JPH06138319A - Pva based film and optical film - Google Patents

Abstract

PURPOSE:To provide a PVA (polyvinylalcohol) based film having an excellent optical homogeneity, a PVA based polarizing film and a PVA based phase difference film. CONSTITUTION:The PVA based film having a <=1.0X10<-3> average double refractive index (DELTAn) and a <=0.13X10<-3> double refractive index variation (Rn), preferably has a 20 to 100mum average 'thickness (t) and a <=3% thickness variation (Rt). The polarizing film using the PVA based film has a <=0.5 % monochromatic transmittance variation (Ry) and a <=2.5 dichroism ratio variation (DELTARd). The phase difference film using the PVA based film has a <=2% phase difference variation (Re).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 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 shielding function, and a retardation plate having a light phase correcting function are a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. Is. This LCD
The applicable fields of are from small devices such as calculators and watches in the early days,
It has been expanded to high-quality and large-scale devices such as laptop computers, word processors, liquid crystal color projectors, and liquid crystal TVs. Under such circumstances, large-sized products having excellent optical homogeneity as compared with conventional products are required for polarizing plates and retardation plates. Conventionally,
The PVA film used for the polarizing plate and the retardation plate is
It was produced by a casting method (solution casting method) (see, for example, Japanese Patent Publication No. 51-23981) and had low optical homogeneity. Therefore, a PVA polarizing film and a PVA made by using a conventional PVA-based film as a raw material.
Optical films such as retardation films have large optical unevenness. Particularly, the large-sized PVA polarizing film and the PVA retardation film had large optical unevenness at both ends thereof.

[0003]

SUMMARY OF THE INVENTION
The VA film has the following problems. 1) The conventional PVA-based film had a partially different molecular orientation. This molecular orientation unevenness is measured by the birefringence. The conventional PVA-based film has a higher birefringence at both ends in the width direction of the film than that at the center, and therefore has a high average birefringence (Δn) and uneven birefringence (Rn). There was a big problem. 2) The conventional PVA-based film has a large thickness unevenness (Rt), and in the case of a wide PVA-based film, the thickness unevenness (Rt) has been a problem. 3) In the case where the film has a large molecular orientation in the length direction, a stretch ratio at which the film can be stretched in the length direction of the film when processed into a polarizing film (hereinafter, referred to as “maximum stretch ratio”). Is abbreviated as “.”, Or optical unevenness occurs in the obtained polarizing film or the like.

Further, the PVA polarizing film and the PVA retardation film prepared by using the conventional PVA film as a raw material have the following problems. 1) When a conventional PVA-based film having a large unevenness of birefringence (Rn) is used as an original fabric, uneven dyeing in a dyeing process or uneven drawing in a stretching process is likely to occur, and as a result, a conventional PVA polarizing film is , Dichroic ratio unevenness (△ R
d) and the unevenness of transmittance (Ry) were large. The same applies to the case of a PVA retardation film, in which a conventional P using a PVA film having a large unevenness of birefringence (Rn) as a raw material is used.
The VA phase film had large unevenness in phase difference (Re). 2) When a conventional PVA-based film having a large thickness unevenness (Rt) is used as a raw fabric, it is difficult to uniformly stretch the film, and as a result, the conventional PVA polarizing film is Color ratio unevenness (△ Rd) and single transmittance unevenness (Ry)
And the conventional retardation film had a 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 an original fabric, 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 phase difference unevenness (Re) at both ends of the wide PVA phase difference film was large.

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

[0006]

In order to achieve the above object, as a result of extensive studies, the present invention shows that the first invention has an average birefringence (Δn) of 1.0 × 10 ⁻³ or less, And,
P with birefringence unevenness (Rn) of 0.13 × 10 ⁻³ or less
A VA-based film is provided.

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

The average birefringence (Δn) is 1 mm to 10 cm in the width direction (hereinafter abbreviated as TD direction) of at least one point in the film forming direction (hereinafter abbreviated as MD direction) of the PVA type film. It is the average value of the birefringence measured by the above-mentioned measuring method with the pitch fixed in the range.
The birefringence unevenness (Rn) is the difference between the maximum and minimum values 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 following other items, a part of the PVA-based film which is not put to practical use (for example, both ears of the film, an adhesion part of the rolled wound product to the inner cylinder, a wound wound roll product). The end edge) is removed from the measurement point.

Average birefringence (Δn) and uneven birefringence (R
n) represents the optical homogeneity of the PVA-based film, and the smaller each value, the higher the optical homogeneity.
The PVA-based film of the present invention has an average birefringence (Δn) of 1.0 × 10 ⁻³ or less, preferably 0.6 × 10 ⁻³ or less,
More preferably, it is 0.3 × 10 ⁻³ or less, and the birefringence unevenness (Rn) is 0.13 × 10 ⁻³ or less, preferably 0.10 × 10 ⁻³ or less, more preferably 0.07 ×. 1
It is 0 ^-3 or less. Average birefringence (Δn) is 1.0 × 10
If it exceeds ^-3 , the maximum draw ratio of the PVA-based film decreases. Uneven birefringence (Rn) is 0.13 × 10 ^-3
If it exceeds the range, uneven dyeing in the dyeing process or uneven drawing in the drawing process is likely to occur, and as a result, the resulting PVA-based polarizing film has uneven dichroic ratio (ΔRd) and uneven transmittance (Ry). It becomes large and is not preferable in terms of quality. Also,
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, and as a result, the obtained PVA-based retardation film has the phase difference unevenness (Rn).
e) (unevenness of product of birefringence and thickness) becomes large, which is not preferable in terms of quality.

The present invention, as a second invention, is 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 a birefringence unevenness (Rn) is 0.13
It is intended to provide a PVA-based film having a size of × 10 ^-3 or less.

The average thickness (t) in the present invention is measured by using a contact type film thickness continuous measuring instrument (manufactured by Anritsu Electric Co., Ltd.) and applying a measuring load of 30 g to the detection end of a diamond sphere having a diameter of 3 mm. , Continuously measured at a take-off speed of 1.5 m / min, 6 at 20 ° C. and 65% relative humidity.
It is an average value of the values measured over the entire width direction of at least one point in the MD direction of the PVA-based film subjected to time humidity control, and over the length of 1 m in the MD direction of at least one point in the TD direction.

The thickness irregularity (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 formula. Thickness unevenness (Rt) = {(maximum thickness-minimum thickness)
/ Average thickness (t)} × 100 The average birefringence (Δn) and uneven birefringence (Rn) are determined by the method of the first invention.

The PVA film of the present invention has an average thickness (t) in the range of 20 to 100 μm, preferably 50 to 1
00 μm, more preferably 60 to 80 μm, and the thickness unevenness (Rt) is 3% or less, preferably 2.
It is 7% or less, more preferably 2.0% or less. PV
When the average thickness (t) of the A-based film is less than 20 μm, uneven stretching is likely to occur in the stretching step when the PVA-based film is processed into a polarizing film, and the film thickness after stretching becomes thin. It becomes difficult to handle. Even when the thickness t of the PVA-based film exceeds 100 μm, uneven drawing tends to occur in the drawing process.

When the thickness unevenness (Rt) exceeds 3.0%, local stretching unevenness occurs in the stretching process when the PVA film is processed into a polarizing film, and as a result, it is obtained. Further, the polarizing film is not preferable because the dichroic ratio unevenness (ΔRd) and the transmittance unevenness (Ry) become large. Also PVA
The same applies to the case of the phase retardation film, in which the thickness unevenness (Rt) of the original PVA-based film remains as it is and the phase difference unevenness (R
e) becomes large, which is not preferable. Average birefringence (△ n)
And the limiting condition and preferable condition of the birefringence unevenness (Rn) are
It is the same as the first invention.

There is no particular limitation on the length and width of the PVA-based film of the present invention. 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. The upper limit of the width of the PVA-based film is preferably 3 m or less, more preferably 2.5 m or less. The length of PVA film is 1
m or more is preferable, and 10 m or more is more preferable.

There are no particular restrictions on other constituents of the PVA film of the present invention. The degree of polymerization of the PVA-based polymer used in the present invention is preferably 1,000 or more, more preferably 1000 to 20000, and 1500 to 2000.
10000 is more preferable, and 3000-10000 is particularly preferable. The degree of saponification of the PVA-based polymer is not particularly limited, but is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more.

The PVA polymer of the present invention can be obtained by saponifying a polymer of vinyl ester monomer. Vinyl formate monomers include vinyl formate,
Vinyl acetate, vinyl propionate, vinyl valerate,
Examples thereof include vinyl caprate, vinyl laurate, vinyl stearate, vinyl 2,2,4,4-tetramethylvalerate, 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 polymer of the present invention, one having an atactic structure is generally used, but one having a rich isotactic structure or syndiotactic structure is also used.

There is no problem in copolymerizing the above-mentioned vinyl ester-based monomer with a copolymerizable monomer, and 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
Acrylic esters 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 acid esters such as dodecyl methacrylate and octadecyl methacrylate; acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N
Acrylamide derivatives such as dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and its salts, acrylamido propyl dimethyl amine and its salts or its quaternary salts, N-methylol acrylamide and its derivatives; methacrylamide,
Methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or quaternary salts thereof, N-methylolmethacrylamide 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 salt or its ester; itaconic acid and its salt or its ester; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. The content of these copolymerizable monomers is preferably 10 mol% or less, and 5 mol%
The following is more preferable.

Examples of the plasticizer for the PVA polymer include polyhydric alcohol plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol, and mixtures thereof. Among these polyhydric alcohol plasticizers, glycerin is preferable. The plasticizer may or may not be added, but when the 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 polymer.

The PVA-based film of the present invention is characterized by small optical unevenness and uneven thickness (Rt).
As a method for producing the film, the water content of the film when the undiluted solution of the PVA polymer solution is cast on the casting substrate and the film obtained by drying is peeled from the casting substrate is used. It is obtained by setting the content to be less than 10% by weight (hereinafter, the weight% may be abbreviated as "wt%").

Regarding the water content of the film in the present invention, immediately after the film is peeled from the casting substrate, the film is sampled at at least 5 points so as not to be affected by outside air humidity, and the film is dried with an infrared vacuum dryer. About 2 g of the film was dried under reduced pressure of 2 Torr at 50 ° C. for 2 hours, and the weight of the film before and after the drying was measured, which is the average value calculated by the following formula. Moisture content = {(weight before drying−weight after drying) / (weight before drying)} × 100 In this measurement method, the plasticizer such as glycerin contained in the film does not evaporate.

The water content of the film when 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% to 8% by weight. preferable.

When the water content when peeling the film 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 of both ends becomes high, and Even in the central portion, the birefringence unevenness becomes large, and the thickness unevenness also becomes large. If the water content at the time of peeling is less than 3% by weight, the curl of the film may increase and the handling may become difficult in the subsequent manufacturing process.

As a casting drying apparatus for forming a film under the above conditions, there are a drum type film forming machine, a belt type film forming machine, etc., and as a heat treatment apparatus, there are a drum type heat treatment machine, a hot air type heat treatment machine and the like. . PVA in the present invention
An example of the manufacturing process of the base film is shown below.

FIG. 1 shows a belt type film forming machine 11 used for producing the PVA type film of the present invention. This belt type film forming machine 11 has a die 10. The die 10 has P
A stock solution L composed of a VA-based polymer aqueous solution is supplied. The die 10 has a slit-shaped opening that is long in the width direction (direction perpendicular to the paper surface of FIG. 1), and the stock solution L has a uniform thickness in the width direction from the opening and is used as a casting base material. It is poured out on 13.

The belt-type film forming machine 11 has the endless belt 13 which runs by being stretched between a pair of rollers 12, and the stock solution flowing out from the die 10 is cast on the belt 13. It is dried at the same time. The belt 13 is made of stainless steel, for example, and the outer peripheral surface thereof is mirror-finished. Partition walls 14 that partition the space in the traveling direction of the belt 13 are provided on the outer circumference and the inner circumference of the belt 13, respectively.
The outer peripheral surface and the inner peripheral surface of the belt 13 are provided with 80 to 17 from a warm air blower (a warm air blower is omitted in the drawing).
Hot air H of 0 ° C. is blown to accelerate the 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 air C at room temperature.

A peeling roller 15 is provided near the roller 12 on the right side, and the film F dried to a predetermined water content is peeled from the belt 13 by the peeling roller 15. The film F is a heat treatment machine 16 and a humidity controller 1 shown in FIG.
After passing through 7 and the inspection machine 18, it is wound around a winder 19. The heat treatment machine 16 blows hot air of about 100 to 170 ° C. onto the film F to change the crystallinity of the film F and the like. The humidity controller 17 is a film F
The water content is adjusted to, for example, about 5% by weight. The inspection machine 18 is for inspecting physical defects, foreign matter, thickness, moisture and the like.

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

Further, since the belt-type film forming machine 11 of FIG. 1 is not particularly limited in lengthening the belt 13, it is possible to lengthen the drying time by lengthening the belt 13.
Therefore, while the film F is sufficiently dried, the belt speed can be increased to increase the production capacity of the line. The traveling speed of the belt 13 is appropriately selected within the range of about 5 to 50 m / min. The residence time on the belt 13 is appropriately selected within the range of about 1 to 10 minutes.

Further, like this belt type film forming machine 11,
A partition wall 14 is provided in the running direction of the belt 13 to allow hot air H
When is applied to the belt 13, the temperature of the hot air H can be changed between the partition walls 14. Therefore, the optimum temperature can be selected according to the dry 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 figure, the stock solution L obtained through the same steps as in the case of the belt type of FIG. 1 is quantitatively supplied to the die 10, the film is formed on the drum type roll 22, and the film is dried by the drying roll 23. , PVA-based film F is manufactured. Film F is
After passing through the heat treatment machine 16, the humidity control machine 17, and the inspection machine 18, it is wound up on a winder 19.

In the present invention, water is preferably used as the solvent for the PVA polymer. However, when an explosion-proof type film forming apparatus is used, 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, or the like is used. An organic solvent may be used, and among these organic solvents, dimethyl sulfoxide is preferable. Also, a mixture of these solvents may be used.

The present invention provides, as a third invention, a PVA-based polarizing film having a single-element transmittance unevenness (Ry) of 0.5% or less and a dichroic ratio unevenness (ΔRd) of 2.5 or less. It is provided. Uneven transmittance in the present invention (Ry)
The unevenness of dichroic ratio (ΔRd) is calculated by measuring the degree of polarization (V) and the single transmittance (Y) of the PVA-based polarizing film.
The degree of polarization (V) and the single transmittance (Y) are in accordance with Japanese Electronic Machinery Industry Standard ED-2521 and JIS standard Z-870.
1 Applying "Display method of color by 2 degree visual field XYZ system",
The stimulus value (Y) in the “tristimulus value of the transparent object” was defined as the transmittance. Standard light source is C light source, wavelength range is 380-780n
UV, 2200 manufactured by Shimadzu was used as the spectrophotometer. Single transmittance (Y): The light transmittance of one polarizing film was measured. Polarization degree (V): Calculated by the following formula. V = ((Ypara-Ycross) / (Ypara + Ycross)) ^0.5 Ypara is the transmittance when two polarizing films are stacked so that their alignment directions are parallel to each other, and Ycross is the alignment of two polarizing films. It is the transmittance in the case of overlapping so that the directions are orthogonal to each other.

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

The single-body transmittance unevenness (Ry) of the present invention is 0.5.
% Or less, preferably 0.3% or less, more preferably 0.
It is 2% or less, and the unevenness of dichroic ratio (ΔRd) is 2.5 or less, preferably 2.0 or less, more preferably 1.0 or less. When the single-element transmittance unevenness (Ry) exceeds 0.5% or the dichroic ratio unevenness (ΔRd) exceeds 2.5, the polarization performance unevenness is large, and therefore, when it is used for an LCD. Causes display unevenness and is not preferable.

There are no particular restrictions on the other constituents of the PVA type polarizing film of the present invention. As the dichroic substance used in the present invention, so-called dichroic dyes may be used alone or in combination in addition to iodine. The content of the dichroic substance is adjusted in the range of 0.01 to 1% by weight so as to satisfy the polarization degree and the transmittance required for the polarizing film. There is no particular limitation on the compounding components other than the dichroic substance in the PVA-based polarizing film of the present invention, but 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 film thickness of the PVA-based polarizing film in the present invention is not particularly limited, but is preferably 5 to 50 μm, and 10 to 40 μm.
Is more preferable. The width and length of the polarizing film of 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, more preferably 10 m or more.

As a fourth invention, the present invention provides 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. The method for producing the PVA-based polarizing film in the present invention is not particularly limited except the above-mentioned constitutional requirements, but preferred embodiments thereof will be described below. Swelling, dyeing the original PVA film,
A polarizing film is produced by uniaxial stretching, treatment with a boric acid compound, and drying. Dyeing can be performed before stretching, during stretching, or after stretching. As the dye, iodine-potassium iodide or dichroic dyeing can be used.

The uniaxial stretching may be carried out in warm water, or the film after absorbing water may be carried out in air. The original PVA-based film of the present invention can have a higher draw ratio than a conventional film, and is 3 times or more in the uniaxial direction,
It is preferable to stretch 4 times or more, more preferably 5 times or more. The temperature during stretching is 20 to 200
The stretching temperature and the stretching speed vary depending on the temperature conditions, but are 10 to 1 based on the original length of the original PVA film.
It is usual to select from 000% / min.

Examples of the boric acid compound used for the boric acid compound treatment include 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 the iodine compound in the bath during the treatment with the boric acid compound. The uniaxially stretched film treated with the boric acid compound is subjected to a heat treatment which also serves as drying under the conditions of a temperature of 50 to 200 ° C. and a time of 1 to 5 minutes.

PV used as an original fabric in the present invention
Since the A-based film has a low average birefringence (Δn), a small birefringence unevenness (Rn), and a small thickness unevenness,
In the dyeing process, the dye adsorption is good, uneven dyeing is less likely to occur, and in the stretching process, the stretching ratio can be increased,
It is presumed that a polarizing film with less optical unevenness can be obtained because the uneven drawing is reduced.

The present invention, as a fifth invention, includes phase difference unevenness (R
Provided is a polyvinyl alcohol-based retardation film having e) of 2% or less. The phase difference unevenness (Re) in the present invention is P
It is calculated by measuring the retardation (birefringence x film thickness) of the VA-based retardation film. The retardation is measured using a retardation measuring device (KOBRA-21 (trade name) manufactured by Kanzaki Paper Co., Ltd.). Phase difference unevenness (Re) is
The average value of the retardation values measured by the measurement method of the first invention, and the maximum value, with a pitch in the range of 1 mm to 10 cm fixed with respect to the stretching direction of at least one point in the stretching direction of the PVA-based retardation film and the direction orthogonal thereto. It is calculated by the following formula from the difference between the value and the minimum value. Phase difference unevenness (Re) = {(maximum retardation value−
Minimum value of retardation value) / average value of retardation value} × 100

The retardation unevenness (Re) of the present invention is 2% or less, preferably 1.4% or less, and more preferably 1.0.
% Or less. When the retardation unevenness (Re) exceeds 2%, the retardation correction function of the retardation film is inferior, which is not preferable.

There are no particular restrictions on other structural requirements of the PVA-based retardation film of the present invention, and the thickness of the PVA-based retardation film is preferably about 5 to 70 μm. There is no particular limitation on the compounding component of the PVA type retardation film, but boric acid, borax,
An ultraviolet absorber or a stabilizer may be added. The width and length of the retardation film of the present invention are not particularly limited. The lower limit of the width of the retardation film is preferably 40 cm or more, more preferably 60 cm or more. The length of the retardation film is preferably 1 m or more, more preferably 10 m or more.

The present invention provides, as a sixth invention, a method for producing a PVA-based retardation film using the PVA-based film of the first or second invention as a raw material. The method for producing the PVA-based retardation film in the present invention is not particularly limited except the above-mentioned constitutional requirements, but the preferred embodiments will be described below.

The original PVA-based film is uniaxially stretched, dried and heat-set to prepare a PVA-based retardation film. PVA
System film swells in water at 20-50 ° C.
Uniaxially stretched 1.01 to 3 times in air or in water at 50 ° C, dried at 50 to 100 ° C, 50 ° C to 200 ° C
Method of heat fixing with PVA film or 20 ~
Preheat to 100 ° C and 1.01 in 80-180 ° C air
A method of uniaxially stretching to 3 times and heat setting at 50 ° C to 200 ° C can be mentioned.

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. Since the PVA-based film of the present invention has a low average birefringence, little birefringence unevenness, and little thickness unevenness, it can be uniformly stretched, uneven retardation due to stretching unevenness hardly occurs, and it is optically homogeneous. It is presumed that an excellent PVA retardation film can be obtained.

[0048]

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

Average birefringence (Δn) and uneven birefringence (Rn): Sampling was carried out at a pitch of 5 cm in the width direction of the film, and the humidity was controlled for 6 hours in an environment of 20 ° C. and 65% relative humidity. Retardation measuring device (Kanzaki Paper Co., Ltd.)
Manufactured by KOBRA-21 (trade name), the retardation was measured, and the film thickness was measured at the same place by using a micrometer. Next, the birefringence was calculated by dividing the measured retardation value by the measured film thickness. The birefringence is calculated for each point of the sample, the average value is taken as the average birefringence (Δn), the difference between the maximum and minimum birefringence of each point of the sample is calculated, and the birefringence unevenness is calculated. (Rn).

Average thickness (t) and thickness unevenness (Rt): A total of 5 points at equal intervals in the width direction of the film and 5 points at equal intervals in the length direction of the film were sampled for a total of 10 points. After conditioning the humidity for 6 hours in an environment of 20 ° C. and 65% relative humidity, a contact type film thickness continuous measuring instrument (manufactured by Anritsu Electric Co., Ltd.) was used to detect the diamond sphere with a diameter of 3 mm. Applying a measurement load of 30g, 1.5m / min
The film thickness was measured at the take-up speed of. Next,
The average value was calculated from the measured values of the 10-point sample to obtain the average thickness (t), and the difference between the maximum value and the minimum value of the measured values of the 10-point sample was described in the section of the description of the second invention. The thickness unevenness (Rt) was calculated by the equation.

Non-uniform transmittance (Ry) and non-uniform dichroic ratio (ΔRd): By the measuring method described in the section of the description of the third invention, at one point in the stretching direction of the PVA polarizing film,
Single transmittance (Y) at 4 cm pitch in the direction perpendicular to the stretching direction
And the degree of polarization (V) were measured and calculated.

Retardation unevenness (Re): Sampling was performed at a pitch of 5 cm in a direction perpendicular to the stretching direction of one point in the stretching direction of the PVA retardation film, and a retardation measuring device (KOBRA-21 manufactured by Kanzaki Paper Co., Ltd. The phase difference unevenness (Re) was calculated from the difference between the maximum and minimum values of the retardation measured by using the (name)) according to the formula described in the section of the description of the fifth invention.

Water content and water content unevenness: By the method described in the section of the description of the second invention above, the film was sampled at a pitch of 5 cm in the width direction of the PVA-based film, and measured and calculated.

Maximum stretch ratio: The maximum stretch ratio that can be stretched when stretched at a stretching speed of 0.26 m / min using a PVA-based film sample having a width of 15 cm in a 4% by weight boric acid aqueous solution at 35 ° C. Indicated.

Example 1 PVA (degree of polymerization 1750, degree of saponification 99.9 mol%) 1
00 parts by weight and 12 parts by weight of glycerin, and water as a solvent are further added thereto, and a uniform undiluted solution having a water content of 60% wb (weight% in wet base, the same applies hereinafter) is quantitatively supplied to the die.
The drum type film forming machine 21 of FIG. 2 has a thickness of 75 μm and a width of 2.0.
m PVA film was produced. No drying roll was 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 film peeling 8.0wt% Heat treatment machine: Hot air hot air temperature 160 ° C. Treatment time 15 seconds Moisture content of exit film 1.8 wt% Moisture content of film after humidity conditioning 6.5 wt% Physical properties of the film thus obtained are shown in Table 1. This film had small thickness unevenness, average birefringence and birefringence unevenness, and had good stretchability.

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

Example 3 PVA (degree of polymerization 1750, degree of saponification 99.9 mol%) 1
00 parts by weight, and water as a solvent is further added to give a water content of 60%.
A uniform wb stock solution was quantitatively supplied to the die, a belt-type film forming machine 11 shown in FIG. 1 was used to produce a film having a thickness of 75 μm and a width of 1.5 m, and heat treatment was carried out by the heat treatment machine 16. The main manufacturing conditions are shown below. Die: T-type slit die Die temperature 100 ° C. Film forming machine: Stainless belt length 20 m Belt speed 10 m / min Drying temperature 100 ° C. to 150 ° C. Drying time 120 seconds Water content at film peeling 9.0 wt% Heat treatment machine: hot air Formula Hot air temperature 160 ° C. Treatment time 15 seconds Water content of exit film 1.5 wt% Water content of film after humidity conditioning 6.0 wt% Physical properties of the film thus obtained are shown in Table 1. This film had small thickness unevenness, average birefringence and birefringence unevenness, and had good stretchability.

Comparative Example 1 The same stock solution as in Example 1 was quantitatively supplied to the die to produce a film having a thickness of 75 μm and a width of 2.0 m by the drum type film forming machine 21 of 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. Treatment time 15 seconds Water content of exit film 1.5 wt% Water content of film after humidity conditioning 6.3 wt% Physical properties of the film thus obtained are shown in Table 1. . This film has large thickness unevenness, average birefringence and birefringence unevenness, and has a lower stretchability than the examples.

Comparative Example 2 The same stock solution as in Example 1 was quantitatively supplied to the die, a belt type film forming machine 11 of FIG. 1 was used to produce a film having a thickness of 75 μm and a width of 1.5 m, and a heat treatment machine 16 was used for heat treatment. 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 film peeling 20 wt% Heat treatment machine: Hot air hot air temperature 165 ° C. Treatment Time 9 seconds Moisture content of outlet film 5.2 wt% Moisture content of film after humidity conditioning 6.5 wt% Physical properties of the film thus obtained are shown in Table 1. This film has large thickness unevenness, average birefringence and birefringence unevenness, and has a lower stretchability than the examples.

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

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 film of Example 3 was used as a raw fabric. Table 2 shows the physical properties of the polarizing film. Similar to 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 unevenness of transmittance and unevenness of dichroic ratio, and especially at both ends of the polarizing film.

Example 6 Using the raw fabric of Example 3, a retardation film was produced by uniaxial stretching. Through the steps of swelling, stretching, drying and heat setting as a manufacturing process, 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 was 350 nm. Physical properties of raw material after heat treatment and the obtained width 1.2m
Table 3 shows the physical properties of the retardation film. Since the birefringence of the raw fabric was low and the stretching ratio was increased, and the birefringence unevenness of the raw fabric was small and the thickness unevenness was small, the obtained retardation film had little unevenness in retardation.

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 original fabric and the physical properties of the obtained retardation film having a width of 1.2 m. The obtained retardation film had large unevenness in retardation. The product width of the retardation film obtained in Comparative Example 4 was wider than that of Example 6 because the stretching ratio was lower than that of Example 6, but the width was 1.2 m excluding both ends. Each measurement was performed as a retardation film.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

[Table 3]

[0068]

【The invention's effect】

(1) By using a PVA-based film having a small average birefringence and a small unevenness in birefringence, a high-quality PVA-based polarizing film having a small unevenness in polarization performance can be obtained. Further, it is possible to obtain a PVA-based retardation film with less unevenness in retardation. (2) Furthermore, 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) It is possible to obtain a product having high optical homogeneity even for a wide PVA-based polarizing film and a PVA-based retardation film due to the increase in size of LCDs.

[Brief description of drawings]

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

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

[Explanation of symbols]

 11 ... Belt type film forming machine, 21 ... Drum type film forming machine.

Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number in the agency FI Technical display location B29L 7:00 4F C08L 29:00 (72) Inventor Yoshiaki Mukai 892 Sashunichi, Saijo City, Ehime Prefecture Claret Co., Ltd. Within

Claims (6)

[Claims] 1. The average birefringence (Δn) is 1.0 × 10 ^−3.
And the birefringence unevenness (Rn) is 0.13 × 1
A polyvinyl alcohol-based film of 0 ^-3 or less. 2. The polyvinyl alcohol-based film according to claim 1, which has an average thickness (t) of 20 to 100 μm and an uneven thickness (Rt) of 3% or less. 3. A polyvinyl alcohol-based polarizing film having a single-element transmittance unevenness (Ry) of 0.5% or less and a dichroic ratio unevenness (ΔRd) of 2.5 or less. 4. A method for producing a polyvinyl alcohol-based polarizing film according to claim 3, wherein the polyvinyl alcohol-based film according to claim 1 or 2 is used as an original fabric. Method. 5. A polyvinyl alcohol-based retardation film having a retardation unevenness (Re) of 2% or less. 6. The polyvinyl alcohol-based retardation film according to claim 5, wherein the polyvinyl alcohol-based film according to claim 1 or 2 is used as an original fabric to produce the polyvinyl alcohol-based retardation film. Manufacturing method.