WO2018186399A1

WO2018186399A1 - Glass sheet for light diffusion sheet, light diffusion sheet and backlight unit

Info

Publication number: WO2018186399A1
Application number: PCT/JP2018/014271
Authority: WO
Inventors: 和田　直哉; 順子宮坂
Original assignee: Ａｇｃ株式会社
Priority date: 2017-04-06
Filing date: 2018-04-03
Publication date: 2018-10-11

Abstract

A glass sheet for a light diffusion sheet, said glass sheet having two main surfaces facing each other, wherein: the thickness of the glass sheet is 0.3-2.0 mmm inclusive; the average thermal expansion coefficient of the glass sheet at 50-350oC is 60x10-7/K or less; the total light transmittance of the glass sheet at a wavelength of 450 nm, 550 nm or 630 nm is 10-60% inclusive and the sum of the total light transmittance and the total light reflectance at a wavelength of 450 nm, 550 nm or 630 nm is 90% or more; and the glass sheet is formed of a glass which comprises, in terms of mol% on oxide basis, 55-68% of SiO2, 0-9% of Al2O3, 0-19% of B2O3, 4-15% of MgO, 0-4% of BaO and 0-4% of Na2O.

Description

Glass plate for light diffusion plate, light diffusion plate and backlight unit

The present invention relates to a glass plate for a light diffusion plate, a light diffusion plate, and a backlight unit.

In recent years, with the reduction in the weight and size of liquid crystal televisions and liquid crystal monitors, a glass diffusion plate that is highly rigid and difficult to deform by its own weight has been studied as a diffusion plate used in a direct type backlight unit. Furthermore, it is desired to reduce the thickness of the direct backlight unit itself.

Japanese Patent No. 3749568 Japanese Patent No. 3100853 Japanese Unexamined Patent Publication No. 2006-339033

When the distance between the light source and the light diffusing plate approaches as the backlight unit becomes thinner, the temperature of the light diffusing plate increases, and the diffusing plate may be warped as a deformation over time. As a result, problems such as display unevenness and uneven brightness occur in the liquid crystal display device, and this problem may become more conspicuous as the brightness of the light source increases.

An object of the present invention is to provide a glass plate for a light diffusing plate having a sufficient heat-scattering characteristic even if it is thin and having high heat resistance, a light diffusing plate including the same, and a backlight unit.

In order to solve the above-described problem, according to one aspect of the present invention, a glass plate having two main surfaces facing each other, wherein the thickness of the glass plate is 0.3 mm or more and 2.0 mm or less, The glass plate has an average coefficient of thermal expansion of 50 × 10 ⁻⁷ / K or less at 50 ° C. to 350 ° C., and the total light transmittance of the glass plate at wavelengths of 450 nm, 550 nm, and 630 nm is 10% or more and 60% or less, The total of the total light transmittance and the total light reflectance at wavelengths of 450 nm, 550 nm, and 630 nm is 90% or more, the glass plate is expressed in terms of mol percentage based on oxide, SiO ₂ is 55 to 68%, Al the _{_{_{2 O 3 0 ~ 9%,}}} B 2 O 3 0 to 19% of MgO 4 ~ 15%, 0 ~ 4% of BaO, made of glass containing Na ₂ O 0 ~ 4%, the light diffusion plate A glass plate is provided.

According to one aspect of the present invention, there are provided a glass plate for a light diffusion plate having high heat resistance while having sufficient transmission and scattering characteristics even if it is thin, a light diffusion plate including the same, and a backlight unit.

FIG. 1 is a cross-sectional view of a direct type backlight unit using a light diffusing plate including a glass plate for a light diffusing plate of the present invention.

In this specification, the diffusion plate may be read as a diffusion sheet.

The glass plate for a light diffusion plate of the present invention has a thickness of 0.3 mm or more. By setting the thickness of the glass plate to 0.3 mm or more, it is difficult to cause temperature distribution in the surface, and the amount of warpage when used as a light diffusion plate can be suppressed. Further, from the viewpoint of maintaining the strength required when used for the light diffusion plate and exhibiting an appropriate function, the thickness of the glass plate is more preferably 0.4 mm or more, and further preferably 0.5 mm or more. Preferably, it is 0.6 mm or more. Further, from the viewpoint of reducing the weight of the backlight (backlight unit), the plate thickness is 2.0 mm or less. The plate thickness is more preferably 1.8 mm or less, further preferably 1.7 mm or less, further preferably 1.5 mm or less, and particularly preferably 1.3 mm or less.

The glass plate for a light diffusion plate of the present invention is preferably a rectangle (rectangle) having a dimension of at least one side of 200 mm or more. Moreover, it is more preferable that the dimension of at least one side is 400 mm or more, and it is further more preferable that it is 600 mm or more. Further, the dimension of at least one side 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 glass plate for a light diffusion plate of the present invention has an average coefficient of thermal expansion at 50 ° C. to 350 ° C. of 60 × 10 ⁻⁷ / K or less. The warpage is caused by the fact that a temperature distribution is generated in the surface as the temperature of the light diffusion plate rises. If the average thermal expansion coefficient is less than 60 × 10 ⁻⁷ / K, warpage due to temperature distribution can be suppressed, and display unevenness is less likely to occur. The average coefficient of thermal expansion is more preferably 55 × 10 ⁻⁷ / K or less, further preferably 53 × 10 ⁻⁷ / K or less, and particularly preferably 50 × 10 ⁻⁷ / K or less.

The total light transmittance (hereinafter also simply referred to as total light transmittance) at wavelengths of 450 nm, 550 nm, and 630 nm of the glass plate for light diffusion plate of the present invention is 10% or more. If the total light transmittance is 10% or more, the transmittance necessary to function as a direct type backlight can be obtained. The total light transmittance is more preferably 15% or more, and further preferably 20% or more. On the other hand, if the total light transmittance is 60% or less, display unevenness can be suppressed. The total light transmittance is more preferably 55% or less, and further preferably 50%.

The total light reflectance (hereinafter also simply referred to as total light reflectance) at wavelengths of 450 nm, 550 nm, and 630 nm of the glass plate for light diffusion plate of the present invention is preferably 40% or more. If the total light reflectance is 40% or more, the homogeneity necessary to function as a direct type backlight can be obtained. The total light reflectance is more preferably 45% or more, and further preferably 50% or more. On the other hand, the total light reflectance is preferably 90% or less. If the total light reflectance is 90% or less, sufficient luminance can be obtained. The total light reflectance is more preferably 85% or less, and further preferably 80% or less.

The glass plate for a light diffusion plate of the present invention suppresses the amount of light absorbed by the glass plate if the total of the total light transmittance and total light reflectance at each wavelength of 450 nm, 550 nm, and 630 nm is 90% or more. It is preferable because the light quantity of the light source can be used efficiently. The total of the total light transmittance and total light reflectance at each wavelength is more preferably 95% or more, and even more preferably 98% or more.

Examples of the glass having the total light transmittance and the total light reflectance described above include phase separation glass and crystallized glass. When the glass plate for light diffusion plates of the present invention is composed of phase-separated glass, the total light transmittance and total light reflectance can be adjusted by controlling the phase separation state described later. Moreover, when the glass plate for light diffusing plates of this invention consists of crystallized glass, a total light transmittance and a total light reflectance can be adjusted by control of a crystallization state. Below, although the case of phase separation glass is mainly demonstrated, it is not limited to this.

The desired optical properties (total light transmittance and total light reflectance) of the glass constituting the glass plate for a light diffusion plate of the present invention (hereinafter also simply referred to as glass) are a refractive index difference between phases and a high refractive index phase. The volume density, the plate thickness, and the like can be adjusted as appropriate.

In addition, the refractive index difference of the phase separation and the volume density of the high refractive index phase can be adjusted by the composition of the glass and heat treatment conditions (for example, conditions for the phase separation treatment).

The glass plate for light diffusing plates of the present invention is composed of phase-separated glass including two phase-separated phases.
Glass phase separation means that a single-phase glass is divided into two or more glass phases. Examples of the method for phase separation of glass include a method for heat-treating glass.

As a condition for heat treatment for phase separation of glass, typically, the temperature is preferably 50 ° C. higher than the glass transition point, more preferably 75 ° C. higher temperature, more preferably 100 ° C. higher temperature. It is particularly preferred that However, the conditions for the heat treatment are typically preferably 400 ° C. or higher than the glass transition point, more preferably 350 ° C. or higher, and particularly preferably 300 ° C. or lower.

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 phase separation temperature can be adjusted by the composition of the glass. In particular, adjusting the amounts of Al ₂ O ₃ , alkali metal, and alkaline earth metal is effective for adjusting the phase separation temperature. Among alkaline earth metals, adjusting the amount of MgO is effective for adjusting the phase separation temperature. By containing Al ₂ O ₃ , there is an effect of lowering the phase separation temperature. In particular, in a borosilicate glass not containing an alkali metal, if the amount of Al ₂ O ₃ is too large, the phase separation temperature becomes 1000 ° C. or less, and phase separation treatment in a short time becomes extremely difficult.

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. From the viewpoint of improving optical properties, the heat treatment time is preferably 10 hours or less, more preferably 8 hours or less, further preferably 6 hours or less, further preferably 4 hours or less, particularly preferably 2 hours or less, and most preferably 1 hour or less. preferable.
The phase separation temperature is preferably higher than the devitrification temperature. When the phase separation temperature is higher than the devitrification temperature, it becomes easier to form a phase-separated glass.

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 As the state of the separated glass, there are a binodal state and a spinodal state. The binodal state is a state in which one or more generally spherical phase separation structures are formed in a continuous phase by a nucleation-growth mechanism. Further, the spinodal state is a state in which each phase separated has a certain degree of regularity and is intertwined with each other in three dimensions. These phase separation structures exhibit a function as a light scatterer as described below.

Since the light scatterer has a different refractive index from the surroundings, it scatters the incident light. When one or more phase-separated structures are dispersed inside the glass plate (hereinafter also referred to as a dispersed phase), 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 are present inside the glass plate, the light incident from the light source repeats scattering, and the transmitted light can be uniformly dispersed.

In the glass of the present invention, in order to reduce the wavelength dependency of the light scattering property, the average particle diameter of the phase functioning as a light scattering material (hereinafter abbreviated as a light scattering material) in the phase separation state inside the glass is 0. It is preferably 1 μm or more, more preferably 0.2 μm or more, and still more preferably 0.3 μm or more. Moreover, in order to improve light-scattering property, it is preferable that the average particle diameter of the said phase is 1.6 micrometers or less, More preferably, it is 1.0 micrometer or less, More preferably, it is 0.8 micrometer or less. The average particle size of the phase can be measured by SEM observation.

Here, the average particle size in the phase-separated state is an average of the widths of the phases having a small volume fraction in the spinodal state, which are intertwined with each other continuously. When the phase is spherical, the average value of the diameters, and when one phase is elliptical, the average value of the values obtained by adding the major axis and minor axis and dividing by two.

In order to develop an appropriate light scattering property, the volume fraction of the light scatterer in the glass is preferably 5% or more, more preferably 10% or more, and more preferably 15% or more. More preferably, it is particularly preferably 20% or more, particularly preferably 25% or more, and most preferably 30% or more. The volume fraction is preferably 70% or less, more preferably 60% or less, and further preferably 50% or less. The volume fraction of the light scatterer is estimated from the ratio of the dispersed particles by calculating the ratio of the dispersed particles distributed on the glass surface from the SEM observation photograph.

It is known that the refractive index of the whole glass has a positive correlation with the specific gravity. In order to reduce the refractive index and reduce the reflectivity on the surface of the phase separation glass, or to reduce the deflection due to its own weight deformation, the density is preferably 3.0 g / cm ³ or less, and 2.8 g / cm ^3. The following is more preferable, 2.7 g / cm ³ or less is further preferable, and 2.6 g / cm ³ or less is most preferable.

The method for producing the phase-separated glass is not particularly limited. For example, an appropriate amount of various raw materials are prepared, heated to about 1500 to 1800 ° C. and melted, and then homogenized by defoaming, stirring, and the like. Forming into a plate shape or the like by a downdraw method, a press method, a roll-out method, or the like, or a block shape by casting, slowly cooling, processing into an arbitrary shape, and then performing phase separation. In particular, when it is desired to shorten the phase separation time and reduce the cost, various amounts of various raw materials are prepared, heated to about 1500-1800 ° C. and melted, and then homogenized by defoaming, stirring, and the like. After processing to lower and phase-separate, it is formed into a plate shape by the float method, downdraw method, press method or rollout method, etc., or cast into a block shape, and after slow cooling, it is processed into an arbitrary shape Thereafter, a phase separation process may be performed.

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-divided glass by heat processing shall also be included in phase-separated glass, and in this case, the step of phase-separating the glass is included in the step of melting or the like.

The glass plate for light diffusion plates of the present invention may be made of crystallized glass.
The crystallinity of the crystallized glass is preferably 1% or more, more preferably 5% or more, and further preferably 10% or more. The crystallinity is preferably 90% or less, more preferably 60% or less, still more preferably 40% or less, particularly preferably 30% or less, and most preferably 20% or less.

By setting the crystallinity of the crystallized glass to 1% or more, the average thermal expansion coefficient can be reduced, sufficient scattering characteristics can be obtained, the Young's modulus can be improved, 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 by the following equation (1) from the mass ratio b and a of the reference sample and crystallized glass.

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 an average particle diameter 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 refractive index difference 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 from the ratio of the crystal phase by calculating the ratio of the crystal phase distributed on the glass surface from the SEM observation photograph.

In order to further reduce the wavelength dependence of the light scattering property, it is preferable that the particle diameter has a distribution. The difference between the average value Ds of the lower 10% and the average value Dl of the upper 10% (Dl−Ds) of the particle diameter (nm) measured by SEM observation except for a small contribution of less than 50 nm to the optical characteristics in the visible region (Dl−Ds) However, it is preferably 100 nm or more, more preferably 200 nm or more, further preferably 400 nm or more, further preferably 700 nm or more, particularly preferably 1000 nm or more, and 2000 nm or more. Most preferred.

In the case of crystallized glass, the control of the particle size distribution in the glass can be obtained, for example, by controlling the thermal history of the crystallization process. As an example, a particle size distribution in the plate thickness direction is generated by giving a temperature difference to the upper surface, the inside, and the lower surface of the glass. Examples of heating methods that give a temperature difference to the upper, inner, and lower surfaces of the glass include, for example, changing the temperature and number of heating heaters on the upper and lower surfaces, changing the distance between the heater and the glass plate, induction heating, and laser. For example, use of local heating is used.

Also, when crystallization treatment is performed on glass in a molten state, the same effect can be obtained by controlling the flow velocity distribution in the plate thickness direction. Moreover, in order to provide a uniform particle size distribution in the plate thickness direction in the glass, the time for passing through the temperature zone for crystallization treatment may be controlled. By passing slowly through the crystallization temperature zone, the particle size increases, and by passing faster, the particle size decreases. As a method for controlling the time for passing through the crystallization temperature zone, for example, a method for precisely controlling the temperature profile of the heat treatment furnace or a glass flow rate if crystallization is performed in the course of passing through the glass forming process. Can also be obtained.

The glass plate for a light diffusion plate of the present invention preferably has an arithmetic average roughness Ra of at least one main surface of 0.03 nm or more.

The glass plate for a light diffusing plate of the present invention may have an uneven surface on at least one surface in order to increase light diffusibility as a light diffusing plate. When the surface of at least one surface has an uneven surface, the arithmetic average roughness (Ra) of the outer surface is not particularly limited in order to improve the light diffusibility of the light diffusion plate, but is 0.05 nm or more. More preferably, it is 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 average roughness (Ra) of the outer surface is preferably 10 nm or more, more preferably 100 nm or more, still more preferably 1000 nm or more, and most preferably 5000 nm or more.

The arithmetic average roughness Ra can be measured based on Japanese Industrial Standard JIS B0601 (1994). On the other hand, the first main surface and the second main surface may have the same or different arithmetic average roughness Ra.

In order to increase the light diffusibility of the light scattering plate, the glass plate for light diffusing plate of the present invention may have at least one surface concavo-convex by blasting, acid etching or imprinting, or a combination of these methods. . In that case, the half width of the intensity distribution of the transmitted scattered light on the surface (hereinafter also referred to as the half width of the transmitted scattered light) is preferably 5 ° or more, more preferably 10 ° or more, and even more preferably 20 °. That's it. Moreover, although an upper limit is not restrict | limited in particular, in order to maintain the intensity | strength of glass, 40 degrees or less are preferable, More preferably, it is 35 degrees or less.

The half width at half maximum of the transmitted scattered light can be measured using a spectrophotometer with a variable measurement angle. However, it is necessary to distinguish between scattering due to phase separation and scattering due to surface shape. For this purpose, a smooth surface is formed by filling the half-width a ° of the transmitted scattered light, measured with a phase-separated glass having irregularities on at least one surface, and the irregularities with a resin having a refractive index approximately equal to that of the glass matrix. The difference between the measured half-width b ° of the transmitted scattered light and (a−b) ° is defined as the half-width of the transmitted scattered light on the uneven surface.

Examples of the method for adjusting the arithmetic average roughness Ra of the glass surface and the half width at half maximum of scattering on the surface include polishing, blasting, etching and imprinting. The first main surface and the second main surface of the glass may be coated with silica, titania, alumina, or the like.

The composition of the glass of the present invention will be described. In the present specification, the content of the glass component will be described using an oxide-based molar percentage display (%) unless otherwise specified.

SiO ₂ is a component that improves the weather resistance and scratch resistance as glass, and is contained by 55% or more. The content of SiO ₂ is more preferably 57% or more, further preferably 59% or more, and particularly preferably 61% or more. On the other hand, if the content of SiO ₂ is 68% or less, the viscosity of the glass can be lowered to improve productivity. The content of SiO ₂ is more preferably 67% or less, further preferably 66% or less, and particularly preferably 65% or less.

Al ₂ O ₃ is an optional component. When Al ₂ O ₃ is contained, it is preferable to contain 1% or more because the chemical durability of the glass can be improved and the average thermal expansion coefficient can be reduced. The content of Al ₂ O ₃ is more preferably 2% or more, further preferably 3% or more, and particularly preferably 4% or more. On the other hand, if the content of Al ₂ O ₃ is 9% or less, the phase separation treatment can be performed in a short time by increasing the phase separation temperature of the glass. The content of Al ₂ O ₃ is more preferably 8% or less, further preferably 7% or less, and particularly preferably 6% or less.

B ₂ O ₃ is an optional component. When B ₂ O ₃ is contained, it is preferable to contain 5% or more because the viscosity of the glass is lowered, the solubility is improved, and the dispersion stability between SiO ₂ and other components is remarkably improved. The content of B ₂ O ₃ is more preferably 7% or more, further preferably 9% or more, and particularly preferably 11% or more. On the other hand, if the content of B ₂ O ₃ is 19% or less, the chemical durability of the glass can be improved. The content of B ₂ O ₃ is more preferably 18% or less, still more preferably 17% or less, and particularly preferably 16% or less.

MgO is a component that can reduce the viscosity of the glass and reduce the average thermal expansion coefficient, and is contained at 4% or more. The content of MgO is more preferably 5% or more, and further preferably 6% or more. On the other hand, if the content of MgO is 15% or less, the glass can be stabilized by lowering the devitrification temperature. The content of MgO is more preferably 10% or less, further preferably 9% or less, and particularly preferably 8% or less.

BaO is an optional component. When BaO is contained, if the content is 0.5% or more, the viscosity of the glass is lowered, and the average thermal expansion coefficient can be reduced. The content of BaO is more preferably 1% or more. On the other hand, if the content of BaO is 4% or less, the specific gravity can be reduced and deformation of its own weight can be prevented. The BaO content is more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1.5% or less.

Na ₂ O is an optional component. When Na ₂ O is contained, the average thermal expansion coefficient can be reduced if it is 4% or less. The content of Na ₂ O is more preferably 3% or less, further preferably 2% or less, and particularly preferably substantially free.

P ₂ O ₅ is an optional component, but since it is a basic component that promotes phase separation in combination with SiO ₂ , MgO, and Na ₂ O, the phase-separated glass is used as the glass plate for the light diffusion plate of the present invention. When used, it is preferably contained. 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, the content of P ₂ O ₅ is preferably 15% or less, more preferably 14% or less, still more preferably 10% or less, particularly preferably 7% or less, and most preferably 4.5% or less. is there.

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 of the present invention, it may be preferable to contain the following components in addition to the SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , and MgO components. In this case, the total content of the components is preferably 85% or more, and typically 90% or more.

By making the total content of Li ₂ O, Na ₂ O, and K ₂ O 1% or less, the average thermal expansion coefficient can be reduced, which is preferable. The total content of the components is more preferably 0.7% or less, still more preferably 0.5% or less, particularly preferably 0.3% or less, and most preferably substantially free.

ZrO ₂ is an optional component, but is preferably contained in an amount of 1% or more and more preferably 2% or more in order to significantly improve chemical durability. In order to lower the refractive index of the glass and reduce the reflectance on the glass surface, it is preferably 4.5% or less, more preferably 4% or less, and even more preferably 3% or less.

CaO, SrO and BaO are all optional 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, even more preferably Is 1% or more.

When CaO is contained, its content is preferably 7% or less. By setting the content of CaO to 7% or less, the average thermal expansion coefficient can be reduced, and the glass is difficult to devitrify. The content of CaO is more preferably 6% or less, still more preferably 5% or less.

The total content of CaO, SrO and BaO is preferably 12% or less, more preferably 8% or less, further preferably 6% or less, particularly preferably 4% or less, and typically 3% or less. It is. By making the total 12% or less, the glass is less likely to be devitrified.

Further, it is preferable that the value of MgO / (MgO + CaO + SrO + BaO) is 0.2 or more because the viscosity can be reduced while reducing the average thermal expansion coefficient. This value is more preferably 0.3 or more, still more preferably 0.4 or more, and particularly preferably 0.5 or more.

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.

Moreover, the glass of the present invention may contain SO ₃ as a fining agent. In this case, the content of SO ₃ is preferably more than 0% and 0.5% or less in terms of mass percentage. The content of SO ₃ is more preferably 0.4% or less, further preferably 0.3% or less, and further preferably 0.25% or less.

Moreover, the glass of the present invention may contain one or more of Sb ₂ O ₃ , SnO ₂ and As ₂ O ₃ as an oxidizing agent and a fining agent. In this case, the content of Sb ₂ O ₃ , SnO ₂ or As ₂ O ₃ is preferably 0 to 0.5% in terms of mass percentage. The content of Sb ₂ O ₃ , SnO ₂ or As ₂ O ₃ is more preferably 0.2% or less, further preferably 0.1% or less, and still more preferably substantially not contained.

However, since Sb ₂ O ₃ , SnO ₂ and As ₂ O ₃ act as an oxidizing agent for glass, they may be added within the above range depending on the purpose of adjusting the amount of Fe ^{2+ in} the glass. However, As ₂ O ₃ is not positively contained from the environmental viewpoint.

The glass of the present invention may contain _Fe 2 _{O 3.} When Fe ₂ O ₃ is contained, since Fe ₂ O ₃ also functions as a coloring component, the content of Fe ₂ O ₃ is preferably 10 ppm or less with respect to the total amount of the glass composition described above. In particular, Fe ₂ O ₃ is preferably 200 ppm or less, more preferably 100 ppm or less, and more preferably 80 ppm or less from the viewpoint of suppressing a decrease in total light transmittance and obtaining uniform and high light diffusibility. More preferably, it is most preferable to set it as 50 ppm or less.

Moreover, the glass of the present invention may contain NiO. When NiO is contained, since NiO functions also as a coloring component, the content of NiO is preferably 10 ppm or less with respect to the total amount of the glass composition described above. In particular, NiO is preferably 1.0 ppm or less, more preferably 0.5 ppm or less, from the viewpoint of suppressing a decrease in total light transmittance and obtaining uniform and high light diffusibility.

The glass of the present invention may contain Cr ₂ O ₃ . When Cr ₂ O ₃ is contained, Cr ₂ O ₃ also functions as a coloring component. Therefore, the content of Cr ₂ O ₃ is preferably 10 ppm or less with respect to the total amount of the glass composition described above. In particular, Cr ₂ O ₃ is preferably 1.0 ppm or less, more preferably 0.5 ppm or less, from the viewpoint of suppressing a decrease in total light transmittance and obtaining uniform and high light diffusibility.

The glass of the present invention may contain MnO ₂ . When MnO ₂ is contained, since MnO ₂ functions also as a component that absorbs visible light, the content of MnO ₂ is preferably 50 ppm or less with respect to the total amount of the glass composition described above. In particular, MnO ₂ is preferably 10 ppm or less from the viewpoint of suppressing a decrease in total light transmittance and obtaining uniform and high light diffusibility.

The glass of the present invention may contain TiO ₂ . When TiO ₂ is contained, TiO ₂ also functions as a component that absorbs visible light. Therefore, the content of TiO ₂ is preferably 1000 ppm or less with respect to the total amount of the glass composition described above. The content of TiO ₂ is more preferably 500 ppm or less, and particularly preferably 100 ppm or less, from the viewpoint of suppressing a decrease in total light transmittance and obtaining uniform and high light diffusibility. Further, in order to lower the devitrification temperature or to reduce the reflection on the glass surface by lowering the refractive index of the glass, the content of TiO ₂ is preferably 3% or less, more preferably 2% or less. % Or less is more preferable.

The glass of the present invention may contain CeO _2. CeO ₂ has the effect of reducing the redox of iron and can reduce the absorption of glass at a wavelength of 400 to 700 nm. However, if containing CeO ₂ in a large amount, CeO ₂ also functions as a component which absorbs visible light and there is a possibility that excessively lowering the content of divalent iron, not preferred. Therefore, the CeO ₂ content is preferably 1000 ppm or less with respect to the total amount of the glass composition described above. The CeO ₂ content is more preferably 500 ppm or less, further preferably 400 ppm or less, particularly preferably 300 ppm or less, and most preferably 250 ppm or less. However, the content of CeO ₂ must be adjusted so that the content of divalent iron converted to Fe ₂ O ₃ is 1 mass ppm or more and 900 mass ppm or less.

The glass plate for light diffusion plate of the present invention is made of the glass described above. FIG. 1 shows a cross-sectional view of a direct type backlight (direct type backlight unit) constituted by a glass plate for a light diffusion plate made of glass according to an embodiment of the present invention. In the direct type backlight unit 1 shown in FIG. 1, a light source 3 is provided on a reflector 2 having a frame 8 at a predetermined interval, and a light diffusing plate (light diffusing of the present invention) is provided thereon. A light diffusion plate 4 including a glass plate for plates) is provided. 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 glass plate for a light diffusing plate of the present invention can have a function of a light diffusing sheet by coating particles having a particle diameter of 100 nm or more, porous silica, or the like. When the glass plate for a light diffusing plate of the present invention itself has the function of the light diffusing sheet 5, the light diffusing sheet 5 can be omitted.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

As the glass plate for the light diffusing plate, samples of glasses A to I and resins having compositions as shown in Tables 1 and 2 were used. Glasses B to G are examples, and glass A, glass H, glass I, and resin are comparative examples.
Glasses A to I were produced by the following method. First, a glass material prepared in advance was melted, homogenized, and degassed at 1650 ° C. to produce a molten glass. The molten glass was cooled to the phase separation treatment temperature described in Tables 1 and 2 at a cooling rate of 50 ° C. per minute, then held at the phase separation treatment temperature for 30 minutes, poured into a mold, and 1 ° C. at 700 ° C. After maintaining the time, the glass was cooled to room temperature at a cooling rate of 1 ° C. per minute to produce phase-separated glass. It was observed with a scanning microscope that the glass was phase-separated and separated into two phases.
The total light transmittance and total light reflectance were measured using an integrating sphere unit of a spectrophotometer (trade name: Lamda 950) manufactured by PerkinElmer.
The density was measured by the Archimedes method.
The thermal conductivity was measured by a laser flash method.
The average thermal expansion coefficient was measured with a thermomechanical analyzer. Tables 1 and 2 show thermal expansion coefficients at 50 to 350 ° C.
Young's modulus and Poisson's ratio were measured by the ultrasonic method.

(Evaluation of warpage)
As shown in FIG. 1, a plurality of LEDs (light emitting diodes) constituting a plurality of light sources 3 are arranged behind the light diffusion plate 4. One long side of the light diffusing plate 4 is fixed to the frame 8. The distance between the light diffusing plate 4 and each LED was set to 13 mm, and the distance between adjacent LEDs was set to 18 mm. When all the LEDs were turned on, the surface temperature of the LEDs reached 140 ° C. After maintaining the state where the LED was lit for 30 minutes, the light diffusion plate was warped to the side where the LED was not installed. The maximum in-plane curvature at that time was measured with a three-dimensional length measuring device.

The test results are shown in Tables 3 and 4 below. Generally, if the distance between the light diffusing plate and the LED fluctuates by 1 mm or more, it is considered that the uniformity of in-plane luminance is deteriorated. Therefore, a sample whose warpage is less than 1 mm is determined to be appropriate (OK), and the warpage is 1 mm or more. The sample was judged as ineligible (NG). As a comprehensive evaluation, a sample having a thickness of 0.3 mm to 1.5 mm and a warp of 1 mm or less is judged as (OK), and any one or more of the samples having a thickness of 0.3 mm to 1.5 mm is determined. Samples with a warp of 1 mm or more in thickness were judged as non-conforming (NG).

As is clear from Tables 3 and 4, the warpage increases as the plate thickness decreases. Even with a 1.5 mm thick sample made of resin, the maximum warpage amount was 1 mm or more, and display unevenness was large. Samples with a glass thickness of 0.5 mm to 1.5 mm with glass A and glass H had a maximum warpage of less than 1 mm, but samples with a plate thickness of 0.3 mm had a maximum warpage of 1 mm or more. Was NG. It is considered that Glass A and Glass H have an average coefficient of thermal expansion at 50 to 350 ° C., which suggests that the warping amount may or may not be in an appropriate range depending on the plate thickness. Samples with a glass thickness of 1 mm to 1.5 mm in glass I had a maximum warpage of less than 1 mm, but samples with a thickness of 0.3 mm to 0.5 mm had a maximum warpage of 1 mm or more. It was NG. On the other hand, the samples with the glass B to G and the plate thickness of 0.3 mm to 1.5 mm all had a maximum warpage amount of less than 1 mm and the overall evaluation was OK, and uneven brightness could be suppressed.

(Diffusion evaluation)
Furthermore, when the diffuser plate used in VIERA TH-32D300 manufactured by Panasonic was changed to a light diffuser plate made of glass BG, and a backlight unit for diffusivity evaluation was constructed, the shape of the LED was visible. It was not possible to show good diffusibility.
In addition, arithmetic mean roughness Ra of the surface of the glass plate for light diffusing plates by the glass B was 0.2 micrometer.
Therefore, it was found that the light diffusing plate of the present invention includes a glass plate for a light diffusing plate having high heat resistance, so that even if it is thin, it has sufficient diffusibility and can easily achieve uniform luminance.

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. 2017-076105 filed with the Japan Patent Office on April 6, 2017. The entire contents of Japanese Patent Application No. 2017-076105 are incorporated herein by reference. .

DESCRIPTION OF SYMBOLS 1 Direct type backlight unit 2 Reflecting plate 3 Light source 4 Light diffusing plate (Light diffusing plate containing the glass plate for light diffusing plates of this invention)
5 Light diffusion sheet 6 Prism sheet 7 Polarization separation sheet 8 Frame

Claims

A glass plate for a light diffusing plate having two main surfaces facing each other,
The plate thickness of the glass plate is 0.3 mm or more and 2.0 mm or less,
The glass plate has an average coefficient of thermal expansion at 50 ° C. to 350 ° C. of 60 × 10 −7 / K or less,
The total light transmittance of wavelengths of 450 nm, 550 nm, and 630 nm of the glass plate is 10% or more and 60% or less, and the total of the total light transmittance and the total light reflectance of wavelengths of 450 nm, 550 nm, and 630 nm is 90% or more. And
The glass plate is expressed in mol percentage on the basis of oxide, SiO 2 55-68%, Al 2 O 3 0-9%, B 2 O 3 0-19%, MgO 4-15% and BaO. A glass plate for a light diffusing plate made of glass containing 0 to 4% and Na to 4% of Na 2 O.
The glass plate for a light diffusing plate according to claim 1, wherein the glass contains 0 to 1% of the total content of Li 2 O, Na 2 O and K 2 O in terms of mol percentage based on oxide.
The glass plate for a light diffusing plate according to claim 1 or 2, wherein the glass is a phase separation glass.
The glass plate for a light diffusing plate according to any one of claims 1 to 3, wherein a dimension of at least one side is 200 mm or more.
The glass plate for a light diffusing plate according to any one of claims 1 to 4, wherein an arithmetic average roughness Ra of at least one of the main surfaces is 0.03 nm or more.
A light diffusing plate comprising the glass plate for a light diffusing plate according to any one of claims 1 to 5.
A backlight unit comprising the light diffusing plate according to claim 6 and a light source.