JP2016009079A - Optical film and method for manufacturing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film having a good appearance without coating stripes and having high reliability, and a method for manufacturing the optical film.SOLUTION: An optical film 1 comprises a transparent substrate 11, an alignment film 12, and a retardation layer 13 containing a liquid crystal material, layered in this order. The retardation layer 13 is formed by incorporating a solvent having a boiling point of 100°C or higher into the liquid crystal material, applying the liquid crystal material on the alignment film 12 by a die coating process or the like, and drying the coating to obtain a residual solvent amount of 1.0 mg/mor more and 50 mg/m2 or less. The solvent having a boiling point of 100°C or higher is, for example, a ketone solvent or an aromatic solvent.

Description

  The present invention relates to an optical film in which a transparent substrate, an alignment film, and a retardation layer containing a liquid crystal material are laminated, and a method for producing the optical film.

  In recent years, optical films such as retardation films applied to flat panel displays and the like have been provided which provide desired optical characteristics by imparting a desired retardation to transmitted light by a retardation layer (for example, , See Patent Document 1). In this type of optical film, an alignment film is formed on the surface of a substrate made of a transparent film or the like, and a retardation layer is formed on the alignment film.

  The retardation layer formed on the alignment film can be formed by solidifying (curing) the liquid crystal material in a state where the liquid crystal material is aligned by the alignment regulating force of the alignment film. More specifically, this type of retardation layer is formed by laminating and coating a liquid crystal material containing a polymerizable liquid crystal monomer on the alignment film by a method such as a die coating method, and then drying by raising the temperature to the phase transition point. Then, it forms by superposing | polymerizing by ultraviolet irradiation etc. and fixing the orientation state of a liquid crystal.

  However, conventionally, when a liquid crystal material is coated on the alignment film, there is a problem that a coating stripe caused by the liquid crystal material is generated. The coating streak means a streak-like defect that occurs during a coating operation on the film surface. This coating stripe is a film that is transported due to agglomeration and solidification of the liquid crystal material used for coating, for example, adhering to the coating liquid supply part of the coating apparatus such as a die coating apparatus, and the adhering liquid crystal material. It is thought to occur as streak-like defects on the surface. Such a coating stripe deteriorates the appearance of the obtained optical film and causes a deterioration in reliability.

JP-A-10-68816

  The present invention has been proposed in view of the above-described conventional problems, and an object thereof is to provide a highly reliable optical film having no coating streak and good appearance, and a method for producing the optical film. Yes.

  This inventor repeated earnest examination in order to solve the subject mentioned above. As a result, a high-boiling solvent with low volatility is included as a solvent contained in the liquid crystal material constituting the retardation layer, and the amount of residual solvent in the retardation layer is within a predetermined range, thereby generating coating streaks. The present invention was completed by finding that the optical film had a good appearance and high reliability. That is, the present invention provides the following.

(1) In the present invention, a transparent substrate, an alignment film, and a retardation layer containing a liquid crystal material are laminated in this order, and the liquid crystal material contains a solvent having a boiling point of 100 ° C. or higher. The optical film is characterized in that a residual solvent amount in the retardation layer is 1.0 mg / m ² or more and 50 mg / m ² or less.

  (2) Further, in the invention according to (1), the solvent having a boiling point of 100 ° C. or higher is at least one selected from a ketone solvent and an aromatic solvent. It is.

  (3) The present invention is the optical film according to the invention according to (1), wherein the solvent having a boiling point of 100 ° C. or higher is two or more types of ketone solvents.

  (4) Further, the present invention provides the optical film according to any one of (1) to (3), wherein the liquid crystal material has a transition temperature from the liquid crystal phase to the isotropic phase of 80 ° C. or higher. It is.

(5) The present invention is a method for producing an optical film in which a transparent base material, an alignment film, and a retardation layer containing a liquid crystal material are laminated in this order, and the boiling point of the liquid crystal material is 100 ° C. The above-mentioned solvent is contained, the liquid crystal material is applied onto the alignment film, and dried so that the residual solvent amount is 1.0 mg / m ² or more and 50 mg / m ² or less to form the retardation layer. This is a method for producing an optical film.

  (6) Further, the present invention is the method according to (5), wherein the solvent having a boiling point of 100 ° C. or higher is two or more types of ketone solvents.

  (7) Moreover, this invention is a manufacturing method of the optical film characterized by coating the said liquid-crystal material on the said alignment film by the die-coating method in the invention which concerns on (5) or (6).

  According to the present invention, it is possible to provide a highly reliable optical film having no coating streak and good appearance, and a method for producing the optical film.

It is a cross-sectional schematic diagram which shows an example of an optical film. It is a flowchart which shows the flow of the manufacturing process of an optical film.

  Hereinafter, a specific embodiment (hereinafter referred to as “the present embodiment”) of an optical film and a manufacturing method thereof according to the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention.

<< 1. Optical film >>
FIG. 1 is a cross-sectional view schematically showing an example of the optical film 1 according to the present embodiment. As shown in FIG. 1, the optical film 1 is formed by laminating a transparent substrate 11 made of a transparent film material, an alignment film 12, and a retardation layer (liquid crystal layer) 13 containing a liquid crystal material in this order. .

In the optical film 1 according to the present embodiment, the liquid crystal material contained in the retardation layer 13 formed on the alignment film 12 contains a solvent having a boiling point of 100 ° C. or higher (high boiling point solvent). The residual solvent amount in the phase difference layer 13 is in a predetermined range. Specifically, the residual solvent amount in the retardation layer 13 is 1.0 mg / m ² or more and 50 mg / m ² or less.

Thus, the boiling point constitutes the phase difference layer 13 by the liquid crystal material containing a high-boiling solvent or 100 ° C., a range that the residual solvent amount in the phase difference layer 13 is 1.0 mg / ^{m 2} or more 50 mg / ^{m 2} or less As a result, the optical film 1 without appearance defects due to coat stripes or the like is obtained. Coat streaks appearing as appearance defects on the optical film are generated due to the liquid crystal material when the liquid crystal material is coated on the alignment film, for example. At this time, as in this embodiment, when the liquid crystal material is applied onto the alignment film, a high boiling point solvent having a boiling point of 100 ° C. or higher is contained in the liquid crystal material, and the residual solvent amount is 1.0 mg / m ^2. By forming the retardation layer 13 so as to be in the range of 50 mg / m ² or less, it is possible to prevent the occurrence of coat streaks due to the liquid crystal material, and the optical film has a good appearance.

  Hereinafter, the structure of the optical film 1 which concerns on this Embodiment is demonstrated in order.

<1-1. Transparent substrate>
The transparent substrate 11 is a transparent film material that has a function of supporting the alignment film 12 and is formed long. For example, when the optical film 1 is used for transfer, the transparent substrate 11 functions as a releasable support, supports the alignment film 12 and the retardation layer 13 for transfer, and the surface thereof. Those having an adhesive strength that can be peeled off are preferred.

  Examples of the film material constituting the transparent substrate 11 include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, and polyarylate, polyolefins such as polyethylene, polypropylene, and polymethylpentene, triacetyl cellulose, and acrylic. Based polymers. The transparent substrate 11 may be a single layer made of these materials, but may be a laminate in which two or more kinds are laminated. Moreover, when it is set as the laminated body of a some layer, the layer of the same composition may be laminated | stacked.

  Although it does not specifically limit as thickness of the transparent base material 11, For example, it is preferable to set it as the range of 20 micrometers or more and 200 micrometers or less. If the thickness of the transparent substrate 11 is less than 20 μm, the minimum necessary self-supporting property may not be imparted. On the other hand, when the thickness exceeds 200 μm, when the optical film is long, when the long optical film is cut into a single wafer optical film, the processing waste increases or is cut. Blade wear may be accelerated.

  In addition, the base material 11 may be subjected to various anti-blocking treatments. Examples of the anti-blocking process include an easy adhesion process, a process for preventing blocking by kneading a filler and the like, and a knurling process. By applying such an anti-blocking treatment to the transparent base material 11, it is possible to effectively prevent sticking of the base materials when winding the transparent base material 11, so-called blocking, and to increase the productivity of the optical film. Can be manufactured.

<1-2. Alignment film>
The alignment film 12 is obtained by applying and curing the composition for alignment film (alignment film composition) on the transparent base material 11 described above, and expresses the alignment regulating force. Here, the alignment regulating force is a function of arranging (orienting) the liquid crystal compound in a predetermined direction when a layer (retardation layer 13) made of a liquid crystal material (polymerizable liquid crystal compound) is formed on the alignment film 12. Say.

  The alignment film 12 is not particularly limited. For example, the alignment film 12 can be a vertical alignment film that homeotropically aligns the molecular axes of the liquid crystal compound molecules in the retardation layer 13 (vertical alignment). As the vertical alignment film, various vertical alignment films applied to a VA liquid crystal display device or the like can be applied. For example, a polyimide alignment film, an alignment film using an LB film, or the like can be applied.

  The alignment film 12 is not limited to a vertical alignment film, and may be an alignment film that homogeneously aligns (horizontal alignment) the molecular axes of the liquid crystal compound. An orientation film to be oriented) may be used.

  The resin used for the alignment film 12 is not particularly limited, and a cured product obtained by curing a conventionally known monofunctional or polyfunctional (meth) acrylate monomer under a polymerization initiator can be used. Specifically, as the (meth) acrylate monomer, for example, 2-ethylhexyl acrylate, cyclohexyl acrylate, diethylene glycol mono 2-ethylhexyl ether acrylate, diethylene glycol monophenyl ether acrylate, tetraethylene glycol monophenyl ether acrylate, trimethylolpropane triacrylate , Lauryl acrylate, lauryl methacrylate, isobornyl acrylate, isobornyl methacrylate, 2-phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxypropyl acrylate, benzyl acrylate, tetrahydrofurfuryl methacrylate, 2-hydroxyethyl methacrylate, benzyl methacrylate , Cyclo Hexyl methacrylate, methacrylic acid, can be exemplified urethane acrylate. In addition, as resin, one of these may be sufficient and a 2 or more types of mixture may be sufficient.

  The solvent (dilution solvent) used in the alignment film composition is not particularly limited as long as it can dissolve the alignment material at a desired concentration. For example, hydrocarbon solvents such as benzene and hexane, methyl ethyl ketone ( MEK), ketone solvents such as methyl isobutyl ketone (MIBK) and cyclohexanone (CHN), ether solvents such as tetrahydrofuran, 1,2-dimethoxyethane and propylene glycol monoethyl ether, and alkyl halide solvents such as chloroform and dichloromethane Ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, amide solvents such as N, N-dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, anone solvents such as cyclohexane, Lumpur, ethanol can be exemplified an alcohol solvent such as isopropyl alcohol. Moreover, one type of solvent may be sufficient and the mixed solvent of two or more types of solvents may be sufficient.

  Such an alignment film 12 is formed by applying a coating liquid made of an alignment film composition containing the material as described above to the substrate 11 and drying it, and then applying a predetermined curing treatment. The alignment film 12 is constituted by the cured product thus formed.

<1-3. Retardation layer (liquid crystal layer)>
The retardation layer (liquid crystal layer) 13 is composed of a liquid crystal material (liquid crystal composition) made of a polymerizable liquid crystal composition. This liquid crystal material contains a liquid crystal compound exhibiting liquid crystallinity and having a polymerizable functional group in the molecule.

(Liquid crystal compound)
The liquid crystal compound has refractive index anisotropy and has a function of imparting a desired retardation by regularly arranging the liquid crystal compound. Examples of the liquid crystal compound include materials exhibiting a liquid crystal phase such as a nematic phase and a smectic phase, but the nematic phase is easier in order to arrange regularly than liquid crystal compounds exhibiting other liquid crystal phases. It is preferable to use a material exhibiting the above liquid crystallinity. The liquid crystal compound exhibiting a nematic phase is preferably a material having spacers at both ends of the mesogen. Since the liquid crystal compound having spacers at both ends of the mesogen is excellent in flexibility, the optical film 1 can be excellent in transparency.

  Further, for example, when the alignment film 12 described above is made of a vertical alignment film and the liquid crystal compound is homeotropically aligned, the liquid crystal compound is particularly a homeotropic liquid crystal material capable of forming homeotropic alignment. It is not limited. Examples of the homeotropic liquid crystal material include materials that can form homeotropic alignment without using a vertical alignment film, and materials that can form homeotropic alignment by using a vertical alignment film. Either can be used suitably.

  The liquid crystal compound is a polymerizable liquid crystal compound having a polymerizable functional group in the molecule as described above. By having a polymerizable functional group, it is possible to polymerize and fix the liquid crystal compound, so that the alignment stability is excellent and the phase change is less likely to occur over time. The polymerizable liquid crystal compound more preferably has a polymerizable functional group capable of three-dimensional crosslinking in the molecule. By having a polymerizable functional group capable of three-dimensional crosslinking, the sequence stability can be further enhanced. Note that “three-dimensional crosslinking” means that liquid crystal molecules are polymerized three-dimensionally to form a network structure.

  Examples of the polymerizable functional group include those that polymerize by the action of ionizing radiation such as ultraviolet rays and electron beams, or heat. Examples of these polymerizable functional groups include radical polymerizable functional groups and cationic polymerizable functional groups. Representative examples of radically polymerizable functional groups include functional groups having at least one addition-polymerizable ethylenically unsaturated double bond, such as vinyl groups having or without substituents, acrylate groups (acryloyl). Group, methacryloyl group, acryloyloxy group, generic name including methacryloyloxy group) and the like. Moreover, an epoxy group etc. are mentioned as a specific example of a cationically polymerizable functional group. In addition, examples of the polymerizable functional group include an isocyanate group and an unsaturated triple bond. Among them, a functional group having an ethylenically unsaturated double bond is preferably used from the viewpoint of the process.

  The amount of the liquid crystal compound is not particularly limited as long as the viscosity of the retardation layer forming coating liquid (liquid crystal composition) can be adjusted to a desired value according to the coating method applied on the alignment film 12. The amount in the liquid crystal composition can be in the range of about 5 to 40 parts by mass. In addition, a polymeric liquid crystal compound can be used individually by 1 type or in mixture of 2 or more types.

(solvent)
The above-mentioned liquid crystal compound is usually dissolved in a solvent (diluting solvent). In the present embodiment, the liquid crystal material contains a solvent (high boiling point solvent) having a boiling point of 100 ° C. or higher as a diluting solvent for the liquid crystal compound described above.

  Examples of the high-boiling solvent having a boiling point of 100 ° C. or higher include ketone solvents such as cyclohexanone, methylcyclohexanone, methyl hexyl ketone, methyl heptyl ketone, phenylacetone, and acetylacetone, and aromatics such as toluene, xylene, ethylbenzene, cumene, and chlorobenzene. An aromatic solvent containing a ring is exemplified. These solvents can be used alone or in combination of two or more.

  These high-boiling solvents preferably have a boiling point of 110 ° C. or higher, particularly preferably 130 ° C. or higher. And it is preferable to use the 2 or more types of ketone solvent which can illustrate the above various compounds as a high boiling point solvent whose boiling point is 100 degreeC or more. As the ketone solvent, cyclohexanone can be particularly preferably used.

In the present embodiment, a high boiling point solvent having a boiling point of 100 ° C. or higher is thus contained in the liquid crystal material, and the residual solvent amount is 1.0 mg / m ² or more and 50 mg / m ² or less. The retardation layer 13 is formed. By constituting the retardation layer 13 with such a liquid crystal material containing a high-boiling solvent having a boiling point of 100 ° C. or higher, solidification of the liquid crystal material is suppressed, and the liquid crystal material is formed on the alignment film 12 by a die coating method or the like. It is possible to prevent the solidified liquid crystal material from adhering to the head portion or the like of the coating apparatus during coating. The coating streaks generated in the optical film are considered to be caused by the liquid crystal material fixed to the head part of the coating apparatus, etc., and by containing a high boiling point solvent having a boiling point of 100 ° C. or more as a solvent in the liquid crystal material, Since the solvent has low volatility, the liquid crystal material becomes wet and spreads, and solidification of the liquid crystal material can be suppressed to prevent the liquid crystal material from sticking to the head portion.

Therefore, in the optical film 1 according to the present embodiment, the liquid crystal material including the solvent having a boiling point of 100 ° C. or higher is applied on the alignment film 12 and subjected to, for example, a drying process of 80 ° C. or lower, thereby remaining. The retardation layer 13 having a solvent amount of 1.0 mg / m ² or more and 50 mg / m ² or less is formed. In such an optical film 1, no coating streaks are generated, and it has a good appearance and high reliability.

Here, when the residual solvent amount in the retardation layer 13 is less than 1.0 mg / m ² , the liquid crystal material is easily solidified when the liquid crystal material is applied onto the alignment film 12. This means that the generation of coat streaks cannot be effectively suppressed. On the other hand, if the residual solvent amount exceeds 50 mg / m ² , a hue change such as a yellow color of the film obtained by the residual solvent occurs, and a highly reliable optical film cannot be obtained.

  In addition, as a solvent, the mixed solvent of the high boiling point solvent whose boiling point mentioned above is 100 degreeC or more, and another solvent other than that may be sufficient. The other solvent is not particularly limited as long as it can uniformly disperse the liquid crystal compound when used as a mixed solvent. Examples thereof include benzene, methyl ethyl ketone, tetrahydrofuran, 1,2-dimethoxyethane, chloroform, dichloromethane, methyl acetate, ethyl acetate, cyclohexane, methanol, ethanol, isopropyl alcohol and the like. Moreover, these solvents may be used as a mixed solvent with a high boiling point solvent using one kind, or as a mixed solvent with a high boiling point solvent using two or more kinds.

The amount of the solvent in the liquid crystal material containing a high-boiling solvent having a boiling point of 100 ° C. or higher is not particularly limited, and is, for example, about 66 parts by mass to 900 parts by mass with respect to 100 parts by mass of the liquid crystal compound. Can do. If the amount of the solvent is less than 66 parts by mass, the liquid crystal compound may not be dissolved uniformly. On the other hand, when it exceeds 900 parts by mass, the solvent tends to remain, and the possibility that the residual solvent amount exceeds 50 mg / m ² increases, and the reliability decreases. Moreover, there is a possibility that uniform coating may not be possible.

  Further, when the solvent in the liquid crystal material is a mixed solvent of a high-boiling solvent having a boiling point of 100 ° C. or higher and another solvent other than that, the mixing ratio of the high-boiling solvent having a boiling point of 100 ° C. or higher is particularly limited. However, the high boiling point solvent is preferably in the range of 5 to 60 parts by weight and preferably in the range of 10 to 40 parts by weight with respect to 100 parts by weight of the mixed solvent. More preferred.

  With respect to such a liquid crystal material, the liquid crystal phase-isotropic phase transition temperature (transition temperature from the liquid crystal phase to the isotropic phase) is not particularly limited, but is preferably 80 ° C. or higher. As described above, preferably, a liquid crystal material having a liquid crystal phase-isotropic phase transition temperature of 80 ° C. or higher is applied onto the alignment film 12 by a die coating method or the like. By forming the retardation layer 13 by drying at a heating temperature of less than 0 ° C., the generation of coat streaks can be more effectively prevented.

That is, as described above, since the liquid crystal material contains a high boiling point solvent having a boiling point of 100 ° C. or higher, a liquid crystal material having a liquid crystal phase-isotropic phase transition temperature of 80 ° C. or higher is less than 80 ° C. When dried under the drying temperature condition, the retardation layer 13 can be formed such that the amount of residual solvent is more effectively in the range of 1.0 mg / m ^{2 to} 50 mg / m ² . That is, from the viewpoint of containing a high-boiling solvent having a boiling point of 100 ° C. or higher in the liquid crystal material, preferably a liquid crystal material having a liquid crystal phase-isotropic phase transition temperature of 80 ° C. or higher, for example, a drying temperature condition of less than 80 ° C. By drying with, the volatilization of the solvent can be effectively suppressed, and the residual solvent amount can be appropriately controlled. Thereby, the solidification of the liquid crystal material can be suppressed, the sticking to the coating apparatus can be prevented, and the generation of the coating lines resulting therefrom can be more effectively prevented.

(Other compounds)
In addition to the above-described components, the liquid crystal material constituting the retardation layer 13 may contain other compounds as necessary as long as the alignment order of the liquid crystal compounds is not impaired. Examples thereof include a polymerization inhibitor, a plasticizer, a surfactant, and a silane coupling agent.

  The thickness of the retardation layer 13 formed by coating the liquid crystal composition as described above on the alignment film 12 is not particularly limited, but in order to obtain appropriate alignment performance, it is 500 nm. The thickness is preferably about 2000 nm or more.

≪2. Manufacturing method of optical film >>
Next, the manufacturing method of the optical film 1 is demonstrated. FIG. 2 is a flowchart showing the flow of the manufacturing process of the optical film 1. In the following description of the manufacturing method, the case where the alignment film 12 is formed of a vertical alignment film will be described as an example, but the present invention is not limited thereto.

  As shown in FIG. 2, in the manufacture of the optical film 1, first, a transparent substrate 11 such as a PET film is provided from a long film wound around a roll (S1).

  Next, in the alignment film forming step (S2), a coating liquid (alignment film composition) for forming an alignment film is applied onto the transparent base material 11 drawn out from the roll, and after being dried, a curing process is performed. Thereby, the alignment film 12 is formed on the transparent substrate 11.

  Next, in the retardation layer forming step (S3), a coating liquid (a retardation layer forming coating liquid, hereinafter simply referred to as “liquid crystal material”) made of a liquid crystal material (liquid crystal composition) containing a liquid crystal compound is used. Then, coating is performed on the alignment film 12. Then, after performing a drying process under predetermined drying conditions, the retardation layer (liquid crystal layer) 13 is formed by curing by irradiation with ultraviolet rays or the like. In addition, you may make it perform the leveling process for making the layer thickness of the phase difference layer 13 uniform before an ultraviolet irradiation process.

Here, in the present embodiment, the liquid crystal material constituting the retardation layer 13 contains a solvent having a boiling point of 100 ° C. or higher, and a coating liquid made of such a liquid crystal material is applied based on a die coating method or the like. Coating is performed on the alignment film 12 using a processing apparatus. Then, the coating film coated on the alignment layer 12, for example, by the temperature conditions of less than 80 ° C., and dried to a residual solvent amount is 1.0 mg / ^{m 2} or more 50 mg / ^{m 2} or less of the range Thus, the retardation layer 13 is formed.

In the method of manufacturing an optical film according to the present embodiment, a liquid crystal material containing a high boiling point solvent having a boiling point of 100 ° C. or higher is used in the retardation layer forming step, and the residual solvent amount is 1.0 mg / m 2. ^The phase difference layer 13 is formed by drying so as to be in the range of ² or more and 50 mg / m ² or less, so that the liquid crystal material is suppressed from solidifying, and the liquid crystal material in the head portion or the like of the coating apparatus. Can be prevented, and the occurrence of coat streaks during the application of the liquid crystal material can be effectively prevented. Thereby, it is possible to obtain a highly reliable optical film having a good appearance and no coating stripes.

In the retardation layer forming step, the drying temperature (heating temperature) is not particularly limited with respect to the conditions for the drying treatment for the coated liquid crystal material, but it is preferably a temperature condition of less than 80 ° C. In the present embodiment, as described above, the liquid crystal phase-isotropic phase transition temperature of the liquid crystal material is preferably 80 ° C. or higher, and a high boiling point solvent having a boiling point of 100 ° C. or higher is contained in the liquid crystal material. include. From this, the liquid crystal material coated on the alignment film 12 is preferably subjected to a drying treatment under a temperature condition of less than 80 ° C., thereby more effectively eliminating the volatilization of the high-boiling solvent and remaining. The retardation layer 13 can be formed so that the amount of the solvent is in the range of 1.0 mg / m ² or more and 50 mg / m ² or less. Thereby, the solidification of the liquid crystal material can be suppressed to prevent the liquid crystal material from sticking to the coating apparatus, and the generation of coat streaks on the film resulting therefrom can be more effectively prevented.

  Further, regarding the drying treatment conditions, the drying time of the film when drying at the above-described drying temperature is not particularly limited and may be appropriately set according to the drying temperature, for example, 10 seconds to 300 seconds. It can be as follows. In the drying process, the residual solvent amount in the liquid crystal material can be controlled by adjusting the above-described drying temperature and the drying time of the film to be subjected to the drying process.

  As described above, a film in which the substrate 11 / alignment film 12 / retardation layer 13 are laminated in this order is manufactured, and the obtained film is wound up by a take-up reel or the like, and then the desired size is obtained. The cutting process is performed. Through such steps, the optical film 1 is produced.

  The method for applying the liquid crystal material on the alignment film 12 is not particularly limited. For example, a die coating method, a gravure coating method, a reverse coating method, a knife coating method, a dip coating method, a spray coating method, An air knife coating method, a spin coating method, a roll coating method, a printing method, a dipping and lifting method, a curtain coating method, a casting method, a bar coating method, an extrusion coating method, an E-type coating method, and the like can be used.

  Among them, it is particularly preferable to apply the liquid crystal material on the alignment film 12 by a die coating method in that the liquid crystal material can be applied more uniformly.

  Here, the die coating apparatus for coating by the die coating method is generally a backup roll that winds and conveys a sheet-like transparent base material around a part of the outer peripheral surface, and a die head that is disposed opposite to the backup roll. It has. The die head includes a discharge slit for discharging the coating liquid and lips formed on both sides of the tip of the discharge slit, and the lip has, for example, a tip edge portion formed in an arc shape in a side view. In such a die coating apparatus, in particular, the coagulated and solidified liquid crystal material tends to adhere to the lip surface of the die head. In this regard, according to the method of manufacturing an optical film according to the present embodiment, as described above, the solidification of the liquid crystal material can be suppressed, and the fixation to the lip or the like can be effectively prevented. As a result, it is possible to prevent the generation of coat streaks on the obtained optical film, so that the effect is particularly high when the die coating method is used, and the production method is used more suitably than the method using the die coating method. be able to.

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

<< Production of optical film >>
[Example 1]
Using a PET substrate having a thickness of 38 μm, a composition for vertical alignment film was coated on one side so as to have a film thickness of 3 μm, and an alignment film was prepared by irradiating polarized ultraviolet rays of 20 mJ / cm ² . In addition, as the composition for vertical alignment films, 2-phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, dipentaerythritol triacrylate, and bis (2-vinyloxyethyl) ether are 1: 1: 4: 5. A mixture in which LUCIRIN TPO was added at a rate of 4% as a polymerization initiator was used.

  Subsequently, a liquid crystal composition (liquid crystal material) containing a photopolymerizable nematic liquid crystal (manufactured by Merck & Co., RMM28B) was applied onto the alignment film by die coating. Here, in the liquid crystal material, as a solvent, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone (CHN) having a boiling point of 155 ° C. in a weight ratio (MEK: MIBK: CHN) of 35 are used. : A mixed solvent mixed at a ratio of 30:35 was used. And the liquid crystal material prepared so that solid content might be 1-1.5g was apply | coated on the alignment film so that an application quantity might be 4-5g (wet).

  And after apply | coating the liquid-crystal material on alignment film, the drying temperature was 75 degreeC and the drying process was performed for 120 second. Then, it superposed | polymerized by ultraviolet irradiation (UV) irradiation, the 1-micrometer-thick retardation layer was formed, and the optical film was obtained.

Here, with respect to the obtained optical film, the residual solvent amount in the retardation layer was measured by a gas chromatography method and found to be 4.2 mg / m ² .

[Example 2]
In Example 2, a liquid crystal material was applied on the alignment film, and then a drying process was performed at a drying temperature of 75 ° C. and a drying time of 90 seconds. A layer was formed to obtain an optical film.

Here, with respect to the obtained optical film, the residual solvent amount in the retardation layer was measured by a gas chromatography method and found to be 10.5 mg / m ² .

[Example 3]
In Example 3, a liquid crystal material was applied onto the alignment film, and then a drying process was performed at a drying temperature of 75 ° C. and a drying time of 60 seconds. A layer was formed to obtain an optical film.

Here, the amount of residual solvent in the retardation layer of the obtained optical film was measured by a gas chromatography method, and found to be 23.5 mg / m ² .

[Example 4]
In Example 4, a liquid crystal material was applied on the alignment film, and then a drying process was performed at a drying temperature of 75 ° C. and a drying time of 30 seconds. A layer was formed to obtain an optical film.

Here, with respect to the obtained optical film, the residual solvent amount in the retardation layer was measured by a gas chromatography method and found to be 45.2 mg / m ² .

[Comparative Example 1]
In Comparative Example 1, photopolymerizable nematic liquid crystal (manufactured by Merck, RMM28B) is contained as a liquid crystal material, and methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) are mixed at a weight ratio (MEK: MIBK) of 50: A mixed solvent mixed at a ratio of 50 was used. Then, a retardation layer having a thickness of 1 μm is formed in the same manner as in Example 1 except that this liquid crystal material is applied onto the alignment film, and then subjected to a drying treatment at a drying temperature of 75 ° C. and a drying time of 120 seconds. To form an optical film.

Here, about the obtained optical film, when the amount of residual solvents in a phase difference layer was measured by the gas chromatography method, it was 0.6 mg / m < ² >.

[Comparative Example 2]
In Comparative Example 2, a phase difference of 1 μm in thickness was obtained in the same manner as in Example 1 except that after the liquid crystal material was applied on the alignment film, the drying treatment was performed at a drying temperature of 30 ° C. and a drying time of 10 seconds. A layer was formed to obtain an optical film.

Here, with respect to the obtained optical film, the amount of residual solvent in the retardation layer was measured by gas chromatography, and found to be 76.5 mg / m ² .

≪Evaluation≫
About the optical film obtained by each Example and the comparative example, based on the following method, the grade of a hue change, the presence or absence of generation | occurrence | production of a coating stripe, and the optical characteristic (presence or absence of retardation drop generation) were evaluated. Table 1 below shows the evaluation results.

(About hue change)
For evaluation of hue change, first, the surface of the phase difference layer of the obtained optical film was measured using V-7100 manufactured by JASCO Corporation, and set as a value and b value before standing. Next, the a value and the b value were measured after the heat treatment at 85 ° C. for 1000 hours to obtain the values a and b after the heat treatment. The values of Δa and Δb were determined from the values determined by these by the following hue change equation. The a value and the b value are based on the CIE 1976 color system and represent the perceptual chromaticity index.
Hue change formula Δa = 85 ° C., a value after standing at 1000 hrs-a value before standing at left Δb = 85 ° C., b values after standing at 1000 hrs-b value before standing

(About the presence or absence of coat lines)
Regarding the evaluation of the occurrence of coat streaks, the obtained optical film was visually inspected for the presence or absence of streaks on the film surface. As shown in Table 1 below, the case where the coat stripe was confirmed was set as “Yes”, and the case where the coat stripe was not confirmed was set as “None”.

(About optical properties)
The optical properties were evaluated based on the presence or absence of retardation drop. Specifically, the MO series 25 μm thickness manufactured by Lintec Corporation is bonded to a 3 mm square glass having a thickness of 1.1 mm, and the optical film prepared on the PET substrate is further bonded to an adhesive glass. Was peeled off. And the retardation value (Rth) of the optical film was measured using the phase difference measuring apparatus (The Oji Scientific Instruments company make, KOBRA-WR). Next, the retardation value (Rth) after standing at 85 ° C. for 24 hours was measured. And the change ((DELTA) Rth) of the retardation value before and behind neglecting processing was evaluated. As shown in Table 1 below, when the change in retardation value was ΔRth <10 nm, “◯” was given, and the optical properties were evaluated as good.

As shown in the results of Table 1, a liquid crystal material containing a solvent having a boiling point of 100 ° C. or higher as a solvent for dissolving the liquid crystal compound was applied onto the alignment film, and the residual solvent amount was 1.0 mg / m 2. ^In the optical films (Example 1 to Example 4) that are dried so as to be in the range of ^{2 to} 50 mg / m ² and formed with a retardation layer, the occurrence of coat streaks is not confirmed, and the reliability has a good appearance. It was highly probable. This is because the liquid crystal material used in the examples contains a high boiling point solvent and has the property of remaining in the retardation layer moderately, so that it has the property of spreading very wet. This is considered to be because solidification (aggregation) could be suppressed and adhesion to the die head of the die coating apparatus (adhesion of the aggregated liquid crystal material) could be prevented.

  Further, it was found that the optical films obtained in these examples had a good appearance with almost no hue change, and further, retardation retardation did not occur and intended optical characteristics could be maintained.

On the other hand, in Comparative Example 1 in which cyclohexanone was not included as a solvent, the residual solvent amount in the retardation layer was 0.6 mg / m ² , and coating streaks were observed on the film surface, and the appearance was poor and the reliability was low. became. This is because the liquid crystal material is very easy to solidify, so that the liquid crystal material is fixed to the die head of the die coater, resulting in coating streaks on the film when the liquid crystal material is applied. It is thought that I was allowed to.

Moreover, in the optical film of Comparative Example 2, since the liquid crystal material containing a high-boiling solvent was used, the optical film had a property of spreading and wetting, so that the generation of coat streaks could be prevented. However, since the residual solvent amount was 76.5 mg / m ² , the film turned yellow (with a hue change), and the appearance was not good and reliable.

DESCRIPTION OF SYMBOLS 1 Optical film 11 Transparent base material 12 Orientation film 13 Retardation layer (liquid crystal layer)

Claims (7)

A transparent base material, an alignment film, and a retardation layer containing a liquid crystal material are laminated in this order,
The liquid crystal material contains a solvent having a boiling point of 100 ° C. or higher,
The optical film, wherein a residual solvent amount in the retardation layer is 1.0 mg / m ² or more and 50 mg / m ² or less.   2. The optical film according to claim 1, wherein the solvent having a boiling point of 100 ° C. or more is at least one selected from a ketone solvent and an aromatic solvent.   The optical film according to claim 1, wherein the solvent having a boiling point of 100 ° C. or more is two or more types of ketone solvents.   4. The optical film according to claim 1, wherein a transition temperature from the liquid crystal phase to the isotropic phase of the liquid crystal material is 80 ° C. or more. A transparent base material, an alignment film, and a retardation layer containing a liquid crystal material are laminated in this order, and a method for producing an optical film,
Including a solvent having a boiling point of 100 ° C. or higher in the liquid crystal material,
An optical film characterized in that the liquid crystal material is applied onto the alignment film and dried so that the residual solvent amount is 1.0 mg / m ² or more and 50 mg / m ² or less to form the retardation layer. Manufacturing method.   The method for producing an optical film according to claim 5, wherein the solvent having a boiling point of 100 ° C. or higher is two or more types of ketone solvents.   The method for producing an optical film according to claim 5 or 6, wherein the liquid crystal material is applied onto the alignment film by a die coating method.

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