JP2006249407A - Polyvinyl alcohol film and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film used as a raw film for manufacturing a polarizing film which is excellent in light beam transmittance and polarizing performance; and a manufacturing method thereof. <P>SOLUTION: The invention provides a polyvinyl alcohol film containing 100 to 500 ppm of a polyalkylene oxide group containing compound in the film; and a polarizing film comprising the film. The film is manufactured by a process of mixing a polyvinyl alcohol resin with at least one of nonionic surfactants in a manner which satisfies the inequality (1): 0.5≤Σä(HLB of the surfactant)×(an added amount of the nonionic surfactant (% by weight) relative to the amount of the polyvinyl alcohol resin)}≤2, wherein HLB represents the hydrophile-lipophile balance and Σ represents the sum total when two or more nonionic surfactants are incorporated into the composition of the film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyvinyl alcohol film excellent in light transmittance. More specifically, the present invention relates to a polyvinyl alcohol film used as a raw film for producing a polarizing film excellent in light transmittance and polarizing performance, and a method for producing the same.

  Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, then forming a film by a solution casting method (casting method), and drying using a metal heating roll or the like. It is manufactured by doing. The polyvinyl alcohol film thus obtained is used for many applications as a film having excellent transparency, and one of its useful applications is a polarizing film. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to a device requiring high quality and high reliability.

Under such circumstances, with the increase in brightness and definition of screens of liquid crystal televisions and the like, there is a demand for polarizing films that are much more transparent than conventional products and have no optical defects. As countermeasures against such a demand, for example, a polyvinyl alcohol film having 500 or less optical foreign matters of 5 μm or more per 100 cm ² is used (see, for example, Patent Document 1), or 20 μm existing on the surface of the film. It has been proposed to use a polyvinyl alcohol film having a foreign material having a size of 10 or less per square meter (for example, see Patent Document 2).

  However, the cause of optical defects is not only micron-order foreign matter. Additives deposited inside the film during film formation or additives that bleed out on the film surface also cause optical defects. Surfactant deposited inside or on the surface of the film reduces the light transmittance and also causes optical unevenness. In particular, surfactants that bleed out on the surface are dyeable when producing polarizing films. In other words, color unevenness is caused and the polarization performance is deteriorated. Therefore, in order to achieve the recent high brightness and high definition in the liquid crystal display, further improvement of the film has been desired.

JP 2001-316492 A Japanese Patent Laid-Open No. 2004-20631

  An object of the present invention is to provide a polyvinyl alcohol film that can be used as a raw film for producing a polarizing film having high light transmittance and excellent polarization performance, and a method for producing the same. .

  The present invention relates to a polyvinyl alcohol film containing 100 to 500 ppm of a polyalkylene oxide group-containing compound in the film.

Moreover, this invention relates to the manufacturing method of the said polyvinyl alcohol-type film including the process of adding at least 1 sort (s) of nonionic surfactant to polyvinyl alcohol-type resin so that following formula (1) may be satisfied.
0.5 ≦ Σ {(HLB of nonionic surfactant) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (% by weight))} ≦ 2 (1)
(In the formula, HLB means the hydrophilic / lipophilic balance, and Σ means the total when two or more nonionic surfactants are added.)

  The polyvinyl alcohol film is preferably made of a polyvinyl alcohol resin having a weight average molecular weight of 140000 to 260000.

  The polyvinyl alcohol film preferably has a film width of 3.0 m or more.

  The polyvinyl alcohol film preferably has a film thickness of 30 to 70 μm.

  The polyvinyl alcohol film preferably has a film length of 4000 m or longer.

  The polyvinyl alcohol film is preferably used as a raw film for a polarizing film.

  The present invention also relates to a polarizing film comprising the polyvinyl alcohol film.

  Furthermore, the present invention relates to a polarizing plate comprising a protective film provided on at least one surface of the polarizing film.

  By limiting the amount of the polyalkylene oxide group-containing compound present in the film, the polyvinyl alcohol film of the present invention has an excellent light transmittance. Therefore, the polarizing film manufactured using the polyvinyl alcohol film of the present invention as a raw film exhibits excellent light transmittance and polarizing performance.

  The present invention relates to a polyvinyl alcohol film containing 100 to 500 ppm of a polyalkylene oxide group-containing compound in the film.

  In the casting stock solution used for forming a polyvinyl alcohol film, various surfactants such as nonionic, anionic and cationic are usually used for the purpose of improving the film forming property and dyeability. It has been added. However, as described above, these surfactants, when deposited on the inside or the surface of the film, may cause a decrease in the light transmittance of the film, optical unevenness, a decrease in dyeability during production of the polarizing film, and the like. Therefore, it is important to control the type and amount of surfactant used and the polyalkylene oxide group-containing compound derived therefrom.

  Therefore, the polyvinyl alcohol film of the present invention is characterized in that the amount of the polyalkylene oxide group-containing compound present in the film is 100 to 500 ppm. The amount of the polyalkylene oxide group-containing compound is preferably 110 to 300 ppm, more preferably 115 to 200 ppm. When the amount of the polyalkylene oxide group-containing compound is less than 100 ppm, when the polyvinyl alcohol film of the present invention is used as a raw film of a polarizing film, the dye is not sufficiently dyed due to a decrease in hydrophilicity, and the degree of polarization is low. descend. On the other hand, if it exceeds 500 ppm, the light transmittance of the polyvinyl alcohol film decreases due to aggregation of the additive, and the light transmittance of the polarizing film obtained from the polyvinyl alcohol film also decreases.

The production method of the polyvinyl alcohol film of the present invention is not particularly limited. For example, the polyvinyl alcohol resin film is produced by casting and drying a polyvinyl alcohol resin aqueous solution prepared using a polyvinyl alcohol resin. At this time, it is preferable to include a step of adding at least one nonionic surfactant to the polyvinyl alcohol resin so as to satisfy the following formula (1).
0.5 ≦ Σ {(HLB of nonionic surfactant) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (% by weight))} ≦ 2 (1)
(In the formula, HLB means the hydrophilic / lipophilic balance, and Σ means the total when two or more nonionic surfactants are added.)

  Hereinafter, the manufacturing method of the polyvinyl alcohol-type film of this invention including the said process is demonstrated.

  The polyvinyl alcohol film of the present invention is obtained by forming a polyvinyl alcohol resin into a film. As the polyvinyl alcohol resin, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used, but the polyvinyl alcohol film of the present invention is not necessarily limited to this. Instead, a resin obtained by saponifying a copolymer of vinyl acetate and a component copolymerizable with a small amount of vinyl acetate can also be used. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.). , Vinyl ethers, unsaturated sulfonates and the like.

  It is also preferable to use a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain as the polyvinyl alcohol resin. Polyvinyl alcohol resins having a 1,2-glycol bond in the side chain are, for example, (a) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (b) vinyl acetate. Of saponifying and decarboxylating a copolymer of styrene and vinyl ethylene carbonate, (c) saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane And (d) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether.

  Although the weight average molecular weight of polyvinyl alcohol-type resin is not specifically limited, Preferably it is 120000-300000, More preferably, it is 140000-200000, More preferably, it is 160000-200000. When the weight average molecular weight is less than 120,000, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film, and when it exceeds 300,000, stretching becomes difficult when the film is used as a polarizing film, and industrial production. Is difficult and undesirable. The weight average molecular weight of the polyvinyl alcohol resin is measured by gel permeation chromatography-low angle laser light scattering method (hereinafter referred to as GPC-LALLS method).

  The saponification degree of the polyvinyl alcohol resin is preferably 97 mol% or more, more preferably 98 to 100 mol%, and still more preferably 99 to 100 mol%. When the saponification degree is less than 97 mol%, it is not preferable because sufficient optical performance cannot be obtained when an optical film is used.

  Since the polyvinyl alcohol resin usually contains sodium acetate, first, the polyvinyl alcohol resin powder is washed to remove sodium acetate. For washing, methanol or water is used, but the method of washing with methanol requires a solvent recovery, and therefore the method of washing with water is more preferable.

  Next, the water-containing polyvinyl alcohol-based resin wet cake after washing is dissolved to prepare a polyvinyl alcohol-based resin aqueous solution. When the water-containing polyvinyl alcohol-based resin wet cake is dissolved in water as it is, a desired high concentration aqueous solution is obtained. Is not obtained, it is preferable to perform dehydration once. The dehydration method is not particularly limited, but a method using centrifugal force is common. By such washing and dehydration, it is preferable to prepare a wet polyvinyl alcohol resin wet cake having a water content of 50% by weight or less, preferably 30 to 45% by weight. If the water content exceeds 50% by weight, it is difficult to obtain a desired aqueous solution concentration.

  Various surfactants such as nonionic, anionic and cationic are added to the polyvinyl alcohol-based resin aqueous solution for the purpose of improving the film forming property and dyeability of the film. As long as the amount of the polyalkylene oxide group-containing compound present in the obtained polyvinyl alcohol-based film is 100 to 500 ppm, the type and amount of the surfactant to be added are not particularly limited, but the peelability from the cast substrate is not limited. A nonionic surfactant is an essential component in order to ensure slipperiness with a roll in the process, dyeability in the production of a polarizing film, or adhesion of a protective film such as triacetate cellulose (TAC).

  However, if the compatibility between the nonionic surfactant and the polyvinyl alcohol resin aqueous solution is insufficient, the surfactant precipitates in the film or on the surface during the film formation process. In particular, since an aqueous polyvinyl alcohol resin solution is water-soluble, precipitation is unlikely to occur with an anionic or cationic surfactant, but nonionic surfactants are likely to cause precipitation. In order to avoid such precipitation, it is necessary that the added nonionic surfactant has an appropriate hydrophilic portion. The ratio of the hydrophilic portion contained in the surfactant molecule is represented by a hydrophilic lipophilic balance (hereinafter referred to as HLB) obtained by dividing the atomic mass of the hydrophilic portion by the molecular weight. Therefore, by selecting a nonionic surfactant having an appropriate HLB, precipitation on the inside of the film or on the surface can be avoided.

  On the other hand, in order to avoid the precipitation of the surfactant, it is necessary to set not only the surfactant HLB but also an appropriate addition amount. This is because when the amount added is too large, the degree of precipitation increases. Of course, if the amount is too small, the function of the original surfactant is not expressed. That is, the product of the HLB of the nonionic surfactant and the amount added is important for avoiding precipitation.

Therefore, in the method for producing a polyvinyl alcohol film containing 100 to 500 ppm of the polyalkylene oxide group-containing compound of the present invention, at least one nonionic surfactant is preferably used so as to satisfy the following formula (1). Is added so as to satisfy the formula (2), more preferably so as to satisfy the formula (3).
0.5 ≦ Σ {(HLB of nonionic surfactant) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (% by weight))} ≦ 2 (1)
0.5 ≦ Σ {(HLB of nonionic surfactant) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (% by weight))} ≦ 1.3 (2)
0.5 ≦ Σ {(HLB of nonionic surfactant) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (wt%))} ≦ 1.2 (3)
In the formula, HLB means the hydrophilic / lipophilic balance, and Σ means the total when two or more nonionic surfactants are added.

  When Σ {(nonionic surfactant HLB) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (% by weight))} is less than 0.5, the polyvinyl alcohol film is removed from the cast substrate. It is difficult to peel off, and when it exceeds 2, precipitation of the surfactant occurs, which is not preferable because the light transmittance of the film is lowered.

  Specific examples of the nonionic surfactant used in the method for producing the polyvinyl alcohol film of the present invention include polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, and polyoxyethylene nonyl. Ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene stearyl ether, polyoxyethylene octyldodecyl ether, polyoxyethylene eicosyl ether, polyoxy Polyoxins such as ethylene oleyl ether, palm oil reduced alcohol ethylene oxide adduct, beef tallow reduced alcohol ethylene oxide adduct Ethylene alkyl ether, polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene decylamine, polyoxyethylene laurylamine, polyoxyethylene tetradecylamine, polyoxyethylene Hexadecylamine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, polyoxyethylene alkylamines such as polyoxyethyleneeicosylamine, stearic acid amide, oleic acid amide, palmitic acid amide, myristic acid amide, lauric acid amide, capron Acid amide, diethanol lauryl amide, polyoxyethylene caproic acid amide, polyoxyethylene caprylic acid amide, poly Higher fatty acid amides such as xylethylene capric acid amide, polyoxyethylene lauric acid amide, polyoxyethylene myristic acid amide, polyoxyethylene palmitic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene oleic acid amide, glyceryl stearate, And sorbitan stearate. Among these, polyoxyethylene group-containing compounds such as polyoxyethylene lauryl ether, diethanol lauryl amide, and polyoxyethylene lauryl amine are preferable.

In the case of using one kind of nonionic surfactant, the surfactant satisfying the formula (1) and possible addition amount are exemplified as follows.
Diethanol lauryl amide (HLB = 6)
0.1-0.3% by weight
Polyoxyethylene stearyl ether with an average degree of condensation of 3 (HLB = 7)
0.1 to 0.25% by weight
Polyoxyethylene lauryl ether with an average degree of condensation of 3 (HLB = 9)
0.1-0.2% by weight
Polyoxyethylene lauryl ether having an average condensation degree of 4 (HLB = 10)
0.05-0.2% by weight
Polyoxyethylene stearyl ether with an average condensation degree of 7 (HLB = 11)
0.05-0.15% by weight
Polyoxyethylene octyldodecyl ether having an average condensation degree of 10 (HLB = 12)
0.045 to 0.15% by weight
Polyoxyethylene stearyl ether with an average condensation degree of 10 (HLB = 13)
0.04 to 0.15% by weight
Polyoxyethylene laurylamine having an average degree of condensation of 10 (HLB = 14)
0.04 to 0.1% by weight
Polyoxyethylene stearyl ether with an average condensation degree of 17 (HLB = 15)
0.035 to 0.1% by weight
Polyoxyethylene lauryl ether having an average condensation degree of 17 (HLB = 16)
0.035 to 0.1% by weight
Polyoxyethylene lauryl ether having an average degree of condensation of 24 (HLB = 17)
0.03 to 0.1% by weight
Polyoxyethylene lauryl ether having an average degree of condensation of 38 (HLB = 18)
0.03 to 0.1% by weight
Polyoxyethylene lauryl ether with an average degree of condensation of 80 (HLB = 19)
0.03 to 0.1% by weight
It is.

When two or more kinds of nonionic surfactants are used, the surfactant satisfying the formula (1) and possible addition amounts are exemplified as follows.
Diethanol lauryl amide (HLB = 6) 0.1% by weight
Polyoxyethylene laurylamine having an average degree of condensation of 10 (HLB = 14) 0.05% by weight
At this time,
Σ {(nonionic surfactant HLB) × (addition amount of nonionic surfactant to resin (% by weight))} = 6 × 0.1 + 14 × 0.05 = 1.3
Thus, the HLB and the addition amount of these nonionic surfactants satisfy the formula (1).

  Even when only a nonionic surfactant that does not contain a polyalkylene oxide group is added, it is decomposed at the time of film production, and finally a film as a polyalkylene oxide group-containing compound based on the nonionic surfactant When it is contained in 100 to 500 ppm, it is included in the present invention.

  The HLB of the nonionic surfactant alone is preferably 5 to 17, more preferably 7 to 15, and still more preferably 9 to 13. When the HLB is less than 5, the compatibility with the aqueous polyvinyl alcohol resin solution is poor, and when it exceeds 17, the peelability becomes insufficient, which is not preferable.

  One type of nonionic surfactant to be added may be used, or two or more types may be used in combination, but the peelability from the cast substrate, the slippage with the roll in the process, the dyeability in the production of the polarizing film, Or in order to ensure the sticking property of protective films, such as a triacetyl cellulose, it is preferable to use 2 or more types together. The total amount of the nonionic surfactant added is preferably from 0.01 to 0.5% by weight, more preferably from 0.02 to 0.3% by weight, and even more preferably from 0.04 to 0.2% by weight. If it is less than 0.01% by weight, the peelability is insufficient, and if it exceeds 0.5% by weight, the light transmittance is lowered due to precipitation, which is not preferable.

  Thus, the compatibility of nonionic surfactant and polyvinyl alcohol is set by setting the product of HLB and addition amount (% by weight) of the nonionic surfactant added at the time of production of the polyvinyl alcohol film to a specific range. Therefore, precipitation of the nonionic surfactant in the film interior and on the surface after film formation is suppressed, and the light transmittance of the resulting polyvinyl alcohol film is extremely high.

  Examples of the cationic surfactant and anionic surfactant added in the method for producing the polyvinyl alcohol film of the present invention include, for example, dodecylamine acetate, stearylamine acetate, and the like as cationic surfactants. Higher alkyl monoamine salts, alkyl diamine salts such as N-dodecyl-1,3-diaminopropane adipate, N-dodecyl propylene diamine dioleate, quaternary ammonium salts such as dodecyl trimethyl ammonium chloride and behenyl trimethyl ammonium chloride Anionic surfactants include sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, tetradecyl sulfate. Alkyl sulfates such as sodium sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, sodium eicosyl sulfate, polyoxyethylene hexyl ether sodium sulfate, polyoxyethylene heptyl ether sodium sulfate, polyoxyethylene octyl ether sodium sulfate, polyoxyethylene nonyl ether Sodium sulfate, polyoxyethylene decyl ether sodium sulfate, polyoxyethylene dodecyl ether sodium sulfate, polyoxyethylene tetradecyl ether sodium sulfate, polyoxyethylene hexadecyl ether sodium sulfate, polyoxyethylene octadecyl ether sodium sulfate, polyoxyethylene eicosyl Polyoxyethylene alkyl such as sodium ether sulfate Ether sulfate, sodium polyoxyethylene hexyl phenyl ether sulfate, sodium polyoxyethylene heptyl phenyl ether sulfate, sodium polyoxyethylene octyl phenyl ether sulfate, sodium polyoxyethylene nonylphenyl ether sulfate, sodium polyoxyethylene decylphenyl ether sulfate, poly Polyoxy, such as sodium oxyethylene dodecyl phenyl ether sulfate, sodium polyoxyethylene tetradecyl phenyl ether sulfate, sodium polyoxyethylene hexadecyl phenyl ether sulfate, sodium polyoxyethylene octadecyl phenyl ether sulfate, sodium polyoxyethylene eicosyl phenyl ether sulfate Ethylene alkyl phenyl ether sulfate, capro Sodium ethanolamide sulfate, sodium caprylic acid ethanolamide sulfate, sodium capric acid ethanolamide sulfate, sodium lauric acid ethanolamide sulfate, sodium palmitate ethanolamide sulfate, stearic acid ethanolamide sodium sulfate, oleic acid ethanolamide sodium sulfate, etc. Higher fatty acid alkanolamide sulfate, sodium hexyl sulfonate, sodium heptyl sulfonate, sodium octyl sulfonate, sodium nonyl sulfonate, sodium decyl sulfonate, sodium dodecyl sulfonate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, Sodium octadecyl sulfonate, sodium alkyl sulfonate having 6 to 18 carbon atoms And aliphatic alkyl sulfonate, such as a mixture of the like.

  Furthermore, when manufacturing the polyvinyl alcohol-type film of this invention, generally used plasticizers, such as glycerol, are mix | blended with a polyvinyl alcohol-type resin as needed. The compounding quantity of a plasticizer is 30 weight% or less with respect to a polyvinyl alcohol-type resin, Preferably it is 3-25 weight%, More preferably, it is 5-20 weight%. If the blending amount exceeds 30% by weight, the film strength is inferior, which is not preferable.

  The aqueous polyvinyl alcohol resin solution used as a casting stock solution is prepared by dissolving a dehydrated water-containing polyvinyl alcohol resin wet cake, a surfactant, and, if necessary, a plasticizer in water. Such an aqueous polyvinyl alcohol resin solution is an aqueous solution obtained by dissolving a dehydrated polyvinyl alcohol resin wet cake, water, a plasticizer, and a surfactant using a dissolution can by heating, stirring. Alternatively, using a multi-screw extruder, charge the dehydrated polyvinyl alcohol resin wet cake or the dried polyvinyl alcohol resin, and add water, plasticizer, surfactant, etc. by side feed. It may be an aqueous solution obtained by charging an agent, heated, and dissolved while applying shear, but the polyvinyl alcohol-based resin aqueous solution used in the method for producing a polyvinyl alcohol-based film of the present invention is particularly a vertical circulation flow. Water-containing polyvinyl alcohol by blowing water vapor into a melting can equipped with a generation type stirring blade It is preferably an aqueous solution obtained by dissolving system resin wet cake.

  When dissolving the water-containing polyvinyl alcohol-based resin wet cake in a dissolving can equipped with such an up-and-down circulating flow generation type stirring blade, water vapor is blown, but when blowing such water vapor, a desired concentration is obtained. It is also preferred to add water. The amount of water vapor blown is preferably 0.5 to 5 times (by weight) with respect to the polyvinyl alcohol resin to be dissolved, and the blow time is preferably 0.5 to 3 hours. If the blowing amount is less than 0.5 times, the dissolution is insufficient, and if it exceeds 5 times, the amount of drain becomes too large and the desired concentration is not achieved. Further, when steam is blown, it is preferable to blow from the bottom of the can, but the present invention is not limited to this, and it may be blown from the side surface or the like. In addition, it is preferable to start stirring when steam is blown and the resin temperature reaches 40 to 80 ° C., preferably 45 to 70 ° C., from the viewpoint of uniform dissolution. If the resin temperature is less than 40 ° C., the load on the motor increases, and if it exceeds 80 ° C., the polyvinyl alcohol resin is hardened and cannot be uniformly dissolved.

  Furthermore, it is also preferable to pressurize the inside of the can at the time when steam is blown and the resin temperature reaches 90 to 100 ° C., preferably 95 to 100 ° C., from the viewpoint of uniform dissolution. If the resin temperature is less than 90 ° C., undissolved material is formed, which is not preferable. When the resin temperature reaches 130 to 150 ° C., the blowing of water vapor is terminated, and stirring is continued for 0.5 to 3 hours for dissolution. After dissolution, the concentration is adjusted so that the desired concentration is obtained. The concentration of the aqueous solution is adjusted by measuring the concentration using a process refractometer (manufactured by K-PATENTS) while partly extracting and circulating the solution in the can.

  The concentration of the aqueous polyvinyl alcohol resin solution obtained as described above is preferably 15 to 60% by weight, more preferably 17 to 55% by weight, and still more preferably 20 to 50% by weight. If the concentration is less than 15% by weight, the drying load becomes large and the production capacity is inferior. If it exceeds 60% by weight, the viscosity becomes too high and uniform dissolution cannot be achieved.

Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include stationary defoaming and defoaming with a multi-screw extruder, but in the method for producing the polyvinyl alcohol film of the present invention, a method of defoaming with a multi-screw extruder is preferable. . The multi-screw extruder is not particularly limited as long as it is a multi-screw extruder having a vent. Usually, a twin-screw extruder having a vent is used. For defoaming using a multi-screw extruder, a polyvinyl alcohol resin aqueous solution is supplied to the multi-screw extruder, the resin temperature of the vent portion is 105 to 180 ° C., preferably 110 to 160 ° C., and the pressure at the tip of the extruder is 2. It is carried out under the condition of -100 kg / cm ² , preferably 5-70 kg / cm ² .

If the resin temperature of the vent portion is less than 105 ° C., defoaming is insufficient, and if it exceeds 180 ° C., resin degradation occurs. Further, when the pressure at the extruder tip is less than 2 kg / cm ² , defoaming is insufficient, and when it exceeds 100 kg / cm ² , resin leakage or the like occurs in the piping, and stable production cannot be achieved.

Further, a gear pump (P1) and a gear pump (P2) are provided before and after the multi-screw extruder, the polyvinyl alcohol-based resin aqueous solution is supplied to the multi-screw extruder by the gear pump (P1), and the polyvinyl alcohol-based resin aqueous solution is supplied by the gear pump (P2). In the method for producing a polyvinyl alcohol film of the present invention, the inlet pressure of the gear pump (P2) is in the range of ² to 70 kg / cm ² , preferably 5 to 70 kg / cm. Controlling the gear pump (P1) so as to show a constant value in the range of ² is preferable in terms of improving the accuracy of the film thickness. If the inlet pressure is less than 2 kg / cm ² , defoaming is insufficient, and if it exceeds 70 kg / cm ² , the resin comes out from the vent portion, which is not preferable. Further, even if the inlet pressure is in the above range, the film thickness accuracy is insufficient if it does not show a certain value, which is not preferable. Note that the constant value referred to here is within a range of ± 2%, preferably ± 1.5% from the specified value.

  After the defoaming process by the multi-screw extruder, the polyvinyl alcohol-based resin aqueous solution discharged from the multi-screw extruder is cast, film-formed, and dried.

  As the T-type slit die, a T-type slit die having an elongated rectangle is usually used.

  The casting of the polyvinyl alcohol-based aqueous solution is performed by a drum-type roll or an endless belt, but it is preferably performed by a drum-type roll from the viewpoints of widening, lengthening, and film thickness uniformity.

  In casting a film with a drum-type roll, for example, the rotational speed of the drum-type roll is preferably 5 to 30 m / min, and particularly preferably 6 to 20 m / min. The surface temperature of the drum roll is preferably 70 to 99 ° C, more preferably 75 to 97 ° C. If the surface temperature of the drum-type roll is less than 70 ° C., drying is poor, and if it exceeds 99 ° C., foaming is not preferable. Moreover, it is preferable that the resin temperature of a T-type slit die exit is 80-100 degreeC, More preferably, it is 85-98 degreeC. If the resin temperature at the exit of the T-shaped slit die is less than 80 ° C., flow failure occurs, and if it exceeds 100 ° C., foaming is not preferable. Although it does not specifically limit about the magnitude | size of a drum type roll, For example, the diameter of a roll has preferable 2000-4000mm, More preferably, it is 2500-3800mm.

  Drying performed after film formation is performed using, for example, a drying roll. Although the surface temperature of a drying roll is not specifically limited, It is preferable that it is 60-100 degreeC, Furthermore, it is 65-90 degreeC. If the surface temperature is less than 60 ° C., the drying is poor, and if it exceeds 100 ° C., it is too dry, which causes an appearance defect. After drying, it is heat-treated as necessary to form a polyvinyl alcohol film.

  The width of the polyvinyl alcohol film of the present invention obtained as described above is preferably 3.0 m or more, more preferably 3.5 m or more, and still more preferably 4.0 m or more. If the width is less than 3.0 m, the productivity of the polarizing film is inferior, which is not preferable. The length of the film is preferably 4000 m or more, more preferably 4500 m or more, and further preferably 5000 m or more. If the length is less than 4000 m, the productivity of the polarizing film is inferior, which is not preferable. The film thickness is preferably 30 to 100 μm, more preferably 30 to 70 μm, and still more preferably 35 to 55 μm. When the film thickness is less than 30 μm, stretching is difficult when the polyvinyl alcohol film of the present invention is used for producing a polarizing film, and when it exceeds 100 μm, the film thickness accuracy is lowered, which is not preferable.

  The light transmittance of the polyvinyl alcohol film of the present invention is preferably 90% or more, more preferably 91% or more. If it is less than 90%, the light transmittance of the polarizing film is insufficient, which is not preferable. The light transmittance of the polyvinyl alcohol film is measured with a spectrophotometer.

  The polyvinyl alcohol film of the present invention is excellent in light transmittance, excellent in light transmittance, and is a raw material for producing a polarizing film excellent in in-plane uniformity of polarization performance (polarization degree and single transmittance). It is preferably used as an anti-film.

  Hereinafter, the manufacturing method of the polarizing film of this invention using the polyvinyl alcohol-type film of this invention is demonstrated.

  The polarizing film of the present invention is produced through processes such as normal dyeing, stretching, boric acid crosslinking and heat treatment. As a method for producing a polarizing film, a polyvinyl alcohol film is stretched and immersed in an iodine or dichroic dye solution and dyed, and then treated with a boron compound. After stretching and dyeing are performed simultaneously, the boron compound is treated. There are a method, a method of dyeing with iodine or a dichroic dye and stretching, and then a method of treating with a boron compound, a method of dyeing and then stretching in a solution of a boron compound, etc., which can be appropriately selected and used. As described above, the polyvinyl alcohol film (unstretched film) may be stretched and dyed and further subjected to boron compound treatment separately or simultaneously, but during at least one of the dyeing step and the boron compound treatment step. It is desirable from the viewpoint of productivity to carry out uniaxial stretching.

  The stretching is desirably performed in a uniaxial direction by 3 to 10 times, preferably 3.5 to 6 times. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The stretching temperature is preferably selected from 40 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be carried out not only in one stage but also in any stage of the production process.

  The film is dyed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used, the iodine concentration is 0.1 to 2 g / L, the potassium iodide concentration is 10 to 50 g / L, and the potassium iodide / iodine weight ratio is 20 to 100. Is appropriate. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent. As the contact means, any means such as dipping, coating, spraying and the like can be applied.

  The dyed film is then treated with a boron compound. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.5 to 2 mol / L, and it is practically desirable for a small amount of potassium iodide to coexist in the solution. The treatment method is preferably an immersion method, but of course, an application method and a spray method can also be carried out. The temperature during the treatment is preferably about 50 to 70 ° C., and the treatment time is preferably about 5 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

  The light transmittance of the polarizing film of the present invention is preferably 43% or more, more preferably 44% or more. If it is less than 43%, high brightness of the liquid crystal display cannot be achieved. The light transmittance of the polarizing film is a value obtained by measuring the light transmittance of the polarizing film alone using a spectrophotometer.

  Further, the polarization degree of the polarizing film of the present invention is preferably 98% or more, more preferably 99% or more. If it is less than 98%, the definition of the displayed image is inferior, which is not preferable.

  The polarizing film thus obtained can be used as a polarizing plate by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both surfaces thereof. Examples of the protective film include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, cyclo or norbornene polyolefin, A sheet is raised.

  For the purpose of reducing the thickness of the polarizing film, instead of the protective film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied and laminated on one or both surfaces.

  A polarizing film (including at least one surface laminated with a protective film or a curable resin) has a transparent pressure-sensitive adhesive layer formed on a surface of the polarizing film as required by a generally known method. In some cases, it may be put to practical use. Examples of pressure-sensitive adhesive layers include acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α- such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid. Since the main component is a copolymer with a monoolefin carboxylic acid (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene), the polarizing properties of the polarizing film are not impaired. Although it is particularly preferable, the present invention is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether or rubber may be used.

  The polarizing film of the present invention includes an electronic desk calculator, an electronic watch, a word processor, a personal computer, a portable information terminal, a liquid crystal display device such as an instrument for automobiles and machinery, sunglasses, eye protection glasses, stereoscopic glasses, a display element (CRT, Used for reflection-reducing layers for LCD, etc., medical equipment, building materials, toys and the like.

  Hereinafter, the present invention will be specifically described with reference to examples. In the examples, “parts” and “%” are based on weight unless otherwise specified.

(1) Weight average molecular weight It measures on condition of the following by GPC-LALLS method.
1) GPC
Apparatus: Waters type 244 gel permeation chromatograph column: Tosoh Corporation TSK-gel-GMPW _XL (inner diameter 8 mm, length 30 cm, 2 pieces)
Solvent: 0.1 M Tris buffer (pH 7.9)
Flow rate: 0.5 ml / min Temperature: 23 ° C
Sample concentration: 0.040%
Filtration: 0.45 μm Mysori Disc W-25-5 manufactured by Tosoh Corporation
Injection volume: 0.2ml
Detection sensitivity (differential refractive index detector): 4 times 2) LALLS
Apparatus: Chromatrix KMX-6 type low angle laser light scattering photometer Temperature: 23 ° C
Wavelength: 633nm
Second virial coefficient × concentration: 0 mol / g
Refractive index density change (dn / dc): 0.159 ml / g
Filter: MILLIPORE 0.45 μm filter HAWP01300
Gain: 800mV

(2) Quantification of polyalkylene oxide group-containing compound Soxhlet extraction is performed for 6 hours using 1 g of a polyvinyl alcohol-based film and methanol as a solvent. The extract is concentrated to dryness with an evaporator, then made up with methanol, and each additive contained in the film is quantified by the LC-MASS method. The LC-MASS is measured using a high-performance liquid chromatography mass spectrometer “HP1100MSD” manufactured by HEWLETT PACKARD. The measurement conditions are as follows, but the model and measurement conditions are not limited to these.
Column: YMC-Pack ODS-A 150 × 4.6 mm manufactured by YMC Co., Ltd. D.
Column temperature: 30 ° C
Eluent: 0.1 M aqueous ammonium acetate solution / methanol, gradient measurement (25/75 → 0/100 (15 minutes))
Flow rate: 0.7 ml / min Injection volume: 20 μL
MASS: Electron spray ionization method Negative mode

(3) Light transmittance of polyvinyl alcohol film The light transmittance at 550 nm is measured using a spectrophotometer (manufactured by JASCO Corporation, trade name: Ubest-35).

(4) Light transmittance of polarizing film Measured using a high-speed multi-wavelength birefringence measuring apparatus (Otsuka Electronics Co., Ltd .: RETS-2000 wavelength: 550 nm).

(5) Polarization degree of polarizing film Calculated according to the following formula (4).
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2 (4)
H ₁₁ : Light transmittance at 550 nm measured in a state in which two polarizing films are superposed so that their alignment directions are the same direction H ₁ : Two polarizing films in a direction in which the alignment directions are orthogonal to each other The light transmittance at 550 nm measured in the state of being superimposed

Example 1
(Manufacture of polyvinyl alcohol film)
200 kg of 18 ° C. water was placed in a 500 l tank, and while stirring, 40 kg of a polyvinyl alcohol resin having a weight average molecular weight of 166000 and a saponification degree of 99.8 mol% was added and stirring was continued for 15 minutes. Thereafter, after draining water, 200 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated with a super decanter (manufactured by Sakai Kogyo Co., Ltd.) to obtain a polyvinyl alcohol resin wet cake having a water content of 43%.

70 kg of this polyvinyl alcohol-based resin wet cake was put in a dissolution can equipped with a Max blend type wing, and the following two types of nonionic surfactants were added. The value of equation (1) is 0.5.
Diethanol lauryl amide (HLB = 6)
21 g (0.05% based on polyvinyl alcohol resin)
Polyoxyethylene lauryl ether having an average condensation degree of 4 (HLB = 10)
8.5 g (0.02% with respect to polyvinyl alcohol resin)

  Furthermore, 10 kg of water and 4.2 kg of glycerin as a plasticizer were added, and water vapor was blown from the bottom of the can. When the internal resin temperature reaches 50 ° C., stirring (the number of revolutions: 5 rpm) is performed. When the internal resin temperature reaches 100 ° C., the system is pressurized. After the temperature is increased to 150 ° C., steam is blown into the system. Stopped (the amount of steam blown was 75 kg in total). After stirring for 30 minutes (rotation speed: 20 rpm) and uniformly dissolving, a polyvinyl alcohol resin aqueous solution with a resin concentration of 25% was obtained by adjusting the concentration.

Next, the obtained polyvinyl alcohol-based resin aqueous solution (liquid temperature 147 ° C.) was supplied from the gear pump 1 to the twin screw extruder, defoamed, and then discharged from the gear pump 2. The discharged polyvinyl alcohol resin aqueous solution was cast from a T-type slit die (straight manifold die) onto a drum-type roll to form a film. The conditions for such casting film formation are as follows.
Drum type roll Diameter (R1): 3200 mm, width: 4200 mm, rotation speed: 8 m / min, surface temperature: 90 ° C., resin temperature at T-type slit die outlet: 95 ° C.

Drying was performed while the front and back surfaces of the obtained film were alternately passed through a drying roll under the following conditions.
Drying roll Diameter (R2): 320 mm, width: 4200 mm, number (n): 10, rotation speed: 8 m / min, surface temperature: 75 ° C.

  Thereafter, heat treatment (condition: floating dryer (120 ° C., length 6 m)) was further performed to obtain a polyvinyl alcohol film (width 4000 mm, thickness 50 μm, length 5000 m). The obtained film had a light transmittance of 91.4%.

(Manufacture of polarizing film)
Furthermore, after the obtained polyvinyl alcohol film was swollen in a water washing tank (30 ° C.), it was immersed in an aqueous solution of 0.2 g / L of iodine and 15 g / L of potassium iodide at 30 ° C. for 240 seconds. Stretched 1.4 times, then immersed in an aqueous solution (55 ° C.) having a composition of boric acid 60 g / L and potassium iodide 30 g / L, and simultaneously treated with boric acid for 5 minutes while uniaxially stretching 2.3 times. A total of 5.6 times uniaxial stretching was performed. Then, it dried and obtained the polarizing film. The obtained polarizing film had a light transmittance of 44.1% and a polarization degree of 99.9%.

Examples 2 and 3
A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the surfactant shown in Table 1 was used. Table 1 shows the light transmittance of the obtained polyvinyl alcohol film, the light transmittance and the polarization degree of the polarizing film.

Example 4
A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1, except that the conditions for casting film formation were as follows.
Drum type roll Diameter (R1): 3200 mm, width: 4200 mm, rotation speed: 10 m / min, surface temperature: 85 ° C., resin temperature at T-type slit die outlet: 95 ° C.

Drying was performed while the front and back surfaces of the obtained film were alternately passed through a drying roll under the following conditions.
Drying roll Diameter (R2): 320 mm, width: 4200 mm, number (n): 20, rotational speed: 10 m / min, surface temperature: 75 ° C.

  Table 1 shows the light transmittance of the obtained polyvinyl alcohol film, the light transmittance and the polarization degree of the polarizing film.

Comparative Examples 1 and 2
A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the surfactant shown in Table 1 was used. Table 1 shows the light transmittance of the obtained polyvinyl alcohol film, the light transmittance and the polarization degree of the polarizing film.

Claims (9)

A polyvinyl alcohol film comprising 100 to 500 ppm of a polyalkylene oxide group-containing compound in the film. The method for producing a polyvinyl alcohol film according to claim 1, comprising a step of adding at least one nonionic surfactant to the polyvinyl alcohol resin so as to satisfy the following formula (1).
0.5 ≦ Σ {(HLB of nonionic surfactant) × (addition amount of nonionic surfactant to polyvinyl alcohol resin (% by weight))} ≦ 2 (1)
(In the formula, HLB means the hydrophilic / lipophilic balance, and Σ means the total when two or more nonionic surfactants are added.) The polyvinyl alcohol film according to claim 1, comprising a polyvinyl alcohol resin having a weight average molecular weight of 140,000 to 260000. The polyvinyl alcohol film according to claim 1 or 3, wherein the film width is 3.0 m or more. The polyvinyl alcohol film according to claim 1, 3 or 4, wherein the film has a thickness of 30 to 70 µm. 6. The polyvinyl alcohol film according to claim 1, wherein the length of the film is 4000 m or more. 7. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film is used as an original film of a polarizing film. A polarizing film comprising the polyvinyl alcohol-based film according to claim 1, 3, 4, 5, 6 or 7. A polarizing plate comprising a protective film provided on at least one surface of the polarizing film according to claim 8.