JP2016212274A - Method for inspecting polarized film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of inspecting color spots, capable of easily detecting color spots of a polarizer film hardly detected in the conventional inspection method.SOLUTION: A method for inspecting color spots of a polarized film comprises: arranging a light source 1, a first reference polarized film 2, an inspection polarized film 3 to be inspected and a second reference polarized film 4 in this order; and inspecting color spots of the inspection polarized film 3 from the side of the second reference polarized film 4. An angle between the absorption axis of one of the first reference polarized film 2 and the second reference polarized film 4 and that of the inspection polarized film 3 is 75±10 degrees, and an angle between the absorption axis of the other reference polarized film and that of the inspection polarized film 3 is 105±10 degrees.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for inspecting color spots of a polarizing film in the form of a polarizing film, preferably a polarizing film having a protective film bonded to one or both sides thereof.

A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film. As a polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter referred to as “polyvinyl”). alcohol "and" PVA "and is sometimes abbreviated) iodine dye stretched film was oriented uniaxially stretched (I ₃ ^- and I ₅ ^-, etc.), such as a dichroic organic dye dichroic dye is adsorbed What you are doing is the mainstream. Such a polarizing film can be obtained by uniaxially stretching a PVA film preliminarily containing a dichroic dye, adsorbing a dichroic dye simultaneously with uniaxial stretching of the PVA film, or dichroic after uniaxially stretching the PVA film. Manufactured by adsorbing dyes.

  LCDs are used in a wide range of devices such as small devices such as calculators and wrist watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. .

  In recent years, since reduction of power consumption has been particularly demanded, it has become important for LCDs to maintain high screen brightness even when the backlight intensity is low. As a means for achieving this, it is conceivable to improve the light transmittance of the polarizing film and thus the polarizing plate by reducing the thickness of the polarizing film or decreasing the degree of dyeing. A polarizing plate having a high value has a problem that color spots are more conspicuous than a polarizing plate having a low light transmittance. Therefore, the evaluation standard of color spots of polarizing plates performed before being incorporated into LCD has become strict in recent years, and an inspection method capable of detecting even weak color spots that are not detected as color spots conventionally. Is required. In addition, in order to manage color spots, the need for quantitative evaluation of color spots on polarizing plates is also increasing.

  As a method for inspecting the color spots of the polarizing plate or polarizing film, the inspection polarizing plate or inspection polarizing film to be inspected is arranged between two reference polarizing plates, and at this time, the absorption axis of the inspection polarizing plate or inspection polarizing film And an inspection polarizing film or inspection polarizing film arranged between two reference polarizing plates arranged so that the absorption axis of the two reference polarizing plates forms a predetermined angle and the absorption axes are parallel to each other Is known (see, for example, Patent Documents 1 to 3).

JP2011-149741A Special table 2010-534351 gazette JP 2012-233886 A

  However, it has been found that when the level of color spots on the polarizing plate or polarizing film to be inspected is weak, it is difficult for the conventional method to be visually recognized as spots. Therefore, an object of the present invention is to provide a color spot inspection method that can easily detect a color spot of a polarizing film that is difficult to detect by a conventional inspection method.

  As a result of intensive studies by the present inventors to achieve the above object, an inspection polarizing plate to be inspected is arranged so as to be crossed Nicol between two reference polarizing plates arranged in parallel Nicol on the light source. Then, one reference polarizing plate is rotated by a specific angle in a specific direction, the other reference polarizing plate is rotated by a specific angle in the opposite direction, and then color spots are observed. It has been found that it is easy to visually recognize color spots that are difficult to detect. In addition, when the present inventors use a linear light source as the light source and inspect color spots while linearly moving the inspection polarizing plate in a direction parallel to the surface, the light source is caused. It has been found that two-dimensional luminance unevenness can be excluded, and luminance data based on the color spots of the polarizing plate that should be obtained can be easily obtained. The present inventors have further studied based on these findings and completed the present invention.

That is, the present invention
[1] A method for inspecting color spots of a polarizing film, in which a light source, a first reference polarizing film, an inspection polarizing film to be inspected, and a second reference polarizing film are arranged in this order, and second reference polarization Inspect the color unevenness of the inspection polarizing film from the film side, where the absorption axis of the inspection polarizing film of the absorption axis of one of the first reference polarizing film and the second reference polarizing film A method in which the angle with respect to is set to 75 ° ± 10 ° and the angle of the absorption axis of the other reference polarizing film to the absorption axis of the inspection polarizing film is set to 105 ° ± 10 °;
[2] The method according to [1] above, wherein the inspection polarizing film is in the form of a polarizing plate in which a protective film is bonded to one side or both sides thereof;
[3] The above-mentioned [1] or [2], wherein at least one of the first reference polarizing film and the second reference polarizing film is in the form of a polarizing plate in which a protective film is bonded to one side or both sides thereof. Method;
[4] The method according to any one of [1] to [3], wherein the light source is a surface light source;
[5] The method according to [4] above, wherein the luminance of the surface light source is 10,000 cd / m ² or more;
[6] The method according to any one of the above [1] to [5], wherein color spots are inspected by photographing with a photographing means;
[7] The method according to [6] above, wherein the color spot is inspected by displaying the luminance data at each position in the plane of the inspection polarizing film obtained by photographing by the photographing means by the display means;
[8] Any of the above-mentioned [1] to [3], wherein the light source is in a line shape and the inspection polarizing film is continuously inspected by moving the inspection polarizing film in a direction parallel to the surface of the inspection polarizing film. Or one method;
[9] The method according to [8] above, wherein the direction parallel to the surface of the inspection polarizing film is a direction substantially perpendicular to the absorption axis direction of the inspection polarizing film;
[10] The color spot is inspected by photographing with a line-shaped photographing means arranged so as to face the line-shaped light source via the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film. The method of [8] or [9] above; and
[11] The method according to [10] above, wherein the luminance distribution derived from the light source in the longitudinal direction of the linear light source is subtracted from the luminance data at each position in the plane of the inspection polarizing film obtained by photographing by the photographing means;
About.

  According to the method of the present invention, it is possible to easily detect color spots on a polarizing film that are difficult to detect by conventional inspection methods.

It is the figure which showed typically the example of the method of arrangement | positioning of each reference | standard polarizing film and test | inspection polarizing film in the method of this invention. In the method of this invention, it is the figure which showed typically the example of the inspection method of a color spot at the time of using a linear thing as a light source.

The present invention is described in detail below.
The method of the present invention for inspecting the color spots of a polarizing film includes a light source, a first reference polarizing film, a polarizing film to be inspected (inspection polarizing film), and a second reference polarizing film in this order, The color spots of the inspection polarizing film are inspected from the side of the second reference polarizing film. In the method of the present invention, the angle of the absorption axis of one of the first reference polarizing film and the second reference polarizing film with respect to the absorption axis of the inspection polarizing film is set to 75 ° ± 10 °. And the angle of the absorption axis of the other reference polarizing film with respect to the absorption axis of the inspection polarizing film is set to 105 ° ± 10 °.

  In the conventional inspection method, the reference polarizing film and the inspection polarizing film are arranged so that the angles formed by the respective absorption axes are 0 degrees and 90 degrees, and therefore it is difficult to detect color spots with weak levels. In addition, it is difficult to detect color spots to be detected because color spots such as stained spots that are difficult to be practically used are easily detected. In contrast, in the method of the present invention, the absorption axis of one reference polarizing film is inclined within a range of 75 ° ± 10 ° with respect to the absorption axis of the inspection polarizing film to be inspected, and the other This is different from the conventional inspection method in that the color of the inspection polarizing film is inspected with the absorption axis of the reference polarizing film tilted within a range of 105 ° ± 10 °. By adopting such a method of the present invention, it is possible to easily detect color spots on the polarizing film that are difficult to detect by the conventional inspection method.

  In the method of the present invention for inspecting the color spots of the polarizing film, as described above, the inspection polarization of the absorption axis of one of the first reference polarizing film and the second reference polarizing film. The angle with respect to the absorption axis of the film is set to 75 ° ± 10 °, and the angle of the absorption axis of the other reference polarizing film with respect to the absorption axis of the inspection polarizing film is set to 105 ° ± 10 °. Here, the angle of the absorption axis of each reference polarizing film with respect to the absorption axis of the inspection polarizing film is set to the same rotational direction angle with respect to the absorption axis of the inspection polarizing film. That is, when viewed toward the light source (when viewed from the second reference polarizing film toward the first reference polarizing film), the angle of the absorption axis of one reference polarizing film is absorbed by the inspection polarizing film. In the case of 75 degrees ± 10 degrees counterclockwise with respect to the axis, the angle of the absorption axis of the other reference polarizing film is 105 degrees ± 10 degrees counterclockwise as described above with respect to the absorption axis of the inspection polarizing film. To be. In addition, the absorption axis of a polarizing film means the direction in which a polarizing film absorbs light, and the said absorption axis normally respond | corresponds to the extending | stretching direction at the time of polarizing film manufacture.

  In FIG. 1, the example of the arrangement | positioning method of each reference | standard polarizing film and test | inspection polarizing film in the method of this invention is shown typically, (a) is the 1st reference | standard polarizing film, test | inspection polarizing film, and It is the figure which mounted the 2nd reference | standard polarizing film in this order, and was seen from the upper diagonal front, (b) is a 1st reference | standard polarizing film, a test | inspection polarizing film, and a 2nd reference | standard polarizing film on a light source It is the figure which showed the relationship of the absorption axis of each polarizing film at the time of mounting these in this order and seeing these from upper direction. In addition, in (a), it has shown in the form which fully opened the space | interval between each polarizing film for convenience. In FIG. 1, the angle θ1 of the absorption axis d1 of the first reference polarizing film 2 with respect to the absorption axis d0 of the inspection polarizing film 3 is 75 degrees ± 10 degrees, and the absorption axis d2 of the second reference polarizing film 4 is The angle θ2 with respect to the absorption axis d0 of the inspection polarizing film 3 is set to 105 ° ± 10 °.

  In the method of the present invention, the angle of the absorption axis of one of the first reference polarizing film and the second reference polarizing film with respect to the absorption axis of the inspection polarizing film is set to 75 ° ± 10 °, In addition, the angle of the absorption axis of the other reference polarizing film with respect to the absorption axis of the inspection polarizing film is 105 degrees ± 10 degrees, but the angle of 75 degrees ± 10 degrees makes it easier to detect color spots. Therefore, it is preferably 75 ° ± 8 °, more preferably 75 ° ± 5 °, and further preferably 75 ° ± 3 °. Similarly, the angle of 105 ° ± 10 ° is preferably 105 ° ± 8 °, more preferably 105 ° ± 5 °, because color spots are more easily detected. More preferably, the degree is ± 3 degrees.

  In the method of the present invention, the light source, the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film are arranged in this order, and the color spots of the inspection polarizing film are inspected from the second reference polarizing film side. The inspection polarizing film and each reference polarizing film may be arranged spatially apart from each other, but the first reference polarizing film and the inspection polarizing film may be in contact with each other, or the second reference polarizing film and the inspection polarizing film may be in contact with each other. The polarizing film may be in contact. The distance between the first reference polarizing film and the second reference polarizing film can be, for example, 30 cm or less, 10 cm or less, and further 5 cm or less. Each surface of the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film is substantially parallel to each other (for example, within a range of 0 ° ± 20 °, and further within a range of 0 ° ± 10 °). It is preferable to arrange in such a manner.

  There is no restriction | limiting in particular in the kind of light-emitting body in the light source used in the method of this invention, A fluorescent lamp, LED lighting, a halogen lamp, a sodium lamp etc. can be used, A fluorescent lamp and LED lighting are preferable.

  As the light source, a surface light source is preferably used from the viewpoint that the entire inspection target region can be irradiated. A surface light source is a light source capable of emitting light in a planar shape. For example, a light source having a configuration in which a light diffusing plate or the like is installed on the upper surface of a light emitter to emit light uniformly in a planar shape, or a light guide plate The light source of the structure which installs a light in the edge and converts light guide into surface light emission etc. can be mentioned.

Brightness of the surface light source, from the viewpoint of facilitating more detecting color spots, is preferably 10,000cd / ^{m 2} or more, more preferably 12,000cd / ^{m 2} or more, 15,000Cd / More preferably, it is m ² or more. There is no particular limitation on the upper limit of the luminance, the luminance example 100,000cd / ^{m 2} or less, further may be a 50,000cd / ^{m 2} or less.

  By the method of the present invention, the presence or absence of color spots and the degree of color spots on the inspection polarizing film can be inspected. The color spots can be inspected by visually observing the transmitted light that has passed through the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film in order from the light source. If the image is taken by means, the luminance data of the transmitted light at each position in the obtained inspection polarizing film plane can be analyzed and recorded quantitatively. The luminance data can be analyzed using, for example, an image processing system using a computer. The luminance data can be inspected for the presence or absence of color spots and the like after being displayed by display means such as various displays and projectors after being analyzed as necessary.

  In the method of the present invention, it is also preferable to move the inspection polarizing film in a direction parallel to the surface of the inspection polarizing film after using a linear light source. Here, the moving direction of the inspection polarizing film is a direction substantially perpendicular to the absorption axis direction of the inspection polarizing film (for example, within a range of 90 ° ± 20 °, and further within a range of 90 ° ± 10 °). Is preferred. The polarizing film often has linear color spots parallel to the absorption axis direction. However, if the moving direction as described above is adopted, it becomes easier to detect such linear color spots. The linear light source may be arranged such that its longitudinal direction is substantially perpendicular to the moving direction of the polarizing film (for example, within a range of 90 ° ± 20 °, and further within a range of 90 ° ± 10 °). preferable.

  In the above case using a line-shaped light source, a line-shaped photographing means (line camera) is provided so as to face the line-shaped light source via the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film. Etc.), and the transmitted light transmitted through the line-shaped light source in the order of the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film is preferably continuously photographed by the line-shaped photographing means. This is preferable because the two-dimensional luminance data of the transmitted light at each position in the obtained inspection polarizing film plane can be quantitatively analyzed and recorded. The obtained luminance data can be analyzed using, for example, a computer image processing system.

When the above method using a line-shaped light source is adopted, the luminance of the light source in the moving direction of the inspection polarizing film becomes constant, so only the one-dimensional luminance distribution derived from the light source in the longitudinal direction of the line-shaped light source is considered. You can do it. Therefore, it is possible to exclude two-dimensional luminance unevenness caused by a light source in the case of using a normal surface light source, and it is possible to easily acquire luminance data based on the color spots of the inspection polarizing film to be originally obtained. .
Specifically, by subtracting the luminance distribution derived from the light source in the longitudinal direction of the line-shaped light source from the luminance data at each position in the inspection polarizing film plane obtained by photographing with the line-shaped photographing means, Luminance data based on the color spots of the inspection polarizing film to be obtained can be easily obtained. Here, the luminance distribution derived from the light source can be obtained, for example, as follows.

  That is, a specific section (for example, a section having a length of 0.1 to 5 m) that is continuous in the moving direction of the inspection polarizing film is defined, and the specific section at each position in a direction perpendicular to the moving direction of the inspection polarizing film. By obtaining the average value of the luminance data at 1, a one-dimensional luminance distribution derived from the light source in the longitudinal direction of the line-shaped light source can be obtained.

  After subtracting the luminance distribution derived from the light source obtained as described above from the luminance data at each position in the inspection polarizing film plane obtained by photographing with the line-shaped photographing means, noise removal is further performed. Is preferred. As a method for removing the noise, for example, an approximate curve is created in the moving direction of the inspection polarizing film, and a difference (brightness deviation) from the approximate curve is obtained. A specific number (for example, continuous in the moving direction of the inspection polarizing film) (30 to 30) data is averaged into one of the continuous specific number of data (moving averaging), etc., and one or more of these are employed. be able to. Before removing the noise, average in a continuous specific section (for example, a section having a length of 1 to 10 cm) in a direction perpendicular to the moving direction of the inspection polarizing film, and set the moving direction of the inspection polarizing film on the horizontal axis. It is preferable to create a graph with the averaged value on the vertical axis, and to remove the noise from the graph.

  After performing noise removal as described above, if the color spot index is defined using the obtained distance between peaks or luminance deviation, the color spot of the inspection polarizing film can be quantitatively evaluated.

  As the inspection polarizing film to be inspected in the present invention, for example, a film in which a dichroic dye such as an iodine-based dye or a dichroic organic dye is adsorbed on a stretched film obtained by uniaxially stretching a PVA film. Can be mentioned. In addition, any one of the first reference polarizing film and the second reference polarizing film used in the present invention, preferably both, iodine-based stretched film obtained by uniaxially stretching the PVA film. What adsorb | sucks dichroic dyes, such as a pigment | dye and a dichroic organic dye, can be used.

Examples of PVA constituting the PVA film include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropenyl acetate. What can be obtained by saponifying the polyvinyl ester obtained by superposing | polymerizing 1 type (s) or 2 or more types of ester can be used. Among the above-mentioned vinyl esters, a compound having a vinyloxycarbonyl group (H ₂ C═CH—O—CO—) in the molecule is preferable from the viewpoint of ease of production of PVA, availability, cost, etc. More preferred is vinyl acetate.

  The polyvinyl ester is preferably obtained using only one or two or more vinyl esters as monomers, and more preferably obtained using only one vinyl ester as a monomer. However, as long as the effect of the present invention is not significantly impaired, a copolymer of one or more vinyl esters and other monomers copolymerizable therewith may be used.

  Examples of other monomers copolymerizable with the vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate and octadecyl (meth) acrylate; (meth) acrylamide; N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl (Meth) acrylamide derivatives such as amide, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamidepropyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; halogenated vinyl such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; vinegar Allyl compounds such as allyl acid and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids or salts thereof And so on. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer.

  The proportion of structural units derived from the other monomers in the polyvinyl ester is preferably 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester, and is preferably 10 mol% or less. More preferably, it is more preferably 5 mol% or less.

  As the above-mentioned PVA, those not graft-copolymerized can be preferably used, but PVA can be used for one or more kinds of graft copolymer as long as the effects of the present invention are not significantly impaired. It may be modified with a monomer. The said graft copolymerization can be performed with respect to at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

  In the PVA, a part of the hydroxyl group may be cross-linked or may not be cross-linked. The PVA may have a hydroxyl group partially reacted with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure. Also good.

  The degree of polymerization of the above PVA is not particularly limited, but is preferably 1,000 or more. When the degree of polymerization of PVA is 1,000 or more, the polarizing performance of the obtained polarizing film can be further improved. If the degree of polymerization of PVA is too high, it tends to lead to an increase in the production cost of PVA and poor processability during film formation, so the degree of polymerization of PVA is in the range of 1,000 to 10,000. Is more preferable, it is still more preferable to be in the range of 1,500 to 8,000, and it is particularly preferable to be in the range of 2,000 to 5,000. In addition, the polymerization degree of PVA as used in this specification means the average degree of polymerization measured according to description of JISK6726-1994.

  The degree of saponification of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more because the heat and heat resistance of the resulting polarizing film is improved. 99.3 mol% or more is particularly preferable. In this specification, the saponification degree of PVA refers to the vinyl alcohol unit relative to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification of PVA. Refers to the proportion (mol%) occupied by the number of moles. The degree of saponification can be measured according to the description of JIS K6726-1994.

  The PVA film may contain a plasticizer together with the above PVA. When the PVA film contains a plasticizer, it is possible to improve the handleability and stretchability of the PVA film. As the plasticizer, polyhydric alcohol is preferably used, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. PVA film Can contain one or more of these plasticizers. Among these, glycerin is preferable because the stretchability of the PVA film becomes better.

  The content of the plasticizer in the PVA film is preferably 2 to 20 parts by mass with respect to 100 parts by mass of PVA, more preferably 3 to 17 parts by mass, and still more preferably 4 to 14 parts by mass. . When the content of the plasticizer in the PVA film is 2 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability of the PVA film is improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less with respect to 100 parts by mass of PVA, the plasticizer bleeds out on the surface of the PVA film and the handling property of the PVA film is reduced. be able to.

  In addition, when a PVA film is produced using a film-forming stock solution for producing a PVA film, which will be described later, the film-forming property is improved and the occurrence of film thickness unevenness is suppressed, and a metal roll is used for film-forming. Since a PVA film can be easily peeled off from these metal rolls and belts when a belt or a belt is used, it is preferable to add a surfactant to the film-forming stock solution. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film may contain a surfactant. There are no particular limitations on the type of surfactant that is blended in the film-forming stock solution for producing the PVA film, and thus the surfactant contained in the PVA film, but from the viewpoint of releasability from a metal roll or belt, an anion is used. Surfactants or nonionic surfactants are preferred, and nonionic surfactants are particularly preferred.

  As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; a sulfonic acid type such as dodecylbenzene sulfonate and the like are suitable.

Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene laurylamino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxy An allyl phenyl ether type such as alkylene allyl phenyl ether is preferred.
These surfactants can be used alone or in combination of two or more.

  When a surfactant is blended in a film-forming stock solution for producing a PVA film, the content of the surfactant in the film-forming stock solution, and thus the content of the surfactant in the PVA film is determined as the film-forming stock solution or the PVA film. It is preferable that it exists in the range of 0.01-0.5 mass part with respect to 100 mass parts of PVA contained in, and it is more preferable that it exists in the range of 0.02-0.3 mass part. When the content of the surfactant is 0.01 parts by mass or more with respect to 100 parts by mass of PVA, the film forming property and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less with respect to 100 parts by mass of PVA, the surfactant bleeds out on the surface of the PVA film, resulting in blocking, and handling properties are reduced. Can be suppressed.

  The PVA film may be composed only of PVA, or may be composed only of PVA and the above-described plasticizer and / or surfactant. If necessary, an antioxidant, an antifreeze agent, a pH adjuster, You may contain other components other than above-mentioned PVA, a plasticizer, and surfactant, such as a masking agent, a coloring inhibitor, and an oil agent.

  The PVA content in the PVA film is preferably in the range of 50 to 100% by mass, more preferably in the range of 80 to 100% by mass, and in the range of 85 to 100% by mass. Is more preferable.

  The thickness of the PVA film is not particularly limited, but if it is too thick, drying when producing the polarizing film is difficult to be performed quickly, while if too thin, the film breaks during uniaxial stretching when producing the polarizing film. Since it tends to occur, it is preferably 5 μm or more, more preferably 8 μm or more, further preferably 10 μm or more, particularly preferably 12 μm or more, and preferably 150 μm or less. 120 μm or less is more preferable, 80 μm or less is further preferable, and 50 μm or less is particularly preferable.

  Although there is no restriction | limiting in particular in the shape of a PVA film, Since a polarizing film can be manufactured continuously with sufficient productivity, it is preferable that it is a long film. The length of the long film is not particularly limited, but a more uniform PVA film can be produced continuously and smoothly, and it can also be used continuously when a polarizing film is produced using it. Therefore, it is preferably within a range of 5 to 50,000 m, and more preferably within a range of 100 to 20,000 m. The width of the long film is not particularly limited, and can be, for example, 50 cm or more. However, in recent years, liquid crystal televisions and monitors have become larger, so that they can be used effectively for them. Preferably, it is preferably 2 m or more, more preferably 4 m or more. Moreover, when manufacturing a polarizing film with a realistic production machine, if the width of the film is too wide, uniform uniaxial stretching may be difficult. Therefore, the width of the PVA film is preferably 8 m or less.

  There is no particular limitation on the form of the PVA film, either in the form of a single layer or in the form of a laminate such as a PVA film formed on a thermoplastic resin film by a coating method or the like. However, a single-layered form is preferable from the viewpoints of complicated laminating (coating and the like) work and cost of the thermoplastic resin film.

  The production method of the PVA film is not particularly limited, and a production method in which the thickness and width of the film after film formation are more uniform can be preferably adopted. For example, the above-described PVA constituting the PVA film, and as necessary In addition, a film-forming stock solution in which one or more of plasticizers, surfactants and other components are dissolved in a liquid medium, PVA, and optionally plasticizers, surfactants, other It can be produced using a film-forming stock solution containing one or more of components and liquid medium and in which PVA is melted. When the film-forming stock solution contains at least one of a plasticizer, a surfactant and other components, it is preferable that these components are uniformly mixed.

  Examples of the liquid medium used for the preparation of the membrane forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of them can be used. Among these, water is preferable from the viewpoint of a small environmental load and recoverability.

  The volatile fraction of the film-forming stock solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation during film formation in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc. It is preferably in the range of 95% by mass, more preferably in the range of 55-90% by mass, and still more preferably in the range of 60-85% by mass. When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the production of an industrial PVA film becomes easy.

  Examples of the film forming method for forming a PVA film using the above-described film forming stock solution include a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, and the like. A membrane method and an extrusion film forming method are preferred. These film forming methods may be used alone or in combination of two or more. Among these film forming methods, the extrusion film forming method is more preferable because a PVA film having a uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat-treated as necessary.

  Examples of the film forming method for forming a PVA film using the above-described film forming stock solution include a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, and the like. A membrane method and an extrusion film forming method are preferred. These film forming methods may be used alone or in combination of two or more. Among these film forming methods, the extrusion film forming method is more preferable because a PVA film having a uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat-treated as necessary.

  A polarizing film manufactured using the above PVA film as a raw fabric can be used as an inspection object in the present invention. In addition, the first reference polarizing film and / or the second reference polarizing film used in the present invention can be manufactured using the PVA film as a raw fabric. In order to produce a polarizing film using the above PVA film as a raw material, for example, using the above PVA film, a swelling treatment, a dyeing treatment, a stretching treatment, and, if necessary, a crosslinking treatment, a fixing treatment, A polarizing film can be manufactured by performing a drying process, heat processing, etc. In this case, the order of each process such as the swelling process, the dyeing process, the stretching process, and the fixing process is not particularly limited, and one or two or more processes can be performed simultaneously. Also, one or more of each process can be performed twice or more.

  The swelling treatment can be performed by immersing the PVA film in water. The temperature of water when immersed in water is preferably in the range of 20 to 40 ° C, more preferably in the range of 22 to 38 ° C, and preferably in the range of 25 to 35 ° C. Further preferred. Moreover, as time to immerse in water, for example, it is preferably within a range of 0.1 to 5 minutes, and more preferably within a range of 0.5 to 3 minutes. In addition, the water at the time of immersing in water is not limited to a pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

  The dyeing process is preferably performed using an iodine-based dye as a dichroic dye, and the dyeing time may be any stage before the stretching process, at the stretching process, or after the stretching process. Dyeing is generally performed by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath, and such a dyeing method is also preferably used in the present invention. . The iodine concentration in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the potassium iodide concentration is preferably in the range of 0.01 to 10% by mass. Moreover, it is preferable that the temperature of a dyeing bath shall be 20-50 degreeC, especially 25-40 degreeC.

  In addition, a dichroic organic dye (for example, DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37, 39, 79) , 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; Direct Yellow 8 , 12, 44, 86, 87; dichroic dyes such as Direct Orange 26, 39, 106, 107) may be used. A dichroic dye may be used individually by 1 type, or may use 2 or more types together.

  The crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. When the crosslinking treatment is performed, crosslinking is introduced into the PVA film, and it is possible to effectively prevent the PVA from being eluted into water when the stretching treatment is performed at a relatively high temperature and wet. From such a viewpoint, the crosslinking treatment is preferably performed after the dyeing treatment. As a crosslinking agent used, 1 type (s) or 2 or more types of boron compounds, such as boric acid salts, such as boric acid and borax, can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably in the range of 1 to 15% by mass, and more preferably in the range of 2 to 7% by mass. The aqueous solution containing a crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the crosslinking agent is preferably in the range of 20 to 50 ° C, and more preferably in the range of 25 to 40 ° C.

  The stretching treatment may be performed by either a wet stretching method or a dry heat stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, or can be carried out in the dyeing bath described above or in a fixing treatment bath described later. Moreover, in the case of a dry-type extending | stretching method, it can carry out in air using the PVA film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, It is especially preferable to be within the range of ˜4.0% by mass. Moreover, the boric acid aqueous solution may contain potassium iodide, and the concentration is preferably in the range of 0.01 to 10% by mass.

  Although the extending | stretching temperature in an extending | stretching process is not specifically limited, In the case of a wet extending | stretching method, it is preferable to exist in the range of 30-90 degreeC, it is more preferable to exist in the range of 40-70 degreeC, and 45-65 degreeC. It is more preferable that it is within the range, and in the case of the dry heat stretching method, it is preferably within the range of 50 to 180 ° C.

In addition, the stretching ratio in the stretching process (the total stretching ratio obtained by multiplying the stretching ratios when performing multi-stage uniaxial stretching) is as much as possible until the film is cut from the point of polarization performance of the polarizing film to be obtained. More specifically, it is preferably 4 times or more, more preferably 5 times or more, and still more preferably 5.5 times or more. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, but is preferably 8 times or less in order to perform uniform drawing. In addition, the draw ratio in this specification is based on the length of the film before extending | stretching, and the state which is not extending | stretched corresponds to 1 time of draw ratios.
The thickness of the stretched film (polarizing film) is preferably 3 to 35 μm, particularly 5 to 30 μm.

  There is no particular limitation on the stretching direction when stretching a long PVA film, and uniaxial stretching or lateral uniaxial stretching in the length direction can be adopted, but the length is obtained because a polarizing film that is superior in polarization performance is obtained. Uniaxial stretching in the direction is preferred. Uniaxial stretching in the length direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, lateral uniaxial stretching can be performed using a tenter type stretching machine.

  In the production of the polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dichroic dye to the film. The fixing treatment can be carried out by immersing a film in an aqueous solution containing one or more boron compounds such as boric acid and borax in a fixing treatment bath. In the fixing treatment bath, an iodine compound or a metal compound may be added as necessary. The concentration of the boron compound in the fixing treatment bath is generally about 2 to 15% by mass, particularly about 3 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C, particularly preferably 25 to 40 ° C.

  The drying treatment (heat treatment) is preferably performed in the range of 30 to 150 ° C, particularly in the range of 50 to 140 ° C. By performing a drying treatment (heat treatment) at a temperature within the above range, a polarizing film excellent in dimensional stability can be easily obtained, and a decrease in polarizing performance can be effectively suppressed.

  Although the polarizing film obtained as described above can be used as an inspection object in the present invention as it is, an inspection object in the form of a polarizing plate in which a protective film is bonded to one or both surfaces of the polarizing film. It is preferable that Moreover, although the polarizing film obtained as mentioned above can be used as it is as the first reference polarizing film and / or the second reference polarizing film in the present invention, it is a protective film on one side or both sides of the polarizing film. It is preferable to use the thing of the form of the polarizing plate on which the is bonded as the 1st standard polarizing film and / or the 2nd standard polarizing film in the present invention. The first reference polarizing film and the second reference polarizing film are more preferably in the form of polarizing plates.

  As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive agent for bonding a protective film, a PVA adhesive agent, a urethane adhesive agent, etc. are mentioned, Among these, a PVA adhesive agent is preferable.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

[Production Example] Production of inspection polarizing film PVA film raw material containing PVA and glycerin obtained by saponifying polyvinyl acetate (polymerization degree of PVA 2,400, saponification degree of PVA 99.9 mol%, glycerin) A polarizing film was prepared by subjecting a content of 12% by mass, a thickness of 60 μm, a width of 65 cm, and a roll shape (length: 1,000 m) to swelling, dyeing, crosslinking, stretching, fixing, and drying.
As the swelling treatment, the PVA film was immersed in distilled water (temperature: 30 ° C.) for 1 minute, and stretched at a stretch ratio of 2 during that time. In addition, as a dyeing treatment, an aqueous solution containing iodine pigment (concentration of iodine used: 0.05 mass%, concentration of potassium iodide used: 1.2 mass%, temperature: 30 ° C.) for 2 minutes. It was immersed and stretched at a stretch ratio of 1.2 times during that time. Further, as a crosslinking treatment, the film was immersed in an aqueous boric acid solution (boric acid concentration: 2.6 mass%, temperature: 30 ° C.) for 2 minutes, and stretched at a stretching ratio of 1.1 times during that time. Subsequently, as a stretching treatment, uniaxial stretching was performed at a stretching ratio of 2.4 times in a boric acid aqueous solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5% by mass, temperature: 57 ° C.) (total stretching). (Magnification is 6.3 times). Further, as a fixing treatment, it was immersed in an aqueous boric acid solution (boric acid concentration: 1.5%, potassium iodide concentration: 5%, temperature: 22 ° C.) for 10 seconds. Finally, as a drying treatment, the stretched PVA film was dried at 60 ° C. for 1 minute to obtain a polarizing film.
Next, a TAC film (thickness 80 μm) was bonded to both surfaces of the obtained polarizing film using a PVA aqueous solution as an adhesive and dried at 70 ° C. for 3 minutes to obtain an inspection polarizing film in the form of a polarizing plate.

[Examples 1 and 2 and Comparative Examples 1 to 3]
(1) Visual inspection of color spots (visibility)
As shown in FIG. 1, in a dark room, a first reference polarizing film (in the form of a polarizing plate; single transmission) on a surface light source (Dentsu Sangyo Co., Ltd., DSK-7040HF45W18-LC50K-FF-KU) 43%), the inspection polarizing film manufactured in the manufacturing example, and the second reference polarizing film (in the form of polarizing plate; single transmittance 43%) were placed in this order. Table 1 shows the angle (θ1) of the absorption axis of the first reference polarizing film with respect to the absorption axis of the inspection polarizing film and the angle (θ2) of the absorption axis of the second reference polarizing film with respect to the absorption axis of the inspection polarizing film, respectively. The angles of the first reference polarizing film and the second reference polarizing film were adjusted so that the indicated values were obtained.
Next, light (luminance 20,000 cd / m ² ) is irradiated from a surface light source, and observed visually from directly above the inspection polarizing film (1 m height from the inspection polarizing film), and the color spots of the inspection polarizing film are visually recognized. The sensory evaluation was performed based on the following criteria. The results are shown in Table 1.
A: Conspicuous color spots are visually recognized.
○: Color spots are visually recognized but are hardly noticeable.
X: Color spots are hardly visible.

(2) Color spot inspection using a line camera (color spot index)
As shown in FIG. 2, a linear light source (manufactured by Sumita Optical Glass Co., Ltd., transmission light: TF-750CL, metal halide light source: LS-M210) is irradiated in the horizontal direction and light is irradiated to the front side in the horizontal direction The first reference polarizing film (in the form of a polarizing plate; single transmittance 43%) and the second reference polarizing film (in the form of a polarizing plate) from the line-shaped light source toward the front side And a line camera (manufactured by Coretec Corporation, CLC-3M575CL-TC54) were arranged in this order. In addition, each reference | standard polarizing film was arrange | positioned perpendicularly so that one surface might face the horizontal direction front side. Further, the line camera was arranged so that its longitudinal direction corresponds to the longitudinal direction of the line-shaped light source and is opposed to the line-shaped light source.

  Further, the inspection polarizing film unwound from the unwinding roll is unwound upward so that the inspection polarizing film can move between the first reference polarizing film and the second reference polarizing film and be wound on the winding roll. A roll and a winding roll were respectively arranged on the lower side. Here, the plane of the moving inspection polarizing film is parallel to the planes of both reference polarizing films, and the moving direction of the inspection polarizing film is perpendicular to the longitudinal direction of the line light source and the line camera. (So that the inspection polarizing film moves downward).

  Next, one short side (side of 50 cm) of a dummy film (PET film) cut to a width of 50 cm and a length of 3 m was attached to the unwinding roll. Similarly, one short side (side of 50 cm) of another dummy film (PET film) cut to a width of 50 cm and a length of 3 m was attached to the winding roll. And the direction which is not affixed on the roll in each dummy film so that the test | inspection polarizing film manufactured in the manufacture example between these dummy films (the test | inspection polarizing film of the full width cut to 50 cm in the absorption-axis direction) may be arrange | positioned A side of 50 cm of the inspection polarizing film was attached to the short side. Thereafter, the dummy film, the inspection polarizing film, and the dummy film were manually wound around the unwinding roll in this order.

Next, Table 1 shows the angle (θ1) of the absorption axis of the first reference polarizing film with respect to the absorption axis of the inspection polarizing film and the angle (θ2) of the absorption axis of the second reference polarizing film with respect to the absorption axis of the inspection polarizing film. The angles of the first reference polarizing film and the second reference polarizing film were adjusted so as to have the values shown in FIG.
And in the state irradiated with light from the linear light source, the dummy film, the inspection polarizing film, and the dummy film are moved in this order at a speed of 5 m / min from the unwinding roll to the winding roll, and the inspection polarized light Images were taken with the line camera as the film passed between the line-shaped light source and the line camera.

  The obtained image was converted into two-dimensional luminance data corresponding to the position in the inspection polarizing film plane, and luminance data was obtained at a pitch of 0.5 mm with respect to each of the absorption axis direction and the width direction of the inspection polarizing film. Next, a one-dimensional luminance distribution derived from the line camera in the longitudinal direction of the line camera is obtained from the obtained luminance data and subtracted from the luminance data to obtain two-dimensional luminance deviation data (1). It was. Here, the luminance distribution derived from the line camera was obtained as follows. That is, a 25 cm continuous section is defined in the moving direction of the luminance data, and the luminance data in the continuous 25 cm section at each position in the direction perpendicular to the moving direction of the inspection polarizing film (longitudinal direction of the line camera). By obtaining the average value, a one-dimensional luminance distribution derived from the line camera was obtained.

  From the two-dimensional brightness deviation data (1) obtained above, a 20 mm long section perpendicular to the moving direction of the inspection polarizing film (the length of the moving direction of the inspection polarizing film is the above line camera). 25 cm) determined when obtaining the one-dimensional luminance distribution of origin, and luminance deviation data for 20 mm in the direction perpendicular to the moving direction of the inspection polarizing film at each position in the moving direction of the inspection polarizing film Was obtained, and a graph of one-dimensional luminance deviation data (2) was obtained with the moving direction of the inspection polarizing film on the horizontal axis and the averaged value on the vertical axis. A cubic polynomial approximate curve was obtained from this graph, and the difference was used as a graph of luminance deviation data (3). Next, a graph of the luminance deviation data (4) obtained by moving and averaging 10 points was obtained from the graph of the luminance deviation data (3). Here, the 10-point moving averaging is performed on the luminance deviation data (3) of each 10 points continuous in the moving direction (in the horizontal axis direction of the graph) of the inspection polarizing film, and the fifth point is moved 10 points from one end. As the reference point for averaging, the average value of 10 points was used as the luminance deviation data of the fifth point.

  In the graph of the luminance deviation data (4) obtained above, 5 points (section of 2 cm in total) are extracted at a pitch of 5 mm in the moving direction of the inspection polarizing film (horizontal axis direction of the graph), and the luminance at the 5 points is extracted. When the deviation data (4) is set to a1, a2, a3, a4 and a5 from one end, the moving direction of the inspection polarizing film giving the a3 such that a1 <a2 <a3> a4> a5 (in the graph) The position in the horizontal axis direction) is the bright peak point, and the position in the moving direction of the inspection polarizing film giving the a3 such that a1> a2> a3 <a4 <a5 (horizontal axis direction in the graph) is the dark peak point, The maximum value of the difference between both luminance deviation data (4) at the peak where the distance between adjacent peaks including the bright peak and the dark peak is 40 mm or less was taken as the color spot index of the inspection polarizing film. The results are shown in Table 1.

  According to the method of the present invention, it is possible to easily detect the color spots of the polarizing film that are difficult to detect by the conventional inspection method. For example, the method is used for inspection means when manufacturing a polarizing film or a polarizing plate. be able to.

DESCRIPTION OF SYMBOLS 1 Light source 2, 7 1st reference polarizing film 3, 8 Inspection polarizing film 4, 9 2nd reference polarizing film 5 Direction to inspect 6 Line-shaped light source 10 Line camera 11, 12 Dummy film 13 Unwinding roll 14 Winding up Roll d0 Absorption axis d1 of inspection polarizing film Absorption axis d2 of first reference polarizing film Absorption axis θ2 of second reference polarizing film Angle θ1 of absorption axis of first reference polarizing film with respect to absorption axis of inspection polarizing film Inspection polarization The angle of the absorption axis of the second reference polarizing film with respect to the absorption axis of the film

Claims (11)

  A method for inspecting color spots of a polarizing film, wherein a light source, a first reference polarizing film, an inspection polarizing film to be inspected, and a second reference polarizing film are arranged in this order, and the second reference polarizing film side Inspect the color unevenness of the inspection polarizing film, where the angle of the absorption axis of the reference polarizing film of one of the first reference polarizing film and the second reference polarizing film with respect to the absorption axis of the inspection polarizing film is determined. A method in which the angle is set to 75 ° ± 10 ° and the angle of the absorption axis of the other reference polarizing film to the absorption axis of the inspection polarizing film is set to 105 ° ± 10 °.   The method according to claim 1, wherein the inspection polarizing film is in the form of a polarizing plate in which a protective film is bonded to one side or both sides.   The method according to claim 1 or 2, wherein at least one of the first reference polarizing film and the second reference polarizing film is in the form of a polarizing plate in which a protective film is bonded to one side or both sides thereof.   The method according to claim 1, wherein the light source is a surface light source. The method according to claim 4, wherein the luminance of the surface light source is 10,000 cd / m ² or more.   The method according to any one of claims 1 to 5, wherein color spots are inspected by photographing with a photographing means.   The method according to claim 6, wherein the color spots are inspected by displaying the luminance data at each position in the plane of the inspection polarizing film obtained by photographing by the photographing means by the display means.   4. The color spot is continuously inspected by moving the inspection polarizing film in a direction parallel to the surface of the inspection polarizing film, wherein the light source is in a line shape. 5. Method.   The method according to claim 8, wherein the direction parallel to the surface of the inspection polarizing film is a direction substantially perpendicular to the absorption axis direction of the inspection polarizing film.   The color spot is inspected by photographing with a line-shaped photographing means arranged so as to face the line-shaped light source through the first reference polarizing film, the inspection polarizing film, and the second reference polarizing film. Or the method according to 9;   The method according to claim 10, wherein the luminance distribution derived from the light source in the longitudinal direction of the linear light source is subtracted from the luminance data at each position in the plane of the inspection polarizing film obtained by photographing with the photographing means.