WO2010110103A1 - Process for producing light-diffusing element, light-diffusing element, and processes for producing polarizing plate with light-diffusing element and liquid-crystal display device - Google Patents

Abstract

A process for producing a light-diffusing element is provided by which a light-diffusing element having a high haze and high diffusing properties and reduced in backward scattering can be produced at low cost with high productivity. The process for producing a light-diffusing element comprises a step in which a matrix-forming material comprising a resin-ingredient precursor and an ultrafine-particle ingredient is brought into contact with fine light-diffusing particles, a step in which at least some of the precursor is infiltrated into an inner part of the fine light-diffusing particles, and a step in which the precursor that has infiltrated into the inner part of the fine light-diffusing particles and the precursor that has not infiltrated into the fine light-diffusing particles are simultaneously polymerized to form a matrix comprising the resin ingredient and the ultrafine-particle ingredient and simultaneously form a concentration gradation region in the vicinity of the inner side of the surface of the fine light-diffusing particles.

Description

Manufacturing method of light diffusing element, light diffusing element, polarizing plate with light diffusing element, and manufacturing method of liquid crystal display device

The present invention relates to a method for manufacturing a light diffusing element, a light diffusing element, a polarizing plate with a light diffusing element, and a method for manufacturing a liquid crystal display device.

Light diffusing elements are widely used in lighting covers, projection television screens, surface light emitting devices (for example, liquid crystal display devices), and the like. In recent years, light diffusing elements have been increasingly used for improving display quality of liquid crystal display devices and the like, and improving viewing angle characteristics. As the light diffusing element, an element in which fine particles are dispersed in a matrix such as a resin sheet has been proposed (for example, see Patent Document 1). In such a light diffusing element, most of the incident light is scattered forward (exit surface side), but a part is scattered backward (incident surface side). The greater the difference in refractive index between the fine particles and the matrix, the greater the diffusivity (for example, haze value). On the other hand, when the difference in refractive index is large, backscattering increases. When backscattering is large, when a light diffusing element is used in a liquid crystal display device, the screen becomes whitish when external light is incident on the liquid crystal display device, so that it is difficult to display a contrast image or image.

As a means to solve the above problems, based on the concept of suppressing reflection at the interface between the fine particles and the matrix, the core-shell fine particles having different refractive indexes of the core and the shell, or continuous from the center of the fine particles toward the outside It has been proposed to disperse gradient refractive index fine particles such as so-called GRIN (gradient index) fine particles whose refractive index changes in a resin (see, for example, Patent Documents 2 to 4). However, these fine particles are not practical because the production process is more complicated than ordinary fine particles, resulting in insufficient productivity.

Japanese Patent No. 3071538 JP-A-6-347617 JP 2003-262710 A JP 2002-212245 A

The present invention has been made to solve the above-described conventional problems. The object of the present invention is to reduce a light diffusing element having a high haze value, strong diffusibility, and suppressed backscattering. The object is to provide a method of manufacturing a light diffusing element that can be manufactured at low cost and high productivity.

The method for producing a light diffusing element of the present invention comprises a step of bringing a matrix-forming material containing a precursor of a resin component and an ultrafine particle component into contact with a light diffusing fine particle, and at least a part of the precursor being the light diffusing fine particle. A matrix containing a resin component and an ultrafine particle component by simultaneously polymerizing a step of permeating the inside of the light diffusing fine particles and a precursor that has penetrated into the light diffusing fine particles and a precursor that has not penetrated into the light diffusing fine particles. And forming a concentration modulation region in the vicinity of the surface of the light diffusing fine particles simultaneously with the formation.
In a preferred embodiment, the production method impregnates the precursor from the surface of the light diffusing fine particles to a range of 10% to 95% of the average particle diameter of the light diffusing fine particles in the infiltration step.
In a preferred embodiment, the production method comprises bringing the precursor of the resin component into contact with the light diffusing fine particles for a time longer than a time until the particle size of the light diffusing fine particles is substantially maximized. .
In a preferred embodiment, the resin component is an ionizing radiation curable resin, and the production method polymerizes the precursor of the resin component by irradiating the ionizing radiation.
According to another aspect of the present invention, a light diffusing element is provided. This light diffusing element is obtained by the above-described method, and has a matrix containing a resin component and an ultrafine particle component, and light diffusing fine particles dispersed in the matrix, inside the vicinity of the surface of the light diffusing fine particles. It has a concentration modulation region formed by permeation of the resin component.
According to another situation of this invention, the manufacturing method of a polarizing plate with a light-diffusion element is provided. This method uses the manufacturing method of the light diffusing element.
According to still another aspect of the present invention, a method for manufacturing a liquid crystal display device is provided. This method uses the manufacturing method of the light diffusing element.

According to the present invention, by using a specific matrix resin component (substantially a precursor thereof) and specific light diffusing fine particles in combination, when the light diffusing element is manufactured, The precursor of the matrix resin component can be infiltrated. By polymerizing this precursor, a matrix can be formed, and at the same time, a concentration modulation region can be formed in the vicinity of the surface of the light diffusing fine particles (that is, a matrix and a concentration modulation region can be formed in one batch). Can do). As described above, according to the present invention, since no special treatment or operation is required for forming the density modulation region, the light diffusing element can be manufactured at low cost and high productivity. In addition, since the light diffusing element obtained by the manufacturing method of the present invention has a concentration modulation region formed in the vicinity of the surface of the light diffusing fine particles, the refractive index is gradually increased in the vicinity of the interface between the light diffusing element and the matrix. Or it can be changed substantially continuously. Therefore, reflection at the interface between the matrix and the light diffusing fine particles can be satisfactorily suppressed, and backscattering can be suppressed. Furthermore, according to the present invention, the refractive index of the matrix can be easily adjusted by using the ultrafine particle component having a specific refractive index and a specific compatibility with the resin component. In particular, according to the present invention, since the resin component permeates the light diffusing fine particles, the concentration of the ultra fine particle component in the matrix can be increased, so that the refractive index difference between the matrix and the light diffusing fine particles can be reduced. Can be easily enlarged. As a result, the light diffusing element obtained by the production method of the present invention has a high haze value, strong diffusibility, and suppressed backscattering.

It is a schematic diagram for demonstrating the dispersion state of the resin component of a matrix and the light diffusible microparticles | fine-particles in the light-diffusion element obtained by the manufacturing method by preferable embodiment of this invention. (A) is a conceptual diagram for demonstrating the refractive index change from the center part of light diffusable microparticles | fine-particles in the light diffusing element of this invention to a matrix, (b) is a matrix from the center part of microparticles | fine-particles in the conventional light diffusing element. It is a conceptual diagram for demonstrating the refractive index change until. It is a graph which shows the relationship between a drying temperature and the diffusion half-value angle obtained about the coating liquid from which stationary time differs. It is a schematic sectional drawing of the polarizing plate with a light-diffusion element obtained by the manufacturing method by preferable embodiment of this invention. It is a schematic sectional drawing of the liquid crystal display device obtained by the manufacturing method by preferable embodiment of this invention. It is a schematic diagram for demonstrating the method of calculating a light-diffusion half-value angle. 6 is a transmission micrograph showing a concentration modulation region for light diffusing elements of Examples 1, 3 and 4. FIG.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these specific embodiments.

A. Method for Producing Light Diffusing Element The method for producing a light diffusing element of the present invention comprises a step (referred to as step A) of contacting a matrix-forming material containing a precursor of a resin component and an ultrafine particle component with light diffusing fine particles, A step of allowing at least a part of the precursor to penetrate into the light diffusing fine particles (referred to as Step B), and polymerizing the precursor to form a matrix containing a resin component and an ultrafine particle component, and at the same time, the light Forming a concentration modulation region in the vicinity of the surface of the diffusible fine particles (referred to as step C).

A-1. Process A
In step A, typically, a coating liquid is prepared in which a matrix-forming material containing a precursor of a resin component and an ultrafine particle component and light diffusing fine particles are dissolved or dispersed in a volatile solvent. Typically, the coating liquid is a dispersion in which ultrafine particle components and light diffusing fine particles are dispersed in a precursor and a volatile solvent. Any appropriate means (for example, ultrasonic treatment) can be adopted as means for dispersing the ultrafine particle component and the light diffusing fine particles. In the coating liquid, the light diffusing fine particles come into contact with the precursor of the resin component.

A-1-1. Resin Component The resin component is composed of any appropriate material as long as the concentration modulation region is satisfactorily formed. Preferably, the refractive index of the resin component satisfies the relationship of the following formula (1):
0 <| n _P −n _A | (1)
In formula (1), n _A represents the refractive index of the resin component of the matrix, and n _P represents the refractive index of the light diffusing fine particles. | N _P −n _A | is preferably 0.01 to 0.10, more preferably 0.01 to 0.06, and particularly preferably 0.02 to 0.06. If | n _P −n _A | is less than 0.01, the concentration modulation region may not be formed. When | n _P −n _A | exceeds 0.10, backscattering may increase.

Preferably, the resin component is composed of a compound similar to the light diffusing fine particles. More preferably, the resin component is composed of a highly compatible compound among the same compounds as the light diffusing fine particles. Thereby, the precursor (monomer) of the resin component can permeate into the light diffusing fine particles due to the fact that the resin component is the same material as the light diffusing fine particles. As a result of the polymerization of the precursor (monomer) described later, a concentration-modulated region by the resin component can be favorably formed in the vicinity of the surface of the light diffusing fine particles. In the present specification, “same system” means that chemical structures and properties are equivalent or similar, and “different system” means something other than the same system. Whether or not they are related may differ depending on how the reference is selected. For example, when organic or inorganic is used as a reference, the organic compounds are the same type of compounds, and the organic compound and the inorganic compound are different types of compounds. When the polymer repeat unit is used as a reference, for example, an acrylic polymer and an epoxy polymer are different compounds despite being organic compounds, and when a periodic table is used as a reference, alkali metals and transition metals are used. Is an element of a different system despite being inorganic elements.

The resin component is preferably composed of an organic compound, more preferably an ionizing radiation curable resin. The ionizing radiation curable resin is excellent in the hardness of the coating film. Examples of the ionizing rays include ultraviolet rays, visible light, infrared rays, and electron beams. Preferably, it is ultraviolet rays, and therefore the resin component is particularly preferably composed of an ultraviolet curable resin. Examples of the ultraviolet curable resin include radical polymerization monomers or oligomers such as acrylate resins (epoxy acrylate, polyester acrylate, acrylic acrylate, ether acrylate). The molecular weight of the monomer component (precursor) constituting the acrylate resin is preferably 200 to 700. Specific examples of the monomer component (precursor) constituting the acrylate resin include pentaerythritol triacrylate (PETA: molecular weight 298), neopentyl glycol diacrylate (NPGDA: molecular weight 212), dipentaerythritol hexaacrylate (DPHA: molecular weight 632). ), Dipentaerythritol pentaacrylate (DPPA: molecular weight 578), and trimethylolpropane triacrylate (TMPTA: molecular weight 296). Such a monomer component (precursor) is preferable because it has a molecular weight and a three-dimensional structure suitable for penetrating into the crosslinked structure (three-dimensional network structure) of the light diffusing fine particles. An initiator may be added as necessary. Examples of the initiator include a UV radical generator (Irgacure 907, 127, 192, etc., manufactured by Ciba Specialty Chemicals) and benzoyl peroxide. The resin component may contain another resin component in addition to the ionizing radiation curable resin. Another resin component may be an ionizing radiation curable resin, a thermosetting resin, or a thermoplastic resin. Representative examples of other resin components include aliphatic (for example, polyolefin) resins and urethane resins. In the case of using another resin component, the type and blending amount thereof are adjusted so that the concentration modulation region is well formed and the refractive index satisfies the relationship of the above formula (1).

The refractive index of the resin component is preferably 1.40 to 1.60.

The blending amount of the resin component in the coating solution is preferably 20 to 80 parts by weight, more preferably 45 to 65 parts by weight with respect to 100 parts by weight of the formed matrix.

A-1-2. Ultrafine particle component The above ultrafine particle component can typically function as a component that adjusts the refractive index of the matrix. By using the ultrafine particle component, the refractive index of the matrix can be easily adjusted, and the refractive index difference between the light diffusing fine particles and the matrix can be increased. In particular, according to the present invention, since the resin component permeates the light diffusing fine particles, the concentration of the ultra fine particle component in the matrix can be increased, so that the refractive index difference between the matrix and the light diffusing fine particles can be reduced. Can be easily enlarged. As a result, it is possible to obtain a light diffusing element having a high haze value (strong diffusibility) while being a thin film. Preferably, the ultrafine particle component has a refractive index n _B satisfying the following formula (2):
0 <| n _P −n _A | <| n _P −n _B | (2)
In Formula (2), n _A and n _P are as described above. | N _P −n _B | is preferably 0.10 to 1.50, more preferably 0.20 to 0.80. If | n _P −n _B | is less than 0.10, the haze is often 90% or less. As a result, when incorporated in a liquid crystal display device, the light from the light source cannot be sufficiently diffused, The corner may be narrowed. When | n _P −n _B | exceeds 1.50, backscattering may increase.

Preferably, the ultrafine particle component is composed of a compound of a system different from the resin component and the light diffusing fine particles, and more preferably composed of an inorganic compound. Examples of preferable inorganic compounds include metal oxides and metal fluorides. Specific examples of the metal oxide include zirconium oxide (zirconia) (refractive index: 2.19), aluminum oxide (refractive index: 1.56 to 2.62), and titanium oxide (refractive index: 2.49 to 2.19). 74) and silicon oxide (refractive index: 1.25 to 1.46). Specific examples of the metal fluoride include magnesium fluoride (refractive index: 1.37) and calcium fluoride (refractive index: 1.40 to 1.43). These metal oxides and metal fluorides have a refractive index that is difficult to be expressed by organic compounds such as ionizing radiation curable resins and thermoplastic resins in addition to low light absorption. The difference in refractive index from the matrix can be increased. In addition, these metal oxides and metal fluorides are separated from the vicinity of the interface between the light diffusing fine particles and the matrix (periphery of the light diffusing fine particles) due to the appropriate dispersibility with the resin component. Concentration modulation regions can be formed. By forming such another concentration modulation region outside the light diffusing fine particles, backscattering can be further suppressed as compared with the case where the concentration modulation region is formed only inside the light diffusing fine particles. . A particularly preferred inorganic compound is zirconium oxide. This is because the difference in refractive index from the light diffusing fine particles is large and the dispersibility with the resin component is appropriate, so that another concentration modulation region having the desired characteristics (or structure) can be satisfactorily formed. is there. In the present invention, the concentration modulation region may be formed in the vicinity of the surface of the light diffusing fine particles, and the other concentration modulation region may not be formed.

The refractive index of the ultrafine particle component is preferably 1.40 or less or 1.60 or more, more preferably 1.40 or less or 1.70 to 2.80, and particularly preferably 1.40 or less or 2 .00 to 2.80. If the refractive index exceeds 1.40 or less than 1.60, the difference in refractive index between the light diffusing fine particles and the matrix becomes insufficient, and the resulting light diffusing element is used as a liquid crystal display device of a collimated backlight front diffusion system. When used, the light from the collimated backlight may not be sufficiently diffused and the viewing angle may be narrowed.

The ultrafine particle component may be made porous to lower the refractive index.

The average particle size of the ultrafine particle component is preferably 1 nm to 100 nm, more preferably 10 nm to 80 nm, and still more preferably 20 nm to 70 nm. In this way, by using an ultrafine particle component having an average particle diameter smaller than the wavelength of light, no geometrical optical reflection, refraction, or scattering occurs between the ultrafine particle component and the resin component, and an optically uniform matrix. Can be obtained. As a result, an optically uniform light diffusing element can be obtained.

The ultrafine particle component preferably has good dispersibility with the resin component. In the present specification, “good dispersibility” means that a coating liquid obtained by mixing the resin component, the ultrafine particle component, and a volatile solvent (if necessary, a small amount of UV initiator) is applied, It means that the coating film obtained by drying and removing the solvent is transparent.

Preferably, the ultrafine particle component is surface-modified. By performing the surface modification, the ultrafine particle component can be favorably dispersed in the resin component, and the other concentration modulation region can be favorably formed. Any appropriate means can be adopted as the surface modifying means as long as the effects of the present invention can be obtained. Typically, the surface modification is performed by applying a surface modifier to the surface of the ultrafine particle component to form a surface modifier layer. Specific examples of preferable surface modifiers include coupling agents such as silane coupling agents and titanate coupling agents, and surfactants such as fatty acid surfactants. By using such a surface modifier, the wettability between the resin component and the ultrafine particle component is improved, the interface between the resin component and the ultrafine particle component is stabilized, and the ultrafine particle component is improved in the resin component. It is possible to disperse and form the other density modulation region favorably.

The blending amount of the ultrafine particle component in the coating solution is preferably 10 to 70 parts by weight, more preferably 35 to 55 parts by weight with respect to 100 parts by weight of the formed matrix.

A-1-3. Light Diffusing Fine Particles The light diffusing fine particles are composed of any appropriate material as long as the concentration modulation region is satisfactorily formed. Preferably, the light diffusing fine particles have a refractive index satisfying the relationship of the formula (1). Preferably, as described above, the light diffusing fine particles are composed of a compound similar to the resin component of the matrix. For example, when the ionizing radiation curable resin constituting the resin component of the matrix is an acrylate resin, the light diffusing fine particles are also preferably composed of an acrylate resin. More specifically, when the monomer component of the acrylate resin constituting the resin component of the matrix is, for example, PETA, NPGDA, DPHA, DPPA and / or TMPTA as described above, the acrylate constituting the light diffusing fine particles The base resin is preferably polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), and a copolymer thereof, and a cross-linked product thereof. Examples of the copolymer component with PMMA and PMA include polyurethane, polystyrene (PSt), and melamine resin. Particularly preferably, the light diffusing fine particles are composed of PMMA. This is because the relationship between the refractive index and thermodynamic characteristics with the resin component of the matrix is appropriate. Further preferably, the light diffusing fine particles have a cross-linked structure (three-dimensional network structure). The light diffusing fine particles having a crosslinked structure can swell. Therefore, unlike such dense or solid inorganic particles, such light diffusing fine particles can satisfactorily permeate a resin component precursor having appropriate compatibility. The crosslink density of the light diffusing fine particles is preferably small (coarse) so that a desired penetration range (described later) is obtained. For example, the degree of swelling of the light diffusing fine particles with respect to the resin component precursor (which may contain a solvent) when applying the coating liquid is preferably 110% to 200%. Here, the “swelling degree” refers to the ratio of the average particle size of the swollen particles to the average particle size of the particles before swelling.

The light diffusing fine particles have an average particle size of preferably 1 μm to 5 μm, more preferably 1.5 μm to 4.0 μm, still more preferably 2.0 μm to 3.0 μm, and particularly preferably 2 μm. .1 μm to 2.4 μm. The average particle diameter of the light diffusing fine particles is preferably ½ or less (for example, ½ to 1/20) of the thickness of the light diffusing element. If the average particle diameter has such a ratio with respect to the thickness of the light diffusing element, a plurality of light diffusing fine particles can be arranged in the thickness direction of the light diffusing element, so that incident light passes through the light diffusing element. In the meantime, the light can be diffused multiple times, and as a result, sufficient light diffusibility can be obtained.

The standard deviation of the weight average particle size distribution of the light diffusing fine particles is preferably 1.0 μm or less, more preferably 0.5 μm or less. If a large number of light diffusing fine particles having a small particle size with respect to the weight average particle size are mixed, the diffusibility may be excessively increased and the backscattering may not be suppressed well. If a large number of light diffusing fine particles having a large particle diameter with respect to the weight average particle diameter are mixed, a plurality of light diffusing elements cannot be arranged in the thickness direction of the light diffusing element, and multiple diffusion may not be obtained. , The light diffusibility may be insufficient.

As the shape of the light diffusing fine particles, any appropriate shape can be adopted depending on the purpose. Specific examples include a true sphere shape, a flake shape, a plate shape, an elliptic sphere shape, and an indefinite shape. In many cases, spherical fine particles can be used as the light diffusing fine particles.

The refractive index of the light diffusing fine particles is preferably 1.30 to 1.70, more preferably 1.40 to 1.60.

The blending amount of the light diffusing fine particles in the coating liquid is preferably 10 parts by weight to 100 parts by weight, more preferably 15 parts by weight to 40 parts by weight with respect to 100 parts by weight of the matrix to be formed. . For example, a light diffusing element having a very excellent light diffusibility can be obtained by incorporating light diffusing fine particles having an average particle diameter in the above preferred range with such a blending amount.

A-1-4. Overall Configuration of Coating Liquid Any appropriate solvent can be adopted as the volatile solvent as long as the above components can be dissolved or uniformly dispersed. Specific examples of the volatile solvent include ethyl acetate, butyl acetate, isopropyl acetate, 2-butanone (methyl ethyl ketone), methyl isobutyl ketone, cyclopentanone, toluene, isopropyl alcohol, n-butanol, cyclopentane, and water.

The coating liquid may further contain any appropriate additive depending on the purpose. For example, when the ultrafine particle component is used, a dispersant can be suitably used in order to disperse the ultrafine particle component satisfactorily. Other specific examples of the additive include an antioxidant, a modifier, a surfactant, a discoloration inhibitor, an ultraviolet absorber, a leveling agent, and an antifoaming agent.

The solid concentration of the coating solution can be adjusted to be preferably about 10% to 70% by weight. If it is such solid content concentration, the coating liquid which has a viscosity with easy coating can be obtained.

A-2. Process B
A typical example of means for allowing at least a part of the precursor to penetrate into the light diffusing fine particles in the step B is to leave the coating solution standing. The resin component and the light diffusing fine particles are preferably composed of the same material, and more preferably composed of a highly compatible material, so that the coating liquid is allowed to stand to perform a special treatment or operation. Even if not, the precursor (monomer) of the resin component penetrates into the light diffusing fine particles. That is, by bringing the precursor of the resin component and the light diffusing fine particles into contact with each other for a predetermined time, the precursor of the resin component penetrates into the light diffusing fine particles. The standing time is preferably longer than the time until the particle size of the light diffusing fine particles is substantially maximized. Here, “the time until the particle size of the light diffusing fine particles is substantially maximized” means that the light diffusing fine particles swell to the maximum extent and do not swell any more (that is, reach an equilibrium state). (Hereinafter also referred to as the maximum swelling time). By bringing the resin component precursor into contact with the light diffusing fine particles for a time longer than the maximum swelling time, the penetration of the resin component precursor into the light diffusing fine particles becomes saturated. It becomes unincorporated into the structure. As a result, the concentration modulation region can be formed satisfactorily and stably in the vicinity of the surface of the light diffusing fine particles by the polymerization step described later. The maximum swelling time can vary depending on the compatibility between the resin component and the light diffusing fine particles. Therefore, the standing time can vary depending on the constituent material of the resin component and the light diffusing fine particles. For example, the standing time is preferably 1 hour to 48 hours, more preferably 2 hours to 40 hours, still more preferably 3 hours to 35 hours, and particularly preferably 4 hours to 30 hours. . When the standing time is less than 1 hour, the precursor may not sufficiently penetrate into the light diffusing fine particles, and as a result, the concentration modulation region may not be satisfactorily formed. If the standing time exceeds 48 hours, the light diffusing fine particles aggregate due to the physical interaction between the light diffusing fine particles, and the viscosity of the coating liquid may increase, resulting in insufficient coating properties. There is. The standing may be performed at room temperature, or may be performed under a predetermined temperature condition set according to the purpose and the material used.

In step B, the precursor only needs to permeate from the surface of the light diffusing fine particles into a part of the light diffusing fine particles. For example, the precursor preferably permeates to a range of 10% to 95% of the average particle diameter. . When the permeation range is less than 10%, the concentration modulation region is not formed well, and backscattering may not be sufficiently reduced. Even when the permeation range exceeds 95%, the concentration modulation region is not formed well as in the case where the permeation range is small, and the backscattering may not be sufficiently reduced. The permeation range can be controlled by adjusting the resin component and the material of the light diffusing fine particles, the crosslinking density of the light diffusing fine particles, the standing time, the standing temperature, and the like.

In the present invention, it is important to control the penetration of the precursor into the light diffusing fine particles. For example, as shown in FIG. 3, when a light diffusing element is formed by applying to a substrate immediately after preparing the coating solution, the diffusion half-value angle varies greatly depending on the drying temperature (the drying process will be described later). To do). On the other hand, when the light-diffusing element is formed by applying the coating liquid to the substrate after standing for 24 hours, for example, the diffusion half-value angle is substantially constant regardless of the drying temperature. This is considered to be because the precursor penetrates into the light diffusing fine particles to a saturated state by standing, so that the formation of the concentration modulation region is not affected by the drying temperature. Therefore, as described above, the standing time is preferably longer than the maximum swelling time. By setting the standing time in this way, it is possible to obtain a substantially constant and good diffusion half-value angle regardless of the drying time, so that a highly diffusive light diffusing element can be stably produced without variation. . Furthermore, since it can manufacture by 60 degreeC low temperature drying, it is preferable also from the surface of safety | security or cost. On the other hand, if the time until the permeation reaches a saturated state can be determined according to the type of the precursor and the light diffusing fine particles, the standing time can be shortened by appropriately selecting the drying temperature. However, a light diffusing element having high diffusibility can be stably manufactured without variation. For example, even when a light diffusing element is formed by applying it to a substrate immediately after preparing a coating solution, the precursor is infiltrated into the light diffusing fine particles by setting the drying temperature to 100 ° C. Thus, it is possible to stably produce a light diffusing element having a high diffusibility by forming a density modulation region.

A-3. Process C
Typically, before the step C (step of polymerizing the precursor), the coating liquid is applied to the substrate. Any appropriate film can be adopted as the substrate as long as the effects of the present invention can be obtained. Specific examples include a triacetyl cellulose (TAC) film, a polyethylene terephthalate (PET) film, a polypropylene (PP) film, a nylon film, an acrylic film, and a lactone-modified acrylic film. If necessary, the base material may be subjected to surface modification such as easy adhesion treatment, and may contain additives such as a lubricant, an antistatic agent, and an ultraviolet absorber. The base material may function as a protective layer in the polarizing plate with a light diffusing element described later.

As a method for applying the coating liquid to the base material, a method using any appropriate coater can be employed. Specific examples of the coater include a bar coater, a reverse coater, a kiss coater, a gravure coater, a die coater, and a comma coater.

Next, the precursor is polymerized. As the polymerization method, any appropriate method can be adopted depending on the type of the resin component (and hence its precursor). For example, when the resin component is an ionizing radiation curable resin, the precursor is polymerized by irradiating the ionizing radiation. When ultraviolet rays are used as the ionizing ray, the integrated light quantity is preferably 200 mJ to 400 mJ. The transmittance of the ionizing rays to the light diffusing fine particles is preferably 70% or more, more preferably 80% or more. For example, when the resin component is a thermosetting resin, the precursor is polymerized by heating. The heating temperature and the heating time can be appropriately set according to the type of the resin component. Preferably, the polymerization is performed by irradiating with ionizing radiation. With ionizing ray irradiation, the coating film can be cured while maintaining a favorable refractive index distribution structure (concentration modulation region), so that a light diffusing element having good diffusion characteristics can be produced. By polymerizing the precursor, a matrix is formed, and at the same time, a concentration modulation region is formed in the vicinity of the surface of the light diffusing fine particles. More specifically, the concentration modulation region is formed by polymerization of a precursor that has penetrated into the light diffusing fine particles; the matrix is formed by polymerization of a precursor that has not penetrated into the light diffusing fine particles. . That is, according to the production method of the present invention, the precursor that has penetrated into the light diffusing fine particles and the precursor that has not penetrated into the light diffusing fine particles are simultaneously polymerized, so that the inside of the light diffusing fine particles near the surface. A matrix can be formed simultaneously with the formation of the density modulation region. In one embodiment, another concentration modulation region may be further formed in the vicinity of the interface between the light diffusing fine particles and the matrix (peripheral portion of the light diffusing fine particles). Another concentration modulation region can be formed mainly due to the compatibility of the resin component, the ultrafine particle component, and the light diffusing fine particles.

It goes without saying that the method for manufacturing a light diffusing element of the present invention can include any appropriate process, process and / or operation at any appropriate time in addition to the above-mentioned processes A to C. The type of such a process and the time when such a process is performed can be appropriately set according to the purpose. For example, the method for producing a light diffusing element of the present invention further includes a step of drying a coating liquid applied on the substrate, if necessary. Such drying may be performed, for example, before the polymerization step or after the polymerization step.

Any appropriate method can be adopted as a method for drying the coating liquid. Specific examples include natural drying, heat drying, and vacuum drying. Heat drying is preferable. The heating temperature is, for example, 60 ° C. to 150 ° C., and the heating time is, for example, 30 seconds to 5 minutes.

Thus, the light diffusing element is formed on the substrate. The obtained light diffusing element may be peeled off from the substrate and used as a single member, or may be used as a light diffusing element with a substrate, transferred from the substrate to a polarizing plate, etc. It may be used as a polarizing plate with a light diffusing element) or may be used as a composite member (for example, a polarizing plate with a light diffusing element) by being attached to a polarizing plate or the like together with the substrate. When the base material is attached to a polarizing plate or the like and used as a composite member (for example, a polarizing plate with a light diffusing element), the base material can function as a protective layer for the polarizing plate.

B. Light Diffusing Element The light diffusing element of the present invention can be obtained by the method described in the above items A-1 to A-3. The light diffusing element of the present invention has a matrix containing a resin component and an ultrafine particle component, and light diffusing fine particles dispersed in the matrix. The light diffusing element of the present invention exhibits a light diffusing function due to a difference in refractive index between the matrix and the light diffusing fine particles. FIG. 1 is a schematic diagram for explaining a dispersion state of a resin component of a matrix and light diffusing fine particles in a light diffusing element obtained by a manufacturing method according to a preferred embodiment of the present invention. The light diffusing element 100 of the present invention includes a matrix 10 including a resin component 11 and an ultrafine particle component 12 and light diffusing fine particles 20 dispersed in the matrix 10. Preferably, the resin component of the matrix and the light diffusing fine particles have a refractive index satisfying the following formula (1):
0 <| n _P −n _A | (1)
The ultrafine particle component has a refractive index satisfying the following formula (2):
0 <| n _P −n _A | <| n _P −n _B | (2)
By using the resin component of the matrix having the relationship of the above formula (1) and the light diffusing fine particles, and by using the ultrafine particle component having the relationship of the above formula (2), it is possible to prevent backscattering while maintaining high haze. A suppressed light diffusing element can be obtained.

In the light diffusing element of the present invention, the concentration modulation region 30 is formed in the vicinity of the surface of the light diffusing fine particles 20. The concentration modulation region 30 is formed by polymerizing the precursor (monomer) of the resin component 11 after penetrating into the light diffusing fine particles 20 as described in the above sections A-1 to A-3. In one embodiment, the weight concentration of the resin component 11 is substantially constant in the concentration modulation region 30. In another embodiment, in the concentration modulation region 30, the weight concentration of the resin component 11 decreases with increasing distance from the surface of the light diffusing fine particles 20 (that is, toward the center of the light diffusing fine particles 20). Preferably, if the concentration modulation region 30 is formed inside the light diffusing fine particles 20, the effect is exhibited. For example, the concentration modulation region is formed from the surface of the light diffusing fine particles 20 to a range of 10% to 95% of the average particle diameter of the light diffusing fine particles. The thickness of the concentration modulation region 30 (distance from the surface of the light diffusing fine particle to the innermost portion of the concentration modulation region) may be constant or may vary depending on the position of the surface of the light diffusing fine particle. The thickness of the concentration modulation region 30 is preferably 100 nm to 4 μm, more preferably 100 nm to 2 μm. When the resin component 11 permeates to form the concentration modulation region 30, the following effects can be obtained: (1) The refractive index is stepwise or substantially continuous in the vicinity of the interface between the light diffusing fine particles and the matrix. (See FIG. 2A). On the other hand, in the conventional light diffusing element, such a concentration modulation region is not formed, and the interface between the fine particles and the matrix is clear. Therefore, the refractive index is discontinuous from the refractive index of the fine particles to the refractive index of the matrix. It changes (refer FIG.2 (b)). As shown in FIG. 2A, by forming a concentration modulation region 30 and changing the refractive index stepwise or substantially continuously in the vicinity of the interface between the matrix 10 and the light diffusing fine particles 20, the matrix 10 is changed. Even if the refractive index difference between the light diffusing element 20 and the light diffusing element 20 is increased, reflection at the interface between the matrix and the light diffusing fine particles can be suppressed, and back scattering can be suppressed. On the other hand, as shown in FIG. 2 (b), according to the conventional light diffusing element, when an attempt is made to impart strong diffusivity (high haze value) by increasing the refractive index difference, the refractive index gap at the interface. Can not be resolved. As a result, backscattering due to interface reflection becomes large; (2) when another concentration modulation region mainly resulting from the ultrafine particle component is formed, the formation can be promoted; (3) resin component When 11 permeates into the light diffusing fine particles 20, the concentration of the resin component 11 in the matrix 10 becomes lower than in the case where it does not permeate. As a result, the contribution of the refractive index of the ultrafine particle component 12 to the refractive index of the entire matrix increases, so that the refractive index of the entire matrix increases when the refractive index of the ultrafine particle component is large (in contrast, the ultrafine particle component When the refractive index is small, the refractive index of the entire matrix is small), and the refractive index difference between the matrix and the light diffusing fine particles is further increased. Therefore, even higher diffusivity (haze value) can be realized as compared with the case where the resin component does not penetrate.

The concentration modulation region is formed by appropriately selecting the resin component of the matrix and the constituent material of the light diffusing fine particles, as well as the chemical and thermodynamic characteristics, as described in the above items A-1 to A-3. Can be formed. For example, the concentration modulation region can be satisfactorily formed by configuring the resin component and the light diffusing fine particles with materials having high compatibility among the similar materials. The thickness and concentration gradient of the concentration modulation region can be controlled by adjusting the chemical and thermodynamic characteristics of the resin component of the matrix and the light diffusing fine particles.

By appropriately selecting the ultrafine particle component in accordance with the type of the resin component and the light diffusing fine particles, it is separately provided in the vicinity of the interface between the matrix 10 and the light diffusing fine particles 20 (the periphery of the light diffusing fine particles). The concentration modulation region may be further formed (not shown). For example, by configuring the resin component and the light diffusing fine particles with the same material (for example, organic compounds), and configuring the ultra fine particle component with a system material (for example, an inorganic compound) different from the matrix and the light diffusing fine particles, Another density modulation region can be formed satisfactorily. More specifically, in the vicinity of the light diffusing fine particles, the resin component should surround the light diffusing fine particles only with the resin component, rather than being uniformly dissolved or dispersed with the ultra fine particle component. The energy of the whole system is stabilized. As a result, the weight concentration of the resin component is higher than the average weight concentration of the resin component in the entire matrix in the closest region of the light diffusing fine particles, and decreases as the distance from the light diffusing fine particles increases. Therefore, another density modulation region can be formed.

In the other concentration modulation region, as the distance from the light diffusing fine particles 20 increases, the weight concentration of the resin component 11 decreases and the weight concentration of the ultrafine particle component increases. In other words, the ultrafine particle component is dispersed at a relatively low concentration in the closest region of the light diffusing fine particle 20 in another concentration modulation region, and the concentration of the ultra fine particle component increases as the distance from the light diffusing fine particle 20 increases. Increase. For example, in the closest region of the light diffusing fine particles 20 in another concentration modulation region, the weight concentration of the resin component is higher than the average weight concentration of the resin component in the entire matrix, and the weight concentration of the ultrafine particle component is in the entire matrix. Lower than the average weight concentration of the ultrafine particle component. On the other hand, in the farthest region from the light diffusing fine particles 20 in another concentration modulation region, the weight concentration of the resin component is equal to or lower than the average weight concentration of the resin component in the entire matrix. The weight concentration of is equal to the average weight concentration of the ultrafine particle component in the entire matrix or higher depending on the case. By forming such another concentration modulation region outside the light diffusing fine particles, the region where the refractive index changes stepwise or substantially continuously can be enlarged (that is, light diffusibility). The refractive index can be changed stepwise or substantially continuously from the concentration modulation region inside the fine particle to another concentration modulation region outside the light diffusing fine particle, so that the concentration modulation region is only inside the light diffusing fine particle. In addition, the backscattering can be further suppressed as compared with the case where the weight concentration of the ultrafine particle component having a refractive index significantly different from that of the light diffusing fine particles 20 is relative to the outside of the other concentration modulation region. Therefore, the difference in refractive index between the matrix 10 and the light diffusing fine particles 20 can be increased, and as a result, high haze (strong diffusibility) can be realized even with a thin film. Kill. Such a feature is particularly suitable in applications where a strong diffusibility as a light diffusing element used in collimated backlight front diffusing system (haze 90% or higher) is required.

The thickness of the other concentration modulation region (distance from the surface of the light diffusing fine particle to the other concentration modulation region end) may be constant (that is, the other concentration modulation region is concentric around the light diffusing fine particle). The thickness may be different depending on the position of the surface of the light diffusing fine particles (for example, it may be like an outer shape of confetti). Preferably, the thickness of another concentration modulation region varies depending on the position of the surface of the light diffusing fine particles. With such a configuration, the refractive index can be changed more continuously in the vicinity of the interface between the matrix 10 and the light diffusing fine particles 20. If another concentration modulation region is formed with a sufficient thickness, the refractive index can be changed smoothly and continuously at the periphery of the light diffusing fine particles, and the backscattering can be suppressed very effectively. Can do. On the other hand, if the thickness is too large, another concentration modulation region occupies the region where the light diffusing fine particles should originally exist, and sufficient light diffusibility (for example, haze value) may not be obtained. Therefore, the thickness of another concentration modulation region is preferably 10 nm to 500 nm, more preferably 20 nm to 400 nm, and still more preferably 30 nm to 300 nm. Further, the thickness of the other concentration modulation region is preferably 10% to 50%, more preferably 20% to 40% with respect to the average particle diameter of the light diffusing fine particles.

The light diffusing element preferably has a higher haze, specifically, preferably 90 to 99%, more preferably 92 to 99%, still more preferably 95 to 99%, and particularly preferably. Is 97 to 99%. When the haze is 90% or more, it can be suitably used as a front light diffusing element in a collimated backlight front diffusing system. The collimated backlight front diffusion system is a liquid crystal display device that uses collimated backlight light (backlight light with a narrow luminance half-value width condensed in a certain direction) and the front light on the viewing side of the upper polarizing plate. A system provided with a diffusing element.

The diffusion characteristic of the light diffusing element is preferably 10 ° to 150 ° (5 ° to 75 ° on one side), more preferably 10 ° to 100 ° (5 ° to 50 ° on one side), in terms of a light diffusion half-value angle. And more preferably 30 ° to 80 ° (15 ° to 40 ° on one side).

The thickness of the light diffusing element can be appropriately set according to the purpose and desired diffusion characteristics. Specifically, the thickness of the light diffusing element is preferably 4 μm to 50 μm, more preferably 4 μm to 20 μm. According to the present invention, a light diffusing element having such a very high haze as described above can be obtained despite such a very thin thickness.

The light diffusing element is suitably used for a viewing side member of a liquid crystal display device, a backlight member of a liquid crystal display device, and a diffusing member for a lighting fixture (for example, an organic EL or LED), and is a front of a collimated backlight front diffusion system It is particularly preferably used as a diffusing element. The light diffusing element may be provided alone as a film-like or plate-like member, or may be provided as a composite member by being attached to any appropriate base material or polarizing plate. An antireflection layer may be laminated on the light diffusing element.

C. Polarizing plate with light diffusing element C-1. Overall Configuration of Polarizing Plate with Light Diffusing Element The manufacturing method of the polarizing plate with a light diffusing element of the present invention is performed using the manufacturing method of the light diffusing element of the present invention described in the above sections A-1 to A-3. . The polarizing plate with a light diffusing element obtained by the production method of the present invention is typically disposed on the viewing side of the liquid crystal display device. FIG. 4 is a schematic cross-sectional view of a polarizing plate with a light diffusing element according to a preferred embodiment of the present invention. The polarizing plate with a light diffusing element 200 includes a light diffusing element 100 and a polarizer 110. The light diffusing element 100 is the light diffusing element of the present invention described in the above items A-1 to A-3 and B. The light diffusing element 100 is disposed so as to be the most visible side when the polarizing plate with the light diffusing element is disposed on the viewing side of the liquid crystal display device. In one embodiment, a low reflection layer or an antireflection treatment layer (antireflection treatment layer) is disposed on the viewing side of the light diffusing element 100 (not shown). In the illustrated example, the polarizing plate with a light diffusing element 200 has protective layers 120 and 130 on both sides of the polarizer. The light diffusing element, the polarizer and the protective layer are attached via any appropriate adhesive layer or pressure-sensitive adhesive layer. At least one of the protective layers 120 and 130 may be omitted depending on the purpose, the configuration of the polarizing plate, and the configuration of the liquid crystal display device. For example, when the base material used when forming the light diffusing element can function as a protective layer, the protective layer 120 can be omitted. The polarizing plate with a light diffusing element of the present invention can be particularly suitably used as a viewing side polarizing plate in a liquid crystal display device employing a collimated backlight front diffusion system.

C-2. Polarizer Any appropriate polarizer may be adopted as the polarizer 110 depending on the purpose. For example, dichroic substances such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And polyene-based oriented films such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product and a polyvinyl chloride dehydrochlorinated product. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol film and uniaxially stretching is particularly preferable because of its high polarization dichroic ratio. The thickness of these polarizers is not particularly limited, but is generally about 1 to 80 μm.

A polarizer uniaxially stretched by adsorbing iodine to a polyvinyl alcohol film can be produced, for example, by dyeing polyvinyl alcohol in an aqueous iodine solution and stretching it 3 to 7 times the original length. . If necessary, it may contain boric acid, zinc sulfate, zinc chloride or the like, or may be immersed in an aqueous solution such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing.

By washing the polyvinyl alcohol film with water, not only can the surface of the polyvinyl alcohol film be cleaned and the anti-blocking agent can be washed, but also the effect of preventing unevenness such as uneven dyeing can be obtained by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

C-3. Protective layer The protective layers 120 and 130 are formed of any appropriate film that can be used as a protective layer of a polarizing plate. Specific examples of the material as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Further, a polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the resin composition.

The protective layer (inner protective layer) 130 is preferably optically isotropic. Specifically, the thickness direction retardation Rth (550) of the inner protective layer is preferably −20 nm to +20 nm, more preferably −10 nm to +10 nm, particularly preferably −6 nm to +6 nm, and most preferably −3 nm to +3 nm. It is. The in-plane retardation Re (550) of the inner protective layer is preferably 0 nm or more and 10 nm or less, more preferably 0 nm or more and 6 nm or less, and particularly preferably 0 nm or more and 3 nm or less. Details of the film that can form such an optically isotropic protective layer are described in Japanese Patent Application Laid-Open No. 2008-180961, which description is incorporated herein by reference.

D. Liquid Crystal Display Device The method for producing a liquid crystal display device of the present invention is performed using the method for producing a light diffusing element of the present invention described in the above items A-1 to A-3. FIG. 5 is a schematic cross-sectional view of a liquid crystal display device obtained by the manufacturing method of a preferred embodiment of the present invention. The liquid crystal display device 500 includes a liquid crystal cell 510, polarizing plates 520 and 530 disposed on both sides of the liquid crystal cell, a backlight unit 540 provided outside the polarizing plate 530, and the outside (viewing side) of the polarizing plate 520. The light diffusing element 100 is provided. Any appropriate optical compensation plate (retardation plate) may be disposed between the liquid crystal cell 510 and the polarizing plates 520 and / or 530 depending on the purpose. The liquid crystal cell 510 includes a pair of substrates (typically, glass substrates) 511 and 512 and a liquid crystal layer 513 that includes liquid crystal serving as a display medium and is disposed between the substrates 511 and 512.

The light diffusing element 100 is the light diffusing element of the present invention described in the above items A-1 to A-3 and B. Alternatively, instead of the light diffusing element 100 and the viewing side polarizing plate 520, the polarizing plate with a light diffusing element of the present invention described in the above section C may be disposed. The light diffusing element transmits and diffuses light that has passed through the liquid crystal cell (typically, collimated light as described below).

The backlight unit 540 is a parallel light source device that emits collimated light toward the liquid crystal cell 510. The backlight unit may have any suitable configuration that can emit collimated light. For example, the backlight unit includes a light source and a condensing element that collimates light emitted from the light source (none of which is shown). In this case, any appropriate condensing element capable of collimating light emitted from the light source can be employed as the condensing element. If the light source itself can emit collimated light, the condensing element can be omitted. Specific configurations of the backlight unit (parallel light source device) include, for example, the following: (1) A light shielding layer on a portion other than the focal point of the lens on the flat surface side of the lenticular lens or the bullet-type lens. Alternatively, a configuration in which a condensing element provided with a reflective layer is disposed on the liquid crystal cell side of a light source (for example, a cold cathode fluorescent lamp) (for example, JP-A-2008-262012); (2) a sidelight type LED light source; The light guide plate and a structure having a convex surface formed on the light guide plate side and a variable angle prism disposed on the liquid crystal cell side of the light guide plate (in this configuration, an anisotropic diffusion element is further used as necessary. For example, Japanese Patent No. 3442247); (3) A louver layer in which a light-absorbing resin and a transparent resin are alternately formed in a stripe shape is provided between a backlight and a backlight-side polarizing plate. (4) Configuration using a bullet-type LED as a light source (for example, JP-A-6-130255); (5) Fresnel lens and, if necessary, A configuration using a diffusion plate (for example, JP-A-1-126627). The above publication describing these detailed configurations is incorporated herein by reference.

Preferably, the liquid crystal layer 513 includes liquid crystal molecules vertically aligned during black display. As a driving mode of a liquid crystal cell having such a liquid crystal layer, for example, an MVA (multi-domain vertical alignment) mode, a PVA (pattern VA) mode, a TN (twisted nematic) mode, an ECB (electric field control birefringence) mode, An OCB (bend nematic) mode may be mentioned.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. Evaluation methods in the examples are as follows. Unless otherwise specified, “parts” and “%” in the examples are based on weight.

(1) Thickness of the light diffusing element The total thickness of the base material and the light diffusing element is measured with a microgauge thickness meter (manufactured by Mitutoyo Corporation), and the thickness of the light diffusing element is subtracted from the total thickness. Was calculated.
(2) Presence / absence of concentration modulation region While the laminate of the light diffusing element and the substrate obtained in Examples and Comparative Examples was cooled with liquid nitrogen, sliced to a thickness of 0.1 μm with a microtome, and a measurement sample It was. Using a transmission electron microscope (TEM), the state of fine particles in the light diffusing element portion of the measurement sample was observed. The case where the contrast due to the penetration of the precursor inside the fine particles could be confirmed was “concentration modulation region present”, and the case where the contrast could not be confirmed inside the fine particles and the color was uniform was designated “no concentration modulation region”.
(3) Haze The haze was measured using a haze meter (trade name “HN-150”, manufactured by Murakami Color Science Laboratory Co., Ltd.) according to the method defined in JIS 7136.
(4) Light diffusion half-value angle Laser light is irradiated from the front of the light diffusing element, and the diffusion luminance with respect to the diffusion angle of the diffused light is measured every 1 ° with a goniophotometer. As shown in FIG. The diffusion angle at which the luminance is half the maximum value of the light diffusion luminance excluding the straight transmitted light is measured on both sides of the diffusion, and the sum of the angles on both sides (angle A + angle A ′ in FIG. 6) is the light diffusion half value. It was a corner.
(5) Backscattering rate The laminated body of the light diffusing element and the base material obtained in the examples and comparative examples was placed on a black acrylic plate (trade name “SUMIPEX” (registered trademark) manufactured by Sumitomo Chemical Co., Ltd.) through a transparent adhesive. ) And a thickness of 2 mm) to obtain a measurement sample. The integrated reflectance of this measurement sample was measured with a spectrophotometer (trade name “U4100”, manufactured by Hitachi Keiki Co., Ltd.). On the other hand, using a coating liquid obtained by removing fine particles from the light diffusing element coating liquid, a laminate of a substrate and a transparent coating layer was prepared as a control sample, and the integrated reflectance ( That is, the surface reflectance was measured. The backscattering rate of the light diffusing element was calculated by subtracting the integrated reflectance (surface reflectance) of the control sample from the integrated reflectance of the measurement sample.
(6) Infiltration range of precursor Ten light diffusing fine particles were randomly selected from a TEM photograph taken by the procedure described in (2) above. For each selected light diffusing fine particle, measure the particle size of the light diffusing fine particle and the particle size of the part where the precursor of the light diffusing fine particle has not penetrated (non-penetrating part), and permeate with the following formula: Range was calculated. The average of 10 light diffusing fine particles was defined as the penetration range.
(Penetration range) = {1− (particle size of non-penetrating portion / particle size of light diffusing fine particles)} × 100 (%)

<Example 1: Production of light diffusing element>
Resin for hard coat containing 62% of zirconia nanoparticles (average particle diameter 60 nm, refractive index 2.19) as an ultrafine particle component (trade name “OPSTAR KZ6661” (MEK / MIBK included)) 18.2 6.8 parts of 50% MEK solution of pentaerythritol triacrylate (trade name “Biscoat # 300” manufactured by Osaka Organic Chemical Industry Co., Ltd., refractive index 1.52) as a precursor of the resin component was started in the part. Agent (Ciba Specialty Chemicals, trade name “Irgacure 907”) 0.068 parts, Leveling agent (DIC, trade name “GRANDIC PC 4100”) 0.625 parts, and light diffusing fine particles Polymethyl methacrylate (PMMA) fine particles (manufactured by Negami Kogyo Co., Ltd., trade name “Art Pearl J4P”, average particle size 2.1 μm, 2.5 parts of refractive index 1.49) were added. This mixture was sonicated for 5 minutes to prepare a coating solution in which the above components were uniformly dispersed. The coating solution is applied onto a TAC film (trade name “Fujitac”, manufactured by Fuji Film Co., Ltd.) using a bar coater, dried at 100 ° C. for 1 minute, and then irradiated with ultraviolet light with an integrated light amount of 300 mJ to obtain a thickness. A 15 μm light diffusing element was obtained. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1 together with the results of Examples 2 to 4 described later. Further, a TEM photograph of a cross section of the light diffusing element is shown in FIG. From the TEM photograph, it was confirmed that a concentration modulation region was formed inside the light diffusing fine particles.

<Example 2: Production of light diffusing element>
A coating solution was prepared in the same manner as in Example 1. The coating liquid was allowed to stand for 4 hours, and then coated in the same manner as in Example 1. A light diffusing element was obtained in the same manner as in Example 1 except that the drying temperature after coating was 60 ° C. and the thickness was 10 μm. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1.

<Example 3: Production of light diffusing element>
A light diffusing element was obtained in the same manner as in Example 1 except that the drying temperature after coating the coating solution was 60 ° C. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1. Further, a TEM photograph of a cross section of the light diffusing element is shown in FIG. From the TEM photograph, it was confirmed that a concentration modulation region was formed inside the light diffusing fine particles.

<Example 4: Production of light diffusing element>
A light diffusing element was obtained in the same manner as in Example 1 except that PMMA fine particles (MX180TA, manufactured by Soken Chemical Co., Ltd.) were used as the light diffusing fine particles, and the thickness was 20 μm. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1. Further, a TEM photograph of a cross section of the light diffusing element is shown in FIG. From the TEM photograph, it was confirmed that a concentration modulation region was formed inside the light diffusing fine particles.

<Example 5: Production of light diffusing element>
A coating solution was prepared in the same manner as in Example 1. The coating liquid was allowed to stand for 2 hours, and then a light diffusing element was obtained in the same manner as in Example 2. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1.

<Example 6: Production of light diffusing element>
A coating solution was prepared in the same manner as in Example 1. The coating liquid was allowed to stand for 7 hours, and then a light diffusing element was obtained in the same manner as in Example 2. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1.

<Example 7: Production of light diffusing element>
A coating solution was prepared in the same manner as in Example 1. The coating liquid was allowed to stand for 24 hours, and then a light diffusing element was obtained in the same manner as in Example 2. The obtained light diffusing element was subjected to the evaluations (1) to (6) above. The results are shown in Table 1.

<Example 8: Production of liquid crystal display device>
The liquid crystal cell was taken out from a commercially available liquid crystal television (manufactured by Sony, BRAVIA 20 type, trade name “KDL20J3000”) having a multi-domain VA mode liquid crystal cell. A commercially available polarizing plate (trade name “NPF-SEG1423DU” manufactured by Nitto Denko Corporation) was bonded to both sides of the liquid crystal cell so that the absorption axes of the respective polarizers were orthogonal to each other. More specifically, the absorption axis direction of the polarizer of the backlight side polarizing plate is the vertical direction (90 ° with respect to the long side direction of the liquid crystal panel), and the absorption axis direction of the polarizer of the viewing side polarizing plate is the horizontal direction. Bonding was performed so as to be (0 ° with respect to the long side direction of the liquid crystal panel). Further, the light diffusing element of Example 1 was transferred from the base material and bonded to the outside of the viewing side polarizing plate to produce a liquid crystal panel.

On the other hand, a lenticular lens pattern was melt-heat transferred onto one side of a PMMA sheet using a transfer roll. An aluminum pattern is deposited on the surface (smooth surface) opposite to the surface on which the lens pattern is formed so that light is transmitted only through the focal point of the lens, and the area ratio of the opening is 7% (the area ratio of the reflection section is 93). %) Of the reflective layer. In this way, a light collecting element was produced. A cold cathode fluorescent lamp (manufactured by Sony Corporation, BRAVIA20J CCFL) was used as the light source of the backlight, and a condensing element was attached to the light source to produce a parallel light source device (backlight unit) that emits collimated light.

The above backlight unit was incorporated into the above liquid crystal panel to produce a liquid crystal display device of a collimated backlight front diffusion system. About the obtained liquid crystal display device, white display and black display were performed in a dark place, and the display state was visually observed. As a result, when viewed from an oblique direction, the black display in the bright place was black and the brightness of the white display in the dark place was high.

<Evaluation>
As is apparent from the description of the procedures of the examples and Table 1, according to the method of manufacturing the light diffusing element of the present invention, the light diffusing fine particles and the matrix resin are substantially not performed without any special treatment or operation. After mixing with the precursors of the components, the light diffusing element having the concentration modulation region could be manufactured simply by polymerizing the precursor. By using such a light diffusing element for a liquid crystal display device of a collimated backlight front diffusing system, a liquid crystal display having good display characteristics that black display in a bright place is black and white display brightness in a dark place is high. A device was obtained. Further, as apparent from comparison between Examples 1 to 3 and 5 to 7, the longer the standing time, the higher the diffusibility until the penetration of the precursor into the light diffusing fine particles reaches a saturated state. When a light diffusing element is obtained and reaches a saturated state, it can be seen that the diffusibility of the obtained light diffusing element is substantially constant even if the standing time is increased. Furthermore, it is understood that a light diffusing element having a high haze value can be obtained even when dried at a low temperature by securing a predetermined standing time and forming a concentration modulation region (low temperature drying is a cost in production and It is preferable because it is excellent in safety).

The light diffusing element and the polarizing plate with a light diffusing element obtained by the production method of the present invention are a viewing side member of a liquid crystal display device, a backlight member of a liquid crystal display device, and a diffusing member for a lighting fixture (for example, organic EL, LED). And can be particularly preferably used as a front diffusion element of a collimated backlight front diffusion system.

DESCRIPTION OF SYMBOLS 10 Matrix 11 Resin component 20 Light diffusing fine particle 30 Density modulation area 100 Light diffusing element 110 Polarizer 120 Protective layer 130 Protective layer 200 Polarizing plate 500 with light diffusing element Liquid crystal display device

Claims (7)

1. Contacting the matrix-forming material containing the precursor of the resin component and the ultrafine particle component with the light diffusing fine particles;
   Allowing at least a portion of the precursor to penetrate into the light diffusing fine particles;
   The precursor that has penetrated into the light diffusing fine particles and the precursor that has not penetrated into the light diffusing fine particles are simultaneously polymerized to form a matrix containing a resin component and an ultrafine particle component, and at the same time, the light diffusibility Forming a concentration modulation region in the vicinity of the surface of the fine particles,
   Manufacturing method of light diffusing element.
2. 2. The light diffusing element according to claim 1, wherein in the infiltration step, the precursor is infiltrated from a surface of the light diffusing fine particles to a range of 10% to 95% of an average particle diameter of the light diffusing fine particles. Method.
3. The light diffusion according to claim 1 or 2, wherein the precursor of the resin component and the light diffusing fine particles are brought into contact with each other for a time longer than a time until the particle size of the light diffusing fine particles is substantially maximized. Device manufacturing method.
4. The method for producing a light diffusing element according to any one of claims 1 to 3, wherein the resin component is an ionizing radiation curable resin, and the precursor of the resin component is polymerized by irradiating the ionizing radiation.
5. A light diffusing element obtained by the method according to claim 1,
   A matrix containing a resin component and an ultrafine particle component, and light diffusing fine particles dispersed in the matrix,
   A light diffusing element having a concentration modulation region formed by penetration of the resin component in the vicinity of the surface of the light diffusing fine particles.
6. A method for producing a polarizing plate with a light diffusing element, wherein the method for producing a light diffusing element according to any one of claims 1 to 4 is used.
7. The manufacturing method of a liquid crystal display device using the manufacturing method of the light-diffusion element in any one of Claim 1 to 4.
   
   

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