WO2018025884A1 - Light diffuser plate, backlight, and method for manufacturing light diffuser plate - Google Patents

Abstract

This light diffuser plate is configured from a glass plate containing light scattering bodies therein. The light diffuser plate satisfies the following formula (1): 30 − 10 × (d − 2.2) − 7 × v − 50 × D ≤ 17 … (1) wherein d (g / cm³) represents the density of the light diffuser plate, v (%) represents the volume fraction of the light scattering bodies in the glass plate, and D (µm) represents the average grain diameter of the light scattering bodies.

Description

Light diffusing plate, backlight and manufacturing method of light diffusing plate

The present invention relates to a light diffusing plate, a backlight, and a method for manufacturing the light diffusing plate.

As the material of the light diffusing plate used in direct type backlight units such as LCD TVs and liquid crystal monitors, if a transparent material is used, the light source can be seen through because it transmits light. A material that does not impair the brightness of the light source without causing the shape of the light source to be recognized is used. Here, the light source is a light emitting diode (LED) or the like.

In addition, as a material of a light diffusing plate used for an edge light type backlight unit such as a liquid crystal television and a liquid crystal monitor, if a transparent material is used, uneven brightness of the light guide plate that emits light incident on the diffusing plate can be seen. Therefore, a material that does not recognize the luminance unevenness of the light guide plate behind the light diffusion plate is used. Since the diffuser plate used in the direct type backlight has the same problem, the following description will be made in detail by taking the direct type as an example, but is not limited to the direct type. Further, the diffusion plate may be read as a diffusion sheet.

Patent Document 1 discloses a light diffusing member using crystallized glass containing a predetermined component and having an average crystal particle diameter of a crystal phase and an average linear expansion coefficient at a predetermined temperature in a predetermined range. . With such a configuration, a light diffusing member has been proposed that has excellent light diffusibility, excellent heat resistance, low expansion characteristics, high rigidity, and excellent dimensional stability.

Patent Document 2 discloses a light diffusing plate for a direct type backlight device having a diffused light transmittance of 55% or less and a thickness of 2.5 mm or more. A light diffusing plate for a direct type backlight device and a direct type backlight device capable of obtaining sufficiently high luminance and sufficiently suppressing luminance unevenness have been proposed.

Japanese Unexamined Patent Publication No. 2006-206412 Japanese Unexamined Patent Publication No. 2009-21118

In recent years, liquid crystal televisions, liquid crystal monitors, and the like have a tendency to increase in size, and light diffusion plates used in backlight units are required to have high luminance distribution uniformity (hereinafter also referred to as luminance uniformity) and strength. In order to improve the light diffusing performance and to further reduce the thickness of the design, there is a demand for reducing the distance between the light source and the light diffusing plate.

However, the conventional resin light diffusing plate has low heat resistance and light resistance, so if the distance between the light source and the light diffusing plate is too close, it will be deformed over time, and the shape of the light source will become conspicuous, There are problems such as difficulty in maintaining uniformity of brightness. In addition, since the coefficient of thermal expansion is large, it is necessary to secure space for expansion corresponding to the temperature rise and space for heat dissipation, and it is difficult to narrow the frame. Further, the resin light diffusing plate has a low rigidity and has a problem that the strength of the outer frame must be increased. Furthermore, since the resin light diffusing plate has low water resistance, there is a problem that when it is stored for a long period of time, water that has entered from the periphery of the light diffusing plate absorbs water and swells and deforms.

Furthermore, the liquid crystal display device has a problem of deterioration in display quality that the color tone appears to change as a whole when viewed from an oblique direction as compared to when viewed from the front.

However, a light diffusing plate that can easily suppress the deterioration of display quality when viewed from an oblique direction while solving the problems such as ensuring the above-described strength and uniformity of brightness has not been realized yet.

Therefore, an object of the present invention is to provide a light diffusing plate that can easily suppress deterioration of display quality when viewed from an oblique direction while ensuring excellent strength, luminance uniformity, and the like.

The present inventor has shown that the display quality when viewed from an oblique direction in a liquid crystal display device is affected by a chromaticity difference of transmitted light when incident on the light diffusion plate from a vertical direction and an oblique direction, and the chromaticity The difference affects the density (g / cm ³ ) of the light diffusing plate, the volume fraction v (%) of the light scatterer in the light diffusing plate in the glass plate, and the average particle diameter D (μm) of the light scatterer. I found it to be received. And it discovered that the said subject could be solved by controlling the result which these factors interacted to the specific range, and completed this invention.

That is, according to one aspect of the present invention, a light diffusing plate composed of a glass plate containing a light scatterer therein, having a haze of 50% or more, relative to the first main surface of the light diffusing plate. When calculating the chromaticity (x, y) of the XYZ color system when the D65 light source is used from the wavelength dependence of the transmittance of transmitted light in the same direction as the incident direction, The difference Δxy = {(x _{0 °} − between the chromaticity coordinates of transmitted light of light incident from the direction of _{0 °} and the transmitted light of light incident from the direction of 60 ° with respect to the normal of the main surface x _{60 °} ) ² + (y _{0 °} -y _{60 °} ) ² } ^1/2 is 0.020 or less, the density of the light diffusing plate is d (g / cm ³ ), and the light scatterer is in the glass plate. A light diffusing plate satisfying the following formula (1) is provided when the volume fraction of the light scattering medium is v (%) and the average particle diameter of the light scatterer is D (μm): .
30-10 × (d-2.2) -7 × v-50 × D ≦ 17 (1)
Moreover, according to 1 aspect of this invention, a backlight provided with said light diffusing plate and a light source is provided.
Furthermore, according to one aspect of the present invention, the glass plate is a method for producing a light diffusing plate containing phase separation glass, and is an average cooling from a phase separation temperature to a glass transition point, which is a heat treatment condition of the phase separation glass. A method of manufacturing a light diffusing plate having a speed of 2 to 300 ° C./min is provided.

Since the light diffusing plate of the present invention includes a glass plate having high heat resistance and light resistance, the distance between the light source and the light diffusing plate can be reduced when used in a backlight, and the luminance distribution is homogenized. Easy to achieve, thin and narrow frame. In addition, since the light diffusing plate of the present invention includes a glass plate, it is superior in rigidity compared to a resin light diffusing plate, is less likely to generate static electricity, has a high surface hardness, and is not easily damaged. If it is, it is easy to handle in the manufacturing process.

Furthermore, since the light diffusing plate of the present invention includes a glass plate, it has higher water resistance than a resin light diffusing plate, and when used in a backlight, it swells even when stored for a long period of time. This is advantageous in that it is difficult to deform, is difficult to deform, and is less likely to cause display unevenness.

Furthermore, the light diffusing plate of the present invention controls the density of the light diffusing plate, the volume fraction of the light scatterer in the light diffusing plate in the glass plate, and the average particle diameter of the light scatterer to a specific range, so A reduction in display quality when viewed from the direction can be suppressed.

FIG. 1 is a sectional view of a direct type backlight using the light diffusion plate of the present invention. FIG. 2 is a graph obtained by plotting the C value and Δxy obtained for each sample. FIG. 3 is a diagram showing transmitted light that diffuses and transmits through the light diffusion plate. FIG. 4 is a diagram showing the measurement of the transmittance of the light diffusing plate using a spectrophotometer, and FIG. 4A is a diagram showing a state in which light incident on and emitted from the light diffusing plate in the vertical direction is measured. FIG. 6B is a diagram illustrating a state in which light incident and emitted from an angle inclined by 60 ° from the vertical direction with respect to the light diffusion plate is measured. FIG. 5 is a diagram showing an example of the result of transmittance measurement. FIG. 6 is a diagram showing an example of the relationship between the average particle diameter D of the light scatterer and the average cooling rate f.

The present invention is a light diffusing plate composed of a glass plate that includes a light scatterer therein, and has a haze of 50% or more, makes light incident on the first main surface of the light diffusing plate, When calculating the chromaticity (x, y) of the XYZ color system using the D65 light source from the wavelength dependence of the transmittance of transmitted light in the same direction as the direction, the normal to the first principal surface Difference Δxy = {(x _{0 °} -x _{60 °} ) ² + () between the chromaticity coordinates of transmitted light of light incident from the direction of 0 ° and the transmitted light chromaticity coordinates of light incident from the direction of _{60 °} y _{0 °} -y _{60 °} ) ² } ^1/2 is 0.020 or less, the density of the light diffusing plate is d (g / cm ³ ), and the volume fraction of the light scatterer in the glass plate is v ( %), When the average particle diameter of the light scatterer is D (μm), the present invention relates to a light diffusion plate in which the following formula (1) is established.

30-10 × (d-2.2) -7 × v-50 × D ≦ 17 (1)
Furthermore, this invention relates to a backlight provided with this light diffusing plate and a light source.

Hereinafter, the left side of Equation (1) is referred to as a C value. The C value is a value indicating the correlation properties of the density d of the light diffusing plate, the volume fraction v of the light scatterer, and the average particle diameter D of the light scatterer. If the C value is 17 or less, the light diffuser is incident from the vertical direction (0 °) and transmitted in the same direction as the incident direction, and the incident light is incident from the direction inclined by 60 ° (oblique direction). The change in color (Δxy) between the transmitted light transmitted in the same direction as the direction can be suppressed to 0.020 or less. For example, when the light diffusing plate of the present invention is used in a liquid crystal display device or the like, it is possible to suppress a decrease in display quality when viewed from an oblique direction.
The C value is more preferably 16.5 or less, and even more preferably 16.0 or less, in order to further reduce the angle dependency of the hue. When the light scatterer is grown by heat treatment, the C value is preferably −50 or more, more preferably −30 or more, and more preferably 0 or more in order to shorten the time required for the heat treatment.

Density d of the light diffuser plate of the formula (1), from the viewpoint of reducing the C value, is preferably 2.3 g / cm ³ or more, 2.35 g / cm ³ or more, more preferably, 2.4 g / cm ³ or more is more preferable, 2.5 g / cm ³ or more is most preferable, and 2.6 g / cm ³ or more is more preferable. On the other hand, in order to reduce brittleness, the density is preferably 3.0 g / cm ³ or less, more preferably 2.8 g / cm ³ or less, and 2.6 g / cm ³ or less. Is more preferable, and is most preferably 2.5 g / cm ³ or less.

Phase-separated glass or crystallized glass, includes a high concentration of SiO ₂ phases, and a low concentration of SiO ₂ phases. In a glass composition containing many components having a high density, that is, in a glass having a high density, a phase having a low SiO ₂ concentration contains many components having a high refractive index. It became clear that In the case of an average particle diameter equal to or smaller than the wavelength range of visible light, it is known that the scattering intensity of small particles is weak, so that the wavelength dependence of the scattering intensity is likely to occur, but the density is 2.3 g / cm ³ or more. In this case, a sufficient difference in refractive index is obtained, so that the scattering intensity increases even with a small average particle diameter, and the wavelength dependence of the scattering intensity decreases. In order to control the density, it is preferable to use an oxide having a large molecular weight. For example, CaO, SrO, BaO, and the like _Al 2 _{O 3.} Since the density of SiO ₂ is 2.2, the difference (d−2.2) is one term representing the correlation.

The glass plate in the light diffusion plate of the present invention has a first main surface and a second main surface. Here, the first main surface of the glass plate is a surface on the light source side when used in a direct type backlight. The 2nd main surface of a glass plate is a surface which opposes a 1st main surface, and when it uses for a direct type | mold backlight, it is a surface which becomes a liquid crystal panel side. Further, when used in an edge light type backlight, the first main surface of the glass plate is a surface on the light guide plate side, and the second main surface of the glass plate faces the first main surface. This is the surface that is on the liquid crystal panel side.

The glass plate in the light diffusion plate of the present invention has a haze of 50% or more when incident light from the normal direction of the first main surface passes through the glass plate. The haze is preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, and most preferably 95% or more. When the haze is 50% or more, moderate diffusibility can be secured when used in a direct type backlight.

The haze can be measured based on the method described in JIS K7136 (2000).
The glass plate in the light diffusing plate of the present invention transmits incident light to the first main surface from the second main surface while diffusing it. Here, “transmitting light incident on the first main surface from the second main surface while diffusing” means that appropriate light scattering properties are exhibited by having an appropriate haze, and an appropriate total light beam. By having a transmittance, it means expressing appropriate transparency.

The light diffusion plate of the present invention contains a light scatterer inside the glass plate. Since the light scatterer has a different refractive index from the surroundings, the light scatterer scatters the incident light. When there is a dispersed phase inside the glass plate and there is a continuous phase around it, the dispersed phase is called a light scatterer. In addition, when there is a continuously entangled phase inside the glass plate, a phase with a small volume fraction is called a light scatterer. When a large number of light scatterers exist inside the glass plate, the light incident from the light source repeats scattering in the many light scatterers, and finally is uniformly dispersed inside the glass plate.

The light diffusion performance of the light diffusion plate depends on the size of the light scatterer. In order to represent the size of the light scatterer, the size of the light scatterer and the average value of the size are called the particle size and the average particle size of the scatterer, respectively, and are defined below. When the light scatterer is spherical, the diameter is taken as the particle diameter. When the light scatterer is not spherical, the value obtained by adding the long side and the short side of the cross section of the light scatterer and dividing by 2 is taken as the particle size of the light scatterer. In the case of a phase in which the light scatterers are continuously entangled, the width of the phase is the particle diameter of the light scatterers. What averaged the particle diameter of the light-scattering body in a glass plate is made into the average particle diameter of a light-scattering body.

The average particle diameter of the light scatterer of formula (1) is preferably 80 nm (0.08 μm) or more, more preferably 100 nm or more, in order to reduce the wavelength dependency of light scattering properties, and 125 nm. More preferably, it is more preferably 150 nm or more, further preferably 175 nm or more, and most preferably 200 nm or more. In order to enhance the light scattering property, it is preferable that the average particle diameter of the light scatterer is appropriately large. Specifically, it is preferably 10000 nm or less, more preferably 7500 nm or less, further preferably 5000 nm or less, further preferably 4000 nm or less, particularly preferably 3000 nm or less, 2000 nm Most preferably: Typically, it is 200 nm or more or 2000 nm or less.
In particular, when a light scatterer is grown by heat treatment or when it is desired to shorten the time required for heat treatment, it is preferably 700 nm or less, more preferably 500 nm or less, further preferably 400 nm or less, and most preferably 350 nm or less. The average particle diameter of the light scatterer can be measured by SEM observation.

Incidentally, in the C value of the left side of the equation (1) = 30−10 × (d−2.2) −7 × v−50 × D, since the influence of the average particle diameter D of the light scatterer is the largest, The coefficient is large.

Specifically, glass containing phase-separated glass (also referred to as phase-separated glass) or crystallized glass as a glass plate allows light incident on the first main surface to be diffused and transmitted from the second main surface. A board is obtained. This is because the phase-separated glass and the crystallized glass have appropriate haze and transmittance orientation distribution, so that appropriate light scattering properties are exhibited and moderate transparency is obtained by having appropriate total light transmittance. This is because it has the characteristic of being expressed.

«Glass phase separation means that a single-phase glass is divided into two or more glass phases.

Whether the glass is phase-separated or not can be determined by SEM (scanning electron microscope, scanning electron microscope). That is, when the glass is phase-separated, it can be observed that it is divided into two or more phases when observed with an SEM.

状態 Examples of the state of phase-separated glass include a binodal state and a spinodal state. The binodal state is a phase separation by a nucleation-growth mechanism and is generally spherical. The spinodal state is a state in which the phase separation is intertwined with each other in three dimensions with some degree of regularity. These phase separations exhibit a function as a light scatterer.

In order to control the average particle diameter D, the time and temperature for the phase separation process may be controlled. In general, the glass is held for a certain time at a temperature lower than the phase separation temperature. As a condition for heat treatment for phase separation of glass, typically, the temperature is preferably 50 ° C. higher than the glass transition point Tg (hereinafter also simply referred to as Tg), and more preferably 100 ° C. higher. Preferably, the temperature is 200 ° C. higher.
The time for heat treating the glass is preferably 1 to 64 hours, more preferably 2 to 32 hours. From the viewpoint of mass productivity, it is preferably 24 hours or less, and more preferably within 12 hours. In order to phase separate the glass in a shorter time, it is preferable to use a glass having a phase separation temperature of 1000 ° C. or higher and heat-treat at 1000 ° C. or higher. The heat treatment time is 5 seconds or more in order to control the size of the phase separation structure. Preferably it is 10 seconds or more, More preferably, it is 1 minute or more, More preferably, it is 30 minutes or more. When the heat treatment time is long, it becomes difficult to achieve an appropriate light scattering property suitable for a light diffusion plate. Therefore, the heat treatment time is preferably 10 hours or less, more preferably 8 hours or less, further preferably 6 hours or less, and more preferably 4 hours or less. Even more preferred is 2 hours or less, most preferred is 1 hour or less.

Or, after melting and homogenizing the glass, the phases can be separated in the process of cooling. By reducing the average cooling rate from the phase separation temperature to Tg, the average particle size increases. At this time, the phase separation temperature is higher than Tg. For example, it can also be obtained by heating in an infrared heating furnace or passing through an electric furnace having a different temperature range. In order to grow the phase separation structure, the average cooling rate from the phase separation temperature to Tg is preferably 300 ° C./min or less, more preferably 200 ° C./min or less, and further preferably 100 ° C./min or less. From the viewpoint of manufacturability, it is preferably 2 ° C./min or more, more preferably 5 ° C./min or more, and further preferably 10 ° C./min or more.
When the glass was melted and homogenized at a temperature equal to or higher than the phase separation temperature and then cooled to Tg at a constant rate, the size of the phase separation particles D changed according to the equation (2).
D = (1 / f) ^1/3 + α Expression (2)
According to Formula (2), the average cooling rate f of the phase separation glass can be calculated from the average particle size of the phase separation. α is an arbitrary constant.
Here, the expression (2) is obtained by the following method.
A plurality of glasses having the same composition are prepared. First, after melting and homogenizing one of the glasses at a temperature higher than the phase separation temperature, the glass is cooled to Tg at a certain average cooling rate f to obtain a sample A of phase separation glass. The cross section of the obtained sample A is observed with a scanning electron microscope (SEM), and the average particle size of the phase separation is calculated.
Next, using another glass having the same composition, except that the average cooling rate f is the same, two or more samples B, C, etc., each having an average cooling rate f different from the sample A, are prepared. The average particle size is calculated. The average cooling rate f of each sample is preferably different from each other by about 5 to 50 times. Next, a relational expression between D and (1 / f) ^1/3 is obtained by fitting (FIG. 6).
In the case of phase-separated glass whose average cooling rate f is unknown, the average cooling rate f can be calculated from the average particle diameter and the relational expression corresponding to the formula (2) obtained from phase-separated glass having the same composition.

Moreover, in order to express an appropriate light scattering property by having an appropriate haze, it is preferable that the difference in refractive index between one phase in the phase-separated glass and the surrounding phase is large. The refractive index difference is preferably 0.0001 or more, more preferably 0.001 or more, still more preferably 0.01 or more, particularly preferably 0.03 or more, and most preferably 0.06. That's it. If the difference in refractive index is too large, the diffusion performance is too high and the transparency is deteriorated. Therefore, the difference in refractive index is preferably 0.3 or less, more preferably 0.2 or less, further preferably 0.16 or less, 0.14 The following is particularly preferable, and 0.12 or less is most preferable. The refractive index difference can be estimated by the Appen equation using the composition analysis result by SEM-EDAX or the wet method.

Next, the volume fraction v in the formula (1) means the volume fraction that the light scatterer in the light diffusion plate occupies in the glass plate. The volume fraction is preferably large from the viewpoint of reducing the C value. Moreover, in order to express moderate light-scattering properties by having an appropriate haze, the phase functioning as a light scatterer inside the glass in the phase-divided glass is 5% or more of the volume fraction in the glass plate. It is preferably 10% or more, more preferably 15% or more, particularly preferably 20% or more, particularly preferably 25% or more, and 30% or more. Most preferably it is.

The volume fraction v can be controlled by changing the composition of the glass. In the case of phase-separated glass, it is divided into a phase having a high SiO ₂ concentration and a phase having a low SiO ₂ concentration, so that the volume fraction v is increased by increasing the components other than SiO ₂ . In particular, the volume fraction v can be effectively increased by increasing the components of alkaline earth metals and alkali metals that are poorly compatible with SiO ₂ . In the case of crystallized glass, the volume fraction v can be increased by performing heat treatment in a temperature range for generating crystal nuclei and then performing heat treatment in a temperature range for crystal growth. Here, the volume ratio of the particles of the dispersed phase is estimated by calculating the ratio of the dispersed particles distributed on the glass surface from the SEM observation photograph.

There are no particular restrictions on the method of producing the phase-separated glass, but for example, various amounts of various raw materials are prepared, heated to about 1500-1800 ° C. and melted, and then homogenized by defoaming, stirring, etc. A drawing method, a press method, a roll-out method, or the like is used to form a plate or the like and cast into a block shape. After slow cooling, it is processed into an arbitrary shape and then subjected to phase separation.

In the present invention, the glass is melted, homogenized, molded, slowly cooled, or shaped without any special phase separation process in steps such as melting, homogenizing, molding, annealing, or shaping. What phase-separated glass by heat processing shall also be included in phase-separated glass, and the process of phase-separating glass in this case shall be included in processes, such as above-mentioned melting | fusing.

Crystallized glass is a glass in which a fine crystalline phase is precipitated, has high mechanical strength and hardness, and has excellent heat resistance, electrical characteristics, and chemical durability. Expresses a function as a light scatterer. However, in the case of a conventional light diffusion plate made of crystallized glass, it is important to achieve excellent display quality while keeping the distance between the light source and the light diffusion plate, the transmittance orientation distribution and the color of the light diffusion plate itself There was a problem in the control and light resistance.

Examples of the crystallized glass used for the glass plate in the light diffusion plate of the present invention include the following (1) to (9). (1) Crystallized glass containing nepheline solid solution crystal (2) Crystallized glass containing lithium disilicate (Li ₂ Si ₂ O ₅ ), pyroxene (MgSiO ₃ ), and wollastonite (CaSiO ₃ ) (3) Li ₂ O—Al ₂ O ₃ —SiO ₂ , MgO—Al ₂ O ₃ —SiO ₂ , and Al ₂ O ₃ — having crystalline phases including stuffed β-quartz, β-lysianite, cordierite, and mullite Crystallized glass containing aluminosilicate crystals such as SiO ₂ (4) Fluorosilicates such as alkali and alkaline earth mica, and chain silicates such as potassium richerlite and canasite (5) Spinel solid solution [eg (Zn, Mg ) _Al 2 _{O 4]} and quartz (glass based on SiO ₂₎ - silicates such as ceramic host moth A crystallized glass (6) and a heat treatment at a softening point or higher temperatures soften and deform while its surface toward the interior acicular crystals have the property of growing deposit containing oxide crystal in the scan, CaO-Al ₂ O ₃ -SiO ₂ system or _CaO-Al 2 _{O 3} based crystallized glass _{(7) SiO 2, Al 2} O 3, MgO, ZnO, B 2 O 3, Na 2 O, the glass containing TiO ₂ as a main component melting, forming, the crystallized glass obtained by heat-treating (8) enstatite (MgSiO ₃₎ and Jiopusaito (MgCaSi ₂ O) crystallized glass containing (9) enstatite (MgSiO _3), and gahnite (ZnO · _Al 2 O ₃ ), crystallized glass containing rutile (TiO ₂ )

The crystallinity of the crystallized glass is preferably 1% or more, more preferably 5% or more, and further preferably 10% or more. Moreover, it is preferable that it is 90% or less, More preferably, it is 60% or less, More preferably, it is 40% or less, More preferably, it is 30% or less, More preferably, it is 20% or less.

By setting the crystallinity of the crystallized glass to 1% or more, the thermal expansion coefficient can be decreased, sufficient scattering characteristics can be obtained, the Young's modulus can be increased, and the Vickers hardness can be increased. Further, by setting the crystallinity of the crystallized glass to 90% or less, sufficient rigidity can be obtained and productivity can be improved.

The crystallinity C of the crystallized glass is determined by performing X-ray diffraction measurement in addition to the crystallized glass to be measured using a crystal other than the crystal that is the main component of the crystallized glass to be measured as a reference sample. The ratio a of the X-ray diffraction intensity of the crystal, which is the main component of the crystallized glass, is obtained, and is calculated from the mass ratio b and a of the reference sample and crystallized glass by the following formula. C = A × a × (b / 1−b)

Here, A is a constant referred to as a reference intensity ratio (RIR), and the PowderDiffertFractionPriffDriffrFriffDrfDrFriffDrFriffDrDrFriffDrFrIDPrDiffrFriffDrDrFrIDPrDrFriffDrPtDrDrFrFrDrFrDrFrPDrFrPDFrFrDrPrDrFrPDrFrPDRdPrFrDrFrPtDrFrFrDFrFrPDrFrPDPrDrFrPDRtFrPDFrPtDrFrFrDtPrDrFrPDRdPrFtDrFrFrPdDrFrFrDtPrFtDrPFrDiFrPdFrPtDrFrFrPtDrFrPDRtFrAPFrFtDrFrFrPdDrFrDtFrCDP -2 Use the value shown in Release 2006.

The average particle diameter in the crystallized glass is preferably 50 nm or more, more preferably 100 nm or more, and further preferably 200 nm or more. Moreover, it is preferable that it is 10,000 nm or less, More preferably, it is 50000 nm or less, More preferably, it is 20000 nm or less.

Here, the average particle diameter in the crystallized glass is an average value of the diameter when the dispersed crystal phase is spherical, and in the case of an elliptical sphere, a value obtained by adding the major axis and the minor axis and dividing by two. The average value, which is not spherical, is the average value of the values obtained by adding the long and short sides of the crystal phase cross section and dividing by two.

When the average particle diameter in the crystallized glass is 50 nm or more, moderate light scattering is expressed by having an appropriate haze. Further, when the average particle diameter is 10,000 nm or less, appropriate transparency is exhibited by having an appropriate total light transmittance. The average particle diameter in the crystallized glass can be measured by a scanning electron microscope (also referred to as Scanning Electron Microscope, SEM).

From the viewpoint of expressing an appropriate light scattering property by having an appropriate haze, it is preferable that the difference in refractive index between the crystal phase in the crystallized glass and the surrounding amorphous glass phase is large. The difference in refractive index is preferably 0.0001 or more, more preferably 0.001 or more, and still more preferably 0.01 or more. The refractive index difference can be estimated from the difference between the refractive index of the crystal based on the crystal data and the refractive index of the residual glass estimated by the Appen equation using the composition analysis value of the residual glass phase.

From the viewpoint of expressing an appropriate light scattering property by having an appropriate haze, the volume ratio of the crystal phase in the crystallized glass is preferably 10% or more, and more preferably 20% or more. Here, the volume ratio of the crystal phase is estimated by calculating the ratio of the crystal phase distributed on the glass surface from the SEM observation photograph.

The thermal expansion coefficient of the glass plate in the light diffusing plate of the present invention is −100 × 10 ⁻⁷ / ° C. or higher, preferably −10 × 10 ⁻⁷ / ° C. or higher, from the viewpoint of productivity and cost. × more preferably ^{10 -7} / ° C. or higher, further preferably 50 × ^{10 -7} / ° C. or higher. The thermal expansion coefficient is 500 × 10 ⁻⁷ / ° C. or less, preferably 300 × 10 ⁻⁷ / ° C. or less, more preferably 200 × 10 ⁻⁷ / ° C. or less, and 150 × 10 ⁻ More preferably, it is ⁷ / ° C. or less.

If the thermal expansion coefficient of the glass plate is in the above range, it is possible to suppress deformation when the distance between the light source and the light diffusion plate is too close in order to enhance the light diffusion performance, and the shape of the light source becomes less noticeable and the brightness Can be homogenized. In addition, an extra space in anticipation of deformation is not required, and it is possible to cope with narrowing and thinning of the frame.

In the present invention, “thermal expansion coefficient” means a value obtained by measurement based on ISO 7991 (1987). The thermal expansion coefficient of the glass plate can be adjusted by the glass composition, precipitated crystal species, crystallinity, degree of phase separation, heat treatment temperature, cooling rate, and the like.

The glass plate in the light diffusion plate of the present invention preferably has a glass transition point Tg of 200 ° C. or higher, more preferably 300 ° C. or higher, further preferably 400 ° C. or higher, and further preferably 500 ° C. or higher. . Moreover, it is preferable that it is 850 degrees C or less, More preferably, it is 800 degrees C or less, More preferably, it is 750 degrees C or less, More preferably, it is 700 degrees C or less.

When the glass transition point Tg of the glass plate is 200 ° C. or higher, the glass plate is not easily deformed by heat, and therefore, when used in a direct type backlight, it is possible to reduce the distance between the light source and the light diffusion plate, Compared with resin light diffusion plate, it is easy to make the brightness uniform. Moreover, productivity of glass improves that the glass transition point Tg is 850 degrees C or less.

In the present invention, the “glass transition point” is a differential thermal dilatometer, which is used to measure the elongation rate of glass when heated from room temperature at a rate of 5 ° C./minute up to the yield point using quartz glass as a reference sample. Means the temperature corresponding to the inflection point in the obtained thermal expansion curve.

From the viewpoint of reducing the thickness and suppressing coloring of light emitted in an oblique direction, the thickness of the light diffusion plate is preferably 0.4 to 3 mm.

The desired properties (thermal expansion coefficient, glass transition point) of the glass plate in the light diffusing plate of the present invention are the composition of the glass, heat treatment conditions (for example, phase separation treatment conditions in the case of phase separation glass, or crystallization). In the case of glass, it can be appropriately adjusted depending on the crystallization conditions.

The glass plate in the light diffusing plate of the present invention has a wavelength of 450, 550, and 630 nm transmitted in the incident direction, out of the incident light from the normal direction of the first main surface, in order to obtain luminance necessary as a backlight. The total light transmittance is preferably 4% or more. More preferably, it is 5% or more, further preferably 10% or more, particularly preferably 20% or more, and most preferably 30% or more.

Also, if the total light transmittance is 90% or less, the diffusibility is not impaired. 85% or less is preferable, 80% or less is more preferable, 75% or less is further preferable, 70% or less is more preferable, and 65% or less is more preferable 60% or less is particularly preferable, and 55% or less is most preferable.

In FIG. 3, L ₀ is irradiation light incident perpendicularly to the light incident surface 31 of the light diffusing plate 30, and L ₁ is an incident direction from the light emitting surface 32 of the light diffusing plate 30 that is L _0. Each represents the same transmitted light. L ₂ represents irradiation light incident at an angle of 60 ° with respect to the light incident surface 31 with respect to the light incident surface 31, and L ₃ represents transmitted light whose emission direction from the light emission surface 32 is the same as that of L _2. To express.

The transmittance of light transmitted through the glass plate by incident light inclined by 60 ° from the normal direction of the first main surface depends on the thickness of the glass plate, but the thickness of the glass plate of the present invention is the target light diffusion. Let it be the thickness of the plate, and the transmittance at the thickness of the light diffusing plate be the transmittance.

FIG. 4 is a diagram showing the measurement of the transmittance of the light diffusing plate 30 using a spectrophotometer. The light emitted from the light source 40 and passed through the light diffusing plate 30 is detected by the detector 41. 4 in (a), _{L 5} whereas the light incident surface 31 of the light diffusion plate 30, the illumination light incident perpendicularly, _{L 6} has emission direction from the light exit surface 32 of the light diffusion plate 30, _{L 5} Each of the transmitted light is the same as the incident direction. In FIG. 4B, L ₇ is irradiation light incident from an angle inclined by 60 ° with respect to the light incident surface 31 with respect to the light incident surface 31, and L ₈ is an emission direction from the light emission surface 32 that is the incident direction of L _7. Each represents the same transmitted light.

From the wavelength dependence of the measured transmittance as shown in FIG. 5, the chromaticity of the XYZ color system when a D65 light source is used based on the color display method standardized in JIS (JISZ8701). Coordinates (x, y) are calculated for the vertical direction (0 °) and 60 ° from the vertical direction and when incident from an angle, respectively, (x _{0 °} , y _{0 °} ), (y _{0 °,} y _{60 °} ). A difference Δxy = {(x _{0 °} −x _{60 °} ) ² + (y _{0 °} −y _{60 °} ) ² } ^1/2 between the chromaticity coordinates can be calculated.

As a result, a change in color tone, so-called Δxy, is measured between the transmitted light that is incident and transmitted from the vertical direction of the light diffusing plate and the transmitted light that is incident and transmitted from a direction inclined at 60 ° (oblique direction). it can. Since the light diffusing plate of this invention satisfy | fills Formula (1), it can suppress (DELTA) xy below to a predetermined value. That is, it is possible to suppress a change in color due to the wavelength dependence of the scattering intensity between the transmitted light transmitted through the light diffusion plate in the vertical direction and the transmitted light transmitted in a direction inclined at 60 ° (oblique direction). As compared with the video display when viewed from the front direction, deterioration of the video display viewed from the oblique direction can be suppressed.

x _{0 ° and} x _{60 °} are preferably 0.30 to 0.40, and more preferably 0.32 to 0.35. If it is 0.30 to 0.40, the color reproducibility of the LED light source is improved.

y _{0 ° and} y _{60 °} are preferably 0.31 to 0.42, and more preferably 0.32 to 0.37. If it is 0.31 to 0.42, the color reproducibility of the LED light source is improved.

Δxy is 0.020 or less, more preferably 0.018 or less, further preferably 0.015 or less, and most preferably 0.010 or less. If it is 0.020 or less, the quality of video display when viewed from an oblique direction is maintained.

The haze of the glass plate in the light diffusing plate of the present invention is the glass composition, heat treatment conditions (for example, conditions for phase separation treatment in the case of phase separation glass, or conditions for crystallization conditions in the case of crystallized glass). It can be adjusted as appropriate.

Specifically, for example, when the glass plate is a phase separation glass, the incident light out of the incident light from the normal direction of the first main surface, depending on the glass composition and phase separation treatment conditions in the following range. The haze at wavelengths 450, 550, and 630 nm transmitted in the direction can be adjusted to 50% or more.

(Glass composition)
In terms of oxide-based mole percentage, SiO ₂ is 40 to 80%, Al ₂ O ₃ is 0 to 30%, MgO is 0 to 30%, Na ₂ O is 1 to 30%, and P ₂ O ₅ is 0.00. Phase separation glass containing 5 to 15%.
Alkali metal oxide containing 40 to 80% SiO ₂ , 0 to 30% Al ₂ O ₃ , 0 to 30% MgO and 10 to 35% B ₂ O ₅ in terms of mole percentage based on oxide Phase-separated glass substantially free of

(Phase separation processing conditions)
A temperature 100 to 800 ° C. higher than the glass transition point Tg is preferable, and a temperature 200 to 700 ° C. is more preferable. The time for heat-treating the glass is preferably 0.1 to 64 hours, and more preferably 1 to 32 hours. From the viewpoint of mass productivity, it is preferably 24 hours or less, and more preferably within 12 hours.

For example, when the glass plate is crystallized glass, the incident light from the normal direction of the first main surface is transmitted in the incident direction according to the following glass composition and crystallization conditions. The haze at a wavelength of 400 nm to 700 nm can be adjusted to 50% or more.

(Glass composition)
Expressed in terms of mole percentage based on oxide, SiO ₂ is 65 to 75%, Al ₂ O ₃ is 10 to 29%, Li ₂ O 5 to 15%, TiO ₂ is 1 to 3%.

(Crystallization conditions)
(1) First, as a heat treatment condition in which the original glass is heated to a temperature within or slightly higher than the transition range to generate nuclei in the glass, the temperature is preferably 950 ° C. or less, and 900 ° C. or less. It is more preferable that The heat treatment time is preferably 1 to 10 hours, more preferably 2 to 6 hours. (2) Heat treatment conditions for heating the glass to a higher temperature, sometimes higher than its softening point, to grow crystals on the nuclei formed in (1) are: 850-1200 ° C. Preferably, the temperature is 900 to 1150 ° C. The heat treatment time is preferably 1 to 10 hours, more preferably 2 to 6 hours.

The glass plate in the light diffusion plate of the present invention may have an uneven surface on the surface of the first main surface in order to increase the light diffusibility of the light diffusion plate. When the surface of the first main surface has an uneven surface, the lower limit of the arithmetic average roughness (Ra) of the first main surface is not particularly limited in order to improve the light diffusibility of the light diffusing plate. It is preferably 0.05 nm or more, more preferably 0.1 nm or more. The upper limit is not particularly limited, but is preferably 10,000 nm or less, more preferably 7000 nm or less, still more preferably 3000 nm or less, particularly preferably 2000 nm or less, and most preferably 1000 nm or less. In order to reduce the influence of scratches generated during handling, the arithmetic mean roughness (Ra) of the first main surface is preferably 10 nm or more, more preferably 100 nm or more, further preferably 1000 nm or more, and more preferably 5000 nm or more. Most preferred.

The arithmetic average roughness Ra of the glass plate on the first main surface of the glass plate can be adjusted by selecting polishing conditions. Further, the first main surface and the second main surface of the glass plate may be coated with silica, titania, alumina or the like.

The arithmetic average roughness Ra of the first main surface of the glass plate can be measured based on Japanese Industrial Standard JIS B0601 (1994). On the other hand, the arithmetic mean roughness Ra of the second main surface of the glass plate is not particularly limited, and may be the same as or different from the first main surface.

The composition of the glass plate will be described. In the present specification, the content of the glass component will be described using a mole percentage display unless otherwise specified.

SiO ₂ is a basic component that forms a network structure of glass. That is, it has an amorphous structure and exhibits excellent mechanical strength, weather resistance, or gloss as glass. The content of SiO ₂ is preferably 40 to 80%.

By making the content of SiO ₂ 40% or more, the weather resistance and scratch resistance as glass are improved. More preferably, it is 50% or more, more preferably 55% or more, particularly preferably 60% or more, and most preferably 66% or more. On the other hand, the productivity of glass can be improved by setting it as 80% or less. More preferably, it is 75% or less, More preferably, it is 73% or less, Most preferably, it is 72% or less.

Al ₂ O ₃ is preferably 0 to 35%. When Al ₂ O ₃ is 0 to 35%, it does not need to contain Al ₂ O ₃ , but when it is contained, it must be 35% or less (the same applies hereinafter).

Al ₂ O ₃ improves the chemical durability of the glass, lowers the coefficient of thermal expansion, significantly improves the dispersion stability of SiO ₂ and other components, and makes the phase separation of the glass uniform. There is an effect of imparting a function, and when the content of Al ₂ O ₃ is 0.5% or more, the effect is easily obtained. Is 1% or more, more preferably 4% or more.

When the content of Al ₂ O ₃ is too large, the melting temperature of the glass is high, and becomes phase separation hardly occurs, the haze is too low. More preferably, it is 28% or less, more preferably 20% or less, further preferably 10% or less, particularly preferably 8% or less, more preferably 6% or less, still more preferably 5% or less, and most preferably 4% or less. .

The MgO content is preferably 0 to 30%. Since MgO has the effect of reducing the thermal expansion coefficient of glass and promoting phase separation in combination with SiO ₂ and Na ₂ O, it is preferably contained when the phase-separated glass is used for the glass plate. . The content of MgO is more preferably 5% or more, further preferably 9% or more, particularly preferably 13% or more, and most preferably 15% or more.

By making the content of MgO 30% or less, the glass can be stabilized. The content of MgO is more preferably 27% or less, further preferably 25% or less, particularly preferably 24% or less, and most preferably 18% or less.

In addition, when considering MgO in terms of mass percentage, it is preferable to contain more than 10%. By containing MgO more than 10%, solubility can be improved. Preferably it is 12% or more.

The ratio MgO / SiO ₂ between the MgO content and the SiO ₂ content is preferably 0.14 or more and 0.45 or less, and more preferably 0.15 or more and 0.40 or less. In MgO / SiO ₂ 0.14 or more, and has the effect of or to improve promote whiteness phase separation by 0.45 or less.

The content of Na ₂ O is preferably 0 to 30%. By containing Na ₂ O, the meltability of the glass can be improved. When Na ₂ O is contained, the content is preferably 1% or more, more preferably 2% or more, still more preferably 4% or more, and particularly preferably 8% or more. Further, the Na ₂ O content is more preferably 15% or less, further preferably 14% or less, and particularly preferably 13% or less.

By making the content of Na ₂ O 1% or more, the meltability of the glass can be improved. Further, by 30% or less and the content of Na 2 _O, it can improve the weather resistance of the glass.

Since P ₂ O ₅ is a basic component that promotes phase separation in combination with SiO ₂ , MgO, and Na ₂ O, it is included when the phase-separated glass is used for the glass plate in the light diffusion plate of the present invention. It is preferable. When P ₂ O ₅ is contained, the content of P ₂ O ₅ is preferably 0.5% or more, more preferably 1% or more, still more preferably 3% or more, and particularly preferably 4% or more. is there. Further, it is preferably 15% or less, more preferably 14% or less, further preferably 10% or less, particularly preferably 7% or less, and most preferably 4.5% or less.

By setting the content of P ₂ O ₅ to 0.5% or more, a light diffusion function can be sufficiently obtained. Further, by setting the content of P ₂ O ₅ to 15% or less, volatilization hardly occurs, and unevenness in luminance hardly occurs when used as a light diffusion plate.

In the glass plate used for the light diffusion plate of the present invention, it may be preferable to contain the following components in addition to the five components. Even in this case, the total content of the five components is preferably 90% or more, and typically 94% or more.

ZrO ₂ is not an essential component, but is preferably 4.5% or less, more preferably 4% or less, and even more preferably 3% or less in order to significantly improve chemical durability. It is possible to prevent the light diffusing function is reduced by setting the content of ZrO ₂ 4.5% or less.

CaO, SrO, and BaO are not essential components, but in order to improve the light diffusion function, it is preferable to contain one or more of these components in an amount of 0.2% or more, more preferably 0.5% or more, and still more preferably Is 1% or more.

When CaO is contained, its content is preferably 3% or less. By making the content of CaO 3% or less, the glass becomes difficult to devitrify.

The total content of CaO, SrO and BaO is preferably 12% or less, more preferably 8% or less, 6% or less, 4% or less, and typically 3% or less. By making the total 12% or less, the glass becomes difficult to devitrify.

B ₂ O ₃ may be contained up to 40% in order to increase the meltability of the glass, improve the whiteness of the glass, lower the thermal expansion coefficient, and further improve the weather resistance. 30% or less, more preferably 25% or less, and particularly preferably 20% or less. By setting the content of B ₂ O ₃ to 40% or less, unevenness in luminance is less likely to occur when used as a light diffusing plate. In order to promote phase separation and improve the light diffusion function, the content is preferably 5% or more, more preferably 8% or more, and still more preferably 10% or more. In order to improve chemical durability, it is preferably 20% or less, more preferably 15% or less. In order to suppress volatilization, the alkaline component _{(Li 2 O, Na 2 O} , K 2 O) is preferably not contained with. Here, the phrase “not contained together” means that either B ₂ O ₃ or the alkali component is 0.1 mol% or less.

La ₂ O ₃ is suitable in terms of improving the light diffusion function of the glass, and can be contained in an amount of 0 to 5%, preferably 3% or less, more preferably 2% or less. By making the content of La ₂ O ₃ 5% or less, the glass can be prevented from becoming brittle. TiO ₂ is suitable for promoting phase separation or crystallization, and is preferably contained in an amount of 0.5 to 10%. In order to suppress coloring, it is preferably 5% or less, more preferably 3% or less, further preferably 2% or less, and most preferably 1% or less.

The glass plate used for the light diffusing plate of the present invention may contain other components in addition to the above components as long as the object of the present invention is not impaired. For example, Co, Mn, Fe, Ni, Cu, Cr, V, Zn, Bi, Er, Tm, Nd, Sm, Sn, Ce, Pr, Eu, Ag, or Au may be contained as a coloring component. In that case, it is preferable that the sum of these coloring components is typically 5% or less in terms of the mole percentage based on the minimum valence oxide.

Fe ₂ O ₃ can be contained in a weight ppm of 1 ppm or more, more preferably 10 ppm or more, still more preferably 20 ppm or more, and even more preferably 30 ppm or more in order to easily dissolve the glass melt uniformly. By setting the content of Fe ₂ O ₃ to 5000 ppm or less, more preferably 3000 ppm or less, still more preferably 2000 ppm or less, and even more preferably 1500 ppm or less, an excessive decrease in transmittance can be prevented.

CoO can be contained in a weight ppm of 0.01 ppm or more, more preferably 0.05 ppm or more, and even more preferably 0.1 ppm or more, from the viewpoint of controlling the color of the glass. By setting the CoO content to 30 ppm or less, more preferably 25 ppm or less, more preferably 20 ppm or less, and even more preferably 10 ppm or less, an excessive decrease in transmittance can be prevented.

The glass plate used for the light diffusing plate of the present invention has a thickness of 0.05 mm or more in order to maintain the strength as the light diffusing plate and exhibit an appropriate function. It is preferably 0.1 mm or more, more preferably 0.3 mm or more, further preferably 0.4 mm or more, and particularly preferably 0.5 mm or more. In order to sufficiently weaken the stress due to the temperature distribution in the plate thickness direction due to heat from the light source by setting the plate thickness of the glass plate to 0.05 mm or more, the plate thickness is 3 mm or less. It is preferably 2.8 mm or less, more preferably 2.5 mm or less, still more preferably 2.3 mm or less, still more preferably 2.1 mm or less, and 2.0 mm or less. Is particularly preferred.

The glass plate used for the light diffusion plate of the present invention preferably has a dimension of at least one side of 200 mm or more, more preferably 400 mm or more, and further preferably 600 mm or more. Further, it is preferably 2500 mm or less, more preferably 2200 mm or less, further preferably 2000 mm or less, and particularly preferably 1800 mm or less. By setting the size of at least one side of the glass plate to 200 mm or more, a light diffusing plate utilizing the rigidity of the glass can be provided.

The wavelength dependency of the total light transmittance of the glass plate used in the light diffusing plate of the present invention is the light that has passed through the light diffusing plate and other optical sheets from the viewpoint of the wavelength spectrum of the emission line of the LED that is the light source used. It is preferable that the total light transmittance of the light diffusing plate has a wavelength dependency so that the color of the light diffusing plate itself is controlled.

In order to prevent the color of the light source from changing due to light absorption by the light diffusion plate, the glass plate used for the light diffusion plate is standardized by the CIE (International Lighting Commission) when using a D65 light source. However, in the L * a * b * color system standardized by JIS (JISX8729), (a ^{* 2} + b ^{* 2} ) ^1/2 is preferably 5 or less, more preferably 2 or less, 1 or less is more preferable, and 0.5 or less is particularly preferable.

The wavelength dependence of the total light transmittance of the glass plate used for the light diffusion plate of the present invention is the composition of the glass, heat treatment conditions (for example, in the case of phase separation glass, phase separation treatment conditions, or crystallized glass). In such a case, it can be appropriately adjusted depending on the crystallization conditions). Specifically, for example, when the blue color of the light source is strong, from the viewpoint of suppressing blue, crystallized glass and phase-separated glass are preferable, and crystallized glass is more preferable. For example, in the case of a light source having excellent whiteness, it is desirable that the light diffusing plate itself is white, and thus phase-separated glass is more preferable.

The light diffusion plate of the present invention can be suitably used for a direct type backlight unit such as a liquid crystal television or a liquid crystal monitor. FIG. 1 shows a cross-sectional view of a direct type backlight using the light diffusion plate of the present invention. In the direct type backlight 1 shown in FIG. 1, a light source 3 is provided on a reflecting plate 2 at a predetermined interval, and a light diffusing plate 4 is provided thereon. The light emitted from the light source 3 is diffused by the light diffusion plate 4.

On the light diffusing plate 4, a light diffusing sheet 5, a prism sheet 6, and a polarization separating sheet 7 are provided in this order. Although not shown in FIG. 1, an electromagnetic wave shielding sheet for shielding electromagnetic waves emitted from the light source may be provided between the light diffusion plate 4 and the light diffusion sheet 5.

The light diffusing plate of the present invention has high heat resistance and light resistance, and the light diffusing property and transmittance orientation distribution are controlled. Therefore, when used in a backlight, the distance between the light source and the light diffusing plate is reduced. Thus, it is possible to improve the uniformity of brightness. Therefore, the light diffusion plate of the present invention can homogenize the luminance distribution as compared with the conventional resin light diffusion plate. In order to achieve a thinner backlight, the distance between the light source 3 and the light diffusing plate 4 is preferably 10 mm or less, more preferably 8 mm or less, and most preferably 6 mm or less.

Furthermore, according to the present invention, high display quality can be secured when applied to a liquid crystal display device while adopting a glass plate excellent in mechanical properties such as ensuring high strength and suppressing thermal expansion compared to resin and the like. A light diffusing plate is provided. In other words, since the change in color between the light emitted in the normal direction and the light emitted in the oblique direction is suppressed, there is little difference between the image quality seen from the front and the image quality seen from the oblique direction, and a high-quality device Will contribute.

[Manufacture of glass]
Glass raw materials were appropriately selected and melted, homogenized and degassed at 1650 ° C. The mixture was poured into a mold material, held at a temperature 30 ° C. higher than the glass transition temperature for 1 hour, and then cooled to room temperature at a cooling rate of 1 ° C. per minute. The obtained glass was processed into a plate shape having a thickness of 2 mm. In order to achieve the desired average particle size of the light scatterer by phase separation, the following heat treatment was performed. It heated to 1500 degreeC with the infrared heating furnace, hold | maintained for 1 minute, and it temperature-falls from 1500 degreeC to Tg with the average cooling rate of Table 1, and phase-divided glass. In any composition, since the phase separation temperature is lower than 1500 ° C., the glass is not phase-separated while being held at 1500 ° C. and is transparent, phase separation occurs in the process of lowering the temperature, and light scattering. The body generated.

The prepared 12 samples of Examples 1-1 to 2-3 and Examples 3 to 8 were analyzed by the following evaluation method.

(1) Density Density was measured by Archimedes method.

(2) Glass transition point (Tg) and thermal expansion coefficient (α)
It was measured by TMA (differential thermal dilatometer). As the thermal expansion coefficient, an average thermal expansion coefficient of 50 to 350 ° C. was calculated.

(3) Haze The haze value was measured using a haze computer (HZ-2) manufactured by Suga Test Instruments Co., Ltd.

(4) Transmittance distribution The transmittance distribution was measured with an ultraviolet-visible infrared spectrophotometer (manufactured by JASCO Corporation: V-670DS) and an automatic absolute reflectance measuring unit (manufactured by JASCO Corporation: ARMN-735). Light was incident from the normal direction (0 °) or an angle inclined by 60 ° with respect to the first main surface of the light diffusion plate, and the transmittance of each light transmitted in the same direction as the incident direction was measured.

(5) Chromaticity and chromaticity difference From the transmittance distribution, based on the color display method standardized in JIS (JISZ8701), the chromaticity coordinates (x, y) of the XYZ color system when the D65 light source is used. ) Was calculated for each of the 0 ° and 60 ° directions. A difference Δxy = {(x _{0 °} -x _{60 °} ) ² + (y _{0 °} -y _{60 °} ) ² } ^1/2 between the chromaticity coordinates was calculated.

(6) D (average particle diameter) and v (volume fraction) of the light scatterer
The glass surface was optically polished and then observed with a scanning electron microscope (SEM). The average value was calculated from 30 or more arbitrarily selected particle sizes, except for less than 50 nm, which has a small contribution to the optical properties in the visible range.

The density d (g / cm ³ ), the volume fraction v (%) of the light scatterer, and the average particle diameter D (μm) of the light scatterer were measured, and from these measured values, the C value = 30-10 × (D-2.2) -7 × v-50 × D was calculated. Further, light is incident from a normal direction (0 °) or an angle inclined by 60 ° with respect to the first main surface of the light diffusion plate, and the transmittance for each wavelength of the light transmitted in the same direction as the incident direction, The chromaticity difference Δxy was calculated. The results are shown in Table 1 and FIG. FIG. 5 shows the transmittance distribution at 0 ° and 60 ° incidence in Examples 1-1 and 1-2.

The straight line in FIG. 2 is obtained from the result of Table 1 by fitting using the least square method. As can be seen from the graphs in Table 1 and FIG. 2, the samples of Examples 1-1 and 2-1, Examples 3, 4 and 5 have a calculated C value = 30−10 × (d−2.2) −7 × Both v-50 × D were 17 or less and the measured Δxy was 0.020 or less, and coloring of the outgoing light in the oblique direction could be suppressed.
On the other hand, the samples of Examples 1-2, 1-3, 2-2, 2-3, Examples 6, 7, and 8 all have C values exceeding 17, and Δxy exceeds 0.020. Therefore, it is difficult to suppress coloring of the outgoing light in the oblique direction.

In the phase-separated glass, since the SiO ₂ concentration is high and the SiO ₂ concentration is low, the refractive index difference between the two phases is more likely to occur as the density of the light diffusion plate increases. It is estimated that the scattering efficiency is increased even with a light scatterer having a small size.
From the results of Examples 1-1 to 1-3 and Examples 2-1 to 2-3, the average particle size and the volume fraction of particles can be obtained by optimizing the average cooling rate f even with the same glass composition. It is estimated that Δxy was suppressed to 0.02 or less after being adjusted to a suitable region.
In FIG. 6, in order to show the relationship between the average particle diameter D and the average cooling rate f, D is plotted against f ^{1/3 in} Examples 1-1, 1-2, and 1-3 having the same composition. . The same procedure was performed in Examples 2-1, 2-2, and 2-3. Here, glass1 shows the results of Examples 1-1, 1-2, and 1-3, and glass2 shows the results of Examples 2-1, 2-2, and 2-3. D = f ^1/3 + α (α is an arbitrary constant). When the glass composition is the same, the average particle size D and the average cooling rate f obtained by changing the average cooling rate f are shown. It is shown that the unknown average cooling rate f can be obtained from the average particle diameter D by using the relational expression.

Although the invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application claims priority based on Japanese Patent Application No. 2016-154684 filed with the Japan Patent Office on August 5, 2016, and the entire contents of Japanese Patent Application No. 2016-154684 are incorporated herein by reference. .

1 Direct type backlight (backlight)
2 Reflecting plate 3 Light source 4 Light diffusing plate 5 Light diffusing sheet 6 Prism sheet 7 Polarized light separating sheet

Claims (8)

A light diffusing plate composed of a glass plate containing a light scatterer inside,
Haze is 50% or more,
The chromaticity of the XYZ color system when light is incident on the first main surface of the light diffusing plate and the D65 light source is used from the wavelength dependence of the transmittance of transmitted light in the same direction as the incident direction ( When calculating x, y), the chromaticity coordinates of the transmitted light incident from the direction of 0 ° with respect to the normal of the first main surface and the transmitted light color of the light incident from the direction of 60 ° The difference Δxy = {(x _{0 °} -x _{60 °} ) ² + (y _{0 °} -y _{60 °} ) ² } ^1/2 is 0.020 or less,
When the density of the light diffusing plate is d (g / cm ³ ), the volume fraction occupied by the light scatterer in the glass plate is v (%), and the average particle diameter of the light scatterer is D (μm) A light diffusing plate in which the following expression (1) is established.
30-10 × (d-2.2) -7 × v-50 × D ≦ 17 (1) The light diffusing plate according to claim 1, wherein the density is 2.3 to 3.0 cm ³ . The light diffusing plate according to claim 1 or 2, wherein the thickness is 0.4 to 3 mm. The light diffusion plate according to any one of claims 1 to 3, wherein an average particle diameter D of the light scatterer is 0.08 µm or more. The light diffusing plate according to any one of claims 1 to 4, wherein the glass plate includes phase-separated glass. The light diffusing plate according to claim 5, wherein a volume fraction v of the light scatterer is 5% or more. A backlight comprising the light diffusing plate according to any one of claims 1 to 6 and a light source. The manufacture of a light diffusion plate for manufacturing a light diffusion plate according to claim 5 or 6, wherein an average cooling rate from a phase separation temperature, which is a heat treatment condition of the phase separation glass, to a glass transition point is 2 to 300 ° C / min. Method.

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