TWI671555B - Polarizing film and method for producing same - Google Patents

Abstract

In the method for producing a polarizing film in which at least a swelling step, a dyeing step, a first crosslinking stretching step, and a second crosslinking stretching step are sequentially applied to a polyvinyl alcohol film, the polyethylene contained in the polyvinyl alcohol film is The average degree of polymerization of the alcohol is 2500 to 3500. In the aforementioned first cross-linking stretching step, in a 40-55 ° C aqueous solution containing 1 to 5 mass% of boric acid, the stretching ratio in this step becomes 1.1 to Uniaxial stretching is performed so that the total stretching ratio is 1.3 times and the total stretching ratio is 2.5 to 3.5 times. In the second cross-linking stretching step, in a 60 to 70 ° C aqueous solution containing 1 to 5 mass% of boric acid, In this step, uniaxial stretching is performed so that the stretching ratio becomes 1.8 to 3.0 times and the total stretching ratio becomes 6 to 8 times. Thereby, a polarizing film having excellent polarizing performance and low shrinkage stress can be manufactured.

Description

Polarizing film and manufacturing method thereof

The present invention relates to a polarizing film including a polyvinyl alcohol film containing an iodine-based dichroic dye and a method for producing the same.

A polarizing plate having a function of transmitting and shielding light, and a liquid crystal that changes a polarization state of light, are basic constituent elements of a liquid crystal display (LCD). 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. As a polarizing film, the mainstream is a substrate obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" is simply referred to as "PVA") (uniaxially stretched for orientation) film) dye adsorbed iodine (I ₃ ^-, I ₅ ^-, etc.) persons. This polarizing film is obtained by uniaxially stretching a PVA film containing a dichroic pigment in advance, or by simultaneously adsorbing a dichroic pigment while the PVA film is uniaxially stretched, or by uniaxially stretching the PVA film. Thereafter, it is manufactured by adsorbing a dichroic dye or the like.

LCDs are used in a wide range of applications, including small devices such as computers and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and measurement equipment used indoors and outdoors. In response to the high performance of displays in recent years, a polarizing film having excellent optical performance is required.

In order to obtain a polarizing film having excellent optical properties, various manufacturing methods have been proposed. Patent Documents 1 to 4 describe a polarizing film in which a PVA film is immersed in water for swelling treatment, dyed with an iodine-based dichroic dye, and then crosslinked in a boric acid aqueous solution and stretched. In the manufacturing method, a polarizing film having excellent polarization characteristics, uniform optical characteristics, and excellent appearance is obtained by performing swelling treatment in a plurality of grooves having different conditions. In these patent documents, various methods are described about the process of performing a crosslinking process in the boric-acid aqueous solution, and performing a stretching process. The example of patent document 1 describes the method of extending | stretching 1.5 times by immersing in the boric-acid aqueous solution at 50 degreeC. The Example of Patent Literature 2 describes a method of immersing in a boric acid aqueous solution at 55 ° C. and stretching it by 2.5 times. The Example of Patent Document 3 describes a method of immersing in a boric acid aqueous solution at 40 ° C and then stretching in a boric acid aqueous solution at 55 ° C. Moreover, the Example of patent document 4 describes the method of extending | stretching to 1.33 times in the 30 degreeC boric acid aqueous solution, and extending | stretching 1.5 times in the 60 degreeC boric acid aqueous solution.

In addition, Patent Document 5 describes a method for producing a polarizing film capable of reducing the shrinkage of the TD direction (the direction orthogonal to the long-side direction) when exposed to high temperature conditions. Specifically, a method is proposed in which a PVA film is immersed in water for swelling treatment, dyed with an iodine-based dichroic pigment, and then cross-linked in a boric acid aqueous solution and stretched. In the swelling treatment, the shrinkage in the TD direction can be reduced by stretching at a ratio of 50% or more of the total stretching ratio. The example of Patent Document 5 describes a step of immersing in an aqueous solution of boric acid at 56.5 ° C. However, no stretching is applied to the aqueous solution. Stretch. The shrinkage ratio in the MD direction (longitudinal direction of the film) was not measured.

In recent years, LCDs have been used for portable applications such as notebook computers and mobile phones. This type of portable LCD is used in a variety of environments, and therefore requires a polarizing film that is excellent in dimensional stability even at high temperatures. For this reason, a polarizing film having a small shrinkage stress at high temperature is desirable. However, the methods described in the aforementioned Patent Documents 1 to 5 cannot obtain a polarizing film that can sufficiently have both excellent polarizing performance and small shrinkage stress. This is because the shrinkage stress becomes larger if the polarization performance is to be improved, and the polarization performance is lowered if the shrinkage stress is to be reduced. Therefore, it is a difficult problem to solve the problem of manufacturing a polarizing film with high polarization performance and small shrinkage stress.

Prior art literature Patent literature

Patent Document 1 Japanese Patent Laid-Open No. 2006-65309

Patent Document 2 Japanese Patent Application Publication No. 2014-197050

Patent Document 3 Japanese Patent Laid-Open No. 2006-267153

Patent Document 4 Japanese Patent Application Publication No. 2013-140324

Patent Document 5 Japanese Patent Application Publication No. 2012-3173

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a polarizing film having excellent polarization performance and low shrinkage stress, and a method for producing the same.

The above-mentioned problem is solved by providing a method for manufacturing a polarizing film, which is a method in which at least a swelling step, a dyeing step, a first crosslinking stretching step, and a second crosslinking stretching are applied to a polyvinyl alcohol film in order. The stretching step is characterized in that the thickness of the polyvinyl alcohol film is 5 to 100 μm, and the average degree of polymerization of the polyvinyl alcohol contained in the polyvinyl alcohol film is 2500 to 3500. In the swelling step, immersion in 10 to Water at 50 ° C to swell the polyvinyl alcohol film. In the dyeing step, immersion in an aqueous solution at 10 to 50 ° C containing a total of 0.5 to 3% by mass of iodine and potassium iodide to impregnate the iodine-based dichroic pigment Polyvinyl alcohol film is uniaxially stretched so that the total stretching ratio becomes 2 to 3 times. In the first cross-linking and stretching step described above, at 40 to 55 ° C. containing 1 to 5 mass% of boric acid. In the aqueous solution, uniaxial stretching is performed so that the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 2.5 to 3.5 times. Then, in the second cross-linking stretching step described above, 1 is included. ~ 5 mass% of boric acid in 60 ~ 70 ℃ aqueous solution In step draw ratio becomes 1.8 to 3.0 times and a total draw ratio of 6 to 8 times uniaxially stretched manner.

In this case, it is preferable that the maximum tensile stress in the second crosslinking stretching step is 15 N / mm ² or less. It is also preferable to obtain a polarizing film having a monomer transmittance of 42 to 45% and a polarization degree of 99.980% or more. It is also preferable to obtain a polarizing film having a shrinkage stress of 45 N / mm ² or less.

The above-mentioned problem is also solved by providing a polarizing film, which is a polarizing film including a polyvinyl alcohol film containing an iodine-based dichroic pigment, and is characterized in that the polarization degree at a single transmittance of 43.5% is 99.990 Above, and the content ratio (C _A ) of the construction factor A measured by wide-angle X-ray diffraction is 3 ~ 4.5%, the content ratio (C _B ) of the construction factor B is 2.0 ~ 8.5%, and the ratio (C _A / C _B ) is 0.4 or more.

In addition, the above-mentioned problem is also solved by providing a polarizing film, which is a polarizing film including a polyvinyl alcohol film containing an iodine-based dichroic pigment, which is characterized in that the monomer transmittance is 42 to 45%, The degree of polarization is above 99.980%, and the content rate (C _A ) of the construction factor A measured by wide-angle X-ray diffraction is 3 to 4.5%, and the content rate (C _B ) of the construction factor B is 2.0 to 8.5%, and the ratio ( C _A / C _B ) is 0.4 or more.

In each of the above stretched films, the structural factor A is a highly-aligned structural factor derived from a polyvinyl alcohol-boron agglomerated structure, and the structural factor B is a highly-aligned structural factor derived from an amorphous polyvinyl alcohol. In addition, the degree of polymerization of the polyvinyl alcohol contained in each of the stretched films is preferably 2500 to 3500. The shrinkage stress of the polarizing film is also preferably 45 N / mm ² or less.

The polarizing film of the present invention has excellent polarization performance and low shrinkage stress. Therefore, it can be suitably used for a high-performance liquid crystal display, especially a liquid crystal display which may be used at a high temperature. Moreover, according to the manufacturing method of this invention, such a polarizing film can be manufactured.

1‧‧‧ Schematic diagram of polarizing film manufacturing equipment

2‧‧‧PVA film roll

3‧‧‧ Swelling step

4‧‧‧ Dyeing steps

5‧‧‧The first cross-linking stretching step

6‧‧‧ 2nd cross-linking stretching step

7‧‧‧ Cleaning steps

8‧‧‧ drying step

9‧‧‧ polarizing film roll

FIG. 1 is a schematic diagram of a polarizing film manufacturing apparatus.

FIG. 2 is a graph depicting the degree of polarization corresponding to the shrinkage stress at a single transmittance of 43.5% of the polarizing films obtained in Example 1 and Comparative Examples 1 to 4, 7, and 8.

FIG. 3 is a drawing in which an underline straight line is drawn in an I (2θ) profile.

Fig. 4 is a diagram obtained by separating the corrected I (2θ) curve graph into "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomeration structure".

Fig. 5 is a graph depicting the integrated intensity values (A) of "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomerated structure" obtained by waveform separation analysis corresponding to azimuth angles.

FIG. 6 is a diagram in which an integrated intensity value (A) is separated into an alignment component and a non-alignment component.

FIG. 7 is a graph depicting the content rate (C _A ) of the construction factor _A and the content rate (C _B ) of the construction factor B as a function of shrinkage stress.

FIG. 8 is a graph depicting a ratio (C _A / C _B ) corresponding to shrinkage stress.

Forms for implementing the invention

The polarizing film of the present invention is a polarizing film including a polyvinyl alcohol film containing an iodine-based dichroic pigment, and has excellent polarizing performance and low shrinkage stress. Such a polarizing film can be prepared by applying a specific process to a polyvinyl alcohol film (PVA film) at least in the order of a swelling step, a dyeing step, a first crosslinking stretching step, and a second crosslinking stretching step. Manufacturing conditions. Hereinafter, the manufacturing method of the polarizing film of this invention is demonstrated in detail.

As the PVA contained in the PVA film used in the production of the polarizing film of the present invention, a PVA obtained by saponifying a polyvinyl ester obtained by polymerizing one or two or more vinyl esters can be used. Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl tert-carbonate, vinyl laurate, vinyl stearate, and benzoic acid. Among them, vinyl acetate, isopropenyl acetate, and the like are preferred from the viewpoints of ease of production, availability, and cost of PVA.

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

Examples of other monomers that can be copolymerized with vinyl esters include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth) acrylic acid or a salt thereof; Base) methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (Meth) acrylates such as tert-butyl (meth) 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) acrylamidoamine, (meth) acrylamidopropylsulfonic acid or a salt thereof, (meth) acrylamidopropyldimethylamine or a salt thereof, N-methylol (methyl) (Meth) acrylamide derivatives such as acrylamide or derivatives thereof; N-vinylfluorenamines such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl Vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl Vinyl ethers such as vinyl ethers and stearyl vinyl ethers; vinyl cyanide (meth) acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl acetate, Allyl compounds such as chloropropene; maleic acid or its salt, ester or anhydride; itaconic acid or its salt, ester or anhydride; vinyl silicon compounds such as vinyltrimethoxysilane; unsaturated sulfonic acid and the like. The polyvinyl ester can have one or two or more structural units derived from the other monomers.

The proportion of the structural units derived from other monomers in the polyvinyl ester is preferably 15 mol% or less, and more preferably 10 mol% or less, based on the molar numbers of all the structural units constituting the polyvinyl ester. Still more preferably, it is 5 mol% or less.

In particular, when the other monomer is a water-soluble monomer that can promote the obtained PVA, such as (meth) acrylic acid, unsaturated sulfonic acid, or the like, in order to prevent the dissolution of PVA during the production of the polarizing film The proportion of the structural units derived from these monomers in the polyvinyl ester is preferably 5 mol% or less, and more preferably 3 mol% or less, based on the mole numbers of all the structural units constituting the polyvinyl ester.

As long as the effect of the present invention is not impaired, the PVA used in the present invention may be a PVA modified by one or two or more kinds of graft copolymerizable monomers. As the graft copolymer Examples of the combined monomers 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 derived from the graft copolymerizable monomer (the structural unit in the graft modification portion) in the PVA is preferably 5 mol% or less based on the number of moles of all the structural units constituting the PVA. .

PVA may be a part of the hydroxyl group of which is crosslinked or uncrosslinked. The PVA may have an acetal structure formed by reacting a part of the hydroxyl groups with aldehyde compounds such as acetaldehyde and butyraldehyde, or may not form an acetal structure without reacting with these compounds.

The average degree of polymerization of PVA is preferably 2500 to 3500. The average degree of polymerization is more preferably 2600 or more, and even more preferably 3300 or less. When the average degree of polymerization is 2500 or more, a polarizing film having excellent polarizing performance can be easily obtained in the second crosslinking stretching step even when stretched at a high temperature. On the other hand, when the average polymerization degree exceeds 3500, it may become difficult to reduce the shrinkage stress of the obtained polarizing film. Here, the average degree of polymerization of PVA means the average degree of polymerization measured in accordance with the description of JIS K6726-1994. Moreover, although PVA in a polarizing film contains the crosslinked structure by a boric acid, the average polymerization degree of PVA itself does not change substantially if a boric acid ester is hydrolyzed and unlocked.

The degree of saponification of PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and still more preferably 99 mol% or more from the viewpoint of the polarization performance of the polarizing film. When the degree of saponification is less than 98 mol%, PVA may easily dissolve during the manufacturing process of the polarizing film, and the dissolved PVA may adhere to the film to reduce the polarizing performance of the polarizing film. The saponification degree of PVA in the present specification means that The total number of moles of the structural units (typically vinyl ester units) and vinyl alcohol units that can be converted to vinyl alcohol units by saponification, and the proportion of the moles of the vinyl alcohol units (Mole %). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

In consideration of the ease of manufacturing a desired polarizing film, etc., the content of PVA in the PVA film used in the present invention is preferably in the range of 50 to 99% by mass. The content is more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more. In addition, it is more preferably 98% by mass or less, still more preferably 96% by mass or less, and particularly preferably 95% by mass or less.

The PVA film preferably contains a plasticizer from the viewpoint of improving the stretchability when it is stretched. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. PVA films One or two or more of these plasticizers can be contained. Among them, glycerin is preferred from the viewpoint of the effect of improving the stretchability.

The content of the plasticizer in the PVA film is preferably within a range of 1 to 20 parts by mass relative to 100 parts by mass of the PVA contained therein. When the content is 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the PVA film from becoming too soft and lowering the operability. The content of the plasticizer in the PVA film is more preferably 2 parts by mass or more, still more preferably 4 parts by mass or more, and particularly preferably 5 parts by mass or more with respect to 100 parts by mass of PVA. The content of the plasticizer is more preferably 15 parts by mass or less, and still more preferably 12 parts by mass or less. Also, although it depends on the manufacture of the polarizing film Etc., but the plasticizer contained in the PVA film may be dissolved during the production of the polarizing film, so the total amount of the plasticizer remaining in the polarizing film is not limited.

The PVA film may further include components such as an antioxidant, an antifreezing agent, a pH adjuster, a masking agent, an anti-staining agent, an oil agent, and a surfactant, as necessary.

The thickness of the PVA film used in the manufacturing method of the present invention is 5 to 100 μm. With a thickness of 100 μm or less, a thin polarizing film can be easily obtained. The thickness of the PVA film is preferably 60 μm or less. On the other hand, when the thickness is less than 5 μm, in addition to the difficulty in manufacturing the polarizing film, uneven dyeing tends to occur. The thickness of the PVA film is preferably 7 μm or more. Here, the thickness means a thickness of the PVA layer in the case of a multilayer film.

The PVA film may be a single-layer film, or a multilayer film having a PVA layer and a substrate resin layer may be used. In the case of a single-layer film, in order to ensure handleability, the thickness of the film is preferably 20 μm or more, and more preferably 30 μm or more. On the other hand, in the case of a multilayer film, the thickness of the PVA layer can be made 20 μm or less, or 15 μm or less. The thickness of the base resin layer in the multilayer film is usually 20 to 500 μm.

In the case where a multilayer film having a PVA layer and a substrate resin layer is used as the PVA film, the substrate resin must be capable of being stretched together with the PVA. Polyester and polyolefin resins can be used. Among them, an amorphous polyester resin is preferred, and copolymerized components such as polyethylene terephthalate, isophthalic acid, and 1,4-cyclohexanedimethanol are suitable. An amorphous polyester resin copolymerized therewith. It is preferable to produce a multilayer film by applying a PVA solution to a base resin film. At this time, in order to improve the adhesion between the PVA layer and the base resin layer, the surface of the base resin film may be modified, or an adhesive layer may be formed between the two layers.

The shape of the PVA film is not particularly limited, and since it can be continuously supplied at the time of manufacturing a polarizing film, a long PVA film is preferred. The length (length in the longitudinal direction) of the long PVA film is not particularly limited, and can be appropriately set according to the purpose of the polarizing film to be produced, and for example, it can be within a range of 5 to 20,000 m.

The width of the PVA film is not particularly limited, and can be appropriately set according to the use of the produced polarizing film and the like. In recent years, large screens of liquid crystal televisions and liquid crystal monitors have been developed. Therefore, if the width of the PVA film is set to 0.5 m or more, and more preferably 1.0 m or more, these applications are suitable. On the other hand, if the width of the PVA film is too large, it becomes difficult to uniformly stretch the polarized film when using a device that has already been put into practical use. Therefore, the width of the PVA film is preferably 7 m or less.

The polarizing film of the present invention can be produced using the PVA film described above as a raw material. Specifically, at least a swelling step, a dyeing step, a first crosslinking stretching step, and a second crosslinking stretching step may be sequentially applied to produce a polarizing film. It is also preferable to apply a washing step and a drying step after the aforementioned second crosslinking stretching step. Hereinafter, each step will be described in detail.

In the manufacturing method of the present invention, a PVA film is first supplied to a swelling step. In the swelling step, immerse in water at 10 ~ 50 ℃, To swell the PVA film. The temperature of water is preferably 20 ° C or higher, and more preferably 40 ° C or lower. By immersing water in this temperature range, the PVA film can be efficiently and uniformly swelled. The time for immersing the PVA film in water is preferably in the range of 0.1 to 5 minutes, and more preferably in the range of 0.5 to 3 minutes. By setting such a dipping time, the PVA film can be efficiently and uniformly swelled. The water used to impregnate the PVA film is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and a water-soluble organic solvent. In the swelling step, uniaxial stretching is preferably applied to the PVA film. The stretching ratio in this case is not particularly limited, but is preferably 1.2 to 2.8 times. The draw ratio is more preferably 1.5 times or more, and even more preferably 2.5 times or less.

In the manufacturing method of the present invention, after the aforementioned swelling step, it is supplied to a dyeing step. In the dyeing step, immerse in a 10-50 ° C aqueous solution containing a total of 0.5 to 3% by mass of iodine and potassium iodide, impregnate the iodine-based dichroic pigment in the PVA film, and increase the total draw ratio by 2 to 3 Way for uniaxial stretching. Thereby, the PVA film is dyed with an iodine-based dichroic dye, and the molecular chains of PVA in the film are aligned, and the iodine-based dichroic dye is also aligned.

The dyeing is performed by immersing a PVA film in a dyeing bath containing an iodine-based dye. The dyeing bath is prepared by mixing iodine (I ₂ ) and potassium iodide (KI) with water. By mixing iodine and potassium iodide with water, iodine-based pigments such as I ₃ ^- and I ₅ ^- can be produced. The total content of iodine and potassium iodide in the dyeing bath is 0.5-3% by mass of their total. The total content of iodine and potassium iodide is preferably 0.8% by mass or more, and more preferably 2.5% by mass or less. By performing dyeing in this concentration range, efficient and uniform dyeing can be performed. The mass ratio of potassium iodide to iodine (KI / I ₂ ) is preferably 10 to 200, and more preferably 15 to 150. The dyeing bath may contain boron compounds such as boric acid such as boric acid and borax. In terms of boric acid, the content is usually less than 5% by mass, and preferably 1% by mass or less.

The temperature of the dyeing bath is 10-50 ° C. The temperature is preferably 15 ° C or higher, and more preferably 20 ° C or higher. The temperature is preferably 40 ° C or lower, and more preferably 30 ° C or lower. By dyeing in this temperature range, the PVA film can be dyed efficiently and uniformly. The time for immersing the PVA film in the dyeing bath is preferably in the range of 0.1 to 10 minutes, and more preferably in the range of 0.2 to 5 minutes. By setting such a time range, the PVA film can be dyed without spots.

In the dyeing step, the PVA film is dyed and uniaxially stretched so that the total stretching ratio becomes 2 to 3 times. A PVA film having such a total stretching ratio is then subjected to a two-stage cross-linking stretching step, so that a polarizing film having excellent polarization performance and low shrinkage stress can be obtained. What is necessary is just to perform it so that the total stretching ratio which passed the previous process including a swelling process and a dyeing process may be 2 to 3 times. The stretching ratio in the dyeing step may be more than 1 times, and more preferably 1.05 times or more.

In the production method of the present invention, the dyeing step is followed by the first cross-linking and stretching step and the second cross-linking and stretching step. The two-stage cross-linking and stretching steps with different application conditions can control the crystal state and alignment state of the obtained polarizing film, and can obtain a polarizing film having excellent polarization performance and low shrinkage stress. Hereinafter, these two steps of crosslinking and stretching will be described.

In the first crosslinking and stretching step, in a 40 to 55 ° C aqueous solution containing 1 to 5 mass% of boric acid, the stretching ratio in this step becomes 1.1 to 1.3 times and the total stretching ratio becomes 2.5 to 3.5. Uniaxial stretching. The boric acid aqueous solution in which the PVA film is impregnated contains 1 to 5 mass% of boric acid. The concentration of boric acid is preferably 1.5% by mass or more, and more preferably 4% by mass or less. With such a concentration, an intermolecular cross-linking reaction by boric acid can proceed at an appropriate rate. The boric acid may be any of boric acid or boric acid ions in an aqueous solution, and any one of boric acid and borate can be used, and boric acid is preferred. In the case of using a borate, the concentration is calculated by mass conversion of boric acid (H ₃ BO ₃ ). The boric acid aqueous solution may contain potassium iodide, and the concentration in this case is preferably in the range of 0.01 to 10% by mass. By including potassium iodide, the polarization performance of the obtained polarizing film can be adjusted. Potassium iodide may be contained in the first crosslinking stretching step, potassium iodide may be contained in the second crosslinking stretching step described later, or both steps may be contained.

The temperature of the boric acid aqueous solution in the first crosslinking and stretching step was 40 to 55 ° C. The temperature is preferably 42 ° C or higher, and more preferably 53 ° C or lower. When this temperature is too low, the progress of the crosslinking reaction by boric acid becomes insufficient, and the polarization of the obtained polarizing film is reduced. On the other hand, when the temperature is too high, PVA may be eluted from the film. Therefore, under such temperature conditions, uniaxial stretching is performed so that the stretching ratio becomes 1.1 to 1.3 times and the total stretching ratio becomes 2.5 to 3.5 times. The total draw ratio is preferably 2.6 times or more, and also preferably 3.4 times or less. In this manner, in the first cross-linking and stretching step, the boric acid cross-linking reaction proceeds while performing uniaxial stretching only slightly to properly align it. With this, even In the case where the boric acid aqueous solution was immersed in the high temperature in the subsequent second crosslinking and stretching step, PVA was not dissolved from the film into the boric acid aqueous solution, and the strength of the film was greatly reduced, and the film could be stretched at a higher rate. .

Then, in the second crosslinking and stretching step, in a 60 to 70 ° C. aqueous solution containing 1 to 5 mass% of boric acid, the stretching ratio in this step becomes 1.8 to 3.0 times and the total stretching ratio becomes 6 ~ 8x way for uniaxial stretching. The composition of the boric acid aqueous solution to be used can be the same as that used in the first crosslinking and stretching step.

In the second crosslinking stretching step, the temperature of the boric acid aqueous solution is 60 to 70 ° C. The temperature is preferably 62 ° C or higher, and also preferably 68 ° C or lower. If the temperature is too low, the shrinkage stress will increase. On the other hand, if the temperature is too high, the PVA is eluted from the film into the boric acid aqueous solution, and the degree of polarization is reduced. Then, in the aforementioned temperature range, uniaxial stretching is performed so that the total stretching ratio becomes 1.8 to 3.0 times and 6 to 8 times. The stretching ratio in the second crosslinking stretching step is preferably 2 times or more, and also preferably 2.8 times or less. The total stretching ratio is preferably 6.2 times or more, and also preferably 7.8 times or less. That is, in a high-temperature boric acid aqueous solution, the boric acid cross-linking reaction proceeds while being stretched at a high magnification. As a result, the crystallization and immobilization of the aligned PVA are promoted in the drying step. Thereby, a polarizing film with high polarization performance and small shrinkage stress can be manufactured.

The maximum tensile stress in the second crosslinking stretching step is preferably 15 N / mm ² or less. Here, the maximum tensile stress refers to a value obtained by dividing the tensile force applied between the adjacent rollers by the cross-sectional area of the PVA film of the raw material in the second crosslinking stretching step. When three or more rollers are used, the maximum tensile force is used. By reducing the maximum tensile stress, a polarizing film having a small shrinkage stress can be obtained. The maximum tensile stress is more preferably 10 N / mm ² or less. The maximum tensile stress is usually 1 N / mm ² or more.

In the first and second cross-linking and stretching steps, when the PVA film is uniaxially stretched, a stretching device having a plurality of rolls parallel to each other in a water bath can be used to change the rolls. The peripheral speed is used.

It is preferable that it is supplied to a washing | cleaning process after the said 2nd crosslinking | crosslinking drawing process. In the cleaning step, unnecessary chemicals and foreign substances on the surface of the film are removed, and the optical properties of the finally obtained polarizing film are adjusted. The cleaning step can be performed by immersing the PVA film in a cleaning bath, or by dispersing a cleaning solution in the PVA film. Water can be used as a cleaning solution, but they can also be made to contain potassium iodide. When it contains potassium iodide, the hue of a polarizing film can be adjusted. The content of potassium iodide is preferably 0.1 to 10% by mass. The temperature of the cleaning solution is usually 10 to 40 ° C, preferably 15 to 30 ° C. You can use multiple baths instead of just one bath. When a plurality of tanks are used, the composition of the cleaning liquid in each tank can be adjusted according to the purpose.

It is preferable to supply the drying step after the aforementioned washing step. The temperature in the drying step is not particularly limited, but is preferably 30 to 150 ° C, and more preferably 50 to 130 ° C. It is easy to obtain a polarizing film excellent in dimensional stability by drying at the temperature in the said range.

The thickness of the polarizing film of the present invention thus obtained is preferably 1 to 30 μm. When the thickness is less than 1 μm, it is difficult to speed up For production, it is more suitable to be 3 μm or more. On the other hand, when the thickness exceeds 30 μm, the tensile tension during stretching processing may increase and the device may be damaged, and more preferably 25 μm or less. Here, the thickness means a thickness of the PVA layer in the case of a multilayer film.

When the obtained polarizing film is a single-layer film of PVA, in order to ensure handleability, the thickness of the polarizing film is preferably 5 μm or more, and more preferably 7 μm or more. On the other hand, in the case of a polarizing film including a multilayer film, the thickness of the PVA layer can be 5 μm or less, or 3 μm or less. The thickness of the base resin layer in the multilayer film is usually 10 to 250 μm.

The monomer transmittance of the polarizing film of the present invention is preferably 42 to 45%. When the unit transmittance is less than 42%, the brightness of the liquid crystal display is reduced. The monomer transmittance is more preferably 42.5% or more. On the other hand, it is difficult to obtain a polarizing film with a high degree of polarization for a polarizing film having a monomer transmittance exceeding 45%, and the monomer transmittance is more preferably 44.5% or less. The degree of polarization of the polarizing film of the present invention is preferably 99.980% or more. With a polarization degree of 99.980% or more, it becomes an excellent image quality of a liquid crystal display. The degree of polarization is more preferably 99.982% or more.

The shrinkage stress of the polarizing film of the present invention is preferably 45 N / mm ² or less. Since the shrinkage stress is small, it is excellent in dimensional stability even when it is used at a high temperature. The shrinkage stress is more preferably 40 N / mm ² or less. Here, the shrinkage stress refers to a value obtained by dividing the tension of a polarizing film fixed as a sample by maintaining it at 80 ° C. for 4 hours by the cross-sectional area of the sample.

The polarizing film of the present invention preferably has a "polarization degree at a single transmittance of 43.5%" of 99.990% or more. This value is obtained by calculating the degree of polarization when a single transmittance (T) of the polarizing film is not 43.5%, and assuming 43.5%. When the monomer transmittance is 43.5%, the polarization degree is more preferably 99.991% or more, and even more preferably 99.992% or more.

The calculation method of "polarization at a single transmittance of 43.5%" is as follows. First, the relationship between the transmittance (T ') excluding the surface reflection and the unit transmittance (T) is expressed by the formula (1). At this time, the refractive index of the PVA was set to 1.5, and the reflectance of the surface was set to 4%. The relationship between the transmittance (T '), the degree of polarization (V), and the dichroic ratio (R) is expressed by the formula (2), and the formula (2) is modified by the formula (3). Here, the dichroic ratio (R) can be treated as a constant in a range where the monomer transmittance (T) does not change significantly, for example, in a range of 42 to 45% because it hardly changes due to the dye concentration. Therefore, after measuring the individual transmittance (T) and polarization degree (V), the equations (1) and (2) are solved using those values, so that the dichroism ratio (R) of the polarizing film can be made constant And figure it out. From the formulas (3) and (1) substituted with this R, the polarization degree (V) at T = 43.5 (%) can be obtained.

T '= T / (1-0.04) ² (1)

R = {-ln [T ’(1-V)]} / {-ln [T’ (1 + V)]} (2)

T '= [1-V] ^{1 / (R-1)} / [1 + V] ^{R / (R-1)} (3)

In addition, when the polarizing film of the present invention was subjected to structural analysis by wide-angle X-ray diffraction (WAXD) measurement, it was found that the polarizing film has structural features different from those of the conventional polarizing film. Hereinafter, it demonstrates.

The polarizing film of the present invention was subjected to WAXD measurement to prepare a graph of X-ray intensity versus diffraction angle (2θ). Then, following In the method described in Example 1, peak division is performed. First, it is divided into three components: "PVA crystal", "PVA amorphous", and "PVA-boric acid aggregation structure". Here, "PVA crystal" means a PVA chain in a crystalline state, and "PVA amorphous" means a PVA chain in an disordered state that is not in a crystalline state. In addition, the peaks derived from the "PVA-boric acid agglomeration structure" are known to appear in the case where boric acid is added to PVA, and are considered to be diffraction signals from the structure formed by the interaction between PVA and boric acid.

Next, for the three components divided by the above method, an X-ray intensity versus an azimuth angle is prepared. Graph. These were further divided into three components each having no alignment component, low alignment component, and high alignment component, so that all components were divided into nine components. By operating in this manner, the ratio (%) of each component when the entire 9 component is set to 100% can be obtained. Then, the high-alignment component of the "PVA-boric acid agglomerate structure" is set to the structural factor A, and the high-alignment component of the "PVA amorphous" is set to the structural factor B. This time, I know the structure required by the construction factor A to improve the polarization performance, and the construction of the shrinkage stress of the construction factor B.

Tectonic factor A is a structure in which boric acid stabilizes the aligned PVA chain intra- or intermolecularly to stabilize it. D. Fujiwara et al., Polymer Preprints, Japan, 59, 2, 3043, 2010; D. Fujiwara et al., Polymer Preprints, Japan, 60, 2, 3393, 2011; K. Ohishi et al., Polymer, 51, 687-693, 2010 and others. In order to achieve high polarization performance, it is necessary to keep more polyiodide ions in the film. In the highly-aligned "PVA-boric acid agglomeration structure", boric acid has the effect of stabilizing polyiodide ions because it inhibits the thermal movement of PVA chains and relaxes the orientation. As a result, a large number of polyiodide ions can be stably maintained.

The construction factor B is a structure in which the PVA chain is highly aligned due to stretching and is directly frozen as it is. It is a producer of uncrystallized PVA chains. At a temperature higher than the glass transition temperature of PVA, molecular mobility is improved by thermal movement. In addition, there is no restraint caused by crystallization and boric acid, so alignment relaxation is easy. The tectonic factor B is highly oriented, so the force during orientation relaxation is large.

The structural factor A and the structural factor B can be controlled using various conditions when a polarizing film is manufactured from a PVA film. For example, the construction factor A depends on the boric acid concentration of the cross-linking tank containing boric acid, and the higher the boric acid concentration, the more the construction factor A is. In addition, for example, the construction factor B depends on the draw ratio. By reducing the draw ratio, the orientation of the PVA chain can be suppressed, and the construction factor B can be reduced.

However, if the boric acid concentration is increased, there are problems such that the stretchability during processing is reduced, or the structural factor B is increased. On the other hand, if the draw ratio is reduced, there is a problem that the structural factor A decreases and a film with high polarization performance cannot be obtained. That is, it is difficult to obtain a polarizing film that satisfies both high polarization performance and low shrinkage stress.

This time, by using the manufacturing method described above, it is possible to manufacture a polarizing film having a higher content rate of the structural factor A than the conventional polarizing film and a lower content rate of the structural factor B than the conventional polarizing film. Thereby, it is possible to obtain a polarizing film which has been difficult to manufacture so far, has excellent polarizing performance, and has low shrinkage stress. Specifically, the content ratio (C _A ) of the construction factor A that can be measured by wide-angle X-ray diffraction is 3 to 4.5%, and the content ratio (C _B ) of the construction factor B is 2.0 to 8.5%, and the ratio (C _A / C _B ) is a polarizing film of 0.4 or more.

The content rate (C _A ) of the structural factor A is preferably 3 to 4.5%. When the content rate (C _A ) is 3% or more, excellent polarizing performance can be obtained. On the other hand, the content rate (C _B ) of the structural factor B is preferably 2.0 to 8.5%, more preferably 2.5 to 8.5%, even more preferably 3.0 to 8.5%, and particularly preferably 4.5 to 8.5%. When the content rate (C _B ) is 8.5% or less, shrinkage stress can be reduced. Therefore, the ratio (C _A / C _B ) of these two is preferably 0.4 or more. By adopting a larger value of the ratio (C _A / C _B ), a polarizing film having excellent polarization performance and low shrinkage stress can be obtained.

A preferred aspect of the polarizing film of the present invention is a polarizing film comprising a polyvinyl alcohol film containing an iodine-based dichroic pigment, and the polarizing degree at a transmittance of 43.5% of the polarizing film-based monomer is 99.990% or more, and The content ratio (C _A ) of the construction factor A determined by wide-angle X-ray diffraction is 3 to 4.5%, the content ratio (C _B ) of the construction factor B is 2.0 to 8.5%, and the ratio (C _A / C _B ) is 0.4. the above.

Another preferred aspect of the polarizing film of the present invention is a polarizing film comprising a polyvinyl alcohol film containing an iodine-based dichroic pigment, the polarizing film-based monomer having a transmittance of 42 to 45% and a polarization degree of 99.980. Above, and the content ratio (C _A ) of the construction factor A measured by wide-angle X-ray diffraction is 3 ~ 4.5%, the content ratio (C _B ) of the construction factor B is 2.0 ~ 8.5%, and the ratio (C _A / C _B ) is 0.4 or more.

Another preferable aspect of the polarizing film of the present invention is a polarizing film comprising a polyvinyl alcohol film containing an iodine-based dichroic pigment, and the polarizing degree at a transmittance of 43.5% of the polarizing film-based monomer is 99.990% or more , And the shrinkage stress is 45N / mm ² or less.

Another preferred aspect of the polarizing film of the present invention is a polarizing film comprising a polyvinyl alcohol film containing an iodine-based dichroic pigment, the polarizing film-based monomer having a transmittance of 42 to 45% and a polarization degree of 99.980. % Or more, and the shrinkage stress is 45 N / mm ² or less.

The polarizing film of the present invention is generally used by forming a polarizing plate by laminating a protective film on both sides or one side thereof. Examples of the protective film include a protective film which is optically transparent and has mechanical strength. Specifically, for example, a cellulose triacetate (TAC) film, a cellulose acetate-butyrate (CAB) film, Acrylic film, polyester film, etc. Examples of the adhesive used for bonding include PVA-based adhesives, urethane-based adhesives, and UV-curable adhesives.

The polarizing plate thus obtained can be used for a high-performance liquid crystal display (LCD). It can provide a polarizing plate that is bright, has good polarization characteristics, and has excellent dimensional stability even under high temperature conditions.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited to these examples at all. The analysis methods and evaluation methods used in the following examples and comparative examples were performed according to the methods shown below.

[Optical characteristics of polarizing film]

A rectangular sample of 3 cm in the longitudinal direction of the polarizing film and 1.5 cm in the vertical direction was taken from the central portion in the width direction of the polarizing film obtained in the following examples and comparative examples. The meter ("V7100" manufactured by JASCO Corporation) was subjected to correction of visual sensitivity in accordance with JIS Z 8722 (method for measuring the color of an object), and then the unit transmittance (T) and polarization (V) were measured.

From the values of T and V thus obtained, the following equations (1) and (2) are solved to calculate the dichroic ratio (R) of the polarizing film, and the equations (3) and ( 1) to obtain the degree of polarization at T = 43.5%. Here, the refractive index of PVA is set to 1.5, and the reflectance of the surface is set to 4%. In addition, the dichroic ratio (R) can be treated as a constant in a range where the transmittance of the monomer does not change significantly, for example, in a range of 42 to 45%, which does not change due to the dye concentration.

T '= T / (1-0.04) ² (1)

R = {-ln [T ’(1-V)]} / {-ln [T’ (1 + V)]} (2)

T '= [1-V] ^{1 / (R-1)} / [1 + V] ^{R / (R-1)} (3)

"Wide-angle X-ray diffraction (WAXD) measurement of polarizing film"

Wide Angle X-Ray Diffraction (WAXD) measurement was performed using a D8 Discover device made by Bruker AXS. The incident X-ray wavelength was set to 0.154 nm (copper target). For the detector, Hi-STAR, a position-sensitive 2D gas detector, was used, and the camera distance (distance between the sample and the detector) was set to approximately 150 mm. The filament current of the X-ray generator was set to 110 mA, the voltage was set to 45 kV, and the diameter of the collimator was 0.5 mm.

The polarizing film was cut into a rectangle with a short side of 5 mm and a long side of 20 mm. At this time, the longitudinal direction is consistent with the stretching direction of the polarizing film. Attach a double-sided tape to the sample holder attached to the device to fix the cut polarizing film. In this measurement, instead of overlapping a plurality of polarizing films, one polarizing film was attached to a sample holder. It has been confirmed in advance that the signal of the polarizing film is sufficiently strong compared to background scattering and electrical noise of the detector. However, the intensity of the diffraction signal from the polarizing film is weak. In this case, a plurality of films can be stacked and measured. In this case, the polarizing films should be attached so that the stretching directions of the respective polarizing films are completely consistent.

The sample holder was mounted on the stage of the X-ray device in such a manner that the stretching direction of the polarizing film was the same as the Y-axis direction of the D8 Discover with GADDS device. At this time, the normal line with respect to the surface of the polarizing film is set so as to coincide with the direction of X-ray incidence. The X-axis, Y-axis, and Z-axis of the device were adjusted so that X-rays were irradiated onto the polarizing film from the aforementioned incident direction.

The WAXD measurement is performed under the following conditions. Set the ω axis of the sample (the axis set so that the angle between the normal to the polarizing film surface and the incident direction of X-rays becomes ω. Generally, it is often called the θ axis) is set to 11 °. The 2θ axis (an axis set such that the angle between the normal to the detector surface and the incident X-ray direction is 2θ) is set to 22 °, and the equivalent of the rotation in the plane of the polarizing film is The axis is set to 90 ° or 0 °. The axis is aligned with the azimuth direction in the plane of the polarizing film. When the stretching direction of the polarizing film is set to the meridian direction and the vertical direction of the in-plane is set to the equatorial line direction, if If the axis is 90 °, the diffraction information in the direction of the equator can be obtained. If the axis is 0 °, the diffraction information in the meridian direction can be obtained. The diffraction or scattering system observed by the detector satisfies Bragg's conditions. In the case of this measurement condition, for example, the detected 110-diffraction signal from the PVA crystal is a diffraction produced by (110) approximately the same as the thickness direction of the polarizing film. will The axis was set at 90 ° or 0 °, and the X-ray exposure time was measured at 60 minutes.

[WAXD measurement data analysis of polarizing film]

Using GADDS (General Area Detector Diffraction System) software, the 2D photos of the WAXD obtained were converted into a 1D graph with X-ray intensity I (2θ) corresponding to 2θ. The 2θ range is set to 5 ° to 35 °. Sampling steps are set at 0.05 ° intervals. Consistent with azimuth direction Axis range is -5 ° to 5 °, 5 ° to 15 °, 15 ° to 25 °, 25 ° to 35 °, 35 ° to 45 °, 45 ° to 55 °, 55 ° to 65 °, 65 ° to 75 °, 75 ° to 85 °, 85 ° to 95 °, 95 ° to 105 °, 105 ° to 115 °, 115 ° to 125 °, 125 ° to 135 °, 135 ° to 145 °, 145 ° to 155 ° , 155 ° to 165 °, 165 ° to 175 °, and 175 ° to 185 °. In the azimuth direction, the azimuth range of 10 ° is divided to obtain I (2θ) curves. The stretching direction of the polarizing film corresponds to 0 °, and the vertical direction thereof corresponds to 90 °. The same operation was also applied to the background scattering data (data that were measured under the same conditions without installing a polarizing film).

The analysis of the I (2θ) graph was performed in the following procedure. First, from the I (2θ) curve obtained from the measurement on the polarizing film, the I (2θ) curve obtained from the same azimuth range measured on the background is subtracted. For the I (2θ) curve with the background scattering subtracted, as shown in Figure 3, create a bottom line connecting the intensity value I (6.5) at 2θ position and 6.5 (30.5) at 2θ position. It is further subtracted from the I (2θ) curve with the background scattering subtracted. On the coordinates of I (2θ) -2θ, the bottom line is a linear function that passes through (6.5, I (6.5)) and (30.5, I (30.5)) 2 points. In addition, in order to suppress the influence of the variation of the measured data on the bottom line, I (6.5) is set to the arithmetic mean of I (6.0) to I (7.0), and I (30.5) is set to I (30.0) to I (31.0 ) Arithmetic mean. Here, in the direction of the meridian, that is, the azimuth is around 0 ° For the I (2θ) curve of Fig., The diffraction peaks of polyiodide ions aligned in the stretching direction are observed around 28 ° at the 2θ position, so I (30.5) will be generated by polyiodide ions. The effect of diffraction peaks. Therefore, when a diffraction peak generated by a polyiodide ion is observed, the diffraction peak is removed in advance. The diffraction peak shape is regarded as a person who can be represented by a Gaussian function, and adjusts the peak top position x, the peak height h, and the width of the Gaussian function (the standard deviation of the normal distribution) in such a way that the influence on the I (2θ) curve disappears. σ), and appropriately subtract the Gaussian function from the I (2θ) curve. This operation is performed on the I (2θ) graphs of all the azimuth angles. After that, the line with the bottom line subtracted is called a corrected I (2θ) curve.

Fig. 4 shows a corrected I (2θ) curve obtained by measuring polarizing film and polyvinyl alcohol film raw materials. The wide and diffuse scattering components observed in the range of 2 ° from 10 ° to 30 ° are mainly from the amorphous producers of PVA. The peak-like composition observed in a range of 19 ° to 21 ° in 2θ is generated from the diffractions of (1-10) and (110) of the PVA crystal. On the other hand, the peak-shaped component observed in the range of 2 ° from 21 ° to 23 ° in 2θ is known to appear when boric acid is added to PVA, and it is considered to originate from the structure formed by the interaction between PVA and boric acid. Radio signal. The structure formed by the interaction between this PVA and boric acid is called "PVA-boric acid aggregate structure". That is, the corrected I (2θ) curve obtained by measuring the polarizing film can be separated into three components: "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomeration structure". Therefore, the waveform separation analysis is applied to the corrected I (2θ) graph.

It is assumed that the scattering or diffraction signals from "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomeration structure" can be expressed by Gaussian functions. Set as Gaussian function A, Gaussian function B, and Gaussian function C, respectively. The parameters defining the shape of the Gaussian function are set as the peak top position x, the peak height h, and the width of the peak (here, it means the standard deviation σ of the normal distribution). The calculated-I (2θ) curve system representing the sum of the three Gaussian functions of each component is consistent with the corrected I (2θ) curve. The peak top positions x, peak heights h, The width of the peak is used as a variable parameter, and all parameters are optimized by least squares fitting. The results are shown in Fig. 4. In this waveform separation and analysis, the calculated-I (2θ) curve must not be affected by the variation of the measurement data, the error caused by the analysis, and the systematic error of the fit. Instead, three calculation methods are used to reflect the structure of the polarizing film. The Gaussian function is appropriately represented. Therefore, in this experiment, the following restrictions (a) to (f) were introduced into the waveform separation analysis and implemented.

(a) Signals in the range of 13 ° to 16 ° and 25 ° to 28 ° in 2θ are regarded as scattering from "PVA amorphous", so I reproduced in the same 2θ range using only Gaussian function A corrected I (2θ) graph.

(b) Signals in the range of about 17 ° to 21 ° in 2θ are scattered and diffracted from "PVA amorphous" and "PVA crystal", and particularly contribute to "PVA crystal". The diffraction peak position generated by the crystallization is known, so the peak top position x of the Gaussian function B is fixed.

(c) Signals in the range of approximately 20 ° to 23 ° in 2θ are scattering and diffraction from "PVA amorphous" and "PVA-boric acid agglomerates". In particular, the contribution of "PVA-boric acid agglomeration structure" is large. Therefore, the peak position x of the Gaussian function C is fixed.

(d) In order to properly separate the "PVA crystal" and the "PVA-boric acid agglomeration structure", the widths of the peaks of the Gaussian function B and the Gaussian function C are set to the same value. It is because it is estimated that regardless of which polarizing film is measured, the diffraction intensities of 17 ° to 21 ° and 20 ° to 23 ° are about the same. There is not much difference in the shape of the radio wave peaks.

(e) Based on the above (a) to (d), explore the calculated-I (2θ) graphs such as the sum of the three Gaussian functions, and reproduce the three corrected Gaussian functions of each of the corrected I (2θ) graphs. The optimum values of the peak top position x and the peak width σ. As a result, we know that when Gaussian function A uses x = 20.0 and σ = 4.0, Gaussian function B uses x = 19.7 and σ = 1.3, and Gaussian function C uses x = 22.0 and σ = 1.3. The waveforms of all the corrected I (2θ) curves can be separated without contradiction and well. The peak top position x and the peak width σ are fixed at the optimum values described above.

(f) For all corrected I (2θ) curves, the peak height h of the three Gaussian functions is set as a variable parameter and least square fitting is performed. The fitting range is set from 6.5 ° to 30.5 °.

Also, in the I (2θ) curve in the direction of the equator, that is, near the azimuth angle of 90 °, a diffraction peak of 100 caused by PVA crystals aligned in the tensile direction was observed around 11 ° at the 2θ position. When a diffraction peak of 100 is observed, the diffraction peak shape is regarded as a person that can be expressed by a Gaussian function, and is included in the waveform separation analysis of the I (2θ) curve. That is, the peak top position x, the crest height h, and the crest width σ of the Gaussian function are appropriately adjusted to perform least square fitting.

After the least squares fit, the areas of the three Gaussian functions were calculated and regarded as the integral intensity values (A) of the signals generated from "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomeration structure". When a 100 diffraction peak is observed, the integrated intensity value of the 100 diffraction peak is included in "PVA amorphous". The above-mentioned waveform separation analysis was performed on the corrected I (2θ) graphs of all the azimuth angles, and the integrated intensity values (A) of "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomeration structure" were calculated. These analyses were performed using Excel software made by Microsoft.

The plot of the integrated intensity value (A) of "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomerate structure" obtained by waveform separation analysis is shown in Figure 5. Here, the azimuth is defined as follows. For example, the analysis result of the corrected I (2θ) curve in the azimuth range of -5 ° to 5 ° is plotted corresponding to the azimuth angle of 0 °, and the corrected I ( 2θ) The analysis result of the graph is drawn corresponding to the azimuth angle of 90 °.

Azimuth scatter plot A ( ) Reflects the alignment state of each component of the polarizing film with respect to the stretching direction. When the resolved scattered or diffracted signals observed in the 2θ range are considered to be mainly caused by interference between PVA molecular chains, the ratio of the signals observed at an azimuth angle of 90 ° is approximately the same as that of PVA molecules The proportions of the components in which the chains are aligned in the stretching direction are equal. The proportion of the signal observed at an azimuth angle of 0 ° is approximately equal to the proportion of the components in which the PVA molecular chains are arranged in a direction perpendicular to the stretching direction. That is, Fig. 5 is a distribution function f ( ). When the PVA is completely non-orientated, there is no azimuth dependency of the distribution function. On the other hand, if PVA is aligned with distribution in the stretching direction, the distribution function shows a peak shape with a maximum intensity of 90 °.

Therefore, the azimuth dispersion plot of the integrated intensity value is plotted as A ( Distribution function f1 ( ) And the distribution function f2 ( ). Since the distribution function without orientation component has no azimuth dependence, it is set to f2 ( ) = C (C is a constant). As shown in FIG. 6, the component that becomes a constant C regardless of the azimuth angle is f2 ( ), The component with probability distribution at a specific azimuth is f1 ( ). Knowing that for any polarizing film, disperse the drawing A from the azimuth F1 with good accuracy ), The data processing can be performed in the following order. Assume that the distribution function f1 of the alignment components of "PVA crystal" and "PVA-boric acid agglomeration structure" ( ) Can be expressed by Lorenz function, the peak position is set to 90 °, the peak height h and the full width at half maximum of the peak are set as variable parameters. Suppose the distribution function f1 of the alignment component of "PVA amorphous" ( ) Can use the shape and expression of two Gaussian functions, set the peak top position to 90 °, and set the peak height h and the full width at half maximum of each function as variable parameters. Take f1 ( ) And f2 ( ) And reproduce A ( ) Method to perform the least square fitting to obtain the optimal solution of the constant C, the peak height h, and the FWHM of the peak. Fitting is performed in an azimuth range from 0 ° to 180 °.

Here, the distribution function f1 ( ), Azimuth A range of 80 ° to 100 °, that is, a ratio of a highly-aligned component is determined as follows. First, in the range of azimuths from 0 ° to 180 °, find the distribution function f1 of the alignment component ( ). Set it to F1. Next, calculate the distribution function f1 ( Azimuth in) The integral value in the range of 80 ° to 100 ° is set to F1a. F1-F1a is an integrated value of 0 ° to 80 ° and 100 ° to 180 °, and it is set to F1b. F1b is an alignment component with a small degree of alignment. Calculate the distribution function f2 with no alignment component in the azimuth range from 0 ° to 180 ° ( ) Integral value F2. The values of F1a, F1b, and F2 were obtained for "PVA amorphous", "PVA crystal", and "PVA-boric acid agglomeration structure", respectively. F1a is an amount proportional to the high alignment component, F1b is an amount proportional to the low alignment component, and F2 is an amount proportional to the non-aligned component.

"PVA amorphous", "PVA crystal", and "PVA-boric acid agglomerate structure" have high-alignment component, low-alignment component, and non-alignment component, that is, the existence ratio of 9 components is as follows, and each component is regarded as relative to each component The ratio of the sum of the integral values. Set them as F1a-PVA amorphous, F1b-PVA amorphous, F2-PVA amorphous, F1a-PVA crystal, F1b-PVA crystal, F2-PVA crystal, F1a-PVA-boric acid agglomerate structure, F1b-PVA-boric acid Aggregation structure, F2-PVA-boric acid aggregation structure.

Among them, it is known that the highly-aligned component F1a-PVA-boric acid agglomeration structure of "PVA-boric acid agglomeration structure" has a high correlation with the polarization performance of a polarizing film, as described above. This is because the boron-acid interaction stabilizes the PVA chain that is highly aligned and stretched by stretching, thereby promoting the formation and retention of polyiodide ions. The highly-aligned component of the "PVA-boric acid agglomerate structure" is set to the structure factor A. On the other hand, it was found that the highly aligned F1a-PVA amorphous system of "PVA amorphous" is highly related to the shrinkage stress of the polarizing film. This is because the PVA chain which is highly aligned and stretched by stretching is easy to thermally move due to an increase in temperature, and has a strong force for slack alignment, which is a cause of shrinkage. The highly-aligned component of "PVA amorphous" is set to the construction factor B.

For a sample of a polarizing film manufactured under various conditions, the graph showing the content rate (C _A ) of the structural factor _A and the content rate (C _B ) of the structural factor B corresponding to the shrinkage stress according to the method described above is shown in FIG. 7. In addition, a graph in which the drawing ratio (C _A / C _B ) corresponds to the shrinkage stress is shown in FIG. 8. It is known that the shrinkage stress, the content ratio of structural factor A (C _A ), the content ratio of structural factor B (C _B ), and the ratio (C _A / C _B ) are very relevant.

[Shrinkage stress of polarizing film]

Shrinkage stress was measured using Shimadzu Corporation's Autograph AG-X with a constant temperature bath and a video-type stretcher TR ViewX120S. The measurement system used a polarizing film that was humidified at 20 ° C / 20% RH for 18 hours. After setting the thermostatic bath of the Autograph AG-X to 20 ° C, the polarizing film (15 cm in the length direction and 1.5 cm in the width direction) was mounted on a jig (fixture interval of 5 cm), and the thermostat was started to rise to 80 ° C simultaneously with the start of stretching. . The polarizing film was stretched at a speed of 1 mm / min, and the stretching was stopped when the tension reached 2 N, and the tension was measured in this state to 4 hours later. At this time, the distance between the clamps changes due to thermal expansion. Therefore, attach a reticule sticker to the clamp, and use the video-type stretcher TR ViewX120S to correct the amount between the clamps by an amount corresponding to the movement of the reticule sticker attached to the clamp. The distance is operated to measure. The value obtained by subtracting the initial tension 2N from the measured value of the tension after 4 hours was defined as the shrinkage force of the polarizing film, and the value divided by the cross-sectional area of the sample was defined as the shrinkage stress (N / mm ² ).

[Maximum tensile stress in the second crosslinking stretching step]

The maximum tensile stress in the second cross-linking and stretching step is measured in the second cross-linking and stretching step by using a tension roller provided between adjacent rollers to apply a tensile tension between the adjacent rollers. Divide the raw PVA thin The value of the cross-sectional area of the film. When three or more rollers are used, the maximum tensile force among them is used.

[Example 1]

100 parts by mass of PVA (saponified polymer of vinyl acetate polymer, degree of polymerization 3000, degree of saponification 99.9 mole%), 10 parts by mass of glycerin as a plasticizer, and polyoxyethylene lauryl ether sulfate as a surfactant Sodium: 0.1 parts by mass of a film-forming stock solution with water, and cast film to obtain a roll of a PVA film having a thickness of 45 μm. For this PVA film, a swelling step, a dyeing step, a first crosslinking stretching step, a second crosslinking stretching step, a cleaning step, and a drying step were sequentially performed to produce a polarizing film. The schematic diagram of a polarizing film manufacturing apparatus is shown in FIG.

Specifically, it operates as follows to manufacture a polarizing film. First, in the swelling step, the above-mentioned PVA film was uniaxially stretched in the longitudinal direction (MD) to twice the original length while being immersed in water at a temperature of 30 ° C for 1 minute. . Then, in the dyeing step, uniaxial stretching is performed in the longitudinal direction (MD) while immersing in a 30 ° C aqueous solution containing 0.06% by mass of iodine and 1.4% by mass of potassium iodide for 1 minute (second stage stretching). ) To 2.4 times the original length. Then, in the first crosslinking stretching step, uniaxial stretching was performed in the longitudinal direction (MD) while immersed in an aqueous solution of 50 ° C containing boric acid at a concentration of 2.6% by mass for 2 minutes (the third stage stretching Extension) to 3 times the original length. Then, in the second cross-linking and stretching step, the monolayer was immersed in the lengthwise direction (MD) while immersed in a 65 ° C aqueous solution containing boric acid at a concentration of 2.8 mass% and potassium iodide at a concentration of 5% by mass. Axial stretching (4th stretch) to 7 times the original length. The maximum tensile stress in the second crosslinking stretching step was 5.5 N / mm ² . Then, in the cleaning step, the film was washed by immersing in a 22 ° C. aqueous solution containing boric acid at a concentration of 1.5% by mass and potassium iodide at a concentration of 5% by mass for 10 seconds. Then, in a drying step, drying was performed with a dryer at 80 ° C. for 90 seconds, thereby producing a polarizing film having a thickness of 13.9 μm.

Using the obtained polarizing film, the degree of polarization and shrinkage stress at the time of the structural factors A and B, the transmittance of the monomer, the degree of polarization, and the transmittance of the monomer of 43.5% were measured by the methods described above. The content ratios of the high-alignment component, the low-alignment component, and the non-alignment component of the PVA crystal were 5.4%, 2.8%, and 15.1%, respectively. The PVA-boric acid agglomerated structure contains 3.2%, 1.4%, and 4.6% of the high, low, and non-aligned components. The content ratios of the PVA amorphous high-alignment component, low-alignment component, and non-alignment component were 8.0%, 10.3%, and 49.3%, respectively. That is, the content rate (C _A ) of the construction factor _A is 3.2%, the content rate (C _B ) of the construction factor B is 8.0%, and the ratio (C _A / C _B ) is 0.4. The unit transmittance is 43.73%, the polarization is 99.982%, the unit transmittance is 43.5%, the polarization is 99.993%, and the shrinkage stress is 34.5N / mm ² . These evaluation results are shown in Table 2.

[Comparative Examples 1 to 8]

In addition to changing the thickness and degree of polymerization of the PVA film as shown in Table 1, the temperature of the boric acid aqueous solution in the first crosslinking stretching step, the total stretching ratio after the first crosslinking stretching step, and the second crosslinking stretching step A polarizing film was produced in the same manner as in Example 1 except for the temperature of the boric acid aqueous solution and the total stretching ratio after the second cross-linking stretching step. Table 1 shows the values of the maximum tensile stress in the second crosslinking stretching step.

Using the obtained polarizing film, the monomer transmittance, polarization degree, and polarization degree at 43.5% of the monomer transmittance, the shrinkage stress, the content factor (C _A ) of the structural factor _A , and the structural factor B were measured in the same manner as in Example 1. Content (C _B ). These evaluation results are arranged and shown in Table 2. In addition, a graph depicting the degree of polarization corresponding to the shrinkage stress at a single transmittance of 43.5% of the polarizing films obtained in Example 1 and Comparative Examples 1 to 4, 7, and 8 is shown in FIG. 2. If you look at Figure 2, you will understand the following. That is, in Comparative Examples 1 to 8, if the polarization degree at 43.5% of the monomer transmittance is increased, the shrinkage stress becomes large. In contrast to this, Example 1 is significantly different from Comparative Examples 1 to 8, and even if the degree of polarization at 43.5% of the monomer transmittance is increased, the shrinkage stress can be reduced. Moreover, the polarized light at the transmittance of 43.5% of Comparative Examples 5 and 6 monomers was less than 99.950%, and deviated from the lower range of the figure.

Claims (7)

A method for manufacturing a polarizing film is to apply at least a swelling step, a dyeing step, a first cross-linking stretching step, and a second cross-linking stretching step to a polyvinyl alcohol film in this order, characterized in that the thickness of the polyvinyl alcohol film is It is 5 to 100 μm. The average degree of polymerization of polyvinyl alcohol contained in the polyvinyl alcohol film is 2500 to 3500. In the swelling step, the polyvinyl alcohol film is immersed in water at 10 to 50 ° C. to swell the polyvinyl alcohol film. In this dyeing step, the polyvinyl alcohol film is impregnated with an aqueous solution of 10 to 50 ° C. containing a total of 0.5 to 3% by mass of iodine and potassium iodide, and the polyvinyl alcohol film is impregnated with a total stretching ratio of 2 to Uniaxial stretching is performed three times. In this first cross-linking stretching step, in a 40-55 ° C aqueous solution containing 1 to 5 mass% of boric acid, the stretching ratio in this step becomes 1.1 to Uniaxial stretching was performed so that the total stretching ratio was 1.3 times and the total stretching ratio was 2.5 to 3.5 times. Then, in this second cross-linking stretching step, an aqueous solution of 60 to 70 ° C. containing 1 to 5 mass% of boric acid was used. , Uniaxially performed such that the stretching ratio in this step becomes 1.8 to 3.0 times and the total stretching ratio becomes 6 to 8 times. Stretch. The method for producing a polarizing film according to claim 1, wherein the maximum tensile stress is 15 N / mm ² or less in the second cross-linking and stretching step. For example, the method for manufacturing a polarizing film according to claim 1 or 2 can obtain a polarizing film having a single transmittance of 42 to 45% and a polarization degree of 99.980% or more. According to the method for producing a polarizing film according to claim 1 or 2, a polarizing film having a shrinkage stress of 45 N / mm ² or less is obtained. A polarizing film is a polarizing film comprising a polyvinyl alcohol film containing an iodine-based dichroic pigment, characterized in that the polarization degree at a single transmittance of 43.5% is 99.990% or more, and a structure for measuring a wide-angle X-ray diffraction. The content ratio (C _A ) of the factor A is 3 to 4.5%, the content ratio (C _B ) of the structural factor B is 2.0 to 8.5%, and the ratio (C _A / C _B ) is 0.4 or more. The degree of polymerization of the contained polyvinyl alcohol is 2500 to 3500. Here, the structural factor A is a highly directional structural factor derived from the polyvinyl alcohol-boron agglomerated structure, and the structural factor B is a high degree derived from the amorphous polyvinyl alcohol. Constructive factors of alignment. A polarizing film is a polarizing film comprising a polyvinyl alcohol film containing an iodine-based dichroic pigment, characterized in that the monomer transmittance is 42 to 45%, the polarization degree is 99.980% or more, and the wide-angle X-ray diffraction measurement The content rate (C _A ) of the construction factor A is 3 to 4.5%, the content rate (C _B ) of the construction factor B is 2.0 to 8.5%, and the ratio (C _A / C _B ) is 0.4 or more, and the polarizing film The degree of polymerization of polyvinyl alcohol contained in it is 2500 ~ 3500. Here, the structural factor A is a highly-aligned structural factor derived from the polyvinyl alcohol-boron agglomerated structure, and the structural factor B is derived from amorphous polyvinyl alcohol. Highly directional construction factor. The polarizing film according to claim 5 or 6, wherein the shrinkage stress is 45 N / mm ² or less.