JP2008197510A - Method for producing polarizer, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizer of which the change in polarization degree is made very small under a moisture-resistant condition and which can be prevented from being colored under high-temperature condition. <P>SOLUTION: The method for producing the polarizer comprises a dyeing step of dyeing a film of a hydrophilic polymer with a dichroic substance, a stretching step of stretching the dyed film of the hydrophilic polymer, and a cross-linking step of cross-linking the stretched hydrophilic polymer by using trialdehyde, and a post-step of bringing the film of the hydrophilic polymer after the cross-linking step into contact with alcohol. Triformyl methane is used as the trialdehyde and lower alcohol is used as the alcohol. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a polarizer used in a liquid crystal display device or the like.

Conventionally, as an optical member such as a liquid crystal display device, a polarizer (also referred to as a polarizing film) having polarization characteristics that transmits light in a specific vibration direction is known.
As such a polarizer, generally, a stretched film of polyvinyl alcohol type dyed with iodine or the like (in this specification, “polyvinyl alcohol” may be abbreviated as “PVA”) is widely used.
Such a polarizer generally includes a swelling step in which a PVA-based film is swollen with water, a dyeing step in which the film is impregnated with an iodine solution, and a fixing step in which the film is impregnated in a boric acid solution and fixed. The film is manufactured through a stretching process for stretching the film, a washing process for washing the film, and a drying process for drying the film (for example, Patent Document 1). The polarizer is usually put to practical use in which protective films such as triacetyl cellulose are laminated on both sides.

However, since PVA is a hydrophilic polymer, it absorbs moisture over time. As a result, there is a problem that the orientation of the polymer is disturbed and the degree of polarization decreases.
Conventionally, a polarizer obtained by crosslinking a dyed PVA film with a dialdehyde such as glyoxal for the purpose of improving the dimensional stability of the PVA film polarizer is known (Patent Document 2).

JP 2003-270440 A Japanese Patent No. 3357109

  The present inventors have conducted various studies on dyed PVA film polarizers to prevent a decrease in the degree of polarization over time under high humidity conditions. As a result, the present inventors obtain a polarizer excellent in moisture resistance and durability when the polymer is crosslinked using a trialdehyde that is not disclosed in Patent Document 2 because the change in polarization degree with time is reduced. I found out that I can. This polarizer is excellent in moisture resistance and durability, but may be colored when exposed to a high temperature for a long time. When a polarizer that can be colored at such a high temperature is mounted on an image display device, it is not preferable because the polarizer may be colored when the device is operated.

  Therefore, an object of the present invention is to provide a method for producing a polarizer that is excellent in moisture resistance and can prevent coloring at high temperatures.

  The method for producing a polarizer of the present invention includes a dyeing process for dyeing a hydrophilic polymer film with a dichroic substance, a stretching process for stretching the hydrophilic polymer film, and a crosslinking process for crosslinking the hydrophilic polymer with trialdehyde. And a post-process of immersing the hydrophilic polymer film in an alcohol solution after the cross-linking process.

  In the polarizer obtained by the above production method, the hydrophilic polymer is cross-linked with trialdehyde and then treated with alcohol, so that the degree of polarization is hardly lowered under high humidity conditions. It is hard to produce coloring in.

The preferable aspect of this invention is a manufacturing method of the said polarizer in which the said trialdehyde contains a triformyl methane.
Furthermore, the preferable aspect of this invention is a manufacturing method of the said polarizer in which the said alcohol contains a lower alcohol (C1-C4).
Moreover, the preferable aspect of this invention is a manufacturing method of the said polarizer whose said post process is what immerses a hydrophilic polymer film in the alcohol solution whose alcohol concentration is 3 mass%-20 mass%.
Furthermore, the preferable aspect of this invention is a manufacturing method of the said polarizer whose said hydrophilic polymer film is a polyvinyl alcohol-type film.
Moreover, the preferable aspect of this invention is a manufacturing method of the said polarizer which has a fixing process which fixes a hydrophilic polymer with the compound containing boron or a boron before the said bridge | crosslinking process.

  Moreover, the image display apparatus of this invention is equipped with the polarizer obtained by one of the said manufacturing methods, It is characterized by the above-mentioned.

According to the method for producing a polarizer of the present invention, it is possible to easily produce a polarizer that is excellent in moisture resistance and difficult to be colored at high temperatures.
The obtained polarizer is processed into a polarizing plate, for example, and mounted on an image display device such as a liquid crystal display device.
In addition, since the image display device of the present invention includes a polarizer that has excellent moisture resistance and is difficult to be colored, a good image can be displayed over a long period of time under normal use conditions.

In the method for producing a polarizer of the present invention, a hydrophilic polymer film dyed with a dichroic substance is subjected to a crosslinking treatment using trialdehyde, and then the film is brought into contact with alcohol.
Hereinafter, the manufacturing method of the polarizer of this invention is demonstrated concretely.

  The method for producing a polarizer of the present invention includes, for example, a swelling process, a dyeing process, a fixing process, a stretching process, a crosslinking process, a post-process, a washing process, and a drying process described below. In this production method, a long polarizer can be produced.

FIG. 1 is a schematic diagram showing the concept of a typical manufacturing process of a long polarizer.
In FIG. 1, a long hydrophilic polymer film 20 wound in a roll shape is fed from a feeding portion 21 and immersed in a swelling bath 31 and a dyeing bath 32 containing iodine and the like, and the speed ratio is different. Swelling treatment and dyeing treatment are performed while tension is applied in the longitudinal direction of the film with the rolls 311, 312, 321 and 322. Next, the long film 20 subjected to the swelling treatment and the dyeing treatment is immersed in the first fixing bath 33 and the second fixing bath 34 containing boric acid and the like, and rolls 331, 332, 341, and 342 having different speed ratios are used. Then, a fixing process and a final stretching process are performed while tension is applied in the longitudinal direction of the film. The fixed long film 20 is immersed in a crosslinking bath 35 containing trialdehyde by rolls 351 and 352. Thereafter, the long film 20 is immersed in the after-bath 36 containing alcohol by the rolls 361 and 362 and then immersed in the water-washing bath 37 by the rolls 371 and 372 and subjected to a water-washing treatment. The long film 20 that has been washed with water is dried by the drying means 38, so that the moisture content is adjusted to, for example, 10% to 30%, and is wound up by the winding unit 22.

(Hydrophilic polymer film)
The hydrophilic polymer film used in the present invention is not particularly limited, and generally a film obtained by forming a resin composition containing a polymer having a hydrophilic group is used. Examples of the film include a PVA film, a partially formalized PVA film, polyethylene terephthalate, an ethylene / vinyl acetate copolymer film, and a partially saponified film thereof. Besides these, polyene oriented films such as PVA dehydrated products and polyvinyl chloride dehydrochlorinated products can also be used. Among these, a PVA polymer film is preferable because it is excellent in dyeability with a dichroic substance. PVA is a polymer obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. As the PVA polymer, modified PVA containing a component copolymerizable with vinyl acetate of PVA can also be used. Examples of the copolymerizable component include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, derivatives thereof, and α-olefins having 2 to 30 carbon atoms. As the PVA polymer, modified PVA containing acetoacetyl group, sulfonic acid group, carboxyl group, etc., modified PVA containing polyvinyl fulmar, polyvinyl acetal, ethylene copolymer and the like can also be used.

  When a PVA polymer is used, the polymer can be obtained, for example, by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer such as vinyl acetate. As for the degree of saponification and degree of polymerization, PVA having a high degree of saponification and a high degree of polymerization is preferably used from the viewpoint of good heat resistance and the like. The degree of saponification of PVA is not particularly limited, but usually those having a saponification degree of 90 mol% or more, preferably 95 mol% or more, more preferably 98% or more are used. The degree of saponification can be determined according to JIS K 6726-1994. Although the average degree of polymerization of PVA is not particularly limited, the average degree of polymerization is usually 500 or more, preferably 2,400 or more because a polarizer having high polarization performance can be produced. The upper limit of the average degree of polymerization is usually 8,000 or less, preferably 5,000 or less. The average degree of polymerization can be determined according to JIS K 6726-1994.

The PVA-based film is obtained by dissolving a resin composition containing a PVA-based polymer in water or / and an appropriate organic solvent such as DMSO, and coating the resin solution on an appropriate substrate by a casting method or the like. be able to. In addition to the casting method, the PVA film may be a film formed by a known film forming method such as an extrusion method.
You may mix | blend suitable additives, such as a plasticizer and surfactant, with the resin composition containing the said PVA-type polymer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. By adding these plasticizers and surfactants, a PVA film excellent in dyeability and stretchability can be obtained. The addition amount of the plasticizer and the surfactant is about 1 to 10 parts by mass with respect to 100 parts by mass of the PVA polymer.
As the hydrophilic polymer film, a long film is usually used. In addition, long means that a length dimension is sufficiently larger than a width dimension. The winding length of the long hydrophilic polymer film is preferably 300 m or more, and more preferably 1,000 m to 50,000 m.

(Swelling process)
The swelling step is a step of swelling the hydrophilic polymer film. What was illustrated above etc. can be used suitably for a hydrophilic polymer. In addition, in the specific description about each process below, it demonstrates centering on the case where the PVA-type film which is a preferable example of a hydrophilic polymer film is used. But the hydrophilic polymer film used for the manufacturing method of the polarizer of this invention is not limited to a PVA-type film.

In the production method of the present invention, an unstretched film is usually used as the PVA film. The PVA-based film is wound up in a roll shape, and the film roll is set on the upstream side of the swelling bath and guided into the swelling bath through the transport roll.
The swelling bath is filled with water as a swelling liquid. In addition, other substances besides water may be added to the swelling bath as long as the effects of the present invention are not impaired.
The water used in each bath such as the swelling bath and the dyeing bath described later is preferably pure water. Moreover, the liquid temperature of the swelling bath is preferably about 20 to 50 ° C, more preferably about 30 to 40 ° C. The time for immersing the PVA film in the swelling bath is approximately 1 to 7 minutes.

  The film may be stretched in a swelling bath, and the stretch ratio at this time is about 1.1 to 4.0 times. Further, the swelling step is usually performed in one bath of a swelling bath, but two or more baths may be used.

  By immersing the PVA film in the swelling bath before the dyeing step, dirt on the surface of the film can be removed, and the PVA film can be swollen with water to prevent uneven introduction of the dichroic material described later.

(Dyeing process)
The dyeing step is a step of impregnating (also referred to as adsorption) a dichroic substance into the PVA film after swelling.
The swollen PVA-based film is drawn out of the swelling bath and then guided to a dyeing bath.
The dyeing bath is filled with a dyeing solution in which a dichroic substance is dissolved in a solvent. As this solvent, water is generally used, but an organic solvent compatible with water may be added.
In the dyeing bath, the concentration of the dichroic substance is not particularly limited, but is preferably 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 7% by mass, and particularly preferably. Is 0.02 mass% to 5 mass%.

As the dichroic substance, conventionally known substances can be used, and examples thereof include iodine and organic dyes. Examples of organic dyes include polymethine dyes, cyanine dyes, merocyanine dyes, rhodacyanine dyes, trinuclear merocyanine dyes, allopolar dyes, hemicyanine dyes, styryl dyes, azo dyes, and others shown in the following color index (CI). Things.
C. I. Direct Yellow 8, C.I. I. Direct Yellow 12, C.I. I. Direct Yellow 28, C.I. I. Direct Yellow 86, C.I. I. Direct Blue 1, C.I. I. Direct Blue 71, C.I. I. Direct Blue 78, C.I. I. Direct Blue 168, C.I. I. Direct Blue 202, C.I. I. Direct Red 2, C.I. I. Direct Red 31, C.I. I. Direct Red 79, C.I. I. Direct Red 81, C.I. I. Direct Red 117, C.I. I. Direct Red 247, C.I. I. Direct Violet 9, C.I. I. Direct violet 51, C.I. I. Direct Orange 26, C.I. I. Direct Orange 39, C.I. I. Direct Orange 72, C.I. I. Direct Orange 106, C.I. I. Direct Orange 107 etc.
Iodine is preferably used as the dichroic material because it exhibits good polarization characteristics in visible light. A dichroic substance may be used alone or in combination of two or more.

  The dichroic material is preferably water-soluble. For this reason, organic dyes, for example, are those in which hydrophilic substituents such as sulfonic acid groups, amino groups, and hydroxyl groups are introduced, in the form of free acids and alkali metal salts, ammonium salts, and amines. It is preferable to use it.

Further, since the dyeing efficiency of the dichroic substance can be further improved, a reaction aid may be added to the dyeing solution. When iodine is used as the dichroic substance, the reaction aid is preferably a boron compound such as boric acid or borax. When an organic dye is used as the dichroic substance, it is preferable to use, for example, boric acid (sodium sulfate) as the reaction aid. When using these dyeing assistants, the concentration is preferably 0.1% by mass to 10% by mass.
When iodine is used as the dichroic substance, iodide may be added to the dyeing solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Etc. The addition ratio of iodide is preferably such that the ratio (mass ratio) of iodine and iodide is in the range of 1: 5 to 1: 100.

  The immersion time of the PVA film in the dyeing bath is not particularly limited, but is preferably about 20 seconds to 1,800 seconds. Moreover, the liquid temperature of the dyeing bath is preferably about 20 ° C to 80 ° C, and more preferably about 40 ° C to 60 ° C. This is because if the temperature of the dyeing bath is too high, the film may melt, and if it is too low, the dyeability is lowered.

In addition, you may extend | stretch a film in this dyeing bath, and the draw ratio at this time is about 1.1 to 4.0 times.
In addition, the dyeing process may be performed separately in two or more tanks.
Moreover, as a dyeing | staining process, the method of apply | coating or spraying the aqueous solution containing a dichroic substance on a PVA-type film other than the method of immersing in the above dyeing baths may be sufficient, for example.

(Fixing process)
The fixing step is a step of impregnating a PVA film impregnated with a dichroic substance with a fixing agent containing boron.
The PVA film impregnated with the dichroic material is drawn out from the dyeing bath and then guided to the fixing bath.
The fixing bath is filled with a fixing solution in which a fixing agent is dissolved in a solvent. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further added. Although the density | concentration of the fixing agent in a solution is not specifically limited, Preferably it is 2 mass%-15 mass%, More preferably, it is 5 mass%-12 mass%.

  As the fixing agent, conventionally known substances can be used, and examples thereof include compounds containing boron such as boric acid and borax. The fixing agent may be used alone or in combination of two or more. When two or more types are used in combination, for example, a combination of boric acid and borax is preferable. The addition ratio (molar ratio) of boric acid and borax is preferably 4: 6 to 9: 1, more preferably 5.5: 4.5 to 7: 3, and particularly preferably 6: 4.

  Iodide may be added to the fixing agent-containing solution from the viewpoint that uniform characteristics in the plane of the polarizer can be obtained. As this iodide, what was illustrated at the said dyeing | staining process can be used suitably. The concentration of iodide is preferably 0.5% by mass to 15% by mass, and more preferably 1% by mass to 10% by mass.

Although the liquid temperature of a fixed bath is not specifically limited, The range of 20-70 degreeC is preferable. The immersion time of the film is not particularly limited, but is preferably about 30 seconds to 1,200 seconds, and more preferably about 60 seconds to 400 seconds.
Moreover, you may perform a fixing process by dividing into 2 or more tank fixing baths.
In addition, the fixing process may use a method of applying or spraying a fixing agent-containing solution as in the dyeing process. Further, the film may be stretched in this fixing bath, and the stretching ratio at this time is about 1.1 to 4.0 times.
By performing the fixing treatment, the tensile strength of the unstretched PVA-based film can be improved, and the film can be prevented from being damaged during the stretching treatment.

(Stretching process)
The stretching step is a step of uniaxially stretching the PVA film.
The stretching treatment can be performed in any step between the swelling step and the fixing step, or in two or more steps selected between the swelling step and the fixing step. In addition, the stretching process can be performed, for example, before the fixing process, or after the fixing process (after the dyeing process if the fixing process is omitted), a stretching process is separately provided. Can also be done. Among them, it is preferable to perform a stretching process simultaneously with the fixing process, or to perform a stretching process by providing a separate stretching process after the fixing process. When a separate stretching step is provided, the presence or absence of a stretching process in each step before the separate stretching step is arbitrary.
Stretching treatment is about 2 to 7 times the original length of the PVA film (PVA film before being introduced into the swelling process) (in addition, when stretching is performed in two or more processes, total stretching is performed) It is preferable that the film is stretched to a magnification (hereinafter the same), more preferably about 2.5 to 6 times, and more preferably about 3 to 5 times. If the total draw ratio is less than 2 times, it is difficult to obtain a polarizer having a high degree of polarization, and if it exceeds 7 times, the film may be broken.

  When a separate stretching step is provided, the stretching method may be any of a wet stretching method in which a PVA film is stretched in a stretching bath and a dry stretching method in which a PVA film after moisture is stretched in air. good. In the case of the wet stretching method, the solution of the stretching bath is not particularly limited, and for example, a solution to which various metal salts, boron, boric acid, iodide, zinc compound, and the like are added can be used. As a solvent of this solution, water, ethyl alcohol or various organic solvents are appropriately used. The liquid temperature of this extending | stretching bath is the range of 30-80 degreeC, for example, Preferably it is 40-65 degreeC. On the other hand, when dry-drawing, 50-150 degreeC is preferable.

(Crosslinking process)
The crosslinking step is a step of impregnating a PVA film impregnated with a dichroic substance with a crosslinking agent containing trialdehyde.
The PVA-based film is guided to a crosslinking bath.
The crosslinking bath is filled with a crosslinking solution in which trialdehyde is dissolved in a solvent. In addition to the trialdehyde, an appropriate additive (for example, the above iodide) may be added to the crosslinking solution.
As the solvent, for example, water can be used, but an organic solvent compatible with water may be further added. The concentration of trialdehyde in the solution is not particularly limited, but is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and particularly preferably 0.5% by mass. ˜5 mass%. This is because if the trialdehyde concentration is less than 0.01%, the amount of trialdehyde impregnated in the film decreases, and a sufficient crosslinking effect may not be obtained. On the other hand, even if the concentration of trialdehyde exceeds 20%, the crosslinking effect does not change, which is disadvantageous in terms of cost.

The trialdehyde is not particularly limited as long as it has three CHO groups. For example, a chain or cycloaliphatic trialdehyde, an aromatic trialdehyde, a heterocyclic trialdehyde, a condensed ring compound Various trialdehydes such as trialdehyde can be used. Trialdehyde having a molecular weight of 300 or less is preferably used. This is because the aldehyde itself is relatively excellent in stability and can penetrate well between molecules of the PVA polymer.
Specific examples of the trialdehyde include triformylmethane represented by the following structural formula (a) and tris (3-oxopropyl) isocyanurate represented by the structural formula (b). Trialdehyde may be used alone or in combination of two or more. Among them, it is preferable to use at least triformylmethane because a polarizer excellent in moisture resistance and durability can be produced and the occurrence of coloring can be remarkably suppressed by performing an alcohol treatment.

Although the liquid temperature of a crosslinking bath is not specifically limited, Preferably it is the range of 20-70 degreeC, More preferably, it is 30-60 degreeC. Although the immersion time of a film is not specifically limited, Preferably it is about 10 second-300 second, More preferably, it is about 10 second-about 60 second.
The cross-linking step may be performed separately in two or more baths. In the cross-linking step, a slight stretching process may be performed.

In the crosslinking step, instead of immersing the PVA film in a crosslinking bath containing trialdehyde as described above, trialdehyde is attached to the PVA film and contained in the film (crosslinking step). Other embodiments).
Specific examples of other embodiments of the crosslinking step include the following methods, for example.
a) A method of applying a trialdehyde solution to one or both sides of a PVA film by a spray method,
b) A method in which a trialdehyde solution is applied to one or both sides of a PVA film by a printing method such as a gravure plate,
c) The method of apply | coating a trialdehyde solution to the single side | surface or both surfaces of a PVA-type film with various coating methods, etc. are mentioned.
As the trialdehyde solution, the cross-linking solutions exemplified above can be used.
The trialdehyde attached to the surface of the PVA film is contained in the film and crosslinks the PVA polymer.

(Post-process)
The post-process is a process of impregnating a PVA-based film containing trialdehyde with alcohol.
The PVA-based film is guided to a post bath.
The post-bath is filled with an alcohol solution in which alcohol is dissolved in water. In addition, you may add an appropriate additive (for example, the said iodide etc.) to an alcohol solution.

  Although the alcohol concentration of the said alcohol solution is not specifically limited, Preferably it is 3 mass%-20 mass%, More preferably, it is 5 mass%-15 mass%. If the concentration is too low, the PVA film cannot be impregnated with alcohol, whereas if the concentration is too high, it is not preferable in terms of cost effectiveness.

  As the alcohol, a monovalent or polyvalent alcohol can be used. As the alcohol, a higher alcohol having 5 or more carbon atoms and a lower alcohol having 1 to 4 carbon atoms can be used. Among them, since it is easy to impregnate a PVA film and easily react with trialdehyde, a lower alcohol having 1 to 4 carbon atoms is preferably used as the alcohol, and more preferably a lower monohydric alcohol having 1 to 4 carbon atoms. Is used. Preferable examples of the lower monohydric alcohol having 1 to 4 carbon atoms include methyl alcohol, ethyl alcohol, isopropyl alcohol, propyl alcohol and the like, and methyl alcohol and ethyl alcohol are particularly preferable. Alcohol may be used alone or in combination of two or more.

Although the liquid temperature of the said postbath is not specifically limited, Preferably it is the range of 20-70 degreeC, More preferably, it is 30-60 degreeC. Although the immersion time of a film is not specifically limited, Preferably it is about 10 second-300 second, More preferably, it is about 10 second-about 60 second.
In addition, you may divide and perform a post process in the post-bath of 2 or more tanks. In the post-process, stretching may be performed slightly.

In the post-process, instead of the method of immersing the PVA-based film in the bath after filling the alcohol solution as described above, the alcohol is attached to the PVA-based film and contained in the film (the post-process Other embodiments) may be used.
Specific examples of other embodiments of the post-process include the following methods.
a) A method of applying an alcohol solution to one or both sides of a PVA film by a spray method,
b) A method of applying an alcohol solution to one or both sides of a PVA film by a printing method such as a gravure plate,
c) The method of apply | coating an alcohol solution to the single side | surface or both surfaces of a PVA-type film with various coating methods etc. are mentioned.
As the alcohol solution, the alcohol solution exemplified above can be used.
Alcohol adhering to the surface of the PVA-based film is contained in the film and comes into contact with the PVA-based polymer.

(Cleaning process)
The cleaning treatment is a step of washing away unnecessary residues such as boron adhering to the PVA film that has undergone the above-described steps.
The crosslinked PVA-based film is drawn out from the crosslinking bath and then guided to a washing bath.
Water is generally used for the washing bath, and appropriate additives may be added as necessary.
The liquid temperature of the washing bath is preferably about 10 ° C to 60 ° C, and more preferably about 15 ° C to 40 ° C. Further, the number of times of the cleaning treatment is not particularly limited and may be performed a plurality of times.

(Drying process)
A drying process is a process of drying the PVA-type film after washing | cleaning.
The washed PVA-based film is drawn from the washing bath and then guided to a drying device.
As a drying method, an appropriate method such as natural drying, air drying, heat drying, or the like can be used. Usually, heat drying is preferably used. In the case of heat drying, the heating temperature is preferably about 20 to 80 ° C., and the drying time is preferably about 1 to 10 minutes. Furthermore, it is preferable to carry out the drying at a relatively low temperature in order to prevent the polarizer from being deteriorated regardless of the drying method. Accordingly, the heating temperature is more preferably 60 ° C. or less, and particularly preferably 45 ° C. or less.

A polarizer (dyed PVA-based film) is obtained through each processing step as described above.
According to the method for producing a polarizer of the present invention, it is possible to obtain a polarizer having excellent moisture resistance and a small change in polarization over time in a relatively short time. Although this effect is not clear, trialdehyde enters between the molecules of the hydrophilic polymer oriented in one direction by stretching, and the CHO group of the trialdehyde binds to the OH group of the hydrophilic polymer to part each polymer chain. This is presumed to be due to cross-linking. For example, when the hydrophilic polymer is a PVA polymer, it is presumed that the OH group of the side chain adjacent to the polymer and the CHO group of trialdehyde acetalize to form a strong crosslink.

  Moreover, the manufacturing method of this invention can obtain the polarizer which is hard to produce coloring on high temperature conditions by performing alcohol treatment after bridge | crosslinking with a trialdehyde. The cause of the coloration of the trialdehyde-crosslinked polarizer is not clear, but among the CHO groups of the trialdehyde contained in the film, the hydrophilic polymer and unbonded CHO groups absorb light at high temperatures. It is assumed that coloring occurs. By treating with alcohol as described above, the unbound CHO group dehydrates with the OH group of the alcohol, and the unbound CHO group is substituted with an alcohol-derived alkyl group, etc., thereby preventing coloring of the polarizer. It is assumed that it can be done.

(Optical characteristics of polarizer)
The polarizer obtained by the production method of the present invention has a polarization degree of preferably 99% or more, more preferably 99.5% or more, and its single transmittance is preferably 40% or more, more preferably 42%. That's it.
The amount of change in the degree of polarization of the polarizer of the present invention is preferably −1.0% or less, more preferably −0.8% or less.
However, the degree of polarization, the single transmittance, and the amount of change in the degree of polarization are numerical values obtained according to the conditions of the following examples.
The thickness of the polarizer is about 10 to 70 μm.

(Application of polarizer)
Although the polarizer of the present invention can be used as it is, it is usually used as an optical film subjected to various optical treatments in practical use. The optical processing is not particularly limited as long as the required optical characteristics are satisfied. For example, the following processing is exemplified. a) A transparent protective layer for the purpose of protecting the polarizer is laminated on one side or both sides of the polarizer. b) The surface of the transparent protective layer (the side opposite to the side that adheres to the polarizer) or polarized light. Applying surface treatment such as hard coat treatment, antireflection treatment, and antisticking treatment on one or both sides of the child, c) laminating an alignment liquid crystal layer for viewing angle compensation, etc., d) laminating other films And the like.

  Furthermore, one or more optical members used for forming an image display device or the like may be laminated on a polarizer or a polarizing plate in which a polarizer and a protective layer are laminated. Examples of the optical member include a polarization conversion element, a reflection plate, a semi-transmission plate, a phase difference plate (including wavelength plates such as 1/2 and 1/4), a viewing angle compensation film, and a brightness enhancement film. Among these, a reflective polarizing plate or a transflective polarizing plate in which a reflective plate or a transflective plate is laminated on a polarizing plate in which a polarizer and a transparent protective layer are laminated is preferable. Further, an elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is laminated on a polarizing plate in which a polarizer and a transparent protective layer are laminated is preferable. Furthermore, a wide viewing angle polarizing plate in which a viewing angle compensation layer or a viewing angle compensation film is laminated on a polarizing plate in which a polarizer and a transparent protective layer are laminated is preferable. Further, a polarizing plate in which a brightness enhancement film is laminated on a polarizing plate in which a polarizer and a transparent protective layer are laminated is preferable.

  Examples of the transparent protective layer provided on one or both sides of the polarizer include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate; cellulose polymers such as diacetyl cellulose and triacetyl cellulose; acrylic polymers such as polymethyl methacrylate; Examples thereof include styrene polymers such as polystyrene and acrylonitrile / styrene copolymer (AS resin); films such as polycarbonate polymers.

Next, an elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is laminated on a polarizing plate will be described. When changing linearly polarized light into elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light into linearly polarized light, or changing the polarization direction of linearly polarized light, a phase difference plate is used. In particular, a so-called quarter-wave plate (also referred to as a λ / 4 plate) is used as a retardation plate that changes linearly polarized light into circularly polarized light or changes circularly polarized light into linearly polarized light. A half-wave plate (also referred to as a λ / 2 plate) is usually used when changing the polarization direction of linearly polarized light.
As a retardation plate, a birefringent film formed by uniaxially or biaxially stretching a polymer material, an alignment film obtained by aligning a liquid crystal monomer and then fixing and polymerizing, an alignment film of a liquid crystal polymer, an alignment of a liquid crystal polymer Examples include those in which the layer is supported by a film.

Various polarizing plates, such as the polarizer of the present invention, the optical film containing the polarizer, and the circularly polarizing plate, can be used as an optical member of an image processing apparatus, for example. The usage and arrangement thereof are the same as those of a conventionally known image processing apparatus.
A typical example of the image processing device is a liquid crystal display device. Other image processing devices include self-luminous devices such as an organic electroluminescence (EL) display, a plasma display (PDP), and a field emission display.
When the polarizer, polarizing plate or the like of the present invention is used in a liquid crystal display device, the polarizer or the like is provided, for example, on one side or both sides of a liquid crystal cell, particularly at least on the display screen side.

  Next, Examples and Comparative Examples of the present invention will be shown to further explain the present invention. However, the present invention is not limited to the following examples.

(Various measurement methods)
(1) Measurement of parallel transmittance, polarization degree and single transmittance:
The parallel transmittance, the degree of polarization, and the single transmittance are spectrophotometers (trade name: DOT-3C, manufactured by Murakami Color Research Laboratory, in accordance with Japan Electronic Machinery Industry Standard (EIAJ) LD-201-1983. Error ± 0. 03%), and measurement was performed under the conditions of a C light source, a 2-degree visual field, and 25 ° C. The measured values of the degree of polarization and single transmittance were based on a wavelength of 550 nm.
Degree of polarization (%) = {(H ₀ −H ₉₀ ) / (H ₀ + H ₉₀ )} ^1/2 × 100 The parallel transmittance (H ₀ ) is a transmittance value of a parallel laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are parallel to each other. The orthogonal transmittance (H ₉₀ ) is a transmittance value of an orthogonal laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are orthogonal to each other.
(2) Measurement of change in polarization degree:
According to the measurement method of the degree of polarization, the degree of polarization of the polarizing plate before the environmental test (this degree of polarization is referred to as “polarization degree P1”) and the degree of polarization of the polarizing plate after the environmental test (this degree of polarization is referred to as “polarization degree P2”). ”) Was measured.
The degree of polarization change was obtained by substituting the measurement results of the degree of polarization P1 and the degree of polarization P2 into the following formula.
Formula: Polarization degree change amount (%) = polarization degree P2−polarization degree P1.
(3) Measurement of thickness:
Measurement was performed using an Anritsu digital micrometer "KC-351C type".

(Example 1)
Example 1 A polyvinyl alcohol film (trade name: Vinylon # 7500, manufactured by Kuraray Co., Ltd.) having a thickness of 75 μm was treated in the order of a swelling process, a dyeing process, a fixing process, a stretching process, a crosslinking process, and a drying process under the following conditions. The polarizer which concerns on was obtained.
a) Swelling step:
While immersing the PVA film in pure water (liquid temperature 30 ° C.) for 36 seconds, the film was stretched uniaxially to 2.2 times the original length.
b) Dyeing process:
The PVA film after swelling was immersed for 32 seconds in a 0.04 mass% iodine solution (liquid temperature 30 ° C.) in which iodine was dissolved in pure water, and the film was uniaxially stretched to 3.3 times the original length.
c) Fixing process:
While immersing the dyed PVA film for 20 seconds in a solution of boric acid and potassium iodide dissolved in pure water (boric acid concentration 3 mass%, potassium iodide concentration 3 mass%, liquid temperature 30 ° C.), The film was stretched in a uniaxial direction up to 3.6 times the original length.
d) Stretching process:
The PVA film after the immobilization treatment is immersed for 70 seconds in a solution in which boric acid and potassium iodide are dissolved in pure water (boric acid concentration 4 mass%, potassium iodide concentration 5 mass%, liquid temperature 60 ° C.). However, the film was stretched uniaxially up to 5.9 times the original length.
e) Crosslinking step:
The PVA fill was immersed for 30 seconds in a solution of triformylmethane and potassium iodide dissolved in pure water (triformylmethane 1 mass%, potassium iodide 4 mass%, liquid temperature 30 ° C.).
f) Post process:
The PVA film was immersed for 30 seconds in a solution of ethyl alcohol and potassium iodide dissolved in pure water (ethyl alcohol 10 mass%, potassium iodide 4 mass%, liquid temperature 30 ° C.).
g) Drying process:
The film was dried by exposure to hot air at 60 ° C. for about 120 seconds.
The thickness of the polarizer obtained as described above was 27 μm.

A triacetyl cellulose film (manufactured by Fuji Film Co., Ltd., trade name: T-80UZ) having a thickness of 80 μm was laminated on both surfaces of the polarizer via an adhesive to produce a polarizing plate.
The single-piece transmittance of the polarizing plate (made by laminating a triacetyl cellulose film on a polarizer) immediately after production was 44.3%, and the degree of polarization P1 was 99.85%.
Further, the parallel transmittance at each wavelength was measured for the polarizing plate immediately after production. The result is shown in FIG.

  Next, this polarizing plate was left for 1000 hours in an environment of a temperature of 80 ° C. and a humidity of substantially 0%. The parallel transmittance of the polarizing plate after the high temperature environment test was measured. The result is shown in FIG.

Further, the polarizing plate immediately after the production was left in an environment of a temperature of 60 ° C. and a humidity of 90% for 1000 hours. The parallel transmittance of the polarizing plate after the high humidity environment test was measured. The result is shown in FIG. Furthermore, when the polarization degree P2 was measured about the polarizing plate after this high humidity environment test, polarization degree P2 was 99.188%. However, the degree of polarization was also measured during the middle of the environmental test (500 hours), as shown in FIG.
From the above, the degree of polarization change (P2-P1) of the polarizing plate of Example 1 was −0.662.

(Comparative Example 1)
F) A polarizer was produced in the same manner as in Example 1 except that no post-process was performed (alcohol treatment was not performed).

The thickness of the obtained polarizer was 27 μm.
A triacetyl cellulose film was laminated on both sides of this polarizer in the same manner as in Example 1 to produce a polarizing plate.
About the polarizing plate of this comparative example 1, it carried out similarly to Example 1, and measured the single-piece | unit transmittance | permeability and polarization degree P1 immediately after preparation. As a result, the single transmittance of the polarizing plate immediately after production was 44.0%, and the degree of polarization P1 was 99.92%.
Further, the parallel transmittance at each wavelength was measured for the polarizing plate immediately after production. The result is shown in FIG.

  The polarizing plate of Comparative Example 1 was subjected to a high temperature environment test (temperature 80 ° C., humidity 0%, 1000 hours) in the same manner as in Example 1, and the parallel transmittance of the polarizing plate after the high temperature environment test was measured. did. The result is shown in FIG.

Further, the polarizing plate of Comparative Example 1 was subjected to a high humidity environment test (temperature 60 ° C., humidity 90%, 1000 hours) in the same manner as in Example 1, and the polarizing plate after the high humidity environment test was parallel. The transmittance was measured. The result is shown in FIG. Furthermore, when the polarization degree P2 was measured about the polarizing plate after this high-humidity environment test, polarization degree P2 was 99.846%. However, the degree of polarization was also measured during the middle of the environmental test (500 hours), as shown in FIG.
From the above, the degree of polarization change (P2-P1) of the polarizing plate of Comparative Example 1 was −0.074.

(Comparative Example 2)
A polarizer was prepared in the same manner as in Example 1 except that e) no triformylmethane was added in the crosslinking step and f) ethyl alcohol was not added in the subsequent step. .

The thickness of the obtained polarizer was 27 μm.
A triacetyl cellulose film was laminated on both sides of this polarizer in the same manner as in Example 1 to produce a polarizing plate.
About the polarizing plate of this comparative example 2, it carried out similarly to Example 1, and measured the single-piece | unit transmittance | permeability and polarization degree P1 immediately after preparation. As a result, the single transmittance of the polarizing plate immediately after production was 44.6%, and the polarization degree P1 was 99.80%.
Further, the parallel transmittance at each wavelength was measured for the polarizing plate immediately after production. The result is shown in FIG.

  The polarizing plate of Comparative Example 2 was subjected to a high temperature environment test (temperature 80 ° C., humidity 0%, 1000 hours) in the same manner as in Example 1, and the parallel transmittance of the polarizing plate after the high temperature environment test was measured. did. The result is shown in FIG.

Further, the polarizing plate of Comparative Example 2 was subjected to a high humidity environment test (temperature 60 ° C., humidity 90%, 1000 hours) in the same manner as Example 1, and the polarizing plate after the high humidity environment test was parallel to the polarizing plate. The transmittance was measured. The result is shown in FIG. Furthermore, when the polarization degree P2 was measured about the polarizing plate after this high-humidity environment test, polarization degree P2 was 97.743%. However, the degree of polarization was also measured during the middle of the environmental test (500 hours), as shown in FIG.
From the above, the degree of polarization change (P2-P1) of the polarizing plate of Comparative Example 2 was −2.057.

(Evaluation)
It is clear that the polarizer containing trialdehyde (Example 1 and Comparative Example 1) has a very small change in polarization degree under high humidity conditions and is excellent in moisture resistance durability. In addition, the alcohol-treated polarizer (Example 1) was not colored under high temperature conditions. On the other hand, as shown in FIG. 3, the polarizer of Comparative Example 1 that was not subjected to alcohol treatment had extremely low transmittance and coloration under high temperature conditions.

The reference drawing which shows an example of the production process of a polarizer. The graph which shows the parallel transmittance | permeability in each wavelength before the environmental test of each polarizing plate of Example 1 and Comparative Examples 1 and 2. FIG. The graph which shows the parallel transmittance | permeability in each wavelength after the high temperature environmental test of each polarizing plate of Example 1 and Comparative Examples 1 and 2. FIG. The graph which shows the parallel transmittance | permeability in each wavelength after the high humidity environment test of each polarizing plate of Example 1 and Comparative Examples 1 and 2. FIG. The graph which shows the polarization degree change amount of each polarizing plate of Example 1 and Comparative Examples 1 and 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Hydrophilic polymer film, 31 ... Swelling bath, 32 ... Dyeing bath, 33, 34 ... Fixing bath, 35 ... Crosslinking bath, 36 ... Post bath, 37 ... Washing bath, 38 ... Drying means

Claims (7)

A dyeing process for dyeing a hydrophilic polymer film with a dichroic substance;
A stretching step of stretching the hydrophilic polymer film;
A crosslinking step of crosslinking the hydrophilic polymer with trialdehyde;
After the cross-linking process, a post-process for contacting the hydrophilic polymer film with alcohol;
A method for producing a polarizer, comprising:   The method for producing a polarizer according to claim 1, wherein the trialdehyde contains triformylmethane.   The manufacturing method of the polarizer of Claim 1 or 2 with which the said alcohol contains a C1-C4 lower alcohol.   The said post process is a manufacturing method of the polarizer in any one of Claims 1-3 which immerses the said hydrophilic polymer film in the solution of alcohol concentration 3 mass%-20 mass%.   The method for producing a polarizer according to claim 1, wherein the hydrophilic polymer film is a polyvinyl alcohol film.   The manufacturing method of the polarizer in any one of Claims 1-5 which has a fixing process which fixes a hydrophilic polymer with the compound containing boron or a boron before the said bridge | crosslinking process.   An image display apparatus provided with the polarizer obtained by the method in any one of Claims 1-6.

Images