WO2015186379A1 - Method for manufacturing phase difference film and method for manufacturing layered polarizing plate - Google Patents

Abstract

　This method for manufacturing a phase difference film has a step for applying a resin solution on a support body film (1), and a step for heat-drying the resin solution and forming a layered body (2) in which the coating is bonded to and layered on the support body film (1). It is preferable that the method for manufacturing the phase difference film additionally have a step for stretching the layered body (2) in at least one direction and imparting the coating with optical anisotropy, the support body being peeled from the layered body after stretching. The support body film used in this manufacturing method has a tensile modulus of elasticity at 140°C of 200-1200 MPa prior to the application step.

Description

Method for producing retardation film and method for producing laminated polarizing plate

The present invention relates to a method for producing a retardation film. Furthermore, the present invention relates to a method for producing a laminated polarizing plate in which a polarizer and a retardation film are laminated.

For a display such as a liquid crystal display device, a retardation film is used for the purpose of performing optical compensation such as improving contrast and widening the viewing angle (see, for example, Patent Document 1). The retardation film has a positive A plate (nx> ny = nz) and a negative A plate (nz = nx> ny) depending on the magnitude relationship between the refractive index (nx, ny) in the in-plane direction and the refractive index (nz) in the thickness direction. ), Positive C plate (nx = ny <nz), negative C plate (nx = ny> nz), positive B plate (nz> nx> ny), negative B plate (nx> ny> nz) ) And Z plates (nx> nz> ny) and the like.

As the resin material constituting the positive A plate, negative C plate, and negative B plate, a polymer having positive intrinsic birefringence is generally used. On the other hand, a polymer having negative intrinsic birefringence is generally used as the resin material constituting the negative A plate, positive C plate, and positive B plate. Note that “having positive intrinsic birefringence” means that when the polymer is oriented by stretching or the like, the refractive index in the orientation direction becomes relatively large. “Having negative intrinsic birefringence” refers to a polymer having a relatively low refractive index in the orientation direction when the polymer is oriented by stretching or the like.

The retardation film used for optical compensation is required to have a uniform film thickness and optical characteristics. Therefore, the solution casting method is widely used for forming the retardation film. In the solution casting method, a resin solution (dope) in which a polymer is dissolved in a solvent is applied onto a support, and then the solvent is removed by heat drying or the like, and a coating film is adhered and laminated on the support. Is formed.

In film formation by the solution film formation method, stress is generated due to volume shrinkage when the resin solution is dried on the support, and the molecular chains of the polymer tend to be oriented in the in-plane direction. Therefore, when a polymer having a high birefringence property is used as the resin material, the coating film formed on the support may have a large thickness direction birefringence due to a shrinking action during drying. In this case, the coating film can be used as a positive C plate or a negative C plate as it is. For example, Patent Document 2 discloses that polyarylate having a predetermined substituent has high birefringence and that a coating film after applying the polymer on a substrate can be used as a negative C plate. .

Various optical anisotropies can be imparted by stretching or shrinking a coating film (film) formed by the solution casting method in at least one direction. When a retardation film is produced by stretching a coating film formed by a solution casting method, in general, a method of stretching a coating film alone by peeling the support from a laminate of the support and the coating film Is adopted. In particular, when the resin solution is applied onto an endless support such as an endless belt or a film forming drum, it is necessary to perform stretching after peeling the coating film from the support.

On the other hand, in the case where an end support made of a resin film or the like is used as the support for solution casting, the laminated body of the support and the coating film is stretched or contracted to impart optical anisotropy. Has also been done. In particular, when the film thickness of the coating film is small (for example, 30 μm or less), or when a resin material with low spreadability (brittle) is used, the coating film has low self-supportability and is difficult to handle. A method of stretching or shrinking the laminate of the used support and coating film is employed.

When optical anisotropy is imparted by stretching or shrinking a laminate of a support and a coating film used for film formation, as disclosed in Patent Document 3, without peeling the support from the laminate. , A method of using the laminate of the support and the coating film as a laminated phase difference plate as it is, and a method of peeling the support from the stretched laminate and using only the stretched coating film as a retardation film for practical use There is. In Patent Document 4, a coating film is formed by solution casting using a heat-shrinkable film as a support, the laminate is heated and shrunk, and then the support is peeled off, whereby nx> nz> ny optical. A method of forming a retardation film (Z plate) having anisotropy is disclosed.

The support used for solution casting is required to have solvent resistance to solvents and heat resistance during heat drying. Moreover, when using the laminated body after extending | stretching as a retardation film as it is, without peeling a support body and a coating film, it is calculated | required that a support body is optically uniform.

On the other hand, when the support is peeled from the stretched laminate and only the stretched coating film is used as the retardation film, the support is a process member not included in the retardation film as the final product. In this case, the support is not necessarily optically uniform, and is required to be as inexpensive as possible as long as it has solvent resistance and heat resistance that can withstand processing such as film formation and stretching.

Therefore, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene (PP) or the like is generally used as a support for forming a retardation film by solution casting. In particular, PET film is widely used as a support for solution casting because it is highly versatile and has excellent heat resistance and solvent resistance. Patent Document 4 discloses an example in which an amorphous polyester (A-PET) film is used as a support for solution casting.

JP 2009-139747 A JP 2009-80440 A Japanese Patent Laid-Open No. 2004-46068 JP2011-227430A

In recent years, with the progress of high-quality displays, the required performance for retardation films has also increased. At the same time, there is an increasing demand for lighter and thinner displays, and retardation films having a smaller film thickness than conventional ones have been used. However, a film with a small film thickness generally has poor self-supporting properties, and the film tends to be difficult to handle. In addition, a negative A plate, a positive C plate, a positive B plate and the like using a polymer having negative intrinsic birefringence have been put into practical use. However, polymers having negative intrinsic birefringence often have low mechanical strength and poor self-supporting properties due to their molecular structure.

When a film with low self-supporting properties is subjected to stretching, problems relating to handling properties such as wrinkling of the film and breakage during stretching are likely to occur. Therefore, for the production of a film having a small film thickness or a resin material having a low mechanical strength, as disclosed in Patent Document 3, a dope is applied on the resin film support, A method in which a coating film is formed on the substrate, the laminate of the coating film and the support is integrally stretched, and then the support is peeled off is suitable.

Generally, a general-purpose film such as polyethylene terephthalate (PET) is used as the resin film support. However, when a coating film with a small film thickness is formed on a support such as a general-purpose PET film, when the laminate of the coating film and the support is stretched, the stretch processability is poor and stretching cannot be performed. It has been found that there are problems such as the appearance of defects and appearance defects such as waves.

On the other hand, when an amorphous polyester film such as A-PET was used as the support, the birefringence expression of the retardation film formed on the support tended to decrease. For this reason, in order to obtain a retardation film having an intended retardation, it has been found that there is a problem that the film thickness has to be increased, and there is a problem of going against the required characteristics of thinning.

In view of the above problems, an object of the present invention is to provide a manufacturing method for producing a retardation film having a large birefringence and having a high retardation even when it is thinned.

As a result of studies by the present inventors, it has been found that the above-mentioned problems can be solved by using a resin film support having predetermined mechanical characteristics, and the present invention has been achieved. The method for producing a retardation film of the present invention includes a step in which a resin solution is applied on a support film (application step), and a laminate in which the resin solution is dried by heating and a coating film is adhered and laminated on the support film. It has the process (drying process) in which a body is formed in this order. The support film used in the production method of the present invention has a tensile elastic modulus at 140 ° C. of 200 MPa to 1000 MPa before the coating step.

The manufacturing method of the present invention is particularly suitable for manufacturing a retardation film having a small film thickness. In one Embodiment of this invention, the film thickness after the support body peels, ie, the film thickness of retardation film, is 30 micrometers or less.

In one embodiment of the present invention, drying is performed at a temperature of 100 ° C. or higher in the drying step. By drying at a high temperature of 100 ° C. or higher, drying in a short time is possible, and the productivity of the retardation film is increased. Moreover, in this invention, since the support body whose tensile elasticity modulus is in the said range is used, even when it dries at high temperature, the coating film after drying has big thickness direction birefringence. Therefore, a retardation film having a large retardation even with a small film thickness can be obtained.

In one embodiment of the production method of the present invention, after the drying step, the laminate is stretched in at least one direction, and a step (stretching step) in which optical anisotropy is imparted to the coating film is performed. After stretching the laminate of the support film and the coating film, the support is preferably peeled from the laminate.

In one embodiment, free end uniaxial stretching is performed in the stretching step. In one embodiment, the stretched film on the support, that is, the retardation film is stretched so as to have an optical anisotropy of nx> ny> nz or nz> nx> ny. Note that nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the coating film, respectively, and nz is the refractive index in the thickness direction of the coating film.

Furthermore, the present invention relates to a method for producing a laminated polarizing plate in which a polarizer and a retardation film are laminated. In the method for producing a laminated polarizing plate of the present invention, a polarizer is laminated on the retardation film produced by the above method. In addition, as long as it is after the said extending | stretching process, you may laminate | stack a retardation film and a polarizer before and after the said peeling process.

According to the present invention, since a coating film is formed by a solution casting method on a support film having a tensile modulus in a predetermined range under a heating environment, the coating film after film formation has a large thickness direction birefringence. . Therefore, even when the film thickness is small, a retardation film having a large retardation can be produced with a high yield. Moreover, since the elastic modulus of the support in a heating environment is within a predetermined range, a retardation film having excellent workability during stretching, high uniformity, and reduced appearance defects can be obtained.

It is a figure which represents typically one Embodiment of an application | coating process and a drying process. It is a figure which represents typically one Embodiment of an extending process and a peeling process.

In the present invention, as the resin material constituting the retardation film, a polymer having excellent transparency, mechanical strength, and thermal stability is preferably used. Specific examples of such polymers include cellulose resins such as acetyl cellulose, polyester resins, polycarbonate resins, polyamide resins, polyimide resins, maleimide resins, polyolefin resins, (meth) acrylic resins, cyclic Examples thereof include polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, polysulfone resins, and mixtures or copolymers thereof.

The polymer may have a positive intrinsic birefringence or a negative intrinsic birefringence. A retardation film having a refractive index nz smaller in the thickness direction than a refractive index nx in the slow axis direction in the plane of the retardation film, that is, a positive A plate (nx> ny = nz), a negative C plate (nx = ny> nz) and negative B plates (nx> ny> nz) are preferably made of polymers having positive intrinsic birefringence. On the other hand, a retardation film in which the refractive index nz in the thickness direction is larger than the refractive index ny in the fast axis direction in the plane of the retardation film, that is, a negative A plate (nz = nx> ny), a positive C plate ( For the production of nx = ny <nz) and positive B plates (nz> nx> ny), polymers having negative intrinsic birefringence are preferably used.

Here, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the coating film, respectively, and nz is the refractive index in the thickness direction of the coating film. In this specification, the in-plane birefringence Δn _in , the in-plane retardation Re, the thickness direction birefringence Δn _out , the thickness direction retardation Rth, and the Nz coefficient have the following relationships, respectively.

Re = Δn _in × d = (nx−ny) × d
Rth = Δn _out × d = (np−nz) × d
Nz = (nx−nz) / (nx−ny)
However, of nx and ny, the one with the larger difference from nz is defined as np.

In the present specification, the description of “ny = nz” in the positive A plate or the description of “nz = nx” in the negative A plate refers to the in-plane refractive index (nx or ny) and the refractive index in the thickness direction (nz). ) Does not have to match exactly. If the Nz coefficient is in the range of 0.97 to 1.03, it can be regarded as a positive A plate with ny = nz, and if the Nz coefficient is in the range of −0.03 to 0.03, It can be regarded as a negative A plate of nz = nx. Similarly, in the negative C plate and the positive C plate, the description “nx = ny” means that the in-plane slow axis direction refractive index (nx) and fast axis direction refractive index (ny) are not necessarily completely different. It is not necessary to match, and if the Nz coefficient is 20 or more or −20 or less, it can be regarded as a C plate of nx = ny. In the present specification, the refractive index and retardation are values at a wavelength of 590 nm.

In the production method of the present invention, first, a solution (dope) of a resin material constituting a retardation film is applied on a support film (application step). The dope applied on the support is dried by heating to form a laminate in which a coating film of a resin material is closely laminated on the support film (drying step). Since molecular orientation of the polymer in the coating film occurs during drying, the coating film after drying can be used as it is as a retardation film.

Preferably, the laminated body in which the coating film is formed on the support is stretched in at least one direction, whereby optical anisotropy is imparted to the coating film (stretching step). The laminated body after stretching can be used as a retardation film as it is. Moreover, a support body is peeled from the laminated body after extending | stretching (peeling process), and the coating film after peeling can also be used as a phase difference film.

From the viewpoint of increasing the productivity of the retardation film, each of the above steps is preferably performed by roll-to-roll. In roll-to-roll, a long support film is used. The application, drying and stretching are performed while the support is transported along the longitudinal direction. Moreover, it is preferable that peeling of the coating film from a support body is also performed by roll-to-roll. Below, the manufacturing method of this invention is demonstrated along each process centering on embodiment by the roll-to-roll method.

[Support]
In the roll-to-roll method, film formation is performed while the support film is conveyed along the longitudinal direction. Therefore, a wound body (roll) of a long film is used as the support film. Moreover, in the manufacturing method of this invention, after a coating film is formed on a support body by a solution casting method, the laminated body of a support body and a coating film is used for an extending process. Therefore, it is preferable that the support film has flexibility, excellent thermal stability and mechanical strength, and can be stretched. From this viewpoint, a resin film is used as the support film. Hereinafter, the support film may be simply referred to as “support”.

The support used in the present invention preferably has a tensile elastic modulus at 140 ° C. of 100 Mpa to 1000 MPa. The tensile elastic modulus at 140 ° C. of the support is more preferably from 200 MPa to 900 MPa, further preferably from 300 MPa to 800 MPa.

If the elastic modulus at 140 ° C. of the support is 100 MPa or more, the birefringence in the thickness direction of the resin coating film formed thereon tends to increase, especially when drying is performed at a high temperature of 100 ° C. or more. The trend is remarkable. On the other hand, when the elastic modulus at 140 ° C. of the support is 1000 MPa or less, the workability during stretching is excellent, and appearance defects such as the generation of waves in the stretching direction are suppressed.

When the support is a stretched film, the elastic modulus may have anisotropy due to a difference in stretch ratio between the longitudinal direction (MD) and the width direction (TD). When the tensile elastic modulus of MD and TD of the support is different, the tensile elastic modulus of MD may be in the above range, but preferably the elastic modulus of MD and TD at 140 ° C. are both in the above range.

The tensile elastic modulus at 140 ° C. of a general-purpose biaxially stretched PET film is about 1200 MPa. As described above, when a film having a high elastic modulus at a high temperature is used as a support, stretching processability when stretching a laminate of a coating film and a support is poor, and stretching may not be performed. It is easy to cause problems such as poor appearance.

On the other hand, when an amorphous polyester film such as A-PET is heated to 140 ° C., it becomes a rubber state exceeding the glass transition point, and the tensile elastic modulus is reduced to several MPa to several tens of MPa. A coating film obtained by heating a resin solution coated on such a low elastic support to a high temperature and drying tends to reduce birefringence in the thickness direction. Therefore, if the elastic modulus at 140 ° C. of the support is excessively small, it tends to be difficult to obtain a retardation film having a small retardation and a large retardation.

The resin material constituting the support is not particularly limited as long as the tensile elastic modulus at 140 ° C. is in the above range. For example, polyester, polyolefin, polycycloolefin, polyamide, polycarbonate, vinyl chloride, vinylidene chloride, imide-based polymer, Examples include sulfone polymers. Among these, those that do not dissolve in the solvent during solution casting are preferably used.

In particular, a crystalline polyester resin is preferably used as a resin material having the above-described tensile elastic modulus and high solvent resistance. As the crystalline polyester resin, the glycol component of the monomer unit constituting the polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) and / or a part of the dicarboxylic acid is used as another monomer component. A copolyester substituted with is preferably used. For polyesters with substituted glycol components, 1,2-cyclohexanedimethanol or 1,4-cyclohexanedimethanol replaces part of linear glycols such as PET ethylene glycol and PBE 1,4-butanediol. Glycol modified polyester and the like. Examples of the polyester substituted with the dicarboxylic acid component include PET terephthalic acid and PEN 2,6-naphthalenedicarboxylic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, And dicarboxylic acid-modified polyester substituted with 1,5-naphthalenedicarboxylic acid.

Among these, a polyethylene-terephthalate / isophthalate copolymer in which a part of terephthalic acid in PET is substituted with isophthalic acid is preferably used. Polyethylene-terephthalate / isophthalate copolymer can adjust the mechanical and thermal properties such as elastic modulus by changing the ratio of terephthalic acid component to isophthalic acid component, and increase the ratio of isophthalic acid component Thereby, the elasticity modulus in 140 degreeC can be made smaller than PET. In addition, since the polyethylene-terephthalate / isophthalate copolymer can be crystallized by stretching in the same way as PET, it has excellent mechanical strength and high solvent resistance. It is suitable as.

The thickness of the support is not particularly limited, but is preferably 30 μm or more, more preferably 35 μm or more, and even more preferably 40 μm or more from the viewpoint of providing the support with self-supporting properties and suppressing the generation of waves during stretching. . On the other hand, if the thickness of the support is excessively large, the tension during stretching increases, and the optical properties of the retardation film may become nonuniform. Therefore, the thickness of the support is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

The support may be colorless and transparent, and may be colored or opaque. The surface of the support may be subjected to easy adhesion treatment, mold release treatment, antistatic treatment, antiblocking treatment and the like. Moreover, the embossing (knurling) etc. may be given to the edge part of the width direction of a support body for the objectives, such as blocking prevention.

The thickness of the support is not particularly limited as long as it has both self-supporting properties and flexibility. The thickness of the support is generally about 20 μm to 200 μm, preferably 30 μm to 150 μm, and more preferably 35 μm to 100 μm. The width of the support is not particularly limited, but is preferably 300 mm or more, more preferably 500 mm or more, more preferably 700 mm or more, and particularly preferably 1000 mm or more. Increasing the width of the support increases the mass productivity of the retardation film.

The support is preferably a stretched film stretched in at least one direction. In particular, when the material constituting the support is a crystalline polymer, as described above, the crystallinity of the polymer is enhanced by stretching the film, and the heat resistance and solvent resistance can be improved along with the mechanical strength. . In particular, from the viewpoint of improving mechanical strength, heat resistance, solvent resistance, and the like, the support is preferably a biaxially stretched film stretched in both the longitudinal direction (MD) and the width direction (TD). Although a draw ratio is not specifically limited, From the said viewpoint, what was extended | stretched 2 times or more to each of MD and TD is used preferably.

[Film forming process and drying process]
In the film forming step, the resin solution (dope) is applied on the support while the support is transported along the longitudinal direction (MD). Thereafter, the resin solution is dried by heating to form a long laminate in which the coating film is closely laminated on the support. FIG. 1 is a process conceptual diagram schematically showing an embodiment of a film forming process and a drying process by a roll-to-roll method.

First, the wound body 10 of the long support 1 is set on the feeding portion 11 of the film forming apparatus. The support 1 unwound from the winding body 10 is continuously conveyed from the feeding section 11 to the downstream side of the film forming apparatus, and passes through the guide rollers 201 to 205, and is then provided on the downstream side. The film is transported to 110 and film formation is performed. The guide roller may constitute a nip roll pair like the rollers 203 and 204.

In the film forming part 110, the dope 118 is spread on the support 1, and film formation is performed according to a conventional method. In FIG. 1, a knife roll coater is illustrated. In this roll coater, the thickness of the coating film is adjusted by bringing the support 1 into contact with the dope 118 in the liquid dam 117 while bringing the support 1 into contact with the backup roll 112 and draining the dope with the knife roll 111. The film forming method in the film forming unit 110 is not limited to knife roll coating, and various methods such as kiss roll coating, gravure coating, reverse coating, spray coating, Meyer bar coating, air knife coating, curtain coating, lip coating, and die coating. Is used.

The dope 118 is a resin material solution for forming a retardation film, and contains a resin material (polymer) and a solvent. The dope may contain additives such as a leveling agent, a plasticizer, an ultraviolet absorber, and a deterioration inhibitor as necessary. As the resin material for forming the retardation film, either a polymer having positive intrinsic birefringence or a polymer having negative intrinsic birefringence is used depending on the optical anisotropy of the target retardation film. it can. Further, a plurality of resin materials can be mixed and used according to the optical characteristics of the target retardation film. The solid content and viscosity of the dope are appropriately set according to the type and molecular weight of the resin, the thickness of the retardation film, the film forming method, and the like.

The film forming thickness is set so that, for example, the film thickness after drying is about 1 μm to 100 μm according to the optical characteristics (retardation value) required for the retardation film. Since the present invention stretches a laminate of a support and a coating film formed thereon, the coating film alone has a small film thickness, and even if handling is difficult, processing such as stretching is easy It can be done. Therefore, when the film thickness of the coating film is preferably 30 μm or less, more preferably 20 μm or less, further preferably 15 μm or less, particularly preferably 10 μm or less, the film thickness is small when the production method of the present invention is applied, In addition, a retardation film having excellent optical characteristics and appearance characteristics can be easily obtained.

[Drying process]
The dope layer applied on the support 1 is transported into the drying furnace 120 together with the support 1, the solvent is removed, and a laminate 2 in which a coating film is formed on the support 1 is obtained. The laminated body 2 is conveyed downstream from the drying furnace 120, passed through the guide rollers 211 to 215, and taken up by the take-up unit 21 to obtain the wound body 20 of the laminated body 2 of the support and the coating film.

The heating temperature (drying temperature) and drying time in the drying process are not particularly limited. From the viewpoint of shortening the drying time and improving the production process, it is preferable that the drying temperature is as high as possible within a range in which appearance defects such as bubbles do not occur. Specifically, the drying temperature is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, and further preferably 120 ° C. or higher. On the other hand, if the drying temperature is excessively high, bubbles may be generated in the coating film due to bumping of the solvent, or the elastic modulus of the support may be reduced, and the dimensional change of the substrate may occur due to the transport tension. Therefore, the drying temperature is preferably 230 ° C. or lower, more preferably 200 ° C. or lower, and further preferably 180 ° C. or lower.

When the drying temperature is increased, productivity can be improved by shortening the drying time, but the thickness direction retardation of the coating film after drying tends to decrease. On the other hand, in the present invention, by using a support having an elastic modulus at a high temperature (140 ° C.) of a predetermined value or more, a decrease in retardation is suppressed even when drying is performed at 100 ° C. or more. Therefore, according to the production method of the present invention, a retardation film having a large retardation can be obtained while improving productivity by drying at a high temperature.

The heating temperature in the drying process is adjusted by an appropriate heating means such as an air circulating fence oven in which hot or cold air circulates, a heater using microwaves or far infrared rays, a roll heated for temperature adjustment, a heat pipe roll, etc. Can be done. The temperature in the furnace does not need to be constant throughout the furnace, and may have a temperature profile that increases or decreases in steps. For example, the furnace can be divided into a plurality of zones, and the set temperature can be changed for each zone. In addition, from the viewpoint of suppressing poor appearance such as wrinkles due to temperature changes at the entrance and exit of the heating furnace and poor conveyance due to temperature changes at the entrance and exit of the heating furnace, temperatures near the entrance and exit of the heating furnace A preheating zone or a cooling zone can be provided so that the change is moderate.

When the temperature in the entire drying furnace is not constant, the drying temperature refers to the temperature in the furnace at the highest temperature (that is, the atmospheric temperature in the furnace). In the present invention, The maximum temperature is preferably 100 ° C or higher, more preferably 110 ° C or higher, and further preferably 120 ° C or higher. In the drying step, the heating time in the above temperature range is preferably 10 seconds or more, more preferably 20 seconds or more, and further preferably 30 seconds or more. The heating time can be adjusted by the length of the transport path of the support in the heating furnace (furnace length) and the transport speed of the support.

As described above, in the present invention, since a support having predetermined mechanical properties is used, the birefringence in the thickness direction of the coating film after drying can be increased. Therefore, the laminate in which the coating film is closely laminated on the support, or the coating after the support is peeled off from the laminate can be practically used as a retardation film.

[Stretching process]
In the present invention, the laminate 2 having a coating film formed on the support 1 is preferably stretched in at least one direction in the stretching step. FIG. 2 is a diagram schematically illustrating an embodiment of the stretching process and the peeling process. In the form shown in FIG. 2, the wound body 20 of the laminate 2 is set on the feeding portion 22 of the stretching apparatus. The laminated body 2 unwound from the wound body 20 is continuously conveyed from the feeding section 22 to the heating furnace 139 of the downstream stretching section 130 via the guide rollers 221 and 222. 1 and 2, after the laminated body 2 after drying the dope is once wound up by the winding unit 21 of the film forming apparatus, the wound body 20 of the laminated body 2 is transferred to the feeding unit 22 of the stretching apparatus. However, the laminate may be subjected to the stretching step as it is without winding the laminate after the film forming and drying steps.

The laminate 2 is stretched in at least one direction at the stretching portion 130. The term “stretched in at least one direction” means that the distance between two points is increased in at least one direction in the plane. In the form shown in FIG. 2, in the extending | stretching part 130, the example which performs free end uniaxial stretching (longitudinal stretching) in the longitudinal direction (MD) by the float method is illustrated. The stretching unit 130 includes a heating furnace 139, nip rolls 231 and 232 are provided on the upstream side (inlet) of the heating furnace 139, and nip rolls 236 and 237 are provided on the downstream side (outlet).

In free end uniaxial stretching, the film is stretched in the longitudinal direction without gripping the end of the laminate in the width direction. In the form shown in FIG. 2, the laminate 2 is stretched in the longitudinal direction by making the peripheral speed of the nip rolls 236 and 237 on the downstream side of the heating furnace 139 larger than the peripheral speed of the nip rolls 231 and 232 on the upstream side. .

In free end uniaxial stretching, a shrinkage action occurs in the width direction and the thickness direction as the laminate is stretched in the longitudinal direction. Therefore, when the polymer constituting the coating film has positive intrinsic birefringence, the refractive index (nx) in the longitudinal direction is large, the refractive index (ny) in the width direction and the refractive index (nz) in the thickness direction are small. Become. On the other hand, when the polymer constituting the coating film has negative intrinsic birefringence, the refractive index (ny) in the longitudinal direction is small, the refractive index (nx) in the width direction and the refractive index (nz) in the thickness direction are large. Become.

In the form shown in FIG. 2, hot air blowing nozzles (floating nozzles) 131 to 137 are arranged in a staggered manner in the heating furnace 139 above and below the transport path of the laminate, and stretching is performed under heating with hot air. The film transport method in the heating furnace (stretching furnace) 139 is not limited to the float method, and an appropriate transport method such as a roll transport method or a tenter transport method is employed. Stretching in the width direction (TD) can be performed while the film is conveyed in the longitudinal direction (MD) by tenter conveyance. Further, simultaneous biaxial stretching in the conveying direction and width direction or oblique stretching may be performed in the heating furnace 139. Furthermore, after stretching in the longitudinal direction in the heating furnace 139, sequential biaxial stretching may be performed by stretching in the width direction in another heating furnace (not shown).

The heating temperature (stretching temperature) in the stretching step is not particularly limited, but is preferably a temperature at which both the support and the coating film formed thereon can be stretched. Specifically, when the glass transition temperature of the coating film formed on the support is Tg, the stretching temperature is preferably (Tg-50) ° C. or higher, more preferably (Tg-40) ° C. or higher, ( Tg-30) ° C. or higher is more preferable. If the stretching temperature is too low, peeling of the coating film from the support may occur, retardation may be non-uniform, and appearance defects such as haze increase may occur. On the other hand, if the stretching temperature is too high, the orientation of the polymer constituting the coating film is lowered, and the desired retardation may not be obtained.

The stretching temperature is set according to the type of polymer constituting the coating film (retardation film), the thermal characteristics of the support, and the like. The stretching temperature is generally about 100 ° C. to 220 ° C., preferably about 120 ° C. to 200 ° C. The temperature in the heating furnace 139 does not need to be constant throughout the furnace, and may have a temperature profile that increases or decreases in steps. For example, the furnace can be divided into a plurality of zones, and the set temperature can be changed for each zone. In addition, from the viewpoint of suppressing problems such as a rapid change in dimensions of the laminate 2 due to temperature changes at the entrance and exit of the heating furnace 139, causing wrinkles and poor conveyance, the vicinity of the entrance and exit of the heating furnace A preheating zone and a cooling zone, or a heating roll and a cooling roll can also be provided so that the temperature change at 1 is moderate.

The draw ratio in the drawing step is preferably 1.01 or more, and more preferably 1.03 or more. In free end uniaxial stretching, in-plane birefringence (Δn _in ) tends to increase as the draw ratio increases. When the draw ratio is excessively large, the coating film may be broken or the optical characteristics may be non-uniform. Therefore, the draw ratio is preferably 3 times or less, more preferably 2.5 times or less, and further preferably 2 times or less.

Optical properties such as in-plane retardation Re, thickness direction retardation Rth, and Nz coefficient of the retardation film are appropriately selected according to the use of the retardation film, and the stretching method and stretching ratio in the stretching process are It can be adjusted according to the optical characteristics.

As described above, in free-end uniaxial stretching (longitudinal stretching), the refractive index in the stretching direction increases (or decreases), whereas the refractive index in the direction orthogonal to the stretching direction, that is, the width direction and the thickness direction decreases. (Or increase). In general, in the free end uniaxial stretching, the shrinkage rate in the width direction and the shrinkage rate in the thickness direction are the same, and the decrease rate (or increase rate) in the width direction and the refractive index in the thickness direction are the same. Therefore, when a polymer having positive intrinsic birefringence is used as the material for the retardation film, the retardation film obtained by free-end uniaxial stretching is generally a positive having a refractive index anisotropy of nx> ny = nz. A plate.

In addition, when the molecular chain of the polymer is oriented in the in-plane direction at the time of solution casting, when the birefringence in the thickness direction of the coating film is large, that is, the coating film has a negative refractive index anisotropy of nx = ny> nz. In the case of a C plate, when the coating film is peeled off from the support, if the coating film after peeling is subjected to free end uniaxial stretching alone, the shrinkage rate in the width direction tends to be larger than the shrinkage rate in the thickness direction. . Therefore, the reduction rate of the refractive index ny in the width direction during stretching is larger than the reduction rate of the refractive index nz in the thickness direction, and the refractive index anisotropy of ny> nz is eliminated. The film becomes a positive A plate having a refractive index anisotropy of nx> ny = nz.

On the other hand, when a laminate having a coating film closely laminated on a support is subjected to free-end uniaxial stretching, the shrinkage in the width direction of the laminate is greatly influenced by the mechanical properties and thermal characteristics of the support, The effect of refractive index anisotropy is small. Therefore, when a coating film made of a polymer having positive intrinsic birefringence formed on a support has a refractive index anisotropy of nx = ny> nz, a refractive index anisotropy of ny> nz is A negative B plate that is held before and after stretching and has a refractive index anisotropy of nx> ny> nz is obtained. According to the same principle, when a polymer having negative intrinsic birefringence is used as the material of the retardation film, a positive B plate having a refractive index anisotropy of nz> nx> ny is obtained by free end uniaxial stretching.

As described above, in the present invention, since a support having predetermined mechanical properties is used, the birefringence in the thickness direction of the coating film after drying can be increased. Therefore, a negative B plate and a positive B plate can be obtained by subjecting the laminate in which the coating film is closely laminated on the support to free end uniaxial stretching. Moreover, since it is suppressed that the tension | tensile_strength at the time of extending | stretching becomes too large, external appearance defects, such as a wave, do not produce easily, and the phase difference film excellent in the uniformity of an external appearance and an optical characteristic is obtained.

When a negative B plate having a refractive index anisotropy of nx> ny> nz is produced by the method of the present invention, the Nz coefficient of the retardation film is preferably larger than 1.03, 1.05 or more Is more preferable, and 1.10 or more is more preferable. When a positive B plate having a refractive index anisotropy of nz> nx> ny is produced by the production method of the present invention, the Nz coefficient of the retardation film is preferably smaller than −0.03, −0 .05 or less is more preferable, and -0.10 or less is more preferable. The stretching method for obtaining the negative B plate and the positive B plate is not limited to free end uniaxial stretching, and may be fixed end uniaxial stretching (lateral stretching) or sequential or simultaneous biaxial stretching.

The draw ratio in the drawing step is preferably 1.01 or more, and more preferably 1.03 or more. In free end uniaxial stretching, in-plane birefringence (Δn _in ) tends to increase as the draw ratio increases. When the draw ratio is excessively large, the coating film may be broken or the optical characteristics may be non-uniform. Therefore, the draw ratio is preferably 3 times or less, more preferably 2.5 times or less, and further preferably 2 times or less.

[Peeling process]
The laminated body 3 after stretching can be used as a retardation film as it is. Preferably, the support 6 after stretching is peeled from the laminated body 3 after stretching, and the coating film 4 after peeling the support is used as a retardation film. In this case, the support is a process member that is not included in the retardation film that is the final product. Therefore, the support need not be optically uniform, and an inexpensive support can be used.

The laminated body 3 after stretching may be wound up into a roll once, and can be subjected to a peeling process continuously from the stretching process. In FIG. 2, the form by which the peeling process is performed in the peeling part 160 continuously after an extending process is illustrated. The peeling method of the support 6 after stretching and the coating film (retardation film 4) is not particularly limited, but from the viewpoint of performing uniform peeling, the laminate 3 is sandwiched between nip rolls 261 and 262, and on the downstream side thereof. The support 6 and the retardation film 4 are preferably transported along the upper roll 261 and the lower roll 262 and then peeled off. The support 6 after peeling is wound up by the winding unit 61 by an appropriate method.

[Other processes]
The retardation film can be further subjected to another process after the stretching process or the peeling process. For example, in the form shown in FIG. 2, the retardation film 4 after peeling off the support 6 is inspected by the inspection unit 170 and then bonded to another film 9 by the bonding unit 190, and then the retardation film. 4 and the laminated body 5 of the film 9 are wound up by the winding part 51, and the wound body 50 is formed.

<Inspection process>
The inspection unit includes an inspection device for inspecting the retardation film. In the form shown in FIG. 2, the inspection unit 170 includes a phase difference meter 171 and a defect detection unit 172. The retardation meter 171 detects the retardation of the retardation film 4 and the orientation angle of the slow axis. The retardation can be kept constant by feeding back the measured retardation value to the roll peripheral speed or the like in the stretching section 130. From the viewpoint of accurately measuring the retardation of the retardation film 4, it is preferable that the retardation measurement is performed after the support 6 is peeled off.

The defect detection unit is configured to detect defects such as foreign matter existing in or on the surface of the retardation film, uneven defects such as dents, and scratches. By detecting the defect after the support 6 is peeled off, the defect of the retardation film 4 can be selectively detected without detecting the defect included only in the support 6, so that the defect detection accuracy is improved.

<Bonding process>
In the bonding part 190, the phase difference film 4 is bonded with the other film 9, and the laminated body 5 is formed. Examples of the film 9 include a protective film (separator) temporarily attached to the retardation film 4 and other optical films (retardation film, polarizer, etc.). It is preferable that lamination | stacking with retardation film and another film is performed through a suitable adhesive agent.

A laminated polarizing plate including a retardation film can be formed by laminating a polarizer on the retardation film. In addition, a polarizer may be laminated | stacked by itself on a retardation film, and what laminated | stacked the transparent protective film and the other retardation film on the polarizer may be laminated | stacked.

The thickness of the polarizer laminated on the retardation film is not particularly limited, but is generally about 1 μm to 50 μm. In particular, from the viewpoint of obtaining a thin laminated polarizing plate, the thickness of the polarizer is preferably 15 μm or less, more preferably 10 μm or less, and preferably 8 μm or less. By reducing the thickness of the polarizer, it is possible to reduce the influence of the stress caused by the dimensional change of the polarizer accompanying changes in the surrounding environment such as heat and humidity on the adjacent retardation film or the like. Therefore, by reducing the thickness of the polarizer laminated on the retardation film, a laminated polarizing plate in which changes in optical characteristics due to changes in the surrounding environment are small even when the thickness of the retardation film is small.

The pressure-sensitive adhesive layer for bonding with another optical film, a liquid crystal cell, or the like may be laminated on the surface of the retardation film 4. For example, an adhesive layer can be laminated | stacked on a phase difference film, for example by bonding together the surface by the side of an adhesive layer of an adhesive sheet with which the adhesive layer was attached on the appropriate separator, and retardation film.

When the thickness of the retardation film 4 after peeling the support 6 from the laminate 3 is 30 μm or less, the retardation film 4 itself has a small self-supporting property and an insufficient handling property. By adhering, handling property can be improved. In FIG. 2, a form in which the film 9 is bonded only to one side of the retardation film 4 is illustrated, but a film, an adhesive layer, or the like may be bonded to both sides of the retardation film 4.

Further, before the support 6 is peeled from the laminate 3 at the peeling portion 160, another film or an adhesive layer may be bonded to the surface of the laminate 3 on the phase difference film 4 side. Before the support 6 is peeled off, another film, a pressure-sensitive adhesive layer, or the like is bonded onto the retardation film 4, so that it is not necessary to transport the retardation film alone. Therefore, even when the thickness of the retardation film is small, handling properties are improved. After laminating another film or pressure-sensitive adhesive layer on the surface of the laminate 3 on the phase difference film 4 side, the support 6 is peeled off, and another film or An adhesive layer may be laminated.

<Winding process>
The retardation film 4 after peeling off the support 6 is subjected to an inspection process or a bonding process as necessary, and then wound up by the winding unit 51 to form a wound body of the retardation film. As shown in FIG. 2, the retardation film 4 may be wound up by a winding unit 51 as a laminated body 5 (for example, a laminated polarizing plate) laminated with another film 9. Moreover, the phase difference film 4 after peeling the support body 6 may be cut into a sheet body as it is, without providing for a winding process. FIG. 2 illustrates a mode in which the support 6 is peeled off by the peeling portion 160 without being wound on the wound body after the laminate 3 having the coating film adhered and laminated on the support is stretched. The laminate 3 can be once wound on a wound body, and then the peeling step can be performed by an apparatus different from the stretching step.

[Application and optical properties of retardation film]
Although the use of the retardation film obtained by the above production method is not particularly limited, it is suitably used for optical compensation of a liquid crystal display device. When the retardation film is used for optical compensation of a liquid crystal display device, the retardation film is disposed between the liquid crystal cell and the polarizer.

Optical characteristics such as in-plane retardation Re and thickness direction retardation Rth of the retardation film are appropriately selected according to the driving method of the liquid crystal cell, the retardation value of the cell, and the like. For example, in an in-plane switching (IPS) type liquid crystal display device, the black luminance increases when the screen is viewed from an oblique direction with an azimuth angle of 45 ° with respect to the absorption axis direction of the polarizing plate. By disposing the retardation film between the cell and the polarizer, the black luminance in the oblique direction can be reduced and the contrast can be improved. In the optical compensation of the IPS liquid crystal display device, two or more retardation films can be used in combination as disclosed in, for example, the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 2009-139747).

When two or more retardation films are used for optical compensation of a liquid crystal display device, the retardation film according to the production method of the present invention is used for at least one retardation film. For example, as disclosed in Japanese Patent Application Laid-Open No. 2009-139747, when a positive B plate and a negative B plate are used, the manufacturing method of the present invention is applied to one or both B plates. Can do. As described above, according to the manufacturing method of the present invention, a positive B plate and a negative B plate can be manufactured by free end uniaxial stretching.

The liquid crystal display device can be manufactured, for example, by appropriately assembling the retardation film of the present invention, another optical film such as a polarizer, a liquid crystal cell, and an optical member such as a backlight and incorporating a drive circuit. When laminating the retardation film and the liquid crystal cell, from the viewpoint of improving the uniformity in the alignment axis direction and simplifying the production process, as described above, the laminated polarizing plate obtained by laminating the retardation film and the polarizer, etc. The liquid crystal cell is preferably bonded through an appropriate adhesive layer such as an adhesive.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

[Measuring method]
The thickness of the film was calculated from the interference pattern of the reflectance using a film thickness measurement system (MCPD manufactured by Otsuka Electronics). Using a polarization / phase difference measurement system (Axometrics product name “AxoScan”), in a 23 ° C. environment, the front wavelength is measured at a measurement wavelength of 590 nm, and the film is tilted by 40 ° with the slow axis direction as the center of rotation. The retardation in the obtained state was measured, and the birefringence and thickness direction retardation of the film were calculated from these measured values.
The elastic modulus of the base film was measured according to JIS K7127 under the conditions of a temperature of 140 ° C. and a tensile speed of 10 mm / min using an autograph with a thermostatic bath (manufactured by Shimadzu Corporation).

[Synthesis Example A] Synthesis of Fumarate Ester Resin (Polymer Having Negative Birefringence) and Dope Preparation Into an autoclave equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe and a thermometer, 48 g of trade name Metrose 60SH-50), 15601 g of distilled water, 8161 g of diisopropyl fumarate, 240 g of 3-ethyl-3-oxetanylmethyl acrylate and 45 g of t-butyl peroxypivalate as a polymerization initiator, and 1 bubbling of nitrogen. After carrying out the time, radical suspension polymerization was carried out by maintaining at 49 ° C. for 24 hours while stirring at 200 rpm. Subsequently, it cooled to room temperature and centrifuged the produced | generated suspension containing the polymer particle. The polymer particles obtained were washed twice with distilled water and twice with methanol, and then dried under reduced pressure at 80 ° C. (yield 80%).

The obtained fumaric acid ester resin was dissolved in a toluene / methyl ethyl ketone mixed solution (toluene / methyl ethyl ketone 50 wt% / 50 wt%) to obtain a 20% solution. Furthermore, 5 parts by weight of tributyl trimellitate as a plasticizer was added to 100 parts by weight of the fumaric acid ester resin to prepare a dope.

[Reference Example A] Application on glass plate The dope was applied on a glass plate having a thickness of 1 mm with an applicator, and the whole glass plate was dried in a hot air oven at 140 ° C for 5 minutes. The dried film was peeled from the glass plate, and the film thickness and retardation were measured.

[Comparative Example A1]
A biaxially stretched PET film having a thickness of 50 μm was cut into an A4 size having MD as a long side, and the short side was bonded onto a glass plate using a heat-resistant tape. The above-mentioned dope is applied onto a PET film bonded to a glass plate using an applicator, and the whole glass plate is dried in a hot air oven at 140 ° C. for 5 minutes to form a laminate in which a coating film is formed on the PET film. Was made. This laminate was cut into a strip shape having a length of 20 cm and a width of 10 cm. Although the short side of the strip-shaped sample was fixed between the chucks and an attempt was made to stretch in the length direction in a hot air oven at 165 ° C., the sample was detached from the chuck and could not be stretched.

[Examples A1 to A3 and Comparative Example A2]
Instead of the biaxially stretched PET film, a biaxially stretched film of polyethylene-terephthalate / isophthalate copolymer was used. The elastic modulus of the biaxially stretched film used in each example and comparative example was as shown in Table 1. On this film, the dope was applied and dried in the same manner as in Comparative Example A1.

<Stretching and peeling>
The above laminate is cut into a strip shape having a length of 20 cm and a width of 10 cm, the short side of the strip sample is fixed between chucks, and is 1.05 times in the length direction in a hot air oven at 165 ° C. When free end uniaxial stretching was performed, all of them could be stretched without problems.

[Synthesis Example B] Synthesis of polyarylate resin (polymer having positive birefringence) In a reaction vessel equipped with a stirrer, 54.0 g of 2,2-bis (4-hydroxyphenyl) -4-methylpentane, benzyl 1.2 g of triethylammonium chloride was dissolved in 500 ml of 1M sodium hydroxide solution. A solution prepared by dissolving 30.4 g of terephthalic acid chloride and 10.2 g of isophthalic acid chloride in 600 ml of chloroform was added to this solution all at once with stirring, and the mixture was stirred at room temperature for 90 minutes. Thereafter, the polymerization solution was allowed to stand to separate the chloroform solution containing the polymer, then washed with acetic acid water, washed with ion-exchanged water, and then poured into methanol to precipitate the polymer. The precipitated polymer was washed with pure water and methanol and then dried under reduced pressure to obtain 68.2 g (yield 92%) of a white polymer.

The obtained polyarylate resin was dissolved in cyclopentanone to prepare a dope having a solid concentration of 20%.

[Reference Example B] Application on a glass plate The above dope is applied on a glass plate with an applicator, dried with a hot air oven at 140 ° C for 5 minutes together with the glass plate, and the dried film is peeled off from the glass plate. The film thickness and retardation were measured.

[Examples B1 to B3 and Comparative Examples B1 and B2]
Except for using the dope obtained in Synthesis Example B above, the dope was applied and dried in the same manner as in Examples A1 to A3 and Comparative Examples B1 and B2, and the stretchability of the obtained laminate was It was confirmed.

[Evaluation results]
Table 1 shows the mechanical properties of the support used in each of the above Examples, the optical properties of the coating film after drying at 140 ° C. for 5 minutes, and the stretchability of the laminate. In Table 1, Δn is the absolute value of the thickness direction birefringence Δn _out . In Reference Example A, Examples A1 to A3, and Comparative Examples A1 and A2 using a fumarate ester resin (polymer having negative birefringence), Δn _out is negative, and polyarylate resin (positive birefringence) In Reference Example B, Examples B1 to B3, and Comparative Examples B1 and B2 using a polymer having refraction, Δn _out was positive.

[Delta] n / [Delta] n ₀ in Table 1, and [Delta] n of the coating film in each Example and Comparative Example, the ratio of [Delta] n ₀ of the coating film of Reference Example was performed coated on a glass plate. Table 1 also shows the absolute value Δn of the birefringence in the thickness direction of the coating film when the drying condition in each reference example and example is changed to 50 ° C. for 30 minutes.

The stretch workability in Table 1 was determined to be good when stretched and poor when stretched.

In Reference Example A, Examples A1 to A3, and Comparative Examples A1 and A2 in which a polymer having negative birefringence was used, there was no significant difference in Δn when drying was performed at 50 ° C. . On the other hand, when drying on the support is performed at a high temperature (140 ° C.), Δn tends to decrease as the elastic modulus of the support at 140 ° C. decreases. In Comparative Example A2, Δn is a reference. It was reduced to about half of Example A. From this result, it can be seen that in order to obtain a retardation film having a small film thickness and a large birefringence, it is necessary to use a support having a high elastic modulus near the drying temperature.

On the other hand, in Comparative Example A1 having an elastic modulus at 140 ° C. exceeding 1000 MPa, it was difficult to stretch the support and the coating film integrally. The same was true for Comparative Example B1.

In Examples B1 to B3 and Comparative Example B2 in which a polymer having positive birefringence was used, as the elastic modulus of the support at 140 ° C. decreased, as in Examples A1 to A3 and Comparative Example A2 above. In addition, a decrease in Δn of the coating film after drying at 140 ° C. was observed. From these results, regardless of the type of polymer, by using a support having a predetermined elastic modulus, the retardation film has high birefringence and stretching when the support and the coating film are stretched integrally. It can be seen that the processability is excellent.

DESCRIPTION OF SYMBOLS 1,6 Support body 2,3 Lamination body 4 Phase difference film 9 Film 5 Lamination body 10 Support body winding body 20 Lamination body winding body 50 Retardation film lamination body winding body 11,22 Feeding part 21,51 Winding up Part 110 Film-forming part 120 Drying furnace 130 Stretching part 139 Heating furnace 160 Peeling part 170 Inspection part 171 Phase difference meter 172 Defect detection part 190 Bonding part

Claims (8)

1. A coating step in which a resin solution is applied onto a support film; and a drying step in which the resin solution is dried by heating to form a laminate in which a coating film is closely laminated on the support film. Have
   The support film is a method for producing a retardation film, wherein a tensile elastic modulus at 140 ° C. is 200 Mpa to 1000 MPa before the coating step.
2. The method for producing a retardation film according to claim 1, further comprising a stretching step in which the laminated body is stretched in at least one direction after the drying step and optical anisotropy is imparted to the coating film.
3. The method for producing a retardation film according to claim 2, further comprising a peeling step in which the support is peeled from the laminate.
4. The method for producing a retardation film according to claim 2, wherein free end uniaxial stretching is performed in the stretching step.
5. The rank according to any one of claims 2 to 4, wherein in the stretching step, the coating is stretched so as to have an optical anisotropy of nx> ny> nz or nz> nx> ny. A method for producing a retardation film (where nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the coating film, respectively, and nz is the refractive index in the thickness direction of the coating film).
6. The method for producing a retardation film according to any one of claims 1 to 5, wherein a film thickness of the coating film after drying is 30 μm or less in the drying step.
7. The method for producing a retardation film according to any one of claims 1 to 6, wherein the drying is performed at a temperature of 100 ° C or higher in the drying step.
8. A method for producing a laminated polarizing plate in which a polarizer and a retardation film are laminated,
   A retardation film is produced by the method according to any one of claims 1 to 7,
   An optical film containing a polarizer is laminated on the retardation film. A method for producing a laminated polarizing plate.

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