JP2001091744A - Optical compensation film, optical compensation polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical compensation film which hardly changes its birefringent characteristics by external stimulation such as humidity and which has excellent stability. SOLUTION: The optical compensation film 1 is produced by laminating and supporting a birefringent phase difference layer 12 with a transparent film material 11 having <=1.0% water absorption (at 23 deg.C for 24 hours) and <=30×10-12 m2/N modulus of photoelasticity. The optical compensation polarizing plate 5 consists of a laminated body including the aforementioned optical compensation film having the phase difference layer consisting of a liquid crystal polymer, and a polarizing plate 3. The liquid crystal display device has the optical compensation film or that film with a polarizing plate on at least one side of a liquid crystal cell. Thus, a liquid crystal display device showing a stable compensation effect even on a large screen and having excellent uniformity in the display quality and good visibility characteristic can be formed with high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation film capable of forming a liquid crystal display device having good visibility and exhibiting stable birefringence characteristics against external stimuli such as humidity, and a polarizing plate laminated with the optical compensation film.

[0002]

BACKGROUND OF THE INVENTION Hitherto, there has been known an optical compensation film in which a tilted alignment layer of a discotic liquid crystal polymer is provided on a cellulose-based film substrate. This has the advantage that the viewing angle showing good visibility can be expanded by compensating for the phase difference of the liquid crystal cell by the phase difference characteristic based on the in-plane main refractive index being inclined with respect to the substrate surface. ing. However, such an optical compensatory film has a problem that the dimensions change due to an external stimulus such as humidity, the birefringence characteristics are likely to change, and the compensation effect is partially different, so that the display is likely to be distorted.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to develop an optical compensation film whose birefringence characteristics are hardly changed by an external stimulus such as humidity and whose stability is excellent.

[0004]

The present invention has a water absorption of 1.0% (23%).
C., 24 hours) and a photoelastic coefficient of 30 × 10
An optical compensatory film comprising a birefringent retardation layer adhered and supported by a transparent film substrate of ^-12 m ² / N or less, and the optical compensation film wherein the retardation layer is composed of a liquid crystal polymer; An optical compensation polarizing plate comprising a laminate of polarizing plates, and a liquid crystal display device comprising the optical compensation film or the optical compensation film and the polarizing plate on at least one side of a liquid crystal cell.

[0005]

According to the present invention, it is possible to obtain an optical compensatory film whose birefringence characteristics are hardly partially changed by an external stimulus such as humidity. As a result, a liquid crystal display device having excellent display quality uniformity and good visibility characteristics can be formed with high reliability, because the water absorption of the transparent film substrate in the optical compensation film is controlled.

That is, the present inventors have made intensive studies to overcome the above-mentioned problem of change in birefringence characteristics.
In conventional optical compensatory films, the size of the cellulosic polymer forming the transparent film substrate changes greatly due to the change in water absorption, and it is determined that the change in the size affects the birefringence characteristics. By controlling the water absorption of the transparent film substrate within the above range, the change in the birefringence characteristics was successfully suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical compensation film according to the present invention comprises
A birefringent retardation layer was tightly supported by a transparent film substrate having a water absorption of 1.0% or less (23 ° C., 24 hours) or less and a photoelastic coefficient of 30 × 10 ⁻¹² m ² / N or less. Consist of things. An example is shown in FIG. 1 is an optical compensation film, 11 is a transparent film substrate, and 12 is a birefringent retardation layer. FIG. 1 shows an optical compensation polarizing plate 5, in which 3 is a polarizing plate, and 2 and 4 are adhesive layers. Also 5
1 is a separator for temporarily protecting the adhesive layer 4.

[0008] The transparent film substrate in the optical compensation film has a water absorption of 1.0% for the purpose of tightly supporting the retardation layer.
Hereinafter, a film made of a transparent polymer having a photoelastic coefficient of 30 × 10 ⁻¹² m ² / N or less is used. This makes it possible to make the birefringence characteristics uniform over the entire surface stable with respect to external stimuli such as humidity. The above water absorption is based on the weight change due to water absorption when immersed in water at 23 ° C. for 24 hours (the same applies hereinafter).

From the viewpoint of maintaining birefringence characteristics by preventing dimensional change due to water absorption, a transparent film substrate having a water absorption of 0.8% or less, preferably 0.6% or less, particularly 0.4% or less is preferred. Things. Further, a transparent film substrate which is preferable from the viewpoint of stability of birefringence characteristics, has a photoelastic coefficient of 20 × 10
^{It is} less than ⁻¹² m ² / N, especially less than 15 × 10 ⁻¹² m ² / N, especially less than 10 × 10 ⁻¹² m ² / N.

A transparent film substrate satisfying the above-mentioned water absorption and photoelastic coefficient has a bulky saturated cyclic structure in the molecule, such as an acrylic polymer having an alicyclic structure or a hydrogenated norbornene polymer. It can be formed from a polymer containing no hydrophilic group or having two or less hydrophilic groups per component monomer unit.

The transparent film substrate can be obtained by forming a polymer into a film by an appropriate method. For example, it is excellent in uniformity of thickness formed by a casting method or the like, and has a good retardation. As small as possible can be preferably used.
The thickness of the transparent film substrate can be appropriately determined according to the strength and the like, but is generally 500 μm or less for the purpose of weight reduction and the like.
Especially, it is 5 to 300 μm, especially 10 to 200 μm.

The birefringent retardation layer adhered and supported by the transparent film substrate compensates for the retardation caused by the birefringence of the liquid crystal cell, thereby preventing coloring or the like due to a change in viewing angle based on the retardation, and providing good visibility. The purpose is to increase the viewing angle or the like, and can be formed by an appropriate birefringent retardation layer such as a stretched film layer or an alignment layer of a liquid crystal polymer according to the purpose. . Incidentally, a tilted alignment layer of a discotic liquid crystal polymer or the like can be advantageously used for expanding the viewing angle.

The support of the birefringent retardation layer in close contact with the transparent film substrate is performed by an appropriate method such as a film adhesion method via an adhesive layer or a polymer liquid coating method as necessary. In the alignment treatment of the liquid crystal polymer, an alignment film such as a rubbing treatment layer can be interposed as necessary. The thickness of the retardation layer can be appropriately determined according to the intended retardation or the like, but is generally 300 μm or less, preferably 0.1 to 100 μm, particularly 0.5 μm.
５０50 μm.

The optical compensatory film according to the present invention can be preferably used for forming a liquid crystal display device and the like. In practical use, the optical compensatory film is used as an optical compensatory polarizing plate 5 which is laminated with a polarizing plate 3 as shown in FIG. You can also. Such lamination can be performed at the time of assembling the display device. However, the method of laminating the optically compensating polarizing plate in advance has advantages such as prevention of variation in quality and improvement of assembling efficiency of the liquid crystal display device.

As the above-mentioned polarizing plate, an appropriate polarizing plate can be used, and the type thereof is not particularly limited. By the way, as examples, polyvinyl alcohol-based film and partially formalized polyvinyl alcohol-based film,
A film obtained by adsorbing iodine and / or a dichroic dye on a hydrophilic polymer film such as an ethylene / vinyl acetate copolymer partially saponified film or a cellulose film,
Examples of the polarizing film include a polyene oriented film such as a polyvinyl alcohol dehydration product and a polyvinyl chloride dehydrochlorination product. The thickness of the polarizing film is usually 5 to 80 μm, but is not limited thereto.

The polarizing plate may be a polarizing film itself or a polarizing film provided with a transparent protective layer on one side or both sides. In addition, the polarizing plate may include various anti-reflection films such as an interference film for the purpose of suppressing surface reflection, and various optical layers such as various light diffusion layers for the purpose of anti-glare due to diffusion of surface reflected light. It may be provided.

The transparent protective layer can be formed by an appropriate method such as a film laminating method or a coating method, and an appropriate transparent resin can be used for the formation. Preferred transparent protective layers are excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, isotropy, and the like. For example,
Cellulose resins such as cellulose triacetate and polyester, polycarbonate and polyamide, polyimide and polyether sulfone, polysulfone and polystyrene, plastics such as acrylic resin and polyolefin, acrylic and urethane, acrylic urethane and epoxy,
Examples thereof include those made of a thermosetting resin or an ultraviolet curable resin such as a silicone resin.

The optical compensation film 1 and the polarizing plate 3 can be adhered by an appropriate method to form an optically compensating polarizing plate 5 composed of a laminate thereof. From the viewpoints of simplicity of the bonding process and stable maintenance of optical characteristics in practical use, the bonding process using the pressure-sensitive adhesive layer 2 as shown in the figure is preferred. For the formation of the adhesive layer, for example, acrylic or silicone, polyester or polyurethane, polyamide or polyether,
An appropriate pressure-sensitive adhesive such as a rubber-based adhesive can be used. Above all, an acrylic pressure-sensitive adhesive can be preferably used in terms of optical transparency, pressure-sensitive adhesive properties, weather resistance and the like.

The adhesion of the pressure-sensitive adhesive layer to the optical compensation film or / and the polarizing plate may be performed, for example, by applying a pressure-sensitive adhesive solution to a predetermined surface of the optical compensation film or / and the polarizing plate by an appropriate developing method such as a casting method or a coating method. It can be carried out by an appropriate method such as a method of directly attaching, or a method of forming an adhesive layer on a separator and transferring it to a predetermined surface of an optical compensation film and / or a polarizing plate according to the method. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the adhesive strength and the like, and is generally 1 to 500 μm, preferably 5 to 500 μm.
It is 200 μm, especially 10 to 100 μm.

The optically compensating polarizing plate may be provided with a pressure-sensitive adhesive layer 4 for adhering and fixing it to a liquid crystal cell or the like as shown in the drawing. The adhesive layer is usually provided on an optical compensation film of an optical compensation polarizing plate. The formation and attachment of such an adhesive layer can be performed according to the above-mentioned adhesive layer 2, and the attachment can be provided in advance on an optical compensation film and used for forming an optical compensation polarizing plate.

As shown in FIG. 1, a separator 51 and the like are temporarily attached to the pressure-sensitive adhesive layer 4 if necessary for the purpose of preventing a decrease in the adhesive force due to contamination or the like until the adhesive layer 4 is bonded. And so on. As the separator, for example, a suitable thin leaf such as a plastic film or a rubber sheet, paper or cloth, a nonwoven fabric or a net, a foamed sheet or a metal foil, a laminate thereof, or the like, if necessary, may be a silicone-based, long-chain alkyl-based, An appropriate one according to the related art, such as one coated with an appropriate release agent such as a system, may be used.

In the above, the polarizing plate 3 is provided on the transparent film substrate side 11 or the retardation layer side 12 of the optical compensation film 1.
May be provided in any of the above. The optical axes of the optical compensation film and the polarizing plate when they are laminated can be set at an appropriate angle depending on the intended retardation characteristics and the like.

The transparent film substrate, the retardation layer, the polarizing plate, its transparent protective layer, the adhesive layer (adhesive layer), etc., which form the optical compensation film or the optically compensating polarizing plate, may be, for example, a salicylic acid ester compound, if necessary. Benzophenone compounds,
It may have ultraviolet absorption ability by a method of treating with an ultraviolet absorber such as a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound.

The liquid crystal display device according to the present invention has the optical compensation film according to the present invention or the polarizing plate on at least one side of the liquid crystal cell, and the polarizing plate can be provided as the above-mentioned optical compensation polarizing plate. The formation of the liquid crystal display device can be performed according to a conventional method. That is, a liquid crystal display device generally includes a liquid crystal cell, a polarizing plate, an optical compensation film,
It is formed by appropriately assembling components such as a lighting system as necessary and incorporating a drive circuit.In the present invention, in particular, except that the optical compensation film according to the present invention or the polarizing plate and the polarizing plate are used. There is no limitation, and it can be in accordance with the prior art.

Therefore, an appropriate liquid crystal display device such as a liquid crystal display device having a polarizing plate disposed on one or both sides of a liquid crystal cell or a device using a backlight or a reflector for an illumination system can be formed. In that case, the optical compensation film or the like according to the present invention can be installed on one side or both sides of the liquid crystal cell, and the optical compensation film is located between the polarizing plate and the liquid crystal cell from the viewpoint of the compensation effect, especially at least on the viewing side of the liquid crystal cell. It is preferable that the optical compensation film is located at the position.

FIGS. 2 and 3 show examples of the structure of the above-mentioned liquid crystal display device. 5 is an optical compensation polarizing plate, 6 is a liquid crystal cell, 7 is a backlight system, and 9 is a reflective layer. Reference numeral 8 denotes a light diffusion plate. 2 is a backlight illumination type in which optical compensation polarizers 5 are arranged on both sides of a liquid crystal cell 6, and FIG. 3 has an optical compensation polarizer arranged only on one side of the liquid crystal cell. Reflective illumination type.

The liquid crystal cell may be of any type such as TN type, STN type, and π type.
In forming a liquid crystal display device, one or two or more appropriate optical layers such as a diffusion plate, an antiglare layer, an antireflection film, and a protective plate can be disposed at appropriate positions.

[0028]

EXAMPLE 1 A 100 μm thick film substrate (Optrez, manufactured by Hitachi Chemical Co., Ltd.) made of an alicyclic acrylic resin having a water absorption of 0.6% and a photoelastic coefficient of 2 × 10 ⁻¹² m ² / N. 0.5 μm thick) consisting of a rubbed film of polyvinyl alcohol
A liquid mixture of a triphenylene-based discotic liquid crystal having a UV-curable functional group and a benzoin ether-based photoinitiator is applied thereon, and heated to 150 ° C. or higher to form a discotic nematic phase. After that, the film was cured by ultraviolet rays to obtain an optical compensation film in which a birefringent retardation layer composed of a liquid crystal polymer layer having a thickness of 2.5 μm was tightly supported by a transparent film substrate. In the liquid crystal polymer layer, the in-plane main refractive index of the liquid crystal molecules was parallel to the film substrate side, and the liquid crystal polymer layer was inclined with respect to the substrate on the free interface side in contact with the air layer.

Next, a polarizing plate (Nitto Denko Corp., provided with an adhesive layer) on the optical compensation film with respect to its in-plane slow axis.
HEG1425DU) was adhered and laminated so that the polarization axes thereof coincided with each other, and an acrylic pressure-sensitive adhesive layer was provided on the optical compensation film side to obtain an optical compensation polarizing plate.

Example 2 A 100 μm thick film substrate made of a maleimide resin (TI-160, manufactured by Tosoh Corporation) having a water absorption of 0.5% and a photoelastic coefficient of 7 × 10 ⁻¹² m ² / N was used. Otherwise, an optical compensation film was obtained in the same manner as in Example 1, and an optical compensation polarizing plate was obtained using the optical compensation film.

COMPARATIVE EXAMPLE A tilted alignment layer of discotic liquid crystal polymer was tightly supported by a transparent film substrate made of triacetyl cellulose having a water absorption of 3.5% and a photoelastic coefficient of 5 × 10 ⁻¹² m ² / N. Optical compensation film (Fuji Photo Film, W
An optically compensatory polarizing plate was obtained according to Example 1, except that VA02A) was used.

Evaluation Test The optically compensating polarizing plates obtained in Examples and Comparative Examples were adhered to both sides of a glass plate via their adhesive layers so that the polarizing plates were in a crossed Nicols state (black at 45 ° and 135 ° in the polarization axis). Display state), subjected to a durability test in which it was left in an atmosphere of 60 ° C. and 90% RH for 120 hours (moisture resistance) or in an atmosphere of 80 ° C. for 120 hours (heat resistance), and then subjected to a uniform black state on a light table. The display quality was evaluated by visually observing the properties and light leakage.

The results are shown in the following table. Moisture resistance Heat resistance Example 1 Good (* 1) Good (* 1) Example 2 Good (* 1) Good (* 1) Comparative example Light leakage defect (* 2) Light leakage defect (* 2) * 1: Uniform black state, no light leakage * 2: Partial light leakage, which is visually recognized as unevenness

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 3 is a cross-sectional view of another example of a liquid crystal display device.

[Explanation of symbols]

 5: Optically compensating polarizing plate 1: Optically compensating film 11: Transparent film substrate 12: Birefringent retardation layer 2, 4: Adhesive layer 3: Polarizing plate 6: Liquid crystal cell

 ──────────────────────────────────────────────────の Continuing on the front page F term (reference) 2H042 AA04 AA26 2H049 BA06 BA24 BA42 BB03 BC22 2H091 FA08X FA08Z FA11X FA11Z FB02 FD06 FD15 GA17 JA01 LA06 LA19 4F100 AK01B AK01E AK21 AK25 AK80 AR00E00 AT00 AS00 AT00 AR00 AT00 AS00 AT00 AT00 BA05 BA06 BA07 BA10A BA10E CB03 CC02 EJ27 GB41 JA11 JN01C JN01E JN10A JN10E JN18 JN18B JN18C JN18E JN30 JN30B JN30C JN30E

Claims (3)

[Claims] 1. A water absorption rate of 1.0% (23 ° C., 24 hours)
An optical compensation film comprising: a transparent film substrate having a photoelastic coefficient of 30 × 10 ⁻¹² m ² / N or less and a birefringent retardation layer being closely supported. 2. An optically compensatory polarizing plate, comprising: the optical compensation film according to claim 1, wherein the retardation layer comprises a liquid crystal polymer. 3. A liquid crystal display device comprising the optical compensation film according to claim 1 or a polarizing plate and the optical compensation film on at least one side of a liquid crystal cell.