JP2006137078A - Polymer film and its production method, polarizing plate and liquid crystal display using the film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new polymer film which is excellent in optical characteristics and in adhesion to a polarizer and improved in tensile strength at break and a method for producing the film. <P>SOLUTION: The polymer film is obtained by molding a polymer solution comprising polyvinyl acetal, a crosslinking agent, and an organic solvent into a film by a solvent cast method. The polymer film obtained by crosslinking the polyvinyl acetal to the degree of crosslinking of 1-60% in a process for volatilizing the organic solvent in the polymer solution and/or a process after the polymer film is obtained and the method for producing the film are disclosed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a crosslinked polyvinyl acetal film and a method for producing the same, a polarizing plate using the polyvinyl acetal film as a protective film, and a liquid crystal display device using the polarizing plate.

Liquid crystal display devices are being replaced by CRTs with large screens, research and development for higher image quality, and cost reductions that meet market requirements. Along with this, with respect to the protective film of the polarizing plate constituting the liquid crystal display device, the light transmittance is improved, the birefringence is reduced, and the adhesion with the polarizer is improved (from the poor adhesion between the polarizer and the protective film). Reduction of defective product rate), improvement of film strength accompanying the reduction of the thickness of the protective film, and the like, and cellulose ester such as triacetate cellulose is used as the protective film (see, for example, Patent Document 1).
JP2004-131737

  The present invention provides a novel polymer film having excellent optical properties and adhesion to a polarizer, and improved tensile strength at break.

  The present inventors have found that when producing a polymer film by a solvent casting method, these problems can be solved by including a crosslinking agent in the polymer solution and causing the polymer to undergo a crosslinking reaction at a specific degree of crosslinking, The present invention has been completed.

  That is, the present invention is a polymer film obtained by forming a polymer solution comprising a polyvinyl acetal, a cross-linking agent and an organic solvent into a film by a solvent casting method, and volatilizing the organic solvent in the polymer solution And / or a polymer film obtained by crosslinking reaction of polyvinyl acetal to a crosslinking degree of 1 to 60% in a step after obtaining the polymer film, and a method for producing the polymer film. Moreover, this invention is a liquid crystal display device using the polarizing plate which used these polymer films as a protective film, and this polarizing plate.

  The film obtained by the production method of the present invention has the effect of being excellent in optical properties, adhesion to a polarizer, yield point strength and breaking strength.

  As the polymer in the present invention, polyvinyl acetal having an appropriate amount of hydroxyl groups in the molecule is used. Polyvinyl acetal is a polymer having a cyclic acetal structure obtained by reaction of polyvinyl alcohol and aldehydes.

  As a method for producing polyvinyl acetal, an aldehyde and an acid catalyst are added in a state where a polyvinyl alcohol aqueous solution obtained by dissolving polyvinyl alcohol in hot water is maintained at a predetermined temperature selected from a range of 0 to 95 ° C. A method of obtaining a powder polymer by advancing the acetalization reaction while stirring to form a cyclic acetal structure in the molecule, then raising the temperature and aging to complete the reaction, followed by neutralization, washing with water and drying There is. Also, powdered polyvinyl alcohol is dispersed in an organic solvent such as methanol or ethanol, and an acid catalyst and an aldehyde are added in a normal state maintained at a predetermined temperature selected from the range of 0 to 60 ° C., and acetalized with stirring. The reaction proceeds to a solution, and then the reaction temperature is raised to complete the reaction, followed by neutralization, and a precipitation solvent such as water is added to precipitate the polymer, followed by washing with water and drying to obtain a powder polymer. is there.

  The polyvinyl alcohol preferably has an average degree of polymerization of 1000 to 5000, more preferably 1500 to 4500. In order to develop the excellent mechanical strength (yield point strength, breaking strength) of the film, it is preferable to use polyvinyl alcohol having a high degree of polymerization. The degree of saponification of polyvinyl alcohol is 90 mol%, preferably 98 mol% or more, from the viewpoint of transparency and heat resistance of the obtained polyvinyl acetal.

  As the aldehyde, acetaldehyde is preferably used from the viewpoint of heat distortion temperature and ease of handling. In addition, a small amount of other aldehyde which is a raw material used for the synthesis of ordinary polyvinyl acetal may be used in a range not impairing the heat distortion temperature. For example, formaldehyde, propyl aldehyde, n-butyraldehyde, t- Aliphatic aldehydes such as butyraldehyde, amylaldehyde, hexylaldehyde, 2-ethylhexylaldehyde, alicyclic aldehydes such as cyclohexylaldehyde, aromatic aldehydes such as benzaldehyde, alkyl-substituted benzaldehyde, halogen-substituted benzaldehyde, and phenyl-substituted alkylaldehyde and so on. In the following description, polyvinyl acetal obtained using acetaldehyde as an aldehyde is often abbreviated as acetoacetal resin.

  As the acid catalyst, for example, hydrochloric acid, phosphoric acid, sulfuric acid, citric acid, p-toluenesulfonic acid and the like are used singly or in combination. These acid catalysts are generally added in an appropriate amount so that the pH of the reaction solution is 0.3 to 2.0.

  As the cross-linking agent, a known compound group that reacts with a hydroxyl group in the polymer to form a covalent bond, for example, those described in the cross-linking agent handbook (Taisei Co., Ltd .; Shinzo Yamashita, edited by Kaneko Tosuke) can be used.

  Examples of the crosslinking agent include dihalogen compounds, dicarboxylic acid anhydrides, dialdehyde compounds, boron compounds, silicon compounds, diisocyanate compounds, divinyl compounds, diazo compounds, metal alkoxide compounds, and the like. In particular, from the viewpoints of solubility and dispersibility with organic solvents, reactivity, ease of handling, etc., boric acid or a boron compound having a functional group that can be converted to a boric acid ester, having a functional group that can be converted to a siloxy group A silicon compound and a block type polyfunctional isocyanate compound in which an active group is protected are preferably used.

  The boron compound having a functional group that can be converted into a borate ester in the presence of a hydroxyl group has a bond between B and a different element such as O, N, H, Cl, Br, I, and the borate ester ( That is, it represents a boron compound having a functional group that can be converted to a B—O) group. Examples of the functional group that can be converted to a borate ester in the presence of a hydroxyl group include a B—O—C group, a B—OC (═O) — group, a B—N group, a B—H group, a B—Cl group, B-Br group, BI group, etc. are mentioned. These functional groups can be bonded to one B element in an amount of 1 to 3 under acidic conditions and 1 to 4 under alkaline conditions. It may be.

  Examples of the boron compound include dimethylmethoxyborane, dimethylethoxyborane, dimethylisopropoxyborane having one alkoxy group bonded thereto, methyldimethoxyborane, methyldiethoxyborane, methyldiisopropoxyborane having two alkoxy groups bonded thereto, and alkoxy. Examples thereof include trimethoxyborane, triethoxyborane, triisopropoxyborane having three groups bonded thereto, sodium tetramethoxyborate, sodium tetraethoxyborate, sodium tetraisopropoxyborate having four alkoxy groups bonded thereto. Further, there are dimethylacetoxyborane in which one carboxy group is bonded, methyldiacetoxyborane in which two carboxy groups are bonded, and triacetoxyborane in which three carboxy groups are bonded. An example of a halogen element bonded is dimethylborane chloride. In addition, there are trimethylborane and the like. Among these boron compounds, functional groups that can be converted to boric acid esters in the presence of hydroxyl groups include B-O due to the ease of conversion to boric acid esters and the characteristics of the products generated by the conversion reaction to boric acid esters. A -C bond is preferred. Among boric acid esters, those having a functional group such as a methoxy group, an ethoxy group, and an isopropoxy group are particularly preferable.

  A silicon compound having a functional group that can be converted to a siloxy group in the presence of a hydroxyl group has a bond between Si and a heterogeneous element such as O, N, H, Cl, Br, or I. Siloxy (ie, Si— The silicon compound which has a functional group which can be converted into O) group is shown. Examples of functional groups that can be converted to a siloxy group in the presence of a hydroxyl group include an alkoxysilyl (Si—O—C) group, a carboxysilyl (Si—OC (═O) —) group, a silazyl (Si—N) group, and a hydrosilyl group. (Si—H) group, chlorosilyl (Si—Cl) group, bromosilyl (Si—Br) group, iodosilyl (Si—I) group and the like can be mentioned. One to four of these functional groups can be bonded to one Si element, and a plurality of types of the corresponding functional groups may be bonded.

  Examples of the silicon compound include trimethylmethoxysilane, dimethyl tertiary butylmethoxysilane, triethylmethoxysilane, triphenylmethoxysilane, trimethylethoxysilane, triethylethoxysilane, and triphenylethoxysilane to which one alkoxy group is bonded. Further, there are dimethyldimethoxysilane, diethyldimethoxysilane, diphenyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, diphenyldiethoxysilane and the like in which two alkoxy groups are bonded. Further, there are methyltrimethoxysilane, ethyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, etc. to which three alkoxy groups are bonded. Further, there are tetramethoxysilane, tetraethoxysilane, tetranormalbutoxysilane, tetraphenoxysilane, and the like in which four alkoxy groups are bonded. In addition, there are trimethylacetoxysilane, triethylacetoxysilane, triphenylacetoxysilane, and the like to which one carboxy group is bonded. Further, there are dimethyldiacetoxysilane, diethyldiacetoxysilane, diphenyldiacetoxysilane and the like in which two carboxy groups are bonded. Further, there are methyltriacetoxysilane, ethyltriacetoxysilane, phenyltriacetoxysilane and the like in which three alkoxy groups are bonded. Further, there are tetraacetoxysilane, tetraformateoxysilane, tetrapropionateoxysilane and the like in which four carboxy groups are bonded. In addition, trimethylsilyldimethylamide, trimethylsilyldiethylamide, trimethylsilyldinormalbutyramide, one amino group bonded, dimethylsilylbis (dimethylamide), diethylsilylbis (dimethylamide), diethylsilylbis ( Diethylamide) and the like. Examples of the halogen element bonded include trimethylsilane chloride, trimethylsilane bromide, trimethylsilane iodide, dimethyldichlorosilane, methyltrichlorosilane, triphenylsilane chloride, dichlorodiphenylsilane, and trichlorophenylsilane. Among these silicon compounds, the functional group that can be converted to a siloxy group in the presence of a hydroxyl group includes a Si—O—C bond due to the ease of conversion to the siloxy group and the characteristics of the product generated by the conversion reaction to the siloxy group. Is preferably a siloxy group having a basic bond, or a carboxy group. Moreover, in a siloxy group, a methoxy group, an ethoxy group, and an isopropoxy group are preferable.

  The blocked isocyanate compound is a compound in which an isocyanate group is masked with a blocking agent. Takenate B-830, B-815N, B-842N, B-846N, B-870N, B-874N, B-882N manufactured by Mitsui Takeda Chemical and so on. When these compounds are used, metal catalysts are preferably used in combination for the purpose of lowering the blocking agent dissociation temperature. For example, Formate TK-1, Formate K, MT-Olestar M8 manufactured by Mitsui Takeda Chemical is there.

  The crosslinking agent is added in an amount of 0.01 to 10% by mass, preferably 0.1 to 5% by mass, based on the polymer. If the amount added is small, the mechanical strength may not be improved. If the amount added is too large, the mechanical strength may be impaired, or the film surface may bleed to deteriorate the film appearance or adhesion to other films. There is a case to let you.

  As the organic solvent, for example, alcohols such as methanol and ethanol, aromatic hydrocarbons such as toluene and xylene, halogenated solvents such as chloroform and methylene chloride, and the like can be used as appropriate. These solvents can be used alone or in combination of two or more. In these solvents, it is desirable to select a good solvent for both the polyvinyl acetal and the crosslinking agent.

  The crosslinking degree of the polymer film is preferably 1 to 60%, more preferably 2 to 50%. If the degree of crosslinking is less than 1%, the effect of improving the tensile break strength of the polymer film may not be obtained. If it exceeds 60%, the optical properties deteriorate or the tensile break strength decreases rather. May end up. The degree of crosslinking refers to a value obtained by dividing the insoluble content of the organic solvent in the polymer film by the mass of the original polymer film. The organic solvent used here is the same as the organic solvent used in the solvent casting method when the polymer film was prepared.

  As a method for producing the polymer film, a known solvent casting method (polymer solution film forming method) can be employed. Specifically, a polymer solution is prepared by dispersing or dissolving a polymer and a crosslinking agent, and if necessary, an ultraviolet absorber, an antioxidant, a plasticizer, etc. in an organic solvent, and casting this onto a support. In this method, a film-like material is formed, and then introduced into a heating step to volatilize and remove the solvent to obtain a polymer film. As the support, a metal drum, a metal belt, a glass plate, various plastic films and the like can be used.

  The polymer film thickness can be controlled to a desired value by adjusting the concentration of the polymer solution and the casting die lip gap. In addition, it is desirable to set the polymer concentration as high as possible from the viewpoint of suppressing foaming on the film surface in the process of volatilization of the solvent, and it is preferable to adjust the polymer concentration to 10 to 15% by mass.

  The heating and drying temperature and the heating time are appropriately selected in consideration of the thickness of the film-like material, the organic solvent type, and the crosslinking agent type. For example, the heating and drying temperature is in the range of 60 to 150 ° C., and the heating time is 5 to 60. The range of minutes. The heating temperature can be changed stepwise or continuously. In addition, when the polymer film once obtained is heated again for a crosslinking reaction, the heating temperature is, for example, in the range of 80 ° C. to 150 ° C., and the heating time is in the range of 0.1 second to 60 minutes, preferably in the range of 1 second to 10 minutes. is there. According to these heating conditions, the degree of crosslinking of the polymer film can be adjusted to 1 to 60%.

  In addition to the crosslinking agent, an ultraviolet absorber, an antioxidant, a plasticizer, and other additives can be added to the polymer solution. Examples of the ultraviolet absorber include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α′dimethylbenzyl) phenyl] -2H-benzotriazole. 2- (3,5-di-tert-butyl-2-hydroxyphenyl) benzotriazole, 2- (3-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- ( 3,5-di-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di-tert-amyl-2-hydroxyphenyl) benzotriazole, 2- ( 2'-hydroxy-5'-t-octylphenyl) benzotriazole UV absorbers such as benzotriazole, 2,2,6,6-tetramethyl- 4-piperidylbenzoate, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) -2- (3,5- Di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate, 4- (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy) -1- (2- (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy) ethyl) -2,2,6,6-tetramethylpiperidine and other hindered amine ultraviolet absorbers, 2,4-di- Benzoate UV absorbers such as t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate, hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate Etc. there is. These ultraviolet absorbers can be used alone or in combination of two or more. The compounding quantity of a ultraviolet absorber is 0.001-10 mass parts with respect to 100 mass parts of polyvinyl acetals, Preferably it is the range of 0.01-1 mass part.

  Antioxidants include, for example, phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. Among them, phenolic antioxidants are preferable, and alkyl-substituted phenolic antioxidants are particularly preferable. . A conventionally well-known thing can be used as a phenolic antioxidant, for example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 Acrylate compounds such as 1,4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate, 2,6-di-t-butyl- 4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, octadecyl-3- (3,5-) di-t-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene- Bis (4-methyl-6-tert-butylphenol), 4,4′-butylidene-bis (4-methyl-6-tert-butylphenol), 4,4′-butylidene-bis (6-tert-butyl) -M-cresol), 4,4′-thiobis (3-methyl-6-tert-butylphenol), bis (3-cyclohexyl-2-hydroxy-5-methylphenyl) methane, 3,9-bis (2- ( 3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy) -1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane, 1, 1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4 -Hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate) methane, triethylene glycol bis (3- (3-t- Alkyl-substituted phenolic compounds such as til-4-hydroxy-5-methylphenyl) propionate), 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bis-octylthio-1,3 , 5-triazine, 6- (4-hydroxy-3,5-dimethylanilino) -2,4-bis-octylthio-1,3,5-triazine, 6- (4-hydroxy-3-methyl-5- t-butylanilino) -2,4-bis-octylthio-1,3,5-triazine, 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1,3 , 5-triazine and other triazine group-containing phenol compounds.

  Examples of phosphorus antioxidants include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, and tris (2-t-butyl). -4-methylphenyl) phosphite, tris (cyclohexylphenyl) phosphite, 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite, 9,10-dihydro-9-oxa-10- Phosphaphenanthrene-10-oxide, 10- (3,5-di-tert-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy -9,10-dihydro-9-oxa-10-phosphine Monophosphite compounds such as phenanthrene, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecylphosphite), 4,4′-isopropylidene-bis (phenyl-di) -Alkyl (C12-C15) phosphite), 4,4'-isopropylidene-bis (diphenylmonoalkyl (C12-C15) phosphite), 1,1,3-tris (2-methyl-4-di-tri) Examples thereof include diphosphite compounds such as decyl phosphite-5-t-butylphenyl) butane and tetrakis (2,4-di-t-butylphenyl) -4,4′-biphenylene phosphite. Of these, monophosphite compounds are preferred.

  Examples of the sulfur-based antioxidant include dilauryl 3,3′-thiodipropionate, distearyl 3,3′-thiodipropionate, lauryl stearyl 3,3′-thiodipropionate, pentaerythritol-tetrakis- (Β-lauryl-thiopropionate), 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane. These antioxidants can be used alone or in combination of two or more. The compounding quantity of antioxidant is 0.001-5.0 mass part with respect to 100 mass parts of polyvinyl acetals, Preferably it is the range of 0.01-1.0 mass part.

  Examples of the plasticizer include ethylene glycol-di-2-ethyl butyrate, 1,3-propylene glycol-2-ethyl butyrate, 1,4-propylene glycol-2-ethyl butyrate, 1,2-propylene glycol. 2-ethylbutyrate, diethylene glycol-2-ethylbutyrate, diethylene glycol-2-ethylhexoate, triethyleneglycol-2-ethylbutyrate, triethyleneglycol-2-ethylhexoate, tetraethyleneglycol-2 -Ethyl butyrate. A small amount can be added as long as the mechanical strength of the film is not impaired.

  The polymer film may be subjected to a surface treatment. As the surface treatment method, any conventionally known method can be adopted, for example, electrical treatment such as colloidal discharge treatment, plasma treatment under low pressure or normal pressure, ultraviolet ray in the presence or absence of ozone. Irradiation treatment, acid treatment with chromic acid, etc., primer treatment such as silane primer or titanium primer, and the like. It is also possible to perform a coating process such as a hard coat.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, these Examples do not limit this invention. In the following examples, “part” and “%” are based on mass unless otherwise specified.

[Example 1]
(Adjustment of acetoacetal resin)
In a 150 L dissolution tank, 90000 parts by mass of pure water and 10000 parts of polyvinyl alcohol having an average degree of polymerization of 1700 and a degree of saponification of 98.8 mol% are added and heated to complete dissolution to obtain a 10% polyvinyl alcohol. An aqueous solution was prepared. Acetaldehyde was charged into a storage tank with a refrigerant jacket and maintained at an internal temperature of 5 ° C.
A 3 L cylindrical glass reactor (with two rod baffles) having three supply ports at the bottom of the reactor and one discharge port at the top of the reactor was prepared. The reactor was filled with pure water, and the internal temperature was maintained at 33 ° C. while stirring (anchor blade, 350 rpm).
The acetoacetal produced while feeding from the bottom of the reactor so that the feed rates of 10% polyvinyl alcohol aqueous solution, 35% hydrochloric acid and acetaldehyde were 9.0 kg / hr, 0.33 kg / hr and 0.55 kg / hr, respectively. The reaction solution (hereinafter referred to as slurry) was discharged from the top of the reactor. When 1 hour has passed since the start of discharge, the slurry was transferred to a separately prepared 9 L aging tank (transfer amount 5 kg), aged at 55 ° C. for 3 hours with stirring, and then aged at 65 ° C. for 4 hours to react. Was completed. The agitation tank had three agitating blades and a stirring speed of 200 rpm.
Next, an aqueous sodium hydroxide solution was added to adjust the pH to 8.0, and the mixture was cooled to room temperature. The obtained slurry was dehydrated with a centrifuge to a water content of 48%, diluted by adding 10 times the amount of pure water to the resin content, stirred for 30 minutes and washed with water. This dehydration and water washing operation was repeated three times, and the resulting slurry was dehydrated again, and then the inside of the system was sealed with nitrogen and hot air dried to prevent dust explosion to obtain a powdery acetoacetal resin. The degree of acetalization was 77 mol%.

(Sample adjustment)
15.5 parts by mass of an acetoacetal resin, 42.8 parts by mass of ethanol as an organic solvent, 42.8 parts by mass of toluene, 0.08 part by mass of boric acid as a crosslinking agent (0.54 mass with respect to the acetoacetal resin) %) Was added to a mixing tank and stirred at room temperature to prepare a polymer solution. During the series of operations, the system was sealed with nitrogen to prevent moisture from entering.
The obtained polymer solution is cast from a lip die having a width of 300 mm to a plastic film (PET film having a thickness of 50 μm) as a continuous support, and then introduced into a heating and drying process, while peeling the PET film as a support. A polymer film (thickness 40 ± 1 μm) was continuously wound up. The take-up speed was 0.5 m / min, and the drying zone length was 4 m (residence time 8 minutes). The drying zone was divided into two sections of 2 m each, and the temperature was controlled (first zone 75 ° C., second zone 95 ° C.). The obtained samples were evaluated as shown below, and the results are shown in Table 1.

[Total light transmittance and haze]
It is a value measured in an atmosphere of a temperature of 23 ° C. ± 1 ° C. and a humidity of 50% ± 5% using a Nippon Denshoku haze meter NDH2000.

[Birefringence]
Using a birefringence measuring apparatus ABR-10A manufactured by UNIOPTO, measuring temperature 23 ° C. ± 1 ° C., vertical direction, wavelength 633 nm (He—Na light source), film piece 20 mm × 20 mm square frame, total 25 in total increments It is an average value measured at points.

[Adhesion]
The film of the present invention is placed on one side of a commercially available PVA film (Kuraray vinylon film “Claria HH (thickness 70 μm)”) that assumes a polarizing plate, and the two films are brought into close contact with each other using a hand roller. Bonding was performed while foaming was performed at a hand roller of about 1 kg / cm ² , a roller speed of 1 m / min, an ambient temperature of 25 ° C., and a humidity of 50 ± 5%. After holding for a minute, the film was taken out and allowed to cool.The film edge of this bonded sample was opened while holding it with both hands, and the peeled state and the degree of material destruction were observed and judged. ○, a case where a part of the material was broken was indicated by Δ, and a case where the material was easily peeled was indicated by ×.

[Thickness and tensile strength at break]
The thickness of the polymer film is a value measured according to JISK7130. The tensile strength at break of the polymer film is a value measured according to JISK7127 and 7161, with a test piece having a width of 10 mm, a chuck interval of 110 mm, and a tensile speed of 5 mm / min, and n = 8.

[Measurement of degree of crosslinking]
About 0.5 g of a film piece was cut into about 5 mm square and weighed accurately. 25 g of ethanol and 25 g of toluene were placed in an Erlenmeyer flask, the film strip was added, and the contents were held at room temperature for 1 day while stirring with a stir bar. After the stirring was stopped and the mixture was allowed to stand, the content liquid was filtered through a 200 mesh wire mesh. The wire mesh to which insoluble matter (gel) was adhered was dried at 110 ° C. for 1 hour, then allowed to cool in a desiccator for 30 minutes, and the mass was measured. The mass of the insoluble matter was calculated from the mass difference before and after filtration of the wire mesh. The degree of crosslinking was determined from the initial mass of the film piece used for the measurement and the mass of the insoluble matter.

[Example 2]
In the preparation of the sample of Example 1, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene 0.31 was further used as an antioxidant. Part by mass, 0.20 part by mass of 2- [2-hydroxy-3,5-bis (α, α′dimethylbenzyl) phenyl] -2H-benzotriazole as an ultraviolet absorber, and triethylene glycol di-2- This is a blend of 1.0 part by mass of ethyl hexoate. Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Example 3]
In the preparation of the sample of Example 1, boric acid as a crosslinking agent was changed to 0.19 parts by mass of triethoxyborane (about 1.27% by mass with respect to the acetoacetal resin). Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Example 4]
In the preparation of the sample of Example 1, boric acid as a crosslinking agent was changed to 0.27 parts by mass of tetraethoxysilane (about 1.8% by mass with respect to the acetoacetal resin). Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Example 5]
In the preparation of the sample of Example 1, 3.5 parts by mass of blocked isocyanate B-846N (manufactured by Mitsui Takeda Chemical Co., Ltd.) and 0.14 parts by mass of catalyst formate TK-1 were added as a crosslinking agent.
In this example, the PET film as a support is continuously wound up without being peeled off, the sample is directly introduced into another heating tank and continuously heated, and then cooled to room temperature. A PET film was peeled to obtain a sample. The heating temperature in the heating tank was 140 ° C., and the residence time in the heating tank was 15 minutes.
Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Example 6]
In the preparation of the sample of Example 1, boric acid as a crosslinking agent was changed to 0.15 parts by mass. Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Example 7]
In the preparation of the acetoacetal resin of Example 1, polyvinyl alcohol was changed to one having an average polymerization degree of 3500 and a saponification degree of 99.0 mol%. Evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Comparative Example 1]
In Example 1, no crosslinking agent was added.

The polymer film of the present invention is excellent in optical properties and adhesion to a polarizer and excellent in mechanical strength, and can be used as an optical film around a liquid crystal device, particularly as a protective film for a polarizing plate.

Claims (10)

  A polymer film obtained by forming a polymer solution comprising a polyvinyl acetal, a crosslinking agent, and an organic solvent into a film by a solvent casting method, wherein the organic solvent in the polymer solution is volatilized and / or the polymer film A polymer film obtained by crosslinking reaction of polyvinyl acetal to a degree of crosslinking of 1 to 60% in the step after obtaining.   The crosslinking agent is at least one selected from boric acid, a boron compound having a functional group that can be converted into a boric acid ester, a silicon compound having a functional group that can be converted into a siloxy group, and a blocked isocyanate compound. The polymer film according to claim 1.   The polymer film according to claim 1 or 2, wherein the polymer solution further contains an ultraviolet absorber and / or an antioxidant.   The polymer film according to any one of claims 1 to 3, further comprising a plasticizer in the polymer solution.   A polymer film production method for producing a polymer film by a solvent casting method from a polymer solution comprising a polyvinyl acetal, a cross-linking agent, and an organic solvent, the step of volatilizing the organic solvent in the polymer solution and / or the polymer film A method for producing a polymer film, wherein the polyvinyl acetal is subjected to a crosslinking reaction to a degree of crosslinking of 1 to 60% in the subsequent step.   The crosslinking agent is at least one selected from boric acid, a boron compound having a functional group that can be converted into a boric acid ester, a silicon compound having a functional group that can be converted into a siloxy group, or a blocked isocyanate compound The method for producing a polymer film according to claim 5.   The method for producing a polymer film according to claim 5 or 6, wherein the polymer solution further contains an ultraviolet absorber and / or an antioxidant.   The method for producing a polymer film according to any one of claims 5 to 7, wherein a plasticizer is further contained in the polymer solution.   The polarizing plate obtained by sticking the film as described in any one of Claims 1-4 on the single side | surface or both surfaces of a polarizer. A liquid crystal display device using the polarizing plate according to claim 9.