JP2003170448A - Manufacturing method for vinyl alcohol polymer film, and polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive method of manufacturing a vinyl alcohol polymer film excellent in terms of process passing properties in a film-making process and a yield in a process of preparing a polarizing film. <P>SOLUTION: In this method of manufacturing the vinyl alcohol polymer film, a film-making material containing a vinyl alcohol polymer is cast or discharged onto an endless belt and dried by hot air and then the vinyl alcohol polymer film is peeled off from the endless belt. After both end parts in the width direction of the film are removed by 5 cm or more in total, the film is subjected to post-drying or heat treatment at a temperature lower than the maximum temperature of the hot air. <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 an optical film and has excellent process passability in the film-forming process, and a polarized light produced using the same. It's about film.

[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 vinyl alcohol-based polymer film for polarizing films, which is spread over a wide range of applications such as word processors, liquid crystal color projectors, in-vehicle navigation systems, and liquid crystal televisions, and which is cheaper 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 hot air is blown onto an endless belt to dry it, and then heat treatment is performed with hot air at a higher temperature. However, in these prior documents, a uniform PV
It is disclosed that in order to obtain the A film, post-drying or heat treatment is performed at a temperature lower than the maximum warm air temperature blown during the drying on the endless belt, and the widthwise ends of the PVA film are removed. Not not.

[0005]

In order to promote application development of polarizing plates, it is necessary to be able to supply inexpensive polarizing plates, and for that purpose, PVA films can be obtained at low cost and processing into polarizing films is possible. Improving the yield in the process is a very important point.

Therefore, an object of the present invention is to provide a method for producing a PVA film which is excellent in terms of the process passability in the film forming step for supplying an inexpensive PVA film and the yield in the step of producing a polarizing film. To provide.

[0007]

In order to solve the above problems, a method for producing a PVA film according to the present invention is
The film-forming raw material containing is cast or discharged onto an endless belt and dried with warm air, then the PVA film is peeled off from the endless belt, and both end portions in the film width direction are removed by 5 cm or more in total, and then the warm air is removed. The PVA film is post-dried or heat-treated at a temperature lower than the maximum temperature of the above.

At this time, it is preferable to carry out post-drying or heat treatment of the PVA film by using a floating dryer, a heating furnace or a heating roll alone or in combination thereof. Also, after post-drying or heat treatment, PVA
It is further preferable that both end portions in the width direction of the film are removed again and the total width with the total width obtained by removing both end portions in the film width direction before the post-drying or heat treatment step is 10 cm or more. A polarizing film is obtained using this PVA film.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The method for producing the PVA film of the present invention includes PV
A film-forming raw material containing A is cast or discharged onto an endless belt and dried with warm air, then the PVA film is peeled off from the endless belt, and both ends in the film width direction are removed by 5 cm or more in total, and then hot air is blown. Post-drying or heat-treating the PVA film at a temperature lower than the maximum temperature is important as a production method for obtaining a PVA film which is a raw material of a good polarizing film and has excellent process passability.

A melt extrusion film forming method in which a water-containing PVA (which may contain an organic solvent or the like) is melted as a film forming raw material, and a PVA solution in which PVA is dissolved in a solvent such as water is used as a film forming raw material. The casting film forming method used is important for obtaining a PVA film as a raw material of a good polarizing film. A uniform PVA film cannot be obtained when the film is first dried only with hot air as in the inflation film forming method. In other film forming methods, a large amount of energy required for film formation is required, and it is difficult to obtain a PVA film having a uniform thickness, and thus the PVA film cannot be manufactured at low cost.

The belt film forming machine requires two or more rolls to move the endless belt at a constant speed, and it is difficult to move the endless belt at a uniform speed with only one roll. If the number of rolls is too large, the equipment cost increases, so five or less rolls are preferable, and it is preferable that the rolls are in contact with the same surface of the endless belt. Further, it is preferable that the endless belt is made of metal, particularly mirror-finished stainless steel in order to obtain a uniform PVA film. The film-forming raw material containing the PVA-based polymer is usually cast or discharged onto the endless belt through a slit-shaped opening elongated in the width direction of the endless belt, and dried by blowing hot air. It is preferable that the drying chamber is installed so as to surround the endless belt and is divided into 5 to 16 rooms so that the temperature of the warm air blown into each room can be changed.

Prior to post-drying or heat-treating the PVA film peeled from the endless belt, it is important to remove both end portions in the width direction of the PVA film in total by 5 cm or more, more preferably 6 cm or more, further preferably 8 cm or more. Is. Total width to remove both ends in the width direction is 5c
When post-drying or heat treatment is performed with the thickness less than m, both ends of the film are caught by the device due to wrinkles caused by the thickness unevenness of the film, or due to thickness unevenness at both ends in the width direction or a difference in heat history. However, post-drying or heat treatment cannot be performed uniformly. Here, it is preferable to use a knife as a method for removing both ends of the PVA film in the width direction,
In the fusion cutting with a heating metal wire or the cutting with a laser beam, the PVA film may be easily broken in the step of processing the polarizing film.

The apparatus used for post-drying or heat treatment is
A floating dryer, a heating furnace, a heating roll, etc. can be used alone or in combination. A device for post-drying or heat treatment that can be preferably used is a floating dryer, and it is more preferable to use a plurality of heating rolls and a floating dryer in series. When the drying is performed only with the endless belt and the post-drying or heat treatment is not performed, the PVA film is curled in the polarizing plate manufacturing process using the film as a raw material, and uniform stretching cannot be performed, resulting in a polarizing plate yield. It may decrease. When the post-drying or heat treatment is carried out by a method of immersing the PVA film in a heating liquid such as silicon oil or bringing it into contact with a heating plate,
In some cases, post-drying or heat treatment cannot be performed uniformly, or problems such as scratches on the film surface occur.

The temperature of the post-drying or heat treatment is lower than the maximum temperature of the warm air blown during the drying on the endless belt, more preferably 10 ° C. or higher, further preferably 20 ° C. or higher, particularly preferably 30. It is important to carry out at a temperature lower than 70 ° C to 70 ° C. When the temperature of the post-drying or heat treatment is the same as or higher than the maximum temperature of the warm air blown during the drying on the endless belt, the PVA film is curled in the manufacturing process of the polarizing plate and the uniform stretching is performed. It cannot be processed and the yield of the polarizing plate is reduced. In addition, cracks may occur on the surface of the film. Also,
If the temperature of the post-drying or heat treatment is lower than the maximum warm air temperature blown during the drying on the endless belt by 70 ° C. or more, the effect of the post-drying or heat treatment may not be obtained.

The post-drying or heat treatment may cause a difference in heat history between the both end portions and the central portion in the film width direction, and uniform stretching may not be possible. It is preferable to remove. 10 cm or more is preferable and 15 cm or more is more preferable for the total total width of the width for removing both ends in the film width direction before post-drying or heat treatment and the width for removing both ends in the film width direction again after post-drying or heat treatment. , 20 cm
The above is more preferable. If the total width is less than 10 cm, the curl or the like of the end portion may be large and uniform stretching may not be possible. Further, it may be cut from the end during stretching. Here, in order to remove both ends in the width direction of the PVA film, it is preferable to use a knife, and in the case of fusing with a heating metal wire or cutting with a laser beam, the PVA film is easily broken in the step of processing into a polarizing film. There is.

PVA that can be used in the present invention
Is produced, for example, by converting all or part of the ester groups of the polyvinyl ester obtained by polymerizing vinyl ester into hydroxyl groups. Further, modified PVA obtained by graft-copolymerizing PVA with unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, olefin, etc., vinyl ester and unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, olefin Modified PVA produced by converting all or part of the ester groups of modified polyvinyl ester obtained by copolymerizing the above to hydroxyl groups, or so-called polyvinyl acetal resin obtained by crosslinking unmodified or modified PVA with aldehydes in a part of the hydroxyl groups. And so on.

Examples of the vinyl ester 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 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 within 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, Examples thereof include nitriles, vinyl halides, allyl compounds, vinylsilyl compounds, and fatty acid isopropenyl, and one or more of these can be used.

When the modified PVA is used, the modification amount is preferably 15 mol% or less, more preferably 5 mol% or less. 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, particularly 9 from the viewpoint of polarization performance and durability.
Most preferably, it is 9.5 mol% or more.

The above-mentioned degree of saponification indicates the proportion of units actually saponified 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 JI
The measurement was performed by the method described in S.

From the viewpoint of polarization performance and durability, the degree of polymerization of PVA is preferably 1000 or more, more preferably 2500 or more, and most preferably 3500 or more. The upper limit of the degree of PVA polymerization is preferably 8000 or less, more preferably 6000 or less.

The degree of polymerization (Po) of the PVA is JIS
It is measured according to K 6726. That is, PVA is re-saponified, purified, and then calculated from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30 ° C. by the following formula. Po = ([η] × 10 ³ /8.29)
^{(1 / 0.62)}

As the solvent for dissolving PVA used in producing the PVA film, known solvents can be used, but dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used. The water-containing PVA used in the production of the PVA film may include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, if necessary. Solvents such as trimethylolpropane, ethylenediamine, diethylenetriamine, and diglycerin may be contained in one kind or two or more kinds.

The PVA concentration of the PVA solution or the hydrous PVA used for producing the PVA film is preferably 10 to 70% by weight, more preferably 10 to 60% by weight, and 13 to 55% by weight. More preferred, 1
Most preferred is 5 to 50% by weight. If necessary, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, or the like.

It is preferable to add a polyhydric alcohol such as glycerin as a plasticizer when the PVA film is produced. The amount of polyhydric alcohol added is PVA1
The amount is preferably 30 parts by weight or less, more preferably 3 to 25 parts by weight, and most preferably 5 to 20 parts by weight with respect to 00 parts by weight. If it exceeds 30 parts by weight, the PVA film may become too flexible and the handleability may deteriorate.

When producing a PVA film, it is preferable to add a surfactant. The type of surfactant is not particularly limited, but anionic or nonionic surfactant is preferable. The amount of surfactant added is
It is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.5 part by weight, based on 100 parts by weight of PVA,
Most preferably 0.05 to 0.3 parts by weight. If it is less than 0.01 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.

The thickness of the PVA film is 10 μm to 1
50 μm is preferable, and 20 μm to 80 μm is more preferable. If the thickness of the PVA film is less than 10 μm, the PVA film is likely to be cut during uniaxial stretching during the production of the polarizing film, while if it exceeds 150 μm, stretching unevenness occurs during the uniaxial stretching, and the resulting polarizing film has dyeing unevenness or optical unevenness. May occur easily.

The PVA film thus obtained is preferably wound around a cylindrical core made of metal or plastic, and stored in a moisture-proof package in a suspended state.

The PV obtained by the method of the present invention
In order to produce a polarizing film from the A film, for example, the PVA film may be dyed, uniaxially stretched, fixed, dried, and optionally heat-treated, and there are no particular restrictions on the order of dyeing, uniaxial stretching and fixing. Absent. Also, each operation may be performed twice or more.

Dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. As a dye, iodine-
Potassium iodide or a dichroic direct dye can be used. Usually, the dyeing is generally performed by immersing the 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 a PVA film or forming a film by mixing with a PVA film.

The uniaxial stretching can be performed 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 treatment bath described later) or in air using a PVA film after absorbing water. be able to. The stretching temperature is not particularly limited, but is preferably 30 ° C. to 90 ° C. when the PVA film is stretched in warm water (wet stretching), and is preferably 50 ° C. to 180 ° C. when dry heat stretching. The stretching ratio of uniaxial stretching (in the case of multi-stage uniaxial stretching, the total stretching ratio) is preferably 4 times or more from the viewpoint of polarization performance, and is 4.5.
It is more preferably at least twice, and most preferably at least five times.
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 is more preferable.

Fixing treatment is often carried out for the purpose of strengthening the adsorption of the above dye on 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 performed at 30 ° C. to 150 ° C., more preferably 50 ° C. to 150 ° 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 both sides or one side 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.

[0036]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Example 1 PVA10 having a saponification degree of 99.9 mol% and a polymerization degree of 1750
P containing 10 parts by weight of glycerin to 0 parts by weight, P
Using a hopper plate, an aqueous solution having a VA concentration of 15% by weight was cast onto a metal endless belt moving at a constant speed and suspended at a pair of heated metal rolls, and the temperature was 130 ° C.
Dried with warm air. Peel off the PVA film from the endless belt, and put 10 cm each on both ends in the film width direction.
20 cm in total width was removed. This PVA film is 6
Re-dry using a heating roll at 0 ° C and a floating dryer at 100 ° C, and apply 5 to each end of the film in the width direction.
cm, total width 10 cm removed. The total width obtained by removing both ends in the width direction of the film was 30 cm.

This PVA film having a thickness of 75 μm was processed in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. That is, the PV
The A film was immersed in water at 30 ° C. for 5 minutes to be pre-swelled, and immersed in an aqueous solution of iodine concentration of 0.4 g / liter and potassium iodide concentration of 40 g / liter at 35 ° C. for 3 minutes. Subsequently, it was uniaxially stretched 5.5 times in a 40 ° C. aqueous solution with a boric acid concentration of 4% to give a potassium iodide concentration of 40 g.
/ Liter, boric acid concentration of 40 g / liter, and zinc chloride concentration of 10 g / liter were immersed for 5 minutes in an aqueous solution at 30 ° C. to perform the fixing treatment. After this, the stretched film was taken out, dried with hot air at 40 ° C. under a fixed length, and further at 100 ° C. for 5
Heat treatment was performed for a minute to obtain a polarizing film. The stretching was stable and could be performed uniformly.

Example 2 PVA10 having a saponification degree of 99.9 mol% and a polymerization degree of 4000
0 parts by weight, 10 parts by weight of glycerin, and 110 parts by weight of water were melt-kneaded by an extruder, and using a T-die, on an endless belt that was moved at a constant speed and was laid between a pair of heated metal rolls. It was extruded and dried with hot air at 150 ° C. The PVA film was peeled off from the endless belt, and both end portions in the film width direction were removed by 5 cm each and a total width of 10 cm. This PVA film was heated with a heating roll at 70 ° C.
Re-dry using a floating dryer at 0 ° C, 5 cm each on both ends in the width direction of the film, 10 cm in total width
Removed. The total width obtained by removing both ends in the width direction of the film was 20 cm.

Using this PVA film having a thickness of 75 μm, the procedures other than the above were the same as in Example 1 to obtain a polarizing film. The stretching was stable and could be performed uniformly.

Example 3 In Example 2, the total removal width before re-drying was 10 cm,
After re-drying, the polarizing film was obtained in the same manner as in Example 2 except that both end portions in the width direction of the film were not removed and the total width was 10 cm. At the time of stretching, both ends of the film tended to curl, and the stretching sometimes became unstable.

Example 4 A polarizing film was obtained in the same manner as in Example 1, except that the heating plate at 110 ° C. was rubbed and redried instead of the heating roll and the floating dryer. It was On the resulting polarizing film, very thin and thin scratches usable in low grade LCD grade were observed.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the PVA film was peeled off from the endless belt and both widthwise end portions of the film were not removed before post-drying. Although an attempt was made to obtain a PVA film, both ends in the width direction of the film were caught in the post-drying process in the floating dryer, and stable operation could not be performed.

Comparative Example 2 A PVA film was obtained by the same procedure as in Example 1 except that the post-drying temperature was 190 ° C. This film was broken during stretching and a polarizing film could not be obtained.

[0044]

As described above, according to the present invention, a PVA film roll for stretching which is useful as a raw material for manufacturing a polarizing film and which can be uniformly stretched easily can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 7:00 B29L 7:00 C08L 29:04 C08L 29:04 Z (72) Inventor Iso ▲ Zaki ▼ Takanori 1621 Sakazu, Kurashiki-shi, Okayama, Kuraray Co., Ltd. (72) Inventor, Satoshi Fujita, 892, Sakusui-shi, Saijo-shi, Ehime F-term (in reference) 2H049 BA02 BB43 BC03 BC09 BC22 4F071 AA14X AA23X AA29 AA30X AA31X AA35X AA36X AA39X AF35 AG27 AH12 BA02 BB02 BC01 BC12 4F205 AA19 AC05 AG01 AH73 GA07 GB02 GC07 GN21 GW05 GW23

Claims (5)

[Claims] 1. A film-forming raw material containing a vinyl alcohol-based polymer is cast or discharged onto an endless belt and dried with warm air, and then the vinyl alcohol-based polymer film is peeled from the endless belt, and the width direction of the film is measured. A method for producing a vinyl alcohol-based polymer film, which comprises post-drying or heat-treating the vinyl alcohol-based polymer film at a temperature lower than the maximum temperature of the warm air after removing both ends in total by 5 cm or more. 2. The vinyl alcohol-based polymer according to claim 1, wherein the vinyl alcohol-based polymer film is subjected to post-drying or heat treatment by using a floating dryer, a heating furnace or a heating roll alone or in combination thereof. Film manufacturing method. 3. The total width obtained by removing both ends in the width direction of the vinyl alcohol-based polymer film again after the post-drying or heat treatment and removing the both ends in the width direction of the film before the post-drying or heat treatment step. The method for producing a vinyl alcohol polymer film according to claim 1 or 2, wherein the width is 10 cm or more. 4. The method for producing a vinyl alcohol-based polymer film according to claim 1, which is for optical use. 5. A polarizing film produced by using the vinyl alcohol polymer film obtained by the production method according to claim 4.