TWI668472B - Polarizing film and manufacturing method - Google Patents

Abstract

The present invention provides a polarizing film with less blue light leakage in a crossed Nicol state.

The present invention is a polarizing film, which is a polarizing film in which an iodine-based pigment is adsorbed on a substrate containing PVA. The cross-section of the polarizing film is measured from the side of the film into the thickness direction by Raman spectrometry. in terms relative to the thickness of the portion of the 10% signal intensity 310cm ^-1 (Int ³¹⁰⁾ is M and 210cm ^-1 in signal intensity (Int ²¹⁰⁾ of the ratio (Int ³¹⁰ / Int ^210), from the other films facing into the interior of one side in the thickness direction with respect to a portion of a thickness of 10% in terms of the signal strength of 310cm ^-1 (Int ³¹⁰⁾ to 210cm ^-1 in a ratio of signal intensity (Int ²¹⁰⁾ of (Int ³¹⁰ / Int ²¹⁰ ) When N (but M ≦ N), M / N is 0.91 or less.

Description

Polarizing film and manufacturing method

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

A polarizing plate with light transmission and shielding functions is the same as the basic constituent elements of a liquid crystal display (LCD), as are liquid crystals that change 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 a polarizing film, and a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" is also simply referred to as "PVA") Unipolarly stretched substrates (stretched films oriented by uniaxial stretching) in which iodine-based pigments (I ₃ ^- or I _5- ^, etc.) are adsorbed have become mainstream as polarizing films constituting polarizing plates. Such a polarizing film is obtained by uniaxially stretching a PVA film pre-containing an iodine-based pigment, or by adsorbing an iodine-based pigment while uniaxially stretching the PVA film, or after uniaxially stretching the PVA film. It is produced by adsorbing an iodine-based dye or the like.

LCDs are used in a wide range of small devices such as computers and watches, notebook computers, liquid crystal displays, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and measuring instruments for indoor and outdoor use. In particular, it has been used in mobile applications such as small notebook computers and mobile phones, and thinning of polarizing plates has been strongly demanded.

As a method for reducing the thickness of a polarizing film constituting a polarizing plate, it is known to stretch, dye, and dry a laminate having a PVA layer formed on one side of a thermoplastic resin film, and then stretch the stretched thermoplastic resin film as necessary. A method for peeling and removing the layers (refer to Patent Documents 1 and 2 and the like).

Prior art 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 conventionally known method, there is often a problem that a large amount of blue light leaks in a crossed Nicols state. Here, an object of the present invention is to provide a polarizing film with less blue light leakage in a crossed Nicols state and a method for manufacturing the same.

In order to achieve the above-mentioned object, the inventors and the like devoted themselves to conducting repeated reviews, and found that when the laminated body having a PVA layer and a thermoplastic resin film layer is dyed and stretched to manufacture a polarizing film, the used iodine is contained The temperature of the dye-based dyeing bath and the immersion time in the dyeing bath are set in a specific range. It is easy to obtain the measurement results near the surface of the film obtained by Raman spectrometry. The state of blue light leakage in the state is less than that of a polarizing film that has not been seen before, and based on this knowledge, it is further reviewed repeatedly to complete the present invention.

That is, the present invention relates to: [1] A polarizing film, which is a polarizing film in which an iodine-based pigment is adsorbed on a matrix containing PVA, and the cross section of the polarizing film is measured from one side of the film by Raman spectrometry. the access to the interior face in the thickness direction with respect to a portion of a thickness of 10% in terms of 310cm in signal intensity (Int ^{310) -1} and 210cm in the ratio of the signal intensity (Int ²¹⁰⁾ of ^-1 (Int ³¹⁰ / Int ²¹⁰⁾ to M, from entering the other side face in the thickness direction of the film thickness with respect to the inner 10% in terms of signal intensity portion 310cm ^-1 (Int ³¹⁰⁾ and 210cm ^-1 in signal intensity (Int ²¹⁰ When the ratio (Int ³¹⁰ / Int ²¹⁰ ) is set to N (but M ≦ N), M / N is 0.91 or less; [2] A polarizing film as described in [1] above, in which the The ratio (A / B) of the absorbance (A) at a wavelength of 480nm to the absorbance (B) at a wavelength of 700nm is 1.40 or more; [3] The polarizing film as described in [1] or [2] above, whose thickness is 15 μm or less; [4] ] The polarizing film according to any one of [1] to [3] above, which has a monomer transmittance of 40 to 45%; [5] A manufacturing method including a layer having a PVA layer and a thermoplastic resin film layer A method for manufacturing a polarizing film in which a laminated body is dyed and stretched, wherein the dyeing is performed by immersing the laminated body in a dyeing bath containing an iodine-based dye, the dyeing bath temperature is 25 ° C or lower, and the immersion time is 2.5 minutes [6] The manufacturing method as described in [5] above, wherein the thickness of the PVA layer is 30 μm or less.

According to the present invention, it is possible to provide a polarizing film with less blue light leakage in a crossed Nicols state. Moreover, according to this invention, the manufacturing method which can manufacture this polarizing film easily can be provided.

Hereinafter, the present invention will be described in detail.

(Polarizing film)

The polarizing film of the present invention has an iodine-based pigment adsorbed on a substrate containing PVA. In addition, the cross-section of the polarizing film was measured by Raman spectroscopy, and the signal intensity (Int ³¹⁰ ) of ³¹⁰ cm ^-1 from the side of the film that entered the thickness direction to the inside to 10% of the thickness was 310 cm ^-1 The ratio (Int ³¹⁰ / Int ²¹⁰ ) to the signal intensity (Int ²¹⁰ ) at 210cm ^-1 is set to M, and the thickness of the part from the other side of the film into the interior is 10% relative to the thickness. 310cm ^-1 signal intensity (Int ³¹⁰⁾ at 210cm ^-1 and the signal intensity (Int ²¹⁰⁾ of the ratio (Int ³¹⁰ / Int ²¹⁰⁾ is set to N (provided that M ≦ N), M / N is 0.91 or less.

When the cross-section of the polarizing film is measured by Raman spectrometry, it is only necessary to perform Raman spectrometry with a Raman spectrophotometer using a sample obtained by slicing the polarizing film of the object in its thickness direction. Specifically, it is only necessary to use A laser Raman spectrometer, such as a micro-laser Raman spectrometer “LabRAM ARAMIS VIS” manufactured by Horiba, can irradiate laser light having a wavelength of 532 nm to the Raman spectrometer to measure the portion of the sample to be measured. Then, from the signal intensity (Int ³¹⁰ ) of ³¹⁰ cm ^{-1 and} the signal intensity (Int ²¹⁰ ) of ²¹⁰ cm ^-1 of each measurement target portion obtained in this way, the ratio of the portion (Int ³¹⁰ / Int ^{210) was obtained.} ). More specific measurement methods and conditions when determining the ratio (Int ³¹⁰ / Int ²¹⁰ ) of each part of the film can be used in the following examples in the examples. In addition, the portion specified in the present invention that enters the interior from each side of the film in the thickness direction to 10% with respect to the thickness. When, for example, a polarizing film having a thickness of 10 μm, the portion is equivalent to that from the polarizing film. Each face goes into the thickness to a part of 1 μm (10 μm × 10% = 1 μm). Although there is no any limitation to the present invention, then the ratio of the film that (Int ³¹⁰ / Int ²¹⁰⁾ depending on the parts of the portion of the line I ₅ ^- present in an amount relative to the I ₃ ^- the ratio of the amount present.

In the polarizing film of the present invention, the M / N is 0.91 or less. When M / N is 0.91 or less, it becomes a polarizing film with little blue light leakage in a crossed Nicols state. Based on the availability of polarizing films with less blue light leakage in the crossed Nicols state, M / N is preferably 0.85 or less, more preferably 0.76 or less, and even more preferably 0.72 or less. Further, from the viewpoint of reducing the red light leakage in the crossed Nicols state, M / N is preferably 0.01 or more, more preferably 0.1 or more, and more preferably 0.5 or more.

A polarizing film having an iodine-based pigment adsorbed on a substrate can be formed by stretching a PVA film containing an iodine-based pigment in advance, or by simultaneously adsorbing an iodine-based pigment with a PVA film, or by stretching a PVA film. After that, it is manufactured by adsorbing iodine-based dyes and the like. More specifically, it can be produced by uniaxially stretching a laminate having a PVA layer (equivalent to a PVA film) containing a iodine-based dye in advance and a thermoplastic resin film layer. After the laminate of the PVA layer and the thermoplastic resin film layer is stretched, the PVA layer absorbs iodine-based pigments, or after the laminate having the PVA layer and the thermoplastic resin film layer is stretched, the matrix formed from the PVA layer adsorbs iodine-based pigments. Pigments and the like.

As the PVA system, vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl versatate, and vinyl laurate can be used. Polyvinyl ester obtained by polymerizing one or more vinyl esters such as vinyl stearate, vinyl benzoate, and isopropenyl acetate, etc., obtained by saponification. Among the above-mentioned vinyl esters, vinyl acetate is preferred from the viewpoints of ease of production, availability, and cost of PVA.

The above-mentioned polyvinyl ester may be obtained by using only one or more vinyl esters as monomers, but as long as the effect of the present invention is not impaired, it may be a copolymer with other monomers copolymerizable therewith.

Examples of the other monomers copolymerizable 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) acrylates (meth) acrylates such as tert-butyl acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and octadecyl (meth) acrylate; (meth) Acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl Amidoamine, (meth) acrylamidopropanesulfonic acid or a salt thereof, (meth) acrylamidopropyldimethylamine or a salt thereof, N-methylol (meth) acrylamidoamine or a derivative thereof (Meth) acrylamide derivatives; N-vinylmethylamine, N-vinylacetamide, N-vinylpyrrolidone, etc .; methylvinyl ether, ethyl Vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl Vinyl ether, isobutyl vinyl ether, third butyl Vinyl ethers, vinyl ethers such as dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide (meth) acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride Ethylene halides, etc .; Allyl compounds such as allyl acetate, allyl chloride; maleic acid or its salt, ester or anhydride; Iconic acid or its salt, ester or anhydride; vinyl trimethoxysilane, etc. Vinyl silane compounds; and unsaturated sulfonic acids. The polyvinyl ester may have one or two or more structural units derived from the other monomers.

The proportion of the structural units derived from the other monomers in the above-mentioned polyvinyl esters is preferably 15 mol% or less, and may also be 10 mol% according to the number of moles of all the structural units constituting the polyvinyl ester. Below, even below 5 mole%.

In particular, if the other monomers are water-soluble monomers that can promote the obtained PVA, such as (meth) acrylic acid, unsaturated sulfonic acid, etc., in order to prevent the dissolution of PVA during the manufacture of polarizing films, The proportion of the structural units derived from these monomers is preferably 5 mol% or less, and more preferably 3 mol% or less, according to the number of moles of all the structural units constituting the polyvinyl ester.

As long as the PVA is within a range that does not impair the effect of the present invention, it may be one modified by one or more types of monomers that can be graft copolymerized. 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 the structural unit (the structural unit in the graft modification section) derived from the graft copolymerizable monomer in the PVA is preferably 5 mol% or less according to the number of moles of all the structural units constituting the PVA.

In the PVA, some of the hydroxyl groups may or may not be crosslinked. In addition, in the PVA, a part of the hydroxyl groups may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure.

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 preferably 1,500 or more, more preferably 2,000 or more, and more preferably 9,200 or less, and more preferably 6,000 or less. With an average degree of polymerization of 1,000 or more, the polarization performance of a polarizing film can be improved. On the other hand, when the average degree of polymerization is 9,500 or less, the productivity of PVA can be improved. The average degree of polymerization of PVA can be measured in accordance with JIS K6726-1994.

From the viewpoint of the polarizing performance of the polarizing film, the saponification degree of the PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and more preferably 99 mol% or more. When the saponification degree is less than 98 mol%, PVA will be easily dissolved during the manufacturing process of the polarizing film, and the dissolved PVA will adhere to the film, which may reduce the polarizing performance of the polarizing film. In addition, the degree of saponification of PVA in this specification refers to the relative molar number of structural units (typically vinyl ester units) and vinyl alcohol units that PVA has with respect to saponification to vinyl alcohol units. Mole ratio of vinyl alcohol unit (mole%). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The above-mentioned iodine-based dye include: I ₃ ^- or I ₅ ^- and the like. Examples of such relative cations include alkali metals such as potassium. The iodine-based pigment can be obtained, for example, by contacting iodine (I ₂ ) 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 5 μm or less, based on the ease of obtaining a thin polarizing plate required in recent years. In addition, since a polarizing film having an excessively thin thickness is difficult to manufacture, the thickness of the polarizing film is, for example, 0.5 μm or more (in one example, 2.5 μm or more). From the viewpoint of manufacturing, the thickness may be 4 μm or more and 5 μm or more. Even 6 μm or more.

From the viewpoint of reducing the blue light leakage of the polarizing film 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 the crossed Nicols state is 1.40 or more Preferably, it is more preferably 1.41 or more, more preferably 1.42 or more, particularly preferably 1.45 or more, and may be 1.50 or more, or even 1.55 or more. On the other hand, when the ratio (A / B) is too high, there is a tendency that the red light leakage increases. Therefore, the ratio (A / B) is preferably 2 or less, more preferably 1.8 or less, and 1.6 or less. Even better. 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.

From the viewpoint of polarizing performance, the monomer transmittance of the polarizing film of the present invention is preferably in the range of 40 to 45%, and the monomer transmittance is more preferably 41% or more, and 42% or more. More preferably, it is more preferably 44% or less. The monomer transmittance of a polarizing film can be measured by the method mentioned later in an Example.

(Manufacturing method of polarizing film)

The method for manufacturing the polarizing film of the present invention is not particularly limited. A PVA film can be used as a raw material film, and can be manufactured by dyeing and stretching. For example, for one side of a PVA film used as a raw material film. The dyeing solution containing the iodine-based pigment is spread on the surface at a specific amount and concentration; the roller coated with the dyeing solution containing the iodine-based pigment is brought into contact with one side of the PVA film used as the raw material film; immersed in a dyeing liquid containing an iodine-based dye impregnated body made of surface contact with the PVA film is the film used as the raw material of the other side of the polarizing film obtained in each of the vicinity of surface I ₅ ^- present in an amount relative to the I ₃ ^- There is a difference in the proportion of the amount, and it is easy to manufacture, but it is preferable that the polarizing film of the present invention can be manufactured more easily according to the following manufacturing method of the present invention.

That is, the manufacturing method of the present invention includes a step of dyeing and stretching a laminated body having a PVA layer and a thermoplastic resin film layer, wherein the dyeing is performed by immersing the laminated body in a dyeing bath containing an iodine-based pigment. The temperature was 25 ° C or lower, and the immersion time was 2.5 minutes.

Examples of the thermoplastic resin constituting the thermoplastic resin film layer include polyethylene, polypropylene, polymethylpentene, polystyrene, polycarbonate, polyvinyl chloride, methacrylic resin, nylon, and polyethylene terephthalate. Various types of thermoplastic resins such as diesters, and copolymers having a plurality of monomer units constituting these thermoplastic resins. The thermoplastic resin film layer may contain one or more thermoplastic resins. Among these, in terms of having high heat resistance and stretchability, polyethylene terephthalate is preferable, and amorphous polyethylene terephthalate is more preferable.

The thickness of the thermoplastic resin film layer is preferably in the range of 20 to 250 μm, more preferably in the range of 30 to 230 μm, and even more preferably in the range of 50 to 200 μm. With thermoplastic resin thin The thickness of the film layer is more than 20 μm, which can effectively prevent the occurrence of wrinkles 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 the tension from becoming too high when the laminate is stretched.

In the description of the polarizing film of the present invention, the PVA constituting the PVA layer can be made the same as described above, and therefore repeated descriptions are omitted here.

From the viewpoint of improving the stretchability during stretching, it is preferable that the PVA layer contains a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The PVA layer may include Among these plasticizers, one or two or more of them are preferably glycerin from the viewpoint of the effect of improving the stretchability.

The content of the plasticizer in the PVA layer is preferably within a range of 1 to 20 parts by mass relative 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 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 operability from being lowered because the PVA layer is too soft. The plasticizer content in the PVA layer is more preferably 2 parts by mass or more, more preferably 4 parts by mass or more, particularly preferably 5 parts by mass or more, and 15 parts by mass based on 100 parts by mass of PVA. The following is more preferable, and the content is preferably 12 parts by mass or less.

In addition, although it depends on the manufacturing conditions of the polarizing film, etc., the plasticizer contained in the PVA layer may be dissolved out during the manufacture of the polarizing film, so the total amount may not only remain in the polarizing film.

If necessary, the PVA layer may further include ingredients such as an antioxidant, an antifreeze, a pH adjuster, a masking agent, an anti-colorant, an oil agent, a surfactant, and the like.

The content of the PVA in the PVA layer is preferably within a range of 50 to 99% by mass based on the ease of modulation of the desired polarizing film, and the content is preferably 75% by mass or more and 80% by mass. The above is more preferable, more preferably 85% by mass or more, and more preferably 98% by mass or less, more preferably 96% by mass or less, and particularly preferably 95% by mass or less.

The thickness of the PVA layer is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less, based on the ease of obtaining a thin polarizing film. In addition, since a laminated body having an excessively thin PVA layer is difficult to manufacture, the thickness of the PVA layer is, for example, 1 μm or more (one example is 5 μm or more). From the viewpoint of manufacturing, the thickness can be 8 μm or more, 10 μm or more, or even 12 μm or more.

The layer structure of the laminated body is not particularly limited, and a polarizer film and the like of the present invention can be manufactured more easily, and a two-layer structure having one PVA layer and one thermoplastic resin film layer is preferred.

The shape of the laminated body is not particularly limited, and it is preferable to use a long laminated body because it can be continuously used in the manufacture of a polarizing film. The length of the long laminated body (length in the long direction) is not particularly limited, and it can be appropriately set depending on the application of the polarizing film to be manufactured, and it is preferably set within a range of 5 to 20,000 m, for example.

The width of the laminated body is not particularly limited, and can be appropriately set according to the use of the polarizing film to be manufactured, but in recent years, from the point of popularization of large screens of liquid crystal televisions and liquid crystal displays, as long as the laminated body is preliminarily used, If the width is set above 0.5m, more preferably above 1.0m, it is suitable for these applications. On the other hand, if the width of the laminate is too wide, When the polarizing film is manufactured with a practical device, it tends to be difficult to stretch uniformly, and the width of the laminated body is preferably 7 m or less.

Examples of the method for manufacturing the laminated body include a method of forming a PVA layer on a thermoplastic resin film, and specifically, a method of dissolving PVA in a liquid medium and further dissolving the above-mentioned plasticizers such as the plasticizer as required. A method for coating a raw solution made of other components on a thermoplastic resin film and drying it; extruding a raw solution prepared by melt-mixing PVA, a liquid medium, and further melt-mixing other components on a thermoplastic resin film as required And a method for further drying; a method for producing a PVA film containing PVA and further containing other components as required, and then bonding the thermoplastic resin film, and the like. Among them, from the point that a thin PVA layer can be easily prepared and the uniformity of the thickness of the obtained PVA layer, it is formed by dissolving PVA in a liquid medium and further dissolving other components as required. The method of coating the original solution on a thermoplastic resin film and drying it is preferred.

Examples of the liquid medium include water, dimethylmethylene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, and diethylene glycol. , Triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., one or more of these can be used. Among them, water is preferred in terms of environmental load and recyclability.

The volatile content of the original solution (the content of the volatile components in the liquid solution such as the liquid medium that is removed by volatilization or drying when forming the PVA layer), although it also depends on the method of forming the PVA layer and the forming conditions It varies with each other, but it is more preferably within a range of 50% by mass to 98% by mass, and more preferably within a range of 55% by mass to 95% by mass. The volatile content of the original solution is 50% by mass or more, and its viscosity is not too high, which can smoothly perform filtering and defoaming during the preparation of the original solution, and easily form a PVA layer with few foreign matter and defects, and can also improve the coating. Sex. On the other hand, since the volatile matter content of the stock solution is 98% by mass or less, the concentration of the stock solution is not excessively low, and the industrial production of the laminated body can be facilitated.

Examples of the coating method when the stock solution is applied on the thermoplastic resin film include a die coating method, a comma blade coating method, and a dip coating method. Among these, the point of uniformity of the thickness of the obtained PVA layer is preferably a die coating method.

It is preferable that the thermoplastic resin film used in the production of the laminated body is subjected to a hydrophilization treatment on at least one surface in advance. By forming the PVA layer in contact with such a hydrophilized surface, the adhesion between the thermoplastic resin film layer and the PVA layer will be improved. Examples of the hydrophilization treatment include corona treatment, plasma treatment, and anchor coating treatment. Among these, corona treatment is preferable because it is easy to adjust the hydrophilicity.

It is preferable to adjust the contact angle of the surface of the thermoplastic resin film to 55 to 70 ° through the above-mentioned hydrophilization treatment, to adjust the contact angle to 57 ° or more, more preferably to 59 ° or more, and more preferably, It is more preferable to adjust it to 69 ° or less, and it is more preferable to adjust it to 68 ° or less. When the contact angle is less than 55 °, the bonding strength between the thermoplastic resin film layer and the PVA layer tends to be too strong, and it may be difficult to peel off the stretched thermoplastic resin film layer after the laminate is stretched. . On the other hand, the When the contact angle is higher than 70 °, the PVA layer tends to be easily peeled off or cracked from the thermoplastic resin film layer during stretching of the laminate, and tends to be difficult to stretch at a high stretching ratio. In addition, the contact angle on the surface of the thermoplastic resin film refers to the angle formed by the water surface and the surface of the thermoplastic resin film (the angle taken inside the water) where the free surface of the water contacts the thermoplastic resin film. It was measured by the method described later in the examples.

The conditions of the corona treatment when the contact angle of the surface of the thermoplastic resin film is adjusted to the above range by the corona treatment are not particularly limited, but because the contact angle of the surface of the thermoplastic resin film can be easily adjusted to the above range, the following The discharge capacity shown in formula (1) is between 180 and 350W. It is preferably in the range of minutes / m ² to 190 to 320W. Min / m ² is more preferably in the range of 200 to 300W. In the range of minutes / m ^2, it is even more preferable.

Discharge (W.min / m ² ) = Output (W / m) / Processing speed (m / min) (1)

The drying conditions after the dope is applied or extruded on the thermoplastic resin film are not particularly limited, but in order to prevent the thermoplastic resin film from wrinkling, it is preferable to perform drying at a temperature below the glass transition temperature of the thermoplastic resin film.

The manufacturing method of the present invention includes a step of dyeing the above-mentioned laminated body (dyeing step) and a stretching step (drawing step). In addition to the dyeing step and the stretching step, the manufacturing method may further include: An insolubilization step, a swelling step, a crosslinking step, a fixing treatment step, a washing step, a drying step, and the like. The order of each step can be appropriately changed as required, and each step can be performed more than two times, or different steps can be performed simultaneously. In addition, according to the above-mentioned manufacturing method, The polarizing film formed on the stretched thermoplastic resin film layer is obtained, but it may include a step of peeling the stretched thermoplastic resin film as needed.

As an example of the manufacturing method of the present invention, the following methods can be enumerated: firstly subjecting the laminated body to an insolubilization step, if necessary, to a swelling step, then to a dyeing step, if necessary, to a crosslinking step, and then to a stretching step, if necessary Then, a fixing process step and / or a cleaning step are performed, and then a drying step is performed. Through these series of steps, a polarizing film formed on the stretched thermoplastic resin film layer is obtained, and the stretched The thermoplastic resin film layer was peeled.

The main purpose of the insolubilization treatment is to prevent the PVA contained in the PVA layer from dissolving in water. Examples of the insolubilization treatment include a method of applying heat treatment to the laminate, and a method of immersing the laminate in an aqueous solution containing one or two or more boron compounds such as boric acid such as boric acid and borax. Among them, a method using an aqueous solution containing a boron compound is preferable because heat may be applied to the laminated body in accordance with the size change of the thermoplastic resin film layer. The heat treatment may be performed at a temperature in a 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 laminated body. And, in the method using an aqueous solution containing a boron compound, the temperature of the aqueous solution is preferably in a range of 20 to 40 ° C, more preferably in a range of 22 to 38 ° C, and in a range of 25 to 35 ° C. Inside is even better. By setting the temperature in the range of 20 to 40 ° C, it is possible to prevent dissolution of PVA and to have insolubilization efficiency. The immersion time in an aqueous solution containing a boron compound is, for example, 0.1 to Within 5 minutes. By setting it in the range of 0.1 to 5 minutes, insolubilization can be performed 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, and even more preferably in the range of 1.5 to 4.0% by mass. . By setting the concentration in the range of 0.5 to 6.0% by mass, dissolution of PVA can be prevented and insolubilization can be efficiently performed.

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

The swelling step can be performed by immersing the laminate in water. When immersed in water, the temperature of the water is preferably in the range of 20 to 40 ° C. The temperature is preferably 22 ° C or higher, more preferably 25 ° C or higher, and more preferably 38 ° C or lower. It is even better below 35 ° C. By setting the temperature in the range of 20 to 40 ° C, the PVA layer can be effectively swollen. 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 setting it within the range of 0.1 to 5 minutes, the PVA layer can be effectively swollen. In addition, the water when immersed 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 laminate in a dyeing bath containing an iodine-based dye. At this time, the temperature of the dyeing bath must be 25 ° C or lower, and the dipping time must be 2.5 minutes or shorter.

When the temperature of the dyeing bath exceeds 25 ° C, the blue light leakage of the obtained polarizing film in the crossed Nicols state will increase. From such a point of view, the temperature of the dyeing bath is preferably 23 ° C or lower, more preferably 21 ° C or lower, even more preferably 18 ° C or lower, or 15 ° C or lower, or even 10 ° C or lower. In particular, when a laminated body having a thinner PVA layer is used, the intended polarizing film can be obtained more effectively by further lowering the temperature of the dyeing bath. On the other hand, when the temperature of the dyeing bath is too low, speckles may be generated 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 immersion time of the laminated body in the dyeing bath exceeds 2.5 minutes, the blue light leakage of the obtained polarizing film in the crossed Nicols state also increases. From this point of view, the dipping time is preferably 2.0 minutes or less, more preferably 1.5 minutes or less, and may be 0.8 minutes or less, 0.3 minutes or less, or even 0.2 minutes or less. In particular, when a PVA having a thin layer is used, In the case of a laminated body, the intended polarizing film can be obtained more effectively by further shortening the immersion time. On the other hand, if the immersion time is too short, speckles may be generated in the obtained polarizing film. Therefore, the immersion time is preferably 0.01 minutes or more, and more preferably 0.05 minutes or more.

Typical examples of the dyeing bath include those obtained by mixing iodine (I ₂ ) and potassium iodide with water. When iodine and potassium iodide are mixed with water, iodine-based pigments 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, but the concentration of iodine is based on the ratio of the mass of iodine used to the mass of the dyeing bath obtained, and it is compared in the range of 0.01 to 2% by mass. Better, in the range of 0.02 to 1% by mass, and the concentration of potassium iodide is in the range of 10 to 300 parts by mass based on the ratio of the mass of potassium iodide to the mass of iodine used above It is preferably within the range of 15 to 150 parts by mass. The dyeing bath may contain boron compounds such as boric acid and boric acid.

When the laminate is crosslinked, the dissolution of PVA in water during wet stretching at higher temperatures can be more effectively prevented. 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 two or more kinds of boron compounds such as borate such as boric acid and borax can be used. The concentration of the crosslinking agent in the crosslinking bath is preferably in the range of 1 to 15% by mass, more preferably 2% by mass or more, and more preferably 7% by mass or less, and more preferably 6% by mass or less. . When the concentration of the crosslinking agent is in the range of 1 to 15% by mass, sufficient stretchability can be maintained. The crosslinking bath may contain auxiliary agents such as potassium iodide. The temperature of the crosslinking bath is preferably within a range of 20 to 50 ° C, and particularly preferably within a range of 25 to 40 ° C. By setting the temperature in the range of 20 to 50 ° C, crosslinking can be effectively performed.

The stretching method of the laminated body during stretching is not particularly limited, and it can be performed by any of a wet stretching method and a dry stretching method. In the case of the wet stretching method, it may be carried out 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 above-mentioned dyeing bath or a fixed treatment bath described later. get on. Further, in the case of the dry stretching method, stretching may be performed at room temperature directly, or stretching while heating, or stretching after absorbing water. Among these, from the viewpoint of thickness uniformity in the width direction of the obtained polarizing film, a wet stretching method is preferred, and stretching in a boric acid aqueous solution is more preferred. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass. 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. It is more preferably 4.0% by mass or less. borrow 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 above-mentioned boron compound-containing aqueous solution may contain potassium iodide, and its concentration is preferably in a 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 when stretching the laminated body is preferably in the range of 5 to 90 ° C. The temperature is preferably 10 ° C or higher, and more preferably 85 ° C or lower, and more preferably 80 ° C or lower. 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 stretching the laminate, the stretching ratio is preferably 4 times or more, more preferably 5 times or more, and more preferably 6 times or more. By setting the stretch ratio of the laminated body within the above range, a polarizing film having more excellent polarizing performance can be obtained. The upper limit of the stretch ratio of the laminated body is not particularly limited, but it is preferably 8 times or less. The stretching of the laminated body can be performed once or divided into a plurality of times, and when divided into a plurality of times, as long as the total stretching ratio multiplied by the stretching ratio of each stretching is within the above range. In addition, the stretching ratio in this specification is based on the length of the laminated body before stretching, and the unstretched state is equivalent to 1 stretching ratio.

The stretching of the laminated body is preferably uniaxially stretched from the viewpoint of the performance of the obtained polarizing film. The direction of uniaxial stretching when stretching a long laminated body is not particularly limited. Uniaxial stretching in the longitudinal direction or uniaxial stretching in the transverse direction can be used, but based on the polarizing film that can obtain more excellent polarizing performance It is better to uniaxially stretch in the length direction. Uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the rollers by using a stretching device having a plurality of rollers parallel to each other. On the other hand, transverse uniaxial stretching can be performed using a tenter-type stretching machine.

The fixing treatment step is mainly used to enhance the adsorption of iodine-based pigments by the PVA layer. The fixing treatment step can be performed by immersing the laminated body before, during or after stretching in a fixing treatment bath. As the fixed treatment bath, an aqueous solution containing one or two or more boron compounds such as borate such as boric acid and borax can be used. Moreover, an iodine compound or a metal compound may be added to a fixed processing bath as needed. The concentration of the boron compound in the aqueous solution containing the boron compound used as the fixed treatment bath is generally preferably in the range of 0.1 to 15% by mass, and particularly preferably in the range of 1 to 10% by mass. By setting the concentration in the range of 0.1 to 15% by mass, the adsorption of the iodine-based pigment can be further enhanced. The temperature of the fixed treatment bath is preferably within a range of 10 to 60 ° C, and particularly preferably within a range of 15 to 40 ° C. By setting the temperature in the range of 10 to 60 ° C., the adsorption of the iodine-based pigment can be further enhanced.

The cleaning step is performed to remove unnecessary drugs or foreign substances on the surface of the film, or to adjust the optical properties of the finally obtained polarizing film. The washing step can be performed by immersing the laminated body in a washing bath, or by dispersing the laminated body in a cleaning solution. Bathing and cleaning liquids can use water, or these can contain potassium iodide.

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

Through the above operations, a polarizing film formed on the stretched thermoplastic resin film layer can be obtained. The use of such a polarizing film The method is not particularly limited, for example, without stretching the stretched thermoplastic resin film layer, it can be directly used as a polarizing plate, or an optically transparent and mechanically strong protective film can be bonded to the polarizing film side as desired to form a polarizing plate. ; Or, after the protective film is laminated on the opposite side of the stretched thermoplastic resin film layer, the stretched thermoplastic resin film layer can be peeled off, and it can be directly used as a polarizing plate or pasted on the peeling surface as desired. A polarizing plate is formed by combining another protective film. The protective film may be a cellulose triacetate (TAC) film, an acetate / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like. In addition, examples of the adhesive used for bonding include PVA-based adhesives and polyurethane-based adhesives. PVA-based adhesives are suitable.

[Example]

Hereinafter, the present invention will be described more specifically with reference to the examples, but the present invention is not limited in any way by these examples.

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

(Contact angle of thermoplastic resin film surface)

"Drop Master 500" manufactured by Kyowa Interface Science Co., Ltd. was used to measure the contact angle after extruding 2 μL of pure water from a needle with an inner diameter of 0.4 mm on the surface of a thermoplastic resin film under an environment of 20 ° C and 65% RH. .

(Absorbance and monomer transmittance of polarizing film)

From the center of the width direction (TD) of the polarizing film obtained in the following examples and comparative examples, a 2 cm sample was taken in the length direction (MD) of the polarizing film, and a spectrophotometer with an integrating sphere (Japan Spectrophotometer Co., Ltd.) was used. Have Co., Ltd. ("V7100"), and set the polarizer of this sample to the cross-Nicol state of this spectrophotometer, and measure the absorbance (A) at 700nm and the absorbance (B) at 700nm. Then, using the same sample and spectrophotometer and in accordance with JIS Z 8722 (method for measuring the color of an object), the visual sensitivity of the visible light region of the light source C and a 2 ° field of view was corrected. The light transmittance at 45 ° and the light transmittance at -45 ° are inclined, and the average value (%) of these is taken as the unit transmittance of the polarizing film.

(M / N of polarizing film)

For the polarizing films obtained in the following examples and comparative examples, a small piece of MD × TD = 2mm × 10mm was cut from the central portion in the width direction (TD) at any position in the length direction (MD), and the small piece was The two sides were supported by two pieces of polyethylene terephthalate with a thickness of 100 μm and mounted on a microtome. This strip was sliced from polyethylene terephthalate parallel to the MD at an interval of 20 μm, and samples with a size of MD × TD = 2 mm × 20 μm were collected.

For this sample, a micro-laser Raman spectrometer "LabRAM ARAMIS VIS" manufactured by Horiba, was used to perform Raman spectroscopic measurement on a measurement target portion on a cross section generated by a microtome slice, and irradiated with laser light having a wavelength of 532 nm. in this case the observed signal, the signal strength from the 310cm ^-1 (Int ³¹⁰⁾ with the signal intensity of 210cm ^-1 (Int ^210), calculates the ratio (Int ³¹⁰ / Int ²¹⁰⁾ the portion. In addition, the above-mentioned measurement target portion is a portion that enters the interior from each side of the polarizing film toward the thickness direction of the film to 10% with respect to the thickness, and the obtained two ratios (Int ³¹⁰ / Int ²¹⁰ ) are based on In a manner satisfying M ≦ N, each value is set to M or N, and M / N is calculated using these M and N.

[Example 1]

(1) Hydrophilic treatment of thermoplastic resin film

The thermoplastic resin film uses an amorphous polyethylene terephthalate film (A-PET sheet manufactured by Teijin Chemicals Co., Ltd .; FR thickness 150 μm), and the discharge capacity of 280 W on one side of the thermoplastic resin film. Corona treatment was performed per minute / m ² (output of 280 W / m and processing speed of 1.0 m / minute). The contact angle on 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

It contains 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 mole%, and a content rate of an ethylene unit of 2.5 mole%), and 10 masses of glycerin as a plasticizer. 0.1 parts by weight of sodium polyoxyethylene lauryl ether sulfate as a surfactant and an aqueous solution of water to prepare a stock solution for forming a PVA layer.

(3) Production of laminated body

On the corona-treated surface of the thermoplastic resin film subjected to the hydrophilization treatment in (1), the stock solution prepared in (2) was applied with a die coater, and then dried at 80 ° C. for 240 seconds to produce an amorphous polymer. A multilayer structure (a long multilayer body having a width of 0.5 m) of a two-layer structure of an ethylene terephthalate film layer and a PVA layer having a thickness of 15 μm.

(4) Manufacturing of polarizing film

With respect to the laminated body produced in (3), an insolubilization step, a dyeing step, a crosslinking step, a stretching step, a fixing treatment step, and a drying step are performed to produce a polarizing film. That is, the laminated body was immersed in an insolubilization bath at a temperature of 32 ° C. containing boric acid at a concentration of 3% by mass for a period of 1 minute. At this time, uniaxial stretching was performed in the length direction (MD) until the original length was doubled (the first stage stretching), and then the water was mixed with water at a concentration of 0.035 mass% iodine and 0.8 mass% of potassium iodide. During immersion in a dyeing bath at a temperature of 20 ° C for 0.5 minutes, uniaxial stretching was performed in the longitudinal direction (MD) until the original length was three times (second stage stretching), and then a concentration of 2.5 mass% of boric acid was contained. It was immersed in a crosslinking bath at a temperature of 32 ° C for 2 minutes, and uniaxially stretched in the longitudinal direction (MD) until it became 3.6 times the original length (third stage stretching), and further contained 2.8% by mass of boric acid and potassium iodide. During immersion in a boric acid / potassium iodide solution having a concentration of 5 mass% at a temperature of 60 ° C, uniaxial stretching was performed in the longitudinal direction (MD) until it became 6 times the original length (fourth-stage stretching). The film was immersed in an aqueous potassium iodide solution at a temperature of 22 ° C. containing a concentration of 1.5 mass% of boric acid and 5 mass% of potassium iodide for 5 seconds to clean the film, and then dried in a dryer at 60 ° C. for 240 seconds to obtain a stretched amorphous material. Polyethylene terephthalate film A polarizing film having a thickness of 8 μm was formed.

With respect to the obtained polarizing film (the stretched amorphous polyethylene terephthalate film layer was peeled off), the absorbance, monomer transmittance, and M / N were measured and calculated by the methods described above. The results are shown in Table 1.

[Examples 2 to 5 and Comparative Examples 1 to 3]

Except that the thickness of the PVA layer in the laminated body, the temperature of the dyeing bath, the immersion time in the dyeing bath, and the composition of the dyeing bath were changed to those shown in Table 1, the same operations as in Example 1 were performed, and the production had A polarizing film having a thickness shown in Table 1.

About the obtained polarizing film (a stretched amorphous polyethylene terephthalate film layer was peeled), the absorbance, the monomer transmittance, and M / N were measured and calculated by the method described above. The results are shown in Table 1.

Claims (7)

A polarizing film is a polarizing film in which an iodine-based pigment is adsorbed on a matrix containing polyvinyl alcohol. The cross-section of the polarizing film is measured from Raman spectroscopy and enters the interior from the side of the film to the thickness direction. For 10% of the thickness of the portion of the signal intensity 310cm ^-1 (Int ³¹⁰⁾ is M and 210cm ^-1 in signal intensity (Int ²¹⁰⁾ of the ratio (Int ³¹⁰ / Int ^210), from the other films the side facing into the interior in the thickness direction with respect to a portion of a thickness of 10% in terms of the signal strength of 310cm ^-1 (Int ³¹⁰⁾ to 210cm ^-1 in a ratio of signal intensity (Int ²¹⁰⁾ of (Int ³¹⁰ / Int ²¹⁰ ) Is set to N (but M ≦ N), 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 Nicol state is 1.40 or more. The polarizing film of claim 1 or 2 has a thickness of 15 μm or less. If the polarizing film of claim 1 or 2 has a monomer transmittance of 40 to 45%. For example, the polarizing film of claim 3 has a monomer transmittance of 40 to 45%. A method for producing a polarizing film according to any one of claims 1 to 5, which is a method for producing a polarizing film including the steps of dyeing and stretching a laminated body having a polyvinyl alcohol layer and a thermoplastic resin film layer, wherein The dyeing is performed by immersing the multilayer body in a dyeing bath containing an iodine-based dye, the dyeing bath temperature is 18 ° C. or lower, and the immersion time is 0.3 minute or shorter. The manufacturing method according to claim 6, wherein the thickness of the polyvinyl alcohol layer is 30 µm or less.