TW201514556A - Polarizing film - Google Patents

Abstract

To provide a thin polarizing film that leaks little blue light when in a crossed Nicols state. A polarizing film has a thickness of 25 [mu]m or less with a matrix including PVA having iodine-based dyes adsorbed thereinto. The ratio (A/B) of an absorbance (A) at a wavelength of 480 nm to an absorbance (B) at a wavelength of 700 nm in the crossed Nicols state is 1.42 or more. Alternatively, 2 x L / (M + N) <= 0.91 (M <= N) is satisfied, where L represents the ratio (Int310 / Int210) of a signal intensity (Int310) at 310 cm-1 to a signal intensity (Int210) at 210 cm-1 at the center in the thickness direction, said signal intensities being acquired by measuring the cross section of the polarizing film using a Raman spectroscopy; M represents the ratio at a position at 10 % of the thickness inward from one surface of the film; and N represents the ratio at a position at 10 % of the thickness inward from the other surface of the film.

Description

Polarized film

The present invention relates to a thin polarizing film in which blue light leakage is small in a state of a crossed polarizer and a method of manufacturing the same.

A polarizing plate having a light transmitting and shading function is a basic constituent element of a liquid crystal display (LCD) as a liquid crystal that changes a polarized state of light. Most of the polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of the polarizing film, and a polarizing film constituting the polarizing plate is a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be omitted as "PVA"). The uniaxially stretched matrix (the uniaxially stretched 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 dye in advance, and uniaxially stretching the PVA film while adsorbing the iodine-based dye or uniaxially stretching the PVA film to adsorb an iodine-based dye or the like.

LCD is widely used in small machines such as computers and watches, notebook computers, LCD screens, liquid crystal color projectors, LCD TVs, car navigation systems, mobile phones, and measurement machines for indoor and outdoor use. In recent years, it has been used especially for small notes. For mobile applications such as computers and mobile phones, the requirements for thinning polarizers are enhanced.

A method of thinning a polarizing film constituting a polarizing plate is conventionally known for forming a PVA layer on one surface of a thermoplastic resin film. After the layer is stretched, dyed, and dried, a method of peeling off the stretched thermoplastic resin film layer is required (see Patent Documents 1 and 2, etc.).

[Previous 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 produced according to a conventional method, there is a problem that blue light leaks in a state of a crossed polarizer. Here, an object of the present invention is to provide a thin polarizing film having a small amount of blue light leakage in a state of a crossed polarizer and a method of manufacturing the same.

In order to achieve the above object, the inventors of the present invention actively repeated the investigation and found that when a thin PVA film is dyed and stretched to produce a polarizing film, the temperature of the dye bath containing the iodine-based dye and the dye bath immersion time are set. For a specific range, the measurement results obtained by Raman spectroscopy in the central portion of the film thickness direction and the vicinity of the surface satisfy a specific relationship, and the blue light leakage in the state of the orthogonal polarizer which is not existing in the past can be easily obtained. The invention is completed by further revisiting based on such knowledge with few polarizing films.

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 a substrate containing PVA and having a thickness of 25 μm or less. In the polarizer state, the ratio (A/B) of the absorbance at a wavelength of 480 nm (A) to the absorbance at a wavelength of 700 nm (A/B) is 1.42 or more; [2] a polarizing film (hereinafter also referred to as "polarized film (2)"), which A polarizing film having a thickness of 25 μm or less adsorbed on a substrate containing PVA, wherein a cross section of the polarizing film is subjected to Raman spectroscopy, and a 310 cm ^-1 signal intensity (Int ³¹⁰ ) and 210 cm at a central portion in the thickness direction of the film are obtained ^. The ratio of ¹ signal intensity (Int ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is L, and one side of the film enters inward in the thickness direction to 310 cm ^-1 signal intensity (Int ³¹⁰ ) and 210 cm ^-1 with respect to 10% of the thickness. The ratio of signal intensity (Int ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is M, and the other side of the film enters inward in the thickness direction to 310 cm ^-1 signal intensity (Int ³¹⁰ ) and 210 cm ^-1 signal with respect to 10% of the thickness. When the ratio of intensity (Int ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is N (only M≦N), 2× L/(M+N) is 0.91 or less; [3] The polarizing film according to the above [2], wherein the ratio of the absorbance at a wavelength of 480 nm (A) to the absorbance at a wavelength of 700 nm (A/) in a crossed polarizer state (A/) The polarizing film according to any one of the above [1] to [3] wherein the polarizing film contains an alkali metal content of X mol/kg and the polarizing film has a thickness of Y μm. The polarizing film of any one of the above [1] to [4], wherein the monomer light transmittance is 40 to 45%; [Z] is as shown in the above-mentioned [1] to [4]; 6) A method for producing a polarizing film, which comprises a method for producing a polarizing film comprising a step of dyeing and stretching a PVA film having a thickness of 50 μm or less, wherein the dyeing is performed by impregnating a PVA film in a dye bath containing an iodine-based dye. The dye bath temperature is 25 ° C or less, and the immersion time is 1.5 minutes or less.

According to the present invention, there is provided a thin polarizing film in which blue light leakage is small in the state of a crossed polarizer. Moreover, according to the present invention, there is provided a method of producing a polarizing film which can easily produce the polarizing film.

[Formation of the Invention]

The invention is described in detail below.

(polarized film)

The polarizing film of the present invention is an iodine-based dye adsorbed on a matrix containing PVA. Such a polarizing film can be produced by stretching a PVA film containing an iodine-based dye in advance, stretching an PVA film while adsorbing an iodine-based dye, or stretching a PVA film to form a matrix, and then adsorbing an iodine-based dye.

The polarizing film of the present invention has a thickness of 25 μm or less. By having a thickness of 25 μm or less, a thin polarizing plate which is 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. Further, the polarizing film having a too small thickness is difficult to manufacture, and the thickness of the polarizing film is, for example, 1 μm or more (an example is 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 in a crossed polarizer state is 1.42 or more. By the ratio (A/B) being 1.42 On the top, it becomes a polarizing film with less leakage of blue light. From this point of view, 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, red light leakage tends to increase. Therefore, the ratio (A/B) is preferably 2 or less, more preferably 1.8 or less, and still more preferably 1.6 or less. Further, 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 ^When the ratio of ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is N (only M≦N), 2×L/(M+N) is 0.91 or less.

When Raman spectroscopy is used for the cross section of the polarizing film, for example, a sample in which the polarizing film of the object is sliced in the thickness direction thereof can be used, and Raman spectroscopy can be performed by a Raman spectrophotometer. Specifically, it can be produced by using a field-making apparatus. A laser Raman spectrometer such as a micro-laser Raman spectrometer "LabRAM ARAMIS VIS" is used to measure Raman spectroscopy by irradiating a laser beam having a wavelength of 532 nm to a measurement target portion of the sample. Thereafter, the ratio (Int ³¹⁰ /Int ²¹⁰ ) of the portion was calculated from the ³¹⁰ cm ^-1 signal intensity (Int ³¹⁰ ) and the 210 cm ^-1 signal intensity (Int ²¹⁰ ) of each of the measurement target portions thus obtained. As the specific measurement method and conditions for determining the ratio of each portion of the film (Int ³¹⁰ /Int ²¹⁰ ), the following examples in the examples can be used. Further, the respective faces of the film specified in the polarizing film (2) are formed 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 each side of the polarizing film. A portion of 1 μm (10 μm × 10% = 1 μm) was entered in the thickness direction toward the inside. It is not considered to limit the invention, but the ratio of each portion of the film (Int ³¹⁰ /Int ²¹⁰ ) depends on the ratio of the amount of I ₅ ^- present in the portion relative to the amount of I ₃ ^- 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, a polarizing film having less blue light leakage in the state of a crossed polarizer is obtained. From the viewpoint of obtaining a polarizing film having less blue light leakage in the state of the crossed polarizer, 2 × L / (M + N) is preferably 0.88 or less, and more preferably 0.85 or less. Further, from the viewpoint of reducing red light leakage in the state of the crossed polarizer, 2 × L / (M + N) is preferably 0.01 or more, more preferably 0.1 or more, and more preferably 0.5 or more.

The polarizing film (2) is preferably a ratio of the wavelength 480 absorbance (A) to the absorbance (B) at a wavelength of 700 nm (A/B) in the state of the crossed polarizer from the viewpoint of reducing the leakage of the blue light, and is preferably 1.42 or 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, red light leakage tends to increase. Therefore, the ratio (A/B) is preferably 2 or less, more preferably 1.8 or less, and still more preferably 1.6 or less.

The aforementioned PVA may use vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl neodecanoate, vinyl dodecate, vinyl octadecate, vinyl benzoate. Polycondensation of one or more kinds of vinyl esters such as esters and isopropenyl acetate The vinyl ester is obtained by saponification. Among the vinyl esters, vinyl acetate is preferred from the viewpoints of ease of production, availability, cost, and the like of PVA.

The polyvinyl ester may be one obtained by using only one or two or more kinds of vinyl esters as a single amount. However, one or two or more kinds of vinyl esters may be used as long as the effects of the present invention are not impaired. Copolymers of other single monomers with which they are copolymerized.

The other monomer which can be copolymerized with the vinyl ester may, for example, be an α-olefin having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene or isobutylene; (meth)acrylic acid or a salt thereof; (methyl) Methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (A) (meth)acrylate such as tert-butyl acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth) acrylate Indoleamine, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone (meth)propene Hydrazine, (meth) acrylamide sulfonate or a salt thereof, (meth) acrylamide dimethylamine or a salt thereof, and N-methylol (meth) acrylamide or a derivative thereof (Methyl) acrylamide derivatives; N-vinylamine, N-vinylacetamide, and N-vinylamine such as 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, t-butyl vinyl ether, dodecyl vinyl ether and octadecyl vinyl ether; vinyl cyanide such as (meth)acrylonitrile; vinyl chloride, dichloroethylene, fluorine Ethylene halide such as ethylene and difluoroethylene; propylene compound such as allyl acetate and chloropropene; An enedioic acid or a salt, ester or anhydride thereof; methylene succinic acid or a salt, ester or anhydride thereof; an ethylene oxime compound such as ethylene trimethoxy hydride; an unsaturated sulfonic acid or the like. The polyvinyl ester may have one or two or more kinds of structural units derived from the other monovalent bodies.

In the polyvinyl ester, the structural unit occupancy ratio from the other monomer is preferably 15 mol% or less, or 10 mol% or less, based on the total number of structural units constituting the polyvinyl ester, and further may be 10 mol% or less. It is 5 mol% or less.

In particular, when the other monoliths described above are (meth)acrylic acid, unsaturated sulfonic acid or the like which may promote the water solubility of the obtained PVA, in order to prevent PVA dissolution during the production of the polarizing film, the polyvinyl ester is derived from The structural unit ratio of the monoliths is preferably 5 mol% or less, and more preferably 3 mol% or less, based on the number of moieties of the entire structural unit constituting the polyvinyl ester.

The PVA may be denatured by one or two or more kinds of graft-copolymerizable units, without departing from the effects of the present invention. The graft copolymerizable monomer may, for example, be an unsaturated carboxylic acid or a derivative thereof; an unsaturated sulfonic acid or a derivative thereof; an α-olefin having 2 to 30 carbon atoms. The ratio of the structural unit (the structural unit of the graft denatured portion) derived from the graft-polymerizable monovalent body in the PVA is preferably 5 mol% or less based on the total structural unit molar number constituting the PVA.

In the aforementioned PVA, one of the hydroxyl groups may be crosslinked or not crosslinked. Further, in the above PVA, a part of the hydroxyl group may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not react with the compounds to form an acetal structure.

The average polymerization degree of the aforementioned PVA is preferably 1,000 to 9,500 In the range, the average degree of polymerization is preferably 1,500 or more, more preferably 2,000 or more, and still more preferably 9,200 or less, more preferably 6,000 or less. By making the average degree of polymerization 1,000 or more, the polarizing performance of the polarizing film is improved. On the other hand, by making the average degree of polymerization to 9,500 or less, the productivity of PVA is improved. Further, the average degree of polymerization of PVA can be measured in accordance with 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 polarizing performance of the polarizing film. When the degree of saponification is less than 98 mol%, PVA is easily eluted during the production of the polarizing film, and the eluted PVA adheres to the film to lower the polarizing performance of the polarizing film. In addition, the degree of saponification of PVA in the present specification is a molar amount of a structural unit (typically a vinyl ester unit) which can be converted into a vinyl alcohol unit by saponification with respect to PVA, and a vinyl alcohol unit. The molar ratio of the unit is occupied (% by mole). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

Examples of the iodine-based dye include I ₃ ^- and I ₅ ^- . The counter cations may, for example, be an alkali metal such as potassium. The iodine dye can be obtained, for example, by bringing iodine (I ₂ ) into contact 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) and Z is 0.19 or less, the heat resistance of the polarizing film is obtained. It is suitable for improving the heat and humidity resistance. From this point of view, Z is preferably 0.185 or less, and more preferably 0.175 or less. Further, in view of the fact that the blue light leakage in the state of the crossed polarizer can be further reduced, Z is preferably 0.15 or more, and more preferably 0.16 or more. Alkali metals can be listed For example, sodium and potassium, etc., should be potassium. This content can be determined by, for example, ICP-MS measurement.

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

(Polarization film manufacturing method)

The method for producing the polarizing film of the present invention is not particularly limited, and a PVA film can be used as a raw material film, which can be produced by dyeing and stretching, and can be dispersed in a specific amount and concentration by, for example, a PVA film used as a raw material film. a dyeing solution for an iodine-based dye; a roller coated with an iodine-based dyeing solution is brought into contact with a PVA film used as a raw material film; a dyeing liquid containing an iodine-based dye is impregnated into a porous body such as a sponge, and the impregnated body is brought into contact as a raw material film. The PVA film or the like used has a difference in the ratio of the amount of I ₅ ⁻ present in the central portion of the obtained polarizing film to the vicinity of the surface with respect to the amount of I ₃ ^— , which is easy to manufacture, but according to the following manufacturing method of the present invention Further, it is more convenient to manufacture the polarizing film of the present invention.

That is, the production method of the present invention comprises a step of dyeing and stretching a PVA film having a thickness of 50 μm or less, and the dyeing is carried out by immersing the PVA film in a dye bath containing an iodine-based dye, the dye bath temperature is 25 ° C or less, and the immersion time is 1.5 minutes. the following.

As described above, the production method of the present invention contains a step of dyeing and extending a PVA film having a thickness of 50 μm or less. The PVA film to be used may be a single layer, or may be described in Patent Documents 1 and 2, and a thermoplastic resin group may be used. The material is laminated on the substrate, but it is preferably a single layer.

The PVA constituting the PVA film may be the same as those described above in the description of the polarizing film of the present invention, and thus the description thereof will be omitted.

The PVA film preferably contains a plasticizer from the viewpoint of improving elongation at the time of stretching. Examples of such plasticizers include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and the PVA film may contain these. One type or two or more types of plasticizers. Among these, glycerin is preferred from the viewpoint of the effect of the elongation enhancement.

The content of the plasticizer of the PVA film is preferably in the range of 1 to 20 parts by mass based on 100 parts by mass of the PVA contained therein. When the content is 1 part by mass or more, the elongation of the PVA film can be improved. On the other hand, when the content is 20 parts by mass or less, the PVA film can be prevented from being too soft and the workability can be lowered. The content of the plasticizer of the PVA film is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, particularly preferably 5 parts by mass or more, and more preferably 15 parts by mass or less, more preferably 12 parts by mass based on 100 parts by mass of the PVA. Below the mass.

In addition, the plasticizer contained in the PVA film is eluted during the production of the polarizing film, and the total amount does not necessarily remain in the polarizing film.

The PVA film may further contain an antioxidant, a cryoprotectant, a pH adjuster, a masking agent, a coloring inhibitor, an oil agent, and a surfactant, as needed.

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

The PVA film used in the production method of the present invention has a thickness of 50 μm or less. By making the thickness 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 still more preferably 10 μm or less. Further, the PVA film having an excessively thin thickness is difficult to manufacture, and the thickness of the PVA film is, for example, 2 μm or more (an example is 5 μm or more).

The shape of the PVA film is not particularly limited, but from the viewpoint of continuous use in producing a polarizing film, it is preferably a long PVA film. The length of the long PVA film (length in the strip direction) is not particularly limited, and may be appropriately set depending on the use of the polarizing film to be produced, and may be, for example, in the range of 5 to 20,000 m.

The width of the PVA film is not particularly limited, and may be appropriately set according to the use of the polarizing film to be manufactured. From the viewpoint of the development of the liquid crystal television and the liquid crystal screen in recent years, if the width of the PVA film is 0.5 m or more, it is preferably 1.0 m or more. It is then suitable for such purposes. On the other hand, when the width of the PVA film is too wide, it is difficult to uniformly extend the polarizing film by a practical device. Therefore, the width of the PVA film is preferably 7 m or less.

The manufacturing method of the present invention comprises the steps of dyeing a PVA film (dyeing step) and the step of extending (extension step) as described above, and the manufacturing method may further include, if necessary, a dyeing step and an extending step. a swelling step, a crosslinking step, a fixing treatment step, a washing step, a drying step, and the like. The order of the steps may be appropriately changed according to the needs, and each step may be performed twice or more, and different steps may be simultaneously performed.

For the manufacturing method of the present invention, for example, the PVA film is first supplied to the swelling step, and then to the dyeing step, and further needs to be supplied to the crosslinking step, and then supplied to the stretching step, and further provided for the fixing treatment step and/or Or a washing step and then a method for the drying step.

The swelling step can be carried out by immersing the PVA film in water. When immersed in water, the water temperature is preferably in the range of 20 to 40 ° C, and the temperature is preferably 22 ° C or more, more preferably 25 ° C or more, and more preferably 38 ° C or less, more preferably 35 ° C or less. By setting the temperature to a range of 20 to 40 ° C, the PVA film can be effectively swollen. Moreover, the time of immersion in water is preferably in the range of 0.1 to 5 minutes, preferably in the range of 0.5 to 3 minutes. The PVA film can be effectively swollen by dipping in the range of 0.1 to 5 minutes. Further, when immersed in water, it is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

In the production method of the present invention, the dyeing is carried out by immersing the PVA film in a dye bath containing an iodine-based dye. Here, the dye bath temperature is 25 ° C or lower, and the immersion time is 1.5 minutes or less.

If the dye bath temperature is greater than 25 ° C, the resulting polarizing film will increase in blue light leakage in the state of the crossed polarizer. From this point of view, the dye bath temperature is preferably 23 ° C or less, preferably 21 ° C or less, more preferably 18 ° C or less, 15 ° C or less, or 10 ° C or less, especially when used thinner. By reducing the dyeing of the PVA film The bath temperature can be used to obtain the polarizing film of the purpose more efficiently. On the other hand, if the temperature of the dyeing bath is too low, the polarizing film obtained may be unevenly formed. Therefore, the temperature of the dyeing bath is preferably 3 ° C or more, and more preferably 5 ° C or more.

When the PVA film is immersed in the dye bath, if the immersion time is more than 1.5 minutes, the blue light leakage of the obtained polarizing film in the state of the crossed polarizer also increases. From such a viewpoint, the immersion time is preferably 1.3 minutes or less, more preferably 1.1 minutes or less, and may be 0.8 minutes or less, 0.5 minutes or less, or further 0.3 minutes or less, particularly when a thin PVA film is used. By shortening the immersion time, the objective polarizing film can be obtained more efficiently. On the other hand, if the immersion time is too short, the polarizing film obtained may be unevenly formed. Therefore, the immersion time is preferably 0.05 minutes or more, and more preferably 0.1 minute or more.

Representative examples of the dyeing bath include those obtained by mixing iodine (I ₂ ) and potassium iodide with water. By mixing iodine and potassium iodide with water, an iodine-based dye such as I ₃ ^- and I ₅ ^- can be produced. The concentration of iodine and potassium iodide in the dyeing bath is not particularly limited, and the iodine concentration of the iodine mass ratio used is preferably in the range of 0.01 to 2% by mass, preferably in the range of 0.02 to 0.5% by mass, relative to the quality of the dyeing bath obtained, The potassium iodide concentration of the potassium iodide mass ratio used is preferably in the range of 10 to 200 mass times, more preferably in the range of 15 to 150 mass times, relative to the mass of the iodine used. The dye bath may also contain a boron compound such as a borate such as boric acid or borax.

By performing the crosslinking step on the PVA film, it is possible to more effectively prevent the PVA from eluting into the water when the wet stretching is performed at a higher temperature. From this point of view, the crosslinking step is preferably carried out after the dyeing step and before the stretching step. The crosslinking step can be performed by immersing the PVA film in a water-soluble solution containing a crosslinking agent. The liquid is cross-linked in a bath. One or two or more kinds of boron compounds such as a borate such as boric acid or borax may be used. The crosslinking agent concentration of the crosslinking bath is preferably in the range of 1 to 15% by mass, more preferably 2% by mass or more, still more preferably 7% by mass or less, and more preferably 6% by mass or less. The cross-linking agent concentration can maintain sufficient elongation in the range of 1 to 15% by mass. The crosslinking bath may also contain an auxiliary agent such as potassium iodide. The cross-linking bath temperature is in the range of 20 to 50 ° C, and particularly preferably in the range of 25 to 40 ° C. The temperature is effectively crosslinked in the range of 20 to 50 °C.

The stretching method when the PVA film is extended is not particularly limited, and any of the wet stretching method and the dry stretching method can be carried out. In the case of the wet stretching method, one or two or more kinds of boron compounds such as boric acid such as boric acid and borax may be used, or may be carried out in the dye bath or in a fixed treatment bath to be described later. Further, in the case of the dry stretching method, it may be carried out at room temperature, or may be extended while being heated, or may be extended after water absorption. Among them, from the viewpoint of thickness uniformity of the obtained polarizing film in the width direction, it is preferably a wet stretching, and it is preferably extended in an aqueous boric acid solution. The boric acid concentration in the aqueous boric acid solution is preferably in the range of 0.5 to 6.0% by mass, and the concentration is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and 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 excellent in thickness uniformity in the width direction can be obtained. The aqueous solution containing the boron compound may further contain potassium iodide, and the concentration thereof 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 having a good polarizing property can be obtained.

The temperature of the PVA film when extending is preferably in the range of 5 to 90 ° C, and the temperature is preferably 10 ° C or more, and more preferably 80 ° C or less, more preferably Below 70 °C. When the temperature is in the range of 5 to 90 ° C, a polarizing film excellent in thickness uniformity in the width direction can be obtained.

The stretching ratio of the PVA film when stretching is preferably 4 times or more, more preferably 5 times or more, more preferably 6 times or more. When the PVA film stretching ratio is within the above range, a polarizing film having excellent polarizing performance can be obtained. The upper limit of the stretching ratio of the PVA film is not particularly limited, and is preferably 8 times or less. The PVA film extension can be carried out once, or can be divided into a plurality of times, and when it is divided into a plurality of times, the total stretching ratio multiplied by the stretching ratio of each extension can be within the above range. Further, in the present specification, the stretching ratio is based on the length of the PVA film before stretching, and the unstretched state corresponds to a stretching ratio of 1 time.

The extension of the PVA film is preferably uniaxially stretched from the viewpoint of the performance of the obtained polarizing film. When the long P4-shaped film is extended, the direction of the uniaxial stretching is not particularly limited, and a uniaxial stretching or a horizontal uniaxial stretching along the longitudinal direction may be employed, and from the viewpoint of obtaining a polarizing film having excellent polarizing performance, it is preferable to Uniaxial extension of the strip direction. The uniaxial extension along the longitudinal direction can be performed by using an extension device having a plurality of rollers parallel to each other, by changing the rotational speed between the rollers. On the other hand, the horizontal uniaxial extension can be carried out using a tenter type stretcher.

The fixing treatment step is mainly used to consolidate the adsorption of the iodine pigment on the PVA film. The fixing treatment step can be carried out by immersing the PVA film before stretching, extending or extending in a fixed treatment bath. As the fixed treatment bath, one type or two or more types of aqueous solutions containing a boron compound such as a borate such as boric acid or borax may be used. Further, an iodine compound or a metal compound may be added to the fixed treatment bath as needed. The concentration of the boron compound in the aqueous solution of the boron-containing compound used in the fixed treatment bath is generally 0.1 to 15 Within the range of mass%, it is particularly preferably in the range of 1 to 10% by mass. By the concentration 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 the temperature in the range of 10 to 60 ° C, the adsorption of the iodine-based pigment can be consolidated.

Most of the washing steps are performed by removing unnecessary chemicals or foreign matters on the surface of the film and adjusting the optical properties of the finally obtained polarizing film. The washing step can be carried out by immersing the PVA film in a washing bath or by dispersing the washing liquid in the PVA film. Water may be used for the washing bath or the washing liquid, and potassium iodide may also be contained.

The drying conditions in the drying step are not particularly limited, and are carried out in the range of 30 to 150 ° C, particularly preferably in the 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 excellent in dimensional stability.

(usage form)

The polarizing film is usually used as a polarizing plate by bonding a protective film on both sides or a single side thereof. The protective film may be optically transparent and has mechanical strength. Specifically, for example, a cellulose triacetate (TAC) film, a cellulose acetate butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. Moreover, the adhesive agent to be bonded may, for example, be a PVA-based adhesive or a urethane-based adhesive, and is preferably a PVA-based adhesive.

[Examples]

The invention is specifically illustrated by the following examples, but the invention is not limited by the examples.

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

[Absorbance of polarizing film and monomer transmittance]

From the center of the width direction (TD) of the polarizing film obtained in the following examples, comparative examples, or reference examples, a rectangular sample of 2 cm was taken along the longitudinal direction (MD) of the polarizing film, and a spectrophotometer with an integrating sphere was used. The company's "V7100") was set to a crossed polarizer state with respect to the spectrophotometer polarizing plate, and measured the absorbance at a wavelength of 480 nm (A) and the absorbance at a wavelength of 700 nm (B). Then, using the same sample and a spectrophotometer, according to JIS Z 8722 (measurement method of object color), the C-light source and the visible light field in the 2° field of view are corrected for the visibility, and when the sample is tilted with respect to the longitudinal direction by 45°, the sample is measured. The light transmittance at a light rate of -45°, and the average value (%) of the light as the monomer transmittance of the polarizing film.

[Alkali metal content in polarizing film]

It was determined by ICP-MS measurement. Further, in any of the examples, the comparative examples and the reference examples, 99 mol% or more of the alkali metal to be measured was potassium.

[2×L/(M+N) of polarizing film]

In the polarizing film obtained in the following examples, comparative examples, or reference examples, a piece of MD × TD = 2 mm × 10 mm was cut out from the center of the width direction (TD) at any position in the longitudinal direction (MD). The two sides of the fine piece were sandwiched between two sheets of polyethylene terephthalate film having a thickness of 100 μm, and placed on a microtome. The fine piece was sliced from the polyethylene terephthalate film in parallel with MD at intervals of 20 μm, and a sample having a size of MD × TD = 2 mm × 20 μm was taken.

For the sample, a laser Raman spectrometer "LabRAM ARAMIS VIS" manufactured by Horiba, Ltd. was used, and Raman spectra were irradiated with laser light having a wavelength of 532 nm on a portion to be measured on a section produced by slicing a slicer. determination, the observed signal of this time, the signal strength from the 310cm ^-1 (Int ³¹⁰⁾ and 210cm ^-1 signal intensity (Int ^210), calculates the ratio (Int ³¹⁰ / Int ²¹⁰⁾ the portion. In addition, the measurement target portion is a central portion in the thickness direction of the polarizing film and a portion from the surface of the polarizing film toward the inside in the thickness direction to a portion having a thickness of 10%, and a ratio is obtained from the central portion in the thickness direction of the polarizing film (Int ³¹⁰ /Int ²¹⁰ ) is L, and, in relation to the ratio (Int ³¹⁰ /Int ²¹⁰ ) obtained from the respective faces of the polarizing film in the thickness direction toward the inside to the portion corresponding to the thickness of 10% (Int ³¹⁰ /Int ²¹⁰ ), the values are satisfied in the form of M≦N Set to M or N, and calculate 2 × L / (M + N) using these L, M, and N.

[Example 1]

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%, an ethylene unit content of 2.5 mol%), 100 parts by mass, and 10 parts by mass of glycerin as a plasticizer, poly 0.1 parts by mass of oxyethylene lauryl ether sulfate as a film-forming stock solution composed of a surfactant and water, a PVA film having a thickness of 30 μm was obtained by casting, and a swelling step, a dyeing step, a crosslinking step, an extending step, and fixing were carried out. The polarizing film is produced by a treatment step and a drying step.

That is, the PVA film is immersed in water at a temperature of 30 ° C for 1 minute, and uniaxially stretched in the longitudinal direction (MD) (first stage extension) to 2 times the original length, and then used in an amount of 0.03 mass % of iodine and potassium iodide. 0.7% by mass concentration in water and immersed in a dye bath at 20 ° C for 1 minute. Longitudinal direction (MD) uniaxial extension (2nd stage extension) to 3 times of the original length, followed by immersion in a 32 °C cross-linking bath containing 2.5% by mass of boric acid for 2 minutes, uniaxial along the length direction (MD) Extension (3rd stage extension) to 3.6 times of the original length, further immersed in a boric acid/potassium iodide aqueous solution containing a concentration of 2.8 mass% of boric acid and 5 mass% of potassium iodide, and uniaxially extending along the length direction (MD) 4 stages of extension) to 6 times the original length, after which the film was washed by immersion for 5 seconds in a 22 ° C potassium iodide aqueous solution containing a concentration of boric acid of 1.5% by mass and potassium iodide concentration of 5 % by mass, followed by drying by a dryer at 60 ° C A polarizing film of 13 μm was produced in 240 seconds.

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

[Comparative Examples 1 to 4 and Reference Example 1]

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

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

Claims (6)

A polarizing film which is a polarizing film having a thickness of 25 μm or less adsorbed on a substrate containing polyvinyl alcohol and having a thickness of 25 μm or less, wherein the ratio of the absorbance at a wavelength of 480 nm (A) to the absorbance at a wavelength of 700 nm (B) in a crossed polarizer state ( A/B) is 1.42 or more. A polarizing film which is a polarizing film having a thickness of 25 μm or less adsorbed on a substrate containing polyvinyl alcohol and having a thickness of 25 μm or less, wherein a cross section of the polarizing film is measured by Raman spectroscopy, and a central portion of the film in the thickness direction is 310 cm ^{- The ratio of the} signal intensity (Int ³¹⁰ ) to the 210 cm ^-1 signal intensity (Int ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is L, and one side of the film enters toward the inside in the thickness direction to 310 cm ^-1 with respect to the thickness of 10%. The ratio of the signal intensity (Int ³¹⁰ ) to the 210 cm ^-1 signal intensity (Int ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is M, and the other side of the film enters inward in the thickness direction to a 310 cm ^-1 signal with respect to a thickness of 10%. The ratio of the intensity (Int ³¹⁰ ) to the 210 cm ^-1 signal intensity (Int ²¹⁰ ) (Int ³¹⁰ /Int ²¹⁰ ) is N (only M≦N), and 2×L/(M+N) is 0.91 or less. The polarizing film of claim 2, wherein the ratio (A/B) of the absorbance at a wavelength of 480 nm (A) to the absorbance at a wavelength of 700 nm (A/B) is 1.42 or more in a state of a crossed polarizer. The polarizing film according to any one of claims 1 to 3, wherein the polarizing film contains an alkali metal content of X mol/kg, and the polarizing film has a thickness of Y μm, wherein: Z = X × log (Y) The Z is 0.19 or less. The polarizing film according to any one of claims 1 to 4, wherein the monomer transmittance is 40 to 45%. A method for producing a polarizing film, which comprises a thickness of 50 μm or less A method for producing a polarizing film in a step of dyeing and stretching a polyvinyl alcohol film, wherein the dyeing is carried out by impregnating a polyvinyl alcohol film with a dye bath containing an iodine-based dye, the dye bath temperature is 25 ° C or less, and the immersion time is 1.5 minutes or less. .