JP2015191049A - Long retardation film, polarizing plate, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long retardation film without having phase difference and optical axis deviation even when using an acryl resin substrate.SOLUTION: A long retardation film has an alignment layer and a retardation layer in this order on a long acryl resin substrate. The long acryl resin substrate may have an inner ring part at the end part in a short-size direction perpendicular to a long-size direction. When a section ab having an arbitrary width 100 mm is provided in the short-size direction center part side portion rather than the inner ring portion in the acryl resin substrate when the acryl resin substrate has the inner ring, or in the whole surface of the acryl resin substrate when the acryl resin substrate does not have the inner ring, a difference between the maximum value and the minimum value is 2 μm or less.

Description

  The present invention relates to a long retardation film, a polarizing plate, and an image display device.

Conventionally, in a liquid crystal display device, various techniques have been developed in order to improve the problem of viewing angle dependency. As one of them, a retardation film having a retardation layer exhibiting birefringence is used as a liquid crystal cell. Liquid crystal display devices disposed between polarizing plates are known (for example, Patent Documents 1 and 2).
As the retardation film having the retardation layer, an alignment layer having an alignment regulating force for aligning liquid crystalline compounds in a certain direction on a resin substrate, and formed on the alignment layer and arranged in a certain direction Those having a retardation layer containing a liquid crystal compound are used.

  Conventionally, as a flat panel display, a two-dimensional display has been mainstream, but in recent years, a flat panel display capable of three-dimensional display has begun to attract attention. Further, in future flat panel displays, it is a natural tendency to be capable of three-dimensional display, and flat panel displays capable of three-dimensional display are being studied in a wide range of fields.

In order to perform three-dimensional display on a flat panel display, it is usually necessary to display a right-eye video and a left-eye video separately to the viewer in some manner. As a method for separately displaying the right-eye video and the left-eye video, for example, a passive method is known. Such a passive three-dimensional display method will be described with reference to the drawings. FIG. 8 is a schematic view showing an example of a liquid crystal display device capable of displaying a three-dimensional image by a passive method. As shown in FIG. 8, in this method, first, the pixels constituting the flat panel display are classified into two types of pixels, a right-eye video display pixel and a left-eye video display pixel, and the right-eye pixel is displayed in the display display area. And the left-eye pixels are arranged in a pattern so that they are adjacent to each other. One group of pixels displays a right-eye image, and the other group of pixels displays a left-eye image. Also, using a linear retardation plate and a pattern retardation film (hereinafter sometimes simply referred to as a pattern retardation film) in which a patterned retardation layer corresponding to the arrangement pattern of the pixel is formed, The image and the image for the left eye are each converted into circularly polarized light. In addition, the viewer wears circularly polarized glasses that employ a right-eye lens and a left-eye lens, and the right-eye image passes only through the right-eye lens, and the left-eye image passes only through the left-eye lens. Like that. In this way, the right-eye video reaches only the right eye, and the left-eye video reaches only the left eye, thereby enabling three-dimensional display.
Such a passive method has an advantage that three-dimensional display can be easily performed by using the pattern retardation film and the corresponding circular polarizing glasses.

  As the above-mentioned pattern retardation film, for example, in Patent Document 3, a photo-alignment layer in which the alignment regulating force is controlled in a pattern on a glass substrate, and the alignment of the liquid crystalline compound formed on the photo-alignment layer are described above. A pattern retardation plate having a retardation layer (liquid crystal layer) patterned so as to correspond to the pattern of the photo-alignment layer is disclosed.

  As a resin base material used for such a retardation film, a triacetyl cellulose (TAC) base material has been mainly used from the viewpoint of optical isotropy and the like (Patent Documents 4 to 6).

  In both of the retardation film and the pattern retardation film, the liquid crystalline compounds are arranged in a certain direction by the alignment layer, and the optical axis is required to be constant throughout the film or in each pattern in the film.

JP-A-3-67219 JP-A-4-322223 JP 2005-49865 A JP 2008-122918 A JP 2002-122733 A JP 2010-85802 A

Conventionally, as a resin base material used for a retardation film, a triacetyl cellulose (TAC) base material has been mainstream.
In order to further improve the optical performance of the retardation film, the present inventor studied using an acrylic resin substrate having a smaller retardation in the film thickness direction than the TAC substrate.
However, when an acrylic resin base material was used, it was found that retardation retardation and optical axis misalignment that did not occur when a TAC base material was used may occur in the retardation film.

  The present invention has been made in view of the above circumstances, and even when an acrylic resin substrate is used, a long retardation film having no retardation unevenness or optical axis deviation, a polarizing plate without light leakage, and a display An object is to provide an image display device with excellent quality.

The retardation film according to the present invention is a long retardation film having an alignment layer and a retardation layer in this order on a long acrylic resin substrate,
The long acrylic resin substrate may have a knurling portion at the end in the short direction perpendicular to the long direction,
When the acrylic resin base material does not have the knurling portion, the entire surface of the acrylic resin base material, and when the acrylic resin base material has the knurling portion, the shorter central portion side than the knurling portion in the acrylic resin base material. When a section ab having an arbitrary width of 100 mm is taken in the short direction in the portion, the difference between the maximum value and the minimum value of the length of the long acrylic resin substrate in the section ab is 2 μm or less. And

The polarizing plate according to the present invention includes the retardation film according to the present invention on at least one surface of a polarizer.
The image display device according to the present invention includes the retardation film according to the present invention.

  According to the present invention, there is provided a long retardation film having no retardation unevenness or optical axis deviation even when an acrylic resin substrate is used, a polarizing plate without light leakage, and an image display device having excellent display quality. Can be provided.

FIG. 1 is a schematic cross-sectional view showing an example of a retardation film. FIG. 2 is a schematic cross-sectional view showing another example of the retardation film. FIG. 3 is a schematic cross-sectional view used for explaining a method for measuring the thickness of an acrylic resin substrate. FIG. 4 is a schematic cross-sectional view showing an example of a polarizing plate. FIG. 5 is a schematic cross-sectional view showing another example of a polarizing plate. FIG. 6 is a diagram showing the measurement results of the thickness distribution in the short direction of the acrylic resin substrate A used in Example 1. FIG. 7 is a diagram showing the measurement results of the thickness distribution in the short direction of the acrylic resin substrate D used in Comparative Example 1. FIG. 8 is a schematic diagram illustrating an example of a liquid crystal display device capable of displaying a three-dimensional image in a passive manner.

Hereinafter, the retardation film according to the present invention, the manufacturing method thereof, the polarizing plate, and the image display device will be described in order.
In the present invention, the optical axis means a slow axis.
In the present invention, the alignment regulating force means an interaction that aligns liquid crystal compounds in the retardation layer in a specific direction.
In the present invention, the retardation film includes a pattern retardation film unless otherwise specified.
In the present invention, curability refers to the property of solidifying through a chemical reaction.
In the present invention, (meth) acryl represents each of acryl or methacryl, and (meth) acrylate represents each of acrylate or methacrylate.

[Phase difference film]
The retardation film according to the present invention is a long retardation film having an alignment layer and a retardation layer in this order on a long acrylic resin substrate,
The long acrylic resin substrate may have a knurling portion at the end in the short direction perpendicular to the long direction,
When the acrylic resin base material does not have the knurling portion, the entire surface of the acrylic resin base material, and when the acrylic resin base material has the knurling portion, the shorter central portion side than the knurling portion in the acrylic resin base material. When a section ab having an arbitrary width of 100 mm is taken in the short direction in the portion, the difference between the maximum value and the minimum value of the length of the long acrylic resin substrate in the section ab is 2 μm or less. And

The retardation film according to the present invention will be described with reference to the drawings. 1 and 2 are schematic cross-sectional views illustrating an example of a retardation film according to the present invention.
As illustrated in FIG. 1, the retardation film 10 of the present invention includes an orientation layer 2 and a retardation layer 3 provided in this order on at least one surface side of the specific acrylic resin substrate 1. is there.
Further, as illustrated in FIG. 2, the retardation film of the present invention has an orientation different from the first orientation region 4 </ b> A and the first orientation region 4 </ b> A as the orientation layer 2 on the one surface side of the specific acrylic substrate. The second alignment region 4B having the second alignment region 4B having the property, and the liquid crystal compound is arranged in the direction different from the first retardation region 5A and the first retardation region as the retardation layer 3 The pattern retardation film 20 having the pattern retardation layer 5 having the retardation region 5B may be used.

  The retardation film of the present invention has a portion of the acrylic resin base material excluding the knurling portion, and when the section ab having a width of 100 mm is arbitrarily taken in the short direction, the long acrylic resin base material in the section ab By selecting and using an acrylic resin base material having a difference between the maximum value and the minimum value of 2 μm or less, a phase difference layer free from alignment unevenness can be formed, and there is no phase difference unevenness or optical axis misalignment. A retardation film can be obtained.

  In order to further improve the optical performance of the retardation film, the present inventor has studied to produce a retardation film using an acrylic resin substrate having a smaller retardation in the film thickness direction than the TAC substrate. However, the inventor has found that when an acrylic resin base material is used, the retardation film may cause retardation unevenness and optical axis deviation that did not occur when a TAC base material was used. Got. As a result of intensive studies, the present inventor has obtained knowledge that the cause of phase difference unevenness and optical axis deviation that occurs when an acrylic resin base material is used is caused by a minute thickness variation in the acrylic resin base material. When TAC base material is used, phase difference unevenness and optical axis deviation do not occur, and when acrylic resin base material is used, the cause of phase difference unevenness and optical axis deviation is unclear, but acrylic resin base material In the manufacturing process, thickness variation is likely to occur, and deformation is easily caused by stress generated during transportation, and therefore, it is estimated that fine variation in thickness occurs in the acrylic resin base material.

The liquid crystalline compound contained in the retardation layer forming composition undergoes a phase transition by heating and is aligned in a certain direction according to the alignment regulating force of the alignment layer. It is estimated that a relatively thin portion of the acrylic resin base material having a variation in thickness is easily affected by heat from the base material side. When the variation of the thickness of the acrylic resin base material is large, it is estimated that uneven heating of the retardation layer easily occurs according to the variation of the thickness. For this reason, it is presumed that the greater the variation in the thickness of the acrylic resin substrate, the more likely the phase difference unevenness and the optical axis deviation occur.
As a result of further study by the present inventors based on these findings, when the acrylic resin base material does not have a knurling part, the entire acrylic resin base material has a knurling part. When the section ab having a width of 100 mm is arbitrarily taken in the short direction in the short direction central portion side portion of the acrylic resin base material from the knurling part, the maximum thickness of the long acrylic resin base material in the section ab When an acrylic resin substrate having a difference between the value and the minimum value of 2 μm or less was used, it became clear that retardation unevenness and optical axis deviation were suppressed. In the acrylic resin base material in which the difference in thickness is suppressed to 2 μm or less in the section having a width of 100 mm, it is estimated that the influence of heating unevenness is reduced because the thickness gradient with respect to the short direction is reduced.
As will be described in detail later, since the acrylic resin base material has a tendency that the variation in the thickness in the short direction tends to be larger than the variation in the thickness in the long direction from the manufacturing method thereof, the acrylic resin base material has an arbitrary width of 100 mm in the short direction. When the section ab is taken, if the difference between the maximum value and the minimum value of the length of the long acrylic resin base material in the section ab is 2 μm or less, the section having an arbitrary width of 100 mm also in the longitudinal direction When the value is taken, the difference between the maximum value and the minimum value of the thickness is suppressed to 2 μm or less.
As described above, the retardation film of the present invention has the long shape in the section ab when the section ab having a width of 100 mm is arbitrarily taken in the short direction in the portion excluding the knurling part of the acrylic resin base material. By selecting and using an acrylic resin base material in which the difference between the maximum value and the minimum value of the acrylic resin base material is 2 μm or less, a retardation film free from retardation unevenness and optical axis deviation can be obtained.

  The retardation film of the present invention has at least an acrylic resin substrate, an alignment layer, and a retardation layer, and further has other layers as necessary within the range not impairing the effects of the present invention. It may be. Hereinafter, the configuration of the retardation film of the present invention will be described.

<Acrylic resin base material>
In the present invention, the acrylic resin base material may have a knurling portion at an end portion in a short direction perpendicular to the long direction, and the acrylic resin base material when the acrylic resin base material does not have the knurling portion. When the acrylic resin base material has the knurling part over the entire surface, when the section ab having a width of 100 mm is arbitrarily taken in the short direction in the short direction center part of the acrylic resin base material, A long acrylic resin substrate in which the difference between the maximum value and the minimum value of the thickness of the long acrylic resin substrate in the section ab is 2 μm or less is selected and used.

  As a material of the acrylic resin base material, for example, a base material formed from an acrylic resin obtained by polymerizing monomers such as (meth) acrylic acid ester, acrylamide, acrylonitrile, (meth) acrylic acid or a derivative thereof. Can be mentioned. Among these, in terms of transparency and weather resistance, polymethyl methacrylate, a copolymer having a methyl methacrylate unit as a main constituent, or a styrene-methyl methacrylate copolymer substrate is preferable.

The acrylic resin base material preferably has a transmittance in the visible light region of 80% or more, and more preferably 90% or more. Here, the transmittance of the long acrylic resin substrate can be measured by JIS K7361-1 (a test method for the total light transmittance of plastic-transparent material).
The acrylic resin base material preferably has a low retardation. More specifically, the in-plane retardation value (Re value) of the acrylic resin substrate is preferably in the range of 0 nm to 10 nm, more preferably in the range of 0 nm to 5 nm, and 0 nm to 3 nm. More preferably, it is in the range.

  The thickness of the acrylic resin substrate can be appropriately set within a range in which the necessary self-supporting property can be imparted to the retardation film, depending on the use of the retardation film. It is preferable that the average thickness of the acrylic resin base material is 50 μm or less from the viewpoint that transparency and high quality retardation film can be obtained. Especially, the average thickness of the acrylic resin base material is 25 to 50 μm. Is more preferable, and it is still more preferable that it is 30-40 micrometers. If it is more than the said lower limit, the retardation film without a phase difference nonuniformity or an optical axis shift will be easy to be obtained, and it is excellent in the self-supporting property of a phase difference film. Moreover, if it is below the said upper limit, while being able to obtain retardation film with high visible light transmittance and low in-plane retardation, processing, such as cutting, is easy.

(Method for evaluating thickness of acrylic resin substrate)
A method for measuring the thickness of the acrylic resin substrate in the present invention will be described with reference to the drawings. FIG. 3 is a schematic cross-sectional view used for explaining a method for measuring the thickness of an acrylic resin substrate. The cross section of the acrylic resin base material 1 in FIG. 3 is a schematic cross-sectional view in the short direction of the long acrylic resin base material.
The thickness of the long acrylic resin substrate is measured along the short direction of the long acrylic resin substrate, that is, the direction perpendicular to the flow direction of the long substrate. The thickness can be measured using a thickness measuring instrument (for example, a rotary caliper meter RC-1 manufactured by Meisho Co., Ltd.). Thickness measurement has a large effect on the measurement result even if the foreign matter is fine on the surface of the base material, so remove the foreign matter before measuring the thickness of the long acrylic resin base material. Measure from Examples of the method for removing foreign substances include a method of wiping with a cloth such as a nonwoven fabric or pulp from which fibers are not detached, and a method of removing foreign substances by blowing off air.

In order to prevent sticking of the substrates to each other at the time of winding, a knurling process such as a fine concavo-convex shape may be applied to the end in the short direction of the long acrylic resin substrate. Since the end in the short direction having such a knurling portion 21 is usually a portion where the optical function of the retardation film is not expected, in the present invention, the acrylic resin base material has the knurling portion 21. The thickness of the acrylic resin base material is evaluated at the central portion 22 in the short direction from the knurling portion 21. Accordingly, in the example of FIG. 3, the thickness measurement range is set to the central portion 22 in the short direction rather than the knurling portion 21 at the end in the short direction to which the fine uneven shape is given.
When the thickness measurement range is determined, the thickness is measured at regular intervals within the measurement range, and, for example, n measurement values h _{1 to} h _n (μm) are recorded. The measurement interval is preferably 1 mm or less and more preferably 0.5 mm or less from the viewpoint of detecting minute variations. On the other hand, the lower limit of the measurement interval may be 0.1 mm or more.

Next, a section ab having a width of 100 mm is arbitrarily taken in the short direction, and evaluation is performed based on a measurement record of the thickness in the section ab. The lower part of FIG. 3 shows a partially enlarged view of the long acrylic resin base material including the section ab. In the example of FIG. 3, x measurement values h _{k1 to} h _kx are included in the section ab. Select the maximum value and minimum value from the measured values h _{k1 to} h _kx to calculate (maximum value – minimum value), and determine whether the (maximum value – minimum value) is 2 μm or less To do. When the determination is repeated for an arbitrary section ab, and when it is determined that the difference between the maximum value and the minimum value is 2 μm or less in all the sections ab, the section ab having an arbitrary width of 100 mm is taken in the short direction The difference between the maximum value and the minimum value of the long acrylic resin substrate in the section ab is evaluated to be 2 μm or less, and can be used as the acrylic resin substrate of the present invention. On the other hand, when the difference between the maximum value and the minimum value exceeds 2 μm in at least one section ab, it is determined that the acrylic resin base material of the present invention is not suitable.

  In addition, a long acrylic resin base material is generally manufactured along the long direction by a melt extrusion molding method, wound into a roll, and stored. In the acrylic resin base material manufactured by the melt extrusion molding method, the short direction cross section at a certain point in the long direction and the short direction cross section at another point in the long direction have substantially the same cross sectional shape. In a state of being wound in a roll shape, relatively thick portions tend to overlap and relatively thin portions tend to overlap in the short direction. Therefore, the acrylic resin base material wound up in a roll shape tends to amplify the variation in thickness in the short direction, and as a result, the base material is likely to be deformed such as wrinkles. Therefore, in the present invention, the long acrylic resin base material can be evaluated for flatness of the acrylic resin base material by measuring the variation in the short length direction with an arbitrary one point in the long direction as a representative. .

  When evaluating in a state where the long acrylic resin base material is cut into a single sheet, any direction of the single acrylic resin base material is in the long acrylic resin base material. It may be unclear whether it corresponds to the long direction. In this case, the thickness in the long direction and the thickness in the direction perpendicular to the long direction in the single-piece acrylic resin base material are respectively measured, and the one with the larger variation is in the long acrylic resin base material. It is estimated that the direction was short.

  In the present invention, when the acrylic resin base material has a section ab having a width of 100 mm arbitrarily in the short direction, the difference between the maximum value and the minimum value of the long acrylic resin base material in the section ab is 2 μm. The difference between the maximum value and the minimum value of the thickness of the acrylic resin base material is preferably 1.5 μm or less from the viewpoint that retardation unevenness and optical axis deviation are less likely to occur. More preferably, it is 0 μm or less.

  In the present invention, the manufacturing method of the acrylic resin base material takes a maximum value and a minimum value of the thickness of the long acrylic resin base material in the section ab when a section ab having a width of 100 mm is arbitrarily taken in the short direction. Any method can be used as long as the difference can be set to 2 μm or less. For example, it can be manufactured with reference to Japanese Patent Application Laid-Open No. 2006-301570. Further, when a commercially available product is evaluated by the above measuring method and a section ab having a width of 100 mm is arbitrarily taken in the short direction, the maximum value and the minimum value of the thickness of the long acrylic resin base material in the section ab Those whose difference is evaluated to be 2 μm or less can be used.

<Alignment layer>
The alignment layer is formed on the alkali resin base material, and is a layer for arranging the liquid crystalline compounds contained in the retardation layer described later in a certain direction. In the present invention, the alignment layer comprises an alignment layer forming composition or a cured product thereof.

The composition for forming an alignment layer can be appropriately selected from conventionally known ones. The composition of the alignment layer forming ink is not particularly limited, and is appropriately selected depending on the combination with a means for imparting alignment regulating force.
Means for imparting alignment regulating force to the alignment layer can be conventionally known, and examples thereof include a rubbing method, a photo-alignment method, and a shaping method.
In the present invention, it is preferable to use a photoalignment composition containing a photoalignment material described later as the composition for forming an alignment layer. This is because according to the present invention, the alignment layer formed by the photo-alignment method can be made uniform.

  When the alignment layer is formed by a photo-alignment method, a photo-alignment composition containing a photo-alignment material that exhibits an alignment regulating force when irradiated with polarized light is used as the alignment layer-forming composition. The photo-alignment material may be a photodimerization type material or a photoisomerization type material. Specifically, for example, cinnamate, coumarin, benzylidene phthalimidine, benzylidene acetophenone, diphenylacetylene, stilbazole, uracil, quinolinone, maleimide, or a polymer having a cinnamylideneacetic acid derivative, among others, cinnamate, or A polymer having at least one of coumarin, a polymer having cinnamate and coumarin, and derivatives thereof are preferably used. Specific examples of such a photodimerization type material are described in, for example, JP-A-9-118717, JP-T-10-506420, JP-T2003-505561, and WO2010 / 150748. A compound can be mentioned.

  The photoalignment composition may contain a compound other than the photoalignment material as necessary. Such a compound is not particularly limited as long as it does not impair the alignment regulating force of the alignment layer. For example, a monomer or oligomer having a polymerizable group (hereinafter, simply referred to as a polymerizable monomer or a polymerizable oligomer) may be used. Preferably used.

  Examples of the polymerizable monomer or polymerizable oligomer used in the present invention include a monofunctional monomer having one (meth) acrylate group (for example, ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methylstyrene, N-vinylpyrrolidone) and polyfunctional monomers having two or more (meth) acrylate groups (for example, polymethylolpropane tri (meth) acrylate, hexanediol (meth) acrylate, triethylene (polypropylene) glycol diacrylate, tripropylene glycol) Di (meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6-hexanediol di (Meth) acrylate, neopentyl glycol di (meth) acrylate, isocyanuric acid poly (meth) acrylate (for example, isocyanuric acid EO diacrylate)) and bisphenol fluorene derivatives (for example, bisphenoxyethanol full orange (meth) acrylate, bisphenol full) Orange epoxy (meth) acrylate) and the like can be used alone or in combination of two or more.

  Further, the composition for forming an alignment layer usually contains a solvent. The solvent used in the composition for forming an alignment layer can be appropriately selected from solvents that do not react with each component in the composition and can dissolve or disperse each component. Specific examples of the solvent used in the composition for forming an alignment layer include hydrocarbon solvents such as benzene and hexane, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, tetrahydrofuran, 1,2-dimethoxyethane, propylene glycol. Ether solvents such as monoethyl ether (PGME), alkyl halide solvents such as chloroform and dichloromethane, ester solvents such as methyl acetate, ethyl acetate, butyl acetate and propylene glycol monomethyl ether acetate, N, N-dimethylformamide, etc. Amide solvents, sulfoxide solvents such as dimethyl sulfoxide, anone solvents such as cyclohexane, alcohol solvents such as methanol, ethanol, and propanol. Not shall. The solvent may be used alone or as a mixed solvent of two or more solvents.

  The alignment layer forming composition absorbs ultraviolet rays as necessary, a polymerization initiator, a polymerization inhibitor, an antioxidant for suppressing changes to oxygen, a light stabilizer for suppressing changes to light. Even if it contains an ultraviolet absorber, a viscosity modifier for adjusting the viscosity, a refractive index modifier for adjusting the refractive index, a fluorine-based or silicon-based lubricant for improving moldability, etc. good. These may be appropriately selected from conventionally known materials.

  The thickness of the alignment layer is not particularly limited as long as liquid crystal compounds in a retardation layer described later can be aligned in a certain direction, and may be set as appropriate. The thickness of the alignment layer is usually in the range of 1 nm to 1000 nm, and preferably in the range of 60 nm to 300 nm.

<Phase difference layer>
In the present invention, the retardation layer is a layer in which liquid crystal compounds are regularly arranged and phase retardation is imparted by the alignment regulating force of the alignment layer. In the present invention, the retardation layer is usually composed of a retardation layer forming composition or a cured product thereof.
The composition for forming a retardation layer usually contains a liquid crystal compound, and usually further contains a solvent. Further, other components may be included as long as the alignment of the liquid crystal compound is not inhibited.
Since a liquid crystalline compound generally has a large refractive index anisotropy, it is easy to impart a desired retardation to a retardation film.

  Examples of the liquid crystal compound include a nematic liquid crystal compound, a cholesteric liquid crystal compound, a chiral nematic liquid crystal compound, a smectic liquid crystal compound, and a discotic liquid crystal compound. Moreover, what has a polymerizable functional group in a liquid crystal molecule is used suitably. If it has a polymerizable functional group, the stability of the retardation film is improved because the liquid crystalline compound can be cross-linked by the action of radicals generated from the photopolymerization initiator by irradiation of light or electron beam. To do.

  In the present invention, it is preferable to use a liquid crystalline compound having a phase transition temperature of 40 to 115 ° C., and a liquid crystalline compound having a temperature of 60 to 90 ° C. It is more preferable to use In the present invention, the phase transition temperature of the liquid crystal compound refers to a temperature at which the liquid crystal compound changes from a so-called liquid crystal phase having optical anisotropy to an isotropic phase having no optical anisotropy.

  Specific examples of the liquid crystalline compound used in the present invention include compounds represented by the following formulas (1) to (17).

  In the present invention, the liquid crystalline compounds can be used singly or in combination of two or more.

  The composition for forming a retardation layer usually contains a solvent. The solvent used in the composition for forming a retardation layer does not react with each component used in the composition for forming a retardation layer, and can be appropriately selected from solvents that can dissolve or disperse each component. . Specifically, it can be the same as the solvent used in the composition for forming an alignment layer.

  Moreover, the composition for forming the retardation layer may further contain other components as necessary. Examples of other components include a polymerization initiator, a polymerization inhibitor, a plasticizer, a surfactant, and a silane coupling agent.

  What is necessary is just to adjust suitably content of the said liquid crystalline compound in the composition for phase difference layer formation in the range which does not impair applicability | paintability. Especially, it is preferable that the content rate of the liquid crystalline compound with respect to the said whole composition for phase difference layer formation exists in the range of 5 mass%-40 mass%, and it exists in the range of 10 mass%-30 mass%. More preferred.

  What is necessary is just to determine the thickness of a phase difference layer suitably according to the kind etc. of the said liquid crystalline compound so that a desired in-plane retardation value may be obtained. Especially, it is preferable that it exists in the range of 0.5 micrometer-4 micrometers, it is more preferable in the range of 1 micrometer-3 micrometers, and it is further more preferable in the range of 1 micrometer-2 micrometers.

<Method for producing retardation film>
A method for producing the retardation film may be a conventionally known method, and is not particularly limited. For example, the long acrylic resin base material may have a knurling portion at an end in a short direction perpendicular to the long direction, and when the acrylic resin base material does not have the knurling portion, When the acrylic resin base material has the knurling part on the entire surface of the acrylic resin base material, a section ab having a width of 100 mm is arbitrarily taken in the short direction in the short side central part of the acrylic resin base material from the knurling part. A step of preparing a long acrylic resin base material in which the difference between the maximum value and the minimum value of the long acrylic resin base material in the section ab is 2 μm or less;
An alignment layer forming step of coating the alignment layer forming composition on one side of the long acrylic resin substrate and continuously forming the alignment layer;
A method for producing a retardation film includes a retardation layer forming step of coating a retardation layer forming composition on the alignment layer and continuously forming a retardation layer.

  According to the method for producing a retardation film, a retardation film having no retardation unevenness and optical axis deviation can be obtained even when an acrylic resin substrate is used.

In the method for producing a retardation film of the present invention, first, when a section ab having a width of 100 mm is arbitrarily taken in the short direction, the maximum value and the minimum value of the thickness of the long acrylic resin base material in the section ab A long acrylic resin base material having a difference of 2 μm or less is prepared.
The said specific acrylic resin base material can be prepared by selecting according to the evaluation method of the thickness of the above-mentioned acrylic resin base material.
The thickness of the acrylic resin substrate may be measured immediately before the production of the retardation film, or may be measured during the production of the long acrylic resin substrate.

(Alignment layer formation process)
The alignment layer forming step of the present invention is a step in which an alignment layer is continuously formed by coating the alignment layer forming composition on one side of the long acrylic resin substrate.
In the alignment layer forming step, in addition to the step of coating the alignment layer forming composition on the long acrylic resin substrate, if necessary, the step of drying the coating film of the alignment layer forming composition, You may have other processes, such as a process of hardening the composition for alignment layer formation.

  The method for applying the composition for forming the alignment layer may be any method as long as the composition for forming the alignment layer can be uniformly applied onto the long acrylic resin substrate. What is necessary is just to select suitably from these coating methods. For example, gravure coating method, reverse coating method, knife coating method, dip coating method, spray coating method, air knife coating method, spin coating method, roll coating method, printing method, dip pulling method, curtain coating method, die coating method, casting Various coating mechanisms used in the method, the bar coating method, the extrusion coating method, the E-type coating method and the like can be mentioned.

In the present invention, usually, the alignment layer forming composition is continuously applied by continuously conveying the long acrylic resin substrate to the application mechanism.
As a method for transporting the long acrylic resin base material, a conventionally known method capable of continuously transporting the long base material may be appropriately selected and used. Specifically, for example, a roll toe using a winder that continuously feeds a long acrylic resin base material in a roll shape, a winder that winds up the long acrylic resin base material, and the like. In the roll system, combining various transport mechanisms such as a belt conveyor, a transport roll, and a floating transport table that transports a long acrylic resin substrate in a state of being floated by discharging and sucking air. The method to use etc. are mentioned.

The alignment layer forming step may further include a drying step for removing the solvent.
The coating film drying process may be performed using a known drying mechanism such as a heat drying mechanism, a reduced pressure drying mechanism, a gap drying mechanism, etc., and the drying temperature, drying time, and solvent atmosphere of the drying zone are adjusted to each drying mechanism. What is necessary is just to adjust a density | concentration etc. suitably. From the viewpoint of drying the coating film continuously and uniformly, it is preferably used in combination with the transport mechanism.

In the case of using the photoalignable composition as the composition for forming an alignment layer, it usually has a polarization exposure step of exposing polarized light in order to express the alignment regulating power. The polarization exposure process is usually performed after the drying process. In the case of forming a patterned alignment layer, for example, the first polarized ultraviolet ray is irradiated to the coating film of the alignment layer forming ink containing the photoalignable material through a mask having a desired pattern. Then, a polarized light exposure step of forming an alignment layer imparted with an alignment regulating force in a pattern by irradiating the second polarized ultraviolet light having a polarization axis different from the polarization axis of the first polarized ultraviolet light without passing through a mask It is good. As such a polarization exposure process, for example, a method described in JP 2012-14064 A can be used. As a polarization exposure apparatus used in the polarization exposure process, a conventionally known apparatus may be appropriately selected and used. When a patterned alignment layer is formed, for example, as described in JP-A-2012-14064 An apparatus can be used.
The polarized light exposure step is preferably used in combination with the transport mechanism.

(Retardation layer forming process)
The retardation layer forming step is a step in which the retardation layer forming composition is applied onto the alignment layer formed in the alignment layer forming step to continuously form the retardation layer.
The method for applying the composition for forming the retardation layer may be any method as long as it can accurately apply the alignment layer having a desired thickness, and can be the same method as the method for applying the composition for forming the alignment layer. .

Next, in order to remove the solvent while aligning the liquid crystal compound in the composition for forming a retardation layer in a specific direction, it usually has a drying step.
The drying step is preferably heat drying from the viewpoint of aligning the liquid crystalline compound in the retardation layer-forming coating film. The heating temperature varies depending on the liquid crystal compound used, but is preferably 0 to 10 ° C. higher than the phase transition temperature of the liquid crystal compound.

  In the case of using a composition for forming a retardation layer containing a liquid crystalline compound having a photopolymerizable functional group, it may have an exposure step of irradiating the retardation layer-forming coating film with ultraviolet rays or the like. The exposure process is usually performed after the drying process. Since the liquid crystalline compound can be crosslinked by the exposure step, the stability of the retardation film is improved. As the exposure apparatus used in the above exposure process, a conventionally known exposure apparatus may be appropriately selected and used, and examples thereof include an ultraviolet irradiation apparatus.

[Polarizer]
The polarizing plate according to the present invention includes the retardation film according to the present invention on at least one surface of a polarizer.

The polarizing plate of this invention is demonstrated with reference to FIG.4 and FIG.5. 4 and 5 are schematic cross-sectional views showing an example of the polarizing film 30 of the present invention. As shown in the examples of FIGS. 4 and 5, the polarizing film 30 of the present invention includes the retardation film 10 of the present invention on at least one surface side of the polarizer 6. As shown in the example of FIG. 4, the substrate 1 side surface of the retardation film 10 and the polarizer 6 may be in contact with each other. As shown in the example of FIG. The surface of the phase difference layer 3 side and the polarizer 6 may be in contact with each other. Although not shown, an adhesive layer or the like may be provided between the polarizer 6 and the retardation film 10.
Since the polarizing plate of the present invention has the retardation film according to the present invention having no retardation unevenness or optical axis deviation as an optical compensation film on at least one surface side of the polarizer, the polarizing plate does not leak light. it can.

  In the present invention, the polarizer can be appropriately selected from conventionally known polarizers. For example, a polyvinyl alcohol film, a polyvinyl formal film, a polyvinyl acetal film, an ethylene-vinyl acetate copolymer saponified film, which is dyed with iodine or a dye and stretched can be used.

[Image display device]
The image display device according to the present invention includes the retardation film according to the present invention.
As the image display device of the present invention, (1) a polarizing plate provided with the retardation film according to the present invention instead of the polarizing plate used in a conventionally known liquid crystal display device, and (2) a conventionally known liquid crystal display device. Instead of the pattern phase difference film used in the passive three-dimensional display type image display, those using the phase difference film according to the present invention as the pattern phase difference film, and combinations thereof can be mentioned.

  The image display device of the above (1) uses an polarizing plate provided with a retardation film having no retardation unevenness and optical axis deviation, thereby suppressing light leakage and providing an image display device with excellent display quality. it can. Further, the image display device of (2) described above uses a pattern retardation film without phase difference unevenness and optical axis deviation, so that a right-eye image can be transmitted through a left-eye lens, or a left-eye image can be transmitted. Transmission of the right-eye lens (so-called crosstalk) can be suppressed, and an image display device with excellent display quality can be obtained.

  Hereinafter, the present invention will be specifically described with reference to examples. These descriptions do not limit the present invention.

(Test example)
Four types of long acrylic resin substrates A to D having a width (length in the short direction) of 1330 mm and a length in the long direction of 50 m and having a knurling portion were prepared, and foreign matters were removed by blowing air onto the surface. Next, a thickness measuring instrument is set along the short direction along the short direction, with the length direction central portion side portion (a range excluding 30 mm at both ends in the short length direction) from the knurling portion of the long acrylic resin base materials A to D. The thickness was measured at intervals of 0.5 mm using (Marisan Co., Ltd., rotary caliper meter RC-1). The results of the acrylic resin substrates A and D are shown in FIGS. 6 and 7 as representatives. Table 1 shows the result of the maximum value of the difference between the maximum value and the minimum value when the section ab having a width of 100 mm is arbitrarily taken in the short direction.

  From the results in Table 1, the acrylic resin base materials A, B, and C had a maximum difference between the maximum value and the minimum value of 2 μm or less when the section ab having a width of 100 mm was arbitrarily taken in the short direction. It was shown that the difference between the maximum value and the minimum value of the thickness in an arbitrary section ab is 2 μm or less. On the other hand, in the acrylic resin base material D, the maximum difference between the maximum value and the minimum value exceeds 2 μm, and the difference between the maximum value and the minimum value of the thickness exceeds 2 μm in at least one section ab. It was evaluated.

(Example 1)
A photo-dimerization reaction type photo-alignment material is contained as a photo-alignment material on one surface side of the acrylic resin substrate A that is shown to have a difference between the maximum value and the minimum value of 2 μm or less in an arbitrary section ab. The composition for forming an alignment layer was applied and dried at 100 ° C. to obtain a coating film having a thickness of 150 nm after drying. The coating layer was irradiated with polarized ultraviolet rays to form an alignment layer.
Next, on the alignment layer, a retardation layer forming composition containing a polymerizable liquid crystal compound and methyl isobutyl ketone is applied and cured by irradiating with ultraviolet rays to form a retardation layer having a thickness of 1 μm. A retardation film 1 was obtained.

(Example 2)
In Example 1, instead of the acrylic resin base material A, except that the acrylic resin base material B in which the difference between the maximum value and the minimum value of the thickness in an arbitrary section ab was 2 μm or less was used, A retardation film 2 was obtained in the same manner as in Example 1.

(Example 3)
In Example 1, instead of the acrylic resin base material A, except that the acrylic resin base material C in which the difference between the maximum value and the minimum value of the thickness in an arbitrary section ab was 2 μm or less was used, A retardation film 3 was obtained in the same manner as in Example 1.

(Comparative Example 1)
In Example 1, instead of the acrylic resin substrate A, the acrylic resin substrate D evaluated that the difference between the maximum value and the minimum value of the thickness exceeds 2 μm in at least one section ab was used. In the same manner as in Example 1, a retardation film 4 was obtained.

<Evaluation of orientation and retardation>
Two polarizing plates are arranged in crossed Nicols, and the retardation films 1 to 4 obtained in Examples 1 to 3 and Comparative Example 1 are respectively put between two polarizing plates and rotated, and alignment defects are visually observed. Observed.
As a result, no alignment failure was observed in the retardation films 1 to 3 of Examples 1 to 3. On the other hand, in the retardation film 4 of Comparative Example 1, orientation failure was observed.
When a misalignment portion observed in the phase difference film 4 was measured with a phase difference measurement device (Axostep, manufactured by AXOMETRIC), the phase difference was ± 2 to 4 nm different from the normal portion. Phase difference unevenness was observed.

DESCRIPTION OF SYMBOLS 1 Acrylic resin base material 2 Alignment layer 3 Phase difference layer 4 Pattern alignment layer 4A 1st alignment area 4B 2nd alignment area 5 Pattern phase difference layer 5A 1st phase difference area 5B 2nd phase difference area 6 Polarizer 10 Phase difference film 20 Pattern retardation film 21 Knurling part 22 Short direction center part side part 30 Polarizing plate

Claims (3)

A long retardation film having an alignment layer and a retardation layer in this order on a long acrylic resin substrate,
The long acrylic resin substrate may have a knurling portion at the end in the short direction perpendicular to the long direction,
When the acrylic resin base material does not have the knurling portion, the entire surface of the acrylic resin base material, and when the acrylic resin base material has the knurling portion, the shorter central portion side than the knurling portion in the acrylic resin base material. When a section ab having an arbitrary width of 100 mm is taken in the short direction in the portion, the difference between the maximum value and the minimum value of the length of the long acrylic resin substrate in the section ab is 2 μm or less. A long retardation film.   A polarizing plate comprising the retardation film according to claim 1 on at least one surface of a polarizer.   An image display device comprising the retardation film according to claim 1.