KR102516908B1 - Method for producing phase-difference film and method for producing laminated polarizing plate - Google Patents

Abstract

In the manufacturing method of the retardation film of the present invention, while a support film made of a long biaxially oriented film is conveyed in the longitudinal direction, a resin solution is applied on the support film, the resin solution on the support is dried by heating, and the support film A layered body in which a coating film is adhered to and laminated thereon is formed. After drying, the laminate is stretched in at least one direction, and optical anisotropy is imparted to the coating film. Prior to application of the resin solution, heat treatment of the support film is performed. The heat treatment is performed in a state in which tension is applied to the support film in the longitudinal direction. INDUSTRIAL APPLICABILITY According to the present invention, a retardation film having a small variation in orientation angles of optical axes in the width direction can be obtained.

Description

Manufacturing method of retardation film and manufacturing method of laminated polarizing plate {METHOD FOR PRODUCING PHASE-DIFFERENCE FILM AND METHOD FOR PRODUCING LAMINATED POLARIZING PLATE}

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

BACKGROUND ART Retardation films are used in displays such as liquid crystal display devices for the purpose of performing optical compensation such as contrast enhancement and viewing angle expansion (see Patent Document 1, for example). Retardation films used for optical compensation require uniformity in film thickness and optical properties. Therefore, the solution film forming method is widely used for film formation of the retardation film. In the solution film forming 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 heating and drying or the like to form a layered product in which a coating film is tightly laminated on the support.

As described in Patent Literature 2, the coating film (film) formed by the solution film forming method can be used as a retardation film as it is. In addition, various optical anisotropies can be imparted by stretching the coating film formed by the solution film forming method in at least one direction. When a retardation film is produced by stretching a coating film formed by a solution film forming method, a method in which the support is separated from the laminate of the support and the coating film and the coating film is stretched as a single unit is generally employed.

On the other hand, when a support made of a resin film or the like is used as a support for solution film formation, it is also practiced to impart optical anisotropy by stretching a laminate of the support and the coating film. In particular, when the film thickness of the coating film is small (for example, 30 μm or less) or when a resin material having low malleability (soft) is used, since the self-supporting property of the coating film is low and handling is difficult, the support used for film formation is difficult. A method of stretching a laminate of a coating film and a coating film is employed. In this case, as disclosed in Patent Document 3, a method of using a laminate of a support and a coating film as it is for practical use as a laminated retardation plate without peeling the support from the laminate, and peeling the support from the stretched laminate , There is a method of using only the coated film after stretching as a retardation film for practical use. Further, in Patent Literature 4, a coating film is formed by solution film formation using a heat-shrinkable film as a support, and after heat-shrinking the laminate, the support is peeled off to form a retardation film having an optical anisotropy of nx > nz > ny A method of doing so is disclosed.

Solvent resistance with respect to a solvent and heat resistance at the time of heat drying are calculated|required of the support body used for solution film formation. In addition, when using the laminated body after extending|stretching as it is as a retardation film, without peeling a support body and a coating film, it is required that a support body be optically uniform. On the other hand, in the case where the support is separated from the stretched laminate and only the stretched coating film is used as the retardation film, the support is a process member that is not included in the retardation film as the final product. In this case, the support does not necessarily have to be optically uniform, and is preferably as inexpensive as possible within the range of having solvent resistance and heat resistance that can withstand processing such as film formation and stretching.

Japanese Unexamined Patent Publication No. 2009-139747 Japanese Unexamined Patent Publication No. 2009-80440 Japanese Unexamined Patent Publication No. 2004-46068 Japanese Unexamined Patent Publication No. 2011-227430

In recent years, along with the progress of high-definition display, the required performance of the retardation film is also increasing. At the same time, the demand for weight reduction and thinning of displays has also increased, and retardation films having a smaller film thickness than before have been used. As described above, in the production of a film with a small film thickness or a film made of a resin material with a low mechanical strength, dope is applied on a resin film support, a coating is formed on the support, and then the support and the coating are laminated. A method in which the sieve is integrally stretched and the support is peeled off is suitable.

The support is preferably inexpensive and has high mechanical strength. Generally, a biaxially oriented stretched film made of a general-purpose resin such as polyethylene terephthalate (PET) or polypropylene (PP) is used. However, according to the study of the present inventors, when a laminate of a support made of a biaxially oriented film and a coating film formed thereon is integrally stretched, the deviation in the width direction of the orientation angle of the optical axis of the coated film after stretching, that is, the retardation film, is It has been found that there may be cases of enlargement.

In addition, as another problem in the case of using a general-purpose biaxially oriented PET film or the like as a support, stretching may not be possible due to insufficient stretching processability when a laminate of a coating film and a support is stretched, or a web or the like may cause appearance defects. The inventors of the present invention found that the above problems in stretching workability can be solved by using a support having high processability at a heating temperature (for example, around 140° C.) when a laminate of a support and a coating film is stretched. paid However, when a support having high processability was used, a tendency for the deviation of the orientation angle of the optical axis of the retardation film to become larger was found.

In view of these, the present invention is to improve the accuracy of the orientation angle of the optical axis of the retardation film after stretching in a method for manufacturing a retardation film in which a biaxially oriented support film and a laminate of a coating film formed thereon are integrally stretched. The purpose.

In the manufacturing method of the retardation film of the present invention, while the support film is conveyed in the longitudinal direction, a resin solution is applied on the support film (application step), and the resin solution applied on the support film is dried by heating (drying step). ). Through these steps, a layered product in which a coating film is adhered and laminated on a support film is formed. The film thickness of the coating film after drying is preferably 30 μm or less.

In the production method of the present invention, heat treatment of the support film is performed prior to application of the resin solution onto the support. According to the inventors' examination, it was found that the orientation angle of the optical axis of the retardation film after stretching became uniform by heat-processing the support before coating film formation. The heat treatment is performed in a state in which tension is applied to the support film in the longitudinal direction.

Optical anisotropy is given to the coating film by extending|stretching in at least one direction the laminated body in which the coating film was laminated closely on the support film (stretching process), and a phase difference film is obtained. In one embodiment, in the stretching step, the laminate is stretched in either the longitudinal direction or the width direction, and contracted in a direction orthogonal to the stretching direction. For example, by performing free end uniaxial stretching (longitudinal stretching) in the longitudinal direction in a state where both ends in the width direction of the laminate are not gripped, the laminate can be contracted in a direction orthogonal to the stretching direction. Further, the laminate can be contracted in a direction orthogonal to the stretching direction by stretching the laminate in the width direction and shrinking the laminate in the longitudinal direction in a state where both ends in the width direction of the laminate are held.

As the support film, a biaxially oriented film is used. The support film is preferably a biaxially stretched film. When a polyester film is used as the support film, it is preferable that the glass transition temperature Tg of the support film is 110°C or less from the viewpoint of improving workability during stretching. Moreover, it is preferable that the tensile elasticity modulus in 140 degreeC of a support body film is 1000 Mpa or less. The support film may be a heat-shrinkable film.

The heating temperature _TH in the heat treatment is preferably 80°C or higher, and the heating time t _H is preferably 8 seconds or higher. In addition, even when the heating temperature is less than 80°C, the same effect as in the case of heat treatment at 80°C or higher may be obtained by lengthening the heating time. The heat treatment temperature may be set based on the glass transition temperature of the support film.

Further, the present invention relates to a method for manufacturing a laminated polarizing plate. A laminated polarizing plate is obtained by laminating an optical film containing a polarizer on the retardation film obtained by the above manufacturing method.

According to the present invention, the alignment angle deviation of the optical axis of the retardation film obtained by stretching the laminate of the support and the coating film can be reduced by performing heat treatment on the support film before film formation. In particular, when a support film having a low tensile modulus excellent in processability during stretching is used, the effect of reducing the deviation of the orientation angle is great. Therefore, a retardation film having a small film thickness and excellent uniformity in optical properties can be produced with a high yield.

1 is a diagram schematically showing an embodiment in which an application step and a drying step are continuously performed after heat treatment.
Fig. 2 is a diagram schematically showing an embodiment in which a stretching step, a peeling step, and a bonding step are continuously performed.
3 is a diagram schematically showing one embodiment in which a bonding process and a peeling process are continuously performed after an extending process.
Fig. 4 is a diagram for explaining a study of a factor causing the orientation angle of the retardation film to be non-uniform in the width direction. Fig. 4A schematically shows a line drawn on the support before heating (bottom) and an orientation angle (upper) on the support before heating. 4B1 and B2 are photographs showing the dimensional change behavior of the support after heating.
5 : is distribution of the orientation angle of the optical axis of the width direction of the coating film (after extending|stretching) in manufacture example A.
(A): Preparation Example A1 (tensile modulus of elasticity at 140 ° C. of support: 800 MPa)
(B): Production Example A2 (tensile modulus of elasticity at 140 ° C. of support: 600 MPa)
(C): Preparation Example A3 (tensile modulus of elasticity at 140 ° C. of support: 200 MPa)
6 is distribution of the optical axis orientation angles in the width direction of the retardation film in Production Example B, (A) before stretching and (B) after stretching.

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 a polymer include cellulose-based resins such as acetyl cellulose, polyester-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, maleimide-based resins, polyolefin-based resins, and (meth)acrylic-based resins. , cyclic polyolefin resins (norbornene-based resins), polyallylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, polysulfone-based resins, and mixtures or copolymers thereof.

The polymer may have positive intrinsic birefringence or may have negative intrinsic birefringence. In the production of a retardation film having a refractive index nz in the thickness direction smaller than the refractive index nx in the in-plane slow axis direction of the retardation film, that is, a positive A plate (nx > ny = nz) and a negative B plate (nx > ny > nz), A polymer having positive intrinsic birefringence is preferably used. On the other hand, the refractive index nz in the thickness direction is greater than the refractive index ny in the in-plane fast axis direction of the retardation film, that is, negative A plate (nz = nx > ny), and positive B plate (nz > nx > ny) Production of , a polymer having negative intrinsic birefringence is preferably used.

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

Re = Δn _in × d = (nx - ny) × d

Rth = Δn _out × d = (np - nz) × d

NZ = (nx - nz)/(nx - ny)

However, among nx and ny, the one with the larger difference from nz is referred to as np.

In the manufacturing method of the present invention, a solution (dope) of a resin material constituting the retardation film is applied onto the support film (application step). The dope applied on the support film is dried by heating, and a laminate is formed in which the coating film of the resin material is adhered and laminated on the support film (drying step). Optical anisotropy is provided to a coating film by extending|stretching the laminated body in which the coating film was formed on the support film in at least one direction (stretching process).

Before application of the dope onto the support film, heat treatment is performed in a state where tension is applied to the support film in the longitudinal direction. By heat-processing the support film before forming the coating film, a retardation film having a small variation in orientation angle is obtained.

In addition, in the stretching step, “stretched in at least one direction” refers to processing such that the distance between two points increases in at least one direction within the plane, and stretching in the longitudinal direction (MD) of the film (longitudinal stretching) , stretching of the film in the transverse direction (TD) (transverse stretching), stretching in both the longitudinal and transverse directions (biaxial stretching), and stretching in an oblique direction. In longitudinal stretching and transverse stretching, the film may be shrunk in a direction orthogonal to the stretching direction.

For example, when stretching in the longitudinal direction (free-end longitudinal stretching) is performed in a state where both ends of the film in the width direction are not held, the film shrinks in the width direction. Generally, in free-end longitudinal stretching, the shrinkage rate in the width direction and the shrinkage rate in the thickness direction are equal, and the rate of decrease (or increase rate) of the refractive index in the width direction and the refractive index in the thickness direction are equal. On the other hand, by using a heat-shrinkable film as a support film and using the shrinkage force of the heat-shrinkable film, the rate of decrease (or increase) of the refractive index in the width direction can be made greater than the rate of decrease (or increase) of the refractive index in the thickness direction. In this way, a retardation film having an optical anisotropy of nx > nz > ny can also be obtained by actively performing shrinkage in a direction orthogonal to the stretching direction.

Further, when stretching in the width direction (fixed-end transverse stretching) is performed while holding both ends of the film in the width direction with a tenter clip or the like, if a simultaneous biaxial stretching machine is used, the film is stretched in the width direction and the length direction. Stretching or shrinking the film in the longitudinal direction while extending in the width direction is also possible. Furthermore, as described in Patent Document 4 (Japanese Unexamined Patent Publication No. 2011-227430), the shrinkage rate in the longitudinal direction is increased by using a heat-shrinkable film as a support film and using the shrinkage force of the heat-shrinkable film, By stretching, a retardation film having an optical anisotropy of nx > nz > ny can also be obtained.

The laminated body after extending|stretching can be used as retardation film as it is. Preferably, the support film is peeled from the laminate after stretching (peeling step), and the coated film after peeling is used as a retardation film.

From the viewpoint of increasing the productivity of the retardation film, it is preferable that the heating, application, and drying are performed by a roll-to-roll method. In the roll-to-roll method, a long support film is used. Further, it is preferable that stretching and peeling of the coating film from the support after stretching are also carried out by roll-to-roll. Below, the manufacturing method of this invention is demonstrated along each process centering on embodiment by roll-to-roll.

1 is a process conceptual diagram schematically showing an example of an embodiment in which a heat treatment, a film forming process, and a drying process are continuously performed by a roll-to-roll method. As shown in FIG. 1, the winding object 10 of the elongate support body 1 is set in the feed-out part 11. The support 1 unwound from the winding body 10 is sequentially conveyed from the drawing-out unit 11 to the heating furnace 101, the film forming unit 110, and the drying furnace 120 located on the downstream side of the conveyance path, Film forming on the support is performed.

[Support film]

In the roll-to-roll method, film formation is performed while conveying the support film along the longitudinal direction. Therefore, as a support film, a winding object (roll) of a long film-like film is used. Below, a support body film may be simply described as a "support body".

In the manufacturing method of the present invention, after the coating film is formed on the support body by the solution film forming method, the laminate of the support body and the coating film is subjected to the stretching step. Therefore, it is preferable that the support has flexibility and is excellent in thermal stability and mechanical strength. From this point of view, as the support, a biaxially oriented film is used. In particular, when the material constituting the support is a crystalline polymer, the biaxial orientation of the film increases the crystallinity of the polymer, and it is possible to improve heat resistance and solvent resistance as well as mechanical strength.

A biaxially oriented film is obtained, for example, by biaxially stretching a film. Examples of the biaxial stretching include vertical and horizontal sequential biaxial stretching and vertical and horizontal simultaneous biaxial stretching. In vertical and horizontal sequential biaxial stretching, the film is stretched in the longitudinal direction (MD) by roll stretching or the like without fixing the film in the width direction (TD) (longitudinal stretching), and then the film is gripped at both ends in the width direction by a tenter or the like. Stretching in the width direction (transverse stretching) is performed in a fixed state. In simultaneous biaxial stretching, in a state where both ends of the film are held in the width direction by tenter clips or the like, a driving method such as a linear motor method, a pantograph method, or a motor chain method is used to change the lengthwise tenter clip spacing while changing the length of the film. By increasing the distance between the clips in the direction, longitudinal stretching and transverse stretching are performed simultaneously.

Further, a method in which the film is stretched in the longitudinal direction (longitudinal stretching) while holding both ends in the width direction with tenter clips or the like, or a state in which shrinkage in the width direction is suppressed by bringing the film into contact with a hot roll or the like A biaxially oriented film can also be obtained by a method of performing longitudinal stretching in the above. The biaxially oriented film may be one obtained by further stretching (or shrinking) a stretched film.

The resin material constituting the support is not particularly limited, and examples thereof include polyester, polyolefin, polycycloolefin, polyamide, polycarbonate, polyvinyl chloride, polyvinylidene chloride, imide polymer, and sulfone polymer. can Among these, those which do not dissolve in the solvent at the time of solution film formation are preferably used. Among them, as a resin material having high solvent resistance, a crystalline polyester resin is preferably used.

Examples of the crystalline polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), as well as glycol components and/or dicarboxylic acids of the monomer units constituting these polyesters. and polyesters in which part or all of are substituted with other monomer components.

The support is preferably one having excellent stretching processability at a heating temperature (for example, around 140°C) in the stretching step after coating film formation. For example, the tensile modulus of elasticity at 140°C of a general-purpose biaxially stretched PET film is about 1200 MPa. In this way, when a film having a high elastic modulus at a high temperature is used as a support, the stretching processability when stretching the laminate of the coating film and the support may be insufficient, and stretching may not be performed, or the appearance of the web or the like may be poor. There are cases.

From the viewpoint of stretchability, the support preferably has a tensile modulus of elasticity of 1000 MPa or less at 140°C. When the tensile modulus of elasticity at 140°C of the support is 1000 MPa or less, workability during stretching is excellent, and appearance defects such as generation of a web in the stretching direction are suppressed. From the viewpoint of improving the stretchability, the tensile modulus of elasticity at 140°C of the support is more preferably 900 MPa or less, and still more preferably 800 MPa or less.

The lower limit of the tensile modulus of elasticity of the support is not particularly limited. If the tensile modulus of elasticity of the support is excessively small, imparting optical anisotropy to the coating film by stretching is insufficient, or the orientation angle of the optical axis of the coating film (retardation film) after stretching (hereinafter, simply referred to as "orientation angle") ) may become non-uniform. Therefore, the tensile modulus of elasticity at 140°C of the support is preferably 100 MPa or more, more preferably 200 MPa or more, and still more preferably 300 MPa or more.

A biaxially oriented film may have anisotropy in tensile modulus due to a difference in draw ratio between the machine direction (MD) and the width direction (TD). When the tensile modulus of elasticity of MD and TD of the support body is different, it is preferable that the tensile modulus of elasticity of MD at 140°C is in the above range. It is more preferable that the elastic moduli at 140 degreeC of both MD and TD fall within the said range.

Further, from the viewpoint of improving the stretching processability, the glass transition temperature Tg of the support is preferably lower than the heating temperature (stretching temperature) in the stretching step. When the support is a polyester film, the glass transition temperature Tg is preferably 110°C or lower, more preferably 105°C or lower, and still more preferably 100°C or lower. The lower limit of the glass transition temperature Tg of the support is not particularly limited, but if the glass transition temperature is excessively low, the elastic modulus of the support during stretching is small, so optical anisotropy is not sufficiently imparted to the coating film by stretching or The orientation angle of the coating film may become non-uniform. When the support is a polyester film, the glass transition temperature Tg is preferably 50°C or higher, and more preferably 60°C or higher. The glass transition temperature is a measured value by the load tensile mode of thermomechanical analysis (TMA).

As the crystalline polyester film having the tensile modulus and glass transition temperature, a crystalline polyester obtained by substituting some or all of the glycol component and/or dicarboxylic acid of the monomer unit constituting the polyester with another monomer component. A biaxially stretched film is preferably used. As the polyester in which the glycol component is substituted, a part of the linear glycol such as ethylene glycol of PET or 1,4-butanediol of PBT is mixed with 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, etc. and glycol-modified polyesters substituted with . In addition, as the polyester in which the dicarboxylic acid component is substituted, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 1, and dicarboxylic acid-modified polyesters substituted with 4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and the like.

Among the above, a polyethylene-terephthalate/isophthalate copolymer in which a part of terephthalic acid in PET is substituted with isophthalic acid is preferably used. The polyethylene-terephthalate/isophthalate copolymer can adjust mechanical properties such as elastic modulus and thermal properties by changing the ratio of the terephthalic acid component and the isophthalic acid component, and by increasing the ratio of the isophthalic acid component, at 140 ° C. The modulus of elasticity can be made smaller than that of PET. In addition, since polyethylene-terephthalate/isophthalate copolymer can be crystallized by stretching in the same way as PET, it is excellent in mechanical strength and has high solvent resistance, so it is preferable as a support for solution film formation.

The support may be colorless or transparent, or may be colored or opaque. The surface of the support may be subjected to an adhesion-facilitating treatment, a release treatment, an antistatic treatment, an antiblocking treatment, or the like. Further, for the purpose of blocking prevention or the like, embossing (knurling) or the like may be applied to the end portion of the support in the width direction.

The thickness of the support body 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, still more preferably 700 mm or more, and particularly preferably 1000 mm or more. By enlarging the width|variety of a support body, while mass productivity of retardation film improves, application to a large-screen display becomes possible.

[Heat Treatment]

In the production method of the present invention, before dope is applied on the support 1 in the film forming unit 110, the support 1 is subjected to heat treatment. By performing the heat treatment, the variation in the width direction of the orientation angle of the retardation film obtained by stretching the coating film formed on the support body together with the support body can be reduced.

The heat treatment is performed in a state in which tension is applied to the support in the longitudinal direction. For example, a method of continuously conveying the support 1 to the downstream side while unwinding it from the winding body 10 of a long support body, heating the support within the heating furnace 101, or heating by bringing it into contact with a heating roll methods and the like. By conveying the support in the longitudinal direction, conveying tension, that is, tension in the longitudinal direction is applied.

The heating of the support is preferably performed in a state in which dimensional change in the width direction of the support is allowed while tension is applied to the support in the longitudinal direction of the support. Therefore, heating is preferably performed while conveying the support in the longitudinal direction in a state where both ends in the width direction of the support are not gripped by a roll conveyance method, a float conveyance method, or the like.

The tension at the time of heat treatment is not particularly limited as long as the support can be transported in the longitudinal direction, and an appropriate value may be set depending on the thickness, tensile modulus, coefficient of linear expansion, and the like of the support. For example, when the support is a biaxially stretched film of crystalline polyester, the tension per unit width of the support is set in the range of about 25 N/m to 500 N/m. When the tension in the longitudinal direction is too small, conveyance of the film during heat treatment may be difficult, or the effect of reducing the variation in orientation angle of the coated film after stretching may be insufficient. On the other hand, if the tension in the longitudinal direction during heat treatment is too large, the elongation may increase, resulting in scratches and wrinkles in the support, and poor appearance of the coating film formed thereon. The rate of dimensional change in the longitudinal direction of the support before and after the heat treatment is preferably within 10%, more preferably within 5%, and still more preferably within 3%.

It is said that the reason why the variation in the orientation angle of the retardation film is reduced by performing the heat treatment of the support before applying the dope is related to the uniformity of the dimensional change behavior of the support during heat drying after dope application and subsequent stretching. It is estimated.

4, an overview of the study of factors causing non-uniformity in the orientation angle of the retardation film obtained by stretching the laminate of the support and the coating film in the width direction will be described. 4B1 and B2 are photographs showing the results of confirmation of dimensional change behavior of the biaxially stretched polyester film by heating. In this experiment, a biaxially stretched film is divided into a plurality of test pieces in the width direction, and a straight line extending in MD and TD and a circle centered on the intersection of these straight lines are drawn on each test piece (see the lower part of Fig. 4A). , and heated for 5 minutes in an oven at 140°C. Fig. 4 B1 is a photograph of a test piece at an end portion in the width direction after heating, and Fig. 4 B2 is a photograph after heating of a test piece at a central portion in the width direction. In Fig. 4 B1 and B2, straight lines and circles in the MD direction in the test piece before heating are drawn as dotted lines, and the shrinkage direction due to heating is indicated by arrows in the figure.

In the sample at the center of the width direction (FIG. 4 B2), slight shrinkage was observed in the MD by heating, but the angle of the straight line in the MD hardly changed before and after heating. On the other hand, in the sample at the edge in the width direction (FIG. 4 B1), it is found that shrinkage occurs in an oblique direction due to heating, and the angle of the straight line of MD is changed after heating. From these results, it can be seen that in the biaxially oriented film, the direction of shrinkage of the film due to heating is arcuately distributed (so-called "bowing") in the width direction, as schematically shown in the upper part of Fig. 4A. can

In this way, when the dimensional change behavior by heating is different in the width direction of the support body, the dimensional change behavior of the support body is different in the width direction at the time of heating or stretching at the time of drying after dope coating. Therefore, it is considered that the orientation angle of the retardation film stretched together with the support is likely to become non-uniform in the width direction. On the other hand, in the present invention, the support is subjected to heat treatment, the dimensional change of the support as shown in FIG. do. In this way, by subjecting the base material to a heat treatment beforehand to change the size of the substrate to relieve bowing, variation in dimensional change behavior of the support at the time of drying after dope coating and subsequent stretching is reduced, and the orientation angle of the retardation film is uniform. It is thought to increase the

In the production of a general-purpose biaxially stretched film, for the purpose of suppressing dimensional change due to heating and mitigating bowing, heating is performed in a state where the film is held in the width direction after transverse stretching by a tenter. There are cases where fixation (heat set) is performed. However, general-purpose films do not require high alignment angle accuracy as in optical films such as retardation films, so even when a biaxially oriented film whose dimensional change behavior is suppressed by heat setting is used as a support, there is a phase difference formed thereon. The film tends to have a large variation in orientation angles in the width direction. On the other hand, in the present invention, since the heat treatment of the support is performed in a state in which contraction in the width direction is possible while applying tension in the longitudinal direction, the dimensional change is more precise than the heat setting treatment in the production of the biaxially stretched film. It is thought that the behavior can be made uniform, and the orientation angle of the retardation film formed on the support becomes uniform in the width direction.

The heat treatment temperature and time are not particularly limited, and the orientation angle deviation of the retardation film after stretching is adjusted to be within a predetermined range in consideration of the material of the support, the glass transition temperature, the orientation (stretch magnification and orientation accuracy), and the like. The higher the heat treatment temperature and the longer the heating time, the smaller the variation in the orientation angle of the retardation film after stretching tends to be.

As a standard, the heating temperature _TH of the support is preferably 60°C or higher, more preferably 80°C or higher, still more preferably 90°C or higher, and particularly preferably 100°C or higher. By raising the heating temperature, the heating time required to improve the uniformity of the orientation angle of the retardation film can be shortened. In addition, the heating temperature _TH of the support body may be set according to the glass transition temperature Tg of the support body. The heating temperature _TH is preferably Tg - 15°C or higher, more preferably Tg - 5°C or higher, and even more preferably Tg or higher. For example, since the glass transition temperature of polyethylene terephthalate or a polyethylene-terephthalate/isophthalate copolymer is about 75°C to 80°C, the heating temperature is preferably 60°C or higher, and more preferably 80°C or higher. In particular, when the heating temperature _TH is equal to or higher than Tg+15°C, the heating time tends to be shortened.

On the other hand, when the heating temperature is excessively high, melting of the film, decrease in dimensional stability, decrease in strength, and the like may occur. In addition, when the polyester film is heated to a high temperature, oligomers precipitate, which may cause poor appearance of the coating film formed on the support. Therefore, the heating temperature _TH is preferably 180°C or less, more preferably 160°C or less, and still more preferably 150°C or less.

The heating temperature can be adjusted by appropriate means. For example, when the support is heated by contact between the heat roll and the support, the heating temperature can be adjusted by changing the temperature of the heat medium supplied into the heat roll. When the support is heated by transportation in a heating furnace, an air circulation type constant temperature oven in which hot or cold air is circulated, a heater using microwaves or far-infrared rays, a roll heated for temperature control, a heat pipe roll, etc. are appropriately heated. By means, the heating temperature can be adjusted. The heating temperature does not have to be constant within the furnace, and may have a temperature profile in which the temperature is raised or lowered step by step.

As described above, the heating time t _H may be set according to the type of the support or the heating temperature _TH . For example, when the heating temperature _TH is 80°C or higher, the heating time t _H is preferably 8 seconds or longer, more preferably 12 seconds or longer, and still more preferably 15 seconds or longer. When the heating temperature _TH is 60°C or more and less than 80°C, the heating time _tH is preferably 23 seconds or longer, more preferably 30 seconds or longer, and still more preferably 40 seconds or longer.

The heating time can also be set based on the relationship between the glass transition temperature Tg of the support and the heating temperature _TH . For example, when the heating temperature _TH is Tg+15°C or higher, the heating time t _H is preferably 8 seconds or longer, more preferably 12 seconds or longer, and still more preferably 15 seconds or longer. When the heating temperature _TH is in the range of Tg - 15°C or more and less than Tg + 15°C, the heating time t _H is preferably {(Tg - T _H ) × 2 + 38} seconds or more, {(Tg - T _H ) × 2 + 45} seconds or longer is more preferred, and {(Tg - T _H ) × 2 + 45} seconds or longer is still more preferred.

The heating time is obtained by dividing the length of the heating furnace (the length of the film transport path in the heating furnace) or the outer circumferential length of the hot roll (the length of the contact portion between the roll and the support in the circumferential direction of the roll) by the transport speed of the support. will be. In the case of using the same equipment, since the length of the heating furnace and the outer circumferential length of the hot roll are constant, it is necessary to reduce the transport speed of the support in order to lengthen the heating time t _H . As shown in FIG. 1, when the heat treatment of the support and the coating and drying of the dope are continuously performed in-line, if the conveyance speed of the support is reduced in order to lengthen the heating time t _H , the film forming process and drying performed continuously The efficiency of the process is also reduced. On the other hand, even if the heating time is excessively long, the effect of suppressing the deviation of the orientation angle is limited to a certain range. Therefore, from the viewpoint of improving productivity, it is preferable that the heating time be as short as possible within a range in which the effect of uniformizing the desired orientation angle is obtained. When the heat treatment and the application step are performed continuously, the heating time is preferably 300 seconds or less, more preferably 150 seconds or less, and still more preferably 100 seconds or less.

[Other processes before the coating process]

Other steps may be performed before the heat treatment or before the application step after the heat treatment. For example, an activation treatment such as corona treatment, plasma treatment, saponification treatment, or low-pressure UV treatment may be applied to the surface of the support for the purpose of improving the adhesion between the support and the coating film. Further, for the purpose of removing foreign substances adhering on the support, etc., the support may be washed.

<Cleaning treatment>

Examples of methods for cleaning the support include a non-contact method in which ultrasonic air or cleaning gas is sprayed, a contact method with a cleaning roll such as an adhesive roll, and a contact method by contact with a liquid. The washing of the support before dope application may be performed either on the dope-applied surface or the back surface, or both surfaces of the support may be washed. By washing the dope-coated surface, introduction into the film of foreign matter or the like adhering on the support is reduced, so that a retardation film with few optical defects is obtained. In addition, by washing the back surface of the support body, foreign matter caught between the back-up roll and the support body during film formation is suppressed.

If a foreign substance exists between the back-up roll and the support at the time of film formation, the film formation surface side of the support is deformed into a convex shape by the pressurization, and the dope is applied thereon, so that the coating thickness of the portion where the support is deformed is locally reduced. It becomes small, and a defect such as point-like interference nonuniformity (hereinafter sometimes referred to as "spot nonuniformity") may occur. In particular, when the film thickness of the coating film is small, spot unevenness due to local film thickness reduction tends to be easily recognized as a defect. By in-line washing the surface (rear surface) on the opposite side to the film forming surface of the support from the time the support is drawn out to the time of application of the dope, the occurrence of spot unevenness can be reduced. In particular, by performing wet cleaning while bringing the back surface of the support and the cleaning roll into contact with a cleaning liquid, the effect of reducing spot unevenness tends to be remarkable.

The cleaning roll preferably has a concave-convex pattern on its surface, and among these, a convex portion of the concave-convex pattern extends non-parallel to the circumferential direction of the roll is preferably used. As a roll which has a convex part extended in the direction non-parallel to the circumferential direction, a gravure roll, a meyer bar roll, an embossing roll etc. are mentioned, for example. As the cleaning roll, a gravure roll and a meyer bar roll are particularly preferably used in that the cleaning liquid is applied to the back surface of the support and spreads without damaging the support. By carrying out wet cleaning while bringing the cleaning roll and the back surface of the support into contact with each other via a cleaning liquid, foreign matter adhering to the back surface of the support is efficiently removed, and occurrence of spot unevenness can be suppressed.

The cleaning liquid supplied between the cleaning roll and the support is not particularly limited as long as it is a liquid and does not dissolve the support, and water, an organic solvent, a mixture of water and an organic solvent, or the like is used. From the viewpoint of efficiently performing in-line cleaning, a liquid having a boiling point lower than that of water is preferably used as the cleaning liquid. In addition, a surfactant, a hydrophilic organic compound, or the like may be added to the cleaning liquid for the purpose of improving cleaning power or the like. Examples of the hydrophilic organic compound include organic compounds having a hydroxyl group, an amino group, an amide group, an imino group, an imide group, a nitro group, a cyano group, an isocyanate group, a carboxyl group, an ester group, an ether group, a carbonyl group, a sulfonic acid group, an SO group, and the like. can

The support after cleaning by contact with the cleaning liquid may be dried from the cleaning liquid adhering to the surface until the dope is applied. The drying method is not particularly limited, and a method of blowing clean air, a method of passing through a heating oven, and the like are exemplified. In addition, the heat treatment may be performed also as drying the washing liquid adhering to the surface of the support. Since the manufacturing process is simplified by carrying out heat treatment concurrently with drying after washing, it is possible to obtain a retardation film in which variation in orientation angles in the width direction is reduced and occurrence of spot irregularities is suppressed with high productivity.

[Film forming process and drying process]

In the film forming step, a resin solution (dope) is applied thereon while conveying the support body 2 after heat treatment along the longitudinal direction (MD). Thereafter, the resin solution is dried by heating, and a long laminated body in which the coating film is tightly laminated on the support is formed.

In the form shown in FIG. 1 , the support 2 subjected to the heat treatment in the heating furnace 101 is transported via the guide roller 207 to the film forming unit 110 formed on the downstream side, and film forming is performed. . 1 shows a form in which film formation is continuously performed in the film forming unit 110 after the heat treatment in the heating furnace 101, but the heat treatment and the film formation do not necessarily need to be performed continuously. For example, film formation may be performed while once winding up the support body after heat treatment in the form of a roll, unwinding the support body from the winding body of the support body after heat treatment, and transporting it to the downstream side.

In the film forming unit 110, the dope 118 is applied to the support 2 and spread, and film forming is performed according to a conventional method. In Figure 1, a knife roll coater is shown. In this roll coater, the support 2 is brought into contact with the dope 118 in the liquid dam 117 while being brought into contact with the backup roll 112, and the dope liquid is removed with the knife roll 111, thereby reducing the thickness of the coating film. is adjusted The film forming method in the film forming unit 110 is not limited to knife roll coating, but kiss roll coat, gravure coat, reverse coat, spray coat, meyer bar coat, air knife coat, curtain coat, lip coat, die coat, etc. A variety of methods are used.

Dope 118 is a solution of a resin material for forming a retardation film, and contains a resin material (polymer) and a solvent. Additives, such as a leveling agent, a plasticizer, a ultraviolet absorber, and a deterioration inhibitor, may be contained in dope as needed. As the resin material for forming the retardation film, either a polymer having positive intrinsic birefringence or a polymer having negative intrinsic birefringence can be used depending on the desired optical anisotropy of the retardation film. In addition, a plurality of resin materials may be mixed and used according to the optical characteristics of the retardation film as the objective. The type of solvent is not particularly limited as long as it dissolves the resin material and does not dissolve the support, and various solvents generally used for solution film formation can be used. Solid content, viscosity, etc. of dope are suitably set according to the kind and molecular weight of resin, the thickness of retardation film, a film forming method, etc.

The film thickness is set so that, for example, the film thickness after drying is about 1 μm to 100 μm, depending on the optical properties (retardation value) and the like required of the retardation film. In the present invention, since the laminate of the support and the coating film formed thereon is stretched, processing such as stretching can be facilitated even when handling is difficult due to the small film thickness of the single coating film. Therefore, even when the film thickness of the coating film is 30 μm or less, by applying the manufacturing method of the present invention, a retardation film having a small film thickness and excellent uniformity of orientation angle can be easily obtained.

The dope layer applied on the support body 2 is conveyed into the drying furnace 120 together with the support body, the solvent is removed, and the laminate 3 in which the coating film adheres on the support body 2 is formed is obtained. The layered product 3 is conveyed downstream from the drying furnace 120, passed through the guide rollers 211 to 215, and wound up by the winding unit 21, and the rolled body of the layered body 3 of the support body and the coating film (20) is obtained.

The heating temperature (drying temperature) and drying time in the drying process are not particularly limited. In general, drying is performed at a higher temperature than near the boiling point of the solvent constituting the dope or higher than the boiling point of the solvent. From the viewpoint of shortening the drying time and enhancing the production process, the drying temperature is preferably as high as possible within a range in which appearance defects such as bubbles do not occur. Specifically, the drying temperature is preferably 70°C or higher, more preferably 80°C or higher, still more preferably 90°C or higher, and particularly preferably 100°C or higher. On the other hand, when the drying temperature is excessively high, bubbles may be generated in the coating film or dimensional change of the support may occur due to the bumpy flow of the solvent. Therefore, the drying temperature is preferably 230°C or lower, more preferably 200°C or lower, and still more preferably 180°C or lower.

In the conventional manufacturing method, when the drying temperature after dope coating onto the biaxially oriented support is increased, the variation in the orientation angle of the retardation film in the width direction tends to increase. In the manufacturing method of the present invention, since non-uniformity in dimensional change of the support in the drying step can be eliminated by performing heat treatment in advance, even when the drying temperature is high, the orientation angle of the retardation film can be made uniform. .

The heating temperature in the drying step can be adjusted by the same method as described above for the heat treatment. The temperature inside the furnace does not have to be constant throughout the inside of the furnace, and may have a temperature profile in which the temperature is raised or lowered step by step. For example, the inside of 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 sudden dimensional change of the support due to temperature change at the inlet or outlet of the heating furnace, a preliminary heating zone or a cooling zone is formed so that the temperature change in the vicinity of the inlet and outlet of the furnace is moderated. You may.

In the case where the temperature throughout the drying furnace is not constant, the drying temperature refers to the temperature within the furnace at the highest temperature (ie, atmospheric temperature within the furnace). In the drying step, the heating time in the above temperature range is preferably 10 seconds or longer, more preferably 20 seconds or longer, and still more preferably 30 seconds or longer. The heating time can be adjusted according to the length of the transport path of the support in the heating furnace (furnace length) and the transport speed of the support.

Upon drying of the coating film on the support, the molecular chains of the polymer tend to be oriented in the in-plane direction. When a polymer having positive intrinsic birefringence is oriented in-plane, the thickness direction refractive index nz of the coating film becomes large relative to the in-plane refractive index (nx and ny), and the coating film exhibits a refractive index anisotropy of nx = ny > nz (where Rth is a positive value) Negative C plate characteristics are expressed. When a polymer having negative intrinsic birefringence is oriented in-plane, the thickness direction refractive index nz of the coating film becomes relatively small with respect to the in-plane refractive index, and a positive C plate characteristic having a refractive index anisotropy (Rth is a negative value) of nx = ny < nz this is manifested

Since the rate of dimensional change of the biaxially oriented film is different depending on the direction when heated, when the coating film formed on the support is dried at a high temperature, due to the anisotropy of the dimensional change of the support, the coating film generates in-plane refractive index anisotropy. There are cases. When the support is contracted in an oblique direction by heating during drying, as shown in FIG. 4B1 , the coating film formed thereon is also contracted in an oblique direction and may have an optical axis in the oblique direction. Therefore, if the shrinkage rate or shrinkage direction of the support is non-uniform in the width direction, the optical axis of the coating film becomes non-uniform in the width direction. On the other hand, in the present invention, as described above, since the support is subjected to heat treatment in advance, the dimensional change behavior of the support becomes uniform in the width direction, and as a result, the coating film formed thereon also changes the orientation angle of the optical axis. It becomes uniform in this width direction.

[stretching process]

The layered product 3 in which the coating film is formed in close contact with the support 2 after the heat treatment is stretched in at least one direction in the stretching step. 2 : is a figure which shows typically one form of an extending process and a peeling process. In the form shown in FIG. 2, the winding object 20 of the laminated body 3 is set in the feed-out part 22 of a stretching apparatus. The laminated body 3 unwound from the winding object 20 is conveyed continuously from the drawing-out part 22 to the heating furnace 139 of the extending part 130 on the downstream side via the guide rollers 221 and 222. Moreover, in FIG. 1 and FIG. 2, after the laminated body 3 after drying dope is once rolled up in the take-up part 21 of the film forming apparatus, the winding object 20 of the laminated body 3 is drawn out of the stretching apparatus Although the form of being set and unwound on the portion 22 is shown, the laminate may be directly used in the stretching step without winding the laminate after the film forming and drying steps.

In the form shown in FIG. 2, in the extending|stretching part 130, the example which implements free-end uniaxial stretching (longitudinal stretching) in the longitudinal direction (MD) by the float method is shown. The stretching unit 130 has a heating furnace 139, nip rolls 231 and 232 are formed on the upstream side (entrance) of the heating furnace 139, and nip rolls 236 and 237 are provided on the downstream side (exit) this is formed In the free-end uniaxial stretching, the film is stretched in the longitudinal direction without gripping the edge of the laminate in the width direction. In the form shown in FIG. 2, by making the circumferential speed of the nip rolls 236 and 237 on the downstream side of the heating furnace 139 larger than the circumferential speed of the nip rolls 231 and 232 on the upstream side, the laminated body 3 has a length stretched in the direction

In the form shown in FIG. 2, in the heating furnace 139, hot air spray nozzles (floating nozzles) 131 to 137 are arranged in a zigzag pattern above and below the transport path of the laminate, and stretching is performed under heating by hot air. It is carried out. The conveyance method of the film in the heating furnace (stretching furnace) 139 is not limited to the float method, and an appropriate conveyance method such as a roll conveyance method or a tenter conveyance method is employed. Stretching in the transverse direction (TD) can also be performed while conveying the film in the longitudinal direction (MD) by tenter conveyance. In the heating furnace 139, simultaneous biaxial stretching in the longitudinal direction and width direction or oblique direction stretching may be performed. Furthermore, after extending|stretching in the longitudinal direction within the heating furnace 139, you may perform sequential biaxial stretching by extending|stretching in the width direction with another heating furnace (not shown), etc.

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, and the type of polymer constituting the coating film (retardation film), the thermal properties of the support, etc. set according to The stretching temperature is generally about 100°C to 220°C, and preferably about 120°C to 200°C. When the glass transition temperature of the coating film formed on the support is tg, the stretching temperature is preferably (tg - 100) ° C or higher, more preferably (tg - 90) ° C or higher, and (tg - 80) ° C or higher more preferable When the stretching temperature is too low, peeling of the coating film from the support may occur, retardation may become non-uniform, or appearance defects such as haze increase may be caused. On the other hand, when the stretching temperature is too high, the orientation of the polymer constituting the coating film may decrease, and desired retardation may not be obtained.

The temperature inside the heating furnace 139 does not have to be constant throughout the inside of the furnace, and may have a temperature profile in which the temperature is raised or lowered step by step. For example, the inside of 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 sudden dimensional change of the laminate due to a temperature change at the inlet or outlet of the heating furnace 139, causing wrinkles or conveying defects, the vicinity of the inlet and outlet of the heating furnace A preliminary heating zone or a cooling zone may be formed, or a heating roll or cooling roll may be formed so that the temperature change in is moderate.

In free-end uniaxial stretching, as the laminate is stretched in the longitudinal direction, contraction action occurs in the width direction and thickness direction. Therefore, when the polymer constituting the coating film has positive intrinsic birefringence, the refractive index (nx) in the longitudinal direction is increased, and the refractive index (ny) in the width direction and the refractive index (nz) in the thickness direction are decreased. On the other hand, when the polymer constituting the coating film has negative intrinsic birefringence, the refractive index ny in the longitudinal direction decreases, and the refractive index nx in the width direction and the refractive index nz in the thickness direction increase. In free-end uniaxial stretching, generally, the shrinkage rate in the width direction and the shrinkage rate in the thickness direction are equal, and the rate of decrease (or increase rate) of the refractive index in the width direction and the refractive index in the thickness direction are equal. Therefore, when using a polymer having positive intrinsic birefringence as the material of the retardation film, the retardation film obtained by free-end uniaxial stretching has a refractive index anisotropy of nx > ny = nz. It becomes a positive A plate. On the other hand, when using a polymer having negative intrinsic birefringence, the retardation film obtained by free-end uniaxial stretching becomes a negative A plate having a refractive index anisotropy of nz = nx > ny.

Further, when a layered product in which a coating film is formed in close contact with a support body is subjected to free-end uniaxial stretching, the shrinkage rate in the width direction of the layered body largely depends on the mechanical properties and thermal characteristics of the support body, so the shrinkage rate and thickness of the coating film in the width direction There are cases in which the shrinkage rates in the directions are different. In addition, when the coating film on the support is dried, the molecular chains of the polymer are oriented in the in-plane direction, so that the thickness direction refractive index nz of the coating film is relatively large or small with respect to the in-plane refractive index, and the coating film has a refractive index of nx = ny > nz It may have negative C plate characteristics with anisotropy (Rth is a positive value) or positive C plate characteristics with a refractive index anisotropy (Rth is a negative value) of nx = ny < nz. Therefore, when the coating film made of a polymer having positive intrinsic birefringence formed on the support has a refractive index anisotropy of nx = ny > nz, the refractive index anisotropy of ny > nz is maintained before and after stretching, and the refractive index of nx > ny > nz A negative B plate having anisotropy may be 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 may be obtained by free-end uniaxial stretching in some cases.

As described above, in free-end uniaxial stretching, contraction in the width direction occurs along with stretching of the support body and the coating film to be stretched, and optical anisotropy is imparted. In the present invention, by performing heat treatment on the support before forming the coating film on the support, in addition to uniforming the dimensional change behavior during drying, the dimensional change behavior during stretching also becomes uniform, so that the optical axis of the retardation film The orientation angle can be made uniform in the width direction.

The draw ratio in the stretching step is preferably 1.01 times or more, and more preferably 1.03 times or more. In free-end uniaxial stretching, in-plane birefringence (Δn _in ) tends to increase as the stretching ratio increases. When the draw ratio is excessively large, breakage of the coating film may occur or optical properties may become non-uniform. Therefore, the draw ratio is preferably 3 times or less, more preferably 2.5 times or less, and still more preferably 2 times or less. The stretching method and the stretching ratio in the stretching step can be adjusted according to the target optical characteristics. In-plane retardation Re of retardation film is about 15 nm - 400 nm, for example. Optical properties such as thickness direction retardation Rth of the retardation film and NZ coefficient are appropriately set depending on the use of the retardation film and the like.

[Peel process]

The layered product 4 after stretching can be used as a retardation film as it is. Preferably, the support 7 after the stretch is peeled off from the laminate 4 after the stretch, and the coating film 5 after the support is peeled off is used as a retardation film. In this case, the support is a process member that is not included in the retardation film as the final product. Therefore, the support does not have to be optically uniform, and an inexpensive support can be used.

The laminated body 4 after extending|stretching may be once rolled up in roll shape, and it may use for a peeling process continuously from an extending process. In FIG. 2, the form in which the peeling process is performed in the peeling part 160 continuously after the extending process is shown. The peeling method of the support body 7 and the coating film (retardation film 5) after stretching is not particularly limited. , It is preferable to convey each of the support body 7 and the retardation film 5 along the upper roll 261 and the lower roll 262 on the downstream side thereof, and to peel them. The support body 7 after peeling is wound up in the take-up part 71 by an appropriate system.

[Other processes after the stretching process]

After the stretching process or the peeling process, the retardation film may be subjected to another process. For example, in the form shown in FIG. 2, after the retardation film 5 after peeling the support body 7 is inspected by the inspection unit 170, and then bonded to another film 9 by the bonding unit 190, The laminate 6 of the retardation film 5 and the film 9 is wound up in a winding unit 51 to form a winding object 50 .

<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 5 and the orientation angle of the slow axis. The retardation can be kept constant by feeding back the measured retardation value to the roll circumferential speed or the like in the stretching unit 130 . From the viewpoint of accurately measuring the retardation of the retardation film 5, it is preferable that the retardation measurement is performed after the support 7 is peeled off.

The defect detection unit is configured to be capable of detecting defects such as concavo-convex defects such as foreign substances, dents, and scratches existing inside or on the surface of the retardation film. Since defects of the retardation film 5 can be selectively detected without detecting defects contained only in the support 7 by performing defect detection after peeling the support 7, the defect detection accuracy increases.

<Bonding process>

In the bonding part 190, the retardation film 5 is bonded together with the other film 9, and the laminated body 6 is formed. Examples of the film 9 include a protective film (separator) temporarily bonded to the retardation film 5 and other optical films (retardation film, polarizer, etc.). Lamination of the retardation film and other films is preferably performed through an appropriate adhesive agent.

A laminated polarizing plate having a retardation film can be formed by laminating a polarizer on the retardation film. Further, on the retardation film, a polarizer may be laminated alone, or on the polarizer, a transparent protective film or another retardation film bonded together may be laminated.

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 25 μm or less, more preferably 15 μm or less, and preferably 8 μm or less. By reducing the thickness of the polarizer, the influence of the stress generated by the dimensional change of the polarizer due to environmental changes such as heat and humidity can be reduced. Therefore, by reducing the thickness of the polarizer laminated on the retardation film, even when the thickness of the retardation film is small, a laminated polarizing plate with little change in optical characteristics due to changes in the surrounding environment can be obtained.

On the surface of the retardation film 5, an adhesive layer for bonding with another optical film or liquid crystal cell may be laminated. For example, an adhesive layer can be laminated|stacked on retardation film by bonding the retardation film with the surface of the adhesive layer side of the adhesive sheet in which the adhesive layer was provided on the suitable separator.

When the thickness of the retardation film 5 after peeling the support 7 from the laminate 3 is 30 μm or less, the self-supporting property of the retardation film 5 alone is insufficient and the handling property is not sufficient. By bonding together with the pressure-sensitive adhesive layer, handling properties are improved. In addition, although the form in which the film 9 is bonded only to one side of the retardation film 5 is shown in FIG. 2, a film or an adhesive layer may be bonded to both sides of the retardation film 5.

In addition, before the support body 7 is peeled off from the laminated body 3 in the peeling part 160, another film or adhesive layer may be bonded to the surface of the laminated body 3 on the side of the retardation film 5. Before the support body 7 is peeled off, it is not necessary to transport the retardation film alone by bonding another film, an adhesive layer, or the like onto the retardation film 5 . Therefore, even when the thickness of the retardation film is small, the handling property is improved. After laminating another film or pressure-sensitive adhesive layer on the surface of the layered product 3 on the side of the retardation film 5, the support 7 is peeled off, and another film is placed on the exposed surface of the retardation film 5 after the release. Alternatively, an adhesive layer may be laminated.

<Winding process>

After the retardation film 5 after peeling the support body 7 is used for an inspection process or a bonding process as needed, it is wound up in the winding unit 51 to form a winding body of the retardation film. As shown in FIG. 2 , the retardation film 5 may be wound up by the take-up unit 51 as a laminate 6 (for example, a laminated polarizing plate) laminated with another film 9 . In addition, the retardation film 5 after peeling the support body 7 may be cut into a single sheet as it is, without subjecting it to the winding-up step.

In FIG. 2, after stretching the layered product 3 in which the coating film was laminated in close contact with the support, the state in which the support 7 is peeled at the peeling part 160 without being wound into a wound body is shown, but the layered product after the stretching After (4) is once wound into a winding object, the peeling step may be performed with an apparatus different from the stretching step. Moreover, bonding with another film may be performed before peeling a support body from a laminated body.

For example, after once winding up the laminated body 4 after extending|stretching in the shape of a roll, as shown in FIG. 3, while unwinding and conveying the winding object 340 of a laminated body from the drawing|feeding part 342 of a bonding/peeling apparatus, , bonding with another film 309 and peeling of the support 307 may be performed in this order. In the form shown in FIG. 3 , the laminate 304 after stretching unwinded from the winding object 340 is laminated at the bonding section 390 on the downstream side via the guide rollers 321 and 322 from the drawing-out section 342. Another film 309 (for example, a polarizing plate) is bonded to the surface of the body 304 on the opposite side to the support body, and a laminate 308 is formed. Further, in the peeling unit 360 on the downstream side, the support 307 is peeled from the laminate to obtain a laminate 306 (for example, a laminated polarizing plate) to which the retardation film and other films are bonded. The laminate 306 to which the retardation film and other films are bonded is subjected to inspection by the inspection unit 470 as necessary, and then is wound up by the winding unit 351 to form a winding object 350.

In this aspect, the retardation film formed on the support is transferred to the other film by peeling the support after bonding the retardation film and the other film. In this way, if bonding with another film is performed before the support is separated from the laminate, there is no need to handle the retardation film alone. Therefore, even when the film thickness of the coating film formed on the support is small and it is difficult to handle the coating film alone, the productivity and yield of the laminated optical film in which the retardation film and other films are laminated can be increased.

[Embodiment using heat-shrinkable support]

Although the example of manufacturing the A plate or the B plate by stretching has been mainly described, by using a heat-shrinkable film as a support, nx > nz > ny having a refractive index anisotropy (NZ coefficient greater than 0 and less than 1) retardation film can also be manufactured. In the case of using a heat-shrinkable film as the support, in the stretching step, the laminate of the support and the coating film is stretched in one direction and shrinked in a direction perpendicular to the stretching direction using the shrinkage force of the support, thereby forming a layer perpendicular to the stretching direction. The rate of decrease (or increase rate) of the refractive index in the direction (contraction direction) can be greater than the rate of decrease (or increase rate) of the refractive index in the thickness direction.

The heat-shrinkable film serving as the support is not particularly limited as long as it has biaxial orientation and heat-shrinks in a direction orthogonal to the stretching direction in the stretching step. The heat-shrinkable film preferably has a shrinkage ratio (length after shrinkage/length before shrinkage) of 0.50 to 0.99, preferably 0.60 It is more preferably from 0.98 to 0.98, and more preferably from 0.70 to 0.95.

The heat-shrinkable film may have different shrinkage ratios in the stretching direction and the shrinking direction in the stretching step. For example, when the laminate is stretched in the width direction and contracted in the longitudinal direction in the stretching step, a heat-shrinkable film that is more easily contracted in the longitudinal direction may be used. As an example, when manufacturing a heat-shrinkable film, both ends of the film are gripped with a tenter clip or the like, and the clips are moved so that the distance between the clips in the longitudinal direction is increased while maintaining the distance between the clips in the width direction. Shrinkage in the longitudinal direction A heat-shrinkable film that tends to be obtained is obtained.

The material constituting the heat-shrinkable film as the support is not particularly limited, and the materials described above can be used as the material of the support. Especially, polyolefins, such as the said polyester and polyethylene, a polypropylene, are used preferably.

In the case of using a heat-shrinkable film as the support, the heat treatment of the support and application and drying of the dope on the support may be carried out in the same manner as described above. As a standard, the heating temperature _TH during the heat treatment is preferably 60°C or higher, more preferably 80°C or higher, still more preferably 90°C or higher, and particularly preferably 100°C or higher. By raising the heating temperature, variation in shrinkage behavior of the support is alleviated and the orientation angle of the coating film formed thereon becomes uniform, so the orientation angle of the retardation film after stretching also tends to become uniform. On the other hand, if the heat treatment temperature is too high, shrinkage in the stretching step may not occur easily because the support is thermally contracted or heat-set during the heat treatment. Therefore, it is preferable that heating temperature _TH is lower than the heating temperature in an extending process. Similarly, it is preferable that the drying temperature after apply|coating dope on a support body is also lower temperature than the heating temperature in an extending process.

In the stretching step, the laminate of the support and the coating film is stretched in one direction, and the laminate is contracted in a direction orthogonal to the stretching direction. Stretching and shrinking may be performed separately, but preferably performed simultaneously. By simultaneously performing both, the orientation developed by contraction and stretching can be maintained without relaxing. By using a heat-shrinkable film as a support, since the heat-shrinkable film shrinks in a direction orthogonal to the stretching direction by heating during stretching, stretching and shrinkage are performed simultaneously, the coating film formed on the support (heat-shrinkable film), It may be stretched in one direction and contracted in a direction orthogonal to the stretching direction. As described above, even in a stretching method such as free end uniaxial stretching, shrinkage occurs in the width direction (direction orthogonal to the stretching direction) along with stretching in the longitudinal direction, but equivalent shrinkage also occurs in the thickness direction. . In contrast, when a heat-shrinkable film is used, since the amount of shrinkage in the direction orthogonal to the stretching direction is greater than the amount of shrinkage in the thickness direction, a retardation film having optical anisotropy of nx > nz > ny can be manufactured.

As a method of simultaneously stretching and contracting in a direction orthogonal to the stretching direction, a method of stretching in the longitudinal direction (MD) and simultaneously contracting in the width direction (TD), or simultaneously with stretching in the width direction (TD) A method of shrinking in the longitudinal direction (MD) is preferred. Among them, from the viewpoint of securing the width of the retardation film to facilitate application of the retardation film to a large screen display or from the viewpoint of improving area efficiency when cutting the retardation film to fit the screen size, simultaneously with stretching in the width direction A method of shrinking in the longitudinal direction is preferred.

In order to shrink in the width direction simultaneously with stretching in the longitudinal direction, free end uniaxial stretching (longitudinal stretching) may be performed using a roll stretching machine, for example. Alternatively, stretching may be performed in the longitudinal direction using a biaxial stretching machine, gripping both ends in the width direction and controlling the shrinkage rate in the width direction. When shrinking in the longitudinal direction simultaneously with stretching in the width direction, stretching in the longitudinal direction may be performed while holding both ends in the width direction and controlling the shrinkage rate in the width direction. In order to simultaneously stretch in the width direction and shrink in the longitudinal direction, for example, using a biaxial stretching machine, while holding both ends in the width direction of the film with a tenter clip or the like, while stretching in the width direction, clip in the length direction It is only necessary to move the clip so that the distance between them becomes smaller.

[Usage and optical properties of retardation film]

Although the use of the retardation film is not particularly limited, it is preferably 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 properties 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 or the retardation value of the cell. For example, in an in-plane switching (IPS) type liquid crystal display device, black luminance increases when the screen is visually viewed from an oblique direction at an azimuth angle of 45° with respect to the direction of the absorption axis of the polarizing plate, but the liquid crystal cell and the polarizer By disposing the retardation film therebetween, the black luminance in the oblique direction can be reduced and the contrast can be improved. In optical compensation of an IPS system liquid crystal display device, as disclosed in, for example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2009-139747), two or more retardation films may be used in combination. When two or more retardation films are used for optical compensation of a liquid crystal display device, the retardation film according to the manufacturing method of the present invention is used for at least one retardation film.

In addition, the number of retardation films used for optical compensation of the liquid crystal display device is not limited to two, but may be one or three or more. For example, if a retardation film having a refractive index anisotropy of nx > nz > ny obtained by using a heat-shrinkable film as a support and shrinking the laminate in a direction orthogonal to the stretching direction is used, with one retardation film, IPS type Optical compensation of the liquid crystal display device can be performed.

A liquid crystal display device can be manufactured, for example, by properly assembling the retardation film of the present invention, other optical films such as a polarizer, a liquid crystal cell, and optical members such as a backlight and attaching a driving circuit thereto. At the time of bonding the retardation film and the liquid crystal cell, from the viewpoint of improving the uniformity in the orientation axis direction and simplifying the manufacturing process, as described above, the laminated polarizing plate and the liquid crystal cell to which the retardation film and the polarizer are bonded are mixed with an appropriate adhesive such as It is preferable to bond through an adhesive layer.

(Example)

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[measurement method]

The elastic modulus of the film was measured according to JIS K 7127 using an autograph (manufactured by Shimadzu Corporation) equipped with a thermostat under conditions of a temperature of 140°C and a tensile rate of 10 mm/min. The retardation of the retardation film and the orientation direction of the optical axis were measured in a 23°C environment using a polarization/phase difference measuring system (manufactured by Axometrics, product name "AxoScan") (measurement wavelength: 590 nm).

The glass transition temperature of the support was measured according to the TMA method described in JIS C 6481 (1996 edition).

[Synthesis Example A: Synthesis of fumaric acid ester-based resin (polymer having negative birefringence) and preparation of dope]

In an autoclave equipped with a stirrer, cooling pipe, nitrogen inlet pipe and thermometer, 48 parts by weight of hydroxypropylmethylcellulose (manufactured by Shin-Etsu Chemical, trade name Metroz 60SH-50), 15601 parts by weight of distilled water, 8161 parts by weight of diisopropyl fumarate 240 parts by weight of 3-ethyl-3-oxetanylmethyl acrylate and 45 parts by weight of t-butylperoxypivalate as a polymerization initiator were added, nitrogen bubbling was carried out for 1 hour, and then maintained at 49 ° C. for 24 hours while stirring, Radical suspension polymerization was carried out. It was then cooled to room temperature, and the resulting suspension containing polymer particles was centrifuged. After washing the obtained polymer twice with distilled water and twice with methanol, it was dried under reduced pressure.

The obtained fumaric acid ester type resin was dissolved in a mixed solution of toluene/methyl ethyl ketone (50% by weight/50% by weight of toluene/methylethyl ketone) to obtain a 20% solution. Furthermore, dope was prepared by adding 5 parts by weight of tributyl trimellitate as a plasticizer to 100 parts by weight of fumaric acid ester-based resin.

[Retardation film production examples A1 to A3]

In retardation film production example A, a polyester (polyethylene-terephthalate/isophthalate copolymer) biaxially stretched film (thickness: 75 μm, width: 1350 mm) was used as the support film. Using three types of supports having different terephthalate/isophthalate content ratios in polyester, the heat treatment conditions of each support were changed, and the orientation angle of the optical axis of the retardation film after stretching was evaluated. The tensile elastic modulus (MD) at 140 degreeC of the support body used by manufacture example A1, A2, and A3 was 800 Mpa, 600 Mpa, and 200 Mpa, respectively.

<Heat treatment, coating, drying>

The winding body of the support film was set in the drawing out part of the film forming apparatus, the support film was drawn out, and heat treatment was performed with a heating furnace while conveying it to the downstream side. The heat treatment temperature was adjusted by changing the atmospheric temperature in the heating furnace. The heating time was adjusted by changing the transport speed of the support. On the support after heat treatment, the dope prepared in Synthesis Example A was applied so that the film thickness after drying was 6 μm, and dried at 140°C. The coated film after drying was rolled up as a laminate together with the support.

<Stretching and peeling>

Free end uniaxial stretching was performed within a drawing furnace at a temperature of 140°C, while setting the said layered product in the feeding part of the stretching apparatus, feeding out the layered product and conveying it to the downstream side. The support was peeled from the laminate after stretching to obtain a phase difference film. The draw ratio was adjusted so that the in-plane retardation of the retardation film after peeling the support body might be set to 35 nm.

The orientation angle of the optical axis of the retardation film obtained above was measured at intervals of 10 mm in the width direction (measurement range: 1230 mm in the center of the width direction), and the difference between the maximum value and the minimum value was taken as the deviation range of the optical axis. Table 1 shows the variation range of the orientation angle (°) of the optical axis with respect to the heat treatment time and heat treatment temperature of the support in Production Example A1 (140°C tensile modulus of support: 800 MPa). In addition, the results of Production Example A2 (140°C tensile modulus of support: 600 MPa) and Production Example A3 (140°C tensile modulus of support: 200 MPa) are shown in Table 2 and Table 3, respectively. Moreover, in Tables 1-3, time 0 second shows the range of deviation of an orientation angle in the case where heating furnace 101 is set to room temperature and heat processing is not performed. In addition, the measurement results (partial excerpts) of the orientation angles of the retardation films of Production Examples A1 to A3 are shown in Figs. 5(A) to (C), respectively.

<Evaluation result>

In any of Production Examples A1, A2 and A3, it can be seen that the higher the heat treatment temperature of the support and the longer the heat treatment time, the smaller the deviation of the orientation angle of the retardation film. In Production Example A3 (Table 3) in which the tensile modulus of elasticity at 140 ° C. of the support is 200 MPa, when the support is not subjected to heat treatment, the heat treatment temperature is increased relative to the orientation angle deviation of 20 °, It can be seen that the variation can be reduced to 1° or less by lengthening the heating time. From this result, it can be seen that when the tensile modulus of elasticity of the support is small, the effect of equalizing the orientation angle by heat treatment of the support is particularly large.

[Synthesis Example B: Synthesis of polyallylate-based resin (polymer having positive birefringence) and preparation of dope]

In a reaction vessel equipped with a stirring device, 54.0 g of 2,2-bis(4-hydroxyphenyl)-4-methylpentane and 12 parts by weight of benzyltriethylammonium chloride were dissolved in a 1 M sodium hydroxide solution. To this solution, a solution in which 406 parts by weight of terephthalic acid chloride was dissolved in chloroform was added at once while stirring, and stirred at room temperature for 90 minutes. Thereafter, the polymerization solution was subjected to static separation to separate the chloroform solution containing the polymer, followed by washing with acetic acid water and ion-exchanged water, and then poured into methanol to precipitate the polymer. The precipitated polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure.

The obtained polyallylate-type resin was dissolved in cyclopentanone to prepare dope having a solid content concentration of 20%.

[Phase difference film production example B]

In retardation film production examples B1 and B2, a heat-shrinkable film was used as the support film. As the heat-shrinkable film, both ends of an unstretched polypropylene film in the width direction are held with tenter clips of a simultaneous biaxial stretching machine, and a biaxially oriented film is used by stretching it in the longitudinal direction while maintaining a distance between the clips in the width direction. did

<Heat treatment, coating, drying>

In Production Example B1, the roll 10 of the heat-shrinkable support film (600 mm in width) was set in the feeding unit 11 of the film forming apparatus schematically shown in FIG. 1, and the support film 1 was fed out, Heat treatment was performed at 110°C for 60 seconds in a heating furnace while conveying to the downstream side. On the support after heat treatment, the dope prepared in Synthesis Example B was applied so that the film thickness after drying was 15 μm, and dried at 100°C. The coated film after drying was rolled up as a laminate together with the support. In Production Example B2, coating and drying of the dope onto the support was performed in the same manner as in Production Example B1 except that the heating furnace was set to room temperature (that is, no heating was performed). The support was peeled from the obtained layered product, and the orientation angle of the optical axis of the coating film was measured at intervals of 2 mm in the width direction (measurement range: 530 mm in the center of the width direction). The measurement result of the orientation angle with heat treatment (production example B1) and without heat treatment (production example B2) is shown in FIG. 6(A).

<Stretching and peeling>

The laminate was stretched 1.2 times in the width direction using a biaxial stretching machine at a temperature of 145° C., while reducing the distance between clips in the longitudinal direction, and shrinking it by 0.75 times. The phase difference film after peeling the support had an in-plane retardation of 270 nm and NZ = 0.5. The optical axis of this retardation film was measured at intervals of 2 mm in the width direction (measuring range: 150 mm in the center of the width direction). The measurement result of the orientation angle of the retardation film with heat treatment (production example B1) and without heat treatment (production example B2) is shown in FIG. 6(B). Table 4 also lists the deviations in orientation angles (°) of the optical axes before and after stretching in Production Examples B1 and B2.

From the comparison between FIG. 6(A) and FIG. 6(B) , it can be seen that in both Production Example B1 (with heat treatment) and Production Example B2 (without heat treatment), the orientation angle deviation tends to be reduced by stretching. can In Production Example B2 in which the heat treatment of the support was not performed, since the variation in the orientation angle of the coating film after applying and drying the dope is large (FIG. 6(A)), the tendency remains even after stretching, and the variation in the orientation angle of the retardation film It is considered that is large (FIG. 6(B)). On the other hand, in Production Example B1, by applying and drying the dope after the heat treatment of the support, the orientation angle variation of the coating film is small, and the orientation angle variation is further reduced by stretching. From these results, it can be seen that even when a heat-shrinkable film is used as the support, a retardation film having a small variation in orientation angle in the width direction can be obtained by heat-treating the support before forming the film.

1, 2, 7: support
3, 4, 6: laminated body
5: retardation film
10: support winding body
20: laminate winding body
50: retardation film laminate winding body
11, 22: extraction unit
21, 51: winding unit
101: heating furnace
110: Unveiling
120: drying furnace
130: stretching unit
139: heating furnace (stretching furnace)
160: peeling unit
170: inspection department
171: phase shifter
172: defect detection unit
190: joining part

Claims (14)

Process in which the support film which is a long biaxially stretched film is heat-processed;
an application step in which a resin solution is applied on the support film while the support film is conveyed in the longitudinal direction;
a drying step in which the resin solution is dried by heating to form a layered body in which a coating film is tightly laminated on the support film; and
After the drying step, the layered product is stretched in at least one direction, and the coating film is provided with an extending step in which optical anisotropy is imparted in this order,
The heat treatment is performed in a state in which tension is applied to the support film in the longitudinal direction. According to claim 1,
The method for producing a phase difference film in which the heating temperature _TH in the heat treatment is 80°C or higher and the heating time t _H is 8 seconds or higher. According to claim 1,
The method for producing a phase difference film, wherein a heating temperature _TH in the heat treatment is 60°C or more and less than 80°C, and a heating time t _H is 23 seconds or more. delete According to claim 1,
The manufacturing method of the retardation film of which the heating temperature TH in the said heat treatment is Tg-15 degreeC or more, taking Tg as the glass transition temperature measured by _TMA of the said support body. According to claim 5,
In the above heat treatment, the heating temperature _TH is Tg + 15 ° C or more and the heat treatment time t _H is 8 seconds or more, or the heating temperature _TH is Tg - 15 ° C or more and less than Tg + 15 ° C, and the heat treatment time t A method for producing a retardation film in which _H is {(Tg - T _H ) × 2 + 38} seconds or more. According to claim 1,
The method for producing a retardation film according to claim 1 , wherein the support film is a polyester film having a glass transition temperature Tg of 110° C. or lower as measured by TMA. According to claim 1,
The method for producing a phase difference film, wherein the support film has a tensile modulus of elasticity at 140°C of 1000 MPa or less before the heat treatment. According to claim 1,
The manufacturing method of the retardation film whose film thickness of the coating film after drying in the said drying process is 30 micrometers or less. According to claim 1,
The manufacturing method of the retardation film whose in-plane retardation of the coating film after the said extending|stretching is 15 nm - 400 nm. According to claim 1,
In the stretching step, the laminate is stretched in either the longitudinal direction or the width direction, and the laminate is contracted in a direction orthogonal to the stretching direction. According to claim 11,
In the stretching step, in a state in which both ends in the width direction of the laminate are not gripped, uniaxial stretching of the free end is performed in the longitudinal direction. According to claim 11,
In the stretching step, the multilayer body is stretched in the width direction and the multilayer body is contracted in the longitudinal direction while holding both ends in the width direction of the multilayer body. A method for manufacturing a laminated polarizing plate in which a polarizer and a retardation film are laminated,
A retardation film is manufactured by the method according to any one of claims 1 to 3 and 5 to 13,
A method for manufacturing a laminated polarizing plate, characterized in that an optical film including a polarizer is laminated on the retardation film.

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