JPWO2016060097A1 - POLYVINYL ALCOHOL FILM, PROCESS FOR PRODUCING THE SAME, POLARIZING FILM, POLARIZING PLATE - Google Patents

Abstract

The present invention is a polyvinyl alcohol film obtained by forming a film-forming material containing a polyvinyl alcohol resin (A), and the polyvinyl alcohol film is 0 in a 5% by weight boric acid aqueous solution at 56 ° C. After immersion for 5 minutes (initial state), boric acid aqueous solution with true stress (Xa) when stretched 2.5 times the initial state at a stretching speed of 70 mm / sec in boric acid aqueous solution and continuing stretching Among them, a polyvinyl alcohol film satisfying the following formula (1) in true stress (Xc) when stretched 4.3 times in the initial state. For this reason, it is possible to obtain a polarizing film having excellent optical characteristics without increasing the stretching ratio, thereby shortening the conventional stretching time and improving productivity, and accompanying high stretching. It also has the effect of reducing the burden on the stretching device due to an increase in film tension and reducing the breakage due to high stretching. 5.0 ≦ Xc / Xa ≦ 9.0 (1)

Description

  The present invention relates to a polyvinyl alcohol film, in particular, a polyvinyl alcohol film for a polarizing film. More specifically, when producing a polarizing film, a polarizing film having excellent optical properties can be obtained without increasing the draw ratio. The present invention relates to a polyvinyl alcohol film that can be produced, a method for producing the same, a polarizing film, and a polarizing plate using 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 in 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 constituent element of a liquid crystal display, and in recent years, its use has been expanded to equipment 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 a polarizing film that is further superior in optical properties than conventional products.
Since the dichroic dye is oriented by dyeing and stretching the polyvinyl alcohol film, which is the raw material, with a dichroic dye such as iodine, the polarizing film is for improving the orientation, that is, the polarizing performance. It was necessary to increase the draw ratio.

  However, increasing the draw ratio improves the optical properties, which is one of the required properties of the polarizing film, but increases the productivity burden due to high stretching, and breaks the film due to high stretching. There is a problem that a problem occurs or a yield rate is reduced due to an increase in neck-in (width shrinkage).

  For this reason, as a means for solving the problem of film breakage due to high stretching, for example, a polyvinyl alcohol film having a swelling degree (A) of 190 to 230% and a thickness of 40 μm or less, A polyvinyl alcohol film having a degree of swelling (B) of 260% or more after stretching at a stretching ratio of 3 in water at 30 ° C. has been proposed (for example, Patent Document 1).

  On the other hand, as means for obtaining a polarizing film having excellent optical characteristics without increasing the draw ratio, for example, polyvinyl alcohol resin (X) and a polyvinyl alcohol system containing a 1,2-diol bond in the side chain. It is proposed to use a polyvinyl alcohol-based film made of a resin (Y), and a polyvinyl alcohol-based film in which the weight swelling degree (W) of the polyvinyl alcohol-based film obtained from this polyvinyl alcohol-based resin is 200 to 300% by weight. (For example, Patent Document 2).

International Publication No. 2014/50697 JP 2009-13368 A

  However, in general, when manufacturing a polarizing film, the optical characteristics are intended to be improved by increasing the draw ratio, whereas the technique disclosed in Patent Document 1 reduces the stretch stress. Since it is intended to reduce the breakage during stretching, a satisfactory polarizing film cannot be obtained with a film having a low stretch ratio. Actually, also in the Example of the said patent document 1, when manufacturing a polarizing film, it is performed by high stretch ratios, such as 6.4 times instead of a low stretch ratio. For this reason, neck-in (width shrinkage) due to high stretching becomes large, and there is a concern over the recent increase in the size of liquid crystal screens.

  Moreover, in the disclosed technique of Patent Document 2, although a polarizing film is manufactured at a low stretch ratio such as 4 to 6 times as compared with the conventional technique, the optical characteristics are not yet satisfactory, Further improvements were required.

  In view of this, the present invention provides a polyvinyl alcohol film capable of obtaining a polarizing film having excellent optical characteristics without increasing the draw ratio when manufacturing a polarizing film, and a method for manufacturing the same. Furthermore, it is an object of the present invention to provide a polarizing film comprising such a polyvinyl alcohol film and a polarizing plate.

  However, as a result of intensive studies by the present inventors to solve the above problems, the true stress at the time of stretching at each stretching ratio when the polyvinyl alcohol film is stretched in a boric acid aqueous solution under predetermined conditions. By setting the ratio (Xc / Xa) of the true stress (Xc) at the time of 4.3 times to the true stress (Xa) at the time of 2.5 times the stretching (Xc / Xa), In addition to the setting, the ratio (Xc / Xa) of the true stress (Xc) at the 4.3 times stretching to the true stress (Xa) at the 2.5 times stretching is the true stress at the 2.5 times stretching. By setting the ratio (Xb / Xa) or more of the true stress (Xb) at the time of stretching 3.4 times to the stress (Xa), it is a polarization having excellent optical characteristics without increasing the stretching ratio as in the prior art. A polyvinyl alcohol film capable of obtaining a film is obtained. Heading the door, and have completed the present invention.

  That is, in general, when the polyvinyl alcohol film is thick, the film is unlikely to break even at a high draw ratio such as a draw ratio exceeding 6 times, for example, a draw ratio of 6.4 times. However, the thinner the film, the greater the possibility of breakage due to stretching, and it becomes difficult to perform high stretching such that the stretching ratio exceeds 6 times. When the draw ratio is 6 times and 6.4 times, it is merely a difference of 0.4 on the numerical value, but even if the difference in the numerical value of the draw ratio becomes smaller as the film becomes a thin film, the industrial production This is a very big difference. From this, when the same optical characteristics are desired, it is desired that the draw ratio is as low as possible. In the present invention, based on such circumstances, as a result of repeated research on the characteristics of the polyvinyl alcohol-based film, the above-described characteristics can be obtained by changing the heat roll temperature and the like to film forming conditions suitable for thin films. The present invention has been found that a polyvinyl alcohol film can be obtained as a polarizing film material excellent in optical properties without having a high draw ratio as in the prior art.

<Summary of the present invention>
That is, the present invention is a polyvinyl alcohol film obtained by forming a film forming material containing the polyvinyl alcohol resin (A), and the polyvinyl alcohol film is 56 ° C. in a 5% by weight boric acid aqueous solution. After being soaked for 0.5 minutes (initial state), in the boric acid aqueous solution, the true stress (Xa) when stretched 2.5 times the initial state at a stretching speed of 70 mm / sec, A polyvinyl alcohol film satisfying the following formula (1) in the true stress (Xc) when stretched 4.3 times in the initial state in an acid aqueous solution is defined as a first gist.
5.0 ≦ Xc / Xa ≦ 9.0 (1)

Furthermore, the present invention relates to a polyvinyl alcohol film obtained by forming a film forming material containing the polyvinyl alcohol resin (A), wherein the polyvinyl alcohol film is contained in a 5% by weight boric acid aqueous solution. After being immersed for 0.5 minutes at 0 ° C. (initial state), the true stress (Xa) when stretched 2.5 times in the initial state at a stretching speed of 70 mm / sec in a boric acid aqueous solution, and continuing the stretching, True stress (Xb) when stretched 3.4 times in the initial state in an aqueous boric acid solution and true stress (Xc) when stretched 4.3 times in the initial state in an aqueous boric acid solution while further stretching. ), A polyvinyl alcohol film satisfying the following formulas (1) and (2) is defined as a second gist.
5.0 ≦ Xc / Xa ≦ 9.0 (1)
Xb / Xa ≦ Xc / Xa (2)

  The present invention is a method for producing the polyvinyl alcohol-based film, which comprises casting an aqueous solution of a film-forming material containing the polyvinyl alcohol-based resin (A) onto a first hot roll to form a film. [I], a step [II] of peeling the film from the first hot roll, and a step [III] of alternately passing the front and back of the film through a second hot roll group having a roll surface temperature of 30 to 95 ° C. The third gist is a method for producing a polyvinyl alcohol film comprising the step [IV] of heat-treating the film having passed through the second heat roll group in an atmosphere of 60 to 145 ° C.

  The present invention also provides a polarizing film comprising the polyvinyl alcohol film and a polarizing plate comprising a protective film provided on at least one surface of the polarizing film.

  In the present invention, when a polyvinyl alcohol film is stretched in a boric acid aqueous solution under a predetermined condition, the true stress generated at the time of stretching is larger than that in the past, and from this, molecules in the film It is presumed that the chain orientation is good, and therefore, it is presumed that a polarizing film having excellent optical properties can be obtained without increasing the draw ratio.

  Since the polyvinyl alcohol film of the present invention has the above properties, it is possible to obtain a polarizing film having excellent optical properties without increasing the stretching ratio, thereby shortening the conventional stretching time and improving productivity. In addition, there are also effects such as a reduction in the burden on the stretching apparatus due to an increase in film tension accompanying high stretching and a reduction in breakage due to high stretching. And the polyvinyl alcohol-type film of this invention is the original film used for the original film of a polarizing film used for liquid crystal display devices, such as polarized sunglasses and a liquid crystal television, a 1/2 wavelength plate, and a 1/4 wavelength plate, It is very useful as an original film of a retardation film used in a liquid crystal display device.

The present invention is described in detail below.
The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film obtained by forming a film forming material containing a polyvinyl alcohol resin (A), and has the following characteristics.

That is, the polyvinyl alcohol film is immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes (initial state). Thereafter, the stretching is continued in a boric acid aqueous solution at a stretching speed of 70 mm / sec, and the initial stress in the boric acid aqueous solution is maintained with the true stress (Xa) when stretched 2.5 times in the initial state and continuing the stretching. In the true stress (Xc) when the state is stretched 4.3 times, the following formula (1) is satisfied. Furthermore, the polyvinyl alcohol film is immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes (initial state). After that, in the boric acid aqueous solution, the stretching was continued at a stretching speed of 70 mm / sec, and the true stress (Xa) when stretched 2.5 times of the initial state and the initial state in the boric acid aqueous solution while continuing the stretching. The true stress (Xb) when stretched by 3.4 times and the true stress (Xc) when stretched by 4.3 times in the initial state in an aqueous boric acid solution while further stretching is expressed by the following formula (1) ) And (2) are satisfied.
5.0 ≦ Xc / Xa ≦ 9.0 (1)
Xb / Xa ≦ Xc / Xa (2)

In addition to the above properties, the polyvinyl alcohol film of the present invention is immersed in a 5 wt% boric acid aqueous solution at 56 ° C. for 0.5 minutes (initial state), and then in the boric acid aqueous solution. The true stress (Xa) when stretched 2.5 times in the initial state at a stretching speed of 70 mm / sec and the true stress when stretched 3.4 times in the initial state in an aqueous boric acid solution while continuing to stretch. In (Xb), what satisfies the following formula (3) is preferable.
1.9 ≦ Xb / Xa ≦ 3.0 (3)

Furthermore, in addition to the above properties, the polyvinyl alcohol film of the present invention is continuously stretched after being immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes (initial state). However, the true stress (Xb) when stretched 3.4 times in the initial state in the boric acid aqueous solution and the true stress when stretched 4.3 times in the initial state in the boric acid aqueous solution while further stretching. In stress (Xc), it is preferable to satisfy | fill following formula (4).
2.0 ≦ Xc / Xb ≦ 3.5 (4)

  The true stresses Xa, Xb and Xc in the above formulas (1), (2), (3) and (4) are 0.5% at 56 ° C. in a 5% by weight boric acid aqueous solution, respectively. After soaking for a minute (this is referred to as “initial state”), while continuing stretching at a stretching speed of 70 mm / sec in an aqueous boric acid solution, 2.5 times the initial state, 3.4 times the initial state, And each true stress (MPa) when extending | stretching to 4.3 time of the said initial state is said. Here, the stress is generally an engineering (nominal) stress, which is a value obtained by dividing the tension by the cross-sectional area before stretching. However, since the polyvinyl alcohol film shrinks in the width direction along with stretching, and the cross-sectional area decreases accordingly, the true stress cannot be calculated even if the tension at each stretching ratio is divided by the cross-sectional area before stretching. . Therefore, in the present invention, the true stress is used as the stress, the measurement is performed by the following measurement method, and the calculated stress is used as the true stress. Further, the above “while continuing stretching” refers to a state in which stretching is continued continuously (not intermittently) without interrupting the stretching process.

<Measurement method of true stress>
The true stress (MPa) is measured as follows. That is, a polyvinyl alcohol-based film was prepared, and the film was cut in the center with respect to the width direction so that the width (TD) direction was 2 cm × the machine (MD) direction was 12.5 cm, and both long sides were oily markers. After coloring, the thickness is measured with a micrometer at five points.

  Next, stretching in a 5% by weight boric acid aqueous solution is performed by fixing the cut out film to a predetermined jig so that both ends on the short side are 96 mm, and a 5% by weight boric acid aqueous solution at 56 ° C. Soak in for 0.5 minutes (this is referred to as “initial state”). During immersion, the grip interval is widened to the extent that no force is applied to remove the slack in the film. Then, the tension | tensile_strength with respect to a draw ratio is measured continuously, continuously uniaxially extending in a machine (MD) direction at a drawing speed of 70 mm / sec. And the tension | tensile_strength when a draw ratio is 2.5 times, 3.4 times, and 4.3 times is each read, continuing uniaxial stretching continuously.

  A tensile tester is used for measuring the tension. An example of such a tensile testing machine is a testing machine having a configuration in which a gate-type chuck is attached to a water tank having a glass window on the bottom so that the film can be stretched in water. In the above-mentioned testing machine, one end of the film is fixed in a 5% by weight boric acid aqueous solution, and the opposite side can be operated. In order to calculate the true stress, it is necessary to measure the width of the film sample being stretched, and a video camera for measuring the film sample width is installed in the water tank. During stretching, the center of the film in the MD direction moves with stretching, so a video camera for measuring the film sample width is also installed so that it moves in synchronization with the stretching speed, and the width at the center of the film can always be measured. It is like that. Using the rate of change in width calculated from the change in width during stretching, which is taken with a camera at the same time as stretching, the tension measured with such a testing machine is taken as the true stress (MPa). In the present invention, the same measurement is performed three times, and the average value is adopted.

Each true stress (Xa, Xb and Xc) (MPa) = tension (F) / cross-sectional area during stretching (S)
Cross-sectional area during stretching (S) = Sample cross-sectional area before stretching (S0) x Rate of change in width (W / W0)
Here, W is a sample (film) width during stretching, and W0 is a sample (film) width before stretching.

  In the formula (1), as described above, Xc / Xa is required to be 5.0 to 9.0, preferably 5.2 to 8.5, particularly preferably 5.4 to 8.0. It is. If this value is less than the above range, the orientation of the molecular chain in the film at the time of stretching will be poor and the polarizing performance will be reduced. If it exceeds the above range, the film will break at the time of stretching.

  Then, the true stress (Xa) in the above formula (1), that is, in the initial state, while continuously uniaxially stretching the polyvinyl alcohol film in a 5 wt% boric acid aqueous solution at a stretching rate of 70 mm / sec. The true stress (Xa) (MPa) when stretched 5 times is preferably 4.0 to 7.0 MPa, particularly 4.4 to 6.9 MPa, more preferably 4.6 to 6.8 MPa. Preferably there is. If the range is too small, swelling at the film end tends to progress and workability tends to be reduced. If it is too large, shrinkage in the width (TD) direction of the film increases and the yield tends to decrease. .

  In addition, the true stress (Xc) in the above formula (1), that is, the polyvinyl alcohol film was continuously uniaxially stretched in a 5% by weight boric acid aqueous solution at a stretching speed of 70 mm / sec, while the initial state was 4. The true stress (Xc) (MPa) when stretched 3 times is preferably 35.0 to 45.0 MPa, particularly 36.0 to 44.0 MPa, more preferably 37.0 to 43.0 MPa. Preferably there is. When the range is too small, the performance of the polarizing film tends to be lowered due to the decrease in the orientation of molecular chains in the film, and when it is too large, the film tends to break.

  Further, the true stress (Xb) in the above formula (1), that is, the initial state of the polyvinyl alcohol film, while continuously uniaxially stretching in a 5 wt% boric acid aqueous solution at a stretching speed of 70 mm / sec, The true stress (Xb) (MPa) when stretched 4 times is preferably 11.0 to 15.0 MPa, particularly 11.5 to 14.8 MPa, more preferably 12.0 to 14.5 MPa. Preferably there is. When this range is too small, there is a tendency that uneven polarization of the polarizing film is caused by stretching unevenness, and when it is too large, stretchability tends to be lowered (cannot be stretched to a predetermined stretching ratio).

  In the formula (2), as described above, the value of Xc / Xa is preferably not less than the value of Xb / Xa, more preferably 2.0 to 3.5 times the value of Xb / Xa, particularly 2. 5 to 3.3 times is preferable. When Xc / Xa is smaller than Xb / Xa, there is a tendency that the polarizing performance of the polarizing film is remarkably lowered or it is difficult to obtain the polarizing film.

  In the formula (3), as described above, Xb / Xa is preferably 1.9 to 3.0, more preferably 2.0 to 2.8, and particularly 2.1 to 2.7. Is preferred. When this value is too small, there is a tendency to cause uneven coloring of the polarizing film due to stretching unevenness during film stretching, and when it is too large, there is a tendency for stretchability to decrease.

  In the formula (4), as described above, Xc / Xb is preferably 2.0 to 3.5, more preferably 2.3 to 3.4, and particularly 2.5 to 3.3. Is preferred. If this value is too small, the performance of the polarizing film tends to deteriorate due to insufficient film stretching. If the value is too large, the polarizing film tends to break.

  The polyvinyl alcohol film of the present invention having the above properties is cast using a film forming material containing the polyvinyl alcohol resin (A).

<Polyvinyl alcohol resin (A)>
As the polyvinyl alcohol resin (A), an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of vinyl acetate and a copolymerizable component may be used. it can. 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.

  Moreover, as a polyvinyl alcohol-type resin (A), the polyvinyl alcohol-type resin which has a 1, 2- glycol bond in a side chain can also be used. Such a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain is, for example, (i) a method for saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method of saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate, (iii) saponifying and depolymerizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glyceryl monoallyl ether, or the like.

The average saponification degree of the polyvinyl alcohol resin (A) used in the present invention is usually preferably 90 mol% or more, particularly preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 99 mol%. The mol% or more, more preferably 99.5 mol% or more. When the average saponification degree is too small, there is a tendency that sufficient optical performance cannot be obtained when a polyvinyl alcohol resin is used as a polarizing film.
Here, the saponification degree in the present invention is obtained by analyzing the alkali consumption required for hydrolysis of residual vinyl acetate.

  Further, the viscosity of the polyvinyl alcohol resin (A) is preferably 8 to 500 mPa · s, particularly 20 to 400 mPa · s, more preferably 40 to 400 mPa, as a 4 wt% aqueous solution viscosity at 20 ° C. -S is preferable. If the viscosity of the 4% by weight aqueous solution is too small, the stretchability at the time of forming the polarizing film tends to decrease, and if too large, the flatness and transparency of the film tend to decrease.

  As a polyvinyl alcohol-type resin (A) used for this invention, in the said polyvinyl alcohol-type resin, you may use together 2 or more types from which modified | denatured seed | species, an average saponification degree, a viscosity, etc. differ.

  In this invention, a polyvinyl alcohol-type film is manufactured using the film forming material containing the said polyvinyl alcohol-type resin (A). In film production, for example, a known compounding agent such as a plasticizer (B) or a surfactant (C) is blended and manufactured.

  The plasticizer (B) generally contributes effectively to stretchability when producing a polarizing film. For example, glycerins such as glycerin, diglycerin, triglycerin, ethylene glycol, diethylene glycol, triglycerin. Examples thereof include alkylene glycols or polyalkylene glycols such as ethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol and polypropylene glycol, and trimethylolpropane. These plasticizers (B) can be used alone or in combination of two or more. Among them, particularly preferred are glycerin alone, glycerin and diglycerin, or a combination of glycerin and trimethylolpropane. When glycerin and diglycerin are used in combination, usually glycerin / diglycerin (weight ratio) = 20/80 to 80/20, and when glycerin and trimethylolpropane are used in combination, it is usually glycerin / trimethylolpropane (weight ratio). ) = 20/80 to 80/20.

  As content of this plasticizer (B), it is preferable that it is 1-35 weight part with respect to 100 weight part of polyvinyl alcohol-type resin (A), 3-30 weight part especially, Furthermore, 7-25 weight. Part. When there is too little content of a plasticizer (B), there exists a tendency for a drawability to fall at the time of preparation of a polarizing film, and when too much, there exists a tendency for the temporal stability of the polyvinyl alcohol-type film obtained to fall.

  In addition, the surfactant (C) generally has a function of suppressing film surface smoothness and adhesion between films when wound into a roll. For example, an anionic surfactant or a nonionic interface An active agent can be used individually or in combination of 2 or more types. In particular, the combined use of an anionic surfactant and a nonionic surfactant is preferable from the viewpoint of the transparency of the film.

  Examples of such anionic surfactants include aliphatic alkyl sulfonates, alkyl sulfate esters, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phenyl ether sulfates, higher fatty acid alkanolamide sulfates, and the like. In addition to these anionic surfactants, sulfate esters such as sulfated oils, higher alcohol ethoxy sulfates, monoglyculates, fatty acid soaps, N-acyl amino acids and salts thereof, polyoxyethylene alkyls Carboxylate types such as ester carboxylates, acylated peptides, alkylbenzene sulfonates, alkylnaphthalene sulfonates, naphthalene sulfonic acid salt formalin polycondensates, melamine sulfonic acid salt formalin condensates, dialkyl sulfosuccinic acid Steric salts, sulfosuccinic acid alkyl disalts, polyoxyethylene alkyl sulfosuccinic acid disalts, alkyl sulfoacetates, α-olefin sulfonates, N-acylmethyl taurates, dimethyl-5-sulfoisophthalate sodium salts, etc. Examples thereof include anionic surfactants such as salt type, phosphoric acid ester salt type such as polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, and alkyl phosphate.

  On the other hand, as the nonionic surfactant, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, higher fatty acid mono- or dialkanolamide, higher fatty acid amide, polyoxyethylene alkylamine, polyoxyethylene higher fatty acid amide, And amine oxides. In addition to these nonionic surfactants, ethylene oxide derivatives of alkylphenol formalin condensates, polyoxyethylene polyoxypropylene block polymers, polyoxyethylene glycerin fatty acid esters, polyoxyethylene castor oil and hydrogenated castor oil, poly Ether-type surfactants such as oxyethylene sorbitan fatty acid esters and polyoxyethylene sorbitol fatty acid esters, and ester-type surfactants such as polyethylene glycol fatty acid esters, sorbitan fatty acid esters, fatty acid monoglycerides, propylene glycol fatty acid esters, and sucrose fatty acid esters , Etc.

  As content of this surfactant (C), it is preferable that it is 0.01-1 weight part with respect to 100 weight part of polyvinyl alcohol-type resin (A), Most preferably, it is 0.02-0.5 weight. Parts, more preferably 0.03 to 0.2 parts by weight. If the content of the surfactant (C) is too small, the anti-blocking effect tends to be difficult to obtain, and if it is too large, the transparency of the film tends to decrease.

  When an anionic surfactant and a nonionic surfactant are used in combination, the anionic surfactant is 0.01 to 1 part by weight, particularly 100 parts by weight of the polyvinyl alcohol resin (A). 0.02 to 0.2 parts by weight, more preferably 0.03 to 0.1 parts by weight, and nonionic surfactant is 0.01 to 1 part by weight, particularly 0.02 to 0.2 parts by weight. It is preferable that it is a weight part, Furthermore, it is 0.03-0.1 weight part. If the amount of the anionic surfactant is too small, the dispersibility of the dye at the time of preparing the polarizing film tends to decrease, and the dyeing spots tend to increase.If the amount is too large, foaming occurs when the polyvinyl alcohol resin is dissolved, and bubbles are generated in the film. It tends to be mixed and cannot be used as an optical film. If the nonionic surfactant is too small, it is difficult to obtain an anti-blocking effect, and if it is too much, the transparency and flatness of the film tend to be lowered.

  In the present invention, it is also useful to add an antioxidant in order to prevent yellowing of the film. Examples of the antioxidant include phenolic antioxidants, and 2,6-di- -T-butyl-p-cresol, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol) and the like are preferable. The antioxidant is preferably used in the range of about 2 to 100 ppm with respect to the polyvinyl alcohol-based resin (A).

  Thus, in the present invention, a film-forming material is prepared using the polyvinyl alcohol-based resin (A). Preferably, the polyvinyl alcohol-based resin (A) further includes at least a plasticizer (B) and a surfactant (C). One is used to prepare a film-forming material. And this film forming material is formed into a film and a polyvinyl alcohol-type film is obtained.

<Method for producing polyvinyl alcohol film>
Hereinafter, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated concretely.

  In the present invention, a film-forming material is prepared using at least one of a polyvinyl alcohol-based resin (A), preferably a plasticizer (B) and a surfactant (C), and an aqueous solution of the film-forming material is used as a drum-type roll. Alternatively, it is cast on an endless belt, preferably a drum-type roll, formed into a film, dried, and then heat-treated to produce a polyvinyl alcohol film.

  In the production method of the present invention, first, the polyvinyl alcohol-based resin (A) powder is washed in order to remove sodium acetate usually contained in the resin. In washing, methanol or water is used for washing. However, the method of washing with methanol requires solvent recovery and therefore, the method of washing with water is more preferable.

  Next, the water-containing polyvinyl alcohol-based resin (A) wet cake after washing is dissolved to prepare a polyvinyl alcohol-based resin (A) aqueous solution. When the water-containing polyvinyl alcohol-based resin (A) wet cake is dissolved in water as it is, Since a desired high-concentration aqueous solution cannot be obtained, it is preferable to perform dehydration once. The dehydration method is not particularly limited, but a method using centrifugal force is common.

  By the washing and dehydration, a wet polyvinyl alcohol resin (A) wet cake having a water content of 50% by weight or less, preferably 30 to 45% by weight, is preferred. If the water content is too high, it tends to be difficult to obtain a desired aqueous solution concentration.

  Next, an aqueous solution of a film forming material used for forming a polyvinyl alcohol film is prepared by adding water, water-containing polyvinyl alcohol resin (A) wet cake after dehydration, plasticizer (B), and surfactant in a dissolution tank. (C) and the like are prepared, heated, stirred and dissolved. In the production method of the present invention, it is particularly preferable in terms of solubility that water-containing polyvinyl alcohol resin (A) wet cake is dissolved by blowing water vapor in a dissolution tank equipped with a vertical circulation flow generation type stirring blade. .

  When the water-containing polyvinyl alcohol resin (A) wet cake is dissolved by blowing water vapor in a dissolution tank equipped with a vertical circulation flow generation type stirring blade, water vapor is blown and the resin temperature is 40 to 80 ° C., preferably 45 Starting at the time when the temperature reaches ˜70 ° C. is preferable in that it can be uniformly dissolved. If the resin temperature is too low, the load on the motor tends to increase. If the resin temperature is too high, the polyvinyl alcohol resin (A) tends to be hardened and cannot be uniformly dissolved. Furthermore, it is also preferable from the viewpoint that uniform melting can be achieved by blowing water vapor and pressurizing the inside of the tank when the resin temperature is usually 90 to 100 ° C, preferably 95 to 100 ° C. If the resin temperature is too low, undissolved products tend to be formed. Then, when the resin temperature reaches 130 to 150 ° C., the blowing of water vapor is finished, and stirring is continued for 0.5 to 3 hours to perform dissolution. After dissolution, the concentration is adjusted so that the desired concentration is obtained.

  The concentration of the aqueous solution of the film-forming material thus obtained is preferably from 10 to 50% by weight, more preferably from 15 to 40% by weight, especially considering that the physical properties (each true stress, etc.) are satisfied. Preferably it is 20-30 weight%. If the concentration is too high or too low, it is difficult to form a uniform film, and the stress during stretching may be increased or decreased due to film thickness unevenness.

  Next, the aqueous solution of the obtained film forming material is defoamed. Examples of the defoaming method include stationary defoaming and defoaming with a multi-screw extruder, but in the production method of the present invention, there is a method of defoaming using a multi-screw extruder in terms of productivity. preferable.

  After the defoaming treatment, the aqueous solution of the film forming material discharged from the multi-screw extruder is introduced into a T-type slit die by a certain amount and cast onto a drum-type roll or an endless belt to form a film, Dry and heat treated.

  As the T-type slit die, a T-type slit die having an elongated rectangle is usually used. The resin temperature at the exit of the T-type slit die is usually preferably 80 to 100 ° C, more preferably 85 to 98 ° C. If the resin temperature at the exit of the T-type slit die is too low, there is a tendency to cause poor flow, and if it is too high, there is a tendency to foam.

  The casting is performed with a drum-type roll or an endless belt, but it is preferably performed with a drum-type roll in terms of widening, lengthening, film thickness uniformity, and the like.

  In casting the film with the drum-type roll, for example, the rotation speed of the drum is preferably 5 to 30 m / min, and particularly preferably 6 to 20 m / min. The surface temperature of the drum-type roll is preferably 50 to 99 ° C, more preferably 60 to 97 ° C. If the surface temperature of the drum-type roll is too low, drying tends to be poor, and if it is too high, foaming tends to occur.

  Drying of the polyvinyl alcohol film formed by the drum-type roll is performed by alternately passing the front and back surfaces of the film through a plurality of heat roll groups. The surface temperature of the heat roll group is preferably set to a low temperature compared to the conventional one, specifically preferably 30 to 95 ° C, more preferably 40 to 85 ° C, particularly 45 to 75. It is preferable that it is ° C. If the surface temperature is too low or too high, the molecular orientation becomes random and the stress tends to decrease.

  In the present invention, heat treatment is performed after the drying.

  The heat treatment is preferably performed at a relatively high temperature such as 60 to 145 ° C., more preferably 90 to 140 ° C., and particularly preferably 100 to 135 ° C. If the heat treatment temperature is too low, the film moisture and the degree of swelling tend to increase and the stress tends to decrease too much. If too high, the film moisture and the degree of swelling tend to decrease and the stress tends to become too high. Moreover, as a heat processing method, for example, (1) The method of passing the roll (1-30 pieces) 0.2-2m in diameter which carried out the hard chrome plating process or the mirror surface process, (2) Floating type dryer (long And the like, and the like.

  Thus, a polyvinyl alcohol-based film can be obtained. In the present invention, among the above production methods, the following formulas [I] to [IV] are included, and the relational expression of the true stress, which is a feature of the present invention, is shown below. It is preferable in that it can be satisfied.

  That is, a step [I] of casting an aqueous solution of a film-forming material containing a polyvinyl alcohol-based resin (A) onto a first hot roll to form a film, and a step of peeling the film from the first hot roll [II] and a step [III] in which the front and back of the film are alternately passed through a second hot roll group having a roll surface temperature of 30 to 95 ° C., and a film that is passed through the second hot roll group is 60 to 145. It includes a step [IV] of performing a heat treatment in an atmosphere of ° C.

  In the step [I], the first heat roll is a drum-type roll or an endless belt, and an aqueous solution of the film forming material is cast onto the first heat roll (drum-type roll or endless belt).

  And in the said process [II], it dries on a 1st heat roll, and it peels in the state where the film moisture content becomes like this. Preferably it is 10-25%, More preferably, it is 12-20%. If the moisture content is too low, the tension at the time of peeling tends to be high and the film tends to stretch, and if it is too high, the film tends to become uneven in the width direction at the time of peeling.

  Next, in the step [III], the film peeled from the first heat roll is sent to at least five or more second heat roll groups so that the front surface and the back surface of the film are alternately passed. At this time, the surface temperature of at least 5 or more second heat roll groups is preferably 30 to 95 ° C as described above, more preferably 40 to 85 ° C, and particularly preferably 45 to 75 ° C. It is.

  Furthermore, in the said process [IV], the film which passed the said 2nd heat roll group is heat-processed in comparatively high temperature atmosphere compared with the past. As described above, the heat treatment conditions at this time are preferably 60 to 145 ° C., further 90 to 140 ° C., and particularly 100 to 135 ° C.

  Further, in the present invention, the film forming material is cast, dried and heat-treated, and the film is wound up. The draw ratio at this time is preferably 0.9 to 1.1, particularly preferably. Is from 0.95 to 1.07, more preferably from 0.98 to 1.05. If the draw ratio is too low, the film tends to be loosened during film transportation and wrinkles are liable to occur. Tend to be higher.

  Here, the draw ratio refers to a ratio determined by the film winding speed / the rotation speed of the first heat roll. The draw ratio is conventionally in the range of 0.9 to 1.1. In the present invention, the draw ratio is set lower than in the past from the viewpoint of suppressing swelling unevenness in the film width direction. It is preferable.

<Polyvinyl alcohol film>

  The polyvinyl alcohol film of the present invention thus obtained has a thickness of usually 5 to 50 μm, particularly 10 to 45 μm, more preferably 15 to 40 μm, for example, when the polarizing film application is considered. preferable.

  Further, the polyvinyl alcohol film of the present invention thus obtained has a retardation value of 10 to 50 nm, particularly 10 to 30 nm, more preferably 10 to 25 nm in that it is uniformly stretched in the width direction. preferable.

  In the polyvinyl alcohol film of the present invention, the degree of weight swelling (W) at 30 ° C. is preferably 190 to 240% from the viewpoint of dyeability of the dye, particularly 190 to 230%, more preferably 195. It is preferably 225%, in particular 195 to 220%. If the weight swelling degree (W) is too small, the stretchability at the time of producing the polarizing film tends to be lowered. If it is too large, the stretchability is improved, but the polarizing performance of the polarizing film tends to be lowered.

  In order to control the weight swelling degree (W) within the above range, for example, the following method is used. The film forming material containing the polyvinyl alcohol resin (A) is cast on a drum-type roll or an endless belt, preferably a drum-type roll, and then the front and back surfaces are alternately dried by a plurality of rotary heating roll groups, so that the moisture content is After continuously forming a 5 to 30% by weight polyvinyl alcohol film, the temperature of the floating dryer or rotary heating roll is adjusted by heat treatment in the range of 100 to 135 ° C. If the moisture content in the film is too high, the crystallization rate of the polyvinyl alcohol-based resin (A) is slowed, so that it is difficult to obtain a heat treatment effect. If the moisture content is too low, heat treatment at 150 ° C. or higher is required. Therefore, the quality of the film tends to be lowered, for example, the degree of weight swelling of the film becomes too low or the film tends to yellow.

  However, without being limited to these methods, the same heat treatment conditions can be adjusted depending on the type and amount of the plasticizer. Generally, if the amount of the plasticizer added is increased, the crystallinity of the polyvinyl alcohol-based resin (A) decreases, so that the degree of weight swelling (W) tends to decrease. Moreover, even if the addition amount of a plasticizer is the same, it is possible to adjust the crystallinity degree of polyvinyl alcohol-type resin (A) with the kind of plasticizer, and it is compatible with polyvinyl alcohol-type resin (A). A good plasticizer has a high effect of lowering the crystallinity, and therefore the weight swelling degree (W) can be adjusted by reducing the amount added. On the other hand, plasticizers with poor compatibility have a low effect of reducing the crystallinity, so that the degree of weight swelling (W) can be adjusted by increasing the amount of plasticizer added.

  Furthermore, even if it is the same heat processing temperature, a weight swelling degree (W) can be adjusted with the saponification degree and polymerization degree of polyvinyl alcohol-type resin (A). Further, the degree of weight swelling (W) may also be adjusted by drying conditions during film formation, for example, conditions for drying moisture in the film such as high temperature drying, low temperature drying, and high humidity drying. Among them, in terms of productivity, it is preferable to adjust the degree of weight swelling (W) by heat treatment after the moisture content during film formation becomes 5 to 30% by weight, and glycerin is mainly used as a plasticizer. More preferably, the degree of weight swelling (W) is adjusted in the range of 100 to 135 ° C. for heat treatment.

Here, the weight swelling degree (W) is measured as follows.
That is, the film is cut into 10 cm × 10 cm and immersed in an ion exchange water bath adjusted to 30 ° C. for 15 minutes. Next, the film is taken out and spread out on the filter paper (5A), and the filter paper (5A) is overlaid on the film, and 15 cm × 15 cm × 0.4 cm (4.4 g / cm ² ) thereon. The SUS plate is placed for 5 seconds to remove water adhering to the film surface. This film is immediately put into a weighing bottle, the weight is measured, and this is defined as the film weight A at the time of swelling. The above operation is performed in an environment of 23 ° C. and 50% RH.
Next, the film is left in a drier at 105 ° C. for 16 hours to remove moisture in the film, and then the film is taken out, immediately put into a weighing bottle, weighed, and dried. Let it be weight B. And it calculates | requires from the following Formula based on the film weight A at the time of swelling, and the film weight B after drying.
Weight swelling degree (W) (%) = A / B × 100

  In the polyvinyl alcohol film of the present invention, the area swelling degree (Y) at 30 ° C. is preferably 130 to 170% from the viewpoint of dyeability of the dye, particularly 135 to 165%, more preferably 140. It is preferably ˜160%. If the area swelling degree (Y) is too small, the stress during stretching increases rapidly and tends to break, and if it is too large, the stress during stretching does not rise and orientation tends to decrease.

  In order to control the degree of area swelling (Y) within the above range, for example, the following method is used. The film forming material containing the polyvinyl alcohol resin (A) is cast on a drum-type roll or an endless belt, preferably a drum-type roll, and then the front and back surfaces are alternately dried by a plurality of rotary heating roll groups, so that the moisture content is After continuously forming a 5 to 30% by weight polyvinyl alcohol film, the temperature of the floating dryer or rotary heating roll is adjusted by heat treatment in the range of 100 to 135 ° C. If the moisture content in the film is too high, the crystallization rate of the polyvinyl alcohol-based resin (A) is slowed, so that it is difficult to obtain a heat treatment effect. If the moisture content is too low, heat treatment at 150 ° C. or higher is required. Therefore, the area swelling degree (Y) of the film tends to be too low, or the film tends to yellow, and the quality tends to decrease.

  However, without being limited to these methods, the same heat treatment conditions can be adjusted depending on the type and amount of the plasticizer. Generally, since the crystallinity of polyvinyl alcohol-type resin (A) will fall if the addition amount of a plasticizer is increased, there exists a tendency for an area swelling degree (Y) to become low. Moreover, even if the addition amount of a plasticizer is the same, it is possible to adjust the crystallinity degree of polyvinyl alcohol-type resin (A) with the kind of plasticizer, and it is compatible with polyvinyl alcohol-type resin (A). A good plasticizer has a high effect of lowering the crystallinity. Therefore, the area swelling degree (Y) can be adjusted by reducing the amount of addition. Conversely, plasticizers with poor compatibility have a low effect of reducing the degree of crystallinity, and therefore the area swelling degree (Y) can be adjusted by increasing the amount of plasticizer added.

  Furthermore, even at the same heat treatment temperature, the area swelling degree (Y) can be adjusted by the saponification degree and the polymerization degree of the polyvinyl alcohol-based resin (A). Also, the area swelling degree (Y) may be adjusted by drying conditions during film formation, for example, conditions for drying moisture in the film such as high temperature drying, low temperature drying, and high humidity drying. Among them, in terms of productivity, it is preferable to adjust the area swelling degree (Y) by heat treatment after the moisture content during film formation becomes 5 to 30% by weight, and glycerin is mainly used as a plasticizer. More preferably, the area swelling degree (Y) is adjusted in the range of 100 to 135 ° C.

Here, the area swelling degree (Y) is measured as follows.
That is, the film is cut into a 10 cm × 10 cm square so as to be parallel to the machine (MD) direction and the width (TD) direction, placed on a flat glass plate, and the dimensions in the MD direction and the TD direction are measured. Next, after immersing in an ion exchange water bath adjusted to 30 ° C. for 5 minutes, the film is taken out and immediately placed on a flat glass plate, and the dimensions in the MD direction and the TD direction are measured with calipers, Obtained by the following formula. The above operation is performed in an environment of 23 ° C. and 50% RH.
Swelling degree in MD direction ( _XMD ) (%)
= (Dimension in MD direction after immersion / Dimension in MD direction before immersion) × 100
Swelling degree in TD direction (X _TD ) (%)
= (Dimension in TD direction after immersion / Dimension in TD direction before immersion) × 100
Area swelling degree (Y) (%)
= (MD swelling degree (X _MD ) / 100) × (TD swelling degree (X _TD ) / 100) × 100

  In the present invention, the syndiotacticity of the polyvinyl alcohol film is preferably 40 to 60%, particularly 45 to 55%, more preferably 50 to 54%. If the syndiotacticity is too small, However, if it is too large, the stretchability tends to be lowered and the film tends to break.

  In order to control the syndiotacticity within the above range, for example, a method of blending a polyvinyl alcohol resin having a high syndiotacticity with a polyvinyl alcohol resin having a low syndiotacticity, or a polymerization temperature of vinyl acetate is set. There are a method of saponifying a changed one, a method of saponifying a polymer of vinyl ester such as vinyl pivalate, vinyl trifluoroacetate, vinyl trichloroacetate and the like.

Here, syndiotacticity is measured as follows. That is, it is a value by a dyad display obtained by measuring a polyvinyl alcohol film in a solvent (D ₂ O) by ¹³ C-NMR method.

Furthermore, the obtained polyvinyl alcohol film has a light transmittance of 90% or more in the entire visible light range, and is very useful as an optical polyvinyl alcohol film.
Therefore, the polyvinyl alcohol film of the present invention is preferably used as a raw film for an optical film, particularly as a raw film for a polarizing film.

<Polarizing film and polarizing plate>
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 dyed by dipping in an iodine or dichroic dye solution, and then treated with a boron compound. After stretching and dyeing at the same time, a boron compound treatment is performed. 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 in terms of productivity to perform uniaxial stretching.

  Stretching is desirably 2.5 to 10 times, preferably 2.8 to 7 times, in the uniaxial direction. In the present invention, a polarizing film having excellent optical properties even when stretching is particularly up to 6 times. can do. 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 20 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing 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 0.3 to 2 mol / L, and it is practically desirable that 10 to 100 g / L of potassium iodide 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 20 to 60 ° C., and the treatment time is preferably about 3 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

  The polarizing film of the present invention 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 sides thereof. As a protective film used for the polarizing plate of the present invention, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, cyclo type Or a film or sheet of norbornene-based polyolefin.

  In addition, for the purpose of thinning 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 side or both sides.

  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 is an electronic desk calculator, electronic clock, word processor, personal computer, television, portable information terminal, liquid crystal display device such as automobiles and machinery instruments, sunglasses, eyeglasses, stereoscopic glasses, display element ( CRT, LCD, etc.) for reflection reduction layer, medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis.
Each physical property was measured and calculated as follows.

(1) Average saponification degree (mol%) of polyvinyl alcohol resin
The analysis was carried out with the alkali consumption required for hydrolysis of the residual vinyl acetate units.

(2) 4% aqueous solution viscosity (mPa · s) of polyvinyl alcohol resin
The water temperature was adjusted to 20 ° C. and measured with a Heppler viscometer.

(3) Each true stress (Xa, Xb, Xc) and each true stress ratio (Xc / Xa, Xb / Xa, Xc / Xb)
A polyvinyl alcohol-based film was prepared, and the center of the film was cut out with respect to the width direction so as to be 2 cm in the width (TD) direction × 12.5 cm in the machine (MD) direction, and both long sides were colored with oily markers. Thereafter, the thickness was measured at five points with a micrometer.

  Next, stretching in a 5% boric acid aqueous solution is performed by fixing the cut out film to a predetermined jig so that both ends on the short side are 96 mm, and in a 5% boric acid aqueous solution at 56 ° C. Immersion for 0.5 minutes (this is referred to as “initial state”). During dipping, the grip interval was widened to the extent that no force was applied to remove the slack in the film. Then, the tension | tensile_strength with respect to a draw ratio was measured continuously, uniaxially stretching in a machine (MD) direction at a drawing speed of 70 mm / sec. And the tension | tensile_strength when a draw ratio is 2.5 times, 3.4 times, and 4.3 times was each read, continuing uniaxial stretching continuously.

  For the measurement of the tension, a testing machine equipped with a configuration in which a gate-type chuck was attached to a water tank having a glass window on the bottom so that the film could be stretched in water or the like. In the above tester, one end of the film is fixed in a 5% boric acid aqueous solution, and the opposite side can be operated. In order to calculate the true stress, it was necessary to measure the width of the film sample during stretching, and a video camera for measuring the film sample width was installed in the water tank. During stretching, the center of the film in the MD direction moves with stretching, so a video camera for measuring the film sample width is also installed so that it moves in synchronization with the stretching speed, and the width at the center of the film can always be measured. It is like that. The tension measured by such a testing machine is divided by the cross-sectional area after stretching taken by the camera at the same time as stretching, and the value calculated by the following formula is defined as true stress (MPa). And the same measurement was performed 3 times and the average value was employ | adopted.

Each true stress (Xa, Xb and Xc) (MPa) = tension (F) / cross-sectional area after stretching (S)
Cross-sectional area after stretching (S) = sample cross-sectional area before stretching (S0) × rate of change in width (W / W0)
Here, W is the sample (film) width after stretching, and W0 is the sample (film) width before stretching.
Xc / Xa
= True stress (Xc) when stretched to 4.3 times / True stress (Xa) when stretched to 2.5 times
Xb / Xa
= True stress when stretched to 3.4 times (Xb) / True stress when stretched to 2.5 times (Xa)
Xc / Xb
= True stress (Xc) when stretched to 4.3 times / True stress (Xc) when stretched to 3.4 times

(4) Area swelling degree (Y) (%)
The film was cut into a 10 cm × 10 cm square so as to be parallel to the machine (MD) direction and the width (TD) direction, placed on a flat glass plate, and the dimensions in the MD direction and the TD direction were measured with calipers. Next, after immersing in an ion exchange water bath adjusted to 30 ° C. for 5 minutes, the film is taken out and immediately placed on a flat glass plate, and the dimensions in the MD direction and the TD direction are measured with calipers, Calculated by the following formula. The above operation was performed in an environment of 23 ° C. and 50% RH.
Swelling degree in MD direction ( _XMD ) (%)
= (Dimension in MD direction after immersion / Dimension in MD direction before immersion) × 100
Swelling degree in TD direction (X _TD ) (%)
= (Dimension in TD direction after immersion / Dimension in TD direction before immersion) × 100
Area swelling degree (Y) (%)
= (MD swelling degree (X _MD ) / 100) × (TD swelling degree (X _TD ) / 100) × 100

(5) Weight swelling degree (W) (%)
The film was cut into 10 cm × 10 cm and immersed in an ion exchange water bath adjusted to 30 ° C. for 15 minutes. Next, the film is taken out, and the film is spread on the filter paper (5A). Further, the filter paper (5A) is overlaid on the film, and 15 cm × 15 cm × 0.4 cm (4.4 g / cm ² ) thereon. The SUS plate was placed for 5 seconds to remove water adhering to the film surface. This film was immediately put into a weighing bottle, the weight was measured, and this was defined as the film weight A at the time of swelling. The above operation was performed in an environment of 23 ° C. and 50% RH.
Next, the film is left in a drier at 105 ° C. for 16 hours to remove moisture in the film, and then the film is taken out, immediately put into a weighing bottle, weighed, and dried. Weight B. And it calculated | required from the following Formula based on the film weight A at the time of swelling, and the film weight B after drying.
Weight swelling degree (W) (%) = A / B × 100

(6) Retardation value (nm)
The retardation value of the center part of the width direction of a polyvinyl alcohol-type film was measured using the retardation measuring apparatus ("KOBRA-WFD" Oji Scientific Instruments company measurement wavelength: 590nm).

[Example 1]
In a 200 L tank, 4% aqueous solution viscosity of 64 mPa · s as polyvinyl alcohol resin, 42 kg of polyvinyl alcohol resin (A) having an average saponification degree of 99.8 mol%, 100 kg of water, and glycerin as plasticizer (B) 2 kg, 21 g of sodium dodecyl sulfonate as surfactant (C) and 8 g of polyoxyethylene dodecylamine were added, and the mixture was heated to 150 ° C. with pressure and heating while stirring to dissolve uniformly. A 26% aqueous solution of film forming material was obtained.

  Next, an aqueous solution of the film forming material (liquid temperature 147 ° C.) was supplied to a twin screw extruder and defoamed. The defoamed aqueous solution of the film forming material was cast from a T-type slit die (straight manifold die) to a drum-type roll (heat roll: R1) to form a film.

The conditions for the casting film formation are as follows.
Drum type roll (heat roll: R1)
Diameter: 3200 mm, width: 4.3 m, rotation speed: 15 m / min, surface temperature: 75 ° C., resin temperature at the exit of the T-type slit die: 90 ° C.
In addition, when the film moisture content at the time of peeling from a drum-type roll was measured, it was 17%.

Drying was performed while the front and back surfaces of the obtained film were alternately passed through a drying roll under the following conditions.
-1st to 15th drying roll (heat roll: R2 to R16)
Diameter: 320 mm, width: 4.3 m, rotation speed: 15 m / min, surface temperature: 60 ° C.
In addition, when the film was sampled after drying and the film moisture content was measured, it was 7%.

After drying, the membrane is continuously heat treated at 130 ° C. by a floating dryer (length 12 m) that blows warm air from both sides, and the polyvinyl alcohol system has a width of 4 m, a length of 4000 m, and a thickness of 30 μm at the center of the film. A film was obtained.
The physical properties of the obtained polyvinyl alcohol film are shown in Table 1 below.

  Using the polyvinyl alcohol film of the present invention obtained above, a polarizing film was obtained in the following manner, and the following evaluation was performed. The evaluation results are shown in Table 1 below.

The obtained polyvinyl alcohol film was stretched 1.5 times while being immersed in a water bath having a water temperature of 30 ° C. Next, it is stretched 1.3 times while being immersed for 240 seconds in a dyeing tank (30 ° C.) consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide, and further 50 g / L of boric acid and 30 g of potassium iodide. / L was immersed in a boric acid treatment tank (50 ° C.) and boric acid treatment was performed for 5 minutes while uniaxially stretching 2.8 times. Thereafter, it was dried to obtain a polarizing film having a total draw ratio of 5.5 times.
In addition, a polarizing film having a total draw ratio of 5.8 times was obtained by carrying out in the same manner except that it was uniaxially drawn by 2.97 times in the boric acid treatment tank.

<< Evaluation of Polarizing Film >>
From the central part in the width direction of each polarizing film obtained above (polarizing film having a total draw ratio of 5.5 times, polarizing film having a total draw ratio of 5.8 times), 4 cm × 4 cm in parallel to the orientation direction of the polarizing film A square sample was taken.
About these samples, the transmittance | permeability (%), polarization degree (%), and dichroic ratio of the obtained polarizing film were measured using the spectrophotometer V-7070 by JASCO Corporation.

[Example 2, Comparative Examples 1-3]
In Example 1, it carried out similarly except having changed the film forming conditions as shown in following Table 1, and obtained the polyvinyl-alcohol-type film, Furthermore, it carried out similarly to Example 1, and obtained the polarizing film.
About the obtained polyvinyl alcohol-type film and polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Table 1 below.

  From the results of the above Examples and Comparative Examples, it can be seen that, for the Example products, since the Xc / Xa is within a predetermined range, the dichroic ratio in the polarizing film is a high polyvinyl alcohol film even at a low draw ratio. . On the other hand, in the comparative product, a polarizing film having excellent optical properties could not be obtained at a low stretch ratio of about 5.5 times or 5.8 times. Particularly, in the case of Comparative Example 3, the film was broken.

  In the said Example, although the specific form in this invention was shown, the said Example is only a mere illustration and is not interpreted limitedly. Various modifications apparent to those skilled in the art are contemplated to be within the scope of this invention.

  The polyvinyl alcohol film of the present invention can obtain a polarizing film having excellent polarization performance even when stretched at a low stretch ratio. An electronic desk calculator, an electronic clock, a word processor, a personal computer, a TV, a portable information terminal, an automobile, Liquid crystal display devices such as instrumentation for machinery, sunglasses, eye protection glasses, stereoscopic glasses, reflection reduction layers for display elements (CRT, LCD, etc.), raw materials for polarizing films used in medical equipment, building materials, toys, etc. It is very useful as an original film used for a half-wave plate or a quarter-wave plate or a retardation film used for a liquid crystal display device.

Claims (15)

A polyvinyl alcohol film formed by forming a film-forming material containing a polyvinyl alcohol resin (A), wherein the polyvinyl alcohol film is immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes. After the initial state, the true stress (Xa) when stretched 2.5 times the initial state at a stretching speed of 70 mm / sec in the boric acid aqueous solution and the initial state in the boric acid aqueous solution while continuing the stretching A polyvinyl alcohol film characterized by satisfying the following formula (1) in true stress (Xc) when stretched 4.3 times:
5.0 ≦ Xc / Xa ≦ 9.0 (1) A polyvinyl alcohol film formed by forming a film-forming material containing a polyvinyl alcohol resin (A), wherein the polyvinyl alcohol film is immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes. After the initial state, the true stress (Xa) when stretched 2.5 times the initial state at a stretching speed of 70 mm / sec in the boric acid aqueous solution and the initial state in the boric acid aqueous solution while continuing the stretching The true stress (Xb) when stretched by 3.4 times and the true stress (Xc) when stretched by 4.3 times in the initial state in an aqueous boric acid solution while further stretching is expressed by the following formula (1) ) And (2).
5.0 ≦ Xc / Xa ≦ 9.0 (1)
Xb / Xa ≦ Xc / Xa (2)   3. The polyvinyl alcohol film according to claim 1 or 2, wherein the true stress (Xa) is 4.0 to 7.0 MPa.   True stress (Xc) is 35.0-45.0 MPa, The polyvinyl alcohol-type film as described in any one of Claims 1-3 characterized by the above-mentioned.   True stress (Xb) is 11.0-15.0 MPa, The polyvinyl alcohol-type film as described in any one of Claims 2-4 characterized by the above-mentioned. When polyvinyl alcohol film is immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes (initial state) and then stretched 2.5 times the initial state in a boric acid aqueous solution at a stretching speed of 70 mm / sec. The true stress (Xa) and the true stress (Xb) when stretched 3.4 times in the initial state in an aqueous boric acid solution while continuing stretching satisfy the following formula (3): The polyvinyl alcohol-type film as described in any one of Claims 2-5.
1.9 ≦ Xb / Xa ≦ 3.0 (3) When the polyvinyl alcohol film is immersed in a 5% by weight boric acid aqueous solution at 56 ° C. for 0.5 minutes (initial state) and then stretched 3.4 times the initial state in the boric acid aqueous solution while continuing to be stretched The true stress (Xb) and the true stress (Xc) when stretched 4.3 times in the initial state in a boric acid aqueous solution while continuing the stretching satisfy the following formula (4): The polyvinyl alcohol-type film as described in any one of Claims 2-6.
2.0 ≦ Xc / Xb ≦ 3.5 (4)   Thickness is 5-50 micrometers, The polyvinyl alcohol-type film as described in any one of Claims 1-7 characterized by the above-mentioned.   The degree of area swelling (Y) when the polyvinyl alcohol film is immersed in water at 30 ° C for 5 minutes to swell is 130 to 170%, according to any one of claims 1 to 8, Polyvinyl alcohol film.   The polyvinyl alcohol film according to any one of claims 1 to 9, wherein the degree of weight swelling (W) at 30 ° C is 190 to 240%.   Retardation value is 10-50 nm, The polyvinyl alcohol-type film as described in any one of Claims 1-10 characterized by the above-mentioned.   It is used as a raw film of a polarizing film, The polyvinyl alcohol-type film as described in any one of Claims 1-11 characterized by the above-mentioned.   It is a method of manufacturing the polyvinyl alcohol-type film as described in any one of Claims 1-12, Comprising: The aqueous solution of the film formation material containing the said polyvinyl alcohol-type resin (A) is cast to a 1st heat roll. Then, the front and back of the film are alternately placed in the step [I] for forming a film into the film, the step [II] for peeling the film from the first heat roll, and the second heat roll group having a roll surface temperature of 30 to 95 ° C. And a step [IV] of heat-treating the film passed through the second heat roll group in an atmosphere of 60 to 145 ° C. [III]. Method.   A polarizing film comprising the polyvinyl alcohol film according to any one of claims 1 to 12.   A polarizing plate comprising a protective film provided on at least one surface of the polarizing film according to claim 14.