WO2018142721A1 - Light-diffusing particles, light-diffusing and -transmitting sheet, and method for producing light-diffusing particles - Google Patents

Abstract

Light-diffusing particles (10) that comprise a core (10c) and a shell (10s). The core (10c) is formed from a first binder (11) and first fine particles (12). The first fine particles (12) include a low-refractive-index fine particle (12a) that has a lower refractive index than the first binder (11). The first fine particles (12) contact and are covered by the first binder. The shell (10s) contacts an outer surface of the core (10c) and covers the core (10c). The shell (10s) includes spherical particles (13) that have a particle diameter of 50–450 nm and give the shell (10s) surface roughness (A).

Description

Light diffusing particles, light diffusing and transmitting sheet, and method for producing light diffusing particles

The present invention relates to a light diffusing particle, a light diffusing and transmitting sheet, and a method for producing the light diffusing particle.

Demand for light diffusing and transmitting sheets having high light diffusing characteristics is increasing in order to spatially homogenize the light emitted from the backlight of the liquid crystal display as the image quality of the liquid crystal display increases. In addition, from the viewpoint of reducing energy consumption, there is an increasing demand for light diffusing and transmitting sheets having high luminance characteristics.

Patent Document 1 describes a light diffusing and transmitting sheet provided with a resin as a base material and silica composite particles dispersed in the resin. The silica composite particles include titanium oxide fine particles having an average particle diameter of 100 nm or less. The light diffusion transmission sheet described in Patent Literature 1 exhibits high total light transmittance and haze ratio. The refractive index of titanium oxide is larger than that of silica.

Patent Document 2 describes a transmissive screen for visually recognizing an image projected from a projector. The transmission screen has a light diffusion layer containing light diffusion fine particles and xerogel. It is described that as the light diffusing fine particles, composite particles composed of organic fine particles and a small amount of inorganic fine particles or composite particles composed of inorganic fine particles and a small amount of organic polymer can be used. Examples of the composite particles composed of organic fine particles and a small amount of inorganic fine particles include composite particles in which the surface of fine particles such as melamine resin or acrylic resin is coated with inorganic fine particles such as silica. In general, the refractive index of melamine resin and the refractive index of acrylic resin are higher than the refractive index of silica.

Patent Document 3 describes an optical laminate having a light-transmitting substrate and an internal scattering layer. Patent Document 3 describes that this optical laminate exhibits excellent contrast and antiglare effect while maintaining good antiglare properties. The internal scattering layer contains internal scattering particles. The internal scattering particles include fine particles having an average particle diameter of 5 to 300 nm. The refractive index n _A of the fine particles encapsulated in the internal scattering particles is larger than the refractive index n _B of components other than the fine particles encapsulated in the internal scattering particles.

Patent Document 4 describes a light diffusing plate having a light diffusing layer made of a transparent base material containing a transparent resin. The light diffusion layer includes first light diffusion particles and second light diffusion particles present inside the transparent substrate. The refractive index of the second light diffusing particles is larger than the refractive index of the first light diffusing particles. The refractive index of the first light diffusing particles is 1.4 to 1.7, and the refractive index of the second light diffusing particles is larger than 2.

JP 2014-48427 A JP 2013-195548 A JP 2009-42554 A JP 2008-40479 A

The techniques described in Patent Documents 1 to 4 are not necessarily advantageous in providing high luminance characteristics to a product including a layer or sheet in which particles described in Patent Documents 1 to 4 are dispersed. In addition, Patent Documents 1 to 4 do not discuss any water retention on the particle surface.

Therefore, the present invention provides light diffusing particles having a surface that is advantageous for imparting high luminance characteristics to a light diffusing and transmitting sheet and that is difficult to retain water.

The present invention
A core formed of a first binder and a first fine particle comprising low refractive index fine particles having a refractive index lower than the refractive index of the first binder, and being covered in contact with the first binder;
A shell that contacts the outer surface of the core and covers the core, the spherical particles having a particle diameter of 50 nm to 450 nm and imparting surface irregularities to the shell, and a second that is in contact with the outer surface of the spherical particles A shell including a binder,
Provide light diffusing particles.

The present invention also provides:
With the base material,
The light diffusion particles dispersed in the base material,
A light diffusing and transmitting sheet is provided.

Furthermore, the present invention provides:
A method for producing light diffusing particles having a core-shell structure,
Preparing a first dispersion in which raw materials of the first binder and first fine particles including low refractive index fine particles having a refractive index lower than the refractive index of the first binder are dispersed,
A core is formed by adding a crosslinking agent for crosslinking the raw material of the first binder to the first dispersion to crosslink the raw material of the first binder,
Preparing a second dispersion in which the core and spherical particles having a particle diameter of 50 nm to 450 nm are dispersed;
Spray drying the second dispersion;
Provide a method.

The above light diffusing particles are advantageous for imparting high luminance characteristics to the light diffusing and transmitting sheet in which the light diffusing particles are dispersed, and water hardly stays on the surface of the light diffusing particles. Moreover, according to said method, the light-diffusion particle | grains which have a core shell structure and have the surface which is hard to hold | maintain water can be manufactured by one spray drying.

FIG. 1 is a cross-sectional view schematically showing the structure of a light diffusing particle according to an example of the present invention. FIG. 2 is a diagram schematically showing an optical path of light incident on a fine particle having a high refractive index. FIG. 3A is a diagram schematically illustrating an optical path of light incident on a low refractive index fine particle. FIG. 3B is a diagram schematically illustrating an optical path of light incident on another low refractive index fine particle. FIG. 4 is a diagram schematically showing light diffusing particles having a surface that is easy to retain water. FIG. 5 is a diagram schematically illustrating the difficulty of water retention on the surface of the light diffusion particle according to an example of the present invention. FIG. 6A is a diagram schematically illustrating the vicinity of the surface of a light diffusion particle according to an example of the present invention. FIG. 6B is a diagram showing a change in refractive index in the section y0 to y2 shown in FIG. 6A. FIG. 7 is a cross-sectional view showing a light diffusing and transmitting sheet according to an example of the present invention. FIG. 8 is a scanning electron microscope (SEM) photograph of the light diffusing particles according to Example 3. FIG. 9 is an SEM photograph of the light diffusing particles according to Comparative Example 1.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description relates to an example of the present invention, and the present invention is not limited to these.

As shown in FIG. 1, the light diffusion particle 10 includes a core 10 c and a shell 10 s. The core 10 c is formed by the first binder 11 and the first fine particles 12. The first fine particles 12 include low refractive index fine particles 12 a having a refractive index lower than that of the first binder 11. In addition, the first fine particles 12 are covered in contact with the first binder 11. The shell 10s contacts the outer surface of the core 10c and covers the core 10c. The shell 10 s includes spherical particles 13 and a second binder 15. The spherical particles 13 have a particle diameter of 50 nm to 450 nm, and give the surface irregularities A to the shell. The second binder 15 is in contact with the outer surface of the spherical particle 13. In the present specification, “particle diameter” means the maximum diameter. “Spherical particle” means a particle having an aspect ratio (ratio of maximum diameter to minimum diameter) of 1.3 or less.

The silica composite particles described in Patent Document 1 include titanium oxide fine particles having an average particle diameter of 100 nm or less. The refractive index of titanium oxide is larger than that of silica. For this reason, in the silica composite particles, titanium oxide fine particles having a high refractive index are encapsulated in silica having a low refractive index. As shown in FIG. 2, when light enters a high refractive index fine particle PH from a relatively low refractive index medium, a part of the light incident on the fine particle PH is repeatedly reflected inside the fine particle PH and inside the fine particle PH. It is easy to be trapped in. In this specification, such a phenomenon is called an “optical confinement phenomenon”. In the silica composite particles described in Patent Document 1, a light confinement phenomenon is likely to occur, and it is difficult to say that the technique described in Patent Document 1 is advantageous for imparting high luminance characteristics to the light diffusion transmission sheet. The same applies to the techniques described in Patent Documents 2 and 3. Moreover, although the composite particle is not described in Patent Document 4, since the refractive index of the second light diffusion particle is larger than 2, it is considered that the light confinement phenomenon is likely to occur in the second light diffusion particle.

In contrast, for example, as shown in FIGS. 3A and 3B, when light is incident on the low-refractive-index fine particles PL1 or the fine particles PL2 from a medium having a relatively high refractive index, the “light confinement phenomenon” occurs in the fine particles PL1 and PL2. Is unlikely to occur. 3A, the difference obtained by subtracting the refractive index of the fine particle PL1 from the refractive index of the medium around the fine particle PL1 is 0.01. In FIG. 3B, the refractive index of the fine particle PL2 is determined from the refractive index of the medium around the fine particle PL2. The difference minus the rate is 0.1. In the light diffusion particle 10, the low refractive index fine particles 12 a have a refractive index lower than that of the first binder 11 and are covered with the first binder 11. Therefore, the light confinement phenomenon hardly occurs in the low refractive index fine particles 12a, and the light diffusing particles 10 are advantageous for imparting high luminance characteristics to the light diffusing and transmitting sheet in which the light diffusing particles 10 are dispersed.

Next, the reason why water hardly stays on the surface of the light diffusion particle 10 will be described. The conditions for capillary condensation are described by the following equation [1]. Here, p, p _s , σ, V, r, R, and T are respectively the vapor pressure when the liquid is a plane, the vapor pressure in the capillary, the surface tension, the molecular volume, the radius of the capillary, the gas constant, And absolute temperature.
log ₁₀ (p / p _s ) = (− 2σV / rRT) [1]

From equation [1], the radius r of the capillary where capillary condensation occurs when the liquid is water in an environment of 25 ° C. and a relative humidity of 50% RH (p / p _s = 0.5) is estimated. In this estimation, σ, V, r, R, and T are 72 × 10 ⁻³ [N · m ⁻¹ ], 18 × 10 ⁻⁶ [m ³ · kg ⁻¹ ], and 8.31 [J · mol, respectively. ⁻¹ K ⁻¹ ] and 298 [K]. In this case, the capillary radius r = 3.5 nm. Capillary condensation occurs in a standard environment of 25 ° C. and a relative humidity of 50% RH, and the radius of the capillary is 3.5 nm. Therefore, if there is a recess with a width of several nanometers near the particle surface, water vapor in the air Capillary condensation may occur in the recess.

For example, as shown in FIG. 4, when a concave portion having a width of several nanometers is present close to the surface of the particle, a large amount of water W stays on the surface of the particle due to capillary condensation of water vapor in the concave portion. In the shell 10 s of the light diffusing particle 10, surface irregularities A are given by the spherical particles 13. As shown in FIG. 1, the surface irregularities A reflect the shape of the spherical particles 13. As shown in FIG. 5, the concave portions of the surface irregularities A are sparsely present in the vicinity of the surface of the light diffusing particles 10 because the spherical particles 13 have a particle diameter of 50 nm to 450 nm. For this reason, sites where capillary condensation of water vapor occurs only sparsely exist in the vicinity of the surface of the light diffusing particle 10, and the light diffusing particle 10 has a surface that hardly retains water. Thereby, when manufacturing a light diffusion transmission sheet using the light diffusion particle 10, it can prevent that the quality of a light diffusion transmission sheet falls with a water | moisture content.

The spherical particles 13 desirably have a particle diameter of 50 nm to 350 nm. In this case, the convex part of the surface irregularity A has a width (for example, 50 nm to 350 nm) that is about half or less of the upper limit of the wavelength of visible light. As shown in FIG. 6A, consider the case where the shell 10s (refractive index Ns) of the light diffusing particle 10 is in contact with the medium M (refractive index Nm> Ns). In this case, in the radial direction of the light diffusion particle 10, the specific position inside the shell 10 s is y 0, the position of the medium M near the top of the convex portion of the surface unevenness A is y 1, and the top of the convex portion of the surface unevenness A The position of the medium M that is radially outward from y1 is defined as y2. The ratio of the space occupied by the surface irregularities A in the vicinity of the surface of the light diffusion particle 10 gradually decreases between y0 and y1. As a result, as shown in FIG. 6B, the apparent refractive index in the vicinity of the surface of the light diffusing particle 10 gradually changes in the interval from y0 to y1. For example, if the light diffusing particles do not have such surface irregularities A, the refractive index changes abruptly in a step shape at the interface between the light diffusing particles and the medium M. It is easy to be reflected on the surface of the light diffusion particle. On the other hand, according to the light diffusing particle 10 in which the spherical particle 13 has a particle diameter of 50 nm to 350 nm, incident light is not easily reflected on the surface of the light diffusing particle 10. For this reason, the light diffusing particles 10 are more advantageous in giving high luminance characteristics to the light diffusing and transmitting sheet in which the light diffusing particles 10 are dispersed.

The content of the spherical particles 13 in the components other than the second binder of the shell 10s is, for example, 25% by mass to 70% by mass, and preferably 40% by mass to 60% by mass. Accordingly, the surface irregularities A are easily formed appropriately on the entire surface of the shell 10 s by the spherical particles 13. As a result, the light diffusing particles 10 have a surface that is more difficult to retain water more reliably. In addition, high luminance characteristics can be more reliably imparted to the light diffusing and transmitting sheet in which the light diffusing particles 10 are dispersed. Moreover, when the content rate of the spherical particles 13 in the shell 10 s has the above upper limit, it is possible to suppress a decrease in the haze ratio of the light diffusion transmission sheet in which the light diffusion particles 10 are dispersed.

As shown in FIG. 7, the light diffusing and transmitting sheet 100 includes a base material 20 and light diffusing particles 10 dispersed in the base material 20. Since the light diffusing and transmitting sheet 100 includes the light diffusing particles 10, it can exhibit high luminance characteristics.

The base material 20 is not particularly limited, but is, for example, a resin having excellent dispersibility of the light diffusing particles 10 and having transparency to visible light, weather resistance, moisture resistance, and heat resistance. For example, as the base material 20, polyester polyol, linear polyester, acrylic resin, amino resin, epoxy resin, melamine resin, silicone resin, urethane resin, vinyl acetate resin, norbornene resin, and polycarbonate resin And the like. Various thermosetting resins and various ultraviolet curable resins can also be used. These resins may be appropriately added with an isocyanate-based curing agent and various dispersants. The light diffusing and transmitting sheet 100 may further include a substrate (not shown) such as a PET (polyethylene terephthalate) film, and the base material 20 in which the light diffusing particles 10 are dispersed may be formed in layers on the substrate.

It is desirable that the average particle diameter of the light diffusing particles 10 be within a predetermined range so that the light diffusing particles 10 can be uniformly dispersed in the base material 20. From such a viewpoint, the average particle diameter of the light diffusing particles 10 is, for example, 4 μm to 10 μm, desirably 4 μm to 8 μm, and more desirably 4 μm to 7 μm. Thereby, the spatial dispersion | variation in the optical characteristic in the light diffusion transmission sheet 100 can be prevented. In addition, it is possible to reduce light reflection loss due to light entering a gap between primary particles generated when the light diffusion particles 10 aggregate. As a result, the luminance characteristics of the light diffusing and transmitting sheet 100 can be improved. Furthermore, it is possible to sufficiently secure an interface where light is refracted in the light diffusing and transmitting sheet 100. Thereby, the light-diffusion characteristic of the light-diffusion transmission sheet 100 can be improved. In the present specification, the “average particle diameter” is 50 visible when the cross section of the light diffusing and transmitting sheet 100 or the light diffusing particles 10 is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It is obtained as an average value of the maximum diameters of one or more particles. The “average particle size” may be a volume-based D50 measured by a laser diffraction method.

The shape of the light diffusing particles 10 is preferably granular having an aspect ratio of 1 to 2 from the viewpoint of imparting spatially uniform light diffusing characteristics to the light diffusing and transmitting sheet 100.

As shown in FIG. 1, the shell 10s covers, for example, the entire outer surface of the core 10c. The light diffusion particle 10 includes, for example, one or a plurality of cores 10c.

The refractive index of the first binder 11 is, for example, 1.49 to 1.60, and preferably 1.50 to 1.55. The refractive index of the low refractive index fine particles 12a is, for example, 1.35 to 1.59, and preferably 1.35 to 1.49. Desirably, the difference n _B −n _F obtained by subtracting the refractive index n _F of the low refractive index fine particles 12a from the refractive index n _B of the first binder 11 is 0.01 or more. Thereby, the refractive index difference between the first binder 11 and the low refractive index fine particles 12a becomes large, and the light incident on the low refractive index fine particles 12a is likely to diffuse (scatter). For this reason, the light diffusion transmission sheet 100 has high luminance characteristics and good light diffusion characteristics.

The first binder 11 can cover the outer surface of the first fine particles 12 and has transparency to visible light. The first binder 11 is preferably selected from the group consisting of an acrylic resin, a polyurethane resin, and nylon from the viewpoint of reducing the hardness of the light diffusing particles 10 and reducing the possibility of damaging a member that contacts the light diffusing and transmitting sheet 100. At least one polymer. Among these, the first binder 11 is preferably a polyurethane resin.

The low refractive index fine particles 12a have a particle diameter of 4 nm to 9 μm, for example. Thereby, the light confinement phenomenon is less likely to occur in the low refractive index fine particles 12a. The average particle diameter of the low refractive index fine particles 12a is desirably 4 nm to 4 μm, and more desirably 0.1 μm to 4 μm. Thereby, the low refractive index fine particles 12a are easily dispersed uniformly in the core 10c.

The low refractive index fine particles 12a are made of, for example, a polymer. In this case, the density of the low refractive index fine particles 12a is small, and the light diffusing particles 10 and thus the light diffusing and transmitting sheet 100 can be easily reduced in weight. In addition, the light diffusing particles 10 can impart to the light diffusing and transmitting sheet 100 such that the low refractive index fine particles 12a are easily deformed by an external force, and the members that are in contact with the light diffusing and transmitting sheet 100 are not easily damaged. The low refractive index fine particles 12a are preferably made of a crosslinked polymer. In this case, the light diffusion particle 10 tends to have heat resistance. The crosslinked polymer is, for example, a crosslinked acrylic resin or a crosslinked styrene resin. Crosslinked acrylic resins also have good solvent resistance. Cross-linked styrene resin has excellent heat resistance. The low refractive index fine particles 12a may be made of an inorganic material such as silica and magnesium fluoride depending on circumstances.

As shown in FIG. 1, the shell 10s further includes, for example, second particles 14 having a particle diameter of 4 nm to 15 nm in addition to the spherical particles 13. Since the second fine particles 14 have a particle diameter smaller than that of the spherical particles 13, a large number of the second fine particles 14 are arranged in the gaps between the spherical particles 13 in the shell 10s. Thereby, since the number of sites where light scattering occurs increases, the light diffusing particles 10 easily exhibit good light diffusibility.

The content of the second fine particles 14 in the shell 10s is, for example, 20% by mass to 60% by mass, and more preferably 32% by mass to 48% by mass. Thereby, it is easy for the light-diffusion particle 10 to exhibit favorable light diffusibility more reliably.

The spherical particles 13 have a refractive index lower than that of the second binder 15, for example. Thereby, the light confinement phenomenon hardly occurs in the spherical particles 13 in the shell 10s, and the light diffusing particles 10 more easily impart high luminance characteristics to the light diffusing and transmitting sheet 100 more reliably. The second binder 15 covers at least a part of the outer surface of the spherical particle 13. The second binder 15 desirably covers the entire outer surface of the spherical particle 13.

The second fine particles 14 have a refractive index lower than that of the second binder 15, for example. Thereby, the light confinement phenomenon hardly occurs in the second fine particles 14, and the light diffusing particles 10 can easily impart high luminance characteristics to the light diffusing and transmitting sheet 100 more reliably. The second binder 15 covers at least a part of the outer surface of the second fine particle 14. The second binder 15 desirably covers the entire outer surface of the second fine particle 14.

The refractive index of the second binder 15 is, for example, 1.49 to 1.60, and preferably 1.50 to 1.55. The refractive index of the second binder 15 is desirably greater than or equal to the refractive index of the first binder 11. Thereby, the light-diffusion particle 10 tends to exhibit a desired optical characteristic. The refractive index of the spherical particles 13 is, for example, 1.35 to 1.59, and preferably 1.35 to 1.49. The refractive index of the second fine particles 14 is, for example, 1.35 to 1.59, preferably 1.35 to 1.49.

The second binder 15 is, for example, a resin having transparency with respect to visible light. The second binder 15 is preferably selected from the group consisting of acrylic resin, polyurethane resin, and nylon from the viewpoint of reducing the hardness of the light diffusing particles 10 and reducing the possibility of damaging the member that contacts the light diffusing and transmitting sheet 100. At least one polymer. Among these, the second binder 15 is preferably a polyurethane resin.

It is desirable that the spherical particles 13 hardly aggregate when the spherical particles 13 are mixed with the raw material of the second binder 15. From such a viewpoint, when the second binder 15 is a resin such as a polyurethane resin, the spherical particles 13 are desirably silica.

The content of the light diffusing particles 10 in the light diffusing and transmitting sheet 100 is, for example, 55% by mass or more, desirably 60% by mass or more, and more desirably 64% by mass or more. Thereby, the light diffusion transmission sheet 100 surely has high luminance characteristics and has good light diffusion characteristics. Moreover, the content rate of the light-diffusion particle | grains 10 in the light-diffusion transmission sheet 100 is 70 mass% or less, for example, desirably 68 mass% or less, More desirably, it is 66 mass% or less. Thereby, the light diffusing particles 10 are well dispersed in the base material 20 and, for example, the light diffusing particles 10 can be prevented from being exposed on the surface of the light diffusing and transmitting sheet 100.

The ratio of the mass of the core 10c to the mass of the light diffusion particle 10 is, for example, 8% to 30%, desirably 9% to 25%, and more desirably 9% to 21%. On the other hand, the ratio of the mass of the shell 10s to the entire mass of the light diffusing particles 10 is, for example, 70% to 92%, desirably 75% to 91%, and more desirably 79% to 91%. Thereby, the light-diffusion transmission sheet 100 can exhibit a high luminance characteristic more reliably.

The content of the first fine particles 12 in the core 10c is, for example, 50% by mass to 80% by mass, desirably 50% by mass to 75% by mass, and more desirably 50% by mass to 70% by mass. The content of the first binder 11 in the core 10c is, for example, 20% by mass to 50% by mass, desirably 25% by mass to 50% by mass, and more desirably 30% by mass to 50% by mass. Thereby, the light-diffusion transmission sheet 100 can exhibit a high luminance characteristic more reliably.

The content of the low refractive index fine particles 12a in the core 10c is, for example, 4% by mass to 80% by mass, desirably 4% by mass to 10% by mass, and more desirably 5% by mass to 7% by mass. Thereby, the light diffusion transmission sheet 100 can exhibit a high luminance characteristic more reliably.

As shown in FIG. 1, the first fine particles 12 may contain fine particles of a different type from the low refractive index fine particles 12a. For example, the first fine particles 12 are at least one selected from the group consisting of silica, silicone, fluororesin, titanium dioxide, zinc oxide, zirconium oxide, calcium carbonate, barium sulfate, zinc sulfide, aluminum hydroxide, glass, and extender. It may further contain seed microparticles. Thereby, a light diffusion transmission sheet having higher luminance characteristics or a light diffusion transmission sheet having various optical characteristics can be provided.

The average particle diameter of the fine particles other than the low refractive index fine particles 12a contained in the first fine particles 12 is, for example, 4 nm to 500 nm, desirably 4 nm to 20 nm, and more desirably 4 nm to 15 nm. Thereby, fine particles other than the low refractive index fine particles 12 a included in the first fine particles 12 are easily dispersed uniformly in the first binder 11.

The first fine particles 12 desirably include only fine particles having a refractive index lower than that of the first binder 11. Thereby, since it is difficult to confine light inside the first fine particles 12, it is possible to more reliably impart high luminance characteristics to the light diffusion transmission sheet 100.

Next, an example of a method for manufacturing the light diffusing particles 10 and the light diffusing and transmitting sheet 100 will be described. A dispersion liquid in which the raw material of the first binder 11 and the first fine particles 12 including the low refractive index fine particles 12a are dispersed is prepared. The dispersion is prepared, for example, by mixing an emulsion containing the raw material of the first binder 11 and a dispersion containing the low refractive index fine particles 12a. If necessary, a fluorescent dye, a fluorescent brightener, a dye, or a pigment may be dispersed in the dispersion. The core 10c can be obtained by performing spray drying using the prepared dispersion. By adjusting the content of the solid component in the dispersion and the spraying conditions in the spray drying, aggregation of primary particles can be suppressed and the particle diameter of the core 10c can be adjusted to an appropriate range.

Further, instead of performing spray drying, the core 10c may be formed by adding a predetermined crosslinking agent to the dispersion and heating to crosslink the raw material of the first binder 11.

Further, the first fine particles 12 including the low refractive index fine particles 12a are added to the resin used as the raw material of the first binder 11, and if necessary, a fluorescent dye, a fluorescent brightener, a dye, or a pigment is added and mixed. Smelt and mix these additives uniformly into the molten resin. The core 10c can also be obtained by crushing the lump of resin obtained in this way and adjusting it to a predetermined particle diameter. However, from the viewpoint of uniformly dispersing the first fine particles 12 in the first binder 11 or efficiently producing the core 10c having a desired particle diameter and shape, by preparing a dispersion and spray drying or adding a crosslinking agent. It is desirable to produce the core 10c.

Next, a dispersion in which the core 10c and the spherical particles 13 are dispersed is prepared. Typically, the raw material of the second binder 15 is added to this dispersion, and the second fine particles 14 are added as necessary. By performing spray drying using the prepared dispersion, the light diffusing particles 10 having a core-shell structure can be produced. By adjusting the content of the solid component in the dispersion and the spraying conditions in the spray drying, the light diffusing particles 10 having a desired particle size and desired characteristics can be produced.

When the core 10c is formed by adding a predetermined crosslinking agent, the raw material of the first binder 11 and the first fine particles 12 including the low refractive index fine particles 12a having a refractive index lower than the refractive index of the first binder 11 are dispersed. A first dispersion is prepared. Next, the core 10c is formed by adding a crosslinking agent for crosslinking the raw material of the first binder 11 to the first dispersion to cross-link the raw material of the first binder 11. Then, a second dispersion in which the core 10c and the spherical particles 13 are dispersed is prepared, and the second dispersion is spray-dried. In this case, the light diffusion particle 10 having a core-shell structure can be manufactured. The raw material of the second binder 15 is typically added to the second dispersion, and the second fine particles 14 are added as necessary.

The light diffusion particles 10 produced as described above are uniformly dispersed in a fluid containing the raw material of the base material 20. In this manner, an ink containing the light diffusing particles 10 and the base material 20 is prepared. The light diffusing and transmitting sheet 100 can be manufactured by applying this ink on a substrate such as a PET film and solidifying the ink.

The present invention will be described in detail using examples. However, the present invention is not limited to the following examples. First, an evaluation method for each example and comparative example will be described.

<Measurement of luminance characteristics and chromaticity>
The luminance characteristics and chromaticity of the sample according to each example and the sample according to the comparative example were measured using a luminance measuring device (product name: RISA-COLOR ONE, manufactured by Highland). The backlight of Apple's iPhone 5 was used as the light source. “IPhone” is a registered trademark of Apple Inc. Moreover, the measurement position of brightness | luminance and chromaticity was located on the opposite side to the light source of a sample, and the distance of the measurement position of brightness | luminance and chromaticity and a sample was 100 cm. The evaluation results of each sample are shown in Table 1. In Table 1, the luminance value when the relative luminance value is 100% is 10 ⁴ cd / cm ² .

<Measurement of haze ratio>
Using a spectrophotometer (manufactured by Shimadzu Corporation, product name: UV-3600) and an integrating sphere, the haze ratio of the sample according to each example and the sample according to the comparative example with respect to incident light having a wavelength of 555 nm was measured. The results are shown in Table 1.

<Change in weight before and after drying>
The light diffusing particles according to each Example and Comparative Example were allowed to stand under the same conditions (48 to 30 hours in an environment of 20 to 30 ° C. and 30 to 80% relative humidity) and then dried for 1 hour in an environment of 110 ° C. ± 5 ° Treated. The weight change of each light diffusion particle before and after the drying treatment was measured, and the moisture content was calculated based on the following formula. Here, ΔW and Wb are the weight change of the light diffusing particles before and after the drying treatment and the weight of the light diffusing particles before the drying treatment, respectively. The results are shown in Table 1.
Moisture content [%] = 100 × ΔW / Wb

Example 1
A water dispersion of fine particles of cross-linked acrylic resin (manufactured by Soken Chemical Co., Ltd., KMR-3TA, refractive index: 1.49, average particle size: 3 μm) was prepared by colloidal silica A (Nissan Chemical Industries, Snowtex XS, silica). Refractive index: about 1.45, average particle diameter of silica fine particles: 4 to 6 nm), colloidal silica B (manufactured by Nippon Chemical Industry Co., Ltd., silica doll 30S, silica refractive index: about 1.45, average particle of silica fine particles (Diameter: 7 to 10 nm), and polyurethane emulsion (Mitsui Chemicals Takelac W-6020: refractive index 1.50 to 1.55 and Takelac WS-6021: refractive index 1.50 to 1.55). Thereby, the dispersion liquid for cores was produced. The core dispersion was prepared so that the solid content of the crosslinked acrylic resin fine particles was 6% by mass and the solid content of the polyurethane was 50% by mass.

After adding a cross-linking agent (Nisshinbo Chemical Co., Ltd., Carbodilite E-05) to the core dispersion, the core dispersion was heated in an environment of 80 ° C. for 2 hours. Thereby, the dispersion liquid in which the polyurethane was crosslinked to form the core was obtained. 20 mass parts of crosslinking agents were added with respect to 100 mass parts of solid content of polyurethane. Next, the core-formed dispersion, colloidal silica A (manufactured by Nissan Chemical Industries, Snowtex XS, silica refractive index: about 1.45, silica fine particle average particle size: 4 to 6 nm), colloidal Silica C (Nissan Chemical Industries, Snowtex ZL, silica refractive index: about 1.45, silica spherical particles average particle size: 70-100 nm) and polyurethane emulsion (Mitsui Chemicals Takelac W-6020: Refraction) A dispersion for light diffusing particles was prepared by mixing the ratios 1.50 to 1.55 and Takelac WS-6021: refractive index 1.50 to 1.55). The compounding ratio of silica in colloidal silica A and silica in colloidal silica C was 50:50 on a mass basis. Further, in the dispersion for light diffusing particles, a dispersion for light diffusing particles was prepared so that the solid content of the core was 20% by mass and the solid content of polyurethane other than the core was 20% by mass. The dispersion liquid for light diffusion particles was spray-dried using a micro mist spray dryer (product name: MDL-050, manufactured by Fujisaki Electric Co., Ltd.) to obtain light diffusion particles according to Example 1 having a core-shell structure. The average particle diameter of the light diffusing particles according to Example 1 was 5 μm.

The ink was prepared by dispersing the light diffusing particles according to Example 1 in an acrylic resin. The ink was applied to a PET film having a thickness of 20 μm by a doctor blade method and solidified to produce a sample according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 2)
In the preparation of the dispersion liquid for light diffusing particles, Example 2 was carried out in the same manner as in Example 1 except that the mixing ratio of silica in colloidal silica A and silica in colloidal silica C was changed to 75:25 on a mass basis. Such light diffusing particles were prepared. The average particle diameter of the light diffusing particles according to Example 2 was 5 μm. A sample according to Example 2 was produced in the same manner as in Example 1 except that the light diffusing particles according to Example 2 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 3)
In preparing the dispersion liquid for light diffusion particles, instead of colloidal silica C, colloidal silica D (manufactured by Nissan Chemical Industries, MP-2040, refractive index of silica: about 1.45, average particle diameter of silica spherical particles: 170 to 230 nm), and the light diffusing particles according to Example 3 were the same as Example 1 except that the compounding ratio of silica in colloidal silica A and silica in colloidal silica D was adjusted to 50:50 on a mass basis. Was made. The average particle diameter of the light diffusing particles according to Example 3 was 5 μm. In FIG. 8, the SEM photograph of the light-diffusion particle which concerns on Example 3 is shown. As shown in FIG. 8, the light diffusing particles according to Example 3 had surface irregularities derived from the silica spherical particles contained in the colloidal silica D. A sample according to Example 3 was produced in the same manner as in Example 1 except that the light diffusing particles according to Example 3 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

Example 4
In preparing a dispersion for light diffusing particles, instead of colloidal silica C, colloidal silica E (manufactured by JGC Catalysts & Chemicals, Cataloid SS-300J, silica refractive index: about 1.45, average particle diameter of silica spherical particles) : 280 to 300 nm), and the light diffusion according to Example 4 was performed in the same manner as in Example 1 except that the compounding ratio of silica in colloidal silica A and silica in colloidal silica E was adjusted to 50:50 on a mass basis. Particles were made. The average particle size of the light diffusing particles according to Example 4 was 5 to 6 μm. A sample according to Example 4 was produced in the same manner as in Example 1 except that the light diffusing particles according to Example 4 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 5)
In preparing the dispersion liquid for light diffusion particles, instead of colloidal silica C, colloidal silica F (manufactured by Nippon Chemical Industry Co., Ltd., MP-4540M, silica refractive index: about 1.45, average particle diameter of silica spherical particles: 450 nm), the compounding ratio of silica in colloidal silica A and silica in colloidal silica F was adjusted to 50:50 on a mass basis, and the solid content of the core was adjusted to 10% by mass. In the same manner as in Example 1, light diffusing particles according to Example 5 were produced. The average particle size of the light diffusing particles according to Example 5 was 5 to 6 μm. A sample according to Example 5 was produced in the same manner as in Example 1 except that the light diffusing particles according to Example 5 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Comparative example)
In the same manner as in Example 1, a dispersion in which a core was formed was prepared. Next, the core-formed dispersion, colloidal silica A (manufactured by Nissan Chemical Industries, Snowtex XS, silica refractive index: about 1.45, silica fine particle average particle size: 4 to 6 nm), colloidal Silica B (Nippon Kagaku Kogyo Co., Ltd., Silica Doll 30S, silica refractive index: about 1.45, silica fine particle average particle size: 7 to 10 nm) and polyurethane emulsion (Mitsui Chemicals Takelac W-6020: refractive index) 1.50 to 1.55 and Takelac WS-6021: refractive index 1.50 to 1.55) were mixed to prepare a dispersion liquid for light diffusing particles. The compounding ratio of silica in colloidal silica A and silica in colloidal silica B was 22:78 on a mass basis. Further, in the dispersion for light diffusing particles, a dispersion for light diffusing particles was prepared so that the solid content of the core was 20% by mass and the solid content of polyurethane other than the core was 20% by mass. The dispersion liquid for light diffusion particles was spray-dried using a micro mist spray dryer (product name: MDL-050, manufactured by Fujisaki Electric Co., Ltd.) to obtain light diffusion particles according to a comparative example having a core-shell structure. The average particle diameter of the light diffusing particles according to the comparative example was 5 μm. FIG. 9 shows an SEM photograph of the light diffusing particles according to the comparative example. As shown in FIG. 9, the surface of the light diffusing particle according to the comparative example was smoother than that of the light diffusing particle according to Example 3.

Example A sample according to the comparative example was produced in the same manner as in Example 1 except that the light diffusing particle according to the comparative example was used instead of the light diffusing particle according to the example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

As shown in Table 1, the moisture content of the light diffusion particles according to Examples 1 to 5 was lower than the moisture content of the light diffusion particles according to the comparative example. This suggests that the light diffusing particles according to Examples 1 to 5 have a surface on which water hardly stays compared to the light diffusing particles according to the comparative example. In addition, the samples according to Examples 1 to 5 showed a high relative luminance value of 101.6 or more. In particular, the samples according to Examples 1 to 4 showed higher luminance characteristics than the sample according to the comparative example.

Claims (11)

A core formed of a first binder and a first fine particle comprising low refractive index fine particles having a refractive index lower than the refractive index of the first binder, and being covered in contact with the first binder;
A shell that contacts the outer surface of the core and covers the core, the spherical particles having a particle diameter of 50 nm to 450 nm and imparting surface irregularities to the shell, and a second that is in contact with the outer surface of the spherical particles A shell including a binder,
Light diffusing particles. 2. The light diffusing particle according to claim 1, wherein the spherical particle has a particle diameter of 50 nm to 350 nm. The light diffusing particles according to claim 1 or 2, wherein the content of the spherical particles in components other than the second binder of the shell is 25% by mass to 70% by mass. The light diffusing particle according to any one of claims 1 to 3, wherein the light diffusing particle has an average particle diameter of 4 袖 m to 10 袖 m. The light diffusing particles according to any one of claims 1 to 4, wherein the low refractive index fine particles have a particle diameter of 4 nm to 9 µm. The light diffusing particle according to any one of claims 1 to 5, wherein the shell further includes second fine particles having a particle diameter of 4 nm to 15 nm. The light diffusing particle according to any one of claims 1 to 6, wherein the first binder includes at least one polymer selected from the group consisting of an acrylic resin, a urethane resin, and nylon. The light diffusing particle according to any one of claims 1 to 7, wherein the spherical particle has a refractive index lower than that of the second binder. The light diffusing particle according to any one of claims 1 to 8, wherein the second binder contains at least one polymer selected from the group consisting of an acrylic resin, a urethane resin, and nylon. With the base material,
The light diffusing particles according to any one of claims 1 to 9, which are dispersed in the base material,
Light diffusion transmission sheet. A method for producing light diffusing particles having a core-shell structure,
Preparing a first dispersion in which raw materials of the first binder and first fine particles including low refractive index fine particles having a refractive index lower than the refractive index of the first binder are dispersed,
A core is formed by adding a crosslinking agent for crosslinking the raw material of the first binder to the first dispersion to crosslink the raw material of the first binder,
Preparing a second dispersion in which the core and spherical particles having a particle diameter of 50 nm to 450 nm are dispersed;
Spray drying the second dispersion;
Method.

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