JP2002267818A - Light diffusible sheet and optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusible sheet which maintains antiglare character istic, suppresses glittering phenomenon of a picture, and scarcely causes white blurring even when the sheet is applied to a high definition liquid crystal display(LCD) and to further provide an optical element which is furnished with the light diffusible sheet. SOLUTION: The light diffusible sheet in which a light diffusion layer composed of resin film layer having a surface in a shape of fine ruggedness is formed on at least one side of a transparent substrate, is characterized in that the ratio of the internal haze value described hereunder to the total haze value described hereunder (internal haze value/total haze value) is >=0.5 and <1 and the total haze value is >=35% and <=50%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing sheet used in liquid crystal displays (LCDs), ELs, PDPs and the like to suppress a reduction in screen visibility.
The present invention relates to an optical element provided with the light diffusing sheet.

[0002]

2. Description of the Related Art Conventionally, in an image display device such as an LCD, the visibility of an image is hindered by room lighting such as a fluorescent lamp, sunlight incident from a window, and a shadow of an operator on the surface of the display device. Can be Therefore, on the display surface, in order to improve the visibility of the image, the surface reflected light is diffused, the specular reflection of external light can be suppressed, and reflection of the external environment can be prevented (having anti-glare properties). A light diffusion layer having an uneven structure is provided. As a method of forming the light diffusion layer, a method of forming a resin film layer by coating a resin in which fine particles are dispersed has been mainly used because the structure can be easily miniaturized and the productivity is good.

However, high definition (for example, 100 ppi)
In the case of the above LCD, when the light diffusion layer is attached,
There is a problem that glare (a portion having a high or low luminance), which is considered to be caused by a fine uneven structure formed by particles protruding from the surface of the light diffusion layer, is generated on the LCD surface, thereby lowering visibility. In addition, from the viewpoint of ergonomics such as easy eyestrain, improvement of the glare is required.

In order to improve the glare phenomenon, there has been proposed a method of continuously forming a large number of fine irregularities by means such as dispersing a large amount of fine particles in a resin film layer. According to this method, the antiglare effect also increases.
However, according to this method, glare is improved and irregular surface reflection of external light occurs, and a phenomenon called so-called white blur occurs that the display screen becomes whitish. In particular, white blur appears remarkably at the time of black display, which causes a problem such as a decrease in contrast of screen display.

For this reason, in the design of a light diffusing sheet used for a high-definition LCD, it is necessary to control the internal diffusivity for achieving a glare preventing effect and the surface diffusivity for achieving a white blur preventing effect. ing. For example, Japanese Patent Application Laid-Open No. H11-305010 describes that the surface haze value and the internal haze value of the light diffusing sheet are in the range of 7 to 20% and 1 to 15%, respectively. However, the light-diffusing sheet having the internal haze value cannot exhibit a sufficient anti-glare effect. It is also described that the light-diffusing sheet increases surface blur when the sum of the surface haze value and the internal haze value exceeds 30, and adjusts the surface haze value and the internal haze value to the above range. However, it has been difficult to provide an excellent antiglare effect and an anti-blur effect.

[0006]

SUMMARY OF THE INVENTION The present invention provides a high definition L
When applied to a CD, a light-diffusing sheet which suppresses glare on a screen while maintaining anti-glare properties and hardly recognizes white blur, and an optical element provided with the light-diffusing sheet The purpose is to provide.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have found that the above object can be achieved by a light diffusing sheet having the following characteristics, and completed the present invention. I came to.

That is, the present invention provides a light diffusing sheet having a light diffusing layer formed of a resin film layer having fine irregularities on at least one surface of a transparent substrate. Light diffusion characterized in that the ratio of the haze value to the following internal haze value (internal haze value / total haze value) is 0.5 or more and less than 1, and the total haze value is 35% or more and 50% or less. Sheet. Total haze value: Haze value of the light diffusing sheet. Internal haze value: on the surface of fine irregularities of the light diffusing sheet,
A value obtained by subtracting a haze value of 11% from a haze value of a state where a transparent sheet with an adhesive having a haze value of 11% is stuck.

The light diffusing sheet of the present invention has a total haze value of 35% or more and 50% or less and a ratio (internal haze value /
By setting the total haze value to 0.5 or more and less than 1, a light diffusing sheet having a good balance between the glare preventing effect and the white blur preventing effect is obtained.

[0010] If the total haze value is less than 35%, glare in the case of high definition cannot be suppressed. 38% total haze
It is preferable to make the above. On the other hand, when the total haze value increases, the transmittance decreases. Therefore, the total haze value is preferably 42% or less.

When the ratio (internal haze value / total haze value) is less than 0.5, the ratio of the internal haze value is so small that glare in the case of high definition cannot be suppressed. Ratio (internal haze value /
The total haze value is preferably 0.6 or more. on the other hand,
When the ratio (internal haze value / total haze value) increases, the effect of preventing white blurring decreases, so that the ratio (internal haze value / total haze value) is preferably set to 0.8 or less. The internal haze value is not particularly limited as long as the ratio satisfies the above ratio in relation to the total haze value.
About 40%, preferably 20 to 30%.

The total haze value is, as shown in FIG.
The haze value is a haze value of a light-diffusing sheet provided with a light-diffusing layer 4 composed of a resin film layer 2 having fine irregularities on at least one surface of the transparent substrate 1. Figure 2 shows the internal haze value.
A haze value of 11 was obtained from the haze value measured for a state in which a transparent sheet 5 with a pressure-sensitive adhesive layer (haze value: 11%) was attached to the finely uneven surface of the light-diffusing sheet shown in FIG.
It is a value obtained by subtracting%. The type of the pressure-sensitive adhesive 5b and the transparent sheet 5a is not limited as long as the haze value of the transparent sheet with a pressure-sensitive adhesive is 11%.

In the light diffusing sheet, it is preferable that the resin film layer contains fine particles, and that the surface irregularities of the resin film layer are formed by the fine particles. The fine particles contained in the resin film layer are preferably organic fine particles. Further, it is preferable that the resin film layer is formed of an ultraviolet curable resin.

By using fine particles, a resin film layer having an uneven surface can be easily and reliably realized, and the haze value can be easily adjusted. In particular, when organic fine particles are used as fine particles, it is effective in suppressing glare. In addition, a resin film layer (light diffusion layer) can be efficiently formed from a UV-curable resin by a simple processing operation in a curing treatment by irradiation with UV light.

Further, the present invention is characterized in that a low refractive index layer having a refractive index lower than the refractive index of the resin film layer is provided on the uneven surface of the resin film layer of the light diffusing sheet. Light-diffusing sheet.

An antireflection function can be provided by the low refractive index layer, and white blur on the screen due to irregular reflection on the image surface of a display or the like can be effectively suppressed.

Further, the present invention relates to an optical element, wherein the light diffusing sheet is provided on one side or both sides of the optical element.

The light-diffusing sheet of the present invention can be used for various applications, for example, for optical elements.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a light diffusing sheet in which a light diffusion layer 4 composed of a resin film layer 2 in which fine particles 3 are dispersed is formed on a transparent substrate 1, and fine particles dispersed in the resin film layer 2. 3 is a light diffusion layer 4
Has an uneven shape on its surface. Although FIG. 3 shows a case in which the resin film layer 2 is a single layer, a resin film layer containing fine particles is separately formed between the resin film layer 2 and the transparent substrate 1 to form a resin film layer. The light diffusion layer may be formed by a plurality of resin film layers.

Examples of the transparent substrate 1 include transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers and acrylic polymers such as polymethyl methacrylate. Film. Also, styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymer, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin-based polymers such as ethylene-propylene copolymer, vinyl chloride-based polymers, nylon and aromatic polyamides And a film made of a transparent polymer such as an amide-based polymer. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers A film made of a transparent polymer such as a polymer, an epoxy-based polymer, or a blend of the above polymers may also be used. In particular, those having low optical birefringence are preferably used.

The thickness of the transparent substrate 1 can be determined as appropriate, but is generally about 10 to 500 μm in view of strength, workability and other workability, and thin layer properties. Especially 20-300μ
m is preferable, and 30 to 200 μm is more preferable.

Resin coating layer 2 having fine uneven structure surface 2
The method of forming is not particularly limited as long as it is formed on the transparent substrate 1, and an appropriate method can be adopted.
For example, the surface of the film used for forming the resin coating layer 2 is previously subjected to a roughening treatment by an appropriate method such as sand blasting, embossing roll, or chemical etching to give a fine uneven structure to the film surface. And a method of forming the surface of the material itself for forming the resin film layer 2 into a fine uneven structure. Further, there is a method in which a resin film layer is separately applied on the resin film layer 2 to give a fine uneven structure to the surface of the resin film layer by a transfer method using a mold or the like. Also, as shown in FIG.
And a method of imparting a fine uneven structure by dispersing the fine particles. These fine concavo-convex structures may be formed by combining two or more methods to form a layer in which the surfaces of the fine concavo-convex structures in different states are combined. The resin film layer 2
Among them, the method of providing the resin film layer 2 containing the fine particles 3 dispersed therein is preferable from the viewpoint of the formability of the surface of the fine uneven structure and the like.

Hereinafter, a method for dispersing and containing the fine particles 3 to provide the resin coating layer 2 will be described. The resin film layer 2
The fine particles 3 can be dispersed as a resin for forming a resin film, and a resin having sufficient strength as a film after forming the resin film layer and having transparency can be used without any particular limitation. Examples of the resin include a thermosetting resin, a thermoplastic resin, an ultraviolet curable resin, an electron beam curable resin, a two-component mixed resin, and the like. An ultraviolet curable resin that can efficiently form a light diffusion layer by a processing operation is preferable.

Examples of the UV-curable resin include polyester, acrylic, urethane, amide, silicone, and epoxy resins, and include UV-curable monomers, oligomers, and polymers. The UV-curable resin preferably used is, for example, a resin having a UV-polymerizable functional group, among which those containing a component of an acrylic monomer or oligomer having two or more, especially 3 to 6 functional groups are mentioned. . Further, an ultraviolet polymerization initiator is blended with the ultraviolet curing resin.

The UV-curable resin (formation of the resin film layer 2) may contain additives such as a leveling agent, a thixotropic agent, and an antistatic agent. The use of a thixotropic agent is advantageous for forming protruding particles on the surface of the fine uneven structure. 0.1 μm as thixotropic agent
The following silica, mica and the like can be mentioned. Usually, the content of these additives is preferably about 1 to 15 parts by weight based on 100 parts by weight of the ultraviolet curable resin.

As the fine particles 3, those having transparency such as various metal oxides, glass and plastic can be used without any particular limitation. For example, silica and alumina, titania and zirconia, calcium oxide and tin oxide,
Inorganic fine particles that may be conductive, such as indium oxide, cadmium oxide, and antimony oxide, crosslinked or uncrosslinked from various polymers such as polymethyl methacrylate, polystyrene, polyurethane, acrylic-styrene copolymer, benzoguanamine, melamine, and polycarbonate. Organic fine particles and silicone fine particles. One or more of these fine particles 3 can be appropriately selected and used, but organic fine particles are preferable. The average particle diameter of the fine particles is 1 to 10 μm, preferably 2 to 5 μm
It is.

The method for forming the resin film layer 2 containing the fine particles 3 is not particularly limited, and an appropriate method can be adopted. For example, a resin containing fine particles 3 (for example, an ultraviolet curable resin: a coating liquid) is applied on the transparent substrate 1, dried, and then cured to form a resin film layer having an uneven surface. 2 is performed. In addition,
The coating liquid is applied by an appropriate method such as fountain, die coater, casting, spin coating, fountain metalling, and gravure.

In order to adjust the haze value of the surface of the formed light diffusion layer 4 to the above range, the average particle diameter and ratio of the fine particles 3 contained in the coating liquid and the thickness of the resin film layer 2 are appropriately adjusted. I do.

Although the ratio of the fine particles 3 contained in the coating liquid is not particularly limited, it is 1 to 2 parts by weight based on 100 parts by weight of the resin.
It is preferably 0 parts by weight, more preferably 5 to 15 parts by weight, in order to satisfy the characteristics such as glare and blurring. Also,
Although the thickness of the resin film layer 2 is not particularly limited, it is 1 to 10 μm.
m, particularly preferably 4 to 8 μm.

A low refractive index layer having an antireflection function can be provided on the uneven surface of the resin film layer 2 on which the light diffusion layer 4 is formed. The material of the low refractive index layer is a resin film layer 2
It is not particularly limited as long as it has a lower refractive index than
For example, a low refractive index material such as a fluorine-containing polysiloxane can be used. The thickness of the low refractive index layer is not particularly limited, but is about 0.05 to 0.3 μm, particularly 0.1 to 0.3 μm.
It is preferably 0.3 μm.

An optical element can be bonded to the transparent substrate 1 of the light diffusing sheet shown in FIG. 3 (not shown). Examples of the optical element include a polarizing plate, a retardation plate, an elliptically polarizing plate, a polarizing plate with optical compensation, and the like, and these can be used as a laminate. Adhesion of the optical element can be carried out through an appropriate adhesive layer having excellent transparency and weather resistance, such as an acrylic, rubber, or silicone adhesive or a hot-melt adhesive, if necessary.

As the polarizing plate, iodine or a dye was adsorbed on a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer-based partially saponified film, and stretched. And polarizing films such as dehydration products of polyvinyl alcohol and dehydrochlorination products of polyvinyl chloride. Examples of the retardation plate include a uniaxially or biaxially stretched film of a polymer film exemplified as the transparent substrate and a liquid crystal polymer film. The retardation plate may be formed as a superimposed body of two or more stretched films. Elliptical polarizing plates and polarizing plates with optical compensation
It can be formed by laminating a polarizing plate and a retardation plate. The elliptically polarizing plate and the polarizing plate with optical compensation have a light diffusion layer formed on the surface on the polarizing plate side.

[0033]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 An average particle size of 100 parts of an acrylic urethane-based UV-curable resin (urethane acrylate-based monomer) was 3.
A coating solution containing 40 parts by weight of a solid content of 40 parts by weight in which 12 parts of 5 μm polystyrene particles, 5 parts of a benzophenone-based photopolymerization initiator, and 2.5 parts of a thixotropic agent (mica) are mixed via a toluene solvent is applied to a triacetyl cellulose film (80 μm in thickness).
m) was applied thereon, dried at 120 ° C. for 5 minutes, and then cured by irradiation with ultraviolet rays to prepare a light diffusing sheet having a resin film layer having a fine unevenness surface with a film thickness of 7 μm.

Example 2 A light diffusing sheet was prepared in the same manner as in Example 1, except that the thickness of the coating film formed on the triacetyl cellulose film was changed to 6 μm.

Example 3 A light diffusing sheet was prepared in the same manner as in Example 1 except that the thickness of the coating film formed on the triacetyl cellulose film was changed to 5 μm.

Example 4 In Example 1, a low refractive index layer having a refractive index lower than the refractive index (1.52) of the resin film layer (Nissan Chemical Industries, Ltd.) LR-202
And a light diffusing sheet was prepared in the same manner as in Example 1 except that 0.1 μm was used.

Comparative Example 1 A light diffusing sheet was produced in the same manner as in Example 1 except that the thickness of the coating film formed on the triacetyl cellulose film was changed to 3 μm.

Comparative Example 2 The same coating liquid as in Example 1 was used except that the amount of polystyrene particles used was changed to 4 parts by weight, and no thixotropic agent was used. A light diffusing sheet was prepared in the same manner as in Example 1 except that the thickness of the coating film formed on the substrate was changed to 1 μm.

Comparative Example 3 The same coating liquid as in Example 1 was used except that the amount of polystyrene particles used was changed to 8 parts by weight and no thixotropic agent was used. A light diffusing sheet was prepared in the same manner as in Example 1 except that the thickness of the coating film formed on the substrate was changed to 1 μm.

Comparative Example 4 The same coating solution as in Example 1 was used except that the amount of polystyrene particles used was changed to 8 parts by weight, and no thixotropic agent was used. A light-diffusing sheet was produced in the same manner as in Example 1 except that the thickness of the coating film formed in Example 1 was changed to 3 μm.

The total haze value and the internal haze value of the light diffusing sheets obtained in Examples and Comparative Examples were measured, and the ratio (internal haze value / total haze value) was determined. The haze value in Example 4 is a value when the low refractive index layer is not provided. Further, the obtained light diffusing sheet was evaluated for glare and white blur. Table 1 shows the results.

(Total Haze Value) The haze value of the light-diffusing sheet was measured with a haze meter manufactured by Suga Test Instruments Co., Ltd. according to JIS-K7105.

(Internal Haze Value) A haze value was obtained for a light-diffusing sheet having a fine irregular surface formed by adhering a polyethylene terephthalate film with an adhesive having one surface coated with an acrylic adhesive (haze value: 11%). Was measured. The value obtained by subtracting 11% from the value was defined as the internal haze value. The measurement of the haze value and the internal haze of the polyethylene terephthalate film with an adhesive is the same as the measurement of the total haze value.

(Glitter) A sample in which a light diffusing sheet was adhered to a polarizing plate (185 μm) which had not been subjected to a surface treatment was adhered to a glass plate having a thickness of 1.1 mm.
This sample was set on a grid pattern placed on the backlight. The grid pattern has openings of 90 μm × 2
Those having 0 μm, a vertical line width of 20 μm, and a horizontal line width of 40 μm were used. The distance from the grating pattern to the light diffusion layer is 1.3m
m, distance from backlight to grid pattern is 1.5
mm. The glare state at that time was visually evaluated according to the following criteria.

：: Little glare. Δ: There is glare, but there is no practical problem without being bothered. ×: A level at which the glare is severe and there is a practical problem.

(Blur) A black tape was adhered to the glass surface of the sample subjected to the glare evaluation, and was 30 ° from the vertical direction of the polarizing plate and 1 azimuth to the incident light under a fluorescent lamp.
From the direction of 80 °, it was visually evaluated according to the following criteria.

A: A state in which almost no white blur occurs. Δ: A level that is not bothersome but practically problematic, though there is white blur. X: A level with a practical problem with white blur.

[0049]

[Table 1] As shown in Table 1, the light-diffusing sheets of the examples are excellent in both the glare preventing effect and the whitening preventing effect and have good balance. On the other hand, the light diffusing sheet of the comparative example does not satisfy at least one of both the glare preventing effect and the white blur preventing effect. The reflection (anti-glare property) under a fluorescent lamp was good.

[Brief description of the drawings]

FIG. 1 is an example of a cross-sectional view of a light-diffusing sheet used for measurement of all haze values.

FIG. 2 is an example of a cross-sectional view of a light diffusing sheet used for measuring an internal haze value.

FIG. 3 is an example of a cross-sectional view of the light diffusing sheet of the present invention.

[Explanation of symbols]

 1: transparent substrate 2: resin layer 3: fine particles 4: light diffusion layer 5: transparent sheet with adhesive layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Shibata 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Tomomori Masada 1-1-1-2 Shimohozumi, Ibaraki-shi, Osaka No. Nitto Denko Corporation F term (reference) 2H042 BA02 BA03 BA12 BA14 BA20 2H049 BA02 BA04 BA06 BA27 BB03 BB63 BC03 BC22 2H091 FA31X FA31Z FB02 FB12 FC23 FC25 FD06 LA03 2K009 AA04 BB28 CC09 CC24 CC26 CC42AT02 DD02 DD02 DD02 BA02 BA03 BA04 BA05 BA06 BA07 BA10B BA10C BA10D BA10E BA26 DD01B DD01C EH46 EH462 EJ86 EJ862 GB41 JB14B JB14C JN01A JN02B JN02C JN06 JN18B JN18C JN18D JN18E

Claims (6)

[Claims] 1. A light-diffusing sheet having a light-diffusing layer formed of a resin film layer having fine irregularities on at least one surface of a transparent substrate, wherein the light-diffusing sheet has the following total haze value and the following haze value: A light-diffusing sheet characterized in that the ratio of internal haze value (internal haze value / total haze value) is 0.5 or more and less than 1 and the total haze value is 35% or more and 50% or less. Total haze value: Haze value of the light diffusing sheet. Internal haze value: on the surface of fine irregularities of the light diffusing sheet,
A value obtained by subtracting a haze value of 11% from a haze value of a state where a transparent sheet with an adhesive having a haze value of 11% is stuck. 2. The light diffusing sheet according to claim 1, wherein the resin film layer contains fine particles, and the surface unevenness of the resin film layer is formed by the fine particles. 3. The light diffusing sheet according to claim 2, wherein the fine particles are organic fine particles. 4. The light diffusing sheet according to claim 1, wherein the resin film layer is formed of an ultraviolet curable resin. 5. A low refractive index layer having a refractive index lower than the refractive index of the resin film layer is provided on the uneven surface of the resin film layer of the light diffusing sheet according to any one of claims 1 to 4. A light diffusing sheet, characterized in that: 6. An optical element, wherein the light diffusing sheet according to claim 1 is provided on one side or both sides of the optical element.