WO2018212112A1 - Circularly polarizing film, circularly polarizing film with adhesive layer, and image display device - Google Patents

Abstract

The present invention relates to a circularly polarizing film which is provided with a polarizer, a retardation film that is arranged on one side of the polarizer, and a protective layer that is arranged on the other side of the polarizer, and which is characterized in that: the retardation film has a function of converting linearly polarized light to circularly polarized light or elliptically polarized light; the retardation film has a thickness of 35 μm or less; both surfaces of the retardation film have different fracture initiation loads in a scratch test; and if the first surface has a higher fracture initiation load and the second surface has a lower fracture initiation load, the polarizer is bonded to the first surface of the retardation film. A circularly polarizing film according to the present invention has excellent impact resistance and excellent reworkability, and is able to suppress curling.

Description

Circular polarizing film, circular polarizing film with pressure-sensitive adhesive layer, and image display device

The present invention relates to a circularly polarizing film. Moreover, this invention relates to the circularly-polarizing film with an adhesive layer using the said circularly-polarizing film. Furthermore, it is related with the image display apparatus using the said circularly-polarizing film or the circularly-polarizing film with an adhesive layer. The circularly polarizing film of the present invention is suitably used for an image display device, and can be particularly suitably used for an image display device that visually recognizes a display screen through a polarizing lens such as polarized sunglasses.

In recent years, image display devices such as mobile phones, smartphones, tablet personal computers (PCs), car navigation systems, digital signage, window displays, etc. have been increasingly used under strong external light. When the image display device is used outdoors as described above, when the viewer views the image display device wearing polarized sunglasses, the transmission axis direction of the polarized sunglasses and the emission of the image display device depend on the viewing angle. As a result, the screen becomes black and the display image may not be visually recognized. In order to solve such a problem, a technique has been proposed in which a circularly polarizing film (a polarizing film for polarizing sunglasses) is disposed on the viewing-side surface of the image display device (Patent Document 1). Further, the image display device as described above is easily subjected to external impact such as dropping or collision, and the circularly polarizing film is also required to have impact resistance.

In addition, when an optical film such as a circularly polarizing film is bonded to a liquid crystal cell or the like, the optical film is peeled off from the liquid crystal panel even when the bonding position is wrong or a foreign object is caught in the bonding surface. In some cases, liquid crystal cells or the like are reused. In such a peeling step, re-peelability (reworkability) that can peel the entire optical film from the liquid crystal panel without adhesive residue is required.

In the circularly polarizing film, a retardation film having a circularly polarizing function or an elliptical polarizing function may be used as a protective film provided on one side of the polarizer. As the retardation film, a stretched polycarbonate film and a stretched norbornene polymer film are known. However, polycarbonate films and norbornene-based polymer films are low in moisture permeability and have good dimensional stability in a humidity environment. On the other hand, when polycarbonate films are used, in-plane retardation Re due to a large photoelastic coefficient is uneven. There was a serious problem that occurred. Moreover, when using a norbornene film as the retardation film on the viewing side (further viewing side than the polarizer) than the optical cell (for example, a liquid crystal cell), sebum or detergent adheres to the norbornene film, There has been a serious problem that the norbornene-based film is cracked or dissolved by the solvent contained in the interlayer resin when the circularly polarizing film is fully laminated.

On the other hand, a cellulose ester film such as a cellulose acetate film or a cellulose acetate propionate film can be used as the retardation film of the circularly polarizing film. Since the cellulose ester film has a small photoelastic coefficient, unevenness of the in-plane retardation Re is unlikely to occur, and it is possible to suppress the generation and dissolution of cracks even when touched by sebum, detergent, or solvent (patent) Reference 2). Moreover, the retardation film obtained by extending | stretching a cellulose-ester type film is usually used for TV, and the thickness is generally 40 μm or more.

JP 2014-16425 A JP 2016-177165 A

Incidentally, recent image display devices are required to be thin, and the retardation film is also required to be thin. Further, since the retardation film is obtained by stretching, curling is likely to occur, and a reduction in thickness is also required from the viewpoint of curling. However, a circularly polarizing film in which a retardation film obtained by stretching a cellulose ester film is bonded to a polarizer is in the vicinity of the surface where the retardation film and the polarizer are bonded during external impact or rework. There was a problem of peeling off.

The present invention is a circularly polarizing film comprising a polarizer, a retardation film disposed on one side of the polarizer, and a protective layer disposed on the other side of the polarizer, An object of the present invention is to provide a circularly polarizing film that is excellent in impact properties and reworkability and can suppress curling.

Another object of the present invention is to provide a circularly polarizing film with an adhesive layer using the circularly polarizing film, and further to provide an image display device using the circularly polarizing film or the circularly polarizing film with an adhesive layer. And

As a result of intensive studies, the inventors of the present application have found that the above-described problems can be solved by the following circularly polarizing film and the like, and have reached the present invention.

That is, the present invention comprises a polarizer, a retardation film disposed on one side of the polarizer, and a protective layer disposed on the other side of the polarizer,
The retardation film has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light, has a thickness of 35 μm or less, and
When both sides of the retardation film have different fracture start loads in the scratch test, the side having the higher fracture start load is the first surface and the lower side is the second surface.
The said polarizer is related with the circularly-polarizing film characterized by being bonded by the 1st surface of the said retardation film.

In the circularly polarizing film, it is preferable that the fracture start load on the first surface of the retardation film is 55 mN or more.

The circularly polarizing film may have a surface functional layer on the second surface of the retardation film.

In the circularly polarizing film, an angle formed between the absorption axis of the polarizer and the slow axis of the retardation film is preferably 35 ° to 55 °. When the circularly polarizing film is long, the angle formed between the slow axis of the retardation film and the long direction is preferably 35 ° to 55 °.

In the circularly polarizing film, the retardation film is a stretched product of a resin film molded on a casting body by a solution casting method, and is suitable when the casting body side surface of the resin film is the first surface. It is.

In the circularly polarizing film, the retardation film can be a cellulose ester film.

In the circularly polarizing film, a film in which the polarizer, the retardation film and the protective layer are bonded through an adhesive layer can be used.

The present invention also relates to a circularly polarizing film with an adhesive layer, characterized by having the circularly polarizing film and an adhesive layer.

Furthermore, the present invention provides a circularly polarizing film or a circularly polarizing film with an adhesive layer on the viewing side of the optical cell, and the retardation film is disposed on the viewing side with respect to the polarizer. Device.

Polycarbonate films and norbornene-based polymer films are generally formed by a melt extrusion method, and there is no difference in physical properties on both sides of the film obtained by such a film formation method. On the other hand, a film forming method using a solution casting method is generally used for the cellulose ester film. In the solution casting method, a resin solution (dope) is poured onto a smooth drum (casting drum) or stainless steel smooth belt, and the film is formed by evaporating the solvent through a heating process. To do. In such a solution casting method, the solvent removal proceeds quickly on the side not in contact with the belt or drum surface (air side). Therefore, when forming a thin film, the air side is in contact with the belt or drum surface. It is easier to cure than the side it is on (there is something like a skin burr on the surface). As a result, it was found that the film obtained by the solution casting method has different physical properties on both sides. Moreover, when bonding the film obtained by a solution casting method to another film, it also turned out that the said air side is bonded together for convenience.

Further, the retardation film used for the circularly polarizing film can be obtained by subjecting it to an oblique stretching treatment so that the angle formed by the width direction and the in-plane slow axis is within a predetermined range. Therefore, when the film having different physical properties on both sides as described above is subjected to high stretching by the oblique stretching, the air side of the obtained retardation film is mechanically brittle compared to the opposite surface. I understood that. In particular, in the case of a thin film, the mechanical properties on the air side were fragile. As a result, when a thin retardation film is bonded to the polarizer, it is presumed that peeling occurred at the time of impact or rework.

From the above findings, in the circularly polarizing film of the present invention, when a retardation film having a different physical property on both sides (having a function of converting linearly polarized light into circularly polarized light or elliptically polarized light) is disposed in the polarizer, the retardation is measured. In the film, the side having a high mechanical characteristic, that is, the side having a high fracture start load was bonded to the polarizer using the fracture start load in the scratch test as an index. Although thinning of the film is not preferable from the viewpoint of impact resistance and reworkability, in the present invention, by adopting such a configuration, a retardation film having a thickness of 35 μm or less is used. In addition, it is possible to provide a circularly polarizing film that is less likely to cause cohesive failure near the bonded surface of the retardation film and the polarizer even during impact or rework, and that is excellent in impact resistance and reworkability. In the present invention, curling can be suppressed by using a retardation film having a thickness of 35 μm or less.

It is a schematic sectional drawing which shows an example of the structure cross section of the circularly-polarizing film of this invention. It is an image which shows the scratch mark in the measurement of a fracture start load before the fracture start (non-destructive part). It is an image which shows the scratch mark in the fracture start point of the measurement of a fracture start load.

(Definition of terms and symbols)
The definitions of terms and symbols in this 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 maximum (ie, the slow axis direction), and “ny” is the direction orthogonal to the slow axis in the plane (ie, the fast axis direction). “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 determined by the formula: Re = (nx−ny) × d, where d (nm) is the thickness of the film.
(3) Thickness direction retardation (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 determined by the formula: Rth = (nx−nz) × d, 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 expressions “substantially orthogonal” and “substantially orthogonal” include the case where the angle between 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 between two directions is 0 ° ± 10 °, preferably 0 ° ± 7 °, more preferably 0 ° ± 5 °. Further, in the present specification, the term “orthogonal” or “parallel” may include a substantially orthogonal state or a substantially parallel state.
(6) Angle When referring to an angle in this specification, unless otherwise specified, the angle includes angles in both clockwise and counterclockwise directions.
(7) Long shape “Long shape” means a long and narrow shape that is sufficiently long with respect to the width. Includes shape.

<Overall configuration of polarizing film>
FIG. 1 is a schematic cross-sectional view showing an example of the cross-section of the circularly polarizing film of the present invention. A circularly polarizing film F of FIG. 1 includes a polarizer 1, a retardation film 2 disposed on one side of the polarizer 1, and a protective layer 3 disposed on the other side of the polarizer 1. The retardation film 2 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. Therefore, the circularly polarizing film of the present invention means a circularly polarizing film or an elliptically polarizing film. The circularly polarizing film F is typically disposed on the viewing side of the image display device. In this case, it arrange | positions so that the phase difference film 2 may become a visual recognition side. With the configuration as described above, excellent visibility can be realized even when the display screen is viewed through a polarizing lens such as polarized sunglasses. Therefore, the circularly polarizing film F can be suitably applied to an image display device that can be used outdoors.

As the retardation film 2, films having different fracture starting loads in the double-side scratch test are used. In the retardation film 2, the side with the higher fracture start load is the first surface 2 a and the side with the lower fracture load is the second surface 2 b. As shown in FIG. 1, the polarizer 1 is bonded to the first surface 2 a side of the retardation film 2.

The circularly polarizing film F may further include a surface functional layer 4 on the second surface 2b (the side opposite to the polarizer 1) of the retardation film 2 as necessary. Furthermore, the circularly polarizing film F may include another retardation film (not shown). The number of different retardation films, arrangement position, optical characteristics (for example, refractive index ellipsoid, in-plane retardation, thickness direction retardation, wavelength dispersion characteristics), mechanical characteristics, etc. can be appropriately set according to the purpose. .

The polarizer 1 and the retardation film 2 are laminated so that the absorption axis of the polarizer 1 and the slow axis of the retardation film 2 form a predetermined angle. The angle formed by the absorption axis of the polarizer 1 and the slow axis of the retardation film 2 is preferably 35 ° to 55 °, more preferably 38 ° to 52 °, still more preferably 40 ° to 50 °. Particularly preferably, it is 42 ° to 48 °, and particularly preferably around 45 °. By arranging the retardation film 2 on the viewing side with respect to the polarizer 1 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 polarizing film according to the embodiment of the present invention can be suitably applied to an image display device that can be used outdoors.

The circularly polarizing film F may be a single wafer or a long shape (for example, a roll). When the circularly polarizing film F is long, the absorption axis direction of the long polarizer may be the long direction or the width direction. Preferably, the absorption axis direction of the polarizer is a long direction. This is because the polarizer can be easily manufactured, and as a result, the manufacturing efficiency of the circularly polarizing film is excellent. When the circularly polarizing film is long, the angle θ formed between the slow axis of the retardation film 2 and the long direction is preferably 35 ° to 55 °, more preferably 38 ° to 52 °, and further The angle is preferably 40 ° to 50 °, particularly preferably 42 ° to 48 °, and particularly preferably around 45 °. As described later, by forming the retardation film constituting the retardation film by oblique stretching, a long retardation film (retardation film) having a slow axis in the oblique direction can be formed. As described above, a long circularly polarizing film can be realized. Since such a long circularly polarizing film can be produced by roll-to-roll, productivity is remarkably improved.

The total thickness of the circularly polarizing film is typically 40 μm to 300 μm, preferably 40 μm to 160 μm, more preferably 50 μm to 140 μm, and further preferably 60 μm to 120 μm. According to the embodiment of the present invention, it is possible to obtain a circularly polarizing film that has such a very thin thickness and is curled well. The total thickness of the circularly polarizing film refers to the total thickness of the polarizer, the retardation film, the protective layer, the surface functional layer if present, and the adhesive layer for laminating them.

Hereinafter, each layer constituting the circularly polarizing film according to the embodiment of the present invention will be described.

<Polarizer>
Any appropriate polarizer can be adopted as the polarizer 1. 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 polarizers composed of a single layer resin film include high hydrophilicity such as polyvinyl alcohol (PVA) resin film, partially formalized PVA resin film, ethylene / vinyl acetate copolymer partially saponified film, etc. Examples of molecular films that have been dyed and stretched with dichroic substances such as iodine and dichroic dyes, polyene-based oriented films such as PVA dehydrated products and polyvinyl chloride dehydrochlorinated products It is done. Preferably, a polarizer obtained by dyeing a PVA resin film with iodine and uniaxially stretching is used because of excellent optical properties.

The dyeing with iodine is performed, for example, by immersing a PVA resin film in an aqueous iodine 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. Moreover, you may dye | stain after extending | stretching. If necessary, the PVA-based resin film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, and the like. For example, by immersing the PVA resin film in water and washing it before dyeing, the PVA resin film surface can be cleaned of stains and anti-blocking agents, and the PVA resin film can be swollen and dyed. Unevenness can be prevented.

As a specific example of a polarizer obtained by using a laminate, a laminate of a resin substrate and a PVA resin layer (PVA resin film) laminated on the resin substrate, or a resin substrate and the resin Examples thereof include a polarizer obtained by using a laminate with a PVA resin layer applied and formed on a substrate. For example, a polarizer obtained by using a laminate of a resin base material and a PVA resin layer applied and formed on the resin base material may be obtained by, for example, applying a PVA resin solution to a resin base material and drying it. A PVA-based resin layer is formed thereon to obtain a laminate of a resin base material and a PVA-based resin layer; the laminate is stretched and dyed to make the PVA-based resin layer a polarizer; obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. Furthermore, the stretching may further include, if necessary, stretching the laminate in the air at a high temperature (for example, 95 ° C. or higher) before stretching in the aqueous boric acid solution. The obtained resin base material / polarizer laminate may be used as it is (that is, the resin base material may be used as a protective layer of the polarizer), and the resin base material is peeled from the resin base material / polarizer laminate. Any appropriate protective layer according to the purpose may be laminated on the release surface. Details of a method for manufacturing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. This publication is incorporated herein by reference in its entirety.

The thickness of the polarizer is preferably 15 μm or less, more preferably 13 μm or less, still more preferably 10 μm, and particularly preferably 8 μm or less. The lower limit of the polarizer thickness is 2 μm in one embodiment and 3 μm in another embodiment. According to the embodiment of the present invention, even when the thickness of the polarizer is very thin, curling when the polarizing film is heated can be satisfactorily suppressed.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 42.0% to 45.5%, more preferably 42.5% to 45.0%. According to the present invention, it is possible to realize a polarizing film that is very thin and curl-suppressed, and further, in such a polarizing film, excellent single transmittance as described above can be realized.

As described above, the degree of polarization 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 a polarizing film that is very thin and curl-suppressed, and further, in such a polarizing film, the above-described excellent degree of polarization can be realized.

<Phase difference film>
As described above, the retardation film 2 has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light. That is, the retardation film 2 typically has a relationship in which the refractive index characteristic is 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 elliptical polarization performance can be obtained with excellent productivity and reasonable cost. As a result, a polarizing film that can ensure good visibility even when the display screen is viewed through a polarizing lens such as polarized sunglasses can be obtained with excellent productivity and reasonable cost.

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

The retardation film 2 is composed of any appropriate retardation film that can satisfy the optical characteristics as described above. In addition, as the retardation film 2, films having different fracture start loads in the double-side scratch test are used. As described above, in the retardation film 2, the side with the higher fracture start load is the first surface 2 a and the side with the lower fracture load is the second surface 2 b. The fracture start load of the first surface 2a is preferably 55 mN or more. When the fracture start load satisfies 55 mN or more, cohesive failure in the vicinity of the surface of the first surface 2a is unlikely to occur, and the impact resistance and reworkability of the circularly polarizing film obtained by bonding to the polarizer are satisfied. Is preferable. The fracture start load of the first surface 2a is preferably 58 mN or more, more preferably 60 mN or more, and further preferably 70 mN or more.

A typical example of the resin forming the retardation film is a cellulose ester resin (hereinafter, also simply referred to as cellulose ester).

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. Cellulose esters may be used alone or in combination.

Cellulose ester is an acyl group such as an acetyl group or a propionyl group in which some or all of the free hydroxyl groups (hydroxyl groups) at the 2nd, 3rd and 6th positions in the glucose unit constituting cellulose by β-1,4-glycoside bonds It is a polymer esterified by (polymer). Here, the “acyl group substitution degree” represents the total of the ratio of hydroxyl groups esterified with respect to the 2nd, 3rd and 6th positions of glucose as a repeating unit. Specifically, the degree of substitution is 1 when the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are each 100% esterified. Therefore, when all of the 2nd, 3rd and 6th positions of cellulose are 100% esterified, the degree of substitution is 3 at the maximum. The “average acyl group substitution degree” refers to an acyl group substitution degree in which the acyl group substitution degree of a plurality of glucose units constituting the cellulose ester resin is expressed as an average value per unit. The degree of acyl group substitution 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, and isobutanoyl. Group, tert-butanoyl group, cyclohexanecarbonyl group, oleoyl group, benzoyl group, naphthylcarbonyl group, 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).
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) includes a cellulose ester resin satisfying the following formula (1a) and the above formula (2), and a cellulose ester resin satisfying the following formula (1b): , Containing.
Formula (1a): 2.0 ≦ (X + Y) <2.5
Formula (1b): 2.5 ≦ (X + Y) ≦ 2.8 Note that “acetyl group substitution degree” and “propionyl group substitution degree” are more specific indicators of the above-mentioned acyl group substitution degree. The “group substitution degree” represents the sum of the ratios of hydroxyl groups esterified with acetyl groups at the 2-position, 3-position and 6-position of glucose of the repeating unit, and “propionyl group substitution degree” The total of the ratio by which the hydroxyl group is esterified by the acetyl group about 2nd-position, 3rd-position, and 6th-position of glucose is represented.

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

Arbitrary appropriate cellulose can be used as a cellulose of the raw material of a cellulose ester resin. Specific examples include cotton linters, wood pulp, and kenaf. A cellulose ester resin 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 comprising the following procedures: raw 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 cellulose triester, the three hydroxyl groups (hydroxyl groups) of the glucose unit are substituted with an acyl acid of an organic acid. When two types 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 prepared. Next, a cellulose ester having a desired degree of acyl group substitution is synthesized by hydrolyzing the cellulose triester. Thereafter, a cellulose ester resin can be obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying.

The retardation film 2 (retardation film) is typically produced by stretching a resin film formed from the resin as described above in at least one direction.

Arbitrary appropriate methods can be employ | adopted as a formation method of a resin film. For example, a melt extrusion method (for example, a T-die molding method), a cast coating method (for example, a casting method), a calendar molding method, a hot press method, a co-extrusion method, a co-melting method, a multilayer extrusion method, an inflation molding method, etc. It is done. Preferably, a T-die molding method, a casting method, and an inflation molding method are used.

As the resin film used for the retardation film used in the present invention (those having different fracture initiation loads in the double-side scratch test), those obtained by a solution casting method are preferably used. In the solution casting method, a resin solution (dope) is poured onto a casting body (casting drum or stainless steel smooth belt) having a smooth surface, and the solvent is evaporated through a process of heating the film to form a film. Mold. In such a solution casting method, since solvent removal proceeds faster on the side not in contact with the casting body (air side), the fracture start load of the obtained resin film is smaller on the air side than on the casting body side. In a retardation film obtained by stretching a resin film obtained by such a solution casting method, the surface on the casting body side of the resin film becomes the first surface.

The thickness of the resin film (unstretched film) can be set to any appropriate value according to desired optical characteristics, stretching conditions described later, and the like. The thickness is preferably 50 μm to 250 μm, more preferably 80 μm to 200 μm.

Any appropriate stretching method and stretching conditions (for example, stretching temperature, stretching ratio, stretching direction) may be employed 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 singly or simultaneously or sequentially. The stretching direction can also be performed in various directions and dimensions such as a horizontal direction, a vertical direction, a thickness direction, and a 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 (as a result, a retardation film) having the desired optical properties (for example, refractive index ellipsoid, in-plane retardation, Nz coefficient) is obtained. Can do.

In one embodiment, the retardation film 2 is produced by uniaxially stretching a resin film or uniaxially stretching a fixed end. As a specific example of uniaxial stretching, there is a method of stretching in the longitudinal direction (longitudinal direction) while running the resin film in the longitudinal direction. Another specific example of the uniaxial stretching includes a method of stretching in the transverse direction using a tenter. The draw ratio is preferably 10% to 500%.

In another embodiment, the retardation film 2 is produced by continuously stretching a long resin film obliquely in the direction of the angle θ with respect to the long direction. By adopting oblique stretching, a long stretched film having an orientation angle of an angle θ with respect to the longitudinal direction of the film can be obtained. For example, roll-to-roll is possible when laminating with a polarizer. Can be simplified. The angle θ is as described above.

Examples of the stretching machine used for the oblique stretching include a tenter type stretching machine capable of adding feed forces, pulling forces, or pulling forces at different speeds in the lateral and / or longitudinal directions. The tenter type stretching machine includes a horizontal uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, but any suitable 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, JP-A-2002-86554, Examples thereof include the method described in JP-A-2002-22944.

The thickness of the retardation film (for example, the stretched film) is 35 μm or less. As the thickness increases, shrinkage and expansion tend to increase, and when the thickness exceeds 40 μm, the amount of panel warpage (curl) in reliability of heating and humidity increases. The thickness is preferably 38 μm or less, and more preferably 35 μm or less. On the other hand, when the thickness is reduced, the load is reduced even on the surface with the large fracture start load (first surface), and the peel force is reduced. Therefore, the thickness is preferably 15 μm or more, and more preferably 20 μm or more. Is preferred.

As the retardation film constituting the retardation film 2, a commercially available film may be used as it is as long as it satisfies the requirements of the present invention, and the commercially available film is subjected to secondary processing (for example, stretched). Treatment, surface treatment).

The surface of the retardation film 2 on the polarizer 1 side may be subjected to 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 in which discharge is performed in normal pressure air by a corona treatment machine. As the plasma treatment, for example, a method of discharging in a normal pressure air by a plasma discharge machine can be mentioned. An example of the frame treatment is 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 or the like with a solvent and coating the diluted solution thinly. Examples of the saponification treatment include a method of immersing in a sodium hydroxide aqueous solution. Corona treatment and plasma treatment are preferable.

<Protective layer>
The protective layer 3 is formed of any appropriate film that can be used as a protective layer for a polarizer. Specific examples of the material as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyvinyl alcohols, polycarbonates, nylons and aromatic polyamides. Such as polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin such as ethylene / propylene copolymer, cycloolefin or cycloolefin having a norbornene structure, (meth) acrylic And transparent resins such as acetates. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included.

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, and particularly preferably 130 ° C. or higher. It is because it can be excellent in durability. Although the upper limit of Tg of the said (meth) acrylic-type resin is not specifically limited, From viewpoints of a moldability etc., Preferably it is 170 degrees C or less.

As said (meth) acrylic-type resin, arbitrary appropriate (meth) acrylic-type resins can be employ | adopted within the range which does not impair the effect of this invention. For example, poly (meth) acrylate 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, (meth) acrylic acid methyl-styrene copolymer (MS resin, etc.), polymer having alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymer) And methyl methacrylate- (meth) acrylate norbornyl copolymer). Preferably, poly (meth) acrylate C _1-6 alkyl such as poly (meth) acrylate methyl is used. More preferred is a methyl methacrylate resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight).

Specific examples of the (meth) acrylic resin include (meth) acrylic resins having a ring structure in the molecule described in, for example, Acrypet VH and Acrypet VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and JP-A-2004-70296. Examples of the resin include 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 that it has high heat resistance, high transparency, and high mechanical strength.

Examples of the (meth) acrylic resin having the lactone ring structure include JP 2000-230016, JP 2001-151814, JP 2002-120326, JP 2002-254544, and JP 2005. Examples thereof include (meth) acrylic resins 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), preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, still more preferably 10,000 to 500,000. Preferably it is 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, still more preferably 130 ° C. or higher, particularly preferably 135 ° C., most preferably. Is 140 ° C. or higher. It is because it can be excellent in durability. The upper limit of Tg of the (meth) acrylic resin having the lactone ring structure is not particularly limited, but is preferably 170 ° C. or less from the viewpoint of moldability and the like.

In this specification, “(meth) acrylic” refers to acrylic and / or methacrylic.

The protective layer 3 is preferably optically isotropic. In this 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 protective layer is preferably 5 μm to 60 μm, more preferably 10 μm to 40 μm.

<Surface functional layer>
A surface functional layer 4 can be provided on the second surface of the retardation film 2. Examples of the surface functional layer include a hard coat layer, an antireflection layer, an antisticking layer, a diffusion layer, and an antiglare layer. The functional layers such as the hard coat layer, the antireflection layer, the antisticking layer, the diffusion layer and the antiglare layer can be provided on the retardation film itself, and separately provided separately from the retardation film. You can also.

As the surface functional layer, for example, a hard coat layer is preferably applied. The hard coat layer has a function of imparting chemical resistance, scratch resistance and surface smoothness to the circularly polarizing film and improving dimensional stability under high temperature and high humidity. Any appropriate configuration can be adopted as the hard coat layer. The hard coat layer is, for example, a cured layer of any appropriate ultraviolet curable resin. Examples of the ultraviolet curable 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 ° C. to 300 ° C., more preferably 130 ° C. to 250 ° C. If it is such a range, the polarizing film excellent in the dimensional stability under high temperature can be obtained. The hard coat layer may contain any appropriate additive as required. Representative examples of the additive include inorganic fine particles and / or organic fine particles.

Note that details of the hard coat layer are described in, for example, Japanese Patent Application Laid-Open No. 2007-171943, and the description thereof is incorporated herein by reference.

The thickness of the surface functional layer 4 is preferably 10 μm or less, more preferably 1 μm to 8 μm, and further preferably 2 μm to 7 μm.

<Adhesive layer>
Arbitrary appropriate adhesive layers (not shown) are used for bonding of the layers constituting the circularly polarizing film according to the embodiment of the present invention. The adhesive layer may be a pressure-sensitive adhesive layer or an adhesive layer. The adhesive layer is formed of an adhesive. The type of the adhesive is not particularly limited, and various types can be used. The adhesive layer is not particularly limited as long as it is optically transparent. Examples of the adhesive include water-based, solvent-based, hot-melt-based, active energy ray-curable types, and the like. Or an active energy ray hardening-type adhesive agent is suitable.

Typically, the polarizer 1, the retardation film 2 and the protective layer 3 are bonded together with an aqueous adhesive. Any appropriate aqueous adhesive can be adopted as the aqueous adhesive. Preferably, an aqueous adhesive containing a PVA resin is used. The average degree of polymerization of the PVA resin contained in the aqueous adhesive is preferably about 100 to 5500, more preferably 1000 to 4500 from the viewpoint of adhesiveness. The average saponification degree is preferably about 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, from the viewpoint of adhesiveness.

The PVA resin contained in the aqueous adhesive preferably contains an acetoacetyl group. This is because the adhesion between the polarizer, the retardation film and the protective layer is excellent and the durability can be excellent. The acetoacetyl group-containing PVA resin can be obtained, for example, by reacting a PVA resin and diketene by an arbitrary method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, more preferably 1 mol% to 20 mol. %, Particularly preferably 1 mol% to 7 mol%. The degree of acetoacetyl group modification 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. If solid content concentration is such a range, there exists an advantage that the dimensional control rate of a polarizing plate is easy to control. If the solid content concentration is too low, the water content of the obtained polarizing film 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 increases, and the productivity of the polarizing film may be insufficient.

The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.05 μm to 5 μm, still more preferably 0.05 μm to 2 μm, and particularly preferably 0.1 μm to 1 μm. If the thickness of the adhesive layer is too thin, the cohesive force of the adhesive itself cannot be obtained, and the adhesive strength may not be obtained. If the thickness of the adhesive layer is too thick, the circularly polarizing film may not satisfy the durability.

The pressure-sensitive adhesive layer can be provided on one side or both sides of the circularly polarizing film F (not shown). For example, since the pressure-sensitive adhesive layer is provided in advance on the protective layer 3 side of the circularly polarizing film F, it can be easily bonded to another optical member (for example, a liquid crystal cell or an organic EL panel). In addition, it is preferable that the peeling film is bonded together on the surface of this adhesive layer until it uses. On the other hand, the adhesive layer on the viewing side (retardation film 2 side) is suitable for members such as an input device such as a touch panel applied on the viewing side of an image display device, a transparent substrate such as a cover glass and a plastic cover, for example. Can be applied.

<Method for producing circularly polarizing film>
About an example of the manufacturing method of the circularly-polarizing film by embodiment of this invention, only a characteristic part is demonstrated easily. This manufacturing method produces the laminated body which has the polarizer 1 and the phase difference film 2 arrange | positioned at one side of the polarizer 1, and the protective layer 3 arrange | positioned at the other side of the polarizer 1, And the said laminated body is heated at the temperature of 85 degreeC or more, for example (henceforth a high temperature heating may be included hereafter). 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 for the high temperature heating is preferably 3 minutes to 10 minutes, more preferably 3 minutes to 6 minutes. You may heat a laminated body at the temperature below 85 degreeC (low temperature heating) before and / or after high temperature heating. The heating temperature and heating time of the low-frequency heating can be appropriately set according to the purpose and desired characteristics of the obtained polarizing film. The high temperature heating and / or low temperature heating may also serve as a drying treatment of the adhesive in the lamination of the polarizer, the retardation film (retardation film) and the protective layer (protective film). In addition, as for the formation method of a polarizer, retardation film (retardation film), and a protective layer (protective film), any appropriate method may be employ | adopted as mentioned above. Arbitrary appropriate methods can also be employ | adopted for the lamination | stacking method of a polarizer, retardation film (retardation film), and a protective layer (protective film).

<Image display device>
The image display device according to the embodiment of the present invention includes a circularly polarizing film on the viewing side of the optical cell. The circularly polarizing film is disposed so that the retardation film is closer to the viewing side than the polarizer. As a typical example of an image display device including an optical cell, a liquid crystal display device and an organic electroluminescence (EL) display device can be given. 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 providing the polarizing film on the viewing side. Therefore, such an image display device can be suitably used even outdoors.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In addition, the evaluation items in the examples are as follows.

<Fracture start load>
A nano scratch tester manufactured by CSM Instruments SA was used as a measuring device for the fracture initiation load. The first surface or the second surface of each retardation film (sample) was affixed to a slide glass, and the other surface (second surface or first surface) was faced upward, and fixed to the stage of the measuring apparatus. Using a cantilever ST-150 equipped with a conical diamond indenter (tip radius of curvature 10 μm) in a measurement environment of 23 ° C. and 50% RH, a load of 0 to 300 mN was applied in the continuous load mode of the above apparatus. A scratch test was carried out by rubbing in one direction while increasing (scratch load).
Using the optical microscope (manufactured by Nikon Corporation) attached to the apparatus, the scratch marks were observed on the surface of the sample subjected to the scratch test with an objective lens 20 times. Then, the first location where the back layer is peeled longer than 2 μm in the scratch direction on the scratch mark is taken as the fracture start point, and the scratch load corresponding to the center of the length of the fracture start point in the scratch direction (destruction length) is The fracture start load was used. FIG. 2 is an image showing scratch marks before the start of destruction (non-destructive portion), and FIG. 3 is an image showing scratch marks at the start point of destruction.
As a result of measuring the above sample, the surface having a large fracture start load was designated as the first surface, and the surface having the small fracture load was designated as the second surface. The results are shown in Table 1.

(Production of polarizer)
A polyvinyl alcohol film having a polymerization degree of 2400, a saponification degree of 99.9 mol%, and a thickness of 30 μm is immersed in warm water at 30 ° C. and swollen, and the length of the polyvinyl alcohol film becomes 2.0 times the original length. Uniaxial stretching was performed as described above. Next, it is immersed in an aqueous solution (dye bath) having a concentration of a mixture of iodine and potassium iodide (weight ratio 0.5: 8) of 0.3% by weight, and the length of the polyvinyl alcohol film is 3.0 times the original length. Dyeing was performed while uniaxially stretching. Thereafter, the film was stretched so that the length of the polyvinyl alcohol film was 3.7 times the original length while immersed in an aqueous solution (crosslinking bath 1) of 5% by weight boric acid and 3% by weight potassium iodide. In an aqueous solution (crosslinking bath 2) of 4% by weight boric acid and 5% by weight potassium iodide, the polyvinyl alcohol film was stretched so that its length was 6 times the original length. Then, after performing an iodine ion impregnation process with an aqueous solution (iodine impregnation bath) of 3% by weight of potassium iodide, it was dried in an oven at 60 ° C. for 4 minutes to obtain a long (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 film obtained by obliquely stretching a long triacetylcellulose (TAC) film obtained by a solution casting method was used. The thickness of the stretched film (the stretched product of the TAC film) was 35 μm, 32 μm, 28 μm, 25 μm, 20 μm, and 40 μm, respectively.
Each stretched film (a stretched product of a TAC film) was provided with a hard coat layer having a thickness of 5 μm on the first surface or the second surface (the surface not bonded to the polarizer).
Each stretched film (a stretched product of the TAC film) was adjusted so that the in-plane retardation Re (550) was 105 nm, and the angle formed between the slow axis and the longitudinal direction was 45 °. .

(Protective layer: protective film)
A long cycloolefin (COP) film (thickness 13 μm, trade name: ZF14-013, manufactured by Nippon Zeon Co., Ltd.) was used.

(Preparation of aqueous adhesive)
A polyvinyl alcohol-based resin containing acetoacetyl groups (average degree of polymerization: 1200, degree of saponification: 98.5 mol%, degree of acetoacetylation: 5 mol%) is dissolved in pure water at a temperature of 30 ° C., A water-based adhesive was obtained by adjusting the solid content concentration to 4%.

Example 1
(Production of circularly polarizing film)
As the retardation film, a stretched film having a thickness of 35 μm (a stretched product of a TAC film) provided with a hard coat layer on the second surface was used. The first surface of the retardation film was applied so that the thickness of the adhesive layer after drying the aqueous adhesive was 80 nm. Similarly, the aqueous adhesive was applied to the protective film so that the thickness of the adhesive layer after drying was 80 nm. Next, the retardation film with adhesive and the protective film are bonded to both sides of the polarizer under a temperature condition of 23 ° C. with a roll machine, and then dried at 55 ° C. for 4 minutes and at 86 ° C. for 4 minutes. A polarizing film was produced. The polarizer, the retardation film with an adhesive, and the protective film were bonded so that the polarizer and the adhesive layer of the protective film were in contact with each other. In the obtained circularly polarizing film, the absorption axis direction of the polarizer was parallel to the long direction, and the angle formed between the slow axis of the retardation film and the long direction was 45 °.

Examples 2-5, Comparative Examples 1-7
In Example 1, the circularly polarizing film was obtained in the same manner as in Example 1 except that the thickness of the stretched film used for the retardation film and the surface on which the retardation film was bonded to the polarizer were changed as shown in Table 1. Obtained.
The retardation films having the same thickness used in Examples 1 to 5 and Comparative Examples 1 to 5 are the same retardation film, and only the surface bonded to the polarizer is different. Moreover, the retardation film of the same thickness used by the comparative example 6 and the comparative example 7 is the same retardation film, and only the surface bonded together to the polarizer is different.

The following evaluation is shown in Table 1 for the circularly polarizing films obtained in the above Examples and Comparative Examples.

<Peel force measurement method>
About the obtained circularly-polarizing film, the peel force was measured by the following method.
Cut out the circularly polarizing film into a size of 200 mm parallel to the stretching direction of the polarizer and 15 mm in the orthogonal direction, and cut it with a cutter knife between the retardation film and the polarizer. Laminated to a glass plate. With Tensilon, the protective film and the polarizer were peeled off in the 90-degree direction at a peeling speed of 3000 mm / min, and the peel strength (N / 15 mm) was measured. About the peeling surface after peeling, the infrared absorption spectrum was measured by ATR method, and it was confirmed that it was a cohesive failure (film breakage) of a retardation film.
The peel force is preferably 0.8 N / 15 mm or more, more preferably 1 N / 15 mm or more, and further preferably 1.5 N / 15 mm or more. In Table 1, when the peel force is 0.8 N / 15 mm or more, “◯” is indicated, and when the peel force is less than 0.8 N / 15, “X” is indicated.
When the fracture start load on the surface where the retardation film is bonded to the polarizer is 55 mN or more, the peeling force from the polarizer can satisfy 0.8 N / 15 mm.

<Length in curl direction>
The obtained circularly polarizing film was cut out to 112 mm × 65 mm (5 inch size) so that the absorption axis direction of the polarizer was a long side. The cut circularly polarizing film was allowed to stand on a horizontal plane with the hard coat layer facing upward, and the height at which the end of the sample curled and floated from the plane was measured. The case where the height of the largest floating part (maximum floating height) was 3 mm or less was marked with ◯, and the case where the maximum floating height exceeded 3 mm was marked with x.

F Circularly polarizing film 1 Polarizer 2 Retardation film 3 Protective layer 4 Surface functional layer

Claims (10)

1. A polarizer, a retardation film disposed on one side of the polarizer, and a protective layer disposed on the other side of the polarizer,
   The retardation film has a function of converting linearly polarized light into circularly polarized light or elliptically polarized light, has a thickness of 35 μm or less, and
   When both sides of the retardation film have different fracture start loads in the scratch test, the side having the higher fracture start load is the first surface and the lower side is the second surface.
   The said polarizer is bonded by the 1st surface of the said retardation film, The circularly-polarizing film characterized by the above-mentioned.
2. The circularly polarizing film according to claim 1, wherein the fracture start load on the first surface of the retardation film is 55 mN or more.
3. The circularly polarizing film according to claim 1 or 2, further comprising a surface functional layer on the second surface of the retardation film.
4. The circularly polarizing film according to any one of claims 1 to 3, wherein an angle formed between an absorption axis of the polarizer and a slow axis of the retardation film is 35 ° to 55 °.
5. The circularly polarizing film according to any one of claims 1 to 4, wherein the circularly polarizing film has a long shape, and an angle formed between a slow axis of the retardation film and a long direction is 35 ° to 55 °.
6. The phase difference film is a stretched product of a resin film molded on a casting body by a solution casting method, and the surface on the casting body side of the resin film is the first surface. 6. The circularly polarizing film according to any one of 5 above.
7. The circularly polarizing film according to any one of claims 1 to 6, wherein the retardation film is a cellulose ester film.
8. The circularly polarizing film according to any one of claims 1 to 7, wherein the polarizer, the retardation film and the protective layer are bonded together via an adhesive layer.
9. A circularly polarizing film with an adhesive layer, comprising the circularly polarizing film according to any one of claims 1 to 8 and an adhesive layer.
10. The circularly polarizing film according to any one of claims 1 to 8 or the circularly polarizing film with an adhesive layer according to claim 9 is provided on the viewing side of an optical cell, and the retardation film is on the viewing side with respect to the polarizer. An image display device characterized by being arranged.
    
    

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