WO2017130868A1

WO2017130868A1 - Light diffusion plate

Info

Publication number: WO2017130868A1
Application number: PCT/JP2017/002012
Authority: WO
Inventors: 雄一 ▲桑▼原
Original assignee: 旭硝子株式会社
Priority date: 2016-01-25
Filing date: 2017-01-20
Publication date: 2017-08-03
Also published as: JP2019053093A

Abstract

The objective of the present invention is to provide a light diffusion plate used in a direct backlight unit, the light diffusion plate: having high heat resistance, light resistance, and water resistance; exhibiting excellent rigidity and display quality; and being suitable for designing thinner plates, narrower bezels, and increased size. A light diffusion plate provided with a glass plate having a first main surface and a second main surface, the heat expansion coefficient of the glass plate being -100×10^-7 to 500×10^-7/°C, a light dispersion film that includes a matrix and particles being provided on at least one main surface of the glass substrate, the matrix including an organic-inorganic composite compound, the particles being inorganic oxide particles having a lower refractive index than the refractive index of the matrix, and light incident on the first main surface being transmitted from the second main surface while being diffused.

Description

Light diffusion plate

The present invention relates to a light diffusing plate used for a direct type or edge light type backlight unit in a display element such as a liquid crystal television and a liquid crystal monitor.

As a material for the light diffusing plate used in direct-type backlight units in display elements such as liquid crystal televisions and liquid crystal monitors, the use of a transparent material allows light to pass through because it transmits light. A material is used that does not impair the brightness of the light source without recognizing the shape of the light source behind the plate. 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 in a display element such as a liquid crystal television and a liquid crystal monitor, the luminance unevenness of the light guide plate that emits light incident on the diffusing plate when a transparent material is used. Therefore, a material that does not recognize the luminance unevenness of the light guide plate behind the light diffusion plate is used. Since the diffusion plate used in the direct type backlight unit also has the same problem, the direct type backlight unit will be described below as an example, but is not limited to the direct type backlight unit.

As a material for the light diffusing plate, in the prior art, a material in which a polymer or inorganic particle having a refractive index different from that of a thermoplastic resin forming a continuous phase is blended as a dispersed phase is used (Patent Literature). 1). Patent Document 2 discloses a light diffusion plate made of a polycarbonate resin in which diffusivity, reflectance, and luminance unevenness are in specific ranges.

Japanese Patent No. 3100853 JP 2006-339033 A

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 brightness uniformity. 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, which makes it 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.

These problems are caused by the increase in size of liquid crystal televisions and liquid crystal monitors, and in-plane temperature distribution and inflow distribution of moisture from the outside air are likely to occur, and display unevenness due to warping of the resin light diffusion plate. This is likely to occur.

Therefore, the present invention provides a light diffusing plate used in a backlight unit that has high heat resistance, light resistance and water resistance, exhibits excellent rigidity and display quality, and is suitable for thin plate, narrow frame size and large size. The purpose is to do.

The present inventors have a first main surface and a second main surface facing the first main surface as a member of a light diffusion plate used in a backlight unit, and the first main surface The present invention has been completed by finding that the above-mentioned problems can be solved by using a glass plate having a thermal expansion coefficient in a specific range while transmitting the incident light to the second main surface while diffusing it.

That is, this invention provides the light diffusing plate which has the following structures, and its manufacturing method.
[1] A glass plate having a first main surface and a second main surface facing the first main surface, the second main surface being diffused while diffusing light incident on the first main surface. A light diffusing plate to be emitted from a surface,
The glass plate is provided with a light scattering film on at least one of the first main surface and the second main surface, and has a thermal expansion coefficient of −100 × 10 ⁻⁷ / ° C. to 500 × 10 ⁻⁷ / ° C. And
The light scattering film includes a matrix and particles, the matrix includes an organic-inorganic composite compound, and the particles are inorganic oxide particles having a refractive index smaller than that of the matrix. Diffusion plate.
[2] The light diffusing plate according to [1], wherein the light scattering film has a thickness of 0.1 to 100 μm.
[3] The light diffusing plate according to [1] or [2], wherein the organic-inorganic composite compound is an organopolysiloxane.
[4] The inorganic oxide particles according to any one of [1] to [3], having an average particle diameter of 0.1 to 50 μm and fine pores having a pore diameter peak value of 2 to 50 nm. The light diffusing plate of description.
[5] The light diffusing plate according to any one of [1] to [4], wherein the volume ratio of the inorganic oxide particles in the light scattering film is 25 to 95 vol%.
[6] The light diffusing plate according to any one of [1] to [5], wherein a haze is 90% or more when incident light from a normal direction to the first main surface of the glass plate is transmitted.
[7] Of the incident light from the normal direction to the first main surface of the glass plate, the average value of the total light transmittance at a wavelength of 400 to 700 nm transmitted in the incident direction is 4% or more. ] The light diffusing plate according to any one of [6] to [6].
[8] Of the incident light from the normal direction to the first principal surface of the glass plate, the average transmittance of light having a wavelength of 400 to 700 nm transmitted in the direction of 30 ° with respect to the normal of the glass plate is The light diffusing plate according to any one of [1] to [7], which is 0.2% or more.
[9] Ratio of total light reflectance and total light transmittance in a wavelength range of 400 to 700 nm when incident light from the normal direction to the first main surface of the glass plate is transmitted (total light reflectance / total The light diffusing plate according to any one of [1] to [8], wherein the light transmittance) is 0.25 or more.
[10] Transmittance in the direction of 30 ° with respect to the normal in the wavelength range of 400 to 700 nm when incident light from the normal direction to the first main surface of the glass plate is transmitted (30 ° transmission) The light diffusion plate according to any one of [1] to [9], wherein a ratio of the transmittance in the straight direction (straight forward transmittance) (30 ° transmittance / straight forward transmittance) is 0.05 or more .
[11] The light diffusing plate according to any one of [1] to [10], wherein the glass plate has a thickness of 0.05 to 3 mm.
[12] The light diffusing plate according to any one of [1] to [11], wherein a dimension of at least one side of the glass plate is 200 mm or more.
[13] A light diffusing plate for applying a dispersion containing an organopolysiloxane precursor and inorganic oxide particles having a refractive index of 1.45 or less to a glass plate, and curing the dispersion to form a light scattering film. Production method.
[14] The method for producing a light diffusing plate according to [13], wherein the dispersion is cured by heat and the heat is cured at a heat treatment temperature of 100 to 800 ° C.

According to the light diffusing plate of the present invention, by including a glass plate having high heat resistance and light resistance, it becomes possible to reduce the distance between the light source and the light diffusing plate when used in the backlight unit. Homogeneity, thinning, and narrow frame are easy to achieve. Moreover, since the light diffusing plate of this invention contains a glass plate, it is excellent in rigidity compared with a resin-made light diffusing plate, and when used in a backlight unit, it is easy to handle in the manufacturing process.

FIG. 1 is a schematic cross-sectional view of a direct type backlight using the light diffusion plate of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the light diffusion plate of the present invention.

The present invention comprises a glass plate having a first main surface and a second main surface opposite to the first main surface, and the second main surface while diffusing light incident on the first main surface. The present invention relates to a light diffusing plate emitted from a main surface. In the light diffusion plate of the present invention, a light scattering film is provided on at least one of the first main surface and the second main surface of the glass plate, and the thermal expansion coefficient of the glass plate is −100 × 10 ⁻⁷ to 500 × 10. ^-7 / ° C. The light diffusing plate of the present invention is useful as a member of a backlight unit in a display element such as a liquid crystal television and a liquid crystal monitor.

Here, the first main surface of the glass plate is a surface on the light source side when used in the backlight unit. The 2nd main surface of a glass plate is a surface which opposes a 1st main surface, and when it uses for a backlight unit, it is a surface used as the liquid crystal panel side.

FIG. 1 shows a cross-sectional view of a backlight unit using the light diffusion plate of the present invention. In the backlight unit 1 shown in FIG. 1, the light source 3 is provided on the reflecting plate 2 at a predetermined interval, and the light diffusion plate 4 is provided thereon. Light emitted from the light source 3 is diffused by the light diffusion plate 4. The light diffusing plate 4 includes a glass plate, and the surface of the glass plate on the light source 3 side is the first main surface.

The light diffusing plate of the present invention transmits incident light to the first main surface while diffusing it from the second main surface. Here, “transmitting from the second main surface while diffusing the incident light to the first main surface” means that the light diffusing plate has an appropriate haze by having an appropriate haze, By having an appropriate total light transmittance, it means expressing an appropriate light transmittance.

FIG. 2 is a schematic cross-sectional view showing an example of the light diffusion plate of the present invention. The light diffusing plate 4 shown in FIG. 2 has a glass plate 40 and a light scattering film 41 provided on one main surface of the glass plate 40. The surface of the glass plate 40 on which the light scattering film 41 is provided may be the first main surface, the second main surface, or both main surfaces of the glass plate 40. Moreover, although the light-scattering film | membrane 41 shown in FIG. 2 contains the matrix 42 and the particle | grains 43, this invention is not limited to this.

The thermal expansion coefficient of the light diffusing plate of the present invention can be made a preferable thermal expansion coefficient when the thermal expansion coefficient of the glass plate is −100 × 10 ⁻⁷ to 500 × 10 ⁻⁷ / ° C.

The thermal expansion coefficient of the glass plate is −100 × 10 ⁻⁷ to 500 × 10 ⁻⁷ / ° C., preferably −10 × 10 ⁻⁷ to 300 × 10 ⁻⁷ / ° C., and more preferably 1 × 10 10 ^{It is −7} to 200 × 10 ⁻⁷ / ° C., and more preferably 50 × 10 ⁻⁷ to 150 × 10 ⁻⁷ / ° C. When the thermal expansion coefficient of the glass plate is 500 × 10 ⁻⁷ / ° C. or lower, the deformation when the distance between the light source and the light diffusion plate is reduced can be suppressed to improve the light diffusion performance, and the shape of the light source is less noticeable. Therefore, the luminance uniformity can be achieved. 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. Further, it is preferable that the thermal expansion coefficient of the glass plate is −100 × 10 ⁻⁷ / ° C. or higher because productivity is improved and costs are reduced.

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.

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 the glass transition point Tg of the said glass plate is 850 degrees C or less, More preferably, it is 800 degrees C or less, More preferably, it is 750 degrees C or less, Most 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 backlight unit, the distance between the light source and the light diffusion plate can be reduced. Uniformity in brightness is easy to achieve compared to a light diffuser made of light. Moreover, productivity of glass improves that a glass transition point is 850 degrees C or less.

In the present invention, “glass transition point” means a temperature corresponding to a bending point in a thermal expansion curve.

The glass plate in the light diffusion plate of the present invention preferably has a yield point of 200 ° C. or higher, more preferably 300 ° C. or higher, and still more preferably 400 ° C. or higher. The yield point of the glass plate is preferably 950 ° C. or lower. When the yield point of the glass plate is 200 ° C. or higher, the glass plate is excellent in heat resistance as compared with the resin light diffusion plate, and it is easy to achieve luminance uniformity. The yield point of a glass plate can be measured using a differential thermal dilatometer.

The glass plate in the light diffusing plate of the present invention preferably has a Young's modulus of 10 GPa or more, more preferably 20 GPa or more, further preferably 50 GPa or more, and further preferably 70 GPa or more. Moreover, it is preferable that the said glass plate is 500 GPa or less in Young's modulus, More preferably, it is 200 GPa or less, More preferably, it is 150 GPa or less.

When the Young's modulus of the glass plate is 10 GPa or more, the light diffusion plate is excellent in rigidity, and when used in a backlight unit, it is easier to handle than a resin light diffusion plate. Moreover, it is excellent in productivity as the Young's modulus of the said glass plate is 500 GPa or less.

The bending strength of the glass plate in the light diffusing plate of the present invention is preferably 10 MPa or more, more preferably 20 MPa or more, further preferably 30 MPa or more, and further preferably 100 MPa or more. When the bending strength of the glass plate is 10 MPa or more, excellent rigidity is obtained, and when used in a backlight unit, the glass plate is easier to handle than a resin light diffusion plate. Further, the bending strength of the glass plate is usually 300 MPa or less. The bending strength of the glass plate can be measured by the method described later in the examples.

The glass plate in the light diffusing plate of the present invention preferably has a surface resistance value of 1.0 × 10 ⁵ Ω / □ or more, more preferably 1.0 × 10 ⁷ Ω / □ or more, and further preferably 1 0.0 × 10 ⁹ Ω / □ or more, more preferably 1.0 × 10 ¹¹ Ω / □ or more. Further, it is preferably 1.0 × 10 ¹⁵ Ω / □ or less, more preferably 1.0 × 10 ¹⁴ Ω / □ or less, and further preferably 1.0 × 10 ¹³ Ω / □ or less.

When the surface resistance value of the glass plate is 10 ⁵ Ω / □ or more, the leakage current is reduced and the safety is improved. Further, when it is 1.0 × 10 ¹⁵ Ω / □ or less, static electricity is hardly generated, and handling is easy as compared with a light diffusion plate made of resin. The surface resistance value of the glass plate can be measured by the method described in JIS K6911 (2006).

Specifically, the glass plate is preferably silicate glass. Examples of the silicate glass include soda lime silicate glass (hereinafter referred to as soda lime glass), alkali aluminosilicate glass, alkali-free aluminosilicate glass, and alkali borosilicate glass. By appropriately selecting the glass composition, a diffusion plate having physical properties suitable for the light diffusion plate can be obtained.
For example, for soda lime glass, SiO ₂ is 60 to 75%, Al ₂ O ₃ is 2 to 12%, MgO is 2 to 11%, CaO is 0 to 10%, and SrO is expressed in terms of mass percentage based on oxide. Examples include a composition containing 0 to 3%, BaO 0 to 3%, Na ₂ O 10 to 18%, K ₂ O 0 to 8%, and ZrO ₂ 0 to 4%. 100% or less, usually 95% or more).
Alkali aluminosilicate glass is SiO ₂ 61 to 70%, Al ₂ O ₃ 1 to 18%, MgO 0 to 15%, CaO 0 to 5%, SrO 0 The composition contains ~ 1%, BaO 0 ~ 1%, Na ₂ O 8 ~ 18%, K ₂ O 0 ~ 6%, ZrO ₂ 0 ~ 4%, B ₂ O ₃ 0 ~ 8%. Can be mentioned.
The alkali-free aluminosilicate glass is expressed in terms of mass percentage on the basis of oxide, with SiO ₂ being 39 to 70%, Al ₂ O ₃ being 3 to 25%, B ₂ O ₃ being 1 to 30%, and MgO being 0 to 10 %, CaO 0 to 17%, SrO 0 to 20% and BaO 0 to 30%.
In addition, as alkali borosilicate glass, SiO ₂ is 65 to 78%, B ₂ O ₃ is 8 to 30%, Li ₂ O + Na ₂ O + K ₂ O is 1 to 18%, Al _{2 in} terms of mass percentage based on oxide. the ₂ O ₃ 0 ~ 10%, the CeO ₂ 0 ~ 5% of SnO ₂ 0 ~ 2% total of CaO 0-7 percent composition containing the like (or more components is 100% or less, It is usually 95% or more).

The method for producing a glass plate in the present invention is not particularly limited. For example, a suitable amount of various raw materials are prepared, heated to about 1500 to 1800 ° C. and melted, and then homogenized by defoaming, stirring, etc. It is produced by forming into a plate shape or the like by casting down, pressing or rolling out, or forming into a block shape after slow cooling and then processing into an arbitrary shape.

In the present invention, a light scattering film is provided on at least one main surface of the glass plate. As a result, a light diffusing plate that diffuses the incident light on the first main surface and transmits the light from the second main surface is obtained. The light scattering film may be provided on both main surfaces of the glass plate. When light scattering films are provided on both main surfaces of the glass plate, a plurality of light scattering layers having different characteristics can be provided at regular intervals.

The light scattering film used in the light diffusion plate of the present invention preferably has a thickness of 0.1 to 100.0 μm, more preferably 1 to 30 μm. When the film thickness of the light scattering film is within the above range, excellent diffusion performance can be secured.

The light scattering film preferably contains a matrix and particles. The matrix preferably contains an organic-inorganic composite compound. The particles are preferably inorganic oxide particles, and the refractive index of the particles is preferably smaller than the refractive index of the matrix.
Since the matrix constituting the light scattering film contains an organic-inorganic composite compound, the matrix has higher heat resistance than a conventional organic film, and cracks are less likely to occur as compared with a film made of only an inorganic material.

The light scattering film preferably has a weight change rate of 10% or less when heated at 400 ° C. for 30 minutes, more preferably 5% or less. Further, it is preferable that the color does not change when heated at 400 ° C. for 30 minutes. Such a film has high heat resistance and can be used in the immediate vicinity of a backlight.

As said organic inorganic composite compound, organopolysiloxane is preferable at the point which is excellent in stability. The organopolysiloxane can be obtained, for example, by hydrolytic condensation of one or more alkoxysilanes in a mixed solution of water and alcohol. As the alkoxysilane, a compound represented by the following formula (1) is preferable.
(R ¹ ) _4-n- Si- (OR ² ) _n (1)
(In the formula (1), n is an integer of 0 to 4, and R ¹ is an alkyl group having 1 to 3, 6, 8, or 10 carbon atoms, a vinyl group, an amino group, a styryl group, a methacryl group, an acrylic group, An organic group such as an epoxy group or a phenyl group, preferably a methyl group, an ethyl group, a propyl group or a phenyl group, and R ² is a methyl group, an ethyl group or a propyl group, preferably a methyl group or an ethyl group.

As the alkoxysilane, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, phenyltrimethoxysilane and the like are more preferable. These may be used alone or in combination of two or more. As the alkoxysilane, a cohydrolyzed condensate of tetraethoxysilane and methyltrimethoxysilane is more preferable.
The molar ratio of tetraethoxysilane to methyltrimethoxysilane in the cohydrolyzed condensate is particularly preferably 2/8 to 8/2. If tetraethoxysilane is in this range, the mechanical strength is improved, and if methyltrimethoxysilane is in this range, cracks are difficult to occur, and a decrease in light scattering due to cracks can be suppressed.

Inorganic oxide particles are preferred because they are stable to heat. The refractive index of the inorganic oxide particles is preferably smaller than the refractive index of the matrix. If the refractive index of the inorganic oxide particles is smaller than that of the matrix, excessive refraction of light can be suppressed and light can be diffused forward. However, inorganic oxide particles having a refractive index higher than that of the matrix may be included as long as the forward diffusion of light is not inhibited.
Examples of the inorganic oxide include silica, alumina, titania, and zirconia. The inorganic oxide particles may be composite oxide particles such as mullite, calcite, dolomite, forsterite, enstatite, cordierite, and steatite. Inorganic oxide particles are particularly preferred because of their low refractive index and availability.

When the matrix contains organopolysiloxane, the refractive index of the inorganic oxide particles is preferably 1.45 or less. In the present specification, “refractive index” means a refractive index at a wavelength of 550 nm.

In order to develop an appropriate light scattering property, it is preferable that the refractive index difference between the inorganic oxide particles in the light scattering film and the surrounding matrix 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 average particle diameter of the inorganic oxide particles is preferably 0.1 μm or more and more preferably 0.2 μm or more in order to obtain good light scattering properties. In order to obtain a homogeneous dispersion, the average particle diameter of the inorganic oxide particles is preferably 50 μm or less, and more preferably 10 μm or less.
The “average particle size” means the median size (50% particle size of the integrated particle size distribution curve) in the volume-based particle size distribution measured by the dynamic light scattering method.
The inorganic oxide particles preferably have fine pores having a pore diameter peak value of 2 to 50 nm. The peak value of the pore diameter is preferably 2 nm or more and more preferably 3 nm or more in order to obtain good light scattering properties. Further, in order to obtain good mechanical strength, the peak value of the pore diameter is preferably 50 nm or less, and more preferably 40 nm or less.
The “peak value of pore diameter” means the most frequent pore diameter in the pore diameter distribution measured by a mercury porosimeter.

In order to express an appropriate light scattering property, the volume ratio of the inorganic oxide particles in the light scattering film is preferably 25 vol% or more, and more preferably 30 vol% or more. In order to increase the film strength, the volume ratio of the inorganic oxide particles in the light scattering film is preferably 95% by volume or less, more preferably 80% by volume or less. Here, the volume ratio of the inorganic oxide particles is obtained from the ratio of the particles by calculating the ratio of the particles distributed on the glass surface from the SEM observation photograph.

The light diffusion plate of the present invention preferably has a water absorption of less than 0.1%, more preferably 0.01% or less, and even more preferably 0.001% or less. By setting the water absorption rate of the glass plate to less than 0.1%, there is no risk of water absorption and swelling when used in a backlight unit, so performance can be maintained even when stored for a long period of time. The light diffusing plate is hardly warped, display unevenness is reduced, and display quality is improved.
In the present invention, the water absorption is a value measured based on JIS K7209 (2000).

In the light diffusion plate of the present invention, the pencil hardness of the light scattering film is preferably HB or more, more preferably 2H or more. If the pencil hardness is HB or higher, damage to the film being handled can be suppressed.

The light diffusing plate of the present invention preferably has a haze of 90% or more, more preferably 93% or more when incident light from the normal direction to the first main surface of the glass plate is transmitted. Preferably it is 96% or more. When the haze is 90% or more, moderate diffusibility can be secured when used in a backlight unit.

In the light diffusing plate of the present invention, it is preferable that the average value of the straight transmittance at a wavelength of 400 to 700 nm transmitted in the incident direction out of the incident light from the normal direction to the first main surface is 15% or less. More preferably, it is 10% or less, More preferably, it is 5% or less. When the average value of the straight transmittance is 15% or less, luminance unevenness hardly occurs when the light diffusing plate is used in the backlight unit.

The average value of the straight transmittance can be obtained from the following equation by measuring the straight transmittance Ts at a wavelength of 400 to 700 nm for each wavelength of 1 nm.

In the above formula, n is an integer of 400 to 700.

In the light diffusing plate of the present invention, of the incident light from the normal direction to the first main surface, the average value of the total light transmittance at a wavelength of 400 to 700 nm transmitted in the incident direction is 4% or more. Preferably, it is 5% or more, more preferably 10% or more, particularly preferably 20% or more, and most preferably 30% or more.

When the average value of the total light transmittance is 4% or more, a luminance preferable for a backlight can be obtained. The average value of the total light transmittance is preferably as high as possible, but it is preferably 90% or less because the diffusibility is not impaired. More preferably, it is 85% or less, More preferably, it is 80% or less, Most preferably, it is 75% or less.

The average value of the total light transmittance can be obtained from the following equation by measuring the total light transmittance Tt for each wavelength of 1 nm at a wavelength of 400 to 700 nm.

In the above formula, n is an integer of 400 to 700.
The total light transmittance of the glass at a wavelength of 400 nm to 700 nm can be measured with a spectrophotometer or the like.

The difference in the definition of the two types of transmittance (straight-line transmittance Ts and total light transmittance Tt) described in the present invention will be described. When light hits an object, a part of the light is reflected, a part of the light entering the object is absorbed in the object, and the rest is emitted as transmitted light. The transmittance of this transmitted light is defined as the total light transmittance Tt. The total light transmitted light is divided into diffuse transmitted light diffused by the object and straight transmitted light that travels straight in the incident direction, and the transmittance of the straight transmitted light is defined as a straight transmitted transmittance Ts.

The light diffusing plate of the present invention preferably has a total light reflectance of 10% or more in a wavelength range of 400 to 700 nm when incident light from a normal direction to the first main surface is transmitted through the glass plate. More preferably, it is 20% or more, more preferably 25% or more, and further preferably 30% or more. Moreover, it is preferable that it is 96% or less, More preferably, it is 95% or less, More preferably, it is 90% or less.

Since the total light reflectance when incident light from the normal direction to the first main surface is transmitted is 10% or more, luminance unevenness hardly occurs when the light diffusing plate is used in the backlight unit. Further, when the total light reflectance is 90% or less, luminance necessary for a backlight can be obtained.

In the present invention, the total light reflectance when incident light from the normal direction to the first main surface is transmitted means the average value of the reflectance of each wavelength measured in the wavelength range of 400 nm to 700 nm. *

The light diffusing plate of the present invention has an average transmittance of incident light from the normal direction to the first principal surface at a wavelength of 400 to 700 nm transmitted in the direction of 30 ° with respect to the normal of the glass plate. Is preferably 0.2% or more, more preferably 0.3% or more, and still more preferably 0.4% or more. Further, it is preferably 10% or less, more preferably 8% or less, and further preferably 5% or less.

The average value of the transmittance of incident light from the normal direction to the first main surface at a wavelength of 400 to 700 nm transmitted in the direction of 30 ° with respect to the normal line of the glass plate is 0.2% or more. Thus, the luminance necessary for the backlight can be obtained. Moreover, moderate light diffusibility can be ensured because the transmittance is 10% or less.

The transmittance of light transmitted in the direction of 30 ° with respect to the normal of the glass plate by incident light from the normal direction to the first main surface at a wavelength of 400 to 700 nm depends on the thickness of the glass plate. The thickness of the glass plate is the thickness of the target light diffusion plate, and the transmittance at the thickness of the light diffusion plate is the transmittance.

The light diffusing plate of the present invention is a ratio of the total light reflectance to the total light transmittance in the wavelength range of 400 to 700 nm when the incident light from the normal direction to the first main surface is transmitted (total light reflectance / The total light transmittance) is preferably 0.25 or more, more preferably 0.3 or more, and still more preferably 0.4 or more. When the ratio is 0.25 or more, luminance necessary for a backlight can be obtained. Although an upper limit is not specifically limited, It is preferable that it is 2 or less.

The light diffusing plate of the present invention has a transmittance (30 ° in the direction of 30 ° with respect to the normal in the wavelength range of 400 to 700 nm when incident light from the normal direction to the first main surface is transmitted. The ratio between the transmittance) and the transmittance in the straight line direction (straight forward transmittance) (30 ° transmittance / straight forward transmittance) is preferably 0.05 or more, more preferably 0.2 or more, and still more preferably. It is 0.5 or more. When the ratio is 0.05 or more, light from the backlight can be diffused favorably.

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 arithmetic average roughness (Ra) of the first main surface is not particularly limited, but is preferably 0.05 nm or more, more preferably 0.1 nm or more. It is. Moreover, although an upper limit is not specifically limited, It is preferable that it is 3000 nm or less, More preferably, it is 2000 nm or less, More preferably, it is 1000 nm or less.

The arithmetic average roughness Ra of the glass plate on the first main surface of the glass plate can be adjusted by selecting the abrasive grains or the polishing method. The light diffusing plate of the present invention has a light scattering film on at least one of the first main surface and the second main surface of the glass plate, and the main surface having or not having the light scattering film. Alternatively, other coatings may be applied as necessary. Examples of other coatings include silica, titania, and alumina coatings.

The arithmetic average roughness Ra of the first main surface of the glass plate can be measured based on 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 glass plate used for the light diffusing plate of the present invention preferably has a thickness of 0.05 to 3 mm, more preferably 0.1 to 2.5 mm, and still more preferably 0.5 to 2 mm. . By setting the thickness of the glass plate to 0.05 mm or more, the strength as a light diffusion plate can be maintained and an appropriate function can be exhibited. Moreover, the stress by the temperature distribution of the thickness direction by the heat | fever from a light source can fully be weakened by the plate | board thickness of a glass plate being 3 mm or less.

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 240 mm or more. Moreover, it is preferable that it is 2500 mm or less. By setting the size of at least one side of the glass plate to 200 mm or more, it is possible to provide a diffusion plate that takes advantage of the rigidity of the glass.

The wavelength dependence of the total light transmittance of the glass plate used in the light diffusing plate of the present invention is that when the light source used is an LED, it passes through the light diffusing plate and other optical sheets from the viewpoint of the wavelength spectrum of the emission line. It is preferable that the total light transmittance of the light diffusing plate has wavelength dependency so that the emitted light is white.

The wavelength dependency of the total light transmittance of the glass plate used for the light diffusing plate of the present invention can be adjusted as appropriate depending on the glass composition.

The light diffusion plate of the present invention can be suitably used for a backlight unit such as a liquid crystal television or a liquid crystal monitor. In the backlight unit 1 shown in FIG. 1, a light diffusion sheet 5, a prism sheet 6, and a polarization separation sheet 7 are sequentially provided on the light diffusion plate 4. 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 can have the function of a light diffusing sheet. When the light diffusing plate of the present invention has the function of the light diffusing sheet 5, the light diffusing sheet 5 can be omitted.

Since the light diffusion plate of the present invention has high heat resistance and light resistance, when used in a backlight unit, the distance between the light source and the light diffusion plate can be reduced to improve the luminance uniformity. Therefore, the light diffusing plate of the present invention can improve the uniformity of luminance as compared with the conventional resin light diffusing plate. Specifically, the distance between the light source and the light diffusion plate is preferably less than 10 mm.

Next, the manufacturing method of the light diffusing plate of this invention is demonstrated.
The production method of the present invention includes a step of applying a dispersion containing an organopolysiloxane precursor and particles to a glass plate, and a step of obtaining a light scattering film by curing the dispersion applied to the glass plate.

Since the glass plate has already been described, the description thereof is omitted.
The dispersion includes an organopolysiloxane precursor and inorganic oxide particles. The organopolysiloxane precursor is a substance that forms an organopolysiloxane by dehydration condensation by hydrolysis, and is specifically alkoxysilane. As the alkoxysilane, a compound represented by the following formula (1) is preferable.
(R ¹ ) _4-n- Si- (OR ² ) _n (1)
(In the formula (1), n is an integer of 0 to 4, and R ¹ is an alkyl group having 1 to 3, 6, 8, or 10 carbon atoms, a vinyl group, an amino group, a styryl group, a methacryl group, an acrylic group, An organic group such as an epoxy group or a phenyl group, preferably a methyl group, an ethyl group, a propyl group, or a phenyl group, and R ² is a methyl group, an ethyl group, or a propyl group, preferably a methyl group or an ethyl group.

As the alkoxysilane, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane and the like are more preferable. These may be used alone or in combination of two or more as long as they form an organopolysiloxane by dehydration condensation. More preferred is a mixture of tetraethoxysilane and methyltrimethoxysilane.
The molar ratio of tetraethoxysilane to methyltrimethoxysilane in the above mixture is particularly preferably 2/8 to 8/2. If tetraethoxysilane is in this range, the mechanical strength is improved, and if methyltrimethoxysilane is in this range, cracks are difficult to occur, and a decrease in light scattering due to cracks can be suppressed.

The refractive index of the inorganic oxide particles is preferably 1.45 or less, more preferably 1.43 or less. Since the inorganic oxide particles have already been described, the description thereof will be omitted.

In the step of applying the dispersion on the glass plate, the application method is not particularly limited, and examples thereof include spin coating, spray coating, die coating, roll coating, bar coating, squeegee coating, and ink jet method. It is done.

In the step of curing the dispersion applied to the glass plate to obtain a light scattering film, the method for curing the dispersion is not particularly limited, and photocuring or heat curing can be applied. As light curing, ultraviolet curing is preferable. Thermosetting is more preferable.

The heat curing is preferably performed at 100 ° C. to 800 ° C. The heat treatment temperature is more preferably 150 ° C. to 700 ° C., further preferably 200 ° C. to 600 ° C. When the heat treatment temperature is 100 ° C. or higher, sufficient film strength can be easily obtained, and by increasing the heat treatment temperature, the organic components in the organopolysiloxane are thermally decomposed to improve water resistance and light resistance. If the heat treatment temperature is 800 ° C. or lower, breakage and deformation of the glass plate can be suppressed.

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

[Manufacture of light diffusion plate]
(Example 1)
0.54 parts by mass of 11.31 parts by mass of water and 10% by mass nitric acid aqueous solution were added to 49.69 parts by mass of industrial alcohol (manufactured by Nippon Alcohol Sales Co., Ltd., trade name: Solmix AP1). Thereafter, 19.42 parts by mass of tetraethoxysilane (TEOS) and 19.04 parts by mass of methyltrimethoxysilane (MTMS) were added and stirred at room temperature for 1 hour to obtain a binder liquid. This binder liquid contains 14.0 mass% of solid content converted to silica in 100 mass% of the binder liquid, and the molar ratio of MTMS to TEOS (MTMS / TEOS) is 6/4. This binder liquid forms an organic-inorganic composite compound (organopolysiloxane) by hydrolysis and condensation.
60 parts by mass of the obtained binder liquid, 24 parts by mass of porous silica particles (manufactured by Nissan Chemical Industries, trade name: Light Star LA-23A) and 36 parts by mass of 2-propanol were mixed to obtain a dispersion. The porous silica particles have an average particle diameter of 0.65 μm, a specific surface area of 240 m ² / g, and a peak value of pore diameter of 16 nm.
The above dispersion was applied to the surface of a 2 mm thick soda lime glass plate (Asahi Glass Co., Ltd., trade name: transparent float plate glass AS) using a bar coater (Imoto Seisakusho Co., Ltd., product number: DOS50), and then at 150 ° C. Sample 1 was obtained by heat treatment for 10 minutes, then at 300 ° C. for 30 minutes, and further at 150 ° C. for 10 minutes.

(Example 2)
48.54 parts by mass of TEOS was added to 39.61 parts by mass of industrial alcohol (Japan Alcohol Sales Company, trade name: Solmix AP1) to obtain a binder liquid. Sample 2 was obtained in the same manner as in Example 1 except that this binder solution was used. This binder liquid forms an organic-inorganic composite by hydrolysis condensation.
(Examples 3 to 5)
The amounts of TEOS and MTMS were adjusted so that the molar ratio of MTMS to TEOS (MTMS / TEOS) in the binder solution was the value shown in Table 1, respectively. Samples 3 to 5 were obtained in the same manner as in Example 1 except that this binder solution was used. These binder liquids form an organic-inorganic composite compound (organopolysiloxane) by hydrolysis and condensation.

(Examples 6 and 7)
The amount of porous silica particles added to the binder liquid was changed so that the particle content in the dispersion would be the value shown in Table 2, respectively.

Samples

6 and 7 were obtained in the same manner as in Example 1 except that this binder solution was used.
(Examples 8 and 9)
Samples 8 and 9 were obtained in the same manner as in Example 1 except that the bar coater used when applying the dispersion was changed and the film thickness was changed to the value shown in Table 2. In Example 8, the bar coater used was Imoto Seisakusho, product number: DOS30, and in Example 9, Imoto Seisakusho, product number: DOS9.

(Example 10)
A sample was obtained in the same manner as in Example 1 except that 60 parts by mass of the binder liquid, 24 parts by mass of spherical titania particles (product number: ST-41, manufactured by Ishihara Sangyo Co., Ltd.) and 36 parts by mass of 2-propanol were mixed. 10 was obtained. The spherical titania particles used are not porous but dense.
(Example 11)
Sample 11 was obtained in the same manner as in Example 1 except that polyvinyl alcohol (trade name; polyvinyl alcohol 2000, manufactured by Kanto Chemical Co., Inc.) was used instead of the binder liquid.

[Evaluation methods]
The characteristics of the obtained samples of Examples 1 to 11 were evaluated by the following methods.
In addition, the thickness of the glass plate and the light scattering film of the obtained light diffusing plate was obtained by cutting a part of the light diffusing plate with a cutter and measuring the difference in height between the exposed glass plate surface and the light scattering film surface with a laser microscope (Keyence Corporation). (Trade name: Laser microscope VK-X110).

(1) Heat resistance A part of the light scattering film was peeled off from each sample using a cutter knife. The peeled light scattering film was heated from room temperature to 400 ° C. at a heating rate of 10 / min using a thermal analyzer (trade name: TG-DTA Thermoplus EVO, manufactured by Rigaku Corporation) and then held at 400 ° C. for 30 minutes. The weight change rate was measured. Moreover, the color of the light-scattering film | membrane after a measurement was observed visually.
(2) Pencil hardness The pencil hardness of the light scattering film was measured according to JIS K5600-5-4 (1999). For the measurement, a load variation type friction wear system (manufactured by Shinto Kagaku Co., Ltd., trade name: HHS-2000) was used.
(3) Haze The haze value of the light diffusing plate was measured by a haze meter (trade name: HZ-2, manufactured by Suga Test Instruments Co., Ltd.) by a method based on JIS K7136 (2000).

(4) Total light transmittance The light is incident on the surface of each sample where the light scattering film is formed, and the total light transmittance is measured using an integrating sphere in the wavelength range of 400 nm to 700 nm. The average value of transmittance was determined. A spectrophotometer (trade name: U-4100, manufactured by Hitachi, Ltd.) was used for the measurement.
(5) Total light reflectivity Light is incident on the surface of each sample on which the light scattering film is formed at an incident angle of 5 °, and the total light is applied using an integrating sphere in the wavelength range of 400 nm to 700 nm. The reflectance was measured, and the average value of the reflectance at each wavelength was determined. A spectrophotometer (trade name: U-4100, manufactured by Hitachi, Ltd.) was used for the measurement.

(6) Straight transmittance and 30% transmittance Installed so that light is incident on the side where the light scattering film of each sample is formed, and 0 ° (straight transmittance) on the same horizontal plane with respect to the normal of the sample. The transmittance of light having a wavelength of 400 nm to 700 nm transmitted in the direction of 30 ° (30% transmittance) was measured, and the average value of the transmittance at each wavelength was determined. For the measurement, an ultraviolet-visible infrared spectrophotometer (manufactured by JASCO Corporation, product name: V-670DS) and an automatic absolute reflectance measurement unit (manufactured by JASCO Corporation, product number: ARMN-735) were used.
(7) Cracks The film surface of each sample was observed at a magnification of 100 times using an optical microscope to determine the presence or absence of cracks.

The above evaluation results are shown in Tables 1 and 2. In Tables 1 and 2, “-” indicates that it has not been evaluated.

In Example 2 in which MTMS was not used, cracks occurred. Since the matrix of the light-scattering film is an inorganic substance (silica), the Young's modulus is increased, and the stress generated by solvent drying or film curing shrinkage cannot be alleviated and cracks are likely to occur.
Example 11 using polyvinyl alcohol instead of the binder liquid showed a large weight reduction and discoloration in the heat resistance test. It is considered that the heat resistance was insufficient because the matrix of the light scattering film was made of an organic substance.

Example 10 using dense titania particles has higher total light reflectivity than total light transmittance compared to Example 13 and the like. It is considered that light is refracted excessively and returns to the incident light side because the refractive index of the particles is large with respect to the matrix.

The light diffusing plate of the present invention is useful as a member of a backlight unit in a display element such as a liquid crystal television and a liquid crystal monitor.
It should be noted that the entire content of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2016-11213 filed on January 25, 2016 is cited herein as the disclosure of the specification of the present invention. Incorporate.

1: Direct type backlight unit, 2: Reflecting plate, 3: Light source, 4: Light diffusion plate, 5: Light diffusion sheet, 6: Prism sheet, 7: Polarization separation sheet, 40: Glass plate, 41: Light scattering film 42: Matrix 43: Particles

Claims

A glass plate having a first main surface and a second main surface opposite to the first main surface is provided, and is emitted from the second main surface while diffusing light incident on the first main surface. A light diffusing plate,
The glass plate is provided with a light scattering film on at least one of the first main surface and the second main surface, and has a thermal expansion coefficient of −100 × 10 −7 to 500 × 10 −7 / ° C. ,
The light scattering film includes a matrix and particles, the matrix includes an organic-inorganic composite compound, and the particles are inorganic oxide particles having a refractive index smaller than that of the matrix. Diffusion plate.
2. The light diffusing plate according to claim 1, wherein the light scattering film has a thickness of 0.1 to 100 μm.
The light diffusing plate according to claim 1 or 2, wherein the organic-inorganic composite compound is an organopolysiloxane.
The inorganic oxide particles according to any one of claims 1 to 3, wherein the inorganic oxide particles have fine pores having an average particle diameter of 0.1 to 50 µm and a peak value of the pore diameter of 2 to 50 nm. Light diffusion plate.
The light diffusion plate according to any one of claims 1 to 4, wherein the volume ratio of the inorganic oxide particles in the light scattering film is 25 to 95 vol%.
The light diffusing plate according to any one of claims 1 to 5, wherein a haze is 90% or more when incident light from a normal direction to the first main surface of the glass plate is transmitted.
The incident light from the normal direction to the first main surface of the glass plate has an average value of total light transmittance of 4% or more at a wavelength of 400 to 700 nm transmitted in the incident direction. The light diffusing plate according to any one of the above.
Of the incident light from the normal direction to the first main surface of the glass plate, the average transmittance of light having a wavelength of 400 to 700 nm transmitted in the direction of 30 ° with respect to the normal of the glass plate is 0.2. The light diffusion plate according to any one of claims 1 to 7, wherein the light diffusion plate is at least%.
Ratio of total light reflectance and total light transmittance in a wavelength range of 400 to 700 nm when incident light from the normal direction to the first main surface of the glass plate is transmitted (total light reflectance / total light transmittance). The light diffusing plate according to any one of claims 1 to 8, wherein) is 0.25 or more.
A transmittance in a direction of 30 ° with respect to the normal (30 ° transmittance) in a wavelength range of 400 to 700 nm when incident light from the normal direction to the first main surface of the glass plate is transmitted; The light diffusing plate according to any one of claims 1 to 9, wherein a ratio of transmittance in a straight traveling direction (straight traveling transmittance) (30 ° transmittance / straight traveling transmittance) is 0.05 or more.
The light diffusing plate according to any one of claims 1 to 10, wherein a thickness of the glass plate is 0.05 to 3 mm.
The light diffusing plate according to any one of claims 1 to 11, wherein a dimension of at least one side of the glass plate is 200 mm or more.
A method for producing a light diffusing plate, wherein a dispersion containing an organopolysiloxane precursor and inorganic oxide particles having a refractive index of 1.45 or less is applied to a glass plate, and the dispersion is cured to form a light scattering film.
The method for producing a light diffusing plate according to claim 13, wherein the dispersion is cured by thermosetting, and the thermosetting is performed at a heat treatment temperature of 100 to 800 ° C.