JP3476135B2 - Method for producing polyvinyl alcohol film for polarizing film - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyvinyl alcohol film which is excellent in thickness uniformity and is useful as a raw material for producing a polarizing 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 has expanded from a small device such as a calculator and a wristwatch in the early stages of development to a wide range of laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, etc. in recent years.
With the increase in the size of liquid crystal display screens, there is a demand for a polarizing plate that is more excellent in polarization performance over a larger area than conventional products.

A polarizing plate is generally a polyvinyl alcohol film (hereinafter, polyvinyl alcohol is referred to as "PVA",
A polyvinyl alcohol film may be abbreviated as “PVA film”) is uniaxially stretched and dyed to form a polarizing film, and a protective film such as a cellulose triacetate (TAC) film is attached to both surfaces of the polarizing film. ing.

[0004]

By the way, in order to make the polarization performance of the polarizing plate uniform, there are many precautions such as uniformly stretching the PVA film and evenly bonding the PVA film. The dots are the PV of the polarizing plate base.
It is the uniformity of the thickness of the A film. If the thickness of the PVA film is not uniform, even if precision stretching is performed, uniform polarization performance cannot be obtained in a large area. In order to obtain a uniform thickness of a PVA film, it has been conventionally known that a PVA dilute solution is used for casting, but it was not possible to obtain sufficient thickness uniformity in a large area. .

An object of the present invention is to provide a method for producing a polyvinyl alcohol film which has excellent thickness uniformity over a large area and is useful as a raw material for producing a polarizing film.

[0006]

In order to achieve the above object, the method for producing a PVA film for a polarizing film according to the present invention uses a film-forming raw material containing PVA and has a surface roughness of 3S or less. Obtained after film formation on a metal surface and drying
It is characterized in that the film thickness is uniform . According to this invention, it is possible to obtain a PVA film for a polarizing film, which has excellent thickness uniformity in a large area. Here, the unit "S" of the surface roughness indicates the degree of unevenness on the surface, and the roughness is displayed by the maximum height. "Maximum height" means, when the extracted part is sandwiched by two straight lines that are parallel to the average line of the part extracted by the reference length from the sectional curve of the object, the interval between these two straight lines is measured in the vertical direction, The value is expressed in units of microns (μm). The surface roughness 3S means that the maximum height is 3 μm.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The metal material used in the method for producing the PVA film for a polarizing film of the present invention is not particularly limited, but usually stainless steel is preferably used. This metal surface is preferably metal-plated to prevent scratches. As the type of metal plating, for example, chrome plating, chrome oxide plating, nickel plating, zinc plating and the like are preferably used. It can be used alone or in combination of two or more kinds of layers, but it is particularly preferable that the outermost surface is chrome-plated from the viewpoint of easy surface smoothing and durability thereof.

The roughness of the metal surface including the metal plating surface is 3S or less, preferably 2S or less, more preferably 1S or less, still more preferably 0.5S or less, and 0.3S.
The following are the most preferable. The smaller the surface roughness of the metal surface in contact with the film-forming raw material containing PVA, the better the thickness uniformity of the PVA film obtained after drying. Therefore, the smaller the surface roughness of the metal surface, the more preferable. Since the smaller the value, the more difficult the production is, 0.01S or more is usually preferable. If the roughness of the metal surface exceeds 3S, the required thickness uniformity of the PVA film cannot be obtained.

The metal surface is preferably flat, but industrially it may be in the shape of a metal drum or a metal belt. The metal belt is particularly preferably a metal drum because cracks are likely to occur on the metal surface due to deterioration over time and the surface roughness tends to increase.

As the PVA, for example, a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer is saponified, and the vinyl ester unit is used as a vinyl alcohol unit. Examples of the vinyl ester-based monomer include vinyl formate, vinyl acetate,
Examples thereof include vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Among these, vinyl acetate is preferably used.

When the vinyl ester-based monomer is polymerized, if necessary, other copolymerizable monomers may be added within a range that does not impair the effects of the invention (preferably 15 mol% or less, more preferably 5 mol% or less). It is also possible to copolymerize.

Examples of the monomer copolymerizable with the vinyl ester monomer include olefins having 3 to 30 carbon atoms 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, acrylic acid 2
-Acrylic acid esters such as ethylhexyl, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate. , I-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, and other methacrylate esters; acrylamide,
Acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts, N-methylolacrylamide and its derivatives; methacryl Amide, N-
Methacrylic amide derivatives such as methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid and its salts, methacrylamide dimethylamine and its salts, N-methylol methacrylamide and its derivatives; N-vinylformamide, N-vinyl. N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-
Propyl vinyl ether, n-butyl vinyl ether,
Vinyl ethers such as i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; Examples include allyl compounds such as allyl acetate and allyl chloride; maleic acid and salts thereof or esters thereof; itaconic acid and salts thereof or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like.

The degree of polymerization of PVA is preferably 500 or more from the viewpoint of film strength, more preferably 1000 or more from the viewpoint of polarization performance, further preferably 2000 or more, 35
00 or more is most preferable. Further, the upper limit of the degree of polymerization of PVA is preferably 10,000 or less from the viewpoint of film forming property of the film.

The degree of polymerization Po of the PVA is determined according to JIS K 6
It is measured according to 726. 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)}

From the viewpoint of the durability of the polarizing film, the degree of saponification of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, most preferably 98 mol% or more. Further, from the viewpoint of dyeability of the film, it is preferably 99.99 mol% or less.

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 saponification. The saponification degree of PVA was measured by the method described in JIS.

It is preferable to add a polyhydric alcohol as a plasticizer when producing a PVA film. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol,
Triethylene glycol, tetraethylene glycol,
Examples thereof include trimethylolpropane, and of these, one kind or two or more kinds can be used. Among these, ethylene glycol or glycerin is preferably used because of the effect of improving stretchability.

The amount of polyhydric alcohol added is PVA1.
1 to 30 parts by weight is preferable with respect to 00 parts by weight, and 3 to 2 parts
5 parts by weight is more preferable, and 5 to 20 parts by weight is particularly preferable. If it is less than 1 part by weight, the dyeability and stretchability may be lowered, and if it is more than 30 parts by weight, the film may be too soft and the handleability may be lowered.

It is preferable to add a surfactant during the production of the PVA film. The type of surfactant is not particularly limited, but anionic or nonionic surfactant is preferable. As the anionic surfactant, for example, carboxylic acid type anionic surfactants such as potassium laurate, sulfate ester type such as octyl sulfate, and sulfonic acid type anionic surfactants such as dodecylbenzene sulfonate are suitable. Examples of the nonionic surfactant include alkyl ether type such as polyoxyethylene oleyl ether, alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, alkyl ester type such as polyoxyethylene laurate, and polyoxyethylene lauryl amino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.

The amount of surfactant added is PVA10.
0.01 to 1 part by weight is preferable with respect to 0 part by weight, and 0.
More preferably from 02 to 0.5 parts by weight, 0.05 to 0.3
Most preferred is parts by weight. If less than 0.01 parts by weight,
The effect of improving the stretchability and the dyeability is less likely to appear, and if it is more than 1 part by weight, it may be eluted on the film surface to cause blocking and the handleability may be deteriorated.

As the method for producing the PVA film, for example, a PVA solution in which PVA is dissolved in a solvent is used, and a casting film forming method, a wet film forming method (discharging into a poor solvent),
Dry-and-wet film forming method, gel film forming method (method in which PVA aqueous solution is once cooled and gelled, and then solvent is extracted and removed to obtain a PVA film), and a method by a combination thereof, or water-containing PVA (including an organic solvent, etc. It is also possible to employ a melt-extrusion film-forming method, which is carried out by melting. Among these, the casting film-forming method and the melt-extrusion film-forming method are preferable since a highly transparent PVA film can be obtained.

The volatile matter concentration of the PVA solution or the water-containing PVA used in producing the PVA film is 50 to 90.
Weight% is preferable, and 55-80 weight% is more preferable. If the concentration of volatile components is less than 50%, the viscosity becomes high and film formation becomes difficult. When the volatile content concentration is higher than 90%, the viscosity is low and the film thickness uniformity is easily impaired, which is not preferable.

The thickness of the PVA film is preferably 5 to 150 μm, more preferably 30 to 100 μm.

In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be dyed, uniaxially stretched, fixed and dried, and optionally heat-treated. The order of each step is not particularly limited, and two steps such as dyeing and uniaxial stretching may be performed at the same time. Also, each step may be repeated a plurality of times.

Dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching, but PVA is uniaxially stretched because uniaxial stretching tends to increase the crystallinity and may reduce the dyeability. It is preferable to dye in any preceding step or during the uniaxial stretching step. Dyes used for dyeing include 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 other dichroic dyes can be used. The dyeing can be usually performed by immersing the PVA film in a solution containing the above dye, but the processing conditions and the processing method are not particularly limited.

The uniaxial stretching can be carried out by a wet stretching method or a dry heat stretching method, and it should be 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. You can The draw ratio is preferably 4 times or more, particularly preferably 5 times or more. When the draw ratio is less than 4 times, it is difficult to obtain practically sufficient polarization performance and durability performance. The stretching temperature is not particularly limited, but is 30 to 9 when the PVA film is stretched in wet water (wet stretching).
0 ° C. is suitable, and 50 to 180 ° C. is suitable for dry heat drawing. The thickness of the stretched PVA film is 3 to 75 μm.
m is preferable, and 10 to 50 μm is more preferable.

A fixing treatment is carried out for the purpose of strengthening the adsorption of the above dyes on the PVA film. Boric acid and 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.

The polarizing film drying treatment (heat treatment) is 30
It is preferable to carry out at 150 to 150 ° C, more preferably at 50 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 As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The dichroic ratio in the examples was evaluated by the following method.

Dichroic ratio: The dichroic ratio was used as an index for evaluating the polarization performance of the obtained polarizing film. This dichroic ratio is based on the Japan Electronic Machinery Manufacturers Association Standard (EIAJ) LD-2.
The transmittance Ts (%) obtained by measuring and calculating in a C light source and a 2 degree visual field using a spectrophotometer according to 01-1983.
And the polarization degree P (%) were used to obtain the value from the following formula. Dichroic ratio = log (Ts / 100−Ts / 100 × P /
100) / log (Ts / 100 + Ts / 100 × P /
100)

Example 1 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, 0.1 parts by weight of lauric acid diethanolamide and water were dissolved in a tank at 100 ° C. to prepare a PVA solution having a volatile content of 80% and heated to 90 ° C. The film was cast on a metal roll surface plated and then chrome plated to form a drum film. The surface roughness of the chrome-plated surface was 0.1S. Furthermore, the PVA film on the surface of the metal roll is heated to 100 ° C.
To obtain a PVA film having an average thickness of 75 μm. When a 1 m square PVA film was cut into strips and the film thickness was measured at 1 cm intervals, the difference between the maximum thickness and the minimum thickness was 1.9 μm.

This 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 30 ° C
Immersed in water for 3 minutes for pre-swelling, iodine concentration 0.4
It was immersed for 4 minutes in a 40 ° C. aqueous solution having a g / l concentration and a potassium iodide concentration of 40 g / l. Then boric acid 4
Uniaxially stretched 5.5 times in a 50% aqueous solution of 50%, and immersed in an aqueous solution of 40 g / liter of potassium iodide and 40 g / liter of boric acid at 30 ° C. for 5 minutes for fixing treatment. The film was taken out, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes. The thickness of the obtained polarizing film was 27 μm. The 10 cm square polarizing film had an average transmittance of 43.2%, an average degree of polarization of 99.7%, and an average dichroic ratio of 45.0. 10
The transmittance of a polarizing film of square cm is calculated by RE manufactured by Otsuka Electronics.
When measured with a light source having a diameter of 100 μm at 1 cm intervals using TS-2000, the difference between the maximum transmittance and the minimum transmittance was 0.5%. When the obtained polarizing film was placed at an angle of 45 ° between two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, almost no optical unevenness was observed.

Example 2 PVA10 having a saponification degree of 99.9 mol% and a polymerization degree of 2400
Volatile component 70 consisting of 0 part by weight, 10 parts by weight of glycerin, 0.1 part by weight of polyoxyethylene lauryl ether and water
% Water-containing chips were melted by heating at 100 ° C., and extruded onto a surface of a metal roll, which was heated at 90 ° C. and had a stainless base material plated with chrome, to form a film. The surface roughness of the chrome-plated surface was 0.3S. Further, the PVA film on the surface of the metal roll is dried with hot air at 100 ° C. to have a thickness of 75 μm.
m PVA film was obtained. When a 1 m square PVA film was cut into strips and the film thickness was measured at 1 cm intervals, the difference between the maximum thickness and the minimum thickness was 2.6 μm.

This 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 30 ° C
Immersed in water for 3 minutes for pre-swelling, iodine concentration 0.4
It was immersed for 4 minutes in a 40 ° C. aqueous solution having a g / l concentration and a potassium iodide concentration of 40 g / l. Then boric acid 4
% Uniaxially stretched in 50% aqueous solution at 50 ° C., and immersed in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 30 ° C. for 5 minutes for fixing treatment. The film was taken out, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes. The polarizing film obtained had a thickness of 30 μm. The 10 cm square polarizing film had an average transmittance of 42.7%, an average degree of polarization of 99.6%, and an average dichroic ratio of 39.9. 10
The transmittance of a polarizing film with a square area of
When measured with a light source having a diameter of 100 μm at 1 cm intervals using TS-2000, the difference between the maximum transmittance and the minimum transmittance was 0.8%. When the obtained polarizing film was placed at an angle of 45 ° between two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, almost no optical unevenness was observed.

Example 3 PVA10 having a saponification degree of 99.9 mol% and a polymerization degree of 1700
A water-containing chip consisting of 0 part by weight, 10 parts by weight of glycerin, 0.1 part by weight of polyoxyethylene lauryl ether sulfate, and 60% of volatile matter was heated and melted at 100 ° C.
A film was formed by extrusion on a surface of a metal roll in which a stainless base material at 90 ° C. was nickel-plated and then chrome-plated. The surface roughness of the chrome-plated surface was 1S. Further, the PVA film on the surface of the metal roll was dried with hot air at 100 ° C. to obtain a PVA film having a thickness of 75 μm. 1m
When the PVA film on four sides was cut into strips and the film thickness was measured at 1 cm intervals, the difference between the maximum thickness and the minimum thickness was 6.3 μm.

This PVA film was processed by 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 30 ° C
Immersed in water for 3 minutes for pre-swelling, iodine concentration 0.4
It was immersed for 4 minutes in a 40 ° C. aqueous solution having a g / l concentration and a potassium iodide concentration of 40 g / l. Then boric acid 4
% Uniaxially stretched in 50% aqueous solution at 50 ° C., and immersed in an aqueous solution of 40 g / liter potassium iodide and 40 g / liter boric acid at 30 ° C. for 5 minutes for fixing treatment. The film was taken out, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes. The thickness of the obtained polarizing film was 36 μm. The 10 cm square polarizing film had an average transmittance of 42.3%, an average degree of polarization of 99.5%, and an average dichroic ratio of 35.1. 10
The transmittance of a polarizing film of square cm is calculated by RE manufactured by Otsuka Electronics.
When measured with a light source having a diameter of 100 μm at 1 cm intervals using TS-2000, the difference between the maximum transmittance and the minimum transmittance was 1.3%. When the obtained polarizing film was placed at an angle of 45 ° between the two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, a small optical unevenness was observed.

Comparative Example 1 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, 0.1 parts by weight of lauric acid diethanolamide and water were dissolved in a tank at 100 ° C. to prepare a PVA solution having a volatile content of 80%, and an unplated stainless metal at 90 ° C. It was cast on a roll surface to form a drum film. The surface roughness of the metal roll surface was 4S. Furthermore, 100 PVA film on the surface of the metal roll
It was dried with hot air at ℃ to obtain a PVA film having an average thickness of 75 μm. When a 1 m square PVA film was cut into strips and the film thickness was measured at 1 cm intervals, the difference between the maximum thickness and the minimum thickness was 12.8 μm.

A polarizing film was prepared by subjecting this PVA film to pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment in this order. That is, the PVA film is 30 ° C
Immersed in water for 3 minutes for pre-swelling, iodine concentration 0.4
It was immersed for 4 minutes in a 40 ° C. aqueous solution having a g / l concentration and a potassium iodide concentration of 40 g / l. Then boric acid 4
Uniaxially stretched 5.5 times in a 50% aqueous solution of 50%, and immersed in an aqueous solution of 40 g / liter of potassium iodide and 40 g / liter of boric acid at 30 ° C. for 5 minutes for fixing treatment. The film was taken out, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes. The thickness of the obtained polarizing film was 29 μm. The 10 cm square polarizing film had an average transmittance of 43.1%, an average degree of polarization of 99.7%, and an average dichroic ratio of 44.3. 10
The transmittance of a polarizing film of square cm is calculated by RE manufactured by Otsuka Electronics.
When measured with a light source having a diameter of 100 μm at 1 cm intervals using TS-2000, the difference between the maximum transmittance and the minimum transmittance was 4.2%. When the obtained polarizing film was placed at an angle of 45 ° between two polarizing plates in the crossed Nicols state and the transmitted light was visually observed, large optical unevenness was observed.

[0040]

As described above, according to the present invention, it is possible to produce a PVA film for a polarizing film, which has excellent thickness uniformity in a large area. Further, this PVA film is also excellent in optical characteristics such as polarization degree and transmittance and durability performance (particularly resistance to moist heat).

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI // B29K 29:00 B29K 29:00 B29L 7:00 B29L 7:00 C08L 29:04 C08L 29:04 (56) References Kaihei 5-239229 (JP, A) JP-A-3-219928 (JP, A) JP-A-6-138319 (JP, A) JP-B-45-6971 (JP, B1) (58) Fields investigated (58) Int.Cl. ⁷ , DB name) B29C 41/00-41/52

Claims (4)

(57) [Claims] 1. A film-forming raw material containing polyvinyl alcohol is used to form a film on a metal surface having a surface roughness of 3 S or less, and the film thickness obtained after drying is uniform.
A method for producing a polyvinyl alcohol film for a polarizing film, comprising: 2. The method for producing a polyvinyl alcohol film for a polarizing film according to claim 1, wherein the metal surface is plated with metal. 3. The method for producing a polyvinyl alcohol film for a polarizing film according to claim 2, wherein the metal plating is chrome plating. 4. The volatile content of the film-forming raw material containing polyvinyl alcohol according to claim 1, which is 50 to 50.
90% by weight of the method for producing a polyvinyl alcohol film for a polarizing film .