CN109917506B

CN109917506B - Polarizing film

Info

Publication number: CN109917506B
Application number: CN201910090674.8A
Authority: CN
Inventors: 大园达也; 风藤修
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2014-03-04
Filing date: 2015-02-23
Publication date: 2022-05-24
Anticipated expiration: 2035-02-23
Also published as: TW201539064A; CN106062596A; CN106062596B; JP6618890B2; CN109917506A; KR102411225B1; KR20160129004A; JPWO2015133304A1; TWI668472B; WO2015133304A1

Abstract

[ problem ] to]A polarizing film with less leakage of blue light in a cross prism state is provided. [ solution means ] to]A polarizing film in which an iodine dye is adsorbed to a matrix comprising PVA, wherein a cross section of the polarizing film is subjected to Raman spectroscopy, and the polarizing film is disposed at a position of 310cm from one surface of the film to 10% of the thickness of the polarizing film from the inside in the thickness direction^‑1Signal intensity of Down (Int)³¹⁰) And 210cm^‑1Signal intensity of Down (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) Denoted as M, is to be taken from the other side of the film to the inside in the thickness direction to 310cm at a portion of 10% of the thickness^‑1Lower signal intensity (Int)³¹⁰) And 210cm^‑1Lower signal intensity (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) When the notation is N, (wherein, M is less than or equal to N), M/N is less than or equal to 0.91.

Description

Polarizing film

This application is a divisional application of PCT application filed on 2015, 2/23, application No. 201580011559.7, entitled "polarizing film".

Technical Field

The present invention relates to a polarizing film with less leakage of blue light in a cross prism state and a method for manufacturing the same.

Background

A polarizing plate having light transmitting and light blocking functions and a liquid crystal for changing the polarization state of light are the basic components of a Liquid Crystal Display (LCD). Many types of polarizing plates have a structure in which a protective film such as a Triacetylcellulose (TAC) film is attached to the surface of a polarizing film, and as a polarizing film constituting a polarizing plate, a substrate (a stretched film in which a polyvinyl alcohol film (hereinafter, polyvinyl alcohol is abbreviated as "PVA") is uniaxially stretched and an iodine-based dye (I) is adsorbed to the substrate₃ ^-、I₅ ^-Etc.) becomes the mainstream. Such a polarizing film is manufactured as follows: uniaxially stretching a PVA film containing an iodine-based dye in advance, adsorbing an iodine-based dye while uniaxially stretching a PVA film, or uniaxially stretching a PVA filmAdsorbing iodine-based pigments, etc.

LCDs are increasingly used in a wide range of small-sized devices such as calculators and wristwatches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car navigation systems, mobile phones, and measuring devices used indoors and outdoors, and in recent years, in particular, in mobile applications such as small-sized notebook computers and mobile phones, a demand for thinning of polarizing plates has been increasing.

As a method for thinning a polarizing film constituting a polarizing plate, there are known: a method in which a laminate obtained by forming a PVA layer on one surface of a thermoplastic resin film is stretched, dyed, and dried, and then the stretched thermoplastic resin film is peeled off as necessary (see patent documents 1 and 2, etc.).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2010/100917

Patent document 2: specification of japanese patent No. 4691205.

Disclosure of Invention

Problems to be solved by the invention

However, when a thin polarizing film is manufactured by a conventionally known method, there is a problem that leakage of blue light is large in a cross prism state. Accordingly, an object of the present invention is to provide a polarizing film with less leakage of blue light in a cross prism state and a method for manufacturing the same.

Means for solving the problems

The present inventors have made extensive studies to achieve the above object, and as a result, have found that: when a polarizing film is produced by dyeing and stretching a laminate comprising a PVA layer and a thermoplastic resin film layer, it is possible to easily obtain a conventionally nonexistent polarizing film in which each measurement result in the vicinity of the film surface obtained by raman spectroscopic measurement of a cross section satisfies a specific relationship and leakage of blue light in a cross-prism state is small by setting the temperature of a dyeing bath containing an iodine-based dye used and the immersion time in the dyeing bath to specific ranges, and further studies have been repeated based on this finding, thereby completing the present invention.

Namely, the present invention relates to the following technical means:

[1]a polarizing film in which an iodine dye is adsorbed to a matrix comprising PVA, wherein a cross section of the polarizing film is subjected to Raman spectroscopy, and the polarizing film is disposed at a position of 310cm from one surface of the film to 10% of the thickness of the polarizing film from the inside in the thickness direction^-1Signal intensity of Down (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) M, which is 310cm at a portion 10% of the thickness of the film from the other surface of the film toward the inside in the thickness direction^-1Signal intensity of Down (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) When the notation is N, (wherein, M is less than or equal to N), M/N is less than or equal to 0.91;

[2] the polarizing film according to the above [1], wherein a ratio (A/B) of an absorbance (A) at a wavelength of 480nm to an absorbance (B) at a wavelength of 700nm in a cross prism state is 1.40 or more;

[3] the polarizing film according to the above [1] or [2], wherein the thickness is 15 μm or less;

[4] the polarizing film according to any one of the above [1] to [3], wherein the monomer transmittance is 40 to 45%;

[5] a method for producing a polarizing film comprising a step of dyeing and stretching a laminate comprising a PVA layer and a thermoplastic resin film layer, wherein the dyeing is carried out by immersing the laminate in a dyeing bath containing an iodine-based dye, the temperature of the dyeing bath being 25 ℃ or less and the immersion time being 2.5 minutes or less;

[6] the production method according to the above [5], wherein the PVA layer has a thickness of 30 μm or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a polarizing film with less leakage of blue light in a cross prism state is provided. In addition, according to the present invention, a method for manufacturing a polarizing film is provided, which can easily manufacture the polarizing film.

Detailed Description

The present invention will be described in detail below.

(polarizing film)

The matrix containing PVA in the polarizing film of the present invention adsorbs an iodine-based dye. Then, a portion of 310cm at a portion of 10% of the thickness from one surface of the film to the inside in the thickness direction, which portion was obtained by measuring the cross section of the polarizing film by raman spectroscopy^-1Lower signal intensity (Int)³¹⁰) And 210cm^-1Lower signal intensity (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) Denoted as M, is to be taken from the other side of the film to the inside in the thickness direction to 310cm at a portion of 10% of the thickness^-1Lower signal intensity (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) When the notation is N, (wherein, M is less than or equal to N), M/N is less than or equal to 0.91.

In the case of raman spectroscopy of the cross section of the polarizing film, for example, a sample obtained by slicing the polarizing film to be measured in the thickness direction thereof may be used, and raman spectroscopy may be performed by a raman spectrometer, and specifically, a laser beam having a wavelength of 532nm may be irradiated to a portion to be measured of the sample to be measured and raman spectroscopy may be performed by using a laser raman spectroscopy apparatus such as a micro laser raman spectroscopy apparatus "LabRAM ARAMIS VIS" manufactured by horiba ltd. 310cm of each of the measurement target portions obtained by the above operation^-1Signal intensity of Down (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) The ratio (Int) of the fractions is calculated³¹⁰/Int²¹⁰). As the ratio (Int) of each part of the film³¹⁰/Int²¹⁰) More specific measurement methods and/or conditions in the case of the above-mentioned measurement can be the same as those described in examples. In the case of a polarizing film having a thickness of 10 μm, for example, a portion entering 10% of the thickness from each surface of the film toward the inside in the thickness direction defined in the present invention corresponds to a portion entering 1 μm (10 μm × 10% =1 μm) from each surface of the polarizing film toward the inside in the thickness direction. Albeit at the end ofWithout limiting the invention at all, it is believed that: ratio of portions of the film (Int)³¹⁰/Int²¹⁰) Depending on the I of the moiety₅ ^-Is present in an amount relative to I₃ ^-The ratio of the amounts present.

The polarizing film of the present invention has an M/N ratio of 0.91 or less. When the M/N is 0.91 or less, the polarizing film is reduced in leakage of blue light in the cross prism state. Since a polarizing film with less leakage of blue light in the cross prism state can be obtained, M/N is preferably 0.85 or less, more preferably 0.76 or less, and further preferably 0.72 or less. From the viewpoint of reducing leakage of red light in the cross prism state, M/N is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.5 or more.

The polarizing film having the iodine-based dye adsorbed on the matrix can be produced by stretching a PVA film containing the iodine-based dye in advance, or by simultaneously adsorbing the iodine-based dye while stretching the PVA film, or by forming a matrix by stretching the PVA film and then adsorbing the iodine-based dye, and more specifically, can be produced by: the substrate may be produced by stretching a laminate comprising a PVA layer (corresponding to a PVA film) containing an iodine-based dye in advance and a thermoplastic resin film layer, or by allowing the PVA layer to adsorb the iodine-based dye while stretching a laminate comprising the PVA layer and the thermoplastic resin film layer, or by stretching a laminate comprising the PVA layer and the thermoplastic resin film layer, and then allowing a matrix formed from the PVA layer to adsorb the iodine-based dye or the like.

As the PVA, a PVA obtained by saponifying polyvinyl ester obtained by polymerizing 1 or 2 or more vinyl esters selected from vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropenyl acetate can be used. Among the vinyl esters, vinyl acetate is preferable from the viewpoint of ease of production, availability, cost, and the like of PVA.

The polyvinyl ester may be a copolymer of 1 or 2 or more kinds of vinyl esters and another monomer copolymerizable therewith as long as the effect of the present invention is not impaired.

Examples of the other monomer copolymerizable with the vinyl ester include an α -olefin having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutylene; (meth) acrylic acid or a salt thereof; (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and octadecyl (meth) acrylate; (meth) acrylamide derivatives such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamidopropanesulfonic acid or a salt thereof, (meth) acrylamidopropyldimethylamine or a salt thereof, and N-methylol (meth) acrylamide or a derivative thereof; n-vinylamides such as N-vinylformamide, N-vinylacetamide and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; ethylene cyanide such as (meth) acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester or anhydride thereof; itaconic acid or a salt, ester or anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids, and the like. The above polyvinyl esters may have 1 or 2 or more kinds of structural units derived from the aforementioned other monomers.

The proportion of the structural unit derived from the other monomer in the polyvinyl ester is preferably 15 mol% or less, may be 10 mol% or less, and further may be 5 mol% or less based on the number of moles of the total structural units constituting the polyvinyl ester.

In particular, when the other monomers are monomers which are likely to promote the water solubility of the PVA to be obtained, such as (meth) acrylic acid, unsaturated sulfonic acid, and the like, the proportion of the structural units derived from these monomers in the polyvinyl ester is preferably 5 mol% or less, more preferably 3 mol% or less, based on the number of moles of the total structural units constituting the polyvinyl ester, in order to prevent dissolution of the PVA during the production of a polarizing film.

The PVA may be modified with 1 or 2 or more kinds of graft-copolymerizable monomers within a range not to impair the effects of the present invention. Examples of the graft-copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; an unsaturated sulfonic acid or a derivative thereof; alpha-olefins having 2 to 30 carbon atoms, and the like. The proportion of the structural unit derived from a graft-copolymerizable monomer (the structural unit in the graft-modified portion) in the PVA is preferably 5 mol% or less based on the number of moles of the total structural units constituting the PVA.

The hydroxyl groups in the PVA may be partially crosslinked or uncrosslinked. The hydroxyl group in the PVA may partially react with an aldehyde compound such as acetaldehyde or butylaldehyde to form an acetal structure, or may not react with such a compound to form an acetal structure.

The average polymerization degree of the PVA is preferably in the range of 1,000 to 9,500, and the average polymerization degree is more preferably 1,500 or more, further preferably 2,000 or more, and further preferably 9,200 or less, further preferably 6,000 or less. By setting the average polymerization degree to 1,000 or more, the polarization performance of the polarizing film is improved. On the other hand, when the average degree of polymerization is 9,500 or less, the productivity of PVA is improved. The average degree of polymerization of PVA can be measured according to JIS K6726-1994.

The saponification degree of the PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and even more preferably 99 mol% or more, from the viewpoint of the polarizing performance of the polarizing film and the like. When the saponification degree is less than 98 mol%, the PVA is easily eluted during the production of the polarizing film, and the eluted PVA adheres to the film to deteriorate the polarizing performance of the polarizing film. The saponification degree of PVA in the present specification means: the proportion (% by mole) of the number of moles of the vinyl alcohol unit is based on the total number of moles of the structural unit (typically, a vinyl ester unit) that can be converted into a vinyl alcohol unit by saponification and the vinyl alcohol unit in the PVA. The degree of saponification can be measured according to JIS K6726-1994.

The iodine-based dye may be represented by I₃ ^-、I₅ ^-And the like. Examples of the counter cation include alkali metals such as potassium. The iodine-containing dye can be prepared by, for example, adding iodine (I)₂) By contacting with potassium iodide.

Since a thin polarizing plate which has been demanded in recent years can be easily obtained, the thickness of the polarizing film of the present invention is preferably 15 μm or less, more preferably 12 μm or less, further preferably 8 μm or less, and particularly preferably 5 μm or less. Since it is difficult to manufacture a polarizing film having an excessively thin thickness, the thickness of the polarizing film is, for example, 0.5 μm or more (2.5 μm or more in one example), and may be 4 μm or more, 5 μm or more, and further 6 μm or more from the viewpoint of the manufacture.

From the viewpoint of reducing leakage of blue light, the polarizing film of the present invention has a ratio (a/B) of absorbance (a) at a wavelength of 480nm to absorbance (B) at a wavelength of 700nm in a cross prism state of preferably 1.40 or more, more preferably 1.41 or more, still more preferably 1.42 or more, particularly preferably 1.45 or more, and may be 1.50 or more, and further 1.55 or more. On the other hand, when the ratio (a/B) is too high, leakage of red light tends to increase, and therefore, the ratio (a/B) is preferably 2 or less, more preferably 1.8 or less, and still more preferably 1.6 or less. The absorbance (a) and the absorbance (B) can be determined using a spectrophotometer, and specifically can be determined by the method described later in examples.

From the viewpoint of polarization performance, the single transmittance of the polarizing film of the present invention is preferably in the range of 40 to 45%, more preferably 41% or more, further preferably 42% or more, and further preferably 44% or less. The cell transmittance of the polarizing film can be measured by the method described later in examples.

(method for producing polarizing film)

The method for producing the polarizing film of the present invention is not particularly limited, and the polarizing film can be produced by using a PVA film as a raw material web (raw material web) film, dyeing and stretching the PVA film, for example, by dispersing a dyeing liquid containing an iodine-based pigment in a specific amount and concentration on one surface of the PVA film used as the raw material web film, bringing a roller coated with the dyeing liquid containing the iodine-based pigment into contact with one surface of the PVA film used as the raw material web film, bringing an impregnated body obtained by impregnating a porous body such as sponge with the dyeing liquid containing the iodine-based pigment into contact with one surface of the PVA film used as the raw material web film, and the like, and bringing the I near each surface of the obtained polarizing film into contact with one surface of the PVA film used as the raw material web film₅ ^-Is present in an amount relative to I₃ ^-The polarizing film of the present invention can be produced more easily by the following production method of the present invention, and therefore, it is preferable.

That is, the production method of the present invention includes a step of dyeing and stretching a laminate having a PVA layer and a thermoplastic resin film layer, the dyeing being performed by immersing the laminate in a dyeing bath containing an iodine-based dye, the temperature of the dyeing bath being 25 ℃ or less, and the immersion time being 2.5 minutes or less.

Examples of the thermoplastic resin constituting the thermoplastic resin film layer include various thermoplastic resins such as polyethylene, polypropylene, polymethylpentene, polystyrene, polycarbonate, polyvinyl chloride, methacrylic resin, nylon, and polyethylene terephthalate, and copolymers having a plurality of monomer units constituting these thermoplastic resins. In the thermoplastic resin film layer, the thermoplastic resin may include only 1 kind, or may include 2 or more kinds, either one of which may be included. Among these, from the viewpoint of having high heat resistance and stretchability, polyethylene terephthalate is preferable, and amorphous polyethylene terephthalate is more preferable.

The thickness of the thermoplastic resin film layer is preferably in the range of 20 to 250. mu.m, more preferably in the range of 30 to 230. mu.m, and still more preferably in the range of 50 to 200. mu.m. By setting the thickness of the thermoplastic resin film layer to 20 μm or more, wrinkles can be effectively prevented from occurring when the PVA layer is formed. On the other hand, by setting the thickness of the thermoplastic resin film layer to 250 μm or less, it is possible to suppress an excessive increase in tension when stretching the laminate.

The PVA constituting the PVA layer may be the same PVA as that already described in the description of the polarizing film of the present invention, and the redundant description thereof is omitted here.

From the viewpoint of improving stretchability upon stretching, the PVA layer preferably contains a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and the PVA layer may contain 1 or 2 or more of these plasticizers. Among these, glycerin is preferable from the viewpoint of the effect of improving stretchability.

The content of the plasticizer in the PVA layer is preferably in the range of 1 to 20 parts by mass with respect to 100 parts by mass of PVA contained therein. By setting the content to 1 part by mass or more, the stretchability of the PVA layer and/or the laminate can be further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the PVA layer from being too soft and thus the handleability from being lowered. The content of the plasticizer in the PVA layer is more preferably 2 parts by mass or more, further preferably 4 parts by mass or more, and particularly preferably 5 parts by mass or more, and further preferably 15 parts by mass or less, further preferably 12 parts by mass or less, with respect to 100 parts by mass of PVA.

The plasticizer contained in the PVA layer is dissolved out during the production of the polarizing film, and therefore, is not limited to being completely left in the polarizing film, although the plasticizer may be left in the polarizing film depending on the production conditions of the polarizing film.

The PVA layer may contain components such as an antioxidant, an antifreeze, a pH adjuster, a masking agent, a stainblocker, an oil agent, and a surfactant, if necessary.

From the viewpoint of ease of production of a desired polarizing film, the content of PVA in the PVA layer is preferably in the range of 50 to 99% by mass, more preferably 75% by mass or more, further preferably 80% by mass or more, particularly preferably 85% by mass or more, and further more preferably 98% by mass or less, further preferably 96% by mass or less, particularly preferably 95% by mass or less.

Since a thin polarizing film can be easily obtained, the thickness of the PVA layer is preferably 30 μm or less, more preferably 25 μm or less, further preferably 15 μm or less, and particularly preferably 10 μm or less. Since a laminate having a PVA layer with an excessively thin thickness is difficult to manufacture, the thickness of the PVA layer is, for example, 1 μm or more (5 μm or more in one example), and may be 8 μm or more, 10 μm or more, and further 12 μm or more from the viewpoint of manufacturing.

The layer structure of the laminate is not particularly limited, and since the polarizing film and the like of the present invention can be produced more easily, a 2-layer structure of 1 PVA layer and 1 thermoplastic resin film layer is preferable.

The shape of the laminate is not particularly limited, and a long laminate is preferable because the laminate can be continuously used in the production of a polarizing film. The length of the long laminate (length in the long direction) is not particularly limited, and may be appropriately set according to the application of the polarizing film to be produced, and may be, for example, in the range of 5 to 20,000 m.

The width of the laminate is not particularly limited, and can be appropriately set according to the application of the polarizing film to be produced, and in recent years, from the viewpoint of the gradual increase in the screen size of liquid crystal televisions and liquid crystal monitors, the width of the laminate is set to 0.5m or more, and more preferably 1.0m or more, and is suitable for these applications. On the other hand, when the width of the laminate is too wide, it tends to be difficult to uniformly stretch the polarizing film in the production of a device to be used in practice, and therefore, the width of the laminate is preferably 7m or less.

Examples of the method for producing the laminate include a method of forming a PVA layer on a thermoplastic resin film, and specifically, the following methods: a method of coating a thermoplastic resin film with a dope obtained by dissolving PVA and optionally other components other than PVA such as the plasticizer in a liquid medium and drying the dope; a method in which a dope obtained by melt-kneading PVA, a liquid medium, and, if necessary, other components is extruded onto a thermoplastic resin film, and further dried if necessary; a method of producing a PVA film containing PVA and, if necessary, other components by a known method and then bonding the PVA film to a thermoplastic resin film. Among these, from the viewpoint of easily preparing a thin PVA layer and the viewpoint of thickness uniformity of the PVA layer to be obtained, a method of coating and drying a dope obtained by dissolving PVA and other components further added as necessary in a liquid medium on a thermoplastic resin film is preferable.

Examples of the liquid medium include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, and the like, and 1 or 2 or more of these can be used. Among them, water is preferable from the viewpoint of the burden on the environment and the recyclability.

The volatilization fraction of the stock solution (the content of volatile components such as a liquid medium removed by volatilization, drying, or the like when forming the PVA layer in the stock solution) varies depending on the method of forming the PVA layer, the formation conditions, and the like, and is preferably in the range of 50 mass% to 98 mass%, more preferably 55 mass% to 95 mass%. When the volatile fraction of the stock solution is 50 mass% or more, the viscosity is not excessively high, filtration and defoaming during preparation of the stock solution are smoothly performed, a PVA layer with few foreign matters and defects is easily formed, and the coatability is also improved. On the other hand, when the volatilization fraction of the stock solution is 98 mass% or less, the concentration of the stock solution is not excessively low, and the industrial production of the laminate is facilitated.

Examples of a coating method when the dope is coated on the thermoplastic resin film include a die coating method, a comma coating method, a dip coating method, and the like. Among these, the die coating method is preferable from the viewpoint of the thickness uniformity of the PVA layer to be obtained.

The thermoplastic resin film used for producing the laminate is preferably subjected to a hydrophilization treatment on at least one surface in advance. By forming the PVA layer so as to contact such a hydrophilized surface, the adhesion between the thermoplastic resin film layer and the PVA layer is improved. Examples of the hydrophilization treatment include corona discharge treatment, plasma treatment, anchor coating treatment, and the like. Among these, corona discharge treatment is preferable from the viewpoint of easy adjustment of hydrophilicity.

The surface contact angle of the thermoplastic resin film is preferably adjusted to 55 to 70 °, more preferably to 57 ° or more, further preferably to 59 ° or more, further preferably to 69 ° or less, further preferably to 68 ° or less by the hydrophilization treatment. When the contact angle is less than 55 °, the adhesion strength between the thermoplastic resin film layer and the PVA layer tends to become too strong, and peeling may be difficult when the stretched thermoplastic resin film layer is peeled off after stretching the laminate. On the other hand, when the contact angle is higher than 70 °, the following tendency is exhibited: in the stretching of the laminate, the PVA layer is easily peeled or chipped from the thermoplastic resin film layer, and it is difficult to perform the stretching at a high stretching ratio. The surface contact angle of the thermoplastic resin film means: the angle (angle inside water) formed between the water surface of the portion where the free surface of water contacts the thermoplastic resin film and the surface of the thermoplastic resin film can be measured by the method described later in examples.

The conditions of the corona discharge treatment when the surface contact angle of the thermoplastic resin film is adjusted to the above range by the corona discharge treatment are not particularly limited, and the surface contact angle of the thermoplastic resin film can be easily adjusted to the above range, and therefore, the discharge amount represented by the following formula (1) is preferably 180 to 350W · min/m²More preferably 190 to 320 W.min/m²More preferably 200 to 300 W.min/m²Within the range of (1).

Discharge capacity (W.min/m)²) = output power (W/m)/processing speed (m/min) (1).

The drying conditions after coating or extruding the dope on the thermoplastic resin film are not particularly limited, and in order to prevent the thermoplastic resin film from being wrinkled, it is preferable to dry the thermoplastic resin film at a temperature not higher than the glass transition temperature thereof.

The production method of the present invention comprises a step of dyeing the laminate (dyeing step) and a step of stretching the laminate (stretching step), and may further comprise an insolubilization step, a swelling step, a crosslinking step, a fixing step, a washing step, a drying step, and the like, if necessary, in addition to the dyeing step and the stretching step. The order of the steps may be changed as needed, and the steps may be performed 2 or more times, or different steps may be performed simultaneously. In addition, according to the above-described manufacturing method, the polarizing film formed on the stretched thermoplastic resin film layer can be obtained, but a step of peeling off the stretched thermoplastic resin film layer may be included as necessary.

As an example of the production method of the present invention, the following method can be mentioned: first, the laminate is subjected to an insolubilization step, if necessary, a swelling step, a dyeing step, if necessary, a crosslinking step, a stretching step, if necessary, a fixing step and/or a cleaning step, and a drying step, and through these series of steps, a polarizing film formed on a stretched thermoplastic resin film layer is obtained, and the stretched thermoplastic resin film layer is further peeled off if necessary.

The insolubilization treatment is mainly performed to prevent the PVA contained in the PVA layer from dissolving out into water. Examples of the insolubilization treatment include a method of subjecting the laminate to a heat treatment; a method of immersing the laminate in an aqueous solution containing 1 or 2 or more kinds of boron compounds such as boric acid and borates such as borax as an insolubilizing bath. Among these, when the laminate is subjected to heat treatment, wrinkles may occur due to dimensional changes of the thermoplastic resin film layer, and therefore, a method using an aqueous solution containing a boron compound is preferred. The heat treatment may be performed at a temperature in the range of 80 to 200 ℃. From the viewpoint of preventing wrinkles, the heat treatment is preferably performed under the condition that tension is applied to the laminate. In the method of using the aqueous solution containing the boron compound, the temperature of the aqueous solution is preferably in the range of 20 to 40 ℃, more preferably in the range of 22 to 38 ℃, and still more preferably in the range of 25 to 35 ℃. By setting the temperature within the range of 20 to 40 ℃, the PVA can be prevented from dissolving and can be efficiently insolubilized. The time for immersing in the aqueous solution containing the boron compound is, for example, in the range of 0.1 to 5 minutes. The insolubilization can be efficiently performed by setting the time to be in the range of 0.1 to 5 minutes. The concentration of the boron compound in the aqueous solution containing the boron compound is preferably in the range of 0.5 to 6.0 mass%, more preferably in the range of 1.0 to 5.0 mass%, and still more preferably in the range of 1.5 to 4.0 mass%. When the concentration is in the range of 0.5 to 6.0 mass%, PVA can be prevented from dissolving and can be efficiently insolubilized.

The insolubilization treatment is preferably performed before the dyeing step, and more preferably before the swelling step.

The swelling step may be performed by immersing the laminate in water. The temperature of water when immersed in water is preferably in the range of 20 to 40 ℃, and the temperature is more preferably 22 ℃ or higher, further preferably 25 ℃ or higher, and further preferably 38 ℃ or lower, further preferably 35 ℃ or lower. When the temperature is set within the range of 20 to 40 ℃, the PVA layer can be efficiently swelled. The time for immersing in water is preferably in the range of 0.1 to 5 minutes, and more preferably in the range of 0.5 to 3 minutes. When the time is in the range of 0.1 to 5 minutes, the PVA layer can be efficiently swelled. The water to be immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

In the production method of the present invention, dyeing is performed by immersing the laminate in a dyeing bath containing an iodine-based dye, and here, the temperature of the dyeing bath needs to be 25 ℃ or less, and the immersion time needs to be 2.5 minutes or less.

When the temperature of the dyeing bath exceeds 25 ℃, leakage of blue light of the obtained polarizing film in a cross prism state becomes large. From this viewpoint, when the temperature of the dyeing bath is preferably 23 ℃ or lower, more preferably 21 ℃ or lower, further preferably 18 ℃ or lower, and may be 15 ℃ or lower, further 10 ℃ or lower, and particularly when a laminate having a thinner PVA layer is used, the temperature of the dyeing bath is further lowered, whereby the polarizing film of interest can be obtained more efficiently. On the other hand, when the temperature of the dyeing bath is too low, the polarizing film obtained may be mottled, and therefore, the temperature of the dyeing bath is preferably 3 ℃ or more, more preferably 5 ℃ or more.

When the immersion time when the laminate is immersed in the dyeing bath exceeds 2.5 minutes, leakage of blue light in a cross prism state of the obtained polarizing film also increases. From this viewpoint, the immersion time is preferably 2.0 minutes or less, more preferably 1.5 minutes or less, and may be 0.8 minutes or less, 0.3 minutes or less, and further 0.2 minutes or less, and particularly, when a laminate having a thinner PVA layer is used, the immersion time is further shortened, whereby the objective polarizing film can be more effectively obtained. On the other hand, if the immersion time is too short, the polarizing film obtained may be mottled, and therefore, the immersion time is preferably 0.01 minutes or more, more preferably 0.05 minutes or more.

As a representative example of the dyeing bath, iodine (I) is used₂) And a dyeing bath obtained by mixing potassium iodide with water. I can be produced by mixing iodine and potassium iodide with water₃ ^-And I₅ ^-Iodine-based pigments such as iodine-based pigments. The concentration of iodine and potassium iodide in the dyeing bath is not particularly limited, but the concentration of iodine is preferably in the range of 0.01 to 2% by mass, more preferably 0.02 to 1% by mass, in terms of the ratio of the mass of iodine used to the mass of the dyeing bath obtained, and the concentration of potassium iodide is preferably in the range of 10 to 300 times by mass, more preferably 15 to 150 times by mass, in terms of the ratio of the mass of potassium iodide used to the mass of iodine used. The dyeing bath may contain boric acid, borate such as borax, etc.

By performing the crosslinking step on the laminate, it is possible to more effectively prevent the PVA from dissolving out into water when wet stretching is performed at a relatively high temperature. From this viewpoint, the crosslinking step is preferably performed after the dyeing step and before the stretching step. The crosslinking step may be performed by immersing the laminate in an aqueous solution containing a crosslinking agent as a crosslinking bath. As the crosslinking agent, 1 or 2 or more kinds of boron compounds such as boric acid and borate such as borax can be used. The concentration of the crosslinking agent in the crosslinking bath is preferably in the range of 1 to 15% by mass, more preferably 2% by mass or more, and further more preferably 7% by mass or less, and further more preferably 6% by mass or less. By setting the concentration of the crosslinking agent within the range of 1 to 15 mass%, sufficient stretchability can be maintained. The crosslinking bath may contain an auxiliary such as potassium iodide. The temperature of the crosslinking bath is preferably in the range of 20 to 50 ℃, particularly preferably in the range of 25 to 40 ℃. By setting the temperature within the range of 20 to 50 ℃, crosslinking can be efficiently performed.

The stretching method for stretching the laminate is not particularly limited, and may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, the stretching may be carried out in an aqueous solution containing 1 or 2 or more kinds of boron compounds such as boric acid and borates such as borax, or may be carried out in the above-mentioned dyeing bath or in a fixing treatment bath to be described later. In the case of the dry stretching method, stretching may be performed at room temperature as it is, or may be performed with heat applied, or may be performed after water absorption. Among these, from the viewpoint of the thickness uniformity of the polarizing film obtained in the width direction, wet stretching is preferable, and stretching in an aqueous boric acid solution is more preferable. The boric acid concentration in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0 mass%, more preferably 1.0 mass% or more, further preferably 1.5 mass% or more, and further preferably 5.0 mass% or less, further preferably 4.0 mass% or less. By setting the boric acid concentration within the range of 0.5 to 6.0 mass%, a polarizing film having excellent thickness uniformity in the width direction can be obtained. The aqueous solution containing a boron compound may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10 mass%. By setting the concentration of potassium iodide within the range of 0.01 to 10 mass%, a polarizing film having a better polarizing performance can be obtained.

The temperature at which the laminate is stretched is preferably in the range of 5 to 90 ℃, more preferably 10 ℃ or higher, still more preferably 85 ℃ or lower, and still more preferably 80 ℃ or lower. When the temperature is set within the range of 5 to 90 ℃, a polarizing film having excellent thickness uniformity in the width direction can be obtained.

The stretching ratio in stretching the laminate is preferably 4 times or more, more preferably 5 times or more, and further preferably 6 times or more. When the stretch ratio of the laminate is within the above range, a polarizing film having more excellent polarizing performance can be obtained. The upper limit of the stretch ratio of the laminate is not particularly limited, but is preferably 8 times or less. The laminate may be stretched once or in multiple times, and in any case, when the laminate is stretched in multiple times, the total stretch ratio obtained by adding the stretch ratios of the individual stretches may be within the above range. In the present specification, the stretch ratio is based on the length of the laminate before stretching, and the unstretched state corresponds to a stretch ratio of 1.

The stretching of the laminate is preferably uniaxial stretching from the viewpoint of the performance of the obtained polarizing film. The direction of uniaxial stretching in stretching the long laminate is not particularly limited, and uniaxial stretching or transverse uniaxial stretching in the long direction may be used, and since a polarizing film having more excellent polarizing performance can be obtained, uniaxial stretching in the long direction is preferable. The uniaxial stretching in the longitudinal direction can be performed by using a stretching apparatus including a plurality of parallel rolls and changing the peripheral speed between the rolls. On the other hand, the transverse uniaxial stretching may be performed using a tenter type stretching machine.

The fixing treatment step is mainly performed to firmly adsorb the iodine-based dye to the PVA layer. The fixing treatment step may be performed by immersing the laminate before, during, or after stretching in a fixing treatment bath. As the fixing treatment bath, an aqueous solution containing 1 or 2 or more kinds of boron compounds such as boric acid and borate such as borax may be used. Further, an iodine compound or a metal compound may be added to the fixing treatment bath as needed. The concentration of the boron compound in the aqueous solution containing the boron compound used as the fixing treatment bath is usually in the range of 0.1 to 15 mass%, particularly preferably in the range of 1 to 10 mass%. When the concentration is in the range of 0.1 to 15% by mass, the adsorption of the iodine-based dye can be further stabilized. The temperature of the fixing treatment bath is preferably within a range of 10 to 60 ℃, particularly preferably within a range of 15 to 40 ℃. By setting the temperature within the range of 10 to 60 ℃, the adsorption of the iodine-based dye can be further stabilized.

The cleaning step is often performed to remove unnecessary chemicals and foreign substances on the film surface or to adjust the optical properties of the polarizing film finally obtained. The cleaning step may be performed by immersing the laminate in a cleaning bath or by spreading a cleaning liquid into the laminate. As a cleaning bath or a cleaning liquid, water may be used, and potassium iodide may be contained therein.

The drying conditions in the drying step are not particularly limited, and the drying is preferably performed at a temperature in the range of 30 to 150 ℃, particularly preferably in the range of 50 to 130 ℃. The polarizing film having excellent dimensional stability can be easily obtained by drying at a temperature in the range of 30 to 150 ℃.

By the above operation, a polarizing film formed on the stretched thermoplastic resin film layer can be obtained. The method of using the polarizing film in this form is not particularly limited, and for example, the polarizing film may be used as it is without peeling off the stretched thermoplastic resin film layer, or may be used as a polarizing plate after attaching an optically transparent protective film having mechanical strength to the polarizing film side as necessary; the polarizing plate may be produced by attaching a protective film to the side opposite to the side having the stretched thermoplastic resin film layer, peeling off the stretched thermoplastic resin film layer, and then using the resultant as it is, or by attaching another protective film to the peeled surface as desired. As the protective film, a Triacetylcellulose (TAC) film, a Cellulose Acetate Butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. The adhesive used for the adhesion may be a PVA adhesive, a polyurethane adhesive, or the like, and is preferably a PVA adhesive.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples at all.

The following are the methods for measuring the surface contact angle of the thermoplastic resin film, and the methods for measuring and/or calculating the absorbance, the monomer transmittance, and the M/N of the polarizing film, which are used in the following examples and comparative examples.

[ surface contact Angle of thermoplastic resin film ]

The contact angle was measured by extruding 2. mu.L of pure water from a needle having an inner diameter of 0.4mm to the surface of the thermoplastic resin film at 20 ℃ and 65% RH using "DropMaster 500" manufactured by Kyowa interfacial science corporation.

[ Absorbance and monomer transmittance of polarizing film ]

A 2cm rectangular sample was collected from the center in the width direction (TD) of the polarizing film obtained in the following examples or comparative examples along the longitudinal direction (MD) of the polarizing film, and the sample was set in a cross prism state with respect to a polarizing plate of a spectrophotometer using a spectrophotometer with an integrating sphere ("V7100" manufactured by japan spectrographic corporation), and absorbance (a) at a wavelength of 480nm and absorbance (B) at a wavelength of 700nm were measured. Next, using the same sample and a spectrophotometer, visibility correction was performed in the visible light region of a 2 ° field of view using a C light source according to JIS Z8722 (method for measuring object color), and with respect to the sample, the light transmittance at an inclination of 45 ° and the light transmittance at an inclination of-45 ° with respect to the longitudinal direction were measured, and the average (%) of these values was taken as the monomer transmittance of the polarizing film.

[ M/N of polarizing film ]

In the polarizing films obtained in the following examples and comparative examples, at any position in the longitudinal direction (MD), a thin piece having a dimension of MD × TD =2mm × 10mm was cut from the central portion in the width direction (TD), and both surfaces of the thin piece were sandwiched by two pieces of polyethylene terephthalate film having a thickness of 100 μm, and mounted on a microtome. The chips were cut at 20 μm intervals from a polyethylene terephthalate film in parallel with the MD, and samples having dimensions MD × TD =2mm × 20 μm were collected.

The sample was irradiated with a wave at a portion to be measured on a cross section obtained by slicing with a microtome using a micro laser Raman Spectroscopy apparatus "LabRAM ARAMIS VIS" manufactured by horibaRaman spectroscopy was carried out using a laser beam of 532nm, and the intensity of the signal obtained at this time was measured at 310cm^-1Signal intensity of Down (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) The ratio (Int) of the fractions is calculated³¹⁰/Int²¹⁰). The measurement target portion is a portion that enters 10% of the thickness of the polarizing film from each surface thereof along the thickness direction of the film, and the two ratios (Int) obtained are set as the above measurement target portion³¹⁰/Int²¹⁰) M/N is calculated using M and N, where M is equal to or greater than N.

[ example 1]

(1) Hydrophilization treatment of thermoplastic resin film

As the thermoplastic resin film, an amorphous polyethylene terephthalate film (A-PET シート FR manufactured by Denko Co., Ltd. having a thickness of 150 μm) was used, and one surface of the thermoplastic resin film was coated with a solution of 280 W.min/m²The corona discharge treatment was carried out at a discharge rate (output: 280W/m, treatment speed: 1.0 m/min). The contact angle of the surface of the thermoplastic resin film after the corona discharge treatment was 60 ° (the contact angle before the corona discharge treatment was 79 °).

(2) Preparation of stock solution

An aqueous solution composed of 100 parts by mass of PVA (saponified product of a copolymer of vinyl acetate and ethylene, having an average polymerization degree of 2,400, a saponification degree of 99.4 mol%, and a content of ethylene units of 2.5 mol%), 10 parts by mass of glycerin as a plasticizer, 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and water was prepared as a stock solution for forming a PVA layer.

(3) Production of laminate

The dope prepared in (2) was applied to the corona discharge treated surface of the thermoplastic resin film hydrophilized in (1) using a die coater, and then dried at 80 ℃ for 240 seconds to produce a 2-layer laminate (a long laminate having a width of 0.5 m) comprising an amorphous polyethylene terephthalate film layer and a PVA layer having a thickness of 15 μm.

(4) Production of polarizing films

The polarizing film is produced by subjecting the laminate produced in (3) to an insolubilization step, a dyeing step, a crosslinking step, a stretching step, a fixing treatment step, and a drying step. That is, the laminate was uniaxially stretched in the longitudinal direction (MD) to 2 times the original length in a period of 1 minute in an insolubilization bath containing boric acid at a concentration of 3 mass% and having a temperature of 32 ℃ (first stage stretching), then was uniaxially stretched in the longitudinal direction (MD) to 3 times the original length in a period of 0.5 minutes in a dyeing bath containing iodine at a concentration of 0.035 mass% and potassium iodide at a concentration of 0.8 mass% in water and having a temperature of 20 ℃ (second stage stretching), then was uniaxially stretched in the longitudinal direction (MD) to 3.6 times the original length in a period of 2 minutes in a crosslinking bath containing boric acid at a concentration of 2.5 mass% and having a temperature of 32 ℃ (third stage stretching), and was further immersed in an aqueous solution of boric acid/potassium iodide containing boric acid at a concentration of 2.8 mass% and potassium iodide at a concentration of 5 mass% and having a temperature of 60 ℃ (, the film was uniaxially stretched in the longitudinal direction (MD) to 6 times the original length (fourth-stage stretching), and then immersed in an aqueous solution of potassium iodide containing boric acid at a concentration of 1.5 mass% and potassium iodide at a concentration of 5 mass% and at a temperature of 22 ℃ for 5 seconds to clean the film, followed by drying in a dryer at 60 ℃ for 240 seconds to obtain a polarizing film having a thickness of 8 μm formed on the stretched amorphous polyethylene terephthalate film layer.

The absorbance, the monomer transmittance and M/N of the obtained polarizing film (film obtained by peeling off the stretched amorphous polyethylene terephthalate film layer) were measured and/or calculated by the above-described method. The results are shown in Table 1.

Examples 2 to 5 and comparative examples 1 to 3

Polarizing films having thicknesses shown in table 1 were produced in the same manner as in example 1, except that the thicknesses of the PVA layers in the laminate, the temperature of the dyeing bath, the immersion time in the dyeing bath, and the composition of the dyeing bath were changed as shown in table 1.

[ Table 1]

Claims

1. A method for producing a polarizing film comprising a step of dyeing and stretching a laminate comprising a polyvinyl alcohol layer and a thermoplastic resin film layer, wherein the thermoplastic resin film has a contact angle of 55 to 70 DEG, the dyeing is carried out by immersing the laminate in a dyeing bath containing an iodine-based dye, the temperature of the dyeing bath is 18 ℃ or lower, the immersion time is 0.3 minutes or less, the polyvinyl alcohol layer has a thickness of 30 [ mu ] m or less,

310cm of a portion entering 10% of the thickness from one surface of the film to the inside in the thickness direction, which is obtained by measuring the cross section of the polarizing film obtained by the above production method by raman spectroscopy^-1Signal intensity of Down (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) Denoted as M, is to be taken from the other side of the film to the inside in the thickness direction to 310cm at a portion of 10% of the thickness^-1Signal intensity of Down (Int)³¹⁰) And 210cm^-1Signal intensity of Down (Int)²¹⁰) Ratio of (Int)³¹⁰/Int²¹⁰) When denoted by N, the ratio M/N is 0.91 or less.