TWI628471B - Polarizing film and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a thin polarizing film with a small amount of blue light leakage in a crossed polarizer state.

The solution of the present invention is a polarizing film, which is a polarizing film having a thickness of 25 μm or less by adsorbing iodine-based pigments on a substrate containing PVA. In the state of an orthogonal polarizer, the absorbance at a wavelength of 480 nm (A) and the absorbance at a wavelength of 700 nm (B ) Ratio (A / B) is 1.42 or more, or the cross section of the polarizing film is measured by Raman spectroscopy, and the 310cm ^-1 signal strength (Int ³¹⁰ ) and 210cm ^-1 signal strength at the central portion of the thickness direction are obtained. The ratio of (Int ²¹⁰ ) (Int ³¹⁰ / Int ²¹⁰ ) is L, from the one side of the thickness direction to the inside to the 10% thickness year-on-year rate M, and the other side of the thickness direction to the inside to the thickness. When the year-on-year rate for the 10% part is N (only M ≦ N), 2 × L / (M + N) is 0.91 or less.

Description

Polarizing film and manufacturing method thereof

The invention relates to a thin polarizing film with less blue light leakage under the state of a cross polarizer and a manufacturing method thereof.

The polarizing plate with the function of transmitting light and shading is the basic constituent element of a liquid crystal display (LCD), as is the liquid crystal that changes the polarization state of light. Most polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is laminated on the surface of the polarizing film. The polarizing film constituting the polarizing plate is a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be omitted as "PVA") A uniaxially-stretched substrate (uniaxially-oriented stretched film) adsorbs iodine-based pigments (I ₃ ^- or I ₅ ^- etc.) as the mainstream. Such a polarizing film is produced by uniaxially stretching a PVA film containing an iodine-based pigment in advance, simultaneously adsorbing an iodine-based pigment while uniaxially stretching the PVA film, or adsorbing an iodine-based pigment after uniaxially stretching the PVA film.

LCDs are widely used in small devices such as computers and watches, notebook computers, LCD screens, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and measuring devices for indoor and outdoor use. In recent years, LCDs have been used especially for small notes. Mobile computers and mobile phones, while increasing the requirements for thinner polarizers.

As a method for reducing the thickness of a polarizing film constituting a polarizing plate, it is known to construct a PVA layer on one side of a thermoplastic resin film. After the layer body is stretched, dyed, and dried, the stretched thermoplastic resin film layer is peeled and removed as necessary (see Patent Documents 1 and 2).

[Prior technical literature] [Patent Literature]

[Patent Document 1] International Publication No. 2010/100917

[Patent Document 2] Japanese Patent No. 4691205

However, when a thin polarizing film is manufactured by a conventional method, there is a problem that blue light leaks out in a state of a cross polarizer. Here, an object of the present invention is to provide a thin polarizing film with less blue light leakage in a cross-polarizer state and a method for manufacturing the same.

The present inventors have actively and repeatedly investigated the results in order to achieve the foregoing objects, and found that when a thin PVA film is dyed and stretched to produce a polarizing film, the temperature of the dyeing bath containing the iodine-based dye and the dye bath immersion time are set. For a specific range, the measurement results of the central portion of the film thickness direction and the vicinity of the surface obtained by Raman spectroscopy in the cross section will satisfy a specific relationship, and blue light leakage in the state of a cross polarizer that did not exist in the past can be easily obtained. Based on this knowledge, a few polarizing films are further repeated to complete the present invention.

In other words, the present invention relates to: [1] A polarizing film (hereinafter also referred to as "polarizing film (1)"), which is a polarizing film having a thickness of 25 μm or less adsorbed on an iodine-based pigment on a substrate containing PVA, which is orthogonal In the state of a polarizer, the ratio (A / B) of the absorbance (A) at a wavelength of 480nm to the absorbance (B) at a wavelength of 700nm is 1.42 or more; [2] a polarizing film (hereinafter also referred to as "polarizing film (2)"), which A polarizing film with an iodine-based pigment adsorbed on a substrate containing PVA and having a thickness of 25 μm or less, wherein the cross-section of the polarizing film was measured by Raman spectroscopy, and the signal strength (Int ³¹⁰ ) and 210 cm ^{−1 of the} central portion of the film thickness direction were obtained ^{. 1} The ratio of signal strength (Int ²¹⁰ ) (Int ³¹⁰ / Int ²¹⁰ ) is L, and one side of the film enters in the thickness direction toward the inside to 310cm ^{-1 with} signal strength (Int ³¹⁰ ) and 210cm ^-1 The ratio of signal strength (Int ²¹⁰ ) (Int ³¹⁰ / Int ²¹⁰ ) is M, and the other side of the film enters in the thickness direction toward the inside to 310cm ^-1 signal strength (Int ³¹⁰ ) and 210cm ^-1 signal with respect to the thickness of 10%. When the ratio of the intensity (Int ²¹⁰ ) (Int ³¹⁰ / Int ²¹⁰ ) is N (only M ≦ N), 2 × L / (M + N) is less than 0.91; [3] The polarizing film as described in [2] above, wherein the ratio of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm (A / B) is 1.42 or more; [4] The polarizing film according to any one of the above [1] to [3], wherein the content of the alkali metal contained in the polarizing film is X mol / kg, and when the thickness of the polarizing film is Y μm, the formula : Z = X × log (Y), Z is 0.19 or less; [5] The polarizing film according to any one of [1] to [4] above, in which the monomer light transmittance is 40 to 45%; [ 6] A method for producing a polarizing film, which is a method for producing a polarizing film including a step of dyeing and extending a PVA film having a thickness of 50 μm or less, wherein the dyeing is performed by impregnating a PVA film in a dyeing bath containing an iodine-based pigment, The temperature of the dyeing bath is 25 ° C or lower, and the immersion time is 1.5 minutes or shorter.

According to the present invention, a thin polarizing film with less blue light leakage in a cross-polarizer state is provided. In addition, according to the present invention, a method for manufacturing a polarizing film capable of easily manufacturing the polarizing film is provided.

[Form of Implementing Invention]

The present invention is described in detail below.

(Polarizing film)

The polarizing film of the present invention is based on a substrate containing PVA to adsorb iodine-based pigments. Such a polarizing film can be produced by extending a PVA film containing an iodine-based pigment in advance, adsorbing an iodine-based pigment while extending the PVA film, or adsorbing an iodine-based pigment after extending the PVA film to form a matrix.

The thickness of the polarizing film of the present invention is 25 μm or less. With a thickness of 25 μm or less, a thin polarizing plate required in recent years can be easily obtained. From such a viewpoint, the thickness of the polarizing film is preferably 23 μm or less, more preferably 20 μm or less, more preferably 10 μm or less, and particularly preferably 5 μm or less. In addition, since a polarizing film having an excessively thin thickness is difficult to manufacture, the thickness of the polarizing film is, for example, 1 μm or more (for example, 2.5 μm or more).

In the polarizing film (1) constituting one aspect of the present invention, the ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm is 1.42 or more in the state of a cross polarizer. With the ratio (A / B) of 1.42 to It becomes a polarizing film with less blue light leakage. From such a viewpoint, the ratio (A / B) is preferably 1.43 or more, and more preferably 1.44 or more. On the other hand, if the ratio (A / B) is too high, the red light leakage tends to increase. Therefore, the ratio (A / B) is preferably 2 or less, more preferably 1.8 or less, and even more preferably 1.6 or less. The absorbance (A) and the absorbance (B) can be obtained by using a spectrophotometer, and specifically, can be obtained by a method described later in the examples.

And constituting the other side of the polarizing film of the present invention (2), the cross-section of the polarizing film measured for Raman scattering, ^-1 signal strength of a film thickness direction central portion 310cm (Int ³¹⁰⁾ the signal strength obtained 210cm ^-1 (Int ²¹⁰⁾ of the ratio (Int ³¹⁰ / Int ²¹⁰⁾ into the side to a thickness of 310cm ^-1 with respect to the signal intensity (Int ³¹⁰⁾ 10% part of the signal intensity of 210cm ^-1 L, the film thickness direction toward the inside ( int ²¹⁰⁾ of the ratio (int ³¹⁰ / int ²¹⁰⁾ is M, a film thickness direction toward the other side into the interior to 310cm ^-1 with respect to the thickness of the signal intensity (int ³¹⁰⁾ 10% of the 210cm ^-1 portion signal intensity (int ²¹⁰ ) When the ratio (Int ³¹⁰ / Int ²¹⁰ ) is N (only M ≦ N), 2 × L / (M + N) is 0.91 or less.

When measuring the Raman spectrum of a polarizing film's cross section, for example, a sample obtained by slicing the polarizing film of the object along its thickness direction can be used to measure Raman spectrum by a Raman spectrophotometer. Specifically, a display made by Horiba Ltd. can be used. A laser Raman spectrometry apparatus such as a micro-laser Raman spectrometer, such as "LabRAM ARAMIS VIS", irradiates laser light having a wavelength of 532 nm to the Raman spectrometer to measure the target portion of the sample. Then, from the thus obtained 310 cm ^-1 signal strength (Int ³¹⁰ ) and 210 cm ^-1 signal strength (Int ²¹⁰ ) of each measurement target portion, the ratio (Int ³¹⁰ / Int ²¹⁰ ) of the portion was calculated. As specific measurement methods and conditions for obtaining the ratio (Int ³¹⁰ / Int ²¹⁰ ) of each part of the film, those described later in the examples may be adopted. In addition, each side of the film specified in the polarizing film (2) enters in the thickness direction toward the inside to a portion of 10% with respect to the thickness. For example, when the thickness of the polarizing film is 10 μm, the portion corresponds to the sides of the polarizing film. A portion of 1 μm (10 μm × 10% = 1 μm) is entered in the thickness direction toward the inside. Hereby that the present invention is not limited, but the ratio of the film portions (Int ³¹⁰ / Int ²¹⁰⁾ depends on the section I ₅ ^- present in an amount relative to ₃ I ^- the ratio of the amount present.

The aforementioned 2 × L / (M + N) of the polarizing film (2) is 0.91 or less. When 2 × L / (M + N) is 0.91 or less, it becomes a polarizing film with little blue light leakage in a cross polarizer state. From the viewpoint of obtaining a polarizing film with less blue light leakage in a cross-polarizer state, 2 × L / (M + N) is preferably 0.88 or less, and more preferably 0.85 or less. In addition, from the viewpoint of reducing the red light leakage in the state of the cross polarizer, the 2 × L / (M + N) is preferably 0.01 or more, more preferably 0.1 or more, and more preferably 0.5 or more.

Polarizing film (2) From the viewpoint of reducing blue light leakage, the ratio (A / B) of the wavelength 480 absorbance (A) to the wavelength 700nm absorbance (B) in the state of the orthogonal polarizer should be 1.42 or more, more preferably 1.43 The above is more preferably 1.44 or more. On the other hand, if the ratio (A / B) is too high, the red light leakage tends to increase. Therefore, the ratio (A / B) is preferably 2 or less, more preferably 1.8 or less, and even more preferably 1.6 or less.

As the PVA, vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl neodecanoate, vinyl dodecanoate, vinyl octadecanoate, and vinyl benzoate can be used. Polymers obtained by polymerizing one or more vinyl esters such as esters and isopropenyl acetate Vinyl esters are obtained by saponification. Among the aforementioned vinyl esters, vinyl acetate is preferred from the viewpoints of easy manufacturability, availability, and cost of PVA.

The polyvinyl ester may be obtained by using only one or two or more vinyl esters as a single amount, but may be one or two or more vinyl esters and may be used as long as the effect of the present invention is not impaired. Copolymers of other monomers with which it is copolymerized.

The aforementioned other monomers that can be copolymerized with vinyl esters include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth) acrylic acid or a salt thereof; (meth) Methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (formyl) (Meth) acrylic acid esters such as tert-butyl acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and stearyl (meth) acrylate; (meth) acrylic acid; Ammonium amine, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone alcohol (meth) acryl Amidoamine, (meth) acrylamidopropanesulfonic acid or a salt thereof, (meth) acrylamidopropanedimethylamine or a salt thereof, and N-methylol (meth) acrylamidoamine or a derivative thereof, etc. (Meth) acrylamide derivatives; N-vinylamines such as N-vinylmethylamine, N-vinylacetamide, and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, N-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, Vinyl ethers such as butyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, and octadecyl vinyl ether; vinyl cyanide (meth) acrylonitrile; vinyl chloride, dichloroethylene, fluorine Halogenated ethylene such as ethylene and difluoroethylene; propylene compounds such as allyl acetate and chloropropylene; butane Adipic acid or its salt, ester or anhydride; methylene succinic acid or its salt, ester or anhydride; ethylene silicon compounds such as ethylene trimethoxysilane; unsaturated sulfonic acid and the like. The polyvinyl ester may have one kind or two or more kinds of structural units derived from the other monobases.

In the aforementioned polyvinyl ester, the proportion of the structural unit derived from the aforementioned other single body is based on the molar number of the entire structural unit constituting the polyvinyl ester, and is preferably 15 mol% or less, and may also be 10 mol% or less. It is 5 mol% or less.

In particular, when the aforementioned other monomers are (meth) acrylic acid, unsaturated sulfonic acid, etc., which may promote the water solubility of the obtained PVA, in order to prevent the dissolution of PVA during the production of polarizing films, The ratio of the structural units of these singular bodies is preferably 5 mol% or less, and more preferably 3 mol% or less, based on the number of moles of all the structural units constituting the polyvinyl ester.

As long as the effect of the present invention is not impaired, the aforementioned PVA may be denatured by one or more kinds of graft copolymerizable monomers. Examples of the graft copolymerizable monomer include an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, and an α-olefin having 2 to 30 carbon atoms. The ratio of the structural units (structural units of the graft-denatured part) derived from the graftable copolymerizable monomer in the PVA is preferably 5 mol% or less based on the number of moles of the total structural units constituting the PVA.

In the PVA, a part of the hydroxyl group may be crosslinked or non-crosslinked. Also, in the aforementioned PVA, a part of the hydroxyl group may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or it may not react with these compounds to form an acetal structure.

The average degree of polymerization of the aforementioned PVA should be between 1,000 and 9,500 Within the range, the average degree of polymerization is more preferably 1,500 or more, more preferably 2,000 or more, more preferably 9,200 or less, and even more preferably 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 in accordance with JIS K6726-1994.

The saponification degree of the aforementioned 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 polarization performance of the polarizing film. If the saponification degree is less than 98 mol%, the PVA is easily dissolved during the manufacture of the polarizing film, and the dissolved PVA is attached to the film, which may reduce the polarizing performance of the polarizing film. In addition, the so-called saponification degree of PVA in this specification refers to the total number of moles of the structural unit (typically, a vinyl ester unit) and a vinyl alcohol unit that can be converted to a vinyl alcohol unit by saponification with respect to PVA. Molar number occupancy ratio of the unit (Molar%). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

An iodine-based dye include the I ₃ ^- and I ₅ ^- and the like. Examples of such counter cations include alkali metals such as potassium. The iodine-based pigment can be obtained, for example, by contacting iodine (I ₂ ) with potassium iodide.

When the content of the alkali metal contained in the polarizing film of the present invention is X mol / kg and the thickness of the polarizing film is Y μm, if the formula: Z = X × log (Y) shows that Z is 0.19 or less, the heat resistance of the polarizing film And it is suitable to improve moist heat resistance. From such a viewpoint, Z is preferably 0.185 or less, and more preferably 0.175 or less. In addition, from the viewpoint that the leakage of blue light under the state of the cross polarizer can be further reduced, Z is preferably 0.15 or more, and more preferably 0.16 or more. Examples of alkali metals For example, sodium and potassium are preferably potassium. This content rate can be calculated | required by ICP-MS measurement, for example.

The monomer light 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 monomer transmittance is more preferably 41% or more, more preferably 42% or more, and more preferably Below 44%. The individual light transmittance of the polarizing film can be measured by a method described later in the examples.

(Polarizing film manufacturing method)

The method for manufacturing the polarizing film of the present invention is not particularly limited. It can be produced by dyeing and stretching using a PVA film as a raw material film, and can be dispersed, for example, in a specific amount and concentration for a PVA film used as a raw material film. Dyeing solution of iodine-based pigment; contact the roller coated with iodine-based dyeing solution with the PVA film used as the raw material film; impregnate the dyeing solution containing iodine-based dye into porous bodies such as sponges, and contact the permeate as the raw material film the PVA film used, so that the thickness of the polarizing film and the vicinity of the surface of the central portion of each of the obtained I ₅ ^- present in an amount relative to the I ₃ ^- present in an amount ratio of a difference, and easy to manufacture, but if the production method according to the present invention the following , The polarizing film of the present invention can be manufactured more easily and is suitable.

That is, the manufacturing method of the present invention includes the steps of dyeing and stretching a PVA film having a thickness of 50 μm or less. The dyeing is performed by immersing the PVA film in a dyeing bath containing an iodine dye. the following.

As described above, the manufacturing method of the present invention includes a step of dyeing and stretching a PVA film having a thickness of 50 μm or less. The PVA film used may be a single layer, or a thermoplastic resin-based resin may be used as described in Patent Documents 1 and 2. Materials such as materials are laminated on the substrate, but a single layer is preferred.

In the description of the polarizing film of the present invention, the PVA constituting the PVA film can use the same materials as described above, and therefore redundant descriptions are omitted here.

The PVA film preferably contains a plasticizer from the viewpoint of improving stretchability during stretching. Examples of such plasticizers include polyhydric alcohols such as ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. PVA films may contain One or more plasticizers. Among these, glycerin is preferred from the viewpoint of elongation-improving effects.

The plasticizer content of the PVA film is preferably within a range of 1 to 20 parts by mass relative to 100 parts by mass of the PVA contained therein. When the content is 1 part by mass or more, the stretchability of the PVA film can be relatively improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the PVA film from being too soft and lowering the operability. The plasticizer content of PVA film is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, more preferably 5 parts by mass or more, 15 parts by mass or less, and more preferably 12 parts by mass relative to 100 parts by mass of PVA. Mass parts or less.

In addition, although it varies depending on the manufacturing conditions of the polarizing film, etc., the plasticizer contained in the PVA film will be dissolved out during the production of the polarizing film, so the entire amount may not remain in the polarizing film.

The PVA film may further contain ingredients such as an antioxidant, an antifreeze, a pH adjuster, a masking agent, an anti-colorant, an oil agent, and a surfactant, as required.

PVA content of PVA film, from the desired polarizing film In terms of ease of modulation, it is preferably in the range of 50 to 99% by mass, and the content ratio is more preferably 75% by mass or more, more preferably 80% by mass or more, particularly 85% by mass or more, and more preferably 98% by mass. Mass% or less, more preferably 96 mass% or less, and particularly preferably 95 mass% or less.

The thickness of the PVA film used in the manufacturing method of the present invention is 50 μm or less. When the thickness is 50 μm or less, the aforementioned thin polarizing film can be easily obtained. From such a viewpoint, the thickness of the PVA film is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. In addition, since a PVA film having an excessively thin thickness is difficult to manufacture, the thickness of the PVA film is, for example, 2 μm or more (for example, 5 μm or more).

The shape of the PVA film is not particularly limited, but from the viewpoint of continuous use when manufacturing a polarizing film, it is preferably a long PVA film. The length of the strip-shaped PVA film (length in the strip direction) is not particularly limited, and can be appropriately set according to the application of the polarizing film to be manufactured, for example, it can be within a range of 5 to 20,000 m.

There is no particular limitation on the width of the PVA film, and it can be appropriately set according to the application of the polarizing film to be manufactured. From the viewpoint of the development of large-screen LCD TVs and LCD screens in recent years, if the width of the PVA film is 0.5 m or more, it is more preferably 1.0 m or more It is suitable for those uses. On the other hand, if the width of the PVA film is too wide, it may be difficult to stretch uniformly when manufacturing a polarizing film by a practical device. Therefore, the width of the PVA film is preferably 7 m or less.

As described above, the manufacturing method of the present invention includes a step of dyeing the PVA film (dyeing step) and an extending step (elongation step). The manufacturing method may further include a dyeing step and an extending step as required. Swelling step, crosslinking step, fixing treatment step, washing step, drying step, and the like. The order of each step can be appropriately changed according to needs, each step can be performed more than two times, and different steps can be performed at the same time.

In the manufacturing method of the present invention, for example, the PVA film is firstly supplied to the swelling step, then to the dyeing step, further to the cross-linking step if necessary, and then to the extension step, and further to the fixing treatment step if necessary, and / Or the method of washing step and then supplying to the drying step.

The swelling step can be performed by immersing the PVA film in water. When immersed in water, the water temperature should be in the range of 20 to 40 ° C. The temperature is preferably above 22 ° C, more preferably above 25 ° C, more preferably below 38 ° C, and more preferably below 35 ° C. By setting the temperature in the range of 20 to 40 ° C, the PVA film can be effectively swelled. In addition, the time of 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 dipping in the range of 0.1 to 5 minutes, the PVA film can be effectively swelled. The immersion in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

In the manufacturing method of the present invention, the dyeing is performed by immersing the PVA film in a dyeing bath containing an iodine-based dye. Here, it is necessary that the temperature of the dyeing bath is 25 ° C or lower and the immersion time is 1.5 minutes or shorter.

If the temperature of the dyeing bath is higher than 25 ° C, the blue light leakage of the obtained polarizing film in the state of the cross polarizer will increase. From this point of view, the temperature of the dyeing bath is preferably 23 ° C or lower, more preferably 21 ° C or lower, more preferably 18 ° C or lower, 15 ° C or lower, and even 10 ° C or lower, especially when used thinner. Dyeing of PVA film The temperature of the bath can more effectively obtain the intended polarizing film. On the other hand, if the temperature of the dyeing bath is too low, unevenness 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.

When the PVA film is immersed in a dyeing bath, if the immersion time is longer than 1.5 minutes, the blue light leakage of the obtained polarizing film in the state of the cross polarizer will also increase. From this point of view, the immersion time should be 1.3 minutes or less, more preferably 1.1 minutes or less, 0.8 minutes or less, 0.5 minutes or less, and further 0.3 minutes or less, especially when a thin PVA film is used By shortening the immersion time, the intended polarizing film can be obtained more efficiently. On the other hand, if the immersion time is too short, unevenness may occur in the obtained polarizing film. Therefore, the immersion time is preferably 0.05 minutes or more, and more preferably 0.1 minutes or more.

Typical examples of the dyeing bath include those obtained by mixing iodine (I ₂ ) and potassium iodide with water. By mixing water with iodine and potassium iodide, may generate I ₃ ^- and I ₅ ^- and other iodine-based dye. The concentration of iodine and potassium iodide in the dyeing bath is not particularly limited. Relative to the quality of the dyeing bath obtained, the iodine concentration of the mass ratio of iodine used should be within the range of 0.01 to 2% by mass, and more preferably within the range of 0.02 to 0.5% by mass. Relative to the mass of iodine used previously, the potassium iodide concentration of the mass ratio of potassium iodide used is preferably within a range of 10 to 200 times the mass, and more preferably within a range of 15 to 150 times the mass. The dyeing bath may contain boron compounds such as boric acid such as boric acid and borax.

By performing a cross-linking step on the PVA film, the PVA can be more effectively prevented from dissolving into water when wet stretching is performed at a higher temperature. From this point of view, the crosslinking step is preferably performed after the dyeing step and before the extending step. The cross-linking step can be performed by dipping the PVA film in a water-soluble solution containing a cross-linking agent. Performed in a liquid crosslinking bath. As the cross-linking agent, one or two or more boron compounds such as borate such as boric acid and borax can be used. The concentration of the crosslinking agent in the crosslinking bath should be in the range of 1 to 15% by mass, more preferably 2% by mass or more, 7% by mass or less, and more preferably 6% by mass or less. A crosslinker concentration in a range of 1 to 15% by mass can maintain sufficient extensibility. The crosslinking bath may also contain auxiliary agents such as potassium iodide. The temperature of the crosslinking bath is in the range of 20 to 50 ° C, and particularly preferably in the range of 25 to 40 ° C. This temperature can be effectively cross-linked in the range of 20 ~ 50 ° C.

There is no particular limitation on the stretching method when the PVA film is stretched, and either a wet stretching method or a dry stretching method can be performed. The wet elongation method can be performed in an aqueous solution containing one or two or more boron compounds such as boric acid such as boric acid and borax, or in the aforementioned dyeing bath or a fixed treatment bath described later. Further, in the case of the dry stretching method, it can be performed at room temperature, it can also be extended while heating, or it can be extended after absorbing water. Among them, from the viewpoint of the thickness uniformity of the obtained polarizing film in the width direction, wet stretching is preferable, and stretching in a boric acid aqueous solution is more suitable. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass, and the concentration is more preferably 1.0% by mass or more, more preferably 1.5% by mass or more, more preferably 5.0% by mass or less, and more 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 aforementioned boron-containing compound aqueous solution may also contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass. If the concentration of potassium iodide is in the range of 0.01 to 10% by mass, a polarizing film with better polarization performance can be obtained.

The temperature when the PVA film is stretched should be in the range of 5 ~ 90 ° C. The temperature is preferably more than 10 ° C, and more preferably 80 ° C or less, and more preferably Below 70 ° 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.

When the PVA film is stretched, the stretching ratio should be 4 times or more, more preferably 5 times or more, and more preferably 6 times or more. By extending the PVA film within the aforementioned range, a polarizing film with excellent polarizing performance can be obtained. The upper limit of the stretching ratio of the PVA film is not particularly limited, and should preferably be 8 times or less. PVA film stretching can be carried out once or divided into multiple times. When divided into multiple times, as long as the total stretching ratio multiplied by the stretching ratio of each stretching is within the aforementioned range. In this specification, the stretching ratio is based on the length of the PVA film before stretching, and the unstretched state is equivalent to 1 times the stretching ratio.

From the viewpoint of the performance of the obtained polarizing film, the extension of the PVA film is preferably uniaxial. When the elongated PVA film is stretched, the direction of uniaxial extension is not particularly limited. Uniaxial extension in the longitudinal direction or transverse uniaxial extension can be used. From the viewpoint of obtaining a polarizing film with excellent polarizing performance, it is preferably Uniaxial extension in strip direction. The uniaxial extension in the long direction can be performed by changing the rotation speed between the rollers by using an extension device having a plurality of rollers parallel to each other. On the other hand, horizontal uniaxial stretching can be performed using a tenter type stretching machine.

The fixing treatment step is mainly used to consolidate the adsorption of the iodine-based pigment on the PVA film. The fixing treatment step can be performed by immersing the PVA film before, during, or after stretching in the fixing treatment bath. As the fixed treatment bath, an aqueous solution containing one or more boron compounds such as borate such as boric acid and borax can be used. If necessary, an iodine compound or a metal compound may be added to the fixed treatment bath. In the boron-containing compound aqueous solution used in the fixed treatment bath, the concentration of the boron compound is generally 0.1 to 15 In the range of mass%, it is particularly preferable to be 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 pigment can be consolidated. The temperature of the fixed treatment bath is in the range of 10 to 60 ° C, and particularly preferably in the range of 15 to 40 ° C. By this temperature in the range of 10 ~ 60 ° C, the adsorption of iodine-based pigments can be consolidated.

The cleaning step is mostly used to remove unnecessary drugs or foreign materials on the surface of the film, and to adjust the optical properties of the finally obtained polarizing film. The washing step can be performed by immersing the PVA film in a washing bath, or spraying a washing solution on the PVA film. Water can be used as a washing bath or a washing liquid, and potassium iodide can also be contained in the washing bath or washing liquid.

The drying conditions in the drying step are not particularly limited, and are in the range of 30 to 150 ° C, and particularly suitable for drying in the temperature range of 50 to 130 ° C. By drying at a temperature in the range of 30 to 150 ° C, it is easy to obtain a polarizing film having excellent dimensional stability.

(Usage form)

A polarizing film is usually used as a polarizing plate by laminating a protective film on both sides or one side. Examples of the protective film include those that are optically transparent and have mechanical strength. Specifically, for example, a cellulose triacetate (TAC) film, a cellulose acetate ‧ butyrate (CAB) film, an acrylic film, a polyester film, and the like can be used. In addition, the adhesive for bonding includes PVA-based adhesives or urethane-based adhesives, and is preferably a PVA-based adhesive.

[Example]

Hereinafter, the present invention is specifically described by examples, but the present invention is not limited in any way by these examples.

In addition, the bias used in the following examples, comparative examples, and reference examples Each measurement or calculation method of the light film absorbance, monomer light transmittance, alkali metal content, and 2 × L / (M + N) is shown below.

[Absorbance of polarizing film and light transmittance of monomer]

From the center of the width direction (TD) of the polarizing film obtained from the following examples, comparative examples, or reference examples, take a rectangular sample of 2 cm along the length direction (MD) of the polarizing film, and use a spectrophotometer with an integrating sphere (Japan Spectroscopy Co., Ltd. "V7100" made by the company), the sample was set to the cross polarizer state with respect to the spectrophotometer polarizer, and the absorbance (A) and 700 nm (B) were measured at a wavelength of 480 nm. Next, using the same sample and spectrophotometer, in accordance with JIS Z 8722 (method for measuring the color of an object), the visual sensitivity correction in the visible light region with a C light source and a 2 ° field of view was performed. The light transmittance and the light transmittance at an inclination of -45 °, and the average value (%) of these is taken as the unit light transmittance of the polarizing film.

[Content ratio of alkali metal contained in polarizing film]

It was calculated | required by ICP-MS measurement. In addition, in any of the examples, comparative examples, and reference examples, more than 99 mol% of the alkali metals measured were potassium.

[2 × L / (M + N) of polarizing film]

For the polarizing films obtained in the following examples, comparative examples, or reference examples, at any position in the longitudinal direction (MD), cut out a piece of MD × TD = 2mm × 10mm size from the central portion in the width direction (TD). The two sides of the fine sheet were sandwiched between two polyethylene terephthalate films having a thickness of 100 μm, and set on a microtome. This fine piece was sliced from a polyethylene terephthalate film at an interval of 20 μm parallel to the MD, and a sample having a size of MD × TD = 2 mm × 20 μm was taken.

For this sample, a micro-laser Raman spectrometer "LabRAM ARAMIS VIS" manufactured by Horiba was used to irradiate laser light with a wavelength of 532 nm to the Raman spectrum of the measurement target portion on the cross-section generated by the slicer slice. In the measurement, at this time, from the signal intensity of 310cm ^-1 (Int ³¹⁰ ) and the signal intensity of 210cm ^-1 (Int ²¹⁰ ), the ratio (Int ³¹⁰ / Int ²¹⁰ ) of this part is calculated. In addition, the aforementioned measurement target portions are the central portion in the thickness direction of the polarizing film and the portion that goes from the sides of the polarizing film in the thickness direction to the inside to 10% relative to the thickness. The ratio (Int ³¹⁰ / Int) is obtained from the central portion in the thickness direction of the polarizing film. ²¹⁰ ) is L, and the ratio of 2 (Int ³¹⁰ / Int ²¹⁰ ) obtained by entering from the sides of the polarizing film inwardly in the thickness direction to the part with a thickness of 10% is to satisfy M ≦ N. Set it to M or N, and use these L, M, and N to calculate 2 × L / (M + N).

[Example 1]

Using 100 parts by mass of PVA (saponified product of a copolymer of vinyl acetate and ethylene, an average degree of polymerization of 2,400, a degree of saponification of 99.4 mol%, and an ethylene unit content of 2.5 mol%) and 10 parts by mass of glycerin as a plasticizer. 0.1 parts by mass of sodium oxyethylene lauryl ether sulfate is used as a surfactant and a film-forming dope composed of water, and a PVA film having a thickness of 30 μm is obtained by casting and film formation, and is subjected to a swelling step, a dyeing step, a crosslinking step, an extension step, and a fixing The processing step and the drying step produce a polarizing film.

That is, the aforementioned PVA film is immersed in water at a temperature of 30 ° C for 1 minute, during which the uniaxial extension (the first stage extension) in the longitudinal direction (MD) is doubled to the original length, and the usage amount is 0.03% by mass of iodine and potassium iodide. 0.7% by mass mixed with water and immersed in a dyeing bath at a temperature of 20 ° C for 1 minute. The length direction (MD) is uniaxially extended (second stage extension) to three times the original length, and then immersed in a crosslinking bath containing a concentration of 2.5 mass% of boric acid at 32 ° C for 2 minutes, during which the axis is uniaxially extended in the length direction (MD). Extend (3rd stage extension) to 3.6 times the original length, and immerse it in a 57 ° C aqueous solution of boric acid / potassium iodide containing 2.8% by mass of boric acid and 5% by mass of potassium iodide, extending uniaxially in the lengthwise direction (MD) 4 steps extended) to 6 times the original length. Thereafter, the film was washed by immersing in a 22 ° C potassium iodide aqueous solution for 5 seconds at a concentration of 1.5 mass% of boric acid and 5 mass% of potassium iodide, and then dried by a 60 ° C dryer. A polarizing film of 13 μm was produced in 240 seconds.

Using the obtained polarizing film, the absorbance, monomer light transmittance, alkali metal content, and 2 × L / (M + N) were measured or calculated by the methods described above. The results are shown in Table 1.

[Comparative Examples 1 to 4 and Reference Example 1]

The thickness of the PVA film, the temperature of the dyeing bath, the immersion time of the dyeing bath, and the composition of the dyeing bath were changed as shown in Table 1, and a polarizing film having the thickness shown in Table 1 was produced in the same manner as in Example 1.

Using the obtained polarizing film, the absorbance, monomer light transmittance, alkali metal content, and 2 × L / (M + N) were measured or calculated by the methods described above. The results are shown in Table 1.

Claims (5)

One kind of polarizing film, which is a polyvinyl alcohol-based matrix containing adsorbed iodine-based dye, a thickness of 25μm or less of the polarizing film, wherein the cross section of the polarizing film for Raman spectrometry (Raman), 310cm central portion in the thickness direction of the obtained film ^{- 1 The ratio of the} signal strength (Int ³¹⁰ ) to 210cm ^-1 (Int ²¹⁰ ) (Int ³¹⁰ / Int ²¹⁰ ) is L, and one side of the film enters in the thickness direction toward the inside to 310cm ^-1 relative to the 10% thickness portion. The ratio of the signal strength (Int ³¹⁰ ) to 210cm ^-1 signal strength (Int ²¹⁰ ) (Int ³¹⁰ / Int ²¹⁰ ) is M. The other side of the film enters in the thickness direction toward the inside to a signal of 310cm ^-1 relative to the thickness of 10%. When the ratio (Int ³¹⁰ / Int ²¹⁰ ) of the intensity (Int ³¹⁰ ) to the signal intensity (Int ²¹⁰ ) of 210cm ^-1 is N (only M ≦ N), 2 × L / (M + N) is 0.91 or less. For example, the polarizing film of claim 1, wherein the ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm in a crossed polarizer state is 1.42 or more. For example, the polarizing film of claim 1 or 2, where the content of alkali metal contained in the polarizing film is X mol / kg, and the thickness of the polarizing film is Y μm, the formula: Z = X × log (Y), where Z is 0.19 the following. For example, the polarizing film of item 1 or 2 in which the monomer light transmittance is 40 to 45%. A method for producing a polarizing film, which is a method for producing a polarizing film according to any one of claims 1 to 4 including a step of dyeing and extending a polyvinyl alcohol film having a thickness of 50 μm or less, wherein the dyeing is performed by using an iodine-based pigment The dyeing bath is impregnated with a polyvinyl alcohol film, and the mass ratio of iodine to the mass of the dyeing bath is in a range of 0.01 to 0.5% by mass. The temperature of the dyeing bath is 25 ° C or lower and the immersion time is 1.5 minutes or shorter.