Optical film and backlight device

Abstract

To provide an optical film capable of inhibiting a coloring when viewed in an oblique direction with regard to light transmitted through a color conversion element.SOLUTION: An optical film includes a pigment dispersion layer including a polymer matrix and dispersion particles including a dichroic dye and a polymerization product of a polymerizable liquid crystal component and dispersed in the polymer matrix. The polymerization product and the dichroic dye are aligned in a prescribed direction in at least part of a region of the pigment dispersion layer. An absorption spectrum of light incident at an incident angle 60° onto the at least part of the region has an absorption maximum wavelength within a range of wavelengths 340 nm to 800 nm. An absorbancy of light at the absorption maximum wavelength incident at an incident angle 60° onto the at least part of the region is larger than an absorbancy of light at the absorption maximum wavelength incident at an incident angle 0°.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical film and a backlight device. [Background technology]

[0002] Multicolor technology using a color conversion method is often applied to image display devices such as organic EL display devices and liquid crystal display devices. For example, by combining a color conversion element that converts blue light emission into green light emission or red light emission with a blue light source, it is possible to extract the three primary colors of blue, green, and red from the blue light source, thereby enabling full-color display or extraction of white light (for example, Patent Document 1).

[0003] However, light transmitted through a color conversion element may have undesired coloring, especially when viewed from an oblique direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2019 / 146332A1 Summary of the Invention [Problem to be solved by the invention]

[0005] A primary object of the present invention is to provide an optical film that can suppress coloring of light that has passed through a color conversion element or the like when viewed from an oblique direction. [Means for solving the problem]

[0006] [1] According to one aspect of the present invention, there is provided an optical film having a pigment-dispersed layer including a polymer matrix and dispersed particles that are dispersed in the polymer matrix and contain a polymerization product of a polymerizable liquid crystal component and a dichroic pigment, wherein in at least a partial region of the pigment-dispersed layer, the polymerization product and the dichroic pigment are oriented in a predetermined direction, and the absorption spectrum of light incident on the at least partial region at an incident angle of 60° has an absorption maximum wavelength in a wavelength range of 340 nm to 800 nm, and the absorbance of light at the absorption maximum wavelength that is incident on the at least partial region at an incident angle of 60° is greater than the absorbance of light at the absorption maximum wavelength that is incident at an incident angle of 0°. [2] In the optical film according to the above [1], the dispersed particles may have an average particle size of 1 μm or less. [3] In the optical film according to the above [1] or [2], the dispersed particles may have an average particle size of 300 nm or less. [4] In the optical film according to any one of [1] to [3] above, the dispersed particles may further contain a non-polymerizable liquid crystal component. [5] In the optical film described in [4] above, the content of the dichroic dye in at least a portion of the dye-dispersed layer may be 0.1 wt % to 10 wt % relative to the total content of the polymerization product and the non-polymerizable liquid crystal component. [6] In the optical film according to any one of the above [1] to [5], the thickness of the dye-dispersed layer may be 3 μm to 30 μm. [7] The optical film according to any one of [1] to [6] above may further comprise a supporting substrate disposed on one or both sides of the dye-dispersed layer. [8] In the optical film according to any one of [1] to [7] above, the total light transmittance of light incident on the at least partial region at an incident angle of 0° may be 50% or more. [9] In the optical film according to any one of [1] to [8] above, the haze of light incident on the at least partial region at an incident angle of 0° may be 5% or less.

[10] In the optical film according to any one of [1] to [9] above, the absorbance of light having the maximum absorption wavelength incident on the at least a portion of the region at an incident angle of 60° may be 0.12 or more.

[11] According to another aspect of the present invention, there is provided a backlight device comprising a monochromatic light source, a color conversion element, and the optical film according to any one of [1] to

[10] above. [Effects of the Invention]

[0007] The optical film according to the embodiment of the present invention contains a dichroic dye oriented in a predetermined direction, and thus can absorb more incident light of a predetermined wavelength in an oblique direction than in a frontal direction. Therefore, by using the optical film according to the embodiment of the present invention in combination with a monochromatic light source and a color conversion element, it is possible to effectively suppress coloring of light transmitted through the color conversion element when viewed from an oblique direction. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of an optical film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the absorption of incident light in the optical film shown in FIG. [Figure 3] FIG. 1 is a schematic diagram illustrating one step in a method for producing an optical film according to one embodiment of the present invention. [Figure 4] 1(a) and 1(b) are a schematic plan view and a schematic cross-sectional view, respectively, illustrating the configuration of an optical film according to one embodiment of the present invention. [Figure 5] 1(a) and 1(b) are a schematic plan view and a schematic cross-sectional view, respectively, illustrating the configuration of an optical film according to one embodiment of the present invention. [Figure 6] FIG. 2 is a schematic diagram illustrating a method for measuring transmitted light. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. Furthermore, each embodiment can be combined as appropriate. In order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention. In this specification, the symbol "to" indicating a numerical range includes the upper and lower limit values.

[0010] A. Optical film A-1. Overall structure of optical film FIG. 1 is a schematic cross-sectional view illustrating the configuration of an optical film according to one embodiment of the present invention. Optical film 100A includes a pigment-dispersed layer 30 containing a polymer matrix 10 and dispersed particles 20, which are dispersed in polymer matrix 10 and contain a polymerization product of a polymerizable liquid crystal component (hereinafter sometimes referred to as a liquid crystal polymer) 22 and a dichroic dye 24. Dispersed particles 20 further contain a non-polymerizable liquid crystal component 26, which is an optional component. Therefore, dispersed particles 20 do not necessarily contain the non-polymerizable liquid crystal component 26. In optical film 100A, the entire pigment-dispersed layer 30 is configured as a region (region A) in which the liquid crystal polymer 22, the dichroic dye 24, and the non-polymerizable liquid crystal component 26 are aligned in the thickness direction. In region A having such a configuration, as shown in FIG. 2, absorption of light L1 incident from the front direction is suppressed, while light of a predetermined wavelength among light L2 incident from an oblique direction can be absorbed by the dichroic dye. Therefore, typically, the total light transmittance of light L2 incident on region A from an oblique direction (for example, at an incident angle of 60°) is lower than the total light transmittance of light L1 incident from the front direction (in other words, at an incident angle of 0°). The total light transmittance can be measured in accordance with JIS K 7361.

[0011] The optical film 100A further includes, as supporting substrates, a first substrate 40 disposed on one side of the pigment-dispersion layer 30 and a second substrate 50 disposed on the other side. Either or both of these substrates may be omitted depending on the purpose.

[0012] The total light transmittance of light incident on the region A at an incident angle of 0° is, for example, 50% or more, and may be 60% or more, and is, for example, 99% or less, and may be 90% or less.

[0013] The haze of light incident on the region A at an incident angle of 0° is, for example, 5% or less, and may be 3% or less or 2% or less, and may be, for example, 0.1% or more, and may be 1% or more. Haze can be measured in accordance with JIS K 7136.

[0014] In one embodiment, the absorption spectrum of light incident on region A at an incident angle of 60° has a maximum absorption wavelength in the wavelength range of 340 nm to 800 nm. The maximum absorption wavelength is derived from the dichroic dye. The absorbance of light at the maximum absorption wavelength (λmax) incident on region A at an incident angle of 60° can vary depending on the purpose, and is, for example, 0.12 or more, or may be, for example, 0.2 or more, or may be, for example, 0.4 or less, or may be, for example, 0.3 or less.

[0015] The absorbance of light of the absorption maximum wavelength incident on region A at an incident angle of 60° is typically greater than the absorbance of light of the absorption maximum wavelength incident at an incident angle of 0°. The ratio of the absorbance of light of the absorption maximum wavelength incident on region A at an incident angle of 60° to the absorbance of light of the absorption maximum wavelength incident on region A at an incident angle of 0° (Y60° / Y0°) can vary depending on the purpose and may be, for example, 1.2 or more, or may be 1.6 or more, or may be, for example, 4.0 or less, or may be 2.0 or less.

[0016] The thickness of the optical film 100A is, for example, 30 μm to 250 μm, and preferably 50 μm to 150 μm.

[0017] [Dye dispersion layer] The pigment dispersion layer 30 includes a polymer matrix 10 and dispersed particles 20, which are dispersed in the polymer matrix 10 and contain a liquid crystal polymer 22 and a dichroic dye 24. In the illustrated example, the dispersed particles 20 further contain a non-polymerizable liquid crystal component 26. The inclusion of the non-polymerizable liquid crystal component 26 in the dispersed particles 20 can improve the alignment of the liquid crystal polymer 22 and the dichroic dye 24. In the illustrated example, the liquid crystal polymer 22, the dichroic dye 24, and the non-polymerizable liquid crystal component 26 are all oriented in the thickness direction, but the alignment direction is not limited to the thickness direction as long as the effects of the present invention can be obtained. Note that "oriented in the thickness direction" includes a state in which each component is oriented generally in the thickness direction as a whole.

[0018] The average particle diameter of the dispersed particles may be, for example, 10 μm or less, preferably 1 μm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. The average particle diameter may be, for example, 100 nm or more, or, for example, 150 nm or more. A small average particle diameter of the dispersed particles reduces scattering, making it possible to obtain an optical film with high transparency. The average particle diameter of the dispersed particles is the volume-average particle diameter of the dispersed particles when viewed from a direction perpendicular to the main surface of the optical film.

[0019] The polymer matrix may be composed of any appropriate resin. The resin for forming the polymer matrix may be appropriately selected depending on factors such as light transmittance, the refractive index of the liquid crystal polymer or non-polymerizable liquid crystal component, and adhesion to the first substrate and / or second substrate. For example, water-soluble or water-dispersible resins such as urethane-based resins, polyvinyl alcohol-based resins, polyethylene-based resins, polypropylene-based resins, and acrylic-based resins may be preferably used. The polymer matrix-forming resins may be used alone or in combination. The difference between the refractive index of the polymer matrix-forming resin and the ordinary or extraordinary refractive index of the liquid crystal component may be, for example, 0.05 or less, preferably 0.0 to 0.05.

[0020] Liquid crystal polymers are the polymerization products of polymerizable liquid crystal components and are non-liquid crystal. That is, in liquid crystal polymers, for example, the transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is unique to liquid crystal compounds, does not occur. As the polymerizable liquid crystal component constituting the liquid crystal polymer, any polymerizable liquid crystal compound can be used alone or in combination of two or more depending on the birefringence, dichroic dye, and compatibility with the non-polymerizable liquid crystal component. In the following description, the properties of the liquid crystal component (birefringence, dielectric constant, etc.) refer to the properties of the liquid crystal component as a whole, which may contain two or more liquid crystal compounds.

[0021] The dielectric anisotropy of the polymerizable liquid crystal component may be positive or negative. The polymerizable liquid crystal component may contain a bifunctional or higher crosslinked liquid crystal compound. Examples of the polymerizable liquid crystal component include polymerizable mesogen compounds described in JP-A-2002-533742 (WO 00 / 37585), EP 358208 (US 5,211,877), EP 66137 (US 4,388,453), WO 93 / 22397, EP 0261712, DE 19504224, DE 4408171, and GB 2280445. Nematic liquid crystal monomers are preferred as the polymerizable liquid crystal component.

[0022] The birefringence Δn (=ne−no; ne is the extraordinary refractive index of the liquid crystal component, and no is the ordinary refractive index of the liquid crystal component) of the polymerizable liquid crystal component at a wavelength of 589 nm is preferably 0.05 to 0.50, more preferably 0.10 to 0.45.

[0023] As the non-polymerizable liquid crystal component, any non-polymerizable liquid crystal compound can be used alone or in combination of two or more depending on the birefringence, compatibility with the polymerizable liquid crystal component and the dichroic dye, etc. The dielectric anisotropy of the non-polymerizable liquid crystal component may be positive or negative. The non-polymerizable liquid crystal component may be, for example, a nematic, smectic, or cholesteric liquid crystal component. It is preferable to use a nematic liquid crystal component because it can achieve high transparency in the aligned state.

[0024] Examples of nematic liquid crystal compounds include biphenyl-based compounds, phenylbenzoate-based compounds, cyclohexylbenzene-based compounds, azoxybenzene-based compounds, azobenzene-based compounds, azomethine-based compounds, terphenyl-based compounds, biphenylbenzoate-based compounds, cyclohexylbiphenyl-based compounds, phenylpyridine-based compounds, cyclohexylpyrimidine-based compounds, cholesterol-based compounds, fluorine-based compounds, etc. These liquid crystal compounds may be used alone or in combination.

[0025] The birefringence Δn of the non-polymerizable liquid crystal component at a wavelength of 589 nm is preferably 0.05 to 0.50, and more preferably 0.10 to 0.45.

[0026] Any appropriate dichroic dye can be used as the dichroic dye as long as it has absorption in a desired wavelength range (e.g., a desired maximum absorption wavelength) and is compatible with the liquid crystal component. The dichroic dye may have a positive or negative Δε. The dichroic dye itself may exhibit liquid crystallinity. Only one dichroic dye may be used, or two or more dichroic dyes may be used in combination. For example, if light transmitted through a color conversion element is yellow when viewed from an oblique direction, the coloring can be offset by selecting a dichroic dye having absorption in the range of 500 nm to 580 nm and a dichroic dye having absorption in the range of 580 nm to 700 nm.

[0027] Specific examples of dichroic dyes include azo dyes, anthraquinone dyes, naphthoquinone dyes, perylene dyes, quinophthalone dyes, tetrazine dyes, and benzothiadiazole dyes. Among these, from the viewpoints of absorption coefficient, solubility in liquid crystal components, lightfastness, and the like, it is preferable that the dichroic dye contains anthraquinone dyes or azo dyes. For example, the azo dyes, anthraquinone dyes, or mixtures thereof described in "Liquid Crystal Device Handbook," edited by the 142nd Committee of the Japan Society for the Promotion of Science, Japan Industrial Newspaper Co., Ltd. (1989), pages 192-196 and 724-730, can be used. Various dichroic dyes are commercially available, and these can be used as appropriate.

[0028] The content of the polymer matrix in the pigment dispersion layer is, for example, 30 to 70% by weight, preferably 35 to 65% by weight, and more preferably 40 to 60% by weight. If the content of the polymer matrix is ​​within this range, good mechanical strength can be obtained, and effects such as prevention of liquid crystal leakage from the edges can be obtained.

[0029] The total content of the liquid crystal polymer and the non-polymerizable liquid crystal component in the dye-dispersed layer is, for example, 30% to 70% by weight, preferably 35% to 65% by weight, and more preferably 40% to 60% by weight. The content of the dichroic dye in the dye-dispersed layer is, for example, 0.1% to 10% by weight, preferably 1% to 10% by weight, and more preferably 3% to 10% by weight, based on the total content of the liquid crystal polymer and the non-polymerizable liquid crystal component.

[0030] The weight ratio of the liquid crystal polymer to the non-polymerizable liquid crystal component in the dye-dispersion layer (former:latter) is, for example, 5:95 to 100:0, preferably 7:93 to 80:20, and more preferably 10:90 to 50:50. The weight ratio of the polymer matrix content to the total content of the liquid crystal polymer, dichroic dye, and non-polymerizable liquid crystal component in the dye-dispersion layer (former:latter) is, for example, 30:70 to 70:30, preferably 35:65 to 65:35, and more preferably 40:60 to 60:40.

[0031] The total content of the polymer matrix, liquid crystal polymer, dichroic dye, and non-polymerizable liquid crystal component in the dye-dispersed layer can be, for example, 80% by weight or more, preferably 90% to 99.9% by weight, and more preferably 95% to 99.9% by weight.

[0032] The dye-dispersion layer may further contain any appropriate component, if necessary, such as a surfactant, a leveling agent, a crosslinking agent, etc.

[0033] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. The content of the surfactant in the dye-dispersed layer is, for example, 1% by weight to 15% by weight, and preferably 2% by weight to 10% by weight.

[0034] Examples of the leveling agent include an acrylic leveling agent, a fluorine-based leveling agent, a silicone-based leveling agent, etc. The content of the leveling agent in the dye-dispersed layer is, for example, 0.1 to 10% by weight, and preferably 0.5 to 5% by weight.

[0035] Examples of the crosslinking agent include an aziridine-based crosslinking agent, an isocyanate-based crosslinking agent, etc. The content of the crosslinking agent in the pigment-dispersed layer is, for example, 0.5% by weight to 20% by weight, and preferably 1% by weight to 10% by weight.

[0036] The thickness of the pigment dispersion layer is typically 2 μm to 40 μm, preferably 3 μm to 30 μm, and more preferably 4 μm to 20 μm.

[0037] [Base material] The first substrate 40 and the second substrate 50 (hereinafter sometimes collectively referred to as "substrates") may each be formed using any suitable material capable of supporting a pigment-dispersion layer. Specific examples of the substrate include glass films and polymer films. Polymer films are preferred because of their excellent smoothness and the ability to significantly improve productivity through continuous production using rolls.

[0038] The substrate is typically a polymer film primarily composed of a thermoplastic resin. Examples of thermoplastic resins include polyester resins; cycloolefin resins such as polynorbornene; acrylic resins; polycarbonate resins; and cellulose resins. Of these, polyester resins, cycloolefin resins, and acrylic resins are preferred. These resins are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and the like. The above thermoplastic resins may be used alone or in combination of two or more.

[0039] The haze of the substrate is preferably 20% or less, more preferably 10% or less, and even more preferably 0.1% to 10%.

[0040] The total light transmittance of the substrate is preferably 30% or more, more preferably 60% or more, and even more preferably 80% or more.

[0041] The thickness of the substrate is, for example, 200 μm or less, preferably 3 μm to 100 μm, and more preferably 5 μm to 50 μm.

[0042] The first substrate and the second substrate may be formed of the same or different materials and may have the same or different thicknesses.

[0043] A-2. Optical film manufacturing method The optical film can be produced by any suitable production method. In one embodiment, the method for producing the optical film includes the following steps: (Step A) applying a coating liquid containing a polymer matrix-forming resin, a polymerizable liquid crystal component, a dichroic dye, and a solvent to a first substrate to obtain a coating layer; (Step B) drying the coating layer to obtain a polymer dispersed liquid crystal (PDLC) layer containing a polymer matrix and liquid crystal droplets containing a polymerizable liquid crystal component and a dichroic dye dispersed in the polymer matrix; (Step C) laminating a second substrate onto the PDLC layer; and (Step D) applying a voltage to the PDLC layer and irradiating it with active energy rays to form dispersed particles containing a liquid crystal polymer, which is a polymerization product of the polymerizable liquid crystal component, and a dichroic dye; Includes:

[0044] [Process A] In step A, a coating liquid containing a polymer matrix-forming resin, a polymerizable liquid crystal component, a dichroic dye, and a solvent is applied to a first substrate to obtain a coating layer. The coating liquid preferably further contains a non-polymerizable liquid crystal component and a polymerization initiator, and may further contain any appropriate additives depending on the purpose.

[0045] The coating liquid is preferably an emulsion in which liquid crystal particles containing a polymerizable liquid crystal component, a dichroic dye, and an optional non-polymerizable liquid crystal component are dispersed in a solvent (hereinafter, this may be referred to as an "emulsion coating liquid"). In one embodiment, the coating liquid is an emulsion coating liquid in which polymer matrix-forming resin particles and liquid crystal particles containing a polymerizable liquid crystal component, a dichroic dye, and an optional non-polymerizable liquid crystal component are dispersed in a solvent.

[0046] The solvent is preferably water or a mixture of water and a water-miscible organic solvent, such as C1-3 alcohol, acetone, or DMSO.

[0047] As the polymerization initiator, any appropriate photopolymerization initiator can be used depending on the purpose, desired properties, and the like. Specific examples of photopolymerization initiators include 2,2-dimethoxy-2-phenylacetophenone, acetophenone, benzophenone, xanthone, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, benzoin propyl ether, benzil dimethyl ketal, N,N,N',N'-tetramethyl-4,4'-diaminobenzophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-dipentoxyphenylphosphine oxide, bis(2,6-dimethoxy-benzoyl)-(2,4,4-trimethyl-pentyl)-phosphine oxide, and thioxanthone compounds. The photopolymerization initiators may be used alone or in combination of two or more. The content of the photopolymerization initiator is, for example, 0.1 to 10 parts by weight, and preferably 0.5 to 5 parts by weight, relative to 100 parts by weight of the polymerizable liquid crystal component.

[0048] The polymer matrix-forming resin, dichroic dye, non-polymerizable liquid crystal component, polymerizable liquid crystal component, and additives, as well as their content ratios, are as described above, except that the content ratio of the polymerizable liquid crystal component may correspond to the content ratio of the liquid crystal polymer.

[0049] The average particle size of the liquid crystal particles may be, for example, 10 μm or less, preferably 1 μm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. The average particle size may be, for example, 100 nm or more, or, for example, 150 nm or more. The average particle size of the liquid crystal particles is the volume average particle size. The average particle size of the liquid crystal particles in the coating liquid may roughly correspond to the average particle size of the dispersed particles in the pigment dispersion layer.

[0050] The average particle diameter of the resin particles for forming a polymer matrix is ​​preferably 10 nm to 500 nm, more preferably 30 nm to 300 nm, and even more preferably 50 nm to 200 nm. Two or more types of resin particles differing in type and / or average particle diameter may be used. The average particle diameter of the resin particles for forming a polymer matrix means the volume-average median diameter and can be measured using a dynamic light scattering particle size distribution analyzer.

[0051] The emulsion coating liquid can be prepared, for example, by mixing a resin emulsion or resin solution containing polymer matrix-forming resin particles, a liquid crystal emulsion containing liquid crystal particles, and optional additives. If necessary, a solvent may be added during mixing. Alternatively, the emulsion coating liquid can be prepared by adding a polymerizable liquid crystal component, a dichroic dye, an optional non-polymerizable liquid crystal component, polymer matrix-forming resin particles, and optional additives to a solvent and mechanically dispersing the mixture.

[0052] The resin emulsion and liquid crystal emulsion can be prepared by, for example, a mechanical emulsification method, a microchannel method, a membrane emulsification method, or the like. Among these, the liquid crystal emulsion is preferably prepared by the membrane emulsification method. The membrane emulsification method can suitably produce an emulsion with a uniform particle size distribution. For details of the membrane emulsification method, reference can be made to the disclosures of JP-A-4-355719 and JP-A-2015-40994 (which are incorporated herein by reference).

[0053] The solid content concentration of the emulsion coating liquid can be, for example, 20% to 60% by weight, and preferably 30% to 50% by weight.

[0054] The viscosity of the emulsion coating liquid can be appropriately adjusted to ensure successful application to the first substrate. The viscosity of the emulsion coating liquid during application is preferably 20 mPa·s to 400 mPa·s, more preferably 30 mPa·s to 300 mPa·s, and even more preferably 40 mPa·s to 200 mPa·s. If the viscosity is less than 20 mPa·s, convection of the solvent becomes significant during drying, which may result in an unstable thickness of the PDLC layer. If the viscosity exceeds 400 mPa·s, the beading of the emulsion coating liquid may become unstable. The viscosity of the emulsion coating liquid can be measured, for example, using an Anton Paar MCR302 rheometer. The viscosity used here is the shear viscosity value at 20°C and a shear rate of 1000 (1 / s).

[0055] Any appropriate method can be used to apply the emulsion coating liquid to the first substrate. Examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). Among these, roll coating is preferred. For example, the description of JP-A-2019-5698 can be referenced for application by roll coating using a slot die.

[0056] The thickness of the coating layer is preferably 3 μm to 50 μm, more preferably 4 μm to 40 μm, and even more preferably 5 μm to 30 μm.Within this range, a PDLC layer with excellent thickness uniformity can be obtained.

[0057] [Process B] In step B, the coating layer is dried to obtain a PDLC layer containing a polymer matrix and liquid crystal droplets containing a polymerizable liquid crystal component, a dichroic dye, and an optional non-polymerizable liquid crystal component dispersed in the polymer matrix. The solvent is removed from the coating layer by drying, forming a PDLC layer having a structure in which liquid crystal droplets are dispersed in a polymer matrix.

[0058] The coating layer can be dried by any appropriate method. Specific examples of the drying method include natural drying, heat drying, hot air drying, etc. When the emulsion coating liquid contains a crosslinking agent, a crosslinked structure of the polymer matrix can be formed during drying.

[0059] The drying temperature is preferably 20° C. to 150° C., more preferably 25° C. to 80° C. The drying time is preferably 1 minute to 100 minutes, more preferably 2 minutes to 10 minutes.

[0060] [Process C] In step C, a second substrate is laminated on the PDLC layer, thereby obtaining a PDLC film having the first substrate, the PDLC layer, and the second substrate in this order.

[0061] To ensure sufficient adhesion, the second substrate is preferably laminated onto the PDLC layer using a laminator while applying a laminating pressure of 0.006 MPa / m to 7 MPa / m, more preferably 0.06 MPa / m to 0.7 MPa / m.

[0062] [Process D] In step D, the PDLC layer is irradiated with active energy rays while a voltage is applied to form dispersed particles containing a liquid crystal polymer, which is a polymerization product of the polymerizable liquid crystal component, a dichroic dye, and any non-polymerizable liquid crystal component.

[0063] FIG. 3 is a schematic diagram illustrating an example of step D. In the embodiment shown in FIG. 3, a PDLC film 100a includes a PDLC layer 30a including a polymer matrix 10 and liquid crystal droplets 20a dispersed in the polymer matrix 10, the liquid crystal droplets 20a including a polymerizable liquid crystal component 28, a dichroic dye 24, and a non-polymerizable liquid crystal component 26; a first substrate 40; and a second substrate 50. A first electrode 210 is disposed on the first substrate 40 side of the PDLC film 100a, and a second electrode 220 is disposed on the second substrate 50 side. The second electrode 220 is transmissive to actinic rays. A voltage is applied between the first electrode 210 and the second electrode 220. The polymerizable liquid crystal component 28, the dichroic dye 24, and the non-polymerizable liquid crystal component 26 are aligned in the direction of the electric field (i.e., the thickness direction) generated by the voltage application. Then, actinic rays (UV irradiation in the illustrated example) are applied from the second electrode 220 side (upper diagram).

[0064] The irradiation of the active energy rays polymerizes the polymerizable liquid crystal component 28 in an oriented state, thereby producing a liquid crystal polymer 22 in which the oriented state is fixed. Furthermore, the dichroic dye 24 and the non-polymerizable liquid crystal component 26 are also oriented along the liquid crystal polymer 22 whose orientation in the thickness direction is fixed. As a result, a dye-dispersed layer 30 is formed (see the lower diagram) containing dispersed particles 20 containing the liquid crystal polymer 22, the dichroic dye 24, and the non-polymerizable liquid crystal component 26, which are oriented in the thickness direction even after the electric field is removed.

[0065] The voltage applied during irradiation with active energy rays is not limited as long as the desired orientation is achieved, and can be, for example, 10V to 200V, and preferably 20V to 100V.

[0066] Examples of usable active energy rays include ultraviolet rays, infrared rays, X-rays, α-rays, β-rays, γ-rays, and electron beams. Of these, ultraviolet rays are preferred. Furthermore, the active energy rays are preferably collimated light that travels in a straight line from the irradiation source.

[0067] The ultraviolet irradiation conditions can be appropriately set depending on the type of polymerizable liquid crystal component, the transmittance of the substrate, the absorption wavelength of the polymerization initiator, etc. The irradiation intensity is, for example, 0.1 mW / cm 2 ~1000mW / cm2 , preferably 1 mW / cm 2 ~100mW / cm 2 The irradiation dose can be, for example, 10 mJ / cm 2 ~10,000mJ / cm 2 , preferably 100 mJ / cm 2 ~5000mJ / cm 2 The irradiation temperature can be, for example, from -20°C to 80°C, and preferably from -20°C to 60°C.

[0068] A-3. Modification 1 of Optical Film 4(a) and 4(b) are a schematic plan view and a schematic cross-sectional view, respectively, illustrating the configuration of an optical film according to one embodiment of the present invention. Optical film 100B has a polymer matrix 10 and a pigment-dispersed layer 30 containing dispersed particles 20, including a liquid crystal polymer 22, a dichroic dye 24, and an optional non-polymerizable liquid crystal component 26, dispersed in the polymer matrix 10. The pigment-dispersed layer 30 of optical film 100B has a region A containing dispersed particles 20, including liquid crystal polymer 22, dichroic dye 24, and optional non-polymerizable liquid crystal component 26, which are aligned in the thickness direction, and a region B containing liquid crystal droplets 20a containing polymerizable liquid crystal component 28, dichroic dye 24, and optional non-polymerizable liquid crystal component 26, which are in a non-oriented state. In the optical film 100B having such a configuration, in region A, the dichroic dye can absorb light of a predetermined wavelength among light incident from oblique directions while suppressing absorption of light incident from the front direction, while dispersion due to the difference in refractive index between the polymer matrix 10 and the liquid crystal droplets 20a and absorption by the dichroic dye occur in region B. As a result, region B can exhibit higher haze and lower total light transmittance than region A for light incident at an incident angle of 0°.

[0069] The same explanation as for the region A of the optical film 100A can be applied to the region A.

[0070] The total light transmittance of light incident on region B at an incident angle of 0° may be, for example, 40% or more, 50% or more, or 55% or more, and may be, for example, 80% or less, 75% or less, or 70% or less. The difference between the total light transmittance of light incident on region A at an incident angle of 0° and the total light transmittance of light incident on region B at an incident angle of 0° may be, for example, 5% or more, 10% or more, or 15% or more, and may be, for example, 35% or less, 30% or less, or 20% or less.

[0071] The haze of light incident on region B at an incident angle of 0° may be, for example, 10% or more, 20% or more, or 30% or more, or may be, for example, 99% or less, 90% or less, or 80% or less. The difference between the haze of light incident on region A at an incident angle of 0° and the haze of light incident on region B at an incident angle of 0° may be, for example, 10% or more, or may be, for example, 95% or less, 80% or less, or 70% or less.

[0072] In one embodiment, the absorption spectrum of light incident on region B at an incident angle of 60° may have a maximum absorption wavelength derived from the dichroic dye. The ratio (Y60° / Y0°) of the absorbance of light of the maximum absorption wavelength incident on region B at an incident angle of 60° to the absorbance of light of the maximum absorption wavelength incident on region B at an incident angle of 0° may be a smaller value than Y60° / Y0° in region A, and may be, for example, 1.3 or less, 1.2 or less, or 1.1 or less, or may be, for example, 0.9 or more, 0.95 or more, or 1 or more.

[0073] The optical film 100B can be produced by irradiating the PDLC layer with active energy rays through a photomass having a desired pattern while applying a voltage to the PDLC layer in step D of the above-described optical film production method. As a result, the region irradiated with active energy rays becomes region A, and the region not irradiated with active energy rays becomes region B, where the polymerizable liquid crystal component remains unreacted and the components are in a non-oriented state when no voltage is applied.

[0074] A-4. Modified Example 2 of Optical Film 5(a) and 5(b) are a schematic plan view and a schematic cross-sectional view, respectively, illustrating the configuration of an optical film according to one embodiment of the present invention. Optical film 100C has a polymer matrix 10 and a pigment-dispersed layer 30 containing dispersed particles 20, 20b, which are dispersed in polymer matrix 10 and contain a liquid crystal polymer 22, a dichroic dye 24, and an optional non-polymerizable liquid crystal component 26. The pigment-dispersed layer 30 of optical film 100C has a region A containing dispersed particles 20 containing liquid crystal polymer 22, dichroic dye 24, and optional non-polymerizable liquid crystal component 26, which are aligned in the thickness direction, and a region C containing dispersed particles 20b containing liquid crystal polymer 22, dichroic dye 24, and optional non-polymerizable liquid crystal component 26, which are in a non-oriented state. In optical film 100C having such a configuration, in region A, absorption of light incident from the front direction is suppressed, and among light incident from oblique directions, light of a predetermined wavelength can be absorbed by the dichroic dye, while in region C, dispersion due to the difference in refractive index between polymer matrix 10 and dispersed particles 20b and absorption by the dichroic dye occur. As a result, region C can exhibit higher haze and lower total light transmittance than region A for light incident at an incident angle of 0°.

[0075] The same explanation as for the region A of the optical film 100A can be applied to the region A.

[0076] The total light transmittance of light incident on region C at an incident angle of 0° may be, for example, 40% or more, 50% or more, or 55% or more, and may be, for example, 80% or less, 75% or less, or 70% or less. The difference between the total light transmittance of light incident on region A at an incident angle of 0° and the total light transmittance of light incident on region C at an incident angle of 0° may be, for example, 5% or more, 10% or more, or 15% or more, and may be, for example, 35% or less, 30% or less, or 20% or less.

[0077] The haze of light incident on region C at an incident angle of 0° may be, for example, 10% or more, 20% or more, or 30% or more, or may be, for example, 99% or less, 90% or less, or 80% or less. The difference between the haze of light incident on region A at an incident angle of 0° and the haze of light incident on region C at an incident angle of 0° may be, for example, 10% or more, or may be, for example, 95% or less, 80% or less, or 70% or less.

[0078] In one embodiment, the absorption spectrum of light incident on region C at an incident angle of 60° may have a maximum absorption wavelength derived from the dichroic dye. The ratio (Y60° / Y0°) of the absorbance of light of the maximum absorption wavelength incident on region C at an incident angle of 60° to the absorbance of light of the maximum absorption wavelength incident on region C at an incident angle of 0° may be a smaller value than Y60° / Y0° in region A, and may be, for example, 1.3 or less, 1.2 or less, or 1.1 or less, or may be, for example, 0.9 or more, 0.95 or more, or 1 or more.

[0079] Optical film 100C can be produced by irradiating the PDLC layer with active energy rays while applying a voltage through a photomask having a desired pattern, followed by irradiating the unirradiated portion with active energy rays without applying a voltage, in step D of the optical film manufacturing method. The region irradiated with active energy rays while applying a voltage through the photomask to the PDLC layer becomes region A. The unirradiated region is then irradiated with active energy rays without applying a voltage (i.e., while the polymerizable liquid crystal component, dichroic dye, and non-polymerizable liquid crystal component are in a non-oriented state). This fixes the polymerizable liquid crystal component as a liquid crystal polymer while remaining in a non-oriented state, and the dichroic dye and non-polymerizable liquid crystal component also remain in a non-oriented state. This forms region C, where liquid crystal polymer 22, dichroic dye 24, and non-polymerizable liquid crystal component 26 are in a non-oriented state.

[0080] B. Backlight device According to another aspect of the present invention, there is provided a backlight device having a monochromatic light source, a color conversion element, and the optical film described in Section A. In the optical film, in the dye-dispersion layer, in region A where the liquid crystal polymer, the dichroic dye, and any non-polymerizable liquid crystal component are oriented in a predetermined direction, the dye-dispersion layer can suppress absorption of light incident from the front direction while allowing the dichroic dye to absorb light of a predetermined wavelength among light incident from oblique directions. Therefore, a backlight device in which the optical film is arranged on the emission surface side of the monochromatic light source (typically a blue light source) and the color conversion element can suitably suppress coloring when the light emitted from the color conversion element is viewed from an oblique direction. [Example]

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

[0082] (1) Thickness Measurement was carried out using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). (2) Volume average particle size of liquid crystal particles in liquid crystal emulsion The volume average particle diameter was calculated using a particle size distribution measuring device (manufactured by Microtrac, "MT3300EXII"). (3) Average particle size of resin particles A measurement sample was prepared by adding a few drops of the resin dispersion to 100 mL of water. Using a dynamic light scattering particle size distribution analyzer (Microtrac, device name "Nanotrac150"), the measurement sample was placed in the measurement holder of the device, and measurements were performed after checking on the device monitor that the concentration was measurable. (4) Average particle size of dispersed particles The volume average particle diameter was calculated using a particle size distribution measuring device (Microtrac, "MT3300EXII"). (5) Total light transmittance and haze Measurements were carried out using a Nippon Denshoku product, product name "NDH4000", in accordance with JIS K 7136 or JIS K 7361. (6) Maximum absorption wavelength The light transmittance from 340 nm to 800 nm was measured using an ultraviolet-visible spectrophotometer (Hitachi High-Tech Science Corporation, model number "UH4150"), and the wavelength at the absorption maximum (maximum absorption wavelength) was taken as the absorption maximum wavelength.

[0083] [Example 1] 1. Preparation of emulsion coating liquid A liquid crystal emulsion was prepared by mixing 31.7 parts of a non-polymerizable liquid crystal component (JNC Corporation, product name "LX-153XX," birefringence Δn = 0.149 (ne = 1.651, no = 1.502), viscosity = 48.5 mPa·s), 3.5 parts of a polymerizable liquid crystal component (BASF, product name "PALIOCOLOR LC-242"), 1.1 parts of a dichroic dye (Hayashibara Co., Ltd., product name "G470"), 0.1 parts of a photoinitiator (IGM, product name "OMNIRAD651"), 60.0 parts of purified water, and 3.6 parts of a dispersant (Dai-ichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") in a homogenizer at 100 rpm for 10 minutes. The average particle size of the resulting liquid crystal particles in the liquid crystal emulsion was 192 nm. An emulsion coating solution was prepared by mixing 38.4 parts of the liquid crystal emulsion, 19.1 parts of a polyether-based polyurethane resin aqueous dispersion (DSM, product name "NeoRez R967," average polymer particle size: 80 nm, CV value = 0.27, solid content: 40 wt%), 17.0 parts of a polyester-based polyurethane resin aqueous dispersion (Sanyo Chemical Industries, Ltd., product name "Eu-Coat C-102," average polymer particle size: 168 nm, CV value = 0.23, solid content: 45 wt%), 0.1 parts of a leveling agent (DIC, product name "F-444"), 1.1 parts of a crosslinker (tris[3-(2-methylaziridin-1-yl)propionic acid] = propylidinetrimethyl), and 24.3 parts of pure water. The amount of dichroic dye in the emulsion coating solution was 3 wt% based on the combined weight of the non-polymerizable liquid crystal component and the polymerizable liquid crystal component.

[0084] 2. Formation of PDLC layer The emulsion coating liquid was applied to one side of a resin film (product name "G-film", thickness 13 μm) as a first substrate using a wire bar to form a coating layer with a thickness of 30 μm, which was then dried at room temperature for 60 minutes to form a PDLC layer with a thickness of 6 μm to 7 μm.

[0085] 3. PDLC Film Fabrication A resin film (product name "G-film", thickness 13 μm) was laminated on the PDLC layer as a second substrate using a laminator at a lamination pressure of 0.4 MPa / m, thereby obtaining a PDLC film with a structure of [first substrate / PDLC layer / second substrate].

[0086] 4.UV irradiation A flat metal electrode was placed on the first substrate side of the PDLC film, and an ITO-coated glass electrode was placed on the second substrate side. While applying a voltage of 3.5 kV to these electrodes, UV irradiation was performed from the second substrate side through a photomask with a predetermined pattern. Specifically, UV-LED lamps (manufactured by Hamamatsu Photonics, product name "C11924-101", peak wavelength 365 nm) were used at 60°C, providing 10 mW / cm². 2 The film was exposed to light for 5 minutes at 1000 W. This formed region A, which contained liquid crystal polymer aligned in the thickness direction, dichroic dye, and dispersed particles containing non-polymerizable liquid crystal components. Next, the region that was not irradiated with UV light in the above exposure process was subjected to a similar exposure process with no voltage applied. This formed region C, which contained non-aligned liquid crystal polymer, dichroic dye, and dispersed particles containing non-polymerizable liquid crystal components.

[0087] In this manner, an optical film 1 having a structure of [first substrate / pigment-dispersed layer having region A and region C / second substrate] was obtained.

[0088] [Example 2] Optical film 2 was obtained in the same manner as in Example 1, except that the coating thickness of the emulsion coating liquid was changed to form a PDLC layer (resulting in a pigment dispersion layer) having a thickness of 3 μm to 4 μm.

[0089] [Example 3] An optical film 3 was obtained in the same manner as in Example 1, except that the amount of the dichroic dye was 1.5 wt % based on the total amount of the non-polymerizable liquid crystal component and the polymerizable liquid crystal component.

[0090] [Example 4] Optical film 4 was obtained in the same manner as in Example 1, except that the coating thickness of the emulsion coating liquid was changed to form a PDLC layer (resulting in a pigment dispersion layer) with a thickness of 3 μm to 4 μm, and the amount of dichroic pigment was 1.5 wt % relative to the total amount of the non-polymerizable liquid crystal component and the polymerizable liquid crystal component.

[0091] The transmittance of light incident at an incident angle of 0° was measured for Region A and Region C of the optical film obtained in the above example, as shown in Figure 6 (in the figure, "100" indicates the optical film and "D" indicates the detector). The absorbance of light at the maximum absorption wavelength incident at incident angles of 0° and 60° was also measured. The results are shown in Table 1, along with the haze measured at an incident angle of 0°. The absorbance of light at the maximum absorption wavelength incident at an incident angle of 60° in Region A of Optical Films 1, 2, 3, and 4 was 0.475, 0.388, 0.339, and 0.252, respectively. The absorbance ratio (Y60° / Y0°) at λmax in Region C of Optical Film 1 was 1.03.

[0092] [Table 1] [Industrial Applicability]

[0093] The optical film of the present invention can be used as a color compensation film for a backlight unit or a light source unit using a color conversion element in an image display device such as an organic EL display device or a liquid crystal display device. [Explanation of symbols]

[0094] 10 Polymer matrix 20 Dispersed particles 22 Liquid Crystal Polymer 24 Dichroic dyes 26 Non-polymerizable liquid crystal components 28 Polymerizable liquid crystal components 30 Dye dispersion layer 40 First base material 50 Second base material 100 Optical Film

Claims

1. a pigment dispersion layer including a polymer matrix and dispersed particles that are dispersed in the polymer matrix and contain a polymerization product of a polymerizable liquid crystal component and a dichroic pigment; the polymerization product and the dichroic dye are oriented in a predetermined direction in at least a partial region of the dye-dispersion layer; an absorption spectrum of light incident on the at least a portion of the region at an incident angle of 60° has a maximum absorption wavelength in a wavelength range of 340 nm to 800 nm; the absorbance of light having the absorption maximum wavelength incident on the at least a portion of the region at an incident angle of 60° is greater than the absorbance of light having the absorption maximum wavelength incident on the at least a portion of the region at an incident angle of 0°; Optical film.

2. 2. The optical film according to claim 1, wherein the dispersed particles have an average particle size of 1 μm or less.

3. The optical film according to claim 1 , wherein the dispersed particles have an average particle size of 300 nm or less.

4. The optical film of claim 1 , wherein the dispersed particles further comprise a non-polymerizable liquid crystal component.

5. 5. The optical film according to claim 4, wherein a content ratio of the dichroic dye in the at least partial region of the dye-dispersed layer is 0.1% by weight to 10% by weight with respect to a total content of the polymerization product and the non-polymerizable liquid crystal component.

6. 2. The optical film according to claim 1, wherein the thickness of the pigment-dispersed layer is 3 μm to 30 μm.

7. The optical film of claim 1 , further comprising a supporting substrate disposed on one or both sides of the pigment-dispersed layer.

8. The optical film according to claim 1 , wherein the total light transmittance of light incident on the at least a portion of the region at an incident angle of 0° is 50% or more.

9. The optical film according to claim 1 , wherein the haze of light incident on the at least a portion of the region at an incident angle of 0° is 5% or less.

10. 2. The optical film according to claim 1, wherein the absorbance of light having the absorption maximum wavelength incident on the at least a portion of the region at an incident angle of 60° is 0.12 or more.

11. A backlight device comprising a monochromatic light source, a color conversion element, and the optical film according to claim 1.

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