JP2018092031A - Optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film including a retardation layer having a good orientation.SOLUTION: An optical film includes: a substrate made of polycarbonate having reverse wavelength dispersion; an intermediate layer laminated on one surface of the substrate; and a retardation layer laminated on the intermediate layer and containing liquid crystal. The intermediate layer contains an ultraviolet-curing polyfunctional monomer whose average molecular weight is 400 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical film having a retardation layer made of liquid crystal.

  As an optical film applied to an image display device or the like, there is an optical film that imparts a desired retardation to incident light by a retardation layer (for example, Patent Document 1). In such an optical film, a retardation layer is produced by laminating a liquid crystal material on one surface side of a substrate.

Although the liquid crystal material applied to such a retardation layer usually has a positive wavelength dispersion characteristic, in recent years, a liquid crystal material having a wavelength dispersion characteristic (reverse wavelength dispersion characteristic) opposite to this has been applied. Has been proposed (for example, Patent Documents 2 and 3). Here, the reverse wavelength dispersion characteristic is a wavelength dispersion characteristic in which the phase difference in transmitted light is smaller as the wavelength is shorter, more specifically, retardation at a wavelength of 450 nm (Re ₄₅₀ ) and retardation at a wavelength of 550 nm ( Re ₅₅₀ ) is a chromatic dispersion characteristic in which Re ₄₅₀ <Re ₅₅₀ .

In the image display device, a retardation layer having a positive A characteristic, a retardation layer having a negative A characteristic, a retardation layer having a positive C characteristic, and a retardation layer having a negative C characteristic are provided alone. Alternatively, a method for improving various optical characteristics such as viewing angle characteristics and color has been proposed in combination as necessary.
Here, the characteristics of positive A are the refractive index in the X-axis direction along the layer surface is Nx, the refractive index in the Y-axis direction perpendicular to the X-axis in the direction along the layer surface is Ny, and the refractive index in the layer thickness direction. When Nz, Nx> Ny≈Nz, and the optical axis is in the Nx direction.
The characteristic of negative A is a relationship of Nz≈Nx> Ny and has a feature that the optical axis is in the Ny direction.
The characteristics of the positive C have a relationship of Nz> Nx≈Ny and have a feature that the optical axis is in the Nz direction.
The characteristic of negative C is a relationship of Nx≈Ny> Nz and has a feature that the optical axis is in the Nz direction.

  For example, Patent Document 4 discloses a technique relating to optical compensation of an IPS liquid crystal display device using a retardation layer having such retardation characteristics.

JP-A-10-68816 U.S. Pat. No. 8,119,026 Japanese translation of PCT publication No. 2010-52892 JP-T 2006-520008

  However, in the past, when a liquid crystal layer was laminated on the surface of the substrate, the alignment of the liquid crystal was sometimes inhibited.

  An object of this invention is to provide the optical film provided with the phase difference layer which has favorable orientation in view of the said problem.

  As a result of intensive studies, the present inventor has determined that the base material is made of polycarbonate having reverse wavelength dispersion characteristics, and that a layer having positive C characteristics due to liquid crystal having good orientation is laminated on the base material, the orientation of the liquid crystal is changed. Obtained the knowledge to inhibit. This is considered due to the fact that the surface of the polycarbonate is dissolved in the liquid crystal solvent. The solvent of the liquid crystal may be changed to a solvent that does not dissolve the polycarbonate, but the solvent is limited to some extent in consideration of the solubility and orientation of the liquid crystal. Accordingly, the inventor completed the present invention by solving the problem by providing an intermediate layer as a layer (barrier layer) that barriers the liquid crystal solvent.

  One aspect of the present invention includes a base material made of polycarbonate having reverse wavelength dispersion, an intermediate layer laminated on one surface of the base material, a retardation layer containing a liquid crystal laminated on the intermediate layer, The intermediate layer is an optical film containing an ultraviolet curable polyfunctional monomer having an average molecular weight of 400 or less.

  In this optical film, the polyfunctional monomer can have a structure capable of hydrogen bonding. Further, the intermediate layer may contain a leveling agent.

  The liquid crystal of the optical film may be made of a polymerizable liquid crystal composition.

  Further, the intermediate layer can be configured not to contain a solvent for dissolving the polycarbonate.

  ADVANTAGE OF THE INVENTION According to this invention, the optical film which has the reverse dispersion performance provided with the phase difference phase containing the liquid crystal which shows favorable orientation can be provided. Furthermore, it becomes possible to effectively adhere the base material made of polycarbonate and the retardation layer.

1 is a diagram illustrating an example of a layer configuration of an optical film 10. FIG. It is a figure explaining the layer structure of the liquid crystal display device 1 to which the optical film 10 is applied.

  Hereinafter, the present invention will be described in detail with specific embodiments. However, the present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.

FIG. 1 is a diagram illustrating a layer configuration of an optical film 10 according to one embodiment. In this embodiment, for example, with respect to the image display device, various optical characteristics can be improved by arranging the optical film 10 together with various other optical films on the liquid crystal display panel. Examples of the optical characteristics include an improvement in viewing angle characteristics, optical compensation for reducing light leakage in an oblique direction, and color correction.
As can be seen from FIG. 1, the optical film 10 of this embodiment includes a base material 11, a retardation layer 12, and an intermediate layer 13.

  The base material 11 is made of a film that serves as a base material for the retardation layer 12 and exhibits reverse wavelength dispersion characteristics. Specifically, polycarbonate is used as the material. Thereby, the optical anisotropy is small, and the optical film 10 as a whole can be suitably functioned as a film having a positive C characteristic.

  The retardation layer 12 is a layer having a positive C characteristic and carrying an optical function, and is a liquid crystal material used for producing retardation layers of various optical films, and has a chromatic dispersion characteristic such as a reverse dispersion characteristic. It is comprised by the polymeric liquid crystal composition containing a certain liquid crystal compound. In the retardation layer 12, the liquid crystal compound is vertically (homeotropic) aligned.

  Specifically, the polymerizable liquid crystal composition exhibits liquid crystallinity and contains a liquid crystal compound (rod-like compound) having a polymerizable functional group in the molecule.

  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 to arrange regularly than liquid crystal compounds exhibiting other liquid crystal phases. It is more preferable to use the liquid crystal compound shown. As the liquid crystal compound exhibiting a nematic phase, it is preferable to use a material having spacers at both ends of the mesogen. A liquid crystal compound having spacers at both ends of the mesogen is excellent in flexibility.

  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 alignment 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 radically polymerizable functional groups. Representative examples of radically polymerizable functional groups include functional groups having at least one addition-polymerizable ethylenically unsaturated double bond, and specific examples include vinyl groups and acrylate groups with or without substituents. (Generic name including acryloyl group, methacryloyl group, acryloyloxy group, methacryloyloxy group) and the like.

  The liquid crystal compound is particularly preferably one having a polymerizable functional group at the terminal. By using such a liquid crystal compound, for example, it can be polymerized three-dimensionally to form a network structure, so that it has stability and excellent optical characteristics. A film can be formed.

  The content of the liquid crystal compound in the polymerizable liquid crystal composition is not particularly limited as long as the viscosity of the polymerizable liquid crystal composition can be adjusted to a desired value according to the coating method applied to the intermediate layer 13. The liquid crystal composition preferably contains 5 to 40 parts by mass, and more preferably contains 10 to 30 parts by mass. If the amount of the liquid crystal compound is less than 5 parts by mass, there is a possibility that the incident light to the retardation layer 12 cannot be properly aligned because the content is too small. On the other hand, when it exceeds 40 mass parts, since the viscosity of the polymeric liquid crystal composition will become high too much, workability | operativity will worsen.

  In addition, a liquid crystal compound can be used individually by 1 type or in mixture of 2 or more types.

The liquid crystal compound described above is usually dissolved in a solvent. As the solvent, it is necessary to be able to uniformly disperse the liquid crystal compound described above, but a known solvent can be used. Examples of such solvents include hydrocarbons such as toluene and xylene, ketones such as acetone, methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone, ethers such as tetrahydro, 1-methoxy-2-propanol, 1-methoxypropyl-2- Examples include glycol ethers such as acetate, and esters such as methyl acetate, ethyl acetate, and butyl acetate.
In this embodiment, the influence of the solvent on the base material 11 can be prevented by the intermediate layer 13 (the surface of the base material 11 can be prevented from being dissolved by the solvent for the liquid crystal layer 12), and the orientation of the liquid crystal Is not hindered, so that the orientation can be improved.

  The content of the solvent in the polymerizable liquid crystal composition is preferably 66 parts by mass to 900 parts by mass with respect to 100 parts by mass of the liquid crystal compound. 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 mass parts, a part of solvent may remain and reliability may fall, and it may be unable to apply uniformly.

  The polymerizable liquid crystal composition can contain other additives as necessary. The other compound is not particularly limited as long as it does not impair the arrangement order of the liquid crystal compound described above, and examples thereof include a plasticizer, a surfactant, and a silane coupling agent.

  The intermediate layer 13 is a layer disposed between the base material 11 and the retardation layer 12. When the retardation layer 12 is formed by the intermediate layer 13, the solvent contained in the composition prevents dissolution of the surface of the base material 11, thereby improving the orientation. When the surface of the base material 11 is dissolved, the orientation is lowered, and the performance of the retardation layer 12 may not be fully exhibited. The intermediate layer 13 prevents this. That is, the intermediate layer 13 is a layer that functions as a barrier layer.

The material constituting the intermediate layer 13 can be dammed without causing the solvent contained in the composition forming the retardation layer 12 to permeate the base material 11 from the viewpoint of exhibiting its function (high barrier property). Is.
In addition to this, the interlayer 13 and the base material 11 and the so-called interlayer adhesion of the interlayer 13 and the retardation layer 12 are also required to be high.

  From the above viewpoint, an ultraviolet curable resin is preferable as a material constituting the intermediate layer 13. Thereby, necessary barrier properties and adhesion with other layers can be ensured. Further, since the ultraviolet curable resin is excellent in moldability, productivity can be increased.

  Therefore, the composition constituting the intermediate layer 13 can be a solventless ultraviolet curable resin or a solvent containing an ultraviolet curable monomer in a solvent. However, from the viewpoint of preferably reducing the viscosity from the viewpoint of coating properties (coating properties), a composition containing an ultraviolet curable monomer in the solvent is preferable.

  Although a well-known thing can be applied as an ultraviolet curable monomer, it is preferable that it is a polyfunctional monomer whose average molecular weight is 400 or less from a viewpoint of improving the above-mentioned performance. Here, “polyfunctional” means a trifunctional or higher functional group. Examples of such polyfunctional monomers include neopentyl glycol diacrylate (average molecular weight 212), trimethylolpropane triacrylate (average molecular weight 286), pentaerythritol triacrylate (average molecular weight 298), pentaerythritol tetraacrylate (average molecular weight 352). ) And glycerin triacrylate (average molecular weight 254).

  Among these, those capable of hydrogen bonding are more preferable, and from this viewpoint, pentaerythritol triacrylate is more preferable. This enables hydrogen bonding by the structure having OH at the terminal.

  The solvent for the ultraviolet curable monomer is preferably an alcohol. An example of this is isopropyl alcohol (IPA). Moreover, the material which does not melt | dissolve the polycarbonate of a base material as another solvent can be used.

Furthermore, this composition may contain a polymerization initiator and a leveling agent. The polymerization initiator can efficiently cure the composition. Examples of such a polymerization initiator include Irgacure 127 and Irgacure 907 (BASF Japan Ltd.).
On the other hand, the leveling agent functions as a surface conditioner, and the planarization and hydrophobicity are improved, and the orientation of the liquid crystal in the retardation layer can be further enhanced.

  The optical film 10 as described above has a positive C characteristic as a whole, and has a wavelength dispersion characteristic of reverse wavelength dispersion. As the wavelength λ increases, the phase difference (Reθ (λ)) of the oblique incident angle θ (θ> 0) increases, thereby functioning as a film exhibiting reverse dispersion characteristics. From this, the image display apparatus provided with this optical film can ensure desired optical characteristics in a wide wavelength band.

By providing the intermediate layer 13, dissolution of the surface of the base material 11 when the retardation layer 12 is laminated and formed in the manufacturing process is prevented, so that the liquid crystal orientation of the retardation layer 12 is better. Can be. Further, conventionally, in order to suppress the dissolution (control to a predetermined range), it was necessary to dry the composition constituting the retardation layer immediately after coating, but in the present embodiment, it is not necessary, It can be said that productivity is good.
Thereby, it becomes possible to effectively adhere the substrate and the retardation layer, and provide an optical film exhibiting good orientation.

  Next, the manufacturing method of the optical film 10 is demonstrated. For example, the optical film 10 includes a base material supplying step, an intermediate layer forming step, and a retardation layer forming step.

  In the base material supplying step, the base material 11 made of polycarbonate is provided by a roll.

  In the intermediate layer forming step, the intermediate layer 13 is formed on one surface of the substrate 11. Specifically, it is as follows.

  The base material 11 is pulled out from the supply reel, and the intermediate layer forming composition is laminated on the base material 11. The method for laminating the composition on the substrate 11 is not particularly limited, and examples thereof include a die coating method, a gravure coating method, a reverse coating method, a knife coating method, a dip coating method, a spray coating method, and an air knife coating. Methods such as spin coating, roll coating, printing, dipping and pulling up, curtain coating, casting, bar coating, extrusion coating, and E-type coating can be used.

Then, the laminated composition is cured by irradiating with ultraviolet rays to obtain the intermediate layer 13. Low-pressure mercury lamps (sterilization lamps, fluorescent chemical lamps, black lights), high-pressure discharge lamps (high-pressure mercury lamps, metal halide lamps), short arc discharge lamps (ultra-high-pressure mercury lamps, xenon lamps, mercury xenon) Lamp) or the like. Among these, a metal halide lamp, a xenon lamp, a high-pressure mercury lamp, and the like can be preferably used. The wavelength of the ultraviolet ray is appropriately set according to the material constituting the composition, and specifically, the irradiation light having a wavelength of 210 nm to 380 nm, preferably 230 nm to 380 nm, more preferably 250 nm to 380 nm. Is preferably used. The irradiation amount of ultraviolet rays as (integrated light quantity) is not particularly limited, for ^example, is preferably in the range of ^{100mJ / cm 2 ~1500mJ / cm 2} , within a range of 100mJ / cm ² ~800mJ / cm 2 It is more preferable that

  In the phase difference layer forming step, the phase difference layer 12 is formed on the side of the intermediate layer 13 opposite to the side on which the substrate 11 is disposed. The retardation layer can be formed in the same manner as the intermediate layer described above.

  Thus, when producing the optical film 10, it is not always necessary to include a step of drying, and productivity can be improved and the reliability of orientation can be increased.

  Next, an optical functional laminate to which the above-described optical film 10 is applied will be described. In this optical function laminated body, it can arrange | position by including the optical film 10 in one of the structures of the various optical functional laminated bodies arrange | positioned at an image display panel.

  As a more specific example, when applied to a liquid crystal display device provided with the optical film 10, as an optical functional laminate, a film made of a linearly polarizing plate disposed on the exit surface of the liquid crystal display panel, the linearly polarizing plate and a color filter are used. Various configurations such as an integrated film can be widely applied.

  FIG. 2 is a diagram illustrating a layer configuration of the liquid crystal display device 1 including the optical film 10. In this liquid crystal display device 1, the optical functional laminate 6 includes an optical film 10 in the optical functional laminate 6 including a polarizer 7 for linearly polarizing the liquid crystal display panel 3 disposed on the exit surface side. It is an example used for optical compensation.

  The liquid crystal display device 1 is an IPS liquid crystal display device (IPS-LCD), and a liquid crystal display panel 3 is disposed in front of the backlight 2.

  The liquid crystal display panel 3 is provided with a liquid crystal cell 5 made of IPS liquid crystal, and a linearly polarizing plate 4 is provided on the backlight 2 side of the liquid crystal cell 5 with, for example, a pressure-sensitive adhesive layer (not shown). The linearly polarizing plate 4 is configured by sandwiching a polarizer, which is a liquid crystal layer serving as a linearly polarizing plate, between two substrates made of a transparent film.

  In the liquid crystal display panel 3, the optical functional laminate 6 is disposed on the exit surface of the liquid crystal cell 5. The optical functional laminate 6 includes an optical film 10 as an optical compensation layer for optical compensation, a polarizer 7, and a base material (protective film) 8 that is a surface material. As the base material 8, a transparent film such as TAC is applied, and a polarizer 7 (liquid crystal layer) as a linear polarizing plate is provided similarly to the polarizer of the linear polarizing plate 4.

More specifically, the optical functional laminate 6 is laminated in the order of the substrate 11, the intermediate layer 13, the retardation layer 12, the adhesive layer (not shown), the polarizer 7, and the substrate 8 from the liquid crystal cell 5 side. Yes. Thus, the optical film 10 constituting the optical functional laminate 6 functions as a layer having positive C characteristics, and does not include a conventional vertical alignment film on the substrate.
Here, the adhesive layer is laminated on the optical film 10, and the polarizer 7 is attached to the optical film 10 through the adhesive layer. The adhesive layer can be formed mainly by curing a two-component adhesive composition comprising a main agent and a curing agent. Although it does not specifically limit as a main ingredient, For example, it can be set as a UV contact bonding layer using an ultraviolet curable resin. More specifically, examples of ultraviolet curable resins include acrylic resins, silicone resins, ester resins, urethane resins, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, polyfunctional Urethane acrylate or the like is preferably used. Among these, it is particularly preferable to use dipentaerythritol hexaacrylate.

  The polarizer 7 is bonded to an adhesive layer, and is configured to be affixed to the optical film 10 through the adhesive layer. The polarizer 7 is not particularly limited and a known one can be used. For example, a dichroic material such as iodine or a dichroic dye is adsorbed on a hydrophilic polymer film such as a polyvinyl alcohol (PVA) film. And polyene-based oriented films such as those obtained by uniaxial stretching, polyvinyl alcohol dehydrated products, and polyvinyl chloride dehydrochlorinated products.

<Production of optical film>
[Example 1]
(Preparation of base material)
A polycarbonate substrate (manufactured by Teijin Limited) showing reverse wavelength dispersion characteristics was prepared as the substrate.

(Formation of intermediate layer)
Pentaerythritol triacrylate (average molecular weight 298) as an ultraviolet curable monomer was dissolved at 25% by mass in isopropyl alcohol as a solvent to prepare a composition for the intermediate layer. In addition, the composition contained 4.0% by mass of a polymerization initiator (Irgacure 907, BASF Japan Ltd.).
And this composition was applied to one side of the base material so that the layer thickness after curing would be 1 μm, and an intermediate layer was formed by curing by irradiating with an ultraviolet ray of 67 mJ / cm ² . .

(Formation of retardation layer)
A liquid crystal compound (manufactured by DIC Corporation) showing a nematic phase using an organic solvent MIBK (content of 100% by mass in the solvent) as a solvent, and 2-hydroxy-3-phenoxy which is an ultraviolet curable monomer as an additive A polymerizable liquid crystal composition was prepared by dissolving propyl acrylate (M600A, manufactured by Kyoeisha Chemical Co., Ltd.) to a solid content ratio of 24%. In addition, the monomer as an additive was contained so that it might become 2 mass% in solid content.
The prepared polymerizable liquid crystal composition was applied to the intermediate layer formed as described above by a die coating method.

Thereafter, the coating film was cured by irradiating with an ultraviolet ray having a dose of 400 mJ / cm ² . As a result, an optical film in which the retardation layer was laminated on the base material made of polycarbonate via the intermediate layer was obtained.

[Example 2]
In Example 2, in addition to Example 1, the composition for the intermediate layer contained 0.1% by mass of a leveling agent (surface conditioning agent, BYK Japan Japan Co., Ltd., BYK-UV3576). Others are the same as in the first embodiment.

[Comparative Example 1]
In Comparative Example 1, 1,6-hexanediol diacrylate (average molecular weight 226, bifunctional) is used as the UV curable monomer for the intermediate layer, and a mixed liquid of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) is used as the solvent. It was. Further, 0.05% by mass of a leveling agent (F554, DIC Corporation) was contained. Others are the same as in the first embodiment.

[Comparative Example 2]
In Comparative Example 2, dipentaerythritol hexaacrylate (average molecular weight 578) was used as the UV curable monomer for the intermediate layer. Others are the same as in the first embodiment.

<Evaluation>
(Adhesion evaluation)
Interlayer adhesion was evaluated for optical films according to Examples and Comparative Examples. Evaluation of adhesion was performed by carrying out a crosscut (100 squares) according to JIS K5400-8.5 method using a mending tape (manufactured by Sumitomo 3M). The results indicate that 100/100 has the highest adhesion, and the adhesion decreases as the number of molecules decreases toward 0/100.

(Orientation evaluation)
The orientation of the optical films according to Examples and Comparative Examples was evaluated. Evaluation of orientation confirms that the dark state does not change to the bright state due to the in-plane retardation, that is, the liquid crystal compound is oriented vertically, by rotating the optical film under polarizing cross Nicol conditions. Was done. At this time, even when the optical film was rotated, it was always in a dark state, and when the orientation was good, “◯”, and when the light state appeared during rotation and the orientation was not good, “x”.

<Result>
The results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

  As can be seen from Table 1, both adhesion and orientation can be obtained by Example 1 and Example 2. In addition, about orientation, Example 2 using a leveling agent was still more favorable compared with the other examples.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Surface light source device 3 Liquid crystal display panel 4 Linear polarizing plate 5 Liquid crystal cell 6 Optical function laminated body 7 Polarizer 8 Base material 10 Optical film 11 Base material 12 Phase difference layer 13 Intermediate | middle layer (barrier layer)

Claims (5)

A substrate made of polycarbonate having reverse wavelength dispersion;
An intermediate layer laminated on one side of the substrate;
A retardation layer containing liquid crystal laminated on the intermediate layer,
The intermediate layer is an optical film containing an ultraviolet curable polyfunctional monomer having an average molecular weight of 400 or less.   The optical film according to claim 1, wherein the polyfunctional monomer has a structure capable of hydrogen bonding.   The optical film according to claim 1, wherein the intermediate layer contains a leveling agent.   The optical film according to claim 1, wherein the liquid crystal is a polymerizable liquid crystal composition.   The optical film according to claim 1, wherein the intermediate layer does not include a solvent that dissolves the polycarbonate.

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