KR102393476B1 - Light diffusing sheet, and backlight device comprising said sheet - Google Patents

Abstract

An object of the present invention is to provide a light-diffusing sheet in which local luminance unevenness and local light leakage are reduced while suppressing a decrease in luminance in a backlight device as much as possible by having high light diffusivity.
In order to solve the above problems, the light diffusing sheet of the present invention is a light diffusing sheet having a light diffusing layer, wherein the light diffusing layer includes a binder resin, light diffusing resin particles and inorganic fine particles, and the light diffusing sheet includes The Y value according to the D65 light source transmission measurement method of JIS Z 8722: 2000 is 0.3 or more and 2.1 or less, and the inorganic fine particles are, for example, one or two or more of zirconium oxide, titanium oxide, and zinc oxide, and binder resin (solid content) It is characterized in that it contains 40 to 480 parts by weight based on 100 parts by weight.

Description

Light diffusing sheet and backlight device including said sheet

The present invention relates to a light diffusing sheet and a backlight device including the sheet.

There are an edge light type and a direct type backlight device used for display devices and the like, and in recent years, the edge light type has become mainstream due to the demand for thinness and weight reduction of the device. In an edge light type backlight device, a light guide plate is used in combination with a light source such as an LED or a cold cathode tube, and an optical member such as a light diffusing film is inserted on the light guide plate. As the light-diffusing sheet, a high-diffusion type light-diffusing sheet having particularly high diffusivity is often used.

As such a light-diffusing sheet, Patent Document 1 proposes a light-diffusing sheet that improves the luminance in the front direction of the display screen while satisfying the original performance of the light-diffusing sheet for making the pattern installed on the light guide plate invisible.

Japanese Patent Laid-Open No. 6-59107

In recent years, there is a tendency to narrow the frame of the display screen in order to use the display unit of the display device combined with the backlight device as wide as possible. As a result, the portion close to the light source of the backlight device is also included in the display area, and it is desired to reduce the luminance unevenness in the vicinity of the light source of the display unit, for example, and to uniformize the luminance of the entire display surface including making light leakage at the end of the light guide plate inconspicuous. is becoming However, in the case of the light diffusing sheet of Patent Document 1, the problem of reducing the luminance non-uniformity in the vicinity of the light source of the display unit and making the light leakage at the end of the light guide plate inconspicuous is not taken into consideration.

Moreover, in order to achieve uniformity of brightness|luminance in general, it is considered to improve the light diffusivity of the light diffusable sheet|seat, a film, etc. which are inserted into a backlight device. And in order to obtain this high light diffusivity, in the conventional method, the type, particle size, amount, etc. of the resin particles (light diffusing material) in the light diffusing layer were changed in order to make the light diffusing layer a coating film having a high haze value. However, in the case of these means, the haze value reaches a critical point at a certain high value, and even with such a high haze value, a coating film that sufficiently reduces the luminance non-uniformity and light leakage described above cannot be obtained. There were problems such as falling.

An object of the present invention is to provide a light-diffusing sheet having high light diffusivity, thereby suppressing a decrease in brightness in a backlight device as much as possible while reducing local brightness non-uniformity and local light leakage.

In order to achieve the above object, the present inventors, as an indicator of light diffusivity, use "Y value (brightness)" according to the CIE (International Commission on Illumination)-XYZ color system, not the haze value (JIS K7105), which has been widely used in this field. As a result of evaluating "high light diffusivity", it was discovered that the above-mentioned luminance non-uniformity and the light leakage of an edge part can be improved by making Y value into a specific range, and this invention has been reached.

That is, the light diffusing sheet of the present invention is a light diffusing sheet having a light diffusing layer, wherein the light diffusing layer includes a binder resin, light diffusing resin particles and inorganic fine particles, and the light diffusing sheet is JIS Z 8722:2000 It is characterized in that the Y value according to the transmission measurement method of the D65 light source is 0.3 or more and 2.1 or less.

Further, in the light diffusing sheet of the present invention, the inorganic fine particles and the binder can take the following aspects based on the above characteristics.

The inorganic fine particles are high refractive index metal oxides having a higher refractive index than that of the binder resin.

The refractive index of the inorganic fine particles is 1.9 or more.

The high refractive index metal oxide is at least one selected from zirconium oxide, titanium oxide and zinc oxide.

The inorganic fine particles are zirconium oxide, and 120 to 320 parts by weight are included with respect to 100 parts by weight of the binder resin (solid content).

The binder resin includes an acrylic polyol resin having a glass transition temperature of 30° C. or less.

The binder resin further includes an acrylic polyol resin having a glass transition temperature of 40° C. or higher.

When the total of the acrylic polyol resin (solid content) having a glass transition temperature of 30°C or less and the acrylic polyol resin (solid content) having a glass transition temperature of 40°C or higher is 100 parts by weight, the acrylic polyol resin having a glass transition temperature of 30°C or less is 50 more than parts by weight.

In addition, the light diffusing sheet of the present invention is characterized in that the total light transmittance is 45% to 88%.

In addition, the light-diffusing sheet of the present invention is a binder resin, 60 to 120 parts by weight of the light-diffusing resin particles based on 100 parts by weight of the binder resin (solid content), and 40 to 480 parts by weight based on 100 parts by weight of the binder resin (solid content) Including inorganic fine particles, the refractive index of the inorganic fine particles is 1.9 or more, the Y value according to the transmission measurement method of the D65 light source of JIS Z 8722: 2000 is 0.3 or more and 2.1 or less, and the total light transmittance is 45% to 88%. .

In addition, the backlight device of the present invention includes a reflective sheet, a light guide plate provided above the reflection sheet, a light source disposed on a side surface of the light guide plate, a light diffusing sheet disposed on a light exit surface side of the light guide plate, and light output of the light diffusing sheet A prism sheet arranged on a surface side is provided, and the light diffusing sheet of the present invention is used as the light diffusing sheet.

In addition, the backlight device of the present invention includes a light source, a diffusion plate disposed on one side of the light source, a reflective film disposed on the other side of the light source, a light diffusing sheet disposed above the diffusion plate, and a light exit surface of the light diffusing sheet A prism sheet disposed on the side is provided, and the light diffusing sheet of the present invention is used as the light diffusing sheet.

In the present invention, the light-diffusing sheet includes a film-like material, and the light-diffusing sheet of the present invention includes a single layer of a light-diffusing layer and a layer in which a light-diffusion layer is laminated on a support such as a transparent substrate. do.

ADVANTAGE OF THE INVENTION According to this invention, the light-diffusion sheet which has high light-diffusion property can be provided by making Y value into a target range. In addition, it is possible to provide a light diffusing sheet in which local luminance unevenness and local light leakage are reduced while suppressing a decrease in luminance as much as possible when inserted into a backlight device.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows one Embodiment of the light-diffusion sheet of this invention.
Fig. 2 is a schematic diagram showing one embodiment of a backlight device using the light diffusing sheet of the present invention.
Fig. 3 is a schematic view showing another embodiment of a backlight device using the light diffusing sheet of the present invention.
4 is a graph showing the results of Example 15;
5 is a graph showing the results of Examples 17 to 19;

EMBODIMENT OF THE INVENTION Below, embodiment of the light-diffusion sheet of this invention is described.

The light diffusing sheet of the present invention is a light diffusing sheet having a light diffusing layer, wherein the light diffusing layer includes a binder resin, light diffusing resin particles, and inorganic fine particles. The light diffusing sheet has a Y value of 0.3 or more and 2.1 or less according to the D65 light source transmission measurement method of JIS Z 8722:2000. The Y value, which is one of the tristimulus values, takes a value from 0 to 100, and the lower the Y value, the lower the luminous transmittance and the higher the hiding property. In the present invention, by setting the Y value within the above-mentioned range, it is possible to prevent luminance unevenness and light leakage on the display surface without lowering the luminance of a display device to which the light diffusing sheet of the present invention is applied.

The Y value is determined by the elements constituting the light-diffusing sheet, particularly the elements constituting the light-diffusion layer, and by adjusting these, the target Y value can be realized. A specific configuration for realizing the above-described Y value will be described below.

As long as the structure of the light-diffusion sheet of this invention contains a light-diffusion layer, the light-diffusion layer single layer may be sufficient, and the light-diffusion layer laminated|stacked on the support body may be sufficient. Moreover, as long as the function of a light-diffusion layer is not impaired, you may have another layer (a light-diffusion layer is included). For example, as shown in FIG. 1, the light-diffusion sheet|seat of this embodiment may contain the light-diffusion layer 11, the support body 12, and a backcoat layer.

Next, the configuration of the light diffusion layer will be described. The light-diffusion layer contains at least a binder resin, light-diffusing resin particles, and inorganic fine particles.

As binder resin of a light-diffusion layer, an ionizing-radiation-curable resin, a thermosetting resin, a thermoplastic resin, etc. are mentioned.

As the ionizing radiation curable resin, a photopolymerizable prepolymer that can be crosslinked and cured by irradiation with ionizing radiation (ultraviolet rays or electron beams) can be used. As this photopolymerizable prepolymer, two or more acryloyl groups in one molecule are crosslinked and cured to three-dimensionally. The acrylic prepolymer used as a network structure is used especially preferably. As this acrylic prepolymer, urethane acrylate, polyester acrylate, epoxy acrylate, melamine acrylate, polyfluoroalkyl acrylate, silicone acrylate, etc. can be used. In addition, although these acrylic prepolymers can be used individually, it is preferable to add a photopolymerizable monomer in order to improve crosslinking-hardenability and to further improve the hardness of a light-diffusion layer.

Examples of the photopolymerizable monomer include monofunctional acrylic monomers such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and butoxyethyl acrylate, 1,6-hexanediol diacrylate, and neo Bifunctional acrylic monomers such as pentyl glycol diacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate and hydroxypivalate neopentyl glycol diacrylate, dipentaerythritol hexaacrylate, trimethylpropane triacrylate, 1 type, or 2 or more types, such as polyfunctional acrylic monomers, such as pentaerythritol triacrylate, are used.

In addition to the above-mentioned photopolymerizable prepolymer and photopolymerizable monomer, it is preferable to use additives, such as a photoinitiator and a photoinitiator, when hardening by ultraviolet irradiation.

Examples of the photopolymerization initiator include acetophenone, benzophenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoyl benzoate, α-acyloxime ester, and thioxanthone.

In addition, the photopolymerization accelerator is a thing capable of accelerating the curing rate by reducing the polymerization disturbance caused by air during curing, and examples thereof include p-dimethylaminobenzoic acid isoamyl ester and p-dimethylaminobenzoic acid ethyl ester.

As the thermosetting resin, silicone resin, phenol resin, urea resin, melamine resin, furan resin, unsaturated polyester resin, epoxy resin, diallyl phthalate resin, guanamine resin, ketone resin, amino alkyd resin Resin, a urethane-type resin, an acrylic resin, polycarbonate-type resin, etc. are mentioned. Although these can be used individually, it is preferable to add a hardening|curing agent in order to improve crosslinking|crosslinking property and the hardness of a crosslinking-hardened coating film more.

As a hardening|curing agent, compounds, such as a polyisocyanate, an amino resin, an epoxy resin, carboxylic acid, can be used suitably according to suitable resin.

As the thermoplastic resin, ABS resin, norbornene resin, silicone resin, nylon resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polybutylene terephthalate, polyethylene terephthalate, sulfone resin, imi De-based resin, fluorine-based resin, styrene-based resin, acrylic resin, vinyl chloride-based resin, vinyl acetate-based resin, vinyl chloride-vinyl acetate copolymer-based resin, polyester-based resin, urethane-based resin, rubber-based resin, polyvinyl ether, polyvinyl alcohol , polyvinyl butyral, polyvinylpyrrolidone, polyethylene glycol, and the like.

Moreover, it is preferable to use the thermosetting resin of an acrylic resin or a thermoplastic resin among these ionizing-radiation-hardenable resin, a thermosetting resin, or a thermoplastic resin from a viewpoint of obtaining the coating-film strength and favorable transparency when it is set as a resin layer. Moreover, these thermosetting resins or thermoplastic resins can also be used as composite resin which combined multiple types, respectively.

In addition, the binder resin can adjust the properties of the light-diffusion layer by adjusting the glass transition temperature (Tg). For example, depending on the type of inorganic fine particles contained in the light diffusion layer, curling tends to occur when the amount increases. Therefore, from the viewpoint of preventing it, the binder resin preferably has a low glass transition temperature (Tg). Specifically, a low glass transition temperature (Tg) has a glass transition temperature of 30°C or less, preferably 20°C or less. On the other hand, when a binder resin with a high glass transition temperature is used, the front luminance of the light diffusing sheet can be increased. From such a viewpoint, the binder resin preferably has a high glass transition temperature (Tg). Specifically, those having a high glass transition temperature (Tg) have a glass transition temperature of 40°C or higher, preferably 50°C or higher. As the binder resin having the glass transition temperature (Tg), an acrylic polyol resin is preferable.

The glass transition temperature (Tg) of the binder resin can be adjusted by appropriately changing the type and ratio of monomer components such as an acrylic component and a styrene component in the resin, for example, in terms of an acrylic polyol resin. For example, the glass transition temperature of the styrene homopolymer is 100°C, and the glass transition temperature can be adjusted by selecting the acrylic monomer to be copolymerized therewith. Moreover, it is known that there exists a thing from 0 degreeC or less to 100 degreeC or more in an acrylic monomer, and a glass transition temperature can be adjusted by selecting the kind of acryl-type component. As an example, the glass transition temperature of styrene (St): methyl methacrylate (MMA): butyl acrylate (BA) = 20: 55: 25 is 46.2 °C (calculated value), but even with the same monomer composition, St: MMA: BA = In the case of 20:70:10, it can be set to 78.5°C (calculated value).

Representative examples of the monomer of the acrylic component include methacrylate-based monomers such as methyl methacrylate and ethyl methacrylate, acrylate-based monomers such as methyl acrylate and ethyl acrylate, hydroxyethyl methacrylate, and acrylamide. As the styrene-based monomer, styrene, α-methylstyrene, vinyltoluene, and the like can be exemplified as representative examples thereof. In the copolymerization of these monomers, other monomers may be copolymerized as necessary using these as a main component, a styrenic monomer graft-polymerized to a side chain of an acrylic resin, or an acrylic monomer graft-polymerized to a side chain of a styrenic resin.

Examples of commercially available acrylic polyol resins having a glass transition temperature of 30° C. or less include DIC’s brand name Acrydic A811 (Tg: 19° C.), brand name Acrydic 49-394IM (Tg: 16° C.), and brand name Acrydic 52-614 ( Tg: 16 degreeC), brand name Acridic 48-261 (Tg: 30 degreeC), etc. are illustrated.

On the other hand, commercially available acrylic polyol resins having a glass transition temperature of 40°C or higher include, for example, DIC's brand name Acrydic A817 (Tg: 96°C), brand name Acrydic A814 (Tg: 87°C), and brand name Acrydic A815-45 (Tg: 101 degreeC), brand name Acrydic A808 (Tg: 70 degreeC), etc. are illustrated.

In a suitable aspect of this embodiment, the binder resin contains the acrylic polyol resin whose glass transition temperature is 30 degrees C or less as a low glass transition temperature (Tg). In addition, the binder resin may include, in addition to the binder resin having a low glass transition temperature, an acrylic polyol resin having a glass transition temperature of 40° C. or higher as a binder resin having a high glass transition temperature.

When a resin with a low glass transition temperature (Tg) and a resin with a high glass transition temperature are used together, the mixing of both is a resin (solid content) ratio of a resin having a high glass transition temperature: a resin having a low glass transition temperature is 5 The range of :5-0:10 is preferable. In other words, when the total of the resin (solid content) with the low glass transition temperature and the resin (solid content) with the high glass transition temperature is 100 parts by weight, the binder resin preferably contains 50 parts by weight or more of the resin having the low glass transition temperature. For example, when the total of the acrylic polyol resin having a glass transition temperature of 30° C. or less and the acrylic polyol resin having a glass transition temperature of 40° C. or more is 100 parts by weight, the acrylic polyol resin having a glass transition temperature of 30° C. or less is preferably 50 parts by weight or more. Do.

Next, as the light-diffusing resin particles, materials generally used as light-diffusing resin particles can be used, and specifically, resins such as styrene resins, urethane resins, nylon resins, benzoguanamine resins, silicone resins, and acrylic resins. It is also possible to use particles. Among these, it is preferable to use an acrylic resin from a viewpoint of having high light transmittance and improving brightness|luminance performance. It is also possible to use these particle|grains not only by 1 type, but combining multiple types.

The size of the light diffusing resin particles is preferably 0.5 to 10 µm in average particle diameter, and more preferably 1 to 8 µm. By making an average particle diameter into 10 micrometers or less, a light-diffusion sheet|seat can be made thin, and light-diffusion property and front brightness can be made favorable by setting it as 0.5 micrometer or more. In particular, when only one type of average particle diameter is used as the light diffusing resin particles, it is more preferable that the average particle diameter is 1 to 4 µm.

Further, when two or more types of light diffusing resin particles having different average particle diameters are used in combination, it is preferable to combine particles having an average particle diameter of 1 to 4 µm with particles having a larger average particle diameter than that. As particle|grains with a large average particle diameter, it is preferable that it is 4-10 micrometers of average particle diameter, and it is more preferable that it is 5-8 micrometers. It is thought that by adding the particle|grains with a comparatively large average particle diameter, the flaw generation|occurrence|production of the light-diffusion layer by a foreign material etc. is suppressed. In the case of combining both, the ratio of particles with a large average particle diameter is preferably equal to or less than that of particles with a small average particle diameter, and in particular, the ratio of small particles to large particles is preferably in the range of 100:40 to 100:60.

Moreover, although the shape of a light-diffusion resin particle is not specifically limited, A thing close|similar to a true spherical shape particle|grains is preferable. With such a shape, the front luminance can be improved.

The refractive index of the light diffusing resin particles is not particularly limited, but it is preferable that the refractive index difference with the binder resin is small. The difference in refractive index between the binder resin and the particles is preferably 0.03 or less, more preferably 0.02 or less. By setting it as such a range, it is easy to reduce the light transmission loss by the internal haze in a light-diffusion layer. Since the refractive index of the above-mentioned binder resin is about 1.43 to 1.57, specifically, the refractive index of the light diffusing resin particles is preferably 1.40 to 1.60, more preferably 1.45 to 1.55.

The content ratio of the light-diffusing resin particles to the binder resin varies depending on the average particle diameter, but is preferably 60 to 220 parts by weight, more preferably 80 to 200 parts by weight, based on 100 parts by weight of the binder resin (solid content). About the particle|grains of the above-mentioned small average particle diameter, in order to exhibit required light diffusivity, 60-180 weight part is preferable with respect to 100 weight part of binder resin (solid content). It is more preferable to contain 80-120 weight part from a viewpoint of further improvement of front brightness. Since light diffusivity is mainly exhibited by the addition of particles with a small average particle diameter, particles with a large average particle diameter can be added without being limited to the content ratio of 180 parts by weight as long as it is within the range (equivalent to or less) of the ratio with respect to the small particles described above. there is.

The inorganic fine particles are added in order to obtain a predetermined Y value without reducing the luminance, and inorganic fine particles having a higher refractive index than that of the binder resin are preferable, and in particular, a high refractive index metal oxide or metal salt is preferable. 1.9 or more are preferable, as for the refractive index of an inorganic fine particle, 2.0 or more are more preferable, 2.3 or more are especially preferable. When the refractive index increases, the reflectance of light can be increased, and a low Y value can be realized even if the amount of inorganic fine particles added is reduced. In addition, when the light-diffusion layer is formed on the support by reducing the amount of the inorganic fine particles to be added, good adhesion of the light-diffusion layer to the support can be maintained.

As the high refractive index metal oxide or metal salt, lead hydroxycarbonate (2PbCO ₃ Pb(OH) ₂ ) (refractive index 1.94 to 2.09), titanium oxide (refractive index 2.71), zirconium oxide (refractive index 2.4), zinc oxide (refractive index 1.95), aluminum oxide (refractive index 1.76) etc. are used suitably.

Moreover, it is preferable that inorganic fine particles show white in a light-diffusion layer coating film. By using the inorganic fine particles exhibiting white color, the light diffusing sheet exhibits white color, and the effect of reducing the luminance unevenness in the vicinity of the light source of the backlight device can be enhanced to make the light leakage at the end of the light guide plate inconspicuous. Zirconium oxide, titanium oxide, and zinc oxide are particularly suitable among the above-mentioned inorganic fine particles as the inorganic fine particles exhibiting whiteness, and among them, zirconium oxide and titanium oxide are suitable.

The above-mentioned high refractive index metal oxide, metal salt, or white inorganic fine particles can be used not only by one type but also in combination of a plurality of types. By combining a plurality of types, it becomes easy to adjust the content as a whole of the inorganic fine particles, the Y value as a result, and other properties of the light-diffusion layer coating film, for example, the adhesion to the support and the anti-curling property.

The primary particle diameter of the inorganic fine particles is not particularly limited, and those having a range of 10 to 50 nm may be used. Most of these nanometer-order microparticles are contained in the diffusion layer as aggregates in the state dispersed in the light diffusion layer. By including the inorganic fine particles as an aggregate, not only does it become easy to obtain a predetermined Y value, but also the liquid manufacturing process is improved because an excessive dispersion process is not required. The average particle diameter (secondary particle diameter) of the aggregate is preferably 100 to 2,000 nm, more preferably 400 to 1,000 nm, from the viewpoint of obtaining high diffusivity while suppressing the decrease in luminance as much as possible by having a predetermined Y value or a predetermined whiteness. desirable. In addition, the particle diameter of the aggregate in the light diffusion layer can be measured with a transmission electron microscope (TEM), such as a cross section of the coating film.

In order to obtain the desired Y value, the blending amount of the inorganic fine particles to 100 parts by weight of the binder resin (solid content) varies depending on the type of inorganic fine particles, but preferably 40 parts by weight or more and 480 parts by weight or less, and 120 parts by weight or more to 320 parts by weight or more. It is more preferably not more than 160 parts by weight and more preferably from 160 parts by weight to 240 parts by weight or less.

When the inorganic fine particles are zirconium oxide, the lower limit of the blending amount of the inorganic fine particles with respect to 100 parts by weight of the binder resin (solid content) is preferably 120 parts by weight or more, more preferably 140 parts by weight or more, still more preferably 160 parts by weight or more, , the upper limit is preferably 320 parts by weight or less, more preferably 280 parts by weight or less, and still more preferably 240 parts by weight or less. By setting it as 120 parts by weight or more, the uniformity of the luminance is improved. By setting it as 320 parts by weight or less, the Y value is prevented from becoming too low.

When the inorganic fine particles are titanium oxide, the lower limit of the blending amount of the inorganic fine particles with respect to 100 parts by weight of the binder resin (solid content) is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, and the upper limit is preferably 130 parts by weight or less. and 120 parts by weight or less is more preferable, and 110 parts by weight or less is still more preferable. By setting it as 40 parts by weight or more, the uniformity of the luminance is improved. By setting it as 130 weight part or less, it prevents that a light-diffusion layer is colored yellow.

When the inorganic fine particles are zinc oxide, the lower limit of the blending amount of the inorganic fine particles with respect to 100 parts by weight of the binder resin (solid content) is preferably 200 parts by weight or more, more preferably 220 parts by weight or more, and still more preferably 240 parts by weight or more, , the upper limit is preferably 480 parts by weight or less, more preferably 420 parts by weight or less, and still more preferably 360 parts by weight or less. By setting it as 200 parts by weight or more, the uniformity of the luminance is improved. By setting it as 480 parts by weight or less, it is prevented that curling of the light diffusing sheet occurs remarkably.

In addition, as described above, since the range of suitable compounding amounts varies depending on the type of inorganic fine particles, when using a combination of a plurality of types of inorganic fine particles, the range of the total compounding quantity of the inorganic fine particles may be an intermediate range according to each compounding ratio. . As an example, when zirconium oxide and titanium oxide are used together, Preferably it is 80-200 weight part with respect to 100 weight part of binder resin (solid content) in both total, More preferably, it is set as 100-180 weight part.

In the light-diffusion layer, in addition to the binder resin, light-diffusing resin particles, and inorganic fine particles described above, additives such as surfactants such as leveling agents and antifoaming agents, antioxidants, and ultraviolet absorbers may be added.

The thickness of the light-diffusion layer is preferably 10-500 µm, more preferably 10-250 µm, when the light-diffusing sheet of the present invention is formed of a single light-diffusion layer. By making thickness into 10 micrometers or more, coating-film intensity|strength can be made sufficient and handling property can be made favorable. On the other hand, transparency of a light-diffusion layer can be made favorable by making thickness into 500 micrometers or less. Further, when the light diffusion layer is formed on the support, it is preferably 2 to 20 µm, more preferably 3 to 15 µm, from the viewpoint of easily obtaining the desired emission characteristics of the present invention while exhibiting the light diffusion performance. . In addition, the thickness of a light-diffusion layer means the thickness from the front-end|tip of the convex part of the uneven|corrugated surface of a light-diffusion layer to the light-diffusion layer surface opposite to an uneven|corrugated surface.

When the light-diffusing sheet of the present invention has a support, the support is not particularly limited as long as it does not deviate from the range of the Y value, so long as it is a plastic film with high optical transparency, it can be used. For example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, acryl, polyvinyl chloride, norbornene compound, etc. can be used. Among them, a polyethylene terephthalate film subjected to stretching, particularly biaxial stretching, is preferable in terms of excellent mechanical strength and dimensional stability. Moreover, in order to improve adhesiveness with a light-diffusion layer, the thing which corona-discharge-treated on the surface or provided an easily adhesive layer is used suitably. Moreover, it is preferable that the thickness of a support body is about 10-400 micrometers normally.

Further, on the surface opposite to the concave-convex surface of the light diffusing sheet of the present invention, a fine matting treatment may be performed to prevent adhesion with other members, or an antireflection treatment may be performed to improve light transmittance. Furthermore, you may provide a backcoat layer, an antistatic layer (not shown in FIG. 1), or an adhesive layer (not shown in FIG. 1) by the application and drying method as follows.

The basic function of the backcoat layer is to prevent close contact with the opposing member, and it can have both the property of preventing the occurrence of scratches to the opposing member and the diffusibility. Such a backcoat layer has a concave-convex shape on the surface, and includes, for example, a binder resin and particles. As the binder resin and particles, the same binder resin and particles used in the light diffusion layer of the light diffusing sheet described above may be used, and it is preferable to use an appropriate material and an appropriate amount according to the function to be imparted to the backcoat layer.

For example, in the case of a backcoat layer that not only has adhesion prevention properties but also prevents occurrence of scratches on opposing members, nylon resin particles and/or silicone resin particles are preferable from the viewpoints below among those enumerated for the light diffusion layer. You may use these resin particles not only individually but combining them suitably. Moreover, it is preferable to use the thermosetting resin whose glass transition temperature (Tg) is 15-100 degreeC as binder resin. The content ratio of the particles to the binder resin in the backcoat layer is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of the binder resin (solid content), but it is also possible to contain more.

Among the scratch prevention properties, nylon resin particles are particularly preferable from the viewpoint of preventing wear and tear of the light guide plate caused by the light diffusing sheet being in close contact with the light guide plate when the backlight device is used and the members rubbing against each other. The nylon resin particles preferably have an average particle diameter of 1 to 10 µm. In addition, it is preferable to contain 0.1 to 2 parts by weight of the nylon resin particles with respect to 100 parts by weight of the thermosetting resin, but it is also possible to contain more.

In addition, silicone resin particles are preferable from the viewpoint of effectively preventing scratches (pressure scratches) of the light-diffusing sheet and the light-guide plate that may occur when the backlight device is pressed with a finger or the like. The silicone resin particles preferably have an average particle diameter of 1 to 10 µm. It is particularly preferable that the silicone resin particles have a double structure in which a spherical core made of silicone rubber is covered with a silicone resin film. It is preferable to contain 0.1 to 2 parts by weight of the silicone resin particles with respect to 100 parts by weight of the thermosetting resin in order to prevent the occurrence of scratches during pressurization, but it is also possible to contain more silicone resin particles.

In addition, as described above, the back coat layer can be provided with light diffusivity as well as adhesion prevention properties. In this case, the haze of the light-diffusing backcoat layer is preferably lower than the haze of the light-diffusion layer from the viewpoint of improving the light diffusivity while maintaining the front luminance. Specifically, the haze is preferably about 50% to 70%. Moreover, regarding the content ratio of binder resin and particle|grains in the light-diffusion backcoat layer, setting the ratio of particle|grains to be lower than the content ratio of binder resin and particle|grains in a light-diffusion layer is a viewpoint of preventing the frontal brightness from falling. preferred in

The thickness of the backcoat layer is generally preferably 1 to 10 µm. Moreover, it is also possible to contain additives, such as a dispersing agent, an antistatic agent, and a leveling agent, suitably as needed.

As long as the antistatic layer does not deviate from the range of the Y value, a general antistatic layer may be used, and the thickness of the antistatic layer is preferably 0.1 µm or less.

As long as the pressure-sensitive adhesive layer does not deviate from the range of the Y value, it is preferable that the pressure-sensitive adhesive layer has a thickness of 30 µm or less.

The light-diffusing sheet of the present invention can be prepared by dissolving or dispersing the above-described binder resin or particle in a suitable solvent, or a coating solution for a backcoat layer provided as necessary, using a conventionally known method, e.g. For example, it can be manufactured by coating on a support body by a bar coater, a blade coater, a spin coater, a roll coater, a gravure coater, a flow coater, a die coater, spraying, screen printing, etc. and drying it. Moreover, it is also possible to set it as the light-diffusion sheet which consists of a light-diffusion layer single layer by peeling and removing the said support body from what formed the light-diffusion layer on the support body.

The light-diffusing sheet of the present invention has a Y value of 0.3 or more and 2.1 or less based on the D65 light source transmission measurement method of JIS Z 8722:2000, thereby suppressing the decrease in luminance in the backlight device as much as possible while reducing local luminance unevenness and localized luminance. It can be set as the light-diffusion sheet which can improve light leakage. When the measured Y value is too low, light-shielding property increases. From the viewpoint of obtaining sufficient luminance, the lower limit of the Y value is preferably 0.3 or more, more preferably 0.4 or more, still more preferably 0.45 or more, and particularly preferably 0.5 or more. . On the other hand, from the viewpoint of improving local luminance non-uniformity and local light leakage, the upper limit of the Y value is preferably 2.1 or less, more preferably 1.8 or less, still more preferably 1.5 or less, and particularly preferably 1.2 or less.

When the light diffusing sheet of the present invention is inserted as a backlight device, so-called white color is preferable for the light diffusing sheet of the present invention so that no color is generated in the light from the light source. In order to make the light diffusing sheet white, as described above, it is preferable that the inorganic fine particles exhibit white color in the light diffusing layer coating film. The preferable range of the whiteness of the light diffusing sheet of the present invention is the lower limit of the x value of Yxy according to the D65 light source transmission measurement method of JIS Z 8722:2000, preferably 0.30 or more, more preferably 0.31 or more, and the lower limit of the y value. Preferably 0.31 or more, more preferably 0.32 or more, the upper limit of the x value is preferably 0.36 or less, more preferably 0.35 or less, and the upper limit of the y value is preferably 0.37 or less, more preferably 0.36 or less. .

In the light diffusing sheet of the present invention, the lower limit of the total light transmittance range measured based on the JIS K 7105 measurement method is preferably 45% or more, more preferably 54% or more, and still more preferably 60% or more. On the other hand, the upper limit is preferably 88% or less, more preferably 84% or less, and still more preferably 80% or less. Although the total light transmittance of the light-diffusing sheet of the present invention is lowered by keeping the Y value low, the luminance value when inserted into a backlight device hardly falls compared to a high total light transmittance. The reason is considered as follows. In the light-diffusing sheet of the present invention, as the Y value decreases, the whiteness becomes strong, and the total light transmittance itself decreases. On the other hand, when the light-diffusing sheet of the present invention is inserted into a backlight device, the light rays incident on the sheet are repeatedly reflected on the surface of a plurality of inorganic fine particles dispersed in the light-diffusion layer. The inorganic fine particles used in the present invention have high refractive index, that is, high reflectivity, so it is considered that transmission or absorption of light in the fine particle portion hardly occurs. Even if the light is emitted in the front direction during repeated reflection or is reflected by the reflective sheet 36 installed on the back surface of the backlight device, in the end, almost all of the incident light is emitted in the front direction without loss, so the front luminance is decreased. It is thought to remain high.

Next, the backlight device using the light-diffusion sheet of this invention is demonstrated. The backlight device can be applied to both a direct type structure and an edge light type structure. Also, it may be used for both large and small liquid crystal displays.

Fig. 2 shows an edge light type backlight device 30 as one embodiment of a backlight device using the light diffusing sheet of the present invention. This backlight device has a light guide plate 35 as a main configuration, a light source 34 disposed at one end thereof, a reflective sheet 36 disposed under the light guide plate 35 , and a light diffusing sheet 33 disposed above the light guide plate 35 . ) and prism sheets 31 and 32 are provided. In addition, although the case where one light-diffusion sheet|seat 33 is used and the case where two prism sheets 31 and 32 are used in FIG.

The light guide plate 35 has at least one side surface as a light incident surface, and has a substantially flat plate shape formed so that one surface substantially orthogonal thereto is a light exit surface. It consists of a matrix resin selected from highly transparent resins, such as resin. If necessary, resin particles having a refractive index different from the matrix resin may be added. Each surface of the light guide plate may have a complex surface shape instead of a uniform plane, or light diffusion printing such as a dot pattern may be applied thereto.

The light source 34 is disposed on at least one end of the light guide plate 35 , and a cold cathode tube, an LED light source, or the like is mainly used. As a shape of a light source, the thing of a point shape, a linear shape, an L shape, etc. are mentioned.

The reflective sheet 36 is disposed under the light guide plate 35 . The reflective sheet is not particularly limited as long as the luminance value is not lowered. For example, a reflective sheet having a metallic luster on which silver deposition or aluminum is supported is preferably used.

The prism sheets 31 and 32 are disposed on the light diffusing sheet 33 . As the prism sheet, a conventionally known prism sheet may be used as long as the luminance value is not lowered.

In addition to the above-described prism sheet, light diffusing sheet, light guide plate, reflective sheet, and light source, the backlight device includes a polarizing film, an electromagnetic wave shielding film, and the like depending on the purpose.

The backlight device 30 of the present embodiment includes a light guide plate 35 and a light source 34 disposed at at least one end of the light guide plate 35 , and the present invention described above on the light exit surface of the light guide plate 35 . Since the light diffusing sheet 33 and the prism sheets 31 and 32 of It is possible to reduce non-uniformity and make light leakage at the end of the light guide plate 35 inconspicuous.

Next, FIG. 3 shows a direct type backlight device 50 as another embodiment of a backlight device using the light diffusing sheet of the present invention. In this backlight device, a reflective film 56 housed in a chassis 55 as a main configuration, a plurality of light sources 54 are disposed on the reflective film 56, and the light of the present invention is provided via a diffuser plate 53 thereon. It has a structure in which the diffusive sheet 52 is arranged, and the prism sheet 51 is further arranged. In addition, although the case where the light-diffusion sheet|seat 52 and the prism sheet|seat 51 are used one by one in FIG. 3 is shown, you may overlap and use a plurality of sheets, respectively.

The diffusion plate 53 is installed on the light source of the direct backlight device to reduce the pattern of the light source, and is mainly made of synthetic resin. Such a diffuser plate only needs to have a thickness of 1 to 10 mm in order to have light diffusivity, supports the light diffusive sheet, and is different from the light diffusive sheet of the present invention.

Examples of the synthetic resin constituting the diffusion plate 53 include a polyester-based resin, an acrylic resin, an acrylic urethane-based resin, a polyester acrylate-based resin, a polyurethane acrylate-based resin, an epoxy acrylate-based resin, a urethane-based resin, an epoxy-based resin, Thermoplastic resins such as polycarbonate resins, cellulose resins, acetal resins, polyethylene resins, polystyrene resins, polyamide resins, polyimide resins, melamine resins, phenolic resins, silicone resins, thermosetting resins, ionized resins A radiation curable resin etc. are mentioned. Among these, an acrylic resin excellent in an optical characteristic is used suitably.

In the diffuser plate 53, fine particles are added to impart light diffusivity. Examples of the fine particles include inorganic fine particles such as silica, clay, talc, calcium carbonate, calcium sulfate, barium sulfate, aluminum silicate, titanium oxide, synthetic zeolite, alumina, smectite, styrene resin, urethane resin, benzoguanamine resin, silicone resin, acrylic The organic fine particles which consist of resin etc. are mentioned.

As the light source 54, a cold cathode tube, an LED light source, or the like is mainly used. As a shape of a light source, the thing of a point shape, a linear shape, an L shape, etc. are mentioned.

The reflective film 56 may be disposed under the light source 54 . It does not specifically limit as long as a luminance value is not reduced. Specifically, a white film is suitably used.

The prism sheet 51 may be disposed on the light diffusing sheet of the present invention. As long as the luminance value is not lowered, a conventionally known one may be used.

As the chassis 55, a conventionally known one used in a direct type backlight device may be used.

Moreover, it is also possible to use not only the light-diffusion sheet|seat of this invention, but a conventionally well-known optical member combining suitably for a backlight device. For example, the backlight device includes a reflecting plate, a polarizing film, an electromagnetic wave shielding film, etc. according to the purpose in addition to the above-described prism sheet, light diffusing sheet, diffusion plate, reflecting film, and light source.

In the backlight device of the present embodiment, a reflective film 56 housed in a chassis 55, a plurality of light sources 54 are disposed on the reflective film, and the light diffusing sheet of the present invention is interposed thereon via a diffuser plate 53. Since 52 is disposed and the prism sheet 51 has a structure in which the prism sheet 51 is disposed, even if the frame of the display screen of the backlight device is narrowed, the luminance does not decrease much compared to the conventional backlight device, and the It is possible to reduce the luminance non-uniformity and make light leakage at the end of the diffuser plate 53 inconspicuous.

Further, the present invention is characterized by a light diffusing sheet, and the present invention can be suitably applied to a backlight device other than the above-described embodiment and a light source device other than the backlight device as long as the light diffusing sheet of the present invention is used.

Example

The present invention will be further described by way of examples below. In addition, "part" and "%" are made on a weight basis unless otherwise indicated, and all amounts other than a diluent solvent are made into solid amount.

1. Fabrication of light diffusing sheet

<Example 1>

After mixing and stirring the coating solution for the light diffusion layer of the following formulation, it is applied by a bar coating method so that the thickness after drying becomes 5 μm on a support made of a 23 μm thick polyethylene terephthalate film (Lumirer T60: Toray Corporation), It was dried to form a light diffusion layer. Next, on the opposite side to the side on which the light-diffusion layer is formed of the support, the coating solution for a backcoat layer of the following formulation is applied by a bar coating method so that the thickness after drying becomes 5 μm, dried to form a backcoat layer, and the light diffusion of Example 1 got a sex sheet.

<Coating liquid for light-diffusion layer coating film>

・4 parts of acrylic polyol resin

(Acridic A-817: DIC Corporation, solid content 50%, Tg 96°C, refractive index 1.51)

・6 parts of acrylic polyol resin

(Acridic A-811: DIC Corporation, solid content 50%, Tg 19°C, refractive index 1.49)

・2 parts of polyisocyanate

(Takenate D110N: Mitsui Chemicals, 60% solids)

・10 parts of acrylic resin particles

(Polymethyl methacrylate spherical particles, average particle diameter 2-3 μm, refractive index 1.49)

・Zirconium dioxide 14.4 parts

(Zirconium oxide PCS: Nippon Denko Corporation, primary particle diameter 20 nm, refractive index 2.40, specific gravity 6)

・94 parts of dilution solvent

<Coating liquid for backcoat layer of Example 1>

・10 parts of acrylic polyol resin

(Acridic A-807: DIC Corporation, solid content 50%)

・2 parts of polyisocyanate

(Takenate D110N: Mitsui Chemicals, 60% solids)

・0.1 parts of nylon resin particles

(Nylon resin spherical particle: average particle diameter 5 μm)

・38 parts of dilution solvent

<Example 2>

A light-diffusing sheet of Example 2 was obtained in the same manner as in Example 1 except that the weight part of zirconium dioxide in the coating liquid for a light-diffusion layer of Example 1 was changed to 16.8 parts.

<Example 3>

A light-diffusing sheet of Example 3 was obtained in the same manner as in Example 1 except that the weight part of zirconium dioxide in the coating liquid for the light-diffusion layer of Example 1 was changed to 19.2 parts.

<Example 4>

A light-diffusing sheet of Example 4 was obtained in the same manner as in Example 1 except that the weight part of zirconium dioxide in the coating liquid for a light-diffusion layer of Example 1 was changed to 21.6 parts.

<Example 5>

A light-diffusing sheet of Example 5 was obtained in the same manner as in Example 1 except that the weight part of zirconium dioxide in the coating solution for the light-diffusion layer of Example 1 was changed to 24.0 parts.

<Example 6>

Except having changed the coating liquid for light-diffusion layers of Example 1 into the following formulation, it carried out similarly to Example 1, and obtained the light-diffusion sheet|seat of Example 6.

<Coating liquid for light-diffusion layer coating film of Example 6>

・10 parts of acrylic polyol resin

(Acridic A-811: DIC Corporation, solid content 50%, Tg 19°C, refractive index 1.49)

・2 parts of polyisocyanate

(Takenate D110N: Mitsui Chemicals, 60% solids)

・10 parts of acrylic resin particles

(Polymethyl methacrylate spherical particles, average particle diameter 2-3 μm, refractive index 1.49)

· 24.0 parts of zirconium dioxide

(Zirconium oxide PCS: Nippon Denko Corporation, primary particle diameter 20 nm, refractive index 2.40, specific gravity 6)

・94 parts of dilution solvent

<Example 7>

A light-diffusing sheet of Example 7 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating liquid for the light-diffusion layer of Example 6 was changed to 26.4 parts.

<Example 8>

A light-diffusing sheet of Example 8 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating liquid for the light-diffusion layer of Example 6 was changed to 28.8 parts.

<Example 9>

A light-diffusing sheet of Example 9 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating liquid for a light-diffusion layer of Example 6 was changed to 33.6 parts.

<Example 10>

A light-diffusing sheet of Example 10 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating liquid for a light-diffusion layer of Example 6 was changed to 38.4 parts.

<Example 11>

Zirconium dioxide in the coating liquid for the light diffusion layer of Example 6 was changed to titanium dioxide (rutile TiO ₂ ) (tronox R-KB-2, Bayer Corporation, primary particle size 20 nm, refractive index 2.71, specific gravity 4.3), and the weight Except having changed the part into 7.2 parts, it carried out similarly to Example 6, and obtained the light-diffusion sheet|seat of Example 11.

<Example 12>

Light diffusivity of Example 12 in the same manner as in Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to the same titanium dioxide as titanium dioxide used in Example 11, and the weight part was changed to 14.4 parts got a sheet

<Example 13>

Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to zinc oxide (Nanofine 50A, Sakai Chemical Industry, primary particle diameter of 20 nm, refractive index 1.95, specific gravity 5.6), and parts by weight were changed to 28.8 parts It carried out similarly to 6, and the light-diffusion sheet|seat of Example 13 was obtained.

<Example 14>

Light diffusivity of Example 14 in the same manner as in Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to the same zinc oxide used in Example 13, and the weight part was changed to 57.6 parts. got a sheet

<Comparative Example 1>

A light-diffusing sheet of Comparative Example 1 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating solution for the light-diffusion layer of Example 6 was changed to 12.0 parts.

<Comparative Example 2>

A light-diffusing sheet of Comparative Example 2 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating liquid for a light-diffusion layer of Example 6 was changed to 9.6 parts.

<Comparative example 3>

Light diffusivity of Comparative Example 3 in the same manner as in Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to the same zinc oxide used in Example 13, and the weight part was changed to 14.4 parts got a sheet

<Comparative example 4>

Light diffusivity of Comparative Example 4 in the same manner as in Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to the same zinc oxide used in Example 13, and the weight part was changed to 7.2 parts got a sheet

<Comparative example 5>

A light-diffusing sheet of Comparative Example 5 was obtained in the same manner as in Example 6 except that the weight part of zirconium dioxide in the coating liquid for the light-diffusion layer of Example 6 was changed to 48.0 parts.

<Comparative Example 6>

Light diffusivity of Comparative Example 6 in the same manner as in Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to the same titanium dioxide as titanium dioxide used in Example 11, and the weight part was changed to 28.8 parts got a sheet

<Comparative Example 7>

Light diffusivity of Comparative Example 7 in the same manner as in Example 6 except that zirconium dioxide in the coating liquid for light diffusion layer of Example 6 was changed to the same zinc oxide as used in Example 13, and the weight part was changed to 72.0 parts got a sheet

<Example 15>

A light-diffusing sheet was produced in the same manner as in Example 1 except that the coating liquid for the light-diffusion layer of Example 1 was changed to the following formulation. In the following formulation, only the content M of the acrylic resin particle (small particle) was changed to 11.2 parts, 14.4 parts, 18 parts, and 21.6 parts, and 4 types of light-diffusion sheets were obtained.

<Coating liquid for light-diffusion layer coating film of Example 15>

・10 parts of acrylic polyol resin

(Acridic A-811: DIC Corporation, solid content 50%, Tg 19°C, refractive index 1.49)

・2 parts of polyisocyanate

(Takenate D110N: Mitsui Chemicals, 60% solids)

・Acrylic resin particle (small particle) M part

(Polymethyl methacrylate spherical particles, average particle diameter 2-3 μm, refractive index 1.49)

4.8 parts of acrylic resin particles (large particles)

(Polymethyl methacrylate spherical particles, average particle diameter 5 μm, refractive index 1.49)

· Titanium dioxide (rutile TiO ₂ ) 6 parts

(tronox R-KB-2, Bayer, primary particle size 20 nm, refractive index 2.71, specific gravity 4.3)

94 parts of diluent solvent

<Example 16>

A light-diffusing sheet was produced in the same manner as in Example 15 except that the coating liquid for the light-diffusion layer of Example 15 was changed to the following formulation. Among the two types of inorganic fine particles of the following formulation, the zirconium dioxide content L was fixed to 7.2 parts, and the titanium dioxide content N was varied to 4.8 parts, 5.4 parts, and 6 parts, and three types of light diffusive sheets were obtained.

<Coating liquid for light-diffusion layer coating film of Example 16>

・10 parts of acrylic polyol resin

(Acridic A-811: DIC Corporation, solid content 50%, Tg 19°C, refractive index 1.49)

・2 parts of polyisocyanate

(Takenate D110N: Mitsui Chemicals, 60% solids)

9.6 parts of acrylic resin particles (small particles)

(Polymethyl methacrylate spherical particles, average particle diameter 2-3 μm, refractive index 1.49)

4.8 parts of acrylic resin particles (large particles)

(Polymethyl methacrylate spherical particles, average particle diameter 5 μm, refractive index 1.49)

・Zirconium dioxide L part

(Zirconium oxide PCS: Nippon Denko Corporation, primary particle diameter 20 nm, refractive index 2.40, specific gravity 6)

・Titanium dioxide (rutile type TiO ₂ ) N parts

(tronox R-KB-2, Bayer, primary particle size 20 nm, refractive index 2.71, specific gravity 4.3)

94 parts of diluent solvent

<Example 17-19>

A plurality of light-diffusing sheets in which ratios of two kinds of inorganic fine particles (zirconium dioxide and titanium dioxide) were different were produced by the same formulation as in Example 16. In Example 17, in the formulation of Example 16, the content N of titanium dioxide was fixed to 2.4 parts, and the content L of zirconium dioxide was changed to 9.6 parts, 12 parts, 14.4 parts, and 16.8 parts. Moreover, in Example 18, in the prescription of Example 16, content N of titanium dioxide was fixed to 3.6 parts, and content L of zirconium dioxide was made different to 9.6 parts, 12 parts, and 14.4 parts. In Example 19, in the formulation of Example 16, the content N of titanium dioxide was fixed to 4.8 parts, and content L of zirconium dioxide was made different to 8.4 parts, 9.6 parts, 12 parts, 14.4 parts, and 16.8 parts.

<Examples 20 and 21>

The zirconium dioxide content L and the titanium dioxide content N in the coating liquid for the light diffusion layer of Example 16 were fixed to 9.6 parts and 4.8 parts (14.4 parts as the content of inorganic fine particles), respectively, small and large particles of acrylic resin particles A plurality of light-diffusing sheets were prepared by varying the ratio of . In Example 20, the content of large particles was fixed at 4.8 parts as in Example 16, and the content of small particles was changed to 4.8 parts and 7.2 parts. In Example 21, the content of small particles was fixed at 9.6 parts as in Example 16, and the content of large particles was changed to 2.4 parts and 3.6 parts.

2. Fabrication of the backlight device

The light diffusivity of Examples 1-21 and Comparative Examples 1-7 in a 4-inch edge light type backlight (8 LED light sources with a luminous intensity of 1,300 mcd, and a polycarbonate light guide plate with a thickness of 0.5 mm) The backcoat layer of the sheet is inserted so as to face the light guide plate, and a 65 μm thick first prism sheet (TBEF2-GT: Sumitomo 3M Co., Ltd.) and a 68 μm thick second prism are further placed on the light diffusing layer of the light diffusing sheet. Backlight devices of Examples 1-21 and Comparative Examples 1-7 were produced by stacking sheets (TBEF2-GM: Sumitomo 3M Co., Ltd.) on top of each other. In addition, the two prism sheets were arranged so that the ridge lines of each of the structural rows were orthogonal to each other with the structural row facing upward (the emission side).

3. Measurement of Y value

"High light diffusivity" was evaluated by "Y value" according to the CIE-XYZ color system. With a color meter (Nippon Denshoku Kogyo Co., Ltd., ZE-2000), the Y value was measured according to the D65 light source transmission measurement method of JIS Z 8722:2000 using the light diffusing layer of the light diffusing sheet as the light incident surface.

4. Evaluation of luminance uniformity by visual observation

Two prism sheets are removed from the backlight device manufactured in the above "Production of a backlight device" (only the light diffusing sheet), and the luminance of the light diffusing sheets of Examples 1 to 14 and Comparative Examples 1 to 7 near the light source is turned on. Non-uniformity and light leakage at the end of the light guide plate were evaluated by visual observation. The evaluation is that at a distance of approximately 30 cm from the light exit surface of the backlight device, the pattern of the LED light source (point light source) is not seen and there is no light leakage at the end of the light exit surface, so that the overall display surface is uniformly seen as "○", A case where the LED light source pattern was seen or the light leakage of the edge was seen, and the whole display surface was not uniformly seen was made into "x".

5. Measurement of luminance ratio

The backlight device (including two prism sheets) produced in the above "Production of the backlight device" is turned on, and the luminance in the front direction is measured using a color luminance meter CS-200 (manufactured by Konica Minolta), containing inorganic fine particles The luminance ratio of each light-diffusing sheet was calculated by dividing by the measured value (12,000 cd/m ² ) of the front luminance of the light-diffusing sheet that is not. The luminance was measured in a dark room.

<Measurement conditions>

・Measurement distance: 30 cm

・Measuring angle (light-receiving angle): 1 degree

・Measurement point: 1 point in the center

6. Method of measuring total light transmittance (Tt) and haze

Total light transmittance (Tt) with the light diffusing layer of the light diffusing sheet as the light incident surface with a haze meter (Suga Test Engineer, Model HGM-2K) and color computer (Suga Test Engineer, Model SM-4) according to JIS K 7105 measurement method and haze (Haze) were measured.

7. Evaluation

Table 1 shows the measurement results for Examples 1 to 14 and Comparative Examples 1 to 7. In addition, Table 2 shows the result about each typical example about Examples 15-21. In Tables 1 and 2, the amount (phr) is a weight part of the inorganic fine particles with respect to 100 parts by weight of the binder resin (solid content). In addition, 100 parts by weight of the binder resin (solid content) includes the amount of polyisocyanate as a curing agent.

As can be seen from the results of the luminance uniformity evaluation by visual observation in Tables 1 and 2, Examples 1-21 in which the Y value is in the range of 0.3 to 2.1, the luminance non-uniformity in the vicinity of the light source is reduced, and the light leakage degree at the end of the light guide plate decreased. In Examples 1-21, since the luminance ratio hardly changed, the luminance decrease did not occur so much, the luminance non-uniformity in the vicinity of a light source was reduced, and the light leakage at the edge part of a light-guide plate decreased. In addition, these Examples were not inferior in the luminance ratio even when compared with those having a high total light transmittance (Tt).

Comparing Example 5 and Example 6 (which does not include a resin having a high glass transition temperature among the binder resins), Example 5 showed slight concave curling on the light diffusion layer side, but there was no problem at all in actual use. On the other hand, in Example 6, the evaluation and physical properties of Table 1 were the same as those of Example 5, but curling did not occur.

In addition, the light-diffusing sheet|seat of Examples 1-21 was white when visually observed. As a representative, the x-value (small x-value) and y-value (small y-value) of "Yxy" according to the CIE-XYZ color system for Examples 8 and 12 are set to "3. Measurement of Y value" was carried out in the same manner with the color meter described in the section. As a result, the x value of Example 8 was 0.3344, the y value was 0.3430, the x value of Example 12 was 0.3308, and the y value was 0.3433. From the measurement result of the said x-value and y-value, it turned out that the light-diffusion sheet of this invention containing Example 8 and Example 12 has shown white in the CIE-XYZ color system. In addition, when comparing the light diffusing sheet of Examples 1 to 10 containing zirconium dioxide and the light diffusing sheet of Example 12 containing titanium dioxide, the sheet of Examples 1 to 10 showed more whiteness than the sheet of Example 12. was high.

Comparative Examples 1 to 4 did not improve the luminance non-uniformity near the light source and light leakage at the end of the light guide plate because the Y value was outside the range of 0.3 to 2.1. Comparative Examples 5 to 7 improved the luminance non-uniformity near the light source and light leakage at the end of the light guide plate, but the luminance decreased because the Y value was outside the range of 0.3 to 2.1. Comparative Example 5 was not suitable for practical use because curling occurred on the light diffusion layer side. Although curling did not occur in Comparative Example 6, the light-diffusion layer was colored yellow, and thus was not suitable for practical use. In Comparative Example 7, curling occurred and the coating film adhesiveness was also poor. In addition, the reason curling occurred in Comparative Examples 5 and 7 is presumed to be because the content of inorganic fine particles is large, and in preventing curling, the desired effect is obtained with a relatively small content as inorganic fine particles (for example, titanium oxide). ), it can be seen that it is preferable to use

Example 15 is an example in which titanium dioxide was used as inorganic fine particles and two types of resin particles (referred to as small particles and large particles) having different average particle diameters were used as light diffusing resin particles. Compared with Example 11 using the same titanium dioxide, in Example 15, although the total amount of acrylic resin particles was larger than in Example 11, the content of titanium dioxide was small (Example 11 is based on 100 parts of binder resin) 60 parts, Example 15 was 50 parts with respect to 100 parts of binder resin), and the total light transmittance was higher than Example 11, and was about 65% or more as an average of 4 types. Further, as shown in the graph of Fig. 4, it was possible to achieve sufficient uniformity of luminance in the range of approximately 1.0±0.1 also for the Y value. In addition, it was confirmed that the Y value was maintained in the desired range even when large particles were added to prevent the occurrence of scratches. In addition, although there was a tendency for the Y value to decrease with an increase in the content of small particles that mainly contribute to light diffusivity, it was confirmed that an appropriate Y value was maintained in a suitable small particle content range. In addition, in the graph of FIG. 4, the horizontal axis|shaft is the light-diffusion resin particle content of small particle|grains (part with respect to 100 parts of binder resin).

Example 16 is an example in which titanium dioxide was used together under the condition that the amount of zirconium dioxide in the inorganic fine particles was small (7.2 parts: 60 parts with respect to 100 parts of the binder). In Example 16, the Y value decreased from 0.98 to 0.86 as the content of titanium dioxide increased, but all were able to maintain a high luminance ratio and a total light transmittance of 65% or more. That is, the effect of the present invention that the hiding property can be increased without lowering the luminance ratio was confirmed.

In addition, compared with Example 1 using only zirconium dioxide, the Y value fell despite the small content of the inorganic fine particles. From this result, it turns out that high brightness|luminance uniformity can be aimed at without increasing content by using zirconium dioxide and titanium dioxide together.

Examples 17 to 19 are Examples in which the change of Y value when different ratios of titanium dioxide and zirconium dioxide is examined based on the knowledge of Example 16 is studied. The change of the Y value at the time of making the ratio of these two types of inorganic fine particles different is shown in FIG. In Fig. 5, the horizontal axis represents the total content of the two types of inorganic fine particles (parts relative to 100 parts of binder resin). 5, the change of Y value of the light-diffusion sheet of Examples 1-4 (Example of 4 types with different content of zirconium dioxide) is shown as reference.

From the result shown in FIG. 5, when two types of inorganic fine particles are used rather than the case where one type of inorganic fine particles are used, it turns out that the change of the Y value according to content can be moderated, and Y value is easy to adjust. In addition, by combining inorganic particles (eg, zirconium dioxide), which require a relatively large content, with a relatively small content (eg, titanium dioxide) to obtain a suitable Y value, the content of inorganic particles other than the Y value is affected. It is possible to easily adjust the properties of the coating film affecting

In Examples 20 and 21, the content of the two types of inorganic fine particles was fixed at 14.4 parts (120 parts with respect to 100 parts of the binder resin), and the ratio and total content of the two types of light diffusing resin particles were different. From the results of Examples 20 and 21, it was confirmed that even if the amount of light diffusing particles (particularly the content of small particles) was small, if the inorganic fine particles were in an appropriate range, the Y value was at most about 1.16, and it was confirmed that the luminance could be uniformed.

10 light diffusing sheet
11 light diffusion layer
12 support
13 back coat layer
30 edge light type backlight unit
31 prism sheet
32 prism sheet
33 light diffusing sheet
34 light source
35 light guide plate
36 reflective sheet
50 Direct backlight unit
51 prism sheet
52 light diffusing sheet
53 diffuser plate
54 light source
55 chassis
56 reflective film

Claims (18)

A light diffusing sheet having a light diffusing layer, comprising:
The light-diffusion layer includes a binder resin, light-diffusing resin particles and inorganic fine particles,
The inorganic fine particles include zirconium oxide and titanium oxide,
The total content of zirconium oxide and titanium oxide is 80 to 200 parts by weight with respect to 100 parts by weight of solid content of the binder resin, and the weight ratio of zirconium oxide to titanium oxide is 50:50 to 80:20,
The light diffusing sheet has a Y value of 0.3 or more and 2.1 or less according to the D65 light source transmission measurement method of JIS Z 8722:2000. delete The light-diffusing sheet according to claim 1, comprising:
The light-diffusing sheet, characterized in that the refractive index of the inorganic fine particles is 1.9 or more. delete delete delete delete delete The light-diffusing sheet according to claim 1, comprising:
The light-diffusing resin particle comprises two types of resin particles having different average particle diameters. The light-diffusing sheet according to claim 9, comprising:
The light diffusible sheet, wherein in the light diffusing resin particles, a ratio of the resin particles having a larger average particle diameter is equal to or smaller than that of the resin particles having a smaller average particle diameter. The light-diffusing sheet according to claim 10, wherein the resin particles having the smaller average particle diameter have an average particle diameter of 1 µm or more and 4 µm or less. The light-diffusing sheet according to claim 1, comprising:
The light-diffusing sheet, characterized in that the binder resin comprises an acrylic polyol resin having a glass transition temperature of 30° C. or less. A light diffusing sheet according to claim 12, comprising:
The light-diffusing sheet, characterized in that the binder resin further comprises an acrylic polyol resin having a glass transition temperature of 40 °C or higher. The light diffusing sheet according to claim 13, comprising:
When the total of the acrylic polyol resin (solid content) having the glass transition temperature of 30°C or less and the acrylic polyol resin (solid content) having the glass transition temperature of 40°C or higher is 100 parts by weight, the acrylic polyol resin having the glass transition temperature of 30°C or less is A light diffusing sheet, characterized in that 50 parts by weight or more. The light-diffusing sheet according to claim 1, comprising:
A light diffusing sheet having a total light transmittance of 45% to 88%. delete a reflective sheet, a light guide plate provided above the reflection sheet, a light source disposed on a side surface of the light guide plate, a light diffusing sheet disposed on a light exit surface side of the light guide plate, and a prism sheet disposed on a light exit surface side of the light diffusing sheet 16. A backlight device comprising: the light diffusing sheet according to any one of claims 1 to 3 and 9 to 15 used as the light diffusing sheet. a light source, a diffusion plate disposed on one side of the light source, a reflective film disposed on the other side of the light source, a light diffusing sheet disposed above the diffusion plate, and a prism sheet disposed on the light exit surface side of the light diffusing sheet 16. A backlight device provided with the light diffusing sheet, wherein the light diffusing sheet according to any one of claims 1, 3, and 9 to 15 is used as the light diffusing sheet.

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