JPH06347641A - Novel polarizing film - Google Patents

Abstract

PURPOSE:To provide a polarizing film which decreases leaking light in a diagonal direction when the polarizing film is installed in a crossed Nicols state by specifying the double refractive index and thickness of a base material film to respectively specific values. CONSTITUTION:A polarizing in which a dichromatic dyestuff is adsorbed and oriented on the polyvinyl alcoholic base material film. The thickness of the base material film is 1 to 20mum, more preferably 1 to 13mum. The double refractive index of the base material film is >=0.022, more preferably >=0.025. Further, the base material film is uniformly dyed with the dichromatic dyestuff in the thickness direction. The polarizer has a single layer structure in the thickness direction. The thickness of the polarizer is 2 to 20mum and the degree of polarization is >=99.80%. The case where the double refractive index of the base material film is <0.022 is undesirable as the quantity of the leaking light in the perpendicular direction when the polarizing film is put into the crossed Nicols state attains >=3% even when iodine is adsorbed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel polarizing film having little leakage light in an oblique direction when the polarizing film is installed in a crossed Nicol state.

[0002]

2. Description of the Related Art Conventionally, a polarizing film used for a liquid crystal display device or the like is produced by adsorbing a dichroic dye on a stretched and oriented polarizing film substrate film. For the polarizing film, it is general to use a film which is optically transparent on both sides and has no anisotropy as a protective film. An optically transparent triacetyl cellulose film (hereinafter, abbreviated as “triacetate film”) is usually used as the protective film. A polyvinyl alcohol polymer is generally used as the base film.

A conventional polarizing film is generally produced by adsorbing iodine on a stretched polyvinyl alcohol film, treating it with a fixed aqueous solution containing boric acid, and then laminating a protective film made of a triacetate film. It is common. As a general method for producing a dye-based polarizing film, a method of adsorbing a dichroic dye on a polymer film is used (for example, JP-A-3-6890).
No. 2, JP-A-3-89203). As the polymer film used in this case, a polyvinyl alcohol film is preferably used. In particular, a polarizing film prepared by adsorbing iodine on a polyvinyl alcohol film is most excellent in terms of transmittance and degree of polarization, and is most commonly used as a polarizing film.

[0004]

A polarizing film is obtained by uniaxially stretching a polyvinyl alcohol film which is a base polymer, and uniaxially orienting a dichroic dye in accordance with the molecular orientation of the polymer to obtain polarizing performance. Conventionally, the adsorption of the dichroic dye into the polyvinyl alcohol-based substrate film has been performed by immersing the polyvinyl alcohol-based substrate film in a liquid containing the dichroic dye. When observing the cross section of the polyvinyl alcohol-based substrate film obtained by this method with an optical microscope, the part near the surface of the film is dyed with a dichroic dye, but the middle part of the film is dyed with a dichroic dye. The boundary is not clear, but has a clear three-layer structure in the thickness direction of the film. As a problem with the current polarizing film, when the polarizing film is installed in a crossed nicols state, the leakage light from the polarizing film increases when the polarizing film is tilted in a direction other than the optical axis. To be When the leak light is measured by setting the polarizing film in crossed Nicols and changing the azimuth angle and the attack angle, the leak light increases most when the azimuth angle is 45 ° with respect to the polarization axis. In recent years, due to the widespread use of liquid crystal displays and the accompanying technological progress, the problem of light leakage from a polarizing film has been pointed out as one of the factors deteriorating the visual characteristics of liquid crystal displays, and improvements in this respect have been demanded.

[0005]

Means for Solving the Problems The present inventor diligently studied the leakage light of a polarizing film and the structure of the polarizing film in order to achieve the above object. In the polarizing film using the polarizer, the polarizing film in which the birefringence of the base film and the thickness of the base film are controlled was found. Furthermore, the inventors have found a polarizing film having a single-layer structure in which a dichroic dye is uniformly adsorbed in the thickness direction of a polyvinyl alcohol-based substrate film and controlling the thickness of the substrate film.

That is, the present invention provides a polarizing film comprising a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based substrate film, and the thickness of the substrate film is 1 μm or more and 20 μm or less (preferably 1 μm or more and 13 μm
m or less) and the birefringence of the base film is 0.
The polarizing film is 022 or more (preferably 0.025 or more). Furthermore, the present invention is a polarizing film comprising a polarizer in which a dichroic dye is oriented and adsorbed on a polyvinyl alcohol-based substrate film, wherein the substrate film is uniformly dyed with the dichroic dye in the thickness direction. Thus, when the cross section of the substrate film is observed using an optical microscope, the polarizer has a single-layer structure in the thickness direction and the thickness of the polarizer is 2 μm or more and 20 μm or less. And the degree of polarization is 99.
It is a polarizing film of 80% or more.

When a polyvinyl alcohol polarizing film in which iodine is adsorbed and oriented is brought into a crossed Nicol state, the amount of light leaked from the vertical direction is usually 1% or less. In the case of a high contrast type polarizing film, this is set to 0.
It can be reduced to 1% or less. However, even with a polarizing film having such high performance, the amount of leaked light is significantly increased when the light is oblique. For example, under the conditions of an azimuth angle of 45 ° and an angle of attack of 60 °, there is usually 3% or more of leakage light.

In the polarizing film of the present invention, the leakage light in the crossed Nicols state can be significantly reduced. For example, the leakage light with respect to the oblique light under the condition of the azimuth angle of 45 ° and the elevation angle of 60 ° is 2% or less, Alternatively, it can be reduced to 1.5% or less. In addition, the polarizing film of the present invention has the feature of reducing the leaked light, but also has the feature of not changing the color tone of the leaked light, and has the feature that there is no wavelength dependence of the leaked light. Have.

The thickness of the polyvinyl alcohol base film used for the polarizing film of the present invention is 20 μm or less, preferably 16 μm or less, more preferably 13 μm or less. Considering that the thickness of the polyvinyl alcohol-based substrate film used conventionally is 21 μm or more, and generally 28 μm or more, the thickness of the substrate film used for the polarizing film of the present invention is conventionally used. It is much thinner than the base film.

The birefringence of the substrate film must be 0.022 or more. When the birefringence of the base film of the polarizer is less than 0.022, the amount of leaked light in the vertical direction when the polarizing film is in the crossed Nicols state is 3% or more even when iodine is adsorbed. Not preferred because of

The polyvinyl alcohol base film in the present invention is, for example, a polyvinyl alcohol film,
Polyvinyl formal film, polyvinyl acetal film, polyvinyl butyral film, ethylene-
It is a film such as a saponified film of vinyl acetate copolymer. The polyvinyl alcohol-based substrate film preferably has a saponification degree of the resin constituting the film of 85 mol% or more. It is particularly preferably 90 mol% or more, and most preferably 95 mol% or more. When it is less than 85 mol%, the stretchability and dyeability are poor, which is not preferable.

The dichroic dye used in the present invention is not particularly limited as long as it has two or more optical axes having different absorption coefficients in the visible light region in the molecule. For example, I ₃ ^-,
It is possible to use iodine such as I ₅ ^−, dichroic dye such as Congo red, polyene and the like. Alternatively, these may be used in combination. Among these, iodine is preferable because a polarizing film having a high degree of polarization and a high transmittance can be obtained.

The polarizing film of the present invention can be produced, for example, by the method described below, but the invention is not limited thereto. That is, a polyvinyl alcohol film is obtained by casting a stock solution of polyvinyl alcohol having an average polymerization degree of 1500 to 3500 (saponification degree of 85 mol% or more) dissolved in water or a mixed solvent of water and an organic solvent. As the organic solvent used in this case, dimethyl sulfoxide (DMSO), glycerin, ethylene glycol, propylene glycol, ethylenediamine or the like can be used. When an organic solvent is used, the amount of the organic solvent mixed is 10 to 90% (the content of water is 90 to 10).
%) Is good. The concentration of polyvinyl alcohol in the stock solution is preferably 20% or less. Preferably 3 to 15
It is good to set to%. Conventionally, in the case of obtaining a polyvinyl alcohol film for a polarizer, considering that the concentration of polyvinyl alcohol in the stock solution was 20 to 40%, the polyvinyl alcohol film used in the present invention uses a stock solution with a thin polyvinyl alcohol concentration. is doing. By using an undiluted solution having a low polyvinyl alcohol concentration, a polyvinyl alcohol film having a thin and uniform structure can be obtained.

The polarizer used in the polarizing film of the present invention is prepared by dissolving a dichroic dye in a liquid in which polyvinyl alcohol, for example, polyvinyl alcohol having an average polymerization degree of 1500 to 3500 (saponification degree of 85 mol% or more) is dissolved. After that, the solution can also be used for casting to form a film. In this case, as the solvent used, water or a mixed solvent of water and an organic solvent is used as described above. In this case, the concentration of the dichroic dye is preferably 0.05 to 5% by weight with respect to the solvent.

The thickness of a polyvinyl alcohol film which has been conventionally uniaxially stretched is at least 50 μm, preferably 75.
μm was required. A 75 μm film is most commonly used, but the stretch ratio of this film is limited to 6 times, and the normal draw ratio determined from the thickness of the film for neck-in is about 2.9 times. It was When stretched 6 times or more, a uniaxially stretched film having a uniform structure could not be obtained, and the film was cut at a stretch ratio of about 7 times. The thickness of the polyvinyl alcohol film stretched 6 times was 26 μm. When the polyvinyl alcohol film before uniaxial stretching is thinned, thinner uniaxial stretching can be obtained, but when the film becomes thin, stretching becomes difficult to perform, and when a polyvinyl alcohol film having a thickness of 50 μm is used. The limit was 5 times stretching. The thickness of the film at that time was 22 μm.

The concentration of the undiluted solution of polyvinyl alcohol is 20
A polyvinyl alcohol film having a more uniform structure could be obtained by controlling the content to be not more than%. By using this undiluted solution, it is possible to obtain a polyvinyl alcohol film having a thickness of 40 μm or less, which is significantly thinner than the conventional one. By uniaxially stretching the film 5 times or more, a base film having a film thickness of 16 μm or less could be obtained. Further, a uniaxially stretched film having a thickness of 10 μm could be obtained by stretching a film having a thickness of 20 μm 5 times.

In the present invention, the polyvinyl alcohol film may be uniaxially stretched and then dyed with a dichroic dye, or the film before stretching may be dyed with a dichroic dye in advance and then uniaxially stretched. It is difficult to measure the birefringence of a uniaxially stretched film in the visible light region in the state where a dichroic dye is adsorbed, because the absorption of light is large. For this reason, it is preferable to measure the birefringence of the base film in the state where the dichroic dye is not adsorbed. It is estimated that the birefringence of the polyvinyl alcohol-based film adsorbing the dichroic dye matches the birefringence of the base film.

The adsorption of the dichroic dye in the polyvinyl alcohol film is carried out by immersing the polyvinyl alcohol film in a liquid containing the dichroic dye.
As the liquid for dissolving the dichroic dye, it is preferable to use water, ethanol, methanol, ethylene glycol or a mixed solvent thereof. The dichroic dye is preferably used in a concentration of 0.05 to 5%. The adsorption treatment of the dichroic dye may be performed on the unstretched or stretched film, or may be performed simultaneously with the stretching in the liquid bath.

Further, the dichroic dye solution preferably contains a crosslinking agent. The dichroic dye may be adsorbed on the polyvinyl alcohol film and then treated in a solution containing a crosslinking agent. As the cross-linking agent used in this case, boric acid, borax, zirconium compound or the like is used. Adsorption of dichroic dye and crosslinking treatment temperature with crosslinking agent are 30-
It is better to carry out at a temperature of 110 ° C.

On the other hand, as a method for obtaining the polarizer of the present invention,
When the method of casting film formation using a solution in which polyvinyl alcohol is dissolved in a liquid in which a dichroic dye is dissolved in advance, the concentration of polyvinyl alcohol in the solution is 30% by weight.
Even if it is increased to a certain extent, the cast film after casting has a uniform single structure in its thickness direction.

A specific example of the present invention will be described using a polyvinyl alcohol film. In the polarizer of the present invention, an unstretched film of polyvinyl alcohol is stretched 4 to 6 times in the longitudinal direction in water, and then immersed in an aqueous potassium iodide solution containing iodine, and then in an aqueous boric acid solution containing potassium iodide. It can be obtained by treating with. It can also be obtained by immersing an unstretched film of polyvinyl alcohol in an aqueous solution of potassium iodide containing iodine, stretching it 4 to 6 times in the aqueous solution, and then treating it in an aqueous solution of boric acid containing potassium iodide. A protective film layer is formed on one side or both sides of the obtained polarizer to obtain a polarizing film.

[0022]

The present invention will be described in more detail in the following examples. Reference Example 1 5 parts of polyvinyl alcohol having a polymerization degree of 1900 and a saponification degree of 99.5 mol% was dissolved in 95 parts of water to obtain a solution having a polyvinyl alcohol concentration of 5% by weight. This solution was cast on a polyethylene terephthalate film and then dried to obtain a raw film of polyvinyl alcohol having a film thickness of 25 μm. In addition, raw films of polyvinyl alcohol having film thicknesses of 20 μm and 35 μm were also obtained. Next, the experiments of Examples 1 to 6 and Comparative Examples 1 to 4 were conducted using these raw films.

Example 1 A raw film of polyvinyl alcohol having a thickness of 25 μm was immersed in water and then uniaxially stretched 5 times in the longitudinal direction to obtain a uniaxially stretched film having a thickness of 11 μm. Measured later). The birefringence of this film was 0.027. The film was immersed in an aqueous solution containing 0.5% by weight of iodine and 5% of potassium iodide while maintaining a tension state to adsorb the dichroic dye. Furthermore, boric acid 10% and potassium iodide 10%
A cross-linking treatment was carried out for 5 minutes in an aqueous solution of 50 ° C. under tension to obtain a polarizer. When the film thickness of the polarizer after the crosslinking treatment was measured after drying, the film thickness was 12 μm, and there was almost no change in the film thickness as compared with the uniaxially stretched film before adsorption of iodine. Finally, a 80 μm-thick triacetyl cellulose film (Fuji Photo Film, manufactured by Fuji Photo Film Co., Ltd.) was attached to both surfaces of this film using a polyvinyl alcohol-based adhesive to obtain a polarizing film.

When the transmittance and the degree of polarization of this polarizing film were measured, the single transmittance was 41% and the degree of polarization was 99.9%.
(When installed in the crossed Nicols state, the transmittance in the vertical direction was 0.05% or less).

The amount of leaked light in the crossed Nicols state of this polarizing film was 1.6% when the azimuth angle was 45 ° and the angle of attack was 60 °. In addition, the wavelength dependence of leaked light in the wavelength range of 400 nm to 700 nm was measured. The result is shown in FIG. As is clear from FIG. 1, there was no wavelength dependence of the transmitted light.

The transmittance was measured according to the Japan Electronic Machinery Industry Standard (LD-201) (400 nm to 70 nm).
Calculated from the spectral transmittance measured every 10 nm in the wavelength range of 0 nm). The polarization degree is a value obtained from the following formula 1. Polarization degree = [(H ₁ −H ₂ ) / (H ₁ + H ₂ )] ^1/2 where H ₁ ; parallel transmittance (transmission when the two polarizing films are oriented in the same direction) Percentage) H ₂ ; Vertical transmittance (transmittance when the orientation directions of two polarizing films are orthogonal) Shimadzu Ellipsometer AEP for measuring birefringence
-100 was used. The wavelength used for measurement is 632.8.
was nm.

Example 2 Using the polyvinyl alcohol film having a thickness of 20 μm obtained in Reference Example, uniaxial stretching was carried out 5 times in the same manner as in Example 1. The film thickness of the polyvinyl alcohol film after 5 times stretching was 9 μm. The birefringence of this film was 0.028. A polarizing film was obtained in the same manner as in Example 1 except that this uniaxially stretched film was used. The polarizing film had a transmittance of 41% and a polarization degree of 99.9%. The leakage light of this polarizing film at an azimuth angle of 45 ° and an angle of attack of 60 ° was 1.3%. Further, the wavelength dependence of leaked light was not the same as in the case of Example 1.

Example 3 The polyvinyl alcohol film having a thickness of 25 μm obtained in Reference Example was uniaxially stretched 6 times under the same conditions as in Example 1. The film thickness of the obtained film was 10 μm.
The birefringence of this film was 0.030. A polarizing film was produced in exactly the same manner as in Example 1 except that this film was used. The transmittance of this polarizing film was 40%, and the degree of polarization was 99.9%. The leakage light of this polarizing film at an azimuth angle of 45 ° and an angle of attack of 60 ° was 1.7%. Also, there was no wavelength dependence of the leaked light.

Examples 4 to 6 Several kinds of polarizing films were obtained by changing the film thickness and the stretching ratio of the original film and repeating the same method as in Example 1. This property is shown in Table 1.

Reference Example 2 30 parts of polyvinyl alcohol having a polymerization degree of 1900 and a saponification degree of 99.5% was dissolved in 70 parts of water to obtain a solution having a polyvinyl alcohol concentration of 30% by weight. This solution was cast on a polyethylene terephthalate film and dried to give a film thickness of 7
A polyvinyl alcohol original film having a thickness of 5 μm was obtained. Further, a raw film of polyvinyl alcohol having a film thickness of 50 μm was obtained.

Comparative Example 1 The polyvinyl alcohol film having a thickness of 75 μm obtained in Reference Example 2 was uniaxially stretched 5 times in the same manner as in Example 1. The film thickness of the obtained film was 32 μm (the film thickness was measured after drying). The birefringence of this film was 0.027. This film was dyed with iodine under the same conditions as in Example 1, and then cross-linked with boric acid. A triacetyl cellulose film was adhered to both sides of this polarizer to obtain a polarizing film. When the transmittance and the polarization degree of this polarizing film were measured, the transmittance was 40% and the polarization degree was 99.9%. The leaked light in the crossed Nicols state of this polarizing film is converted into azimuth angle 45.
As a result of measurement under conditions of 90 ° and angle of attack of 60 °, leakage light was 3.8.
%Met. There was no wavelength dependence of leaked light (Fig. 1
reference).

Comparative Example 2 The polyvinyl alcohol film having a film thickness of 50 μm obtained in Reference Example 2 was uniaxially stretched 5 times in the same manner as in Example 1. The thickness of the obtained film is 21 μm,
The birefringence was 0.028. Using this film, a polarizer and a polarizing film were obtained in the same manner as in Example 1. When the transmittance and the polarization degree of this polarizing film were measured, the transmittance was 40% and the polarization degree was 99.9%. Also, the leakage light at an azimuth angle of 45 ° and an attack angle of 60 ° is 3.4.
%Met.

Comparative Example 3 A 75 μm thick original film obtained in Reference Example 2 was stretched 6 times to obtain a 30 μm thick uniaxially stretched film. The birefringence of this film was 0.030. Using this film, a polarizing film was obtained in the same manner as in Example 1. The single transmittance of this polarizing film is 41.
%, The degree of polarization was 99.9%, and the leakage light at an azimuth angle of 45 ° and an angle of attack of 60 ° was 3.4%.

Comparative Example 4 The polyvinyl alcohol film having a thickness of 20 μm obtained in Reference Example 1 was stretched 4 times to obtain a film having a thickness of 12 μm. The birefringence of this film was 0.021. Using this film, a polarizing film was obtained in the same manner as in Example 1. The polarization degree of this polarizing film was 96.3%. The leakage light at an azimuth angle of 45 ° and an angle of attack of 60 ° was 6.2%.

The results of Examples 1 to 6 and Comparative Examples 1 to 4 are summarized in Table 1.

[Table 1] As is clear from the results of Table 1, Example 1 of the present invention
When the polarizing films obtained in Examples 6 to 6 were installed in a crossed nicols state, the amount of leaked light in the oblique direction was smaller than that in the polarizing films of Comparative Examples 1 to 4.

Example 7 An aqueous solution containing 0.1% by weight of iodine and 0.5% by weight of potassium iodide was prepared, and 15 parts of polyvinyl alcohol (polymerization degree 1900, saponification degree 99.7%) was added to 85 parts of this solution. Dissolved. This solution was cast on a polyethylene terephthalate film and then dried to obtain a raw film of polyvinyl alcohol dyed with iodine and having a thickness of 40 μm. The raw film was immersed in water and then uniaxially stretched 5 times in the longitudinal direction. Boric acid 1 while maintaining tension
Cross-linking treatment was performed for 5 minutes with an aqueous solution of 0% and 10% potassium iodide at 50 ° C. In this way, a polarizer was obtained. Finally, the polarizer thus obtained is coated with 80
A μm triacetylcellulose film (Fuji Photo Film, manufactured by Fuji Photo Film Co., Ltd.) was attached using a polyvinyl alcohol adhesive. When the transmittance and the polarization degree of this polarizing film were measured, the single transmittance was 39% and the polarization degree was 99.94% (when installed in a crossed Nicol state, the transmittance in the vertical direction was 0.02%. Met).
When the cross section of the polarizer of this polarizing film was observed using an optical microscope, the polarizer was uniformly dyed with iodine. That is, the polarizer had a single-layer structure in the thickness direction. The film thickness of the polarizer was 16 μm. The leaked light in the crossed Nicols state of this polarizing film has an azimuth angle of 4
When measured under the conditions of 5 ° and an angle of attack of 60 °, the leakage light was 1.4%. In addition, wavelength 400nm-700nm
The wavelength dependence of the leaked light in the range was measured.
The result is shown in FIG. As is clear from FIG. 2, there was no wavelength dependence of leaked light. The transmittance was measured in the same manner as in Example 1 according to the Japanese Electronic Machinery Industry Standard (LD-201). The degree of polarization was also determined in the same manner as in Example 1.

Example 8 A polyvinyl alcohol film dyed with iodine and having a thickness of 50 μm was obtained in the same manner as in Example 7. This raw film was stretched 5 times in the same manner as in Example 7, and then a triacetyl cellulose film was adhered to both sides to obtain a polarizing film. The single transmittance of this polarizing film is 37.
%, The polarization degree was 99.97% (when installed in the crossed Nicols state, the transmittance in the vertical direction was 0.01%.
Met). When the cross section of the polarizer of this polarizing film was observed using an optical microscope, the polarizer was uniformly dyed with iodine. That is, the polarizer had a single-layer structure in the thickness direction. The film thickness of the polarizer was 20 μm.
The leakage light in the crossed Nicols state of this polarizing film was measured under the conditions of an azimuth angle of 45 ° and an angle of attack of 60 °. The leaked light was 1.7%, and there was no wavelength dependence of the leaked light.

Example 9 A polarizing film was produced in the same manner as in Example 7 except that the thickness of the polyvinyl alcohol original film dyed with iodine was 25 μm. The draw ratio was 5 times as in Example 7. When the transmittance and the polarization degree of this polarizing film were measured, the single transmittance was 42% and the polarization degree was 99.85.
% (When installed in the crossed Nicols state, the transmittance in the vertical direction was 0.05%). The leakage light measured in the crossed Nicols state of this polarizing film under the conditions of an azimuth angle of 45 ° and an angle of attack of 60 ° was 1.2%.
However, there was no wavelength dependence of the transmitted light. When the cross section of the polarizer of this polarizing film was observed using an optical microscope, the polarizer was uniformly dyed with iodine. The film thickness of the polarizer was 10 μm.

Comparative Example 5 30 parts of polyvinyl alcohol having a polymerization degree of 1900 and a saponification degree of 99.7% was dissolved in 70 parts of water to obtain a solution having a polyvinyl alcohol concentration of 30% by weight. This solution was cast on a polyethylene terephthalate film and dried to give a film thickness of 7
A polyvinyl alcohol original film having a thickness of 5 μm was obtained. After immersing this film in water, it was uniaxially stretched 5 times in the longitudinal direction to obtain a stretched film. While maintaining the tension of this film, iodine 0.5% by weight and potassium iodide 5
% Aqueous solution of 10% boric acid while adsorbing the dichroic dye and maintaining the tension of the film.
Cross-linking treatment was carried out for 5 minutes with an aqueous solution of potassium iodide 10% at 50 ° C. Finally, a 80 μm thick triacetyl cellulose film (Fujitac, Fuji Photo Film) was laminated on both sides of this film using a polyvinyl alcohol adhesive. When the single transmittance and the degree of polarization of this polarizing film were measured, the single transmittance was 40%,
The polarization degree was 99.90% (when installed in the crossed Nicols state, the transmittance in the vertical direction was 0.03%). With respect to this polarizing film, the leakage light measured under the conditions of an azimuth angle of 45 ° and an angle of attack of 60 ° in the crossed Nicols state was 3.8%, and there was no wavelength dependency of the leakage light (FIG. 2). See). The film thickness of the polarizer of this polarizing film was 30 μm. When the cross section of the polarizer of this polarizing film was observed using an optical microscope, both sides of the polarizer were dyed with iodine, but the intermediate portion in the thickness direction was not dyed with iodine. That is, when a polarizer is produced by a conventional method, the structure of the polarizer has a three-layer structure of a portion stained with iodine, a portion not stained with iodine, and a portion stained with iodine, if described in order in the thickness direction. there were. The boundary between the portion stained with iodine and the portion not stained was not clear, and the surface of the polarizer was sufficiently stained with iodine, and the degree of iodine staining decreased toward the inner layer of the polarizer.

Comparative Example 6 A polarizing film was produced in the same manner as in Example 7, except that the thickness of the polyvinyl alcohol original film dyed with iodine was 80 μm. The draw ratio was 5 times. The transmittance and the degree of polarization of this polarizing film were measured. The single transmittance was 34%, and the polarization degree was 99.97% (when installed in the crossed Nicols state, the vertical transmittance was 0.01%). The leaked light of this polarizing film was measured under the conditions of an azimuth angle of 45 ° and an angle of attack of 60 °.
It was 1%. The film thickness of the polarizer was 34 μm.

[0041]

According to the present invention, when the polarizing film is installed in a crossed nicols state, it is possible to obtain a polarizing film with little leak light in the oblique direction.

[Brief description of drawings]

FIG. 1 is a graph showing the wavelength dependence of oblique transmittance of the polarizing films obtained in Example 1 and Comparative Example 1.

FIG. 2 is a graph showing the wavelength dependence of oblique transmittance of the polarizing films obtained in Example 7 and Comparative Example 5.

[Explanation of symbols]

 1 Polarizing Film Obtained by Example 1 2 Polarizing Film Obtained by Comparative Example 3 Polarizing Film 4 Obtained by Example 7 Polarizing Film Obtained by Comparative Example 5

Claims (2)

[Claims] 1. A polarizing film using a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based substrate film, wherein the substrate film has a birefringence of 0.022 or more and the substrate film. Thickness is 1 μm or more 20
A polarizing film having a thickness of not more than μm. 2. A polarizing film using a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based substrate film, wherein the polarizer has a single-layer structure in the thickness direction, and the thickness of the polarizer. Is 2 μm or more and 20 μm or less, a polarizing film having a polarization degree of 99.80% or more.