KR20160112971A - Optical laminate and method of producing the same, and image display device using the optical laminate - Google Patents

Abstract

The present invention provides an optical laminate formed in a thin type, also preventing curl, and having a circle polarization function or an ellipse polarization function. According to an embodiment of the present invention, the optical laminate includes: a polarizer, a phase difference layer disposed on one side of the polarizer, and a protective layer disposed on the other side of the polarizer. The phase difference layer has a function for converting linear polarization into circle polarization or ellipse polarization. According to the optical laminate, the difference ratio between the variation ratio of heating dimension in a first direction and the variation ratio of heating dimension in a second direction is equal to or less than 1.0 %.

Description

TECHNICAL FIELD The present invention relates to an optical laminate, an optical laminate, a method of manufacturing the same, and an image display device using the optical laminate. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to an optical laminate, a manufacturing method thereof, and an image display apparatus using the optical laminate.

2. Description of the Related Art In recent years, opportunities for use of image display devices under strong external light, such as mobile phones, smart phones, tablet-type personal computers (PC), car navigation systems, digital signage, When the image display apparatus is used outdoors in such a manner that the viewer uses polarized sunglasses and views the image display apparatus in accordance with the viewer's viewing angle, the direction of the transmission axis of the polarized sunglasses and the transmission axis direction of the emission side of the image display apparatus The cross-Nicol state is established. As a result, the screen is blackened and the displayed image may not be visually recognized. In order to solve such a problem, a technique has been proposed in which a circularly polarizing plate (polarizing plate for polarizing sunglasses) is arranged on the viewer-side surface of the image display apparatus.

However, a demand for thinning of the image display apparatus has been strengthened, and accordingly, the optical member used in the image display apparatus is also required to be thinned. However, attempting to reduce the thickness of the polarizing plate for polarizing sunglasses as described above has a problem that the curl (in particular, curling in the diagonal direction of the polarizing plate) is remarkable.

Japanese Patent Application Laid-Open No. 2014-16425

An object of the present invention is to provide an optical laminate having a circular polarization function or an elliptically polarizing function which is thin and has curl suppressed.

The optical laminate of the present invention comprises a polarizer, a retardation layer disposed on one side of the polarizer, and a protective layer disposed 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. The optical laminate has a difference in heating dimensional change in the first direction and a heating dimensional change in the second direction substantially orthogonal to the first direction of 1.0% or less.

In one embodiment, the first direction is the slow axis direction or the fast axis direction of the retardation layer, and the second direction is the fast axis direction or the slow axis direction of the retardation layer.

In one embodiment, the angle formed between the absorption axis of the polarizer and the slow axis of the retardation layer is 35 ° to 55 °.

In one embodiment, the optical laminate is an elongated phase, and the angle formed by the slow axis of the retardation layer and the longitudinal direction is 35 ° to 55 °.

In one embodiment, the optical laminate further comprises a hard coat layer on the side opposite to the polarizer of the retardation layer.

In one embodiment, the polarizer, the retardation layer, and the protective layer are bonded to each other with an aqueous adhesive having a solid concentration of 6 wt% or less.

According to another aspect of the present invention, an image display apparatus is provided. This image display apparatus is provided with the optical laminate on the viewing side, and the retardation layer is disposed on the viewer side.

According to an embodiment of the present invention, there is provided an optical laminate having a polarizing element and a retardation layer having a circularly polarizing function or an elliptically polarizing function and a protective layer, wherein the ratio of the heating dimensional change in the first direction and the rate of change in the heating dimension in the first direction are substantially orthogonal By controlling the difference in the heating dimensional change ratio in the first direction and the second direction in which the curling is suppressed. In particular, suppression of curling in the diagonal direction is remarkable.

1 is a schematic sectional view of an optical laminate according to one embodiment of the present invention.
2 is a graph showing the profile of the dimensional change rate in the slow axis direction and the fast axis direction with respect to the temperature in the first embodiment.
3 is a graph showing the profile of the dimensional change rate in the slow axis direction and the fast axis direction with respect to the temperature in Comparative Example 1. FIG.
4 is a graph showing the profile of the dimensional change rate in the slow axis direction and the fast axis direction with respect to the temperature in Comparative Example 2;
5 is a photograph showing the curl state of the optical laminate of Example 1. Fig.
6 is a photograph showing the curl state of the optical laminate of Comparative Example 1. Fig.
7 is a photograph showing the curl state of the optical laminate of Comparative Example 2. Fig.

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 the terms and symbols in the present specification 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 the maximum (that is, the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane Refractive index in the thickness direction.

(2) In-plane retardation (Re)

"Re (λ)" is an in-plane retardation of a film measured at a wavelength of λ nm at 23 ° C. For example, " Re (450) " is the in-plane retardation of the film measured at a wavelength of 450 nm at 23 deg. Re (?) Is obtained by the formula: Re = (nx - ny) xd, where d (nm) is the thickness of the film.

(3) The retardation in the thickness direction (Rth)

"Rth (λ)" is the retardation in the thickness direction of the film measured at a wavelength of 550 nm at 23 ° C. For example, " Rth (450) " is the retardation in the thickness direction of the film measured at a wavelength of 450 nm at 23 deg. Rth (?) Is determined by the formula: Rth = (nx - nz) xd, where d (nm) is the thickness of the film.

(4) Nz coefficient

The Nz coefficient is obtained by Nz = Rth / Re.

(5) substantially orthogonal or parallel

The expression " substantially orthogonal " and " substantially orthogonal " includes the case where the angle formed by the two directions is 90 DEG +/- 10 DEG, preferably 90 DEG +/- 7 DEG, Deg.]. The expression " substantially parallel " and " approximately parallel " include cases where the angle formed by the two directions is 0 deg. 10 deg., Preferably 0 deg. 7 deg. Deg.]. Further, in the present specification, when the terms are simply referred to as " orthogonal " or " parallel, " they may include substantially orthogonal or substantially parallel states.

(6) Angle

In this specification, when referring to an angle, the angle includes angles in both clockwise and counterclockwise directions unless otherwise specified.

(7) Long shrine prize

The term " elongated shape " means a shape having a sufficiently long length with respect to its width. For example, it includes a elongated shape having a length of 10 times or more, preferably 20 times or more.

A. Overall construction of optical laminate

1 is a schematic sectional view of an optical laminate according to one embodiment of the present invention. The optical laminate 100 of this embodiment includes a polarizer 10, a retardation layer 20 disposed on one side of the polarizer 10, and a protective layer 20 disposed on the other side of the polarizer 10, (30). The retardation layer 20 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. Therefore, the optical laminate 100 may be typically a circularly polarizing plate or an elliptically polarizing plate. The optical laminate 100 is typically disposed on the viewer side of the image display apparatus. In this case, the retardation layer 20 is arranged to be on the viewing side. With this configuration, even when a display screen is viewed through a polarizing lens such as polarized sunglasses, excellent visibility can be realized. Therefore, the optical laminate 100 can be preferably applied to an image display apparatus which can be used outdoors.

The optical laminate 100 may further comprise a hard coat layer 40 on the opposite side of the polarizer 10 of the retardation layer 20, if necessary. Further, the optical laminate 100 may have another retardation layer (not shown). The number of the different retardation layers, the arrangement position, optical characteristics (e.g., refractive index ellipsoid, in-plane retardation, thickness retardation, wavelength dispersion characteristics), mechanical properties, and the like can be appropriately set according to the purpose.

The optical laminated body 100 has a difference in heating dimensional change in the first direction and a heating dimensional change in the second direction substantially orthogonal to the first direction of 1.0% or less, preferably 0.8% or less , More preferably not more than 0.6%, and further preferably not more than 0.4%. According to the embodiments of the present invention, it is possible to realize an optical laminated body which is extremely thin and curl is suppressed by controlling the heating dimensional change ratio in two substantially orthogonal directions. 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 rate of change of the heating dimension in the specific two directions, it is possible to further suppress the curl in the 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 between the absorption axis of the polarizer 10 and the slow axis of the retardation layer 20 is preferably 35 to 55 degrees, more preferably 38 to 52 degrees, still more preferably 40 to 50 degrees Particularly preferably 42 DEG to 48 DEG, and particularly preferably 45 DEG. By arranging the retardation layer 20 on the viewing side of the polarizer 10 in such an axial relationship, excellent visibility can be realized even when a display screen is viewed through a polarizing lens such as polarizing sunglasses. Therefore, the optical laminate according to the embodiment of the present invention can also be preferably applied to an image display apparatus that can be used outdoors.

The optical laminate 100 may be a single sheet or a laminate (for example, a roll). In the case where the optical laminate 100 is an elongated phase, the absorption axis direction of the elongated phase polarizer may be a long direction or a width direction. Preferably, the absorption axis direction of the polarizer is a longitudinal direction. This is because the production of the polarizer is easy, and as a result, the production efficiency of the optical laminate is excellent. In the case where the optical laminate is elongated, the angle? Formed by the slow axis of the retardation layer 20 and the longitudinal direction is preferably 35 to 55, more preferably 38 to 52, still more preferably 40 To 50 deg., Particularly preferably 42 deg. To 48 deg., And particularly preferably 45 deg. As described later, by forming the retardation film constituting the retardation layer by oblique stretching, it is possible to form an elongated phase retardation film (retardation layer) having a slow axis in the oblique direction, and consequently to realize an elongated optical laminate have. Such an elongated optical laminate can be produced by roll-to-roll, and therefore, productivity is remarkably excellent.

The total thickness of the optical laminate is typically from 40 탆 to 300 탆, preferably from 60 탆 to 160 탆, more preferably from 80 탆 to 140 탆, and still more preferably from 100 탆 to 120 탆. According to the embodiment of the present invention, an optical laminate having such a very thin thickness and excellent curl suppression can be obtained. 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 any, and the adhesive layer for laminating them.

Each layer constituting the optical laminate according to the embodiment of the present invention will be described below.

A-1. Polarizer

As the polarizer 10, any suitable polarizer may be employed. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

As specific examples of the polarizer composed of the single-layer resin film, a hydrophilic polymer film such as a polyvinyl alcohol (PVA) based resin film, a partially formalized PVA based resin film, and an ethylene / vinyl acetate copolymerization system partially saponified film, Dyes and other dyestuffs, and polyene-based oriented films such as dehydrated PVA and dehydrochlorinated polyvinyl chloride films. Preferably, from the viewpoint of excellent optical characteristics, a polarizer obtained by dying a PVA resin film with iodine and uniaxially stretching is used.

The dyeing by iodine is carried out, for example, by immersing a PVA resin film in an iodine aqueous solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment, or may be performed while dyeing. Further, it may be dyed after stretching. If necessary, swelling treatment, crosslinking treatment, cleaning treatment, drying treatment, and the like are performed on the PVA resin film. For example, before dying, the PVA resin film is immersed in water and washed with water, so that the PVA resin film can be cleaned, and the PVA resin film can be swollen to prevent uneven dyeing have.

As a specific example of the polarizer obtained by using the laminate, a laminate of a resin substrate and a PVA resin layer (PVA resin film) laminated on the resin substrate or a laminate of a PVA resin layer formed on the resin substrate and the resin substrate And a polarizer obtained by using a laminate. A polarizer obtained by using a laminate of a resin substrate and a PVA resin layer formed on the resin substrate can be produced by, for example, applying a PVA resin solution to a resin substrate and drying the PVA resin layer to form a PVA resin layer on the resin substrate , Obtaining a laminate of a resin substrate and a PVA-based resin layer; stretching and staining the laminate to prepare a PVA-based resin layer as a polarizer; In the present embodiment, the stretching typically involves immersing the laminate in an aqueous solution of boric acid and stretching. In addition, the stretching may further include, if necessary, air-stretching the laminate at a high temperature (for example, 95 캜 or higher) before stretching in an aqueous solution of boric acid. The obtained laminate of the resin substrate / polarizer may be used as is (that is, the resin substrate may be the protective layer of the polarizer), the resin substrate is peeled from the laminate of the resin substrate / polarizer, May be laminated and used. Details of the method for producing such a polarizer are described, for example, in Japanese Laid-Open Patent Publication No. 2012-73580. This publication is incorporated herein by reference in its entirety.

The thickness of the polarizer is preferably 15 占 퐉 or less, more preferably 13 占 퐉 or less, further preferably 10 占 퐉, and particularly preferably 8 占 퐉 or less. The lower limit of the thickness of the polarizer is 2 占 퐉 in one embodiment, and 3 占 퐉 in another embodiment. According to the embodiment of the present invention, even when the thickness of the polarizer is very thin as described above, it is possible to satisfactorily suppress curling when the optical laminate is heated.

The polarizer preferably exhibits absorption dichroism at a wavelength of 380 nm to 780 nm. The unit 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 optical laminate that is very thin and curled and curled, and the excellent simple transmittance as described above can be realized in such an optical laminate.

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 laminate which is extremely thin and curl is suppressed, and the above-mentioned excellent polarization degree can be realized in such an optical laminate.

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 exhibits a refractive index characteristic of 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 this range, a retardation film having an appropriate elliptically polarizing performance can be obtained with good productivity and at a reasonable cost. As a result, an optical laminate capable of securing good visibility even when a display screen is viewed through a polarizing lens such as polarizing sunglasses can be obtained with excellent productivity and at a reasonable cost.

The retardation layer 20 represents any suitable refractive index ellipsoid so 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 still more preferably 1 to 1.3.

The retardation layer 20 is composed of any suitable retardation film capable of satisfying the above-described optical characteristics. As a resin for forming the retardation film, a cellulose ester resin (hereinafter, simply referred to as a cellulose ester) is exemplified.

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. Preferably, it is cellulose triacetate, cellulose diacetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate. The cellulose ester may be used alone or in combination.

The cellulose ester is a cellulose ester in which a part or all of the free hydroxyl groups (hydroxyl groups) at the 2-position, the 3-position and the 6-position in the glucose unit constituting the cellulose by the? -1,4-glycoside bond is replaced with an acetyl group, (Polymer) esterified by an acyl group such as < RTI ID = 0.0 > Here, the "acyl group degree of substitution" refers to the sum of the ratios of hydroxyl groups being esterified to the 2-position, 3-position and 6-position of the glucose in the repeating unit. Concretely, when the hydroxyl groups at the 2-position, the 3-position and the 6-position of the cellulose are 100% esterified, the substitution degree is 1, respectively. Therefore, when all of the 2-position, 3-position and 6-position of the cellulose is 100% esterified, the degree of substitution becomes the maximum 3. The "average acyl group substitution degree" refers to an acyl group substitution degree obtained by expressing the degree of acetyl group substitution of a plurality of glucose units constituting the cellulose ester resin as an average value per unit. The acyl group substitution degree can be measured according to ASTM-D817-96.

Examples of the acyl groups include acetyl, propionyl, butanoyl, heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, An octadecanoyl group, an isobutanoyl group, a tert-butanoyl group, a cyclohexanecarbonyl group, an oleyl group, a benzoyl group, a naphthylcarbonyl group and a cinnamoyl group.

In one embodiment, when the acetyl group substitution degree of the cellulose ester resin is X and the propionyl group substitution degree is Y, X and Y preferably satisfy the following formulas (1) and (2) .

Expression (1): 2.0? (X + Y)? 2.8

Equation (2): 0? Y? 1.0

More preferably, the cellulose ester resin satisfying the above-mentioned expressions (1) and (2) is a cellulose ester resin satisfying the following formula (1a) and the formula (2) And a cellulose ester resin.

Formula (1a): 2.0? (X + Y) < 2.5

Expression (1b): 2.5? (X + Y)? 2.8

The " acetyl group degree of substitution " and " propionyl group degree of substitution " are more specific indicators of the above-mentioned acyl group substitution degree, and the " acetyl group degree of substitution " Refers to the sum of the proportion of hydroxyl groups being esterified with an acetyl group and the " propionyl group degree of substitution " means the degree of substitution of the hydroxyl group at the 2-position, 3-position and 6-position of the glucose in the repeating unit with acetyl Represents the sum of the ratios of esterification by the groups.

The cellulose ester resin preferably 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, still more preferably 2.5 to 5.0, and particularly preferably 3.0 ~ 5.0.

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

The cellulose ester resin can be produced by any suitable method. Representative examples include a method comprising the following steps: a step of mixing the raw material cellulose, a predetermined organic acid (e.g., acetic acid, propionic acid), an acid anhydride (e.g. acetic anhydride, propionic anhydride) For example, sulfuric acid) is mixed, the cellulose is esterified, and the reaction is allowed to proceed until the cellulose triester is obtained. In the cellulose triester, the three hydroxyl groups (hydroxyl groups) in the glucose unit are substituted with an acyl acid of an organic acid. When two kinds of organic acids are used at the same time, a mixed ester type cellulose ester (for example, cellulose acetate propionate, cellulose acetate butyrate) can be produced. Subsequently, the cellulose ester having the desired acyl group substitution degree is synthesized by hydrolyzing the cellulose triester. Thereafter, the cellulose ester resin can be obtained through a process such as filtration, precipitation, water washing, dehydration, and drying.

The retardation layer 20 (retardation film) is typically manufactured by stretching a resin film formed of the above-described resin in at least one direction.

As a method of forming the resin film, any appropriate method can be employed. For example, it is possible to use various methods such as a melt extrusion method (for example, a T-die molding method), a cast coating method (for example, a casting method), a calender molding method, a hot pressing method, . Preferably, a T-die molding method, a casting method, and an inflation molding method are used.

The thickness of the resin film (unstretched film) may be set to any appropriate value depending on desired optical properties, stretching conditions to be described later, and the like. Preferably 50 mu m to 300 mu m, and more preferably 80 mu m to 250 mu m.

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

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (for example, refractive index ellipsoid, in-plane retardation, and Nz coefficient) (consequently, a retardation layer) can be obtained.

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

In another embodiment, the retardation layer 20 is produced by obliquely stretching a long-length resin film continuously in the direction of the angle? With respect to the longitudinal direction. By employing the oblique stretching, a elongated stretched film having an orientation angle of angle? With respect to the longitudinal direction of the film is obtained. For example, roll-to-roll can be performed in the lamination with the polarizer, and the manufacturing process can be simplified . The angle &thetas;

Examples of the stretching machine used for oblique stretching include a tenter stretcher capable of imparting a feed force or a pulling force or a pulling force at right and left different velocities in the transverse and / or longitudinal direction. Examples of the tenter-type stretching machine include a transverse uniaxial stretching machine and a simultaneous biaxial stretching machine. However, any suitable stretching machine can be used as long as it can obliquely stretch the elongated resin film continuously.

As the method of oblique stretching, for example, Japanese Patent Application Laid-Open Nos. 50-83482, 2-113920, 3-182701, 2000-9912, Japanese Unexamined Patent Application Publication No. 2002-86554, Japanese Unexamined Patent Publication No. 2002-22944, and the like.

The thickness of the stretched film (consequently, the retardation layer) is preferably 20 to 80 占 퐉, more preferably 30 to 60 占 퐉.

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 used by secondary processing (for example, stretching treatment or surface treatment) depending on the purpose.

The surface of the retardation layer 20 on the polarizer 10 side may be subjected to a surface treatment. Examples of the surface treatment include a corona treatment, a plasma treatment, a frame treatment, a primer coating treatment, and a saponification treatment. As the corona treatment, for example, there is a method of discharging in a normal-pressure air by a corona treatment machine. The plasma treatment may be, for example, a method of discharging in atmospheric air by means of a plasma discharge machine. The frame process may be, for example, a method of bringing the flame directly into contact with the film surface. The primer coating treatment can be performed, for example, by diluting an isocyanate compound, a silane coupling agent, or the like with a solvent and applying the diluted solution thinly. The saponification treatment includes, for example, a method of immersing in an aqueous solution of sodium hydroxide. Preferably, it is a corona treatment or a plasma treatment.

A-3. Protective layer

The protective layer 30 is formed of any suitable film that can be used as the protective layer of the polarizer. Specific examples of the material that becomes the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, And transparent resins such as polystyrene, polystyrene, polynorbornene, polyolefin, (meth) acrylic, and acetate. Further, thermosetting resins such as (meth) acrylic resins, urethane resins, (meth) acrylurethane resins, epoxy resins and silicon resins, and ultraviolet curable resins may also be used. In addition, a glassy polymer such as a siloxane-based polymer may be used, for example. A polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) may also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a phenyl group and a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extrusion molded article of the resin composition.

As the (meth) acrylic resin, Tg (glass transition temperature) is preferably 115 ° C or higher, more preferably 120 ° C or higher, further preferably 125 ° C or higher, particularly preferably 130 ° C or higher. This is because durability can be excellent. The upper limit of the Tg of the (meth) acrylic resin is not particularly limited, but is preferably 170 DEG C or less from the viewpoint of moldability and the like.

As the (meth) acrylic resin, any suitable (meth) acrylic resin may be employed as long as the effect of the present invention is not impaired. Examples thereof include poly (meth) acrylate esters such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymers, methyl methacrylate- (meth) acrylic acid ester copolymers, methyl methacrylate- (Meth) acrylic acid copolymer, a (meth) acrylic acid methyl-styrene copolymer (MS resin and the like), a polymer having an alicyclic hydrocarbon group (for example, a methacrylic acid methyl-methacrylic acid cyclohexyl copolymer, Methyl (meth) acrylate norbornyl copolymer, and the like). Preferable examples include poly (meth) acrylate C _1-6 alkyl such as methyl poly (meth) acrylate. More preferably, the methacrylic acid-based resin having a main component (50 to 100% by weight, preferably 70 to 100% by weight) of methyl methacrylate is exemplified.

Specific examples of the (meth) acrylic resin include, for example, acrylate VH manufactured by Mitsubishi Rayon Co., Ltd., acrylate VRL20A, and (meth) acrylic resin having a ring structure in the molecule described in Japanese Patent Application Laid-Open No. 2004-70296 , And high-Tg (meth) acrylic resins obtained by intramolecular crosslinking or intramolecular cyclization.

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

As the (meth) acrylic resin having the lactone ring structure, there can be mentioned, for example, JP-A 2000-230016, JP-A 2001-151814, JP-A 2002-120326, JP-A 2002-254544, (Meth) acrylic resins having a lactone ring structure described in Japanese Patent Application Laid-Open No. 2005-146084.

The (meth) acrylic resin having a lactone ring structure preferably has a mass average molecular weight (also referred to as a weight average molecular weight) of preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, and still more preferably 10,000 to 500,000 , And particularly preferably from 50,000 to 500,000.

The (meth) acrylic resin having the lactone ring structure preferably has a Tg (glass transition temperature) of preferably 115 ° C or more, more preferably 125 ° C or more, still more preferably 130 ° C or more, particularly preferably 135 ° C or more , And most preferably at least 140 < 0 > C. This is because durability can be excellent. The upper limit of the Tg of the (meth) acrylic resin having the lactone ring structure is not particularly limited, but is preferably 170 占 폚 or less from the viewpoint of moldability and the like.

In the present specification, the term "(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 retardation Rth (550) in the thickness direction is -10 nm to +10 nm.

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

A-4. Hard coat layer

The hard coat layer 40 has functions of imparting chemical resistance, scratch resistance and surface smoothness to the optical laminate, and improving dimensional stability under high temperature and high humidity. As the hard coat layer 40, any suitable configuration may be employed. The hard coat layer is, for example, a cured layer of any suitable UV curable resin. Examples of the ultraviolet ray hardening resin include acrylic resins, silicone resins, polyester resins, urethane resins, amide resins, and epoxy resins. The glass transition temperature of the resin constituting the hard coat layer is preferably 120 占 폚 to 300 占 폚, and more preferably 130 占 폚 to 250 占 폚. With such a range, an optical laminate excellent in dimensional stability under high temperature can be obtained. The hard coat layer may contain any suitable additive, if necessary. Typical examples of the additive include inorganic fine particles and / or organic fine particles.

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

Details of the hard coat layer are described, for example, in Japanese Patent Application Laid-Open No. 2007-171943, the disclosure of which is incorporated herein by reference.

A-5. Adhesive layer

Any suitable adhesive layer (not shown) is used for bonding the respective 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 with an aqueous adhesive. As the water-based adhesive, any suitable water-based adhesive may be employed. Preferably, an aqueous adhesive containing a PVA 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, and more preferably 1000 to 4500, from the viewpoint of adhesiveness. The average degree of saponification is preferably from 85 mol% to 100 mol%, more preferably from 90 mol% to 100 mol%, from the viewpoint of adhesiveness.

The PVA resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because the adhesion between the polarizer and the retardation layer and the protective layer is excellent and the durability is excellent. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by an arbitrary method. The acetoacetyl group-modified degree of the acetoacetyl group-containing PVA-based resin is typically 0.1 mol% or more, preferably 0.1 mol% to 40 mol%, more preferably 1 mol% to 20 mol% Is from 1 mol% to 7 mol%. The degree of modification of the acetoacetyl group 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 still more preferably 0.5% by weight to 6% by weight. When the solid concentration is in this 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 moisture content of the resulting optical laminate increases, and the dimensional change may increase depending on the drying conditions. If the solid content concentration is too high, the viscosity of the adhesive becomes high, and the productivity of the optical laminate may become insufficient.

The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, still more preferably 0.01 μm to 2 μm, particularly preferably 0.01 μm to 1 μm. If the thickness of the adhesive layer is too small, the cohesive force of the adhesive itself can not be obtained, and there is a possibility that the adhesive strength may not be obtained. If the thickness of the adhesive layer is too large, the optical laminate may not be able to satisfy durability.

A-6. Other

In one embodiment, an easy adhesion layer (not shown) may be formed on the surface of the retardation layer 20 on the polarizer 10 side. In the case of forming the adhesion-facilitating layer, the retardation layer 20 may or may not be subjected to the above-described surface treatment. Preferably, the retardation layer 20 is subjected to a surface treatment. By combining the adhesion facilitating layer and the surface treatment, realization of a desired adhesion force between the polarizer 10 and the retardation layer 20 can be promoted. The adhesion facilitating layer preferably contains a silane having a reactive functional group. By forming such an easy-to-adhere layer, realization of a desired adhesion force between the polarizer 10 and the retardation layer 20 can be promoted. The details of the adhesion facilitating layer are described, for example, in Japanese Laid-Open Patent Publication No. 2006-171707.

Practically, a pressure-sensitive adhesive layer (not shown) may be formed on the protective layer 30 side of the optical laminate. Since the pressure-sensitive adhesive layer is formed in advance, it can be easily attached to another optical member (for example, liquid crystal cell, organic EL panel). It is preferable that a release film is adhered to the surface of the pressure-sensitive adhesive layer until it is provided for use.

B. Manufacturing method of optical laminate

Only a characteristic portion will be briefly described with respect to an example of a method for producing an optical laminate according to an embodiment of the present invention. This manufacturing method is a manufacturing method of a laminated body including a polarizer 10, a retardation layer 20 disposed on one side of the polarizer 10, and a protective layer 30 disposed on the other side of the polarizer 10 , And heating the laminate at a temperature of, for example, 85 캜 or higher (hereinafter, sometimes referred to as high-temperature heating). The heating temperature for high temperature heating is preferably 86 DEG C or higher. The upper limit of the heating temperature for high-temperature heating is, for example, 100 占 폚. The heating time for high-temperature heating is preferably 3 minutes to 10 minutes, and more preferably 3 minutes to 6 minutes. The laminate may be heated (low-temperature heating) at a temperature lower than 85 캜 before and / or after the high temperature heating. The heating temperature and the heating time for the low temperature heating can be appropriately set according to the purpose and the desired characteristics of the obtained optical laminate. The high temperature heating and / or low temperature heating may also serve to dry the adhesive in the lamination of the polarizer, the retardation film (retardation film) and the protective layer (protective film). The polarizer, the retardation layer (retardation film), and the protective layer (protective film) may be formed as described above, or any appropriate method may be employed. The lamination method of the polarizer, the retardation layer (retardation film), and the protective layer (protective film) may be any suitable method.

C. Image display device

An image display apparatus according to an embodiment of the present invention includes an optical laminate on the viewing side. The optical laminate is an optical laminate according to the embodiment of the present invention described in the paragraphs A and B above. The optical laminate is arranged such 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 apparatus can provide excellent visibility even when a display screen is viewed through a polarizing lens such as polarizing sunglasses by providing the optical laminate on the viewing side. Therefore, such an image display apparatus can be preferably used also outdoors.

Example

Hereinafter, the present invention will be described in detail 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

The optical laminate obtained in Examples and Comparative Examples was cut into 4 mm 50 mm along the direction of the slow axis and the direction of the fast axis, respectively, to obtain a measurement sample set. Each measurement specimen was chucked with a metal jig so that the length of the measurement part was 20 mm, and put into a heating furnace in this state, and the rate of dimensional change with respect to the temperature change was measured. Specifically, the rate of dimensional change of each measurement sample was measured by changing the temperature from 30 占 폚 to 90 占 폚 at a heating rate of 1.5 占 폚 / min using a thermal analysis system (TMA7100, manufactured by Hitachi High-Tech Science Co., Ltd.). The difference in the dimensional change of the heating dimension was taken as the difference at the temperature at which the difference in the dimensional change rate between the measurement sample cut along the slow axis direction and the measurement sample cut along the fast axis direction was the largest within the measurement temperature range (30 DEG C to 90 DEG C). The profiles of the rate of dimensional change in the direction of the slow axis and the direction of the fast axis with respect to the temperature in Example 1 and Comparative Examples 1 and 2 are shown in Fig. 2 to Fig. 4, respectively.

(2) length in the curl direction

The optical laminate obtained in Examples and Comparative Examples was cut into 112 mm 65 mm (5 inch size) such that the absorption axis direction of the polarizer was at the long side. When the cut optical stacked body was curled, the length of the optical stacked body in the direction of the curl was measured. The larger the measured length, the smaller the curl amount and the better the handling property.

[Example 1]

(Production of Polarizer)

A PVA resin film having a degree of polymerization of 2400, a degree of saponification of 99.9 mol%, and a thickness of 30 탆 was immersed in hot water at 30 캜 and subjected to uniaxial stretching so that the PVA resin film had a length of 2.0 times the original length while swelling. Subsequently, the mixture was immersed in a 0.3% by weight aqueous solution (dyeing bath) of a mixture of iodine and potassium iodide (weight ratio 0.5: 8) and uniaxially stretched so that the length of the PVA resin film was 3.0 times the original length. Thereafter, the PVA resin film was stretched so that the length of the PVA resin film became 3.7 times the original length while immersed in an aqueous solution (crosslinking bath 1) of 5% by weight of boric acid and 3% by weight of potassium iodide. 4% by weight of boric acid at 60 DEG C, In the aqueous solution (crosslinking bath 2) of potassium 5% by weight, the PVA resin film was stretched to have a length of 6 times the original length. Further, iodine ion impregnation treatment was performed with an aqueous solution of 3 wt% potassium iodide (iodine impregnation bath), followed by drying in an oven at 60 ° C for 4 minutes to obtain an elongated (rolled) polarizer. The thickness of the obtained polarizer was 12 占 퐉. The absorption axis of the polarizer was parallel to the longitudinal direction.

(Retardation film)

A long-length triacetylcellulose (TAC) film which was obliquely stretched and on which a hard coat layer was formed was used. The thickness of the TAC film was 40 占 퐉, and the thickness of the hard coat layer was 5 占 퐉. The in-plane retardation Re (550) of the TAC film was 105 nm, and the angle between the slow axis and the longitudinal direction was 45 °.

(Protective film)

A long-form lactonized polymethyl methacrylate film (thickness 30 탆) was used.

(Fabrication of optical laminate)

The polarizer, the protective film and the retardation film were laminated by roll-to-roll through a polyvinyl alcohol adhesive (solid concentration: 5.6 wt%, thickness after drying: 0.08 mu m) to form a hard coat layer / retardation layer / polarizer / Was prepared. ≪ tb > < TABLE > Thereafter, the resulting laminate was dried at 66 DEG C for 4 minutes and at 86 DEG C for 4 minutes to obtain an optical laminate. In the optical laminate thus obtained, the absorption axis direction of the polarizer was parallel to the longitudinal direction, and the angle formed by the slow axis and the longitudinal direction of the retardation layer was 45 DEG. The total thickness of the obtained optical laminate was 97 탆. Further, as a result of providing the obtained optical laminate to the evaluations of the above items (1) and (2), the difference in dimensional change after heating was 0.32% and the length in the curl direction was 102 mm. The curl state is shown in Fig.

[Comparative Example 1]

An optical laminate was obtained in the same manner as in Example 1 except that the drying conditions of the laminate were changed from 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 laminate was 1.03% and the length in the curl direction was 42 mm. The state of curl 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 laminate was 1.10%, and the length in the curl direction was 38 mm. The state of curl is shown in Fig.

[evaluation]

As apparent from Figs. 5 to 7, the optical laminate of the example of the present invention controls the difference in heating dimensional change between the slow axis direction and the fast axis direction, thereby achieving a very thin thickness of 97 mu m in total thickness, It can be suppressed to be suppressed.

Industrial availability

The optical laminate according to the embodiment of the present invention is preferably used for an image display apparatus and can be particularly preferably used for an image display apparatus for viewing 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 (7)

A polarizer, a retardation layer disposed on one side of the polarizer, and a protective layer disposed on the other side of the polarizer,
Wherein the retardation layer has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light,
Wherein a difference between a heating dimensional change ratio in the first direction and a heating dimensional change rate in the second direction substantially orthogonal to the first direction is 1.0% or less. The method according to claim 1,
Wherein the first direction is the slow axis direction or the fast axis direction of the retardation layer and the second direction is the fast axis direction or the slow axis direction of the retardation layer. The method according to claim 1,
And an angle formed by an absorption axis of the polarizer and a slow axis of the retardation layer is 35 ° to 55 °. The method according to claim 1,
And the angle formed by the slow axis of the retardation layer and the longitudinal direction is 35 ° to 55 °. The method according to claim 1,
And a hard coat layer on the side opposite to the polarizer of the retardation layer. The method according to claim 1,
Wherein the polarizer, the retardation layer, and the protective layer are bonded with an aqueous adhesive having a solid concentration of 6 wt% or less. An image display device comprising the optical laminate according to claim 1 on a viewing side and the retardation layer on a viewing side.

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