JP2001264517A - Optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly stable optical sheet with excellent optical transmittance and diffusion properties and maintaining the optical characteristics without damage even under a high temperature and high humidity conditions in the optical sheet used for displays such as an LCD(liquid crystal display) or an EL(electroluminescence) panel. SOLUTION: The optical sheet is characterized by having a translucent substrate and an adhesive layer laminated on the translucent substrate, by having a single layer of spherical fine particles with 0.8-1.0 particle size distribution value buried in the adhesive layer in the state partly protruding from the surface of the adhesive layer and by having the distance from the apexes of the protruding parts of the spherical fine particles to the surface of the translucent substrate being 100-110% of the volume averaged particle diameter of the spherical fine particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to, for example, LCDs,
The present invention relates to an optical sheet that is suitably used for displays such as EL and FED, and particularly exhibits excellent effects of preventing luminance unevenness, improving contrast, and increasing the viewing angle of these displays.

[0002]

2. Description of the Related Art In recent years, displays such as LCDs, ELs, and FEDs have been remarkably developed. In particular, LCDs have become widespread in all fields such as notebook computers and portable terminals, and expectations for the future are great. This LCD is roughly classified into a reflection type and a transmission type according to a method of taking in light for illuminating a liquid crystal panel. In the reflective type, a reflective plate with an aluminum film with high reflectivity is placed on the back of the transmissive / reflective liquid crystal panel, and external light incident from the display surface is reflected by the reflective plate to illuminate the liquid crystal panel and illuminate the liquid crystal. Get an image. On the other hand, the transmission type
In this method, the backlight unit provided on the back of the liquid crystal panel illuminates the liquid crystal panel. For the reflective type,
In order to prevent the background color of aluminum from deteriorating the contrast, a medium that appropriately diffuses light is interposed between the liquid crystal panel and the reflector to bring the background color closer to paper white. ing. In the case of the transmission type, a medium that appropriately diffuses light between the liquid crystal panel and the backlight unit in order to prevent the pattern of the acrylic light guide plate constituting the backlight unit from coming out and deteriorating the visibility. , A uniform planar light illuminates the liquid crystal panel.

As described above, a light diffusing medium (hereinafter, referred to as a light diffusing body) is generally used in both the reflection type and the transmission type. As this light diffuser, by dispersing fine particles in a binder resin, an internal light diffuser that scatters light inside the layer, an external light diffuser that roughens the resin surface and diffuses light as an uneven shape, There is an internal / external light diffuser that makes unevenness by protruding a part of particles on the surface of the binder resin to diffuse light both inside and outside. Of these, it is known that an internal / external light diffuser in which particles are arranged in a single layer on the surface of a resin layer has a small loss of transmitted light due to backward scattering, and has high transmittance and high diffusivity.

[0004]

However, the above-mentioned internal
The external light diffuser has a problem that the optical characteristics gradually change at high temperature and high humidity. The present invention has been made in view of the above circumstances, and has as its object to provide an optical sheet in which high and uniform light transmittance and diffusivity are sufficiently exhibited, and which maintain these optical characteristics even under high temperature and high humidity conditions. And

[0005]

Means for Solving the Problems As a result of intensive studies on the improvement of optical stability, the present inventors have found that under high temperature and high humidity conditions, spherical fine particles sink in the direction of the substrate due to the flow of the binder. It was found to change the optical properties.
Furthermore, it has been clarified that the flow of the binder can be suppressed by reducing the thickness of the binder layer. Therefore, the present inventor suppressed the behavior of the spherical fine particles sinking in the binder by binding the spherical fine particles directly or on a single layer via a very thin binder, thereby reducing the light transmittance. An optical sheet having high diffusivity and high stability of optical characteristics was obtained.

That is, the optical sheet of the present invention has a light-transmitting substrate and a binding layer laminated directly or via another layer on the light-transmitting substrate, and the particle size is formed on the binding layer. 0.8 distribution
Monodisperse spherical fine particles of 1.0 to 1.0 are embedded in a single layer with a part protruding from the surface of the binder layer, and the distance from the top of the protrusion of the spherical fine particles to the surface of the light-transmitting substrate. Is 100% to 110% of the volume average particle diameter of the spherical fine particles. Note that the surface of the binding layer in which the spherical fine particles are embedded may be laminated to improve light diffusion.

[0007]

FIG. 1 is a sectional view schematically showing one example of the optical sheet of the present invention. This optical sheet L
In this method, a binding layer 2 is directly laminated on a light-transmitting substrate 1, and a large number of spherical fine particles 3 are bound on a surface layer of the binding layer 2 in a single layer without being densely overlapped in a plane direction in a thickness direction. It is embedded so that a part thereof protrudes from the surface of the deposition layer. By embedding the spherical fine particles in this way, it is possible to sufficiently obtain uniform light diffusion and light transmittance by the spherical fine particles.
Here, the single layer refers to a state in which the spherical fine particles are embedded in the surface of the binding layer as uniformly as possible without overlapping the spherical fine particles in the thickness direction of the binding layer.

In the present invention, the distance (b in FIG. 1) from the apex of the protrusion of the spherical fine particles to the surface of the light-transmitting substrate is 100% to 110% of the volume average particle diameter of the spherical fine particles (a in FIG. 1).
Must. The distance is at least about 100% of the volume average particle diameter of the spherical fine particles since the spherical fine particles are not embedded in the light-transmitting substrate. Too much resin of the binder layer existing between the optical substrates causes the stability of the optical characteristics under high temperature and high humidity to deteriorate, and practically sufficient optical characteristics cannot be obtained. In the present invention, the "distance from the top of the protruding portion of the spherical fine particles to the surface of the light-transmitting substrate" is:
It corresponds to d ₁ in FIG. 2 and is a value measured by the following method. In FIG. 2, reference numerals 2 and 3 denote a binder layer and spherical fine particles, respectively, as described above. First, after freezing the optical sheet with liquid nitrogen, the optical sheet is divided into two at an arbitrary portion, and five spherical microparticles are randomly extracted from the photograph by using a photograph of a cross section of the fractured surface. Then, a straight line d ₁ orthogonal to the boundary between the light-transmitting substrate and the binder layer is drawn from the apex T ₁ of the protrusion of each spherical fine particle, and the length of the straight line is measured. The average of these values is defined as the distance from the vertex of the protrusion of the particle to the surface of the light-transmitting substrate.

The narrower the particle size distribution of the spherical fine particles is, the more uniform the depth of embedding the spherical fine particles in the binder layer is. The value is preferably 0.8 to 1.0.
More preferably, it is desirable to be 0.9-1.0.
The term “particle size distribution” as used in the present invention is defined by the following formula, and is closer to 1.0 as the particle size distribution becomes monodisperse, and becomes 1.0 for complete monodisperse particles. is there. * Particle size distribution = Number average particle size / Volume average particle size * Number average particle size = Average value of diameters of 100 spherical fine particles randomly extracted from a micrograph of spherical fine particles * Volume average particle size = above The spherical fine particles are regarded as true spheres from the diameter of the spherical fine particles obtained by measuring the number average particle diameter, and the volume of each spherical fine particle is determined. Next, the volumes of the individual spherical fine particles are accumulated to calculate the total volume of 100 spherical fine particles. Then, the volume is accumulated in order of volume from the smallest spherical particle to the largest spherical particle among the 100 spherical particles, and when the accumulated volume becomes 50% of the above total volume. Particle diameter. When the spherical fine particles are not true spheres, the longest diameter is defined as the diameter of the spherical fine particles.

The thickness (c in FIG. 1) of the binder layer can prevent the spherical fine particles from peeling off from the binder layer, and can protrude from the surface of the binder layer to ensure light diffusion. for,
10 to 90% of the diameter of the spherical fine particles, preferably 30 to 8
Desirably, the thickness is 0%. In the present invention,
The “thickness of the binding layer” corresponds to d ₂ in FIG. 3 and is a value measured by the following method. In FIG. 3, reference numerals 2 and 3 mean a binder layer and spherical fine particles, respectively, as described above. First, five spherical microparticles are randomly extracted from the cross-sectional photograph of the optical sheet. Then, a straight line d ₂ perpendicular to the boundary between the translucent substrate and the binding layer is drawn from the point T ₂ where the spherical fine particles contact the binding layer 2 and the spherical fine particle 3, and the length of the straight line d ₂ is measured. . This was measured for each of the left and right sides of the protrusions of the five spherical fine particles, and a total of 1
The average value of zero points is defined as the thickness of the binder layer.

Further, in the present invention, the glass transition point (hereinafter, referred to as “Tg”) of the resin used for the binder layer must be −
It is desirable to be 65 to -15 ° C. Tg is -65 ° C
If the temperature is lower, it is difficult to suppress the change in the optical properties because the binder is too soft.If the temperature is higher than -15 ° C., the spherical particles are hard to be embedded in the binding layer because the binder is hard, It cannot be held firmly. In the present invention, Tg is determined by measuring dynamic viscoelasticity (using Orientec Co., Ltd., using Leopy Bron DDV-II).
The maximum value of an δ was determined, and this was defined as Tg.

Next, suitable materials for forming the optical sheet of the present invention will be described. A transparent film can be used as the translucent substrate of the present invention. Specifically, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetyl cellulose (TAC),
Various resin films made of polyalate, polyimide, polyether, polycarbonate, polysulfone, polyethersulfone, cellophane, polyamide, polyethylene, polypropylene, polyvinyl alcohol, and the like can be suitably used. The present invention is not limited to such a film, and a resin plate made of the above resin or a sheet-shaped member made of a glass material such as quartz glass or soda glass can be used.

As the light-transmitting substrate, a non-transparent substrate can be used as long as it transmits light. However, when it is used for a liquid crystal display or the like, the refractive index (JIS K7142) is used.
Is desirable in the range of 1.42 to 1.60. Specific examples include acrylic resin films such as triacetyl cellulose (TAC) and polymethyl methacrylate. The higher the transparency of these transparent substrates, the better, and the light transmittance (JIS C671)
4) is 80% or more, more preferably 85% or more,
Further, the haze value (JIS K7105) is 3.0 or less,
More preferably, it is preferably 1.0 or less, most preferably 0.5 or less. When used in a small and lightweight liquid crystal display, the light-transmitting substrate is more preferably a film, and the thickness thereof is preferably thinner from the viewpoint of weight reduction. It is preferable to use one having a range of 0.5 μm to 1 mm. Further, a lens having a light collecting property or a diffusing property can be formed on one surface of the light-transmitting substrate on the side opposite to the binding layer.

The binder layer of the present invention is preferably, for example, a pressure-sensitive adhesive layer obtained by coating a pressure-sensitive adhesive on the substrate. As the adhesive, polyester resin,
Resin adhesives such as epoxy resins, polyurethane resins, silicone resins, and acrylic resins can be used. These may be used alone or in combination of two or more. In particular, acrylic pressure-sensitive adhesives are excellent in water resistance, heat resistance, light resistance, etc., and have good adhesive strength and transparency.
When used for a liquid crystal display, it is preferable because the refractive index can be easily adjusted to conform to the refractive index. Examples of the acrylic pressure-sensitive adhesive include homopolymers or copolymers of acrylic monomers such as acrylic acid and esters thereof, methacrylic acid and esters thereof, acrylamide and acrylonitrile, and at least one of the acrylic monomers and acetic acid. Copolymers with aromatic vinyl monomers such as vinyl, maleic anhydride and styrene can be mentioned. In particular, ethylene acrylate, butyl acrylate, 2-ethylhexyl acrylate, and other main monomers that exhibit adhesiveness, vinyl acetate, acrylonitrile, acrylamide, styrene, methacrylate, and methyl acrylate, which are cohesive components, and further improve adhesive strength. Methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl methacrylate to impart a crosslinking origin,
A copolymer comprising a functional group-containing monomer such as hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminomethyl methacrylate, acrylamide, methylolacrylamide, glycidyl methacrylate, and maleic anhydride is preferred. In the pressure-sensitive adhesive, as a curing agent, for example, a metal chelate-based, isocyanate-based, or epoxy-based cross-linking agent may be used alone or in combination of two or more as necessary. Further, a UV curable binder to which a photopolymerizable monomer, oligomer, polymer and photopolymerization initiator are added may be used for the binder layer.

The above-mentioned resin is used for the binder layer of the present invention.
Preferably it is 5 ° C. Since a resin having a Tg lower than -65 ° C. is too soft, the spherical fine particles once adhered are peeled off by an impact particularly at a high temperature and a high humidity, and defects such as color unevenness easily occur. Further, the resin is attached to the spherical fine particles that have been peeled off once, and the spherical fine particles may again adhere to other spherical fine particles, which may adversely affect the optical characteristics. Furthermore, even when the optical sheet is produced, the fixation of the spherical fine particles becomes insufficient, it is difficult to form the spherical fine particles in a single layer on the binder layer, and the light transmittance becomes low, which is not preferable. On the other hand, a resin having a Tg higher than −15 ° C. is not preferable because the spherical fine particles easily fall off due to insufficient tackiness.

The binder layer is made of a resin as described above and has an adhesive strength (JIS Z0237-8) of 100 g / 25 m.
m or more is practically preferable. If the adhesive strength is less than 100 g / 25 mm, detachment of the spherical fine particles may occur or environmental resistance may deteriorate. In particular, under high temperature and high humidity, the binder layer may peel off from the light transmitting substrate. Further, the holding force of the binder layer (JIS Z0237-
11) is preferably 0.5 mm or less. 0.5m holding force
When it is larger than m, the particles are soft, so that the spherical fine particles are liable to form a multilayer as described above.

The spherical fine particles of the present invention include inorganic fillers such as silica and alumina, acrylic resins, polystyrene resins, polyethylene resins, epoxy resins, silicone resins, polyvinylidene fluoride, Teflon (registered trademark), divinylbenzene, and phenol resins. Organic fine particles such as urethane resin, cellulose acetate, nylon, cellulose, benzoguanamine and melamine can be used, but organic fine particles are preferable from the viewpoint of light transmittance and adhesion with the binder layer, and furthermore, in light resistance. Acrylic beads,
Silicone beads are particularly preferred.

Further, as the particle size distribution of the spherical fine particles is narrower as described above, the embedding depth of the spherical fine particles into the binder layer becomes more uniform, and the optical characteristics of the optical sheet become more stable.
0.8 to 1.0 is preferable, and 0.9 to 1.0 is more preferable.
The value of 1.0 is preferable because the organic fine particles having a particle size distribution close to such a monodispersion are easily obtained.
Further, as other layers, for example, an adjustment layer for adjusting the refractive index and transmittance of light on the outermost surface, or an adhesive layer for firmly bonding the base and the binding layer, and the like may be provided as necessary. Is also good.

Next, a method for producing the optical sheet of the present invention will be described. First, on one or both surfaces of the translucent substrate, directly or via another layer, a coating solution in which a resin for forming the binder layer is dissolved in an appropriate solvent is applied and dried to laminate the binder layer. Air doctor coating,
Coating such as blade coating, knife coating, reverse coating, transfer roll coating, gravure roll coating, kiss coating, cast coating, spray coating, slot orifice coating, calendar coating, electrodeposition coating, dip coating, die coating, flexographic printing, etc. Printing, such as letterpress printing, direct gravure printing, intaglio printing such as offset gravure printing, lithographic printing such as offset printing, and stencil printing such as screen printing.In particular, coating using a roll coater has a uniform layer thickness. Is preferred because it is obtained. In addition, in order to mature the binder layer, a heat treatment is performed at a temperature of about 20 to 80 ° C. for about 3 to 14 days in a state where the binder layer is protected with a peelable PET film or the like, and then the process proceeds to the next step. Good.

Next, spherical fine particles are adhered to the surface of the binding layer on the translucent substrate. Examples of the means of adhesion include spraying the spherical fine particles directly onto the binder layer, spraying the fine particles with an air spray, transferring the fine particles from a brush or a roll to which the fine spherical particles are adhered, or coating after dispersing the fine spherical particles in a solvent. In particular, fluid immersion using a fluidized tank is preferable because spherical fine particles are uniformly attached. In addition,
Here, it is sufficient that the spherical fine particles simply adhere to the surface of the binding layer by the adhesive force of the binding layer.

Thereafter, the adhered spherical fine particles are embedded in the binder layer by applying pressure. As a means for pressurizing, there are a rubber press roller and a blow with a pressurized medium. It is necessary to uniformly apply the pressure to the spherical fine particles attached to the binder layer. For this reason, it is preferable to use a method in which spherical particles are used as the pressurizing medium and the spherical fine particles are hit by vibration. The size of the pressurizing medium is appropriately selected depending on the particle size and material of the spherical fine particles, but is generally about 0.3 to 2.0 m.
About m is appropriate. Further, excess spherical fine particles remaining adhering without being embedded in the binder layer are removed by washing away with running water or the like to obtain an optical sheet of the present invention. Further, at a temperature of about 20 to 80 ° C. for 3 to 14 hours for the purpose of aging the embedded fine spherical particles and the binder layer.
The heat treatment may be performed for about a day.

[0022]

Next, an embodiment of the present invention will be described. A. Synthesis of polyacrylate [Synthesis Example 1] Butyl acrylate 62 in a three-necked flask
Parts, methyl acrylate 28 parts, methyl methacrylate 5 parts, azobisisobutyronitrile 2 parts, toluene 20
Add 0 parts and polymerize at 60 ° C. for 5 hours with stirring.
And 0.3 part of a bifunctional isocyanate (trade name: D-
90, manufactured by Soken Chemical Co., Ltd.) to obtain polyacrylate a. After applying this polyacrylate a to the release PET with an applicator roll so that the dry film thickness became 20 μm, the release PET was overlaid thereon, and the polyacrylate was frozen with liquid nitrogen to produce a sheet. Thereafter, this sheet was cut into a size of 4 × 0.5 cm, and the dynamic viscoelasticity was measured with Leo Vibron DDV-II (manufactured by Orientec), and the maximum value of Tan δ was taken as Tg. 34 ° C.

[Synthesis Example 2] In a three-necked flask, 92 parts of 2-ethylhexyl acrylate, 8 parts of acrylic acid, 2 parts of azobisisobutyronitrile, and 200 parts of toluene were added.
Polymerization was performed at 60 ° C. for 5 hours with stirring to obtain polyacrylate b. Synthesis Example 1 of Tg of this polyacrylate b
It was -11 degreeC when it measured by the same method as above.

B. Production of Optical Sheet [Example 1] As a light-transmitting substrate, triacetyl cellulose having a thickness of 80 µm (trade name: Fujitack UVD80, refractive index 1.49, total light transmittance 92.4%, haze value 0.4%).
15, manufactured by Fuji Photo Film Co., Ltd.). On one side of this film, the polyacrylate a was coated with a reverse coater so that the thickness after drying was 1.5 μm, dried at 100 ° C. for 2 minutes, and then aged at 60 ° C. for 7 days. Was performed to form a binder layer.

Next, methyl silicone fine particles (trade name: Tospearl 145, manufactured by GE Toshiba Silicone Co., Ltd.) having a volume average particle size of 4.5 μm and a particle size distribution of 0.94 were used as the spherical fine particles. Was passed through the light-transmissive substrate on which the binder layer was formed, and was adhered thereto. Further, a spherical zirconia sphere having a particle diameter of 0.5 mm is placed in a container as a pressurizing medium, and while the container is being vibrated, the light-transmitting substrate having the spherical fine particles adhered to the container is passed through the container, and the sphere is formed. Fine particles were embedded in the binder layer. After washing to remove excess spherical fine particles, aging was performed for 7 days in a constant temperature bath at 60 ° C., and cooled to room temperature.
Was obtained.

Example 2 The same binder as in Example 1 was coated on one side of the same film as in Example 1 with a reverse coater so that the thickness after drying was 3 μm, and the coating was performed at 100 ° C. for 2 minutes. After drying, aging was performed at 60 ° C. for 7 days to form a binder layer. The subsequent steps were performed in the same manner as in Example 1 except that the spherical fine particles used were changed to methyl methacrylate (trade name: MX-1000, manufactured by Soken Chemical Co., Ltd.) having a volume average particle size of 10.8 μm and a particle size distribution of 0.94. In the same manner as in the above, an optical sheet of Example 2 was obtained.

Example 3 The same binder as in Example 1 was coated on one side with a reverse coater on one side of a film so as to have a thickness of 1 μm after drying, and at 100 ° C. for 2 minutes. After drying, aging was performed at 60 ° C. for 7 days to form a binder layer. In the subsequent step, the spherical fine particles to be used are methyl silicone beads having a volume average particle size of 2.6 μm and a particle size distribution of 0.90 (trade names: Tospearl 130, GE
An optical sheet of Example 3 was obtained in the same manner as in Example 1 except for changing to Toshiba Silicone Co., Ltd.).

Example 4 On one side of the same film as in Example 1, the binder of Example 1 was applied with a reverse coater so that the thickness after drying was 5 μm, and was applied at 100 ° C. for 2 minutes. After drying, aging was performed at 60 ° C. for 7 days to form a binder layer. Next, methyl methacrylate (trade name: MX-1000, manufactured by Soken Chemical Co., Ltd.) having a volume average particle diameter of 10.8 μm and a particle diameter distribution of 0.94 was used as the spherical fine particles, and a fluid tank containing the spherical fine particles was used. Through a light-transmitting substrate on which a binding layer was formed.

Further, as a pressurizing medium, a particle diameter of 0.5 mm
The spherical zirconia spheres were placed in a container, and while the container was being vibrated, a translucent substrate having the spherical particles adhered to the container was passed through the container, and the spherical particles were embedded in the binder layer. After washing to remove excess spherical fine particles,
After aging for 14 days in a constant temperature bath, the mixture was cooled to room temperature to obtain an optical sheet of Example 4.

Comparative Example 1 On one side of the same film as in Example 1, the binder of Example 1 was dried to a thickness of 2.2 μm.
m with reverse coater, 2 at 100 ° C
After drying for 5 minutes, aging was performed at 60 ° C. for 7 days to form a binder layer. Subsequent steps were performed in the same manner as in Example 1 to obtain an optical sheet of Comparative Example 1.

[Comparative Example 2] The binder of Example 1 was dried on one side of the same film as in Example 1 to a thickness of 1.5 μm.
m with reverse coater, 2 at 100 ° C
After drying for 5 minutes, aging was performed at 60 ° C. for 7 days to form a binder layer. The subsequent steps were performed in the same manner as in Example 3, and an optical sheet of Comparative Example 2 was obtained.

Comparative Example 3 The binder of Example 1 was dried on one side of the same film as in Example 1 to a thickness of 1.5 μm.
m with reverse coater, 100 ℃ 2
After drying for 5 minutes, aging was performed at 60 ° C. for 7 days to form a binder layer. The subsequent steps were performed in the same manner as in Example 1 except that the spherical fine particles used were changed to methyl silicone beads having a volume average particle diameter of 4.5 μm and a particle diameter distribution of 0.78, and an optical sheet of Comparative Example 3 was obtained. Was.

Comparative Example 4 On one side of the same film as in Example 1, the above-mentioned polyacrylate b was coated with a reverse coater so that the thickness after drying was 1.5 μm.
After drying at 0 ° C. for 2 minutes, aging was performed at 60 ° C. for 7 days to form a binder layer. Subsequent steps were performed in the same manner as in Example 1 to obtain an optical sheet of Comparative Example 4.

* Observation of Optical Sheet The cross sections of the optical sheets of Examples 1 to 4 and Comparative Examples 1 to 4 were photographed with an electron microscope and observed. Figures 4-7
Are schematic diagrams of cross-sectional photographs of the optical sheets of Examples 1 to 4, and FIGS. 8 to 11 are schematic diagrams of cross-sectional photographs of the optical sheets of Comparative Examples 1 to 4. Table 1 shows the measured values of the distance from the apex of the protrusion of the spherical fine particles specified in the present invention to the light-transmitting substrate and the thickness of the binder layer based on the photograph.

[0035]

[Table 1]

* Optical property test The surface of the sheet comprising the light-transmitting substrate 1, the binder layer 2 and the spherical fine particles 3 as shown in FIG. Total light transmittance: Tt (%), Haze value: H when incident light is applied from the side
z (%) was measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. Next, the above Examples 1-4 and Comparative Examples 1-4
Under high temperature and high humidity (60 ° C., 90%) condition.
After standing for days, Tt and Hz were measured in the same manner as above, and the high-temperature and high-humidity resistance, that is, the reliability under high temperature and high humidity was evaluated. Table 2 shows the measurement results.

[0037]

[Table 2]

As is clear from Tables 1 and 2, when the height from the substrate surface to the apex of the spherical fine particles is 110% or less, which is close to the diameter of the spherical fine particles, good optical characteristics are obtained except for Comparative Example 3. can get. That is, the optical characteristics of the optical sheets of Examples 1 to 4 of the present invention were able to maintain high light transmittance and light diffusion with little change even after being left under high temperature and high humidity. On the other hand, Comparative Example 1 in which the height from the substrate surface to the top of the spherical fine particles exceeds 110% of the diameter of the spherical fine particles
In the optical sheets of Nos. 2 and 4, and the optical sheet of Comparative Example 3 in which the value of the particle size distribution of the spherical fine particles is smaller than 0.78 and 0.80, the frequency was 10 Hz when left at high temperature and high humidity.
% Or more. Further, in the optical sheet of Comparative Example 4,
Since the binder having a high Tg was used, the spherical fine particles were also found to have fallen off after being left under high temperature and high humidity (the value of Tt was large), resulting in a problem that unevenness in optical characteristics was caused. there were.

[0039]

The optical sheet of the present invention comprises a light-transmitting substrate,
A binding layer laminated directly or via another layer on the light-transmitting substrate, and an optical member in which spherical fine particles are spread over the binding layer in a single layer; Since the average height from the surface to the apex protruding from the binding layer of the spherical fine particles is close to the volume average particle size of the spherical fine particles, the stability of the optical characteristics is higher than that of the conventional optical sheet, and the optical characteristics have excellent reliability. A sheet is obtained.

Thus, for example, in a transmission type liquid crystal display, as shown in FIG.
By inserting the optical sheet 11 of the present invention between the liquid crystal cell 2 and the liquid crystal cell 14 held between the polarizing plates 13, it is possible to efficiently diffuse the light while efficiently transmitting the light of the backlight unit. In addition, since the optical characteristics are excellent even under high temperature and high humidity, stable performance can be given to the liquid crystal display for a long period of time. Therefore, the optical sheet of the present invention can be used for applications requiring long-term optical stability, such as various displays such as LCDs, ELs, and FEDs, and has extremely excellent effects.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of an optical sheet of the present invention.

FIG. 2 is a schematic view showing a measurement site of a distance from a vertex of a protruding portion of a spherical fine particle of the optical sheet of the present invention to a surface of a light-transmitting substrate.

FIG. 3 is a schematic view showing a measurement site of a thickness of a binder layer of the optical sheet of the present invention.

FIG. 4 is a schematic diagram of a cross section of an optical sheet according to a first embodiment of the present invention.

FIG. 5 is a schematic view of a cross section of an optical sheet according to a second embodiment of the present invention.

FIG. 6 is a schematic diagram of a cross section of an optical sheet according to a third embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of an optical sheet according to a fourth embodiment of the present invention.

FIG. 8 is a schematic view of a cross section of an optical sheet of Comparative Example 1 of the present invention.

FIG. 9 is a schematic view of a cross section of an optical sheet of Comparative Example 2 of the present invention.

FIG. 10 is a schematic diagram of a cross section of an optical sheet of Comparative Example 3 of the present invention.

FIG. 11 is a schematic view of a cross section of an optical sheet of Comparative Example 4 of the present invention.

FIG. 12 is a schematic diagram for explaining a direction of incident light with respect to an optical sheet.

FIG. 13 is a schematic view showing an example of a method for using the optical sheet of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transparent base | substrate, 2 ... Binder layer, 3 ... Spherical fine particles a ... Volume average particle diameter of spherical fine particles b ... Distance from the vertex of the protrusion of spherical fine particles to the surface of the light transmitting substrate c ... Binding layer thickness L: Optical sheet

Claims (3)

[Claims] 1. A light-transmitting substrate, and a binding layer laminated on the light-transmitting substrate, wherein the particle size distribution of the binder layer is 0.
The spherical fine particles having a particle diameter of 8 to 1.0 are embedded in a single layer in a state where a part thereof protrudes from the surface of the binder layer, and the distance from the top of the protruding portion of the spherical fine particles to the surface of the light-transmitting substrate. Is 100 to 110% of the volume average particle diameter of the spherical fine particles. 2. The optical sheet according to claim 1, wherein the thickness of the binder layer is 10% to 90% of the volume average particle diameter of the spherical fine particles. 3. The optical sheet according to claim 1, wherein the resin used for the binder layer has a glass transition point of −65 ° C. to −15 ° C.