JPH11287906A - Optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element, with which the field of view can be widened together with improvement in the lightness and resolution of a transmission type liquid crystal display device, by composing the optical element of a film having a sea island structure, and setting the absolute value of a refractive index difference among respective phases forming a sea structure and an island structure higher than a specified value. SOLUTION: This optical element is composed of the film having the sea island structure. An island structure 2 makes its lengthwise direction almost parallel with the thickness direction of the film. Plural columnar objects sets the cross-sectional size for the length of a diameter or longest diagonal, preferably, within the range of from 0.5 to 50 μm, more preferably, within the range of from 0.5 to 3 μm. At the same time, the plural columnar objects take random values within this range of the cross-sectional size. Concerning a sea structure 2, the absolute value of the refractive index difference from the island structure 1 is made different more than 0. 1, preferably, than 0.04.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical element for improving a viewing angle characteristic of a liquid crystal display device.

[0002]

2. Description of the Related Art With the development of information processing systems, liquid crystal display devices have been used in a wide range of fields due to advantages such as low power consumption, light weight, and space saving. Recently, demand in the monitor field has been spotlighted, and technology development for enlargement of the screen has been promoted, but the liquid crystal display device for the monitor application has a problem that the viewing angle characteristics are poor. .

As a liquid crystal display device in the above field, for example,
Although an STN liquid crystal display device is used, one of the attempts to solve the above problem is to reduce the angle dependence of the phase difference plate to reduce the angle dependence of the display quality of the liquid crystal display device. Instead of a simple uniaxially stretched film for compensating for the birefringence of an STN liquid crystal display element, a retardation plate using a film whose refractive index is controlled in three dimensions has been used.

However, the use of a retardation plate whose refractive index is controlled three-dimensionally merely improves the viewing angle characteristics in the vertical direction of the screen. Therefore, in order to improve the viewing angle characteristics in the horizontal direction of the screen, for example, Japanese Patent Application Laid-Open No. 3-28
An optical diffraction plate that scatters only light from a specific direction using a diffraction phenomenon disclosed in Japanese Patent No. 4702 or the like must be used in combination with the retardation plate. That is,
By using a combination of the light diffraction plates, display degradation such as grayscale inversion is suppressed, and the viewing angle characteristics are improved.

As shown in FIG. 4, the light diffraction plate c has a structure in which layers a and b having different refractive indices with respect to the light transmission direction of the light diffraction plate are repeatedly laminated at a certain angle. . Therefore, only light rays incident parallel to the layers having different refractive indices cause scattering by diffraction, and incident light from other directions passes through the light diffraction plate c without being scattered. As described above, the single light diffraction plate c can scatter only light rays in a specific direction which are incident parallel to the layers having different refractive indices.
As shown in FIG. 5, in order to improve the viewing angle characteristics in the horizontal direction of the screen, usually, two light diffraction plates c are used in a stacked state. In order to improve the viewing angle characteristics in the vertical direction of the screen at the same time, another set of the laminate shown in FIG. 5 is prepared, and a four-layered light diffraction plate in which the layer directions are shifted by 90 degrees is used. There must be.

The front, rear, left, and right sides of the screen of a conventional liquid crystal display device
In order to improve the viewing angle characteristics in different directions, it is necessary to stack a plurality of types of sheets as described above. The productivity of the liquid crystal display is reduced and the cost is increased. The resulting liquid crystal display is also made thicker by laminating a number of members, and the advantages of the liquid crystal display, such as low power consumption, light weight, and space saving, are significantly reduced. there were.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and has no adverse effects on the advantages of the liquid crystal display device, such as low power consumption, light weight, and space saving.
It is an object of the present invention to provide an optical element which can achieve a high viewing angle as well as a high brightness and a high resolution of a transmission type liquid crystal display device.

[0008]

SUMMARY OF THE INVENTION The present invention is an optical element comprising a film having a sea-island structure, wherein a columnar island structure is formed such that its length direction is substantially parallel to the film thickness direction. In addition, the gist of the present invention is an optical element in which the absolute value of the refractive index difference of each phase forming the sea structure and the island structure is 0.01 or more.

As shown in FIG. 1, the island structure 1 is composed of a plurality of columnar structures whose length direction is substantially parallel to the thickness direction of the film, for example, having a circular or polygonal cross section. The plurality of columnar bodies having a circular or polygonal cross section have a cross sectional size of preferably 0.5 to 50 μm, more preferably 0.5 to 3 μm in diameter or the length of the longest diagonal line.
m, and the plurality of columnar bodies take random values within the range of the cross-sectional size. If the cross-sectional size is less than 0.5 μm, the spread of light due to diffraction is small, and if it exceeds 50 μm, display defects such as the appearance of an abnormal image commonly called a “moire” approaching the pixel size may occur. There is. Further, when the plurality of columnar bodies do not take a random value and consist only of a specific cross-sectional size, the diffraction angle varies depending on the wavelength, and the emitted light may be abnormally colored.

The sea structure 2 differs from the island structure 1 in absolute value of the refractive index difference by 0.01 or more, preferably 0.04 or more. If the absolute value of the refractive index difference between the island structure 1 and the sea structure 2 is less than 0.01, the spread of light due to diffraction is small and high resolution cannot be achieved.

A plurality of columnar island structures 1 whose length direction is substantially parallel to the film thickness direction, for example, having a circular or polygonal cross section, have an absolute value of a refractive index difference of 0.0 from the island structure 1.
Means for producing a sea-island structure dispersed in one or more sea structures 2 is not particularly limited, but will be described by way of example. First, at least two types of photopolymerizable monomers or oligomers are applied on a process paper subjected to a release treatment to a uniform thickness, and circular or polygonal pores randomly set in the range of the above cross-sectional size are formed on the entire surface. Perforate as evenly as possible, cover with a patterned mask for forming a plurality of columnar island structures having a circular or polygonal cross section, and pass through the mask to be substantially perpendicular to the coating film surface The island structure is formed in the coating film by irradiating parallel ultraviolet rays. Next, the mask is removed from the coating surface,
An optical element is produced by irradiating the coating film surface with ultraviolet rays of substantially parallel light from a vertical direction to form a sea structure around the island structure.

The photopolymerizable monomer or oligomer is not particularly limited as long as it produces polymers having different refractive indices, has good compatibility with each other, and has a different photopolymerization reaction rate. Although not limited, for example, polyfunctional acrylates such as polyester acrylate, polyol polyacrylate, modified polyol polyacrylate, polyacrylate with isocyanuric acid skeleton, melamine acrylate, polyacrylate with hydantoin skeleton, polybutadiene acrylate, epoxy acrylate, urethane acrylate, etc. And methacrylates corresponding to these acrylates, tetrahydrofurfuryl acrylate, ethyl carbitol acrylate, dicyclopentenyloxyethyl acrylate,
Phenyl carbitol acrylate, nonylphenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, ω-hydroxyhexanoyloxyethyl acrylate, acryloyloxyethyl succinate, acryloyloxyethyl phthalate, phenyl acrylate, tribromophenyl acrylate, phenoxyethyl Acrylate, tribromophenoxyethyl acrylate, benzyl acrylate, p-
Bromobenzyl acrylate, bisphenol A diacrylate, 2,2-bis (4-methacryloxyethoxy-3,5-dibromophenyl) propane, isobornyl acrylate, lauryl acrylate, 2,2,3,3
-Tetrafluoropropyl acrylate and methacrylates corresponding to these acrylates and styrene,
Vinyl compounds such as p-chlorostyrene, divinylbenzene, vinyl acetate, acrylonitrile, N-vinylpyrrolidone, and vinylnaphthalene; allyls such as diethylene glycol bisallyl carbonate, triallyl isocyanurate, diallylidenepentaerythritol, diallyl phthalate, and diallyl isophthalate And the like.

A photopolymerization initiator is added to the photopolymerizable monomer or oligomer. The photopolymerization initiator is appropriately determined depending on the photopolymerizable monomer or oligomer used, and is not particularly limited. For example, 4- (2-hydroxyethoxy) phenyl (2-hydroxy- Ketones such as 2-propyl) ketone [Darocure 2959: Ciba-Geigy]; α-hydroxy-α, α'-dimethyl-acetophenone [Darocure 1173: Ciba-Geigy], methoxyacetophenone, 2,2-dimethoxy-2- Acetophenones such as phenylacetophenone [Irgacure 651: Ciba-Geigy] and 2-hydroxy-2-cyclohexyl acetophenone [Irgacure 184: Ciba-Geigy]; ketals such as benzyl dimethyl ketal; others, halogenated ketones and acylphosphines Inoxide, acylphosphonate and the like.

The amount of the photopolymerization initiator to be added is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, based on 100 parts by weight of the monomer mixture. When the addition amount of the photopolymerization initiator is less than 0.01 part by weight based on 100 parts by weight of the monomer mixture, a sufficient conversion cannot be obtained because the polymerization reaction hardly proceeds, and the amount exceeds 5 parts by weight. In such a case, the amount of generated radicals becomes too large, and only a low molecular weight polymer can be obtained.

The thickness of the optical element of the present invention is preferably 2
It is 5 to 150 μm, more preferably 50 to 100 μm. If the thickness of the optical element is less than 25 μm, the spread of light due to diffraction is small and high resolution cannot be achieved. or,
When the thickness exceeds 150 μm, the thickness of the liquid crystal display device is increased as a whole, and the characteristics of the liquid crystal display device having advantages of low power consumption, light weight, space saving, and the like are spoiled.

The obtained optical element of the present invention is, for example, as shown in FIG.
A liquid crystal display device is assembled by laminating the polarizing plate B / the liquid crystal cell C / the retardation plate D / the optical element E of the present invention / the polarizing plate B in this order.

The parallel light of the light source used above refers to a substantially parallel light beam in which a light beam incident on the liquid crystal display panel is orthogonal to the liquid crystal display panel surface. This means that the angle between the light beams is 10 degrees or less. The parallel light source device is not particularly limited, and examples thereof include a light condensing device using a lens such as a wave sheet.

As described above, in the optical element of the present invention, the columnar island structure is formed so that the length direction thereof is substantially parallel to the film thickness direction, and the sea structure and the island structure are formed. Since the absolute value of the refractive index difference of each phase is 0.01 or more, it functions as a single optical element for a transmission type liquid crystal display device using parallel light as a light source, and transmits the transmitted light as described above. An optical element with a sea-island structure diffracts concentrically around a columnar body with an island structure and spreads light sufficiently in all directions, so the liquid crystal display device has the advantage of an extremely thin optical element. The liquid crystal display device can achieve high brightness, high resolution, and a wide viewing angle without impairing the advantages of low power consumption, light weight, and space saving.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

(Example) 50 g of polyether urethane acrylate composed of polypropylene glycol having an average molecular weight of 2,000, hydroxyethyl acrylate and isophorone diisocyanate, 50 g of tribromophenoxyisobutyl acrylate and 3 g of hydroxyisobutylphenone were mixed by stirring and a coater was placed on a glass plate. To a thickness of 150 μm. A mask in which black fine particles having an average particle size of 2.1 μm are uniformly coated on a quartz plate on the coating surface is arranged in parallel at a distance of 5 mm from the coating surface, and ultraviolet rays are irradiated from above the mask at 50 W / cm ² for 30 seconds. Then, the mask was removed, and irradiation was performed for another 10 seconds to produce an optical element.

In order to evaluate the performance of the obtained optical element,
As shown in FIG. 2 (1), the obtained optical element is placed with its short side in front and behind and its long side left and right, and the thickness direction of the optical element is used as a base axis. When the intensity of the transmitted light with respect to the incident light was measured using an ellipsometer, there was diffraction and scattering in the range of 0 to 13 degrees in the form of a bell-shaped curve shown in FIG. Showed no scattering. Further, the transmitted light is equivalent to 50% of the transmitted light intensity at the 0 degree, which is the half value width of the incident light from the thickness direction of the optical element, that is, 0 degree, that is, the ellipsometer is moved from the base axis. The so-called half-value angle (θ) for detecting the diffused light intensity was scattered light having a distribution of 13 degrees.

[0022]

Since the optical element of the present invention is configured as described above, the brightness of the transmission type liquid crystal display device can be reduced without impairing the advantages of the liquid crystal display device such as low power consumption, light weight, and space saving. A wide viewing angle as well as a high resolution can be achieved at a high level.

[0023]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing an enlarged perspective view of a fine structure at a molecular level, that is, a sea-island structure, of a film constituting an optical element of the present invention.

FIG. 2A is an explanatory diagram of a test method for evaluating the performance of the optical element of the present invention, and FIG. 2B is a graph showing test results, showing transmission at various angles with respect to incident light. It shows that the light intensity and the half-value angle (θ) are 13 degrees.

FIG. 3 is a perspective view showing an example of a liquid crystal display device using the optical element of the present invention.

FIG. 4 is an explanatory diagram showing the behavior of transmitted light with respect to the angle of incident light of an optical element used in a conventional transmission type liquid crystal display device.

FIG. 5 is a perspective view showing an example of an optical element used in a conventional reflective liquid crystal display device.

[Explanation of symbols]

 a, b layers having different refractive indices c light diffraction plate 1 island structure 2 sea structure A parallel light backlight unit B polarizing plate C liquid crystal cell D retardation plate E Optical element of the present invention

Claims (1)

[Claims] 1. An optical element comprising a film having a sea-island structure, wherein a columnar island structure is formed so that a length direction thereof is substantially parallel to a film thickness direction. An optical element in which the absolute value of the difference in the refractive index of each phase forming (i) is 0.01 or more.