KR20170066253A - Method for manufacturing polarizing film - Google Patents

Abstract

An object of the present invention is to provide a polarizing film producing method capable of obtaining a polarizing film having excellent polarizing properties.
A method for producing a polarizing film in which a resin film is dyed with a dichroic substance while conveying a strip-shaped resin film made of a polyvinyl alcohol-based resin in a longitudinal direction, comprising the steps of: (Crosslinking bath) containing a first crosslinking agent to obtain a crosslinked film in which a resin film dyed with a dichroic substance is crosslinked with a first crosslinking agent; and a step of immersing the crosslinked film in a crosslinking bath containing a second crosslinking agent And the total amount of the first cross-linking agent and the second cross-linking agent contained in the aqueous solution in the cleaning step is controlled so as to fall within a range of not less than 0.003 parts by mass and less than 0.1 part by mass with respect to 100 parts by mass of water, ≪ / RTI >

Description

METHOD FOR MANUFACTURING POLARIZING FILM [0002]

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

The liquid crystal display device is used in a personal computer, a TV, a monitor, a cellular phone, a PDA (Personal Digital Assistant), and the like. In recent years, as the performance and thickness of a liquid crystal display device have become higher, a polarizing film used in a liquid crystal display device has been required to be thin. For example, a thin polarizing film having a thickness of 10 占 퐉 or less can be obtained by dyeing and stretching a laminate having a polyvinyl alcohol-based resin layer on the surface of a thermoplastic resin substrate (substrate) using a dichroic substance One).

[Patent Document 1] Japanese Patent Application Laid-Open No. 2009-098653

As the above-mentioned dichroic substance, for example, iodine is used. Iodine in the polarizing film exists as an iodine complex, and depends on the orientation of the polyvinyl alcohol-based resin, and the iodine complex itself is also oriented. It is known that this iodine complex absorbs light in the visible region and thus the polarizing film exhibits polarization characteristics (polarization degree). For this reason, as a method of improving the degree of polarization of the polarizing film, a method of improving the orientation of the polyvinyl alcohol-based resin is considered.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a polarizing film producing method capable of obtaining a polarizing film having excellent polarizing properties.

As a result of intensive investigations to solve the above-mentioned problems, the inventors of the present invention found that the orientation of the iodine complex is disturbed in the cleaning step in the polarizing film production method, and the polarization degree of the resultant polarizing film is lowered there was. Particularly, when the thickness of the polarizing film is 10 m or less, the iodine complex existing on the surface of the polarizing film increases, as compared with the case where the thickness of the polarizing film exceeds 10 m, It turned out that it can not be overlooked. On the other hand, when the thickness of the polarizing film is more than 10 mu m, since the polarizing film has a sufficient thickness, deterioration of the polarization characteristics in the cleaning process has not been recognized.

The inventors of the present invention have found that the above-mentioned object can be achieved by the production method of the polarizing film described below, and have completed the present invention.

That is, one aspect of the present invention is a method for producing a polarizing film in which a resin film is dyed with a dichroic substance while a strip-shaped resin film comprising a polyvinyl alcohol-based resin is transported in the longitudinal direction A crosslinking step of dipping a resin film dyed with a dichroic material in a crosslinking bath (crosslinking bath) containing a first crosslinking agent to obtain a crosslinked film in which a resin film dyed with a dichroic substance is crosslinked with the first crosslinking agent; Wherein the total amount of the first crosslinking agent and the second crosslinking agent contained in the aqueous solution is 0.003 part by mass or more and 0.1 part by mass or more per 100 parts by mass of the water in the washing step in the washing step of washing the crosslinked film with an aqueous solution containing the second crosslinking agent Of the polarizing film is controlled so as to be in a range of less than a predetermined value.

In one aspect of the present invention, prior to the crosslinking step, a polyvinyl alcohol-based resin solution is applied to one side of a substrate film while the strip-like base film is transported in the longitudinal direction to form a polyvinyl alcohol- A resin layer formed on one side of the stretched base film, and a resin layer formed on the other side of the stretched base film, wherein the base film is stretched while conveying the laminate obtained in the resin layer in the longitudinal direction, And a lamination step of obtaining the laminated laminated film.

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 substance 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 polarizing film producing method capable of obtaining a polarizing film having excellent polarizing properties.

1 is a flow chart showing a method of manufacturing a polarizing film according to a first embodiment of the present invention.
2 is a schematic cross-sectional view showing an example of arrangement of principal devices according to the method for producing a polarizing film of the present invention.
3 is a flowchart showing a method of manufacturing a polarizing film according to a second embodiment of the present invention.

≪ First Embodiment >

Hereinafter, a method of manufacturing a polarizing film according to a first embodiment of the present invention will be described with reference to Figs. 1 and 2, with reference to the symbols appropriately. On the other hand, in all the following drawings, the dimensions, ratios, etc. of the respective components may be appropriately changed in order to facilitate the illustration of the drawings.

[Production method of polarizing film]

1 is a flow chart showing a method of manufacturing a polarizing film according to a first embodiment of the present invention. The polarizing film manufacturing method of the present embodiment includes a crosslinking step including steps S11 and S12 described later, a cleaning step including step S13, and a drying step including step S14.

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

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

Fig. 2 is a schematic cross-sectional view showing one example of arrangement of principal devices according to the method for producing a polarizing film of the present embodiment. 2, in the present embodiment, 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, the resin film 11 is dichroic To prepare a polarizing film 19.

The resin film 11 is fed from one side in a state of being wound on the feeding roll 21. First, the resin film 11 is dyed by dipping in the dyeing tank 23 (step S11). Next, the obtained dyed film 13 is immersed and stretched in the crosslinking bath 25 to obtain a crosslinked film 15 (step S12). Further, the crosslinked film 15 is washed by immersing in the washing tub 27 (step S13). The washed cross-linked film 15 is dried by passing through the drying furnace 29 (step S14). By the above-described processing, the polarizing film 19 is obtained.

[Resin film]

2, the material for forming the resin film 11 according to the present embodiment is conventionally a polyvinyl alcohol (hereinafter referred to as PVA) resin used for a polarizing film. As the PVA resin, a PVA resin or a PVA resin derivative is used.

Examples of the PVA resin derivative include polyvinylformal, polyvinyl acetal, polyvinyl butyral, and modified products thereof. Examples of the modifier include the above-described PVA resin derivatives, modified with an olefin such as ethylene or propylene, an alkyl ester of an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or crotonic acid or an unsaturated carboxylic acid, .

The degree of polymerization of the PVA-based resin is preferably from 1,000 to 10,000, more preferably from 1,500 to 5,000. The saponification degree of the PVA resin is preferably 85 mol% or more, more preferably 90 mol% or more, and further preferably 99 mol% or more.

The above-mentioned resin film (11) may contain an additive such as a plasticizer. Examples of the plasticizer include condensates of polyols or polyols such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. 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 占 퐉, more preferably 5 to 80 占 퐉, and still more preferably 5 to 40 占 퐉.

[Crosslinking Process]

(dyeing)

2, dyeing of the resin film 11 according to the present embodiment is carried out for the purpose of adsorbing and orienting a dichroic substance to the resin film 11. Fig. Specifically, the resin film 11 is dipped in a solution containing a dichroic substance, whereby the resin film 11 is dyed with a dichroic substance.

Examples of the dichroic substance used for dyeing the resin film 11 include known dichroic dyes as iodine and coloring matters for a polarizing film, and iodine is preferable.

Hereinafter, the case where iodine is used as the dichroic substance will be described. For dyeing the resin film 11 according to the present embodiment, an iodine solution is preferably used, and an iodine aqueous solution is preferably used. As the iodine aqueous solution, an iodine and an aqueous solution containing iodide ions dissolved in iodide as a dissolution aid are used. As the iodide, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide or titanium iodide is preferable and potassium iodide is more preferable.

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

In dyeing the resin film 11 according to the present embodiment, the temperature of the iodine solution is preferably 20 to 50 ° C, more preferably 25 to 40 ° C. The time for immersion in the iodine solution is preferably 10 to 300 seconds, more preferably 20 to 240 seconds.

(Bridging)

In Fig. 2, the crosslinking of the dye film 13 according to the present embodiment is performed for the purpose of making the dye film 13 water resistant. Specifically, the dye film 13 is immersed in an iodide aqueous solution containing a first crosslinking agent (hereinafter referred to as a crosslinking bath).

In the present embodiment, the inclusion of iodide in the crosslinking bath makes it possible to uniformize the polarization property of the resulting polarizing film 19 in the plane, and to adjust the color of the polarizing film 19. [ As the iodide contained in the crosslinking bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide or titanium iodide is preferable, More preferable.

The concentration of iodide in the crosslinking bath is preferably 4 mass% or more, more preferably 4 mass% or more and 12 mass% or less, further preferably 4.5 mass% or more and 11 mass% or less, further preferably 5 mass% or more and 10 mass% Is particularly preferable.

In the present embodiment, the PVA resin is crosslinked by including the first crosslinking agent in the crosslinking bath. As the first crosslinking agent contained in the 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, borax, and the like.

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

Here, the mechanism in which the dye film 13 is water-hydrated will be described by exemplifying the case of using PVA as a material for forming the dye film 13 and boric acid as a first cross-linking agent. When the dye film 13 is immersed in a crosslinking bath, the hydroxy group of the PVA reacts with the hydroxyl group of the boric acid ion B (OH) ₄ ^- to form a hydrogen bond or an inorganic acid ester bond. As a result, a stable cyclic ring structure containing these bonds is formed and crosslinked. PVA has a hydroxyl group every one carbon atom, and since each hydroxy group is crosslinked, a plurality of PVA chains are combined to form a mesh-like network. It is believed that the formation of the mesh network in this manner leads to the PVA being hardened or insolubilized in water to improve the water resistance of the dye film 13. Further, it is possible to suppress the outflow of the dyed iodine by the mesh-shaped network, and suppress the deterioration of the polarization characteristic of the obtained polarizing film 19. [

(Stretching)

In Fig. 2, the stretching may be performed together with the crosslinking of the dye film 13 according to the present embodiment. When the stretching is performed together with the crosslinking of the dye film 13, the orientation property of the dichroic substance is improved along with the orientation of the PVA resin, and thus the polarizing property of the resulting polarizing film 19 can be improved. Further, if the orientation of the PVA-based resin is improved by stretching, the dye film 13 is more insolubilized than when the stretching is not performed, and the water resistance is further improved.

The stretching of the dye film 13 according to the present embodiment is preferably a wet uniaxial stretching.

The stretching magnification is preferably 4 to 7 times, more preferably 5 to 6.8 times, and 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 dye film 13 tends to be easily broken. If the stretching magnification is lower than 4 times, the polarization characteristic of the obtained polarizing film 19 may be lowered. The thickness of the resin film 11 obtained by crosslinking and stretching the dye film 13 is preferably 5 to 80 탆.

If the stretching magnification in the crosslinking step of the present embodiment is within the above-mentioned range, it can be carried out in multiple steps in one crosslinking bath. Examples of the multistage stretching method include inter-roll stretching or tenter stretching in which a plurality of pairs of pinch rolls (nip rolls) provided in a crosslinking bath are stretched by a main speed difference.

In the crosslinking of the dye film 13 according to the present embodiment, the temperature of the crosslinking bath is preferably 30 占 폚 or higher, for example, and more preferably 40 to 85 占 폚. The time for immersion in the crosslinking bath is preferably 10 to 1200 seconds, more preferably 30 to 600 seconds.

[Cleaning process]

In Fig. 2, the cleaning step of the present embodiment is carried out for the purpose of reducing the remaining agent in the resin film 11, for example, a surplus dichroic substance or unreacted first cross-linking agent in the above-described process . Specifically, the crosslinked film 15 is immersed in an aqueous solution containing a second crosslinking agent (hereinafter referred to as cleansing bath).

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

The total concentration of the first cross-linking agent and the second cross-linking agent contained in the slush bath is lower than the concentration of the first cross-linking agent in the cross-linking bath. Concretely, the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleansing bath is preferably not less than 0.003 parts by mass, more preferably not less than 0.003 parts by mass and less than 0.1 parts by mass based on 100 parts by mass of water, more preferably 0.005 And more preferably not less than 0.1 part by mass. When the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleansing bath is less than 0.003 parts by mass, the polarizing property of the obtained polarizing film 19 tends to be lowered. If the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleansing bath is 0.1 part by mass or more, washing of the remaining agent in the crosslinked film 15 becomes insufficient, and the contamination of the surface of the obtained polarizing film 19 It causes.

In a conventional method for producing a polarizing film, pure water such as ion-exchanged water or distilled water is used for a cleansing bath in order to obtain a sufficient cleaning effect. However, if the crosslinked film 15 is washed in a pure water washing bath, the first crosslinking agent is removed from the crosslinked structure derived from the first crosslinking agent contained in the crosslinked film 15 by hydrolysis, . By eluting the first crosslinking agent, the crosslinking structure of the crosslinking film 15 is dissolved, and the dichroic substance received in the crosslinking structure is sometimes eluted.

Further, after the first crosslinking agent is desorbed, a hydroxyl group is generated. Further, since the crosslinked film 15 has an unreacted hydroxyl group which is not crosslinked in the crosslinking step in addition to the hydroxyl group, the crosslinked film 15 may swell or partially dissolve in a pure water washing bath. Thereby, the dichroic substance may be eluted.

It is considered that the polarization characteristic of the obtained polarizing film 19 is deteriorated because it depends on the concentration of the dichroic substance.

In the method for producing a polarizing film of the present embodiment, the first crosslinking agent and the second crosslinking agent are contained in the above-mentioned concentration range in the cleansing bath, whereby the elution of the first crosslinking agent and the swelling of the crosslinking film (15) Or dissolution of the polarizing film 19 is suppressed, thereby suppressing the deterioration of the polarization characteristics of the resulting polarizing film 19. [

In the cleaning step of the present embodiment, the first crosslinking agent contained in the crosslinking bath is mixed in the cleansing bath, and the concentration of the first crosslinking agent and the second crosslinking agent contained in the cleansing bath is controlled so as not to exceed 0.1 part by mass do. For example, by adjusting the nip pressure of the nip roll 103 shown in Fig. 2, the mixing amount of the first crosslinking agent in the cleansing bath can be increased or decreased. Also, when replacing with an unused cleansing bath for inspection or replacement of cleansing bath, the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleansing bath is controlled so as not to fall below 0.003 part by mass. For example, a second crosslinking agent may be added in an unused cleansing bath to increase the concentration of the second crosslinking agent in the cleansing bath. By the above method, the total concentration of the first crosslinking agent and the second crosslinking agent contained in the cleansing bath can be controlled within the above-mentioned range.

Further, in the washing step of the present embodiment, iodide is preferably contained in the washing bath. The color of the obtained polarizing film 19 can be prepared by containing iodide in the washing bath.

The iodide contained in the washing bath can be the same as the iodide contained in the crosslinking bath, and examples thereof include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, Calcium, tin iodide or titanium iodide is preferable, and potassium iodide is more preferable.

The concentration of iodide in the lavage bath is preferably 0.8 mass% or more, more preferably 0.8 mass% or more and 5 mass% or less, further preferably 0.8 mass% or more and 4.5 mass% or less, further preferably 0.8 mass% or more and 4.0 mass% Is particularly preferable.

In the cleaning step of the present embodiment, the temperature of the cleansing bath is more preferably 15 to 60 占 폚, and more preferably 20 to 45 占 폚. The immersing time in the cleansing bath is preferably from 1 to 120 seconds, more preferably from 3 to 90 seconds.

The cleaning process of the present embodiment may use a solution in which a liquid alcohol such as methanol, ethanol, isopropyl alcohol, butanol, or propanol is blended to the extent that the effect of the present invention is not impaired. By using the liquid alcohol as described above, the drying of the crosslinked film 15 can be accelerated in a subsequent drying step.

[Drying process]

2, the drying step of the present embodiment is carried out for the purpose of drying the crosslinked film 15 after the washing step to obtain a polarizing film 19 having a desired liquid-impermeability.

In the drying step of the present embodiment, the drying temperature is preferably 70 ° C or lower, more preferably 60 ° C or lower, and further preferably 45 ° C or lower. If the drying temperature is too low, the drying time is prolonged and the production efficiency is lowered. On the other hand, if the drying temperature is too high, the obtained polarizing film 19 deteriorates, and the polarization characteristics and color 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, there is provided a polarizing film producing method capable of obtaining a polarizing film 19 having excellent polarizing properties.

≪ Polarizing plate production method >

A polarizing plate in which a polarizing film 19 and a protective film are laminated is formed by bonding a protective film to at least one surface of the polarizing film 19 produced by the above-described method using an adhesive.

[Protection film]

The material of the protective film of the polarizing plate of the present embodiment is preferably a resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like. Examples thereof include acetylcellulose resins such as triacetylcellulose, cycloolefin resins, Based resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate-based resins; acrylic resins such as polymethyl methacrylate; and non-cyclic olefin-based resins such as polypropylene and polyethylene Resins, and mixtures thereof.

The thickness of the above-mentioned protective film is preferably 1 to 500 占 퐉, more preferably 1 to 300 占 퐉, still more preferably 5 to 200 占 퐉, and particularly preferably 10 to 100 占 퐉.

On the other hand, when a protective film is formed on both sides of the polarizing film 19 in the present embodiment, a protective film made of the same resin material or a different resin material may be used on both sides thereof.

[glue]

As the adhesive for the polarizing plate of the present embodiment, for example, an aqueous adhesive, an ultraviolet curable adhesive or an electron beam curable adhesive is preferable, and an aqueous adhesive is more preferable. As the water-based adhesive, there can be mentioned, for example, an aqueous solution of a polyvinyl alcohol-based resin and an aqueous solution or a urethane-based emulsion adhesive in which a general crosslinking agent is blended in an aqueous solution of a polyvinyl alcohol-based resin.

In addition, the adhesive used in the present embodiment may contain a metal compound filler.

[Polarizing plate production method]

Hereinafter, the polarizing plate of the present embodiment will be described. On the other hand, the case of using an aqueous adhesive will be described below.

The polarizing plate of the present embodiment is manufactured by bonding the protective film and the polarizing film 19 using the adhesive described above. The application of the adhesive may be applied to either the protective film or the polarizing film 19, or both. The polarizing film 19 and the protective film are bonded together and then dried to form an adhesive layer made of the above-described adhesive between the polarizing film 19 and the protective film. The polarizing film 19 and the protective film can be bonded by a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is preferably 30 to 1000 nm. On the other hand, after drying, it may be cured at a temperature of 20 to 45 캜, for example.

The polarizing plate of the present embodiment can be subjected to a surface treatment on the polarizing film 19 or the protective film or both for the purpose of improving the adhesiveness with the adhesive. Examples of the surface treatment include a corona treatment, a plasma treatment, a flame treatment, an ultraviolet ray treatment, a primer treatment, a saponification treatment, a solvent treatment by applying a solvent and drying.

The surface of the protective film on which the polarizing film 19 is not adhered may be subjected to a hard coat treatment, an antireflection treatment, a sticking prevention treatment, a diffusion or antiglare treatment or the like.

≪ Second Embodiment >

Hereinafter, a method of manufacturing a polarizing film according to a second embodiment of the present invention will be described with reference to Figs. 2 and 3. Fig.

[Production method of polarizing film]

3 is a flowchart showing a method of manufacturing a polarizing film according to a second embodiment of the present invention. The manufacturing method of the polarizing film of the second embodiment of the present invention shown in Fig. 3 is the same as that of the flow chart of the polarizing film producing method of the first embodiment shown in Fig. 1 and the steps S11 to S14. The difference between the first embodiment and the second embodiment is that the resin layer forming step including step S21 described later, the lamination step including step S22, and the step S23 are included before the crosslinking step in the first embodiment And the like. Therefore, in the present embodiment, constituent elements common to those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

In step S21, a PVA-based resin solution is applied to at least one surface of the base film while the strip-like base film is transported in the longitudinal direction to form a resin layer made of a PVA-based resin.

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

In step S23, the laminated film is immersed in a insoluble bath containing a third crosslinking agent (insolubilizing bath). By immersing the laminated film in the insoluble bath, a laminated film in which the resin film (11) formed on at least one side of the stretched base film is insoluble is obtained.

[Resin Layer Forming Step]

In the laminate of the present embodiment, the PVA resin layer is formed on at least one surface of the base film, and the base film and the PVA resin layer are integrated. 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 the base film and the PVA resin layer.

(Substrate film)

As the base film of the present embodiment, those conventionally used as a protective film of a polarizing film can be used. As a material for forming the base film, for example, transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, This excellent thermoplastic resin is used. Specific examples of such a thermoplastic resin include cellulose resins such as triacetylcellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamides such as nylon and aromatic polyamides (Norbornene resin) having a cyclo or norbornene structure, a (meth) acrylic resin, a polyarylate resin such as a (meth) acrylic resin, a polyimide resin, a polyolefin resin such as polyethylene, polypropylene, , A polystyrene resin, a polyvinyl alcohol resin, or a mixture thereof.

Here, the thermoplastic resin can be roughly distinguished from being in a crystalline state in which polymers are regularly arranged, and in amorphous or amorphous states in which the polymer does not have regular arrangement, or only a part thereof. Correspondingly, a thermoplastic resin having a property of making 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, a resin which is not in a crystalline state or a resin which does not reach a crystalline state, regardless of whether it is a crystalline resin or an amorphous resin, is called an amorphous or amorphous resin. Here, the amorphous or amorphous resin is used separately from the noncrystalline resin which does not form 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 the polymer is arranged by heating or stretching orientation and crystallization progresses. The physical properties of the resin vary in various ways depending on the degree of crystallization. On the other hand, even when a crystalline resin such as polypropylene (PP) or polyethylene terephthalate (PET) is used, it is possible to inhibit crystallization by inhibiting the arrangement of the polymer caused by heat treatment or stretching orientation. These polypropylene (PP) and polyethylene terephthalate (PET) whose crystallization is inhibited are referred to as amorphous polypropylene and amorphous polyethylene terephthalate, and these are collectively referred to as amorphous olefin resin and amorphous ester resin.

For example, in the case of polypropylene (PP), noncrystalline polypropylene (PP) in which crystallization is suppressed can be produced by making it an atactic structure having no stereoregularity. Further, for example, in the case of polyethylene terephthalate (PET), amorphous polyethylene terephthalate (PET) in which crystallization is suppressed can be produced by copolymerizing molecules which inhibit crystallization of polyethylene terephthalate (PET). Specifically, amorphous polyethylene terephthalate (PET) can be prepared by copolymerizing, for example, isophthalic acid or 1,4-cyclohexanedimethanol as the polymerized monomer.

In the present embodiment, the thickness of the unstretched base film is preferably 10 to 500 占 퐉, more preferably 20 to 300 占 퐉, still more preferably 30 to 200 占 퐉, and particularly preferably 50 to 150 占 퐉. When the thickness of the base film of the non-stretched base is within the above-mentioned range, the strength and workability of the base film are excellent.

(PVA resin solution)

The PVA resin layer of the present embodiment is obtained by applying a PVA resin solution onto at least one surface of a base film and drying it. The PVA resin solution may be coated on both sides of the base film and dried to form the PVA resin layer. As the PVA resin solution, a PVA resin aqueous solution is preferable. The PVA resin aqueous solution can be prepared by swelling the PVA resin powder, pulverized product or cut product with water and then heating and stirring the swollen PVA resin. The concentration of the PVA resin in the PVA resin aqueous solution is preferably from 2 to 20 mass%, more preferably from 4 to 10 mass%.

(apply)

In the present embodiment, the above-mentioned PVA resin solution can be applied by a conventionally known technique. Examples of the method of applying the PVA resin solution include a roll coating method such as a wire bar coating method, a reverse coating method and a gravure coating method, a die coating method, a comma coating method, a lip coating method, a screen coating method, , A spray method, and the like. On the other hand, when the primer layer is formed on the base film, the PVA-based resin solution can be applied directly to the primer layer by the above-mentioned technique.

(dry)

After the PVA resin solution is applied, the laminate is dried using an oven. The drying temperature is preferably 50 to 200 占 폚, more preferably 80 to 150 占 폚. The drying time is preferably 5 to 30 minutes.

[Lamination step]

(Stretching)

The stretching performed in the lamination step of the present embodiment is performed for the purpose of forming a laminated film from the above-mentioned laminate. It is also intended to insolubilize the resulting resin film (11) by improving the orientation of the PVA-based resin by stretching the laminate. It is preferable that drawing performed in the lamination step is dry uniaxial drawing. The draw ratio is preferably 1.3 to 2.2 times, more preferably 1.5 to 2.0 times, and even more preferably 1.8 to 2.0 times, based on the unstretched laminate. If the draw ratio is higher than 2.2 times, the resin film 11 formed on at least one side of the stretched base film tends to be easily broken. If the stretching magnification is lower than 1.3 times, the polarization characteristic of the resulting polarizing film 19 may be lowered.

If the stretching magnification in the lamination step of the present embodiment is within the above-described range, it may be performed in multiple steps. Examples of the multistage stretching method include inter-roll stretching in which a plurality of pairs of pinch rolls (nip rolls) are stretched by a main speed difference, thermal roll stretching as described in Japanese Patent No. 2731813, or tenter stretching.

The drawing temperature in the lamination step of the present embodiment is preferably 80 to 160 占 폚, more preferably 90 to 150 占 폚, and further preferably 100 to 130 占 폚.

[Insolubilization Process]

The insolubilization step of the present embodiment is carried out for the purpose of insolubilizing the resin film 11 in the laminated film in the subsequent steps. The insolubilization step is carried out by immersing the laminated film in a solution containing a third crosslinking agent (hereinafter referred to as insoluble bath). As the third crosslinking agent to be contained in the insoluble 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 non-solubilization step of this embodiment may be the same as the first crosslinking agent used in the subsequent crosslinking step. As the solvent of the insoluble 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. The temperature of the insoluble bath is preferably 25 ° C or higher, more preferably 30 to 85 ° C, and still more preferably 30 to 60 ° C. The immersing time in the insoluble bath described above is preferably 5 to 800 seconds, more preferably 8 to 500 seconds.

According to the present embodiment, there is provided a polarizing film producing method capable of obtaining a polarizing film 19 having excellent polarizing properties. Further, in the present embodiment, it is possible to produce a thin polarizing film having a thickness of 10 mu m or less. In the conventional method of producing a thin polarizing film, since the resin film 11 is formed by applying a PVA resin solution, there is a problem that the resin film 11 is liable to be dissolved in a bath. Particularly, in the cleaning step, the orientation of the dichroic substance is liable to be disturbed, and the polarizing characteristic of the obtained thin polarizing film is likely to be deteriorated. On the other hand, in the method of producing a polarizing film of the present embodiment, the orientation of the dichroic substance is not disturbed in the cleaning step even in the production of the thin polarizing film, and the deterioration of the polarization property of the resulting thin polarizing film can be further suppressed.

<Modifications>

On the other hand, the technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of not impairing the effect of the present invention.

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

Further, for example, in the above-described embodiment, the resin film 11 is stretched together with the crosslinking, but the stretching may be performed before the resin film 11 is crosslinked. When the resin film 11 is stretched before the crosslinking of the resin film 11, the resin film 11 may be stretched before or after dyeing, but it is preferable that the resin film 11 is stretched together with the resin film 11. In the case of drawing before the crosslinking of the resin film 11, the drawing magnification is preferably 4 or less, and more preferably 2.8 to 3.8.

Further, for example, in the above-described embodiment, metal salts may be contained in a solution used in each step (hereinafter referred to as bath). By including the 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 the resin film 11 contains metal ions and therefore has an advantage of improving the color tone and durability of the resin film 11. As the metal salt, 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 and zinc acetate are more preferable Do.

Further, for example, in the second embodiment, the laminated film is insolubilized before dyeing the laminated film, but it may be performed before the laminated film is independently crosslinked. By insolubilizing the laminated film even before crosslinking of the laminated film, it is possible to inhibit the PVA-based resin, which is a material for forming the dye film 13 contained in the laminated film, from dissolving in the crosslinking bath.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

&Lt; Example 1 >

An amorphous polyethylene terephthalate film (NovaClear (registered trademark) manufactured by Mitsubishi Kagaku Kabushiki Kaisha) having a thickness of 200 탆 was prepared as a base film and subjected to corona treatment on one side at a condition of 90 W · min / Respectively. A PVA resin aqueous solution having a degree of polymerization of 4000 and a degree of saponification of 99.0 mol% or more was applied to the surface of the corona-treated substrate film and dried at 65 캜 to form a PVA resin layer having a thickness of 8.3 탆.

The laminate thus obtained was uniaxially stretched at 90 DEG C at a stretching ratio of 1.8 times based on the unstretched laminate by using a stretching device provided in an oven. Next, an aqueous solution (insoluble bath) in which 3 parts by mass of boric acid was blended with 100 parts by mass of water was prepared. The obtained laminated film was immersed for 30 seconds in an insoluble bath controlled at a liquid temperature of 30 占 폚 to insolubilize it.

An iodine aqueous solution was prepared by mixing 0.18 parts by mass of iodine and 1.26 parts by mass of potassium iodide with respect to 100 parts by mass of water. The insolubilized laminated film was immersed in an iodine aqueous solution adjusted to a liquid temperature of 30 캜 for 13 seconds to be dyed with iodine to prepare a polarizing film having a transmittance of about 42.0%.

An aqueous solution (crosslinking bath) was prepared by mixing 3 parts by mass of potassium iodide and 3 parts by mass of boric acid with respect to 100 parts by mass of water. The laminated film stained with iodine was immersed in a crosslinking bath controlled at a liquid temperature of 40 占 폚 for 30 seconds to crosslink.

An aqueous solution was prepared by mixing 4 parts by mass of boric acid and 5 parts by mass of potassium iodide with respect to 100 parts by mass of water. The film was uniaxially stretched in the longitudinal direction (longitudinal direction) while immersing the cross-linked laminated film in an aqueous solution adjusted to a liquid temperature of 75 占 폚, followed by stretching in water. The maximum draw ratio of the obtained laminated film was 5.94 times based on the unstretched laminate.

An aqueous solution (cleansing bath) containing 4 parts by mass of potassium iodide and 0.005 parts by mass of boric acid was prepared with respect to 100 parts by mass of water. The laminated film thus stretched in water was immersed for 5 seconds in a cleansing bath adjusted to a solution temperature of 30 占 폚 to be washed. The washed laminated film was dried with warm air at 60 캜 to prepare a polarizing film on the surface of the base film. The thickness of the polarizing film integrally stretched with the base film was 4.5 占 퐉.

&Lt; Examples 2 to 4, Comparative Examples 1 to 3 >

A polarizing film was produced in the same manner as in Example 1 except that the concentration of boric acid contained in the cleansing bath was changed as shown in Table 1. [

<Production of Polarizer>

First, a 3% by mass PVA resin aqueous solution was prepared by dissolving PVA powder ("KL-318" manufactured by Kabushiki Kaisha Kuraray Co., Ltd., average degree of polymerization: 1800) in hot water at 95 ° C. A crosslinking agent (Sumirez Resin (registered trademark) 650, manufactured by Daoka Kagaku Kogyo K.K.) was mixed in an amount of 1 part by mass with respect to 2 parts by mass of the PVA powder to obtain an adhesive.

The obtained adhesive was applied to the surface of the laminated film produced in the above-mentioned Examples and Comparative Examples, on which the polarizing films were laminated. Next, triacetylcellulose (TAC) ("KC4UY", manufactured by Konica Minolta K.K.) having a thickness of 40 탆 and saponified with an adhesive surface was bonded to the surface to which the adhesive had been applied as a protective film, and the film was laminated using a roll laminator Respectively.

After compression, the polarizing film, the adhesive, and the base film integrated with the TAC were peeled off to produce a polarizing plate.

<Evaluation method>

The presence or absence of dirt adhering to the surfaces of the polarizing films prepared in Examples and Comparative Examples was visually observed. The visual sensitivity-corrected single transmittance and visibility-corrected polarized light intensity were obtained as the polarization characteristics of the obtained polarizing film. On the other hand, the visual sensitivity-corrected single-beam transmittance and visual sensitivity correction polarization degree were obtained by the following methods.

[Measurement of Visible Light Correction Unit Transmittance]

The visibility-correcting simple transmittance of the obtained polarizing film was measured with a spectrophotometer (V7100, manufactured by Nihon Bunko K.K.) having an integrating sphere. The MD transmittance and the 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 the formula (1).

Further, visual sensitivity correction was performed by a 2-degree visual field (C light source) of JIS Z 8701 to obtain a visual sensitivity-corrected single-unit transmittance. Here, the "MD transmittance" indicates the transmittance when the direction of the polarized light emitted from the Grythmoth Prism is parallel to the transmission axis of the polarizing plate sample. The term &quot; TD transmittance &quot; refers to the transmittance when the direction of polarization from the Glan Thompson prism and the transmission axis of the polarizing plate sample are orthogonal.

[Measurement of visibility correction polarization degree]

Based on the above-mentioned MD transmittance and TD transmittance, the degree of polarization at each wavelength was calculated based on the formula (2). Further, visual sensitivity correction was performed by a 2-degree visual field (C light source) of JIS Z 8701 to obtain a visual sensitivity-corrected single-unit transmittance.

Table 1 shows the concentrations of boric acid with respect to 100 parts by mass of water in the cleansing bath used in Examples and Comparative Examples. Table 1 shows the presence or absence of dirt of the polarizing film produced in the examples and the comparative examples and the polarization characteristics (transmittance and visibility correction polarity).

In the present embodiment, when the concentration of boric acid in the cleansing bath is within the range specified in the present invention, a polarizing film excellent in polarization characteristics (transmittance for visible sensitivity correction and visibility correction polarity) is obtained without occurrence of defects such as dirt I could. Specifically, in the polarizing films of Examples 1 to 4, the transparency of the visual sensitivity-corrected single unit was equal to that of the polarizing films of Comparative Examples 1 to 3, and the visibility-correcting polarized light intensity was excellent.

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

11: strip-shaped resin film made of a polyvinyl alcohol-based resin
13: Dyeing film 15: Crosslinked film
19: Polarizing film 21: Feed roll
23: dyeing tank 25: crosslinking tank
27: Washing tank 29: Drying furnace
101 to 105: Nip rolls 111 to 119:

Claims (7)

A method for producing a polarizing film in which the resin film is dyed with a dichroic material while conveying a strip-shaped resin film made of a polyvinyl alcohol-based resin as a material,
The resin film dyed with the dichroic substance is immersed in a crosslinking bath (crosslinking bath) containing a first crosslinking agent to obtain a crosslinked film in which the resin film stained with the dichroic substance is crosslinked with the first crosslinking agent A crosslinking step,
And a cleaning step of cleaning the crosslinked film with an aqueous solution containing a second crosslinking agent,
Wherein the total amount of the first crosslinking agent and the second crosslinking agent contained in the aqueous solution is controlled to fall within a range of not less than 0.003 parts by mass and less than 0.1 part by mass with respect to 100 parts by mass of water in the washing step. The method according to claim 1, wherein, prior to the crosslinking step, a polyvinyl alcohol resin solution is applied to at least one side of the substrate film while the strip-like base film is transported in the longitudinal direction, A resin layer forming step of forming a resin layer made of a polyvinyl alcohol-based resin,
A lamination step of stretching the laminate obtained in the resin layer forming step in the longitudinal direction to obtain a laminated film in which the base film is stretched and the resin film formed on one side of the stretched base film is laminated Of the polarizing film. The method for producing a polarizing film according to claim 1 or 2, wherein the second crosslinking agent is a boron compound. The method of producing a polarizing film according to claim 1 or 2, wherein the first crosslinking agent and the second crosslinking agent are the same compound. The method for producing a polarizing film according to claim 1 or 2, wherein the dichroic substance is iodine. The method of producing a polarizing film according to claim 5, wherein the aqueous solution contains iodide. 7. The method of claim 6, wherein the iodide is potassium iodide.

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