CN108693590B - Optical film, polarizing plate, display device, and method for producing optical film - Google Patents

Abstract

The invention provides an optical film, a polarizing plate, a display device and a method for manufacturing the optical film. The optical film is a film in which the slow phase axis is inclined at 10 to 80 DEG with respect to one side of the film profile in the film surface. The dimensional change rates of the optical film in the phase advancing axis direction and the phase retarding axis direction before and after being left at 90 ℃ for 120 hours were respectively represented by Δ D_F(%) and Δ D_L((%), the optical film satisfies 0% or more ≦ Δ D at the center and both ends in the direction along the one side_F<0.5%, and Δ D_L<0% and a residual solvent content of 60ppm or less.

Description

Optical film, polarizing plate, display device, and method for producing optical film

Technical Field

The present invention relates to an optical film as an obliquely extending film, a polarizing plate provided with the optical film, a display device provided with the polarizing plate, and a method for producing the optical film.

Background

Conventionally, various methods have been proposed for producing an obliquely stretched film by stretching a resin film in an oblique direction with respect to a width direction. For example, in patent document 1, a resin film is drawn out from a direction different from the winding direction of the stretched film, and both ends of the resin film are gripped by a pair of grippers and conveyed. Further, the resin film is extended in an oblique direction by changing the conveying direction of the resin film halfway. Thereby, an obliquely-stretched film having a retardation axis at a desired angle exceeding 0 ° and less than 90 ° with respect to the longitudinal direction or the width direction is produced.

The obliquely-stretched film produced in this manner can be applied to a circularly polarizing plate for preventing reflection of external light, for example, in an organic EL (electroluminescence) display device. The above-described circularly polarizing plate is obtained by laminating a polarizer and an obliquely extending film in a roll-to-roll manner, for example, in such a manner that the retardation axis of the obliquely extending film crosses the absorption axis (or transmission axis) of the polarizer at a desired angle (for example, 45 °) in the film plane. By manufacturing the circularly polarizing plate in a roll-to-roll manner, the productivity of the circularly polarizing plate is dramatically improved as compared with a batch type in which a circularly polarizing plate is manufactured by laminating obliquely oriented films and polarizers of predetermined sizes one by one.

Documents of the prior art

Patent document

Patent document 1: japanese unexamined patent application, first publication No. 2010-173261 (see claim 1, FIG. 1, etc.)

Disclosure of Invention

Technical problem to be solved by the invention

However, as typical methods for producing a resin film (long film) which is a base of an obliquely-stretched film, a solution casting film-forming method and a melt casting film-forming method are known. The solution casting film-forming method is as follows: a resin film is obtained by casting a dope in which a resin and an additive are dissolved in a solvent on a metal support and drying the dope, stretching or holding the width of the cast film after peeling the cast film (web) from the metal support, and then drying the cast film. On the other hand, the melt casting film formation method is a method of: a resin composition containing a resin and an additive is heated and melted to a temperature at which fluidity is exhibited, and thereafter, the melt having fluidity is cast to obtain a resin film.

When a resin film formed by a solution casting film-forming method is obliquely stretched and the obtained obliquely stretched film is bonded to a polarizer to produce a polarizing plate, the obliquely stretched film shrinks in both the slow axis direction and the phase axis direction (a direction perpendicular to the slow axis direction in the film surface) under a high-temperature environment during bonding (for example, under a high-temperature environment due to ultraviolet irradiation when an ultraviolet-curable adhesive is used, or when heated to promote curing, or when a water-based adhesive such as water gel is used, or when heated to promote curing). The inventors of the present application presume the reason as follows.

The resin density of the resin film formed by the solution casting film forming method is lower than that of the resin film formed by the melt casting film forming method. This is because, in the solution casting film-forming method, the solvent contained in the casting film evaporates due to drying of the casting film after stretching, and a gap (space after the solvent evaporates and dissipates) is generated in the film. When a film having a low resin density is obliquely stretched, the film tends to be stretched in the stretching direction (direction inclined with respect to the width direction (slow axis direction)), and further tends to be stretched in the advancing axis direction due to the influence of the stretching caused by the tension acting in the transport direction. Therefore, after the film is obliquely stretched, tensile stress remains in both the slow axis direction and the fast axis direction. In a high-temperature environment, the tensile stress is relaxed, and therefore the film contracts in both the slow axis direction and the phase advance axis direction.

As described above, when the obliquely-stretched film shrinks in both the slow axis direction and the fast axis direction in a high-temperature environment, the entire film undergoes dimensional changes and shrinks. As a result, curling occurs in the polarizing plate obtained by laminating the polarizer and the obliquely-stretched film, the adhesiveness between the polarizer and the obliquely-stretched film is reduced, and the obliquely-stretched film is likely to peel off. As a result, in the organic EL display device to which the polarizing plate is applied, light leakage due to reflection of external light occurs in black display.

Further, from various studies, it has been found that even in the case of producing a polarizing plate by obliquely stretching a resin film formed by a melt casting film-forming method and bonding the obtained obliquely stretched film to a polarizer, depending on stretching conditions in oblique stretching, tensile stress remains in both directions of a slow axis direction and a phase advancing axis direction after oblique stretching, and the obliquely stretched film shrinks in both directions of the slow axis direction and the phase advancing axis direction under a high temperature environment in bonding to cause dimensional change, which causes the same problem as described above.

On the other hand, in a liquid crystal display device, a circularly polarizing plate is arranged on the viewing side with respect to a liquid crystal layer so that an observer can view a display image both in an upright state and in a state where the head is tilted in the lateral direction while wearing a polarized sunglass. In such a structure, when a curl is generated in the circularly polarizing plate due to a dimensional change of the obliquely-stretched film under a high-temperature environment, a distortion is generated in an image seen through the circularly polarizing plate, thereby deteriorating visibility of a display image.

Therefore, in order to suppress light leakage due to reflection of external light in an organic EL display device and to suppress deterioration of visibility of a display image of a liquid crystal display device which should deal with a polarizing sunglass, it is necessary to suppress dimensional change of the entire obliquely extending film under a high-temperature environment when the obliquely extending film and the polarizer are bonded. However, such obliquely-stretched film has not been proposed yet.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical film as an obliquely extending film capable of suppressing a dimensional change in a high-temperature environment, a polarizing plate including the optical film, and a display device including the polarizing plate.

Means for solving the problems

The above object of the present invention is achieved by the following configurations.

1. An optical film having a slow axis inclined by 10 to 80 DEG with respect to one side of the film profile in the film surface,

the dimensional change rates of the optical film in the phase advancing axis direction and the phase retarding axis direction before and after being left at 90 ℃ for 120 hours were respectively represented by Δ D_F(%) and Δ D_L(in%) is in the central part along the one side andtwo end parts satisfy

0％≦ΔD_F<0.5％

ΔD_L<0％，

And the residual solvent content is 60ppm or less.

2. The optical film as described in the above 1, wherein the residual solvent amount is 10ppm or less.

3. The optical film as described in the above 1 or 2, wherein the distances between two points arranged in the phase advancing axis direction in the optical film and before and after the optical film is left at 90 ℃ for 120 hours are a1(mm) and a2(mm), respectively,

and the distances between two points arranged in the slow axis direction in the optical film are b1(mm) and b2(mm) before and after the optical film is left at 90 ℃ for 120 hours,

ΔD_F＝{(a2-a1)/a1}×100

ΔD_L＝{(b2-b1)/b1}×100。

4. the optical film according to any one of claims 1 to 3, wherein a dimensional change rate in a phase advancing axis direction before and after the optical film is left at 90 ℃ for 120 hours in a central portion in a direction along the one side is represented by Δ D_F-C(％)，

And the dimensional change rate of the optical film in the phase advancing axis direction before and after being placed at 90 ℃ for 120 hours at one end part along the one side is set to be delta D_F-E1(％)，

And the dimensional change rate of the optical film in the phase advancing axis direction before and after being left at 90 ℃ for 120 hours at the other end in the direction along the one side is set to be delta D_F-E2When (%), further satisfies

(ΔD_F-E1+ΔD_F-E2)/2＞ΔD_F-C。

5. The optical film according to any one of claims 1 to 4, wherein the optical film is in a long form,

the direction along the one side is a width direction perpendicular to the longitudinal direction within the film surface of the optical film.

6. A polarizing plate comprising the optical film according to any one of 1 to 5 and a polarizer,

the optical film is located on one side with respect to the polarizer in such a manner that a slow phase axis crosses an absorption axis of the polarizer within a film plane.

7. A display device comprising the polarizing plate described in the above item 6 and a display unit,

the polarizing plate is located on a visible side with respect to the display unit.

8. The display device according to claim 7, wherein the optical film of the polarizing plate is located on the display cell side with respect to the polarizer.

9. The display device according to claim 8, wherein the display unit is an organic electroluminescent element.

10. The display device according to claim 7, wherein the optical film of the polarizing plate is located on a side opposite to the display unit with respect to the polarizer.

11. The display device according to claim 10, wherein the display unit is a liquid crystal unit.

12. A method for producing an optical film according to any one of the above 1 to 5,

comprises an obliquely stretching step of obtaining an obliquely stretched film constituting the optical film by grasping both end portions of a long film in a width direction with a pair of grasping members, and bending and conveying the long film in a film surface by advancing one grasping member relative to the other grasping member, thereby stretching the long film in an oblique direction with respect to the width direction,

when forces applied by the holders in the transport direction to the respective ends of the long film in the width direction before the oblique stretching are set to be the same Tr (N),

and forces applied in the transport direction by the relatively delayed-side gripper and the relatively advanced-side gripper at each end in the width direction of the elongated film during the diagonal stretching are to (N) and Ti (N), respectively,

in the oblique stretching process, the requirement of

(Ti-Tr)/Tr≧1.7

(Tr-To)/Tr≧1.5

In the above aspect, the strip film is extended in the oblique direction.

13. The method of manufacturing an optical film according to claim 12, wherein in the oblique stretching step, an end portion of each end portion of the long film in the width direction, which is gripped by the gripper on the retardation side, is cooled.

14. The method of manufacturing an optical film according to claim 12 or 13, wherein in the oblique stretching step, the long film is obliquely stretched so that a slow axis is aligned at an alignment angle larger than a desired alignment angle with respect to a width direction of the long film, and thereafter, the long film is obliquely stretched so that the slow axis is aligned at the desired alignment angle.

Effects of the invention

The optical film is a so-called obliquely extending film in which the slow axis is inclined at 10 to 80 DEG with respect to one side of the film profile in the film surface. The dimension change rate Delta D of the phase advancing axis direction and the phase retarding axis direction is set at the central part and the two end parts of the optical film along the one side_FAnd Δ D_LThe optical film satisfies the above conditional expressions, and expands or does not change in size in the phase advancing axis direction and contracts in the phase retarding axis direction in a high-temperature environment. In this way, since the optical film does not shrink in the phase advancing axis direction under a high temperature environment, even if there is shrinkage in the slow axis direction under a high temperature environment, dimensional change (shrinkage) of the entire film can be suppressed.

Thus, even when a polarizing plate is produced by bonding a polarizer and an optical film at high temperature, the occurrence of curling in the polarizing plate due to dimensional changes of the optical film and the deterioration of the adhesiveness of the optical film to the polarizer can be suppressed. As a result, in the organic EL display device to which the polarizing plate is applied, light leakage due to reflection of external light during black display can be suppressed. In addition, in the liquid crystal display device to which the polarizing plate is applied and which is adapted to the polarized sunglasses, it is possible to suppress distortion from occurring in an image viewed through the polarizing plate, and it is possible to suppress a reduction in visibility of a display image.

Drawings

Fig. 1 is an explanatory view schematically showing a schematic configuration of an apparatus for producing an obliquely-stretched film according to an embodiment of the present invention.

Fig. 2 is a plan view schematically showing an example of a guide rail pattern of an extension part provided in the manufacturing apparatus.

Fig. 3 is a plan view showing the details of the structure of the extension portion.

Fig. 4 is an exploded perspective view showing a schematic structure of the polarizing plate.

Fig. 5 is a sectional view showing a schematic structure of the organic EL display device in an exploded manner.

Fig. 6 is a cross-sectional view showing a schematic configuration of the liquid crystal display device.

Fig. 7 is an explanatory view schematically showing changes in the adhesive and the optical film at the width center portion and the width end portion when the adhesive is cured.

Fig. 8 is an explanatory view schematically showing forces in the conveying direction applied to both ends in the width direction of the long film in the extension section.

Fig. 9 is an explanatory view schematically showing another structure of the extension portion.

Fig. 10 is an explanatory view schematically showing another structure of the extension portion.

Description of the reference numerals

50 polarizing plate

52 polarizer

53 retardation film (optical film)

100 organic EL display device

101 organic EL element (display unit)

301 polarizing plate

311 lambda/4 phase difference film (optical film)

313 polarizer

400 liquid crystal display device

401 liquid crystal cell (display unit)

402 polarizing plate

411 polarizer

413 lambda/4 phase difference film (optical film)

Co holding piece

Ci holding piece

Detailed Description

In one embodiment of the present invention, the following description is made based on the drawings. In the present specification, when a numerical range is denoted by a to B, the numerical range includes values of a lower limit a and an upper limit B. The present invention is not limited to the following.

The obliquely-stretched film of the present embodiment is a long obliquely-stretched film having an in-plane retardation axis at an arbitrary angle with respect to the width direction of the stretched film by obliquely stretching a long resin film, or a sheet-like obliquely-stretched film obtained by cutting the long obliquely-stretched film in the width direction.

Here, the long length means a length of at least 5 times or more, preferably 10 times or more, with respect to the width of the film, and specifically means a length to the extent that the film is wound in a roll shape and stored or transported in a state of being wound in a roll. In the method of manufacturing a long film, the film can be manufactured in a desired arbitrary length by continuously manufacturing the film. In the method for manufacturing a long obliquely-stretched film, after the long film is formed, the long film may be temporarily wound around a winding core to form a wound body (long film roll), and the long film may be supplied from the wound body to the obliquely stretching step to manufacture the obliquely-stretched film, or the long film after the film formation may be continuously supplied from the film forming step to the obliquely stretching step without winding the long film. Since the film forming conditions are changed by feeding back the results of the film thickness and the optical value of the stretched film, and a desired long obliquely stretched film can be obtained, it is preferable to continuously perform the film forming step and the obliquely stretching step.

In the method of manufacturing a diagonally stretched film according to the present embodiment, a long diagonally stretched film having a retardation axis at an angle exceeding 0 ° and less than 90 ° with respect to the width direction of the film (for example, an angle of 10 to 80 ° with respect to the width direction) is manufactured. Here, the angle with respect to the width direction of the film is an angle in the film plane. The slow axis is usually found in the extending direction or in a direction perpendicular to the extending direction, and therefore, in the manufacturing method of the present embodiment, by extending at an angle exceeding 0 ° and less than 90 ° with respect to the width direction of the film, a long obliquely-extended film having the slow axis can be manufactured. The angle formed by the width direction of the long obliquely-stretched film and the slow axis, that is, the alignment angle can be arbitrarily set to a desired angle within a range exceeding 0 ° and less than 90 °. In the present embodiment, the term "long film" refers to a long resin film before being obliquely stretched.

< about Long-strip film >

First, a long film to be stretched in the present embodiment will be described.

The long film of the present embodiment is not particularly limited as long as it is a film made of a thermoplastic resin, and for example, when the stretched film is used for optical applications, a film made of a resin having transparency to a desired wavelength is preferable. Examples of such resins include polycarbonate resins (PC), polyester resins, olefin copolymer resins having an alicyclic structure (cycloolefin resins, COP), polyethersulfone resins, polyethylene terephthalate resins, polyimide resins, polymethyl methacrylate resins, polysulfone resins, polyaryl ester resins, polyethylene resins, and polyvinyl chloride resins.

Polycarbonate resins are polyesters of carbonic acid with a diol or a dihydric phenol, and are polymers having a carbonate bond of-O-CO-O-, most practically used are polymers of bisphenol and carbonate, and are marketed by deltoid corporation (Panlite (registered trademark), PURE-ACE (registered trademark)), kokushi corporation (ELMECH (registered trademark)), mitsubishi engineering plastic corporation (lupilon (registered trademark)), and the like. Of course, a copolymer obtained by copolymerizing a monomer having a fluorenyl group with the monomer (see, for example, Japanese patent application laid-open No. 2005-189632) shows reverse wavelength dispersion of retardation, and such a polycarbonate can be suitably used depending on the application.

Examples of the polyester resin include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), and a copolymer obtained by copolymerizing a monomer having a fluorene group and the monomer has a reverse wavelength dispersion of retardation.

As the polyethylene naphthalate-based resin, for example, polyethylene naphthalate obtained by polycondensing a lower alkyl ester of naphthalenedicarboxylic acid and ethylene glycol can be suitably used. As a commercially available product, Teonex (manufactured by imperial corporation) or the like can be suitably used.

The cycloolefin resin is not particularly limited as long as it has a monomer unit formed of a cyclic olefin (cycloolefin). The cycloolefin resin may be any of a cycloolefin Copolymer (COP) and a cycloolefin copolymer (COC). The cycloolefin-based copolymer is an amorphous cycloolefin-based resin which is a copolymer of a cycloolefin and an olefin such as ethylene.

As the cyclic olefin, there are polycyclic cyclic olefins and monocyclic cyclic olefins. Examples of the polycyclic cyclic olefin include norbornene, methylnorbornene, dimethylnorbornene, ethylnorbornene, ethylidenenorbornene, butylnorbornene, dicyclopentadiene, dihydrodicyclopentadiene, methyldicyclopentadiene, dimethyldicyclopentadiene, tetracyclododecene, methyltetracyclododecene, dimethyltetracyclododecene, tricyclopentadiene and tetracyclopentadiene. Examples of the monocyclic cyclic olefin include cyclobutene, cyclopentene, cyclooctene, cyclooctadiene, cyclooctadectatriene, and cyclododecatriene.

Examples of the cycloolefin resin that can be obtained as a commercially available product include "ZEONOR" manufactured by japanese swiss corporation, "ARTON" manufactured by JSR corporation, "TOPAS" manufactured by precious plastics corporation, "APEL" manufactured by mitsui chemical corporation, and the like.

Further, as the resin constituting the long film, the resin composition described in Japanese patent laid-open No. 2006-45369 and the alkoxycinnamate polymer described in Japanese patent laid-open No. 2016-108544 can be used.

< method for producing long film >

As a method for forming a long film, there are a solution casting film forming method and a melt casting film forming method described below. Hereinafter, each film forming method will be described. In the present embodiment, as described later, in order to obtain the property that the obliquely stretched film does not shrink in the phase advancing axis direction in a high temperature environment, a long film to be obliquely stretched is formed by a melt casting film forming method.

[ solution casting film-making method ]

In a solution casting film-forming method, the following steps are carried out: a step of dissolving a resin and an additive in a solvent to prepare a dope, a step of casting the dope on a belt-shaped or cylindrical metal support, a step of drying the cast dope as a casting film (blank), a step of peeling the blank from the metal support, a step of stretching or holding the blank in width, a step of further drying the blank, and a step of winding the completed film.

The metal support in the casting step is preferably a metal support having a mirror-finished surface, and a cylinder having a surface plated on a stainless steel belt or a casting is preferably used. The surface temperature of the metal support is set to-50 ℃ to a temperature at which the solvent boils and does not foam. The support temperature is preferably high because the drying rate of the material can be increased, but if it is too high, the material may foam or the flatness may deteriorate.

The preferable support temperature is appropriately determined at 0 to 100 ℃, and more preferably 5 to 30 ℃. Alternatively, it is also a preferable method to gel the material by cooling and peel it from the cylinder in a state containing a large amount of residual solvent. The method of controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of bringing warm water into contact with the inside of the metal support. Since the heat transfer is efficiently performed and the time until the temperature of the metal support reaches a certain temperature is shortened, it is preferable to use warm water.

In the case of using warm air, warm air having a temperature higher than the boiling point of the solvent may be used in consideration of the temperature drop of the material due to the latent heat of evaporation of the solvent, and air having a temperature higher than the temperature for the purpose of preventing foaming may be used.

In particular, it is preferable to change the temperature of the support and the temperature of the drying air during the period from the casting to the peeling, thereby efficiently drying the support.

In order to obtain a film having good flatness, the amount of the residual solvent in peeling the preform from the metal support is preferably within a desired range. Here, the residual solvent amount is defined by the following equation.

Residual solvent amount (mass% or%) { (M-N)/N } × 100

In addition, M is the mass (g) of the sample extracted at any time during or after the production of the blank or film, and N is the mass (g) after heating M at 115 ℃ for 1 hour.

In the film drying step, a roll drying method (a method of drying the web by alternately passing the web through a plurality of rollers arranged above and below) or a method of drying the web while conveying the web by a tenter method is generally used.

[ melt casting film-making method ]

A melt-casting film-forming method is a method in which a resin composition containing a resin and an additive such as a plasticizer is heated and melted to a temperature at which fluidity is exhibited, and then the melt having fluidity is cast to form a film. The method of forming by melt casting can be classified into a melt extrusion (molding) method, a press molding method, an inflation molding method, an injection molding method, a blow molding method, an elongation molding method, and the like. Among these methods, a melt extrusion method capable of obtaining a film excellent in mechanical strength, surface accuracy, and the like is preferable. In addition, it is generally preferable that a plurality of raw materials used in the melt extrusion method are kneaded and granulated in advance.

The granulation may be carried out by a known method. For example, the dried resin, plasticizer, and other additives are supplied to an extruder by a feeder, kneaded by a single-screw or twin-screw extruder, extruded into a strand form from a die, cooled with water or air, and cut to prepare pellets.

The additive may be mixed with the resin before being supplied to the extruder, or the additive and the resin may be supplied to the extruder by separate feeders. In addition, in order to uniformly mix the particles and a small amount of additives such as an antioxidant, it is preferable to mix the particles and the additives in advance with the resin.

The extruder is preferably processed at a low temperature so as to be able to pellet the resin without deteriorating the resin (such as lowering of molecular weight, coloring, and formation of colloid). For example, in the case of a twin-screw extruder, it is preferable to use a deep-groove type screw rotating in the same direction. From the viewpoint of kneading uniformity, the mesh type is preferred.

The particles thus obtained were used for film formation. Of course, the film can be formed by directly supplying the powder of the raw material to the extruder by the feeder without granulating the powder.

The melting temperature when the pellets are extruded using a single-screw or twin-screw extruder is set to about 200 to 300 ℃, foreign matter is removed by filtration using a leaf disc type filter or the like, the pellets are cast into a film shape from a T die, and the film is kneaded by a cooling roll and an elastic contact roll and solidified on the cooling roll.

When the pellets are introduced from the hopper into the extruder, it is preferable to prevent oxidative decomposition or the like under vacuum or under a negative pressure in an inert gas atmosphere.

The extrusion flow rate is preferably stably performed by introducing a gear pump or the like. In addition, a stainless steel fiber sintered filter is preferably used as the filter used for removing foreign matter. The stainless fiber sintered filter is a stainless fiber sintered filter in which a stainless fiber body is manufactured in a state of being wound in a complicated manner, and then the stainless fiber body is compressed and sintered at a contact portion to be integrated, and the filtration accuracy can be adjusted by changing the density according to the thickness and the compression amount of the fiber.

Additives such as plasticizers and particles may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. For uniform addition, a mixing device such as a static mixer is preferably used.

The film temperature on the contact roller side when the film is kneaded by the cooling roller and the elastic contact roller is preferably set to Tg (glass transition temperature) or more and Tg +110 ℃ or less of the film. A known roller can be used as the roller having an elastic surface used for such a purpose.

The elastic contact roller is also called a nip rotating body. As the elastic contact roller, a commercially available elastic contact roller can be used.

When the film is peeled from the cooling roll, the tension is preferably controlled to prevent the deformation of the film.

The long film formed by each of the above film-forming methods may be a single-layer film or a laminate film having 2 or more layers. The laminate film can be obtained by a known method such as a coextrusion molding method, a film lamination method, and a coating method. Of these methods, the coextrusion method and the co-casting method are preferable.

< Specification of Long film >

The thickness of the long film of the present embodiment is preferably 30 to 300. mu.m, and more preferably 40 to 150. mu.m. In the present embodiment, from the viewpoint of keeping the film drawing tension at the entrance of the oblique tenter constant so as to stabilize the optical characteristics such as the alignment angle and the optical path difference, the thickness fluctuation σ m in the flow direction (transport direction) of the long film supplied to the stretching region is preferably less than 0.30 μm, more preferably less than 0.25 μm, and still more preferably less than 0.20 μm. When the thickness variation σ m in the flow direction of the long film becomes 0.30 μm or more, the variation in optical characteristics such as the optical path difference and the alignment angle of the long stretched film may deteriorate.

Further, as the long film, a film having a thickness gradient in the width direction may be supplied. By experimentally stretching a film having a thickness gradient varied in various ways, the gradient of the thickness of a long film can be empirically obtained so that the film thickness at the position where the stretching in the subsequent step is completed can be the most uniform film thickness. The inclination of the thickness of the strip film can be adjusted so that, for example, the thickness of the end portion on the side where the thickness is large is about 0.5 to 3% thicker than the end portion on the side where the thickness is small.

The width of the long film is not particularly limited, but may be 500 to 4000mm, preferably 1000 to 2000 mm.

The preferable modulus of elasticity at the stretching temperature in the oblique stretching of the long film is 0.01MPa to 5000MPa, more preferably 0.1MPa to 500MPa, as represented by the young's modulus. When the elastic modulus is too low, the shrinkage rate during and after stretching becomes low, and wrinkles become hard to disappear. If the elastic modulus is too high, the tension applied during stretching becomes large, and the strength of the portion holding both side edge portions of the film needs to be increased, which increases the load on the tenter in the subsequent step.

As the long film, a long film without alignment may be used, or a film with alignment may be supplied in advance. In addition, if necessary, the distribution of the width direction of the alignment of the long films may be arcuate, that is, in a so-called convex belly shape. That is, the alignment state of the long film can be adjusted so that the alignment of the film at the position where the stretching in the subsequent process is completed can be a desired alignment.

Method and apparatus for producing long obliquely-stretched film

Next, a method and an apparatus for producing a long obliquely-stretched film by stretching the long film in a direction oblique to the width direction to produce a long obliquely-stretched film will be described.

(outline of the apparatus)

Fig. 1 is an explanatory view schematically showing a schematic configuration of a production apparatus 1 for an obliquely stretched film. The manufacturing apparatus 1 of the present embodiment includes, in order from the upstream side in the transport direction of the long film: a film feeding section 2, a conveying direction changing section 3, a guide roller 4, an extending section 5, a guide roller 6, a conveying direction changing section 7, a film cutting device 8, and a film winding section 9. The details of the extension 5 will be described later.

The film draw-out section 2 is a film draw-out section that draws out the long film and supplies it to the extension section 5. The film drawing section 2 may be formed separately from the film forming apparatus for the long film or may be formed integrally therewith. In the former case, the long film is temporarily wound around a winding core after being formed into a film, and is wound into a wound body, and the wound body is loaded into the film take-out section 2, whereby the long film is taken out from the film take-out section 2. On the other hand, in the latter case, the film draw-out section 2 draws out the extension section 5 without winding up the long film after the long film is formed.

The conveying direction changing unit 3 is a conveying direction changing unit that changes the conveying direction of the long film drawn out from the film drawing unit 2 to a direction toward the entrance of the extending unit 5 as an obliquely extending tenter. The transport direction changing unit 3 includes, for example, a rotating bar that changes the transport direction by turning back while transporting the film, and a rotating table that rotates the rotating bar in a plane parallel to the film.

By changing the transport direction of the longer film in the above-described manner by the transport direction changing section 3, the width of the entire manufacturing apparatus 1 can be made narrower, and in addition, the feeding position and angle of the film can be finely controlled, and a long stretched film with small variations in film thickness and optical value can be obtained. Further, if the film drawing section 2 and the transport direction changing section 3 are made movable (slidable and rotatable), it is possible to effectively prevent the film from being badly caught by the right and left fasteners (grippers) that sandwich both ends of the elongated film in the width direction in the extending section 5.

The film drawing part 2 may be slidable and rotatable so that the long film is fed out at a predetermined angle with respect to the inlet of the extending part 5. In this case, the conveyance direction changing unit 3 may be omitted.

At least one guide roller 4 is provided on the upstream side of the extension portion 5 in order to stabilize the track when the long film moves. The guide roller 4 may be a pair of upper and lower rollers that sandwich the film, or may be a plurality of roller pairs. The guide roller 4 closest to the entrance of the extension portion 5 is a driven roller that guides the movement of the film, and is rotatably supported via a bearing portion, not shown. As the material of the guide roller 4, a known material can be used. In order to prevent the film from being damaged, it is preferable to reduce the weight of the guide roll 4 by applying a ceramic coating to the surface of the guide roll 4 or applying chrome plating to a light metal such as aluminum.

Further, one of the rollers on the upstream side of the guide roller 4 closest to the inlet of the extension portion 5 is preferably kneaded by pressing a rubber roller. By using such a kneading roller, fluctuation of the drawing tension in the flow direction of the film can be suppressed.

In a pair of bearing portions at both ends (right and left) of the guide roller 4 closest to the inlet of the extension portion 5, first tension detecting means and second tension detecting means are provided as film tension detecting means for detecting tension generated in the film at the roller, respectively. As the film tension detecting means, for example, a load cell can be used. As the load sensor, a known load sensor of a tensile or compressive type can be used. The load sensor is a device that converts a load applied to an application point into an electric signal and detects the load by a strain gauge attached to a strain gauge.

The load cell detects the force applied to the roller by the moving film, that is, the tension in the film traveling direction generated in the vicinity of both edges of the film, independently from each other, by the left and right bearing portions provided on the guide roller 4 closest to the inlet of the extending portion 5. The strain gauge may be directly attached to a support member constituting a bearing portion of the roller, and a load based on the strain generated in the support member, that is, a film tension may be detected. The relationship between the generated strain and the film tension is a known relationship measured in advance.

When the position and the conveying direction of the film supplied from the film feeding section 2 or the conveying direction changing section 3 to the extension section 5 are deviated from the position and the conveying direction toward the entrance of the extension section 5, a difference occurs in the tension near both side edges of the film of the guide roller 4 closest to the entrance of the extension section 5 depending on the amount of deviation. Therefore, by providing such a film tension detection device to detect the tension difference, the degree of the deviation can be determined. That is, if the film transport position and the film transport direction are correct (if the film transport position and the film transport direction are correct, the load acting on the guide roller 4 is roughly equal at both ends in the axial direction, but if the film transport position and the film transport direction are incorrect, a difference occurs in the film tension between the left and right sides.

Therefore, if the film position and the film transport direction (angle with respect to the entrance of the extension portion 5) are appropriately adjusted by the transport direction changing portion 3 so that the difference in the film tension between the left and right sides of the guide roller 4 closest to the entrance of the extension portion 5 becomes equal, for example, the film is stably held by the gripper at the entrance of the extension portion 5, and the occurrence of troubles such as the gripper falling off can be reduced. Further, the physical properties in the width direction of the film after the oblique stretching by the stretching portion 5 can be stabilized.

In order to stabilize the trajectory when the film obliquely stretched by the stretching portion 5 (long obliquely stretched film) moves, at least one guide roller 6 is provided on the downstream side of the stretching portion 5.

The conveying direction changing unit 7 is a conveying direction changing unit that changes the conveying direction of the stretched film conveyed from the stretching unit 5 to a direction toward the film winding unit 9. The transport direction changing section 7 can be constituted by, for example, a folding mechanism that folds the elongated obliquely-stretched film back at least once in a direction parallel or perpendicular to the stretching direction within the surface of the elongated obliquely-stretched film.

Here, in order to cope with fine adjustment of the alignment angle (direction of the in-plane slow phase axis of the film) or product deformation, it is necessary to adjust the angle formed by the film advancing direction at the inlet of the extension portion 5 and the film advancing direction at the outlet of the extension portion 5.

In addition, it is preferable to continuously perform film formation and oblique stretching in terms of productivity and yield. When the film forming process, the oblique stretching process, and the winding process are continuously performed, the direction of travel of the film is changed by the conveying direction changing unit 3 and/or the conveying direction changing unit 7, so that the direction of travel of the film in the film forming process and the winding process is made to coincide, that is, as shown in fig. 1, the direction of travel (the direction of extraction) of the film extracted from the film extracting unit 2 and the direction of travel (the direction of winding) of the film immediately before winding by the film winding unit 9 are made to coincide, whereby the width of the entire apparatus with respect to the direction of travel of the film can be reduced.

The film running directions in the film forming step and the film winding step do not necessarily need to be the same, but it is preferable that the running direction of the film is changed by the transport direction changing unit 3 and/or the transport direction changing unit 7 so that the film drawing unit 2 and the film winding unit 9 do not interfere with each other.

The conveyance direction changing units 3 and 7 can be realized by a known method using an air flow roller or the like.

The film cutting device 8 is a film cutting device that cuts a film (long obliquely-stretched film) stretched by the stretching portion 5 in a predetermined film length (winding length) in the width direction, and includes a cutting member 8 a. The cutting member 8a is constituted by, for example, scissors or a cutter (including a slitter or a band-shaped knife (thomson knife (トムソン edge)), but is not limited thereto, and may be constituted by a rotary circular saw, a laser emitting device, or the like.

The film winding unit 9 is a film winding unit that winds the film fed from the extension unit 5 through the feeding direction changing unit 7, and is configured by, for example, a winding device, a storage device, a driving device, and the like. The film winding section 9 is preferably slidable in the transverse direction to adjust the winding position of the film.

The film winding section 9 can finely control the drawing position and angle of the film so that the film can be drawn at a prescribed angle with respect to the outlet of the extension section 5. This makes it possible to obtain a long stretched film with small variations in film thickness and optical value. In addition, since the occurrence of wrinkles in the film can be effectively prevented and the winding property of the film can be improved, the film can be wound in a long-length manner. In the present embodiment, the drawing tension T (N/m) of the film after stretching is preferably adjusted to be 100N/m < T <700N/m, more preferably 150N/m < T < 250N/m.

When the above-mentioned drawing tension is 100N/m or less, the film tends to be loosened and wrinkled, and the arrangement in the film width direction of the optical path difference and the alignment angle is also deteriorated. Conversely, when the pulling tension is 700N/m or more, there is a case where the deviation of the alignment angle in the film width direction is deteriorated, and the width yield (winding efficiency in the width direction) is deteriorated.

In the present embodiment, it is preferable that the variation in the pull-out tension T is controlled with an accuracy of less than ± 5%, and preferably with an accuracy of less than ± 3%. When the variation of the pulling tension T becomes ± 5% or more, the variation of the optical characteristics in the width direction and the flow direction (transport direction) becomes large. As a method of controlling the variation of the pulling tension T within the above range, there may be mentioned the following method: the load applied to the first roll (guide roll 6) on the exit side of the extending portion 5, that is, the film tension, was measured, and the rotation speed of the take-up roll (winding roll of the film winding portion 9) was controlled by a general PID control method so that the value was constant. As a method for measuring the load, the following methods can be cited: a load sensor is attached to a bearing portion of the guide roller 6 to measure a load applied to the guide roller 6, that is, a film tension. As the load sensor, a known load sensor of a tensile type or a compression type can be used.

The stretched film is released from the gripping by the gripper of the stretching portion 5, discharged from the outlet of the stretching portion 5, trimmed at both ends (both sides) of the film gripped by the gripper, and then sequentially wound around a winding core (winding roller), thereby forming a rewound body of a long obliquely stretched film. The trimming described above may be performed as needed.

Before the long obliquely-stretched film is wound, the masking film may be wound while being overlapped with the long obliquely-stretched film for the purpose of preventing the films from sticking to each other, or the masking film may be wound while bonding a tape or the like to the end portion of at least one (preferably both) of the long obliquely-stretched films overlapped by the winding. The masking film is not particularly limited as long as it can protect the long obliquely-stretched film, and examples thereof include a polyethylene terephthalate film, a polyethylene film, and a polypropylene film.

Further, before the long obliquely-stretched film is wound, a portion (convex portion) called a knurled portion or a boss portion, which is larger than the film surface, is formed at both ends in the width direction of at least one surface (preferably both surfaces) of the film, whereby blocking between the films when the film is wound can be prevented. The height and shape of the knurled section may be different at both ends in the width direction (may be asymmetrical).

(details of the extension)

Next, the details of the extension portion 5 will be described. Fig. 2 is a plan view schematically showing an example of the guide rail pattern of the extension 5. Fig. 3 is a plan view showing the details of the structure of the extension 5. These are merely examples, and the present invention is not limited to these configurations.

The manufacturing apparatus 1 is performed using a diagonally extendable tenter (diagonal stretcher) as the extension section 5. The tenter is a device that heats a long film to an arbitrary temperature at which the film can be stretched and obliquely stretches the film. The stenter includes a heating zone Z, a pair of left and right guide rails Ri, Ro, and a plurality of grippers 15 (fig. 2 shows only a pair of left and right grippers Ci, Co among the plurality of grippers 15 for convenience). The details of the heating zone Z will be described later.

The guide rails Ri and Ro are each configured by coupling a plurality of guide rail portions by coupling portions, and are endless track guide rails (white circles in fig. 2 are an example of the coupling portions). As shown in fig. 3, the guide Ri on one end side (left side) in the film width direction is configured by connecting a forward guide portion 11 for advancing the gripper 15 in the transport direction of the long film and a backward guide portion 12 for advancing the gripper 15 in the direction opposite to the transport direction of the long film. The guide Ro on the other end side (right side) in the film width direction is configured by connecting an outward travel guide portion 13 for advancing the gripper 15 in the transport direction of the long film and a backward travel guide portion 14 for advancing the gripper 15 in the direction opposite to the transport direction of the long film.

The gripping member 15 is composed of a fastener for gripping both ends of the film in the width direction, is provided corresponding to each of the guide rails Ri, Ro, and is provided in plurality at equal intervals along the film transport direction (each of Ri, Ro). One end side in the width direction of the film is gripped by a plurality of grippers 15 arranged along the transport direction (guide rail Ri), and the other end side is gripped by a plurality of grippers 15 arranged along the transport direction (guide rail Ro), and the film is transported by moving the grippers 15 along the guide rails Ri, Ro in this state.

The gripper 15 moving along the left guide Ri moves along the forward guide 11 while gripping one end of the film, releases the gripping of the film near the exit of the extension 5, moves along the backward guide 12, returns to the vicinity of the entrance of the extension 5, and again grips one end of the film, and then repeats the same process (winding along the guide Ri) as described above. On the other hand, the gripper 15 moving along the right guide Ro moves along the forward guide 13 while gripping the other end portion of the film, releases the gripping of the film in the vicinity of the outlet of the extension 5, moves along the backward guide 14, returns to the vicinity of the inlet of the extension 5, and repeats the same process as described above (turns along the guide Ro) after gripping the other end portion of the film again.

In fig. 2, the conveyance direction D1 before the stretching of the long film is different from the conveyance direction D2 after the stretching of the long film, and a draw-out angle θ i is formed between the conveyance direction D1 before the stretching and the conveyance direction D2 after the stretching. The extraction angle θ i can be arbitrarily set to a desired angle within a range exceeding 0 ° and less than 90 °.

In this manner, the conveyance direction D1 before the stretching and the conveyance direction D2 after the stretching are different from each other, and therefore the guide rail pattern of the stenter has a left-right asymmetrical shape. The guide pattern can be manually or automatically adjusted according to the alignment angle θ, the draw ratio, and the like applied to the long obliquely-stretched film to be produced. In the diagonal stretcher used in the present embodiment, it is preferable that the position of each of the rail portions and the rail coupling portions constituting the rails Ri and Ro be freely set, so that the rail pattern can be arbitrarily changed.

In the present embodiment, the gripper 15 moves at a constant speed with a constant interval from the grippers 15 before and after the gripper (grippers 15 on the upstream side and the downstream side in the film transport direction). The moving speed of the gripper 15 can be selected as appropriate, but is usually 1 to 150 m/min. The difference in the moving speed between the pair of left and right grippers (for example, grippers Ci and Co) is usually 1% or less, preferably 0.5% or less, and more preferably 0.1% or less of the moving speed. This is because the speeds of the left and right grips are required to be substantially the same because the stretching step outlet is wrinkled or deflected when there is a difference in the traveling speeds of the left and right films at the stretching step outlet. In a general stenter device or the like, there are speed fluctuations on the order of seconds or less depending on the period of the teeth of the sprocket driving the chain, the frequency of the driving motor, and the like, and fluctuations of several percent are often generated, but these do not conform to the speed difference described in the embodiment of the present invention.

In the oblique stretching machine used in the manufacturing method of the present embodiment, a large curvature is often required in a guide rail that restricts the trajectory of the gripper, particularly in a portion where the film conveyance is inclined. In order to avoid interference between the grippers and local stress concentration caused by sudden bending, the trajectory of the grippers at the bent portion (bent portion) is desirably drawn as a smooth curve.

In the oblique tenter used for imparting oblique alignment to the long film, it is preferable that the alignment angle of the film be freely set by variously changing the guide pattern, and that the alignment axis (slow axis) of the film be uniformly aligned in the left-right direction across the width direction of the film with high accuracy, and that the film thickness and the optical path difference be controlled with high accuracy.

Next, the extending operation at the extending portion 5 will be described based on fig. 2. Both ends of the long film are gripped by the left and right grippers Ci and Co, and the long film is conveyed in the heating zone Z along with the movement of the grippers Ci and Co. The left and right grippers Ci and Co face each other at the inlet (position a in the drawing) of the extension section 5 in a direction substantially perpendicular to the film advancing direction (conveyance direction D1 before extension), move along the left and right asymmetric guide rails Ri and Ro, and release the gripped film in the vicinity of the outlet (position B in the drawing) at the end of extension. The timing of releasing the grip will be described in detail later. The film released from the grippers Ci and Co is wound around the winding core by the film winding unit 9. As described above, the pair of guide rails Ri, Ro each have an annular continuous orbit, and the outside guide rails of the grippers Ci, Co on which the film is released from the outlet portion of the extension portion 5 move and sequentially return to the inlet portion.

At this time, since the guide rails Ri, Ro are asymmetric in the left and right directions, in the example of fig. 2, as the left and right grips Ci, Co facing each other at the position a in the drawing move on the guide rails Ri, Ro, the grip Ci moving on the guide rail Ri side is in a positional relationship that precedes the grip Co moving on the guide rail Ro side.

That is, when one of the grippers Ci and Co in the direction substantially perpendicular to the transport direction D1 before stretching the film reaches the position B at the end of stretching the film at the position a in the drawing, the straight line connecting the grippers Ci and Co is inclined at the angle θ L with respect to the direction substantially perpendicular to the transport direction D2 after stretching the film. By the above operation, the long film is obliquely extended at an angle θ L with respect to the width direction. Here, substantially perpendicular means in the range of 90 ± 1 °.

As described above, the method for producing a diagonally stretched film according to the present embodiment can include a diagonally stretching step of: one end side in the width direction of the film is gripped by the plurality of grippers 15 (including the gripper Ci) and the other end side is gripped by the plurality of grippers 15 (including the gripper Co), and the film can be extended in an oblique direction with respect to the width direction by relatively advancing one of the grippers 15 (for example, the plurality of grippers 15 moving along the guide rail Ri) on the one end side and the other end side and relatively delaying the other gripper 15 (for example, the plurality of grippers 15 moving along the guide rail Ro) to convey the film. In the following description, the side of the one end side and the other end side in the film width direction where the gripper moves relatively early is referred to as the "early side", and the side where the gripper moves relatively late is referred to as the "late side". For example, in fig. 2, in the film width direction, the side where the gripper Ci moves is the leading side, and the side where the gripper Co moves is the trailing side.

Next, the details of the heating zone Z will be described. The heating zone Z of the extension 5 is composed of a preheating zone Z1, an extension zone Z2, and a heat fixing zone Z3. In the extension part 5, the film gripped by the grippers Ci and Co passes through the preheating zone Z1, the extension zone Z2, and the heat fixing zone Z3 in this order.

The preheating zone Z1 is a zone in which the grippers Ci and Co gripping both ends of the film move while holding the film at a constant interval in the left-right direction (in the film width direction) at the entrance of the heating zone Z.

The stretching region Z2 is a region in which the above-described oblique stretching step is performed. At this time, the film may be stretched in the longitudinal or transverse direction before and after the oblique stretching, as necessary.

The heat-fixing zone Z3 is a zone in which a heat-fixing step of fixing the optical axis (slow axis) of the film is performed after the oblique stretching step is completed.

After the stretched film passes through the heat-set zone Z3, the temperature in the zone may be set to a range (cooling zone) of not more than the glass transition temperature Tg (c) of the thermoplastic resin constituting the film. In this case, in consideration of the reduction of the film due to cooling, a guide pattern in which the interval between the opposed grippers Ci and Co is narrowed may be provided in advance.

The temperature of the preheating region Z1 is preferably set to Tg +30 ℃, the temperature of the extension region Z2 is preferably set to Tg +30 ℃, and the temperature of the heat-setting region Z3 is preferably set to Tg-30 to Tg ℃, relative to the glass transition temperature Tg of the thermoplastic resin.

In order to control the thickness fluctuation of the film in the width direction, a temperature difference may be given in the width direction in the extension region Z2. In order to provide a temperature difference in the width direction in the extended region, a known method such as a method of providing a difference in the opening degree of a nozzle for feeding warm air into the thermostatic chamber in the width direction and adjusting the opening degree, or a method of arranging heaters in the width direction and performing heating control can be used. The lengths of the preheating zone Z1, the extension zone Z2, and the heat-setting zone Z3 can be appropriately selected, and the length of the preheating zone Z1 is usually 100 to 150% and the length of the heat-setting zone Z3 is usually 50 to 100% with respect to the length of the extension zone Z2.

Further, when the width of the film before stretching is Wo (mm) and the width of the film after stretching is W (mm), the draw ratio R (W/Wo) in the stretching step is preferably 1.3 to 3.0, more preferably 1.5 to 2.8. When the draw ratio is within this range, the thickness fluctuation in the width direction of the film becomes small, and therefore it is preferable. In the stretching zone Z2 of the diagonal stretching tenter, when a difference is given to the stretching temperature in the width direction, the thickness fluctuation in the width direction can be made to be a more favorable level. The stretch ratio R is set such that the distance W1 between both ends of the fastener gripped at the inlet of the stenter is equal to the ratio (W2/W1) when the distance W2 is set at the outlet of the stenter.

< quality of elongated stretched film >

In the long obliquely-stretched film obtained by the production method according to the embodiment of the present invention, it is preferable that the alignment angle θ is inclined with respect to the winding direction in a range of, for example, greater than 0 ° and less than 90 °, and that the variation in the in-plane retardation Ro in the width direction is 3nm or less and the variation in the alignment angle θ is less than 0.6 ° over a width of at least 1300 mm.

That is, in the long obliquely-stretched film obtained by the manufacturing method according to the embodiment of the present invention, the variation in the in-plane retardation Ro is 3nm or less, preferably 1nm or less at least 1300mm in the width direction. When the deviation of the in-plane retardation Ro is within the above range, when a long obliquely-stretched film is laminated to a polarizer to form a circularly polarizing plate and the circularly polarizing plate is applied to an organic EL display device, color fluctuation due to leakage of external light reflected light during black display can be suppressed. In addition, when the long stretched film is used as, for example, a retardation film for a liquid crystal display device, display quality can be improved.

In the long obliquely-stretched film obtained by the production method according to the embodiment of the present invention, the variation in the alignment angle θ is less than 0.6 °, preferably less than 0.4 °, at least 1300mm in the width direction. When a long obliquely-stretched film having a deviation of an alignment angle θ of 0.6 ° or more is laminated with a polarizer to form a circularly polarizing plate and is mounted on an image display device such as an organic EL display device, light leakage occurs, and contrast between light and dark is reduced.

The in-plane retardation Ro of the long obliquely-stretched film obtained by the manufacturing method according to the embodiment of the present invention is selected to an optimum value according to the design of the display device to be used. The Ro is a value obtained by multiplying a difference between a refractive index nx in the in-plane slow axis direction and a refractive index ny in the in-plane direction orthogonal to the slow axis by the average thickness d of the film (Ro ═ nx-ny) × d).

The average thickness of the long obliquely-stretched film obtained by the production method according to the embodiment of the present invention is preferably 10 to 200 μm, more preferably 10 to 60 μm, and particularly preferably 10 to 35 μm from the viewpoint of mechanical strength and the like. Since the thickness variation in the width direction of the obliquely oriented film affects the winding availability, it is preferably 3 μm or less, and more preferably 2 μm or less.

< polarizing plate >

Fig. 4 is an exploded perspective view showing a schematic configuration of the polarizing plate 50 of the present embodiment. The polarizing plate 50 is formed by laminating a polarizing plate protective film 51, a polarizer 52, and a retardation film 53 in this order. The polarizing plate protective film 51 is made of, for example, a cellulose ester film, but may be made of another transparent resin film (for example, cycloolefin resin). The polarizing plate protection film 51 may be formed of an optical compensation film that compensates for optical characteristics such as viewing angle magnification.

As the polarizer 52, a polarizer in which polyvinyl alcohol doped with iodine or a dichroic dye is stretched can be used. The thickness of the polarizer is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm.

The retardation film 53 is composed of an obliquely extending film which is an optical film of the present embodiment. The retardation axis of the retardation film 53 is inclined by 10 to 80 DEG with respect to one side (for example, side 53a) of the outer shape of the rectangular film in the film surface. The side 53a is a side corresponding to the width direction of the long obliquely-stretched film. The inclination angle of the slow phase axis with respect to the side 53a in the film surface is preferably in the range of 30 to 60 °, and more preferably 45 °. The angle formed by the retardation axis of the retardation film 53 and the absorption axis (or transmission axis) of the polarizer 52 is, for example, 10 to 80 °, preferably 15 to 75 °, more preferably 30 to 60 °, and particularly preferably 45 °.

Other layers (for example, a hard layer, a low refractive index layer, an antireflection layer, and a liquid crystal (positive C-plate)) may be appropriately provided on the surface of the retardation film 53 opposite to the polarizer 52, and an easy-adhesion layer may be provided on the surface of the retardation film 53 on the polarizer 52 side.

The polarizing plate 50 of the present embodiment may be a long polarizing plate in which a long polarizing plate protective film 51, a long polarizer 52, and a long retardation film 53 (long obliquely extending film) are laminated in this order, or may be a sheet-like polarizing plate in which the long polarizing plate 50 is cut in the width direction perpendicular to the longitudinal direction.

The polarizing plate 50 can be manufactured by a general method. For example, the polarizer 52 and the retardation film 53 may be bonded to each other with an ultraviolet curable adhesive (UV adhesive) to produce the polarizing plate 50. The retardation film 53 subjected to the alkali saponification treatment may be bonded to one surface of the polarizing plate 52 using a completely saponified polyvinyl alcohol aqueous solution (water gel), and the polarizing plate 52 may be produced by immersing and stretching a polyvinyl alcohol film in an iodine solution. In addition, an ultraviolet-curable adhesive or a water-based adhesive may be used for adhesion of the polarizer 52 and the polarizing plate protective film 51.

(composition of ultraviolet ray-curable adhesive)

As ultraviolet-curable adhesive compositions for polarizing plates, photoradical polymerization-type compositions using photoradical polymerization, photocation polymerization-type compositions using photocation polymerization, and hybrid-type compositions using both photoradical polymerization and photocation polymerization are known.

As a photoradical polymerization type composition, a composition containing a radical polymerizable compound having a polar group such as a hydroxyl group or a carboxyl group and a radical polymerizable compound having no polar group at a specific ratio is known (described in JP 2008-009329A). In particular, the radical polymerizable compound is preferably a compound having an ethylenically unsaturated bond capable of radical polymerization. Preferred examples of the compound having an ethylenically unsaturated bond capable of radical polymerization include compounds having a (meta) acryloyl group. Examples of the compound having a (meth) acryloyl group include N-substituted (meth) acrylamide compounds and (meth) acryloyl ester compounds. (meta) acrylamide refers to acrylamide monomer or methacrylamide.

Further, as the photo cation polymerization type composition, there can be mentioned an ultraviolet ray curing type adhesive composition containing components of (α) a cation polymerizable compound, (β) a photo cation polymerization initiator, (γ) a sensitizer which exhibits maximum absorption against light having a wavelength of 380nm, and () a naphthalene type photo sensitizer, as disclosed in japanese unexamined patent publication (kokai) No. 2011-028234. However, other ultraviolet-curable adhesives may be used.

(1) Pretreatment step

The pretreatment step is a step of performing an easy adhesion treatment on the adhesion surface of the retardation film and the polarizer protective film (these are collectively referred to as "protective film" herein) to the polarizer. As the easy adhesion treatment, corona treatment, plasma treatment, and the like can be cited.

(Process for applying ultraviolet-curing adhesive)

In the step of applying the ultraviolet-curable adhesive, the ultraviolet-curable adhesive is applied to the adhesive surface of at least one of the polarizer and the protective film. When the ultraviolet-curable adhesive is directly applied to the surface of the polarizer or the protective film, the application method is not particularly limited. For example, various wet coating methods such as a doctor blade, a wire bar, a die coater, a comma knife coater, and a gravure coater can be used. Further, after the ultraviolet curable adhesive is applied (cast) between the polarizer and the protective film, a method of uniformly pressing and expanding the ultraviolet curable adhesive by applying pressure with a roller or the like can be used.

(2) Bonding step

After the ultraviolet-curable adhesive is applied by the above-described method, the adhesive is treated in a bonding step. In this bonding step, for example, when an ultraviolet-curable adhesive is applied to the surface of the polarizer in the previous coating step, the protective film is polymerized thereto. In the case of the method of applying the ultraviolet-curable adhesive to the surface of the protective film, the polarizer is polymerized in this portion. In addition, in the case where the ultraviolet ray hardening type adhesive is cast between the polarizer and the protective film, the polarizer and the protective film are polymerized in this state. In this state, the protective films are generally sandwiched between pressure rollers and the like to apply pressure. The material of the pressure roller may be metal, rubber, or the like. The pressure rollers disposed on both sides may be made of the same material or different materials.

(3) Hardening step

In the curing step, ultraviolet rays are irradiated to the uncured ultraviolet-curable adhesive to cure the ultraviolet-curable adhesive layer containing a cationically polymerizable compound (e.g., an epoxy compound or a hexadecane compound) or a radically polymerizable compound (e.g., an acryl compound or an acrylamide compound), and the polarizer and the protective film polymerized through the ultraviolet-curable adhesive are bonded to each other. In the structure of the present embodiment in which the protective films are bonded to both surfaces of the polarizer, it is advantageous that the ultraviolet-curable adhesive on both surfaces is simultaneously cured by irradiating ultraviolet rays in a state in which the protective films are polymerized via the ultraviolet-curable adhesive on both surfaces of the polarizer.

The ultraviolet irradiation conditions may be any suitable conditions as long as the ultraviolet-curable adhesive can be cured. The ultraviolet irradiation dose is preferably a cumulative dose of 50 to 1500mJ/cm²More preferably, the cumulative light amount is 100 to 500mJ/cm²The range of (1).

When the polarizing plate is manufactured in a continuous line, the line speed is determined by the curing time of the adhesive, but is preferably in the range of 1 to 500m/min, more preferably in the range of 5 to 300m/min, and particularly preferably in the range of 10 to 100 m/min. When the production line speed is 1m/min or more, the productivity can be ensured, and the damage to the protective film can be suppressed, so that the polarizing plate with excellent durability can be manufactured. In addition, when the production line speed is 500m/min or less, the ultraviolet-curable adhesive agent is sufficiently cured, and an ultraviolet-curable adhesive layer having a desired hardness and excellent adhesiveness can be formed.

< organic EL display device >

Fig. 5 is a sectional view showing a schematic exploded structure of an organic EL display device 100 as an example of the display device of the present embodiment. The structure of the organic EL display device 100 is not limited to this.

The organic EL display device 100 is configured by forming a polarizing plate 301 on an organic EL element 101 as a display unit via an adhesive layer 201. The organic EL element 101 is configured by sequentially including a metal electrode 112, a light-emitting layer 113, a transparent electrode (ITO or the like) 114, and a sealing layer 115 on a substrate 111 using glass, polyimide, or the like. The metal electrode 112 may be formed of a reflective electrode and a transparent electrode.

The polarizing plate 301 is formed by laminating a λ/4 retardation film 311, an adhesive layer 312, a polarizer 313, an adhesive layer 314, and a protective film 315 in this order from the organic EL element 101 side, and the polarizer 313 is sandwiched between the λ/4 retardation film 311 and the protective film 315. The polarizing plate 301 (circular polarizing plate) is configured by laminating the transmission axis (or absorption axis) of the polarizer 313 and the retardation axis of the λ/4 retardation film 311 formed of the long obliquely extending film of the present embodiment at an angle of about 45 ° (or 135 °). The protective film 315, the polarizer 313, and the λ/4 retardation film 311 of the polarizing plate 301 correspond to the polarizing plate protective film 51, the polarizer 52, and the retardation film 53 of the polarizing plate 50 of fig. 4, respectively.

A hardened layer is preferably stacked on the protective film 315. The hardened layer has an effect of preventing warpage due to the polarizing plate 301 as well as preventing damage to the surface of the organic EL display device. Further, an antireflection layer may be provided on the hardened layer. The thickness of the organic EL element 101 itself is about 1 μm.

In the above-described structure, when a voltage is applied to the metal electrode 112 and the transparent electrode 114, electrons are injected from the electrode serving as a cathode in the metal electrode 112 and the transparent electrode 114, holes are injected from the electrode serving as an anode, and the electrons and the holes are recombined in the light-emitting layer 113, whereby light emission of visible light corresponding to the light-emitting characteristics of the light-emitting layer 113 is generated. The light generated in the light-emitting layer 113 is extracted to the outside through the transparent electrode 114 and the polarizing plate 301, directly or after being reflected by the metal electrode 112.

In general, in an organic EL display device, a metal electrode, a light-emitting layer, and a transparent electrode are sequentially stacked on a transparent substrate to form an element (organic EL element) as a light-emitting body. The light-emitting layer is a laminate of various organic films, and various combinations of a hole-injecting layer made of triphenylamine derivative or the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of such a light-emitting layer and an electron-injecting layer made of perylene derivative or the like, and a laminate with these hole-injecting layer, light-emitting layer, electron-injecting layer, and the like are known.

The organic EL display device emits light using the following principle: when a voltage is applied to the transparent electrode and the metal electrode, holes and electrons are injected into the light-emitting layer, the energy generated by the recombination of the holes and the electrons excites the fluorescent substance, and when the excited fluorescent substance returns to a normal state, light is emitted. The mechanism of recombination in the middle is the same as that of a general diode, and thus it is also expected that the current and the light emission intensity show strong nonlinearity accompanying rectification with respect to the applied voltage.

In an organic EL display device, at least one of the electrodes needs to be transparent in order to extract light emission in the light-emitting layer, and a transparent electrode formed of a transparent conductor such as Indium Tin Oxide (ITO) is generally used as an anode. On the other hand, in order to facilitate electron injection and improve the light emission efficiency, it is important to use a substance having a small work function for the cathode, and a metal electrode such as Mg — Ag or Al — Li is generally used.

In the organic EL display device having such a structure, the light-emitting layer is formed by an extremely thin film having a thickness of about 10 nm. Therefore, the light-emitting layer transmits light almost completely, as in the case of the transparent electrode. As a result, light incident from the surface of the transparent substrate during non-emission and reflected by the metal electrode through the transparent electrode and the light-emitting layer is emitted again to the surface side of the transparent substrate, and thus the display surface of the organic EL display device looks like a mirror surface when viewed from the outside.

The circularly polarizing plate of the present embodiment is suitable for an organic EL display device in which external light reflection is a problem.

That is, when the organic EL element 101 does not emit light, half of the external light incident from the outside of the organic EL element 101 due to indoor lighting or the like is absorbed by the polarizer 313 of the polarizing plate 301, and the remaining half is transmitted as linearly polarized light and enters the λ/4 retardation film 311. Since the transmission axis of the polarizer 313 and the retardation axis of the λ/4 retardation film 311 cross at 45 ° (or 135 °), light incident to the λ/4 retardation film 311 is converted into circularly polarized light by passing through the λ/4 retardation film 311.

When the circularly polarized light emitted from the λ/4 retardation film 311 is specularly reflected by the metal electrode 112 of the organic EL element 101, the phase is inverted by 180 degrees, and the circularly polarized light is reflected as inverted circularly polarized light. The reflected light is converted into linearly polarized light perpendicular to the transmission axis of the polarizer 313 (parallel to the absorption axis) by entering the λ/4 retardation film 311, and is therefore completely absorbed by the polarizer 313 and is not emitted to the outside. That is, external light reflection in the organic EL element 101 can be reduced by the polarizing plate 301.

< liquid crystal display device >

Fig. 6 is a cross-sectional view showing a schematic configuration of a liquid crystal display device 400 as another example of the display device of the present embodiment. The liquid crystal display device 400 is configured by disposing a polarizing plate 402 on one surface side of a liquid crystal cell 401.

The liquid crystal cell 401 is a display cell in which a liquid crystal layer is sandwiched between a pair of substrates. Note that, although another polarizing plate disposed in a state of being orthogonally polarized to the polarizing plate 402 and a backlight for illuminating the liquid crystal cell 401 are provided on the side of the liquid crystal cell 401 opposite to the polarizing plate 402, these are not illustrated in fig. 6.

The liquid crystal display device 400 may have a front window 403 on the side opposite to the liquid crystal cell 401 with respect to the polarizing plate 402. The front window 403 is an outer cover of the liquid crystal display device 400, and is made of, for example, cover glass. A filler 404 made of, for example, an ultraviolet curable resin is filled between the front window 403 and the polarizing plate 402. In the case where the filler 404 is not present, an air layer is formed between the front window 403 and the polarizing plate 402, and thus the visibility of the display image may be reduced by reflection of light at the interfaces between the front window 403 and the polarizing plate 402 and the air layer. However, since the filler 404 does not form an air layer between the front window 403 and the polarizing plate 402, it is possible to avoid a reduction in visibility of a display image due to reflection of light at the interface.

The polarizing plate 402 has a polarizer 411 that transmits predetermined linearly polarized light. On one surface side (the side opposite to the liquid crystal cell 401) of the polarizer 411, a λ/4 retardation film 413 and a cured layer 414 made of an ultraviolet curable resin are laminated in this order via an adhesive layer 412. Further, a protective film 416 is bonded to the other surface side (liquid crystal cell 401 side) of the polarizer 411 via an adhesive layer 415.

The polarizer 411 is a polarizer obtained by, for example, dyeing a polyvinyl alcohol film with a dichroic dye and stretching it at a high magnification. After the polarizer 411 is subjected to alkali treatment (also referred to as saponification treatment), a λ/4 retardation film 413 is bonded to one surface side via an adhesive layer 412, and a protective film 416 is bonded to the other surface side via an adhesive layer 415. The protective film 416, the polarizer 411, and the λ/4 retardation film 413 of the polarizing plate 402 correspond to the polarizing plate protective film 51, the polarizer 52, and the retardation film 53 of the polarizing plate 50 of fig. 4, respectively. The adhesive layers 412 and 415 are layers made of, for example, a polyvinyl alcohol adhesive (PVA adhesive, water gel), but may be layers made of an ultraviolet-curable adhesive (UV adhesive).

The λ/4 retardation film 413 is a layer that imparts an in-plane retardation of about 1/4 degrees in wavelength to transmitted light, and is composed of the optical film (obliquely-stretched film) of the present embodiment, and has a thickness of, for example, 10 to 70 μm. The angle (crossing angle) formed by the retardation axis of the λ/4 retardation film 413 and the absorption axis of the polarizer 411 is, for example, 30 to 60 °, and more preferably 45 °. Thereby, the linearly polarized light from the polarizer 411 is converted into circularly polarized light or elliptically polarized light by the λ/4 retardation film 413.

The hardened layer 414 (also referred to as a hard layer) is made of an active energy ray-curable resin (e.g., an ultraviolet-curable resin).

The protective film 416 is made of, for example, a cellulose resin (cellulose copolymer), an acrylic resin, a cyclic polyolefin (COP), or a Polycarbonate (PC). The protective film 416 is provided only as a film for protecting the back surface side of the polarizer 411, but may be provided as an optical film that is a retardation film having a desired optical compensation function.

In the case of a liquid crystal display device, the other polarizing plate disposed on the opposite side of the liquid crystal cell 401 (liquid crystal cell) from the polarizing plate 402 is configured to sandwich the surface of the polarizer by two optical films, but as the above-described polarizer and optical films, the same polarizer and optical film as the polarizer 411 and the protective film 416 of the polarizing plate 402 can be used.

An easy-adhesion layer for improving the adhesion of the λ/4 retardation film 413 may be provided on the adhesion layer 412 side of the λ/4 retardation film 413. The easy adhesion layer is formed by performing an easy adhesion treatment on the adhesion layer 412 side of the λ/4 retardation film 413. Examples of the easy adhesion treatment include corona (discharge) treatment, plasma treatment, flame treatment, ITRO treatment, glow treatment, ozone treatment, primer coating treatment, and the like, but at least one of these treatments may be performed. Among these easy adhesion treatments, corona treatment and plasma treatment are preferable as the easy adhesion treatment from the viewpoint of productivity.

In the liquid crystal display device 400 having the polarizing plate 402 positioned on the viewing side with respect to the liquid crystal cell 401 and the λ/4 retardation film 413 of the polarizing plate 402 positioned on the opposite side of the polarizer 411 from the liquid crystal cell 401, the linearly polarized light emitted from the liquid crystal cell 401 and transmitted through the polarizer 411 on the viewing side is converted into circularly polarized light or elliptically polarized light by the λ/4 retardation film 413. Therefore, when the observer views the display image of the liquid crystal display device 400 by wearing the polarized sunglasses, the display image can be observed by guiding the light component parallel to the transmission axis of the polarized sunglasses to the eye of the observer regardless of the angle between the transmission axis of the polarizer 411 and the transmission axis of the polarized sunglasses.

< dimensional change rate of obliquely-stretched film >)

Next, the dimensional change rate of an obliquely stretched film (optical film) used as a retardation film (for example, a λ/4 retardation film) of the above-described polarizing plate will be described.

The optical film of the present embodiment, that is, the optical film in which the slow axis is inclined by 10 to 80 degrees with respect to one side of the film outer shape in the film surface, is set to have a dimension change rate of Δ D in the phase advance axis direction and the slow axis direction before and after being left at 90 ℃ for 120 hours_F(%) and Δ D_L(%). That is, when the distances between two points arranged in the direction of the advancing axis of the optical film and between the points before and after the optical film is left at 90 ℃ for 120 hours are respectively a1(mm) and a2(mm), and the distances between two points arranged in the direction of the retarding axis of the optical film and between the points before and after the optical film is left at 90 ℃ for 120 hours are respectively b1(mm) and b2(mm),

ΔD_F＝{(a2-a1)/a1}×100

ΔD_L＝{(b2-b1)/b1}×100。

in the present embodiment, the film has a shape satisfying both the center and both end portions in the direction along the one side of the outer shape of the film

0％≦ΔD_F<0.5％···(1)

ΔD_L<0％···(2)。

Relates to an optical filmThe dimensional change rate Δ D in the advancing axis direction and the retarding axis direction of_FAnd Δ D_LWhen the above conditional expressions (1) and (2) are satisfied, the optical film expands in the phase advance axis direction or contracts in the phase delay axis direction without changing its size in a high-temperature environment.

The reason why the optical film shrinks in the slow axis direction under a high-temperature environment is as follows. The slow axis direction is the same as the extension direction, and after extension, tensile stress remains in the optical film in the slow axis direction. Since the tensile stress is relaxed in a high-temperature environment, the optical film contracts in the slow axis direction. The reason why the optical film expands or does not change in dimension in the phase advancing axis direction in a high-temperature environment is that a shrinkage stress remains in the phase advancing axis direction after stretching, or a shrinkage stress and a tensile stress do not remain in the phase advancing axis direction, and the dimensional change rate Δ D is realized in such a manner_FThe details of the scheme (A) are described later.

Since the optical film of the present embodiment does not shrink in the phase advancing axis direction under a high temperature environment by satisfying the conditional expressions (1) and (2), even if there is shrinkage in the slow axis direction under a high temperature environment, it is possible to suppress dimensional change (shrinkage) of the entire film as compared with a film that shrinks in both the phase advancing axis direction and the slow axis direction under a high temperature environment. Accordingly, even when the optical film and the polarizer of the present embodiment are bonded to each other with an adhesive so that the retardation axis of the optical film and the absorption axis (or transmission axis) of the polarizer form a desired angle (for example, 45 °), the deterioration of the quality of the polarizing plate, such as the occurrence of curling in the polarizing plate due to dimensional changes of the optical film or the peeling of the optical film from the polarizer due to the decrease in the adhesiveness of the optical film to the polarizer, can be suppressed.

That is, if the adhesive is, for example, an ultraviolet-curable adhesive, the adhesive becomes a high-temperature environment by ultraviolet irradiation or heating for accelerating curing. On the other hand, when the adhesive is a water-based adhesive such as a water gel, the adhesive is heated or dried to promote curing of the adhesive, thereby forming a high-temperature environment. Even in such an environment that becomes a high temperature at the time of bonding, the optical film of the present embodiment can suppress dimensional change (shrinkage) of the entire film without shrinking in the phase axis direction as described above, and thus can suppress curling of the polarizer and deterioration of the adhesiveness of the optical film.

In this way, by suppressing the curl of the polarizing plate, in the organic EL display device to which the polarizing plate is applied, light leakage due to reflection of external light at the time of black state display can be suppressed. In addition, in the liquid crystal display device corresponding to the polarized sunglasses in which the polarizing plate is disposed on the visible side of the liquid crystal cell, distortion can be suppressed from occurring in an image viewed through the polarizing plate, and a decrease in visibility of a display image can be suppressed.

Recently, in order to improve the visibility from an arbitrary angle, a high retardation film composed of polyethylene terephthalate or polyethylene naphthalate and having a retardation of 10000nm or more has been proposed. Even in the case where such a film is used to constitute a polarizing plate, when a curl is generated in the polarizing plate due to a dimensional change of the film, visibility of a display image is lowered. However, even in such a film, since the dimensional change of the entire film under a high temperature environment can be suppressed and the curl of the polarizer can be suppressed by satisfying the above conditional expressions (1) and (2), the deterioration of the visibility can be suppressed even in the above-mentioned liquid crystal display device to which the film having a high retardation is applied.

In addition, the dimensional change rate Δ D in the phase advancing axis direction_FIf the amount is 0.5% or more, the dimensional change (expansion) in the phase advancing axis direction becomes too large with respect to the dimensional change (shrinkage) in the slow phase axis direction in a high temperature environment, and distortion occurs in the optical film, whereby curling occurs in the polarizing plate in the same manner as described above, and peeling of the optical film may occur. Therefore, in the conditional expression (1), the dimensional change rate Δ D in the phase advance axis direction is calculated_FThe upper limit of (B) is defined to be 0.5%.

In addition, since the optical film of the present embodiment has a residual solvent amount of 60ppm or less, it is possible to design a film that satisfies the above conditional expressions (1) and (2) at the same time. As described in more detail below.

In the film formation by the solution casting film formation method, since a solvent is used in the film formation, the residual solvent amount of the film formed is far more than 60 ppm. As described above, a film formed by a solution casting film-forming method has a low resin density and is easily stretched in both the slow axis direction and the fast axis direction during oblique stretching, and therefore, after oblique stretching, tensile stress remains in both the slow axis direction and the fast axis direction. As a result of the relaxation of the tensile stress in a high-temperature environment, the film shrinks in both the slow axis direction and the phase advance axis direction. Therefore, the optical film does not satisfy the conditional expression (1) even if the optical film satisfies the conditional expression (2).

On the other hand, a film having a residual solvent amount of 60ppm or less can be formed by, for example, a melt casting film forming method. A film formed by a melt-casting film-forming method has a higher resin density than a film formed by a melt-casting film-forming method (the same components except for a solvent), and therefore, the film is difficult to stretch in the phase-advancing axis direction during oblique stretching and is forcibly stretched in the phase-retarding axis direction by a force in the stretching direction. Therefore, tensile stress remains in the obliquely-stretched film in the slow axis direction, while it becomes difficult to remain in the phase advancing axis direction. Therefore, even if the film shrinks in the slow axis direction under a high temperature environment, it becomes difficult to shrink in the phase advancing axis direction, so that it becomes possible to design a film that satisfies the conditional expressions (1) and (2) at the same time.

From the viewpoint of reliably increasing the density of the resin contained in the film and thus reliably enabling film design that satisfies both conditional expressions (1) and (2), the preferable range of the residual solvent amount of the optical film of the present embodiment is 10ppm or less.

For example, a transversely stretched film is a film stretched in the width direction, but since a tensile force for transporting the film is applied in the transport direction (longitudinal direction) during stretching, tensile stress remains in both the slow axis direction (width direction as the stretching direction) and the fast axis direction (transport direction) in the stretched film. Therefore, as a result of the film being relaxed in the tensile stress in a high-temperature environment, the film contracts in both the slow axis direction and the phase advance axis direction, and the conditional expression (1) is not satisfied.

The longitudinally stretched film is a film that extends in the conveyance direction (longitudinal direction), and is considered to extend in the longitudinal direction (slow axis direction) and contract in the width direction (advancing axis direction) during stretching, but is considered to not contract positively in the width direction and to have a small contraction force in the advancing axis direction. Therefore, the residual stress in the phase advancing axis direction is small, and even if the residual stress in the phase advancing axis direction of the film in a high-temperature environment is relaxed, the film does not expand in the phase advancing axis direction. On the contrary, in a high-temperature environment, the shrinkage in the slow phase axis direction is large, and therefore the entire film tends to shrink, and therefore, the film is considered to shrink in the phase advancing axis direction although it is only a little. Therefore, the longitudinally stretched film also becomes unsatisfactory in the conditional expression (1).

As described above, the optical film of the present embodiment satisfying both the conditional expressions (1) and (2) is realized by an obliquely-stretched film formed by a stretching method other than the transverse stretching and the longitudinal stretching, that is, by stretching in a direction oblique to the width direction of the long film.

The optical film of the present embodiment preferably further satisfies the following conditional expression (1 a). That is to say that the first and second electrodes,

0％<ΔD_F<0.5％···(1a)。

since the optical film satisfying the conditional expression (1a) expands in the phase advancing axis direction in a high-temperature environment, even if there is shrinkage in the slow axis direction in the high-temperature environment, it is possible to reliably suppress dimensional change (shrinkage) of the entire film as compared with a film that shrinks in both the phase advancing axis direction and the slow axis direction in the high-temperature environment. Accordingly, the curl of the polarizing plate formed by laminating the optical film and the polarizer can be reliably suppressed, and the light leakage due to the reflection of external light when the polarizing plate is applied to an organic EL display device and the deterioration of visibility when the polarizing plate is applied to a liquid crystal display device corresponding to a polarized sunglass can be reliably suppressed.

However, in an optical film (obliquely-stretched film) in which the slow axis is inclined by 10 to 80 ° with respect to one side (for example, a side corresponding to the width direction of a strip film) of the outer shape (for example, a rectangular shape) of the film in the film surface, the dimensional change rate in the direction of the phase advancing axis before and after the optical film is left at 90 ℃ for 120 hours in the central portion along the one side is defined as Δ D_F-C(%) and the dimensional change rate in the phase advancing axis direction before and after the optical film was left at 90 ℃ for 120 hours was Δ D at one end in the direction along the one side (for example, the end on the advancing side in oblique stretching)_F-E1In percent, and the dimensional change rate in the phase advancing axis direction before and after the optical film was left at 90 ℃ for 120 hours at the other end portion (for example, the end portion on the retardation side in the case of oblique stretching) in the direction along the one side is represented by Δ D_F-E2(%), the more preferable results are satisfied

(ΔD_F-E1+ΔD_F-E2)/2＞ΔD _F-C3. c. The reason for this is as follows.

In the case where the optical film of the present embodiment and the polarizer are bonded to each other via an adhesive to form a polarizing plate, the adhesive generally shrinks when cured (in a high-temperature environment) regardless of whether it is an ultraviolet-curable adhesive or a water-based adhesive. In this case, in the bonding using the ultraviolet-curable adhesive, when ultraviolet rays as active energy rays are irradiated, the amount of light received by the ultraviolet rays often differs between the widthwise central portion (corresponding to the widthwise central portion of the optical film) and the widthwise end portions (corresponding to the widthwise end portions of the optical film) of the adhesive, and the amount of light received by the ultraviolet rays is greater in the widthwise central portion than in the widthwise end portions. Therefore, it is estimated that the width end portion is larger than the width center portion with respect to curing shrinkage of the adhesive at the time of ultraviolet irradiation.

The reason why the difference in the amount of ultraviolet light received is present between the width center portion and the width end portion is that, when a UV light source that irradiates ultraviolet light with a width narrower than a required width is used, ultraviolet light is irradiated from both one side and the other side in the width direction with respect to the normal line of the application surface of the adhesive in the width center portion, whereas ultraviolet light is irradiated from only one side in the width direction with respect to the normal line of the application surface of the adhesive in the width end portion. In order to reduce the variation in the width direction of the amount of ultraviolet light received, for example, a method of irradiating ultraviolet light with a width wider than a required width is conceivable, but this method requires a large-sized UV lamp and is not preferable because the cost becomes extremely high.

In addition, it is also known that, when heating is performed to promote curing of an adhesive (ultraviolet-curable adhesive, water gel), heat is more likely to concentrate in the width central portion than in the width end portions, and the temperature is decreased in the width end portions. Therefore, even when heating for promoting curing of the adhesive is performed, the curing shrinkage of the adhesive is estimated to be larger in the width center portion than in the width end portion.

After discussing a method of securing sufficient adhesive force of an adhesive between an optical film and a polarizer and coping with deformation of a polarizing plate caused by curing shrinkage of the adhesive, it is known that curling of the polarizing plate can be more suppressed over the entire region in the width direction by providing a difference in expansion amount in the phase advancing axis direction in the width direction of the optical film. Fig. 7 schematically shows changes in the adhesive and the optical film at the width center portion and the width end portion when the adhesive is cured in the present embodiment. Since the contraction and expansion are changes in opposite directions, for example, when the contraction of the adhesive is large and the expansion of the optical film is large at the same position in the width direction, the polarizing plate curls so that the adhesive side becomes concave (so that the optical film side becomes convex).

By satisfying the above conditional expression (3), the expansion in the phase axis direction of the optical film is small at the width center portion where the shrinkage of the adhesive is large, and the expansion in the phase axis direction of the optical film is large at the width end portion where the shrinkage of the adhesive is small. Thus, the tendency of curling of the polarizing plate due to large shrinkage of the adhesive can be suppressed by small expansion of the optical film in the phase advancing axis direction at the widthwise central portion. Similarly, the tendency of curling of the polarizing plate due to large expansion in the phase axis direction of the optical film can be suppressed by small contraction of the adhesive at the width end portions. As a result, the curl of the polarizing plate can be further suppressed over the entire width direction. Further, by further suppressing curling of the polarizer, it is possible to sufficiently secure adhesion between the optical film and the polarizer by the adhesive, and to reliably suppress peeling of the optical film.

The optical film of the present embodiment is in a long shape, and the direction along the one side of the film outer shape is preferably a width direction perpendicular to the longitudinal direction within the film surface of the optical film. In this case, the dimensional change rate Δ D can be realized at the center portion and both end portions in the width direction_FAnd Δ D_LA long optical film satisfying the above conditional expressions (1) and (2). In addition, the polarizing plate can be manufactured in a roll-to-roll manner by using such a long optical film.

The polarizing plate according to the present embodiment (for example, the polarizing plate 301 in fig. 5 or the polarizing plate 402 in fig. 6) includes the optical film (for example, the λ/4 retardation film 311 or 413) and the polarizer (for example, the polarizer 313 or 411) according to the present embodiment. The optical film is located on one side of the polarizer so that a slow phase axis crosses an absorption axis (or a transmission axis) of the polarizer in a film surface. Since the optical film of the present embodiment does not shrink in the phase advance axis direction under a high temperature environment, and dimensional change of the entire film can be suppressed, even when the polarizing plate is produced by bonding the optical film and the polarizer, curling of the polarizing plate and peeling of the optical film due to dimensional change of the optical film under a high temperature environment at the time of bonding can be suppressed.

Therefore, in the organic EL display device 100 in which the display unit is the organic EL element 101 and the λ/4 retardation film 311 of the polarizing plate 301 is positioned on the organic EL element 101 side with respect to the polarizer 313, by suppressing the curling of the polarizing plate 301, light leakage due to reflection of external light at the time of black state display can be suppressed.

In the liquid crystal display device 400 corresponding to the polarized sunglasses in which the display cell is the liquid crystal cell 401 and the λ/4 retardation film 413 of the polarizing plate 402 is located on the opposite side of the polarizer 411 from the liquid crystal cell 401, the occurrence of distortion in an image viewed through the polarizing plate 402 can be suppressed by suppressing the curl of the polarizing plate 402, and the deterioration of the visibility of the displayed image can be suppressed.

< solution for realizing dimensional change rate in phase advance axis direction >

Next, in the optical film of the present embodiment described above, the dimensional change rate Δ D in the phase advance axis direction defined by the conditional expression (1) is realized_FThe scheme of (2) is specifically explained.

(setting of force (tension) in the conveying direction applied to both ends in the width direction in oblique stretching)

Fig. 8 schematically shows the forces in the conveying direction applied to both ends in the width direction of the long film in the extension portion 5 of the obliquely-stretched film manufacturing apparatus 1 shown in fig. 1. In the extending portion 5, an obliquely extending step of holding both end portions of the long film in the width direction by a pair of holding members Ci and Co is performed, and the long film is bent and conveyed in the film surface by advancing one holding member Ci relative to the other holding member Co, and the long film is extended in an oblique direction with respect to the width direction, thereby obtaining an obliquely extending film constituting the optical film.

Here, forces applied in the transport direction by the gripping of the grips Ci and Co and the movement in the transport direction at the respective ends in the width direction of the long film before the oblique stretching (for example, in the preheating zone Z1) are set to be the same tr (n). In the oblique stretching (for example, in the stretching region Z2), the forces applied in the transport direction by the gripping of the gripper Co on the relatively delay side and the gripper Ci on the relatively advance side and the movement in the transport direction at the respective ends in the width direction of the long film are to (n) and ti (n), respectively. In this case, the above-mentioned oblique stretching step is performed in such a manner as to satisfy

(Ti-Tr)/Tr≧1.7···(A)

(Tr-To)/Tr≧1.5···(B)

In the aspect of (1), the long film is extended in a direction inclined with respect to the width direction.

The conditional expressions (a) and (B) may be modified as described in the following conditional expressions (a ') and (B'), respectively. That is to say that the first and second electrodes,

Ti≧2.7Tr···(A’)

To≦-0.5Tr···(B’)。

the grippers Ci and Co are attached to chains moving along the guide rails Ri and Ro in the extension portion 5, and the chains are moved in the respective zones (the preheating zone Z1, the extension zone Z2, and the heat fixing zone Z3) by the rotation of the drive roller. The forces Tr, Ti, and To may be replaced by the driving force of a motor that rotates the driving roller in each region, and in the present embodiment, the optical film (obliquely-stretched film) satisfying the conditional expressions (a) and (B) is obtained by controlling the driving force.

By satisfying conditional expressions (a) and (B) (or by satisfying conditional expressions (a ') and (B')), the force in the conveyance direction applied during oblique stretching increases at the leading end of the long film in the width direction relative to the force applied before oblique stretching, while the force in the conveyance direction applied during oblique stretching decreases at the trailing end relative to the force applied before oblique stretching, and the amount of change (increase) in the force in the conveyance direction at the leading end and the amount of change (decrease) in the force in the conveyance direction at the trailing end are also large.

By performing the oblique stretching under such conditions, the film is stretched in the oblique stretching direction (slow axis direction) at each position in the width direction of the long film (at least at the center portion and both end portions in the width direction), and on the other hand, the film can be formed in a state of being shrunk against the stretching during the conveyance or in a state of being neither stretched nor shrunk in cooperation with the stretching in the conveyance direction. In this case, the transport direction and the phase advancing axis direction do not necessarily coincide with each other, but even if both are displaced, the amount of displacement is small, and therefore, the film is shrunk in the transport direction, and stress that shrinks in the phase advancing axis direction can be caused to remain in the film. In addition, in the film that neither extends nor shrinks in the conveying direction, a film that neither extends nor shrinks almost in the advancing axis direction can be obtained.

Therefore, in a high-temperature environment, residual stress (shrinkage stress) in the phase advance axis direction is relaxed and the film expandsOr not expanded and contracted, and the dimensional change rate Δ D in the phase advance axis direction defined by the above conditional expression (1) can be realized_F。

(Cooling of the end on the side of the retardation film when obliquely stretched)

Fig. 9 schematically shows other structures of the extension 5. The extension 5 may also have a cooling mechanism 21. The cooling mechanism 21 cools the end portion held by the relatively retarded-side holder Co among the widthwise end portions of the long film in the oblique stretching step by the stretching portion 5. The cooling mechanism 21 can be configured by, for example, an air blowing mechanism (an air conditioner, a fan, or the like) that blows a cool air to the long film.

In the oblique stretching step, the film end on the retardation side is cooled by the cooling mechanism 21, whereby a contraction stress can be applied to the film end. Thus, the contraction stress remaining in the phase advancing axis direction can be further increased by the oblique extension satisfying the conditional expressions (a) and (B) described above. Therefore, in a high-temperature environment, the film can be further expanded by relaxing the residual stress (shrinkage stress) in the phase axis direction of the obliquely-stretched film, and the dimensional change rate Δ D in the phase axis direction defined by the conditional expression (1) can be reliably realized_F。

(multistage diagonal stretching)

Fig. 10 schematically shows another alternative construction of the extension 5. In the oblique stretching step by the stretching portion 5, the long film may be obliquely stretched in the width direction of the long film such that the slow axis is aligned at an alignment angle (for example, 60 °) larger than a desired alignment angle (for example, 45 °), and then the long film may be obliquely stretched such that the slow axis is aligned at a desired alignment angle (for example, 45 °). Such multistage diagonal stretching can be realized by appropriately changing the rail pattern of the stretching portion 5.

In the oblique stretching step, the larger the stretching angle (the turning angle at the time of bending), that is, the larger the alignment angle of the slow axis by oblique stretching, the larger the tensile stress in the slow axis direction and the larger the shrinkage stress in the advancing axis direction. Like thisIn this case, by generating a large shrinkage stress in the phase advance axis direction, even if the extension angle is made small (even if the shrinkage stress is somewhat reduced), the large shrinkage stress can be left. Therefore, in a high-temperature environment, the film can be further expanded by relaxing the residual stress (shrinkage stress) in the phase axis direction of the obliquely-stretched film, and the dimensional change rate Δ D in the phase axis direction defined by the conditional expression (1) can be reliably realized_F. In this case, the aforementioned cooling of the end portion on the side of the retardation side is not essential, but the effect can be further improved by cooling the end portion on the side of the retardation side together with the multi-stage oblique extension.

< example >

Specific examples of the present invention will be described below, but the present invention is not limited to these examples.

[ production of Long film ]

(production of Long film A1)

A polycarbonate resin film (PC film) as the long film a1 was produced by the following production method (melt casting film formation method).

Polymerization was carried out using a batch polymerization apparatus comprising two parts, a stirring blade and a vertical reactor equipped with a reflux cooler controlled to 100 ℃. Reacting 9, 9- [4- (2-hydroxyethoxy) phenyl]Fluorene (BHEPF), Isosorbide (ISB), diethylene glycol (DEG), diphenyl carbonate (DPC), and magnesium acetate tetrahydrate in a molar ratio BHEPF/ISB/DEG/DPC/magnesium acetate of 0.348/0.490/0.162/1.005/1.00 × 10^－5To put in. After the inside of the reactor was sufficiently replaced with nitrogen (oxygen concentration: 0.0005 to 0.001 vol%), the reactor was heated with a heat transfer medium, and stirring was started when the internal temperature became 100 ℃. After 40 minutes from the start of the temperature rise, the internal temperature was brought to 220 ℃ and the pressure was reduced while controlling the temperature so as to be maintained, whereby 13.3kPa was obtained at 90 minutes after the temperature reached 220 ℃. Phenol vapor produced as a by-product of the polymerization reaction was introduced into a reflux condenser at 100 ℃ to return a monomer component contained in the phenol vapor in an amount of several amounts to the reactor, and phenol vapor not condensed was introduced into a condenser at 45 ℃ and recovered.

After nitrogen gas was introduced into the first reactor and the pressure was returned to atmospheric pressure, the reaction solution in the first reactor, which had been oligomerized, was transferred to the second reactor. Then, the temperature increase and pressure reduction in the second reactor were started, and the internal temperature was set to 240 ℃ and the pressure to 0.2kPa at 50 minutes. Thereafter, the polymerization was allowed to proceed until a predetermined stirring power was obtained. When the reactor reached a predetermined power, nitrogen gas was introduced into the reactor and the pressure was increased again, and the reaction mixture was withdrawn in the form of a strand and pelletized with a rotary cutter, thereby obtaining a polycarbonate resin a having a copolymerization composition in which BHEPF/ISB/DEG was 34.8/49.0/16.2[ mol% ]. The polycarbonate-series resin A had a reduced viscosity of 0.430dL/g and a glass transition temperature of 128 ℃.

After the obtained polycarbonate resin A was vacuum-dried at 80 ℃ for five hours, a film-forming apparatus equipped with a uniaxial extruder (25 mm in screw diameter, set temperature in cylinder: 220 ℃ C., manufactured by Kashizu chemical Co., Ltd.), a T die (900 mm in width, set temperature: 220 ℃ C.), a chill roll (set temperature: 120 to 130 ℃ C.), and a winder was used to prepare a polycarbonate resin film having a thickness of 195 μm and a residual solvent amount of 10ppm as a long film A1.

(production of Long film A2)

A polycarbonate resin film (PC film) as the long film a2 was produced by the following production method (solution casting film formation method).

Concentrated liquid composition

Polycarbonate resin A (same resin as used for production of Long film A1)

100 mass part

430 parts by mass of methylene chloride

90 mass fraction of methanol

The composition was put into a closed container, and the mixture was stirred while keeping the temperature at 80 ℃ under pressure until the composition was completely dissolved, thereby obtaining a concentrated solution composition.

Next, the dope composition was filtered, cooled and maintained at 33 ℃, uniformly cast on a stainless steel belt, and dried at 33 ℃ for five minutes. Thereafter, the drying time was adjusted at 65 ℃ to peel the film from the stainless steel tape, and then the drying was completed while conveying the film by a plurality of rollers, thereby obtaining a polycarbonate-based resin film having a film thickness of 75 μm and a residual solvent amount of 110ppm as a long film A2.

(production of Long film B1)

An alicyclic olefin copolymer resin film (COP film) as the elongated film B1 was produced by the following production method (melt casting film formation method).

After 1-hexane 1.2 mass part, dibutyl ether 0.15 mass part, and triisobutylaluminum 0.30 mass part were put into a reactor at room temperature and mixed under a nitrogen atmosphere to a dehydrated cyclohexane 500 mass part, a norbornene monomer mixture and tungsten hexachloride (0.7% toluene solution) 40 mass part were continuously added and polymerized for two hours while maintaining 45 ℃ and the norbornene monomer mixture was composed of: tricyclic [4.3.0.1 ]^2,5]Deca-3, 7-diene (dicyclopentadiene, hereinafter abbreviated to DCP)20 moiety, 1, 4-methylene-1, 4,4a,9 a-tetrahydrofluorene (hereinafter abbreviated to MTF)140 moiety and 8-methyl-tetracyclo [4.4.0.12,5.17,10]-dodec-3-ene (hereinafter abbreviated as MTD)40 mass fraction. Addition of 1.06 parts by mass of glycidyl butyl ether and 0.52 parts by mass of isopropyl alcohol to the polymerization solution deactivated the polymerization catalyst to stop the polymerization reaction.

Next, a cyclohexane 270 mass portion and a nickel-alumina catalyst (manufactured by Nikkiso Kagaku Co., Ltd.) 5 mass portion were added to 100 mass portions of the obtained reaction solution containing the ring-opened polymer, and the mixture was heated to a temperature of 200 ℃ under pressure of 5MPa with hydrogen gas and stirring, and then reacted for four hours to obtain a reaction solution containing 20% of DCP/MTF/MTD ring-opened polymer hydrogenated copolymer.

After removing the hydrogenation catalyst by filtration, a soft polymer (manufactured by Coli, Inc.; SEPTON2002) and an antioxidant (manufactured by Ciba Seikagaku Co., Ltd.; IRGANOX1010) were added to the obtained solutions, respectively, and dissolved (each 0.1 part by mass per 100 parts by mass of the polymer). Then, cyclohexane and other volatile components as a solvent were removed from the solution using a cylinder type concentration dryer (manufactured by Hitachi, Ltd.), and the hydrogenated copolymer was extruded from an extruder in a molten state into a strand shape, cooled, pelletized, and recovered. The copolymerization ratio of each norbornene monomer in the polymer was calculated from the composition of the residual norbornene in the solution after polymerization (by gas chromatography), and it was found to be DCP/MTF/MTD 10/70/20, which was almost equal to the charged composition. The ring-opened polymer had a hydrogen addition, a weight average molecular weight (Mw) of 31,000, a molecular weight distribution (Mw/Mn) of 2.5, a hydrogen addition rate of 99.9%, and a glass transition temperature Tg of 134 ℃.

The obtained pellets of the ring-opened polymer hydrogen additive were dried at 70 ℃ for two hours using a hot air dryer through which air was circulated to remove moisture. Next, the pellets were melt-extruded using a short-shaft extruder (manufactured by Mitsubishi heavy industries, Ltd.; screw diameter: 90mm, T-die lip seal material: tungsten carbide, and peel strength from molten resin: 44N) having a T-die of a coat hanger type, to obtain an alicyclic olefin copolymer resin film (COP film) having a thickness of 75 μm and a residual solvent amount of 10ppm as a long film B1.

(production of Long film B2)

An alicyclic olefin copolymer resin film (COP film) having a residual solvent amount of 110ppm was produced as an elongated film B2 in the same manner as in the production of the elongated film a2 by a solution casting film production method, except that a dope composition was prepared using the hydrogenated copolymer obtained in the production of the elongated film B1 instead of the polycarbonate resin a, and the prepared dope composition was used.

(preparation of Long film C)

A polyethylene naphthalate-based resin film (PEN film) as the long film C was produced by the following production method (melt casting film formation method).

Synthesis of polyethylene naphthalate

A cobalt acetate tetrahydrate salt 0.03 mass part was used as a transesterification catalyst, and a dimethyl-2, 6-naphthalenedicarboxylate 100 mass part and an ethylene glycol 60 mass part were subjected to transesterification reaction in accordance with a conventional method. Thereafter, 0.023 parts by mass of trimethyl phosphate was added to substantially complete the transesterification reaction. Subsequently, 0.024 part by mass of antimony trioxide was added, and polycondensation reaction was performed under high temperature and high vacuum conditions by a conventional method to obtain polyethylene naphthalate having an inherent viscosity (measured at 35 ℃ C. with a phenol/tetrachloroethane mixed solvent (mass ratio 1: 1)) of 0.62 dL/g.

Production of membrane

The pellets of the obtained polyethylene naphthalate were dried at 180 ℃ for three hours and then supplied to a hopper of an extruder. The polyethylene naphthalate-based resin film was obtained as a long film C by melting at 300 ℃ and extruding the molten copolymer through a slit die of 9.0mm onto a rotary cooling drum having a surface temperature of 40 ℃ to obtain a polyethylene naphthalate-based resin film having a residual solvent content of 8 ppm.

(preparation of strip film D)

A cellulose ester resin film (CE film) as the long film D was produced by the following production method (solution casting film formation method).

Fine particle dispersion

Fine particles (AEROSIL R972V, produced by AEROSIL CORPORATION, Japan) 11 parts by mass

Ethanol 89 mass fraction

The above was stirred and mixed for 50 minutes by a vertical disperser, and then dispersed by a homogenizer.

Fine particle additive liquid

The fine particle dispersion was slowly added to a dissolution tank containing methylene chloride with sufficient stirring based on the following composition. Further, the dispersion was carried out by a mill so that the particle diameter of the secondary particles became a predetermined size. This was filtered through a nanocrystalline soft magnetic material (FINEMET) NF manufactured by japan kokai corporation to prepare a fine particle-added liquid.

99 parts by mass of methylene chloride

Fine particle dispersion 5 part by mass

Concentrated liquid of main type

A main dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. Cellulose acetate was put into a pressurized dissolution tank containing a solvent while stirring. The resulting solution was heated and completely dissolved with stirring. This was filtered through an Amur filter paper No.244 manufactured by Amur Filter paper Co., Ltd to prepare a main concentrate. The sugar ester compound was synthesized by the following synthesis examples.

Composition of Main concentrated solution

(Synthesis of sugar ester Compound)

The sugar ester compound was synthesized by the following procedure.

[ solution 1]

34.2g (0.1 mol) of sucrose, 180.8g (0.6 mol) of anhydrous benzoic acid, and 379.7g (4.8 mol) of pyridine were placed in a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube, and the temperature was raised while bubbling nitrogen gas through the nitrogen gas inlet tube under stirring, and esterification reaction was carried out at 70 ℃ for five hours.

Then, the inside of the bottle was depressurized to 4X 10²Pa or less, distilling excess pyridine at 60 deg.C, reducing pressure in the bottle to 1.3 × 10Pa or less, heating to 120 deg.C, and distilling anhydrous benzoic acid and most of generated benzoic acid.

Finally, 100g of water was added to the toluene layer thus separated, and after washing with water at room temperature for 30 minutes, the toluene layer was separated and then subjected to reduced pressure (4X 10)²Pa or less), and toluene was distilled at 60 ℃ to obtain a mixture of compounds A-1, A-2, A-3, A-4 and A-5 (sugar ester compound).

After the obtained mixture was analyzed by HPLC and LC-MASS, A-1, A-2, A-3, A-4, and A-5 were 1.3, 13.4, 13.1, 31.7, and 40.5% by MASS, respectively. The average degree of substitution was 5.5.

HPLC-MS measurement conditions

1) LC part

The device comprises the following steps: column type heating furnace (JASCO CO-965) manufactured by Japan Spectroscopy Co., Ltd.), detector (JASCO UV-970-

Column: inertsil ODS-3 particle size 5 μm 4.6X 250mm (GL Sciences corporation)

Column temperature: 40 deg.C

Flow rate: 1ml/min

Mobile phase: THF (1% acetic acid): h₂O(50：50)

Injection amount: 3 μ l

2) MS part

The device comprises the following steps: LCQ DECA (manufactured by Thermo Quest corporation)

An ionization method: electrospray ionization (ESI) method

Spray Voltage：5kV

Capillary temperature: 180 deg.C

Vaporizer temperature: 450 deg.C

Next, the main dope was uniformly cast on a stainless steel belt support using an endless belt casting apparatus. The solvent was evaporated on the stainless steel belt support until the residual solvent amount in the cast (formed) strip film became 75%, and the drying was terminated while conveying the strip film by a plurality of rollers, thereby obtaining a cellulose ester-based resin film having a film thickness of 75 μm and a residual solvent amount of 600ppm as a strip film D.

[ production of obliquely oriented film ]

(production of obliquely oriented film 101)

The roll of the long film a1(PC film, residual solvent amount: 10ppm) obtained as described above was set in the film draw-out section 2 of the obliquely stretched film manufacturing apparatus 1 shown in fig. 1, and the long film a1 was drawn out from the film draw-out section 2 and supplied to the extending section 5, and obliquely stretched in the extending section 5, thereby obtaining the long obliquely stretched film 101 having a film thickness of 45 μm. Then, the obliquely-stretched film 101 is conveyed to the film winding section 9 and wound into a roll shape. The temperature conditions for stretching in the extension part 5 are appropriately selected from the range of (Tg-10) DEG C to (Tg +30) DEG C of the film.

In addition, when forces applied in the transport direction by the respective grippers Co and Ci are equal To Tr (n) at the respective ends in the width direction of the long film before the oblique stretching, and forces applied in the transport direction by the grippers Co on the relatively delayed side and the grippers Ci on the relatively advanced side at the respective ends in the width direction of the long film during the oblique stretching are To (n) and Ti (n), respectively, the long film is stretched in the oblique direction so as To have (Ti-Tr)/Tr of 1.3 and (Tr-To)/Tr of 1.0 in the oblique stretching step by the stretching section 5. As the forces Tr, Ti, To, a driving force of a motor (readable by a motor control device) for rotating the driving rollers when the chain for conveying the grippers Co, Ci is driven by the driving rollers is applied To the extension portion 5.

In addition, the extension angle of the film in the extension portion 5 was set to 45 °. The stretching angle is an angle (alignment angle) formed by the in-plane retardation axis of the film and the film width direction at the time of completion of the oblique stretching step. The extension angle is adjusted by changing the length, the degree of bending, and the like of the guide rail at the bent portion (extension region Z2) of the extension portion 5.

(production of obliquely oriented film 102)

In the extension portion 5, the long film a1 was extended in an oblique direction (45 ° direction with respect To the width direction) so as To be (Ti-Tr)/Tr of 2.0 and (Tr-To)/Tr of 1.5. Otherwise, the obliquely stretched film 102 was produced in the same manner as the obliquely stretched film 101.

(production of obliquely oriented film 103)

In the extension portion 5, the long film a1 was extended in an oblique direction (45 ° direction with respect To the width direction) so as To be (Ti-Tr)/Tr of 3.0 and (Tr-To)/Tr of 2.0. Otherwise, the obliquely stretched film 103 was produced in the same manner as the obliquely stretched film 101.

(production of obliquely oriented film 104)

In the extension portion 5, the long film a1 was extended in an oblique direction (45 ° direction with respect To the width direction) so as To be (Ti-Tr)/Tr of 3.0 and (Tr-To)/Tr of 3.0. At the same time, of the widthwise ends of the long film a1, the end held by the relatively delayed-side holder Co is cooled by blowing of cooling air. At this time, the end portion gripped by the delay-side gripper Co is cooled to be lower by 10 ℃ than the end portion gripped by the advance-side gripper Ci in the width direction of the long film a 1. Otherwise, the obliquely stretched film 104 was produced in the same manner as the obliquely stretched film 101.

(production of obliquely oriented film 105)

In the extension portion 5, the long film a1 was extended in an oblique direction (45 ° direction with respect To the width direction) so as To be (Ti-Tr)/Tr 3.5, (Tr-To)/Tr 3.5. Meanwhile, the long film a1 was obliquely stretched so that the slow axis was aligned at 60 ° which was larger than a desired alignment angle (here, 45 °) with respect to the width direction of the long film a1, and then the long film a1 was obliquely stretched so that the slow axis was aligned at 45 °. Otherwise, the obliquely stretched film 105 was produced in the same manner as the obliquely stretched film 101.

(production of obliquely oriented film 106)

In the extension portion 5, the long film a1 was extended in an oblique direction (45 ° direction with respect To the width direction) so as To be 4.0 (Ti-Tr)/Tr, (Tr-To)/Tr (4.0). At the same time, of the widthwise ends of the long film a1, the end held by the relatively delayed-side holder Co is cooled by blowing of cooling air. At this time, the end portion gripped by the delay-side gripper Co is cooled to be lower by 10 ℃ than the end portion gripped by the advance-side gripper Ci in the width direction of the long film a 1. Further, at the same time, the long film a1 was obliquely stretched such that the slow axis was aligned at 60 ° which was larger than the desired alignment angle (here, 45 °) with respect to the width direction of the long film a1, and then the long film a1 was obliquely stretched such that the slow axis was aligned at 45 °. Otherwise, the obliquely stretched film 106 was produced in the same manner as the obliquely stretched film 101.

(production of obliquely oriented film 107)

A obliquely oriented film 107 was produced in the same manner as the production of the obliquely oriented film 104, except that the obliquely oriented film A2(PC film, residual solvent amount: 110ppm) was used in place of the elongate film A1.

(production of obliquely oriented film 108)

An obliquely-stretched film 108 was produced in the same manner as the obliquely-stretched film 103 except that the guide pattern in the stretching portion 5 was changed and the obliquely-stretched film was stretched at an alignment angle of 75 °.

(production of obliquely oriented film 109)

An obliquely-stretched film 109 was produced in the same manner as the obliquely-stretched film 103 except that the guide pattern in the stretching portion 5 was changed and the obliquely-stretched film was stretched at an alignment angle of 15 °.

(production of obliquely oriented film 110)

An obliquely stretched film 110 was produced in the same manner as in the production of the obliquely stretched film 103, except that the obliquely stretched film D (CE film, residual solvent amount 600ppm) was used in place of the elongated film a 1.

(production of obliquely oriented film 111)

An obliquely-stretched film 111 was produced in the same manner as the obliquely-stretched film 110 except that the guide pattern in the stretching portion 5 was changed and the obliquely-stretched film was stretched at an alignment angle of 75 °.

(production of obliquely oriented film 112)

A obliquely-stretched film 112 was produced in the same manner as in the production of the obliquely-stretched film 103, except that the elongate film B2(COP film, residual solvent amount 110ppm) was used for oblique stretching instead of the elongate film a 1.

(production of obliquely oriented film 113)

A obliquely-stretched film 113 was produced in the same manner as the production of the obliquely-stretched film 103, except that the elongate film B1(COP film, residual solvent amount 10ppm) was used for oblique stretching instead of the elongate film a 1.

(production of obliquely oriented film 114)

A bias stretched film 114 was produced in the same manner as the production of the bias stretched film 103, except that the bias stretch was performed using the long film C (PEN film, residual solvent amount 8ppm) instead of the long film a 1.

(production of obliquely oriented film 115)

The obliquely-stretched film 115 was produced in the same manner as the production of the obliquely-stretched film 101, except that the long film a1 was stretched in an oblique direction (direction at 45 ° To the width direction) so that (Ti-Tr)/Tr became 2.0 and (Tr-To)/Tr became 2.0 in the stretched portion 5.

(production of obliquely oriented film 116)

The obliquely-stretched film 116 was produced in the same manner as the production of the obliquely-stretched film 101, except that the long film a1 was stretched in an oblique direction (direction at 45 ° To the width direction) so that (Ti-Tr)/Tr became 4.0 and (Tr-To)/Tr became 5.0 in the stretched portion 5.

(production of obliquely oriented film 117)

The obliquely-stretched film 117 was produced in the same manner as the production of the obliquely-stretched film 101, except that the long film a1 was stretched in an oblique direction (direction at 45 ° To the width direction) so that (Ti-Tr)/Tr became 1.7 and (Tr-To)/Tr became 1.5 in the stretched portion 5.

[ rate of change in size Δ D_FMeasurement of Δ DL]

In the center C in the width direction of the obliquely extending films 101 to 117 produced as described above, one end E1 (the end gripped by the leading-side gripper) and the other end E2 (the end gripped by the trailing-side gripper) are marked with two points arranged in the advancing axis direction, the distance a1(mm) between the two points is measured with a ruler or the like, the distance b1(mm) between the two points is measured with a ruler or the like. The slow axis direction is an extending direction (orientation angle direction), and the fast axis direction is a direction perpendicular to the slow axis direction within the film surface, so that the slow axis direction and the fast axis direction are easily defined in the obliquely extending films 101 to 117.

Next, after the obliquely-stretched films 101 to 117 were left at 90 ℃ for 120 hours, the distance a2(mm) between two points aligned in the phase advancing axis direction was measured with a ruler or the like at the center C, one end E1, and the other end E2 in the width direction of each film, and the distance b2(mm) between two points aligned in the phase retarding axis direction was measured with a ruler or the like. And, by the followingThe dimensional change rate Δ D in the phase axis direction was calculated for each of the center C, end E1, and E2 of the film_F(%) and the rate of change in dimension Δ D in the slow axis direction_L(％)。

ΔD_F＝{(a2－a1)/a1}×100

ΔD_L＝{(b2－b1)/b1}×100

Table 1 shows the dimensional change rate Δ D_F、ΔD_LAnd various parameters related to the obliquely extending films 101 to 117. In table 1, the dimensional change rate Δ D in the phase advance axis direction of the center C and the end portions E1 and E2 in the width direction of the film was set to_FBy Delta D_F-C、ΔD_F-E1、ΔD_F-E2The dimensional change rate Δ D in the slow axis direction of the center portion C and the end portions E1 and E2 is shown_LBy Delta D_L-C、ΔD_L-E1、ΔD_L-E2To indicate.

[ Table 1]

[ production of polarizing plate ]

(production of polarizing plate 201)

Manufacture of polaroid

After a long polyvinyl alcohol film having a thickness of 60 μm was continuously fed through a guide roll and immersed in a dyeing bath (30 ℃) containing iodine and potassium iodide to carry out dyeing treatment and stretching treatment 2.5 times, the entire was subjected to stretching treatment and bridging treatment 5 times in an acid bath (60 ℃) containing boric acid and potassium iodide, and the obtained iodine-PVA type polarizer having a thickness of 12 μm was dried at 50 ℃ for 30 minutes in a dryer to obtain a polarizer having a moisture content of 4.9%.

Preparation of ultraviolet-curable adhesive

The following components were mixed to prepare a liquid ultraviolet-curable adhesive (UV adhesive).

40 parts by mass of 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexanecarboxylate

Bisphenol A epoxy resin 60 parts by mass

Diphenyl [4- (phenylthio) phenyl ] azulene hexafluoroantimonate (cationic polymerization initiator) 4.0 parts by mass

Lamination

After the application surface of the obliquely extending film 101 was subjected to corona treatment, the prepared ultraviolet-curable adhesive was coated to a thickness of 3 μm by a coating apparatus equipped with a sealing blade. Further, after the adhesive surface of the protective film 1 (Cornick Mendax TAC KC4UY, thickness 40 μm, manufactured by Konikome Co., Ltd.) was subjected to corona treatment, the above ultraviolet-curable adhesive was coated in a thickness of 3 μm in the same manner.

Immediately thereafter, the obliquely extending film 101 was bonded to one surface of the prepared polarizer by a bonding roller via the coated surface of each ultraviolet curable adhesive, and the protective film 1 was bonded to the other surface. At this time, the obliquely-stretched film 101 and the polarizer were laminated so that the width direction thereof and the absorption axis (or transmission axis) of the polarizer were aligned (the angle formed by the slow axis of the obliquely-stretched film 101 and the absorption axis of the polarizer was 45 °). Then, the metal halide lamp is turned on at a line speed of 20m/min, and the cumulative light amount at a wavelength of 280 to 320nm is 320mJ/cm²The polarizing plate 201 is manufactured by irradiating ultraviolet rays from the obliquely extending film 101 side to cure the adhesive on both sides. Since the polarizing plate 201 is manufactured by a roll-to-roll method, the long polarizing plate 201 is cut in the width direction to obtain a sheet-shaped polarizing plate 201.

(production of polarizing plates 202 to 217)

Polarizing plates 202 to 217 were produced in the same manner as the polarizing plate 201 except that the obliquely-stretched film 101 was changed to the obliquely-stretched films 102 to 117.

(production of polarizing plate 218)

The polarizing plate 218 was produced in the same manner as the polarizing plate 203 except that the obliquely extending film 103 and the polarizer, the polarizer and the protective film 1 were bonded to each other with a water-based adhesive (polyvinyl alcohol adhesive). In order to accelerate the curing of the adhesive, the polarizing plate 218 is dried at 80 ℃ for two minutes.

(production of polarizing plate 219)

A polarizing plate 219 was produced in the same manner as the polarizing plate 203 except that the protective film 2 was used instead of the protective film 1. The protective film 2 is a protective film produced as follows.

Production of protective film 2

Preparation of Fine particle Dispersion

Fine particles (AEROSIL R812, manufactured by AEROSIL corporation, japan) in 11.3 parts by mass and ethanol in 84 parts by mass were stirred and mixed for 50 minutes by a vertical disperser, and then dispersed by a homogenizer to prepare a fine particle dispersion liquid.

Then, 5 parts by mass of the fine particle dispersion was gradually added to the well-stirred methylene chloride (100 parts by mass) in the dissolution tank. Further, the dispersion is performed by an attritor so that the particle size of the secondary particles becomes a predetermined size. This was filtered through a nanocrystalline soft magnetic material (FINEMET) NF manufactured by japan kokai corporation to prepare a fine particle-added liquid.

Preparation of concentrated solution

A main dope having the following composition was prepared. First, dichloromethane and ethanol were added to a pressurized dissolution tank. Then, the cycloolefin resin a (to which the antioxidant has been added), the ultraviolet absorber, and the fine particle additive solution are put into the pressurized dissolving tank while stirring. The resulting solution was heated and dissolved completely with stirring, and filtered through an Anji filter paper No.244 manufactured by Anji Filter paper Co.

The cycloolefin resin a has the following structure.

[ solution 2]

Cycloolefin resin A

Next, the main dope was uniformly cast on a stainless steel belt support at a temperature of 31 ℃ and a width of 1800mm using an endless belt casting apparatus. The temperature of the stainless steel belt was controlled to 28 ℃. The conveying speed of the stainless steel belt was set to 20 m/min.

On the stainless steel belt support, the solvent was evaporated until the amount of the residual solvent in the cast (formed) film became 30%. Next, the casting film was peeled from the stainless steel tape support at a peeling tension of 128N/m. The peeled casting film was extended 2.2 times in the width direction under the condition of 160 ℃. The residual solvent at the start of elongation was 5% by mass. Next, the drying was completed while being conveyed in the drying zone by a plurality of rollers, the end portions sandwiched by the tenter fasteners were slit by a laser cutter, and then the film was wound to obtain a protective film 2 having a film thickness of 40 μm.

[ evaluation ]

(curl amount)

The polarizing plates 201 to 219 thus produced were cut out to a size of 30cm × 30cm, and polarizing plate samples were obtained. The obtained polarizing plate sample was arranged such that the convex side of the sample faces the top surface. Then, the heights from the table surface of the four corners a to d of the polarizing plate sample were measured, and the curl amount C was obtained from the following relational expression.

C＝[(Ha+Hb+Hc+Hd)/4]/L

Wherein the content of the first and second substances,

ha: height (mm) of corner a from the table top

Hb: height (mm) of corner b from the table top

Hc: height (mm) of corner c from the table top

Hd: height (mm) of corner d from the table top

L: the length of the polarizing plate sample (300 mm).

Then, the curl amount of the polarizing plate was evaluated based on the following evaluation criteria.

Reference to evaluation

Very good: the curl amount C is more than 0% and less than 3%.

O: the curling amount C is more than 3% and less than 6%.

Δ: the curl amount C is more than 6% and less than 10%.

X: the curl amount C is 10% or more.

(adhesiveness)

A knife edge of a cutter was inserted between the polarizer and the optical film (obliquely extending film) at the end of each of the produced polarizing plates 201 to 219. Then, the polarizer and the optical film were held in the insertion portion and stretched in opposite directions, and the adhesiveness was evaluated based on the following evaluation criteria.

Reference to evaluation

O: the polarizer or the optical film cannot be torn and peeled off, and the adhesiveness is good.

Δ: a part of the peeling between the polarizer and the optical film was observed, but in the range of no problem.

X: the polarizer and the optical film were all peeled off, and the adhesiveness was poor.

(light leakage)

The obtained polarizing plates 201 to 219 were cut into a predetermined size, and bonded to the viewing side of an organic EL panel (product name 15EL9500 by LG display) via an acrylic adhesive to produce organic EL display devices 301 to 319. In this case, the obliquely extending film is disposed on the organic EL panel side with respect to the polarizer in the polarizing plates 201 to 219. The organic EL panel used for the evaluation was used after peeling off the antireflection film attached to the surface in advance.

Then, the organic EL panel was displayed in a black state, and light leakage due to reflection of external light at this time was visually observed, and the light leakage was evaluated based on the following evaluation criteria.

Reference to evaluation

O. light leakage was not observed at all.

Light leakage was slightly observed, but there was no problem in practical use.

Light leakage was observed, which was problematic in practical use.

(visibility)

In a 21.5-inch liquid crystal display device (IPS226V-PN, produced by LG electronic japan), the polarizing plates on the viewer side (visible side, opposite side to the backlight) of two pairs of polarizing plates provided so as to sandwich a liquid crystal layer were peeled off, and the obliquely extending films of the polarizing plates 201 to 219 produced above were brought into the visible side (opposite side to the liquid crystal cell) with respect to the polarizer, and bonded to the glass of the liquid crystal cell with an optical adhesive, thereby producing liquid crystal display devices 401 to 419. In this case, the visible-side polarizing plate is disposed so that the light transmission axis of the visible-side polarizing plate and the light transmission axis of the backlight-side polarizing plate are orthogonal to each other.

The obtained liquid crystal display devices 401 to 419 were observed through polarized sunglasses to display images, and the visibility was evaluated based on the following evaluation criteria.

Reference to evaluation

Very good: there is no distortion in the displayed image and visibility is very good.

O: the display image is substantially free from distortion and has good visibility.

Δ: there is a slight distortion in the displayed image, but there is no problem in practical use.

X: the display image has distortion and poor visibility.

Table 2 shows the results of various evaluations on the polarizing plates 201 to 219.

[ Table 2]

From tables 1 and 2, the dimensional change rate Δ D in the phase advance axis direction at the center C and the end portions E1 and E2 in the film width direction was used_FAnd a dimensional change rate DeltaD in a slow phase axis direction_LSatisfy the requirement of

0％≦ΔD_F<0.5％

ΔD_L<In the polarizing plate of the obliquely-stretched film having 0% and a residual solvent amount of 60ppm or less (an intermediate value between 110ppm and 10ppm), good results were obtained in terms of both curl amount and adhesiveness (see the obliquely-stretched film and the polarizing plate of the example in the table). This is considered to be because the oblique direction is the same as the oblique directionThe stretched film shrinks in the slow axis direction and does not shrink in the fast axis direction in a high temperature environment, so that the shrinkage of the entire film can be suppressed, and the shrinkage of the entire film can be suppressed even when the high temperature adhesion of the obliquely stretched film and the polarizer is required (in the case of using an ultraviolet-curable adhesive, in the case of ultraviolet irradiation, in the case of using a water-based adhesive, in the case of heating for accelerating the curing, the same applies). As a result, in the organic EL display device using the polarizing plate of the example, reflection of external light (light leakage) was within a range that had no problem in practical use, and in the liquid crystal display device using the polarizing plate of the example, which corresponds to the polarized sunglasses, degradation of visibility due to distortion of a display image was within a range that had no problem in practical use.

In the obliquely-stretched films 107, 110 to 112 obtained by stretching a long film formed by a solution casting film-forming method, the dimensional change rate Δ D in the phase-advancing axis direction_FAll negative, which is a property of shrinking in the phase advance axis direction under a high temperature environment. This is considered to be caused by the following reasons. In the solution casting film formation method, since a solvent is used for film formation, the resin density of the film to be formed is low, and the film is easily stretched in both the slow axis direction and the advancing axis direction in which the direction is close to the transport direction when the film is obliquely stretched. Therefore, after the oblique stretching, a tensile stress remains at least in the phase advancing axis direction, and the tensile stress is relaxed in a high-temperature environment, and as a result, the film shrinks in the phase advancing axis direction.

Therefore, it can be said that the dimensional change rate Δ D in the phase advance axis direction is set to be larger_FIt is preferably 0 or more, and the long film is formed by a film-forming method other than the solution casting film-forming method and obliquely stretched, and particularly, as a result of the obliquely stretched film 102 or the like, the long film formed by the melt casting film-forming method is preferably obliquely stretched. In other words, since the amount of the residual solvent of the long film formed by the melt casting film forming method is 60ppm or less (preferably 10ppm or less), it can be said that the oblique stretching of the long film having the residual solvent amount of 60ppm or less (preferably 10ppm or less) is the dimensional change rate Δ in the direction of the production phase axisD_FThe amount of the film is preferably 0 or more.

In the obliquely stretched film 101 stretched under the conditions of (Ti-Tr)/Tr of 1.3 and (Tr-To)/Tr of 1.0, the long film a1 formed by the melt casting film forming method was obliquely stretched, but the dimensional change rate Δ D in the phase axis direction was observed_FNegative, the phase proceeds to shrinkage in the direction of the phase axis under high temperature environment. This is considered to be caused by the following reasons. That is, in the oblique stretching, since the amount of change (increase) in the force in the transport direction of the leading-side end portion of the film and the amount of change (decrease) in the force in the transport direction of the lagging-side end portion are both small, the film is stretched in the oblique stretching direction (the retarded axis direction), and on the other hand, in the transport direction, a state in which the film is shrunk against the stretching during transport or a state in which the film is neither stretched nor shrunk in cooperation with the stretching is not formed, and thus tensile stress remains in the transport direction and the advancing axis direction close to the transport direction. In addition, the tensile stress is relaxed in a high-temperature environment, and the film shrinks in the phase advance axis direction.

Therefore, as a result of the obliquely extending films 102 to 117 and the polarizing plates 202 to 217, it can be said that it is preferable to satisfy the requirement in the obliquely extending step using the extending portion 5

(Ti-Tr)/Tr≧1.7

(Tr-To)/Tr ≧ 1.5, a long film (formed by a melt casting film-forming method) having a residual solvent amount of 60ppm or less is obliquely stretched.

In addition, the polarizing plates 204 to 206 using the obliquely extending films 104 to 106 have higher evaluation values of curl amount and adhesiveness than other polarizing plates (for example, the polarizing plate 203). This is considered to be because, in the production of the obliquely extending films 104 to 106, the widthwise end portions are cooled in the obliquely extending step, and therefore, a larger shrinkage stress can remain in the widthwise end portions in the phase advancing axis direction, and the obliquely extending film expands in the phase advancing axis direction by being relaxed in a high-temperature environment at the time of bonding with the polarizer, whereby dimensional change (shrinkage) of the entire film can be further suppressed even if the film shrinks in the slow axis direction. In particular, in the production of the obliquely-stretched film 106, since stretching is performed in two stages simultaneously in the obliquely stretching step in addition to the end portion cooling, a larger shrinkage stress can be left in the phase advancing axis direction at the widthwise end portion, and dimensional change (shrinkage) of the entire film in a high-temperature environment at the time of bonding with the polarizer can be further suppressed. Therefore, it is considered that the highest evaluation was obtained in the curl amount and the adhesiveness.

In addition, when using the composition satisfying (Δ D)_F-E1+ΔD_F-E2)/2＞ΔD_F-CThe polarizing plate (for example, the polarizing plate 202) using the obliquely-stretched film under the condition(s) above is higher in the evaluation of the curl amount and the adhesiveness by at least one rank than the polarizing plate (for example, the polarizing plates 215 and 217) using the obliquely-stretched film not satisfying the above-mentioned conditions. This is presumably because, in consideration of uneven curing shrinkage of the adhesive at each position in the width direction, a difference is given to the dimensional change rate (expansion amount) in the phase advance axis direction at the center portion and the end portion in the width direction of the obliquely-stretched film, and therefore, at the width center portion, the curl of the polarizing plate due to large curing shrinkage of the adhesive is suppressed by small expansion in the phase advance axis direction of the obliquely-stretched film, and at the width end portion, the curl of the polarizing plate due to large expansion in the phase advance axis direction of the obliquely-stretched film is suppressed by small curing shrinkage of the adhesive, whereby the curl of the entire polarizing plate in the width direction is reliably suppressed.

Industrial applicability of the invention

The optical film of the present invention can be used, for example, in a circular polarizing plate for preventing reflection of external light of an organic EL display device or a polarizing plate of a liquid crystal display device corresponding to a polarizing sunglass.

Claims (13)

1. An optical film having a slow axis inclined by 10 to 80 DEG with respect to one side of the film profile in the film surface,

the dimensional change rates of the optical film in the phase advancing axis direction and the phase retarding axis direction before and after being left at 90 ℃ for 120 hours were respectively represented by Δ D_F(%) and Δ D_L(%) at the edgeThe central part and two end parts in the direction of the one side satisfy

0％≦ΔD_F<0.5％

ΔD_L<0％，

And the amount of the residual solvent is 60ppm or less,

the dimensional change rate of the optical film in the phase advancing axis direction before and after being placed at 90 ℃ for 120 hours in the central part along the one side is defined as Δ D_F-C(％)，

And the dimensional change rate of the optical film in the phase advancing axis direction before and after being placed at 90 ℃ for 120 hours at one end part along the one side is set to be delta D_F-E1(％)，

And the dimensional change rate of the optical film in the phase advancing axis direction before and after being left at 90 ℃ for 120 hours at the other end in the direction along the one side is set to be delta D_F-E2When (%), further satisfies

(ΔD_F-E1+ΔD_F-E2)/2＞ΔD_F-C。

2. The optical film of claim 1,

the residual solvent content is 10ppm or less.

3. The optical film according to claim 1 or 2,

when the distance between two points arranged in the phase advancing axis direction in the optical film and the distance between the two points before and after the optical film is left at 90 ℃ for 120 hours are respectively set as a1(mm) and a2(mm),

and the distances between two points arranged in the slow axis direction in the optical film are b1(mm) and b2(mm) before and after the optical film is left at 90 ℃ for 120 hours,

ΔD_F＝{(a2-a1)/a1}×100

ΔD_L＝{(b2-b1)/b1}×100。

4. the optical film according to claim 1 or 2,

the optical film is in a strip shape,

the direction along the one side is a width direction perpendicular to the longitudinal direction within the film surface of the optical film.

5. A polarizing plate is characterized in that,

comprising the optical film and the polarizer of any one of claims 1 to 4,

the optical film is located on one side with respect to the polarizer in such a manner that a slow phase axis crosses an absorption axis of the polarizer within a film plane.

6. A display device is characterized in that a display panel is provided,

comprising the polarizing plate and the display unit according to claim 5,

the polarizing plate is located on a visible side with respect to the display unit.

7. The display device of claim 6,

the optical film of the polarizing plate is located on the display unit side with respect to the polarizer.

8. The display device of claim 7,

the display unit is an organic electroluminescent element.

9. The display device of claim 6,

the optical film of the polarizing plate is located on a side opposite to the display unit with respect to the polarizer.

10. The display device of claim 9,

the display unit is a liquid crystal unit.

11. A method for manufacturing an optical film according to any one of claims 1 to 4,

comprises an obliquely stretching step of obtaining an obliquely stretched film constituting the optical film by grasping both end portions of a long film in a width direction with a pair of grasping members, and bending and conveying the long film in a film surface by advancing one grasping member relative to the other grasping member, thereby stretching the long film in an oblique direction with respect to the width direction,

when forces applied by the holders in the transport direction to the respective ends of the long film in the width direction before the oblique stretching are set to be the same Tr (N),

and forces applied in the transport direction by the relatively delayed-side gripper and the relatively advanced-side gripper at each end in the width direction of the elongated film during the diagonal stretching are to (N) and Ti (N), respectively,

in the oblique stretching process, the requirement of

(Ti-Tr)/Tr≧1.7

(Tr-To)/Tr≧1.5

In the above aspect, the strip film is extended in the oblique direction.

12. The method of manufacturing an optical film according to claim 11,

in the oblique stretching step, an end portion of each end portion of the long film in the width direction, which is gripped by the gripper on the retardation side, is cooled.

13. The method for manufacturing an optical film according to claim 11 or 12,

in the oblique stretching step, the long film is obliquely stretched so that the slow axis is aligned at an alignment angle larger than a desired alignment angle with respect to the width direction of the long film, and then the long film is obliquely stretched so that the slow axis is aligned at the desired alignment angle.

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