JP2017102467A - Method for producing polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polarizing film capable of obtaining a polarizing film having excellent polarization characteristics.SOLUTION: There is provided a method for producing a polarizing film that produces a polarizing film obtained by dying a resin film with a dichroic substance while conveying a belt-like resin film containing a polyvinylalcohol-based resin as a formation material in a longitudinal direction which includes: a crosslinking step of immersing a resin film died with a dichroic substance in a crosslinking bath containing a first crosslinking agent, and obtaining a crosslinked film obtained by crosslinking the resin film died with the dichroic substance with a first crosslinking agent; and a cleaning step of cleaning the crosslinked film 1 with an aqueous solution containing a second crosslinking agent, where in the cleaning step, the crosslinked film is controlled so that the total of the first crosslinking agent and the second crosslinking agent contained in the aqueous solution is in a range of 0.003 pts.mass or more and less than 0.1 pts.mass with respect to 100 pts.mass of water.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a polarizing film.

  Liquid crystal display devices are used in personal computers, TVs, monitors, mobile phones, PDAs (Personal Digital Assistants), and the like. In recent years, with the improvement in performance and thickness of a liquid crystal display device, the polarizing film used in the liquid crystal display device is also required to be thin. For example, a thin polarizing film having a thickness of 10 μm or less can be obtained by dyeing and stretching a laminate in which a polyvinyl alcohol-based resin layer is provided on the surface of a thermoplastic resin substrate with a dichroic substance ( Patent Document 1).

JP 2009-0986653 A

  For example, iodine is used as the dichroic substance. Iodine in the polarizing film exists as an iodine complex, and the iodine complex itself is oriented depending on the orientation of the polyvinyl alcohol resin. It is known that this iodine complex absorbs light in the visible region, so that the polarizing film exhibits polarization characteristics (polarization degree). Therefore, as a method for improving the degree of polarization of the polarizing film, a method for improving the orientation of the polyvinyl alcohol resin is conceivable.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the manufacturing method of the polarizing film from which the polarizing film which has the outstanding polarizing characteristic is obtained.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have disturbed the orientation of the iodine complex in the cleaning step in the method for producing a polarizing film, resulting in a decrease in the degree of polarization of the resulting polarizing film. I understood it. In particular, when the thickness of the polarizing film is 10 μm or less, the iodine complex existing on the surface of the polarizing film increases compared to the case where the thickness of the polarizing film exceeds 10 μm. It turns out that it cannot be overlooked. On the other hand, when the thickness of the polarizing film exceeds 10 μm, since the polarizing film has a sufficient thickness, the deterioration of the polarizing property in the washing process has not been recognized.

  The inventors have found that the above-described object can be achieved by the following polarizing film manufacturing method, and have completed the present invention.

  That is, one embodiment of the present invention is a polarizing film manufacturing method for manufacturing a polarizing film in which a resin film is dyed with a dichroic substance while a belt-shaped resin film having a polyvinyl alcohol resin as a forming material is conveyed in the longitudinal direction. A resin film dyed with a dichroic material is immersed in a crosslinking bath containing a first crosslinking agent, and the resin film dyed with a dichroic material is crosslinked with the first crosslinking agent. A crosslinking step for obtaining a crosslinked film; and a washing step for washing the crosslinked film with an aqueous solution containing a second crosslinking agent. In the washing step, the first crosslinking agent and the second crosslinking agent contained in the aqueous solution. The manufacturing method of the polarizing film which manages so that the sum total of it may become the range of 0.003 mass part or more and less than 0.1 mass part with respect to 100 mass parts of water is provided.

  In one embodiment of the present invention, prior to the crosslinking step, a polyvinyl alcohol-based resin solution is applied to one surface of the substrate film while the belt-shaped substrate film is conveyed in the longitudinal direction, and the polyvinyl alcohol-based resin is applied to one surface. A resin layer forming step for forming a resin layer using a resin as a forming material, and a stretched base film in which the laminate obtained in the resin layer forming step is stretched while being conveyed in the longitudinal direction, and the base film is stretched, A laminating step of obtaining a laminated film in which a resin film formed on one surface of the stretched substrate film is laminated.

  In one embodiment of the present invention, the second crosslinking agent is preferably a boron compound.

  In one embodiment of the present invention, the first crosslinking agent and the second crosslinking agent are preferably the same compound.

  In one embodiment of the present invention, the dichroic material is preferably iodine.

  In one embodiment of the present invention, the aqueous solution preferably contains iodide.

  In one embodiment of the present invention, the iodide is preferably potassium iodide.

  According to one aspect of the present invention, there is provided a method for producing a polarizing film from which a polarizing film having excellent polarizing properties can be obtained.

It is a flowchart which shows the manufacturing method of the polarizing film which concerns on 1st Embodiment of this invention. It is a cross-sectional schematic diagram which shows the example of arrangement | positioning of the main apparatuses which concern on the manufacturing method of the polarizing film of this invention. It is a flowchart which shows the manufacturing method of the polarizing film which concerns on 2nd Embodiment of this invention.

<First Embodiment>
Hereinafter, the manufacturing method of the polarizing film which concerns on 1st Embodiment of this invention is demonstrated using a code | symbol suitably, referring FIG. 1 and FIG. In all the following drawings, in order to make the drawings easy to see, the dimensions and ratios of the respective constituent elements may be appropriately changed and illustrated.

[Production method of polarizing film]
FIG. 1 is a flowchart showing a method for manufacturing a polarizing film according to the first embodiment of the present invention. The manufacturing method of the polarizing film of this embodiment is equipped with the bridge | crosslinking process containing step S11 and step S12 mentioned later, the washing | cleaning process containing step S13, and the drying process containing step 14.

  In step S11, a belt-shaped resin film (hereinafter referred to as a resin film) using a polyvinyl alcohol-based resin as a forming material is dyed with a dichroic substance.

  Next, in step S12, a resin film dyed with a dichroic substance (hereinafter, dyed film) is immersed in a crosslinking bath containing a first crosslinking agent. At this time, the resin film is stretched in the longitudinal direction in a crosslinking bath (not shown). By immersing the dyed film in the crosslinking bath, a crosslinked film obtained by crosslinking the dyed film with the first crosslinking agent is obtained.

  Further, in step S13, the crosslinked film is washed with an aqueous solution containing the second crosslinking agent. In step S14, the washed crosslinked film is dried.

  FIG. 2 is a schematic cross-sectional view showing one example of the arrangement of main devices according to the method for manufacturing a polarizing film of the present embodiment. As shown in FIG. 2, in this embodiment, the polarizing film 19 in which the resin film 11 is dyed with a dichroic substance is conveyed while the resin film 11 is conveyed in the longitudinal direction by the nip rolls 101 to 105 and the conveying rolls 111 to 119. To manufacture.

  The resin film 11 is supplied from one side in a state of being wound around the feeding roll 21. First, the resin film 11 is dye | stained by being immersed in the dyeing tank 23 (step S11). Next, the obtained dyed film 13 is immersed and stretched in the crosslinking tank 25, whereby the crosslinked film 15 is obtained (step S12). Further, the crosslinked film 15 is cleaned by immersing it in the cleaning tank 27 (step S13). The washed crosslinked film 15 is dried by passing it through a drying furnace 29 (step S14). The polarizing film 19 is obtained by the above processing.

[Resin film]
In FIG. 2, a material for forming the resin film 11 according to the present embodiment is preferably a polyvinyl alcohol (hereinafter, PVA) resin that has been conventionally used for polarizing films. As the PVA resin, a PVA resin or a PVA resin derivative is used.

  Examples of the PVA resin derivative include polyvinyl formal, polyvinyl acetal, polyvinyl butyral, and modified products thereof. As this modified product, for example, the above-mentioned PVA resin derivative is modified with an olefin such as ethylene or propylene, an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or crotonic acid, or an alkyl ester of an unsaturated carboxylic acid, acrylamide or the like. The thing which was done is mentioned.

  1000-10000 are preferable and, as for the polymerization degree of PVA-type resin, 1500-5000 are more preferable. Moreover, 85 mol% or more is preferable, as for the saponification degree of PVA-type resin, 90 mol% or more is more preferable, and 99 mol% or more is further more preferable.

  The resin film 11 described above may contain an additive such as a plasticizer. Examples of the plasticizer include polyols such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol, and polyol condensates. The content of the plasticizer in the resin film 11 is not particularly limited, but is preferably 20% by mass or less.

  In the present embodiment, the thickness of the unstretched resin film 11 is preferably 5 to 150 μm, more preferably 5 to 80 μm, and further preferably 5 to 40 μm.

[Crosslinking process]
(staining)
In FIG. 2, the resin film 11 according to the present embodiment is dyed for the purpose of adsorbing and orienting the dichroic substance on the resin film 11. Specifically, the resin film 11 is dyed with a dichroic substance by immersing the resin film 11 in a solution containing the dichroic substance.

  As a dichroic substance used for dyeing | staining of the resin film 11, a well-known dichroic pigment | dye is mentioned as a pigment | dye for iodine and a polarizing film, for example, and an iodine is preferable.

  Hereinafter, the description is limited to the case where iodine is used as the dichroic substance. An iodine solution is used for dyeing the resin film 11 according to this embodiment, and an iodine aqueous solution is preferably used. As the iodine aqueous solution, an aqueous solution containing iodine and iodine ions as dissolution aids is used. 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. Is preferred, and potassium iodide is more preferred.

  The concentration of iodine in the iodine solution is preferably 0.01% by mass or more and 0.5% by mass or less, more preferably 0.02% by mass or more and 0.4% by mass or less, and 0.2% by mass or more and 0.38% by mass. % Or less is more preferable, and 0.2% by mass or more and 0.35% by mass or less is particularly preferable. On the other hand, the concentration of iodide in the iodine solution is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.02% by mass or more and 8% by mass or less.

  In the dyeing | staining of the resin film 11 which concerns on this embodiment, 20-50 degreeC is preferable and the temperature of an iodine solution has more preferable 25-40 degreeC. Moreover, 10 to 300 seconds are preferable and, as for the time immersed in an iodine solution, 20 to 240 seconds are more preferable.

(Crosslinking)
In FIG. 2, crosslinking of the dyed film 13 according to this embodiment is performed for the purpose of making the dyed film 13 water resistant. Specifically, the dyed film 13 is immersed in an iodide aqueous solution (hereinafter, a crosslinking bath) containing a first crosslinking agent.

  In the present embodiment, when iodide is contained in the crosslinking bath, the polarization characteristics of the obtained polarizing film 19 can be made uniform in the plane, and the hue of the polarizing film 19 can be prepared. Examples of the iodide contained in the crosslinking bath include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, and iodine. Tin iodide or titanium iodide is preferred, and potassium iodide is more preferred.

  The concentration of iodide in the crosslinking bath is preferably 4% by mass or more, more preferably 4% by mass or more and 12% by mass or less, further preferably 4.5% by mass or more and 11% by mass or less, and 5% by mass or more and 10% by mass or less. The following are particularly preferred:

  In the present embodiment, the PVA-based resin is crosslinked by including the first crosslinking agent in the crosslinking bath. As a 1st crosslinking agent contained in a crosslinking bath, a boron compound, glyoxal, or glutaraldehyde is preferable, and a boron compound is more preferable. Examples of the boron compound include boric acid and borax.

  The concentration of the first crosslinking agent in the crosslinking bath is preferably 2% by mass or more and 8% by mass or less, more preferably 2.5% by mass or more and 7% by mass or less, and further preferably 3% by mass or more and 6% by mass or less. When the concentration of the first cross-linking agent in the cross-linking bath is lower than 2% by mass, the water resistance and the degree of polarization of the obtained polarizing film 19 tend to decrease. On the other hand, when the concentration of the first crosslinking agent in the crosslinking bath is higher than 8% by mass, the resin film 11 tends to be difficult to be stretched.

Here, the mechanism by which the dyed film 13 is water-resistant will be described by exemplifying the case where PVA is used as the forming material of the dyed film 13 and boric acid is used as the first cross-linking agent. When immersing the dyed film 13 in the crosslinking bath, PVA hydroxy group and a borate ion B (OH) ₄ ^- and hydroxy groups react the hydrogen bond or an inorganic acid ester binding occurs. As a result, a stable six-membered ring structure containing these bonds is formed and crosslinked. PVA has a hydroxy group every other carbon atom, and since each hydroxy group is crosslinked, a plurality of PVA chains are combined to form a network network. By forming a network network in this way, it is considered that PVA becomes insoluble or insoluble in water and the water resistance of the dyed film 13 is improved. Moreover, it can suppress that the dye | stained iodine flows out by a network-like network, and can suppress the fall of the polarization characteristic of the polarizing film 19 obtained.

(Stretching)
In FIG. 2, you may extend | stretch with the bridge | crosslinking of the dyeing | staining film 13 which concerns on this embodiment. By extending | stretching with the bridge | crosslinking of the dyeing | staining film 13, since the orientation of a dichroic substance improves with the orientation of PVA-type resin, the polarization characteristic of the polarizing film 19 obtained can be improved. Furthermore, if the orientation of the PVA-based resin is improved by stretching, it is considered that the dyed film 13 becomes more insoluble and the water resistance is further improved as compared with the case where the stretching is not performed.

The stretching of the dyed film 13 according to this embodiment is preferably wet uniaxial stretching.
The draw ratio is preferably 4 to 7 times, more preferably 5 to 6.8 times, still more preferably 5.5 to 6.5 times based on the unstretched resin film 11. If the draw ratio is higher than 7 times, the dyed film 13 tends to break. Moreover, when a draw ratio is lower than 4 times, the polarizing characteristic of the polarizing film 19 obtained may fall. The thickness of the resin film 11 obtained by crosslinking and stretching the dyed film 13 is preferably 5 to 80 μm.

  If the draw ratio in the cross-linking step of the present embodiment is within the above range, it can be performed in a multi-step in one cross-linking bath. Examples of the multistage stretching method include inter-roll stretching or tenter stretching in which stretching is performed with a difference in peripheral speed between a plurality of pinch rolls (nip rolls) provided in a crosslinking bath.

  In the crosslinking of the dyed film 13 according to this embodiment, the temperature of the crosslinking bath is preferably, for example, 30 ° C. or higher, and more preferably 40 to 85 ° C. Further, the immersion time in the crosslinking bath is preferably 10 to 1200 seconds, and more preferably 30 to 600 seconds.

[Washing process]
In FIG. 2, the cleaning process of the present embodiment is used in the above-described process, and is used for the purpose of reducing the agent left on the resin film 11, for example, excess dichroic substance and unreacted first cross-linking agent. Done. Specifically, the crosslinked film 15 is immersed in an aqueous solution containing a second crosslinking agent (hereinafter referred to as a washing bath).

  As the second cross-linking agent contained in the cleaning bath of the present embodiment, the same compound as the first cross-linking agent contained in the cross-linking bath can be used. For example, a boron compound, glyoxal or glutaraldehyde is used. Preferably, a boron compound is more preferable. Examples of the boron compound include boric acid and borax. In the present embodiment, the first crosslinking agent and the second crosslinking agent may be different or the same.

  The total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleaning bath is lower than the concentration of the first crosslinking agent in the crosslinking bath. Specifically, the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleaning bath is preferably 0.003 parts by mass or more, and 0.003 parts by mass or more with respect to 100 parts by mass of water. The amount is more preferably less than 0.1 parts by mass, and further preferably 0.005 parts by mass or more and less than 0.1 parts by mass. When the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleaning bath is less than 0.003 parts by mass, the polarization characteristics of the obtained polarizing film 19 tend to deteriorate. Further, when the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleaning bath is 0.1 parts by mass or more, cleaning of the drug remaining on the crosslinked film 15 becomes insufficient, This causes contamination of the surface of the obtained polarizing film 19.

  In the conventional method for producing a polarizing film, pure water such as ion-exchanged water or distilled water is used for the washing bath for the purpose of obtaining a sufficient washing effect. However, when the crosslinked film 15 is washed in a pure water washing bath, the first crosslinking agent is detached from the crosslinked structure derived from the first crosslinking agent contained in the crosslinked film 15 by hydrolysis, and the first crosslinking agent is obtained. Is easier to elute. When the first crosslinking agent is eluted, the crosslinked structure of the crosslinked film 15 is eliminated, and the dichroic substance incorporated in the crosslinked structure may be eluted.

  Moreover, after the first cross-linking agent is eliminated, a hydroxy group is generated. Furthermore, since the crosslinked film 15 has an unreacted hydroxy group that has not been crosslinked in the crosslinking step in addition to the hydroxy group, the crosslinked film 15 may swell or partially dissolve in a pure water washing bath. . Thereby, a dichroic substance may elute.

  Since the polarization characteristic of the obtained polarizing film 19 depends on the concentration of the dichroic substance, it is considered that the polarization characteristic of the polarizing film 19 is lowered.

  In the manufacturing method of the polarizing film of this embodiment with respect to the above-mentioned subject, the 1st crosslinking agent and the 2nd crosslinking agent are contained in the above-mentioned concentration range in the washing bath, so that the first crosslinking agent It is considered that elution and swelling and dissolution of the crosslinked film 15 are suppressed, and a decrease in polarization characteristics of the obtained polarizing film 19 is suppressed.

  In the cleaning step of the present embodiment, the first cross-linking agent contained in the cross-linking bath is mixed in the cleaning bath, but the first cross-linking agent and the second cross-linking agent contained in the cleaning bath are mixed. The total concentration is controlled so as not to exceed 0.1 parts by mass. For example, the amount of the first crosslinking agent mixed in the cleaning bath can be increased or decreased by adjusting the nip pressure of the nip roll 103 shown in FIG. In addition, when the cleaning bath is replaced with an unused cleaning bath by inspection or replacement, the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleaning bath is less than 0.003 parts by mass. Manage so that there is no. For example, a second crosslinking agent can be added to an unused cleaning bath to increase the concentration of the second crosslinking agent in the cleaning bath. By the above method, the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleaning bath can be controlled within the above range.

  In the cleaning step of the present embodiment, it is preferable that iodide is contained in the cleaning bath. By including iodide in the washing bath, the hue of the obtained polarizing film 19 can be prepared.

  As the iodide contained in the washing bath, the same iodide as that contained in the crosslinking bath can be used, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, iodide. Lead, copper iodide, barium iodide, calcium iodide, tin iodide or titanium iodide are preferred, and potassium iodide is more preferred.

  The concentration of iodide in the cleaning bath is preferably 0.8% by mass or more, more preferably 0.8% by mass or more and 5% by mass or less, and further preferably 0.8% by mass or more and 4.5% by mass or less. It is particularly preferably 8% by mass or more and 4.0% by mass or less.

  In the cleaning step of the present embodiment, the temperature of the cleaning bath is, for example, more preferably 15 to 60 ° C, and more preferably 20 to 45 ° C. Further, the immersion time in the washing bath is preferably 1 to 120 seconds, more preferably 3 to 90 seconds.

  In the present embodiment, the washing step can use a solution in which liquid alcohol such as methanol, ethanol, isopropyl alcohol, butanol, propanol or the like is blended as long as the effects of the present invention are not impaired. By using the liquid alcohol as described above, drying of the crosslinked film 15 can be accelerated in the subsequent drying step.

[Drying process]
In FIG. 2, the drying process of this embodiment is performed for the purpose of obtaining the polarizing film 19 having a desired liquid content by drying the crosslinked film 15 after the cleaning process.

  In the drying step of the present embodiment, the drying temperature is preferably 70 ° C. or less, more preferably 60 ° C. or less, and further preferably 45 ° C. or less. If the drying temperature is too low, the drying time becomes longer and the production efficiency decreases. On the other hand, when the drying temperature is too high, the obtained polarizing film 19 deteriorates, and the polarization characteristics and hue deteriorate. The drying time is preferably 10 minutes or less, more preferably 5 minutes or less. In this way, the polarizing film 19 is obtained.

  According to this embodiment, the manufacturing method of the polarizing film from which the polarizing film 19 which has the outstanding polarizing characteristic is obtained is provided.

<Production method of polarizing plate>
A polarizing plate on which the polarizing film 19 and the protective film are laminated is formed by attaching a protective film to at least one surface of the polarizing film 19 manufactured by the above-described method using an adhesive.

[Protective film]
As a material for the protective film of the polarizing plate of the present embodiment, a resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, and the like is preferable. For example, an acetyl cellulose resin such as triacetyl cellulose , Cycloolefin resins, cycloolefin copolymer resins, polyethylene terephthalate, polyethylene naphthalate, polyester resins such as polybutylene terephthalate, polycarbonate resins, acrylic resins such as polymethyl methacrylate, acyclic olefins such as polypropylene and polyethylene Resin or a mixture thereof.

  1-500 micrometers is preferable, as for the thickness of the above-mentioned protective film, 1-300 micrometers is more preferable, 5-200 micrometers is further more preferable, and 10-100 micrometers is especially preferable.

  In addition, when providing a protective film in the both sides of the polarizing film 19 in this embodiment, the protective film which consists of the same resin material may be used on both surfaces, and the protective film which consists of a different resin material may be used.

[adhesive]
As the adhesive for the polarizing plate of this embodiment, for example, a water-based adhesive, an ultraviolet curable adhesive, or an electron beam curable adhesive is preferable, and a water-based adhesive is more preferable. Examples of the water-based adhesive include an aqueous solution of a polyvinyl alcohol resin, an aqueous solution in which a general crosslinking agent is blended with an aqueous solution of a polyvinyl alcohol resin, and a urethane emulsion adhesive.

  Moreover, the adhesive used in the present embodiment can contain a metal compound filler.

[Production method of polarizing plate]
Hereinafter, the polarizing plate of this embodiment will be described. In the following, the case where an aqueous adhesive is used will be described.

  The polarizing plate of this embodiment is manufactured by bonding the protective film and the polarizing film 19 using the above-described adhesive. Application | coating of an adhesive agent may be performed to any of a protective film and the polarizing film 19, and may be performed to both. By bonding the polarizing film 19 and the protective film and then drying, an adhesive layer made of the above-described adhesive is formed between the polarizing film 19 and the protective film. Bonding of the polarizing film 19 and the protective film can be performed by a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is preferably 30 to 1000 nm. In addition, after drying, you may cure at the temperature of 20-45 degreeC, for example.

  The polarizing plate of this embodiment can perform a surface treatment on the polarizing film 19 and / or the protective film for the purpose of improving the adhesiveness with the adhesive. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, ultraviolet treatment, primer treatment, saponification treatment, solvent treatment by solvent application and drying.

  Further, the surface of the protective film where the polarizing film 19 is not adhered may be subjected to a hard coat treatment, an antireflection treatment, an antisticking treatment, a treatment for diffusion or antiglare, and the like.

Second Embodiment
Hereinafter, the manufacturing method of the polarizing film which concerns on 2nd Embodiment of this invention is demonstrated with reference to FIG. 2 and FIG.

[Production method of polarizing film]
FIG. 3 is a flowchart showing a method for manufacturing a polarizing film according to the second embodiment of the present invention. The polarizing film manufacturing method according to the second embodiment of the present invention shown in FIG. 3 has steps S11 to S14 in common with the flowchart showing the polarizing film manufacturing method according to the first embodiment shown in FIG. The difference between the first embodiment and the second embodiment includes a resin layer forming step including step S21 described later, a laminating step including step S22, and step S23 prior to the crosslinking step in the first embodiment. And an insolubilization step. Therefore, in this embodiment, the same code | symbol is attached | subjected about the component which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

  In step S21, a PVA-based resin solution is applied to at least one surface of the base film while transporting the belt-shaped base film in the longitudinal direction, thereby forming a resin layer using the PVA-based resin as a forming material.

  In step S22, the laminate obtained in step S21 is stretched while being conveyed in the longitudinal direction. By stretching the laminate, a laminated film (hereinafter, laminated film) in which the stretched base film and the resin film 11 formed on at least one surface of the stretched base film are laminated is obtained.

  In step S23, the laminated film is immersed in an insolubilizing bath containing a third crosslinking agent. A laminated film in which the resin film 11 formed on at least one surface of the stretched base film is insolubilized is obtained by immersing the laminated film in an insolubilizing bath.

[Resin layer forming step]
In the laminate of the present embodiment, a PVA resin layer is formed on at least one surface of a base film, and the base film and the PVA resin layer are integrated. In addition, a thin layer such as a primer layer (undercoat layer) may be formed between the base film and the PVA resin layer for the purpose of improving the adhesion between them.

(Base film)
As the base film of this embodiment, what is conventionally used as a protective film of a polarizing film can be used, and as a forming material of the base film, for example, transparency, mechanical strength, thermal stability A thermoplastic resin excellent in moisture barrier properties, isotropic properties, stretchability, and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, and polyamides such as nylon and aromatic polyamide. Resin, polyimide resin, polyethylene resin, polyolefin resin such as polypropylene, ethylene / propylene copolymer, cyclic polyolefin resin having a cyclo or norbornene structure (norbornene resin), (meth) acrylic resin, polyarylate resin, polystyrene resin, polyvinyl Alcohol resins or mixtures thereof are mentioned.

  Here, thermoplastic resins are roughly classified into those in which the polymer is in a crystalline state in which the polymer is regularly arranged and those in which the polymer is in an amorphous or amorphous state with no regular arrangement or only a small part. it can. Correspondingly, a thermoplastic resin having a property of forming a crystalline state is called a crystalline resin, and a thermoplastic resin having no such property is called an amorphous resin. On the other hand, regardless of whether the resin is a crystalline resin or an amorphous resin, a resin that is not in a crystalline state or a resin that does not reach a crystalline state is referred to as an amorphous or amorphous resin. Here, an amorphous or amorphous resin is used in distinction from an amorphous resin having a property of not producing a crystalline state.

  Examples of the crystalline resin include olefin resins including polyethylene (PE) and polypropylene (PP), and ester resins including polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). One of the characteristics of the crystalline resin is that it generally has a property that crystallization proceeds by polymer alignment by heating or stretching orientation. The physical properties of the resin vary depending on the degree of crystallization. On the other hand, for example, even with a crystalline resin such as polypropylene (PP) or polyethylene terephthalate (PET), crystallization can be suppressed by inhibiting the arrangement of the polymers caused by heat treatment or stretching orientation. These polypropylene (PP) and polyethylene terephthalate (PET) whose crystallization is suppressed are called amorphous polypropylene and amorphous polyethylene terephthalate. These are collectively called amorphous olefin resin and amorphous ester type. It is called resin.

  For example, in the case of polypropylene (PP), amorphous polypropylene (PP) in which crystallization is suppressed can be produced by using an atactic structure without stereoregularity. For example, in the case of polyethylene terephthalate (PET), amorphous polyethylene terephthalate (PET) with suppressed crystallization can be prepared by copolymerizing molecules that inhibit crystallization of polyethylene terephthalate (PET). . Specifically, amorphous polyethylene terephthalate (PET) can be produced by copolymerizing, for example, isophthalic acid or 1,4-cyclohexanedimethanol as a polymerization monomer.

  In the present embodiment, the thickness of the unstretched base film is preferably 10 to 500 μm, more preferably 20 to 300 μm, further preferably 30 to 200 μm, and particularly preferably 50 to 150 μm. When the thickness of the unstretched base film is within the above range, the strength and workability of the base film are excellent.

(PVA resin solution)
The PVA-type resin layer of this embodiment is obtained by apply | coating a PVA-type resin solution to the at least one surface of a base film, and drying. A PVA resin layer may be formed by applying a PVA resin solution to both surfaces of a base film and drying it. As the PVA resin solution, a PVA resin aqueous solution is preferable. The PVA-based resin aqueous solution can be prepared by swelling a PVA-based resin powder, a pulverized product, or a cut product with water and then stirring the swollen PVA-based resin with heat. The concentration of the PVA resin in the PVA resin aqueous solution is preferably 2 to 20% by mass, and more preferably 4 to 10% by mass.

(Application)
In the present embodiment, the above-described PVA resin solution can be applied by a conventionally known method. Examples of methods for applying the PVA resin solution include wire bar coating, roll coating such as reverse coating and gravure coating, die coating, comma coating, lip coating, screen coating, fountain coating, and dipping. And the spray method. In addition, when the primer layer is provided in the base film, a PVA-type resin solution can be directly apply | coated to a primer layer with the above-mentioned method.

(Dry)
After applying the PVA resin solution, the laminate is dried using an oven. The drying temperature is preferably 50 to 200 ° C, more preferably 80 to 150 ° C. The drying time is preferably 5 to 30 minutes.

[Lamination process]
(Stretching)
The stretching performed in the laminating process of the present embodiment is performed for the purpose of forming a laminated film from the above-described laminated body. Furthermore, it is carried out for the purpose of insolubilizing the obtained resin film 11 by improving the orientation of the PVA resin by stretching the laminate. The stretching performed in the laminating step is preferably dry uniaxial stretching. The draw ratio is preferably 1.3 to 2.2 times, more preferably 1.5 to 2.0 times, and still more preferably 1.8 to 2.0 times based on the unstretched laminate. When the draw ratio is higher than 2.2, the resin film 11 formed on at least one surface of the stretched base film tends to be easily broken. Moreover, when a draw ratio is lower than 1.3 times, the polarizing characteristic of the polarizing film 19 obtained may fall.

  If the draw ratio in the lamination process of this embodiment is in the above-mentioned range, it can also be performed in multiple steps. Examples of the multistage stretching method include inter-roll stretching in which stretching is performed with a difference in peripheral speed between a plurality of pinch rolls (nip rolls), hot roll stretching or tenter stretching as described in Japanese Patent No. 2731813. Is mentioned.

  80-160 degreeC is preferable, as for the extending | stretching temperature in the lamination process of this embodiment, 90-150 degreeC is more preferable, and 100-130 degreeC is further more preferable.

[Insolubilization process]
The insolubilization step of the present embodiment is performed for the purpose of insolubilizing the resin film 11 in the laminated film in a later step. The insolubilization step is performed by immersing the laminated film in a solution containing a third crosslinking agent (hereinafter referred to as insolubilization bath). As the third crosslinking agent contained in the insolubilizing bath, a boron compound, glyoxal or glutaraldehyde is preferable, and a boron compound is more preferable. As the boron compound, for example, boric acid or borax is preferable, and boric acid is more preferable. The third crosslinking agent used in the insolubilization step of the present embodiment may be the same as the first crosslinking agent used in the subsequent crosslinking step. As the solvent for the insolubilizing bath, water or a mixed solvent of water and an organic solvent is preferable, and water is more preferable.

  The concentration of the boron compound in the insolubilizing bath is preferably 1% by mass or more and 4% by mass or less. Moreover, 25 degreeC or more is preferable, as for the temperature of an insolubilization bath, 30-85 degreeC is more preferable, and 30-60 degreeC is further more preferable. The time for immersion in the insolubilizing bath is preferably 5 to 800 seconds, and more preferably 8 to 500 seconds.

  According to this embodiment, the manufacturing method of the polarizing film from which the polarizing film 19 which has the outstanding polarizing characteristic is obtained is provided. Moreover, in this embodiment, it is possible to manufacture a thin polarizing film having a thickness of 10 μm or less. Conventionally, in the method for producing a thin polarizing film, since the resin film 11 is formed by applying a PVA resin solution, there is a problem that it is easily dissolved in a bath. In particular, in the washing step, the orientation of the dichroic substance is easily disturbed, and the polarization characteristics of the resulting thin polarizing film are liable to deteriorate. In contrast, the polarizing film manufacturing method of the present embodiment reduces the polarization characteristics of the resulting thin polarizing film without disturbing the orientation of the dichroic substance in the washing process even when the thin polarizing film is manufactured. It can be suppressed more.

<Modification>
The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the effects of the present invention.

  For example, in FIG. 1, one tank is provided for each step of the method for manufacturing a polarizing film, but a plurality of tanks may be provided.

  Further, for example, in the above-described embodiment, the stretching is performed together with the crosslinking of the resin film 11, but the stretching may be performed before the crosslinking of the resin film 11. When the stretching is performed before the crosslinking of the resin film 11, the stretching may be performed before or together with the staining of the resin film 11, but it is preferable to perform the stretching together with the staining of the resin film 11. In the case where the stretching is performed before the crosslinking of the resin film 11, the stretching ratio is preferably 4 times or less, and more preferably 2.8 to 3.8 times.

  Furthermore, for example, in the above-described embodiment, a metal salt may be contained in the solution used in each step (hereinafter, in a bath). By including a metal salt in the bath, metal ions can be contained in the resin film 11 when the resin film 11 is immersed in the bath. It is considered that there are advantages such as hue adjustment and durability improvement of the resin film 11 by including metal ions in the resin film 11. As the above-mentioned metal salt, for example, zinc chloride, zinc iodide, zinc sulfate, zinc acetate, cobalt chloride, zirconium chloride, sodium thiosulfate, sodium sulfate or potassium sulfite are preferable, and zinc chloride, zinc iodide, zinc sulfate, Zinc acetate is more preferred.

  Further, for example, in the second embodiment, the insolubilization of the laminated film is performed before the laminated film is dyed, but may be performed independently before the crosslinking of the laminated film. By insolubilizing the laminated film before crosslinking of the laminated film, it is possible to suppress dissolution of the PVA resin, which is a material for forming the dyed film 13 included in the laminated film, in the crosslinking bath.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
As a base film, an amorphous polyethylene terephthalate film (Mitsubishi Chemical Co., Ltd., “Novaclear (registered trademark)”) having a thickness of 200 μm was prepared, and one side was subjected to corona treatment under the condition of 90 W · min / m ² . After applying a PVA resin aqueous solution having a polymerization degree of 4000 and a saponification degree of 99.0 mol% or more to the surface of the corona-treated base film, it is dried at 65 ° C. to form a 8.3 μm thick PVA resin layer. did.

  The obtained laminate was uniaxially stretched 1.8 times using an unstretched laminate at 90 ° C. using a stretching apparatus provided in an oven. Next, an aqueous solution (insolubilized bath) in which 3 parts by mass of boric acid was mixed with 100 parts by mass of water was prepared. The resulting laminated film was insolubilized by immersing it in an insolubilizing bath adjusted to a liquid temperature of 30 ° C. for 30 seconds.

  Furthermore, the iodine aqueous solution which mix | blended 0.18 mass part of iodine and 1.26 mass parts of potassium iodide with respect to 100 mass parts of water was prepared. The insolubilized laminated film was immersed in an aqueous iodine solution adjusted to a liquid temperature of 30 ° C. for 13 seconds to be dyed with iodine to produce a polarizing film having a transmittance of about 42.0%.

  Furthermore, an aqueous solution (crosslinking bath) containing 3 parts by mass of potassium iodide and 3 parts by mass of boric acid with respect to 100 parts by mass of water was prepared. The film was crosslinked by immersing the laminated film dyed with iodine in a crosslinking bath adjusted to a liquid temperature of 40 ° C. for 30 seconds.

  Furthermore, the aqueous solution which mix | blended 4 mass parts boric acid and 5 mass parts potassium iodide with respect to 100 mass parts of water was prepared. While immersing the crosslinked laminated film in an aqueous solution adjusted to a liquid temperature of 75 ° C., the film was stretched in water by uniaxially stretching in the longitudinal direction (longitudinal direction). The maximum draw ratio of the obtained laminated film was 5.94 times based on the unstretched laminate.

  Furthermore, an aqueous solution (cleaning bath) containing 4 parts by mass of potassium iodide and 0.005 parts by mass of boric acid with respect to 100 parts by mass of water was prepared. Washing was performed by immersing the laminated film stretched in water for 5 seconds in a washing bath adjusted to a liquid temperature of 30 ° C. The washed laminated film was dried with hot air at 60 ° C. to produce a polarizing film on the surface of the base film. The thickness of the polarizing film stretched integrally with the base film was 4.5 μm.

<Examples 2-4, Comparative Examples 1-3>
In Example 1, a polarizing film was produced under the same conditions as in Example 1 except that the concentration of boric acid contained in the cleaning bath was changed as shown in Table 1.

<Preparation of polarizing plate>
First, PVA powder (manufactured by Kuraray Co., Ltd., “KL-318”, average polymerization degree 1800) was dissolved in hot water at 95 ° C. to prepare a 3 mass% PVA resin aqueous solution. The resulting PVA resin aqueous solution was mixed with a cross-linking agent (manufactured by Taoka Chemical Co., Ltd., “SUMIREZ RESIN (registered trademark) 650”) at a ratio of 1 part by mass with respect to 2 parts by mass of the PVA powder. It was.

  The obtained adhesive was applied to the surface on which the polarizing film in the laminated film produced in the above-described Examples and Comparative Examples was laminated. Next, as a protective film, a 40 μm thick triacetyl cellulose (TAC) (manufactured by Konica Minolta Co., Ltd., “KC4UY”) whose adhesive surface is saponified is bonded to the surface on which the adhesive is applied, and a roll Crimping was performed using a laminator.

  After pressure bonding, the polarizing film was produced by peeling off the base film integrated with the polarizing film, the adhesive, and the TAC.

<Evaluation method>
The presence or absence of dirt adhered to the surface of the polarizing film prepared in Examples and Comparative Examples was visually observed. Moreover, the visibility correction | amendment single transmittance and the visibility correction | amendment polarization degree were calculated | required as a polarization characteristic of the obtained polarizing film. The visibility corrected single transmittance and the visibility corrected polarization degree were determined by the following methods.

[Measurement of transmittance correction single transmittance]
The visibility corrected single transmittance of the obtained polarizing film was measured with a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, V7100). MD transmittance and TD transmittance were determined in the wavelength range of 380 nm to 780 nm, and the single transmittance at each wavelength was calculated based on Equation (1).
Furthermore, the visibility correction was performed using the JIS Z 8701 twice field of view (C light source), and the visibility corrected single transmittance was obtained. Here, “MD transmittance” indicates the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing plate sample. The “TD transmittance” indicates the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the polarizing plate sample.

[Measurement of polarization correction polarization]
From the above-described MD transmittance and TD transmittance, the degree of polarization at each wavelength was calculated based on Equation (2). Furthermore, the visibility correction was performed using the JIS Z 8701 twice field of view (C light source), and the visibility corrected single transmittance was obtained.

  Table 1 shows the concentration of boric acid with respect to 100 parts by mass of water in the cleaning baths used in the examples and comparative examples. Table 2 shows the presence or absence of dirt on the polarizing films prepared in Examples and Comparative Examples, and the polarization characteristics (luminosity corrected single transmittance and visibility corrected polarization degree).

  In this example, when the concentration of boric acid in the cleaning bath is within the range specified in the present invention, there is no occurrence of defects such as dirt, and polarization characteristics (luminosity corrected single transmittance and visibility corrected polarization degree). An excellent polarizing film was obtained. Specifically, the polarizing films of Examples 1 to 4 had the same visibility-corrected single transmittance as compared with the polarizing films of Comparative Examples 1 to 3, and were excellent in the visibility corrected polarization degree.

  From the above results, it was confirmed that the present invention is useful.

DESCRIPTION OF SYMBOLS 11 ... Strip | belt-shaped resin film which uses polyvinyl alcohol-type resin as a forming material, 13 ... Dye film, 15 ... Crosslinked film, 19 ... Polarizing film, 21 ... Feeding roll, 23 ... Dyeing tank, 25 ... Crosslinking tank, 27 ... Washing tank 29 ... drying furnace, 101-105 ... nip roll, 11
1 to 119 ... transport roll

Claims (7)

A method for producing a polarizing film, comprising producing a polarizing film in which the resin film is dyed with a dichroic substance while conveying a belt-shaped resin film having a polyvinyl alcohol resin as a forming material in the longitudinal direction,
The resin film dyed with the dichroic substance is immersed in a crosslinking bath containing a first crosslinking agent, and the resin film dyed with the dichroic substance is crosslinked with the first crosslinking agent. A crosslinking step for obtaining a crosslinked film;
Washing the crosslinked film with an aqueous solution containing a second crosslinking agent,
In the washing step, the total of the first crosslinking agent and the second crosslinking agent contained in the aqueous solution is in the range of 0.003 parts by mass or more and less than 0.1 parts by mass with respect to 100 parts by mass of water. The manufacturing method of the polarizing film managed. Prior to the crosslinking step, a polyvinyl alcohol-based resin solution is applied to at least one surface of the base film while a belt-shaped base film is conveyed in the longitudinal direction, and a polyvinyl alcohol-based resin is applied to the at least one surface. A resin layer forming step of forming a resin layer as a forming material;
The laminated body obtained in the resin layer forming step is stretched while being conveyed in the longitudinal direction, and the stretched base film on which the base film is stretched, and the resin formed on one surface of the stretched base film The manufacturing method of the polarizing film of Claim 1 which has a lamination process which obtains the laminated | multilayer film which the film laminated | stacked.   The method for producing a polarizing film according to claim 1, wherein the second crosslinking agent is a boron compound.   The method for producing a polarizing film according to claim 1, wherein the first cross-linking agent and the second cross-linking agent are the same compound.   The method for producing a polarizing film according to claim 1, wherein the dichroic substance is iodine.   The method for producing a polarizing film according to claim 5, wherein the aqueous solution contains iodide.   The method for producing a polarizing film according to claim 6, wherein the iodide is potassium iodide.

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