JP2003170451A - Manufacturing method for vinyl alcohol polymer film, and polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a vinyl alcohol polymer film which curls little when immersed in water and which is easy to stretch uniformly and can be made a polarizing film having a uniform polarizing performance. <P>SOLUTION: In the manufacturing method for the vinyl alcohol polymer film wherein a film-making material containing a vinyl alcohol polymer is cast or discharged onto an endless belt and then dried, a drying chamber so provided as to surround the whole of the endless belt is divided into 6 to 16 chambers by partition walls. When the temperatures of hot air sent into three continuous drying chambers A, B and C adjacent to each other, except the chamber located at a position where the film-making material is cast or discharged onto the endless belt and that located at a position where the film is peeled off from the endless belt, are denoted by AT, BT and CT respectively, relational formulas of AT>BT and BT<CT are satisfied by the method. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a vinyl alcohol-based polymer film which is useful as a raw material for producing a polarizing film and is less likely to curl when immersed in water, and a polarizing film produced using the same. It is about.

[0002]

2. Description of the Related Art A polarizing plate having a light transmitting and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The field of application of this LCD is from small devices such as calculators and wristwatches in the early stages of development to laptop computers in recent years.
There is a demand for a polarizing plate which is widely used in word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, and the like, and which has more excellent optical characteristics than ever before.

Generally, a polarizing plate is a vinyl alcohol polymer film (hereinafter, abbreviated as "PVA film", and a vinyl alcohol polymer as a raw material thereof may be abbreviated as "PVA"). Is uniaxially stretched and dyed, and a protective film such as a cellulose triacetate (TAC) film or an acetic acid / cellulose butyrate (CAB) film is laminated on both surfaces of the polarizing film.

Japanese Unexamined Patent Publication No. 5-337967 and Japanese Unexamined Patent Publication 5
JP-A-305642 discloses a method for producing a PVA film in which a partition wall is installed in a drying chamber to change the temperature of hot air blown onto the PVA film on the endless belt. However, in these prior documents, in order to obtain a PVA film in which curling is less likely to occur when immersed in water, the temperature of the hot air blown to a specific drying chamber is the hot air blown to the drying chambers adjacent to both sides. There is no disclosure of lowering the temperature below.

[0005]

In order to make the polarizing performance of the polarizing plate uniform, there are many points such as making the thickness of the PVA film uniform and sticking them evenly, but the most important The point is to stretch the PVA film uniformly. When the PVA film cannot be stretched uniformly, it is difficult to make the polarizing performance of the obtained polarizing plate uniform.

[0006] Therefore, an object of the present invention is to provide a method for producing a PVA film which has a small curl when immersed in water, can be uniformly stretched, and can be a polarizing film having a uniform polarization performance.

[0007]

In order to solve the above problems, in the method for producing a PVA film according to the present invention, a film forming raw material containing a vinyl alcohol polymer is cast or discharged onto an endless belt. In the method for producing a vinyl alcohol-based polymer film to be dried, a drying chamber installed so as to surround the entire endless belt is divided into 6 to 16 chambers by partition walls, and the film-forming raw material is cast or discharged onto the endless belt. Except for the drying chamber at the position and the drying chamber at the position where the film is peeled off from the endless belt, the temperatures of the hot air blown to the three adjacent drying chambers A, B and C are AT, BT and CT, respectively. Then, the relational expressions of AT> BT and BT <CT are to be satisfied.

At this time, except for the drying chamber at the position where the film-forming raw material is cast or discharged onto the endless belt and the drying chamber where the film is peeled from the endless belt, the warm air blown to each drying chamber is used. The maximum temperature difference between the drying chambers is preferably 60 ° C or more. By this method, a PVA film suitable for producing a polarizing film can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a PVA film belt film forming apparatus used in the manufacturing method of the present invention, which contains water-containing P
A melt-extrusion film forming machine for melting and extruding VA (which may contain an organic solvent; the same applies hereinafter) is shown. This film forming machine extrudes a fixed amount of film forming raw material (molten PVA) 2 from an elongated slit-shaped opening 1 in the width direction of the endless belt onto an endless belt 4 which moves at a constant speed, and a part of this endless belt 4 is pushed out. Pass through to dry the PVA film. At this time, the drying chamber 10 installed so as to surround the entire endless belt 4 is divided into eight chambers from the drying chamber 11 to the drying chamber 18 by the partition wall 8. After that, the PVA film 6 passes through a floating dryer, a drying metal roll, an inspection machine, etc., which are not shown, and is wound around a winder.

In the above film forming machine, in the present invention, the drying chamber 11 at the position where the film forming raw material 2 is cast or discharged onto the endless belt 4 and the drying chamber where the PVA film 6 is separated from the endless belt 4. Blowers are blown to three adjacent continuous drying chambers (drying chambers A, B, C) except 18 (there may be the same drying chamber without a partition between the drying chambers 11 and 18). Temperature (BT) of the hot air 9 blown to the drying chamber B among the hot air blown to the drying chambers (drying chambers A and C) adjacent to both sides thereof (AT) (AT
And CT), preferably at least 10 ° C., more preferably 15 ° C., particularly preferably 20 ° C. above the temperature of the hot air on one side (AT or CT).
It is more important to lower the temperature. If there is no drying chamber corresponding to the drying chamber B and having a temperature lower than the temperature of the warm air blown to the drying chambers adjacent to both sides, a PVA film having less curl when immersed in water cannot be obtained. In the present invention, when the temperature of the hot air 9 that is blown to the adjacent divided drying chambers is the same, it is regarded as one drying chamber even if it is divided by the partition walls. Further, the temperature of the warm air blown to the three adjacent drying chambers is AT> BT and BT.
<As long as the relational expression of CT is satisfied, such three adjoining drying chambers have a drying chamber at a position where the film forming raw material is cast or discharged onto the endless belt and the film is an endless belt. Two or more sets may be provided between the drying chambers at positions where they are separated from each other.

Further, in the present invention, the temperature of the hot air blown to the drying chambers other than the drying chamber 11 and the drying chamber 18 and the warm air 9
The maximum temperature difference of the temperature (BT) is preferably 60 ° C. or higher, more preferably 65 ° C. or higher, and most preferably 70 ° C. or higher. If the maximum temperature difference between the drying chambers is less than 60 ° C., curling may occur easily when the obtained PVA film is immersed in water.

Furthermore, it is preferable that the back surface of the endless belt at the position where the film-forming raw material 2 discharged from the slit-shaped opening 1 contacts the endless belt 4 moving at a constant speed is in contact with the roll 3. . When the back surface is not in contact with the roll 3, the thickness uniformity of the PVA film 6 obtained may deteriorate.

The roll 3 includes steam, heat medium, hot water,
Heat with an electric heater. Further, it is preferable to suck air or steam around the PVA film into each of the divided rooms of the drying chamber 10 installed so as to surround the endless belt 4.

The endless belt 4 is preferably made of metal, and particularly preferably made of mirror-finished stainless steel. The width of the endless belt 4 is preferably equal to or smaller than the width of the roll, more preferably 1 cm narrower, and further preferably 5 cm narrower. Endless belt 4
When the width of the PVA film is wider than the width of the roll, the thickness unevenness in the vicinity of both ends of the PVA film in the width direction tends to increase.

In the PVA, for example, a part or all of the ester groups of polyvinyl ester obtained by polymerizing a vinyl ester monomer is converted into hydroxyl groups by a saponification reaction, an alcoholysis reaction, a transesterification reaction, or the like. Manufactured in. Modified PVA obtained by graft-copolymerizing PVA with unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, olefin, etc.
A modified PVA produced by saponifying a modified polyvinyl ester obtained by copolymerizing a vinyl ester-based monomer with an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an olefin, or an unmodified or modified PVA. Examples include so-called polyvinyl acetal resins in which a part of hydroxyl groups is crosslinked with aldehydes.

Examples of the vinyl ester-based monomer include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like. One or more of these can be used, but vinyl acetate is preferred.

On the other hand, the comonomer used in the modified PVA is mainly used for the purpose of modifying the PVA, and is used in a range not impairing the gist of the present invention. Examples of such comonomers include olefins, acrylic acid and its derivatives, methacrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, acrylamide derivatives, methacrylamide derivatives, N-vinylamides, vinyl ethers, Nitriles, vinyl halides, allyl compounds, vinylsilyl compounds, isopropenyl acetate and the like,
These 1 type (s) or 2 or more types can be used.

When modified PVA is used, the modification amount is 15
It is preferably at most mol%, more preferably at most 5 mol%.
As the comonomer, α-olefin having 2 to 30 carbon atoms is preferable, and ethylene is particularly preferable.

The degree of saponification of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, still more preferably 99 mol% or more, and particularly preferably 99.5 mol, from the viewpoint of polarization performance and durability of the obtained polarizing film. % Or more is most preferable, and from the viewpoint of dyeability of the PVA film, 99.99 mol% or less is preferable.

The above-mentioned degree of saponification indicates the proportion of units actually converted into vinyl alcohol units among units which can be converted into vinyl alcohol units by a saponification reaction or the like. The degree of saponification of PVA is JIS
The measurement was performed by the method described.

The degree of polymerization of PVA is preferably 1,000 or more from the viewpoint of the polarization performance and durability of the polarizing film obtained,
2500 or more is more preferable, and 3500 or more is particularly preferable. The upper limit of the degree of PVA polymerization is preferably 8000 or less, more preferably 6000 or less.

The degree of polymerization of PVA is JIS K 67.
It is measured according to 26. That is, it is determined from the intrinsic viscosity measured in 30 ° C. water after re-saponifying PVA and purifying it.

As a method for producing a PVA film using the above PVA, the water-containing PV shown in the embodiment of FIG. 1 is used.
A melt extrusion film forming method in which A (which may contain an organic solvent or the like) is melted, or P in which PVA is dissolved in a solvent such as water
A casting film forming method in which a VA solution is used for casting can be adopted. A good polarizing film cannot be obtained by other methods such as the inflation film forming method.

Solvents for dissolving PVA used in the production of PVA films include, for example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol. , Tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, diglycerin, water and the like, and one or more of them can be used. Among these, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.

The PVA concentration of the PVA solution or water-containing PVA used when producing the PVA film is preferably 10% by weight to 70% by weight, and 10% by weight to 60% by weight.
Is more preferable, 13% by weight to 55% by weight is further preferable, and 15% by weight to 50% by weight is the most preferable.
If necessary, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, or the like.

When manufacturing a PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of this polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, pentaerythritol, sorbitol acetate, sorbitol ethylene oxide adduct, glycerin ethylene oxide adduct. The thing etc. are mentioned and 1 type (s) or 2 or more types can be used among these. Among these, diglycerin, ethylene glycol, and glycerin are preferably used because of the effect of improving stretchability.

The amount of polyhydric alcohol added is PVA.
The amount is preferably 30 parts by weight or less, more preferably 3 parts by weight to 25 parts by weight, most preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight. If it exceeds 30 parts by weight, the PVA film may become too flexible and the handleability may deteriorate.

It is preferable to add a surfactant when the PVA film is produced. The type of surfactant is not particularly limited, but anionic or nonionic surfactant is preferable. As the anionic surfactant, carboxylic acid type, sulfuric acid ester type and sulfonic acid type are preferable. As the nonionic surfactant, alkyl ether type, alkyl ester type, alkyl amide type, polypropylene glycol ether type, alkanol amide type, allyl phenyl ether type are suitable, and these are used alone or in combination of two or more kinds. can do.

The amount of the surfactant added is PVA10.
0.01 to 1 part by weight is preferable with respect to 0 part by weight, 0.02 to 0.5 part by weight is more preferable,
Most preferably 0.05 to 0.3 parts by weight. 0.0
If it is less than 1 part by weight, the effect of improving the stretchability and dyeing property is difficult to appear, and if it exceeds 1 part by weight, it may be eluted on the surface of the PVA film to cause blocking and the handleability may be deteriorated.

In the present invention, when the PVA film is formed, it is more preferable that the PVA film is dried by the belt film forming machine shown in the drawing, and then post-dried or heat-treated by a heat roll and a floating dryer.

The thickness of the PVA film is 10 μm to 150 μm.
μm, preferably 15 μm to 100 μm, 20 μm
It is more preferably m to 80 μm. If the thickness of the PVA film is less than 10 μm, the stretching ratio cannot be increased, and the polarizing performance of the obtained polarizing film will be low. On the other hand, even if the thickness of the PVA film exceeds 150 μm, the polarization performance is not improved and it is not economical, and it is necessary to increase the tension for stretching.

The PVA film thus obtained, after removing both ends in the width direction of the film, is wound up on a cylindrical core made of metal or plastic and stored in a moisture-proof package in a suspended state. Preferably.

For producing a polarizing film from the PVA film obtained by the method of the present invention, for example, PVA
The film may be dyed, uniaxially stretched, fixed, dried, and optionally heat-treated, and dyed, uniaxially stretched,
There is no particular limitation in the order of fixed processing operations. Also, each operation may be performed twice or more.

Dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. As the dichroic dye used for dyeing, iodine-potassium iodide; Direct Black 17, 19, 154; Direct Brown 44,
106, 195, 210, 223; Direct Red
2, 23, 28, 31, 37, 39, 79, 81, 24
0, 242, 247; Direct Blue 1, 15, 2
2, 78, 90, 98, 151, 168, 202, 23
6, 249, 270; Direct Violet 9, 1
2, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107 and the like, and they can be used in one kind or a mixture of two or more kinds. Normal,
Dyeing is generally performed by immersing a PVA film in a solution containing the above dye,
There are no particular restrictions on the processing conditions and processing method, such as coating on the A film or mixing with the PVA film to form a film.

The uniaxial stretching can be carried out by a wet stretching method or a dry heat stretching method, and is carried out in warm water (in a solution containing the dye or in a fixing bath described later) or in the air using a PVA film after absorbing water. be able to. The stretching temperature is not particularly limited, but 30 ° C. to 90 ° C. is preferable when the PVA film is stretched in warm water (wet stretching), and 50 ° C. to 180 ° C. is preferable when the PVA film is dry heat stretched. In addition, the draw ratio for uniaxial stretching (in the case of multi-stage uniaxial stretching, the total draw ratio)
Is preferably 4 times or more, more preferably 4.5 times or more, and most preferably 5 times or more from the viewpoint of polarization performance. The upper limit of the stretching ratio is not particularly limited, but if it is 8 times or less, uniform stretching is easily obtained, which is preferable. The thickness of the stretched film is preferably 3 μm to 75 μm, and 5 μm to 50 μm.
μm is more preferable.

Fixing treatment is often carried out for the purpose of strengthening the adsorption of the above dye to the PVA film. Boric acid and / or a boron compound are usually added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a process bath as needed.

Drying treatment (heat treatment) of the PVA film
Is preferably carried out at 30 ° C to 150 ° C, and 50 ° C to 1
It is more preferable to carry out at 50 ° C.

The polarizing film of the present invention obtained as described above is usually used as a polarizing plate by laminating an optically transparent protective film having mechanical strength on one or both sides thereof. It Examples of the protective film include a fatty acid cellulose-based film, an acrylic film, a polyester-based film, a polyolefin-based film, a polycarbonate-based film, a polyether ether ketone-based film, a polysulfone-based film, and the like, and a cellulose triacetate film is preferable. An ultraviolet absorber may be added to the protective film. In order to increase the adhesive strength between the polarizing film and the protective film, it is preferable to perform surface treatment such as corona treatment or flame treatment on the surfaces of the two films or one of the films to be bonded. Examples of the adhesive for bonding include PVA-based, urethane-based, and acrylic-based adhesives, and among them, PVA-based adhesives are preferable.

[0039]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Example 1 The melt extrusion film forming machine described in FIG. 1 was used. This Example 1
Then, the drying chamber 10 installed so as to surround the endless belt 4 is divided from the drying chamber 11 to the drying chamber 18, and the temperature of the warm air blown to each drying chamber is 40 ° C., 100 ° C.,
120 ° C, 140 ° C, 90 ° C, 160 ° C, 130 ° C, 6
It was set to 0 ° C. Further, the back surface at the position where the film-forming raw material 2 contacts the endless belt is in contact with the roll 3.

Degree of saponification 99.9 mol%, degree of polymerization 1750
An aqueous solution containing 10 parts by weight of glycerin and having a PVA concentration of 15 parts by weight per 100 parts by weight of PVA was cast on a metal endless belt through a slit-shaped opening, dried under the above conditions, and then dried with a floating dryer. The film is dried and both widthwise ends are removed to a thickness of 75 μm.
The PVA film of was obtained. The surface of the PVA film was smooth, and no thickness unevenness was observed.

The PVA film was subjected to pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment in this order to prepare a polarizing film. That is, the PVA film is
It was dipped in water at 0 ° C. for 5 minutes to be pre-swelled, and then dipped for 3 minutes in a 35 ° C. aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter. continue,
Uniaxial stretching was performed 5.5 times in a 40 ° C. aqueous solution with a boric acid concentration of 4%, into a 30 ° C. aqueous solution having a potassium iodide concentration of 40 g / liter, boric acid concentration of 40 g / liter, and zinc chloride concentration of 10 g / liter. Immobilization was carried out by immersing for 5 minutes. After this, the stretched film was taken out and kept at 40 ° C. under a fixed length.
Was dried with hot air at 100 ° C. and further heat treated at 100 ° C. for 5 minutes.

No curl was observed when immersed in water, and uniform stretching was possible. The polarizing film obtained had a thickness of 22 μm and had no color spots.

Example 2 With the apparatus of Example 1, the temperature of warm air was changed to 50 ° C., 100 ° C.,
140 ° C, 60 ° C, 130 ° C, 110 ° C, 90 ° C, 40
It was set to ° C.

Saponification degree 99.9 mol%, degree of polymerization 4000
100 parts by weight of PVA, 10 parts by weight of glycerin, and 110 parts by weight of water are melt-kneaded by an extruder, cast through a slit-shaped opening onto a metal endless belt, dried under the above conditions, and then dried by a floating dryer. After drying, both widthwise end portions of the film were removed to obtain a PVA film having a thickness of 75 μm. The surface of the PVA film was smooth, and no thickness unevenness was observed.

The stretch ratio of the PVA film is 5.6.
A polarizing film was obtained by performing the same processing as in Example 1 except that the number of times was changed. No curl was observed when immersed in water, and uniform stretching was possible. The polarizing film obtained had a thickness of 22 μm and had no color spots.

Example 3 In Example 2, the temperature of the hot air was changed to 50 ° C. and 100, respectively.
℃, 120 ℃, 100 ℃, 130 ℃, 110 ℃, 90
The same processes as in Example 1 were carried out except that the temperature was set to 40 ° C. to obtain a polarizing film. A slight curl was observed when immersed in water, but most of them could be uniformly stretched. The thickness of the obtained polarizing film was 23 μm, and it was confirmed that color spots were not a problem.

COMPARATIVE EXAMPLE 1 In Example 1, the temperature of the hot air was changed to 50 ° C. and 100, respectively.
℃, 140 ℃, 180 ℃, 160 ℃, 150 ℃, 130
It was attempted to obtain a polarizing film by performing the same treatment as in Example 1 except that the temperature was set to 40 ° C. and 40 ° C. However, when it was immersed in water, curling was severe and uniform stretching was impossible.

Comparative Example 2 Except that in Example 1, the number of drying chambers was set to 3, and the temperature of the hot air was set to 20 ° C., 180 ° C., and 20 ° C.
The same treatment as in Example 1 was carried out to obtain a polarizing film, but when it was immersed in water, curling was severe and uniform stretching was impossible.

[0049]

According to the present invention, it is possible to obtain a PVA film which has little curl when immersed in water and is easily stretched uniformly. Further, a polarizing film having uniform polarization performance can be obtained using this PVA film.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a belt film forming machine showing an embodiment when manufacturing a PVA film of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Slit-shaped opening part, 2 ... Film forming raw material, 3, 3 '... A pair of rolls, 4 ... Endless belt, 5 ... Peeling roll,
6 ... Vinyl alcohol polymer film, 7 ... Roll rotation direction, 8 ... Partition wall, 9 ... Warm air, 10 ... Drying chamber installed so as to surround the whole, 11-18 ... Divided drying chamber, 1
1 ... Drying chamber at a position where a film-forming raw material is cast or discharged onto an endless belt, 18 ... Drying chamber at a position where a film is peeled from the endless belt

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 7:00 B29L 7:00 (72) Inventor Iso ▲ Zaki ▼ Takanori 1621 Sakata, Kurashiki, Okayama Co., Ltd. Kuraray (72) Inventor Satoshi Fujita Satoshi-shi, Ehime Prefecture 892 Sakusui-shi, Kuraray Co., Ltd. F-term (reference) 2H049 BA02 BB43 BC03 BC09 BC22 2H091 FA08X FA08Z FB02 FB12 FB13 FC01 FC05 FC22 FD06 LA12 LA30 4F205 AA19 AC AH73 AR06 GA07 GC07 GF24 GN21 GN24

Claims (4)

[Claims] 1. A method for producing a vinyl alcohol polymer film, which comprises casting or discharging a film-forming raw material containing a vinyl alcohol polymer onto an endless belt and then drying the film, which is installed so as to surround the entire endless belt. The drying chamber is divided into 6 to 16 chambers by partition walls, and the drying chamber at the position where the film-forming raw material is cast or discharged onto the endless belt and the drying chamber where the film is peeled from the endless belt are excluded. The temperature of the warm air blown to the three adjacent drying chambers A, B, and C is A, respectively.
If T, BT, CT, then AT> BT and BT <
A method for producing a vinyl alcohol-based polymer film, characterized by satisfying a relational expression of CT. 2. Drying of warm air blown to each drying chamber except a drying chamber at a position where the film-forming raw material is cast or discharged onto the endless belt and a drying chamber where a film is peeled off from the endless belt. The method for producing a vinyl alcohol polymer film according to claim 1, wherein the maximum temperature difference between the chambers is 60 ° C. or more. 3. An optical film as claimed in claim 1 or 2.
The method for producing a vinyl alcohol-based polymer film as described in 1. 4. A polarizing film produced by using the optical film obtained by the production method according to claim 3.