JP2024143490A - Diffusion film, light diffusion device, liquid crystal display device, and method for manufacturing the diffusion film - Google Patents

Abstract

To provide a diffusion film capable of improving in-plane brightness uniformity when combined with a light source unit..SOLUTION: A diffusion film according to an embodiment of the present invention comprises a diffusion layer containing a polymer matrix and dispersion particles dispersed in the polymer matrix, the dispersion particles containing a liquid crystal polymer, or a polymerized product of a polymerizable liquid crystal compound, where the diffusion layer has first regions containing the liquid crystal polymer aligned in a first direction at an angle with a thickness direction.SELECTED DRAWING: Figure 2

Description

The present invention relates to a diffusion film, a light diffusion device, a liquid crystal display device, and a method for manufacturing a diffusion film.

A PDLC film having a polymer dispersed liquid crystal (hereinafter sometimes referred to as "PDLC") layer containing a polymer matrix and droplets of a liquid crystal compound dispersed therein (hereinafter sometimes referred to as "liquid crystal droplets") can cause light scattering because the liquid crystal droplets act as scattering particles due to the difference in refractive index between the polymer matrix and the liquid crystal droplets.

In recent years, display devices that use light-emitting diodes (hereinafter referred to as LEDs) as light sources have become widespread due to their low power consumption and the possibility of making them smaller and thinner. In such display devices, from the viewpoint of uniforming the in-plane luminance, it has been proposed to provide a reflective film on the surface of the LED elements to generate a batwing light distribution (Patent Document 1).

JP 2019-121790 A

The PDLC film can be used as a diffusion film by taking advantage of its scattering properties. On the other hand, when the PDLC film is combined with a light source unit and used as a light diffusion device, the uniformity of the in-plane brightness may be insufficient. Therefore, the main object of the present invention is to provide a diffusion film that can improve the uniformity of the in-plane brightness when combined with a light source unit.

[1] According to one aspect of the present invention, there is provided a diffusion film having a diffusion layer including a polymer matrix and dispersed particles dispersed in the polymer matrix, the dispersed particles including a liquid crystal polymer that is a polymer of a polymerizable liquid crystal compound, the diffusion layer having a first region including the liquid crystal polymer oriented in a first direction, the first direction being inclined with respect to a thickness direction.
[2] In the diffusion film according to the above [1], the diffusion layer may further include a third region having a lower haze than the first region and a second region having a higher haze than the first region.
[3] In the diffusion film according to [2] above, the first region may be disposed between the second region and the third region.
[4] In the diffusion film according to the above [2] or [3], a difference in haze between the second region and the third region may be 10% or more.
[5] In the diffusion film described in any one of [1] to [4] above, the dispersed particles containing the liquid crystal polymer oriented in the first direction may be positioned along the first direction from one side of the diffusion layer to the other side. [6] In the diffusion film described in any one of [1] to [5] above, the dispersed particles may further contain a non-polymerizable liquid crystal compound.
[7] In the diffusion film according to the above [6], the content of the liquid crystal polymer may be 5% by weight or more with respect to the total content of the liquid crystal polymer and the non-polymerizable liquid crystal compound.
[8] The diffusion film according to any one of [1] to [7] above may further include a supporting substrate disposed on one or both sides of the diffusion layer.
[9] According to another aspect of the present invention, there is provided a light diffusion device comprising a light source unit and the diffusion film according to any one of [1] to [8] above.
[10] According to another aspect of the present invention, there is provided a liquid crystal display device comprising, in this order, a light source unit, the diffusion film according to any one of [1] to [8] above, and a liquid crystal panel.
[11] According to another aspect of the present invention, there is provided a method for producing a diffusion film, comprising: step I of applying a coating liquid containing a polymer matrix-forming resin, a polymerizable liquid crystal compound, and a solvent to a first substrate to obtain a coating layer; step II of drying the coating layer to obtain a polymer dispersed liquid crystal layer containing a polymer matrix and droplets dispersed in the polymer matrix, the droplets containing the polymerizable liquid crystal compound; and step III of polymerizing the polymerizable liquid crystal compound to obtain a diffusion layer, wherein step III comprises polymerizing, in a first region of the polymer dispersed liquid crystal layer, at least a portion of the polymerizable liquid crystal compound in a state where the polymerizable liquid crystal compound is aligned in a first direction, and the first direction is inclined with respect to the thickness direction.
[12] In the method for manufacturing a diffusion film described in [11] above, step III may include polymerizing the polymerizable liquid crystal compound in a second region of the polymer dispersed liquid crystal layer in a state where the polymerizable liquid crystal compound has a lower degree of orientation than in the first region.
[13] In the method for manufacturing a diffusion film described in [11] or [12] above, step III may include polymerizing at least a portion of the polymerizable liquid crystal compound in a third region of the polymer dispersed liquid crystal layer while aligning the compound in a second direction, and an angle between the second direction and the thickness direction may be smaller than an angle between the first direction and the thickness direction.
[14] In the method for manufacturing a diffusion film according to any one of [11] to [13] above, step III may comprise polymerizing the polymerizable liquid crystal compound while applying a voltage between electrodes disposed on both sides of the polymer dispersed liquid crystal layer so as not to overlap in a planar view.
[15] In the method for manufacturing a diffusion film according to any one of [11] to [14] above, step III may comprise polymerizing the polymerizable liquid crystal compound in the first region of the polymer dispersed liquid crystal layer while generating an electric field in the first direction.

According to an embodiment of the present invention, a portion of the liquid crystal compound is obliquely aligned in a specific region of the PDLC layer, and the alignment state is fixed. This makes it possible to obtain a diffusion film that has an area where light easily escapes in an oblique direction, and that can improve the uniformity of in-plane luminance when combined with a light source unit.

1 is a schematic plan view of a diffusion film according to one embodiment of the present invention. FIG. 2 is an image diagram illustrating an example of the orientation state of liquid crystal polymers in dispersed particles in a cross section taken along line A1-A1 in region I of the diffusion film shown in FIG. FIG. 4 is an image diagram illustrating an example of the distribution of dispersed particles in a diffusion layer. FIG. 11 is a schematic diagram illustrating an example of step III. FIG. 2 is a schematic diagram illustrating an example of the configuration of an electrode. FIG. 2 is a schematic diagram illustrating an example of the configuration of an electrode. 1 is a schematic cross-sectional view illustrating a configuration of a light diffusing device according to one embodiment of the present invention.

The following describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments. In addition, each embodiment can be combined as appropriate. In this specification, the term "to" indicating a numerical range includes the upper and lower numerical limits.

A. Diffusion Film The diffusion film according to an embodiment of the present invention has a diffusion layer including a polymer matrix and dispersed particles including a liquid crystal polymer, which is a polymer of a polymerizable liquid crystal compound, dispersed in the polymer matrix. The diffusion layer has a first region including the liquid crystal polymer aligned in a first direction, and the first direction is inclined with respect to the thickness direction.

Figure 1 is a schematic plan view of a diffusion film according to one embodiment of the present invention. The diffusion film 100 (more specifically, the diffusion layer) has a first region A, a second region B, and a third region C, each of which has a different haze when viewed in a plan view. The second region B is two-dimensionally arranged at a predetermined interval. The first region A is arranged so as to surround the second region B, and the region outside of the first region A is the third region C. The first region A is arranged between the second region B and the third region C.

The haze of each region of the diffusion film 100 can be appropriately set according to the use of the diffusion film. In one embodiment, the second region B has a higher haze than the third region C. In this embodiment, the haze of the second region can be, for example, 30% to 100%, or, for example, 50% to 100%. The haze of the third region can be, for example, 0% to 70%, or, for example, 0% to 50%. The difference in haze between the second region and the third region can be, for example, 10% or more, preferably 20% to 100%, and more preferably 30% to 100%. The haze of the first region can be greater than the haze of the third region and less than the haze of the second region. For example, the haze of the first region is higher than the haze of the third region and lower than the haze of the second region. The haze of the first region may be uniform or non-uniform. In one embodiment, the first region may have a haze gradient such that the haze gradually decreases from the second region side to the third region side. Haze can be measured according to JIS K 7136.

2 is an image diagram illustrating an example of the orientation state of the liquid crystal polymer in the dispersed particles in the cross section of the diffusion film shown in FIG. 1, cut along the line A1-A1 in the region I surrounded by the dotted line. Specifically, in FIG. 2, one of the dispersed particles contained in each of the first region A, the second region B, and the third region C of the diffusion layer is selected and enlarged to illustrate the orientation state of the liquid crystal polymer therein. In FIG. 2, the diffusion film 100 has a first support substrate 110, a diffusion layer 120, and a second support substrate 130 in this order. The diffusion layer 120 includes a polymer matrix 10 and dispersed particles 20 (20a) dispersed in the polymer matrix 10. The dispersed particles 20 (20a) include a liquid crystal polymer 22. Here, the liquid crystal polymer is a polymer of a polymerizable liquid crystal compound and is non-liquid crystal. That is, in the liquid crystal polymer, for example, the transition to a liquid crystal phase, a glass phase, or a crystalline phase due to temperature changes specific to liquid crystal compounds does not occur.

The first region A includes dispersed particles 20a containing liquid crystal polymer 22 oriented in a first direction (the direction of arrow a). Dispersed particles containing liquid crystal polymer oriented obliquely to the thickness direction make the first region more likely to transmit light along the first direction. The inclination angle (θ°) of the first direction can be appropriately set depending on the application of the diffusion film, etc. The inclination angle of the first direction may be, for example, 10° to 80°, or, for example, 20° to 70°.

In one embodiment, the dispersed particles containing the liquid crystal polymer oriented in the first direction are located along the first direction from one surface to the other surface of the diffusion layer. To explain in detail with reference to an image diagram (FIG. 3) illustrating an example of the distribution of dispersed particles, among the multiple dispersed particles 20 contained in the first region A of the diffusion layer 120, the dispersed particles 20a containing the liquid crystal polymer oriented in the first direction are aligned along the first direction (direction of arrow a) from the second region B side to the third region C side from one surface to the other surface of the diffusion layer 20. When the dispersed particles 20a are aligned in this manner, light is likely to be transmitted along the first direction as a result of the alignment of the dispersed particles 20a. Note that, as long as the effect of the present invention can be obtained, the dispersed particles in the first region may include a liquid crystal polymer that is not oriented in the first direction or a liquid crystal polymer that has a low degree of orientation in the first direction. The first region may also include dispersed particles that do not include a liquid crystal polymer oriented in the first direction. For example, in FIG. 3, the dispersed particles other than dispersed particle 20a in the first region may not contain liquid crystal polymer oriented in the first direction.

On the other hand, in the second region B of the diffusion film 100, the liquid crystal polymer 22 in the dispersed particles 20 is in a non-oriented state. In addition, in the third region C, the liquid crystal polymer 20 in the dispersed particles 20 is oriented in the second direction of the diffusion layer 120 (the thickness direction in the illustrated example). However, as long as the effects of the present invention can be obtained, the orientation states of the liquid crystal polymer in the second and third regions are not limited to the orientation states in the illustrated example, and can be adjusted appropriately depending on the purpose.

The diffusion film 100 having the above configuration can exhibit a higher parallel light transmittance in the oblique direction than in the thickness direction. In this specification, if the diffusion film exhibits a parallel light transmittance higher than the parallel light transmittance in the thickness direction (incident angle 0°) at any oblique angle (incident angle greater than 0° and less than 90°), it can be determined that the dispersed particles contain liquid crystal polymer oriented in an oblique direction, and the direction exhibiting the highest parallel light transmittance can be defined as the first direction. The parallel light transmittance can be measured according to JIS K 7361.

The shape and arrangement pattern of each region can be set appropriately depending on the purpose. For example, the first region and the second region may each be any shape (circular, elliptical, rectangular, polygonal, etc.). Also, for example, the first region may be provided so as to surround the outside of the third region, and the second region may be arranged outside of that.

The thickness of the diffusion film is, for example, 10 μm to 400 μm, preferably 20 μm to 300 μm, and more preferably 30 μm to 150 μm.

<Diffusion layer>
The diffusion layer 120 includes a polymer matrix 10 and dispersed particles 20 that are dispersed in the polymer matrix 10 and include a liquid crystal polymer 22. The dispersed particles 20 may further include a non-polymerizable liquid crystal compound in addition to the liquid crystal polymer 22. When the dispersed particles include a non-polymerizable liquid crystal compound, the orientation of the liquid crystal polymer can be more suitably controlled.

The diffusion layer 120 has a first region including a liquid crystal polymer oriented in a first direction. Preferably, the diffusion layer has a first region A, a second region B, and a third region C, each of which has a different haze when viewed in a plane. The haze of each region of the diffusion layer may be the same as the haze of each region of the diffusion film. The orientation state of the liquid crystal polymer in each region of the diffusion layer is as described above for the diffusion film.

The polymer matrix may be composed of any suitable resin. The resin for forming the polymer matrix may be appropriately selected depending on the light transmittance, the refractive index of the liquid crystal polymer or non-polymerizable liquid crystal compound, the adhesion to the support substrate, and the like. 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 resin for forming the polymer matrix may be used alone or in combination.

The content of the polymer matrix in the diffusion 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, it is possible to obtain effects such as good mechanical strength and prevention of liquid crystal leakage from the edges.

A liquid crystal polymer is a polymer of a polymerizable liquid crystal compound, and as described above, is non-liquid crystal. As the polymerizable liquid crystal compound that constitutes the liquid crystal polymer, any polymerizable liquid crystal compound can be used alone or in combination of two or more types depending on the birefringence, compatibility with the non-polymerizable liquid crystal compound, etc. In the following description, the characteristics of the liquid crystal compound (birefringence, dielectric constant, etc.) refer to the characteristics of the liquid crystal compound as a whole.

The dielectric anisotropy of the polymerizable liquid crystal compound may be positive or negative. The polymerizable liquid crystal compound may be a crosslinked type having two or more functionalities. As the polymerizable liquid crystal compound, for example, the polymerizable mesogen compounds described in JP-A-2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, GB2280445, etc. can be used. As the polymerizable liquid crystal compound, for example, a nematic type liquid crystal monomer is preferable.

The birefringence Δn (=ne-no; ne is the refractive index of the liquid crystal compound molecules in the long axis direction, and no is the refractive index of the liquid crystal compound molecules in the short axis direction) of the polymerizable liquid crystal compound at a wavelength of 589 nm is preferably 0.05 to 0.50, and more preferably 0.10 to 0.45.

As the non-polymerizable liquid crystal compound, 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 compound, etc. The dielectric anisotropy of the non-polymerizable liquid crystal compound may be positive or negative. The non-polymerizable liquid crystal compound may be, for example, a nematic type, a smectic type, or a cholesteric type liquid crystal compound. It is preferable to use a nematic type liquid crystal compound because it can achieve high transparency in the oriented state.

Nematic liquid crystal compounds include biphenyl compounds, phenylbenzoate compounds, cyclohexylbenzene compounds, azoxybenzene compounds, azobenzene compounds, azomethine compounds, terphenyl compounds, biphenylbenzoate compounds, cyclohexylbiphenyl compounds, phenylpyridine compounds, cyclohexylpyrimidine compounds, cholesterol compounds, fluorine compounds, etc. These liquid crystal compounds may be used alone or in combination.

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

The total content of the liquid crystal polymer and the non-polymerizable liquid crystal compound in the diffusion layer is, for example, 30% by weight to 70% by weight, preferably 35% by weight to 65% by weight, and more preferably 40% by weight to 60% by weight. The content of the liquid crystal polymer relative to the total content of the liquid crystal polymer and the non-polymerizable liquid crystal compound in the diffusion layer may be, for example, 5% by weight or more, preferably 7% by weight or more, and more preferably 10% by weight or more, and may be, for example, 100% by weight or less, preferably 80% by weight or less, and more preferably 50% by weight or less. The total content of the polymer matrix, the liquid crystal polymer, and the non-polymerizable liquid crystal compound in the diffusion layer may be, for example, 80% by weight or more, preferably 90% by weight to 99.9% by weight, and more preferably 95% by weight to 99.9% by weight.

The diffusion layer may further contain any suitable additives as necessary. Such additives include polymerization initiators, dispersants, leveling agents, crosslinking agents, dispersion stabilizers, etc. The total content of the additives in the diffusion layer may be, for example, 20% by weight or less, preferably 0.1% by weight to 10% by weight, and more preferably 0.1% by weight to 5% by weight.

The average particle diameter of the dispersed particles may be, for example, 0.2 μm to 9 μm, preferably 0.3 μm to 8 μm. If the average particle diameter of the dispersed particles is too small, the dispersed particle size is smaller than the wavelength of light, so that the light passes through the dispersed particles without being scattered, which may result in a problem of insufficient haze being obtained. If the average particle diameter is too large, the dispersed particle size is larger than the wavelength of light, so that a problem of insufficient haze being obtained may result. The average particle diameter of the dispersed particles in the diffusion layer is the volume average particle diameter of the dispersed particles when viewed from a direction perpendicular to the main surface of the diffusion layer.

The thickness of the diffusion layer is, for example, 3 μm to 60 μm, preferably 5 μm to 55 μm, and more preferably 10 μm to 50 μm.

<Support substrate>
The first supporting substrate and the second supporting substrate (hereinafter, collectively referred to as "supporting substrate") each include a substrate body. The supporting substrate may have a hard coat (HC) layer on one side or both sides of the substrate body as necessary. The first supporting substrate and the second supporting substrate may have the same configuration (material and thickness of the substrate body, presence or absence of an HC layer or material, etc.) or may have different configurations. One or both of the first supporting substrate and the second supporting substrate may be omitted depending on the purpose, etc.

The substrate body may be formed using any suitable material. Specific examples include glass film and polymer film. Polymer films are preferred because they have excellent smoothness and can be used for continuous production using rolls to greatly improve productivity.

The substrate body is typically a polymer film mainly 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, and moisture shielding properties. The above thermoplastic resins may be used alone or in combination of two or more. In addition, optical films such as those used in polarizing plates, such as low retardation substrates, high retardation substrates, retardation plates, absorptive polarizing films, and polarized selective reflection films, can also be used as the substrate body.

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

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

The thickness of the support substrate is, for example, 100 μm or less, preferably 3 μm to 50 μm, and more preferably 5 μm to 30 μm.

B. Method for Producing Diffusion Film According to another aspect of the present invention, there is provided a method for producing a diffusion film. The method for producing a diffusion film according to an embodiment of the present invention includes the steps of:
A step I of applying a coating liquid containing a polymer matrix-forming resin, a polymerizable liquid crystal compound, and a solvent to a first substrate to obtain a coating layer;
Step II of drying the coating layer to obtain a polymer dispersed liquid crystal layer including the polymer matrix and droplets containing the polymerizable liquid crystal compound dispersed in the polymer matrix;
Step III of polymerizing the polymerizable liquid crystal compound to obtain a diffusion layer,
The step III includes polymerizing the polymerizable liquid crystal compound in the first region of the polymer dispersed liquid crystal layer while at least a portion of the polymerizable liquid crystal compound is aligned in a first direction.
According to the manufacturing method of the diffusion film, at least a part of the polymerizable liquid crystal compound is polymerized in a state aligned in a first direction in the first region of the PDLC layer, and thus dispersed particles containing a liquid crystal polymer aligned in the first direction are generated in the first region. Therefore, according to the manufacturing method, the diffusion film described in section A can be suitably manufactured. The manufacturing method may further include, as necessary, disposing a second substrate on the side of the PDLC layer before the polymerizable liquid crystal compound is polymerized or on the side of the diffusion layer after the polymerization opposite to the side on which the first substrate is provided (step IV).

B-1. Step I
In step I, a coating liquid containing a polymer matrix forming resin, a polymerizable liquid crystal compound, and a solvent is applied to a first substrate to obtain a coating layer. The coating liquid typically further contains a polymerization initiator, and may further contain a non-polymerizable liquid crystal compound and/or other additives (such as a dispersant, a leveling agent, a crosslinking agent, and a dispersion stabilizer) as necessary. Hereinafter, the polymerizable liquid crystal compound and the non-polymerizable liquid crystal compound may be collectively referred to as a liquid crystal component.

The coating liquid is preferably an emulsion coating liquid containing liquid crystal particles containing a liquid crystal component as a dispersoid. In one embodiment, the coating liquid is an emulsion coating liquid in which polymer matrix forming resin particles and liquid crystal particles containing a liquid crystal component are dispersed in a solvent. The emulsion coating liquid preferably further contains a polymerization initiator in the liquid crystal particles.

As the solvent, water or a mixed solvent of water and a water-miscible organic solvent can be preferably used. Examples of the water-miscible organic solvent include C1-3 alcohol, acetone, DMSO, etc. The polymerizable liquid crystal compound, non-polymerizable liquid crystal compound, and resin for forming the polymer matrix are as described in Section A.

The content of the liquid crystal component in the solid content of the coating liquid can be, for example, 30% by weight to 70% by weight, preferably 35% by weight to 65% by weight, and more preferably 40% by weight to 60% by weight.

The weight ratio of the polymerizable liquid crystal compound to the non-polymerizable liquid crystal compound in the coating liquid (polymerizable liquid crystal compound:non-polymerizable liquid crystal compound) can be, for example, 5:95 to 100:0, preferably 7:93 to 80:20, and more preferably 10:90 to 50:50.

The content of the polymer matrix-forming resin in the solid content of the coating liquid can be, for example, 30% by weight to 70% by weight, preferably 35% by weight to 65% by weight, and more preferably 40% by weight to 60% by weight.

The weight ratio of the liquid crystal component content to the polymer matrix forming resin content in the coating liquid (liquid crystal component:polymer matrix forming resin) can be, for example, 30:70 to 70:30, preferably 35:65 to 65:35, and more preferably 40:60 to 60:40. The total content of the polymer matrix forming resin and the liquid crystal component in the solid content of the coating liquid can be, for example, 80% by weight or more, preferably 90% by weight to 99.9% by weight, and more preferably 95% by weight to 99.9% by weight.

The average particle diameter of the liquid crystal particles is preferably 0.3 μm or more, more preferably 0.4 μm or more. The average particle diameter of the liquid crystal particles is preferably 9 μm or less, more preferably 8 μm or less. If the average particle diameter of the liquid crystal particles is within this range, the average particle diameter of the dispersed particles in the diffusion layer can be set to a desired range. The average particle diameter of the liquid crystal particles means the volume-based median diameter, and can be measured by a laser diffraction/scattering method using, for example, a particle size distribution measuring device (Microtrac's "MT3300EXII") or the like.

It is preferable that the average particle size of the liquid crystal particles has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the average particle size of the liquid crystal particles may be, for example, less than 0.40, preferably 0.35 or less, and more preferably 0.30 or less.

The average particle size 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 with different resin types and/or average particle sizes may be used. The average particle size of the resin particles for forming a polymer matrix means the volume average particle size, and can be measured by dynamic light scattering using, for example, a particle size distribution measuring device (Microtrac's Nanotrac 150).

As the polymerization initiator, any suitable photopolymerization initiator or thermal polymerization initiator can be used depending on the purpose and desired properties, etc., and a photopolymerization initiator is preferably used. Specific examples of photopolymerization initiators include 2,2-dimethoxy-2-phenylacetophenone, acetophenone, benzophenone, xanthone, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, benzoin propyl ether, benzyl 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 polymerization initiators may be used alone or in combination of two or more. The content of the polymerization initiator is preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, relative to 100 parts by weight of the polymerizable liquid crystal compound.

Examples of dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. The content of the dispersant is preferably 1 to 15 parts by weight, and more preferably 2 to 10 parts by weight, per 100 parts by weight of the solid content of the coating liquid.

Examples of leveling agents include acrylic leveling agents, fluorine-based leveling agents, and silicone-based leveling agents. The content of the leveling agent is preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the solid content of the coating liquid.

Examples of crosslinking agents include aziridine-based crosslinking agents and isocyanate-based crosslinking agents. The content of the crosslinking agent is preferably 0.5 to 20 parts by weight, and more preferably 1 to 10 parts by weight, per 100 parts by weight of the solid content of the coating liquid.

The emulsion coating liquid can be prepared, for example, by mixing a resin emulsion or a resin particle dispersion containing resin particles for forming a polymer matrix, a liquid crystal emulsion containing liquid crystal particles containing a liquid crystal component and a polymerization initiator, and any additives (e.g., a dispersant, a leveling agent, a crosslinking agent). If necessary, a solvent may be further added during mixing. Alternatively, the emulsion coating liquid can be prepared by adding the liquid crystal component, the resin for forming a polymer matrix, the polymerization initiator, and any additives to a solvent and mechanically dispersing them.

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. In particular, the liquid crystal emulsion is preferably prepared by the membrane emulsification method. According to the membrane emulsification method, an emulsion with a uniform particle size distribution can be suitably obtained. For details of the membrane emulsification method, the disclosures of JP-A-4-355719, JP-A-2015-40994, and the like (these are incorporated herein by reference) can be referred to.

The solids concentration of the coating liquid can be, for example, 20% to 60% by weight, preferably 30% to 50% by weight.

The viscosity of the coating liquid can be appropriately adjusted so that the coating on the first substrate is performed satisfactorily. The viscosity of the coating liquid during coating is preferably 20 mPas to 400 mPas, more preferably 30 mPas to 300 mPas, and even more preferably 40 mPas to 200 mPas. If the viscosity is less than 20 mPas, the convection of the solvent becomes significant when the solvent is dried, and the thickness of the PDLC layer (and consequently the diffusion layer) may become unstable. If the viscosity exceeds 400 mPas, the bead of the coating liquid may become unstable. The viscosity of the coating liquid can be measured, for example, by a rheometer MCR302 manufactured by Anton Paar. The viscosity used here is the shear viscosity value at 20°C and a shear rate of 1000 (1/s).

Any suitable substrate may be used as the first substrate. By using the first supporting substrate described in Section A as the first substrate, a diffusion film having a first supporting substrate and a diffusion layer can be suitably obtained. Depending on the purpose, the first substrate may be peeled off and removed from the diffusion layer after completion of step III.

Any appropriate method can be used as the coating method. For example, roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), etc. are included. Among them, roll coating is preferred. For example, the description of JP2019-5698A can be referred to for coating by the roll coating method using a slot die.

The thickness of the coating layer is preferably 40 μm to 300 μm, more preferably 60 μm to 240 μm, and even more preferably 80 μm to 200 μm. Within such a range, a diffusion layer can be obtained that is excellent in improving the uniformity of in-plane luminance and has excellent thickness uniformity.

B-2. Step II
In step II, the coating layer obtained in step I is dried to obtain a PDLC layer containing a polymer matrix and droplets containing a polymerizable liquid crystal compound 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.

The coating layer can be dried by any suitable method. Specific examples of drying methods include natural drying, heat drying, and hot air drying. If the coating liquid contains a crosslinking agent, a crosslinked structure of the polymer matrix can be formed during drying.

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.

B-3. Step III
In step III, the polymerizable liquid crystal compound is polymerized in the PDLC layer obtained in step II, thereby forming a diffusion layer including a polymer matrix and dispersed particles that are dispersed in the polymer matrix and contain a liquid crystal polymer, which is a polymer of the polymerizable liquid crystal compound.

The polymerization of the polymerizable liquid crystal compound is carried out by irradiation with active energy rays, heating, or a combination of these, and is preferably carried out by irradiation with active energy rays.

Examples of active energy rays that can be used include ultraviolet rays, infrared rays, X-rays, alpha rays, beta rays, gamma rays, and electron beams. Of these, ultraviolet rays are preferred. In addition, it is preferable that the active energy rays are collimated light that has a high degree of linearity from the irradiation source.

The ultraviolet irradiation conditions can be appropriately set depending on the type of polymerizable liquid crystal compound, the transmittance of the substrate, the absorption wavelength of the photopolymerization initiator, etc. The irradiation intensity can be, for example, 0.1 mW/cm ² to 1000 mW/cm ² , preferably 1 mW/cm ² to 100 mW/cm ^2. The irradiation amount can be, for example, 10 mJ/cm ² to 10000 mJ/cm ² , preferably 100 mJ/cm ² to 5000 mJ/cm ^2. The irradiation temperature can be, for example, -20°C to 80°C, preferably -20°C to 60°C.

The polymerization is typically carried out in a state where at least a portion of the polymerizable liquid crystal compound is aligned in a first direction in the first region of the PDLC layer. For example, the polymerization can be carried out in a state where electrodes are arranged on both sides of the PDLC layer so that they do not overlap in a planar view, and a voltage is applied between the electrodes. This allows an electric field to be generated in the first region of the PDLC layer in a direction oblique to the thickness direction (e.g., the first direction), and the polymerizable liquid crystal compound can be polymerized in a state where the liquid crystal component is aligned in the electric field direction (e.g., the first direction).

An example of step III will be described below with reference to FIG. 4. In the illustrated example, step IV is performed before step III, and the PDLC film 100a has a PDLC layer 120a, a first support substrate 110 disposed on one side thereof, and a second support substrate 130 disposed on the other side thereof. The PDLC layer 120a includes a polymer matrix 10 and liquid crystal droplets 24 that are dispersed in the polymer matrix 10 and contain a polymerizable liquid crystal compound 26. A first electrode 410 is disposed on the outer side of the first support substrate 110 of the PDLC film 100a, and a second electrode 420 is disposed on the outer side of the second support substrate 130. Unlike the illustrated example, the first support substrate and/or the second support substrate may be omitted.

Figure 5(a) is a schematic plan view of the first electrode 410, and Figure 5(b) is a schematic cross-sectional view of the first electrode 410 shown in Figure 5(a) taken along line A2-A2. The first electrode 410 is flat, and has recesses 410a in a two-dimensional array on one side of the first electrode 410, each recess having a double circular shape in plan view. A preferred example of the first electrode 410 is a metal electrode.

Figure 6(a) is a schematic plan view of the second electrode 420, and Figure 6(b) is a schematic cross-sectional view of the second electrode 420 shown in Figure 6(a) taken along line A3-A3. The second electrode 420 has a flat substrate 422 and an electrode layer 424 provided on one side of the substrate 422. The electrode layer 424 has holes 424a that are circular in plan view and arranged in a two-dimensional array. In the illustrated example, the holes 424a have the same diameter as the outer diameter of the recesses 410a of the first electrode 410, and are arranged in the same pattern as the recesses 410a.

The second electrode is preferably a transparent electrode that can transmit active energy rays. The second electrode can be obtained, for example, by providing a transparent electrode layer 424 such as an ITO layer by sputtering on one side of a substrate 422 made of a glass plate, and then removing the transparent electrode layer 424 at desired locations by etching to form holes 424a. Alternatively, for example, the second electrode can be produced by providing a transparent electrode layer such as an ITO layer by sputtering on one side of a substrate made of a glass plate, and then removing the transparent electrode layer at locations corresponding to the holes together with the glass plate by cutting.

As described above, the holes 424a of the second electrode 420 are provided in the same pattern and have the same diameter as the outer diameter of the recesses 410a of the first electrode 410. Therefore, as shown in Fig. 4, when the first electrode 410 and the second electrode 420 are disposed on the first supporting substrate 110 side and the second supporting substrate 130 side of the PDLC film 100a, respectively, there are regions on both sides of the PDLC layer where the first electrode and the second electrode (more specifically, the electrode layer of the second electrode) are arranged to overlap, and regions where they do not overlap, in a plan view.
In the above configuration, when a voltage is applied between the first electrode and the second electrode, an electric field is generated in the thickness direction (the direction of arrow b) in the region where these electrodes overlap, and the liquid crystal component can be oriented along the electric field direction.
On the other hand, in the region where the electrodes do not overlap, an electric field may be generated in the direction connecting the first electrode and the second electrode. In particular, the strongest electric field may be generated along the direction where the distance between the electrodes is the shortest (i.e., the direction connecting the inner circle portion of the recess 410a of the first electrode 410 and the hole portion 424a side of the electrode layer 424 of the second electrode 420 (the direction of the arrow c)), more specifically, on the line where the distance between the electrodes is the shortest, and the liquid crystal component may be oriented along the electric field direction. Also, in the region where the electrodes do not overlap, the degree of orientation of the liquid crystal component decreases as the distance between the electrodes increases, and may be in a non-oriented state, for example.
In this state, by irradiating the PDLC layer with active energy rays (UV light in the illustrated example) from the second electrode side, at least a portion of the polymerizable liquid crystal compound in the area where the electrodes do not overlap can be polymerized in a state where the polymerizable liquid crystal compound is oriented in the direction that minimizes the distance between the electrodes.
The direction in which the distance between the electrodes is shortest is a direction inclined with respect to the thickness direction, and can correspond to the first direction in the diffusion film described in section A.
4, for regions of the PDLC layer with different electric field strengths, electric field directions, etc., one of the multiple dispersed particles contained in each region is selected and enlarged to illustrate the orientation state of the liquid crystal component therein. In the PDLC layer, the liquid crystal component in the dispersed particles contained in the width (cross-sectional area) of the electric field generated along the line where the distance between the electrodes is the shortest is preferably oriented along the direction of arrow c as shown in the example, and the degree of orientation of the liquid crystal component in the dispersed particles can decrease with increasing distance from the line.

According to the manufacturing method including step III of the illustrated example, it is possible to suitably obtain a diffusion film (as a result, the diffusion film described in section A) having a region corresponding to the double circular recess of the first electrode as a first region, a region corresponding to the inside of the inner circle of the double circular recess as a second region, and a region corresponding to the outside of the outer circle of the double circular recess as a third region.

The orientation state of the liquid crystal polymer in the dispersed particles in the first, second, and third regions of the diffusion layer can be appropriately changed by changing the applied voltage, the distance between the electrodes, etc. to change the electric field strength. For example, in the region where the electrodes overlap (third region), the applied voltage, the distance between the electrodes, etc. can be changed to polymerize the polymerizable liquid crystal compound in a state in which the liquid crystal component in the PDLC layer is aligned in the second direction. The angle between the second direction and the thickness direction is preferably smaller than the angle between the first direction and the thickness direction. Also, for example, in the region where the electrodes do not overlap (second region) that does not include the part where the distance between the electrodes is the shortest, the polymerizable liquid crystal compound can be polymerized in a state with a lower degree of orientation (including a non-aligned state) than in the region where the distance between the electrodes is the shortest (first region).

The difference between the outer diameter and inner diameter of the double circular recess of the first electrode and the depth of the recess can be appropriately set according to the desired diffusion characteristics, applied voltage, PDLC layer thickness, etc. Also, by appropriately changing the shape, arrangement pattern, etc. of the recess of the first electrode and the electrode layer of the second electrode, a diffusion film having a first region, a second region, and a third region in any shape and pattern can be obtained.

B-4. Step IV
In step IV, a second substrate is disposed on the side of the PDLC layer or the diffusion layer opposite to the side on which the first substrate is disposed. Any suitable substrate can be used as the second substrate, and the second supporting substrate described in section A can be preferably used. The timing of carrying out step IV may be before step III, i.e., before polymerizing the polymerizable liquid crystal compound, or after step III, i.e., after polymerizing the polymerizable liquid crystal compound.

According to the method for manufacturing a diffusion film including step IV, by using the first supporting substrate and the second supporting substrate described in section A as the first substrate and the second substrate, respectively, a diffusion film having the first supporting substrate and the second supporting substrate and the diffusion layer directly sandwiched therebetween can be obtained.

In order to obtain sufficient adhesion, the second substrate is laminated onto the PDLC layer or the diffusion layer, preferably using a laminator, while applying a lamination pressure of 0.006 MPa/m to 7 MPa/m, more preferably 0.06 MPa/m to 0.7 MPa/m.

C. Light Diffusion Device The light diffusion device according to an embodiment of the present invention includes the diffusion film described in Section A and a light source unit. Fig. 7 is a schematic cross-sectional view showing the configuration of a light diffusion device according to one embodiment of the present invention. The light diffusion device 300 includes a light source layer 200 and a diffusion film 100 (dispersion particles are not shown) disposed thereon.

The light source layer 200 has a reflective layer 210, a light source section 220 provided on one side of the reflective layer 210, and a sealing resin layer 230 that seals the light source section 220. The reflective layer may include, for example, a metal layer or a foamed resin layer. The light source section 220 is typically composed of a plurality of point light sources. The plurality of point light sources are, for example, two-dimensionally arranged in a predetermined pattern. For example, an LED element can be used as the point light source. The sealing resin layer 230 is, for example, composed of a thermosetting resin such as a silicone resin or an epoxy resin.

In one embodiment, the diffusion film 100 has a second region formed in a pattern corresponding to the arrangement pattern of the point light sources, and a first region and a third region formed in this order to surround the outside of the second region, and can be laminated on the light source layer 200 so that the second region (high haze region) is located above the point light sources. With this configuration, the light emitted from the point light sources can be highly diffused in the second region and can be suitably transmitted through the first and third regions. Furthermore, in the first region, the light can be preferentially transmitted obliquely outward. Therefore, a light diffusion device having this configuration can achieve excellent uniformity of in-plane brightness.

D. Image display device The diffusion film described in Section A and the light diffusion device described in Section C can be preferably used, for example, in a backlight device of an image display device. In one embodiment, the image display device is a liquid crystal display device having a light source unit, the diffusion film described in Section A, and a liquid crystal panel in this order, or a liquid crystal display device having the light diffusion device described in Section C and a liquid crystal panel arranged on the viewing side thereof.

The diffusion film of the present invention is suitable for use in light diffusion devices, etc.

REFERENCE SIGNS LIST 10 Polymer matrix 20 Dispersed particles 22 Liquid crystal polymer 100 Diffusion film 110 First supporting substrate 120 Diffusion layer 130 Second supporting substrate 100 Diffusion film 200 Light source layer 300 Light diffusion device

Claims (15)

A diffusion layer including a polymer matrix and dispersed particles including a liquid crystal polymer that is a polymer of a polymerizable liquid crystal compound and is dispersed in the polymer matrix,
the diffusion layer has a first region including the liquid crystal polymer aligned in a first direction;
A diffusion film, wherein the first direction is inclined with respect to a thickness direction. The diffusion film of claim 1, wherein the diffusion layer further has a third region having a lower haze than the first region and a second region having a higher haze than the first region. The diffusion film of claim 2, wherein the first region is disposed between the second region and the third region. The diffusion film of claim 2, wherein the difference between the haze of the second region and the haze of the third region is 10% or more. The diffusion film according to claim 1, wherein the dispersed particles containing the liquid crystal polymer oriented in the first direction are positioned along the first direction from one surface to the other surface of the diffusion layer. The diffusion film of claim 1, wherein the dispersed particles further comprise a non-polymerizable liquid crystal compound. The diffusion film according to claim 6, wherein the content of the liquid crystal polymer relative to the total content of the liquid crystal polymer and the non-polymerizable liquid crystal compound is 5% by weight or more. The diffusion film according to claim 1, further comprising a support substrate disposed on one or both sides of the diffusion layer. A light diffusion device having a light source unit and a diffusion film according to any one of claims 1 to 8. A liquid crystal display device having, in this order, a light source unit, a diffusion film according to any one of claims 1 to 8, and a liquid crystal panel. A step I of applying a coating liquid containing a polymer matrix-forming resin, a polymerizable liquid crystal compound, and a solvent to a first substrate to obtain a coating layer;
Step II of drying the coating layer to obtain a polymer dispersed liquid crystal layer including a polymer matrix and droplets containing the polymerizable liquid crystal compound dispersed in the polymer matrix;
and step III of polymerizing the polymerizable liquid crystal compound to obtain a diffusion layer,
the step III includes polymerizing, in a first region of the polymer dispersed liquid crystal layer, at least a part of the polymerizable liquid crystal compound in a state where the polymerizable liquid crystal compound is aligned in a first direction;
The method for manufacturing a diffusion film, wherein the first direction is inclined with respect to a thickness direction. The method according to claim 11, wherein step III includes polymerizing the polymerizable liquid crystal compound in the second region of the polymer-dispersed liquid crystal layer in a state in which the degree of orientation is lower than in the first region. the step III includes polymerizing, in a third region of the polymer dispersed liquid crystal layer, at least a part of the polymerizable liquid crystal compound in a state where the polymerizable liquid crystal compound is aligned in a second direction;
The manufacturing method according to claim 11 , wherein an angle between the second direction and the thickness direction is smaller than an angle between the first direction and the thickness direction. The method according to claim 11, wherein step III includes polymerizing the polymerizable liquid crystal compound while applying a voltage between electrodes arranged on both sides of the polymer dispersed liquid crystal layer so as not to overlap in a planar view. The method according to claim 11 , wherein the step III includes polymerizing the polymerizable liquid crystal compound in the first region of the polymer dispersed liquid crystal layer while applying an electric field in the first direction.

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