JP2010060924A - Optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably supply an optical sheet with good contrast. <P>SOLUTION: This optical sheet includes a functional layer on at least one side of a transparent base plate, includes a diffusion element on the uppermost surface of and/or inside the functional layer, includes a relationship of inequality (I): 0.64<Q/P<0.94, and is used for a display element surface. Were P is the total of diffusion transmission intensity of light diffused and transmitted when visible light is emitted normally from the opposite side of an observer's side of the optical sheet measured at each degree between -85° to +85°, and Q (regular transmission intensity) is the diffusion transmission intensity at 0°. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical sheet excellent in contrast.

In the optical sheet used for the surface of the display device, a layer having functions such as antiglare property, antistatic property and antifouling property is laminated as a functional layer on the surface of the transparent substrate on the viewer side. Usually, in order to express the above-mentioned function, for example, in order to impart antiglare properties, a method of imparting uneven shapes to the surface layer or adding diffusion particles to the resin forming the surface layer is used. . In order to impart antistatic properties, methods such as adding conductive fine particles and conductive resin, and in order to impart antifouling properties, a fluorine-containing polymer and an antifouling agent are added. Since these diffusing particles, conductive fine particles, additives and the like are not completely compatible with the resin forming the surface layer, the optical sheet using them has an action of diffusing visible light. The unevenness of the surface layer also has the effect of diffusing visible light.
Furthermore, in order to prevent interference spots between the optical sheets and interference spots between the optical sheet and the display element, the surface layer, the back surface of the transparent substrate, and irregularities having a visible light wavelength or more are provided between the respective layers. However, this unevenness also has the effect of diffusing visible light.

In the present invention, a material that causes the diffusion of visible light as described above is defined as a diffusing element. If such a diffusing element is provided, the optical sheet causes a decrease in contrast due to reflection of external light. That is, the optical sheet is required to prevent a decrease in contrast while maintaining the function of the optical sheet as described above.
As a method for simply evaluating contrast, a haze value or a ratio of internal haze to total haze has been generally used. That is, in the process of manufacturing an optical sheet, it has been considered that an optical sheet with a low contrast can be manufactured by controlling the material specification and manufacturing conditions so as to reduce the haze value (Patent Documents 1 to 3). 3).

JP 2002-267818 A JP2007-334294A JP2007-17626

However, even when the haze value is the same, the contrast is often different. For example, in the production using the haze value and the ratio between the internal haze and the total haze as an index, it is not always possible to stably produce a good optical sheet. I understood it.
An object of the present invention is to provide an optical sheet with good contrast under such circumstances.

Until now, it has been considered that the contrast depends on the haze value. According to JIS K7136: 2000 and ISO 14782: 1999, the haze value is “percentage of transmitted light that has passed through the specimen by 0.044 rad (2.5 degrees) or more from the incident light due to forward scattering. Is defined. That is, the haze value indicates the ratio of scattered light in which incident light is scattered by ± 2.5 degrees or more, and the luminance distribution due to diffusion is not considered at all. In an extreme example, an optical sheet that completely reflects specularly (no diffusion) and no specular reflection, but both optical sheets that diffuse all transmitted light within ± 2.5 degrees have a haze value of 0 It will be.
On the other hand, for example, the optical sheet in which the amount of transmitted light within ± 2.5 degrees is 30% and the transmitted light is scattered to an angle of 70 to 80 degrees, and the amount of transmitted light within ± 2.5 degrees are the same. The optical sheets that scatter the transmitted light at an angle of 5 to 10 degrees at 30% both have a haze value of 70%.

FIG. 1 shows the relationship between the haze value and the contrast, and FIG. 2 shows the result of verifying the relationship between the internal haze / total haze ratio and the contrast by producing optical sheets with different conditions. As shown in FIG. 1 and FIG. 2, it can be seen that there are optical sheets with completely different contrast as evaluated by the observer even if they have the same haze value and ratio of internal haze to total haze. The contrast here refers to bright room contrast.
As a result of intensive studies based on these findings, the present inventors have found that by adding the concept of intensity distribution by diffusion, it is possible to easily perform contrast evaluation that could not be evaluated with conventional haze values. More specifically, the contrast can be easily evaluated by using the sum of diffuse transmission intensities in a specific angle range with the normal transmission direction as the center, and in the optical sheet manufacturing process, As an index, it has been found that an optical sheet with little decrease in contrast can be efficiently and stably manufactured by controlling the identification of materials, manufacturing conditions, and the like. The present invention has been completed based on these findings.

That is, the present invention is characterized by having a functional layer on at least one surface of the transparent substrate, having a diffusion element on the outermost surface and / or inside of the functional layer, and having the relationship of the following formula (I): An optical sheet used for the display element surface is provided.
0.64 <Q / P <0.94 (I)
P: Sum of diffuse transmission intensities Q obtained by measuring the diffusely transmitted light when irradiated with visible light perpendicularly from the surface opposite to the viewer side of the optical sheet in a range of −85 degrees to +85 degrees. (Normal transmission intensity); Diffuse transmission intensity at 0 degree

  According to the present invention, it is possible to easily perform contrast evaluation that cannot be evaluated with a conventional haze value, and to provide an optical sheet with little reduction in contrast.

The optical sheet of the present invention has a functional layer on at least one surface of a transparent substrate, has a diffusing element on the outermost surface and / or inside of the functional layer, and 0.64 <Q / P <0.94. It has the relationship of these.
Hereinafter, a method for measuring diffuse transmission intensity will be described with reference to FIG.
When visible light is irradiated from the direction 5 on the optical sheet as shown in FIG. 3, the light is transmitted in the direction 6 and part of the light is diffused. The transmission intensity in the six directions, that is, 0 degree is the regular transmission intensity Q, and the diffuse transmission intensity from −85 degrees to +85 degrees is 1 degree as shown in FIG. 3 with respect to the regular transmission direction. Measured every time and the sum is P.
In addition, the measurement of diffuse transmission intensity is specifically measured as follows.

(Measurement method of diffuse transmission intensity)
Visible light is irradiated vertically from the back surface of the optical sheet (the surface opposite to the viewer side of the optical sheet). The diffuse transmission intensity is measured by scanning the light receiver at every 1 degree in the range from −85 degrees to +85 degrees with the light beam incident from the optical sheet surface and diffused and transmitted. In addition, although there is no restriction | limiting in particular about the apparatus which measures diffuse transmission intensity, In this invention, Nippon Denshoku Industries Co., Ltd. product "GC5000L" was used.

The reason why the ratio of the regular transmission intensity to the total diffuse transmission intensity of the optical sheet determines whether the contrast is good or bad will be described with reference to FIG. 4 which is a conceptual diagram.
When the surface layer having the diffuse transmission intensity distribution b is laminated on the transparent substrate having the diffuse transmission intensity distribution a in FIG. 4, the decrease rate of the diffuse transmission intensity is larger as it is closer to 0 degrees. The reduction in strength is large, and an optical sheet having a diffuse transmission intensity distribution of c is obtained. That is, when the transmission intensity distribution is widened, the regular transmission intensity Q shows a small value, and when the transmission intensity distribution is narrowed, the regular transmission intensity Q is increased. Further, since the change in the intensity distribution is larger as the diffusion angle is closer to 0 degrees, the total transmission intensity becomes smaller as tailing to a larger diffusion angle. That is, it is analogized that Q / P is an index indicating the relationship between tailing and regular transmission of diffuse transmission intensity of the optical sheet.

The optical sheet of the present invention is characterized by satisfying the following formula (I).
0.64 <Q / P <0.94 (I)
When Q / P exceeds 0.64, an optical sheet with a small reduction in contrast can be obtained. From the viewpoint of suppressing the decrease in contrast, Q / P is preferably more than 0.82, more preferably more than 0.86.
On the other hand, as Q / P increases, the contrast does not decrease, and when Q / P is 1, diffusion of transmitted light is eliminated. The optical sheet of the present invention has a functional layer and some diffusing element, but the upper limit varies depending on the type of the functional layer. In general, Q / P is preferably less than 0.94, and if it is less than 0.94, for example, in the case of an antiglare sheet, sufficient antiglare property can be obtained.

Achieving the formula (I) 0.64 <Q / P <0.94 in the present invention can be achieved by adjusting the transmission luminance distribution and intensity with the internal diffusion element and the external diffusion element.
As a method of adjusting the transmission luminance distribution and intensity by the internal diffusion element, the resin constituting the functional layer may be described as translucent inorganic particles and / or translucent organic particles (hereinafter simply referred to as “translucent particles”). There is a way to disperse. Furthermore, it can be performed by controlling the shape of the transparent resin constituting the functional layer, the shape of the translucent particles dispersed in the transparent resin, the dispersed state, the particle diameter, the addition amount, the refractive index, and the like. Further, the concentration of additives other than the translucent particles that can be added to the transparent resin also affects the diffuse transmission intensity of the internal diffusion element.

On the other hand, as a method of adjusting the diffuse transmission intensity by the external diffusion element, for example,
(1) A method for transferring an uneven shape onto the surface of an optical sheet using a mold having fine unevenness on the surface,
(2) A method of forming irregularities on the surface by curing shrinkage of a resin constituting a functional layer such as an ionizing radiation curable resin,
(3) A method of forming irregularities on the surface by projecting and solidifying translucent fine particles from the surface layer,
(4) There is a method of imparting surface irregularities by external pressure.
As the method of (1), for example, an ionizing radiation curable resin is disposed on a transparent substrate, a mold having fine irregularities is brought into close contact with the coating layer of the ionizing radiation curable resin, and cured by ionizing radiation. Thus, an uneven shape can be provided on the surface of the optical sheet.
The method (2) is effective in preventing glare because fine irregularities having a smooth surface can be obtained, and the method (3) described above is the selection of translucent particles and transparent resin, and the coating film. Since the performance can be adjusted by selecting the thickness, solvent selection, drying conditions, permeability to the transparent substrate, etc., it is effective in that the process is short, the operation is simple, and it can be manufactured at low cost.
It should be noted that the antireflection layer provided on the uneven surface, and the functional layers such as the antifouling layer, the hard coat layer, and the antistatic layer also affect the diffuse transmission intensity by the external diffusion element. Specifically, by providing another functional layer on the uneven surface to form a two-layer structure, the surface unevenness can be moderated and surface diffusion can be suppressed. In addition, by increasing the thickness of the coating film of the other functional layer, the surface unevenness can be moderated, and the surface diffusion can be controlled by the coating solution composition, coating and drying conditions, and the like.

The method (3) for obtaining the above-mentioned external diffusion element is preferable in that the external diffusion and the internal diffusion can be simultaneously applied depending on the kind of the light-transmitting fine particles to be used, and the manufacturing process can be simplified. Is the method.
On the other hand, when using a method other than the above (3), the method of adjusting the diffuse transmission intensity by the external diffusion element and the method of adjusting the diffusion transmission intensity by the internal diffusion element can be designed separately and independently. Other than contrast, it is preferable in terms of easy adjustment of optical performance such as resolution, glare, and antiglare property. In addition, since the diffusion transmission strength can be adjusted by an external diffusion element without considering the optical performance of the resin used, a resin that exhibits physical performance such as hard coat properties, antifouling properties, and antistatic properties of the surface resin. Is easy to select.

[Translucent particles]
The preferable range of the translucent particles dispersed in the transparent resin will be described in detail below.
The translucent particles may be organic particles, inorganic particles, or a mixture of organic particles and inorganic particles.
In the optical sheet of the present invention, the average particle size of the translucent particles used is preferably in the range of 0.5 to 20 μm, more preferably 1 to 10 μm. Within this range, it is possible to adjust the diffuse transmission intensity distribution by internal diffusion and / or external diffusion. In particular, when the average particle diameter of the translucent particles is 0.5 μm or more, the aggregation of the particles does not become excessive and adjustment of the unevenness is facilitated, and when it is 20 μm or less, a glare or rough image is produced. Since it is difficult, a degree of freedom in designing the diffuse transmission intensity distribution is secured.

In addition, the smaller the variation in the particle size of the translucent particles, the less the scattering characteristics, and the easier the diffuse transmission intensity distribution design. More specifically, when the average diameter by weight average is MV, the cumulative 25% diameter is d25, and the cumulative 75% diameter is d75, (d75−d25) / MV is preferably 0.25 or less. More preferably, it is 20 or less. The cumulative 25% diameter means the particle diameter when counted from a particle having a small particle diameter in the particle size distribution to 25% by mass, and the cumulative 75% diameter is similarly counted to 75% by mass. The particle size when
As a method for adjusting the particle size variation, for example, it can be carried out by adjusting the conditions of the synthesis reaction, and classification after the synthesis reaction is also an effective means. In classification, particles having a desired distribution can be obtained by increasing the number of times or increasing the degree. It is preferable to use a method such as an air classification method, a centrifugal classification method, a sedimentation classification method, a filtration classification method, or an electrostatic classification method for classification.

  Furthermore, it is preferable that the refractive index difference between the transparent resin constituting the functional layer and the translucent particles is 0.01 to 0.25. When the difference in refractive index is 0.01 or more, for example, in an antiglare sheet or the like, glare can be suppressed, and when it is 0.25 or less, diffuse transmission intensity distribution design becomes easy. From the above viewpoint, the difference in refractive index is preferably 0.01 to 0.2, and more preferably 0.02 to 0.15. The refractive index of the translucent particles was measured by measuring the turbidity by dispersing an equal amount of the translucent particles in the solvent in which the refractive index was changed by changing the mixing ratio of two types of solvents having different refractive indexes. It is measured by measuring the refractive index of the solvent when the turbidity is minimized with an Abbe refractometer.

In addition, two or more kinds of translucent particles having a specific gravity difference of 0.1 or more are used in combination, or two or more kinds of translucent particles having different particle diameters having a difference in particle diameter of 0.5 μm or more are used in combination. The diffusion transmission intensity can also be adjusted by using two or more kinds of light-transmitting particles having a refractive index difference of 0.01 or more, or by using spherical light-transmitting particles and amorphous light-transmitting particles in combination. Is possible.
Specific gravity is liquid phase substitution method, gas phase substitution method (pycnometer method), particle size is Coulter counter method, light diffraction scattering method, etc., and refractive index is measured directly by Abbe refractometer or spectral reflection It can be quantitatively evaluated by measuring spectrum and spectroscopic ellipsometry.

Translucent organic particles include polymethyl methacrylate particles, polyacryl-styrene copolymer particles, melamine resin particles, polycarbonate particles, polystyrene particles, crosslinked polystyrene particles, polyvinyl chloride particles, benzoguanamine-melamine formaldehyde particles, silicone particles, Fluorine resin particles, polyester resin particles, and the like are used.
Examples of the light-transmitting inorganic particles include silica particles, alumina particles, zirconia particles, titania particles, and inorganic particles having a hollow shape or pores.

Moreover, even if the light-transmitting fine particles have the same refractive index and particle size distribution, the diffuse transmission intensity distribution differs depending on the degree of aggregation of the light-transmitting particles. Therefore, two or more kinds of light-transmitting particles having different aggregation states are used. It is possible to adjust the diffuse transmission intensity distribution by changing the aggregation state by using two or more inorganic particles having different silane coupling treatment conditions.
In addition, the method of adding the silica etc. which have a particle diameter below the wavelength of visible light, for example, a particle diameter of about 50 nm or less, is mentioned suitably for aggregation of a translucent particle.

  In order to obtain the effect of internal diffusion, amorphous translucent particles such as silica having a particle diameter equal to or larger than the wavelength of visible light are effective. This is because amorphous particles have the effect of widening the distribution of transmission diffusion angles compared to spherical particles. However, amorphous translucent particles also have a wide internal reflection distribution, which affects the diffusibility of the coating and may make it difficult to adjust the diffuse transmission intensity. It is preferable to add it according to. More specifically, it is preferable to add the amorphous translucent particles within a range of less than 4% by mass with respect to the total amount of the spherical particles and the amorphous translucent particles.

  It is preferable to mix | blend translucent particle | grains so that 1-30 mass% may be contained in transparent resin (solid content), and the range of 2-25 mass% is more preferable. When it is 1% by mass or more, sufficient antiglare property and light diffusibility can be produced, and good visibility can be obtained. On the other hand, when it is 30% by mass or less, there is no reduction in contrast.

[Transparent resin]
As the transparent resin constituting the functional layer, an ionizing radiation curable resin or a thermosetting resin can be used. In order to form a functional layer, a resin composition containing an ionizing radiation curable resin or a thermosetting resin is applied to a transparent substrate, and monomers, oligomers and prepolymers contained in the resin composition are crosslinked and / or Alternatively, it can be formed by polymerization.
As the functional groups of the monomer, oligomer and prepolymer, those having ionizing radiation polymerization are preferable, and among them, a photopolymerizable functional group is preferable.

Examples of the photopolymerizable functional group include unsaturated polymerizable functional groups such as a (meth) acryloyl group, a vinyl group, a styryl group, and an allyl group.
Examples of the prepolymer and oligomer include acrylates such as urethane (meth) acrylate, polyester (meth) acrylate, and epoxy (meth) acrylate, silicon resins such as siloxane, unsaturated polyester, and epoxy resin.
Monomers include styrene monomers such as styrene and α-methylstyrene; methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, pentaerythritol (meth) acrylate, dipentaerythritol hexa (meth) acrylate, di Acrylic monomers such as pentaerythritol penta (meth) acrylate and trimethylolpropane tri (meth) acrylate; two in a molecule such as trimethylolpropane trithioglycolate, trimethylolpropane trithiopropylate, and pentaerythritol tetrathioglycol Examples include polyol compounds having the above thiol groups.

Moreover, it is also possible to add a polymer to the said resin composition and use it as a binder. Examples of the polymer include polymethyl methacrylate (PMMA). By adding the polymer, it is possible to adjust the viscosity of the coating liquid, and this has the advantage of facilitating the coating and facilitating the adjustment of unevenness formation due to particle aggregation.
Moreover, a radical photopolymerization initiator can be added to the resin composition as necessary. As the radical photopolymerization initiator, acetophenones, benzoins, benzophenones, phosphine oxides, ketals, anthraquinones, thioxanthones, azo compounds and the like are used.
As acetophenones, 2,2-dimethoxyacetophenone, 2,2-diethoxyacetophenone, p-dimethylacetophenone, 1-hydroxy-dimethylphenylketone, 1-hydroxy-dimethyl-p-isopropylphenylketone, 1-hydroxycyclohexylphenyl Ketone, 2-methyl-4-methylthio-2-morpholinopropiophenone, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone, 4-phenoxydichloroacetophenone, 4-t-butyl- Examples of benzoins include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl dimethyl ketal, and benzoin benzene sulfonic acid. Ester, benzoin toluenesulfonic acid ester, benzoin methyl ether, benzoin ethyl ether. Benzophenones include benzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyldiphenyl sulfide, 2,4-dichlorobenzophenone, 4,4-dichlorobenzophenone and p-chlorobenzophenone, 4,4′-dimethylaminobenzophenone. (Michler's ketone), 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone and the like can be used.
Moreover, a photosensitizer can also be mixed and used and the specific example includes n-butylamine, triethylamine, poly-n-butylphosphine, and the like.

Moreover, it is also possible to adjust the diffuse transmission intensity by the internal diffusion element by using a plurality of phase-separable resins as the transparent resin. That is, in the above-mentioned prepolymer, oligomer, monomer, and polymer, it is also possible to adjust the diffuse transmission intensity by the internal diffusion element by using a mixture of a compatible component and an incompatible component. For example, when one resin is a styrene resin (polystyrene, styrene-acrylonitrile copolymer, etc.), the other resin is a cellulose derivative (cellulose ester such as cellulose acetate propionate), a (meth) acrylic resin ( Suitable examples include polymethyl methacrylate), alicyclic olefin resins (polymers having norbornene as a monomer), polycarbonate resins, polyester resins, and the like. When one resin is a cellulose derivative (cellulose ester such as cellulose acetate propionate), the other resin is a styrene resin (polystyrene, styrene-acrylonitrile copolymer, etc.), (meth) acrylic resin. (Polymethyl methacrylate, etc.), alicyclic olefin resins (polymers having norbornene as a monomer, etc.), polycarbonate resins, polyester resins and the like are preferred.
The ratio (mass ratio) of the resin to be combined can be selected from the range of 1/99 to 99/1, preferably in the range of 5/95 to 95/5, more preferably in the range of 10/90 to 90/10, and 20 / The range of 80-80 / 20, especially the range of 30 / 70-70 / 30 is preferable.

  Furthermore, it is also possible to adjust the diffuse transmission intensity by the external diffusion element by using the prepolymer, oligomer and monomer having a large polymerization shrinkage. The larger the polymerization shrinkage, the larger the surface unevenness and the wider the transmission intensity distribution.

  In addition, a solvent is usually used in the radiation curable resin composition in order to adjust the viscosity and to dissolve or disperse each component. The solvent is preferably selected as appropriate in consideration of the fact that the surface state of the coating film varies depending on the coating and drying steps depending on the type of solvent used, and the transmission intensity distribution due to external diffusion can be adjusted. Specifically, it is selected in consideration of saturated vapor pressure, permeability to a transparent substrate, and the like.

The resin composition for forming the functional layer constituting the optical sheet of the present invention preferably contains an ionizing radiation curable resin as a transparent resin, translucent particles, and a solvent. Here, the resin composition impregnates the transparent substrate with a solvent impregnated in the transparent substrate (hereinafter sometimes referred to as “penetrating solvent”) and / or an ionizing radiation curable resin impregnated in the transparent substrate. It is preferable to include an ionizing radiation curable resin that is not impregnated into the solvent and / or the transparent substrate that is not impregnated. This is because the thickness of the functional layer can be controlled by adjusting the amount of impregnation into the transparent substrate, and as a result, the diffuse transmission intensity can be adjusted.
More specifically, the diffuse transmission intensity can be controlled by the amount of impregnation into the transparent substrate and the size of the translucent particles. Specifically, when the amount of impregnation of the solvent and / or ionizing radiation curable resin (hereinafter sometimes referred to as “solvent etc.”) into the substrate is small and the translucent particles are small, the solvent Although the functional layer is formed in a form in which most of the particles are embedded in the surface, the translucent particles are likely to aggregate, and the surface irregularities are relatively large. On the other hand, when a solvent having a large amount of impregnation into a transparent substrate and a light-transmitting particle having a small particle diameter are used in combination, the aggregation of the light-transmitting particles is reduced, and the surface unevenness is relatively small. become.
In addition, when a solvent and / or ionizing radiation curable resin with a large amount of impregnation into a transparent substrate is used in combination with a light-transmitting particle having a large particle size, the thickness of the functional layer is reduced. The light-sensitive particles protrude from the functional layer, and surface irregularities resulting from the light-transmitting particles can be obtained. On the other hand, when a solvent having a small amount of impregnation into a transparent substrate and a light-transmitting particle having a large particle size are used in combination, the thickness of the functional layer is increased. Protrusion to the surface is suppressed, and surface irregularities are relatively small.
In this way, by adjusting the amount of impregnation of the solvent and / or ionizing radiation curable resin into the transparent base material and controlling it in combination with the particle size of the translucent particles, various surface irregularities can be formed. Can be formed.
This technique is particularly effective when the transparent substrate is made of a cellulose resin.

Further, as the solvent, one kind can be used alone, or two or more kinds of solvents having different boiling points at room temperature and normal pressure can be contained. By using two or more solvents, the drying speed of the solvent can be controlled in various ways. When the drying speed is high, the particles are volatilized and the solvent is reduced and the viscosity is increased before the particles are sufficiently aggregated, so that further aggregation does not proceed. Therefore, controlling the drying speed will control the particle size of the translucent particles, and as described above, in relation to the degree of penetration of the solvent and / or ionizing radiation curable resin into the substrate, It leads to controlling the diffuse transmission intensity.
Specific solvents can be appropriately selected from the above viewpoints. Specific examples include aromatic solvents such as toluene and xylene, and ketones such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone. Are preferred. These can be used alone or in combination of two or more. It is preferable to use a mixture of at least one aromatic solvent and at least one ketone. In addition, in order to control the drying speed, cellosolves such as methyl cellosolve and ethyl cellosolve and cellosolve acetates, alcohols such as ethanol, isopropanol, butanol, and cyclohexanol may be mixed.

In the optical sheet of the present invention, additives other than translucent particles are blended in the transparent resin as necessary. For example, various inorganic particles can be added to improve physical properties such as hardness, optical properties such as reflectance, and scattering properties.
Examples of inorganic particles include metals such as zirconium, titanium, aluminum, indium, zinc, tin, and antimony, ZrO ₂ , TiO ₂ , Al ₂ O ₃ , In ₂ O ₃ , ZnO, SnO ₂ , Sb ₂ O ₃ , ITO, Examples thereof include metal oxides such as ATO and SiO ₂ . Other carbon, MgF, silicon, BaSO _4, CaCO _3, talc, and the like kaolin.
The particle size of the inorganic particles is preferably as fine as possible in the resin composition when the functional layer is applied in order to reduce the influence on the diffuse transmission intensity distribution, and the average particle size is 100 nm or less. It is preferable that it is the range of these. By miniaturizing the inorganic particles to 100 nm or less, an optical sheet that does not impair transparency can be formed. The particle diameter of the inorganic particles can be measured by a light scattering method or an electron micrograph.

In the present invention, various surfactants can be used to improve the properties such as anti-aggregation effect and anti-settling effect, and other leveling properties. Examples of the surfactant include silicone oil, a fluorine-based surfactant, and preferably a fluorine-based surfactant containing a perfluoroalkyl group.
Furthermore, in the present invention, an antifouling agent, an antistatic agent, a colorant (pigment, dye), a flame retardant, an ultraviolet absorber, an infrared absorber, an adhesion promoter, a polymerization inhibitor, an antioxidant, a surface modifier, etc. Can be added.

The transparent substrate used in the optical sheet of the present invention is not particularly limited as long as it is usually used in an optical sheet, such as a transparent resin film, a transparent resin plate, a transparent resin sheet, or transparent glass.
Transparent resin films include triacetylcellulose film (TAC film), diacetylcellulose film, acetylbutylcellulose film, acetylpropylcellulose film, cyclic polyolefin film, polyethylene terephthalate film, polyethersulfone film, polyacrylic resin film, polyurethane film Resin films, polyester films, polycarbonate films, polysulfone films, polyether films, polymethylpentene films, polyether ketone films, (meth) acrylonitrile films, polynorbornene resin films, and the like can be used. In particular, when the optical sheet of the present invention is used together with a polarizing plate, the TAC film and the cyclic polyolefin film are preferable because they do not disturb the polarization, and polyester films such as a polyethylene terephthalate film are preferable when the mechanical strength and smoothness are important. .

  The transparent substrate may be a multilayer or a single layer, and a primer layer may be provided on the surface for the purpose of adhesion to the coating film. In addition, in order to prevent interference fringes generated at the interface when there is a substantial difference in refractive index between the transparent substrate and the coating layer, for example, interference fringes having an intermediate refractive index between the transparent substrate and the coating layer. It is also possible to provide a prevention layer and to provide unevenness of about 0.3 to 1.5 μm as the surface roughness (ten-point average roughness Rz). Rz is a value measured according to JIS B0601 1994.

The optical sheet of the present invention can have functions such as hard coat properties, antiglare properties, antireflection properties, antistatic properties, and antifouling properties.
Hard coat properties are usually the maximum load at which scratches are not confirmed when a black tape is applied to the backside of the 10-round rubbing test while applying a load with pencil hardness (measured according to JIS K5400) or steel wool # 0000. (Steel wool scuff resistance) In the optical sheet of the present invention, the pencil hardness is preferably H or higher, more preferably 2H or higher. Further, in the steel wool scuff resistance, is preferably 200 g / cm ² or more, more preferably 500 g / cm ² or more, particularly preferably 700 g / cm ² or more.

Next, for the antiglare property, preferably, the transparent resin capable of imparting hard coat properties contains translucent particles for imparting antiglare property, and a solvent, and the projections of the translucent particles themselves. Or it is preferable that the unevenness | corrugation of a surface is formed by the processus | protrusion formed with the aggregate | assembly of a some particle | grain. The antiglare property is evaluated by the following method.
(Anti-glare evaluation method)
A measurement sample is produced by sticking an optical sheet on a flat black acrylic plate. A light source is incident from a direction of 15 degrees with respect to the normal direction of the measurement sample, and a reflection image of the light source is photographed by a CCD camera installed at a position in the mirror surface direction to obtain the maximum peak intensity of the reflected light. When this measurement is performed with two light sources of different sizes, the reflected light peak intensity value when measured with a large light source is P _L , and the reflected light peak intensity value when measured with a small light source is P _S , The antiglare property is evaluated by the formula (IV).
50 × log (P _L / P _S ) (IV)
The larger this value, the higher the antiglare property. In this evaluation, it is preferably 20 or more, more preferably 40 or more, and particularly preferably 60 or more.
Also, a measurement sample is prepared by sticking an optical sheet on a flat black acrylic plate, and a light source of about 900 lux is captured at an angle of, for example, 15 degrees, and the degree of blurring seen from the regular reflection direction is visually observed. May be evaluated.

For antireflection, a low refractive index layer is provided on the outermost surface in order to reduce the reflectance of the sheet. The refractive index of the low refractive index layer is preferably 1.5 or less, and more preferably 1.45 or less.
The low refractive index layer is formed of a material containing silica or magnesium fluoride, a fluororesin that is a low refractive index resin, or the like.
The thickness d of the low refractive index layer preferably satisfies d = mλ / 4n. Here, m represents a positive odd number, n represents the refractive index of the low refractive index layer, and λ represents the wavelength. m is preferably 1, and λ is preferably 480 to 580 nm. Moreover, it is preferable to have a relationship of 120 <n · d <145 from the viewpoint of low reflectance.

Moreover, it is preferable to provide antistatic performance in terms of preventing static electricity on the optical sheet surface. In order to impart antistatic performance, for example, a method of applying a conductive coating liquid containing conductive fine particles, a conductive polymer, a quaternary ammonium salt, thiophene and a reactive curable resin, or a transparent film is formed. Conventionally known methods such as a method of forming a conductive thin film by vapor deposition or sputtering of metal, metal oxide or the like can be mentioned. Further, the antistatic layer can be used as a part of a functional layer such as a hard coat, antiglare and antireflection.
As an index indicating antistatic property, there is a surface resistance value. In the present invention, the surface resistance value is preferably 10 ¹² Ω / □ or less, more preferably 10 ¹¹ Ω / □ or less, and particularly preferably 10 ¹⁰ Ω / □ or less. . The so-called saturation band voltage, which is the maximum voltage that can be stored in the optical film, is preferably 2 kV or less with an applied voltage of 10 kV.

  Further, an antifouling layer can be provided on the outermost surface of the optical sheet of the present invention. The antifouling layer lowers the surface energy and makes it difficult to attach hydrophilic or lipophilic stains. The antifouling layer can be applied by adding an antifouling agent, and examples of the antifouling agent include fluorine compounds, silicon compounds, and mixtures thereof, and compounds having a fluoroalkyl group are particularly preferred.

Hereinafter, the manufacturing method of the optical sheet of the present invention will be described in detail. In the present invention, as described above, it is important to control the manufacturing conditions so as to satisfy the equation 0.64 <Q / P <0.94 as an index.
The optical sheet of the present invention is produced by applying a resin composition constituting a functional layer to a transparent substrate. Various methods can be used as the coating method, such as dip coating, air knife coating, curtain coating, roll coating, wire bar coating, gravure coating, die coating, blade coating, Known methods such as a micro gravure coating method, a spray coating method, and a spin coating method are used.
In the present invention, since the transmission diffusion luminance characteristics vary depending on the coating amount, a roll coating method, a gravure coating method, and a die coating method that can easily obtain the functional layer thickness in a range of 1 to 20 μm are preferable.

After coating by any of the above methods, the solvent is dried by various known methods by being transported to a heated zone to dry the solvent. Here, by selecting the solid content concentration, coating solution temperature, drying temperature, drying air speed, drying time, solvent atmosphere concentration in the drying zone, etc., external diffusion due to the profile of the surface uneven shape and the translucent particles or the above-mentioned The internal diffusion due to the additive can be adjusted. In particular, a method of adjusting the transmission diffusion luminance characteristics by selecting drying conditions is simple and preferable. Specifically, the drying temperature is preferably 30 to 120 ° C., and the drying wind speed is preferably 0.2 to 50 m / s, and the transmission diffusion luminance characteristic can be adjusted by appropriately adjusting within this range.
More specifically, by increasing the drying temperature, the permeability of the resin and the solvent to the base material is improved. That is, by controlling the drying temperature, the permeability of the resin and solvent to the base material can be controlled, and as described above, the diffuse transmission intensity is controlled in relation to the particle size of the translucent particles. It leads to things.
For example, a resin composition for forming a functional layer is composed of a transparent resin, translucent particles, and a solvent, and the refractive index of the transparent resin penetrating component is lower than the refractive index of the translucent particles. When the settling and aggregation of the ring and translucent particles are the same, if the drying time until curing becomes longer, the low refractive component in the transparent resin penetrates the transparent substrate, and the refractive index of the transparent resin increases. Thus, the difference in refractive index from the translucent particles is reduced. On the other hand, since the ratio of the translucent particles to the transparent resin is increased, the translucent particles are likely to protrude on the surface, and surface irregularities are easily developed. Therefore, the longer the drying time, the smaller the internal diffusion and the larger the external diffusion. By using this permeability, the adhesion between the transparent base material and the functional layer due to the anchor effect and the occurrence of interference fringes that become noticeable when the difference in refractive index between the transparent base material and the functional layer is 0.03 or more are prevented. It is also possible to do. This is because the low-refractive component in the transparent resin penetrates the transparent base material, and the permeation layer expresses the function as a refractive index adjustment layer in which the refractive index continuously changes between the transparent base material and the functional layer. This is because it has the effect of eliminating the interface.

  Further, by increasing the drying speed, the aggregation time of the translucent particles is shortened, so that the aggregation does not proceed, and the same effect as when the particle size of the translucent particles that act substantially becomes smaller is exhibited. . That is, by controlling the drying rate, the particle size of the translucent particles that act substantially can be controlled. As described above, the penetration of the solvent and / or ionizing radiation curable resin into the base material is possible. It leads to controlling the diffuse transmission intensity in relation to the degree.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by this example.
(Evaluation methods)
1. Measurement of diffuse transmission intensity The optical sheet produced in each production example was measured by the method described in the specification.
2. Measurement of haze The optical sheet produced in each production example was measured with “Haze Meter HM-150” manufactured by Murakami Color Research Laboratory.
3. Antiglare property For the optical sheet produced in each production example, a measurement sample was prepared by sticking an optical sheet on a flat black acrylic plate, and a 900 lux light source was captured at an angle of 15 degrees. The degree of blurring seen from the reflection direction was visually evaluated. The evaluation 1 is the worst antiglare property, and the evaluation 5 is the best antiglare property.

4). Contrast measurement (light room contrast)
The bright room contrast is expressed by the following equation.
CR (L) = LW (L) / LB (L)
(CR (L): bright room contrast, LW (L): bright room white luminance, LB (L): bright room black luminance)
In general, since the change rate of bright room white luminance is small and the change rate of bright room black luminance is large, the bright room contrast is governed by the bright room black luminance. Further, since the original black luminance of the panel is smaller than the bright room black luminance and can be ignored, the blackness (black luminance) was evaluated in the following manner to substantially evaluate the bright room contrast. For the optical sheet produced in each production example, the back surface (the surface that does not have a surface layer, the surface on the side opposite to the observer side) is pasted on a flat black acrylic plate with no irregularities or warp via a transparent adhesive. To prepare a sample for evaluation. In addition, the black acrylic board used here is for preventing back surface reflection as described above, so that it does not have an air layer on the back surface of the optical sheet and can absorb visible light. There is no particular limitation. This sample is placed on a horizontal surface and sensory evaluation is performed under 30W of three-wavelength fluorescence (irradiates the surface of the optical sheet from the 45 degree direction) (an angle of about 45 degrees above the sample surface and opposite to the fluorescent lamp with respect to the vertical axis) (Visual observation) and blackness was evaluated in five stages. Evaluation 1 means that black is the worst and contrast is low, and evaluation 5 means that black is the best and contrast is high.

Production Example 1
Triacetyl cellulose (manufactured by Fuji Film Co., Ltd., thickness 80 μm) was prepared as a transparent substrate. As a transparent resin, a mixture (mass ratio; PETA / DPHA / PMMA = 86/5/9) of pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), and polymethyl methacrylate (PMMA) is used (refraction) 1.51), polystyrene particles (refractive index 1.6, average particle size 3.5 μm, (d75-d25) / MV is 0.05) and styrene-acrylic copolymer particles (transparent particles). 18.5 and 3.5 parts by mass of a refractive index of 1.56, an average particle diameter of 3.5 μm, and (d75-d25) / MV of 0.04) were added to 100 parts by mass of the transparent resin. A resin composition obtained by adding 190 parts by mass of a mixed solvent (mass ratio 7: 3) of toluene (boiling point 110 ° C.) and cyclohexanone (boiling point 156 ° C.) as a solvent to 100 parts by mass of the transparent resin. Was coated on the transparent substrate, and dried at 70 ° C. at a flow rate of 0.2 m / s for 1 minute. Thereafter, ultraviolet rays were irradiated (200 mJ / cm ² under a nitrogen atmosphere) to cure the transparent resin, and an optical sheet (antiglare sheet) was produced. The coating thickness was 3.5 μm. Table 2 shows the results of evaluating the optical sheet by the above method.

Production Examples 2 to 7 and Production Examples 10 to 19
In Production Example 1, the type of transparent substrate, the type of transparent resin, the type and content of translucent particles, the type and content of solvent, the drying conditions, and the coating thickness change as described in Table 1. Thus, an optical sheet (antiglare sheet) was produced. Table 2 shows the evaluation results for each optical sheet in the same manner as in Production Example 1.

Production Example 8
Triacetyl cellulose (manufactured by Fuji Film Co., Ltd., thickness 80 μm) was prepared as a transparent substrate. Pentaerythritol triacrylate (PETA, refractive index 1.51) was used as a transparent resin, and styrene-acrylic copolymer particles (refractive index 1.51, average particle size 9.0 μm, (d75- d25) / MV is 0.04) and polystyrene particles (refractive index 1.6, average particle size 3.5 μm, (d75-d25) / MV is 0.05), respectively, with respect to 100 parts by mass of the transparent resin. It was made to contain 10.0 mass parts and 16.5 mass parts. A resin composition obtained by adding 190 parts by mass of a mixed solvent (mass ratio 7: 3) of toluene (boiling point 110 ° C.) and cyclohexanone (boiling point 156 ° C.) as a solvent to 100 parts by mass of the transparent resin. Was coated on the transparent substrate, dried at a flow rate of 1 m / s at 85 ° C. for 1 minute. This was irradiated with ultraviolet rays (100 mJ / cm ^{2 in an} air atmosphere) to cure the transparent resin (formation of an antiglare layer).
On the coating layer (antiglare layer), PETA (pentaerythritol triacrylate, refractive index 1.51) as a transparent resin, and a mixed solvent of toluene (boiling point 110 ° C.) and cyclohexanone (boiling point 156 ° C.) as a solvent ( The resin composition obtained by blending 190 parts by mass with respect to 100 parts by mass of the transparent resin at a mass ratio of 7: 3) was applied, and 70 ° C. dry air was circulated at a flow rate of 5 m / s. It was dried for a minute (formation of a hard coat layer). This was irradiated with ultraviolet rays (200 mJ / cm ² under a nitrogen atmosphere) to cure the transparent resin, and an optical sheet (antiglare sheet having a hard coat layer) was produced. The coating thickness was 12.0 μm as a whole. Table 2 shows the evaluation results of this optical sheet in the same manner as in Production Example 1.

Production Example 9
In Production Example 8, the content of polystyrene particles that are translucent particles is 6.5 parts by mass with respect to 100 parts by mass of the transparent resin, and the production thickness is 13.0 μm in total. In the same manner as in Example 8, an optical sheet (antiglare sheet having a hard coat layer) was produced. The results evaluated in the same manner as in Production Example 1 are shown in Table 2.

A: polystyrene particles (refractive index 1.6, average particle size 3.5 μm, (d75-d25) / MV is 0.05)
B: Styrene-acrylic copolymer particles (refractive index 1.56, average particle size 3.5 μm, (d75-d25) / MV is 0.04)
C: Styrene-acrylic copolymer particles (refractive index 1.51, average particle size 9.0 μm, (d75-d25) / MV is 0.04)
D: amorphous silica (refractive index 1.45, average particle size 1.5 μm, (d75-d25) / MV is 0.6)
E: amorphous silica (refractive index 1.45, average particle size 2.5 μm, (d75-d25) / MV is 0.8)
F: Melamine particles (refractive index 1.66, average particle size 2.0 μm, (d75-d25) / MV is 0.2)
M: a mixture of pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), and polymethyl methacrylate (PMMA) (mass ratio; PETA / DPHA / PMMA = 86/5/9) (refractive index 1. 51)
N: Pentaerythritol triacrylate (PET) (refractive index 1.51)
X: Mixture of toluene (boiling point 110 ° C.) and methyl isobutyl ketone (boiling point 116 ° C.) (mass ratio 8: 2)
Y: Mixture of toluene (boiling point 110 ° C.) and cyclohexanone (boiling point 156 ° C.) (mass ratio 7: 3)

In Production Examples 1 to 19, Q / P was calculated from the measurement results of diffuse transmission intensity, and the results of plotting Q / P on the horizontal axis and contrast and antiglare properties on the vertical axis are shown in FIGS. 5 and 6, respectively. . Q / P, contrast, and antiglare properties are correlated. In the present invention, Production Examples 3, 4, 8 to 11, 15, 16, and 18 correspond to Examples satisfying 0.64 <Q / P <0.94, and Production Examples 1, 2, 5 to 5 are satisfied. 7, 12-14, 17 and 19 correspond to comparative examples which do not satisfy the above formula. While the light quality contrast of the optical sheet of the example is good, the light quality contrast of the optical sheet having Q / P of 0.64 or less shows a low value. On the other hand, an optical sheet having a Q / P of 0.94 or more has insufficient antiglare properties.
In Production Examples 1 to 19, the results of plotting haze on the horizontal axis and contrast on the vertical axis from the measurement results of haze values are shown in FIG. Further, the result of plotting haze on the horizontal axis and anti-glare property on the vertical axis is shown in FIG. Furthermore, the result of plotting the ratio of internal haze to total haze on the horizontal axis and the contrast on the vertical axis is shown in FIG. 2. The horizontal axis represents the ratio between internal haze and total haze, and the horizontal axis represents anti-glare properties. The plotted result is shown in FIG. There is no correlation between haze and contrast and antiglare properties, and the ratio of internal haze / total haze to contrast and antiglare properties.

  The optical sheet of the present invention has a small reduction in contrast and good antiglare properties.

It is a figure which shows the relationship between a haze value and contrast. It is a figure which shows the relationship between ratio of internal haze / total haze, and contrast. It is a conceptual diagram which shows the measuring method of the diffuse transmission intensity in this invention. It is a conceptual diagram explaining the principle of the evaluation method of this invention. It is a figure which shows the correlation of Q / P and contrast. It is a figure which shows the correlation of Q / P and anti-glare property. It is a figure which shows the relationship between a haze value and anti-glare property. It is a figure which shows the correlation of ratio of internal haze / total haze, and anti-glare property.

Explanation of symbols

1. Optical sheet Base material 3. Surface layer 4. 4. Translucent particles 5. Direction of incident light beam Functional layer (antiglare layer)
7). Forward transmission direction

Claims (18)

A display element surface characterized by having a functional layer on at least one surface of a transparent substrate, having a diffusion element on the outermost surface and / or inside of the functional layer, and having a relationship of the following formula (I) Optical sheet used.
0.64 <Q / P <0.94 (I)
P: Sum of diffuse transmission intensities Q obtained by measuring the diffusely transmitted light when irradiated with visible light perpendicularly from the surface opposite to the viewer side of the optical sheet in a range of −85 degrees to +85 degrees. (Normal transmission intensity); Diffuse transmission intensity at 0 degree Furthermore, the optical sheet of Claim 1 which has the relationship of following formula (II).
0.82 <Q / P <0.94 (II) Furthermore, the optical sheet of Claim 1 which has the relationship of following formula (III).
0.86 <Q / P <0.94 (III)   The optical sheet according to any one of claims 1 to 3, wherein the functional layer is formed by dispersing translucent inorganic particles and / or translucent organic particles in a transparent resin.   The optical sheet according to claim 1, wherein the functional layer is made of a transparent resin, and the transparent resin is made of a plurality of resins capable of phase separation.   The optical sheet according to claim 4, wherein the transparent resin and the translucent inorganic particles and / or translucent organic particles have different refractive indexes.   The optical sheet according to claim 4 or 6, wherein irregularities are provided on the surface of the functional layer by the light-transmitting inorganic particles and / or the light-transmitting organic particles.   The optical sheet according to claim 6 or 7, wherein a refractive index difference between the transparent resin and the translucent inorganic particles and / or translucent organic particles is 0.01 to 0.25.   The optical sheet according to any one of claims 4 and 6 to 8, wherein an average particle diameter of the translucent inorganic particles and / or translucent organic particles is 0.5 to 20 µm.   When the average diameter of the light-transmitting inorganic particles and / or light-transmitting organic particles is MV, the cumulative 25% diameter is d25, and the cumulative 75% diameter is d75, (d75−d25) / MV is 0. The optical sheet according to any one of claims 4 and 6 to 9, wherein the optical sheet is 25 or less.   The optical sheet according to any one of claims 4 and 6 to 10, wherein 1 to 30% by mass of the translucent inorganic particles and / or translucent organic particles are contained in the transparent resin.   The optical sheet according to any one of claims 1 to 11, wherein the unevenness provided on the surface of the mold is reversely transferred to provide the unevenness on the surface of the functional layer.   5. The transparent resin is an ionizing radiation curable resin, and the functional layer is formed by applying an ionizing radiation curable resin composition containing the ionizing radiation curable resin on a transparent base material and curing by crosslinking. The optical sheet in any one of -12.   The transparent substrate is made of a cellulose-based resin, and the ionizing radiation curable resin composition includes a solvent that impregnates the transparent substrate and / or an ionizing radiation curable resin that impregnates the transparent substrate, and a solvent that does not impregnate the transparent substrate. And / or an ionizing radiation curable resin not impregnated in the transparent substrate, and having the relationship of any one of formulas (I) to (III).   The optical sheet according to claim 14, wherein the transparent substrate is triacetylcellulose.   The optical sheet according to claim 1, wherein the transparent substrate is polyethylene terephthalate. The optical sheet according to claim 1, wherein the functional layer includes a hard coat layer and has a steel wool scuff resistance of 200 g / cm ² or more.   The optical sheet according to any one of claims 1 to 17, wherein an antireflection functional layer is formed on the outermost layer.

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