JP2022049869A - Optical sheet, backlight unit, and liquid crystal display device - Google Patents

Abstract

To provide an optical sheet capable of performing suitable color conversion even when the content of fluorescent agent is relatively low, a backlight unit having the optical sheet, and a liquid crystal display device having the backlight unit.SOLUTION: An optical sheet 10 is disposed in a liquid crystal display device having a plurality of light sources dispersedly arranged on the rear side of a display screen, between the plurality of light sources and a prism sheet, and comprises a color conversion layer 11 containing a fluorescent agent 13 and a diffusing agent 14.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical sheet, a backlight unit, and a liquid crystal display device.

A liquid crystal display device (liquid crystal display) is widely used as a display device in various information devices such as smartphones and tablets. Examples of the backlight used in the liquid crystal display include a direct type method in which a plurality of light sources are arranged on the back side of the liquid crystal panel.

In the direct type backlight, a light emitting diode (LED) element is often used as the light source, and for example, a so-called blue LED element that emits blue light is used. When an LED element is used as the light source, a light emitting device or the like is used in which the light emitted from the light source is color-converted so as to approach white light and emitted.

Examples of the light emitting device for such color conversion include the light emitting device described in Patent Document 1. Patent Document 1 includes a semiconductor light emitting element and a fluorescent member arranged apart from the semiconductor light emitting element, and the fluorescent member absorbs a part of the light emitted from the semiconductor light emitting element and converts it into other light. The fluorescent member can be converted and emit light, and the fluorescent member has a first portion located at a first distance from the semiconductor light emitting element and a second portion located at a position farther than the first distance, and the first portion is a second portion. A light emitting device having a higher absorption rate of light emitted from a semiconductor light emitting element than that of a portion is described.

Japanese Patent Application Laid-Open No. 2003-142737

According to Patent Document 1, the ratio of the amount of light emitted from the light emitting element to the amount of light whose wavelength is converted by the fluorescent member can be made substantially uniform in the entire fluorescent member, and the color rendering property is excellent and the color is uneven. It is disclosed that a small amount of uniform emission color can be obtained. In the light emitting device described in Patent Document 1, a fluorescent substance is contained in a reflector portion formed around the semiconductor light emitting element, and a mixed color light of visible light from the semiconductor light emitting element and visible light from the fluorescent substance is mixed. Is white light. Patent Document 1 also describes that by incorporating a light diffusing agent in the reflector portion, it can be reflected and scattered by the light diffusing agent to obtain a uniform emission color with less color unevenness.

On the other hand, in the direct type backlight unit, unlike the light emitting device described in Patent Document 1, the light emitted from the semiconductor light emitting element is not reflected by the reflector unit, but is between the light source and the prism sheet. It is also conceivable to arrange an optical sheet. Specifically, by arranging an optical sheet capable of converting the color of the transmitted light by transmitting the light emitted from the LED element between the light source and the prism sheet, the light source irradiates the light source. It is also conceivable to color-convert the light to be brought closer to white light. As such a color-convertable optical sheet, it is conceivable to contain a fluorescent agent. In such an optical sheet, in order to transmit the light emitted from the LED element to obtain white light, it is necessary to highly fill the fluorescent agent, but since the fluorescent agent is generally expensive, fluorescence is applied. It is required to reduce the amount of agent used. That is, there is a demand for an optical sheet having excellent color conversion properties so that suitable color conversion can be performed even if the content of the fluorescent agent is relatively small.

The present invention has been made in view of such circumstances, and an optical sheet capable of performing suitable color conversion even when the content of the fluorescent agent is relatively low, a backlight unit provided with the optical sheet, and the backlight. It is an object of the present invention to provide a liquid crystal display device provided with a unit.

As a result of various studies, the present inventors have found that the above object can be achieved by the following invention.

The optical sheet according to one aspect of the present invention is an optical sheet located between the plurality of light sources and a prism sheet in a liquid crystal display device in which a plurality of light sources are dispersedly provided on the back side of a display screen. An optical sheet comprising a color conversion layer containing a fluorescent agent and a diffusing agent.

According to such a configuration, it is possible to provide an optical sheet capable of suitable color conversion even if the content of the fluorescent agent is relatively low. That is, the content of the fluorescent agent can be reduced in order to realize the same degree of color conversion as when the diffuser is not contained.

Further, in the optical sheet, the diffusing agent preferably contains at least one of silicone beads and titanium oxide particles.

According to such a configuration, the content of the fluorescent agent can be further reduced in order to realize the same degree of color conversion as in the case where the diffuser is not contained. Therefore, an optical sheet having excellent color conversion properties can be obtained.

Further, in the optical sheet, the content of the diffusing agent is preferably 0.1 to 30% by mass with respect to the color conversion layer.

According to such a configuration, it is possible to obtain an optical sheet capable of suitable color conversion while suppressing deterioration of processability due to the inclusion of the diffusing agent.

Further, in the optical sheet, the fluorescent agent preferably contains a green fluorescent agent and a red fluorescent agent.

According to such a configuration, an optical sheet capable of more suitable color conversion can be obtained. Specifically, when the light transmitted through the optical sheet is blue light, the blue light is absorbed by the green fluorescent agent contained in the color conversion layer of the optical sheet and converted to the green side from the blue light. Can radiate light. Further, the blue light transmitted through the optical sheet can be absorbed by the red fluorescent agent contained in the color conversion layer of the optical sheet, and the light converted to the red side from the blue light can be emitted. The mixed color light of these converted lights will be converted to the yellow side. Then, the light transmitted through the optical sheet is converted to the white light side by this mixed color light. Therefore, the optical sheet can perform suitable color conversion.

Further, in the optical sheet, the content of the fluorescent agent is preferably 7.5 to 14.5% by mass with respect to the color conversion layer.

According to such a configuration, an optical sheet capable of suitable color conversion can be obtained without increasing the content of the fluorescent agent too much.

Further, it is preferable that the optical sheet further includes a light diffusing layer, and the light diffusing layer is in contact with the color conversion layer.

According to such a configuration, suitable color conversion can be performed, and further, the effect of the light diffusion layer such as increasing the brightness can be exhibited. Further, since the optical sheet is provided with the light diffusion layer in contact with the color conversion layer, a problem occurs due to the combination of the color conversion sheet including the color conversion layer and the light diffusion sheet including the light diffusion layer. Can be suppressed. Specifically, when the color conversion sheet and the light diffusion sheet are combined, it is possible to prevent dust and the like from interposing between the sheets. Further, it is possible to prevent the color conversion sheet and the light diffusion sheet from being damaged due to contact with each other. Therefore, the optical sheet can perform suitable color conversion, can also exert the effect of the light diffusion layer such as increasing the brightness, and further, dust and the like intervening between the layers and damage to each layer. Etc. can be suppressed.

Further, in the optical sheet, the thickness of the color conversion layer is preferably 10 to 1000 μm.

According to such a configuration, an optical sheet capable of suitable color conversion can be obtained.

Further, the backlight unit according to another aspect of the present invention includes a plurality of light sources, a prism sheet, and an optical sheet located between the plurality of light sources and the prism sheet. It is a backlight unit characterized by being the above-mentioned optical sheet.

According to such a configuration, it is possible to provide a backlight unit capable of irradiating light with suitable color conversion.

Further, in the backlight unit, it is preferable that the light source is a light emitting diode element that irradiates blue light.

According to such a configuration, it is possible to provide a backlight unit capable of irradiating blue light from the light source and irradiating white light obtained by appropriately color-converting the irradiated blue light.

Further, the liquid crystal display device according to another aspect of the present invention is a liquid crystal display device including the backlight unit and a liquid crystal panel provided on the prism sheet side of the backlight unit. ..

According to such a configuration, the backlight unit irradiates light with suitable color conversion, so that a liquid crystal display device capable of displaying an image on the liquid crystal panel can be obtained.

According to the present invention, it is possible to provide an optical sheet capable of performing suitable color conversion even if the content of the fluorescent agent is low, a backlight unit including the optical sheet, and a liquid crystal display device including the backlight unit. ..

FIG. 1 is a schematic cross-sectional view of an optical sheet according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a backlight unit including an optical sheet according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing an example of the configuration of a liquid crystal display device including the backlight unit shown in FIG.

Hereinafter, embodiments according to the present invention will be described, but the present invention is not limited thereto.

As shown in FIG. 1, the optical sheet 10 according to an embodiment of the present invention includes a color conversion layer 11 containing a fluorescent agent 13 and a diffusing agent 14. The optical sheet 10 may be a sheet made of the color conversion layer 11, or may be a sheet including the color conversion layer 11 and a layer other than the color conversion layer 11 (the color conversion layer 11). Examples of the layer other than the color conversion layer 11 include a light diffusion layer 12. That is, examples of the optical sheet 10 include, as shown in FIG. 1, an optical sheet 10 including the color conversion layer 11 and the light diffusion layer 12 in contact with the color conversion layer 11. .. Note that FIG. 1 is a schematic cross-sectional view of the optical sheet 10 according to the present embodiment.

The optical sheet 10 is an optical sheet located between the plurality of light sources and a prism sheet in a liquid crystal display device provided with a plurality of light sources dispersed on the back side of a display screen. As the optical sheet 10, for example, as shown in FIGS. 2 and 3, in the backlight unit 20 provided in the liquid crystal display device 30, a plurality of light sources dispersedly provided on the back surface side of the liquid crystal display device 30. It is an optical sheet located between 22 and the prism sheets 24 and 25. Note that FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the backlight unit 20 including the optical sheet 10 according to the present embodiment. Further, FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the liquid crystal display device 30 including the backlight unit 20 shown in FIG. 2.

When the optical sheet 10 contains the fluorescent agent 13, the transmitted light can be color-converted by transmitting the light emitted from the light source in the backlight unit provided in the liquid crystal display device. By containing not only the fluorescent agent 13 but also the diffuser 14, the optical sheet 10 can perform suitable color conversion even if the content of the fluorescent agent 13 is relatively low. That is, in the optical sheet 10, the content of the fluorescent agent 13 can be reduced in order to realize the same degree of color conversion as when the diffusing agent is not contained (conventional color conversion sheet, wavelength conversion sheet, etc.). can. Since fluorescent agents are generally expensive, it is required to reduce the amount of fluorescent agents used, and the optical sheet 10 can achieve this requirement. That is, the amount of expensive fluorescent agent used can be reduced. This is considered to be due to the following. The light transmitted through the optical sheet 10 hits the diffusing agent 14 contained in the optical sheet 10, and the optical path becomes long. In that case, the chance that the transmitted light hits the fluorescent agent 13 increases. From this, it is considered that the color conversion by the fluorescent agent can be suitably performed. Therefore, it is considered that suitable color conversion can be performed even with a relatively small amount of the fluorescent agent.

As shown in FIG. 1, the color conversion layer 11 is not particularly limited as long as it is a layer containing the fluorescent agent 13 and the diffusing agent 14 and capable of transmitting light. The color conversion layer 11 includes, for example, the fluorescent agent 13 and the diffuser 14, and as a binder, a layer further containing a translucent resin, and the fluorescent agent 13, the diffuser 14, and the translucent layer. Examples thereof include a layer made of a resin having a property.

The fluorescent agent 13 is not particularly limited, and examples thereof include a fluorescent agent capable of absorbing light and emitting the absorbed light with a longer wavelength. Examples of the fluorescent agent 13 include a yellow fluorescent agent that is excited by blue light and emits yellow light (a yellow fluorescent agent that can absorb blue light and convert it to a yellow side from the blue light) and blue light. A green fluorescent agent that is excited by and emits green light (a green fluorescent agent that can emit light that absorbs blue light and converts it to the green side from the blue light), and red that is excited by blue light and emits red light. Examples thereof include a fluorescent agent (a red fluorescent agent capable of absorbing blue light and radiating light converted to a red side from the blue light). Examples of the yellow fluorescent agent include YAG and LSN. Examples of the green fluorescent agent include β-SiAlON and LuAG. Examples of the red fluorescent agent include KSF and CASN.

Further, as shown in FIG. 1, the fluorescent agent 13 preferably contains the green fluorescent agent 15 and the red fluorescent agent 16, and the fluorescent agent 13 preferably contains the green fluorescent agent 15 and the red fluorescent agent 16. It may be composed of 16. In such a case, for example, when the light transmitted through the optical sheet is blue light, the blue light may be absorbed by the green fluorescent agent and emitted light converted to the green side from the blue light. can. Further, the blue light transmitted through the optical sheet can be absorbed by the red fluorescent agent contained in the color conversion layer of the optical sheet, and the light converted to the red side from the blue light can be emitted. The mixed color light of these converted lights will be converted to the yellow side. Then, the light transmitted through the optical sheet is converted to the white light side by this mixed color light. Therefore, the optical sheet can perform suitable color conversion. The content ratio of the green fluorescent agent to the red fluorescent agent varies depending on the type of the fluorescent agent and the like, but the mass ratio is preferably 6: 3 to 6:18, preferably 6: 6 to 6:12. Is more preferable, and 6: 9 is particularly preferable. When the content ratio of the green fluorescent agent and the red fluorescent agent is within the above range, the light transmitted through the optical sheet can be suitably converted to the white light side by the mixed color light obtained by the fluorescent agent. can. Therefore, an optical sheet capable of more preferably color conversion can be obtained.

The content of the fluorescent agent 13 varies depending on the type of the fluorescent agent and the like, but is preferably 7.5 to 14.5% by mass with respect to the total amount of the color conversion layer, for example. If the amount of the fluorescent agent is too small, it tends to be difficult to realize a suitable color conversion. That is, although the content of the fluorescent agent can be reduced by containing the diffuser in the optical sheet, if the amount of the fluorescent agent is too small, it becomes difficult to realize suitable color conversion. Further, if the amount of the fluorescent agent is too large, suitable color conversion can be realized, but the requirement for reducing the content of the fluorescent agent cannot be satisfied. Specifically, even if the diffusing agent is not contained, if the content of the fluorescent agent is about 15% by mass, suitable color conversion can be performed, so that the content of the fluorescent agent is higher than 15% by mass. Therefore, the requirement to reduce the content of the fluorescent agent cannot be satisfied. Further, even if the amount of the fluorescent agent is too large, the color conversion effect of the fluorescent agent tends to be saturated. Therefore, in the optical film according to the present embodiment, by containing the diffusing agent, an optical sheet capable of suitable color conversion can be obtained even if the content of the fluorescent agent 13 is within the above range.

The particle size of the fluorescent agent 13 is not particularly limited as long as the color conversion can be realized by containing the fluorescent agent in the optical sheet. The particle size of the fluorescent agent 13 is, for example, preferably 5 to 100 μm in volume average particle size, and more preferably 10 to 40 μm. If the fluorescent agent is too small or too large, there is a tendency that color conversion cannot be performed satisfactorily. It is considered that this is because if the fluorescent agent is too small, it becomes difficult to hit the light transmitted through the optical sheet. Further, it is considered that when the fluorescent agent is too large, the fluorescent agents tend to be separated from each other, which makes it difficult to hit the light transmitted through the optical sheet. Therefore, the fluorescent agent 13 can more preferably perform color conversion of the obtained optical sheet when the particle size is within the above range.

The diffusing agent 14 is not particularly limited as long as it is contained in the optical sheet and exhibits a light diffusing effect. Examples of the diffusing agent 14 include inorganic particles and organic particles contained as a diffusing agent contained in a general light diffusing sheet. Examples of the inorganic particles include silica particles, titanium oxide particles, aluminum hydroxide particles, barium sulfate particles and the like. Examples of the organic particles include acrylic particles, acrylic nitrile particles, silicone beads, polystyrene particles, polyamide particles and the like. Of these, silicone beads and titanium oxide particles are preferable.

The content of the diffusing agent 14 varies depending on the type of the diffusing agent and the like, but is preferably 0.1 to 30% by mass, preferably 0.5 to 30% by mass, based on the total amount of the color conversion layer, for example. % Is more preferable. When the diffusing agent is silicone beads, the content of the diffusing agent is preferably 1 to 30% by mass, preferably 5 to 30% by mass, based on the total amount of the color conversion layer. Is more preferable. When the diffusing agent is titanium oxide particles, the content of the diffusing agent is preferably 0.1 to 10% by mass, preferably 1 to 10% by mass, based on the total amount of the color conversion layer. Is more preferable. If the amount of the diffusing agent is too small, it tends to be difficult to achieve the effect of adding the diffusing agent, that is, the effect that suitable color conversion can be realized even if the content of the fluorescent agent is reduced. Further, if the amount of the diffusing agent is too large, the effect of adding the diffusing agent tends to be saturated. Further, if the amount of the diffusing agent is too large, there is a tendency that problems due to the addition of the diffusing agent, for example, problems such as deterioration of the processability of the obtained optical film, are likely to occur. Therefore, when the content of the diffusing agent is within the above range, an optical sheet capable of suitable color conversion can be obtained while suppressing the occurrence of defects due to the addition of the diffusing agent.

The particle size of the diffusing agent 14 is not particularly limited as long as it can exert a light diffusing effect, and varies depending on the type of the diffusing agent and the like, but is, for example, 0.05 to 10 μm in volume average particle size. Is preferable. When the diffusing agent is silicone beads, the particle size of the diffusing agent is preferably 0.5 to 10 μm in terms of volume average particle size. When the diffuser is titanium oxide particles, the particle size of the diffuser is preferably 0.05 to 1 μm in terms of volume average particle diameter. If the diffusing agent is too small or too large, there is a tendency that color conversion cannot be performed satisfactorily. It is considered that this is because when the diffusing agent is too small, it becomes difficult to hit the light transmitted through the optical sheet, and it becomes difficult to exert the effect of lengthening the optical path by hitting the diffusing agent. Further, if the diffuser is too large, it is considered that the light transmitted through the optical sheet is less likely to hit the fluorescent agent. Further, it is considered that the diffusing agents tend to be separated from each other, which makes it difficult for the light to hit the light transmitted through the optical sheet, and makes it difficult to exert the effect of lengthening the optical path by hitting the diffusing agent. .. Therefore, the diffuser 14 can more preferably perform color conversion of the obtained optical sheet when the particle size is within the above range.

Examples of the binder include a translucent resin (translucent resin) and the like. Examples of the translucent resin include acrylic resin, polystyrene, polycarbonate, methylmethacrylate-styrene copolymer, polyethylene terephthalate, polyethylene naphthate, cellulose acetate, and polyimide. Further, as the translucent resin, it is preferable to use an ultraviolet (UV) curable resin. When a UV curable resin is used as the binder, the fluorescent agent and the diffuser are added to the UV curable resin before curing, and the UV curable resin before curing to which these are added can be used as a substrate or light. It is preferable in that a color conversion layer can be obtained by applying it to a diffusion layer or the like and irradiating it with UV. Examples of the UV curable resin include a UV curable acrylic resin and the like.

As described above, the optical sheet 10 may include the color conversion layer 11 and further include the light diffusion layer 12. As described above, by including the light diffusing layer, the optical sheet can perform suitable color conversion, and can also exert the effect of the light diffusing layer such as increasing the brightness. Further, as shown in FIG. 1, it is preferable that the light diffusion layer 12 is in contact with the color conversion layer 11. In this way, when the light diffusion layer and the color conversion layer are provided in contact with each other, it is possible to suppress the occurrence of defects due to the combination of the color conversion sheet provided with the color conversion layer and the light diffusion sheet provided with the light diffusion layer. .. Specifically, when the color conversion sheet and the light diffusion sheet are combined, it is possible to prevent dust and the like from interposing between the sheets. Further, it is possible to prevent the color conversion sheet and the light diffusion sheet from being damaged due to contact with each other. Therefore, the optical sheet can perform suitable color conversion, can also exert the effect of the light diffusion layer such as increasing the brightness, and further, dust and the like intervening between the layers and damage to each layer. Etc. can be suppressed.

The light diffusing layer 12 is not particularly limited as long as it is a layer that exerts a light diffusing effect, and examples thereof include a general light diffusing sheet. Examples of the light diffusion layer include a layer having at least one surface having an uneven shape. That is. Both surfaces of the light diffusing layer may have an uneven shape, or only one surface may have an uneven shape. In addition, examples of the light diffusion layer include a layer in which one surface of the light diffusion layer has an uneven shape and the other surface has a matte shape. When a layer having an uneven shape on one surface and a mat shape on the other surface is used as the light diffusion layer, the color conversion layer is on the mat shape side of the light diffusion layer as the optical sheet. Examples include sheets provided for.

Examples of the shape of the convex portion in the concave-convex shape include a semicircular spherical shape (spherical shape in the upper half), a conical shape, and a polygonal pyramid shape. Examples of the polygonal pyramid include a triangular pyramid, a quadrangular pyramid, and a hexagonal pyramid. The shape of the convex portion includes a shape that can be approximated to the shape of the convex portion, for example, a shape that can be approximated to a conical shape (substantially conical shape), a shape that can be approximated to a polygonal pyramid shape (substantially polygonal pyramid shape), and the like. It may be. In addition, examples of the shape of the concave portion in the concave-convex shape include a shape corresponding to the shape of the convex portion, for example, an inverted semicircular spherical shape (inverted spherical shape in the upper half), an inverted conical shape, an inverted polygonal pyramid shape, and the like. Can be mentioned. Examples of the inverted polygonal pyramid include an inverted triangular pyramid, an inverted quadrangular pyramid, and an inverted hexagonal pyramid. The shape of the concave portion includes a shape that can be approximated to the shape of the concave portion, for example, a shape that can be approximated to an inverted conical shape (substantially inverted conical shape) and a shape that can be approximated to an inverted polygonal pyramid shape (substantially inverted polygonal pyramid shape). ) Etc. may be used. Further, when a plurality of convex portions and a plurality of concave portions are two-dimensionally arranged in the concave-convex shape, the convex portions and the concave portions may be provided on the front surface of the surface of the light diffusion layer, or may be provided at a constant interval. It may be provided at random intervals, or it may be provided at random intervals.

The light diffusing layer 12 may contain a diffusing agent (second diffusing agent), for example, a layer containing the second diffusing agent and further containing a translucent resin as a binder, and the above. Examples thereof include a layer made of a second diffusing agent and a translucent resin.

The diffusing agent (second diffusing agent) contained in the light diffusing layer 12 is not particularly limited as long as it is contained in the optical sheet and exhibits a light diffusing effect, and is, for example, the color conversion. Examples thereof include the same diffusing agent as the diffusing agent (first diffusing agent) contained in the layer 11, such as silicone beads and titanium oxide particles. Further, the particle size of the second diffusing agent may be the same as that of the first diffusing agent. The content of the second diffusing agent when the second diffusing agent is contained varies depending on the type of the diffusing agent and the like, but is, for example, 4% by mass or less with respect to the total amount of the light diffusing layer. It is preferable, and it is more preferable that it is 2% by mass or less. The second diffusing agent may not be contained (the content of the second diffusing agent may be 0% by mass).

The binder (second binder) contained in the light diffusion layer 12 is not particularly limited as long as it is a translucent resin (translucent resin), and is contained in, for example, the color conversion layer 11. Examples thereof include the same translucent resin as the binder (first binder) to be used. Examples of the second binder include acrylic resin, polystyrene, polycarbonate, methyl methacrylate-styrene copolymer, polyethylene terephthalate, polyethylene naphthate, cellulose acetate, and polyimide.

The thickness of the color conversion layer 11 varies depending on the concentration of the fluorescent agent and the like, and is not particularly limited. The lower limit of the thickness of the color conversion layer 11 is, for example, preferably 10 μm or more, and more preferably 50 μm or more. The upper limit of the thickness of the color conversion layer 11 is, for example, preferably 1000 μm or less, more preferably 500 μm or less, further preferably 300 μm or less, and particularly preferably 200 μm or less. preferable. When the optical sheet 10 does not include another layer such as the light diffusion layer 12, the thickness of the color conversion layer 11 is preferably, for example, 50 to 1000 μm, preferably 100 to 500 μm. Is more preferable. When the optical sheet 10 includes another layer such as the light diffusion layer 12, the thickness of the color conversion layer 11 is preferably, for example, 10 to 500 μm, preferably 50 to 200 μm. More preferred. If the color conversion layer 11 is too thin, the color conversion effect produced by the color conversion layer tends to be insufficiently exhibited. Further, if the color conversion layer 11 is too thin or too thick, there is a risk of problems due to it. For example, the workability of the obtained optical sheet may decrease. Further, if the color conversion layer 11 is too thick, the obtained optical sheet becomes thick, and it becomes difficult to contribute to the miniaturization of the backlight unit and the final product, the liquid crystal display device.

The thickness of the light diffusion layer 12 is not particularly limited, and is preferably, for example, 50 to 1000 μm, more preferably 100 to 500 μm. If the light diffusing layer 12 is too thin, the light diffusing effect exerted by the light diffusing layer tends not to be sufficiently exerted. Further, if the light diffusion layer 12 is too thin or too thick, there is a risk of problems due to it. For example, the workability of the obtained optical sheet may decrease. Further, if the light diffusion layer 12 is too thick, the obtained optical sheet becomes thick, and it becomes difficult to contribute to the miniaturization of the backlight unit and the final product, the liquid crystal display device.

With the above configuration, the optical sheet 10 can perform suitable color conversion even if the content of the fluorescent agent is relatively low. Further, as described above, the optical sheet 10 is an optical sheet located between the plurality of light sources and the prism sheet in a liquid crystal display device in which a plurality of light sources are dispersedly provided on the back side of the display screen. ..

The method for manufacturing the optical sheet 10 is not particularly limited as long as the optical sheet 10 can be manufactured. When the optical sheet 10 includes the color conversion layer 11 and the light diffusing layer 12, as a method for manufacturing the optical sheet 10, for example, a liquid binder to which the fluorescent agent and the diffusing agent are added is used. Examples thereof include a method of manufacturing the optical sheet 10 by forming the color conversion layer 11 on the light diffusion layer 12 by solidifying the binder after coating on the light diffusion layer 12. When a UV curable resin is used as the binder, examples of the solidifying method include a method of irradiating UV to cure the binder.

The backlight unit provided in the liquid crystal display device is not particularly limited as long as it includes the optical sheet. That is, the backlight unit according to the present embodiment includes a plurality of light sources, a prism sheet, and an optical sheet located between the plurality of light sources and the prism sheet, and the optical sheet is the above-mentioned optical sheet. It is a backlight unit. The backlight unit provided with such an optical sheet can irradiate light that has been suitably color-converted. Specifically, as shown in FIG. 2, the backlight unit 20 includes a reflective sheet 21, a plurality of light sources 22, an optical sheet 10, a first prism sheet 24, and a second prism sheet 25. A polarizing sheet 26 is provided. The plurality of light sources 22 are arranged two-dimensionally on the reflective sheet 21. The optical sheet 10 is an optical sheet according to the present embodiment, and is located between the light source 22 and the first prism sheet 24. The first prism sheet 24 and the second prism sheet 25 are located between the optical sheet 10 and the polarizing sheet 26, and the first prism sheet 24 is arranged on the optical sheet 10 side. Therefore, the second prism sheet 25 is arranged on the polarizing sheet 26 side.

The reflective sheet 21 is not particularly limited, and examples thereof include a reflective sheet provided in a general backlight unit. Examples of the reflective sheet 21 include a white polyethylene terephthalate resin film, a silver-deposited film, and the like.

The light source 22 is not particularly limited, and examples thereof include a light source provided in a general backlight unit. As the light source 22, a so-called small light source can be used, and examples thereof include a light emitting diode (LED) element and a laser element. Among these, LED elements are preferably used from the viewpoint of cost, productivity and the like. Further, the light source 22 is preferably a blue LED element that irradiates blue light. The optical sheet can suitably color-convert the blue light emitted from the light source into white light or the like. From this, the backlight unit 20 can irradiate blue light from the light source and irradiate white light obtained by appropriately color-converting the irradiated blue light. Further, the light source 22 may have a rectangular shape when viewed in a plan view, and in that case, the length of one side is preferably 10 μm to 20 mm, more preferably 10 μm to 10 mm, and 50 μm. It is more preferably to 5 mm. When the LED element is used as the light source 22, the LED chips may be arranged on the reflective sheet 21 at regular intervals. Further, a lens may be attached to the LED in order to adjust the emission angle characteristic of the LED element serving as the light source 22.

The first prism sheet 24 and the second prism sheet 25 are not particularly limited, and examples thereof include a prism sheet provided in a general backlight unit. As the first prism sheet 24 and the second prism sheet 25, for example, a plurality of grooves having an isosceles right cross section are formed so as to be adjacent to each other, and the apex angle of a prism composed of a pair of adjacent grooves is formed. Examples thereof include a film formed at about 90 °. Examples of the first prism sheet 24 and the second prism sheet 25 include those obtained by forming a prism shape on a polyethylene terephthalate (PET) film using a UV curable acrylic resin. In the first prism sheet 24 and the second prism sheet 25, each groove formed on the first prism sheet 24 and each groove formed on the second prism sheet 25 are orthogonal to each other. Is placed in. The first prism sheet 24 and the second prism sheet 25 may be integrally formed.

The polarizing sheet 26 is not particularly limited, and examples thereof include a polarizing sheet provided in a general backlight unit. As the polarizing sheet 26, a commercially available product can be used, and examples thereof include the DBEF series manufactured by 3M.

The liquid crystal display device is not particularly limited as long as it includes the backlight unit. That is, the liquid crystal display device according to the present embodiment is a liquid crystal display device including the backlight unit and a liquid crystal panel provided on the prism sheet side of the backlight unit. In such a liquid crystal display device, since the light that has been appropriately color-converted is irradiated from the backlight unit provided with the optical sheet, the image can be suitably displayed on the liquid crystal panel. As shown in FIG. 3, the liquid crystal display device 30 includes a backlight unit 20, a liquid crystal panel 35, and a first polarizing plate 36 and a second polarizing plate 37. The liquid crystal panel 35 is located between the first polarizing plate 36 and the second polarizing plate 37, and the first polarizing plate 36 is arranged on the backlight unit 20 side.

The liquid crystal panel 35 includes a thin film transistor (TFT) substrate 31 and a color filter (CF) substrate 32 provided so as to face each other, and a liquid crystal layer 33 provided between the TFT substrate 31 and the CF substrate 32. To prepare for. Further, the liquid crystal panel 35 further includes a sealing material (not shown) provided in a frame shape for enclosing the liquid crystal layer 33 between the TFT substrate 31 and the CF substrate 32.

The TFT substrate 31 is not particularly limited, and examples thereof include a TFT substrate provided in a general liquid crystal display device. The TFT substrate 31 includes, for example, a glass substrate, a plurality of TFTs provided in a matrix on the glass substrate, an interlayer insulating film provided so as to cover each of the TFTs, and an interlayer insulating film. Examples thereof include a substrate provided with a plurality of pixel electrodes provided in a matrix and connected to each of the plurality of TFTs, and an alignment film provided so as to cover each of the pixel electrodes.

The CF substrate 32 is not particularly limited, and examples thereof include a CF substrate provided in a general liquid crystal display device. The CF substrate 32 includes, for example, a glass substrate, a black matrix provided in a grid pattern on the glass substrate, and a red layer, a green layer, and a blue layer provided between the grids of the black matrix, respectively. Examples thereof include a substrate provided with a color filter, a common electrode provided so as to cover the black matrix and the color filter, and an alignment film provided so as to cover the common electrode.

The liquid crystal layer 33 is not particularly limited, and examples thereof include a liquid crystal layer provided in a general liquid crystal display device. Examples of the liquid crystal layer 33 include a liquid crystal layer made of a nematic liquid crystal material containing liquid crystal molecules having electro-optic characteristics.

The first polarizing plate 36 and the second polarizing plate 37 are not particularly limited, and examples thereof include a polarizing plate provided in a general liquid crystal display device. The first polarizing plate 36 and the second polarizing plate 37 include, for example, a polarizing layer having a polarization axis in one direction and a pair of protective layers provided so as to sandwich the polarizing layer. Examples include boards.

The shape of the display screen 30a of the liquid crystal display device 30 as viewed from the front (upper side in FIG. 3) is not particularly limited. This shape is often rectangular or square, but is not limited to this, and may be any shape such as a rectangular shape with rounded corners, an ellipse, a circle, a trapezoid, or an instrument panel (instrument panel) of an automobile. You may.

The liquid crystal display device 30 applies a voltage of a predetermined magnitude to the liquid crystal layer 33 in each sub-pixel corresponding to each of the pixel electrodes to change the orientation state of the liquid crystal layer 33, and the backlight unit. An image is displayed by adjusting the transmittance of light incident from 20 via the first polarizing plate 36 and emitting it through the second polarizing plate 37.

The liquid crystal display device 30 includes various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, mobile information terminals, portable game machines, copy machines, ticket vending machines, automatic cash deposit / payment machines, etc.). It is used as a display device incorporated in.

Hereinafter, the present invention will be described in more detail by way of examples, but the scope of the present invention is not limited thereto.

[Example 1-1]
As the light diffusion layer, the optical sheet according to Example 1 described in JP-A-2020-86432 was used.

6% by mass of green fluorescent agent (β-SiAlON, volume average particle diameter 16 μm), 9% by mass of red fluorescent agent (KSF, volume average particle diameter 30 μm), diffuser (silicone beads, volume average particle diameter 2 μm). As shown in Table 1, each was added to the (liquid) UV curable resin (UV curable acrylic resin) before curing so as to be 1% by mass. The content of the fluorescent agent was 15% by mass in total of the green fluorescent agent and the red fluorescent agent.

The liquid thus obtained (coating liquid for forming a color conversion layer) was applied to one side of the diffusion plate. At that time, the coating liquid for forming the color conversion layer was applied so that the thickness of the finally obtained color conversion layer was about 130 μm. Then, by irradiating the coated coating liquid for forming a color conversion layer with UV to cure the UV curable resin, an optical sheet having a color conversion layer formed on the diffusion plate was obtained. ..

[Examples 1-2 to 1-7]
Each optical sheet according to Examples 1-2 to 1-7 was manufactured by the same method as in Example 1 except that the content of the silicone beads as a diffusing agent was changed to the content shown in Table 1.

[Comparison example]
For each optical sheet according to the comparative example, an optical sheet was obtained by the same method as in Example 1 except that the coating liquid for forming the color conversion layer did not contain a diffusing agent.

[Examples 2-1 to 2-4]
Each optical sheet according to Examples 2-1 to 2-4 uses titanium oxide particles (volume average particle diameter 0.05 μm) instead of silicone beads as a diffusing agent, and the content thereof is changed to Table 2. It was manufactured by the same method as in Example 1 except for the above.

[evaluation]
(Saturation)
The optical sheet is provided 5 mm from the upper surface of the blue LED elements (blue LED array) arranged in an array, and two prism sheets arranged so that the grooves are orthogonal to each other are placed on the optical sheet. Assembled the backlight unit. The chromaticity (x, y) of the light emitted from this backlight unit was measured with a luminance meter (spectral radiance meter SR-3 manufactured by Topcon Corporation).

(Difference in chromaticity from blue light: Δx, Δy)
Then, the difference (Δx, Δy) between the chromaticity (x, y) of the obtained light and the chromaticity (x_B, y_B) of the light emitted from the blue LED element was calculated from the following formula. Here, the difference (Δx, Δy) from the chromaticity (x_B, y_B) of the light emitted from the blue LED element is defined as the chromaticity difference from the blue light.

Δx = x-x_B
Δy = yy_B
The chromaticity (x_B, y_B) of the light emitted from the blue LED element was 0.1529 for x_B and 0.0281 for y_B.

(Concentration of fluorescent agent)
The fluorescent agent estimated to be necessary to achieve the obtained chromaticity without containing a diffuser was defined as the conversion concentration of the fluorescent agent. That is, if the diffusing agent was not contained, the concentration of the fluorescent agent estimated to be necessary to satisfy the chromaticity of each example (when the diffusing agent was contained) was defined as the conversion concentration of the fluorescent agent. Here, it is estimated assuming that the chromaticity difference from blue light is directly proportional to the concentration of the fluorescent agent. Specifically, the chromaticity difference (Δx_e, Δy_e) from the blue light in the optical sheet according to each embodiment, the chromaticity difference (Δx_c, Δy_c) from the blue light in the optical sheet according to the comparative example, and the fluorescent agent. It was calculated from the following formula using the total concentration Cf. Here, Cf was 15% by mass.

Converted concentration of fluorescent agent (mass%) = 0.5 × (Δx_e / Δx_c + Δy_e / Δy_c) × Cf × 100
(Total concentration of fluorescent agent / conversion concentration)
Next, the ratio of the total concentration of the fluorescent agent to the converted concentration (total concentration of the fluorescent agent / converted concentration) (%) was calculated. It can be seen that, for example, when this ratio is 60%, the chromaticity equivalent to that in the case where the diffusing agent is not contained can be achieved at a concentration of 60% of the concentration of the fluorescent agent required when the diffusing agent is not contained. That is, it can be seen that the lower the ratio (total concentration of fluorescent agent / converted concentration), the more the desired chromaticity can be obtained even if the concentration of the fluorescent agent is lowered.

(Required estimated concentration of fluorescent agent)
The total concentration of the fluorescent agent required to achieve the same chromaticity as the chromaticity in the case where the diffusing agent was not contained (the optical sheet according to the comparative example) was estimated. Specifically, the value obtained by multiplying the total concentration of the fluorescent agents actually used by the ratio (total concentration of the fluorescent agents / converted concentration) was taken as the required estimated concentration (% by mass) of the fluorescent agent.

The above results are shown in Tables 1 and 2.

As can be seen from Tables 1 and 2, when the diffusing agent is contained (Examples 1-1 to 1-7 and Examples 2-1 to 2-4), the case where the diffusing agent is not contained (comparative example) Although the concentration of the fluorescent agent is the same, the difference in chromaticity from the blue light is large, and it can be seen that the color conversion is suitable. Therefore, it can be seen that when the diffusing agent is contained, an optical sheet capable of suitable color conversion can be obtained even if the content of the fluorescent agent is relatively low. This can be seen from the values estimated from the obtained chromaticity differences such as the conversion concentration of the fluorescent agent, the ratio (total concentration of the fluorescent agent / conversion concentration), and the required estimated concentration (mass%) of the fluorescent agent.

Further, from the comparison of Examples 1-1 to 1-7 and the comparison of Examples 2-1 to 2-4, the higher the content of the diffusing agent, the more suitable the fluorescent agent for performing color conversion. It can also be seen that the content tends to be low. On the other hand, it can also be seen that even if the content of the diffusing agent is too high, the effect on color conversion tends to be saturated. Further, it is considered that if the content of the diffusing agent is high, the processability of the obtained optical sheet is lowered. Therefore, when the diffusing agent is silicone beads, it can be seen that the content of the diffusing agent is preferably 1 to 30% by mass with respect to the total amount of the color conversion layer. Further, when the diffusing agent is titanium oxide particles, it can be seen that it is preferably 0.1 to 10% by mass with respect to the total amount of the color conversion layer.

Further, as the diffusing agent, from the comparison between Examples 1-1 to 1-7 and Examples 2-1 to 2-4, the titanium oxide particles have a fluorescent agent content for performing suitable color conversion. It turns out that it may be less. From this, it can be seen that as the diffusing agent, silicone beads and titanium oxide particles are preferable, and titanium oxide particles are more preferable.

Next, in order to further clarify that the content of the fluorescent agent for performing suitable color conversion can be reduced by containing the diffusing agent, the following was confirmed.

[Example 3]
The optical sheet according to Example 3 was the same as in Example 2-4 except that the total concentration of the fluorescent agent was changed to 8.2% by mass without changing the ratio of the green fluorescent agent and the red fluorescent agent. And manufactured.

From Table 3, it can be seen that by containing the fluorescent agent, the same degree of chromaticity can be achieved even if the content of the fluorescent agent is small. Specifically, it can be seen that the content of the fluorescent agent can be reduced to about 55% by containing titanium oxide in an amount of 10% by mass as a diffusing agent.

10 Optical sheet 11 Color conversion layer 12 Light diffusion layer 13 Fluorescent agent 14 Diffusing agent 15 Green fluorescent agent 16 Red fluorescent agent 20 Backlight unit 21 Reflective sheet 22 Light source 24 1st prism sheet 25 2nd prism sheet 26 Polarizing sheet 30 Liquid crystal display Equipment 31 TFT substrate 32 CF substrate 33 Liquid crystal layer 35 Liquid crystal panel 36 First polarizing plate 37 Second polarizing plate

Claims (10)

An optical sheet located between the plurality of light sources and a prism sheet in a liquid crystal display device in which a plurality of light sources are dispersedly provided on the back side of a display screen.
An optical sheet comprising a color conversion layer containing a fluorescent agent and a diffusing agent. The optical sheet according to claim 1, wherein the diffusing agent contains at least one of silicone beads and titanium oxide particles. The optical sheet according to claim 1 or 2, wherein the content of the diffusing agent is 0.1 to 30% by mass with respect to the color conversion layer. The optical sheet according to any one of claims 1 to 3, wherein the fluorescent agent contains a green fluorescent agent and a red fluorescent agent. The optical sheet according to any one of claims 1 to 4, wherein the content of the fluorescent agent is 7.5 to 14.5% by mass with respect to the color conversion layer. With an additional light diffusion layer,
The optical sheet according to any one of claims 1 to 5, wherein the light diffusion layer is in contact with the color conversion layer. The optical sheet according to any one of claims 1 to 6, wherein the color conversion layer has a thickness of 10 to 1000 μm. With multiple light sources
With a prism sheet,
An optical sheet located between the plurality of light sources and the prism sheet is provided.
The backlight unit according to any one of claims 1 to 7, wherein the optical sheet is the optical sheet. The backlight unit according to claim 8, wherein the light source is a light emitting diode element that irradiates blue light. The backlight unit according to claim 8 or 9,
A liquid crystal display device including a liquid crystal panel provided on the prism sheet side of the backlight unit.

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