WO2018142722A1

WO2018142722A1 - Light-diffusing particles, light-diffusing and -transmitting sheet, and method for producing light-diffusing particles

Info

Publication number: WO2018142722A1
Application number: PCT/JP2017/041171
Authority: WO
Inventors: 多佳子岩井; 耕一郎壹岐
Original assignee: 日本板硝子株式会社
Priority date: 2017-01-31
Filing date: 2017-11-16
Publication date: 2018-08-09
Also published as: JP6793211B2; JPWO2018142722A1

Abstract

Light-diffusing particles (10) that comprises a core (10c) and a shell (10s). The core (10c) includes a first binder (11) and a core fine particle (12). The first binder (11) contacts an outer surface of the core fine particle (12). The core fine particle (12) has a lower refractive index than the first binder (11), a circularity of at least 0.85, and a particle diameter of 0.1–4 μm. The core (10c) contacts an outer surface of the core (10c) and covers the core (10c).

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, in Patent Documents 1 to 4, specifically, whether or not the layer or sheet in which particles described in Patent Documents 1 to 4 are in contact with another member is likely to damage the other member. Not considered.

Therefore, the present invention is advantageous for imparting high luminance characteristics to the light diffusing and transmitting sheet, and is also advantageous for imparting the light diffusing and transmitting sheet with characteristics that hardly damage the members in contact with the light diffusing and transmitting sheet. Provides diffusing particles.

The present invention
A first binder, and core fine particles having a refractive index lower than the refractive index of the first binder, a circularity of 0.85 or more, and a particle diameter of 0.1 μm to 4 μm, wherein the first binder is the core A core in contact with the outer surface of the fine particles;
A shell that contacts the outer surface of the core and covers the core;
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,
A first dispersion in which a raw material of the first binder and core fine particles having a refractive index lower than the refractive index of the first binder, a circularity of 0.85 or more, and a particle diameter of 0.1 μm to 4 μm are dispersed. Prepare the liquid,
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 shell material are dispersed;
Spray drying the second dispersion;
Provide a method.

The light diffusing particles described above are advantageous for imparting high luminance characteristics to the light diffusing and transmitting sheet in which the light diffusing particles are dispersed, and exhibiting characteristics that hardly damage the member that contacts the light diffusing and transmitting sheet. It is advantageous to apply to a sheet. Moreover, according to said method, said light-diffusion particle | grains can be manufactured by one spray drying.

FIG. 1A is a cross-sectional view schematically showing the structure of a light diffusing particle according to an example of the present invention. FIG. 1B is a cross-sectional view schematically showing the structure of a light diffusing particle according to another 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. 3 is a diagram schematically showing the optical path of light incident on the low refractive index fine particles. FIG. 4 is a cross-sectional view showing a light diffusing and transmitting sheet according to an example of the present invention. FIG. 5 is a side view of an apparatus for evaluating the scratch imparting characteristics of samples of light diffusing and transmitting sheets according to Examples and Comparative Examples.

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 FIGS. 1A and 1B, the light diffusion particle 10 includes a core 10c and a shell 10s. The core 10 c includes a first binder 11 and core fine particles 12. The core fine particles 12 have (i) a refractive index lower than that of the first binder 11, (ii) a circularity of 0.85 or more, and (iii) a particle diameter of 0.1 μm to 4 μm. The first binder 11 is in contact with the outer surface of the core fine particle 12. The shell 10s contacts the outer surface of the core 10c and covers the core 10c. As used herein, “particle diameter” means the maximum diameter. The “circularity” of the particles can be obtained by the following equation (1). Here, the projected area of the particle and the peripheral length of the projected particle are determined by image processing software (for example, National Institutes of Health (NIH)) using an image of the particle obtained by observing the particle with an optical microscope or a transmission electron microscope. It can be determined by processing using the provided Image J).
Circularity = 4π × (particle projection area) / (peripheral length of particle projection) ² (1)

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.

On the other hand, for example, as shown in FIG. 3, when light is incident on the low-refractive index fine particles PL from a medium having a relatively high refractive index, the “light confinement phenomenon” hardly occurs in the fine particles PL. In FIG. 3, the difference obtained by subtracting the refractive index of the fine particles PL from the refractive index of the medium around the fine particles PL is 0.01. In the light diffusing particle 10, the core fine particle 12 has a refractive index lower than that of the first binder 11 and is covered in contact with the first binder 11. For this reason, the light confinement phenomenon hardly occurs in the core fine particles 12, 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.

Thus, when the core fine particles 12 have a low refractive index, it is advantageous for imparting high luminance characteristics to the light diffusion transmission sheet. Therefore, the present inventor has studied light diffusion particles having a core-shell structure using various low refractive index fine particles. As a result, the present inventors have found that the susceptibility of the member contacting the light diffusing and transmitting sheet in which the light diffusing particles are dispersed differs depending on the difference in the circularity of the fine particles to be arranged in the core. . That is, the present inventors provide a member in which the light diffusing particles 10 are in contact with the light diffusing and transmitting sheet, because the core fine particles 12 in the core 10c have a circularity of 0.85 or more and a particle diameter of 0.1 μm to 4 μm. It has been found that the light diffusive transmission sheet can be imparted with characteristics that are difficult to damage.

As shown in FIG. 1A, when the particle diameter of the core fine particles 12 is 1 μm to 4 μm, in the light diffusing particle 10, the single core fine particles 12 are easily arranged at the center of the core 10 c, and The core 10c is easily formed. On the other hand, as shown in FIG. 1B, when the particle diameter of the core fine particles 12 is in the range of 0.1 μm to 0.5 μm, a plurality (seven in FIG. 1B) of the core fine particles 12 aggregate to form the center of the core 10c. The core 10c is easily formed based on the aggregated core fine particles 12. When the particle diameter of the core fine particles 12 is in the range of 0.5 μm to 1 μm, the arrangement state of the core fine particles 12 in the core 10c can be either the state shown in FIG. 1A or FIG. 1B depending on conditions.

As shown in FIG. 4, the light diffusing and transmitting sheet 100 can be manufactured using the light diffusing particles 10. The light diffusion transmission sheet 100 includes a base material 20 and light diffusion particles 10 dispersed in the base material 20. Since the light diffusing and transmitting sheet 100 includes the light diffusing particles 10, the light diffusing and transmitting sheet 100 can exhibit high luminance characteristics and has a characteristic that the member that contacts the light diffusing and transmitting sheet 100 is hardly damaged.

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. The “average particle diameter” of the light diffusing particles 10 is D50 based on mass (volume) 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.

The core fine particles 12 may be made of an organic material or may be made of an inorganic material such as silica as long as it has the characteristics (i) to (iii) described above. In order to more reliably prevent damage to the member that contacts the light diffusing and transmitting sheet, it is desirable that the core fine particles 12 be soft (easy to be deformed by an external force). For this reason, the core fine particles 12 are preferably made of a polymer. When the core fine particles 12 are made of a polymer, the core fine particles 12 are easily deformed by an external force due to the viscoelasticity of the polymer.

The polymer forming the core fine particles 12 is, for example, an acrylic resin, a silicone resin, or a fluororesin. In this case, the light diffusing particles 10 can more reliably impart the light diffusing and transmitting sheet 100 with the property of hardly damaging the member that contacts the light diffusing and transmitting sheet 100.

The refractive index of the first binder 11 is, for example, 1.49 to 1.60, and preferably 1.50 to 1.55. Further, the refractive index of the core fine particles 12 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 core fine particles 12 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 core fine particles 12 becomes large, and the light incident on the core fine particles 12 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 core 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.

As shown in FIG. 1A and FIG. 1B, the core 10 c may include fine particles 14 of a different type from the core fine particles 12. For example, the core 10c is 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 as the fine particles 14. It may further contain at least one kind of fine particles. Thereby, a light diffusion transmission sheet having higher luminance characteristics or a light diffusion transmission sheet having various optical characteristics can be provided.

The particle diameter of the fine particles 14 other than the core fine particles 12 included in the core 10c is, for example, 4 nm to 100 nm, desirably 4 nm to 20 nm, and more desirably 4 nm to 10 nm. Thereby, the fine particles 14 other than the core fine particles 12 included in the core 10 c are easily dispersed uniformly in the first binder 11.

The fine particles 14 desirably have a refractive index lower than that of the first binder 11. Thereby, since it is difficult to confine light inside the fine particles 14, it is possible to impart high luminance characteristics to the light diffusion transmission sheet 100 more reliably.

As shown in FIGS. 1A and 1B, the shell 10 s is formed of, for example, shell fine particles 13 and a second binder 15. The shell fine particles 13 have a particle diameter of 4 nm to 20 nm, for example. The second binder 15 is in contact with the outer surface of the shell fine particles 13 and covers the shell fine particles 13. Since the particle size of the shell fine particles 13 is smaller than that of the core fine particles 12, the shell fine particles 13 have a characteristic that hardly damages a member that comes into contact with the light diffusion transmission sheet 100 provided to the light diffusion transmission sheet 100 by the light diffusion particles 10. Has little effect. For this reason, the light diffusing particle 10 can more reliably impart the light diffusing and transmitting sheet 100 with a characteristic that hardly damages the member that contacts the light diffusing and transmitting sheet 100. The shell 10 s may contain particles having a particle diameter of more than 20 nm as long as the characteristics that hardly damage the member that contacts the light diffusing and transmitting sheet 100 are not impaired. Further, when the shell fine particles 13 have a particle diameter of 4 nm to 20 nm, the light diffusing particles 10 and thus the light diffusing and transmitting sheet 100 have high light diffusing characteristics.

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 shell fine particles 13 is, for example, 1.35 to 1.59, and preferably 1.35 to 1.49. The refractive index of the shell fine particles 13 is desirably lower than the refractive index of the second binder 15. In this case, the light confinement phenomenon hardly occurs in the shell fine particles 13.

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.

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 20%, and more desirably 9% to 15%. On the other hand, the ratio of the mass of the shell 10s to the total mass of the light diffusing particles 10 is, for example, 70% to 92%, desirably 80% to 91%, and more desirably 85% to 91%. Thereby, the light-diffusion transmission sheet 100 can exhibit a high luminance characteristic more reliably.

The content of the core fine particles 12 in the core 10c is, for example, 4% by mass to 71% by mass, desirably 4% by mass to 10% by mass, and more desirably 5% by mass to 7% by mass. The content of the first binder 11 in the core 10c is, for example, 29% by mass to 50% by mass, desirably 29% by mass to 40% by mass, and more desirably 30% by mass to 31% by mass. The content of the fine particles 14 in the core 10c is, for example, 20% by mass to 67% by mass, desirably 40% by mass to 67% by mass, and more desirably 53% by mass to 66% by mass. Thereby, the light-diffusion transmission sheet 100 can exhibit a high luminance characteristic more reliably.

The content of the shell fine particles 13 in the shell 10 s is, for example, 71% by mass to 79% by mass, desirably 73% by mass to 79% by mass, and more desirably 77% by mass to 79% by mass.

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 core fine particles 12 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 core fine particles 12. You may disperse | distribute the microparticles | fine-particles 14, a fluorescent dye, a fluorescent whitening agent, dye, or a pigment to a dispersion liquid as needed. 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 core fine particles 12 are added to the resin used as the raw material of the first binder 11, and if necessary, the fine particles 14, the fluorescent dye, the fluorescent brightening agent, the dye, or the pigment are added and kneaded. Mix the additive 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 core fine particles 12 in the first binder 11 or efficiently producing the core 10c having a desired particle diameter and shape, the core is prepared by preparing a dispersion and spray drying or adding a crosslinking agent. It is desirable to make 10c.

Next, a dispersion liquid in which the core 10c and the raw material of the shell 10s are dispersed is prepared. If necessary, additives such as fluorescent dyes, fluorescent brighteners, dyes, and pigments may be added to the dispersion. 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, the refractive index lower than the refractive index of the first binder 11, a circularity of 0.85 or more, and 0.1 μm to 4 μm A first dispersion in which core fine particles 12 having a particle diameter are dispersed 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 raw material of the shell 10s are dispersed is prepared, and the second dispersion is spray-dried. Thereby, the light-diffusion particle 10 which has a core-shell structure can be manufactured. Typically, the raw material of the second binder 15 and the shell fine particles 13 are added to the second dispersion. If necessary, additives such as a fluorescent dye, a fluorescent brightener, a dye, and a pigment may be added to the second dispersion.

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.

<Evaluation of scratch imparting characteristics>
Using the apparatus shown in FIG. 5, it was evaluated how much the samples of the light diffusing and transmitting sheets of each Example and each Comparative Example damaged other members due to contact. A commercially available transparent polycarbonate film PF having a length of 100 mm, a width of 30 mm, and a thickness of 0.8 mm was attached on the support base 40 with a double-sided tape. Next, a sample Sa of a light diffusing and transmitting sheet having a length of 20 mm and a width of 15 mm was attached to the planar friction element 31 using a double-sided tape. Further, as shown in FIG. 5, the sample Sa was arranged so that the sample Sa was in contact with the film PF. At this time, a weight 32 was attached to the upper part of the planar friction element 31 so that a load of 150 g was applied to the film PF. In this state, the plane friction element 31 was reciprocated 10 times with a stroke of 80 mm on the film PF at an average speed of 8.7 m / min, and the film PF was rubbed with the sample Sa. The degree of scratching of the film PF after rubbing with the sample Sa was visually evaluated in the following three stages.
A: The film PF is shallowly scratched and has few scratches.
B: The film PF is shallow but has many scratches C: The film PF is deeply scratched

<Measurement of luminance characteristics and chromaticity>
Using a luminance measuring device (product name: RISA-COLOR ONE, manufactured by Highland Co., Ltd.), the luminance characteristics and chromaticity of the sample according to each example and the sample of the light diffusion transmission sheet according to the comparative example were measured. 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 with respect to incident light having a wavelength of 555 nm of the sample of the light diffusion transmission sheet according to each example and each comparative example was measured. . The results are shown in Table 1.

<Average particle size>
Using a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3000, manufactured by Nikkiso Co., Ltd.), the particle size distribution of the light diffusing particles according to each Example and each Comparative Example was measured. The mass-based (volume-based) D50 obtained from the measurement result of the particle size distribution was determined as the average particle diameter of the light diffusing particles according to each Example and each Comparative Example.

Example 1
An aqueous dispersion of fine particles made of cross-linked acrylic resin (manufactured by Soken Chemical Co., Ltd., KMR-3TA, refractive index: 1.49, average particle diameter: 3 μm, typical value of circularity: 0.87) was prepared by colloidal silica A (Nissan Chemical Industries, Snowtex XS, silica refractive index: about 1.45, silica fine particles average particle diameter: 4-6 nm), colloidal silica B (Nippon Chemical Industry Co., Ltd., silica doll 30S, silica refractive index: About 1.45, average particle size of silica fine particles: 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 30% by mass. In addition, the image of 10 cross-linked acrylic resin particles obtained using an optical microscope is processed by image processing software (Image J ver.1.48) provided by NIH, and the projected area of the particle and the surroundings of the projected particle The length was decided. Then, the circularity of each crosslinked acrylic resin fine particle was determined based on the formula (1). The arithmetic average value of the circularity of 10 particles was determined as the representative value of the circularity of fine particles made of crosslinked acrylic resin.

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. 33 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 B (manufactured by Nippon Chemical Industry Co., Ltd., silica doll 30S, silica refractive index: about 1.45, silica fine particle average particle size: 7 to 10 nm), polyurethane Emulsions (Mitsui Chemicals Takelac W-6020: Refractive index 1.50 to 1.55 and Takelac WS-6021: Refractive index 1.50 to 1.55) are mixed, and further 10ppm (parts per million) blue A pigment was added to prepare a dispersion for light diffusing particles. In the dispersion for light diffusing particles, a dispersion for light diffusing particles was prepared so that the solid content of the core was 10% 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 (D50) of the light diffusing particles according to Example 1 was 6.0 μm.

The ink was prepared by dispersing the light diffusing particles according to Example 1 in an acrylic resin. This ink was applied to a PET film having a thickness of 20 μm by a doctor blade method and solidified to prepare a sample of a light diffusing and transmitting sheet 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)
Instead of the crosslinked acrylic resin fine particles used in Example 1, crosslinked acrylic resin fine particles having a representative circularity different from the representative circularity of the particles (KMR-3TA, manufactured by Soken Chemical Co., Ltd.) Example 1 except that the refractive index is 1.49, the average particle size is 3 μm, the typical value of circularity is 0.93), and the solid content of the polyurethane is 50% by mass. A dispersion for the core was prepared. Thereafter, a dispersion having a core formed therein was obtained in the same manner as in Example 1. Light diffusing particles according to Example 2 having a core-shell structure were obtained in the same manner as in Example 1 except that a dispersion liquid for light diffusing particles was prepared so that the solid content of the core was 30% by mass. The average particle diameter (D50) of the light diffusing particles according to Example 2 was 4.7 μm. The circularity of the crosslinked acrylic resin fine particles was determined in the same manner as in Example 1.

A sample of the light diffusing and transmitting sheet according to Example 2 was produced in the same manner as 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 this sample was 10 to 17 μm, and the content of the light diffusing particles in the coating film of the sample was 65% by mass.

(Comparative Example 1)
Colloidal silica A (Nissan Chemical Industry Co., Ltd., Snowtex XS, silica refractive index: about 1.45, silica fine particle average particle diameter: 4 to 6 nm) and colloidal silica B (Nippon Chemical Industry Co., Ltd., Silica Doll 30S) , Silica refractive index: about 1.45, silica fine particle average particle size: 7-10 nm) and polyurethane emulsion (Mitsui Chemicals Takelac W-6020: Refractive index 1.50-1.55 and Takelac WS-6021) : A refractive index of 1.50 to 1.55) to prepare a core dispersion. In the core dispersion liquid, the solid content of the polyurethane was adjusted to 30% by mass.

After adding a crosslinking 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. 33 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 B (manufactured by Nippon Chemical Industry Co., Ltd., silica doll 30S, silica refractive index: about 1.45, silica fine particle average particle size: 7 to 10 nm), polyurethane Emulsions (Mitsui Chemicals' Takelac W-6020: Refractive index 1.50 to 1.55 and Takelac WS-6021: Refractive index 1.50 to 1.55) are mixed, and further 10 ppm of blue pigment is added. A dispersion for light diffusing particles was prepared. In the dispersion for light diffusing particles, a dispersion for light diffusing particles was prepared so that the solid content of the core was 10% 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 Comparative Example 1 having a core-shell structure. The average particle diameter (D50) of the light diffusing particles according to Comparative Example 1 was 5.0 μm.

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

(Comparative Example 2)
An aqueous dispersion of magnesium fluoride particles (manufactured by Kanto Chemical Co., Inc., refractive index: 1.38, average particle size: 0.2 to 0.3 μm, typical value of circularity: 0.71) is colloidal silica A (Nissan) Chemical Industries, Snowtex XS, silica refractive index: about 1.45, silica fine particles average particle diameter: 4-6 nm), colloidal silica B (Nippon Chemical Industry Co., Ltd., silica doll 30S, silica refractive index: About 1.45, average particle size of silica fine particles: 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 8% by mass and the solid content of the polyurethane was 50% by mass. The image of the 10 magnesium fluoride particles obtained using a transmission electron microscope (TEM) was processed by image processing software (Image J ver.1.48) provided by NIH, and the projected area of the particles and the particle The perimeter of the projection was determined. Then, the circularity of each magnesium fluoride particle was determined based on the formula (1). The arithmetic average value of the circularity of 10 particles was determined as the representative value of the circularity of the magnesium fluoride particles.

After adding a crosslinking 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 B (manufactured by Nippon Chemical Industry Co., Ltd., silica doll 30S, silica refractive index: about 1.45, silica fine particle average particle size: 7 to 10 nm), polyurethane Emulsions (Mitsui Chemicals' Takelac W-6020: Refractive index 1.50 to 1.55 and Takelac WS-6021: Refractive index 1.50 to 1.55) are mixed, and further 10 ppm of blue pigment is added. A dispersion for light diffusing particles was prepared. In the dispersion for light diffusing particles, the dispersion for light diffusing particles was prepared so that the solid content of the core was 30% 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 Comparative Example 2 having a core-shell structure. The average particle diameter (D50) of the light diffusing particles according to Comparative Example 2 was 5.2 μm.

A sample of the light diffusing / transmitting sheet according to Comparative Example 2 was prepared in the same manner as in Example 1 except that the light diffusing particles according to Comparative Example 2 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in this sample was 10 to 17 μm, and the content of the light diffusing particles in the coating film of the sample was 65% by mass.

The samples according to Example 1 and Example 2 have the same high luminance characteristics as the sample in which the light diffusion particles according to Comparative Example 2 having magnesium fluoride particles having a refractive index of 1.38 in the core are dispersed. Was.

The samples according to Example 1 and Example 2 were more difficult to damage other members in contact than those of Comparative Examples 1 and 2. The samples according to Example 1 and Example 2 have such characteristics because the light diffusion particles according to Example 1 and Example 2 have a core containing fine particles made of a crosslinked acrylic resin having a high degree of circularity. It is thought. In the light diffusing particles according to Comparative Example 1, since the core does not contain particles having a particle diameter of 0.1 μm to 4 μm, an irregular core is easily formed, and the shape of the light diffusing particles is likely to be irregular. Conceivable. For this reason, it is thought that the sample which concerns on the comparative example 1 was easy to damage other members which contact compared with the sample which concerns on Example 1 and Example 2. In the light diffusing particles according to Comparative Example 2, the magnesium fluoride particles contained in the core had a low circularity and an angular shape. For this reason, it is thought that the sample which concerns on the comparative example 2 was easy to damage other members which contact compared with the sample which concerns on Example 1 and Example 2.

Claims

A first binder, and core fine particles having a refractive index lower than the refractive index of the first binder, a circularity of 0.85 or more, and a particle diameter of 0.1 μm to 4 μm, wherein the first binder is the core A core in contact with the outer surface of the fine particles;
A shell that contacts the outer surface of the core and covers the core;
Light diffusing particles.
The light diffusion particle according to claim 1, wherein the core fine particle is made of a polymer.
The light diffusing particles according to claim 1 or 2, wherein the polymer is an acrylic resin, a silicone resin, or a fluororesin.
The light diffusing particle according to any one of claims 1 to 3, wherein the first binder is made of at least one polymer selected from the group consisting of an acrylic resin, a urethane resin, and nylon.
The shell is formed by shell fine particles having a particle diameter of 4 nm to 20 nm and a second binder that covers the shell fine particles in contact with an outer surface of the shell fine particles. The light diffusing particles described in 1.
The light diffusing particle according to claim 5, wherein the second binder is made of at least one polymer selected from the group consisting of acrylic resin, urethane resin, and nylon.
The light diffusing particle according to any one of claims 1 to 6, which has an average particle diameter of 4 to 10 袖 m.
With the base material,
The light diffusing particles according to any one of claims 1 to 7, which are dispersed in the base material.
Light diffusion transmission sheet.
A method for producing light diffusing particles having a core-shell structure,
A first dispersion in which a raw material of the first binder and core fine particles having a refractive index lower than the refractive index of the first binder, a circularity of 0.85 or more, and a particle diameter of 0.1 μm to 4 μm are dispersed. Prepare the liquid,
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 shell material are dispersed;
Spray drying the second dispersion;
Method.