JP6556693B2 - Polyvinyl alcohol film and method for producing the same - Google Patents

Description

  The present invention relates to a polyvinyl alcohol film and a method for producing the same, and an optical film such as a polarizing film produced from the film. More specifically, the present invention relates to polyvinyl alcohol that provides an optical film such as a polarizing film that has a narrow color spot and is less noticeable as a spot even when the light transmittance is high or the light intensity of the backlight is high. The present invention relates to a film, a manufacturing method thereof, and an optical film such as a polarizing film manufactured from the film.

A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film. As a polarizing film constituting the polarizing plate, a polyvinyl alcohol film is uniaxially stretched. iodine dye stretched film was oriented (I ₃ ^- and I ₅ ^-, etc.) that by adsorbing a dichromatic dye such as or a dichroic organic dye is mainly used. Such a polarizing film is obtained by uniaxially stretching a polyvinyl alcohol film containing a dichroic dye in advance, adsorbing a dichroic dye simultaneously with uniaxial stretching of the polyvinyl alcohol film, or uniaxially stretching the polyvinyl alcohol film. Manufactured by adsorbing dichroic dyes.

  LCDs are used in a wide range of applications, including small devices such as calculators and wristwatches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. . In recent years, since reduction of power consumption is particularly strongly demanded, it has become important for LCDs to maintain high screen brightness even when the light intensity of the backlight is low. As a means for achieving this, it is conceivable to improve the light transmittance of the polarizing film and thus the polarizing plate by reducing the thickness of the polarizing film or decreasing the degree of dyeing. A high-polarizing plate is more prominent in color spots than a polarizing plate having a low light transmittance.

  Conventionally, as a polyvinyl alcohol film for reducing color spots of a polarizing film, a polyvinyl alcohol film (see Patent Document 1) in which birefringence spots and thickness spots are reduced, between two points separated by 1 cm in the width direction of the film A polyvinyl alcohol film having a retardation difference in a specific range (see Patent Document 2), a polyvinyl alcohol film having a thickness variation per mm in the width direction of the film in a specific range (see Patent Document 3), and the like are known. .

  In addition, the inclination of the optical axis over the entire film width direction of the film can be reduced with respect to the longitudinal direction of the film, as it can reduce the generation of wrinkles when the polyvinyl alcohol film swells and streak-like stained spots existing in the longitudinal direction of the polarizing film. A polyvinyl alcohol film of 45 to 135 ° is known (see Patent Document 4).

JP-A-6-138319 JP 2002-28938 A JP 2002-31720 A International Publication No. 2009/028141

  However, the above-mentioned conventional polyvinyl alcohol film has a relatively wide color spot even if the color difference of the color spot can be reduced, for example, when the polarizing film is used for manufacturing a polarizing plate. It has been found that there is a problem that it is easily noticeable as spots.

An object of the present invention is to provide a polyvinyl alcohol film that can easily produce an optical film such as a polarizing film that has a narrow color spot and is less noticeable as a spot, and a method for producing the same.
Furthermore, this invention aims at providing optical films, such as a polarizing film manufactured using the said polyvinyl alcohol film.

As a result of intensive studies by the present inventors to achieve the above object, in the distribution of the orientation axis angle obtained by measuring the orientation axis angle in the plane of the film at a pitch of 0.8 mm in the width direction of the film, A novel polyvinyl alcohol film in which the distance between adjacent peaks was below a specific value could be obtained. And when the polyvinyl alcohol film is used as a raw material, even when a light transmittance is high or a backlight having a higher light intensity is used, the polarizing film has a narrow color spot and is hardly noticeable as a spot. It was found that an optical film such as
Furthermore, when manufacturing the film using the film-forming stock solution containing polyvinyl alcohol, the inventors of the present invention use the film-forming stock solution on a support such as a roll or a belt from a discharge port of a discharge device. It has been found that smooth production can be achieved by blowing a specific wind speed to the discharged film within a specific time after discharging into a film.
The present inventors have further studied based on these findings and completed the present invention.

That is, the present invention
[1] In the distribution of orientation axis angles obtained by measuring the orientation axis angle in the plane of the film at a pitch of 0.8 mm in the width direction of the film, the maximum distance between adjacent peaks is 6 cm or less. It is the characteristic polyvinyl alcohol film.
And this invention,
[2] In the distribution of the orientation axis angles obtained by measuring the orientation axis angles in the plane of the film at a pitch of 0.8 mm in the width direction of the film, the maximum difference between the orientation axis angles in adjacent peaks is 10 ° or less. The polyvinyl alcohol film of [1] above; and
[3] The polyvinyl alcohol film of the above [1] or [2] having a width of 2 m or more;
It is.

Furthermore, the present invention provides
[4] A method of producing a polyvinyl alcohol film by discharging a film-forming stock solution containing polyvinyl alcohol onto a support from a discharge port of a discharge device, and drying the solution, wherein the wind speed is reduced within 10 seconds after discharge. It is a manufacturing method of the polyvinyl alcohol film characterized by having the process of spraying on the film | membrane which discharged the wind of 3-5 m / sec.

The present invention also provides:
[5] An optical film produced using the polyvinyl alcohol film of any one of [1] to [3]; and
[6] The optical film according to [5], which is a polarizing film;
It is.

By using the polyvinyl alcohol film of the present invention as a raw material, even if the light transmittance is high or a backlight having a higher light intensity is used, the polarizing film has a narrow color spot and is hardly noticeable as a spot. An optical film such as can be obtained.
By employing the production method of the present invention, the polyvinyl alcohol film of the present invention having the above-described excellent characteristics can be produced smoothly.

FIG. 1 is a diagram schematically showing an orientation axis angle in a film plane of a polyvinyl alcohol film. FIG. 2 is a schematic view showing an example of measurement points when measuring the orientation axis angle in the film plane of the polyvinyl alcohol film.

The present invention is described in detail below.
The polyvinyl alcohol film of the present invention (hereinafter, polyvinyl alcohol may be referred to as “PVA”) has an orientation axis angle obtained by measuring the orientation axis angle in the plane of the film at a pitch of 0.8 mm in the width direction of the film. In the distribution, the maximum distance between adjacent peaks is 6 cm or less.
In the conventional PVA film, since the said distance is large, in the polarizing film manufactured using it, and a polarizing plate, there existed a problem that the width | variety of a color spot was thick and it was conspicuous as a spot. On the other hand, the PVA film of the present invention has a maximum distance of 6 cm or less, which is different from the conventional PVA film. If such a PVA film of the present invention is used as a raw material, even if a light transmittance is high or a backlight having a higher light intensity is used, the polarization is so narrow that the color spots are narrow and hardly noticeable as spots. An optical film such as a film can be produced.

  The orientation axis angle in the plane of the film in the present invention, as shown in FIG. 1, refers to the angle θ between the longitudinal direction (MD) and the orientation axis (slow axis) in the plane of the film, and the orientation axis angle. It depends on the orientation state of the PVA molecules at the measurement position. The orientation axis angle can be measured based on light (for example, light having a wavelength of 543 nm) traveling in a direction perpendicular to the film surface (film thickness direction) using a birefringence measurement device, a cell gap measurement device, or the like. Specifically, it can be measured by the method described later in the examples.

Below, the measuring method of the "orientation axis angle in the plane of a film" as used in this invention and the method of calculating | requiring the "distance between adjacent peaks" are demonstrated.
As shown in FIG. 2, a virtual straight line A1-A2 in the width direction orthogonal to the length direction of the PVA film is defined at an arbitrary position in the length direction (MD) of the PVA film, and on the virtual straight line A1-A2. Is measured with light traveling in a direction perpendicular to the film surface (thickness direction of the film) at a pitch of 0.8 mm over the entire width of the virtual straight line A1-A2 (full width of the film).
The measurement position for measuring the orientation axis angle is not particularly limited. For example, an arbitrary point (for example, the center) on the imaginary straight line connecting A1 and A2 is A3, and a pitch of 0.8 mm from A3 toward A1. A method of measuring the orientation axis angle at a pitch of 0.8 mm from A3 to A2 and the like can be adopted.
Here, the width direction of the film is a direction (TD) in the plane of the film orthogonal to the length direction (MD) of the film. When an optical film such as a polarizing film is produced using a long PVA film as a raw material, it is usually uniaxially stretched in the length direction (machine flow direction; MD) of the long PVA film. Therefore, normally, the length direction (MD) of the film coincides with the direction in which the PVA film should be uniaxially stretched when producing an optical film such as a polarizing film, and the direction in the plane of the film orthogonal to the length direction. Is the width direction (TD). In the case of a non-long PVA film, the direction to be uniaxially stretched when manufacturing an optical film such as a polarizing film is the length direction (MD) of the film, and the direction in the plane of the film orthogonal thereto The width direction (TD) may be used.

Distribution of orientation axis angles in the width direction obtained by measuring orientation axis angles at a pitch of 0.8 mm over the entire width of the PVA film on a virtual straight line A1-A2 perpendicular to the length direction of the PVA film. It is often difficult to analyze the data indicating as it is due to the influence of long-period noise or the like, particularly when the analysis is performed electronically. Therefore, it is preferable to eliminate long-period noise before obtaining the distance between adjacent peaks. The long-period noise can be eliminated as follows.
That is, for each measurement point, a total of 500 points of 250 points (250 pitches) continuous on one side of the film width direction (TD) and 250 points (250 pitches) continuous on the other side from the measurement points. The average value of the orientation axis angles is obtained, and this average value is subtracted from the orientation axis angle value at the target measurement point. By performing the same calculation for each measurement point, data indicating the variation of the orientation axis angle from which long-period noise has been eliminated can be obtained. The “distance between adjacent peaks” can be obtained by analyzing the data indicating the variation in the orientation axis angle from which long-period noise has been eliminated by the following method. In the case of eliminating the long-period noise, both end portions in the film width direction (TD) without data of orientation axis angles for 250 points continuous on one side in the film width direction (TD). (Each portion having a width of about 20 cm) is often not manufactured because it is usually slit in the optical film manufacturing process, and can therefore be excluded from the analysis of “distance between adjacent peaks”.

  Next, using the analysis software Origin Pro 8.6J (manufactured by OriginLab Corporation), peak detection of the distribution of the orientation axis angle is performed based on the data indicating the change in the orientation axis angle from which the long-period noise has been eliminated. Do. To detect the peak of the distribution of the orientation axis angle, set “constant (average)” as the baseline mode, and set “based on height (threshold height 30%)” as the peak fit filtering method. Peaks smaller than the threshold are excluded. Next, the position in the width direction at each peak is obtained, the distance in the width direction between adjacent peaks is calculated, and this is defined as “distance between adjacent peaks”. In the present invention, the peak in “distance between adjacent peaks” includes a positive peak and a negative peak.

In the PVA film of the present invention, the maximum distance between adjacent peaks obtained as described above is 6 cm or less, and the distance between adjacent peaks is all 6 cm or less. When the maximum value of the distance between adjacent peaks is larger than 6 cm, the width of the color spot becomes thick when the polarizing film and the polarizing plate are used, and the spot becomes easily noticeable as a spot. In this respect, the maximum distance between adjacent peaks in the PVA film is preferably 5.5 cm or less, more preferably 5 cm or less, and in some cases 4 cm or less, 2 cm or less, and further 1 cm or less. It may be.
The lower limit of the maximum distance between adjacent peaks is not particularly limited, but a PVA film having a very small maximum distance between adjacent peaks is difficult to produce with high productivity. The value is preferably 0.1 cm or more, more preferably 0.2 cm or more, and further preferably 0.3 cm or more.

In the PVA film of the present invention, in the distribution of the orientation axis angles, the maximum value of the difference in orientation axis angles at adjacent peaks is preferably 10 ° or less. When the maximum value of the difference in the orientation axis angle between adjacent peaks is 10 ° or less, the difference in color shading when the polarizing film and the polarizing plate are formed can be reduced. From the viewpoint of the productivity of the PVA film, the maximum value of the difference in the orientation axis angle in the adjacent peak is preferably 0.01 ° or more. From this point, in the PVA film of the present invention, the orientation in the adjacent peak is The maximum value of the difference in the shaft angle is more preferably 0.01 to 10 °, further preferably 0.02 to 8 °, and particularly preferably 0.05 to 5 °.
The difference in orientation axis angle between adjacent peaks can be determined from the value of the orientation axis angle at the peak detected in the above-mentioned “distance between adjacent peaks”.

  The thickness of the PVA film of the present invention is not particularly limited, but if it is too thick, drying when producing an optical film such as a polarizing film is difficult to be performed quickly, while if too thin, it is difficult to produce an optical film. Since the film tends to break during uniaxial stretching, the thickness of the PVA film is preferably in the range of 5 to 150 μm, more preferably in the range of 8 to 120 μm, and in the range of 10 to 80 μm. It is more preferable that it is in the range of 12 to 50 μm.

  Although the width of the PVA film of the present invention is not particularly limited, in recent years, liquid crystal televisions and monitors have become larger in screen, so that they can be effectively used for them, preferably 2 m or more. More preferably. In addition, when an optical film such as a polarizing film is manufactured with a realistic production machine, if the width of the film is too wide, uniform uniaxial stretching may be difficult, so the width of the PVA film is 8 m or less. It is preferable.

  The length of the PVA film of the present invention is not particularly limited, but a more uniform PVA film can be continuously and smoothly manufactured, and is also used continuously when an optical film is manufactured using the PVA film. Therefore, it is preferably in the range of 5 to 50,000 m, and more preferably in the range of 100 to 20,000 m.

Examples of PVA constituting the PVA film of the present invention include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate, etc. Those obtained by saponifying a polyvinyl ester obtained by polymerizing one or more of these vinyl esters can be used. Among the above vinyl esters, a compound having a vinyloxycarbonyl group (H ₂ C═CH—O—CO—) in the molecule is preferable from the viewpoint of ease of production of PVA, availability, and cost. More preferred is vinyl acetate.

  The polyvinyl ester is preferably obtained using only one or two or more vinyl esters as monomers, and more preferably obtained using only one vinyl ester as a monomer. However, as long as the effect of the present invention is not significantly impaired, a copolymer of one or more vinyl esters and other monomers copolymerizable therewith may be used.

  Examples of other monomers copolymerizable with the vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide; N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylic (Meth) acrylamide derivatives such as luamide, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamide propyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; halogen such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride Vinyl chloride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters or acid anhydrides; itaconic acid or its salts, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfones An acid or its salt can be mentioned. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer.

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

  As the above-mentioned PVA, those not graft-copolymerized can be preferably used, but PVA can be used for one or more kinds of graft copolymer as long as the effects of the present invention are not significantly impaired. It may be modified with a monomer. The said graft copolymerization can be performed with respect to at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

  In the PVA, a part of the hydroxyl group may be cross-linked or may not be cross-linked. In addition, the PVA may have a hydroxyl group partially reacted with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure. Also good.

  The degree of polymerization of the above PVA is not particularly limited, but is preferably 1,000 or more. When the degree of polymerization of PVA is 1,000 or more, the polarizing performance of the polarizing film obtained from the PVA film can be further improved. If the degree of polymerization of PVA is too high, it tends to lead to an increase in the production cost of PVA and poor processability during film formation, so the degree of polymerization of PVA is in the range of 1,000 to 10,000. Is more preferable, it is still more preferable to be in the range of 1,500 to 8,000, and it is particularly preferable to be in the range of 2,000 to 5,000. In addition, the polymerization degree of PVA as used in this specification means the average degree of polymerization measured according to description of JISK6726-1994.

The degree of saponification of PVA is preferably 98 mol% or more, more preferably 99 mol% or more, since the heat and heat resistance of an optical film such as a polarizing film obtained from the PVA film is improved. More preferably, it is 8 mol% or more, and it is especially preferable that it is 99.9 mol% or more.
In this specification, the degree of saponification of PVA refers to the vinyl alcohol relative to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification of PVA. The ratio (mol%) occupied by the number of moles of units. The degree of saponification can be measured according to the description of JIS K6726-1994.

  The PVA film may contain a plasticizer together with the above PVA. When the PVA film contains a plasticizer, it is possible to improve the handleability and stretchability of the PVA film. As the plasticizer, polyhydric alcohol is preferably used, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. PVA film Can contain one or more of these plasticizers. Among these, glycerin is preferable because the stretchability of the PVA film becomes better.

  The content of the plasticizer in the PVA film is preferably 3 to 20 parts by mass, more preferably 5 to 17 parts by mass, and further preferably 7 to 14 parts by mass with respect to 100 parts by mass of PVA. . When the content of the plasticizer in the PVA film is 3 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability of the PVA film is improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less with respect to 100 parts by mass of PVA, the plasticizer bleeds out on the surface of the PVA film and the handling property of the PVA film is reduced. be able to.

  Moreover, when manufacturing a PVA film using the film forming undiluted solution mentioned later, film forming property improves and generation | occurrence | production of the thickness variation of a film is suppressed, When a metal roll and a belt are used at the time of film forming Since peeling of the PVA film from a metal roll or belt is facilitated, it is preferable to incorporate a surfactant in the film-forming stock solution. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film contains a surfactant. There are no particular limitations on the type of surfactant that is blended in the film-forming stock solution for producing the PVA film, and thus the surfactant contained in the PVA film, but from the viewpoint of releasability from a metal roll or belt, an anion is used. Surfactants or nonionic surfactants are preferred, and nonionic surfactants are particularly preferred.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; a sulfonic acid type such as dodecylbenzene sulfonate and the like are suitable.
Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene Alkylamine types such as laurylamino ether; alkylamide types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; An allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether is preferred.
These surfactants can be used alone or in combination of two or more.

  In the case of using a film-forming stock solution containing a surfactant, the content of the surfactant may be within a range of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of PVA contained in the film-forming stock solution. Preferably, it is in the range of 0.02 to 0.3 parts by mass. When the content of the surfactant is 0.01 parts by mass or more with respect to 100 parts by mass of PVA, the film forming property and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less with respect to 100 parts by mass of PVA, the surfactant bleeds out on the surface of the PVA film, resulting in blocking, and handling properties are reduced. Can be suppressed.

  The PVA film may be composed only of PVA, or may be composed only of PVA and the above-described plasticizer and / or surfactant. If necessary, an antioxidant, an antifreeze agent, a pH adjuster, You may further contain 1 type, or 2 or more types of other components, such as a masking agent, a coloring preventing agent, and an oil agent.

  The PVA content in the PVA film is preferably in the range of 50 to 100% by mass, more preferably in the range of 80 to 100% by mass, and in the range of 85 to 100% by mass. Further preferred.

The manufacturing method in particular of the PVA film of this invention is not restrict | limited, You may manufacture by any method if it is a method which can manufacture the PVA film of this invention. Among them, a method for producing a PVA film by discharging a film-forming stock solution containing PVA onto a support from a discharge port of a discharge device, and drying the film-forming solution 10 seconds after discharging the film-forming solution from the discharge port The manufacturing method which has the process of spraying the wind of a wind speed of 0.3-5 m / second on the discharged | emitted film | membrane is preferably employ | adopted from the point which can manufacture the PVA film of this invention smoothly.
Below, the manufacturing method of the said PVA film which can be employ | adopted suitably in this invention (henceforth "the manufacturing method of this invention") is demonstrated.

  Examples of the film-forming stock solution include PVA and, if necessary, a plasticizer, a surfactant, a film-forming stock solution in which other components are dissolved in a liquid medium, PVA and, if necessary, a plasticizer and an interface. Examples include a film-forming stock solution containing an activator, other components, and a liquid medium and in which PVA is melted. When the film-forming stock solution contains at least one of a plasticizer, a surfactant, and other components, it is preferable that these components are uniformly mixed.

  Examples of the liquid medium used for the preparation of the membrane forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of them can be used. Among these, water is preferable from the viewpoint of a small environmental load and recoverability.

The volatile fraction of the film-forming stock solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation during film formation in the film-forming stock solution) may vary depending on the film-forming method, the film-forming conditions, etc. It is preferably within the range of -95% by mass, more preferably within the range of 55-90% by mass, and even more preferably within the range of 60-85% by mass. When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the production of an industrial PVA film becomes easy.
Moreover, it is preferable that the temperature of film forming undiluted | stock solution shall be 90-110 degreeC.

  Examples of the discharge device for discharging the film-forming stock solution into a film include a T-type slit die, an I-die, and a lip coater die.

  In the manufacturing method of this invention, it has the process of spraying the wind of a wind speed of 0.3-5 m / sec at the time of less than 10 second after discharging a film forming undiluted solution into a film form from an outlet. Since the PVA film of the present invention can be obtained more efficiently, the time when the wind is blown (the time when the wind is first blown to the discharged film) is preferably within 5 seconds after the discharge. Is more preferable, and it is more preferable that the time is immediately after discharge to 1 second. At that time, the length of time for blowing the wind is preferably 0.1 to 10 seconds, more preferably 0.5 to 5 seconds, and further preferably 0.8 to 2 seconds. .

  The wind speed of the wind to be blown is 0.3 to 5 m / second, and since the PVA film of the present invention can be obtained more efficiently, the wind speed is preferably 0.4 m / second or more, and 0.5 m / second. It is more preferably at least 2 seconds, more preferably at least 0.7 m / second, particularly preferably at least 0.77 m / second, and the wind speed is preferably less than 3 m / second, preferably 1 m. Is more preferably less than 0.9 m / sec, and even more preferably less than 0.9 m / sec.

  20-100 degreeC is preferable, as for the temperature of the wind to blow, 30-90 degreeC is more preferable, and 40-80 degreeC is further more preferable. If the temperature of the blowing air is too low, the discharged PVA film tends to be insufficiently dried. On the other hand, if the temperature of the blowing air is too high, foaming tends to occur.

  Although there is no restriction | limiting in particular about the method of blowing the said wind, The structure which reduces the wind speed spot of the wind to blow is preferable, and a nozzle system, a baffle plate system, or those combinations are generally used. Although there is no restriction | limiting in particular in the direction of the wind which blows on a PVA film | membrane, The direction which opposes the non-contact surface (surface opposite to the surface which contacts first) to the support bodies, such as the 1st roll and belt which PVA film | membrane contacts first. It may be a direction substantially along the non-contact surface, or any other method.

  The film forming apparatus to be used only needs to have a support for discharging the film forming stock solution. For example, a drum type film forming apparatus or a belt type film forming apparatus can be used. Among these, since the PVA film of the present invention can be produced more efficiently, a drum-type film forming apparatus is preferable, and in particular, a drum-type film forming apparatus including a plurality of drying rolls whose rotation axes are parallel to each other is more preferably used. By using a drum-type film forming apparatus including a plurality of drying rolls whose rotation axes are parallel to each other, volatile components are evaporated from one surface of the PVA film discharged onto the first roll, followed by drying. The other surface of the discharged PVA film can be dried by passing over the peripheral surface of the heated second roll that rotates.

  The volatile fraction at the time of peeling the PVA film from the first roll is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and further preferably 20 to 30% by mass. . When the volatile content rate at the time of peeling from the first roll is too small, the stretchability tends to deteriorate during the processing to the polarizing film. On the other hand, if the volatile content rate when peeling from the first roll is too large, peeling from the first roll tends to be difficult.

After the film-forming stock solution is dried with the first roll, it is further dried on the peripheral surface of one or a plurality of rotating heated rolls arranged on the downstream side, or further dried by passing through a hot air drying apparatus. Thereafter, a method of winding around a winding device can be preferably employed industrially. Drying with a heated roll and drying with a hot air dryer may be performed in an appropriate combination.
In order to adjust the PVA film to an appropriate state, a device for manufacturing the PVA film is provided with a heat treatment device; a humidity control device; a motor for driving each roll; a speed adjustment mechanism such as a transmission. It is preferable.

The drying temperature during the drying process in the production process of the PVA film is preferably in the range of 50 to 150 ° C, and more preferably in the range of 60 to 120 ° C.
From this point, when manufacturing a PVA film using a drum-type film forming apparatus including a plurality of drying rolls whose rotation axes are parallel to each other, the surface temperature of the first roll and the subsequent roll is set to 50 to 150 ° C., particularly 60 ° C. It is preferable to set it to -120 degreeC.
Moreover, when arrange | positioning a hot air dryer further downstream of a drying roll, it is preferable to make the atmospheric temperature in a hot air dryer into 50-150 degreeC, especially 60-120 degreeC.

  The drying treatment may be performed until the volatile content of the PVA film is 10% by mass or less, further 5% by mass or less, particularly 2 to 4% by mass, such as handleability during the production of an optical film such as a polarizing film. It is preferable from the point.

  Although there is no restriction | limiting in particular in the use of the PVA film of this invention, Even if it is a case where the light transmittance is high or the case where a backlight with higher light intensity is used, the width | variety of a color spot is thin and it is a polarizing film which is not conspicuous as a spot Therefore, the PVA film of the present invention is preferably used as a raw material for producing an optical film. Examples of the optical film include a polarizing film and a retardation film. These optical films can be produced by a production method having a step of uniaxial stretching using the PVA film of the present invention.

  In order to produce a polarizing film using the PVA film of the present invention as a raw fabric, for example, dyeing, uniaxial stretching, fixing treatment, drying treatment and further heat treatment may be performed using the PVA film of the present invention. . The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, dyeing may be performed simultaneously with uniaxial stretching, or dyeing may be performed after uniaxial stretching. In addition, steps such as uniaxial stretching and dyeing may be repeated a plurality of times.

  In dyeing the PVA film, iodine or a dichroic organic dye (for example, DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; Direct Yellow 8, 12, 44, 86, 87; dichroic dyes such as Direct Orange 26, 39, 106, 107) can be used. These dichroic dyes may be used alone or in combination of two or more. Dyeing can usually be performed by immersing the PVA film in a solution containing the above-described dichroic dye, but the treatment conditions and treatment method are not particularly limited.

Uniaxial stretching of the PVA film may be performed by either a wet stretching method or a dry heat stretching method. When uniaxially stretching by a wet stretching method, it may be uniaxially stretched in warm water containing boric acid, or may be uniaxially stretched in a solution containing the above-described dichroic dye or in a fixing treatment bath described later. The PVA film after water absorption may be uniaxially stretched in the air or may be uniaxially stretched by other methods. Although the stretching temperature in the uniaxial stretching treatment is not particularly limited, it is preferably 30 to 90 ° C, more preferably 40 to 70 ° C, and further preferably 45 to 65 ° C when the PVA film is stretched in warm water (wet stretching). The temperature of 50 to 180 ° C. is preferably employed when dry heat stretching is performed. In addition, the stretching ratio of uniaxial stretching (the total stretching ratio in the case of performing uniaxial stretching in multiple stages) is preferably stretched as much as possible from the point of polarization performance until just before the film is cut, and specifically 4 times or more. It is preferably 5 times or more, more preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, but is preferably 8.0 times or less in order to perform uniform stretching. In addition, the draw ratio in this specification is based on the length of the film before extending | stretching, and the state which is not extending | stretched corresponds to 1 time of draw ratios.
The thickness of the stretched film (polarizing film) is preferably 3 to 35 μm, particularly 5 to 30 μm.

  There is no particular limitation on the stretching direction of uniaxial stretching when uniaxially stretching a long PVA film, and uniaxial stretching in the length direction or uniaxial stretching in the lateral direction can be adopted. Therefore, uniaxial stretching in the length direction is preferable. Uniaxial stretching in the length direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, uniaxial stretching in the transverse direction can be performed using a tenter type stretching machine.

  In the production of the polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dichroic dye to the uniaxially stretched film. Examples of the fixing treatment include a method of immersing the film in a fixing treatment bath to which a boron compound such as boric acid or borax is added. In that case, you may add an iodine compound in a fixed treatment bath as needed.

  The film subjected to uniaxial stretching or uniaxial stretching and fixing treatment is preferably subjected to drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably in the range of 30 to 150 ° C, particularly in the range of 50 to 140 ° C. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film tends to be lowered, while if too high, the polarization performance is likely to deteriorate due to decomposition of the dichroic dye.

The polarizing film obtained as described above can be made into a polarizing plate by attaching a protective film that is optically transparent and has mechanical strength to both sides or one side. As the protective film in this case, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, a cycloolefin polymer (COP) film, or the like is used. Moreover, as an adhesive agent for bonding a protective film, a PVA adhesive agent, a urethane adhesive agent, etc. are mentioned, Among these, a PVA adhesive agent is preferable.
The polarizing plate obtained as described above can be used as a component of a liquid crystal display device after being coated with a pressure-sensitive adhesive such as acrylic and then attached to a glass substrate. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, or the like may be bonded.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.
In the following examples and comparative examples, the distance between adjacent peaks in the distribution of orientation axis angles, the difference in orientation axis angles between adjacent peaks, and the color spots of the polarizing film were determined by the following methods.

(1) The distance between adjacent peaks in the distribution of orientation axis angles and the difference in orientation axis angles between adjacent peaks:
(I) Performed by the method described above.
That is, the full width length having a length of 40 mm in the length direction (MD) of the PVA film from an arbitrary position in the length direction (MD) of the long PVA film obtained in each of the following Examples or Comparative Examples A (3 m) tape-shaped sample (a tape having a width of 40 mm and a length of 3 m in terms of the tape shape) was collected. That is, with reference to FIG. 2, the virtual straight line connecting A1 and A2 is defined as a central line so that the virtual straight line connecting A1 and A2 becomes the measurement site of the orientation axis angle, and 20 mm upstream of the virtual straight line. And the tape-shaped sample over the full width of the PVA film was taken so that it might become a total of 40 mm by 20 mm downstream.
(Ii) For the tape-shaped sample collected in (i) above, one measurement position is determined at the center in the width direction of the film (middle point A3 of the imaginary straight line connecting A1 and A2 in FIG. 2), and from this measurement position Toward both ends in the width direction (A3 → A1 and A3 → A2), the measurement positions are determined at a pitch of 0.8 mm, and the orientation axis angle is measured in the film plane at each measurement position. I got the data.
Here, the measurement of the orientation axis angle at each measurement position was performed with light having a wavelength of 543 nm traveling in a direction perpendicular to the film surface using “WPA-100-L” manufactured by Photonic Lattice.
(Iii) For each measurement point, a total of 500 points from the measurement point to 250 points (for 250 pitches) continuous on one side in the film width direction (TD) and 250 points (for 250 pitches) continuous on the other side. The average value of the orientation axis angles of the points was obtained, and this average value was subtracted from the value of the orientation axis angle at the target measurement point. By performing the same calculation for each measurement point, data indicating fluctuations in the orientation axis angle from which long-period noise was eliminated was obtained.
Next, using the analysis software Origin Pro 8.6J (manufactured by OriginLab Corporation), peak detection of the distribution of the orientation axis angle is performed based on the data indicating the change in the orientation axis angle from which the long-period noise has been eliminated. went. To detect the peak of the distribution of the orientation axis angle, set “constant (average)” as the baseline mode, and set “based on height (threshold height 30%)” as the peak fit filtering method. Peaks smaller than the threshold were excluded.
(Iv) Next, the position in the width direction of each peak is obtained, the distance in the width direction between adjacent peaks (between adjacent peaks) is calculated, and is set as the “distance between adjacent peaks”, of which The maximum value was determined.
(V) Further, based on the value of the orientation axis angle at the detected peak, the difference in orientation axis angle between adjacent peaks (between adjacent peaks) is calculated between the respective peaks, The maximum value was determined.

(2) Color spots on the polarizing film:
An polarizing plate for observation (using a polarizing film having a transmittance of about 43%) is placed on a surface light source (backlight) in a dark room, and a polarizing film produced in the following examples or comparative examples on the surface light source (backlight). Was placed so as to be in a crossed Nicol state with respect to the polarizing plate for observation, and then the polarizing film was irradiated with light from the backlight through the polarizing plate for observation (luminance 15,000 cd). The polarizing film was visually observed from the position, and color spots of the polarizing film were evaluated by sensory evaluation based on the following criteria.
A: Color spots are not visually recognized.
○: Color spots are visible, but are not noticeable and are practically acceptable.
X: Color spots of a level causing a practical problem were visually recognized.

[Example 1]
(1) From 100 parts by weight of PVA (saponified vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 99.9 mol%), 12 parts by weight of glycerin, 0.1 parts by weight of lauric acid diethanolamide and water A T-type slit is formed on a first roll (support) of a drum-type film forming apparatus using a film-forming stock solution having a volatile content of 66 mass% and a temperature of 100 ° C., and a plurality of drying rolls whose rotation axes are parallel to each other. Discharge into a film using a die, and start blowing air at a wind speed of 0.81 m / second at 0.1 seconds after discharge (wind blowing direction: against the non-contact surface of the first roll of the PVA film) Almost perpendicular angle), the wind is blown for 0.1 to 1 second after discharge, the volatile content of the PVA film when peeling from the first roll is 22% by mass, and the first roll of PVA film Second of following non-contact surface / contact surface A long PVA film (thickness 60 μm, width 3 m, volatile content 4 mass%) was continuously produced by alternately contacting the rolls after the roll.
With respect to the obtained PVA film, the maximum value of the distance between adjacent peaks in the distribution of orientation axis angles and the maximum value of the difference between orientation axis angles in the adjacent peaks were determined by the method described above. The results are shown in Table 1.

(2) From the central part in the width direction of the PVA film obtained in (1) above, a rectangular test piece having a length direction of 12 cm and a width direction of 20 cm is collected, and both ends in the length direction of the test piece are stretched portions. Is fixed to a stretching jig so that the size of the length is 10 cm in the length direction × 20 cm in the width direction, and the original length of 2. is stretched at a stretching speed of 24 cm / min while being immersed in water at a temperature of 30 ° C. for 38 seconds. After uniaxial stretching (first-stage stretching) twice in the length direction, in an iodine / potassium iodide aqueous solution at a temperature of 30 ° C. containing 0.03% by mass of iodine and 3% by mass of potassium iodide. While immersed for 60 seconds, the film was uniaxially stretched in the lengthwise direction (second stage stretching) to 3.3 times the original length at a stretching speed of 24 cm / min, and then boric acid was added at 3% by mass and potassium iodide. At a temperature of 30 ° C. containing 3% by weight of boric acid / iodide While immersed in an aqueous solution of lithium for about 20 seconds, the film was uniaxially stretched in the longitudinal direction (third-stage stretching) up to 3.6 times the original length at a stretching speed of 24 cm / min. While being immersed in a boric acid / potassium iodide aqueous solution containing 60% by mass and potassium iodide at a concentration of about 5% by mass, the length is increased to 6.5 times the original length at a stretching rate of 24 cm / min. After uniaxial stretching (fourth-stage stretching) in the longitudinal direction, it was fixed by immersing in a potassium iodide aqueous solution containing potassium iodide at a concentration of 3% by mass for 10 seconds. It dried for minutes and the polarizing film (23 micrometers in thickness) was obtained.
About the polarizing film obtained by this, the color spot was evaluated by the above-mentioned method. The results are shown in Table 1.

[Examples 2 to 5 and Comparative Examples 1 to 6]
PVA film in the same manner as in Example 1 except that the wind blowing start time, the wind blowing time, the wind speed, and the volatile content of the PVA film when peeled from the first roll were changed as shown in Table 1. And calculating the maximum value of the distance between adjacent peaks in the distribution of the orientation axis angles of the obtained PVA film and the maximum difference of the orientation axis angles in the adjacent peaks, and the polarization obtained. The color spots of the film were evaluated. The results are shown in Table 1.

As seen in Table 1 above, the PVA films of Examples 1 to 5 have a maximum distance of 6 cm or less between adjacent peaks in the distribution of the orientation axis angles. A high-quality polarizing film having a level in which no color spots are visually recognized or is not noticeable even when the color spots are visually recognized is obtained.
On the other hand, the PVA films of Comparative Examples 1 to 6 have a practically problematic color when a polarizing film is produced because the maximum distance between adjacent peaks in the distribution of orientation axis angles exceeds 6 cm. Spots occurred.

  If the PVA film of the present invention is used, an optical film such as a polarizing film that has a narrow color spot and is not noticeable as a spot even when a light transmittance is high or a backlight having a higher light intensity is used. Therefore, the PVA film of the present invention is extremely useful as a raw film for an optical film such as a polarizing film, and the production method of the present invention allows the PVA film of the present invention to be smoothly and continuously produced with high productivity. It is useful as a method for manufacturing.

Claims (5)

In the distribution of the orientation axis angle was determined by measuring at 0.8mm pitch orientation axis angle in the width direction of the film in the plane of the film state, and are maximum 6cm or less of the distance between adjacent peaks, adjacent peaks The polyvinyl alcohol film characterized in that the maximum value of the difference in orientation axis angle at 10 is 10 ° or less . The polyvinyl alcohol film according to claim 1 , wherein the width is 2 m or more. A method for producing a polyvinyl alcohol film by discharging a film-forming stock solution containing polyvinyl alcohol in a film form from a discharge port of a discharge device onto a support and drying it, wherein the wind speed is 0.3 to 5 m within 10 seconds after discharge. 2. The method for producing a polyvinyl alcohol film according to claim 1, further comprising a step of spraying a film on which air is discharged for 1 second . The optical film produced by using a polyvinyl alcohol film according to claim 1 or 2. The optical film according to claim 4 , which is a polarizing film.

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