JP2010122709A - Optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which is excellent in black color feeling and image sharpness. <P>SOLUTION: The optical sheet is used on a surface of a display element and includes a functional layer on at least one surface of a transparent substrate and a diffusion component on an outermost surface of and/or in the functional layer. The optical sheet satisfies inequality (I): 0.16<R/V<0.71 (I), wherein R is diffusion regular reflection intensity, i.e., intensity in a diffusion regular reflection direction and V is total sum of diffusion reflection intensity measured for each degree between -θ° and +θ° toward the diffusion regular reflection direction when the optical sheet is irradiated with visible rays. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical sheet that is excellent in blackness and image cutout and is suitable for mixed use of a moving image and a still image.

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).
However, even if the haze value is the same, there are many cases where the contrast is different. For example, even if the haze value and the ratio of the internal haze and the total haze are used as an index, a good optical sheet is always stably produced. I found it impossible.

In recent years, with the widespread use of various distribution systems such as 1Seg, opportunities to view both still images and moving images on the same display are increasing. For this reason, the image quality required for the display terminal is also changing, and there is a demand for the development of an optical sheet that is excellent for mixed use of still images and moving images.
As an example, as shown in Patent Documents 4 and 5, the required performance is different between a still image and a moving image, and the viewing state of an observer is also different. As a result of intensive studies on the required performance of the optical sheet for moving images and still images, the present inventors have high contrast as an image quality that can be appreciated for moving images, and increase the teri and brightness of images. I found out that an image with a sense of vigor is required.
In addition, the performance required for such moving images has both dynamic feeling and contrast (for example, it looks glossy black when displaying black, or it looks glossy and lively when displaying skin color, etc.) ) Is called “blackness”.
In addition, for still images, an image with excellent contrast and anti-reflection properties is required, and the performance that combines contrast and anti-reflection properties required for still images is called `` image loss ''. Called. That is, an optical sheet excellent in blackness and image cut is desired.

JP 2002-267818 A JP2007-334294A JP2007-17626 JP 2006-81089 A JP 2006-189658 A

  Under such circumstances, an object of the present invention is to provide an optical sheet that is excellent in blackness and image cutout and is suitable for mixed use of a moving image and a still image.

The present inventors have found that, in order to obtain a moving image with excellent blackness, the normal transmission diffusion of the optical sheet is large, and the stray light component of external light and video light is reduced. .
On the other hand, in order to obtain a still image with excellent image cut-off, it is necessary to achieve both contrast and anti-reflection properties.
However, if the so-called anti-glare property is increased for the purpose of improving the anti-reflection property, the reflection diffusion becomes large, the contrast is lowered, and the cutout of the image is deteriorated.
Therefore, as a result of intensive studies on image cuts, the present inventors have found that the cause of the difficulty in reflection for the observer often matches the external image in which the observer's focus is reflected when viewing the image. It was found that this was because the viewpoint was not fixed on the image.
As a result of further investigation, the outline of the reflected external video is made unclear, so that the reflection does not become difficult and the reduction in contrast can be suppressed, and it is possible to improve the cutout of the image. I found out.
In other words, in order to achieve both the cut-out of images required for still images and the blackness of moving images, the small reflection that suppresses the decrease in regular transmission diffusion and blurs the outline of the reflected external video. It was found that it is important to give diffusion appropriately.
This means that the regular reflection component is converted to diffusion near the regular reflection. Considering the following (a) to (c), it is possible to achieve both compatibility of the still image cut and the blackness of the moving image. This means that the intended optical sheet can be obtained. That is, (a) transmission diffusion is small, (b) regular reflection is small, and (c) conversion to diffusion in the vicinity of regular reflection is satisfied.

Optical sheets generally add conductive particles to provide an antistatic function, and fine particles are often added to prevent glare and surface unevenness shaping. Diffusion due to surface unevenness (hereinafter referred to as external diffusion) In addition to internal diffusion.
Here, when the diffusion due to the internal diffusion factor and the diffusion due to the surface shape are compared, the refractive index ratio between the resin constituting the optical sheet and the internal diffusion factor is significantly larger than the refractive index ratio between the air and the resin on the external surface. Since the surface is small, in the optical sheet having a concavo-convex shape on the surface, the surface shape is dominant in the transmission diffusion strength.

Further, assuming that the exit angle from the inclined plane θ is ψ and the refractive index of the coating film is n, n * sinθ = sinψ from Snell's law, and the exit angle ψ is A · sin (n * sinθ) −θ. It becomes. On the other hand, the reflection shows twice the change of the inclined surface θ according to the law of reflection, so the reflection angle ψ is 2 * θ.
In the case of 1.5, which is the refractive index of a general coating film, the reflection and transmission diffusion angles with respect to the surface tilt angle are shown in FIG. 1 within the surface shape range (within 10 degrees) of the optical sheet. As shown in FIG. 1, the diffusion angle of reflection and transmission is proportional to the surface inclination angle, and it can be seen that the diffusion angle by reflection is always about 30% larger than the diffusion angle by transmission. That is, small transmission diffusion is almost synonymous with small diffuse reflection.
Therefore, since (a) small transmission diffusion is equivalent to (a ′) low reflection diffusion, an optical system that achieves both the above-described anti-reflection characteristics of still images and the blackness of moving images. For the sheet, it is preferable to convert regular reflection into diffusion in the vicinity of regular reflection.
On the other hand, since small diffusion is preferable for blackness, it is important that the conversion to the vicinity of regular reflection is not excessive, and the reflection diffusion intensity is preferably controlled within a specific range.

By the way, the haze value that has been used in the optical sheet so far is the ratio of the light diffused by 2.5 degrees or more from the regular transmission with respect to the total light as shown in JIS K7136. It is impossible to come up with the idea of using diffusion in the vicinity of regular reflection, such as diffusion less than 2.5 degrees.
Here, the diffusion intensity in the vicinity of regular reflection in the case of isotropic diffusion will be considered.
As shown in FIG. 2, when a layer having a diffuse reflection intensity distribution of b is laminated on a transparent substrate having a diffuse reflection intensity distribution of a, the reduction rate of the diffuse reflection intensity is larger as it approaches 0 degrees. The closer to 0 degrees, the greater the decrease in intensity, and the optical sheet has a diffuse reflection intensity distribution of c.
That is, when the total reflected light amount is constant, the total (V) of the reflection intensities measured for each optical sheet with a larger change in the reflection intensity distribution near 0 degrees shows a smaller value, and the reflection intensity near 0 degrees. The sheet becomes smaller as the change in distribution becomes smaller. Further, the optical sheet having a wider reflection intensity distribution from the beginning shows a smaller value of V, and the optical sheet having a narrower reflection intensity distribution from the beginning has a larger V.

More specifically, in FIG. 4 showing the relationship between the reflection diffusion angle and the intensity, the total reflected light amount of each of the optical sheets having the reflection diffusion characteristics aa, bb, and cc is a rotating body around the y axis. When the volume Vaa, Vbb, and Vcc are equal, if the integrated reflectance is equal, Vaa = Vbb = Vcc.
Here, a case is considered where the specular reflection intensity of the optical sheet having the diffusion characteristic aa is reduced to Oh and the diffusion characteristic becomes bb and cc. In the case of bb, the volume Vbaa of the rotating body in the part indicated by the oblique line indicated by bb is reduced, and the part having a larger diffusion than the diffusion angle b has a characteristic of bb having a stronger intensity than aa. At this time, since Vaa = Vbb, Vbaa is distributed to the volume Vhbb of the donut-shaped rotating body.
Similarly, in the case of cc, the volume Vcaa of the rotating body in the portion indicated by the oblique line indicated by cc decreases, and in the portion where the diffusion is larger than the diffusion angle c, the strength of cc is stronger than aa. At this time, since Vaa = Vcc, Vhaa is allocated to the volume Vhcc of the donut-shaped rotating body.
In addition, the amount of light is thought to be proportional to the product of the square of the diffusion angle and the intensity at that diffusion angle. The strength is lower.
That is, the total reflection intensity V is stray light that cannot be ignored even at an intermediate angle between them, as well as anti-glare properties that have a large influence in the vicinity of specular reflection, white turbidity that has a large influence on a portion having a large diffusion angle, etc. It is related to all reflection diffusion angles.
Therefore, R / V indicates the degree to which the regular reflection is changed to the diffusion in the vicinity of the regular reflection, and at the same time, the influence of stray light or the like is taken into account, and the blackness and cut are evaluated with higher accuracy.

The present invention has been completed based on the above findings,
(1) An optical sheet used on a display element surface having a functional layer on at least one surface of a transparent substrate and having a diffusing element on the outermost surface and / or inside of the functional layer, and having the following formula (I) Optical sheet characterized by having a relationship 0.16 <R / V <0.71 (I)
R (diffuse regular reflection intensity); intensity in the diffuse regular reflection direction V: diffuse reflection intensity measured every degree from −θ degree to + θ degree with respect to the diffuse regular reflection direction when the optical sheet is irradiated with visible light And (2) a method for producing an optical sheet having a functional layer on at least one surface of a transparent substrate, and having a diffusing element on the outermost surface and / or inside of the functional layer, the formula (I) The present invention provides a method for producing an optical sheet for use on the surface of a display element, wherein the production conditions are controlled so as to have the following relationship.

  According to the present invention, as can be seen from the graphs of the relationship between blackness and image cut and total haze (FIG. 5), internal haze (FIG. 6), internal haze / total haze (FIG. 7), As can be clearly seen from FIG. 8 showing the relationship between blackness and image cut-off and R / V, evaluation of blackness and image cut-out that could not be evaluated with the haze value can be easily performed. It is possible to provide an optical sheet that is excellent in image quality and excellent in image cutting.

It is a figure which shows the diffusion angle of reflection and permeation | transmission with respect to a surface inclination angle. It is a figure which shows diffusion intensity distribution. It is a conceptual diagram which shows the measuring method of the diffuse reflection intensity in this invention. It is a conceptual diagram which shows the detailed description of diffusion intensity distribution. It is a figure which shows total haze, a black feeling, and a piece. It is a figure which shows an internal haze, a black feeling, and a cut. It is a figure which shows the ratio of an internal haze and a total haze, a black feeling, and a cut. It is a figure which shows R / V, a black feeling, and a cut.

The optical sheet of the present invention is an optical sheet having a functional layer on at least one surface of a transparent substrate, and having a diffusing element on the outermost surface and / or inside of the functional layer, and 0.16 <R / V Control is performed so as to have a relationship of <0.71.
Hereinafter, a method for measuring R and V will be described with reference to FIG. 3. As shown in FIG. 3, when the optical sheet 1 is irradiated with visible light from the direction 4, it is diffusely reflected in the direction 5, and Part of the light is diffused. This direction 5 is the diffuse regular reflection direction, and the intensity of light in the diffuse regular reflection direction is defined as the diffuse regular reflection intensity R.
As will be described later, a visible light absorbing material 8 such as a black acrylic plate is attached to the back surface of the transparent substrate 2 with an adhesive to suppress back surface reflection and match the conditions during actual use. To do.

Next, V is the total obtained by measuring the diffuse reflection intensity from −θ degrees to + θ degrees shown in FIG. With respect to θ for determining the measurement range, the measurement accuracy becomes higher as the angle range is larger, but usually about 45 degrees provides sufficient measurement accuracy. Note that the maximum measurement range of θ can be changed by changing the angle of the incident light.
Then, in the optical sheet manufacturing process, R / V is used as an index to select materials, control manufacturing conditions, and the like to obtain an optical sheet that satisfies the above formula (I).
Specifically, the diffuse reflection intensity is measured as follows.

(Measurement method of diffuse reflection intensity)
A sample for evaluation is prepared by attaching the back surface of the optical sheet (the surface having no surface layer, the surface opposite to the viewer side) to a flat black acrylic plate having no irregularities or warping through a transparent adhesive. .
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.
For example, when measuring in a production line, it is also possible to measure online by a method such as applying a black paint to the back surface of the inspection portion of the optical sheet.
Next, the evaluation sample is installed in a measuring apparatus, and a light beam is incident on the optical sheet side surface of the evaluation sample at an angle of 45 degrees from the normal of the surface. The diffuse reflection intensity is obtained by scanning the light receiver at every time in the range of −θ degrees to + θ degrees with respect to the diffuse regular reflection direction for the light that is incident on the optical sheet surface of the evaluation sample and diffusely reflected. taking measurement.
In addition, 45 degrees which is the regular reflection direction of incident light is defined as a diffuse regular reflection direction. The apparatus for measuring the diffuse reflection intensity is not particularly limited, but in the present invention, Nippon Denshoku Industries (
"GC5000L" manufactured by Co., Ltd. was used.

The present invention is characterized by controlling the following formula (I) as an index.
0.16 <R / V <0.71 (I)
By setting R / V to exceed 0.16, it is possible to obtain an optical sheet that is excellent in blackness and has good image cutting. From the viewpoint of further improving the blackness, R / V is preferably more than 0.20, and more preferably more than 0.31.
Further, from the viewpoint of further improving the cutout of the image, it is more preferable that R / V is less than 0.62.

  Next, the optical sheet of the present invention satisfies the above formula (I). An optical sheet satisfying the above formula (I) has excellent blackness and excellent image cutout.

In order to achieve 0.16 <R / V <0.71 in the present invention, it is important to adjust the reflected luminance distribution and intensity by the internal diffusion element and the external diffusion element.
As a method of adjusting the reflection 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. In addition, the concentration of additives other than the translucent particles that can be added to the transparent resin also affects the diffuse reflection intensity by the internal diffusion element.

On the other hand, as a method of adjusting the diffuse reflection 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 the 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. Thereby, the uneven | corrugated shape can be provided in the surface of an optical sheet.
The method (2) is effective in providing glare prevention and reflection resistance because fine irregularities having a smooth surface can be obtained, and the method (3) described above is performed with translucent particles. Since the performance can be adjusted by selecting transparent resin, coating thickness, solvent selection, drying conditions, permeability to transparent substrate, etc., the process is short and the work is simple, so it can be manufactured at low cost It is effective in.
In addition, 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 reflection 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 reflection intensity by the external diffusion element and the method of adjusting the diffuse reflection intensity by the internal diffusion element can be designed separately and independently. Other than the contrast, it is preferable in terms of easy adjustment of optical performance such as resolution, glare and anti-reflection.
Moreover, since the diffuse reflection intensity can be adjusted by an external diffusion element without considering the optical performance of the resin used, a resin that exhibits physical properties such as hard coat properties, antifouling properties, and antistatic properties of the surface resin. Is easy to select.

[Translucent particles]
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 reflection intensity distribution due to 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 this is difficult, a degree of freedom in designing the diffuse reflection intensity distribution is ensured.

In addition, the smaller the variation in the particle size of the translucent particles, the less the scattering characteristics, and the easier the diffuse reflection intensity distribution design. More specifically, it is preferable that (d75−d25) / MV is not more than 0.25, where MV is an average diameter by weight average, d25 is a cumulative 25% diameter, and d75 is a cumulative 75% diameter. More preferably, it is .20 or less.
The cumulative 25% diameter refers to the particle diameter when counted from a particle having a small particle diameter in the particle size distribution and reaches 25% by mass. The cumulative 75% diameter is similarly counted to 75% by mass. The particle diameter when it becomes%.
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 and the translucent particles constituting the functional layer is 0.01 to 0.25. If the refractive index difference is 0.01 or more, glare can be suppressed, and if it is 0.25 or less, the diffuse reflection 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.

Also, 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 and having a particle diameter difference of 0.5 μm or more are used in combination. Or a combination of two or more kinds of light-transmitting particles having a refractive index difference of 0.01 or more, or a combination of spherical light-transmitting particles and amorphous light-transmitting particles. Adjustments can be made.
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, 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.

Further, even if the light-transmitting fine particles have the same refractive index and particle size distribution, the diffuse reflection intensity distribution varies 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. The diffuse reflection intensity distribution can be adjusted by changing the aggregation state by using two or more kinds of 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 prevention 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 reflection 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 reflection 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, reflection resistance can be obtained. On the other hand, when it is 30% by mass or less, there is little decrease in contrast and good visibility can be obtained.

[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 benzenesulfonic acid. Ether, 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 possible to adjust the diffuse reflection 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 reflection intensity by the internal diffusion element by mixing and using a compatible component and an incompatible composition.
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, the diffuse reflection intensity by the external diffusing element can be adjusted 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 diffuse reflection intensity distribution.
Conversely, addition of a compatible polymer to the ionizing radiation curable resin or thermosetting resin, or addition of fine particles having a wavelength less than or equal to the wavelength of light, for example, fine particles having a wavelength of 100 nm or less, can reduce polymerization shrinkage. It is also possible to adjust the diffuse reflection intensity by the external diffusion element.

  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 type of solvent used and the steps of coating and drying, so that the reflection intensity distribution by external diffusion can be adjusted. Specifically, it is selected in consideration of saturated vapor pressure, permeability to a transparent substrate, and the like.

In the production method of the present invention, the resin composition for forming the functional layer preferably contains an ionizing radiation curable resin as a transparent resin, translucent particles, and a solvent.
Here, the resin composition does not impregnate the transparent base material with the solvent impregnated in the transparent base material (hereinafter sometimes referred to as “permeable solvent”) and / or the ionizing radiation curable resin impregnated in the transparent base material. It is preferable that an ionizing radiation curable resin not impregnated in the solvent and / or the transparent substrate is included.
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 reflection intensity can be adjusted.
More specifically, the diffuse reflection 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 etc. The functional layer is formed in such a manner that most of the particles are embedded therein, but since the translucent particles are likely to aggregate, 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 and / or relative evaporation rates 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 rate 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 reflection intensity.
The relative evaporation rate is a rate obtained by the following equation as shown in ASTM-D3539, and the larger the number, the faster the evaporation. Relative evaporation rate = time required for n-butyl acetate to evaporate / time required for some solvent to evaporate.
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 according to the present invention, additives other than the 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 . In addition, carbon, MgF, silicon, BaSO ₄ , CaCO ₃ , talc, kaolin and the like are included.
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 reflection 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.
When a resin composition containing a solvent is applied and dried, a difference in surface tension or the like occurs between the film surface and the inner surface in the coating film, thereby causing a large number of convections in the film. This convection becomes a yuzu skin and a coating defect.
It also has an adverse effect on blackness and image sharpness. When such a surfactant is used, this convection can be prevented, so that not only a concavo-convex film having no defects or unevenness can be obtained, but also the diffuse reflection intensity characteristics can be easily adjusted.
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, or 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 according to the present invention can be provided with functions such as hard coat properties, anti-reflection properties, antireflection properties, antistatic properties, and antifouling properties.
Hard coat property is usually the maximum load at which scratches are not confirmed when a black tape is applied to the backside of the 10-reciprocal 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 according to the present invention, the pencil hardness is preferably H or higher, more preferably 2H or higher. Further, the steel wool scuff resistance is preferably 200 g / cm ² or more, more preferably 500 g / cm ² or more, and particularly preferably 700 g / cm ² or more.

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, reflection resistance, 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 production conditions so as to satisfy the expression 0.16 <R / V <0.71 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 reflection / diffusion luminance characteristics change depending on the coating amount, a roll coating method, a gravure coating method, and a die coating method, which can easily obtain the thickness of the functional layer 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.
By selecting the solvent relative evaporation rate, solid content concentration, coating solution temperature, drying temperature, drying air velocity, drying time, solvent atmosphere concentration in the drying zone, etc. Internal diffusion due to the light-sensitive particles and the additives can be adjusted.
In particular, a method of adjusting the reflection / diffusion luminance characteristics by selection of drying conditions is simple and preferable. The specific drying temperature is preferably 30 to 120 ° C. and 0.2 to 50 m / s at the drying air speed, and the reflection 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 reflection intensity is controlled in relation to the particle size of the translucent particles. It leads to things.
For example, the resin composition for forming the functional layer is made of a transparent resin, a light-transmitting particle having a higher refractive index than that of the transparent resin, and a solvent, and the refractive index of the component having the permeability of the transparent resin is that of the light-transmitting particle. If the sedimentation and aggregation of the leveling and translucent particles are lower than the refractive index, and the drying time until curing becomes longer, the low refractive component in the transparent resin penetrates the transparent substrate, The refractive index of transparent resin rises and the refractive index difference with translucent particles decreases.
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 generation of interference fringes that become noticeable when the refractive index difference 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.

In addition, 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 is exhibited as when the particle size of the translucent particles that act substantially becomes smaller. .
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 reflection 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 regular reflection intensity and diffuse reflection intensity The optical sheet produced in each production example was measured by the method described in the specification text.
2. Evaluation of blackness and image cutout The polarizing plate on the outermost surface of a liquid crystal television “KDL-40X2500” manufactured by Sony Corporation was peeled off, and a polarizing plate without surface coating was attached.
Subsequently, the transparent adhesive film for optical films (total light transmittance of 91% or more, haze of 0.3% or less, film thickness of 20 to 20%, so that the surface coated surface side is the outermost surface of the sample prepared in each production example thereon. A 50 μm product such as MHM series (manufactured by Niei Engineering Co., Ltd.) was used.
Place the LCD TV in a room with an illuminance of about 1,000 Lx, display the DVD “Phantom of the Opera” by Media Factory, and place it about 1.5 to 2.0 meters away from the LCD TV From the above, the video was viewed by 15 test subjects, and a sensitivity evaluation of a three-step evaluation was performed on the following items. The evaluation criteria are as follows, and the most frequent evaluation result was used as the final result. (1) Blackness feeling: When moving images were displayed, it was determined by whether or not the image had a high contrast, and the images had teri and shine and felt a dynamic feeling.
○: 10 or more who answered good △: 5-9 who answered good ×; 4 or less who answered good (2) Image cuts: High contrast when displaying still images In addition, it was excellent in reflection resistance (a state in which the observer and the background reflection of the observer were not worried) and judged whether or not a still image was visible.
○: 10 or more people who answered good △; 5-9 people who answered good ×; 4 or less people who answered good

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 1.60, 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 size of 3.5 μm, and (d75-d25) / MV of 0.04) were added to 100 parts by mass of the transparent resin.
As a solvent, a mixed solvent (mass ratio 7: 3) of toluene (boiling point 110 ° C., relative evaporation rate 2.0) and cyclohexanone (boiling point 156 ° C., relative evaporation rate 0.32) is used with respect to 100 parts by mass of the transparent resin. The resin composition obtained by blending 190 parts by mass was applied to the transparent substrate, and dried at 70 ° C. at a flow rate of 0.2 m / s for 1 minute.
Thereafter, the transparent resin was cured by irradiating with ultraviolet rays (200 mJ / cm ² under a nitrogen atmosphere) to produce an optical sheet. 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 are listed in Table 1. An optical sheet was prepared by changing. Table 2 shows the evaluation results for each optical sheet in the same manner as in Production Example 1.

Production Example 8
Triacetyl cellulose (Fuji Film Co., Ltd., thickness 80 μm) was prepared as a transparent substrate.
Pentaerythritol triacrylate (PETA, refractive index 1.51) was used as the 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 1.60, 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.
As a solvent, a mixed solvent (mass ratio 7: 3) of toluene (boiling point 110 ° C., relative evaporation rate 2.0) and cyclohexanone (boiling point 156 ° C., relative evaporation rate 0.32) was added to 100 parts by mass of the transparent resin. On the other hand, the resin composition obtained by blending 190 parts by mass was applied to the transparent substrate, and dried at 85 ° C. at a flow rate of 1 m / s for 1 minute.
This was irradiated with ultraviolet rays (100 mJ / cm ^{2 in an} air atmosphere) to cure the transparent resin.
On the coating layer, PETA (pentaerythritol triacrylate, refractive index 1.51) as a transparent resin, and toluene (boiling point 110 ° C., relative evaporation rate 2.0) and cyclohexanone (boiling point 156 ° C., relative evaporation) as a transparent resin. A resin composition obtained by blending 190 parts by mass of a mixed solvent (mass ratio 7: 3) with a speed of 0.32) with respect to 100 parts by mass of the transparent resin was applied at a flow rate of 5 m / s. C. Dry air was circulated and dried for 1 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, thereby producing an optical sheet. The total coating thickness was 12.0 μm. 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 light-transmitting particles was 6.5 parts by mass with respect to 100 parts by mass of the transparent resin, and the coating thickness was 13.0 μm in total. In the same manner as in Example 8, an optical sheet was produced. The results evaluated in the same manner as in Production Example 1 are shown in Table 2.

A: polystyrene particles (refractive index 1.60, 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 diameter 2.5 μm, (d75-d25) / MV is 0.8)
P: 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)
Q: pentaerythritol triacrylate (PETA) (refractive index 1.51)
X: Mixture of toluene (boiling point 110 ° C., relative evaporation rate 2.0) and methyl isobutyl ketone (boiling point 116 ° C., relative evaporation rate 1.6) (mass ratio 8: 2)
Y: Mixture of toluene (boiling point 110 ° C., relative evaporation rate 2.0) and cyclohexanone (boiling point 156 ° C., relative evaporation rate 0.32) (mass ratio 7: 3)

In Production Examples 1 to 19, R / V was calculated from the measurement results of diffuse reflection intensity. It can be seen that the optical sheet satisfying the formula (I) is well-balanced with excellent blackness and image cutout.
In the present invention, Production Examples 1-4, 8-12, 15, 16, and 18 correspond to Examples satisfying 0.16 <R / V <0.71, and Production Examples 5-7, 13, 14, 17, and 19 correspond to comparative examples that do not satisfy the above formula.

  According to the optical sheet of the present invention, it is possible to easily evaluate the blackness and image breakage that could not be evaluated with the conventional haze value, and to stabilize the optical sheet that is excellent in blackness and image breakage. Can be provided.

1. Optical sheet Base material 4. 4. Light incident direction 5. Diffuse regular reflection direction Functional layer (antiglare layer)
7). Translucent particles 8. Visible light absorbing material (black acrylic board)

Claims (18)

An optical sheet for use on a liquid crystal display element surface having a functional layer on at least one surface of a transparent substrate made of triacetylcellulose or cyclic polyolefin, and having a diffusing element inside the outermost surface of the functional layer, and having an internal haze An optical sheet having a value of 1.3 to 16.9 and a relationship of the following formula (I):
0.16 <R / V <0.71 (I)
R (diffuse regular reflection intensity): intensity in diffuse regular reflection direction V diffuse reflection intensity measured every degree from -θ degree to + θ degree with respect to the diffuse regular reflection direction when the optical sheet is irradiated with visible light Total Furthermore, the optical sheet of Claim 1 which has the relationship of following formula (II).
0.20 <R / V <0.62 (II) Furthermore, the optical sheet of Claim 1 which has the relationship of following formula (III).
0.31 <R / V <0.62 (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 any one of claims 1 to 3, 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, wherein unevenness is provided on a 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, wherein the 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 claim 4, 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 claim 4, which is .25 or less.   The optical sheet according to claim 4, wherein the translucent inorganic particles and / or translucent organic particles are contained in the transparent resin in an amount of 1 to 30% by mass.   The optical sheet according to any one of claims 1 to 3, wherein unevenness provided on the surface of the mold is reversely transferred to provide 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 substrate, and crosslinking and curing the composition. The optical sheet according to 1.   The ionizing radiation curable resin composition includes a solvent impregnated in the transparent substrate and / or an ionizing radiation curable resin impregnated in the transparent substrate, a solvent not impregnated in the transparent substrate, and / or the transparent substrate. The optical sheet according to claim 13, comprising an ionizing radiation curable resin that is not impregnated in the composition and controlled to have any one of the formulas (I), (II), and (III). 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 3, wherein an antireflection functional layer is formed on the outermost layer.   The polarizing plate using the optical sheet of any one of Claims 1-16.   An image display device using the polarizing plate according to claim 17.

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