KR20160126987A - Polyvinyl alcohol film and method for manufacturing same - Google Patents

Abstract

(PROBLEMS) To provide a PVA film which can easily produce an optical film such as a polarizing film which is narrow in the width of color unevenness and is inconspicuous as a nonuniformity, and a manufacturing method thereof.
A PVA film in which the maximum value of the distance between adjacent peaks is not more than 6 cm 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 film width direction, A step of spraying a wind with an air velocity of 0.3 to 5 m / sec into the discharged film within 10 seconds after discharging, when the film forming liquid containing PVA is discharged in the form of a film on the support from the discharge port of the discharge device and dried to produce the PVA film ≪ / RTI >

Description

TECHNICAL FIELD [0001] The present invention relates to a polyvinyl alcohol film,

The present invention relates to a polyvinyl alcohol film, a method for producing the same, and an optical film such as a polarizing film produced from the film. More particularly, the present invention relates to a polyvinyl alcohol film which provides an optical film such as a polarizing film which is not conspicuous due to a narrow width of color heterogeneity even when the light transmittance is high or the light intensity of the backlight is high A production method thereof, and an optical film such as a polarizing film produced from the film.

A polarizing plate having light transmission and shielding functions is a fundamental component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Most of the polarizing plates have a structure in which a protective film such as a cellulose acylate (TAC) film is stuck to the surface of the polarizing film. As the polarizing film constituting the polarizing plate, a polyvinyl alcohol film is uniaxially stretched, (I ₃ ^- , I ₅ ^-, etc.) and dichroic organic dyes are adsorbed on a stretched film made of a dichroic dye. Such a polarizing film can be obtained by uniaxially stretching a polyvinyl alcohol film preliminarily containing a dichroic dye, by adsorbing a dichroic dye simultaneously with uniaxial stretching of a polyvinyl alcohol film, or by uniaxially stretching a polyvinyl alcohol film And then adsorbing the dichroic dye or the like.

LCDs have come to be used in a wide range of small-sized devices such as electronic desk calculators and wrist watches, notebook PCs, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, vehicle navigation systems, mobile phones and measuring instruments used indoors and outdoors. In recent years, in particular, it has become important to maintain a high screen brightness even when the light intensity of the backlight is low in an LCD, because reduction of power consumption is particularly strongly demanded. As a means for achieving this, it is conceivable to improve the light transmittance of a polarizing film or a polarizing plate by making the thickness of the polarizing film thinner or weakening the degree of dyeing. However, a polarizing plate having a high light transmittance , And the color unevenness is more conspicuous than a polarizing plate having a low light transmittance.

As a polyvinyl alcohol film for reducing the color unevenness of the polarizing film, a polyvinyl alcohol film (see Patent Document 1) in which the birefringence unevenness and the thickness unevenness are reduced in the prior art, a retardation between two points A polyvinyl alcohol film (see Patent Document 2) in which the difference is within a specific range, and a polyvinyl alcohol film in which the thickness variation per 1 mm in the width direction of the film is within a specific range (see Patent Document 3).

It is also possible to reduce wrinkles at the time of swelling of the polyvinyl alcohol film and uneven dyeing on the stripes existing in the longitudinal direction of the polarizing film. The inclination of the optical axis over the entire film width direction is the length And a polyvinyl alcohol film having an angle of 45 to 135 with respect to the direction of the film is known (see Patent Document 4).

Japanese Patent Application Laid-Open No. 6-138319 Japanese Patent Application Laid-Open No. 2002-28938 Japanese Laid-Open Patent Publication No. 2002-31720 International Publication No. 2009/028141

However, even when the conventional polyvinyl alcohol film can reduce the difference in density of the color unevenness even when used as a polarizing film in the production of a polarizing plate, the width of the color unevenness is relatively large, It was easy to see that there was a problem.

An object of the present invention is to provide a polyvinyl alcohol film which can easily produce an optical film such as a polarizing film which is narrow in width of color unevenness and is uneven and uneven, and a method for producing the same.

It is another object of the present invention to provide an optical film such as a polarizing film produced by using the polyvinyl alcohol film.

As a result of intensive studies conducted by the present inventors to achieve the above object, it has been found that, 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 film width direction, A novel polyvinyl alcohol film having a distance of not more than a specific value could be obtained. As a result of using the polyvinyl alcohol film as a raw material, even when a light transmittance is high or a backlight having a high light intensity is used, a polarizing film or the like which is narrow in the width of the color unevenness and is inconspicuous Was obtained.

Further, the inventors of the present invention have found that, when the film is produced by using the film-forming stock solution containing polyvinyl alcohol, the polyvinyl alcohol film is discharged onto a support such as a roll or a belt from a discharge port of the discharge device , And it is possible to smoothly manufacture by blowing wind of a specific wind speed to a film discharged within a specific time.

The inventors of the present invention have conducted further studies based on these findings and completed the present invention.

That is,

[1] A polyolefin film characterized in that the maximum value of the distance between adjacent peaks 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 film width direction is 6 cm or less. It is a vinyl alcohol film.

The present invention,

[2] In the distribution of the 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 value of the difference in orientation axis angle in the adjacent peaks is 10 By weight of the polyvinyl alcohol film of [1] above; And

[3] a polyvinyl alcohol film according to [1] or [2], wherein the polyvinyl alcohol film has a width of 2 m or more;

to be.

Further, according to the present invention,

[4] A method for producing a polyvinyl alcohol film by discharging a film forming liquid containing polyvinyl alcohol from a discharge port of a discharge device onto a support in the form of a film and drying the film, comprising the steps of: Is sprayed onto the discharged film. The present invention also provides a method for producing a polyvinyl alcohol film.

Further, according to the present invention,

[5] An optical film produced using the polyvinyl alcohol film of any one of [1] to [3] above; And

[6] The optical film of [5], which is a polarizing film;

to be.

By using the polyvinyl alcohol film of the present invention as a raw material, an optical film, such as a polarizing film, which is uneven and uneven in color irregularity width even when a light transmittance is high or a backlight having a higher light intensity is used, Can be obtained.

By adopting the production method of the present invention, the polyvinyl alcohol film of the present invention having the above-described excellent characteristics can be smoothly produced.

BRIEF DESCRIPTION OF DRAWINGS 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 diagram showing an example of a measurement point when measuring the orientation axis angle in the film plane of the polyvinyl alcohol film.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol film (hereinafter sometimes referred to as " PVA ") of the present invention has an orientation axis angle in the plane of the film measured at a pitch of 0.8 mm in the film width direction, The maximum value of the distance between adjacent peaks is 6 cm or less.

In the conventional PVA film, since the distance is large, there is a problem that the polarizing film produced using the polarizing plate, that is, the polarizing plate using the polarizing plate, has a large width of unevenness of color and is easy to notice as unevenness. In contrast, the PVA film of the present invention has a maximum value of the distance of 6 cm or less, which is different from the conventional PVA film. When such a PVA film of the present invention is used as a raw material, an optical film such as a polarizing film which is uneven in appearance due to a narrow width of color unevenness can be obtained even when a light transmittance is high or a backlight having a higher light intensity is used Can be manufactured.

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

Hereinafter, a method for measuring the orientation axis angle in the plane of the film and a method for obtaining the "distance between adjacent peaks" in the present invention will be described.

2, a virtual straight line A1-A2 in the width direction orthogonal to the longitudinal direction of the PVA film is defined at an arbitrary position in the longitudinal direction MD of the PVA film, (The thickness direction of the film) with a pitch of 0.8 mm across the entire width of the virtual straight line A1-A2 (the entire width of the film) .

The measurement position at the time of measurement of the orientation axis angle is not particularly limited. For example, assume that an arbitrary point (for example, center) on a virtual straight line connecting A1 and A2 is A3, A method in which the orientation axis angle is measured at a pitch of mm and the orientation axis angle is measured at a pitch of 0.8 mm from A3 to A2.

Here, the width direction of the film is the direction (TD) in the plane of the film orthogonal to the longitudinal direction (MD) of the film. When an elongate PVA film is used as a raw material to produce an optical film such as a polarizing film, it is usually uniaxially stretched in the longitudinal direction (mechanical flow direction: MD) of a long PVA film. Therefore, the longitudinal direction (MD) of the film usually coincides with the direction in which the PVA film is to be uniaxially stretched when an optical film such as a polarizing film is produced, and the direction in the plane of the film orthogonal to the longitudinal direction is In the width direction (TD). Further, in the case of a non-elongated PVA film, the direction in which the uniaxial stretching should be performed in the longitudinal direction (MD) of the film when producing an optical film such as a polarizing film, and the direction Direction (TD).

A distribution of the orientation axis angle in the width direction obtained by measuring the orientation axis angle at a pitch of 0.8 mm over the entire width of the PVA film on the imaginary line (A1-A2) in the width direction orthogonal to the longitudinal direction of the PVA film In many cases, the data is difficult to interpret as it is due to the influence of noise or the like in the long-term period, particularly in the case of performing analysis electronically. Therefore, it is preferable to exclude noise of a long period before the distance between adjacent peaks is determined. The exclusion of noise in this long-term period may be carried out as follows.

That is, for each measurement point, a total of 500 points (250 pitches) continuous to one side of the film width direction (TD) from the measurement point and 250 points (250 pitches) continuous to the other side The average value of the orientation axis angles is obtained, and the average value is subtracted from the value of the orientation axis angle at the target measurement point. By performing the same calculation for each measuring point, data indicating the variation of the orientation axis angle excluding the long period noise is obtained. By interpreting the data representing the variation of the orientation axis angle from which the noise of the long period is excluded by the following method, " distance between adjacent peaks " is obtained. When the long period of noise is excluded, both end portions of the film in the width direction (TD) of the film without the data of the orientation axis angle of 250 points continuous to one side of the film width direction (TD) Width of about 20 cm) is usually slit in the manufacturing process of the optical film and is not commercialized, and therefore can be excluded from the analysis of " distance between adjacent peaks ".

Next, using the analysis software Origin Pro 8.6J (manufactured by OriginLab Corporation), the peak of the orientation axis angular distribution is detected based on the data indicating the variation of the orientation axis angle excluding the long period noise. In the peak detection of the orientation axis angular distribution, "constant (average)" is set as the baseline mode and "based on height (threshold height 30%)" is set as the filtering method of the peak pit And a peak smaller than the threshold value is excluded. Next, the position in the width direction of each peak is obtained, and the distance in the width direction between peaks adjacent to each other is calculated, and this is referred to as " distance between adjacent peaks ". Further, in the present invention, the peak in the " distance between adjacent peaks " includes a positive peak and a negative peak.

In the PVA film of the present invention, the maximum value of the 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 the adjacent peaks is larger than 6 cm, the width of the color unevenness becomes large when the polarizing film and the polarizing plate are used, and it becomes easy to stand out as unevenness. From this viewpoint, the maximum value of the 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, further 1 cm or less It may be.

The lower limit of the maximum value of the distance between adjacent peaks is not particularly limited. However, since the PVA film having a too small maximum value of the distance between adjacent peaks is difficult to produce with good productivity, the maximum value of the distance between adjacent peaks is 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, it is preferable that, in the distribution of the orientation axis angles, the maximum value of the difference of the orientation axis angles at adjacent peaks is 10 degrees or less. When the maximum value of the difference of the orientation axis angles at the adjacent peaks is 10 DEG or less, the difference in shade of color unevenness when the polarizing film and the polarizing plate are formed can be reduced. From the viewpoint of the productivity of the PVA film, it is preferable that the maximum value of the difference of the orientation axis angles at the adjacent peaks is 0.01 DEG or more. In this regard, in the PVA film of the present invention, More preferably 0.01 to 10 degrees, further preferably 0.02 to 8 degrees, and particularly preferably 0.05 to 5 degrees.

The difference in the orientation axis angles at adjacent peaks can be obtained from the value of the orientation axis angle at the peak detected in the " distance between adjacent peaks ".

Although the thickness of the PVA film of the present invention is not particularly limited, if it is too thick, it is difficult to rapidly dry the optical film such as a polarizing film. On the other hand, when the PVA film is too thin, The thickness of the PVA film is preferably in the range of 5 to 150 占 퐉, more preferably in the range of 8 to 120 占 퐉, more preferably in the range of 10 to 80 占 퐉 More preferably in the range of 12 to 50 mu m, and particularly preferably in the range of 12 to 50 mu m.

The width of the PVA film of the present invention is not particularly limited. However, since the liquid crystal television or monitor has a large screen in recent years, it is preferably 2 m or more and more preferably 4 m or more in order to effectively use them. Further, when an optical film such as a polarizing film is produced with an actual production apparatus, if the width of the film is too wide, uniform uniaxial stretching may become difficult. Therefore, the width of the PVA film is preferably 8 m or less.

The length of the PVA film of the present invention is not particularly limited, but it is preferable that the PVA film of the present invention has a length of 5 < RTI ID = 0.0 > To 50,000 m, and more preferably in the range of 100 to 20,000 m.

Examples of the 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 isobutyrate, And polyvinyl esters obtained by polymerizing one or more vinyl esters can be used. Of the above vinyl esters, compounds having a vinyloxycarbonyl group (H ₂ C = CH-O-CO-) in the molecule are preferable from the viewpoints of easiness in production of PVA, availability and cost, and vinyl acetate is more preferable.

The polyvinyl ester is preferably obtained by using only one kind of vinyl ester or two or more kinds of vinyl esters, more preferably by using only one kind of vinyl ester as a monomer, but it is preferably within a range It may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith.

Examples of other monomers copolymerizable with the vinyl ester include? -Olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (Meth) acrylic acid or a salt thereof; (Meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t- (Meth) acrylic acid esters such as butyl, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate and octadecyl (meth) acrylate; (Meth) acrylamide; (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, ) Acrylamidopropyldimethylamine or a salt thereof, (meth) acrylamide derivatives such as N-methylol (meth) acrylamide or derivatives thereof; N-vinyl amides such as N-vinyl formamide, N-vinylacetamide and N-vinyl pyrrolidone; Vinyl ethers such as 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 and stearyl vinyl ether Ether; Vinyl cyanide such as (meth) acrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; Maleic acid or its salt, ester or acid anhydride; Itaconic acid or its salt, ester or acid anhydride; Vinylsilyl compounds such as vinyltrimethoxysilane; Unsaturated sulfonic acid or a salt thereof. The polyvinyl ester may have a structural unit derived from one or more of the above-mentioned other monomers.

The proportion of the structural unit derived from the other monomer in the polyvinyl ester is preferably 15 mol% or less, more preferably 10 mol% or less, based on the moles of the total structural units constituting the polyvinyl ester, More preferably 5 mol% or less.

As the PVA, those not subjected to graft copolymerization can be preferably used. However, as long as the effect of the present invention is not impaired, the PVA may be one modified by one or more graft copolymerizable monomers. This graft copolymerization can be carried out for at least one of polyvinyl ester and PVA obtained by saponifying it. As the graft copolymerizable monomer, for example, unsaturated carboxylic acid or its derivative; Unsaturated sulfonic acid or a derivative thereof; And? -Olefins having 2 to 30 carbon atoms. The proportion of the structural unit 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 the total structural units constituting the polyvinyl ester or PVA.

A part of the hydroxyl group of the PVA may be crosslinked or may not be crosslinked. In the PVA, a part of the hydroxyl groups may react with an aldehyde compound such as acetaldehyde or butylaldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure.

The degree of polymerization of the PVA is not particularly limited, but is preferably 1,000 or more. Since the degree of polymerization of PVA is 1,000 or more, the polarization performance of the polarizing film obtained from the PVA film can be further improved. If the degree of polymerization of PVA is too high, the production cost of PVA tends to increase and the processability at the time of film formation tends to be poor. Therefore, the polymerization degree of PVA is more preferably in the range of 1,000 to 10,000, more preferably in the range of 1,500 to 8,000 , And particularly preferably within the range of 2,000 to 5,000. The degree of polymerization of PVA referred to in this specification means an average polymerization degree measured in accordance with the description of JIS K 6726-1994.

The degree of saponification of the PVA is preferably 98 mol% or more, more preferably 99 mol% or more, further preferably 99.8 mol% or more, in view of good heat and humidity resistance of the optical film such as polarizing film obtained from the PVA film , And particularly preferably 99.9 mol% or more.

In the present specification, the degree of saponification of PVA means the number of moles of the vinyl alcohol unit in terms of the total mole number of the structural unit (typically, vinyl ester unit) that can be converted into the vinyl alcohol unit by saponification of the PVA and the vinyl alcohol unit (Mol%) of the total amount of the components. The degree of saponification can be measured in accordance with the description of JIS K 6726-1994.

The PVA film may contain a plasticizer together with the above PVA. By containing the plasticizer in the PVA film, the handleability and the stretchability of the PVA film can be improved. As the plasticizer, a polyhydric alcohol is preferably used. Specific examples of the plasticizer include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, May contain one or more of these plasticizers. Of these, glycerin is preferable in that 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. The content of the plasticizer in the PVA film is 3 parts by mass or more based on 100 parts by mass of the PVA, so that the stretching property 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 based on 100 parts by mass of the PVA, the plasticizer is bleed-out on the surface of the PVA film to suppress deterioration of the handleability of the PVA film.

When a PVA film is produced by using a film-forming raw material solution to be described later, the film-forming property is improved to suppress the occurrence of thickness irregularity of the film, and when a metal roll or a belt is used at the time of film formation, It is preferable to incorporate a surfactant into the stock solution for the purpose of facilitating the peeling of the PVA film. When a PVA film is prepared from a film forming stock solution containing a surfactant, the PVA film contains a surfactant. The kind of the surfactant contained in the surfactant to be added to the PVA film-forming stock solution, that is, the surfactant contained in the PVA film is not particularly limited, but from the viewpoint of the releasability from the metal roll or the belt, the anionic surfactant or non- Surfactants are preferred, and nonionic surfactants are particularly preferred.

Examples of the anionic surfactant include carboxylic acid type such as potassium laurate; Sulfuric acid ester type such as octylsulfate; Sulfonic acid type such as dodecylbenzenesulfonate and the like are preferable.

Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether and the like; Alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene lauryl amino ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide types such as diethanolamide laurate, and diethanolamide oleic acid; And allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether.

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

In the case of using a stock solution containing a surfactant, the content of the surfactant is preferably in the range of 0.01 to 0.5 parts by mass, more preferably 0.02 to 0.3 parts by mass, relative to 100 parts by mass of the PVA contained in the stock solution desirable. The content of the surfactant is 0.01 part by mass or more based on 100 parts by mass of the PVA, so that the film formability and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less based on 100 parts by mass of the PVA, the surfactant bleeds out on the surface of the PVA film to prevent blocking due to deterioration of handling properties.

The PVA film may be composed of only PVA or may be composed of PVA and the above plasticizer and / or surfactant. However, if necessary, the PVA film may contain other components such as an antioxidant, a cryoprotectant, a pH adjuster, a masking agent, And may further contain one kind or two or more kinds thereof.

The content of PVA in the PVA film is preferably within a range of 50 to 100 mass%, more preferably within a range of 80 to 100 mass%, and still more preferably within a range of 85 to 100 mass%.

The method for producing the PVA film of the present invention is not particularly limited, and any method may be used as long as the method can produce the PVA film of the present invention. In particular, a method for producing a PVA film by discharging a film forming liquid containing PVA from a discharge port of a discharging device onto a support in the form of a film and drying the PVA film is characterized in that the film discharged within 10 seconds after discharging the film forming solution from the discharge port, And a process of spraying wind at 5 m / sec is preferably adopted because it can smoothly produce the PVA film of the present invention.

Hereinafter, a method for producing the PVA film, which can be preferably employed in the present invention (hereinafter referred to as "the production method of the present invention") will be described.

The film-forming stock solution may be, for example, a PVA and, if necessary, a plasticizer, a surfactant, and other ingredients dissolved in a liquid medium, a PVA and, if necessary, a plasticizer, a surfactant, And a stock solution of a film containing a medium and having PVA melted. When the stock solution for film formation contains at least one of a plasticizer, a surfactant and other components, it is preferable that the components are uniformly mixed.

Examples of the liquid medium used for the preparation of the film-forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, trimethylol propane, ethylenediamine, diethylenetriamine, and the like, and one or more of these may be used. Among them, water is preferable in terms of small load on the environment and recoverability.

The volatilization rate of the undiluted film forming solution (the content ratio of the volatile component such as a liquid medium removed by volatilization or evaporation at the time of film formation in the film forming stock solution) may vary depending on the film forming method, film forming conditions, etc., By mass, more preferably within a range of 55 to 90% by mass, and still more preferably within a range of 60 to 85% by mass. The volatilization ratio of the undiluted solution is 50 mass% or more, so that the viscosity of the undiluted film-forming solution does not become excessively high and filtration and defoaming at the time of preparation of the film-forming solution are smoothly carried out. On the other hand, when the volatile fraction of the undiluted film-forming solution is 95 mass% or less, the concentration of the film-forming solution does not become too low, and the production of an industrial PVA film becomes easy.

The temperature of the film-forming stock solution is preferably 90 to 110 캜.

Examples of the discharging device for discharging the film-forming stock solution in the form of a film include a T-shaped slit die, an I-die, and a lip coater die.

In the production method of the present invention, there is a step of spraying a wind at an air velocity of 0.3 to 5 m / sec at a point within 10 seconds after discharging the film-forming stock solution from the discharge port in a film form. In order to obtain the PVA film of the present invention more efficiently, it is preferable that the time of blowing the wind (the time of first blowing wind on the discharged film) is within 5 seconds after discharge, and within 3 seconds , More preferably at a time point immediately after the ejection to a time of one second. At this time, the length of time for spraying the wind is preferably 0.1 to 10 seconds, more preferably 0.5 to 5 seconds, and even more preferably 0.8 to 2 seconds.

The wind velocity of the blowing air is 0.3 to 5 m / sec. In view of more efficiently obtaining the PVA film of the present invention, the wind velocity is preferably 0.4 m / sec or more, more preferably 0.5 m / sec or more , More preferably 0.7 m / sec or more, particularly preferably 0.77 m / sec or more, and the wind velocity is preferably less than 3 m / sec, more preferably less than 1 m / sec, and less than 0.9 m / More preferable.

The temperature of the blowing air is preferably 20 to 100 占 폚, more preferably 30 to 90 占 폚, and even more preferably 40 to 80 占 폚. If the temperature of the blowing air is too low, drying of the discharged PVA film tends to become insufficient, and if the temperature of the blowing air is excessively high, foaming tends to occur.

The method of spraying the wind is not particularly limited, but a structure for reducing wind velocity unevenness of spraying is preferable, and a nozzle method, a rectifying plate method, or a combination thereof is generally used. There is no particular limitation on the direction of the wind blown onto the PVA film, but the direction of the wind facing the first contact surface (the surface opposite to the first contact surface) to the support such as the first roll or belt, And may be a direction substantially along the non-contact surface, or may be other methods.

The film-forming apparatus to be used may be a drum-shaped film-forming apparatus or a belt-type film-forming apparatus, for example, as long as it has a support for discharging the raw film-forming solution. Among them, a drum type film forming apparatus is preferable in view of more efficiently producing the PVA film of the present invention, and more particularly, a drum type film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other is more preferably used . A volatile component is evaporated from one side of the PVA film discharged on the first roll and dried, and the other surface of the subsequently discharged PVA film is dried by using a drum type film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other, Can be passed over the circumferential surface of the heated second roll to be dried.

The volatile fraction when the PVA film is peeled off from the first roll is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and still more preferably 20 to 30% by mass. If the volatile fraction of the film at the time of peeling from the first roll is too small, the stretchability tends to deteriorate at the time of processing into the polarizing film. On the other hand, if the volatilization ratio at the time of peeling from the first roll is too large, peeling from the first roll tends to become difficult.

After the film-forming raw liquid is dried by the first roll, it is further dried on the circumferential surface of one or a plurality of rotating heated rolls disposed on the downstream side, or is further dried by passing through a hot air drying apparatus, A method in which the film is taken up on an intermediate layer can be industrially favorably employed. The drying by the heated roll and the drying by the hot air drying apparatus may be carried out in appropriate combination.

Apparatus for producing a PVA film may include a heat treatment apparatus; Humidity control system; A motor for driving each roll; A speed adjusting mechanism such as a transmission or the like is preferably provided.

The drying temperature in the production process of the PVA film is preferably in the range of 50 to 150 캜, more preferably in the range of 60 to 120 캜.

In this regard, when a PVA film is produced using a drum-type film-forming apparatus having 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, 120 deg. C is preferable.

In addition, when a hot-air drying apparatus is further disposed downstream of the drying roll, it is preferable that the temperature of the atmosphere in the hot-air drying apparatus is set to 50 to 150 ° C, particularly 60 to 120 ° C.

The drying treatment is preferably carried out until the volatile fraction of the PVA film is 10 mass% or less, more preferably 5 mass% or less, particularly 2 to 4 mass% or less, .

The use of the PVA film of the present invention is not particularly limited, but an optical film such as a polarizing film which is uneven in appearance due to a narrow width of color unevenness is used as the optical film It is preferable that the PVA film of the present invention is used as a raw material for producing an optical film. Examples of the optical film include a retardation film and the like in addition to the polarizing film. These optical films can be produced by a production method having a monoaxial stretching process 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 material, for example, the PVA film of the present invention may be used for dyeing, uniaxial stretching, fixing treatment, drying treatment, . The order of dyeing and uniaxial stretching is not particularly limited and may be dyed before uniaxial stretching, dyeing may be performed simultaneously with uniaxial stretching, or dyeing may be performed after uniaxial stretching. The uniaxial stretching, dyeing, and the like may be repeated a plurality of times.

In the dyeing of 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 , Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270, DirectViolet 9, 12, 51, 98, Direct Green 1, 85, Direct Yellow 8 , 12, 44, 86, 87, DirectOrange 26, 39, 106, 107, etc.) can be used. These dichroic dyes may be used alone, or two or more dyes may be used in combination. The dyeing can be usually carried out by immersing the PVA film in a solution containing the above-mentioned dichroic dye, but the treatment conditions and the treatment method are not particularly limited.

The uniaxial stretching of the PVA film may be carried out by either a wet stretching method or a dry heat stretching method. In the case of uniaxial stretching by wet stretching, it may be uniaxially stretched in hot water containing boric acid, or may be uniaxially stretched in a solution containing the dichroic dye or in a later fixed treatment bath, May be uniaxially stretched in air or may be uniaxially stretched by other methods. When the PVA film is subjected to stretching (wet stretching) in hot water, the stretching temperature in the uniaxial stretching treatment is preferably 30 to 90 占 폚, more preferably 40 to 70 占 폚, still more preferably 45 to 70 占 폚, A temperature of 65 DEG C is adopted, and in the case of dry heat stretching, a temperature of 50 to 180 DEG C is preferably adopted. It is preferable that the stretching magnification (uniaxial stretching ratio in the case of uniaxial stretching in multiple stages) of the uniaxial stretching is as long as possible until the film is cut off from the viewpoint of the polarization performance, More preferably 5 times or more, and still more preferably 5.5 times or more. The upper limit of the draw 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 drawing. The stretching magnification in this specification is based on the length of the film before stretching, and the stretching magnification is equivalent to 1 times the stretching magnification.

The thickness of the stretched film (polarizing film) is preferably from 3 to 35 탆, more preferably from 5 to 30 탆.

There is no particular limitation on the stretching direction of the uniaxial stretching when the long PVA film is uniaxially stretched. Uniaxial stretching in the longitudinal direction and uniaxial stretching in the transverse direction can be employed. However, Uniaxial stretching in the longitudinal direction is preferable in that a film is obtained. The uniaxial stretching in the longitudinal direction can be carried out by changing the peripheral velocity between rolls by using a stretching apparatus having a plurality of rolls parallel to each other. On the other hand, uniaxial stretching in the transverse direction can be carried out using a tenter-type stretching machine.

In the production of the polarizing film, it is preferable to perform fixing treatment to strengthen the adsorption of the dichroic dye to the uniaxially stretched film. As the fixing treatment, a method of immersing the film in a fixed treatment bath to which a boron compound such as boric acid or borax is added may be mentioned. At this time, if necessary, an iodine compound may be added to the fixed treatment bath.

It is preferable that the film subjected to uniaxial stretching or uniaxial stretching and fixing treatment is subsequently subjected to a drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably in the range of 30 to 150 占 폚, particularly preferably in the range of 50 to 140 占 폚. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film tends to be deteriorated. On the other hand, if the temperature is too high, the polarization performance accompanied with the decomposition of the dichroic dye tends to decrease.

A polarizing plate can be formed by adhering a protective film having optically transparent and mechanical strength to both sides or one side of the polarizing film obtained as described above. As the protective film in this case, a cellulose triacetate (TAC) film, a cellulose acetate (CAB) film, an acrylic film, a polyester film, a cycloolefin polymer (COP) film and the like are used. Examples of the adhesive for bonding the protective film include a PVA adhesive and a urethane adhesive, among which a PVA adhesive 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 or the like and then bonded to a glass substrate. A retardation film, a viewing angle improving film, a luminance improving film, or the like may be applied when the polarizing plate is bonded to the glass substrate.

Example

Hereinafter, the present invention will be described concretely with reference to Examples, but the present invention is not limited by the following Examples.

In the following examples and comparative examples, the difference between the adjacent peak distances in the distribution of the orientation axis angles and the orientation axis angle at the adjacent peaks and the color unevenness of the polarizing film were determined by the following method .

(1) Distance between adjacent peaks in the distribution of orientation axis angles and difference in orientation axis angle in adjacent peaks:

(I) the method described above.

That is, from the arbitrary position in the longitudinal direction (MD) of the elongated PVA film obtained in each of the following Examples and Comparative Examples, the total width length (3 m) having a length of 40 mm in the longitudinal direction (MD) (A tape having a width of 40 mm and a length of 3 m in a tape form) on a tape of a tape was taken. 2, a virtual straight line connecting A1 and A2 is defined as a center line so that a virtual straight line connecting A1 and A2 becomes a measurement site of the orientation axis angle, and a center line is defined as 20 mm on the upstream side of the virtual straight line. And 20 mm on the downstream side in total of 40 mm to collect samples on the tape over the entire width of the PVA film.

(Ii) For the sample on the tape taken in (i) above, one measurement position is set at the center in the width direction of the film (intermediate point A3 of a virtual straight line connecting A1 and A2 in Fig. 2) (A3? A1 and A3? A2) are measured at 0.8 mm pitches, and the orientation axis angles in the film plane are measured at the respective measurement positions, and the orientation axis angle data .

Here, the measurement of the orientation axis angle at each measurement position was carried out by using light of 543 nm which propagated in the direction perpendicular to the film surface by using "WPA-100-L" manufactured by Photonic Lattice Co. .

(Iii) For each measurement point, a total of 500 points (250 pitches) continuous to one side of the film width direction (TD) from the measurement point and 250 points continuous to the other side (250 pitches) And the average value is subtracted from the value of the orientation axis angle at the measurement point of interest. By performing the same calculation for each measuring point, data representing the variation of the orientation axis angle excluding the long period noise was obtained.

Next, using the analysis software Origin Pro 8.6J (manufactured by OriginLab Corporation), the peak of the orientation axis angular distribution was detected on the basis of the data indicating the variation of the orientation axis angle excluding the long period noise. In the peak detection of the orientation axis angular distribution, "integer (average)" is set as a baseline mode and "based on height (threshold height 30%)" is set as a filtering method of peak pits, The peak was excluded.

(Iv) Subsequently, the position in the width direction of each peak is obtained, and the distance in the width direction between peaks adjacent to each other (between peaks adjacent to each other) is calculated to obtain "distance between adjacent peaks" .

(v) Further, the difference between the orienting axis angles at peaks adjacent to each other (peaks adjacent to each other) is calculated between peaks, based on the value of the orientation axis angle at the detected peak, The maximum value was obtained.

(2) Color heterogeneity of polarizing film:

A polarizing plate for observation (a polarizing film having a transmittance of about 43% was used) was placed on a surface light source (backlight) in a dark room, and a polarizing film prepared in the following Examples or Comparative Examples was observed The polarizing film was irradiated with light through a polarizing plate for observation from the backlight (luminous intensity: 15,000 ㏅), and the polarizing film was observed with a naked eye at a position of 1 m immediately above the polarizing film , And the color unevenness of the polarizing film was evaluated by sensory evaluation based on the following criteria.

⊚: color irregularity is not recognized.

?: The color unevenness is visually recognized, but is not noticeable and practically no problem level.

X: Color irregularity at a level that is a problem in practice was recognized.

[Example 1]

(1) 100 parts by mass of PVA (saponification of a homopolymer of vinyl acetate, degree of polymerization: 2,400, degree of saponification: 99.9 mol%), 12 parts by mass of glycerin, 0.1 part by mass of diethanolamide laurate, and a volatile matter content of 66% (Substrate) of a drum type film forming apparatus provided with a plurality of drying rolls whose rotating shafts are parallel to each other, using a T-shaped slit die, (Blowing direction of wind: substantially vertical angle with respect to the non-contact surface of the first roll of the PVA film) at a wind speed of 0.81 m / sec and blowing of wind is performed for 0.1 to 1 second after discharge, The volatile fraction of the PVA film at the time of peeling from the first roll was set at 22 mass% and the non-contact surface / contact face of the first roll of the PVA film was alternately brought into contact with the succeeding second roll and subsequent drying rolls, Flow was produced (thickness: 60 ㎛, width of 3 m, volatile content ratio 4%) in a row.

With respect to the thus obtained PVA film, the maximum value of the maximum value of the distance between adjacent peaks in the distribution of the orientation axis angles and the maximum value of the difference between the orientation axis angles at the adjacent peaks were obtained by the above-described method. The results are shown in Table 1.

(2) A rectangular test piece having a size of 12 cm in the longitudinal direction x 20 cm in the width direction was taken from the center in the width direction of the PVA film obtained in the above (1), and both ends in the longitudinal direction of the test piece were measured in the longitudinal direction And then immersed in water at 30 캜 for 38 seconds while being immersed in water at a temperature of 30 캜 at a stretching speed of 24 cm / min, uniaxially stretching in the length direction at a stretch ratio of 2.2 times the original length ), Then immersed in an iodine / potassium iodide aqueous solution having a concentration of 0.03 mass% of iodine and 3 mass% of potassium iodide at a temperature of 30 ° C for 60 seconds, and at a drawing rate of 24 cm / (Second-stage stretching) in the longitudinal direction up to a depth of 5 mm, followed by the addition of 3% by mass of boric acid and 3% by mass of potassium iodide in an aqueous solution of boric acid / potassium iodide (3-stage stretching) in the longitudinal direction up to 3.6 times the original length at a stretching speed of 24 cm / min while immersing the substrate for about 20 seconds. Subsequently, 4% by mass of boric acid and 5% by mass of potassium iodide (4-stage stretching) in the longitudinal direction up to 6.5 times the original length at a stretching speed of 24 cm / min while immersing in a boric acid / potassium iodide aqueous solution having a concentration of 3% by mass of potassium iodide, , And then dried for 4 minutes in a drier at 60 DEG C to obtain a polarizing film (thickness: 23 mu m).

The polarizing film thus obtained was evaluated for color unevenness by the above-described method. The results are shown in Table 1.

[Examples 2 to 5 and Comparative Examples 1 to 6]

A PVA film and a polarizing film were produced in the same manner as in Example 1 except that the blowing start point of the wind, the blowing time of the wind, the wind speed and the volatile fraction of the PVA film at the time of peeling from the first roll were changed as shown in Table 1 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 value of the difference between the orientation axis angles at the adjacent peaks and the evaluation of the color unevenness of the obtained polarizing film Respectively. The results are shown in Table 1.

As shown in Table 1, in the PVA films of Examples 1 to 5, the maximum value of the distance between adjacent peaks in the distribution of the orientation axis angles was 6 cm or less, so that when the polarizing film was produced, Quality polarizing film having no problem in practical use because it is not conspicuous even when color irregularity is visually recognized.

On the other hand, in the PVA films of Comparative Examples 1 to 6, the maximum value of the distance between adjacent peaks in the distribution of the orientation axis angles exceeded 6 cm, causing color heterogeneity which was a practical problem when a polarizing film was produced .

Industrial availability

When the PVA film of the present invention is used, an optical film, such as a polarizing film, which is uneven and uneven due to a narrow width of color heterogeneity can be obtained even when a light transmittance is high or a backlight having a higher light intensity is used, The PVA film of the present invention is very useful as a raw film for an optical film such as a polarizing film, and the production method of the present invention is useful as a method for continuously and continuously producing the PVA film of the present invention with high productivity.

Claims (6)

Wherein the maximum value of the distance between adjacent peaks 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 is 6 cm or less. . The method according to claim 1,
Wherein a distribution of an orientation axis angle obtained by measuring an orientation axis angle in a plane of the film at a pitch of 0.8 mm in the film width direction satisfies a relationship of a poly Vinyl alcohol film. 3. The method according to claim 1 or 2,
A polyvinyl alcohol film having a width of 2 m or more. A method for producing a polyvinyl alcohol film by discharging a film forming liquid containing polyvinyl alcohol from a discharge port of a discharge device onto a support in the form of a film and drying the polyvinyl alcohol film is characterized in that a wind of 0.3 to 5 m / And a step of spraying the polyvinyl alcohol film onto the film. An optical film produced by using the polyvinyl alcohol film according to any one of claims 1 to 3. 6. The method of claim 5,
Polarizing film.

Images