WO2015133304A1

WO2015133304A1 - Polarizing film

Info

Publication number: WO2015133304A1
Application number: PCT/JP2015/054931
Authority: WO
Inventors: 達也大園; 修風藤
Original assignee: 株式会社クラレ
Priority date: 2014-03-04
Filing date: 2015-02-23
Publication date: 2015-09-11
Also published as: CN109917506A; TW201539064A; KR102411225B1; TWI668472B; JP6618890B2; CN106062596B; KR20160129004A; JPWO2015133304A1; CN109917506B; CN106062596A

Abstract

　[Problem] To provide a polarizing film having negligible leakage of blue light in the crossed nicols state. [Solution] Provided is a polarizing film in which an iodine-based pigment is adsorbed onto a matrix that includes PVA, wherein the polarizing film satisfies the relationship M/N ≦ 0.91, where M denotes the ratio (Int³¹⁰/Int²¹⁰ of the signal intensity at 310 cm^-1 ((Int³¹⁰) and the signal intensity at 210 cm^-1 (Int²¹⁰) in a section corresponding to ingress by the equivalent of 10% of thickness, into the interior of the film from one surface thereof in the thickness direction, and N denotes the ratio (Int³¹⁰/Int²¹⁰ of the signal intensity at 310 cm^-1 (Int³¹⁰) and the signal intensity at 210 cm^-1 (Int²¹⁰) in a section corresponding to ingress by the equivalent of 10% of the thickness, into the interior of the film from the other surface thereof in the thickness direction (M ≦ N), obtained through Raman spectrometry of a cross section of the polarizing film.

Description

Polarized film

The present invention relates to a polarizing film with little leakage of blue light in a crossed Nicol state and a method for producing the same.

A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film. As a polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter referred to as “polyvinyl alcohol”). iodine based dye "to the sometimes abbreviated as" PVA ") in a matrix formed by uniaxially stretched (oriented film was oriented by uniaxial stretching) (I ₃ ^- and I ₅ ^-, etc.) those adsorbed Has become the mainstream. Such a polarizing film can be obtained by uniaxially stretching a PVA film preliminarily containing an iodine pigment, adsorbing an iodine pigment simultaneously with uniaxial stretching of a PVA film, or adsorbing an iodine pigment after uniaxially stretching a PVA film. Or manufactured.

LCDs are used in a wide range of devices such as small devices such as calculators and wrist watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. However, in recent years, it is often used for mobile applications such as small notebook personal computers and mobile phones, and there is an increasing demand for thinner polarizing plates.

As a method of thinning a polarizing film constituting a polarizing plate, a thermoplastic resin film is stretched, dyed and dried after being stretched, dyed and dried on a thermoplastic resin film, and then stretched as necessary. A method of peeling and removing a film layer is known (see Patent Documents 1 and 2, etc.).

International Publication No. 2010/100917 Japanese Patent No. 4691205

However, when a thin polarizing film is produced according to a conventionally known method, there is a problem that blue light leaks in a crossed Nicol state. Then, an object of this invention is to provide the polarizing film with little leakage of the blue light in a crossed Nicol state, and its manufacturing method.

As a result of intensive studies to achieve the above object, the present inventors are used when producing a polarizing film by dyeing and stretching a laminate having a PVA layer and a thermoplastic resin film layer. By setting the temperature of the dyeing bath containing iodine dye and the immersion time in the dyeing bath to a specific range, each measurement result in the vicinity of the film surface obtained by Raman spectroscopic measurement of the cross section satisfies a specific relationship. The present inventors have found that an unprecedented polarizing film with less blue light leakage in the Nicol state can be easily obtained, and further studied based on the knowledge to complete the present invention.

That is, the present invention
[1] A polarizing film in which an iodine pigment is adsorbed on a matrix containing PVA, which is obtained by Raman spectroscopic measurement of a cross section of the polarizing film. signal intensity at 310 cm ^-1 in the 10% penetration portion Te ratio of the signal intensity at ^{(Int 310)} and 210cm ^-1 ^{(Int 210)} to ^{^(Int} 310 ^/ Int ²¹⁰⁾ is M, from the other surface of the film The ratio (Int ³¹⁰ / Int ²¹⁰ ) of the signal intensity (Int ³¹⁰ ) at ³¹⁰ cm ⁻¹ and the signal intensity (Int ²¹⁰ ) at ²¹⁰ cm ⁻¹ in the portion that has entered 10% of the thickness in the thickness direction is N A polarizing film in which M / N is 0.91 or less (provided that M ≦ N);
[2] The polarizing film according to the above [1], wherein the ratio (A / B) of the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in the crossed Nicol state is 1.40 or more;
[3] The polarizing film of the above [1] or [2], having a thickness of 15 μm or less;
[4] The polarizing film according to any one of [1] to [3], wherein the single transmittance is 40 to 45%;
[5] A method for producing a polarizing film, including a step of dyeing and stretching a laminate having a PVA layer and a thermoplastic resin film layer, wherein the dyeing is performed by immersing the laminate in a dyeing bath containing an iodine-based pigment. A production method in which the temperature of the dyeing bath is 25 ° C. or less and the immersion time is 2.5 minutes or less;
[6] The method according to [5] above, wherein the PVA layer has a thickness of 30 μm or less;
About.

According to the present invention, a polarizing film with less leakage of blue light in the crossed Nicol state is provided. Moreover, according to this invention, the manufacturing method of the polarizing film which can manufacture the said polarizing film easily is provided.

Hereinafter, the present invention will be described in detail.
(Polarizing film)
In the polarizing film of the present invention, an iodine dye is adsorbed on a matrix containing PVA. Then, a signal intensity (Int ³¹⁰ ) at ³¹⁰ cm ⁻¹ and 210 cm at a portion where 10% of the thickness entered from the one surface of the film in the thickness direction from one surface of the film obtained by Raman spectroscopy measurement of the cross section of the polarizing film. The ratio (Int ³¹⁰ / Int ²¹⁰ ) to the signal intensity at ⁻¹ (Int ²¹⁰ / Int ²¹⁰ ) is M, and the portion at a depth of 310 cm ⁻¹ in the portion entering the thickness direction from the other side of the film to the inside by 10% When the ratio (Int ³¹⁰ / Int ²¹⁰ ) between the signal intensity (Int ³¹⁰ ) and the signal intensity (Int ²¹⁰ ) at 210 cm ⁻¹ is N (where M ≦ N), the M / N is 0. 91 or less.

When performing Raman spectroscopic measurement of the cross section of the polarizing film, for example, Raman spectrophotometry may be performed with a Raman spectrophotometer using a sample obtained by slicing the target polarizing film in the thickness direction. Using a laser Raman spectrometer such as a microscopic laser Raman spectrometer “LabRAM ARAMIS VIS”, the measurement target portion of the sample may be irradiated with laser light having a wavelength of 532 nm to perform Raman spectroscopy. Then, from the signal intensity (Int ³¹⁰ ) at ³¹⁰ cm ⁻¹ and the signal intensity (Int ²¹⁰ ) at ²¹⁰ cm ⁻¹ in each measurement target part obtained in this way, the ratio (Int ³¹⁰ / Int ²¹⁰ ) is calculated. As specific measurement methods or conditions for obtaining the ratio (Int ³¹⁰ / Int ²¹⁰ ) in each part of the film, those described later in the examples can be employed. In addition, in the case of a polarizing film having a thickness of 10 μm, for example, with respect to a portion that has entered 10% of the thickness in the thickness direction from each surface of the film defined in the present invention, the portion corresponds to each surface of the polarizing film. Corresponds to a portion that has entered 1 μm (10 μm × 10% = 1 μm) in the thickness direction. Without limiting the invention in any way, the ratio (Int ³¹⁰ / Int ²¹⁰ ) in each part of the film is considered to depend on the ratio of the amount of I ₅ ^{− to} the amount of I ₃ ⁻ in that part. It is done.

The polarizing film of the present invention has an M / N of 0.91 or less. When M / N is 0.91 or less, a polarizing film with little leakage of blue light in the crossed Nicols state is obtained. Since a polarizing film with less leakage of blue light in the crossed Nicols state is obtained, M / N is preferably 0.85 or less, more preferably 0.76 or less, and 0.72 or less. More preferably. In view of reducing the leakage of red light in the crossed Nicols state, M / N is preferably 0.01 or more, more preferably 0.1 or more, and 0.5 or more. Further preferred.

A polarizing film in which iodine-based dye is adsorbed on a matrix is obtained by stretching a PVA film containing iodine-based dye in advance, adsorbing iodine-based dye simultaneously with stretching of the PVA film, or stretching PVA film to form a matrix. And then, for example, by adsorbing an iodine dye, more specifically, a PVA layer (corresponding to a PVA film) preliminarily containing an iodine dye, a thermoplastic resin film layer, A laminate having a PVA layer and a thermoplastic resin film layer, or a PVA layer and a thermoplastic resin film layer adsorbing iodine pigments simultaneously with the stretching of the laminate having a PVA layer and a thermoplastic resin film layer After stretching the film, it can be produced by, for example, adsorbing an iodine dye to a matrix formed from the PVA layer.

As said PVA, 1 type of vinyl esters, such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate Or what is obtained by saponifying the polyvinyl ester obtained by superposing | polymerizing 2 or more types can be used. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of ease of production of PVA, availability, cost, and the like.

The above-mentioned polyvinyl ester may be obtained using only one or two or more kinds of vinyl esters as a monomer. It may be a copolymer of two or more kinds of vinyl esters and other monomers copolymerizable therewith.

Examples of the other monomer copolymerizable with the vinyl ester include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, (meth) acrylate n-propyl, (meth) acrylate i-propyl, (meth) acrylate n-butyl, (meth) acrylate i-butyl, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide, N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl (Meth) acrylamide derivatives such as amides, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamide propyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters or acid anhydrides; itaconic acid or its salts, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids be able to. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer.

The proportion of structural units derived from the other monomers described above in the polyvinyl ester is preferably 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester, and is preferably 10 mol%. Hereinafter, it may be 5 mol% or less.
In particular, when the other monomer described above is a monomer that may promote the water solubility of the obtained PVA, such as (meth) acrylic acid or unsaturated sulfonic acid, In order to prevent PVA from being dissolved in the production process, the proportion of structural units derived from these monomers in the polyvinyl ester is 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester. It is preferable that it is 3 mol% or less.

The above PVA may be modified with one or two or more types of graft copolymerizable monomers as long as the effects of the present invention are not impaired. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in PVA (structural units in the graft modified portion) is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA. .

The above PVA may have a part of its hydroxyl group cross-linked or not cross-linked. Moreover, said PVA may react with aldehyde compounds, such as acetaldehyde and a butyraldehyde, etc. to form an acetal structure, and the said PVA does not react with these compounds and does not form an acetal structure. May be.

The average degree of polymerization of the PVA is preferably in the range of 1,000 to 9,500. The average degree of polymerization is more preferably 1,500 or more, and further preferably 2,000 or more. Moreover, it is more preferable that it is 9,200 or less, and it is further more preferable that it is 6,000 or less. When the average degree of polymerization is 1,000 or more, the polarizing 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 the description of JIS K6726-1994.

The degree of saponification of the PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and more preferably 99 mol% or more from the viewpoint of the polarizing performance of the polarizing film. preferable. When the degree of saponification is less than 98 mol%, PVA tends to be eluted during the production process of the polarizing film, and the eluted PVA may adhere to the film and reduce the polarizing performance of the polarizing film. In this specification, the degree of saponification of PVA refers to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units of PVA. The proportion (mol%) occupied by the number of moles of vinyl alcohol units. The degree of saponification can be measured according to the description of JIS K6726-1994.

As the iodine-based dye, _{I 3} ^-, and the like ^- and _{I 5.} Examples of these counter cations include alkali metals such as potassium. The iodine dye can be obtained, for example, by bringing iodine (I ₂ ) into contact with potassium iodide.

The thickness of the polarizing film of the present invention is preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 8 μm or less because a thin polarizing plate required in recent years can be easily obtained. Particularly preferably, it is 5 μm or less. In addition, since it is difficult to manufacture a polarizing film that is too thin, the thickness of the polarizing film is, for example, 0.5 μm or more (in one example, 2.5 μm or more), and 4 μm or more from the viewpoint of manufacturing. It may be 5 μm or more, further 6 μm or more.

From the viewpoint of reducing leakage of blue light, the polarizing film of the present invention has a ratio (A / B) of the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in a crossed Nicol state of 1.40. Preferably, it is 1.41 or more, more preferably 1.42 or more, particularly preferably 1.45 or more, 1.50 or more, and further 1.55. It may be the above. On the other hand, if the ratio (A / B) is too high, red light leakage tends to increase. Therefore, the ratio (A / B) is preferably 2 or less, and is 1.8 or less. More preferably, it is more preferably 1.6 or less. In addition, said light absorbency (A) and light absorbency (B) can be calculated | required using a spectrophotometer, and can be specifically calculated | required by the method mentioned later in an Example.

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

(Production method of polarizing film)
The method for producing the polarizing film of the present invention is not particularly limited, and can be produced by dyeing and stretching a PVA film as a raw film, for example, used as a raw film. Disperse the dyeing liquid containing iodine dye on one side of the PVA film in a specific amount and concentration; one side of the PVA film used as a raw film on a roll coated with the dyeing liquid containing iodine dye Contacting one side of a PVA film used as a raw film with an impregnated body in which a porous material such as sponge is impregnated with a dyeing solution containing an iodine-based dye; It can be easily manufactured by making a difference in the ratio of the amount of I ₅ ^{− to} the amount of I ₃ ^{− in} the vicinity of each surface. The following production method of the present invention is preferable because the polarizing film of the present invention can be more easily produced.

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, and the dyeing is performed by immersing the laminate in a dyeing bath containing an iodine-based pigment. The temperature of the dyeing bath is 25 ° C. or less, and the immersion time is 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, polyethylene terephthalate, and their heat. Examples thereof include a copolymer having a plurality of types of monomer units constituting the plastic resin. In the thermoplastic resin film layer, only one kind of thermoplastic resin may be contained, or two or more kinds of thermoplastic resins may be contained. Among these, polyethylene terephthalate is preferable and amorphous polyethylene terephthalate is more preferable because it has high heat resistance and stretchability.

The thickness of the thermoplastic resin film layer is preferably within the range of 20 to 250 μm, more preferably within the range of 30 to 230 μm, and even more preferably within the range of 50 to 200 μm. When the thickness of the thermoplastic resin film layer is 20 μm or more, wrinkles can be effectively prevented when forming the PVA layer. On the other hand, when the thickness of the thermoplastic resin film layer is 250 μm or less, it is possible to suppress an excessive increase in tension when the laminate is stretched.

Since the PVA constituting the PVA layer can be the same as that described above in the description of the polarizing film of the present invention, redundant description is omitted here.

The PVA layer preferably contains a plasticizer from the viewpoint of improving stretchability when stretched. Examples of the plasticizer may include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. One or more of the agents can be included. 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. When the content is 1 part by mass or more, the stretchability of the PVA layer and thus 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 becoming too flexible and handleability from being lowered. The content of the plasticizer in the PVA layer is more preferably 2 parts by mass or more with respect to 100 parts by mass of PVA, further preferably 4 parts by mass or more, and particularly preferably 5 parts by mass or more. The amount is more preferably 15 parts by mass or less, and further preferably 12 parts by mass or less.
Although depending on the manufacturing conditions of the polarizing film, the plasticizer contained in the PVA layer is eluted when the polarizing film is manufactured, so that the total amount does not always remain in the polarizing film.

The PVA layer may further contain components such as an antioxidant, an antifreezing agent, a pH adjuster, a hiding agent, a coloring inhibitor, an oil agent, and a surfactant as necessary.

The content of PVA in the PVA layer is preferably in the range of 50 to 99% by mass in view of ease of preparation of the desired polarizing film, and the content is preferably 75% by mass or more. More preferably, it is more preferably 80% by mass or more, particularly preferably 85% by mass or more, more preferably 98% by mass or less, further preferably 96% by mass or less, 95 It is particularly preferable that the content is not more than mass%.

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 more preferably 10 μm or less because a thin polarizing film can be easily obtained. Particularly preferred. In addition, since it is difficult to manufacture a laminate having a PVA layer that is too thin, the thickness of the PVA layer is, for example, 1 μm or more (in an example, 5 μm or more), and from the viewpoint of manufacturing, 8 μm or more. It may be 10 μm or more, and further 12 μm or more.

Although there is no restriction | limiting in particular in the layer structure of a laminated body, Since the polarizing film of this invention can be manufactured more easily etc., it is preferable that it is a two-layer structure of one PVA layer and one thermoplastic resin film layer. .

The shape of the laminate is not particularly limited, but is preferably a long laminate because it can be used continuously when producing a polarizing film. The length of the long laminate (length in the long direction) is not particularly limited, and can be set as appropriate according to the application of the polarizing film to be produced. For example, the length is in the range of 5 to 20,000 m. It can be.

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. However, in recent years, the laminate has been increasing in screen size for liquid crystal televisions and liquid crystal monitors. If the width is set to 0.5 m or more, more preferably 1.0 m or more, it is suitable for these applications. On the other hand, if the width of the laminated body is too wide, it tends to be difficult to uniformly stretch the polarizing film when the polarizing film is produced by a device that has been put to practical use. Therefore, the width of the laminated body is 7 m or less. Is preferred.

Examples of the method for producing a laminate include a method of forming a PVA layer on a thermoplastic resin film. Specifically, other components other than PVA such as PVA and, if necessary, the above-described plasticizer. A method in which a stock solution dissolved in a liquid medium is coated on a thermoplastic resin film and dried; a stock solution obtained by melting and kneading PVA, the liquid medium and other components as required is applied onto the thermoplastic resin film. Examples include a method of extruding and further drying as required; a method of producing a PVA film containing PVA and, if necessary, further other components by a known method, and laminating it with a thermoplastic resin film. Among these, from the point that a thin PVA layer can be easily prepared and the uniformity of the thickness of the resulting PVA layer, a stock solution in which PVA and, if necessary, further other components are dissolved in a liquid medium is used as a thermoplastic resin film. A method of coating and drying is preferred.

Examples of the liquid medium include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine. Of these, one or more of these can be used. Among these, water is preferable from the viewpoint of environmental load and recoverability.

Although the volatile content rate of the stock solution (the content ratio in the stock solution of volatile components such as a liquid medium that is removed by volatilization or drying during the formation of the PVA layer) varies depending on the formation method and formation conditions of the PVA layer, It is preferably in the range of 50% by mass to 98% by mass, and more preferably in the range of 55% by mass to 95% by mass. When the volatile content of the stock solution is 50% by mass or more, its viscosity does not become too high, and filtration and defoaming during the preparation of the stock solution are smoothly performed, and formation of a PVA layer with less foreign matter and defects is facilitated. At the same time, the coatability is also improved. On the other hand, when the volatile content of the stock solution is 98% by mass or less, the concentration of the stock solution does not become too low, and industrial production of the laminate is facilitated.

Examples of the coating method for coating the stock solution on the thermoplastic resin film include a die coating method, a comma coating method, and a dip coating method. Among these, the die coating method is preferable from the viewpoint of the uniformity of the thickness of the obtained PVA layer.

It is preferable that at least one surface of the thermoplastic resin film used for the production of the laminate is hydrophilized. By forming the PVA layer so as to be in contact with the hydrophilically treated surface, the adhesion between the thermoplastic resin film layer and the PVA layer is improved. Examples of the hydrophilic treatment include corona treatment, plasma treatment, anchor coat treatment, and the like. Among these, corona treatment is preferable from the viewpoint of easy adjustment of hydrophilicity.

It is preferable to adjust the contact angle of the surface of the thermoplastic resin film to 55 to 70 ° by the above-described hydrophilic treatment, more preferably to adjust the contact angle to 57 ° or more, and to adjust to 59 ° or more. More preferably, it is more preferably adjusted to 69 ° or less, and further preferably adjusted to 68 ° or less. When the contact angle is lower than 55 °, the adhesive strength between the thermoplastic resin film layer and the PVA layer tends to be too strong, and it is difficult to peel off the stretched thermoplastic resin film layer after stretching the laminate. May be. On the other hand, if the contact angle is higher than 70 °, the PVA layer tends to peel or tear from the thermoplastic resin film layer during stretching of the laminate, and it tends to be difficult to stretch at a high stretch ratio. is there. The contact angle of the surface of the thermoplastic resin film is the angle formed by the water surface and the surface of the thermoplastic resin film where the free surface of water is in contact with the thermoplastic resin film (takes an angle inside the water) It can measure by the method mentioned later in an Example.

There is no particular restriction on the corona treatment conditions when the surface contact angle of the thermoplastic resin film is adjusted to the above range by corona treatment, but the surface contact angle of the thermoplastic resin film can be easily adjusted to the above range. Therefore, the discharge amount represented by the following formula (1) is preferably in the range of 180 to 350 W · min / m ² , more preferably in the range of 190 to 320 W · min / m ² , More preferably, it is within the range of 200 to 300 W · min / m ² .
Discharge amount (W · min / m ² ) = Output (W / m) / Processing speed (m / min) (1)

There are no particular restrictions on the drying conditions after the stock solution is coated or extruded on the thermoplastic resin film, but in order to prevent wrinkles from entering the thermoplastic resin film, the glass transition temperature is below the glass transition temperature of the thermoplastic resin film. Drying at a temperature is preferred.

The production method of the present invention includes a step of dyeing the laminate (dyeing step) and a step of drawing (stretching step). The production method includes an insolubilization step, a swelling step, and a crosslinking step in addition to the dyeing step and the drawing step. Further, a fixing process, a washing process, a drying process and the like may be further included as necessary. The order of each process may be changed as needed, each process may be performed twice or more, and different processes may be performed simultaneously. Moreover, according to said manufacturing method, although the polarizing film formed on the stretched thermoplastic resin film layer is obtained, the process of peeling the said stretched thermoplastic resin film as needed is included. Also good.

As an example of the production method of the present invention, the laminate is first subjected to an insolubilization process, further subjected to a swelling process as necessary, then subjected to a dyeing process, and further subjected to a crosslinking process as necessary, and then to a stretching process. Then, if necessary, it is further subjected to a fixing treatment step and / or a washing step, and is then subjected to a drying step. By these series of steps, a polarizing film formed on the stretched thermoplastic resin film layer is obtained, The method of peeling the said stretched thermoplastic resin film layer further as needed is mentioned.

The insolubilization treatment is mainly performed to prevent elution of PVA contained in the PVA layer into water. As the insolubilization treatment, for example, a method of performing a heat treatment on the laminate, or an aqueous solution containing one or more of boron compounds such as borate such as boric acid and borax using the laminate as an insolubilizing bath. The method of immersing is mentioned. Among these, a method of using an aqueous solution containing a boron compound is preferable because if the laminate is subjected to a heat treatment, wrinkles may occur with the dimensional change of the thermoplastic resin film layer. The heat treatment can be performed at a temperature in the range of 80 to 200 ° C., for example. From the viewpoint of preventing wrinkles, the heat treatment is preferably performed while applying tension to the laminate. In the method using an aqueous solution containing a boron compound, the temperature of the aqueous solution is preferably within the range of 20 to 40 ° C., more preferably within the range of 22 to 38 ° C., and within the range of 25 to 35 ° C. More preferably. By setting the temperature within the range of 20 to 40 ° C., the PVA can be prevented from dissolving and efficiently insolubilized. The time for immersion in the aqueous solution containing the boron compound is, for example, in the range of 0.1 to 5 minutes. By in the range of 0.1 to 5 minutes, it can be insolubilized efficiently. 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% by mass, more preferably in the range of 1.0 to 5.0% by mass. More preferably, it is in the range of 0.5 to 4.0% by mass. By setting the concentration within the range of 0.5 to 6.0% by mass, the PVA can be prevented from dissolving and efficiently insolubilized.
The insolubilization treatment is preferably performed before the dyeing step and further before the swelling step.

The swelling step can be performed by immersing the laminate in water. The temperature of the water when immersed in water is preferably within a range of 20 to 40 ° C., more preferably 22 ° C. or higher, further preferably 25 ° C. or higher. The temperature is more preferably 38 ° C. or lower, and further preferably 35 ° C. or lower. By setting the temperature within the range of 20 to 40 ° C., the PVA layer can be efficiently swollen. Further, the time for immersion in water is preferably within a range of 0.1 to 5 minutes, and more preferably within a range of 0.5 to 3 minutes. By making it within the range of 0.1 to 5 minutes, the PVA layer can be efficiently swollen. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

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

When the temperature of the dyeing bath exceeds 25 ° C., the resulting polarizing film has more blue light leakage in the crossed Nicol state. From such a viewpoint, the temperature of the dyeing bath is preferably 23 ° C. or less, more preferably 21 ° C. or less, further preferably 18 ° C. or less, 15 ° C. or less, and further 10 ° C. or less. In particular, when a laminate having a thinner PVA layer is used, the target polarizing film can be obtained more efficiently by lowering the temperature of the dyeing bath. On the other hand, if the temperature of the dyeing bath is too low, spots may occur in the obtained polarizing film. Therefore, the temperature of the dyeing bath is preferably 3 ° C. or higher, and more preferably 5 ° C. or higher.

Even when the immersion time when the laminate is immersed in the dyeing bath exceeds 2.5 minutes, the obtained polarizing film has a large amount of leakage of blue light in a crossed Nicol state. From such a viewpoint, the immersion time is preferably 2.0 minutes or less, more preferably 1.5 minutes or less, 0.8 minutes or less, 0.3 minutes or less, and further 0.2 minutes. The following may be sufficient, and when using the laminated body which has a thinner PVA layer especially, the target polarizing film can be obtained more efficiently by making immersion time shorter. On the other hand, if the soaking time is too short, spots may occur in the resulting polarizing film. Therefore, the soaking time is preferably 0.01 minutes or more, and more preferably 0.05 minutes or more.

A representative example of the dyeing bath is that obtained by mixing iodine (I ₂ ) and potassium iodide with water. By mixing the iodine and potassium iodide and water, I ₃ ^- and I ₅ ^- such can generate iodine dye. The concentration of iodine and potassium iodide in the dyeing bath is not particularly limited, but the iodine concentration is within a range of 0.01 to 2% by mass as a ratio of the mass of iodine used to the mass of the resulting dyeing bath. The concentration of potassium iodide is preferably in the range of 0.02 to 1% by mass, and the concentration of potassium iodide is the mass of potassium iodide used relative to the mass of iodine used. The ratio is preferably in the range of 10 to 300 times by mass, and more preferably in the range of 15 to 150 times by mass. The dyeing bath may contain a boron compound such as borate such as boric acid and borax.

By performing a crosslinking step on the laminate, it is possible to more effectively prevent PVA from eluting into water when wet-stretching 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 can be performed by immersing the laminate in an aqueous solution containing a crosslinking agent as a crosslinking bath. As the crosslinking agent, one or more 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, more preferably 7% by mass or less, and 6% by mass or less. More preferably. Sufficient stretchability can be maintained when the concentration of the crosslinking agent is in the range of 1 to 15% by mass. The crosslinking bath may contain an auxiliary agent such as potassium iodide. The temperature of the crosslinking bath is preferably in the range of 20 to 50 ° C., particularly preferably in the range of 25 to 40 ° C. By setting the temperature within the range of 20 to 50 ° C., crosslinking can be performed efficiently.

There is no restriction | limiting in particular in the extending | stretching method at the time of extending | stretching a laminated body, You may carry out by any of a wet extending | stretching method and a dry-type extending | stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing one or more boron compounds such as boric acid such as boric acid and borax, or in the above-described dyeing bath or a fixing treatment bath described later. It can also be done inside. In the case of the dry stretching method, stretching may be performed at room temperature, stretching may be performed while applying heat, or stretching may be performed after water absorption. Among these, the wet stretching method is preferable from the viewpoint of the uniformity of the thickness in the width direction of the obtained polarizing film, and it is more preferable to stretch in a boric acid aqueous solution. The concentration of boric acid 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, and 1.5 mass% More preferably, it is more preferably 5.0% by mass or less, and further preferably 4.0% by mass or less. When the boric acid concentration is in the range of 0.5 to 6.0% by mass, a polarizing film having excellent thickness uniformity in the width direction can be obtained. The aqueous solution containing the boron compound may contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass. When the concentration of potassium iodide is in the range of 0.01 to 10% by mass, a polarizing film with better polarizing performance can be obtained.

The temperature at which the laminate is stretched is preferably in the range of 5 to 90 ° C., more preferably 10 ° C. or more, and more preferably 85 ° C. or less. More preferably, it is not higher than ° C. When the temperature is in the range of 5 to 90 ° C., a polarizing film having excellent thickness uniformity in the width direction can be obtained.

The stretching ratio when stretching the laminate is preferably 4 times or more, more preferably 5 times or more, and further preferably 6 times or more. By making the draw ratio of the laminate within the above range, a polarizing film that is more excellent in polarizing performance can be obtained. Although the upper limit of the draw ratio of the laminate is not particularly limited, it is preferably 8 times or less. The stretching of the laminate may be performed at once or may be performed in multiple times, but when performed in multiple times, the total stretch ratio multiplied by the stretch ratio of each stretch is within the above range. I just need it. In addition, the draw ratio in this specification is based on the length of the laminated body before extending | stretching, and the state which is not extending | stretched corresponds to 1 time of draw ratios.

The stretching of the laminate is preferably uniaxial stretching from the viewpoint of the performance of the obtained polarizing film. There is no particular limitation on the direction of uniaxial stretching in stretching a long laminate, and uniaxial stretching or lateral uniaxial stretching in the longitudinal direction can be adopted, but a polarizing film that is superior in polarization performance can be obtained. Uniaxial stretching in the longitudinal direction is preferred. Uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, lateral uniaxial stretching can be performed using a tenter type stretching machine.

The fixing treatment step is mainly performed in order to strengthen the adsorption of the iodine-based dye to the PVA layer. The fixing treatment step can be performed by immersing the laminate before stretching, during stretching or after stretching in a fixing treatment bath. As the fixing treatment bath, an aqueous solution containing one or more of boron compounds such as boric acid such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed 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 generally within the range of 0.1 to 15% by mass, and particularly preferably within the range of 1 to 10% by mass. By setting the concentration within the range of 0.1 to 15% by mass, the adsorption of the iodine-based dye can be further strengthened. The temperature of the fixing treatment bath is preferably in the range of 10 to 60 ° C, particularly preferably in the range of 15 to 40 ° C. By setting the temperature within the range of 10 to 60 ° C., it is possible to further strengthen the adsorption of the iodine dye.

The cleaning process is often performed to remove unnecessary chemicals and foreign matters on the film surface and to adjust the optical performance of the finally obtained polarizing film. The cleaning step can be performed by immersing the laminate in a cleaning bath or by spraying a cleaning liquid on the laminate. Water can be used as the washing bath or the washing liquid, and potassium iodide may be contained therein.

The drying conditions in the drying step are not particularly limited, but it is preferable to perform the drying at a temperature within the range of 30 to 150 ° C, particularly within the range of 50 to 130 ° C. A polarizing film excellent in dimensional stability can be easily obtained by drying at a temperature in the range of 30 to 150 ° C.

By doing so, a polarizing film formed on the stretched thermoplastic resin film layer can be obtained. The method of using the polarizing film in such a form is not particularly limited. For example, the stretched thermoplastic resin film layer is not peeled off, but is used as it is or optically transparent to the polarizing film side as desired. It is good also as a polarizing plate by laminating | stacking the protective film which has sufficient strength, and after bonding a protective film on the opposite side to the side where the stretched thermoplastic resin film layer is located, the said stretched thermoplastic resin It is good also as a polarizing plate by peeling a film layer and sticking another protective film on the peeling surface as it is, if desired. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. In addition, examples of the adhesive for bonding include a PVA adhesive and a urethane adhesive, and a PVA adhesive is preferable.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In addition, the measurement method of the contact angle of the surface of the thermoplastic resin film and the measurement, calculation methods of absorbance, unit transmittance and M / N of the polarizing film employed in the following examples and comparative examples are as follows. Show.

[Contact angle of thermoplastic resin film surface]
Using a “DropMaster 500” manufactured by Kyowa Interface Science Co., Ltd., in an environment of 20 ° C. and 65% RH, 2 μL of pure water was extruded from the needle with an inner diameter of 0.4 mm onto the surface of the thermoplastic resin film, and the contact angle was measured. .

[Absorbance and single transmittance of polarizing film]
From a central part in the width direction (TD) of the polarizing film obtained in the following Examples or Comparative Examples, a rectangular sample of 2 cm was taken in the length direction (MD) of the polarizing film, and a spectrophotometer with an integrating sphere ( Using “V7100” manufactured by JASCO Corporation, this sample was placed in a crossed Nicol state with respect to the polarizing plate of the spectrophotometer, and the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at 700 nm were measured. It was measured. Next, using the same sample and spectrophotometer, in accordance with JIS Z 8722 (object color measurement method), the visibility correction of the visible light region of the C light source and 2 ° field of view is performed, and the sample is measured in the length direction. The light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and the average value (%) was taken as the single transmittance of the polarizing film.

[M / N of polarizing film]
About the polarizing film obtained by the following example or the comparative example, it is a strip with a size of MD × TD = 2 mm × 10 mm from the central portion in the width direction (TD) at an arbitrary position in the length direction (MD). Was cut out and attached to a microtome with both sides of the strip sandwiched between two 100 μm-thick polyethylene terephthalate films. The strip was sliced from above the polyethylene terephthalate film at intervals of 20 μm parallel to the MD, and a sample having a size of MD × TD = 2 mm × 20 μm was collected.
Using the microscopic laser Raman spectrometer “LabRAM ARAMIS VIS” manufactured by HORIBA, Ltd., the sample to be measured is irradiated with a laser beam having a wavelength of 532 nm on the cross-section to be measured on the cross section produced by the microtome. performed, among the signals observed at that time, because the intensity of the signal at 310cm intensity of the signal at ^-1 ^{(Int 310)} and 210cm ^-1 ^{(Int 210),} the ratio in that portion ^{^(Int} 310 ^/ Int ²¹⁰ ) Was calculated. In addition, said measurement object part shall be a part which penetrated 10% with respect to thickness to the inside in the thickness direction of the film from each surface of the polarizing film, and about the obtained two ratios (Int ³¹⁰ / Int ²¹⁰ ), M ≦ N Each value was set to M or N so as to satisfy, and M / N was calculated using these M and N.

[Example 1]
(1) Hydrophilization treatment of thermoplastic resin film Amorphous polyethylene terephthalate film (A-PET sheet FR thickness 150 μm, manufactured by Teijin Chemicals Ltd.) is used as the thermoplastic resin film, and the amount of discharge on one side of the thermoplastic resin film. Corona treatment was performed at 280 W · min / m ² (output 280 W / m, treatment speed 1.0 m / min). The contact angle of the surface of the thermoplastic resin film after the corona treatment was 60 ° (the contact angle before the corona treatment was 79 °).
(2) Preparation of stock solution PVA (saponified copolymer of vinyl acetate and ethylene, average polymerization degree 2,400, saponification degree 99.4 mol%, ethylene unit content 2.5 mol%) 100 parts by mass An aqueous solution consisting of 10 parts by mass of glycerin as a plasticizer and 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 After coating the stock solution prepared in (2) on the corona-treated surface of the thermoplastic resin film subjected to hydrophilic treatment in (1) using a die coater, it is dried at 80 ° C. for 240 seconds. As a result, a two-layer laminate (a long laminate having a width of 0.5 m) composed of an amorphous polyethylene terephthalate film layer and a PVA layer having a thickness of 15 μm was produced.
(4) Production of Polarizing Film A polarizing film was produced by performing an insolubilization process, a dyeing process, a crosslinking process, a stretching process, a fixing process process, and a drying process on the laminate prepared in (3). That is, while the laminate is immersed in an insolubilization bath containing boric acid at a concentration of 3% by mass at a temperature of 32 ° C. for 1 minute, it is uniaxial in the length direction (MD) up to twice the original length. After stretching (first-stage stretching), the amount used is 0.035% by mass of iodine and potassium iodide is mixed with water at a concentration of 0.8% by mass in water at a temperature of 20 ° C. for 0.5 minutes. While immersed, the film is uniaxially stretched in the length direction (MD) up to 3 times the original length (second-stage stretching), and then crosslinked at a temperature of 32 ° C. containing boric acid at a concentration of 2.5% by mass. While immersed in the bath for 2 minutes, it was uniaxially stretched in the length direction (MD) up to 3.6 times the original length (stretched in the third stage), and further 2.8% by mass of boric acid and potassium iodide. 6 times the original length while immersed in an aqueous solution of boric acid / potassium iodide at a temperature of 60 ° C. containing 5% by mass In a potassium iodide aqueous solution at a temperature of 22 ° C. containing 1.5% by mass of boric acid and 5% by mass of potassium iodide. The film was washed by immersing it in 5 seconds, followed by drying at 60 ° C. for 240 seconds to obtain a polarizing film having a thickness of 8 μm formed on the stretched amorphous polyethylene terephthalate film layer. .
With respect to the obtained polarizing film (after the stretched amorphous polyethylene terephthalate film layer was peeled), the absorbance, single transmittance and M / N were measured or calculated by the methods described above. The results are shown in Table 1.

[Examples 2 to 5 and Comparative Examples 1 to 3]
The thickness shown in Table 1 was the same as in Example 1 except that the thickness of the PVA layer 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. The polarizing film which has was manufactured.
With respect to the obtained polarizing film (after the stretched amorphous polyethylene terephthalate film layer was peeled), the absorbance, single transmittance and M / N were measured or calculated by the methods described above. The results are shown in Table 1.

Claims

A polarizing film in which an iodine-based dye is adsorbed on a matrix containing polyvinyl alcohol, and obtained by Raman spectroscopic measurement of the cross section of the polarizing film. % ratio of the signal intensity at 310 cm -1 in the entrance portion signal intensity at (Int 310) and 210cm -1 (Int 210) to (Int 310 / Int 210) is M, the thickness direction from the other surface of the film internal the ratio of the signal intensity at 310 cm -1 in the 10% penetration portion relative to the thickness signal intensity at (Int 310) and 210cm -1 (Int 210) (Int 310 / Int 210) is N in the On the occasion (however, M ≦ N), M / N is 0.91 or less.
The polarizing film according to claim 1, wherein a ratio (A / B) of absorbance (A) at a wavelength of 480 nm and absorbance (B) at a wavelength of 700 nm in a crossed Nicol state is 1.40 or more.
The polarizing film according to claim 1, wherein the thickness is 15 μm or less.
The polarizing film according to any one of claims 1 to 3, wherein the single transmittance is 40 to 45%.
A method for producing a polarizing film, comprising a step of dyeing and stretching a laminate having a polyvinyl alcohol layer and a thermoplastic resin film layer, wherein the dyeing is performed by immersing the laminate in a dyeing bath containing an iodine pigment. The manufacturing method in which the temperature of the dyeing bath is 25 ° C. or less and the immersion time is 2.5 minutes or less.
The manufacturing method of Claim 5 whose thickness of a polyvinyl alcohol layer is 30 micrometers or less.