TWI785191B - Polarizing film and method for producing same - Google Patents

Abstract

The present invention is a polarizing film, which comprises polyvinyl alcohol (A), at least A polarizing film of a boron-containing compound (B) and boric acid (C), wherein the boron element concentration (α) derived from the boron-containing compound (B) within 1 μm from the surface of the polarizing film is 1 to 7 Atomic %, the boron element concentration (β) derived from the boron-containing compound (B) in the range of 1 μm from the center to the outside is 0.1 to 2 atomic %, and the ratio of the concentration (α) to the concentration (β) (α/ β) is 1.5 or more. The polarizing film has good polarizing performance and hue, and low shrinkage.

[In the formula (I), R1 is ^a divalent organic group with carbon numbers of ¹ to 20, and R1 is connected with two boronic acid groups by a boron-carbon bond. ]

Description

Polarizing film and manufacturing method thereof

The invention relates to a polarizing film with good polarizing performance and hue and low shrinkage force and a manufacturing method thereof.

Polarizing plates with light transmission and shielding functions, and liquid crystals that change the polarization state of light are the basic components of liquid crystal displays (LCDs). In order to prevent the fading of the polarizing film and the shrinkage of the polarizing film, most polarizing plates have a structure in which a protective film such as triacetate cellulose (TAC) film is attached to the surface of the polarizing film, and as the polarizing film constituting the polarizing plate, the mainstream A substrate obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA") to adsorb iodine dyes (I ₃ ^- or I ₅ ^- , etc.).

LCDs are widely used in small devices such as computers and watches, smartphones, notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, and measuring equipment. In recent years, these machines have been required to be thinner and lighter, and the thinning of glass used in LCDs is being developed. However, the warpage of the LCD panel caused by thinning the glass has become a problem. The main cause of LCD panel warping is said to be the shrinkage of the polarizing film at high temperature, so a polarizing film with low shrinkage force is required. In addition, it is required to improve the contrast of LCD, so it is also necessary to improve the polarizing performance and hue of the polarizing film.

Patent Document 1 describes that after the dyeing step, the crosslinking step and the stretching step, the first drying step of drying the PVA film at 25°C or higher and lower than 65°C and the second drying step of drying at 65°C or higher and 115°C or lower The manufacturing method of the polarizing film in the drying step. Patent Document 1 describes that according to this method, the shrinkage of the polarizing film at high temperature can be reduced, and the dimensional stability can be improved. However, since it dries at high temperature, the polarizing performance of the obtained polarizing film becomes low, and there existed a problem that the hue deteriorated.

Patent Document 2 describes a method of preventing shrinkage of the polarizing film and improving heat resistance by treating the PVA film with diboric acid in the swelling step, dyeing step or stretching step. However, this polarizing film has problems of low polarizing performance and poor hue.

Patent Document 3 describes that by reducing the amount of boric acid in the PVA film and setting a step of drying the PVA film between the boric acid treatment step and the water washing step, a polarizing film with low shrinkage force and good hue at high temperature can be obtained. However, if the amount of boric acid in the polarizing film is reduced, the shrinkage force will decrease, but it is difficult to maintain high polarizing performance.

prior art literature patent documents

Patent Document 1 Japanese Patent Application Laid-Open No. 2015-028634

Patent Document 2 KR10-2014-0075154 Publication

Patent Document 3 Japanese Patent Application Laid-Open No. 2013-148806

The object of the present invention is to provide a polarizing film with good polarizing performance and hue and low shrinkage force and a simple manufacturing method thereof.

The above problems are solved by providing a polarizing film comprising PVA (A), selected from the group comprising diboronic acid represented by the following formula (I) and a compound that can be converted into the diboronic acid in the presence of water A polarizing film of at least one boron-containing compound (B) and boric acid (C) in the group, characterized in that the concentration of boron element derived from the boron-containing compound (B) within 1 μm from the surface of the polarizing film ( α) is 1 to 7 atomic %, the boron element concentration (β) derived from the boron-containing compound (B) in the range from the center to the outer 1 μm is 0.1 to 2 atomic %, and the concentration (α) is relative to the concentration (β ) ratio (α/β) is 1.5 or more.

[In the formula (I), R1 is ^a divalent organic group with carbon numbers of ¹ to 20, and R1 is connected with two boronic acid groups by a boron-carbon bond. ]

The content of the boron element derived from the boron-containing compound (B) in the polarizing film is preferably 0.1 to 3.0 parts by mass relative to 100 parts by mass of the PVA (A). Preferably R ¹ is an aliphatic group. Preferably, the total boron element content in the aforementioned polarizing film is 1.0-5.0% by mass.

The above-mentioned problems are also solved by a method of manufacturing the above-mentioned polarizing film, which is a polarizing film including a dyeing process of dyeing a PVA film with a dichroic pigment, and a stretching process of uniaxially stretching the film in an aqueous solution of boric acid. A production method wherein the stretched PVA film having a boron content derived from boric acid of 0.5 to 5.0% by mass is dipped in an aqueous solution having a concentration of 0.1 to 5.0% by mass of the boron-containing compound (B), and heated at 95°C Next, this film is dried.

The polarizing film of the present invention has good polarizing performance and hue, and low shrinkage force. According to the manufacturing method of the present invention, the aforementioned polarizing film can be easily manufactured.

1‧‧‧Derived from the peak value of deuterium water as the determination solvent

2‧‧‧Peak derived from the methine group of PVA

3‧‧‧Peak derived from the methylene group of PVA

4‧‧‧The peak derived from the hydrocarbon group contained in the boron-containing compound overlapped with the peak derived from PVA

5‧‧‧Peaks derived from hydrocarbon groups contained in boron-containing compounds that do not overlap with peaks derived from PVA

FIG. 1 is the ¹ H-NMR spectrum of the polarizing film obtained in Example 1.

Form of implementing the invention

The polarizing film of the present invention comprises PVA (A), at least one selected from the group consisting of diboronic acid represented by the following formula (I) and a compound that can be converted into the diboronic acid in the presence of water In the polarizing film of the boron-containing compound (B) and boric acid (C), the boron element concentration (α) derived from the boron-containing compound (B) in the range of 1 μm from the surface of the polarizing film to the inner side is 1 to 7 atomic %, The concentration (β) of the boron element derived from the boron-containing compound (B) in the range of 1 μm from the center to the outside is 0.1 to 2 atomic %, and the ratio (α/β) of the concentration (α) to the concentration (β) is 1.5 or above.

[In the formula (I), R1 is ^a divalent organic group with carbon numbers of ¹ to 20, and R1 is connected with two boronic acid groups by a boron-carbon bond. ]

The concentration (α) of the boron element derived from the boron-containing compound (B) must be 1 to 7 atomic % within a range of 1 μm from the surface of the polarizing film. When the boron element concentration (α) is less than 1 atomic %, the amount of crosslinking in the vicinity of the surface of the polarizing film is too small, and the polarizing performance becomes insufficient. The boron element concentration (α) is preferably 2 atomic % or more. On the other hand, when the boron element concentration (α) exceeds 7 atomic %, the surface becomes too hard and the polarizing film is easily broken. The boron element concentration (α) is preferably 6 atomic % or less.

In addition, the boron element concentration (β) derived from the boron-containing compound (B) must be 0.1 to 2 atomic % within a range of 1 μm from the center of the polarizing film to the outside. When the boron element concentration (β) exceeds 2 atomic %, the polarizing performance becomes low and the hue deteriorates. The reason for this is unclear, but it is considered that the boron-containing compound (B) inhibits the formation of an iodine complex that absorbs short-wavelength light. The boron element concentration (β) is preferably 1 atomic % or less. On the other hand, when the boron element concentration (β) is less than 0.1 atomic %, the shrinkage force of the polarizing film becomes high. The boron element concentration (α) and boron element concentration (β) in the aforementioned polarizing film can be obtained by using an X-ray photoelectron spectrometer (GCIB XPS) with a gas cluster ion beam gun. Specifically, it can obtain|require by the method described in the Example mentioned later.

The thickness of the aforementioned polarizing film is preferably 5-30 μm. When the thickness is less than 5 μm, elongation fracture tends to occur during production, and there is a possibility that productivity may be lowered. The thickness is preferably 10 μm or more. On the other hand, when the thickness is less than 30 μm, performance required for a polarizing plate such as thinning and weight reduction may not be satisfied.

In the aforementioned polarizing film, the ratio (α/β) of the boron element concentration (α) to the boron element concentration (β) must be 1.5 or more. When this ratio (α/β) is less than 1.5, the polarization performance may become insufficient or the hue may deteriorate. The aforementioned ratio (α/β) is preferably 2 or more, more preferably 3 or more. On the other hand, the aforementioned ratio (α/β) is usually 50 or less.

As mentioned above, the boron element derived from the boron-containing compound (B) has a predetermined concentration distribution in the thickness direction, which is a major feature of the aforementioned polarizing film. When the boron-containing compound (B) is adsorbed on the PVA film by a general method, there is no substantial concentration difference between the surface and the center of the film. Although the effect of reducing the shrinkage force can be obtained, there is a problem that the polarizing performance or the hue is reduced. The inventors of the present case have repeatedly discussed in order to make it have both polarizing performance, hue and shrinkage. As a result, it was found that by making the content of the boron-containing compound (B) in the center of the polarizing film less than that near the surface, the polarization can be suppressed. The performance and hue are reduced, and the shrinkage force is reduced at the same time. The reason for this is not clear, but it is considered that by reducing the content of the boron-containing compound (B) in the central portion of the polarizing film, the formation of iodine complexes that absorb short-wavelength light can be promoted in this portion, so that the polarizing performance and The hue is reduced.

The content of the boron element derived from the boron-containing compound (B) in the polarizing film is preferably 0.1 to 3.0 parts by mass relative to 100 parts by mass of the PVA (A). When the content exceeds 3.0 parts by mass, the amount of crosslinking may become too large, and the polarizing film may be easily brittle and cracked. The content is more preferably at most 2.0 parts by mass. On the other hand, when the content is less than 0.1 parts by mass, the amount of crosslinking may be too small, and the shrinkage force of the polarizing film may become high. The content is more preferably at least 0.3 parts by mass. The boron element content derived from the boron-containing compound (B) can be determined by ¹ H-NMR measurement. Specifically, it can obtain|require by the method described in the Example mentioned later.

Preferably, the total boron element content in the aforementioned polarizing film is 1.0-5.0% by mass. When this content exceeds 5.0 mass %, there exists a possibility that the shrinkage force of a polarizing film may become high. The content is more preferably at most 4.0% by mass, and still more preferably at most 3.0% by mass. On the other hand, when the content is less than 1.0% by mass, there is a possibility that the polarizing performance may become insufficient. The content is more preferably at least 2.0% by mass, and still more preferably at least 2.2% by mass. The total boron content in the polarizing film can be obtained by ICP emission analysis. Specifically, it can obtain|require by the method described in the Example mentioned later.

The boron-containing compound (B) used in the present invention is at least one selected from the group consisting of diboronic acid represented by the following formula (I) and a compound that can be converted into diboronic acid in the presence of water. Diboronic acid is a boron-containing compound having two boronic acid groups [—B(OH) ₂ ] in one molecule. In the formula (I), R ¹ is a divalent organic group with carbon numbers of 1-20, and R ¹ is connected to two boronic acid groups by a boron-carbon bond. The boronic acid group has a structure in which a boron atom is bonded to two hydroxyl groups and a carbon atom. Therefore, boric acid differs in the point of having a boron-carbon bond, compared to boron atoms bonded to three hydroxyl groups in boric acid [B(OH) ₃ ]. And since the boron-carbon bond which a boronic acid group has does not hydrolyze, it is stable even in the environment where water exists.

Also, the hydroxyl group in the boronic acid group can form an ester with alcohol in the same way as the hydroxyl group in the boric acid group. Accordingly, the boron-containing compound (B) used in the present invention has 4 hydroxyl groups that can react with the hydroxyl group of PVA to form an ester. , and the boronic acid groups exist at positions away from each other through R ¹ . Therefore, it is considered that the boron-containing compound (B) used in the present invention can effectively crosslink PVA.

As a boron-containing group which can be converted into a boronic acid group in the presence of water, the following borate ester group is mentioned as a representative thing, but it is not limited to this. The following structural formula (II) is a diboronic acid monoester obtained by reacting one molecule of alcohol (R ² -OH) with boronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, R in the structural formula ( ^II ) is PVA, and the organic group is bonded to the PVA through a boron atom.

The following structural formula (III) is an example of a diboronic acid diester obtained by reacting 2 molecules of alcohol (R ² -OH) with boronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, the two R ² in the structural formula (III) are both PVA chains.

In the above formula (I), R ¹ is a divalent organic group with 1 to 20 carbon atoms. When R ¹ has an appropriate length, the PVA chains can be efficiently cross-linked. The carbon number of R ¹ is preferably at most 10, more preferably at most 6, and even more preferably at most 4. Also, the carbon number of R ¹ is preferably 2 or more. As long as R ¹ is a divalent organic group, and R ¹ and two boronic acid groups are connected by boron-carbon bonds. R ¹ may be a hydrocarbon group, and may also contain heteroatoms such as oxygen, nitrogen, sulfur, and halogen. In consideration of the ease of acquisition, etc., R ¹ preferably does not contain a heteroatom, more preferably R ¹ is a hydrocarbon group.

R ¹ is preferably an aliphatic compound from the viewpoint of being easy to set the boron element concentration (α) or boron element concentration (β) within the above-mentioned range. When R ¹ is an aromatic group, adsorption to the PVA film and diffusion in the PVA film become slow, and it may be difficult to set the boron element concentration (α) or boron element concentration (β) within the above range.

Specific examples of the boron-containing compound (B) include methanediboronic acid, 1,2-ethanediboronic acid, 1,3-propanediboronic acid, 1,4-butanediboronic acid, 1,5-pentanediboronic acid, Alkanediboronic acid, 1,6-hexanediboronic acid, 1,7-heptanediboronic acid, 1,8-octanediboronic acid, 1,9-nonanediboronic acid, 1,10-decanediboronic acid, 1 ,11-undecanediboronic acid, 1,12-dodecanediboronic acid, 1,13-tridecanediboronic acid, 1,14-tetradecanediboronic acid, 1,15-pentadecanediboronic acid, 1 ,16-hexadecane diboronic acid, 1,17-heptadecane diboronic acid, 1,18-octadecane diboronic acid, 1,19-nonadecane diboronic acid, 1,20-eicosane diboronic acid and other Isomers, etc., such as boron-containing compounds where R ¹ is a hydrocarbon group, 2-oxa-1,3-propane diboronic acid, 3-oxa-1,5-pentane diboronic acid, 4-oxa-1,7 -Heptane diboronic acid and these isomers, etc., in which R1 contains ^a heteroatom, boron-containing compounds, 1,4-phenylene diboronic acid and these isomers, etc., R1 is ^an aromatic group-containing compound Boron compounds, etc. Among these, 1,2-ethanediboronic acid, 1,3-propanediboronic acid, and 1,4-butanediboronic acid are preferable.

The degree of polymerization of PVA(A) is preferably in the range of 1,500-6,000, more preferably in the range of 1,800-5,000, and still more preferably in the range of 2,000-4,000. When the degree of polymerization is 1,500 or more, the optical properties of the polarizing film obtained by uniaxially stretching the film can be improved. On the other hand, when the degree of polymerization is 6,000 or less, it is possible to suppress an increase in production cost, a defect in process passability at the time of film formation, and the like. In addition, the polymerization degree of PVA (A) in this invention means the average polymerization degree measured based on the description of JISK6726-1994.

From the viewpoint of water resistance of a polarizing film obtained by uniaxially stretching a PVA film, the degree of saponification of PVA (A) is preferably at least 95%, more preferably at least 96%, and still more preferably at least 98%. Furthermore, the degree of saponification of PVA (A) refers to the structural unit (typically vinyl ester unit) and vinyl alcohol unit that can be converted into vinyl alcohol unit (-CH ₂ -CH(OH)-) by saponification. The total moles of vinyl alcohol units in PVA (A) account for the proportion (%) of the moles of vinyl alcohol units. The saponification degree can be measured according to the description of JIS K6726-1994.

The manufacturing method of PVA (A) is not specifically limited. For example, the method of converting the vinyl ester unit of the polyvinyl ester obtained by polymerizing a vinyl ester monomer into a vinyl alcohol unit is mentioned. Vinyl monomers used in the manufacture of PVA are not particularly limited, and examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, trimethylvinyl acetate, Vinyl neodecanoate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate, etc. From the viewpoint of hydroxylation, vinyl acetate is preferred.

PVA (A) may be obtained by converting vinyl ester units of a polyvinyl ester copolymer obtained by copolymerizing vinyl ester monomers and other monomers copolymerizable therewith into vinyl alcohol units. As other monomers that can be copolymerized with vinyl ester monomers, for example: α-olefins with 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or its salts; Methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate , tertiary butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate and other (meth)acrylates; base) acrylamide; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone (methyl) ) acrylamide, (meth)acrylamidopropanesulfonic acid or its salts, (meth)acrylamidopropyldimethylamine or its salts, N-methylol (meth)acrylamide or its derivatives (meth)acrylamide derivatives such as substances; Propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, secondary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers; (meth)propylene Vinyl cyanide such as nitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salt, ester or anhydride; Itaconic acid or its salt, ester or anhydride; vinyl silane compounds such as ethylene trimethoxysilane; unsaturated sulfonic acid, etc. The above-mentioned vinyl ester copolymer may have structural units derived from one or two or more of the aforementioned other monomers. This other monomer can be used by allowing the vinyl ester monomer to exist in the reaction container beforehand when it is subjected to the polymerization reaction, or by adding it to the reaction container during the polymerization reaction. From the viewpoint of polarizing performance, the content of units derived from other monomers is preferably at most 10 mol%, more preferably at most 5 mol%, and even more preferably at most 2 mol%.

From the point of view of improving the elongation and extending at a higher temperature, and reducing the troubles such as elongation breakage during the production of optical films, and further improving the productivity of optical films, the above-mentioned copolymerization with vinyl ester monomers Among the monomers, ethylene is preferred. When PVA contains ethylene units, the content of ethylene units is preferably 1 to 4 mol% based on the number of moles of the total structural units constituting PVA from the viewpoint of the above-mentioned elongation or elongation temperature. , more preferably 2~3 mol%.

The polymerization method when polymerizing vinyl ester monomers can be batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization, etc. As the polymerization method, block polymerization method, solution polymerization method, suspension polymerization method, etc. Well-known methods, such as a polymerization method and an emulsion polymerization method, are used. Generally, a mass polymerization method or a solution polymerization method in which polymerization is carried out in a solvent such as no solvent or alcohol is used. When it is desired to obtain polyvinyl ester with a high degree of polymerization, emulsion polymerization is preferred. The solvent of the solution polymerization method is not particularly limited, and is, for example, alcohol. Alcohols used as solvents in the solution polymerization method are, for example, lower alcohols such as methanol, ethanol, and propanol. The amount of solvent used in the polymerization solution can be selected in response to the degree of polymerization of the purpose PVA and considering the chain transfer of the solvent. For example, when the solvent is methanol, as the mass ratio of the solvent to all monomers (solvent/total monomers), It is preferably selected from the range of 0.01-10, more preferably selected from the range of 0.05-3.

The polymerization initiator used in the polymerization of vinyl ester monomers can be selected from well-known polymerization initiators according to the polymerization method, such as azo initiators, peroxide initiators, redox initiators, etc. starter. Azo initiators are, for example: 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis( 4-methoxy-2,4-dimethylvaleronitrile).

Peroxide-based initiators are, for example, percarbonate-based compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, etc. ; Secondary butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate and other perester compounds; Acetyl peroxycyclohexylsulfonyl; 2,4,4-Trimethyl Amyl-2-peroxyphenoxyacetate; Acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide and the like may also be used in combination with the aforementioned initiators as a polymerization initiator. The redox-based initiator is, for example, a polymerization initiator that combines the above-mentioned peroxide-based initiator with a reducing agent such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and sodium formaldehyde sulfate. The amount of the polymerization initiator used varies with the type of the polymerization initiator, so it cannot be determined uniformly, but it can be selected according to the polymerization speed. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as a polymerization initiator, it is preferably 0.01 to 0.2%, more preferably 0.02 to 0.15%, based on the vinyl ester monomer. The polymerization temperature is not particularly limited, but room temperature to about 150°C is appropriate, preferably above 40°C and below the boiling point of the solvent used.

Polymerization of vinyl ester monomers can also be carried out in the presence of chain transfer agents. Chain transfer agents include, for example, aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; hypophosphite salts such as sodium hypophosphite monohydrate, etc. . Among them, aldehydes and ketones can be used appropriately. The amount of chain transfer agent used can be determined according to the chain transfer coefficient of the chain transfer agent used and the degree of polymerization of the target PVA. Generally speaking, it is preferably 0.1-10 parts by mass relative to 100 parts by mass of vinyl ester monomer .

The saponification of polyvinyl ester can be carried out, for example, in a state in which the polyvinyl ester is dissolved in alcohol or hydroalcohol. The alcohol used for saponification includes, for example, lower alcohols such as methanol and ethanol, preferably methanol. Alcohol used for saponification may contain, for example, other solvents such as acetone, methyl acetate, ethyl acetate, and benzene in a proportion of 40% by mass or less of the mass. The catalysts used in saponification are, for example, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkali catalysts such as sodium methoxide, and acid catalysts such as mineral acid. The temperature for performing saponification is not limited, but is preferably within a range of 20 to 60°C. When a colloidal product is precipitated due to progress of saponification, PVA can be obtained by pulverizing the product, followed by washing and drying. The saponification method is not limited to the aforementioned method, and a known method can be applied.

The PVA film may contain a plasticizer in addition to the above-mentioned PVA (A). Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, etc. In addition, these plasticizers may contain 1 type or 2 or more types. Among these, glycerin is preferred from the viewpoint of the elongation-enhancing effect.

The content of the plasticizer in the PVA film is preferably in the range of 1 to 20 parts by mass, more preferably in the range of 3 to 17 parts by mass, and even more preferably in the range of 5 to 15 parts by mass relative to 100 parts by mass of PVA(A). within the range of parts by mass. When this content is 1 mass part or more, the extensibility of a film can be improved more. On the other hand, when this content is 20 mass parts or less, it can suppress that a film becomes too soft and the handling property falls.

PVA film, if necessary, can be properly blended with fillers, copper compounds and other processing stabilizers, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, and other thermoplastic resins , Lubricants, fragrances, defoamers, deodorants, extenders, stripping agents, release agents, reinforcing agents, crosslinking agents, antifungal agents, preservatives, crystallization speed retarders and other additives.

The ratio of the total of PVA(A) and the plasticizer in the PVA film is preferably at least 80% by mass, more preferably at least 90% by mass, and still more preferably at least 95% by mass, based on the mass of the PVA film.

The swelling degree of the PVA film is preferably in the range of 160-240%, more preferably in the range of 170-230%, particularly preferably in the range of 180-220%. With a swelling degree of 160% or more, crystallization can be extremely inhibited, and stable extension to high magnification can be achieved. On the other hand, when the degree of swelling is 240% or less, dissolution during stretching can be suppressed, and stretching can be performed even at a higher temperature. The degree of swelling of the PVA film can be determined by the method described in Examples described later.

The thickness of the PVA film is preferably 5-100 μm, more preferably 5-60 μm, particularly preferably about 10-45 μm. When the thickness is too thin, stretch fracture tends to easily occur during a stretching process such as uniaxial stretching for producing a polarizing film. Moreover, when this thickness is too thick, the shrinkage force of a polarizing film may become too large.

The width of the PVA film is not particularly limited, and can be determined according to the application of the manufactured polarizing film. From the viewpoint of increasing the size of liquid crystal televisions and liquid crystal monitors in recent years, if the width of the PVA film used to manufacture the polarizing film is 3 m or more, it is suitable for these applications. On the other hand, if the width of the PVA film used to make the polarizing film becomes too large, it is easy to become difficult to uniformly uniaxially stretch the polarizing film when the polarizing film is made by a practical device. Therefore, the PVA film used to make the polarizing film The width of the film is preferably 7 m or less.

The manufacturing method of PVA thin film is not particularly limited, preferably can adopt the thickness of the thin film after film making and the manufacturing method of wide uniformity, for example, can use the above-mentioned PVA (A ), and if necessary, further dissolve one or two or more of the above-mentioned plasticizers, additives, and surfactants described below, or contain PVA (A), and if necessary, further contain plastic One or two or more of chemical agents, additives, surfactants, and liquid media, etc., and PVA (A) are produced by melting the film-forming stock solution. When the film-forming stock solution contains at least one of a plasticizer, an additive, and a surfactant, it is preferable that these components are uniformly mixed.

As the above-mentioned liquid medium used in the preparation of the membrane-forming stock solution, for example, water, dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, Alcohol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and one or more of these can be used 2 or more. Of these, water is preferred from the viewpoint of environmental load and recyclability.

The volatile content of the film-forming stock solution (the proportion of volatile components in the film-forming stock solution that are removed by volatilization or evaporation during film forming) varies depending on the film-forming method, film-forming conditions, etc., but Generally, it is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass. Since the volatile content of the film-forming stock solution is more than 50% by mass, the viscosity of the film-forming stock solution will not become too high, and the filtration or defoaming during the preparation of the film-forming stock solution can be smoothly performed, and the PVA film with less foreign matter or defects Manufacturing made easy. On the other hand, since the volatile content of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and industrial production of PVA films becomes easy.

The membrane-forming stock solution preferably contains a surfactant. By including the surfactant, the film-forming property is improved, and the occurrence of uneven thickness of the PVA film can be suppressed, and at the same time, the PVA film can be easily peeled off from the metal roll or belt used for film-forming. When producing a PVA film from a film-forming stock solution containing a surfactant, the PVA film may contain a surfactant. The type of the above-mentioned surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferred from the viewpoint of peelability from a metal roll or a belt.

As the anionic surfactant, for example, carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate are suitable.

As nonionic surfactants, for example: alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octylphenyl ether; alkyl ester type such as polyoxyethylene laurate; polyoxyethylene lauryl Alkylamine type such as amine ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanol such as lauric acid diethanolamide and oleic acid diethanolamide Amide type; allyl phenyl ether type such as polyoxyallyl phenyl ether, etc. are suitable.

These surfactants may be used alone or in combination of two or more.

When the film-forming stock solution contains a surfactant, its content is preferably in the range of 0.01 to 0.5 parts by mass, more preferably in the range of 0.02 to 0.3 parts by mass, relative to 100 parts by mass of PVA (A) contained in the film-forming stock solution within, particularly preferably within the range of 0.05 to 0.2 parts by mass. When this content is 0.01 mass part or more, film-forming property and peelability are improved more. On the other hand, when the content is 0.5 parts by mass or less, the surface active agent overflows on the surface of the PVA film to cause sticking, and a decrease in handling properties can be suppressed.

As a film-forming method of using the above-mentioned film-forming stock solution to perform film-forming of a PVA film used to manufacture a polarizing film, for example, a casting film-forming method, an extrusion film-forming method, a wet-type film-forming method, a condensation film-forming method, etc. Glue film method, etc. These film-forming methods may be used alone or in combination of two or more. Among these film forming methods, the casting film forming method and the extrusion film forming method are preferable from the viewpoint of obtaining a PVA film used for producing a polarizing film having uniform thickness and width and good physical properties. The formed PVA film can be dried or heat-treated as needed.

As an example of the specific manufacturing method of the PVA film, it is preferable to adopt in the industry, for example: use a T-shaped slot die, a hopper plate, an I-type die, a lip-shaped coating machine die, etc., to spit out the above-mentioned film-making stock solution evenly or Casting on the peripheral surface of the heated first roll (or belt) in rotation at the uppermost side, and from one side of the film discharged or cast on the peripheral surface of the first roll (or belt) The surface is dried by evaporating the volatile components, and then further dried on the peripheral surface of the heated roller arranged in one or more rotations on the downstream side, or passed through a hot air drying device for further drying , A method of coiling by a coiling device. Drying with a heated roll and drying with a hot air drying device can also be implemented in combination as appropriate. In addition, a layer containing PVA (A) may be formed on one surface of a base film composed of a single resin layer, thereby forming a multilayer PVA film.

The manufacturing method of the polarizing film of the present invention is not particularly limited. A suitable manufacturing method is a manufacturing method of a polarizing film, which is a method of manufacturing a polarizing film comprising dyeing a PVA film with a dichroic pigment, and stretching the film in a uniaxial stretching process, wherein the source The stretched PVA film with a boron element content of 0.5-5.0% by mass of boric acid is dipped in an aqueous solution having a boron-containing compound (B) concentration of 0.1-5.0% by mass, and then dried at 95°C or lower. For the PVA film used in the production of the polarizing film of the present invention, dyeing treatment, stretching treatment, and further swelling treatment, boric acid crosslinking treatment, fixation treatment, cleaning treatment, heat treatment, etc. are given as necessary. At this time, the order of each treatment is not particularly limited, but it is preferably performed in the order of swelling treatment, boric acid crosslinking treatment, stretching treatment, and immobilization treatment. Also, the dyeing treatment is preferably performed before the boric acid crosslinking treatment. Furthermore, one or two or more treatments may be performed simultaneously, or one or two or more treatments may be performed twice or more.

The swelling treatment can be performed by immersing the PVA film in water. The temperature of the water when immersed in water is preferably 20 to 40°C, more preferably 22 to 38°C, and particularly preferably 25 to 35°C. Moreover, as time for immersing in water, for example, 0.1 to 5 minutes are preferable, and 0.2 to 3 minutes are more preferable. In addition, the water at the time of immersion in water is not limited to pure water, and may be: potassium iodide, calcium iodide, zinc chloride, sodium sulfate and other iodides and salt components, or carboxylic acid types such as potassium laurate; polyoxyethylene Sulfate ester type such as lauryl ether sulfate and octyl sulfate; sulfonic acid type anionic surfactants such as dodecylbenzenesulfonate, or alkyl ether type such as polyoxyethylene oleyl ether; polyoxyethylene octylphenyl ether, etc. Alkylphenyl ether type; Alkyl ester type such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene laurylamine ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polyoxyethylene polyoxypropylene ether Such as polypropylene glycol ether type; lauric acid diethanolamide, oleic acid diethanolamide and other alkanolamide type; polyoxyalkylene allyl phenyl ether and other allyl phenyl ether type non-ionic surfactants, etc. The aqueous solution in which the active ingredient is dissolved can also be mixed with dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, Mixture of aqueous media such as ethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane or its structural isomers.

The dyeing process can be performed by bringing a dichroic dye into contact with the PVA film. As a dichroic dye, an iodine-based dye or a dichroic dye is generally used. The dyeing process can be carried out at any stage before stretching treatment, during stretching treatment, and after stretching treatment, but from efficiently adsorbing the dichroic dye to the PVA film to efficiently adsorbing the dichroic dye to the PVA film. From the viewpoint of alignment, it is preferable to perform the dyeing treatment after the swelling treatment and before the stretching treatment. The dyeing process is generally carried out by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide as a dyeing bath, or a solution (especially an aqueous solution) containing a plurality of dichroic dyes. In the case of a solution containing iodine-potassium iodide, the concentration of iodine in the dyeing bath is preferably from 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably from 0.01 to 10% by mass. Moreover, it is preferable to set the temperature of a dyeing bath as 20-50 degreeC, and it is especially preferable to set it as 25-40 degreeC. The suitable dyeing time is 0.2~5 minutes. When a dichroic dye is used, the dichroic dye is preferably an aqueous dye. Moreover, it is preferable that the dye concentration in a dyeing bath is 0.001-10 mass %. Moreover, dyeing auxiliaries can be used as needed, and inorganic salts, such as sodium sulfate, surfactant, etc. can also be used. When sodium sulfate is used, it is preferably 0.1 to 10% by mass. The dyeing temperature is preferably 30~80°C. Specific dichroic dyes include C.I. Direct Yellow 28, C.I. Direct Orange 39, C.I. Direct Yellow 12, C.I. Direct Yellow 44, C.I. Direct Orange 26, C.I. Direct Orange 71, C.I. Direct Orange 107, and C.I. Direct Red 2. , C.I. Direct Red 31, C.I. Direct Red 79, C.I. Direct Red 81, C.I. Direct Red 247, C.I. Direct Green 80, C.I. Direct Green 59, etc., but dichroic dyes developed for the manufacture of polarizing plates are preferred.

By subjecting the PVA film to the boric acid cross-linking treatment, it is possible to effectively prevent the PVA (A) or the dichroic dye adsorbed on the PVA film from being eluted into water during wet stretching at high temperature. From this point of view, the boric acid crosslinking treatment is more preferably performed after the dyeing treatment and before the stretching treatment. The boric acid crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, one or more boron-containing inorganic compounds such as boric acid and borate such as borax can be used. From the viewpoint of ease of handling, the boric acid crosslinking agent is preferably boric acid. The concentration of the boric acid crosslinking agent in the aqueous solution containing the boric acid crosslinking agent is preferably 1 to 10% by mass, more preferably 2 to 7% by mass. Sufficient extensibility can be maintained when the concentration of the boric acid crosslinking agent is 1-10% by mass. When the concentration of the boric acid crosslinking agent exceeds 10% by mass, the crosslinking proceeds excessively and the extensibility decreases, which is not preferable. Also, when the concentration of the boric acid crosslinking agent is less than 1% by mass, the effect of preventing PVA (A) or the dichroic dye adsorbed on the PVA film from elution into water during stretching at high temperature becomes insufficient, which is not preferable. The aqueous solution containing boric acid crosslinking agent may also contain additives such as potassium iodide. The temperature of the aqueous solution containing the boric acid crosslinking agent is preferably 20-50°C, particularly preferably 25-40°C. By making this temperature 20-50 degreeC, boric-acid crosslinking can be performed efficiently.

Different from the stretching treatment described later, the PVA film can also be stretched (pre-stretched) during or between the above-mentioned treatments. As mentioned above, the total stretching ratio of the pre-stretching performed before the stretching treatment (the ratio obtained by multiplying the stretching ratios in each treatment) is based on the pre-stretching ratio from the viewpoint of the polarizing performance of the obtained polarizing film. Based on the original length of the PVA film as the raw material, it is preferably more than 1.5 times, more preferably more than 2.0 times, and more preferably more than 2.5 times. On the other hand, the total elongation ratio is preferably at most 4.0 times, more preferably at most 3.5 times. The elongation ratio in the swelling treatment is preferably 1.05 to 2.5 times. The elongation ratio in the dyeing process is preferably 1.1 to 2.5 times. The elongation ratio in the boron crosslinking treatment is preferably 1.1 to 2.5.

The stretching treatment can be performed by either a wet stretching method or a dry stretching method. In the case of a wet drawing method, it may be performed in an aqueous solution containing a boric acid crosslinking agent, or may be performed in the above-mentioned dyeing treatment bath. In addition, in the case of the dry stretching method, the uniaxial stretching treatment may be performed at room temperature, the uniaxial stretching treatment may be performed while heating, or the uniaxial stretching treatment may be performed in air using a water-absorbed PVA film. Among them, the wet stretching method is preferable, and the uniaxial stretching treatment in an aqueous solution containing a boric acid crosslinking agent is particularly preferable. From the viewpoint of ease of handling, the boric acid crosslinking agent is preferably boric acid. The concentration of boric acid in the aforementioned aqueous solution is preferably 0.5 to 5% by mass, more preferably 2 to 5% by mass. When the concentration of boric acid is less than 0.5% by mass, the content of boric acid in the PVA film becomes too small, and when the stretched PVA film is immersed in an aqueous solution of the boron-containing compound (B), the boron-containing compound (B) will be excessive. adsorption, the polarizing film becomes brittle. On the other hand, when the boric acid concentration exceeds 5% by mass, the boric acid content in the PVA film becomes too much, and when the stretched PVA film is immersed in an aqueous solution of the boron-containing compound (B), the boric acid will excessively hinder the boron-containing compound (B). Adsorption of compound (B). The boric acid aqueous solution may also contain potassium iodide, and the concentration of potassium iodide is preferably 0.01 to 10% by mass. The stretching temperature in the stretching treatment is preferably 30-90°C. The temperature is more preferably at least 40°C, even more preferably at least 50°C. On the other hand, the aforementioned temperature is more preferably not higher than 80°C, further preferably not higher than 70°C. In addition, the stretching ratio in the stretching treatment (total stretching ratio from the raw PVA film) is preferably 2.0 to 4.0 times. From the viewpoint of the polarizing performance of the obtained polarizing film, etc., the elongation ratio is more preferably 2.2 times or more. On the other hand, the elongation ratio is more preferably 3.5 times or less. In addition, from the viewpoint of polarizing performance, the total stretching ratio before the fixing treatment described later is preferably 5 times or more, more preferably 5.5 times or more. The upper limit of the elongation ratio is not particularly limited, but the elongation ratio is preferably 8 times or less.

The direction of the uniaxial stretching treatment in the case of stretching the elongated PVA film is not particularly limited, and the uniaxial stretching process to the elongated direction, the horizontal uniaxial stretching process, or the so-called oblique stretching process can be used, but from From the viewpoint of obtaining a polarizing film excellent in polarizing performance, uniaxial stretching in the longitudinal direction is preferred. Uniaxial stretching in the longitudinal direction can be performed by using a stretching device with a plurality of rollers parallel to each other and changing the peripheral speed between the rollers. On the other hand, the horizontal uniaxial stretching treatment can be performed using a tenter type stretching machine.

When producing a polarizing film, in order to strengthen the adsorption of dichroic dyes (iodine-based dyes, dichroic dyes, etc.) to the PVA film, it is preferable to perform a fixation process after stretching. As the fixation treatment bath used for the fixation treatment, an aqueous solution containing a boron-containing compound (B) is preferable. Also, boric acid, iodine, iodide, metal compounds, etc. may be added to the fixed treatment bath if necessary, and iodides such as potassium iodide are preferably added. The temperature of the fixed treatment bath is preferably 10-70°C, more preferably 20-40°C. As for iodide, it is preferable to add 0.5-10 mass %. The elongation ratio in the fixation treatment is preferably at most 1.3 times, more preferably at most 1.2 times, and still more preferably less than 1.1 times.

The boron-containing compound (B) is adsorbed on the stretched PVA film. If the boron-containing compound (B) is adsorbed before or during the stretching treatment, a large amount of the boron-containing compound (B) will be adsorbed to the center of the polarizing film, and the hue may be deteriorated. In addition, there is a possibility that intermolecular crosslinking becomes excessive and elongation may decrease. The boron-containing compound (B) can be adsorbed on the PVA film in any step of the dyeing treatment, boric acid cross-linking treatment, and fixation treatment as long as it is a step after the stretching treatment, but it never deteriorates the hue or the viewpoint of stretching For this purpose, it is preferable to perform adsorption in the immobilization process. Specifically, it is preferable to adsorb the boron-containing compound (B) on the PVA film by immersing the PVA film in an aqueous solution having a concentration of the boron-containing compound (B) of 0.1 to 5.0% by mass.

When the concentration of the boron-containing compound (B) in the aforementioned aqueous solution is less than 0.1% by mass, there is a possibility that the hue may deteriorate or the effect of reducing the contraction force may not be sufficient. The concentration is more preferably at least 0.2% by mass, and still more preferably at least 0.3% by mass. On the other hand, when the concentration exceeds 5.0% by mass, the boron-containing compound (B) is excessively adsorbed, and the surface of the polarizing film becomes brittle or precipitates of the boron-containing compound (B) are generated on the surface. The aforementioned concentration is more preferably 4% by mass or less. Also, the temperature of the aforementioned aqueous solution is preferably 10 to 70°C. When the temperature is lower than 10°C, there is a possibility that the boron-containing compound (B) may precipitate in the treatment bath. This temperature is more preferably 20° C. or higher. On the other hand, when the said temperature exceeds 70 degreeC, there exists a possibility that wrinkles may become easy to generate|occur|produce in a polarizing film. The aforementioned temperature is more preferably not higher than 60°C, still more preferably not higher than 50°C, and most preferably not higher than 40°C. The time for immersion in the aqueous solution is preferably 5 to 400 seconds. From the viewpoint of improving polarizing performance, the aforementioned aqueous solution preferably contains iodide such as potassium iodide as an auxiliary agent, and the content thereof is preferably 0.5-10% by mass.

The content of the boron element derived from boric acid in the PVA film used for the adsorption of the boron-containing compound (B) must be 0.5 to 5.0% by mass. Thereby, the concentration of the boron-containing compound (B) in the thickness direction of the polarizing film can be adjusted, and the boron element concentration (α) and the boron element concentration (β) derived from the boron-containing compound (B) can be set within the above range . The boric acid in the PVA film properly hinders the adsorption of the boron-containing compound (B), so that the boron-containing compound (B) is easily adsorbed near the surface of the polarizing film and difficult to be adsorbed at the center. When the content of boron element derived from boric acid in the PVA film is less than 0.5% by mass, when the PVA film is immersed in the aqueous solution of the boron-containing compound (B), the boron-containing compound (B) is excessively adsorbed, and the hue is deteriorated or polarized. The surface of the film becomes too hard and becomes brittle. The aforementioned content is preferably at least 1% by mass. On the other hand, when the said content exceeds 5.0 mass %, when a PVA film is immersed in the aqueous solution of a boron-containing compound (B), there exists a possibility that adsorption of a boron-containing compound (B) may be inhibited excessively. Furthermore, the boron content in the PVA film derived from boric acid can be adjusted according to the temperature of the treatment bath, the concentration of boric acid, and the immersion time during the stretching treatment or the boric acid crosslinking treatment.

The content of the boron-containing compound (B) in the polarizing film can be controlled by adjusting the concentration of the boron-containing compound (B) in the aqueous solution in the fixing process, the temperature of the aqueous solution, or the immersion time of the aqueous solution, but adjusting the temperature or immersion Since there is a possibility of wrinkling in the polarizing film, it is preferable to adjust the concentration of the boron-containing compound (B).

Washing treatment may also be performed prior to drying treatment. The cleaning treatment is generally carried out by immersing the PVA film in water, distilled water, pure water, or the like. At this time, from the viewpoint of improving polarizing performance, the aqueous solution used for cleaning treatment preferably contains iodide such as potassium iodide, and the concentration of iodide is preferably 0.5 to 10% by mass. Also, the temperature of the aqueous solution in the cleaning treatment is generally 5 to 50°C, preferably 10 to 45°C, particularly preferably 10 to 40°C. From an economic point of view, it is not preferable that the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, the polarizing performance will be lowered, so it is not preferable.

After the PVA film is immersed in the aqueous solution of the boron-containing compound (B), drying treatment is performed to dry the film at 95° C. or lower. When the drying temperature exceeds 95°C, the hue may deteriorate. The temperature is preferably not higher than 90°C, more preferably not higher than 80°C. On the other hand, when the drying temperature is lower than 40° C., the shrinkage force tends to be high, which is not preferable. This temperature is preferably 50°C or higher. The drying time is preferably 10 to 600 seconds.

By performing heat treatment after drying treatment, a polarizing film having more excellent dimensional stability can be obtained. Here, the heat treatment is a process of further heating the dried polarizing film having a moisture content of 5% or less to improve the dimensional stability of the polarizing film. The heat treatment conditions are not particularly limited, and the heat treatment temperature is preferably 60°C to 95°C, particularly preferably 70°C to 90°C. If the heat treatment is performed at a lower temperature than 60°C, the effect of improving the dimensional stability due to the heat treatment is not sufficient, so it is not good. If the heat treatment is performed at a higher temperature than 95°C, sometimes the polarizing film will be strongly reddened, so less favorable.

The polarizing film obtained as above is usually used as a polarizing plate by bonding an optically transparent protective film having mechanical strength to both surfaces or one surface thereof. As the protective film, cellulose triacetate (TAC) film, cellulose acetate-butyrate (CAB) film, acrylic film, polyester film, etc. are used. Moreover, as an adhesive agent for bonding, a PVA type adhesive agent, an ultraviolet curing type adhesive agent, etc. are mentioned, Among them, a PVA type adhesive agent is preferable.

The polarizing plate obtained as described above can be bonded to a glass substrate after applying an adhesive such as an acrylic system, and can be used as a component of an LCD. At the same time, it can also be laminated with retardation film, viewing angle improvement film, luminance improvement film, etc.

[Example]

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, each measurement or evaluation method used in the following examples and comparative examples is shown below.

[Optical properties of polarizing film]

From the central part of the width direction and the length direction of the polarizing film, take a rectangular sample of 4 cm in the length direction x 2 cm in the width direction of the polarizing film, and use a spectrophotometer V-7100 (manufactured by JASCO Co., Ltd.) with an integrating sphere and An automatic polarizing film measuring device VAP-7070S (manufactured by JASCO Corporation) equipped with a Glan-Taylor polarizer was used to measure the parallel transmittance and crossed Nicolium transmittance of the polarizing film. Furthermore, the measurement wavelength range is set at 380nm~780nm, and the transmittance when the vibration direction of the polarized light incident on the polarizing film through the Glan-Taylor polarizer is parallel to the transmission axis of the polarizing film is defined as the parallel transmittance, The case perpendicular to the transmission axis of the polarizing film is defined as the crossed Nicolium transmittance. After that, use the "Polarizing Film Evaluation Program" (manufactured by JASCO Co., Ltd.), according to JIS Z 8722 (measurement method of object color), perform C light source, visibility correction in the visible light region of 2° field of view, and perform polarizing film Single-body transmittance, degree of polarization, and single-body b value (hue) are calculated, and these three values are obtained as optical characteristics of the polarizing film.

[Contraction force]

Contraction force was measured using Autograph "AG-X" with constant temperature bath and video extensometer "TR ViewX120S" manufactured by Shimadzu Corporation. The measurement system used a polarizing film that was conditioned at about 20°C/20%RH for 18 hours. After setting the constant temperature bath of Autograph "AG-X" at 20°C, install the polarizing film (15cm in the longitudinal direction and 1.5cm in the widthwise direction) on the clamps (5cm between the clamps), and start stretching at 10°C/min. The heating rate starts to raise the temperature of the constant temperature bath to 80°C. The polarizing film was stretched at a rate of 1 mm/min, and the stretching was stopped when the tension reached 2N, and the tension was measured until 4 hours later in this state. At this time, the distance between the grippers will be changed due to thermal expansion, so stick marking stickers on the upper and lower grippers, and move the marking stickers while keeping the distance between the grippers constant using the video extensometer "TR ViewX120S" The amount is corrected while performing the measurement. In addition, when the minimum value of the tension occurs at the initial stage of the measurement (within 10 minutes from the start of the measurement), the minimum value is subtracted from the measured value of the tension after 4 hours, and this value is regarded as the shrinkage force of the polarizing film.

[Concentration of boron element derived from boron-containing compound (B)]

Using an X-ray photoelectron spectrometer (manufactured by ULVAC-PHI Co., Ltd.: PHI5000 VersaProbe II) (GCIB-XPS) with a gas cluster ion beam gun, the concentration of boron element derived from the boron-containing compound (B) in the polarizing film was measured . The measurement system used a polarizing film that was conditioned at about 23°C/50%RH for 16 hours. While neutralizing with the conditions of sputtering ion source Ar2500 ⁺ , accelerating voltage 20keV, and current value 30nA, sputtering was carried out in the range of 2mm×2mm, and every time the sputtering was 50nm in the depth direction, X-ray photoelectron spectroscopy was carried out ( XPS assay). XPS measurement is carried out using monochromatic Al in the X-ray source, the X-ray spot diameter is 100 μm, the X-ray output is 15kV, 25W, and the detection elements are selected from 5 kinds of carbon, boron, oxygen, iodine, and potassium. Furthermore, when a dichroic dye is used as the dichroic dye, elements such as nitrogen and sulfur contained in the dichroic dye must also be appropriately selected as detection elements. Next, use the analysis software "MultiPack" (manufactured by ULVAC-PHI Co., Ltd.) to calculate the boron element concentration (a, atomic %) at each depth of the polarizing film based on 284.8eV, which is the bonding energy of CC and CH bonds. . Then, with respect to the XPS spectrum at each depth, using the table calculation software "Microsoft 2010" (manufactured by Microsoft Corporation), the bonding energy of boron derived from boric acid 192.3eV, and the boron derived from boron-containing compound (B) were set appropriately. The bonding energy of , and using the quasi-Voigt function, the peak separation is performed by the least squares method. In addition, a linear function calculated from the average value of the intensity of the XPS spectrum from 187 to 189 eV and the average value of the XPS spectrum from 195 to 197 eV was used as a baseline. As described above, the peak area ratio (b, %) of boron derived from boron-containing compound (B) relative to the total of boron derived from boric acid and boron-containing compound (B) was calculated, and substituted into the following calculation The formula (1) is used to calculate the concentration of boron element derived from the boron-containing compound (B) in each depth.

Concentration of boron element derived from boron-containing compound (B) (atomic %)=a×b×10 ^-2 (1)

In addition, the bonding energy of boron originating in the boron-containing compound (B) changes according to the structure of the compound. Therefore, it is necessary to appropriately set the aforementioned bonding energy according to the type of the boron-containing compound (B). For example, when the boron-containing compound (B) is 1,4-butanediboronic acid, it is 191.3 eV. Also, when performing peak separation by the least squares method using the pseudo-Voigt function, the Lorentzian function ratio of boric acid was set to 0.115, and ^{2 1/2} ×σ was set to 0.809. In addition, the Lorentzian function ratio and the half-width of the boron-containing compound (B) also vary depending on the structure of the compound. Therefore, depending on the type of the compound, it is necessary to appropriately set the Lorentz function ratio and 2 ^1/2 ×σ. When the boron-containing compound (B) is 1,4-butanediboronic acid, the Lorentzian function ratio is set to 0.263, and ^{2 1/2} ×σ is set to 0.797.

By the method as mentioned above, for both sides of the polarizing film, the concentration of boron element derived from the boron-containing compound (B) is obtained every 1 μm to 50 nm from the surface to the inner side, and the average value is taken as the surface of the polarizing film. The boron element concentration (α, atomic %) derived from the boron-containing compound (B) within the range of 1 μm inside. In addition, for every 1 μm to 50 nm from the center of the polarizing film to the outer sides, the concentration of boron element derived from the boron-containing compound (B) was obtained, and the average value was used as the source of the range of 1 μm from the center of the polarizing film to the outer sides The boron element concentration (β, atomic %) of the self-boron-containing compound (B).

[Content of boron element derived from boron-containing compound (B) relative to 100 parts by mass of PVA (A)]

A polarizing film conditioned at 23° C./50% RH for 16 hours was dissolved in heavy water to about 0.003% by mass, and then concentrated to a solution of about 0.15% by mass by a rotary evaporator, which was used as a ¹ H-NMR measurement sample. ¹ H-NMR (JNM-AL400 manufactured by JEOL Ltd.: 400 MHz) was measured at 80° C., and analyzed by the following method using ALICE2 (manufactured by JEOL Ltd.). For the ¹ H-NMR spectrum obtained by the measurement, the phase was adjusted to smooth the baseline, and the average point was set to 20 to automatically correct the baseline. Next, as a reference, it is automatically set to a position where the peak value of heavy water, which is the measurement medium, becomes 4.65 ppm. Afterwards, as shown in Fig. 1, the hydrogen peaks of the hydrocarbon groups contained in the boron-containing compound (B) are integrated, and the peak areas are calculated. At this time, the sum of the hydrogen peak areas (area c) of the hydrocarbon groups contained in the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA (A) is set as the basis of the peak area, and is set to contain The hydrogen number of the corresponding hydrocarbon of the boron compound (B) is the same as the value of the area c. Next, the hydrogen peak in the range of 1.7ppm to 2.4ppm is regarded as the hydrogen peak derived from the methylene group of PVA(A) and the boron-containing compound overlapping with the hydrogen peak derived from the methylene group of PVA(A) (B) The sum of the hydrogen peaks of the contained hydrocarbon groups is calculated, and the peak area (area d) is obtained. Then, the area e was calculated by subtracting the hydrogen number of the boron-containing compound (B) which overlapped with the hydrogen peak derived from the methylene group of PVA (A) from the area d. The numerical value obtained by these methods was substituted into the following formula, and the content of the boron element originating in the boron-containing compound (B) with respect to 100 mass parts of PVA (A) was calculated. In addition, X and Y in the following formula (2) are respectively the hydrogen number of the hydrocarbon group contained in the boron-containing compound (B) that does not overlap with the peak of PVA, and the boron per molecule of the boron-containing compound (B) number. In addition, formula (2) is a formula used when unmodified PVA is used, but when modified PVA is used as a raw material, formula (2) must be modified suitably.

Boron element content (parts by mass) derived from boron-containing compound (B)={(area c/X)/(area e/2)}×{(10.811×Y)/44.0526}×100 (2)

In the formula (2), 10.811 is the atomic weight of boron, and 44.0526 is the molecular weight per 1 mole of repeating units of unmodified PVA. For example, the ¹ H-NMR spectrum in Figure 1 is for the determination of the polarizing film of Example 1, and the content of boron element derived from the boron-containing compound (B) relative to 100 parts by mass of PVA is unconditionally rounded up to the second place of the decimal point. 0.5 parts by mass.

[Total boron content in polarizing film]

The mass f (g) of the polarizing film adjusted at about 23° C./50% RH for 16 hours was measured, and the polarizing film was dissolved in about 20 mL of distilled water at about 0.005% by mass. The aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and its mass g (g) was measured. Thereafter, the boron concentration h (ppm) of the measurement sample was measured using a polymorphic ICP emission analyzer manufactured by Shimadzu Corporation. Then, the numerical value calculated by substituting a numerical value into following formula (3) was made into the total boron element content (mass %) in a polarizing film.

Total boron content in polarizing film (mass%)=[(h×10 ^-6 ×g)/f]×100 (3)

[Content of boron element derived from boric acid in the stretched PVA film]

Take the PVA film after the stretching treatment and before the fixing treatment, dry it, and adjust the humidity at 23°C/50%RH for 16 hours, measure the mass i (g), and dissolve the PVA film so that the content of the PVA film is about 0.005% by mass In distilled water about 20mL. The obtained aqueous solution was used as a measurement sample, and its mass j (g) was measured. Thereafter, the boron concentration k (ppm) of the measurement sample was measured using a polymorphic ICP emission analyzer manufactured by Shimadzu Corporation. Then, the value calculated by substituting the value in the following formula (4) was defined as the boron element content (% by mass) derived from boric acid in the PVA film after the stretching treatment and before the fixing treatment.

Content of boron element derived from boric acid in PVA film (mass%)=[(k×10 ^-6 ×j)/i]×100 (4)

[Swelling degree of PVA film]

The PVA film was cut into 5 cm×10 cm, and immersed in 1000 mL of distilled water at 30° C. for 30 minutes. Thereafter, the PVA film was taken out, and the moisture on the surface of the PVA film was wiped with filter paper to measure the quality of the PVA film after immersion (mass 1). Thereafter, the PVA film was placed in a dryer at 105° C. and dried for 16 hours, and then the mass (mass m) of the PVA film after drying was measured. The degree of swelling of the PVA film was calculated by substituting the numerical values of mass 1 and mass m in the following formula (5).

Swelling degree (%)=(mass 1/mass m)×100 (5)

[Example 1]

Prepare 100 parts by mass of PVA (saponification degree 99.9%, polymerization degree 2400), 10 parts by mass of glycerol as a plasticizer, and 0.1 part by mass of polyoxyethylene lauryl ether sulfate as a surfactant, and the content of PVA It is a 10% by mass PVA aqueous solution. The film obtained by drying the above-mentioned PVA aqueous solution on a metal roller at 80°C was heat-treated in a hot air dryer (120°C) for 10 minutes to obtain a PVA film with a thickness of 30 μm and a swelling degree of 200%.

A sample of width 5 cm x length 9 cm was cut out from the central part in the width direction of the obtained PVA film so that the range of width 5 cm x length 5 cm could be uniaxially stretched. This sample was dipped in pure water at 30° C. for 30 seconds while being uniaxially stretched 1.1 times in the longitudinal direction to perform swelling treatment. Next, immerse in an aqueous solution (dyeing treatment bath) (temperature 30° C.) containing 0.035% by mass of iodine and 3.5% by mass of potassium iodide for 60 seconds while uniaxially stretching 2.2 times (2.4 times as a whole) in the longitudinal direction to absorb iodine. . Next, while dipping in an aqueous solution containing 3.0% by mass of boric acid and 3% by mass of potassium iodide (boric acid crosslinking treatment bath) (temperature 30°C), uniaxially stretched 1.2 times (2.7 times as a whole) in the longitudinal direction. And dipped in a 60° C. aqueous solution (stretching treatment bath) containing 4.0% by mass of boric acid and 6% by mass of potassium iodide, while performing uniaxial stretching in the longitudinal direction to 6.0 times as a whole. After the uniaxial stretching treatment, immerse in an aqueous solution (fixed treatment bath) (temperature 30° C.) containing 0.5 mass % of 1,4-butanediboronic acid and 2.5 mass % of potassium iodide as the boron-containing compound (B) for 100 seconds . In the fixing process, the PVA film was not stretched (stretching ratio 1.0 times). Finally, it was dried at 60° C. for 240 seconds to produce a polarizing film (thickness 13 μm).

After the stretching treatment, a uniaxially stretched film produced by drying without fixing treatment was carried out, and ICP measurement was performed. As a result, the content of boron element derived from boric acid in the film was 4.5% by mass.

The XPS spectrum of the polarizing film was measured and analyzed. As a result, the boron element concentration (α) derived from the boron-containing compound (B) within 1 μm from the surface of the polarizing film was 5.0 atomic %, and 1 μm from the center of the polarizing film The boron element concentration (β) derived from the boron-containing compound (B) is 0.7 atomic %.

As a result of measuring and analyzing the ¹ H-NMR of the polarizing film, the boron element content derived from the boron-containing compound (B) was 0.5 parts by mass relative to 100 parts by mass of PVA.

The ICP measurement of the polarizing film was carried out. As a result, the total boron element content in the polarizing film was 2.5% by mass.

Using the polarizing film, the optical properties and shrinkage force of the polarizing film were evaluated by the above method. As a result, the transmittance of the polarizing film was 43.96%, the degree of polarization was 99.93%, the b value (hue) of the monomer was 2.1, and the shrinkage force was 6.1N. Table 1 shows the above results.

[Example 2]

A solution containing 0.5% by mass of 1,2-ethanediboronic acid and 4% by mass of potassium iodide (at a temperature of 30° C.) was used in the fixed treatment bath, except that it was carried out in the same manner as in Example 1 to prepare a polarizing film, and each measurement and evaluation. The results are shown in Table 1.

[Example 3]

In the fixed treatment bath, an aqueous solution (temperature 30° C.) containing 0.3 mass % of 1,4-butanediboronic acid and 4 mass % of potassium iodide was used, except that it was carried out in the same manner as in Example 1 to prepare a polarizing film, and each measurement and evaluation. The results are shown in Table 1.

[Example 4]

A polarizing film was produced in the same manner as in Example 1 except that the time of immersion in the fixed treatment bath was changed to 10 seconds, and various measurements and evaluations were performed. The results are shown in Table 1.

[Example 5]

The concentration of boric acid in the stretching treatment bath was changed to 2.0% by mass, the temperature of the stretching treatment bath was changed to 58°C, and the time of immersion in the fixed treatment bath was changed to 10 seconds, except that it was performed in the same manner as in Example 1 to produce a polarizing film. , and carry out various measurements and evaluations. The results are shown in Table 1.

[Comparative example 1]

Using KR10-2014-0075154 as a reference, immerse in pure water at 30°C for 120 seconds, while performing uniaxial stretching in the longitudinal direction to 1.3 times the overall size, and performing swelling treatment. Next, while immersing in an aqueous solution (dyeing treatment bath) (temperature 30°C) containing 10 parts by mass of potassium iodide relative to 1 part by mass of iodine for 240 seconds, uniaxially stretching 1.1 times in the longitudinal direction (1.4 times as a whole) ), while dyeing. Next, uniaxially stretch 4.3 times in the longitudinal direction while dipping in a 50°C aqueous solution (stretching treatment bath) containing 0.5% by mass of 1,4-butanediboronic acid and 5% by mass of potassium iodide for 120 seconds (the overall 6.0 times). Then, it was immersed in 30 degreeC pure water (cleaning process bath) for 10 seconds. Finally, it was dried at 60° C. for 4 minutes to produce a polarizing film. Each measurement and evaluation were performed about the obtained polarizing film. The results are shown in Table 1.

[Comparative example 2]

Except changing the concentration of 1,4-butanediboronic acid in the stretching treatment bath to 0.2% by mass, it carried out in the same manner as in Comparative Example 1, and after producing a polarizing film, various measurements and evaluations were performed. The results are shown in Table 1.

[Comparative example 3]

As for the fixed treatment bath, an aqueous solution (temperature 30° C.) containing 2.0% by mass of boric acid and 3% by mass of potassium iodide was used, except that it was performed in the same manner as in Example 1 to prepare a polarizing film, and perform various measurements and evaluations. The results are shown in Table 1.

[Comparative example 4]

In the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 2.0% by mass of boric acid and 3% by mass of potassium iodide was used, and the time of immersion in the fixed treatment bath was changed to 10 seconds, except that it was the same as in Example 1. Then, a polarizing film was produced, and various measurements and evaluations were performed. The results are shown in Table 1.

[Comparative Example 5]

In terms of the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 1.0% by mass of boric acid and 3% by mass of potassium iodide was used, and the time of immersion in the fixed treatment bath was changed to 10 seconds, except that it was the same as in Example 2. Then, a polarizing film was produced, and various measurements and evaluations were performed. The results are shown in Table 1.

[Comparative Example 6]

In terms of the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 0.5% by mass of boric acid and 3% by mass of potassium iodide was used, and the time of immersion in the fixed treatment bath was changed to 10 seconds, except that it was the same as in Example 1. Then, a polarizing film was produced, and each measurement or evaluation was performed. The results are shown in Table 1.

[Comparative Example 7]

In terms of the fixed treatment bath, use an aqueous solution (30° C. at temperature) containing a ratio of 2% by mass of potassium iodide, and change the time of immersion in the fixed treatment bath to 20 seconds. In addition, it is performed in the same manner as in Example 1 to make a polarizing film. , and carry out various measurements and evaluations. The results are shown in Table 1.

[Comparative Example 8]

In the fixed treatment bath, use the aqueous solution (temperature 30°C) containing boric acid 2.0% by mass and potassium iodide 3% by mass, and change the drying temperature to 100°C, except that it is carried out in the same manner as in Example 1 to make a polarizing film, And each measurement and evaluation were performed. The results are shown in Table 1.

In addition, Examples 2 to 5 and Comparative Examples 3 to 8 were immersed in an aqueous solution (dyeing treatment bath) (at a temperature of 30° C.) of 100 parts by mass of potassium iodide relative to 1 part by mass of iodine in the same manner as in Example 1. Seconds, and at the same time uniaxially stretched 2.2 times (2.4 times as a whole) in the longitudinal direction to adsorb iodine. At this time, the concentration of iodine or potassium iodide in the dyeing treatment bath is adjusted so that the transmittance of the dried polarizing film becomes 43.8% to 44.2%. Comparative Examples 1 and 2 were dipped in an aqueous solution (dyeing treatment bath) (temperature 30° C.) containing 10 parts by mass of potassium iodide relative to 1 part by mass of iodine for 240 seconds, while performing uniaxial stretching 1.1 times in the longitudinal direction. (The whole is 1.4 times), so that iodine is adsorbed. At this time, the concentration of iodine or potassium iodide in the dyeing treatment bath is adjusted so that the transmittance of the dried polarizing film becomes 43.8% to 44.2%.

From the above results, it can be clearly known that the polarizing films of Examples 1 to 5 that meet the requirements of the present invention have a degree of polarization of 99.8% or more, and a monomer b value of 0 to 3. The optical properties of the polarizing film are excellent, and the shrinkage force is also less than 12N, low contraction force. On the other hand, Comparative Examples 1 and 2 in which the boron element concentration (β) derived from the boron-containing compound (B) exceeded 2% in the range of 1 μm from the center of the polarizing film had low shrinkage force but poor optical properties . Also, the polarizing films of Comparative Examples 3 to 8 that did not use the boron-containing compound (B) had high shrinkage (Comparative Examples 3 to 6), or insufficient optical properties (Comparative Examples 7 and 8), and could not be combined. With such.

Claims (5)

A polarizing film comprising polyvinyl alcohol (A), at least one selected from the group consisting of diboronic acid represented by the following formula (I) and a compound that can be converted into the diboronic acid in the presence of water The polarizing film of boron-containing compound (B) and boric acid (C), characterized in that: the boron element concentration (α) derived from boron-containing compound (B) in the range of 1 μm from the surface of the polarizing film to the inner side is 1~ 7 atomic %, the concentration (β) of the boron element derived from the boron-containing compound (B) in the range of 1 μm from the center to the outside is 0.1 to 2 atomic %, and the ratio of the concentration (α) to the concentration (β) (α /β) is more than 1.5, wherein, the boron element concentration (α) and the boron element concentration (β) in the polarizing film are obtained by using an X-ray photoelectron spectrometer with a gas cluster ion beam gun,

[In the formula (I), R1 is ^a divalent organic group with carbon numbers of ¹ to 20, and R1 is connected with two boronic acid groups by a boron-carbon bond]. The polarizing film according to claim 1, wherein the content of boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass relative to 100 parts by mass of polyvinyl alcohol (A). The polarizing film according to claim 1 or 2, wherein R ¹ is an aliphatic group. The polarizing film according to claim 1 or 2, wherein the total boron content in the polarizing film is 1.0-5.0% by mass. A manufacturing method of the polarizing film according to any one of claims 1 to 4 method, which is a method for producing a polarizing film comprising dyeing a polyvinyl alcohol film with a dichroic dye, and stretching the film in an aqueous solution of boric acid to uniaxially stretch it, wherein boron derived from boric acid The stretched polyvinyl alcohol film having an element content of 0.5-5.0% by mass is immersed in an aqueous solution having a boron-containing compound (B) concentration of 0.1-5.0% by mass, and then dried at 95°C or lower.

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