JP2008158020A - Polarizer, manufacturing method of polarizer, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizer which has very small polarization degree change. <P>SOLUTION: The polarizer is constituted to contain trialdehyde in a hydrophilic polymer film that contains a dichroic substance. Trialdehyde is at least either triformylmethane or tris-(3-oxopropyl) isocyanurate. The hydrophilic polymer film that contains the dichroic substance is a poly(vinyl alcohol) film containing a dichroic substance, such as iodine. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarizer used in a liquid crystal display device and the like, a manufacturing method thereof, and 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, for the purpose of improving the dimensional stability of a PVA film polarizer, a polarizer obtained by crosslinking a dyed PVA film with a dialdehyde such as glyoxal is disclosed (Patent Document 2).

JP 2003-270440 A Japanese Patent No. 3357109

As a result of various studies for preventing a decrease in the degree of polarization over time with respect to a polarizer made of a PVA-based film that has been dyed, the present inventors have not disclosed the above-described trio that is not disclosed in Patent Document 2. The inventors have found that a polarizer having a small change in the degree of polarization with time can be obtained by crosslinking with an aldehyde, thereby completing the present invention.
It is an object of the present invention to provide a polarizer having a very small change in polarization degree and a method for manufacturing the polarizer.

Therefore, a first means of the present invention provides a polarizer in which trialdehyde is contained in a hydrophilic polymer film containing a dichroic substance.
The second means of the present invention provides a polarizer obtained by bringing a hydrophilic polymer film dyed with a dichroic substance into contact with trialdehyde and subjecting it to a crosslinking treatment.

A preferred embodiment of the present invention provides the polarizer, wherein the trialdehyde is a trialdehyde having a molecular weight of 300 or less.
Moreover, the preferable aspect of this invention provides the said polarizer whose said trialdehyde is at least any one of a triformyl methane or isocyanuric acid tris (3-oxopropyl).
Furthermore, the preferable aspect of this invention provides the said polarizer in which the said trialdehyde contains 0.07-1.0 mass%.
Moreover, the preferable aspect of this invention provides the said polarizer whose said hydrophilic polymer film is a polyvinyl alcohol-type film.

The third means 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. A method for producing a polarizer is provided.
According to a fourth means of the present invention, after the hydrophilic polymer film is dyed with a dichroic substance, the hydrophilic polymer is fixed with boric acid or a compound containing boric acid, and the hydrophilic polymer film is uniaxially fixed. Provided is a method for producing a polarizer that is stretched and crosslinks the stretched hydrophilic polymer with trialdehyde.

  In a preferred embodiment of the present invention, the crosslinking step includes a step of immersing the hydrophilic polymer film in a crosslinking bath containing trialdehyde, and the trialdehyde concentration in the crosslinking bath is 0.01% by mass to 20% by mass. The manufacturing method of the said polarizer which is is provided.

  The fifth means of the present invention provides an image display device comprising any one of the above polarizers.

The polarizer of the present invention has a very small change in the degree of polarization with time, and is extremely excellent in maintaining water resistance and polarization characteristics.
Moreover, the manufacturing method of the polarizer of this invention can manufacture efficiently the polarizer with a very small change of the polarization degree with progress of time.

In the polarizer of the present invention, trialdehyde is contained in a hydrophilic polymer film containing a dichroic substance. As the polarizer, for example, a film obtained by bringing a hydrophilic polymer film dyed with a dichroic substance into contact with trialdehyde and performing a crosslinking treatment can be used.
Hereinafter, the polarizer of this invention and the manufacturing method of a polarizer are demonstrated.

<Polarizer>
The polarizer of the present invention is composed of a stretched film containing a hydrophilic polymer, trialdehyde, and a dichroic substance. Such a polarizer has excellent water resistance, and the change in the degree of polarization is small even after a long period of 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 hydrophilic polymer to partially bind each polymer chain. It is presumed to be crosslinked.

(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. Components that can be copolymerized with vinyl acetate such as unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, derivatives thereof, α-olefins having 2 to 30 carbon atoms, etc. as PVA polymers Modified PVA containing can also be used. In addition to modified PVA containing an acetoacetyl group, a sulfonic acid group, a carboxyl group, etc., modified PVA such as polyvinyl fulmar, polyvinyl acetal, and ethylene copolymer can be used as the PVA polymer.

  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 film can be obtained by a casting method in which a resin composition containing a PVA polymer is dissolved in water or / and an appropriate organic solvent such as DMSO, and the resin solution is formed into a film. 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.

(Trialdehyde)
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 the molecules of the hydrophilic polymer.
Specific examples of the trialdehyde include triformylmethane and isocyanuric acid tris (3-oxopropyl). These trialdehydes may be contained singly or in combination of two or more.
The content of trialdehyde is not particularly limited, but if it is too small, the crosslinking effect cannot be sufficiently exhibited, and if it is too large, the mechanical strength of the film may be lowered. The content is preferably 0% by mass (ratio to the whole film), more preferably 0.1 to 0.3% by mass.

(Dichroic material)
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 the following color index (CI). There are many 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. The dichroic substance may be contained alone or in combination of two or more.

The polarization degree of the polarizer of the present invention is preferably 99% or more, more preferably 99.5% or more, and the single transmittance thereof is preferably 40% or more, more preferably 42% or more.
The amount of change in polarization degree of the polarizer of the present invention is preferably −0.08% or less, more preferably −0.05% 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.

(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 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. A phase difference plate or the like is used when changing linearly polarized light to elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light to linearly polarized light, or changing the polarization direction of linearly polarized light. 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 For example, 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.

<Method for producing polarizer>
Next, the manufacturing method of the polarizer of this invention is demonstrated.
The polarizer of the present invention can be obtained by impregnating a polymer film containing a hydrophilic polymer as a main component with a dichroic substance, subjecting it to a stretching treatment, and bringing it into contact with trialdehyde. Hereinafter, each step will be described.

(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 the following description of the manufacturing method, the manufacturing method using a PVA film which is a preferred example of the hydrophilic polymer film will be mainly described. But the hydrophilic polymer film used for the manufacturing method of the polarizer of this invention is not limited to a PVA-type film.

As the PVA film, an unstretched film is usually used. 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 is guided into the swelling bath through a conveyance roller.
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, it is preferable that the liquid temperature of the swelling bath is heated to 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.

  Before the dyeing process, the PVA film is immersed in a swelling bath to remove dirt on the surface of the film, and the PVA film is swollen with water to prevent uneven introduction of the dichroic material described later. it can.

(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 a ratio of 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 7% by mass, Especially preferably, it is 0.02 mass%-5 mass%.

  As the dichroic substance, those exemplified above can be used as appropriate. One type of dichroic substance may be used, or two or more types may be used in combination. The dichroic material is preferably water-soluble. For this reason, it is preferable to use, for example, an organic dye or the like into which a hydrophilic substituent such as a sulfonic acid group, an amino group, or a hydroxyl group is introduced in the form of a free acid and its alkali metal salt, ammonium salt, or amine salt.

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. One kind of these may be used, or two or more kinds may be used in combination. When two or more types are used in combination, for example, a combination of boric acid and borax is preferable, and the addition ratio (molar ratio) is preferably in the range of 4: 6 to 9: 1, and 5.5: 4. The range of 5-7: 3 is more preferred, and 6: 4 is most preferred.

  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 polymer 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.

  In addition, when a stretching process is not performed in any step between the swelling process and the fixing process and a separate stretching process is provided, the stretching method is a wet stretching method in which a PVA film is stretched in a stretching bath. Any of the dry stretching methods of stretching the water-containing PVA film in the air may be used. 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, ethanol 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.

As the trialdehyde, those exemplified above can be appropriately used. Trialdehyde may be used alone or in combination of two or more.
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 method for producing a polarizer of the present invention, trialdehyde is used as a crosslinking agent. For this reason, the crosslinking process performed in order to obtain a polarizer excellent in water resistance and having a small change in polarization degree with time can be completed in a relatively short time. That is, since the trialdehyde has three CHO groups, it easily reacts with an OH group such as a PVA polymer and exhibits a crosslinking effect quickly. In addition, aldehydes having a valence of 4 or more have poor stability per se, and are unlikely to exhibit a good crosslinking effect like trialdehyde.

(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 heat drying, for example, 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.
In addition, you may perform a washing | cleaning process between the said bridge | crosslinking process and a drying process. The washing step is a step of washing away unnecessary residues adhering to the film that has undergone each of the above steps. The washing step is usually performed by immersing the film in water.

  A polarizer (dyed PVA-based film) is obtained through each processing step as described above. According to the method for producing a polarizer of this embodiment, it is possible to produce a polarizer having excellent water resistance and a small change in polarization degree with time in a relatively short time. Therefore, according to the production method of the present invention, it is possible to improve the production speed of a polarizer having excellent polarization characteristics.

(Modification of the production method of the present invention)
In the embodiment of the above production method, the method of immersing the hydrophilic polymer film in the crosslinking solution containing trialdehyde was shown, but instead, the trialdehyde was attached to the hydrophilic polymer film and contained in the film. May be.
Specifically, for example, a solution obtained by dissolving trialdehyde in a solvent such as water is applied on one or both sides of a hydrophilic polymer film by a spray method, and b) by a printing method such as a gravure plate. The method of apply | coating to the single side | surface or both surfaces of a hydrophilic polymer film, c) In addition, the method of apply | coating to the single side | surface or both surfaces of a hydrophilic polymer film by various coating methods, etc. are mentioned.
As the solution, the cross-linking solution exemplified in the cross-linking step is used.
Trialdehyde attached to the surface of the hydrophilic polymer film is contained in the film and crosslinks the hydrophilic polymer.
Moreover, you may abbreviate | omit any process among each said process as needed. Further, if necessary, any two or more steps can be performed simultaneously.

  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 polarization degree and single transmittance:
The degree of polarization is determined by using a spectrophotometer (Murakami Color Research Laboratory, trade name: DOT-3C, error ± 0.03%) according to Japan Electronic Machinery Industry Standard (EIAJ) LD-201-1983, using a C light source The measurement was performed under the condition of a 2-degree visual field.
The 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 polarization degree, the polarization degree of the polarizing plate before the test (this polarization degree is referred to as “polarization degree P1”) is measured.
The polarizing plate is held between a pair of mesh sheets and left for 1000 hours in an environment of a temperature of 60 ° C. and a humidity of 90%, and then the polarization degree of the polarizing plate (hereinafter, the degree of polarization after this environmental test). (Referred to as “degree of polarization P2”).
The measurement results of the degree of polarization P1 and the degree of polarization P2 are substituted into the following formula to determine the amount of polarization degree change.
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 30 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) 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 transmittance of this polarizing plate (thick polarizer laminated with a triacetyl cellulose film) was 43.43%, and the degree of polarization P1 was 99.893%.
Next, the polarizing plate was held between a pair of mesh sheets and allowed to stand in an environment of a temperature of 60 ° C. and a humidity of 90% for 1000 hours, and then the degree of polarization P2 of the polarizing plate was measured. As a result, the degree of polarization P2 was 99.871%.
However, for reference, the degree of polarization was also measured during the middle of the environmental test (500 hours) (see FIG. 1).
From the above, the amount of change in polarization degree of the polarizing plate of Example 1 was −0.022.

Moreover, the weight of the polarizer obtained through each said process was measured. This polarizer was immersed in hot water at 95 ° C. for 10 minutes, and the remaining film pulled up from the hot water (film which remained undissolved) was exposed to hot air at 60 ° C. and sufficiently dried. The weight was measured.
As a result, the insolubilization rate calculated | required by the following formula was 66.5% (refer FIG. 2).
Insolubilization rate = (weight of remaining film after hot water treatment / weight of film before hot water treatment) × 100.
However, the amount of change in polarization degree and the insolubilization rate are both average values of two samples.

(Example 2)
A polarizer was produced in the same manner as in Example 1 except that the crosslinking step was changed as follows.
e) Crosslinking step:
In a solution of tris (3-oxopropyl) isocyanurate and potassium iodide dissolved in pure water (1% by mass of tris (3-oxopropyl) isocyanurate, 4% by mass of potassium iodide, liquid temperature 30 ° C.), The PVA fill was immersed for 30 seconds.

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.
For this polarizing plate, the single transmittance and the polarization degrees P1 and P2 were determined under exactly the same conditions as in Example 1, and the insolubilization rate was determined for the polarizer.
As a result, the single transmittance of the polarizing plate was 42.70%, the polarization degree P1 was 99.953%, the polarization degree P2 was 99.922%, and the amount of change in the polarization degree was −0.031. It was.
The insolubilization rate of the polarizer was 77.2%.

  Triformylmethane is represented by the formula (a), and tris (3-oxopropyl) isocyanurate is represented by the formula (b).

(Comparative Example 1)
A polarizer was produced in the same manner as in Example 1 except that the crosslinking step was changed as follows.
e) Crosslinking step:
The PVA film was immersed for 30 seconds in a solution in which glyoxal and potassium iodide were dissolved in pure water (glyoxal 1 mass%, potassium iodide 4 mass%, liquid temperature 30 ° C.).

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.
For this polarizing plate, the single transmittance and the polarization degrees P1 and P2 were determined under exactly the same conditions as in Example 1, and the insolubilization rate was determined for the polarizer.
As a result, the single transmittance of the polarizing plate was 42.40%, the polarization degree P1 was 99.916%, the polarization degree P2 was 99.800%, and the degree of polarization change was −0.116. It was.
The insolubilization rate of the polarizer was 4.4%.

(Comparative Example 2)
A polarizer was produced in the same manner as in Example 1 except that the crosslinking step was changed as follows (no crosslinking agent was added).
e) Crosslinking step:
The PVA film was immersed in pure water at a liquid temperature of 30 ° C. for 30 seconds.

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.
For this polarizing plate, the single transmittance and the polarization degrees P1 and P2 were determined under exactly the same conditions as in Example 1, and the insolubilization rate was determined for the polarizer.
As a result, the single transmittance of the polarizing plate was 42.74%, the polarization degree P1 was 99.961%, the polarization degree P2 was 99.867%, and the degree of polarization change was −0.094. It was.
The insolubilization rate of the polarizer was 0.2%.

(Evaluation)
It is clear that the polarizers (Example 1 and Example 2) containing trialdehyde have a very small amount of change in polarization degree and are excellent in water resistance and polarization characteristics over time. On the other hand, it is clear that the polarizer treated with dialdehyde (Comparative Example 1) and the untreated polarizer (Comparative Example 2) have a very large change in polarization degree and are very fragile due to water absorption.

The graph which shows the polarization degree variation | change_quantity of each polarizer of an Example and a comparative example. The graph which shows the insolubilization rate of each polarizer of an Example and a comparative example.

Claims (10)

  A polarizer characterized in that trialdehyde is contained in a hydrophilic polymer film containing a dichroic substance.   A polarizer obtained by bringing a hydrophilic polymer film dyed with a dichroic substance into contact with trialdehyde to perform a crosslinking treatment.   The polarizer according to claim 1 or 2, wherein the trialdehyde is an aldehyde having a molecular weight of 300 or less.   The polarizer according to any one of claims 1 to 3, wherein the trialdehyde is at least one of triformylmethane and isocyanuric acid tris (3-oxopropyl).   The polarizer according to claim 1, wherein trialdehyde is contained in an amount of 0.07 to 1.0% by mass.   The polarizer according to any one of claims 1 to 5, wherein the hydrophilic polymer film is a polyvinyl alcohol film.   Production of a polarizer comprising a dyeing step for dyeing a hydrophilic polymer film with a dichroic substance, a drawing step for drawing the hydrophilic polymer film, and a crosslinking step for crosslinking the hydrophilic polymer with trialdehyde Method.   After dyeing the hydrophilic polymer film with a dichroic substance, the hydrophilic polymer is fixed with boron or a compound containing boron, the hydrophilic polymer film is stretched in a uniaxial direction, and the stretched hydrophilic polymer is crosslinked with trialdehyde. A method for producing a polarizer, comprising:   The cross-linking step has a step of immersing the hydrophilic polymer film in a cross-linking bath containing trialdehyde, and the trialdehyde concentration in the cross-linking bath is 0.01% by mass to 20% by mass. The manufacturing method of the polarizer of description.   An image display apparatus provided with the polarizer in any one of Claims 1-6.

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