KR20080003152A - Polyvinylalcohol film and polarizing film - Google Patents

Abstract

A polyvinylalcohol film and a polarizing film are provided to have uniform optical property over the large area. According to a polyvinylalcohol film, the difference of hot water extension time along width direction(TD) of the film is below 3 seconds. The difference of the longest hot water extension length along width direction of the film is below 30 mm. The thickness along width direction of the film is 40-150 mum. Thickness difference along width direction of the film is below 3 mum.

Description

Polyvinyl alcohol film and polarizing film {Polyvinylalcohol film and polarizing film}

The present invention relates to a polyvinyl alcohol-based film having a uniform optical performance even in a large area, and a polarizing film for a large-screen liquid crystal display using the same.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display, and its range of use is widespread and is increasingly used as a large screen, so that a polarizing plate having uniform optical performance is required.

A normal polarizing plate is manufactured by apply | coating a protective film, such as a cellulose triacetate (TAC) film, on both surfaces of the polarizing film manufactured by uniaxially stretching and dyeing a polyvinyl alcohol-type film (henceforth PVA-type film).

In order to make the optical performance of the polarizing plate uniform, there are many things to consider, such as using a PVA film having a uniform thickness, uniformly coloring the dichroic dye, and uniformly applying TAC, but PVA film that becomes the material of the polarizing plate Uniformity is the most important factor.

Japanese Patent No. 3476136 describes a polyvinyl alcohol having a polymerization degree of 500 or more and a saponification degree of 90 mol% or more and a film forming raw material containing 1 to 30 parts by weight of a polyhydric alcohol with respect to 100 parts by weight of the polyvinyl alcohol. When manufacturing a polyvinyl alcohol film, the method of manufacturing the polyvinyl alcohol-type film for polarizing films which is excellent in polarizing performance is disclosed by making the temperature difference of the drum temperature surface located in the most upstream which supply a film forming raw material into 2 degrees C or less. .

Japanese Patent No. 3478536 discloses a polyvinyl alcohol-based film, characterized in that the ratio of the tensile elongation in the MD direction and the tensile elongation in the TD direction of the film obtained by drum film formation is 0.7 to 1.3. By appropriately adjusting the error of the ratio of tensile elongation and the ratio of tensile elongation, an optically uniform polyvinyl alcohol film is obtained.

Japanese Patent No. 3283563 discloses a polyvinyl alcohol-based film, wherein the product of the hydrothermal cutting temperature and the weight swelling degree is 13000 or more.

Japanese Patent No. 3487535 discloses a polyvinyl alcohol-based film having a temperature difference of 1.5 ° C. or less after taking samples at regular intervals in a width direction (TD) of a polyvinyl alcohol film having a width of 2 M or more and measuring the same. Here, the hydrothermal cutting temperature is a polyvinyl alcohol film having a width of 2 m or more and is cut into 5 mm in the width direction and 15 cm in the flow direction, and a weighing weight of 0.5 g / 10 μm is installed at one end of the sample and suspended in 40 ° C. It means the hot water temperature when the temperature is raised at a rate of ℃ / min and the sample is cut.

In addition, Japanese Patent Laid-Open No. 2003-268127 forms a film from ethylene-modified polyvinyl alcohol having 1 to 4 mol% of ethylene units, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol%, and a hydrothermal cutting temperature of 66 to 73 ° C. A phosphorus ethylene-modified polyvinyl alcohol film is disclosed, and it is disclosed that it is preferable that the hydrothermal cutting temperature difference between two points separated by 5 cm in the TD direction of the film is 1 ° C or less.

However, the polyvinyl alcohol-based film defined by the above characteristic values is an optically uniform polyvinyl alcohol-based film that reflects all factors such as crystallinity, crystal size, molecular weight, saponification degree, distance and ratio between the crystal region and the amorphous region. There is a limit that cannot be seen as a film.

In particular, when the TD direction hydrothermal cutting temperature difference of a polyvinyl alcohol film is defined, this value does not reflect properly the ratio between the crystal size and the crystalline region and the non-crystalline region, and even if the hydrothermal cutting temperature difference falls within the above range, the optical properties of the polyvinyl alcohol film Uniformity is still a problem.

In addition, in the case of polyvinyl alcohol-based film having a width of 1m or more, the variation of the hydrothermal cutting temperature according to the position is very severe, and it is troublesome to measure the hydrothermal cutting temperature for a plurality of specimens. It is hard to think that they are a proper reflection of them.

On the other hand, as a production method of PVA, a belt film forming method and a drum film forming method in which a PVA solution or a liquid in a molten state (including water) are discharged or extruded and dried on a belt or drum heated from a die are industrially used.

However, the belt film forming method involves various technical difficulties in obtaining a uniform PVA film having a film width of 2 m or more. In particular, in the case of optical PVA film, it is difficult to manufacture a wide and smooth belt because the joint of the belt is required to be uniform, the mirror polished over a length of several tens of meters, and the like. Follow.

On the other hand, in the case of the drum film forming method, a drum which is used for this can be produced industrially as a seamless one having a width of 2 m or more. However, the drum film forming method tends to cause a difference in thickness in the obtained PVA film, and also has insufficient uniformity of retardation. .

Accordingly, the technical problem to be achieved by the present invention is a PVA film suitable for a wide polarizing film having a uniform optical performance even in a large area, especially when manufacturing a wide PVA film by a drum film forming method and a large-screen liquid crystal using the same. It is to provide a polarizing film suitable for display.

In order to achieve the above object, the present invention provides a polyvinyl alcohol-based film having a difference in the width direction (TD direction) hydrothermal extension time of 3 seconds or less.

The polarizing film for liquid crystal display can be obtained using the PVA film which concerns on this invention.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol-based film of the present invention is characterized in that the difference in the hydrothermal extension time in the width direction (TD direction) of the film is 3 seconds or less.

Here, the "difference in hydrothermal extension time" means the difference between the maximum value and the minimum value of the hydrothermal extension time, and the hydrothermal extension time is a test piece having a width of 10 mm and a length of 60 mm at 50 mm intervals in the width direction (TD) of the polyvinyl alcohol-based film. This is the time taken when the specimen is cut or fully extended after cutting in water at 65 ° C by hanging a load of 0.5 g / 10 µm (0.5 g per 10 µm film thickness) at one end after cutting.

In this case, the hydrothermal extension time reflects all the characteristic values such as the crystallinity, crystal size, molecular weight, saponification degree, distance between crystalline and non-crystalline regions, and the ratio of the films. This can be confirmed through. Although the exact value or range of these characteristics can be measured by X-RAY, the method is very difficult and the measurement error is very large.

The average thickness of the PVA film according to the invention is preferably 40-150 μm, more preferably 50-120 μm. If the average thickness is less than 40 μm, stretching burst may occur during uniaxial stretching to produce a polarizing film. When it exceeds 150 micrometers, drawing strength will increase at the time of uniaxial stretching, and work will be very bad.

It is preferable that the difference of the maximum value and minimum value of the TD direction thickness of the PVA film which concerns on this invention is 3 micrometers or less. When the thickness difference exceeds 3 μm, the optical error of the obtained polarizing film may be large.

The width of the PVA film of the present invention is not particularly limited, but when used for the large screen of the LCD, the width is preferably 2 m or more.

As PVA which comprises the PVA film of this invention, what saponified the vinyl ester polymer obtained by superposing | polymerizing a vinyl ester monomer, and which made the vinyl ester unit the vinyl alcohol unit can be used. Examples of such vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and versatate vinyl. And vinyl acetate is most preferred.

When copolymerizing a vinyl ester monomer, if necessary, the copolymerizable monomer can be copolymerized within a range that does not impair the effects of the invention.

As a monomer copolymerizable with said vinyl ester type monomer, For example, C3-C30 olefins, such as ethylene, propylene, 1-butene, isobutene; Acrylic acid and its salts; Acrylic esters such as 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 octadecyl acrylate; Methacrylic acid and its salts; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate; Methacrylic acid esters such as i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; Acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamide propanesulfonic acid and its salts, acrylamide propyl dimethyl amine and its salts, N-methylol acrylamide Acrylamide derivatives such as amides and derivatives thereof; Methacrylamide, N-methylmethacrylamide, N-ethyl methacrylamide, methacrylamide propane sulfonic acid and salts thereof, methacrylamide propyl dimethyl amine and salts thereof, N-methylol methacrylamide and derivatives thereof Krylamide derivatives; N-vinyl amides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; Vinyl such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether Ethers; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; Maleic acid and its salts or esters thereof; Itaconic acid and its salt or its ester; Vinyl silyl compounds such as vinyl trimethoxysilane; N-vinylamides, such as isopropenyl acetate, N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone, are mentioned.

It is preferable that the average degree of polymerization of PVA which comprises the said PVA film is 500 or more from a viewpoint of the intensity | strength of a film, 1000 or more are more preferable and 3500 or more are especially preferable from a polarization performance viewpoint. When the average degree of polymerization is more than 6000, the yield may not be increased without increasing the monomer polymerization, and the work may be difficult due to the large stretching force in the stretching and dyeing process in manufacturing the polarizing plate, and the polarization efficiency may be lowered.

When manufacturing a PVA film, it is preferable to add polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohols include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like, and one or two or more of them can be used.

The amount of the plasticizer added is preferably 1 to 30 parts by weight, more preferably 3 to 25 parts by weight, particularly preferably 5 to 20 parts by weight based on 100 parts by weight of PVA. If it is less than 1 part by weight, the dyeing property and the stretchability may be lowered. If it is more than 30 parts by weight, the film may become too flexible and difficult to handle.

When producing a PVA film it is preferred to add a surfactant. There is no restriction | limiting in particular as a kind of surfactant, Anionic or nonionic surfactant is preferable. As anionic surfactant, carbonic acid type, such as potassium laurate, sulfuric acid ester type, such as octyl sulfate, and sulfonic acid type, such as dodecyl benzenesulfonate, are suitable, for example. As a nonionic surfactant, For example, Alkyl ether type, such as polyoxyethylene oleyl ether, Alkylphenyl ether type, such as polyoxyethylene octylphenyl ether, Alkyl ester type, such as polyoxyethylene laurate, Polyoxyethylene lauryl Alkylamine type, such as amino ether, Alkylamide type, such as polyoxyethylene lauric acid amide, Polypropylene glycol ether type, such as polyoxyethylene polyoxypropylene ether, Alkanolamide type, such as oleic acid diethanamide, Polyoxyalkyl Nonionic surfactants, such as aryl phenyl ether type, such as aryl aryl phenyl ether, are preferable. One type or two types or more of these surfactants can be used in combination.

The amount of the surfactant added is preferably 0.01 to 1 parts by weight, more preferably 0.02 to 0.5 parts by weight, and particularly preferably 0.05 to 0.3 parts by weight based on 100 parts by weight of PVA. If it is less than 0.01 part by weight, the effect of improving the stretchability and the dyeing property does not appear, and if it is more than 1 part by weight, it is eluted to the film surface, causing blocking, and the handleability may be lowered.

As a method for producing a PVA film, there are a drum film forming method for discharging a film forming raw material, which is a PVA solution or a melt, onto a heated drum using a die or the like, and a belt film forming method for discharging a film on a heated endless metal belt. . The drum film forming method is preferable for producing a PVA film having a width of 2 m or more for obtaining a large polarizing film.

 In this case, the drum film forming process is to uniformly discharge the film forming material onto a rotating metal drum for drying, dry and peel the volatiles on the drum circumferential surface, and then further dry with a drying roller or a floating dryer to appropriately control the humidity as necessary. It means to make one film.

In order to make the difference of the hydrothermal extension time of the film width direction into 3 second or less, the film forming raw material is discharged uniformly through a T die etc., and the thickness difference is 3 micrometers or less, and the film raw material has a surface temperature difference of 1 degrees C or less. When discharging to a drum or a belt, or drying using hot air in the film-forming raw material discharged, it is important to make the temperature difference of the hot air uniformly in the entire width direction with the temperature difference of 1 ° C or less. Moreover, it is important to make the temperature difference of a subsequent drying roll or a floating dryer into 5 degrees C or less. In addition, it is important that the difference between the maximum value and the minimum value of the longest hydrothermal extension length in the width direction is 30 mm or less. The longest hydrothermal extension here refers to the length of the longest sample in water.

It is preferable that the thickness of a PVA film is 40-150 micrometers. Thinner than 40 μm may be cut during uniaxial stretching, and thicker than 150 μm may result in stretching deviation and erroneous optical errors during uniaxial stretching.

The polarizing film obtained using the PVA film which concerns on this invention can be used as a polarizing plate by apply | coating the protective film which is optically transparent and mechanical strength on the both surfaces or single side | surface.

Hereinafter, the present invention will be described in more detail with reference to the following Examples, which are intended to illustrate the present invention, but are not intended to limit the scope of the present invention.

In the following example, the hydrothermal extension time and the thickness deviation of the film were performed by the method described below.

Hydrothermal extension time

Cut a specimen 10 mm wide by 60 mm long at 50 mm intervals of the polyvinyl alcohol film (TD), and then suspend a load of 0.5 g / 10 μm (0.5 g per 10 μm film thickness) at one end and in water at 65 ° C. The time taken when the specimen was cut or fully elongated after elongation was measured.

PVA  Film thickness difference

The difference in thickness is to evaluate the thickness uniformity of the PVA film, which was calculated as the difference between the maximum value and the minimum value by measuring the thickness of the film at intervals of 25 mm over the width direction of the PVA film using a thickness gauge (Mitsutoyo). .

Example

Example 1

A solution consisting of 25% by weight of polyvinyl alcohol having a degree of saponification of 99.9 mol% and a degree of polymerization of 3300 and 75% by weight of water using a drum or belt forming machine (ie, a solution having a solid content of 25% by weight). 11 parts by weight of glycerin and 0.1 parts by weight of surfactant were added to 100 parts by weight of polyvinyl alcohol, and then the raw material for film formation was discharged through T-DIE having a temperature of 90 ° C ± 0.5 ° C, and 85 ° C ± 1 ° C. , Dried by hot air having a precision of 3 m / sec, and heat-treated by passing the inside of a floating oven at 130 ° C. for 15 seconds in a portion maintaining a water content of 8 to 12% to obtain a film.

The average hydrothermal extension time of this PVA film was 30 second and hydrothermal extension length was 310 +/- 5 mm, The difference was 0.7 second, the average thickness of 60 micrometers, the thickness difference 2 micrometers, and the PVA film of width 1200mm were obtained.

The polarizing film obtained by processing the PVA film into a polarizing film had a transmittance of 43.1% and a polarization efficiency of 99,97%. The two polarizing plates were inclined at 45 degrees in a cross state and visually observed with the naked eye. (TD) showed uniform optical properties.

Examples 2 and 3 and Comparative Examples 1-3

T-die temperature and temperature deviation, drum surface temperature and temperature deviation, dry hot air temperature and temperature deviation, heat treatment temperature and temperature deviation and heat treatment time in the same manner as in Example 1 except that Film was prepared.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 T-die temperature (℃) / deviation (℃) 90 / ± 0.5 85 / ± 0.3 90 / ± 0.7 90 / ± 2 90 / ± 3 90 / ± 1 Drum surface temperature (℃) / deviation (℃) 90 / ± 0.3 90 / ± 0.5 90 / ± 0.7 90 / ± 1.5 90 / ± 2 90 / ± 1.5 Dry hot air temperature (℃) / deviation (℃) 85 ± 1 90 ± 1 85 ± 1 85 ± 1 85 ± 1.5 85 ± 3 Heat Treatment Temperature (℃) / Deviation (℃) 130 / ± 1 120 / ± 1 120 / ± 1 130 / ± 1 120 / ± 1 130 / ± 2 Heat treatment time (seconds) 15 30 30 15 15 15 Film thickness (μm) / deviation (μm) 60/2 65/1 70/3 60/4 65/5 70/6 Hydrothermal extension time (seconds) / deviation (seconds) 30 / 0.7 31/1 29 / 0.7 31/4 30/5 31/8 Hydrothermal extension length (mm) / deviation (mm) 310/10 313/10 300/16 310/28 310/32 310/40 Polarization efficiency (%) 99.97 99.96 99.98 99.34 99.12 99.11

As can be seen in Table 1, the polyvinyl alcohol-based film according to the present invention can be seen that the polarization efficiency is excellent.

Polyvinyl alcohol-based film according to the present invention is excellent in optical uniformity can be used as a polarizing film for a large-screen liquid crystal display.

Claims (6)

The polyvinyl alcohol film characterized by the difference of the hydrothermal extension time of the width direction (TD) of a film being 3 second or less. The method of claim 1, A polyvinyl alcohol-based film, characterized in that the difference in length in the widthwise longest hydrothermal extension of the film is 30 mm or less. The method of claim 1, The width direction thickness of a film is 40-150 micrometers, The polyvinyl alcohol-type film characterized by the above-mentioned. The method of claim 1, The polyvinyl alcohol-type film whose thickness difference of the width direction of a film is 3 micrometers or less. The width of the film produced by the drum film forming machine is 2 m or more.  Polyvinyl alcohol-based film characterized in that. The polarizing film which consists of a polyvinyl alcohol-type film of any one of Claims 1-5.