JP3342516B2 - Method for producing PVA-based film and optical film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyvinyl alcohol (hereinafter abbreviated as PVA) film, a PVA polarizing film and a PVA retardation film.

[0002]

2. Description of the Related Art A polarizing plate having a light transmitting function and a light blocking function, and a phase difference plate having a light phase correcting function, together with a liquid crystal having a light switching function, are basic components of a liquid crystal display (LCD). It is. This LCD
The field of application is from small devices such as calculators and watches in the early days,
It has been expanded to high-quality and large-size devices such as laptop personal computers, word processors, liquid crystal color projectors, and liquid crystal televisions. Under such circumstances, a large product having better optical homogeneity than a conventional product is required for a polarizing plate and a retardation plate. Conventionally,
PVA-based films used for polarizing plates and retardation plates,
It was produced by a casting method (solution casting method) (for example, see Japanese Patent Publication No. 51-23981) and had low optical homogeneity. Therefore, a PVA polarizing film and PVA made from a conventional PVA-based film
An optical film such as a retardation film had large optical unevenness. In particular, large-sized PVA polarizing films and PVA retardation films had large optical unevenness at both ends.

[0003]

The above prior art P
VA films have the following problems. 1) The conventional PVA-based film had a state where the molecular orientation was partially different. This molecular unevenness is measured by the birefringence. In the conventional PVA-based film, the birefringence at both ends in the width direction of the film is particularly higher than that at the center, so that the average birefringence (Δn) is high and the birefringence unevenness (Rn) is also high. There was a problem of being big. 2) The thickness unevenness (Rt) is large in the conventional PVA-based film, and the thickness unevenness (Rt) is a problem particularly in the case of a wide PVA-based film. 3) In the case where the film has a large molecular orientation in the length direction of the film, when the film is processed into a polarizing film or the like, the stretch ratio at which the film can be stretched in the length direction (hereinafter, referred to as “maximum stretch ratio”). "), And optical unevenness has occurred in the obtained polarizing film and the like.

Further, the following problems have occurred in the PVA polarizing film and the PVA retardation film using the conventional PVA-based film as a raw material. 1) In the case where a conventional PVA-based film having large birefringence unevenness (Rn) is used as a raw material, uneven dyeing in the dyeing process and uneven stretching in the stretching process are likely to occur. , Dichroic ratio unevenness (△ R
d) and transmittance unevenness (Ry) were large. The same applies to the case of a PVA retardation film, and a conventional PA film using a conventional PVA film having a large birefringence unevenness (Rn) as a raw material.
The VA phase film had large phase difference unevenness (Re). 2) When a conventional PVA-based film having a large thickness unevenness (Rt) is used as a raw material, it is difficult to perform uniform stretching in the stretching step. Unevenness in color ratio (△ Rd) and unevenness in single transmittance (Ry)
The conventional retardation film had large retardation unevenness (Re). 3) When a PVA-based film having a high birefringence at both ends in the width direction of the film is used as a raw material, the dichroic ratio unevenness (ΔRd) and the transmittance unevenness at both ends of the wide PVA polarizing film are used. (Ry) is large, and there is a problem particularly in a large LCD. Further, the retardation unevenness (Re) at both ends of the wide PVA retardation film was large.

The present invention has been made in view of the above-mentioned conventional problems, and is intended to provide a PVA-based film and a PVA film having excellent optical homogeneity.
An object of the present invention is to provide a method for producing an A-based polarizing film and a PVA-based retardation film.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present invention provides a first invention as PV
Stock solution consisting of A-based polymer solution on casting substrate
The film obtained by casting and drying
PVA obtained by peeling from a substrate for coating
In the method for producing a base film,
The moisture content of the film when the film is peeled off from the substrate
It is set to less than 10% by weight, and the average birefringence (Δn) is 1.
A PVA-based film for obtaining a film having a birefringence unevenness (Rn) of not more than 0 × 10 ^{−3 and not} more than 0.13 × 10 ^−3.
The present invention provides a method for manufacturing a system.

In the present invention, the average birefringence (Δn) and birefringence unevenness (Rn) are calculated by measuring the birefringence of a PVA-based film. The birefringence in the present invention is measured by a retardation measuring device (KOBRA-2 manufactured by Kanzaki Paper Co., Ltd.).
1 (trade name)), while measuring the retardation of a PVA-based film conditioned for 6 hours in an environment of 20 ° C. and a relative humidity of 65%, and using a micrometer.
It is determined by measuring the thickness of the same portion of the film and dividing the measured value of the retardation by the measured value of the film thickness.

The average birefringence (Δn) is 1 mm to 10 cm in at least one width direction (hereinafter abbreviated as the TD direction) in the film forming direction (hereinafter abbreviated as the MD direction) of the PVA-based film. Is a mean value of the birefringence index measured by the above-described measurement method while fixing the pitch in the range.
The birefringence unevenness (Rn) is the difference between the maximum value and the minimum value of the birefringence measured in the same manner as the measurement of the average birefringence (Δn). In the above-mentioned measuring method and the measuring methods of the other items described below, the portions of the PVA-based film that are not put into practical use (for example, both ears of the film, the bonded portion of the rolled product to the inner cylinder, and the winding of the rolled product) End) is removed from the measurement point.

The average birefringence (Δn) and the birefringence unevenness (R
n) represents the optical homogeneity of the PVA-based film, and it can be said that the smaller the value, the higher the optical homogeneity.
The PVA-based film obtained by the present invention has an average birefringence (Δn) of 1.0 × 10 ⁻³ or less, preferably 0.6 × 10 ⁻³ or less.
10 ⁻³ or less, more preferably 0.3 × 10 ⁻³ or less, and uneven birefringence (Rn) is 0.13 × 10 ⁻³ or less, preferably 0.10 × 10 ⁻³ or less, more preferably Is 0.07 × 10 ⁻³ or less. Average birefringence (△ n)
Exceeds 1.0 × 10 ⁻³ , the maximum stretch ratio of the PVA-based film decreases. If the birefringence index unevenness (Rn) exceeds 0.13 × 10 ⁻³ , uneven dyeing in the dyeing step and uneven stretching in the stretching step are likely to occur, and as a result, the obtained PVA-based polarizing film has two colors. Sex ratio unevenness (△
Rd) and transmittance unevenness (Ry) increase, which is not preferable in terms of quality. The same applies to the case of the PVA-based retardation film, and the birefringence unevenness (Rn) of the original PVA-based film remains as it is. As a result, the obtained PVA-based retardation film has the retardation unevenness (Rn). Re) (unevenness of product of birefringence and thickness)
Is undesirably high in quality.

A feature of the PVA-based film obtained by the present invention is that optical unevenness and thickness unevenness (Rt) are small. As a method for producing the PVA-based film, a stock solution comprising a PVA-based polymer solution is cast. 10% by weight of the film when the film obtained by casting on a substrate for drying and drying is peeled off from the substrate for casting.
(In the following, weight% may be abbreviated as “wt%”).

In the present invention, the moisture content of the film is measured at least at five or more points immediately after the film is peeled off from the casting substrate so as not to be affected by the outside air humidity. About 2 g of the film was dried under reduced pressure of 2 Torr at 50 ° C. for 2 hours, the weight of the film before and after drying was measured, and the average value calculated by the following equation. Water content = ｛(weight before drying-
(Weight after drying) / (weight before drying)｝ × 100 This measurement method is a condition under which the plasticizer such as glycerin contained in the film does not evaporate.

The moisture content of the film when the film is peeled from the casting substrate is not particularly limited as long as it is less than 10% by weight, but is preferably 3% by weight or more and less than 10% by weight, more preferably 5-8% by weight. preferable.

If the moisture content when the film is peeled from the casting substrate is 10% by weight or more, large peeling unevenness occurs at both ends in the TD direction of the film, and the birefringence at both ends becomes high. Even at the center, the birefringence unevenness increases, and the thickness unevenness also increases. When the moisture content at the time of peeling is less than 3% by weight, curling of the film increases, and handling may be difficult in subsequent manufacturing steps.

[0014] Casting dryers for forming a film under the above conditions include a drum type film forming machine and a belt type film forming machine, and examples of the heat treating device include a drum type heat treating machine and a hot air type heat treating machine. . PVA in the present invention
An example of the production process of the base film is shown below.

FIG. 1 shows a method for producing a PVA-based film of the present invention.
1 shows a belt type film forming machine 11 used in the method . The belt type film forming machine 11 has a die 10. A stock solution L composed of a PVA-based polymer aqueous solution is supplied to the die 10. The die 10 has a slit-shaped opening that is long in the width direction (the direction perpendicular to the plane of the paper of FIG. 1). 13.

The belt type film forming machine 11 has the endless belt 13 running across a pair of rollers 12, 12, and the undiluted solution flowing out of the die 10 is cast on the belt 13. And dried. The belt 13 is made of, for example, stainless steel, and its outer peripheral surface is mirror-finished. On the outer circumference and inner circumference of the belt 13, partition walls 14 are respectively provided to partition a space in the traveling direction of the belt 13.
On the outer peripheral surface and the inner peripheral surface of the belt 13, 80 to 17 from the hot air blower (the hot air blower is omitted in the drawing).
Hot air H at 0 ° C. is blown to promote drying of the stock solution. Also, for the purpose of increasing the film strength during peeling,
In the most downstream zone 14A, the film F may be cooled by the normal temperature air C.

A peeling roller 15 is provided near the right roller 12, and the film F dried to a predetermined moisture content is peeled from the belt 13 by the peeling roller 15. The film F is the heat treatment machine 16 and the humidity control machine 1 shown in FIG.
After being passed through 7 and an inspection machine 18, it is taken up by a winder 19. The heat treatment machine 16 changes the crystallinity of the film F by blowing hot air of about 100 to 170 ° C. onto the film F. The humidity controller 17 is provided with a film F
Is adjusted to, for example, about 5% by weight. The inspection device 18 inspects physical defects, foreign matter, thickness, moisture, and the like.

Next, a manufacturing method using the belt type film forming machine 11 will be described. The stock solution L composed of the PVA-based polymer aqueous solution is sent to the die 10 and flows out onto the belt 13. The undiluted solution L that has flowed onto the belt 13 is cast by the belt 13 of FIG. 1 traveling in the direction of arrow A, and drying on the belt 13 is promoted by the hot air H. Here, the belt 13 is different from a drum described later,
Since the film F can be lengthened, the drying time can be extended, and the film F can be sufficiently dried on the belt 13. Therefore, the water content of the film F can be easily reduced to less than 10% by weight, and the film F Can be easily peeled off. Therefore, the birefringence is uniform and low. Moreover, since a film F having a uniform birefringence in the width direction and a low birefringence is obtained, the stretchability of the film in the optical film production process is improved.

In the belt type film forming machine 11 shown in FIG. 1, there is no particular restriction on the length of the belt 13, so that the drying time can be extended by lengthening the belt 13.
Therefore, while the film F is sufficiently dried, the belt speed can be increased, and the production capacity of the line can be increased. The traveling speed of the belt 13 is appropriately selected within a range of about 5 to 50 m / min. The residence time on the belt 13 is appropriately selected within a range of about 1 to 10 minutes.

Further, as in this belt type film forming machine 11,
A partition wall 14 is provided in the running direction of the belt 13 so that the hot air H
Is applied to the belt 13, the temperature of the hot air H can be changed between the partition walls 14. Therefore, it is possible to select an optimum temperature according to the drying state (drying stage) of the film F. Thereby, the stretchability of the film can be further improved.

FIG. 2 shows a drum type film forming machine 21. In the same figure, the undiluted solution L obtained through the same process as the case of the belt type of FIG. 1 is supplied to the die 10, a film is formed on a drum type roll 22, and dried by a drying roll 23. To produce a PVA-based film F. Film F is
After being passed through a heat treatment machine 16, a humidity control machine 17 and an inspection machine 18, it is wound around a winder 19.

The present invention provides, as a second invention, an average thickness (t)
Is 20 to 100 μm, and the thickness unevenness (Rt) is 3
% Or less and the average birefringence (Δn) is 1.0 × 1
0 ^-3 or less, and uneven birefringence index (Rn) is 0.13
Manufacture of PVA-based films to obtain those of ^10-3 or less
It provides a method .

The average thickness (t) in the present invention is determined by applying a measuring load of 30 g to the detection end of a diamond ball having a diameter of 3 mm using a contact type film thickness continuous measuring device (manufactured by Anritsu Electric Co., Ltd.). , Measured continuously at a take-off speed of 1.5 m / min, at a temperature of 20 ° C. and a relative humidity of 65%.
It is the average value of the values measured over the entire width direction of at least one point in the MD direction of the time-humidified PVA-based film, and over a length of 1 m in the MD direction of at least one point in the TD direction.

The thickness unevenness (Rt) is calculated from the maximum value and the minimum value of the thickness measured in the same manner as the measurement of the average thickness (t).
It is calculated by the following equation. Uneven thickness (Rt) = ｛(maximum thickness−minimum thickness)
/ Average thickness (t)} × 100 The average birefringence (Δn) and the birefringence unevenness (Rn) are determined by the method of the first invention.

The PVA-based film obtained according to the present invention has an average thickness (t) in the range of 20 to 100 μm, preferably 50 to 100 μm, more preferably 60 to 80 μm, and uneven thickness (Rt). Is 3% or less, preferably 2.7% or less, more preferably 2.0% or less. When the average thickness (t) of the PVA-based film is less than 20 μm, uneven stretching is likely to occur in a stretching step when the PVA-based film is processed into a polarizing film, and the film thickness after stretching becomes small. Handling becomes difficult.
Even when the thickness t of the PVA-based film exceeds 100 μm, uneven stretching tends to occur in the stretching step.

If the thickness unevenness (Rt) exceeds 3.0%, local stretching unevenness occurs in a stretching step when a PVA-based film is processed into a polarizing film. Such a polarizing film is not preferable because the dichroic ratio unevenness (△ Rd) and the transmittance unevenness (Ry) increase. Also PVA
The same applies to the case of a system retardation film, in which the thickness irregularity (Rt) of the raw PVA-based film remains as it is, and the retardation irregularity (Rt)
e) is undesirably large. Average birefringence (△ n)
And the limiting conditions and preferable conditions of the birefringence unevenness (Rn) are as follows:
This is the same as the first invention.

The length and width of the PVA-based film obtained according to the present invention are not particularly limited. The lower limit of the width of the PVA-based film is preferably 50 cm or more, more preferably 80 cm or more, and particularly preferably 100 cm or more. P
The upper limit of the width of the VA-based film is preferably 3 m or less, more preferably 2.5 m or less. The length of the PVA-based film is preferably 1 m or more, more preferably 10 m or more.

There are no particular restrictions on other constituent requirements of the PVA-based film obtained according to the present invention. The degree of polymerization of the PVA-based polymer used in the present invention is 1000
The above is preferable, 1000 to 20,000 is more preferable, 1500 to 10000 is further preferable, and 3000
Particularly preferred is from 10,000 to 10,000. The saponification degree of the PVA-based polymer is not particularly limited, but is preferably 80 mol% or more.
90 mol% or more is more preferable, and 95 mol% or more is still more preferable.

The PVA polymer of the present invention is obtained by saponifying a polymer of a vinyl ester monomer. Vinyl ester monomers include vinyl formate,
Vinyl acetate, vinyl propionate, vinyl valerate,
Examples include vinyl caprate, vinyl laurate, vinyl stearate, vinyl 2,2,4,4-tetramethyl valerate, vinyl benzoate, vinyl pivalate and vinyl versatate. Of these, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate are preferably used alone or as a mixture.

As the three-dimensional structure of the PVA-based polymer of the present invention, those having an atactic structure are generally used, but those having a rich isotactic structure or a syndiotactic structure are also used.

The vinyl ester monomer may be copolymerized with a monomer copolymerizable with the vinyl ester monomer. Examples of the copolymerizable monomer include olefins such as ethylene, propylene, 1-butene and isobutene; Acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-acrylate
Acrylates such as butyl, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, methacrylic acid i-propyl, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate,
Methacrylic esters such as dodecyl methacrylate and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N
Acrylamide derivatives such as dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, N-methylolacrylamide and its derivatives; methacrylamide;
Methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts or quaternary salts, N-methylol methacrylamide and its derivatives; methyl Vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i
-Butyl vinyl ether, t-butyl vinyl ether,
Vinyl ethers such as dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; Maleic acid and its salts or esters; itaconic acid and its salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate. The content of these copolymerizable monomers is preferably 10 mol% or less, and more preferably 5 mol%.
The following is more preferred.

Examples of the plasticizer for the PVA-based polymer include polyhydric alcohol-based plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol, and mixtures thereof. Among the polyhydric alcohol plasticizers, glycerin is preferred. A plasticizer may or may not be added, but when a plasticizer is added, it is added in an amount of about 2 to 20 parts by weight based on 100 parts by weight of the PVA-based polymer.

In the present invention, water is preferably used as a solvent for the PVA-based polymer. However, when using an explosion-proof film-forming apparatus, as a solvent, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, a diamine compound having 1 to 10 carbon atoms, a triamine compound having 1 to 10 carbon atoms, and the like. An organic solvent may be used, and among these organic solvents, dimethyl sulfoxide is preferred. Further, a mixture of these solvents may be used.

According to a third aspect of the present invention, there is provided a PVA-based composition for obtaining an element having an irregularity in single transmittance (Ry) of 0.5% or less and a dichroic ratio unevenness (ΔRd) of 2.5 or less. It is intended to provide a method for producing a polarizing film. In the present invention, the single transmittance unevenness (Ry) and the dichroic ratio unevenness (△ Rd) are:
It is calculated by measuring the degree of polarization (V) and the single transmittance (Y) of the PVA-based polarizing film. For the degree of polarization (V) and the single transmittance (Y), the JIS standard Z-8701 “Color display method using a two-degree visual field XYZ system” is applied in accordance with Japanese Electronic Machinery Industry Standard ED-2521 and “Transmissible object The stimulus value (Y) in “Tristimulus values” was used as the transmittance. The standard light source is a C light source, the wavelength range is 380 to 780 nm, and the spectrophotometer is UV-
2200 was used. Single transmittance (Y): The transmittance of light of one polarizing film was measured. Degree of polarization (V): determined by the following equation. V = ((Ypara−Ycross) / (Ypara + Ycross)) ^0.5 Ypara is the transmittance when two polarizing films are overlapped so that their orientation directions are parallel, and Ycross is the orientation of the two polarizing films. This is the transmittance when they are superposed so that the directions are orthogonal to each other.

The single transmittance unevenness (Ry) is measured at least at one point in the stretching direction of the PVA-based polarizing film in a direction perpendicular to the stretching direction, with a pitch of 1 mm to 10 cm fixed, and measured by the above-described measuring method. The difference between the maximum value and the minimum value of the single transmittance (Y). Dichroic ratio unevenness (比
Rd) is 1 mm to 1 mm at least at one point in the stretching direction of the PVA-based polarizing film in a direction perpendicular to the stretching direction.
With the pitch in the range of 0 cm fixed, Y and V were measured by the above measurement method, and the dichroic ratio (R
d) is the difference between the maximum value and the minimum value. Rd = Log (Y × (1-V)) / Log (Y × (1 + V))

The non-uniform transmittance irregularity (Ry) of the present invention is 0.5.
%, Preferably 0.3% or less, more preferably 0.1% or less.
2% or less, and the dichroic ratio unevenness (ΔRd) is 2.5 or less, preferably 2.0 or less, more preferably 1.0 or less. When the single transmittance non-uniformity (Ry) exceeds 0.5% or the dichroic ratio non-uniformity (△ Rd) exceeds 2.5, the polarization performance non-uniformity is large. Causes display unevenness, which is not preferable.

There are no particular restrictions on the other components of the PVA-based polarizing film obtained according to the present invention. Contact to the present invention
As the dichroic substance used in addition to iodine, so-called dichroic dyes are used alone or in combination. The content of the dichroic substance is adjusted in the range of 0.01 to 1% by weight so as to satisfy the degree of polarization and transmittance required for the polarizing film. There is no particular limitation on the components other than the dichroic substance in the PVA-based polarizing film in the present invention , and examples thereof include boric acid and metal ions (zinc, cobalt, etc.) added in the dyeing step and the stretching step. There is no particular limitation on the content. The thickness of the PVA-based polarizing film in the present invention is not particularly limited, but is preferably 5 to 50 μm,
0 to 40 μm is more preferable. The width and length of the polarizing film in the present invention are not particularly limited. The lower limit of the width of the polarizing film is preferably 25 cm or more, more preferably 50 cm or more. The length of the polarizing film is preferably 1 m or more,
0 m or more is more preferable.

The present invention is a method for producing a PVA-based film polarizing film using the PVA-based film of the first or second invention as a raw material , and there is no particular limitation other than the above constitutional requirements. The preferred embodiments will be described below. Swell, dye, uniaxially stretch PVA-based film,
A boric acid compound treatment and drying are performed to produce a polarizing film. Dyeing can be performed before, during or after stretching. As the dye, iodine-potassium iodide or dichroic dyeing can be used.

The uniaxial stretching may be performed in warm water, or the film after water absorption may be performed in air. The raw PVA-based film of the present invention can have a larger stretching ratio than a conventional film, and can be three times or more uniaxially.
The stretching is preferably performed at least 4 times, more preferably at least 5 times. The temperature during stretching is 20 to 200
° C, the stretching speed varies depending on the temperature conditions, but is 10 to 1 based on the original length of the raw PVA-based film.
It is usual to choose from 000% / min.

The boric acid compound used in the boric acid compound treatment includes boric acid and borax. The concentration of the boric acid compound aqueous solution is appropriately selected from the range of 1 to 8% by weight, and the temperature of the boric acid compound aqueous solution is appropriately selected from the range of 20 to 60 ° C. It is practically preferable to mix an iodine compound in the bath at the time of the boric acid compound treatment. The boric acid compound-treated uniaxially stretched film is subjected to a heat treatment for drying at a temperature of 50 to 200 ° C. for 1 to 5 minutes.

PV used as a substrate in the present invention
The A-based film has a low average birefringence (Δn), a small birefringence unevenness (Rn), and a small thickness and thin unevenness.
In the dyeing step, the dye has good adsorptivity, and uneven dyeing is unlikely to occur, and in the stretching step, the stretching ratio can be increased,
It is estimated that a polarizing film with less optical unevenness can be obtained because stretching unevenness is reduced.

According to a fourth aspect of the present invention, a phase difference unevenness (R
e) to provide a method for manufacturing polyvinyl alcohol-based retardation film to obtain a not more than 2%. The retardation unevenness (Re) in the present invention is calculated by measuring the retardation (birefringence × film thickness) of the PVA-based retardation film. The retardation is measured using a retardation measuring device (KOZAKI KANSAI PAPER CO., LTD.
BRA-21 (trade name)). The retardation unevenness (Re) was measured by the measurement method of the first invention with a pitch in the range of 1 mm to 10 cm fixed in a direction orthogonal to at least one stretching direction of the stretching direction of the PVA-based retardation film. It is calculated from the average value of the retardation values and the difference between the maximum value and the minimum value according to the following equation. Uneven phase difference (Re) = ｛(maximum retardation value−
(Minimum value of retardation value) / Average value of retardation value x 100

The phase difference unevenness (Re) of the present invention is 2% or less, preferably 1.4% or less, more preferably 1.0% or less.
% Or less. If the phase difference unevenness (Re) exceeds 2%, the function of correcting the phase difference as a phase difference film is inferior, which is not preferable.

There are no particular restrictions on the other constituents of the PVA-based retardation film obtained by the present invention, and the thickness of the PVA-based retardation film is preferably about 5 to 70 μm. PVA
There are no particular restrictions on the components of the system retardation film, but boric acid, borax, an ultraviolet absorber or a stabilizer may be added. The width and length of the retardation film in the present invention are not particularly limited. The lower limit of the width of the retardation film is 4
0 cm or more is preferable, and 60 cm or more is more preferable.
The length of the retardation film is preferably 1 m or more, more preferably 10 m or more.

The present invention is a method for producing a PVA-based retardation film by using the PVA-based film of the first or second invention as a raw material , and there is no particular limitation other than the above constitutional requirements. The preferred embodiments will be described below.

The raw PVA-based film is uniaxially stretched, dried and heat-set to produce a PVA-based retardation film. PVA
Swelling in water at 20-50 ° C.
Stretched in the uniaxial direction 1.03 to 1 times in air or water at 50 ° C, dried at 50 to 100 ° C, and dried at 50 to 200 ° C.
Heat-fixing with PVA-based film
Preheat to 100 ° C and 1.01 in air at 80-180 ° C
A method in which the film is stretched in a uniaxial direction up to 3 times and heat-set at 50 ° C. to 200 ° C.

Examples of the preheating device include a roll preheating device and a hot air preheating device, and examples of the stretching device include a two-roll or multi-stage stretching device and a tenter type stretching device. The PVA-based film obtained by the present invention has a low average birefringence, a small birefringence nonuniformity, and a small thickness and thin nonuniformity. It is presumed that a PVA phase difference film which is uniformly homogeneous can be obtained.

[0048]

The present invention will be described more specifically in the following examples. In addition, the physical properties of the film, the polarizing film, and the retardation film in the following Examples and Comparative Examples were measured by the following methods. In the following measurements, ears of the film, the polarizing film and the retardation film were excluded from sampling.

Average birefringence (Δn) and birefringence unevenness (Rn): Sampling was carried out at a pitch of 5 cm in the width direction of the film, and the film was conditioned at 20 ° C. and 65% relative humidity for 6 hours. Retardation measuring instrument (KOB manufactured by Kanzaki Paper Co., Ltd.)
RA-21 (trade name)), the retardation was measured, and the thickness of the film was measured at the same place using a micrometer. Next, the birefringence was calculated by dividing the measured value of the retardation by the measured value of the film thickness. The birefringence index is determined for each point of the sample, the average value is defined as the average birefringence index (Δn), and the difference between the maximum value and the minimum value of the birefringence index at each point of the sample is determined to obtain birefringence index unevenness. (Rn).

Average thickness (t) and thickness unevenness (Rt): A total of 10 points are sampled, that is, 5 points at full width at equal intervals in the width direction of the film and 5 points at 1 m intervals in the length direction of the film. After adjusting the humidity for 6 hours in an environment of 20 ° C. and a relative humidity of 65%, using a contact type film thickness continuous measuring device (manufactured by Anritsu Electric Co., Ltd.), A measuring load of 30 g is applied, and 1.5 m / min
The film thickness was measured at a take-off speed of. Next,
The average value was calculated from the measured values of the ten samples, and the average thickness (t) was calculated. The difference between the maximum value and the minimum value of the measured values of the ten samples was described in the description of the second invention. The thickness unevenness (Rt) was determined by the equation.

Nonuniform transmittance irregularity (Ry) and dichroic ratio irregularity (△ Rd):
At one point in the stretching direction of the PVA polarizing film, the single transmittance (Y) and the degree of polarization (V) were measured and calculated at a pitch of 4 cm in a direction perpendicular to the stretching direction.

Uneven retardation (Re): Sampling was performed at a pitch of 5 cm in a direction perpendicular to the stretching direction at one point in the stretching direction of the PVA retardation film, and a retardation measuring device (KOBRA-21 manufactured by Kanzaki Paper Co., Ltd. (commercially available)) Phase difference unevenness (Re) was determined from the difference between the maximum value and the minimum value of the retardation measured using the formula (1) according to the equation described in the section of the fourth invention .

Moisture Content and Moisture Content Unevenness: According to the method described in the above-mentioned section of the second invention, PV
The film was sampled at a pitch of 5 cm in the width direction of the A-based film, and measured and calculated.

Maximum stretching ratio: A 15 cm wide PV in a 4% by weight aqueous solution of boric acid at 35 ° C.
Using a sample of A-based film, stretching speed 0.26m
The maximum draw ratio at which the film can be stretched when the film is stretched at / min is shown.

Example 1 PVA (degree of polymerization 1750, degree of saponification 99.9 mol%) 1
00 parts by weight, 12 parts by weight of glycerin and water as a solvent were further added, and a uniform undiluted solution having a water content of 60% wb (% by weight on a wet base, the same applies hereinafter) was quantitatively supplied to a die.
The thickness is 75 μm and the width is 2.0 in the drum type film forming machine 21 shown in FIG.
m of PVA film was produced. Note that a drying roll was not used. The main manufacturing conditions are shown below. Die: T type slit die Die temperature 100 ° C Drum type film forming machine: Cast roll diameter 2m Rotation speed 2m / min Roll temperature 90 ° C Drying time 155 seconds Water content at the time of film peeling 8.0wt% Heat treatment machine: Hot air type Hot air temperature 160 ° C. Treatment time 15 seconds Water content of exit film 1.8 wt% Water content of moisture-conditioned film 6.5 wt% The physical properties of the thus obtained film are shown in Table 1. This film had small thickness unevenness, small average birefringence index and uneven birefringence index, and good stretchability.

Example 2 PVA (degree of polymerization: 4300, degree of saponification: 99.9 mol%) 1
00 parts by weight, glycerin 12 parts by weight, and water as a solvent were further added, and a uniform undiluted solution having a water content of 70% wb was quantitatively supplied to a die, and was fed to a belt-type film forming machine 11 shown in FIG.
A 1.5 m wide PVA film was produced. The main manufacturing conditions are shown below. Note that no heat treatment was performed. Die: T-type slit die Die temperature 100 ° C Belt type film forming machine: Stainless steel belt Length 20m Belt speed 8m / min Drying conditions Air temperature 130-155 ° C Drying time 145 seconds Water content at film peeling 9.8wt% Table 1 shows the physical properties of the obtained film. This film had small thickness unevenness, small average birefringence index and uneven birefringence index, and good stretchability.

Example 3 PVA (degree of polymerization 1750, degree of saponification 99.9 mol%) 1
00 parts by weight, water was further added as a solvent, and the water content was 60%.
A uniform undiluted solution of wb was supplied to the die in a fixed amount, a film having a thickness of 75 μm and a width of 1.5 m was manufactured by the belt type film forming machine 11 in FIG. The main manufacturing conditions are shown below. Die: T-type slit die Die temperature: 100 ° C Film forming machine: Stainless steel belt Length: 20m Belt speed: 10m / min Drying temperature: 100 ° C to 150 ° C Drying time: 120 seconds Water content at the time of film peeling 9.0wt% Heat treatment machine: hot air Formula Hot air temperature 160 ° C Processing time 15 seconds Water content of exit film 1.5 wt% Water content of moisture-conditioned film 6.0 wt% The physical properties of the film thus obtained are shown in Table 1. This film had small thickness unevenness, small average birefringence index and uneven birefringence index, and good stretchability.

Comparative Example 1 The same stock solution as in Example 1 was quantitatively supplied to a die, and a film having a thickness of 75 μm and a width of 2.0 m was produced by the drum type film forming machine 21 shown in FIG. The main manufacturing conditions are shown below. Die: Same as in Example 1 Drum type film forming machine: Cast roll Same as in Example 1 Rotation speed 5 m / min Roll temperature 90 ° C. Drying time 62 seconds Moisture content at film peeling 25 wt% Dry roll Roll temperature 70 ° C. to 110 ° C. Drying time 100 seconds Heat treatment machine: Hot air type Hot air temperature 160 ° C Processing time 15 seconds Water content of outlet film 1.5 wt% Water content of moisture-conditioned film 6.3 wt% The physical properties of the film thus obtained are shown in Table 1. . This film has large thickness unevenness, large average birefringence index and birefringence unevenness, and also has lower stretchability than the examples.

COMPARATIVE EXAMPLE 2 The same stock solution as in Example 1 was quantitatively supplied to a die, and a film having a thickness of 75 μm and a width of 1.5 m was produced by the belt type film forming machine 11 shown in FIG. gave. The main manufacturing conditions are shown below. Die: Same as in Example 2 Film forming machine: Same as in Example 2 Belt speed 16 m / min Drying temperature 100 ° C. to 150 ° C. Drying time 70 seconds Moisture content at the time of film peeling 20 wt% Heat treatment machine: Hot air type Hot air temperature 165 ° C. Treatment Time 9 seconds Water content of outlet film 5.2 wt% Water content of moisture-conditioned film 6.5 wt% The physical properties of the thus obtained film are shown in Table 1. This film has large thickness unevenness, large average birefringence index and uneven birefringence index, and also has lower stretchability than the examples.

Example 4 Using the PVA-based film of Example 1 as a raw material, a polarizing film was produced by wet dyeing with iodine and uniaxially stretching. Through the steps of swelling, dyeing, washing with water, stretching, boric acid treatment and drying, the weight ratio of potassium iodide / iodine in the dyeing solution is fixed at 100, and the iodine concentration is 43% of the single transmittance of the polarizing film. Was adjusted appropriately between 1 and 20 g / liter so as to cover. 4% by weight of boric acid was added to the stretching bath and stretched to the maximum stretching ratio. To the boric acid treatment bath, 4% by weight of boric acid and 4% by weight of potassium iodide were added. Drying was performed with hot air at 50 ° C. By the above operation, a polarizing film having a width of 1.2 m was obtained. Table 2 shows the physical properties of the polarizing film. This PVA polarizing film had small transmittance unevenness and dichroic ratio unevenness.

Example 5 A polarizing film having a width of 0.9 m was obtained in the same manner as in Example 4 except that the PVA-based film of Example 3 was used as a raw material. Table 2 shows the physical properties of the polarizing film. As in Example 4, this polarizing film had small transmittance unevenness and dichroic ratio unevenness.

Comparative Example 3 Using the PVA film of Comparative Example 1 as a raw material, a polarizing film having a width of 1.2 m was obtained in the same manner as in Example 4. Table 2 shows the physical properties of the polarizing film. This polarizing film had large transmittance unevenness and dichroic ratio unevenness, and especially at both ends of the polarizing film.

Example 6 A retardation film was produced by uniaxial stretching using the raw material of Example 3. Through the steps of swelling, stretching, drying, and heat setting as production steps, the swelling and stretching were performed in water at 35 ° C., and the stretching ratio was determined so that the retardation of the retardation film of the product became 350 nm. Physical properties of raw material after heat treatment strengthening and obtained width 1.2m
Table 3 shows the physical properties of the retardation film. Since the birefringence of the raw material was low and the stretch ratio was increased, and the birefringence of the raw material was small and the thickness non-uniformity was small, the obtained retardation film had little phase difference unevenness.

Comparative Example 4 A retardation film was produced in the same manner as in Example 6 using the raw material of Comparative Example 2. Table 3 shows the physical properties of the raw material and the physical properties of the obtained retardation film having a width of 1.2 m. The obtained retardation film had large retardation unevenness. The product width of the retardation film obtained in Comparative Example 4 was wider than that of Example 6 because the draw ratio was lower than that of Example 6, but was 1.2 m in width excluding both ends. Each measurement was performed as a retardation film.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

[Table 3]

[0068]

(1) By using a PVA-based film having a small average birefringence and a small birefringence unevenness, it is possible to obtain a high-quality PVA-based polarizing film with little uneven polarization performance. In addition, a PVA-based retardation film with little phase difference unevenness can be obtained. (2) Further, by using a PVA-based film having a small thickness, the optical homogeneity of the PVA-based polarizing film and the PVA-based retardation film is improved. (3) A product with high optical homogeneity can be obtained even for a PVA-based polarizing film and a PVA-based retardation film having a wide width accompanying an increase in the size of an LCD.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a manufacturing apparatus used in a film manufacturing method according to the present invention.

FIG. 2 is a schematic configuration diagram showing another example of a manufacturing apparatus used in the film manufacturing method according to the present invention.

[Explanation of symbols]

 11: belt type film forming machine, 21: drum type film forming machine.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B29L 7:00 B29L 7:00 C08L 29:00 C08L 29:00 (72) Inventor Yoshiaki Mukai 892 Sakuhichi, Saijo City, Ehime Prefecture Stock (56) References JP-A-4-204802 (JP, A) JP-A-4-173844 (JP, A) JP-A-4-173125 (JP, A) JP-A-64-84203 (JP, A) A) JP-A-63-261201 (JP, A) JP-A-57-212025 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 55/00-55/30 B29C 61 / 00-61/10 C08J 5/00-5/02 C08J 5/12-5/22 G02B 5/30

Claims (4)

(57) [Claims] 1. From a polyvinyl alcohol-based polymer solution
The casting solution is cast on a casting substrate and dried.
The obtained film is peeled off from the casting substrate.
Polyvinyl alcohol-based resin
In the method for producing a film, the casting substrate
The moisture content of the film when the film is peeled from the top is 10
% By weight, and the average birefringence (Δn) is 1.0 ×
10 ⁻³ or less and birefringence index unevenness (Rn) is 0.1
Polyvinyl alcohol to obtain one of 3 × 10 ^-3 or less
Production method of base film . 2. A manufacturing polyvinyl alcohol-based film according to the average thickness (t) is 20 to 100 [mu] m, and <br/> claim 1 in which the thickness irregularity (Rt) to obtain a not more than 3%
Construction method . 3. The method according to claim 1 or 2,
Using the obtained polyvinyl alcohol-based film as a raw material, the single-unit transmittance unevenness (Ry) is 0.5% or less.
And a method for producing a polyvinyl alcohol-based polarizing film having a dichroic ratio unevenness (ΔRd) of 2.5 or less . 4. The method according to claim 1 or 2,
A method for producing a polyvinyl alcohol-based retardation film for producing a polyvinyl alcohol-based retardation film having a retardation unevenness (Re) of 2% or less using the obtained polyvinyl alcohol-based film as a raw material. .