achieved even when the display screen is viewed through a polarizing lens such as polarized sunglasses. Therefore, the optical layered body 100 can be suitably applied to an image display device that can be used outdoors.

The optical layered body 100 may further include a hard coat layer 40 on the side of the retardation layer 20 opposite to the polarizer 10, as necessary. Further, the optical layered body 100 may include another retardation layer (not shown). The number of different retardation layers, arrangement position, optical characteristics (eg, refractive index ellipsoid, in-plane retardation, thickness direction retardation, wavelength dispersion characteristic), mechanical characteristics, etc. can be appropriately set according to the purpose. ..

In the optical layered body 100, the difference between the heating dimensional change rate in the first direction and the heating dimensional change rate in the second direction substantially orthogonal to the first direction is 1.0% or less, and preferably It is 0.8% or less, more preferably 0.6% or less, and further preferably 0.4% or less. According to the embodiment of the present invention, by controlling the heating dimensional change rate in two directions that are substantially orthogonal to each other, it is possible to realize an optical laminate that is extremely thin and has curl suppressed. Typically, the first direction is the slow axis direction or the fast axis direction of the retardation layer 20, and the second direction is the fast axis direction or the slow axis direction of the retardation layer. By controlling the heating dimensional change rate in these two specific directions, curling can be further suppressed in a very thin optical laminate.

The polarizer 10 and the retardation layer 20 are laminated such that the absorption axis of the polarizer 10 and the slow axis of the retardation layer 20 form a predetermined angle. The angle formed by the absorption axis of the polarizer 10 and the slow axis of the retardation layer 20 is preferably 35° to 55°, more preferably 38° to 52°, and further preferably 40° to 50°. , Particularly preferably 42° to 48°, particularly preferably around 45°. By disposing the retardation layer 20 on the viewing side of the polarizer 10 in such an axial relationship, excellent visibility can be realized even when the display screen is viewed through a polarizing lens such as polarized sunglasses. it can. Therefore, the optical laminate according to the embodiment of the present invention can be preferably applied to an image display device that can be used outdoors.

The optical layered body 100 may have a sheet shape or a long shape (for example, a roll shape). When the optical laminated body 100 has a long shape, the absorption axis direction of the long-sized polarizer may be the long direction or the width direction. Preferably, the absorption axis direction of the polarizer is the longitudinal direction. This is because the polarizer can be easily manufactured, and as a result, the manufacturing efficiency of the optical laminate is excellent. When the optical laminate has a long shape, the angle θ between the slow axis of the retardation layer 20 and the long direction is preferably 35° to 55°, more preferably 38° to 52°, and It is preferably 40° to 50°, particularly preferably 42° to 48°, and particularly preferably around 45°. By forming the retardation film constituting the retardation layer by oblique stretching as described below, it is possible to form a long retardation film (retardation layer) having a slow axis in the oblique direction. As a result, a long optical laminate can be realized. Since such a long optical laminate can be produced by roll-to-roll, the productivity is remarkably excellent.

The total thickness of the optical layered body is typically 40 μm to 300 μm, preferably 60 μm to 160 μm, more preferably 80 μm to 140 μm, and further preferably 100 μm to 120 μm. According to the embodiment of the present invention, it is possible to obtain an optical layered body in which curl is excellently suppressed while having such an extremely thin thickness. The total thickness of the optical laminate refers to the total thickness of the polarizer, the retardation layer, the protective layer, the hard coat layer if present, and the adhesive layer for laminating these.

Hereinafter, each layer constituting the optical layered body according to the embodiment of the present invention will be described.

A-1. Polarizer Any appropriate polarizer may be adopted as the polarizer 10. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of the polarizer composed of a single-layer resin film include polyvinyl alcohol (PVA)-based resin film, partially formalized PVA-based resin film, ethylene/vinyl acetate copolymer-based partially saponified film, and the like having high hydrophilicity. Examples include molecular films that have been subjected to dyeing treatment and stretching treatment with a dichroic substance such as iodine or a dichroic dye, polyene oriented films such as PVA dehydration-treated products and polyvinyl chloride dehydrochlorination-treated products. To be Preferably, a polarizer obtained by dyeing a PVA-based resin film with iodine and uniaxially stretching it is used because it has excellent optical properties.

The dyeing with iodine is performed, for example, by immersing the PVA-based resin film in an iodine aqueous solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment or may be performed while dyeing. Further, it may be stretched and then dyed. If necessary, the PVA resin film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment and the like. For example, by immersing the PVA-based resin film in water and washing it before dyeing, it is possible to not only clean the surface of the PVA-based resin film and an anti-blocking agent, but also swell the PVA-based resin film for dyeing It is possible to prevent unevenness.

Specific examples of the polarizer obtained using the laminated body include a laminated body of a resin base material and a PVA-based resin layer (PVA-based resin film) laminated on the resin base material, or a resin base material and the resin. Examples thereof include a polarizer obtained by using a laminate with a PVA-based resin layer formed by coating on a base material. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying the solution. A PVA-based resin layer is formed thereon to obtain a laminate of a resin base material and a PVA-based resin layer; and the PVA-based resin layer is used as a polarizer by stretching and dyeing the laminate. obtain. In the present embodiment, the stretching typically includes dipping the laminate in a boric acid aqueous solution and stretching. Further, the stretching may further include, if necessary, stretching the laminate at high temperature (for example, 95° C. or higher) in air before stretching in the aqueous boric acid solution. The resin base material/polarizer laminate thus obtained may be used as it is (that is, the resin base material may be used as a protective layer of the polarizer), or the resin base material is peeled from the resin base material/polarizer laminate. However, any appropriate protective layer depending on the purpose may be laminated on the peeled surface and used. Details of the method for manufacturing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire disclosure of this publication is incorporated herein by reference.

The thickness of the polarizer is preferably 15 μm or less, more preferably 13 μm or less, further preferably 10 μm, and particularly preferably 8 μm or less. The lower limit of the thickness of the polarizer is 2 μm in one embodiment and 3 μm in another embodiment. According to the embodiment of the present invention, the curl when the optical layered body is heated can be favorably suppressed even though the thickness of the polarizer is thus extremely thin.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 44.0% to 45.5%, more preferably 44.5% to 45.0%. According to the present invention, it is possible to realize an extremely thin optical laminate in which curling is suppressed, and further, in such an optical laminate, it is possible to realize the excellent single transmittance as described above.

As described above, the polarization degree of the polarizer is 98% or more, preferably 98.5% or more, and more preferably 99% or more. According to the present invention, it is possible to realize an optical laminated body that is extremely thin and curl is suppressed, and further, in such an optical laminated body, it is possible to realize the excellent polarization degree as described above.

A-2. Retardation Layer The retardation layer 20 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light as described above. That is, the retardation layer 20 typically shows a relationship that the refractive index characteristics are nx>ny. The in-plane retardation Re(550) of the retardation film is preferably 80 nm to 160 nm, more preferably 90 nm to 120 nm. When the in-plane retardation is in such a range, a retardation film having appropriate elliptically polarizing performance can be obtained with excellent productivity and reasonable cost. As a result, it is possible to obtain an optical layered body that can ensure good visibility even when the display screen is viewed through a polarizing lens such as polarized sunglasses with excellent productivity and at a reasonable cost.

The retardation layer 20 exhibits any suitable index ellipsoid as long as it has a relationship of nx>ny. Preferably, the refractive index ellipsoid of the retardation layer exhibits a relationship of nx>ny≧nz. The Nz coefficient of the retardation layer is preferably 1 to 2, more preferably 1 to 1.5, and further preferably 1 to 1.3.

The retardation layer 20 is composed of any appropriate retardation film that can satisfy the above optical characteristics. As a resin forming the retardation film, a cellulose ester resin (hereinafter, also simply referred to as a cellulose ester) is typically mentioned.

Specific examples of the cellulose ester include cellulose (di,tri)acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. Preferred are cellulose triacetate, cellulose diacetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate. The cellulose ester may be used alone or in combination.

Cellulose ester is an acyl group such as an acetyl group or a propionyl group for a part or all of the free hydroxyl groups (hydroxyl groups) at the 2-position, 3-position and 6-position in a glucose unit that constitutes cellulose with a β-1,4-glycoside bond. Is a polymer esterified by. Here, the “acyl group substitution degree” refers to the total of the proportion of esterified hydroxyl groups at the 2-position, 3-position and 6-position of glucose of the repeating unit. Specifically, the degree of substitution is 1 when the respective 2-position, 3-position and 6-position hydroxyl groups of cellulose are 100% esterified. Therefore, when all of the 2-position, 3-position and 6-position of cellulose are 100% esterified, the substitution degree becomes 3 which is the maximum. The "average degree of acyl group substitution" means the degree of acyl group substitution expressed as the average value of the degree of acyl group substitution of a plurality of glucose units constituting the cellulose ester resin per unit. The acyl group substitution degree can be measured according to ASTM-D817-96.

Examples of the acyl group include acetyl group, propionyl group, butanoyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, isobutanoyl group. Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group.

In one embodiment, when the degree of acetyl group substitution of the cellulose ester resin is X and the degree of substitution of propionyl group is Y, X and Y preferably satisfy the following formulas (1) and (2).
Formula (1): 2.0≦(X+Y)≦2.8
Formula (2): 0≦Y≦1.0
More preferably, the cellulose ester resin satisfying the above formulas (1) and (2) is a cellulose ester resin satisfying the following formulas (1a) and (2), and a cellulose ester resin satisfying the following formulas (1b). Contains.
Formula (1a): 2.0≦(X+Y)<2.5
Formula (1b): 2.5≦(X+Y)≦2.8
The “acetyl group substitution degree” and the “propionyl group substitution degree” are more specific indicators of the acyl group substitution degree, and the “acetyl group substitution degree” means the 2-position and 3-position of glucose as a repeating unit. And the 6-position represents the total of the proportion of the hydroxyl group esterified by the acetyl group, and the "propionyl group substitution degree" means that the hydroxyl group is the acetyl group at the 2-position, 3-position and 6-position of the repeating unit glucose. It represents the sum of the proportions which are esterified by the groups.

The cellulose ester resin has a molecular weight distribution (weight average molecular weight Mw/number average molecular weight Mn) of preferably 1.5 to 5.5, more preferably 2.0 to 5.0, and further preferably 2.5. To 5.0, particularly preferably 3.0 to 5.0.

Any appropriate cellulose can be used as the raw material cellulose of the cellulose ester resin. Specific examples include cotton linter, wood pulp, and kenaf. Cellulose ester resins obtained from different raw materials may be used in combination.

The cellulose ester resin can be produced by any appropriate method. Representative examples include methods that include the following procedures: raw material cellulose, certain organic acids (eg, acetic acid, propionic acid), acid anhydrides (eg, acetic anhydride, propionic anhydride), and catalysts (eg, Sulfuric acid) is mixed to esterify the cellulose and the reaction proceeds until a cellulose triester is obtained. In the cellulose triester, the three hydroxyl groups (hydroxyl groups) of the glucose unit are replaced with an acyl acid of an organic acid. By using two kinds of organic acids at the same time, a mixed ester type cellulose ester (eg, cellulose acetate propionate, cellulose acetate butyrate) can be prepared. Next, the cellulose triester is hydrolyzed to synthesize a cellulose ester having a desired degree of acyl group substitution. Then, the cellulose ester resin can be obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying.

The retardation layer 20 (retardation film) is typically produced by stretching a resin film made of the above resin in at least one direction.

Any appropriate method can be adopted as a method for forming the resin film. For example, melt extrusion method (for example, T die molding method), cast coating method (for example, casting method), calender molding method, hot pressing method, coextrusion method, comelting method, multi-layer extrusion, inflation molding method and the like. To be Preferably, a T-die molding method, a casting method and an inflation molding method are used.

The thickness of the resin film (unstretched film) can be set to any appropriate value depending on desired optical characteristics, stretching conditions described below, and the like. The thickness is preferably 50 μm to 300 μm, more preferably 80 μm to 250 μm.

Any appropriate stretching method and stretching conditions (for example, stretching temperature, stretching ratio, stretching direction) can be adopted for the stretching. Specifically, various stretching methods such as free-end stretching, fixed-end stretching/free-end contraction, and fixed-end contraction can be used alone or simultaneously or sequentially. The stretching direction can also be performed in various directions and dimensions such as horizontal direction, vertical direction, thickness direction and diagonal direction. The stretching temperature is preferably in the range of the glass transition temperature (Tg)±20° C. of the resin film.

By appropriately selecting the stretching method and stretching conditions, a retardation film (as a result, a retardation layer) having the desired optical characteristics (for example, an index ellipsoid, an in-plane retardation, an Nz coefficient) can be obtained. You can

In one embodiment, the retardation layer 20 is produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. Specific examples of the uniaxial stretching include a method of stretching the resin film in the longitudinal direction (longitudinal direction) while running the resin film in the longitudinal direction. Another specific example of the uniaxial stretching is a method of stretching in the transverse direction using a tenter. The draw ratio is preferably 10% to 500%.

In another embodiment, the retardation layer 20 is produced by continuously stretching a long resin film in the direction of an angle θ with respect to the long direction. By adopting oblique stretching, a long stretched film having an orientation angle of θ with respect to the lengthwise direction of the film can be obtained, and for example, roll-to-roll becomes possible when laminating with a polarizer, Can be simplified. The angle θ is as described above.

As a stretching machine used for oblique stretching, for example, a tenter type stretching machine capable of applying a feed force or a pulling force or a pulling force at different speeds in the lateral and/or longitudinal directions can be mentioned. Examples of the tenter type stretching machine include a horizontal uniaxial stretching machine and a simultaneous biaxial stretching machine. Any appropriate stretching machine can be used as long as a long resin film can be continuously stretched obliquely.

Examples of the oblique stretching method include, for example, JP-A-50-83482, JP-A-2-113920, JP-A-3-182701, JP-A-2000-9912, and JP-A-2002-86554. The method described in JP-A-2002-22944 and the like can be mentioned.

The thickness of the stretched film (as a result, the retardation layer) is preferably 20 μm to 80 μm, more preferably 30 μm to 60 μm.

As the retardation film constituting the retardation layer 20, a commercially available film may be used as it is, or a commercially available film may be subjected to secondary processing (for example, stretching treatment, surface treatment) depending on the purpose.

The surface of the retardation layer 20 on the side of the polarizer 10 may be subjected to a surface treatment. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, primer coating treatment, and saponification treatment. Examples of the corona treatment include a method of discharging in a normal pressure air using a corona treatment machine. As the plasma treatment, for example, a method of discharging in atmospheric air by a plasma discharge machine can be mentioned. The flame treatment includes, for example, a method in which a flame is brought into direct contact with the film surface. Examples of the primer coating treatment include a method of diluting an isocyanate compound, a silane coupling agent, and the like with a solvent, and applying the diluted liquid thinly. Examples of the saponification treatment include a method of immersing in a sodium hydroxide aqueous solution. Of these, corona treatment and plasma treatment are preferable.

A-3. Protective Layer The protective layer 30 is formed of any suitable film that can be used as a protective layer of the polarizer. Specific examples of the material that is the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, and polysulfone resins. , Polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, acetate-based transparent resins and the like. Further, a thermosetting resin such as a (meth)acrylic resin, a urethane resin, a (meth)acrylic urethane resin, an epoxy resin, a silicone resin, or an ultraviolet curable resin may be used. In addition to these, for example, a glassy polymer such as a siloxane polymer may be used. Further, the polymer film described in JP 2001-343529 A (WO 01/37007) can also be used. Examples of the material of this film include a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in its side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film can be, for example, an extruded product of the resin composition.

The (meth)acrylic resin has a Tg (glass transition temperature) of preferably 115°C or higher, more preferably 120°C or higher, still more preferably 125°C or higher, and particularly preferably 130°C or higher. This is because it can have excellent durability. The upper limit of Tg of the (meth)acrylic resin is not particularly limited, but is preferably 170° C. or lower from the viewpoint of moldability and the like.

As the (meth)acrylic resin, any appropriate (meth)acrylic resin can be adopted as long as the effects of the present invention are not impaired. For example, poly(meth)acrylic acid ester such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester -(Meth)acrylic acid copolymer, methyl (meth)acrylate-styrene copolymer (MS resin, etc.), alicyclic hydrocarbon group-containing polymer (for example, methyl methacrylate-cyclohexyl methacrylate copolymer) , Methyl methacrylate-(meth)acrylic acid norbornyl copolymer, etc.). Preferable one is C _1-6 alkyl poly(meth)acrylate such as methyl poly(meth)acrylate. More preferably, a methyl methacrylate-based resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight) is used.

Specific examples of the (meth)acrylic resin include, for example, Acrypet VH and Acrypet VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and a (meth)acrylic resin having a ring structure in the molecule described in JP 2004-70296 A. Examples thereof include resins and high Tg (meth)acrylic resins obtained by intramolecular crosslinking or intramolecular cyclization reaction.

As the (meth)acrylic resin, a (meth)acrylic resin having a lactone ring structure is particularly preferable in terms of high heat resistance, high transparency, and high mechanical strength.

Examples of the (meth)acrylic resin having a lactone ring structure include JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, and JP-A-2005. Examples of the (meth)acrylic resin having a lactone ring structure described in JP-A-146084.

The (meth)acrylic resin having a lactone ring structure has a mass average molecular weight (sometimes referred to as a weight average molecular weight) of preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, further preferably 10,000 to 500,000, particularly It is preferably 50,000 to 500,000.

The (meth)acrylic resin having a lactone ring structure has a Tg (glass transition temperature) of preferably 115°C or higher, more preferably 125°C or higher, further preferably 130°C or higher, particularly preferably 135°C, most preferably Is 140° C. or higher. This is because it can have excellent durability. The upper limit of Tg of the (meth)acrylic resin having a lactone ring structure is not particularly limited, but is preferably 170° C. or lower from the viewpoint of moldability and the like.

In addition, in this specification, "(meth)acrylic" means acrylic and/or methacrylic.

The protective layer 30 is preferably optically isotropic. In the present specification, “optically isotropic” means that the in-plane retardation Re(550) is 0 nm to 10 nm and the thickness direction retardation Rth(550) is −10 nm to +10 nm. Say.

The thickness of the inner protective film is preferably 20 μm to 80 μm, more preferably 30 μm to 60 μm.

A-4. Hard Coat Layer The hard coat layer 40 has a function of imparting chemical resistance, scratch resistance and surface smoothness to the optical layered body and improving dimensional stability under high temperature and high humidity. Any appropriate configuration can be adopted as the hard coat layer 40. The hard coat layer is, for example, a cured layer of any appropriate ultraviolet curable resin. Examples of the ultraviolet curable resin include acrylic resin, silicone resin, polyester resin, urethane resin, amide resin, and epoxy resin. The glass transition temperature of the resin constituting the hard coat layer is preferably 120°C to 300°C, more preferably 130°C to 250°C. Within such a range, an optical laminate having excellent dimensional stability at high temperatures can be obtained. The hard coat layer may contain any appropriate additive as necessary. Representative examples of the additive include inorganic fine particles and/or organic fine particles.

The thickness of the hard coat layer 40 is preferably 10 μm or less, more preferably 1 μm to 8 μm, and further preferably 3 μm to 7 μm.

Details of the hard coat layer are described in, for example, JP-A-2007-171943, and the description thereof is incorporated herein by reference.

A-5. Adhesive Layer Any suitable adhesive layer (not shown) is used for bonding the layers constituting the optical laminate according to the embodiment of the present invention. The adhesive layer may be a pressure-sensitive adhesive layer or an adhesive layer. Typically, the polarizer 10, the retardation layer 20, and the protective layer 30 are bonded together with a water-based adhesive. Any appropriate water-based adhesive may be adopted as the water-based adhesive. Preferably, a water-based adhesive containing PVA-based resin is used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100 to 5500, more preferably 1000 to 4500 from the viewpoint of adhesiveness. From the viewpoint of adhesiveness, the average degree of saponification is preferably about 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because the polarizer is excellent in adhesion to the retardation layer and the protective layer, and can be excellent in durability. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting the PVA-based resin with diketene by an arbitrary method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA-based resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, and more preferably 1 mol% to 20 mol. %, particularly preferably 1 to 7 mol %. The acetoacetyl group modification degree is a value measured by NMR.

The solid content concentration of the water-based adhesive is preferably 6% by weight or less, more preferably 0.1% by weight to 6% by weight, and further preferably 0.5% by weight to 6% by weight. When the solid content concentration is in such a range, there is an advantage that the dimensional control rate of the polarizing plate can be easily controlled. If the solid content concentration is too low, the resulting optical layered body will have a high water content and may have a large dimensional change depending on the drying conditions. If the solid content concentration is too high, the viscosity of the adhesive may be high, and the productivity of the optical laminate may be insufficient.

The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, further preferably 0.01 μm to 2 μm, and particularly preferably 0.01 μm to 1 μm. If the thickness of the adhesive layer is too thin, the cohesive force of the adhesive itself may not be obtained, and the adhesive strength may not be obtained. If the thickness of the adhesive layer is too large, the optical layered product may not satisfy the durability.

A-6. Others In one embodiment, an easily adhesive layer (not shown) may be provided on the surface of the retardation layer 20 on the side of the polarizer 10. When the easy-adhesion layer is provided, the retardation layer 20 may or may not be subjected to the above-mentioned surface treatment. Preferably, the retardation layer 20 is surface-treated. By combining the easy-adhesion layer and the surface treatment, realization of a desired adhesive force between the polarizer 10 and the retardation layer 20 can be promoted. The easy-adhesion layer preferably contains a silane having a reactive functional group. By providing such an easy-adhesion layer, it is possible to promote realization of a desired adhesive force between the polarizer 10 and the retardation layer 20. Details of the easy-adhesion layer are described in, for example, JP-A-2006-171707.

Practically, an adhesive layer (not shown) may be provided on the protective layer 30 side of the optical layered body. Since the pressure-sensitive adhesive layer is provided in advance, it can be easily attached to another optical member (for example, a liquid crystal cell or an organic EL panel). A release film is preferably attached to the surface of the pressure-sensitive adhesive layer until it is used.

B. Method for Producing Optical Laminated Body An example of the method for producing an optical laminated body according to the embodiment of the present invention will be briefly described only for characteristic portions. This manufacturing method is to manufacture a laminate having a polarizer 10 and a retardation layer 20 arranged on one side of the polarizer 10 and a protective layer 30 arranged on the other side of the polarizer 10. And heating the laminated body at a temperature of, for example, 85° C. or higher (hereinafter, also referred to as high temperature heating). The heating temperature of the high temperature heating is preferably 86° C. or higher. The upper limit of the heating temperature for high temperature heating is, for example, 100°C. The heating time of high temperature heating is preferably 3 minutes to 10 minutes, more preferably 3 minutes to 6 minutes. Before and/or after the high temperature heating, the laminate may be heated (low temperature heating) at a temperature of less than 85°C. The heating temperature and the heating time of the low-frequency heating can be appropriately set depending on the purpose and the desired characteristics of the resulting optical layered body. The high temperature heating and/or the low temperature heating may also serve as a drying treatment of the adhesive in the lamination of the polarizer, the retardation layer (retardation film) and the protective layer (protection film). The method for forming the polarizer, the retardation layer (retardation film) and the protective layer (protective film) may be as described above or any suitable method. Any appropriate method may be adopted as a method for laminating the polarizer, the retardation layer (retardation film) and the protective layer (protective film).

C. Image Display Device The image display device according to the embodiment of the present invention includes an optical laminate on the viewer side. The optical layered body is the optical layered body according to the embodiment of the present invention described in the above items A and B. The optical layered body is arranged so that the retardation layer is on the viewing side. Typical examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. Such an image display device can realize excellent visibility even when the display screen is viewed through a polarizing lens such as polarized sunglasses by including the above optical laminate on the viewing side. Therefore, such an image display device can be suitably used outdoors.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The evaluation items in the examples are as follows.

(1) Difference in heating dimensional change rate The optical laminates obtained in Examples and Comparative Examples were cut into 4 mm x 50 mm along the slow axis direction and the fast axis direction, respectively, to prepare a measurement sample set. Each measurement sample was chucked with a metal jig so that the length of the measurement portion was 20 mm, and then charged into a heating furnace in that state, and the dimensional change rate with respect to temperature change was measured. Specifically, using a thermal analysis system (TMA7100 manufactured by Hitachi High-Tech Science Co., Ltd.), the temperature is changed from 30° C. to 90° C. at a heating rate of 1.5° C./min, and the dimensional change of each measurement sample is measured. The rate was measured. Within the range of measurement temperature (30°C to 90°C), at the temperature where the difference in dimensional change rate between the measurement sample cut out along the slow axis direction and the measurement sample cut out along the fast axis direction becomes the largest. The difference was defined as the heating dimensional change rate difference. 2 to 4 show profiles of dimensional change rates in the slow axis direction and the fast axis direction with respect to temperature in Example 1 and Comparative Examples 1 and 2, respectively.
(2) Curling direction length The optical laminates obtained in Examples and Comparative Examples were cut into 112 mm×65 mm (5 inch size) so that the absorption axis direction of the polarizer was the long side. When the cut optical laminate curls, the length of the optical laminate in the curl direction was measured. The larger the measured length is, the smaller the curl amount is and the more excellent the handling property is.

[Example 1]
(Production of polarizer)
A PVA-based resin film having a degree of polymerization of 2400, a saponification degree of 99.9 mol% and a thickness of 30 μm is immersed in warm water at 30° C., and the length of the PVA-based resin film is 2.0 times the original length while swelling. Was uniaxially stretched. Next, the mixture of iodine and potassium iodide (weight ratio 0.5:8) is immersed in an aqueous solution (dyeing bath) having a concentration of 0.3% by weight, and the length of the PVA resin film is 3.0, which is the original length. Dyeing was performed while uniaxially stretching so as to double the length. After that, while being immersed in an aqueous solution of 5% by weight of boric acid and 3% by weight of potassium iodide (crosslinking bath 1), the PVA-based resin film was stretched to be 3.7 times its original length, The PVA-based resin film was stretched in an aqueous solution of 4% by weight boric acid and 5% by weight potassium iodide (crosslinking bath 2) at 60° C. so that the length of the PVA-based resin film was 6 times the original length. Furthermore, after performing an iodine ion impregnation treatment with an aqueous solution of 3% by weight potassium iodide (iodine impregnation bath), it was dried in an oven at 60° C. for 4 minutes to obtain a long-length (roll-shaped) polarizer. The thickness of the obtained polarizer was 12 μm. The absorption axis of the polarizer was parallel to the longitudinal direction.
(Retardation film)
A long triacetyl cellulose (TAC) film that was obliquely stretched and on which a hard coat layer was formed was used. The TAC film had a thickness of 40 μm and the hard coat layer had a thickness of 5 μm. The in-plane retardation Re(550) of the TAC film was 105 nm, and the angle formed by the slow axis and the lengthwise direction was 45°.
(Protective film)
A long lactonized polymethylmethacrylate film (thickness 30 μm) was used.

(Preparation of optical laminate)
The above polarizer, the protective film, and the retardation film are bonded together by a roll-to-roll via a polyvinyl alcohol-based adhesive (solid content concentration 5.6% by weight, thickness after drying 0.08 μm) to form a hard coat layer. A laminate having a structure of /retardation layer/polarizer/protective layer was produced. Then, the produced laminated body was dried at 66° C. for 4 minutes and at 86° C. for 4 minutes to obtain an optical laminated body. In the obtained optical layered body, the absorption axis direction of the polarizer was parallel to the longitudinal direction, and the angle formed between the slow axis of the retardation layer and the longitudinal direction was 45°. The total thickness of the obtained optical layered body was 97 μm. Further, when the obtained optical layered body was subjected to the evaluations of (1) and (2) above, the difference in the rate of change in heating dimension was 0.32%, and the length in the curl direction was 102 mm. The curled state is shown in FIG.

[Comparative Example 1]
An optical laminated body was obtained in the same manner as in Example 1 except that the drying conditions of the laminated body were changed to 66° C. for 4 minutes, 70° C. for 2 minutes, and 80° C. for 2 minutes. The difference in heating dimensional change of the obtained optical layered body was 1.03%, and the curl direction length was 42 mm. The curled state is shown in FIG.

[Comparative example 2]
An optical laminate was obtained in the same manner as in Example 1 except that the drying conditions of the laminate were changed to 66° C. for 4 minutes, 70° C. for 17 seconds and 80° C. for 17 seconds. The difference in heating dimensional change of the obtained optical layered body was 1.10%, and the length in the curling direction was 38 mm. The curled state is shown in FIG.

[Evaluation]
As is apparent from FIGS. 5 to 7, the optical layered bodies of the examples of the present invention have a total thickness of 97 μm by controlling the difference in the heating dimensional change rate in the slow axis direction and the fast axis direction. It can be seen that curl can be favorably suppressed even though the thickness is thin.

The optical layered body according to the embodiment of the present invention is suitably used for an image display device, and can be particularly suitably used for an image display device which visually recognizes a display screen through a polarizing lens such as polarized sunglasses.

10 Polarizer 20 Retardation Layer 30 Protective Layer 40 Hard Coat Layer 100 Optical Laminate

Claims (4)

An optical laminate comprising a retardation layer, a polarizer, a protective layer and an adhesive layer in this order,
Retardation layer is formed of a cellulose ester resin film has a function of converting the direct linearly polarized light into circularly polarized light or elliptically polarized light, as well as in-plane retardation Re (550) is 90Nm～120nm,
A heating dimensional change rate of the optical laminate in the slow axis direction or the fast axis direction of the retardation layer and a heating dimensional change rate of the optical laminate in the fast axis direction or the slow axis direction of the retardation layer. der difference of 1.0% or less is,
The optical laminate has a long shape, and an angle formed by the slow axis of the retardation layer and the long direction is 35° to 55°.
Optical stack. The optical laminate according to claim 1, wherein an angle formed by the absorption axis of the polarizer and the slow axis of the retardation layer is 35° to 55°. Wherein the polarizer on the opposite side further comprising a hard coat layer, the optical laminate according to claim 1 or 2 of the retardation layer. Provided on the viewing side of the optical laminate according to any one of claims 1 to 3, wherein the retardation layer is disposed on the viewing side, the image display device.