JP2002228835A - Polarizer, method for manufacturing the same and polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer having a high polarization degree and high transmittance, a method for manufacturing the same and a polarizing plate and a liquid crystal display device using the same. SOLUTION: The polarizer consists of a film comprising a polyvinyl alcohol type film with iodine or a dichroic dye adsorbed thereto and aligned thereon. The birefringence (Δn) of the polyvinyl alcohol type film expressed by an equality (1) is made to satisfy an inequality 0.002<=Δn<=0.01. Δn=ns-nf (1) (in the equality, ns expresses the refractive index in the slow axis direction in the polyvinyl alcohol type film plane and nf expresses the refractive index in the fast axis direction in the polyvinyl alcohol type film plane).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizer used for a liquid crystal display device and the like, a method of manufacturing the same, a polarizing plate using the same, and a liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices include desk-top electronic calculators, electronic clocks, personal computers, word processors,
It is used for instruments of automobiles and machines, and a polarizing plate is used in this liquid crystal display device. As a polarizing plate,
A polarizing film of a polyvinyl alcohol-based film in which iodine or a dichroic dye is adsorbed and aligned, a protective film such as triacetyl cellulose is used on both sides, and a liquid crystal display device having high brightness and high contrast is used. In order to provide such a polarizing plate, a polarizing plate having both a high transmittance and a high degree of polarization is required.

A polarizer obtained by dyeing and stretching a polyvinyl alcohol (PVA) film with iodine or the like having a dichroic property generally has a higher degree of polarization even at the same transmittance by increasing the stretching ratio. It is known that it can be obtained, and as the polyvinyl alcohol-based film, a film obtained by forming a polyvinyl alcohol-based resin having an average degree of polymerization of 500 to 10,000 and a saponification degree of 95 mol% or more is used. However, there is a limit to the draw ratio of a polyvinyl alcohol-based film, and if the draw ratio is too high, the film is cut, and thus the obtained characteristics are also limited. Therefore, it is necessary to obtain a polarizer having a high transmittance and a high degree of polarization without increasing the stretching magnification.

On the other hand, as a method for producing a film having a high degree of polarization and high transmittance, a method of uniaxially stretching a polyvinyl alcohol-based film in a dry system, adsorbing and orienting iodine and the like, and immersing in a boric acid-containing aqueous solution (Japanese Patent Laid-Open No. 8-2407
No. 15), a method in which a polyvinyl alcohol-based film is uniaxially stretched in a dry system, dyed, and further stretched while immersed in a boric acid aqueous solution (JP-A-10-288709, JP-A-11-49878). Proposed. However, there are problems that the degree of polarization is insufficient, and a polarizer with a high transmittance and a high degree of polarization cannot be stably produced.

[0005]

In order to solve the above-mentioned conventional problems, the present inventors have conducted intensive studies. As a result, by using a polyvinyl alcohol-based film having a birefringence within a certain range, the draw ratio cannot be increased. In both cases, they have found that a polarizer and a polarizing plate having a high degree of polarization and a high transmittance can be obtained, and have completed the present invention.

[0006]

In order to solve the above-mentioned problems, a polarizer of the present invention is a polarizer comprising a film in which iodine or a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based film. The birefringence (Δn) of the alcohol-based film represented by the formula (1) is 0.1.
002 ≦ Δn ≦ 0.01. _{Δn = n s -n f (1} ) ( wherein, n _s is a refractive index in a slow axis direction of the polyvinyl alcohol-based film plane, n _f is a fast-axis refractive index of the polyvinyl alcohol-based film plane is there.)

When the birefringence (Δn) of the polyvinyl alcohol-based film is less than 0.002, the degree of polarization becomes insufficient, and when it exceeds 0.01, the film tends to break during stretching, making it difficult to produce a polarizer. . That is, by using the polyvinyl alcohol-based film of the present invention, Δn <0.00 having the same transmittance stretched under the same stretching conditions.
The degree of polarization is higher than that of the polarizer using the polyvinyl alcohol-based film of No. 2. That is, by using a polyvinyl alcohol-based film satisfying 0.002 ≦ Δn, there is an advantage that a polarizer having a high transmittance and a high degree of polarization can be obtained without increasing the stretching magnification.

In the polarizer of the present invention, the polyvinyl alcohol-based film is preferably stretched in the slow axis direction in the film plane, and the stretching ratio is preferably 3 to 7 times.

The polarizing plate of the present invention is characterized in that the polarizer has a protective layer on at least one side of the polarizer.

Next, according to the method for producing a polarizer of the present invention, the birefringence (Δn) represented by the following formula (1) is 0.002 ≦
It is characterized in that a polyvinyl alcohol-based film satisfying Δn ≦ 0.01 is stretched in the slow axis direction of the film in an aqueous solution containing iodine or a dichroic dye. _{Δn = n s -n f (1} ) ( wherein, n _s is a refractive index in a slow axis direction of the polyvinyl alcohol-based film plane, n _f is a fast-axis refractive index of the polyvinyl alcohol-based film plane is there.)

Further, the method for producing a polarizer of the present invention is characterized in that the polyvinyl alcohol-based film is stretched in a boron compound-containing aqueous solution in a slow axis direction of the film.

Further, the polarizing plate of the present invention is characterized in that a polarizer produced by the above method has a protective layer on at least one side.

The polarizing plate of the present invention comprises a laminate of the above-described polarizing plate and at least one optical layer selected from a retardation plate, a reflector, a transflective reflector, a viewing angle compensation film, and a brightness enhancement film. It is characterized by becoming.

Further, the liquid crystal display device of the present invention is characterized in that any one of the polarizing plates is arranged on at least one side of a liquid crystal cell.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizer of the present invention is obtained by adsorbing or aligning iodine or a dichroic dye on a polyvinyl alcohol-based film having a birefringence (Δn) of 0.002 ≦ Δn ≦ 0.01. Made of film. That is, the polyvinyl alcohol-based film is dried after a dyeing step of dyeing with dichroic iodine or a dichroic dye, a crosslinking step of crosslinking with boric acid or borax, and a stretching step of uniaxial stretching. The steps of dyeing, crosslinking, and stretching are as follows:
The steps need not be performed separately and may be performed simultaneously, and the order of each step may be arbitrary. Stretching may be performed two or more times,
It may be performed a plurality of times in the same step, or may be performed in different steps.

The polyvinyl alcohol-based film used in the polarizer of the present invention has a birefringence (Δn) represented by the following formula (1) in a range of 0.002 ≦ Δn ≦ 0.01, preferably 0.005 ≦ Δn ≦ 0.01. ≦ Δn ≦ 0.009. When the birefringence (Δn) is less than 0.002, the degree of polarization becomes insufficient, and when it exceeds 0.01, it is liable to break during stretching, making it difficult to produce a polarizer. _{Δn = n s -n f (1} ) ( wherein, n _s is a refractive index in a slow axis direction of the polyvinyl alcohol-based film plane, n _f is a fast-axis refractive index of the polyvinyl alcohol-based film plane is there.)

The polyvinyl alcohol resin used as the raw material of the polyvinyl alcohol film used in the present invention is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but is not limited thereto. Alternatively, a copolymer of vinyl acetate with a small amount of a copolymerizable monomer such as an unsaturated carboxylic acid, unsaturated sulfonic acid, or a cationic monomer may be used. The degree of polymerization of the polyvinyl alcohol-based polymer is not particularly limited, and any one can be used. The average degree of polymerization is preferably from 500 to 10,000, more preferably from 1,000 to 6,000.
When the average degree of polymerization is less than 500, the film is easily dissolved in water, so that stretching is difficult. When the average degree of polymerization exceeds 10,000, film formation becomes difficult due to high viscosity. Further, from the viewpoint of the solubility of the film in water, the saponification degree is preferably at least 75 mol%, more preferably from 98 to 100 mol%.

As a method for producing a film using a polyvinyl alcohol-based resin, a method of casting an undiluted solution obtained by dissolving a polyvinyl alcohol-based resin in water or an organic solvent to form a film is generally used, but is not limited thereto. . Examples of the solvent used for preparing the stock solution include water, dimethyl sulfoxide, N-methylpyrrolidone, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine,
Examples include diethylenetriamine and mixtures thereof. The concentration of the polyvinyl alcohol-based resin in the stock solution is usually 5 to 20% by mass. When a film is formed from this undiluted solution by a casting method, Δn can be changed by changing the peeling speed from the belt. The thickness of the polyvinyl alcohol-based film is preferably from 10 to 200 μm,
In particular, 30 to 80 μm is preferable. If it is less than 10 μm, stretching becomes difficult, and if it exceeds 200 μm, it is difficult to dry during film formation, and problems such as foaming tend to occur.

The method for adsorbing and orienting iodine or a dichroic dye is not particularly limited. For example, an unstretched polyvinyl alcohol film is uniaxially stretched in water and then dipped in an aqueous solution containing iodine or a dichroic dye. A method in which an unstretched polyvinyl alcohol-based film is immersed in an aqueous solution containing iodine or a dichroic dye and then uniaxially stretched, and a method in which the unstretched polyvinyl alcohol-based film is uniaxially stretched in an aqueous solution containing iodine or a dichroic dye. And the like.

The polyvinyl alcohol-based film is preferably stretched in a slow axis direction in the film plane in order to maximize the orientation. Stretching can be performed once or divided into a plurality of times.
It is preferable that it is twice, especially 4 to 6 times. When the total stretching ratio is less than 3 times, a sufficient degree of polarization cannot be obtained, and problems such as generation of wrinkles due to swelling of the film occur. When the total stretching ratio exceeds 7 times,
Stretch breaks are likely to occur.

Next, a method for producing the polarizer of the present invention will be described.

In the present invention, the birefringence (Δ
A polyvinyl alcohol-based film in which n) satisfies 0.002 ≦ Δn ≦ 0.01 is stretched in an aqueous solution (dye bath) containing iodine or a dichroic dye. The stretching ratio in this step is preferably 3 to 7 times, particularly 4 to 6 times for the above reason, and the stretching direction is preferably the slow axis direction.

The composition of the iodine-containing aqueous solution is usually 100
0.1 to 1.0 part by mass of iodine and 2 to 20 parts by mass of potassium iodide are relative to 1 part by mass of iodine per part by mass.
The temperature of the aqueous solution is usually in the range of 20 to 70C. The composition of the dichroic dye-containing aqueous solution is usually 0.1 to 1.0 part by mass of dichroic dye per 100 parts by mass of water, and sodium sulfate is 2 to 20 parts by mass with respect to 1 part by mass of the dichroic dye. The temperature of the aqueous solution is usually in the range of 20 to 70 ° C. The immersion time is not particularly limited, but is usually 1 minute to 20 minutes.
In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained. Further, the polyvinyl alcohol-based film may be immersed in water before being dyed in an aqueous solution containing iodine or a dichroic dye. The temperature of the water is usually in the range of 20-60C. The immersion time is not particularly limited, but is usually 0.1 minutes to 10 minutes, preferably 0.2 minutes.
Minutes to 5 minutes.

The stretching in an aqueous solution containing iodine or a dichroic dye (dye bath) may be performed, for example, while immersing a polyvinyl alcohol-based film in an aqueous solution containing iodine or a dichroic dye. Alternatively, a method may be used in which an aqueous solution containing iodine or a dichroic dye is applied to a polyvinyl alcohol-based film and stretched while spraying. The stretching method is not particularly limited. For example, the stretching can be performed by a method of appropriately adjusting the tension applied to the film.

Next, the stretched polyvinyl alcohol-based film may be stretched in an aqueous solution containing a boron compound. In this case, the stretching is preferably performed so that the total stretching ratio becomes 3 to 7 times, and particularly preferably 4 to 6 times.
When the total stretching ratio is less than 3 times, a sufficient degree of polarization cannot be obtained, and problems such as generation of wrinkles due to swelling of the film occur. When the total stretching ratio exceeds 7 times, stretching breakage occurs. It is easier.

The composition of the boron compound-containing aqueous solution is usually 1 to 10 parts by mass of boric acid, borax or the like alone or mixed with 100 parts by mass of water, and the temperature of the aqueous solution is usually 20 to 7 parts by mass.
It is in the range of 0 ° C. Immersion time is not particularly limited,
It is usually 0.1 minute to 10 minutes. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained.

The stretching in the boron compound-containing aqueous solution may be performed, for example, by immersing the stretched polyvinyl alcohol-based film in the boron compound-containing aqueous solution. Also, a boron compound-containing aqueous solution, applied to the relaxed polyvinyl alcohol films, or a method of spraying while stretching. The stretching method is not particularly limited. For example, the stretching can be performed by a method of appropriately adjusting the tension applied to the film.

The polyvinyl alcohol-based film that has been subjected to the above-mentioned adsorption orientation treatment is further washed with water and then dried to obtain the polarizer of the present invention. Washing is usually in the range of 10 to 60 ° C, preferably 20 to 50 ° C. The washing time is not particularly limited, but is 0.05 minutes to 1 minute. The drying is usually performed at a temperature in the range of 20 to 80C, preferably 25 to 50C. The drying time is not particularly limited, but is 1 minute to 10 minutes, preferably 3 minutes to 5 minutes. Although the thickness of the polarizer of the present invention is not particularly limited, it is 5 to 80 μm.
Is common, and particularly preferably 10 to 40 μm.

Next, the polarizing plate of the present invention will be described.

The basic structure of the polarizing plate of the present invention is such that a protective layer is provided on one or both sides of a polarizer made of the polarizing film of the present invention via an appropriate adhesive layer, for example, an adhesive layer made of a vinyl alcohol polymer or the like. And a transparent protective film to be bonded.

As a protective film material serving as a transparent protective layer provided on one or both sides of a polarizer (polarizing film), an appropriate transparent film can be used. Above all, a film made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like is preferably used. Examples of the polymer include an acetate resin such as triacetyl cellulose, a polyester resin, a polyethersulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, and an acrylic resin. However, the present invention is not limited to this.

A transparent protective film that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with an alkali or the like. The thickness of the transparent protective film is arbitrary, but is generally 500 μm or less, preferably 5 to 300 μm, and particularly preferably 5 to 1 μm for the purpose of reducing the thickness of the polarizing plate.
It is 50 μm. When transparent protective films are provided on both sides of the polarizing film, the transparent protective films may be made of different polymers on the front and back.

The transparent protective film used for the protective layer is
As long as the object of the present invention is not impaired, a hard coat treatment, an anti-reflection treatment, a treatment for preventing sticking, diffusion or anti-glare, or the like may be performed. The hard coat treatment is performed for the purpose of preventing scratches on the polarizing plate surface and the like.
A cured film excellent in hardness, slipperiness and the like made of a suitable ultraviolet-curable resin such as a urethane-based, acrylic-based, or epoxy-based resin can be formed by a method of adding to the surface of the transparent protective film.

On the other hand, the anti-reflection treatment is performed for the purpose of preventing reflection of external light on the polarizing plate surface, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, anti-sticking is performed to prevent adhesion between adjacent layers, and anti-glare treatment is performed to prevent external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate. For example, the transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a roughening method by a sand blast method or an embossing method or a method of blending transparent fine particles.

Examples of the transparent fine particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 20 μm. Fine particles may be used, or organic fine particles composed of crosslinked or uncrosslinked polymer particles or the like may also be used.
The amount of the transparent fine particles used is 2 per 100 parts by mass of the transparent resin.
It is generally from 70 to 70 parts by weight, especially from 5 to 50 parts by weight.

The anti-glare layer containing the transparent fine particles can be provided as the transparent protective film itself or as a coating layer on the surface of the transparent protective film. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle compensation function) for diffusing light transmitted through the polarizing plate to increase the viewing angle. The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer, and the like can be provided as an optical layer made of a sheet or the like provided with these layers, separately from the transparent protective film.

The bonding treatment between the polarizer (polarizing film) and the transparent protective film as the protective layer is not particularly limited. For example, an adhesive composed of a vinyl alcohol polymer, boric acid or boric acid may be used. It can be carried out via an adhesive or the like comprising at least a water-soluble crosslinking agent of a vinyl alcohol polymer such as sand, glutaraldehyde, melamine, and oxalic acid. This makes it difficult for the film to be peeled off due to the influence of humidity or heat, and can have excellent light transmittance and degree of polarization. Such an adhesive layer is formed as a coating and drying layer of an aqueous solution, and at the time of preparing the aqueous solution, other additives and a catalyst such as an acid can be blended as necessary.

The polarizing plate of the present invention can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited.
Λ plate such as a 波長 wavelength plate and a 波長 wavelength plate), a reflective plate, a semi-transmissive reflective plate, a viewing angle compensation film, a brightness enhancement film, and other suitable liquid crystal display devices. One or two or more optical layers can be used. In particular, an elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate including the above-described polarizer and protective layer, and a reflecting plate or semi-transmissive reflection on the above-described polarizing plate including the polarizer and the protective layer. A reflective polarizing plate or a semi-transmissive reflecting plate type polarizing plate in which plates are laminated, a polarizing plate in which a viewing angle compensation film is further laminated on a polarizer including the above-described polarizer and a protective layer, or the above-described polarizer. A polarizing plate in which a brightness enhancement film is further laminated on a polarizing plate comprising a protective layer is preferable.

Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers, such as a polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate and retardation plate may be used. An optical member in which two or three or more optical layers are laminated can be formed by a method in which the optical members are sequentially laminated separately in a manufacturing process of a liquid crystal display device or the like. This has the advantage that the stability of quality and the workability of assembling are excellent and the manufacturing efficiency of a liquid crystal display device or the like can be improved. Note that an appropriate bonding means such as an adhesive layer can be used for lamination.

The above-mentioned polarizing plate or optical member may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed with an appropriate pressure-sensitive adhesive, such as an acrylic resin, according to the related art. In particular, from the viewpoint of preventing foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of liquid crystal cell warpage, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is high. It is preferable that the pressure-sensitive adhesive layer is low and has excellent heat resistance. In addition, an adhesive layer or the like that contains fine particles and exhibits light diffusivity can also be used. The adhesive layer may be provided on a necessary surface if necessary.For example, if mention is made of a protective layer of a polarizing plate comprising a polarizer and a protective layer, if necessary, an adhesive layer may be provided on one or both sides of the protective layer. May be provided.

When the adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until practical use of the adhesive layer for the purpose of preventing contamination and the like. The separator is formed by a method of providing a release coat with a suitable release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide as necessary, on a suitable thin leaf according to the transparent protective film or the like. be able to.

The layers such as the polarizing film and the transparent protective film, the optical layer and the adhesive layer which form the above-mentioned polarizing plate and optical member are made of, for example, salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds and cyanoacrylate compounds. Compounds having an ultraviolet absorbing ability by an appropriate method such as a method of treating with a compound or a nickel complex salt-based compound or the like may be used.

The polarizing plate of the present invention can be used for forming various devices such as a liquid crystal display device. In particular, a reflection type, a semi-transmission type or a transmission type in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell. It can be preferably used for a liquid crystal display device of the type. The liquid crystal cell forming the liquid crystal display device is optional,
For example, a liquid crystal cell of an appropriate type such as an active matrix driving type represented by a thin film transistor type or a simple matrix driving type represented by a twisted nematic type or a super twisted nematic type may be used.

When polarizing plates and optical members are provided on both sides of the liquid crystal cell, they may be the same or different. Further, in forming the liquid crystal display device, one or more layers of appropriate components such as a prism array sheet, a lens array sheet, a light diffusing plate, and a backlight can be arranged at appropriate positions.
Next, the present invention will be specifically described with reference to examples.

[0045]

Example 1 A polyvinyl alcohol (PVA) film having an average degree of polymerization of 1700 and Δn = 0.0030 was swollen with warm water at 30 ° C. for 1 minute, and potassium iodide / iodine (mass ratio: 10: 1) at 30 ° C. ) Dipped in aqueous solution and stretched 3 times. Then 5
The film is stretched in a 4% boric acid aqueous solution at 0 ° C. so that the total stretching ratio becomes 4 times, and immersed in a 30 ° C. water bath and washed with water.
C. for 4 minutes to obtain a polarizer. The concentration of the potassium iodide / iodine (mass 10: 1) aqueous solution was set to 0.35% by mass of iodine so that the transmittance of the polarizer was 43.5%.

Example 2 A PVA film having an average degree of polymerization of 1700 and Δn = 0.0082 was swollen with warm water at 30 ° C. for 1 minute, and immersed in an aqueous solution of potassium iodide / iodine (mass ratio 10: 1) at 30 ° C. The film was stretched three times. Subsequently, the film was stretched in a 4% aqueous solution of boric acid at 50 ° C. so that the total stretching ratio became 4 times, immersed in a water bath at 30 ° C., washed with water, and dried at 50 ° C. for 4 minutes to obtain a polarizer. . The concentration of the aqueous solution of potassium iodide / iodine (mass ratio 10: 1) was adjusted to 0.39% by mass so that the transmittance of the polarizer was 43.5%.

Comparative Example 1 A PVA film having an average degree of polymerization of 1700 and Δn = 0.0013 was swollen with warm water of 30 ° C. for 1 minute, and immersed in an aqueous solution of potassium iodide / iodine (mass ratio 10: 1) at 30 ° C. The film was stretched three times. Subsequently, the film was stretched in a 4% aqueous solution of boric acid at 50 ° C. so that the total stretching ratio became 4 times, immersed in a water bath at 30 ° C., washed with water, and dried at 50 ° C. for 4 minutes to obtain a polarizer. . The concentration of the aqueous solution of potassium iodide / iodine (mass ratio 10: 1) was adjusted to 0.33% by mass so that the transmittance of the polarizer was 43.5%.

Comparative Example 2 A PVA film having an average degree of polymerization of 1700 and Δn = 0.122 was swollen with warm water at 30 ° C. for 1 minute, and immersed in an aqueous solution of potassium iodide / iodine (mass ratio 10: 1) at 30 ° C. The film was stretched three times. Next, the film was stretched in a 4% aqueous solution of boric acid at 50 ° C. so that the total stretching ratio was 4 times. However, the film was broken during the stretching, and a polarizer could not be obtained.

(Evaluation) Table 1 shows the results obtained by measuring the single transmittance, the parallel transmittance, and the orthogonal transmittance of the polarizers obtained in Examples and Comparative Examples, respectively, and calculating the degree of polarization. The measurement was performed by the following method. The birefringence (Δn) is 5
This is a value obtained by calculating the phase difference value (Δnd) by using the parallel Nicol rotation method with light having a wavelength of 90 nm and dividing the value by the thickness d.

(Transmittance) Measured using a spectrophotometer (DOT-3, manufactured by Murakami Color Research Laboratory) and measured according to JLSZ870.
Y whose luminosity is corrected by a 1-degree field of view (C light source).
Value.

(Degree of Polarization) The transmittance (parallel transmittance: H ₀ ) when two identical polarizing plates are superimposed so that their polarization axes are parallel to the transmittance (orthogonal transmission) when they are superimposed orthogonally. Rate: H ₉₀ ) was measured according to the method for measuring the transmittance, and was determined from the following equation.

(Equation 1)

[0052]

Table 1 Birefringence index (Δn) Total stretching ratio Single transmittance (%) Polarization degree (%) Example 1 0.0030 43.5 96.7 Example 2 0.0082 4 43.5 98.9 Comparative Example 1 0.0013 4 43.5 95.6 Comparative Example 2 0.0122 4 Broken during stretching

As is clear from Table 1, among the polarizers showing the same single transmittance, those using a PVA film satisfying 0.002 ≦ Δn ≦ 0.01 (Examples 1 and 2) have Δn
It was found that it exhibited a higher degree of polarization than the one using <0.002 PVA film (Comparative Example 1). When a PVA film with 0.002 <Δn was used (Comparative Example 2), the film was broken during stretching, and a polarizer could not be obtained.

[0054]

As described above, the birefringence (Δn) represented by the difference between the refractive index in the slow axis direction in the film plane and the refractive index in the fast axis direction in the film plane is 0.002. ≦ Δn ≦
By using a polyvinyl alcohol-based film of 0.01, a polarizer having a high transmittance and a high degree of polarization can be manufactured. Further, according to the method of the present invention, it is not necessary to increase the stretching ratio, so that stable stretching can be performed. Therefore, by using the polarizer of the present invention for a liquid crystal display device, a liquid crystal display device having a high contrast can be provided, and its industrial value is great.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C08L 29:04 C08L 29:04 (72) Inventor ▲ Hama ▼ Eiji Moto 1 Shimohozumi, Ibaraki-shi, Osaka 1-2 1-2 Nitto Denko Co., Ltd. (72) Inventor Seiichi Kusumoto 1-2-1, Shimohozumi, Ibaraki City, Osaka Prefecture 1-22 Nitto Denko Corporation (72) Inventor Yuji Shiki 1-chome Shimohozumi, Ibaraki City, Osaka Prefecture 1-2-2 Nitto Denko Corporation (72) Inventor Yoichiro Sugino 1-2-2 Shimohozumi, Ibaraki-shi, Osaka F-term in Nitto Denko Corporation (reference) 2H049 BA02 BA06 BA26 BA27 BB03 BB43 BC03 BC22 2H091 FA08X FA08Z FA11X FA15Z FA34Z FB02 FB12 FB13 FC07 KA10 LA12 4F071 AA29 AB27 AE09 AF31Y AF35Y AG12 AG35 AH19 BB07 BC01

Claims (9)

[Claims] 1. A polarizer comprising a film in which iodine or a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based film, wherein the polyvinyl alcohol-based film has a birefringence (Δn) represented by the formula (1). Is 0.002 ≦ Δn ≦ 0.01. _{Δn = n s -n f (1} ) ( wherein, n _s is a refractive index in a slow axis direction of the polyvinyl alcohol-based film plane, n _f is a fast-axis refractive index of the polyvinyl alcohol-based film plane is there.) 2. The polarizer according to claim 1, wherein the polyvinyl alcohol-based film is stretched in a slow axis direction in the film plane. 3. The polarizer according to claim 1, wherein the stretch ratio of the polyvinyl alcohol-based film is 3 to 7 times. 4. A polarizing plate having a protective layer on at least one side of the polarizer according to claim 1. 5. A birefringence (Δ) represented by the following equation (1):
n) stretching a polyvinyl alcohol-based film in which 0.002 ≦ Δn ≦ 0.01 in the slow axis direction of the film in an aqueous solution containing iodine or a dichroic dye; Production method. _{Δn = n s -n f (1} ) ( wherein, n _s is a refractive index in a slow axis direction of the polyvinyl alcohol-based film plane, n _f is a fast-axis refractive index of the polyvinyl alcohol-based film plane is there.) 6. The method for producing a polarizer according to claim 5, wherein the polyvinyl alcohol-based film is further stretched in a slow axis direction of the film in an aqueous solution containing a boron compound. 7. A polarizing plate having a protective layer on at least one side of the polarizer produced by the method according to claim 5. Description: 8. A laminate comprising the polarizer according to claim 4 and at least one optical layer selected from a retardation plate, a reflector, a semi-transmissive reflector, a viewing angle compensation film, and a brightness enhancement film. Polarizer. 9. A liquid crystal display device, wherein the polarizing plate according to claim 4, 7 or 8 is arranged on at least one side of a liquid crystal cell.