JP2002311239A - Quarter-wave plate, circularly polarizing plate and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a wave plate functioning as a quarter-wave plate over a wide wavelength region such as a visible ray region and which can be mass- produced and very thin, and to develop a circularly polarizing plate excellent in antireflection for a wide band. SOLUTION: The quarter-wave plate (1) comprises a birefringent layer (12) giving a phase difference of one-half wavelength to a monochromatic ray arranged on a monolayer stretched film (11) giving a phase difference of one- quarter wavelength to a monochromatic ray where the birefringent layer consists of a fixed orientation layer of a liquid crystalline compound. The circularly polarizing plate comprises a polarizing film (3) laminated on the birefringent layer side of the quarter-wave plate. A display device comprises a liquid crystal cell or an organic EL(electroluminescence) element with the quarter-wave plate or the circularly polarizing plate arranged on at least one side thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a quarter-wave plate excellent in thinness that gives a phase difference of four wavelengths, and a circularly polarizing plate that prevents reflection over a wide wavelength range.

[0002]

BACKGROUND OF THE INVENTION Conventionally, as a quarter-wave plate for providing a quarter-wave retardation in a wide wavelength region of visible light, a plurality of stretched films for giving quarter-wave and half-wave retardations have been used. There have been known laminates in which the optical axes are crossed, and laminates in which a transparent support, a liquid crystal compound layer and a birefringent film layer are laminated (JP-A-5-100114, JP-A-13-48).
No. 37).

However, in the former case where the stretched film is laminated, it is difficult to perform continuous processing using a long film, and the lamination work is performed in a batch system, which requires cutting, size adjustment, lamination for each veneer, and mass production. There is a problem that the 性 wavelength plate obtained is poor in quality and the obtained quarter-wave plate is also thick. Also, the latter method has problems in that the number of layers is large, mass productivity is poor, and the obtained quarter-wave plate is thick.

[0004]

SUMMARY OF THE INVENTION The present invention provides a wave plate which functions as a quarter wavelength plate over a wide wavelength range such as a visible light region, and is excellent in mass productivity and thinness, and a circularly polarized light which is excellent in anti-reflection broad band and the like. The task is to develop boards.

[0005]

The present invention provides a birefringent layer which gives a phase difference of 1/2 wavelength to monochromatic light on a monolayer stretched film which gives a phase difference of 1/4 wavelength to monochromatic light. １ ／ wavelength plate characterized in that the birefringent layer is composed of an alignment solidified layer of a liquid crystal compound, and a polarizing film laminated on the birefringent layer side of the ４ wavelength plate And a display device characterized in that the quarter-wave plate or the circular polarizer is disposed on at least one side of a liquid crystal cell or an organic EL element. .

[0006]

According to the present invention, it is possible to obtain a quarter-wave plate which can be continuously manufactured, has excellent mass productivity and is thin, and gives a quarter-wave phase difference in a wide wavelength region such as a visible light region. Can be. Further, a circularly polarizing plate useful as a broadband antireflection filter capable of substantially preventing reflection of light in a wide wavelength range such as a visible range can be obtained by using the quarter wavelength plate.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A quarter-wave plate according to the present invention is provided on a single-layer stretched film that gives a phase difference of one-quarter wavelength to monochromatic light, and a half-wave plate for monochromatic light. A birefringent layer for providing a phase difference is provided, and the birefringent layer is formed of an alignment solidified layer of a liquid crystalline compound. An example is shown in FIG. 1 is a 1/4 wavelength plate, 11 is a stretched film, and 12 is a birefringent layer. The figure shows a circularly polarizing plate, wherein 3 is a polarizing film, 2 and 4 are adhesive layers, and 5 is a separator.

[0008] As a stretched film, 1 to monochromatic light
One that gives a phase difference of / 4 wavelength is used. There is no particular limitation on the monochromatic light or the phase difference, but in general, in consideration of birefringence by liquid crystal when applied to a liquid crystal cell, a position measured with light having a wavelength of about 540 to 560 nm, which is almost in the middle of the visible light range. 80-200 nm, especially 110-145
nm, particularly preferably 120 to 140 nm. The phase difference is based on the front phase difference, that is, the product of the difference between the maximum in-plane refractive index and the refractive index in a direction orthogonal to the direction and the thickness (the same applies hereinafter).

The above-mentioned stretched film also serves to support a birefringent layer composed of an alignment solidified layer of a liquid crystal compound.
For example, it can be obtained by a method of stretching a polymer film uniaxially or biaxially. In that case, it is preferable to perform a stretching treatment so that the longitudinal direction thereof becomes a slow axis from the viewpoint of obtaining a long film from which a circularly polarizing plate can be continuously produced. Vertical using the peripheral speed difference (longitudinal direction of long film)
It can be performed by applying a uniaxial stretching method. In the biaxial stretching method, for example, a long film can be stretched in the longitudinal direction by a uniaxial stretching method, and then stretched in the width direction (short side direction) via a tenter.
In addition, for example, in the uniaxial stretching method, a stretching direction in a width direction by a tenter may be used, and in the biaxial stretching method, a slow axis may be set to a width direction of 90 degrees with respect to the longitudinal direction of a long film by a method of controlling a stretching axis. it can.

There is no particular limitation on the type of polymer forming the stretched film, and those having excellent transparency are preferably used. By the way, examples thereof include polyolefins such as polyethylene, polypropylene and norbornene polymers, polyvinyl chloride and polystyrene, polyacrylonitrile and polysulfone, polyarylate and polyvinyl alcohol, polymethacrylate and polyacrylate, cellulose ester and polycarbonate, polyester, and the like. Examples thereof include polyether sulfone, a mixture of these polymers, and a copolymer of monomers forming these polymers.

From the viewpoint of the stability of optical characteristics and the like, a stretched film made of a polymer having a photoelastic coefficient of 5 × 10 ⁻¹² cm ² / dyn or less is preferable. The polymer film to be stretched can be formed by an appropriate method, but is preferably a polymer film produced by a solvent casting method from the viewpoint of obtaining a stretched film with less birefringence unevenness. The thickness of the polymer film can be appropriately determined according to the draw ratio, the phase difference, and the like, but is generally 20 to 500 μm, preferably 50 to 500 μm.
It is 200 μm, especially 50-100 μm.

The birefringent layer supported by the above-mentioned stretched film is formed by a solidified alignment layer of a liquid crystalline compound. This enables mass production by continuous production while reducing the thickness. Further, the birefringent layer gives a phase difference of 波長 wavelength to the monochromatic light. As a result, 1/1
It can be a quarter-wave plate that provides a phase difference of four wavelengths. The monochromatic light or the phase difference in the birefringent layer is not particularly limited, but generally, in consideration of birefringence due to liquid crystal when applied to a liquid crystal cell, a wavelength of about 540 to 560 nm, which is almost in the middle of the visible light region. The phase difference measured with light is 20
0-300 nm, especially 240-290 nm, especially 250-2
Those having a thickness of 80 nm are preferred.

As the liquid crystalline compound forming the birefringent layer, an appropriate compound that forms an alignment state exhibiting birefringence can be used, and may be any of a low molecular weight or a high molecular weight. Above all, a low-molecular liquid crystal compound capable of fixing an alignment state by a polymerization reaction is preferable, and a rod-like liquid crystal compound is particularly preferable. By the way, as an example of the rod-like liquid crystalline compound,
Azomethines and azoxys, cyanobiphenyls and cyanophenyl esters, benzoic acid esters and cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes and cyano-substituted phenylpyrimidines,
Examples include alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitrile (edited by The Chemical Society of Japan, Quarterly Review of Chemistry, Vol. 22, Liquid Crystal Chemistry (1994), Chapters 4, 7). And Chapter 11, and the 142nd Committee of the Japan Society for the Promotion of Science, Liquid Crystal Device Handbook, Chapter 3).

The birefringent layer is formed as a solidified layer in which a liquid crystalline compound is oriented and its orientation is fixed. It is preferable that the alignment state is as uniform as possible, and it is preferable that the alignment state is fixed. From such a point, it is advantageous that the liquid crystal compound has a homogeneous alignment. The alignment of the liquid crystalline compound is, for example, a rubbed surface by rubbing the surface of a polymer film or the like several times with paper or cloth in a certain direction, or a liquid crystalline compound on an alignment film such as a photo alignment film irradiated with polarized light. Can be carried out by a method of expanding.

The birefringent layer is provided such that its optical axis intersects a stretched film giving a quarter-wave retardation. As a result, it is possible to obtain a device that functions as a quarter-wave plate in a wide wavelength range while suppressing dispersion while controlling the phase difference as a whole to a quarter wavelength. The birefringent layer is usually 0.1 to 50 μm, preferably 0.5 to 20 μm, especially 1 to 10 μm.
With a thickness of μm, a phase difference of 波長 wavelength can be given to monochromatic light. In forming the birefringent layer, the surface of the stretched film may be subjected to an appropriate surface treatment such as a glow discharge treatment, a corona discharge treatment, an ultraviolet irradiation treatment, a flame treatment, etc. for the purpose of improving the adhesion.

The circularly polarizing plate can be formed by laminating the polarizing film 3 on the side of the birefringent layer 12 in the quarter wave plate as shown in the figure. A quarter-wave plate that can be preferably used for forming a circularly polarizing plate has a refractive index difference of birefringent light of ４００n1 at a light of 400 nm and a refractive index difference of birefringent light of ５００n2 at a light of 500 nm. When △ n1 /
The dispersion ratio of the birefringent layer based on n2 is larger than the dispersion ratio of the stretched film. This makes it possible to obtain a device that functions as a circularly polarizing plate in a wide wavelength range.

In the above, it is preferable that the transmission axis of the polarizing film and the slow axis of the stretched film have a parallel relation or an orthogonal relation, rather than a point of continuously manufacturing a circularly polarizing plate using a long film. In this case, the slow axis of the birefringent layer is 22.5 times with respect to the transmission axis or the stretching axis (absorption axis) of the polarizing film.
It is preferable that the temperature is set to be equal to the temperature. However, when applied to a liquid crystal cell, when the liquid crystal exhibits birefringence due to its alignment state, the optical axis relationship can be corrected according to the birefringence.

As the polarizing film, an appropriate film that transmits linearly polarized light and absorbs other light can be used, and the type thereof is not particularly limited. Preferably, a polarizing film or one obtained by protecting one or both surfaces thereof with a transparent protective layer is used. Incidentally, examples of the polarizing film include iodine and / or a dichroic dye on a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene-vinyl acetate copolymer-based partially saponified film. Examples thereof include those subjected to stretching treatment by adsorption, and polyene-based polarizing films. In the case of the above-mentioned stretching polarizing film, the transmission axis is in a direction perpendicular to the stretching direction.

The transparent protective layer provided on one side or both sides of the polarizing film as needed can be formed of an appropriate polymer. Above all, a transparent protective layer made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like is preferable. The transparent protective layer can be formed by an appropriate method such as a method of applying a polymer liquid or an adhesive lamination method of a film. Incidentally, examples of the polymer include a cellulosic polymer such as triacetyl cellulose and those exemplified in the above-mentioned stretched film. The transparent protective layer on one side of the polarizing film can also serve as a stretched film forming a quarter-wave plate for the purpose of thinning.

The laminating of the quarter-wave plate and the polarizing film in the circularly polarizing plate may be in a state of being placed, but the stabilization of the quality by preventing the displacement of the optical axis and the improvement of the assembling efficiency of the display device are performed. From the point of view, it is preferable that they are bonded through a transparent bonding layer 2 as shown in the figure. The type of the adhesive forming the adhesive layer is not particularly limited, and for example, an appropriate adhesive such as a thermosetting type, an energy ray curing type, a hot melt type, a two-liquid mixing type reaction type, and an adhesive type may be used. . Particularly, those having excellent transmittance of light in the visible light region are preferable. Further, it is preferable that the resin does not have absorptivity to light of a specific wavelength from the viewpoint of preventing coloring.

Further, an adhesive layer is preferable from the viewpoint of simplicity of the bonding operation and the like. As the pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer, for example, a pressure-sensitive adhesive having an appropriate polymer such as acrylic, silicone, polyester, polyurethane, polyether, or rubber as a base polymer can be used. A material that does not require a high-temperature process for curing or drying and does not require a long-time curing or drying treatment is preferable from the viewpoint of preventing a change in optical characteristics of a forming material. Further, a material which does not cause a peeling problem such as floating or peeling under heating or humidifying conditions is preferable.

The attachment of the adhesive layer to the quarter-wave plate or the polarizing film can be performed by applying an appropriate method. Incidentally, as an example, a pressure-sensitive adhesive component is dissolved or dispersed in a solvent consisting of an appropriate solvent alone or a mixture of appropriate solvents such as toluene and ethyl acetate to prepare a pressure-sensitive adhesive liquid of about 10 to 40% by weight, and it is cast. Examples thereof include a method in which the adhesive layer is directly provided on the material by an appropriate development method such as a method and a coating method, or a method in which an adhesive layer is formed on a separator and transferred to the material according to the above. The provided adhesive layer may be a superposed layer of different compositions or types.

The thickness of the adhesive layer can be appropriately determined according to the adhesive force and the like, and is generally 1 to 500 μm, preferably 3 to 100 μm,
In particular, it is 5 to 50 μm. To the adhesive layer, if necessary, for example, appropriate addition of fillers, pigments, coloring agents, antioxidants, and the like made of natural and synthetic resins, glass fibers and glass beads, metal powders and other inorganic powders, etc. An agent can also be compounded. Further, an adhesive layer showing light diffusing properties may be formed by containing transparent particles. The transparent particles include, for example, silica and alumina, titania and zirconia, tin oxide and indium oxide, cadmium oxide and antimony oxide, and the like.
Appropriate particles such as inorganic particles which may be conductive, organic particles formed of a crosslinked or uncrosslinked polymer, or the like may be used alone or in combination of two or more.

On one or both sides of the quarter-wave plate or the circularly polarizing plate according to the present invention, an adhesive layer 4, particularly an adhesive layer, for the purpose of adhering to other members such as a liquid crystal cell is provided as necessary, as shown in the figure. It can also be provided. When the adhesive layer is exposed on the surface, the surface may be temporarily covered with a separator 5 or the like for the purpose of protection such as contamination prevention until practical use. When the forming material is exposed on the surface, the exposed surface can be covered with a surface protective film to protect it from being damaged. When forming a circularly polarizing plate, the surface of the polarizing film and / or the birefringent layer may be subjected to an appropriate surface treatment such as the above-described corona discharge treatment for the purpose of improving adhesion and the like.

The quarter wave plate according to the present invention can be used for various conventional purposes such as forming a circularly polarizing plate. Circularly polarizing plates can also be used as antireflection filters or optical members for improving display characteristics in various applications, such as forming liquid crystal display devices such as reflective or high-brightness wide-view devices or display devices such as organic EL elements. it can. The display device can be formed by a conventional method such as a method of disposing a quarter-wave plate or a circularly polarizing plate on one or both sides of a liquid crystal cell or an organic EL element.

Example 1 A film made of an optically isotropic norbornene resin having a thickness of 100 μm, a width of 500 mm, and a length of 500 m wound in a roll shape was rewound at 175 ° C. through a difference in peripheral speed while being rewound through a roll. While forming a stretched film having a phase difference of 140 nm by light having a wavelength of 560 nm continuously, a 1% by weight aqueous solution of polyvinyl alcohol is applied on the stretched film and dried at 90 ° C. 22. A film having a thickness of 0.01 μm was formed, and the surface of the film was formed in the longitudinal direction of the film.
Rubbing treatment was performed in the direction of 5 degrees to sequentially form alignment films.

Further, a mixture of a reactive rod-like nematic liquid crystal having the following structure and a photopolymerization initiator is applied to a thickness of about 3 μm on the alignment film, heated at 90 ° C. for 1 minute, and irradiated with ultraviolet rays. To form a birefringent layer having a phase difference of 270 nm by light having a wavelength of 560 nm.
Four-wavelength plates were obtained continuously.

Further, on the birefringent layer of the 回 wavelength plate, a polarizing film with an adhesive layer (SEG1425DU, manufactured by Nitto Denko Corporation) wound in a roll is passed through the adhesive layer in a roll-to-roll system. By sequentially laminating, a circularly polarizing plate was continuously obtained. This is the slow axis (longitudinal direction) of the stretched film
In contrast, the slow axis of the birefringent layer intersected at an angle of 22.5 degrees, and the transmission axis of the polarizing film was orthogonal.

COMPARATIVE EXAMPLE A film made of an optically isotropic norbornene resin having a thickness of 100 μm, a width of 500 mm and a length of 500 m wound into a roll was rewound through a roll and heated to 175 ° C. through a difference in peripheral speed. A stretched film having a phase difference of 140 nm due to light having a wavelength of 560 nm and a wavelength of 560 nm.
Stretched films having a phase difference of 270 nm with light of nm were separately formed.

Next, the stretched film was cut to obtain a wave plate of a predetermined size. The half-wave plate was cut so as to have an angle of 22.5 degrees with respect to the slow axis formed in the longitudinal direction of the stretched film. Then, these wave plates are adhered via an adhesive layer, and a polarizing film of a predetermined size is adhered on the half-wave plate via the adhesive layer to form a circular polarizer having the same optical axis relationship as in Example 1 for each layer. Obtained.

Evaluation Test As described above, the circular polarizing plate obtained in Example 1 had a total thickness of 3
It was 40 μm, and the circular polarization characteristics were also good. On the other hand, the circularly polarizing plate obtained in Comparative Example exhibited good circularly polarizing characteristics, but had a total thickness of 415 μm. Further, in Example 1, the circularly polarizing plate was efficiently manufactured by the roll-to-roll method, and the mass productivity was excellent and the quality was stable. However, in the comparative example, it was necessary to sequentially stack the pieces cut to a predetermined size, and the manufacturing efficiency was increased. It was poor and the variation in quality was great. From the above, it can be seen that, in the examples, lamination treatment via a roll is possible and excellent in production efficiency, and a circularly polarizing plate having a small thickness and almost the same performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a circularly polarizing plate.

[Explanation of symbols]

 1: 1/4 wavelength plate 11: stretched film 12: birefringent layer 3: polarizing film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA03 BA07 BA25 BA27 BA42 BA47 BB03 BB33 BB43 BB44 BB46 BB48 BB49 BB51 BB63 BC03 BC14 BC22 2H091 FA08X FA08Z FA11X FA11Z FC08 FD14 KA01 LA12

Claims (7)

[Claims] 1. A monolayer stretched film that gives a phase difference of 位相 wavelength to monochromatic light,
A quarter-wave plate comprising a birefringent layer for providing a wavelength phase difference, wherein the birefringent layer comprises a liquid crystal compound alignment solidified layer. 2. The stretched film according to claim 1, wherein the stretched film is made of a polymer having a photoelastic coefficient of 5 × 10 ⁻¹² cm ² / dyn or less.
/ 4 wavelength plate. 3. A circularly polarizing plate, comprising: a polarizing film laminated on a side of the birefringent layer in the quarter-wave plate according to claim 1 or 2. 4. The method according to claim 3, wherein the difference in the refractive index of the birefringent light in the light having a wavelength of 400 nm is Δn1,
光 n2 of the birefringent layer when it is △ n2
A circularly polarizing plate using a 1/4 wavelength plate whose dispersion ratio based on 1 / n2 is larger than that of a stretched film. 5. A circularly polarizing plate according to claim 4, wherein the transmission axis of the polarizing film and the slow axis of the stretched film are in a parallel or orthogonal relationship. 6. A display device comprising the quarter-wave plate according to claim 1 disposed on at least one side of a liquid crystal cell or an organic EL element. 7. A display device comprising the circularly polarizing plate according to claim 3 arranged on at least one side of a liquid crystal cell or an organic EL element.