TW201439599A - Light-diffusing element - Google Patents

Abstract

This invention provides a strongly diffusing and high-haze-value light-diffusing element whereby backscatter is reduced. The light-diffusing element of this invention comprises: a matrix that contains a resin component and an ultrafine-particle component; and light-diffusing fine particles dispersed within the matrix. The mean primary particle diameter of the ultrafine-particle component is less than or equal to 100 nm, and essentially no aggregated ultrafine-particle component is contained. In a preferred embodiment, the mean primary particle diameter of the light-diffusing fine particles is between 1 and 5 ?mu?m; the coefficient of variation of the weight-average particle-diameter distribution of the light-diffusing fine particles is less than or equal to 20%; and there is essentially no aggregation of the light-diffusing fine particles.

Description

Light diffusing element

The present invention relates to a light diffusing element.

Light diffusing elements are widely used in lighting shades, screens for projection televisions, surface emitting devices (such as liquid crystal display devices), and the like. In recent years, the use of light diffusing elements for improvement in display quality of liquid crystal display devices and the like, improvement in viewing angle characteristics, and the like has progressed. As the light-diffusing element, it has been proposed to disperse fine particles in a matrix such as a resin sheet (see, for example, Patent Document 1). However, in such a conventional light diffusing element, since a large amount of fine particles in the light diffusing element are agglomerated and the particle diameter of the fine particles is not uniform, there is a problem that the light diffusibility is insufficient and the backscattering is large.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 3071538

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a light diffusing element having a high haze value, strong diffusibility, and suppression of backscattering.

The light diffusing element of the present invention has a matrix containing a resin component and an ultrafine particle component, and light diffusing fine particles dispersed in the matrix, wherein the ultrafine particle component has an average primary particle diameter of 100 nm or less, and It does not contain agglomerated ultrafine particle components.

In a preferred embodiment, the average light particle diameter of the light diffusing fine particles is 1 μm to 5 μm, and the coefficient of variation of the weight average particle diameter distribution of the light diffusing fine particles is 20% or less, and the light diffusing fine particles are substantially not Condensed.

In a preferred embodiment, the ultrafine particle component has an average primary particle diameter of 30 nm or less.

In a preferred embodiment, the resin component, the ultrafine particle component, and the light diffusing fine particle have a refractive index satisfying the following formula (i), and have a refractive index modulation region near the surface of the light diffusing fine particle, | _P -n _A |<| n _P -n _B |. . . (i)

In the formula (i), n _A represents the refractive index of the resin component of the matrix, n _B represents the refractive index of the ultrafine particle component of the matrix, and n _P represents the refractive index of the light diffusing fine particles.

According to the present invention, by including the ultrafine particle component in the matrix, the difference in refractive index between the matrix and the light diffusing fine particles can be increased, and a light diffusing element having a high haze value and strong diffusibility can be realized. Further, a refractive index modulation region in which the refractive index changes substantially continuously in the vicinity of the surface of the light diffusing fine particles can be formed, and as a result, reflection at the interface between the matrix and the light diffusing fine particles can be suppressed, and backscattering can be suppressed. The above effect is remarkable in that the ultrafine particle component is a small particle diameter and substantially does not contain agglomerated ultrafine particle components. Specifically, the light diffusing element of the present invention can prevent an increase in backscattering which is an extreme concentration gradient generated around the aggregated ultrafine particle component and a decrease in utilization efficiency of light which contributes to light diffusion.

Further, the uniform light-diffusing fine particles are used, and the light-diffusing fine particles are present in a state where they are substantially not aggregated, whereby the above-described effects are further remarkable, and the transmission of light that is not directly diffused and transmitted can be suppressed.

10‧‧‧Material

11‧‧‧Resin composition

12‧‧‧ Ultrafine particle components

20‧‧‧Light diffusing microparticles

30‧‧‧Concentration zone

100‧‧‧Light diffusing elements

Fig. 1 is a schematic view for explaining a state of dispersion of a resin component and a light diffusing fine particle of a matrix of a light diffusing element obtained by the production method of the preferred embodiment of the present invention.

Fig. 2 is a schematic view showing the vicinity of the light diffusing fine particles of the light diffusing element of the present invention.

Fig. 3 is a conceptual diagram for explaining a change in refractive index from a central portion of a light diffusing fine particle to a substrate in the light diffusing element of the present invention.

Figure 4 is a transmission electron microscope image illustrating the area ratio of ultrafine particle components in a matrix.

Fig. 5 is a photograph showing a transmissive 顕 micromirror of a cross section of the light diffusing element obtained in Example 1.

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

A. Light diffusing element A-1. Overall composition

The light diffusing element of the present invention has a matrix containing a resin component and an ultrafine particle component, and light diffusing fine particles dispersed in the matrix. The light diffusing element of the present invention exhibits a light diffusing function by a difference in refractive index between the substrate and the light diffusing fine particles. Fig. 1 is a schematic view for explaining a state in which a resin component, an ultrafine particle component, and a light diffusing fine particle of a matrix in a light diffusing element according to a preferred embodiment of the present invention are dispersed. The light diffusing element 100 of the present invention has a matrix 10 comprising a resin component 11 and an ultrafine particle component 12 having an average primary particle diameter of 100 nm or less, and light diffusing fine particles 20 dispersed in the matrix 10. The light diffusing element of the present invention contains substantially no agglomerated ultrafine particle components.

Preferably, as shown in FIGS. 1 and 2, a refractive index modulation region 30 is formed in the vicinity of the surface of the light diffusing fine particles. Therefore, the substrate is preferably provided with a surface of the light diffusing fine particles A refractive index fixed region of the refractive index modulation region 30 and the outer side of the refractive index modulation region (the side away from the light diffusing fine particles). In the refractive index modulation region 30, the refractive index changes substantially continuously. The portion other than the refractive index modulation region 30 of the matrix is preferably substantially a refractive index fixed region. In the present specification, "the vicinity of the surface of the light-diffusing fine particles" includes the surface of the light-diffusing fine particles, the outside of the vicinity of the surface, and the inside of the vicinity of the surface. That is, the innermost portion of the refractive index modulation region may be located inside the light diffusing fine particles.

In the refractive index modulation region 30, as described above, the refractive index changes substantially continuously. Preferably, the outermost refractive index of the refractive index modulation region is substantially the same as the refractive index of the refractive index fixed region. In other words, in the light diffusing element, the refractive index continuously changes from the refractive index modulation region to the refractive index fixed region, and preferably the refractive index continuously changes from the light diffusing fine particles to the refractive index fixed region ( FIG. 3 ). . The refractive index change is preferably as stable as shown in FIG. That is, the shape of the tangent line is changed on the refractive index change curve at the boundary between the refractive index modulation region and the refractive index fixed region. In the refractive index modulation region, the gradient of the refractive index change preferably becomes larger as it goes away from the light diffusing fine particles. According to the light diffusing element of the present invention, a substantially continuous refractive index change can be realized by appropriately selecting the light diffusing fine particles, the resin component of the matrix, and the ultrafine particle component. As a result, even if the refractive index difference between the substrate 10 (substantially the refractive index-fixed region) and the light-diffusing fine particles 20 is increased, the reflection at the interface between the matrix 10 and the light-diffusing fine particles 20 can be suppressed, and backscattering can be suppressed. . Further, in the fixed refractive index region, since the weight concentration of the ultrafine particle component 12 having a large difference between the refractive index and the light diffusing fine particles 20 is relatively high, the substrate 10 (substantially a refractive index fixed region) and light diffusion can be obtained. The difference in refractive index of the fine particles 20 becomes large. As a result, even if it is a film, a high haze (strong diffusibility) can be achieved. In the present specification, the term "the refractive index changes substantially continuously" means that the refractive index changes substantially continuously from the light-diffusing fine particles to the refractive index-fixed region in the refractive index-modulating region. Therefore, for example, even at the interface between the light diffusing fine particles and the refractive index modulation region, and/or the refractive index modulation region and the refractive index The interface of the fixed region has a refractive index difference within a specific range (for example, a refractive index difference of 0.05 or less), and the difference can be tolerated.

The thickness of the refractive index modulation region 30 (the innermost portion from the innermost portion of the refractive index modulation region to the outermost portion of the refractive index modulation region) may be fixed (that is, the refractive index modulation region may also be expanded around the light diffusing fine particles). The concentric spherical shape may be different in thickness depending on the position of the surface of the light diffusing fine particles (for example, it may be a peripheral shape of the golden sugar).

The average thickness of the refractive index modulation region 30 is preferably from 0.01 μm to 0.6 μm, more preferably from 0.03 μm to 0.5 μm, still more preferably from 0.04 μm to 0.4 μm, still more preferably from 0.05 μm to 0.4 μm. The average thickness is an average thickness when the thickness of the concentration modulation region 30 differs depending on the position of the surface of the light diffusing fine particles, and is the thickness when the thickness is fixed.

As described above, the matrix 10 contains the resin component 11 and the ultrafine particle component 12. The refractive index modulation region 30 is preferably formed in accordance with a substantial gradient of the dispersion concentration of the ultrafine particle component 12 in the matrix 10. Specifically, in the refractive index modulation region 30, the dispersion concentration of the ultrafine particle component 12 (specifically, as defined by the weight concentration) becomes higher as it moves away from the light diffusing fine particles 20 (the weight concentration of the resin component 11) Inevitably lower.) In other words, in the closest region of the light diffusing fine particles 20 of the refractive index modulation region 30, the ultrafine particle component 12 is dispersed at a relatively low concentration, and the concentration of the ultrafine particle component 12 increases as it moves away from the light diffusing fine particles 20. For example, the area ratio of the ultrafine particle component 12 in the matrix 10 obtained by the transmission electron microscope (TEM) image is smaller on the side close to the light diffusing fine particles 20 and larger on the side close to the substrate 10, which is larger. The area ratio changes from a light diffusing fine particle side to a matrix side (refractive index fixed area side) to form a substantial gradient. A TEM image showing a representative dispersed state is shown in Fig. 4 . In the present specification, the "area ratio of the ultrafine particle component in the matrix obtained by the transmission electron microscope image" means in the transmission electron microscope image of the section including the diameter of the light diffusing fine particle. The ratio of the area of the ultrafine particle component to the matrix of a specific range (specific area). Area ratio Corresponding to the three-dimensional dispersion concentration (actual dispersion concentration) of the ultrafine particle component. The area ratio of the ultrafine particle component can be obtained by any appropriate image analysis software. Further, the above area ratio is representatively corresponding to the average shortest distance between the particles of the ultrafine particle component. Specifically, the average shortest distance between the particles of the ultrafine particle component is shortened in the refractive index modulation region as being away from the light diffusing fine particles, and is fixed in the refractive index fixed region (for example, the average shortest distance to the light) The closest region of the diffusing fine particles is about 3 nm to 100 nm, and in the fixed refractive index region, it is 1 nm to 20 nm). With respect to the average shortest distance, the TEM image in the dispersed state of FIG. 4 can be binarized and calculated using, for example, the inter-center distance method of the image analysis software "A-like" (made by Asahi Kasei Engineering Co., Ltd.). As described above, according to the manufacturing method of the present invention, the refractive index modulation region 30 can be formed in the vicinity of the surface of the light diffusing fine particles by the substantial gradient of the dispersion concentration of the ultrafine particle component 12, and thus the GRIN fine particles can be produced by using a complicated manufacturing method. In the case of dispersing the GRIN microparticles, the light diffusing element can be produced in a particularly simple order and at a particularly low cost. Further, by forming the refractive index modulation region by the substantial gradient of the dispersion concentration of the ultrafine particle component, the refractive index can be smoothly changed at the boundary between the refractive index modulation region 30 and the refractive index fixed region. Further, by using an ultrafine particle component having a large difference in refractive index from the resin component and the light diffusing fine particles, the refractive index difference between the light diffusing fine particles and the matrix (substantially a refractive index fixed region) can be increased and the refractive index can be made. The refractive index gradient of the rate modulation region becomes steep.

The refractive index modulation region (substantially the gradient of the dispersion concentration of the ultrafine particle component as described above) can be selected by appropriately selecting the resin component of the matrix, the ultrafine particle component and the constituent material of the light diffusing fine particle, and the chemical and Formed by thermodynamic properties. For example, a resin component and light-diffusing fine particles are formed of a homologous material (for example, an organic compound), and a fine particle component is formed of a material (for example, an inorganic compound) different from the resin component and the light diffusing fine particle, whereby the resin component can be favorably formed. Refractive index modulation area. Further, for example, it is preferred to use a material having a higher compatibility in the homologous material to form a resin with each other. Divided into light diffusing fine particles. The thickness and refractive index gradient of the refractive index modulation region can be controlled by adjusting the chemical and thermodynamic properties of the resin component, the ultrafine particle component, and the light diffusing fine particles of the matrix. In the present specification, the term "same system" means that the chemical structure or characteristics are the same or similar, and the term "different system" means a group other than the same system. The same or not can vary depending on the method of selection of the benchmark. For example, in the case of organic or inorganic based, the organic compounds are compounds of the same type, and the organic compound and the inorganic compound are compounds of different systems. When the repeating unit of the polymer is used as a reference, for example, although the acrylic polymer and the epoxy polymer are the same as the organic compound, they are compounds of different systems, in the case of the periodicity table, although the base is used. The metal and the transition metal are both inorganic elements, but are elements of different systems.

The higher the haze value of the light diffusing element, the better, specifically, 70% or more, more preferably 90% to 99%, further preferably 92% to 99.5%, and further preferably 95% to 99.5. %, especially good is 97%~99.5%, and the best is 98.6%~99.5%. By using a haze value of 70% or more, it can be preferably used as a front light diffusing element in a collimated backlight front diffusion system. In addition, the collimated backlight front diffusing system refers to a collimated backlight (a backlight having a narrow half-width of brightness concentrated in a fixed direction) and a front side on the viewing side of the upper polarizing plate in the liquid crystal display device. A system of light diffusing elements.

The diffusion characteristics of the light diffusing element are preferably 10° to 150° (single side 5° to 75°), more preferably 10° to 100° (one side 5°), as indicated by the light diffusion half angle. ~50°), further preferably 30° to 80° (15° to 40° on one side).

When the parallel light is incident perpendicularly to the light diffusing element, the transmittance of light parallel to the incident light is preferably 2% or less, more preferably 1% or less. In the present invention, since the ultrafine particle component is not contained, the light transmitted through the light diffusing fine particles and the refractive index modulation region can be reduced, and the incident light can be prevented from being directly diffused without being diffused. Further, the light diffusing fine particles are present in a state of not substantially agglomerating, whereby the above effects are more remarkable.

The thickness of the above light diffusing element can be appropriately set depending on the purpose or the desired diffusion characteristics. Specifically, the thickness of the light diffusing element is preferably 4 μm to 50 μm, more preferably 4 μm to 20 μm. According to the present invention, it is possible to obtain a light diffusing element having a very high haze value as described above and excellent in smoothness, although it is a very thin thickness as described above.

The above light diffusing element can be preferably used for a liquid crystal display device, and can be particularly preferably used for a collimated backlight front diffusing system. The light diffusing element may be provided as a film or a plate member alone, or may be attached to any appropriate substrate or polarizing plate as a composite member. Further, an antireflection layer may be laminated on the light diffusing element.

A-2. Matrix

As described above, the substrate 10 preferably contains the resin component 11 and the ultrafine particle component 12. As described above, as shown in FIG. 1 and FIG. 2, the ultrafine particle component 12 is preferably dispersed in the resin component 11 so as to form the refractive index modulation region 30 in the vicinity of the surface of the light diffusing fine particle 20.

A-2-1. Resin composition

The resin component 11 can be composed of any suitable material as long as the effect of the present invention can be obtained. As described above, the resin component 11 is preferably composed of a compound which is the same as the compound of the light diffusing fine particles and which is different from the ultrafine particle component. Thereby, the refractive index modulation region can be favorably formed in the vicinity of the surface of the light diffusing fine particles. Further, it is preferable that the resin component 11 is composed of a compound having high compatibility with a compound of the same type as the light diffusing fine particles. Thereby, a refractive index modulation region having a desired refractive index gradient can be formed. More specifically, the resin component is in a state in which the light-diffusing fine particles are surrounded by the resin component as compared with the state in which the ultrafine particle component is uniformly dissolved or dispersed in the vicinity of the light diffusing fine particles. The energy is more stable. As a result, the weight concentration of the resin component in the closest region of the light diffusing fine particles is higher than the average weight concentration of the resin component of the entire matrix, and becomes lower as it moves away from the light diffusing fine particles. Therefore, the refractive index modulation region can be favorably formed in the vicinity of the surface of the light diffusing fine particles.

The above resin component is preferably composed of an organic compound, more preferably hard free rays Made of a synthetic resin. The free ray-curable resin-based coating film is excellent in hardness. Examples of the free ray include ultraviolet light, visible light, infrared light, and an electron beam. Ultraviolet rays are preferred, and therefore the resin component is preferably composed of an ultraviolet curable resin. The ultraviolet curable resin may, for example, be a resin formed of a radical polymerizable monomer and/or oligomer such as an acrylate resin (epoxy acrylate, polyester acrylate, acrylic acrylate, or ether acrylate). The molecular weight (precursor) constituting the acrylate resin preferably has a molecular weight of 200 to 700. Specific examples of the monomer component (precursor) constituting the acrylate resin include pentaerythritol triacrylate (PETA: molecular weight 298), neopentyl glycol diacrylate (NPGDA: molecular weight 212), and dipentaerythritol hexaacrylate ( DPHA: molecular weight 632), dipentaerythritol pentaacrylate (DPPA: molecular weight 578), trimethylolpropane triacrylate (TMPTA: molecular weight 296). In the precursor, an initiator may also be added as needed. Examples of the initiator include a UV radical generator (Irgacure 907, 127, 192, etc., manufactured by BASF Japan Co., Ltd.) and benzammonium peroxide. The resin component may contain other resin components other than the above-described free ray curable resin. The other resin component may be a free ray curable resin, may be a thermosetting resin, or may be a thermoplastic resin. Representative examples of other resin components include aliphatic (for example, polyolefin) resins and urethane resins. When a resin component is used, the kind or the amount of the compound is adjusted so that the refractive index modulation region is favorably formed.

Preferably, the resin component of the matrix and the light diffusing fine particles have a refractive index satisfying the following formula (1): 0 < | n _{P -} n _A | . . (1)

In the formula (1), n _A represents the refractive index of the resin component of the matrix, and n _P represents the refractive index of the light diffusing fine particles. | n _P -n _A | is preferably from 0.01 to 0.10, more preferably from 0.01 to 0.06, still more preferably from 0.02 to 0.06. If | n _P -n _A | is less than 0.01, there is a case where the refractive index modulation region is not formed. If | n _P -n _A | exceeds 0.10, there is a tendency for backscatter to increase.

The resin component, the ultrafine particle component, and the light diffusing fine particles of the matrix preferably have a refractive index satisfying the following formula (2): 0 < | n _{P -} n _A | < | n _{P -} n _B |. . . (2)

In the formula (2), n _A and n _{P are} as described above, and n _B represents the refractive index of the ultrafine particle component. | n _{P -} n _B | is preferably 0.10 to 1.50, more preferably 0.20 to 0.80. When | n _{P -} n _B | is less than 0.10, the haze value is often 90% or less. As a result, the light from the light source cannot be sufficiently diffused when incorporated into the liquid crystal display device. And there is a narrower perspective. If | n _P -n _B | exceeds 1.50, there is a tendency for backscatter to increase.

When the refractive index of each component is the relationship of the above (1) and (2), a light diffusing element which maintains a high haze and suppresses rear scattering can be obtained.

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

The amount of the above resin component is preferably from 10 parts by weight to 80 parts by weight, more preferably from 20 parts by weight to 80 parts by weight, even more preferably from 20 parts by weight to 65 parts by weight, based on 100 parts by weight of the substrate. It is 45 parts by weight to 65 parts by weight.

The resin component may contain other resin components other than the above-described free ray curable resin. The other resin component may be a free ray curable resin, may be a thermosetting resin, or may be a thermoplastic resin. Representative examples of other resin components include aliphatic (for example, polyolefin) resins and urethane resins. When a resin component is used, the kind or the amount of the compound is adjusted so that the refractive index modulation region is favorably formed.

A-2-2. Ultrafine particle component

As described above, the ultrafine particle component 12 is preferably composed of a compound different from the resin component and the light diffusing fine particles described below, and more preferably an inorganic compound. As a preferable inorganic compound, a metal oxide and a metal fluoride are mentioned, for example. Specific examples of the metal oxide include zirconia (refractive index: 2.19), alumina (refractive index: 1.56 to 2.62), titanium oxide (refractive index: 2.49 to 2.74), and yttrium oxide (refracting Rate: 1.25~1.46). Specific examples of the metal fluoride include magnesium fluoride (refractive index: 1.37) and calcium fluoride (refractive index: 1.40 to 1.43). Since the metal oxide and the metal fluoride are less absorbed by light, and the organic compound such as the free ray-curable resin or the thermoplastic resin has a refractive index which is difficult to express, the ultrafine particle component is separated from the interface with the light diffusing fine particles. The weight concentration is relatively high, whereby the refractive index can be adjusted to be large. By making the refractive index difference between the light-diffusing fine particles and the substrate large, even a thin film can achieve high haze (high light diffusibility), and a refractive index modulation region can be formed, so that the effect of preventing backscattering is also large. A particularly preferred inorganic compound is zirconia.

The above ultrafine particle component preferably also satisfies the above formulas (1) and (2). Moreover, the refractive index of the resin component, the ultrafine particle component, and the light diffusing fine particle is preferably the following formula (3). When the refractive index of the resin component, the ultrafine particle component, and the light diffusing fine particle is in the above relationship, a light diffusing element that maintains a high haze value and suppresses backscattering can be obtained.

| n _P -n _A |<| n _A -n _B |. . . (3)

The refractive index of the ultrafine particle component is preferably 1.40 or less or 1.60 or more, more preferably 1.40 or less or 1.70 to 2.80, particularly preferably 1.40 or less or 2.00 to 2.80. If the refractive index exceeds 1.40 or does not reach 1.60, the difference in refractive index between the light-diffusing fine particles and the substrate becomes insufficient, and sufficient light diffusibility cannot be obtained, and the light diffusing element is used for the front surface of the collimated backlight. In the case of a liquid crystal display device of a diffusion system, there is a possibility that the light from the collimated backlight cannot be sufficiently diffused and the viewing angle is narrowed.

The upper limit of the average primary particle diameter of the above ultrafine particle component is 100 nm, preferably 80 nm, more preferably 60 nm, still more preferably 30 nm. The lower limit of the average primary particle diameter of the above ultrafine particle component is preferably 10 nm, more preferably 15 nm. Thus, by using an ultrafine particle component having an average particle diameter smaller than the wavelength of light, a geometrically uniform matrix can be obtained without geometrical optical reflection, refraction, and scattering between the ultrafine particle component and the resin component. As a result, a light diffusing element having uniform optical properties can be obtained.

The light diffusing element does not substantially contain agglomerated ultrafine particle components. A light diffusing element having a high haze value and a strong diffusibility can be obtained by substantially eliminating the agglomerated ultrafine particle component. In the present specification, the term "substantially free of agglomerated ultrafine particle components" includes not only the case of containing only ultrafine particles existing as primary particles, but also including ultrafine particle components having a particle diameter sufficiently close to the primary particle diameter. The case and the case where the ultrafine particle component of agglomeration is contained in a range which acquires the effect of this invention further. The "ultrafine particle component having a particle diameter sufficiently close to the primary particle diameter" means that the particle diameter is 10 times or less the average primary particle diameter (preferably 8 times or less, more preferably 5 times or less, and still more preferably 3). The ultrafine particle component present in the secondary particle of the following). In addition, in the present specification, "the particle diameter is sufficiently close to the primary particle diameter" is also referred to as "substantially no aggregation". Further, the particle diameter and the average particle diameter of the ultrafine particle component in the light diffusing element can be measured by observing the cross section of the light diffusing element using a transmission electron microscope (TEM).

As described above, the above-mentioned light diffusing element can contain a small amount of agglomerated ultrafine particle component within the range in which the effects of the present invention are obtained. The light diffusing element containing a small amount of agglomerated ultrafine particle component means, for example, a specific measurement field of a transmission electron microscope (TEM) (direct magnification × 1,200, MAGNIFICATION × 10,000 (13.9 μm × 15.5 μm) In the)), the white spot observed by the absence of the ultrafine particle component in the matrix (that is, the white spot other than the whitish portion derived from the light diffusing fine particle in the measurement field) has less than 10 light diffusions. element. This white point is produced by the density (ie, agglomeration) of the ultrafine particle component, and the less the better. The number of white spots is preferably less than 8, more preferably less than 5, and even more preferably less than 3. The best number for this white point is 0. In other words, the ultrafine particle component preferably does not substantially aggregate, and is preferably present as a primary particle.

Preferably, the ultrafine particle component is subjected to surface modification. By performing surface modification, the ultrafine particle component can be well dispersed in the resin component, and the above refractive index modulation region can be favorably formed. As the surface modification means, any appropriate means can be employed as long as the effects of the present invention are obtained. In the representative case, the surface modification is as follows It is carried out by applying a surface modifier to the surface of the ultrafine particle component to form a surface modifier layer. Specific examples of the preferred surface modifier include a coupling agent such as a decane coupling agent or a titanate coupling agent, and a surfactant such as a fatty acid surfactant. By using such a surface modifier, the wettability of the resin component and the ultrafine particle component can be improved, the interface between the resin component and the ultrafine particle component can be stabilized, and the ultrafine particle component can be well dispersed in the resin component and formed well. Refractive index modulation area.

The amount of the ultrafine particle component in the coating liquid is preferably from 10 parts by weight to 70 parts by weight, more preferably from 35 parts by weight to 55 parts by weight, per 100 parts by weight of the substrate to be formed.

A-3. Light diffusing fine particles

Further, the light diffusing fine particles 20 may be formed of any appropriate material as long as the effects of the present invention are obtained. Preferably, as described above, the light diffusing fine particles 20 are composed of a compound which is the same as the resin component of the above-mentioned matrix. For example, when the free ray curable resin constituting the resin component of the matrix is an acrylate resin, the light diffusing fine particles are preferably made of an acrylate resin. More specifically, when the monomer component of the acrylate resin constituting the resin component of the matrix is, for example, PETA, NPGDA, DPHA, DPPA, and/or TMPTA as described above, the acrylate system constituting the light diffusing fine particles The resin is preferably polymethyl methacrylate (PMMA), polymethyl acrylate (PMA) and copolymers thereof, and such crosslinks. Examples of the copolymerization component with PMMA and PMA include polyurethane, polystyrene (PS), and melamine resin. The light diffusing fine particles are particularly preferably composed of PMMA. The reason for this is that the relationship between the refractive index or the thermodynamic properties of the resin component and the ultrafine particle component of the matrix is appropriate. Further, the light diffusing fine particles preferably have a crosslinked structure (stereoscopic network structure). By adjusting the density (crosslinking degree) of the crosslinked structure, the degree of freedom of the polymer molecules constituting the fine particles on the surface of the light diffusing fine particles can be controlled, so that the dispersion state of the ultrafine particle components can be controlled, and as a result, a desired one can be formed. The refractive index modulation region of the refractive index gradient.

Preferably, the resin component penetrates into the light diffusing fine particles, and the light diffusing element contains a resin component in the light diffusing fine particles. When the resin component penetrates into the light-diffusing fine particles, a refractive index modulation region can be formed inside the surface of the light-diffusing fine particles, and a haze value can be obtained, a strong diffusibility can be obtained, and light diffusion of backscattering can be suppressed. element. Further, light-diffusing fine particles having a large average particle diameter can be obtained. The penetration range of the resin component in the light diffusing fine particles is preferably 80% or more, more preferably 85% or more, and still more preferably 85% to 100%, with respect to the average particle diameter of the light diffusing fine particles in the light diffusing element. . When it is in the above range, the refractive index modulation region can be favorably formed to suppress backscattering. The penetration range can be controlled by adjusting the resin component and the material of the light diffusing fine particles, the crosslinking density of the light diffusing fine particles, the type of the organic solvent used in the production, the standing time at the time of production, the standing temperature, and the like.

The average primary particle diameter of the light-diffusing fine particles in the light diffusing element is preferably from 1 μm to 5 μm, more preferably from 2 μm to 5 μm, still more preferably from 2.5 μm to 4 μm. When it is in the above range, a light diffusing element having a high haze value and strong diffusibility and suppressing transmission of direct light can be obtained. In the present specification, the term "light-diffusing fine particles in a light-diffusing element" means that the light-diffusing fine particles are swollen in the production step, that is, the light-diffusing fine particles after swelling, that is, the particle diameter is increased as compared with the addition. Light diffusing fine particles. Further, the average particle diameter of the light diffusing fine particles in the light diffusing element can be measured by observing the cross section of the light diffusing element using a transmission electron microscope (TEM).

It is preferable that the light diffusing fine particles in the light diffusing element do not substantially aggregate. When the light-diffusing fine particles are present in a state of not substantially agglomerating, a light diffusing element having a high haze value and strong diffusibility and suppressing transmission of direct light can be obtained. In the present specification, the term "substantially does not aggregate" means a state in which the particle diameter is sufficiently close to the primary particle diameter. Therefore, the "substantially non-agglomerated" particles include not only the respective separated particles (single particles) but also a plurality of particles in a plurality of aggregated states within the range in which the effects of the present invention are obtained. Specifically, the term "substantially does not condense" light diffusing fine particles, including Light-diffusing fine particles existing as primary particles and light-diffusing fine particles existing as secondary particles having a particle diameter of 2.5 times or less the average primary particle diameter. The particle diameter of the light diffusing fine particles in the light diffusing element is preferably 2 times or less, more preferably 1.5 times or less, of the average primary particle diameter.

The average particle diameter of the light diffusing fine particles in the light diffusing element is preferably 1/2 or less (for example, 1/2 to 1/20) of the thickness of the light diffusing element. If the average particle diameter of the above ratio is set with respect to the thickness of the light diffusing element, the light diffusing fine particles can be arranged in plural in the thickness direction of the light diffusing element, so that the light can be multiplied when the incident light passes through the light diffusing element. The ground spreads, and as a result, sufficient light diffusibility can be obtained.

The standard deviation of the weight average particle diameter distribution of the light-diffusing fine particles in the light diffusing element is preferably 1.0 μm or less, more preferably 0.5 μm or less, and still more preferably 0.1 μm or less. The smaller the standard deviation of the weight average particle diameter distribution of the light diffusing fine particles, the better, but the practical lower limit is, for example, 0.01 μm. Further, the weight average particle diameter distribution of the diffusing fine particles is preferably monodispersed, and for example, the coefficient of variation of the weight average particle diameter distribution ((standard deviation of particle diameter) × 100 / (average particle diameter)) is preferably 20% or less. More preferably, it is 15% or less. The smaller the coefficient of variation of the weight average particle diameter distribution of the diffusing fine particles, the better, but the practical lower limit is, for example, 5%. When a large amount of light-diffusing fine particles having a small particle diameter with respect to the weight average particle diameter is mixed, the diffusibility is excessively increased, and the back scattering cannot be satisfactorily suppressed. When a large amount of light-diffusing fine particles having a large particle diameter with respect to a weight average particle diameter is mixed, there is a case where a plurality of layers cannot be arranged in the thickness direction of the light diffusing element, and multiple diffusion cannot be obtained. As a result, light diffusibility exists. It is not enough.

As the shape of the light diffusing fine particles, any appropriate shape can be adopted depending on the purpose. Specific examples include a spherical shape, a scaly shape, a plate shape, an ellipsoid shape, and an amorphous shape. In many cases, spherical fine particles can be used as the light diffusing fine particles.

It is also preferable that the light diffusing fine particles satisfy the above formulas (1) and (2). The refractive index of the light diffusing fine particles is preferably from 1.30 to 1.70, more preferably from 1.40 to 1.60.

A-4. Method of manufacturing light diffusing element

A method for producing a light diffusing element according to an embodiment of the present invention includes a coating liquid obtained by dissolving or dispersing a resin component precursor (monomer), an ultrafine particle component, and light diffusing fine particles in an organic solvent. a step of coating on a substrate (refer to step A); a step of drying the coating liquid applied to the substrate (refer to step B); and a step of polymerizing the precursor (refer to step C) ).

(Step A)

The resin component precursor, the ultrafine particle component, and the light diffusing fine particles are described in the above items A-2-1, A-2-2, and A-3, respectively. In a representative case, the coating liquid is a dispersion in which an ultrafine particle component and light diffusing fine particles are dispersed in a precursor and a volatile solvent. As means for dispersing the ultrafine particle component and the light diffusing fine particles, a dispersion treatment by a stirrer can be preferably used. This is because the ultrafine particle component and the light diffusing fine particles are sufficiently mixed to obtain an ultrafine particle component and a light diffusing fine particle which are substantially not aggregated. As the agitator, a disperser type mixer can be preferably used. The stirring time is preferably 15 minutes or longer, more preferably 15 minutes to 60 minutes. The dispersion treatment is preferably carried out immediately before the coating liquid is applied onto the substrate.

In one embodiment, the coating liquid is prepared by mixing light diffusing fine particles in an organic solvent and swelling the light diffusing fine particles, and then adding the resin component precursor and the ultrafine particle component to the organic solvent. When the light-diffusing fine particles are mixed in advance in an organic solvent to swell the light-diffusing fine particles, they are supplied to the subsequent step immediately after the preparation of the coating liquid, that is, without standing still. As a result, it is possible to prevent the light diffusing fine particles and the ultrafine particle components from agglomerating.

Specific examples of the organic solvent include butyl acetate, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, 2-butanone (methyl ethyl ketone), cyclopentanone, toluene, and isopropyl ester. Alcohol, n-butanol, cyclopentane, water.

Preferably, the boiling point of the organic solvent is preferably 70 ° C or higher, more preferably 100 ° C. Above, it is preferably 110 ° C or more, and most preferably 120 ° C or more. By using an organic solvent having a relatively low volatility, rapid evaporation can be prevented when the organic solvent is dried, and aggregation of the light diffusing fine particles and the ultrafine particle components can be prevented.

The above coating liquid may further contain any appropriate additives as needed. For example, in order to disperse the ultrafine particle component well, a dispersing agent can be preferably used. Other specific examples of the additive include an ultraviolet absorber, a leveling agent, and an antifoaming agent.

The blending amount of the resin component precursor in the above coating liquid is described in the item A-2-1, and the blending amount of the ultrafine particle component is described in the item A-2-2. The upper limit of the amount of the light-diffusing fine particles is preferably 40 parts by weight, more preferably 30 parts by weight, even more preferably 20 parts by weight, based on 100 parts by weight of the substrate. The lower limit of the amount of the light-diffusing fine particles is preferably 5 parts by weight, more preferably 10 parts by weight, still more preferably 15 parts by weight, based on 100 parts by weight of the substrate.

The solid content concentration of the coating liquid can be adjusted so as to be about 10% by weight to 70% by weight. If it is the above-mentioned solid content density, the coating liquid which has the viscosity which is easy to apply can be obtained.

As the above substrate, any appropriate film can be employed as long as the effects of the present invention are obtained. Specific examples thereof include a cellulose triacetate (TAC) film, a polyethylene terephthalate (PET) film, a polypropylene (PP) film, a nylon film, an acrylic film, a lactone-modified acrylic film, and the like. The substrate may be subjected to surface modification such as easy adhesion treatment as needed, and may include additives such as a lubricant, an antistatic agent, and an ultraviolet absorber.

As a method of applying the coating liquid to the substrate, a method using any appropriate coating machine can be employed. Specific examples of the coater include a bar coater, a reverse coater, a contact coater, a gravure coater, a die coater, and a notch coater.

(Step B)

As the drying method of the above coating liquid, any appropriate method can be employed. Specific examples include natural drying, heat drying, and reduced pressure drying. It is preferably heated and dried. The heating temperature is preferably from 60 ° C to 150 ° C, more preferably from 60 ° C to 100 ° C, and still more preferably from 60 ° C to 80 ° C. When the heating temperature exceeds 150 ° C, the coating liquid surface abruptly changes, and the light diffusing fine particles cannot follow the change of the coating liquid surface, and sufficient smoothness cannot be obtained. The heating time is, for example, 30 seconds to 5 minutes.

(Step C)

The polymerization method may be any appropriate method depending on the kind of the resin component (hence, its precursor). For example, when the resin component is a free ray-curable resin, the precursor is polymerized by irradiation with free rays. When ultraviolet rays are used as the free ray, the cumulative amount of light is preferably from 50 mJ/cm ² to 1000 mJ/cm ² , more preferably from 200 mJ/cm ² to 400 mJ/cm ² . The transmittance of the free ray to the light diffusing fine particles is preferably 70% or more, and more preferably 80% or more. Further, for example, when the resin component is a thermosetting resin, the precursor is polymerized by heating. The heating temperature and the heating time can be appropriately set depending on the type of the resin component. The polymerization is preferably carried out by irradiation with free rays. When it is irradiated with free rays, the refractive index modulation region can be favorably maintained and the coating film can be directly cured, so that a light diffusion element having good diffusion characteristics can be produced. The matrix is formed by polymerizing the precursor while forming a refractive index modulation region in the vicinity of the surface of the light diffusing fine particles. That is, according to the manufacturing method of the present invention, the refractive index can be formed near the surface of the light diffusing fine particles by simultaneously polymerizing the precursor which penetrates into the inside of the light diffusing fine particles and the precursor which does not penetrate into the light diffusing fine particles. The matrix is formed while the regions are changed.

The above polymerization step (step C) may be carried out before the above drying step (step B), or may be carried out after step B. The drying step (step B) is preferably carried out prior to the polymerization step (step C). The reason for this is that the penetration of the resin component precursor into the light diffusing fine particles can be promoted by heating.

Needless to say, in the method of manufacturing the light diffusing element of the present embodiment, in addition to the above steps A to C, any appropriate steps, processes, and/or operations may be included at any appropriate time. The types of such steps, etc., and the timing of such steps, etc. It is set as appropriate according to the purpose. For example, in the case of the step A, when the components are simultaneously mixed, the coating liquid can be allowed to stand for a certain period of time before coating. The resin component precursor can be sufficiently infiltrated into the light diffusing fine particles by standing for a specific period of time. The standing time is preferably from 1 hour to 48 hours, more preferably from 2 hours to 40 hours, further preferably from 3 hours to 35 hours, and particularly preferably from 4 hours to 30 hours.

In the above manner, the light diffusing element described in the above items A-1 to A-3 is formed on the substrate.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the examples. The evaluation methods in the examples are as follows. Further, the "parts" and "%" in the examples are based on weight unless otherwise specified.

(1) Thickness of light diffusing element

The total thickness of the substrate and the light diffusing element was measured by a micrometer thickness gauge (manufactured by Mitutoyo Co., Ltd.), and the thickness of the light diffusing element was calculated by subtracting the thickness of the substrate from the total thickness.

(2) Average particle size and standard deviation of light diffusing fine particles and ultrafine particle components in a light diffusing element

The laminate of the light-diffusing element and the substrate obtained in the examples and the comparative examples was cooled with liquid nitrogen, and cut into a thickness of 0.1 μm by a microtome to obtain a measurement sample. The measurement sample was observed using a transmission electron microscope (TEM), and the particle diameters of the light diffusing fine particles and the ultrafine particle components in the light diffusing element were measured based on the TEM image using an image analysis software. This measurement was carried out at 20 randomly selected points, and the average particle diameter and standard deviation of the light diffusing fine particles and the ultrafine particle components in the light diffusing element were calculated.

(3) Condensation of ultrafine particle components

The laminate of the light-diffusing element and the substrate obtained in the examples and the comparative examples was cooled with liquid nitrogen, and cut into a thickness of 0.1 μm by a microtome to obtain a measurement sample. The cross section of the measurement sample was measured by a transmission electron microscope (TEM) (manufactured by Hitachi, Ltd.). The two-dimensional image was observed by the product name "H-7650" and the acceleration voltage of 100 kV, and the occurrence of density in the light diffusing element of the measurement sample was confirmed. In the measurement field of direct magnification × 1,200, MAGNIFICATION × 10,000 (13.9 μm × 15.5 μm), the portion observed as a white spot in the absence of the ultrafine particle component in the matrix (ie, the light diffusing fine particle in the measurement field of view) The number of white spots other than the whitish part is counted. With respect to the laminate of the light-diffusing element and the substrate obtained in the examples and the comparative examples, the number of white spots was counted at 20 points as described above, and the average value was calculated. The average value is shown in Table 1. The more the number of white spots, the more the density of the ultrafine particle components is evaluated.

(4) Condensation of light diffusing fine particles

TEM observation was carried out in the same manner as in the above (2), and the presence or absence of light-diffusing fine particles (substantial secondary particles) having a particle diameter of 2.5 or more with respect to the average primary particle diameter was confirmed. When no substantial secondary particles were observed, it was judged that the respective particles did not substantially aggregate.

(5) Haze value

The measurement was carried out by a haze meter (manufactured by Murakami Color Research Institute Co., Ltd., trade name "HN-150") according to the method specified in JIS 7136.

(6) Backscattering rate

The laminate of the light-diffusing element and the substrate obtained in the examples and the comparative examples was bonded to a black acrylic plate (manufactured by Sumitomo Chemical Co., Ltd., trade name "SUMIPEX" (registered trademark), thickness: 2 mm) via a transparent adhesive. And as a measurement sample. The integral reflectance of the measurement sample was measured by a spectrophotometer (manufactured by Hitachi Instruments Co., Ltd., trade name "U4100"). On the other hand, a laminate of a substrate and a transparent coating layer was prepared by using a coating liquid from which the fine particles were removed from the coating liquid for a light-diffusing element, and the integrated reflectance was measured in the same manner as above. Surface reflectance). The backscattering ratio of the light diffusing element was calculated by subtracting the integrated reflectance (surface reflectance) of the above-mentioned control sample from the integrated reflectance of the above-mentioned measurement sample.

(Example 1)

15 parts of polymethyl methacrylate (PMMA) fine particles (manufactured by Sekisui Chemicals, Inc., trade name "XX131AA", average particle diameter 2.5 μm, refractive index 1.49) as light diffusing fine particles, and acetic acid as an organic solvent 30 parts of a mixed solvent of butyl ester and MEK (weight ratio 50/50) was mixed, and stirred for 60 minutes to prepare a mixed solution.

Then, a hard coating resin (manufactured by JSR Corporation, trade name "Opstar KZ6661") containing 62% of zirconia nanoparticles as an ultrafine particle component (average particle diameter: 60 nm, refractive index: 2.19) was added to the obtained mixture. (containing MEK/MIBK)) 100 parts of pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #300", refractive index 1.52, molecular weight 298) as a resin component precursor, 22 parts, photopolymerization 0.5 part of a starter (manufactured by Ciba Specialty Chemical Co., Ltd., trade name "Irgacure 907") and 0.5 part of a leveling agent (manufactured by DIC Corporation, trade name "GRANDIC PC 4100") were stirred for 15 minutes using a disperser to prepare a coating liquid.

Immediately after the preparation of the coating liquid, it was applied to a TAC film (manufactured by FUJI FILM Co., Ltd., trade name "Fujitac") using a bar coater, and heated at 60 ° C for 1 minute, and then irradiated with ultraviolet light having a cumulative light amount of 300 mJ to obtain a thickness. 10 μm light diffusing element. The obtained light diffusing element was subjected to the evaluation of the above (2) to (6). Further, a TEM photograph of a cross section of the light diffusing element is shown in Fig. 5 .

(Example 2)

In the first embodiment, a hard coating resin (manufactured by JSR Corporation, trade name "Opstar KZ6661" (with MEK/) containing zirconia nanoparticles (average particle diameter: 60 nm, refractive index: 2.19) containing 62% of the ultrafine particle component is replaced. MIBK)) In the same manner as in Example 1, except that the product name "Opstar KZ6706" (containing PEGME (propylene glycol monomethyl ether)) (having an average particle diameter of 30 nm and a refractive index of 2.19) manufactured by JSR Corporation was used in 100 parts. A light diffusing element is obtained. The obtained light diffusing element was subjected to the evaluation of the above (2) to (6). The results are shown in Table 1.

(Comparative Example 1)

In 100 parts of a hard coating resin (manufactured by JSR Corporation, trade name "Opstar KZ6661" (including MEK/MIBK)) containing 62% of zirconia nanoparticles as an ultrafine particle component (average particle diameter: 60 nm, refractive index: 2.19) Adding pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #300", refractive index 1.52) as a resin component precursor, butyl acetate and MEK mixed solvent 50% solution, 11 parts, photopolymerization 0.5 part of a starter (manufactured by Ciba Specialty Chemical Co., Ltd., trade name "Irgacure 907"), 0.5 part of a leveling agent (manufactured by DIC Corporation, trade name "GRANDIC PC 4100"), and polymethacrylic acid as a light diffusing fine particle Methyl ester (PMMA) fine particles (manufactured by Sekisui Chemicals, Inc., trade name "XX131AA", average particle diameter: 2.5 μm, refractive index: 1.49) were 15 parts. The mixture was subjected to ultrasonic treatment for 5 minutes to prepare a coating liquid in which the above components were uniformly dispersed. The coating liquid was allowed to stand for 24 hours, and then applied to a TAC film (manufactured by FUJI FILM Co., Ltd., trade name "Fujitac") using a bar coater, and heated at 60 ° C for 1 minute, and then irradiated with a cumulative light amount of 300 mJ. Ultraviolet rays were used to obtain a light diffusing element having a thickness of 10 μm. The obtained light diffusing element was subjected to the evaluation of the above (2) to (6). The results are shown in Table 1.

As is clear from the above Table 1, according to the present invention, the ultrafine particle component has a small particle diameter and substantially does not contain agglomerated ultrafine particle components, so that a haze value is high, a strong diffusibility is obtained, and backscattering is suppressed. Light diffusing element.

[Industrial availability]

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

10‧‧‧Material

11‧‧‧Resin composition

12‧‧‧ Ultrafine particle components

20‧‧‧Light diffusing microparticles

30‧‧‧Concentration zone

100‧‧‧Light diffusing elements

Claims (5)

A light diffusing element comprising a matrix containing a resin component and an ultrafine particle component, and light diffusing fine particles dispersed in the matrix, wherein the ultrafine particle component has an average primary particle diameter of 100 nm or less, and substantially does not contain agglomerated super Microparticle composition. The light diffusing element according to claim 1, wherein the light diffusing fine particles have an average primary particle diameter of 1 μm to 5 μm, and the coefficient of variation of the weight average particle diameter distribution of the light diffusing fine particles is 20% or less, and the light diffusing fine particles Essentially not condensed. The light diffusing element of claim 1, wherein the ultrafine particle component has an average primary particle diameter of 30 nm or less. The light diffusing element according to claim 2, wherein the ultrafine particle component has an average primary particle diameter of 30 nm or less. The light diffusing element according to any one of claims 1 to 4, wherein a refractive index of the resin component, the ultrafine particle component, and the light diffusing fine particle satisfies the following formula (i), and is on a surface of the light diffusing fine particle There is a refractive index modulation region nearby, | n _P -n _A |<| n _P -n _B |. . . (i) In the formula (i), n _A represents the refractive index of the resin component of the matrix, n _B represents the refractive index of the ultrafine particle component of the matrix, and n _P represents the refractive index of the light diffusing fine particles.