JP3342517B2 - Method for producing PVA-based film and optical film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 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. 4) The conventional PVA-based film has a large inclination angle (hereinafter, abbreviated as an inclination angle of the optical axis) with respect to the length direction (film forming direction) of the long axis of the birefringent ellipsoid with respect to the film length direction, and its local change. The rate was also large.

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), transmittance unevenness (Ry) was large. The same applies to the case of a PVA retardation film. A conventional PVA film using a conventional PVA-based film having a large birefringence unevenness (Rn) as a raw material is used.
The A 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. The unevenness of the chromaticity ratio (） Rd) and the unevenness of the transmittance (Ry) were large, and the conventional retardation film had a large unevenness of the retardation (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. 4) When a PVA-based film having a large optical axis tilt angle (θ) is used, the tilt angle of the optical axis of the polarizing film obtained after stretching becomes non-uniform, resulting in uneven light transmittance under crossed Nicols. It was big. In the case of a PVA retardation film,
The phase difference unevenness was large.

[0005]

To achieve the above object, according to the solution to ## a result of intensive studies, as the present invention is the first aspect, poly
Cast a stock solution consisting of a vinyl alcohol polymer solution
The film obtained by casting and drying on a substrate for
Obtained by peeling from the casting substrate
Method for producing a polyvinyl alcohol-based film
Then, remove the film from the casting substrate.
Set the moisture content of the film when released to less than 10% by weight
When peeling the film from the casting substrate
Water content unevenness of 1% by weight or less,
The peel tension of the film when peeling the film from the material
0.025 kg / mm ² or less and casting
Straighten the peeling line of the film from the substrate for
The maximum value (Mθ) of the absolute value of the tilt angle (θ) of the major axis of the birefringent ellipsoid with respect to the film length direction is 5 degrees or less, and the local change rate (Rθ) of the tilt angle (θ) The present invention provides a method for producing a PVA-based film , which obtains a film having a temperature of not more than 1 degree.

In the present invention, the maximum value (Mθ) of the absolute value of the inclination angle (θ) of the optical axis and the local change rate (Rθ) of the inclination angle (θ) can be measured by using a polarizing microscope. It is calculated by measuring the tilt angle (θ) of the axis. The inclination angle (θ) of the optical axis of the PVA-based film is determined by controlling the humidity of the PVA-based film for 6 hours in an environment of 20 ° C. and a relative humidity of 65%.
After precisely aligning the film forming direction of the PVA-based film with the vibration direction of the orthogonal Nicol polarizer of the polarizing microscope, rotate the sample stage so that the major axis of the refractive index ellipsoid of the PVA-based film is aligned with the vibration direction of the polarizer. The rotation angle until the coincidence is read is taken as the inclination angle (θ) of the optical axis.

The maximum value (Mθ) of the absolute value of the inclination angle (θ) of the optical axis is determined by the direction in which the PVA film is formed (hereinafter referred to as MD).
Direction) (at least one point in the width direction).
(Abbreviated as D direction) is the maximum value of the absolute value of the inclination angle (θ) of the optical axis measured by the above-described measuring method by selecting a pitch in the range of 1 mm to 1 cm.

The local change rate (Rθ) of the tilt angle (θ)
Is the difference between the maximum value and the minimum value of the optical axis tilt angle (θ) within an arbitrary 5 cm width range measured in the same manner as the method of measuring the absolute value (Mθ) of the optical axis tilt angle (θ). Is the absolute value of In the above-mentioned measuring method and the measuring methods of the other items described below, a portion of the PVA-based film that is not practically used is excluded from the measuring points.

In the present invention, (Mθ) is 5 degrees or less, more preferably 3 degrees or less, and still more preferably 2.degree.
0 degrees or less. In the present invention, (Rθ) is 1 ° or less, more preferably 0.5 ° or less. (M
θ) exceeds 5 degrees, or (Rθ) exceeds 1 degree, the PVA-based film used as a raw material
In the VA-based polarizing film and the PVA-based retardation film, the maximum value of the absolute value of the tilt angle of the optical axis with respect to the stretching direction and the local change rate of the tilt angle are large, and the optical quality is deteriorated.

[0010] There are no particular restrictions on other constituent requirements of the PVA-based film obtained by 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 steric structure of the PVA polymer of the present invention, an atactic structure is generally used, but a polymer rich in an isotactic structure or a syndiotactic structure is also used. It is also possible to copolymerize the monomer copolymerizable with the above-mentioned vinyl ester-based monomer. Examples of these copolymerizable monomers include olefins such as ethylene, propylene, 1-butene and isobutene; acrylic acid and Salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate And acrylates such as octadecyl acrylate; methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, methacrylic acid T-butyl acid, methacrylic acid 2
Methacrylic acid esters such as -ethylhexyl, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and salts thereof, acrylamidopropyl Acrylamide derivatives such as dimethylamine and its salts or quaternary salts thereof, N-methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidopropyl Methacrylamide derivatives such as dimethylamine and its salts or quaternary salts thereof, N-methylol methacrylamide and its derivatives; Vinyl ethers such as toluene ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride; Vinyl halides such as 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; vinyl trimethoxysilane and the like Vinylsilyl compound; isopropenyl acetate and the like. The content of these copolymerizable monomers is preferably 10 mol% or less, more preferably 5 mol% or less.

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 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.

The thickness of the PVA-based film obtained by the present invention is not particularly limited, but is preferably 20 to 100 μm, more preferably 50 to 100 μm, and more preferably 60 to 80 μm.
m is particularly preferred. The length and width of the PVA-based film obtained by the present invention are not particularly limited. The lower limit of the width of the PVA-based film is preferably 50 cm or more.
cm or more is more preferable, and 100 cm or more is particularly preferable. 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 the PVA-based film is preferably 1 m or more, more preferably 10 m or more.

[0015] The PVA-based film obtained by the present invention is characterized by small local optical unevenness and thickness unevenness.
An undiluted solution comprising the A-based polymer solution is cast on a casting substrate, and the film obtained by drying is peeled from the casting substrate to have a water content of 10% by weight (hereinafter referred to as "% by weight"). May be abbreviated as wt%.)
To less than 1% by weight of the moisture content when the film is peeled off from the casting substrate, and 0.025 kg / mm ² or less when the film is peeled off from the casting substrate. And a straight line (preferably a straight line parallel to the TD direction) of the line for peeling the film from the casting substrate. When heat treating a PVA-based film, the tension of the film in the heat treatment machine (the tension of the film during heat treatment)
Is preferably 0.025 kg / mm ² or less.

In the present invention, the moisture content of the film is measured at least 5 points immediately after the film is peeled off from the casting substrate so as not to be affected by the outside humidity. About 2 g of the film was dried at 50 ° C. for 2 hours under a reduced pressure of 2 Torr, the weight of the film was measured before and after drying, and the average value was 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 water content unevenness in the present invention is obtained by measuring the water content of at least five or more arbitrary points of the film immediately after peeling by the measurement method described above, and determining the difference between the maximum value and the minimum value of the measured water content. It is.

The peel tension in the present invention is calculated by the following equation by measuring the peel tension of the film when peeling the film from the casting substrate. Peeling tension = (tension of the entire width of the film at the time of peeling) / {(average thickness of the film) × (full width of the film)}

The film tension during the heat treatment in the present invention is calculated by the following equation by measuring the film tension during the heat treatment. Tension during heat treatment = (Tension of the entire width of the film during heat treatment) /
｛(Average thickness of film) × (full width of film) フ ィ ル ム

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, and 5-8% by weight. More preferred. Moisture content unevenness of the film when the film is peeled off from the casting substrate must be 1.0% by weight or less.
% By weight or less, more preferably 0.5% by weight or less. Peeling tension of the film when peeling the film from the casting base material is required to be below 0.025 kg / mm ^2, preferably 0.012 kg / mm ² or less. Film tension during heat treatment is 0.025kg
/ Mm ² or less, 0.012 kg
/ Mm ² or less.

When 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. Also in the portion, the birefringence unevenness increases, the thickness becomes thin and the unevenness occurs, and the absolute value of the tilt angle of the optical axis and the local change rate of the tilt angle increase. 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. If the moisture content unevenness at the time of peeling the film from the casting substrate exceeds 1% by weight, local unevenness in peeling due to uneven moisture content occurs, and uneven birefringence occurs. When the film peeling tension when the film is peeled from the casting substrate exceeds 0.025 kg / mm ² , the birefringence tends to increase, and when the film is stretched in the length direction, the maximum The stretching ratio decreases, and the absolute value of the tilt angle of the optical axis and the local change rate of the tilt angle increase .

As the casting and drying apparatus for forming a film under the above conditions, there are a drum type film forming machine, a belt type film forming machine and the like, and as the heat treatment apparatus, there are a drum type heat treating machine, a hot air type heat treating machine and the like. . 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 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 (a direction perpendicular to the paper surface of FIG. 1), and the undiluted solution L has a uniform thickness in the width direction through this opening, and a belt 13 as a casting base material is formed. It flows out above.

The belt type film forming machine 11 has the endless belt 13 running between a pair of rollers 12, 12, and the stock 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.
The outer peripheral surface and the inner peripheral surface of the belt 13 are heated from a hot air blower (not shown in the drawing) to 80 ° C.
Hot air H at 170 ° C. is blown to promote drying of the stock solution. Further, in order to increase the film strength at the time of peeling, the film F may be cooled by the normal temperature wind C in the zone 14A which is the most downstream. 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 wound around a winder 19 through a heat treatment machine 16, a humidity control machine 17, and an inspection machine 18 shown in FIG. The heat treatment machine 16 is 100-
The hot air of about 170 ° C. is blown onto the film F to change the crystallinity of the film F and the like. The humidity controller 17 adjusts the water content of the film F to, for example, about 5% by weight. The inspection device 18 inspects physical defects, foreign matter, thickness, moisture, and the like.

Next, a production method using the belt type film forming machine 11 will be described. PV without concentration unevenness
The stock solution L composed of the aqueous solution of the A-based polymer is sent to the die 10 at a constant speed and flows out onto the belt 13. The undiluted solution L that has flowed onto the belt 13 is cast by the belt 13 in FIG. 1 traveling in the direction of the arrow A.
Drying is promoted by the hot air H. Here, the belt 13
Can be lengthened, unlike the drum described later, so that the drying time is extended and the film F
Can be sufficiently dried. Therefore, the water content of the film F is easily reduced to less than 10% by weight, the unevenness of the content at the time of peeling is reduced to 1% by weight or less, and the film F is peeled off from the belt (casting base material) 13. The peel tension of the film F is set to 0.025 kg / mm ²
The film F can be easily peeled off from the belt 13 by making the film F smaller from the belt 13 and making the peeling line of the film F from the belt 13 straight (preferably a straight line parallel to the TD direction). 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 lengthened 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.

Also, 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.

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 second aspect of the present invention, the maximum value (MZ) of the absolute value of the inclination angle (Z) of the major axis of the birefringent ellipsoid with respect to the stretching direction of the polarizing film is 1 degree or less and the angle ( also local rate of change Z) (RZ) is 0.2 degrees or less
And a method for producing a PVA-based polarizing film that obtains

In the present invention, MZ and RZ are calculated by measuring the tilt angle (Z) of the long axis of the birefringent ellipsoid of the PVA-based polarizing film with respect to the polarizing film stretching direction. Z in the present invention
Is measured using a polarizing microscope in the same manner as the method of measuring the inclination angle (θ) of the optical axis described in the section of the first invention.

MZ is the maximum of the absolute value of Z measured by the above-mentioned measuring method, with a fixed pitch of 1 mm to 1 cm in at least one direction perpendicular to the stretching direction of the PVA-based polarizing film. Value.

RZ is the absolute value of the difference between the maximum value and the minimum value in an arbitrary range of 5 cm width measured by the same method as the above-mentioned MZ measurement method.

In the present invention, MZ is 1 degree or less, preferably 0.5 degree or less, and RZ is 0.2 degree or less, preferably 0.1 degree or less. If MZ exceeds 1 degree or RZ exceeds 0.2 degree, P
When a VA-based polarizing film is used under crossed Nicols, light leakage and local unevenness in transmittance occur, which is not preferable in quality.

There are no particular restrictions on other components of the PVA-based polarizing film obtained by the present invention. As the dichroic substance used in the present invention, a so-called dichroic dye is used alone or in combination with iodine. 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 μm is more preferred. 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, and 10 m or more.
The above is more preferable.

The present invention is a method for producing a PVA-based polarizing film using the PVA-based film of the first invention as a raw material , and the production conditions are not particularly limited except for the above constitutional requirements. However, the preferable aspect is shown below. The raw PVA-based film is swelled, dyed, uniaxially stretched, treated with a boric acid compound, and dried 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.

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 in the aqueous solution is appropriately selected from 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 raw material in the present invention
A-based film, since the maximum value of the absolute value of the tilt angle of the optical axis is small and the local change rate of the tilt angle is small,
Even after being processed into a PVA-based polarizing film, the maximum value of the absolute value of the tilt angle of the optical axis of the PVA-based polarizing film is small, and the local change rate of the tilt angle is small. As a result, the optical performance is uniform. It is estimated that

According to a third aspect of the present invention, the maximum value (MΦ) of the absolute value of the tilt angle (Φ) of the major axis of the birefringent ellipsoid with respect to the stretching direction of the retardation film is 3 degrees or less, and Local change rate (RΦ) of angle (Φ) is 0.5 degrees or less
A method for producing a PVA-based retardation film is provided.

MΦ and RΦ in the present invention are calculated by measuring the tilt angle (Φ) of the birefringent ellipsoid of the PVA-based retardation film with respect to the stretching direction of the retardation film. Φ in the present invention
Is measured using a polarizing microscope in the same manner as the inclination angle (θ) of the optical axis described in the section of the first invention.

MΦ is a measurement of the inclination angle described in the column of the first invention, with a pitch in the range of 1 mm to 1 cm fixed in a direction perpendicular to at least one stretching direction of the PVA-based retardation film. The maximum value of the absolute value of Φ measured by the method.

RΦ is the absolute value of the difference between the maximum value and the minimum value in an arbitrary range of 5 cm in width measured by the same method as the method for measuring MΦ described above.

The maximum tilt angle (MΦ) in the present invention is 3
Degrees or less, preferably 2 degrees or less, more preferably 1.5 degrees or less.
Degrees or less. Further, the local change rate (R
Φ) is 0.5 degrees or less, preferably 0.3 degrees or less, and more preferably 0.2 degrees or less. Maximum tilt angle (MΦ)
Exceeds 3 degrees or the local change rate (RΦ) is 0.
If the angle exceeds 5 degrees, local optical unevenness of the PVA-based retardation film becomes large, which is not preferable.

There are no particular restrictions on 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. The present invention
The width and length of the retardation film obtained by the above 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. There are no particular restrictions on the components of the PVA-based retardation film, but boric acid, borax, an ultraviolet absorber or a stabilizer may be added.

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

A 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.
A method in which the film is stretched in the uniaxial direction 1.0 to 3 times in air or water at 50 ° C., dried at 50 to 100 ° C., and heat-set at 50 to 200 ° C.
Preheated to 00 ° C, and in air at 80-180 ° C
A method in which the film is uniaxially stretched three times and heat-set at 50 to 200 ° C. may be used.

Examples of the preheating device include a roll preheating device and a hot air preheating device. As the stretching device, a two-roll or multistage stretching device, a tenter type stretching device, or the like is used. The PVA-based film of the present invention can be stretched uniformly because the maximum value of the absolute value of the tilt of the optical axis is small and the local change rate of the tilt is small, and it is unlikely to cause phase difference unevenness due to uneven stretching. From this, it is estimated that an optically uniform PVA retardation film can be obtained.

[0049]

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 after humidifying for 6 hours in an environment of 20 ° C. and a relative humidity of 65%, Retardation measuring instrument (Kanzaki Paper Co., Ltd.)
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, 5 points in total 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 obtained. The difference between the maximum value and the minimum value of the measured values of the ten samples was obtained, and the thickness unevenness (Rt) was obtained. .

Water content and water content unevenness: The PVA film was sampled at a pitch of 5 cm in the width direction and measured and calculated by the method described in the section of the first invention.

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

The maximum value (Mθ) of the absolute value of the tilt angle (θ) of the optical axis and the local change rate (Rθ) of the tilt angle (θ):
According to the measuring method described in the description of the first invention,
Select one point in the MD direction of the film and 1c in the TD direction
(θ) was measured and calculated at m pitches.

Single transmittance (Y) and degree of polarization (V): JIS standard Z-8701 “Color display method using two-degree visual field XYZ system” is applied in accordance with ED-2521 of the Japan Electronic Machinery Manufacturers Association. The stimulus value (Y) in the “three stimulus values of the transmitted object” was defined as the transmittance. Standard light source is C light source, wavelength range is 3
80-780 nm, spectrophotometer UV-2200 manufactured by Shimadzu
Was used. Single transmittance (Y): The transmittance of one polarizing plate 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 plates are stacked so that their orientation directions are parallel, and Ycross is the two polarizing plates whose orientation is aligned. This is the transmittance when they are superposed so that the directions are orthogonal to each other.

Maximum value (MZ) and local rate of change (RZ) of the absolute value of the tilt angle (Z) of the optical axis: The PVA polarizing film was measured by the measurement method described in the description of the second embodiment. One point in the stretching direction was selected, and Z was measured at a pitch of 1 cm in the direction perpendicular to the stretching direction and calculated.

Retardation and retardation unevenness (Re): One point in the stretching direction of the PVA retardation film was selected, sampling was performed at a pitch of 5 cm in a direction perpendicular to the stretching direction, and a retardation measuring device (manufactured by Kanzaki Paper Co., Ltd.) The average value of retardation (birefringence × film thickness) measured using KOBRA-21 (trade name) is defined as a phase difference, and the difference between the maximum value and the minimum value of the measured retardation values is determined by the phase difference unevenness ( Re).

The maximum value (MΦ) and the local change rate (RΦ) of the absolute value of the tilt angle (Φ) of the optical axis: The PVA phase difference film was measured by the measuring method described in the above-mentioned section of the fourth invention. One point in the stretching direction was selected, and Φ was measured and calculated at a 1 cm pitch in a direction perpendicular to the stretching direction.

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.
75 μm in thickness and 1.5 in width in the belt type film forming machine 11 of FIG.
m of PVA film was produced and heat-treated by a heat treatment machine 16. The main manufacturing conditions are shown below. Film forming machine: Stainless steel belt Length 20 m Belt speed 10 m / min Drying humidity 100-150 ° C. Drying time 120 seconds Moisture content at the time of film peeling 8.5 wt% Moisture content unevenness at the time of film peeling 0.6 wt% Film peeling tension 0.011 kg / mm ² Film peeling line Straight line parallel to the TD direction Heat treatment machine: Hot air type Hot air temperature 160 ° C Processing time 15 seconds Water content of exit film 1.4 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 has small thickness unevenness, average birefringence index and birefringence unevenness, and has a maximum absolute value (M) of the inclination angle (θ) of the optical axis.
θ) was small, the local change rate (Rθ) of (θ) was small, and the optical homogeneity was high.

Example 2 PVA (degree of polymerization 2000, degree of saponification 99.9 mol%) 1
Water as a solvent was added to 00 parts by weight, a uniform undiluted solution having a water content of 65% wb was quantitatively supplied to a die, and a film having a thickness of 75 μm and a width of 2.0 m was manufactured by the drum type film forming machine 21 of FIG. The heat treatment was performed by the heat treatment machine 16. The main manufacturing conditions are shown below. Drum type film forming machine: Cast roll diameter 2m Rotation speed 1.6m / min Roll temperature 90 ° C Drying time 194 seconds Moisture content at film peeling 6.5wt% Moisture content unevenness at film peeling 0.5wt% Film peeling tension 0.010 kg / mm ² Film peeling line Straight line parallel to TD direction Heat treatment machine: Hot air type Hot air temperature 150 ° C Processing time 20 seconds Water content of outlet film 1.2 wt% Water content of moisture-conditioned film 6.2 wt% % The physical properties of the film thus obtained are shown in Table 1. This film had high optical homogeneity as in Example 1.

Example 3 PVA (degree of polymerization 4000, degree of saponification 99.9 mol%) 1
Then, 00 parts by weight, 12 parts by weight of glycerin and water as a solvent were added, and a uniform undiluted solution having a water content of 70% Wb was quantitatively supplied. A PVA film was manufactured and heat-treated by a heat treatment machine 16. The main manufacturing conditions are shown below. Film forming machine: Stainless steel belt Length 20m Belt speed 8m / min Drying humidity 130-155 ° C Drying time 145 seconds Moisture content at film peeling 9.6wt% Moisture content unevenness at film peeling 0.8wt% Film peeling tension 0.024 kg / mm ² film peeling line Straight line parallel to TD direction Heat treatment machine: Hot air type Hot air temperature 160 ° C Processing time 15 seconds Water content of outlet film 1.2wt% Water content of moisture-conditioned film 6.5wt % The physical properties of the film thus obtained are shown in Table 1. This film had high optical homogeneity as in Example 1.

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. gave. The main manufacturing conditions are shown below. Film forming machine: Cast roll diameter 2m Rotation speed 5m / min Roll temperature 85 ° C Drying time 62 seconds Moisture content at film peeling 30.2wt% Moisture unevenness at film peeling 6.2wt% Film peeling tension 0.045kg / mm ² film edged stripping line saw drying roll roll humidity 70 to 110 ° C. drying time 100 sec thermal processor: a water content of 1.8 wt% moisture adjustment of hot air hot air temperature of 160 ° C. treatment time 15 seconds exit film of the film Table 1 shows the physical properties of the film thus obtained. This film has a large average birefringence index and uneven birefringence index, and the maximum value (M) of the absolute value of the inclination angle (θ) of the optical axis.
θ) is large and the local change rate (R) of the inclination angle (θ) is
θ) was large and the optical homogeneity was low.

Comparative Example 2 The same stock solution as in Example 1 was supplied to a 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 shown in FIG. gave. The main manufacturing conditions are shown below. Film forming machine: Stainless steel belt Length 20m Belt speed 10m / min Drying humidity 100-150 ° C Drying time 120 seconds Moisture content at film peeling 15.3wt% Moisture content unevenness at film peeling 1.2wt% Film peeling tension 0.030 kg / mm ² Film peeling line Saw blade Heat treatment machine: Roll heat treatment Roll temperature 140 ° C. Treatment time 15 seconds Water content of exit film 1.6 wt% Water content of moisture-conditioned film 6.0 wt% Table 1 shows the physical properties of the obtained film. This film has relatively small thickness unevenness, average birefringence index, and birefringence unevenness, but has a large absolute value (Mθ) of the absolute value of the tilt angle (θ) of the optical axis, and has a large tilt angle (θ). Had a large local change rate (Rθ) and low optical homogeneity.

Example 4 Using the PVA film of Example 1 as a raw material, a polarizing film was produced by wet dyeing with iodine and biaxial stretching. Through the swelling, dyeing, stretching, boric acid treatment and drying processes, the weight ratio of potassium iodide / iodine in the dyeing solution is 10%.
The iodine concentration was appropriately adjusted between 1 and 20 g / liter so as to cover 43% of the single transmittance of the polarizing film. 4% by weight of boric acid was added to the stretching bath, and the stretching was performed up 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 0.9 m was obtained. Table 2 shows the physical properties of the polarizing film. In this PVA polarizing film, the maximum value (MZ) of the absolute value of the tilt angle (Z) of the optical axis was small, and the local change rate (RZ) of the tilt angle (Z) was small.

Example 5 Using the PVA film of Example 3 as a raw material, a polarizing film having a width of 0.9 m was obtained in the same manner as in Example 4. Table 2 shows the physical properties of the polarizing film. This PVA polarizing film had high optical homogeneity as in Example 4.

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 PVA polarizing film had high MZ and RZ and low optical homogeneity.

Example 6 A retardation film was produced by uniaxial stretching using the raw material of Example 1. 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. Table 3 shows the physical properties of the obtained retardation film having a width of 1.2 m. This retardation film had a small maximum value (MΦ) of the absolute value of the tilt angle (Φ) of the optical axis and a small local change rate (RΦ) of the tilt angle (Φ).

Comparative Example 4 A retardation film was produced in the same manner as in Example 6, except that the raw material of Comparative Example 1 was used. Table 3 shows the physical properties of the obtained retardation film having a width of 1.6 m. This retardation film had large MΦ and RΦ and low optical homogeneity.

[0069]

[Table 1]

[0070]

[Table 2]

[0071]

[Table 3]

[0072]

As described above, according to the present invention,
By using a PVA-based film raw material having a small absolute value (Mθ) of the absolute value of the tilt angle (θ) of the optical axis and a small local change rate (Rθ) of the tilt angle (θ), Provided are a method for producing a PVA-based polarizing film and a PVA-based retardation film that can obtain less disturbance. In addition, a wide and high optical homogeneity which can be suitably used for the enlargement of the LCD is obtained.
And a method for producing a PVA-based polarizing film and a PVA-based retardation film.

[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.

Continuation of the front page (72) Inventor Yoshiaki Mukai 892 Sakuhi-shi, Saijo-shi, Ehime Kuraray Co., Ltd. (56) References JP-A-4-173844 (JP, A) JP-A-4-173125 (JP, A) JP-A-64-84203 (JP, A) JP-A-63-261201 (JP, A) JP-A-57-212025 (JP, A) JP-A-4-204503 (JP, A) (58) (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 (3)

(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
Weight percent, and set the
Moisture content unevenness at the time of peeling the lum is reduced to 1% by weight or less.
When peeling the film from the substrate for casting
The peeling tension of LUM should be 0.025 kg / mm ² or less,
Peeling line for film from the casting substrate
And the maximum value (M) of the absolute value of the inclination angle (θ) of the major axis of the birefringent ellipsoid with respect to the length direction of the film
θ) is 5 degrees or less, and a method of producing a polyvinyl alcohol-based film to obtain a film having a local change rate (Rθ) of the inclination angle (θ) of 1 degree or less. 2. The method according to claim 1, which is obtained by:
Using a polyvinyl alcohol-based film as a raw material , the long axis of the birefringent ellipsoid with respect to the stretching direction of the polarizing film
When the maximum value (MZ) of the absolute value of the tilt angle (Z) is 1 degree or less
And the local change rate (RZ) of the tilt angle (Z) is
Ltd. The polyvinyl alcohol-based polarizing film is 0.2 degrees or less
A method for producing a polyvinyl alcohol-based polarizing film to be produced. 3. The method according to claim 1, which is obtained by the method according to claim 1.
Using a polyvinyl alcohol-based film as a raw material , the long axis of the birefringent ellipsoid in the stretching direction of the retardation film
The maximum value (MΦ) of the absolute value of the tilt angle (Φ) is 3 degrees or less
And the local change rate (RΦ) of the tilt angle (Φ) is
0.5 degree or less polyvinyl alcohol-based retardation film
A method for producing a polyvinyl alcohol-based retardation film to be produced.