JPH06235815A - Polarizing film and its production - Google Patents

Abstract

PURPOSE:To obtain a polarizing film excellent in polarizing characteristics and dimensional stability by subjecting a polyvinylalcohol film to uniaxial orientation by three or more times of stretching, and then crosslinking with polyvalent aldehyde. CONSTITUTION:A polyvinylalcohol(PVA) film is dyed, uniaxially oriented, fixed and crosslinked to obtain a polarizing film. In this method, magnification of stretching for the uniaxial orientation of the film is three or more times, preferably >=3.5 times. The crosslinking treatment with polyvalent aldehyde is effected based on insolubilization of PVA polymer by partial crosslinking, which contributes to dimensional stability. This treatment is performed to obtain 0.01-5wt.% insoluble residue, preferably 0.1-2wt.% in hot water at 100 deg.C in order to obtain excellent dimensional stability without decreasing the polarizing performance. If the insoluble residue is <0.01wt.%, the effect of crosslinking is small and enough dimensional stability is not obtd. If the insoluble residue is >=5wt.%, the polarizing performance decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing film and a method for producing the same, and more particularly to a polarizing film having excellent polarization performance and dimensional stability and an efficient method for producing the same.

[0002]

2. Description of the Related Art A polarizing plate having a light transmitting / shielding function is a liquid crystal display (LCD) together with a liquid crystal having a light switching function.
Is a basic component of. The field of application of this LCD is also
From small devices such as calculators and watches in the early days to laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions and indoor and outdoor measuring devices, the operating conditions range from low to high temperatures and low temperatures. Since it is used under a wide range of conditions from humidity to high humidity, a polarizing plate having high polarization performance and excellent dimensional stability is required.

A polarizing plate is generally prepared by uniaxially stretching and dyeing a polyvinyl alcohol film (which means a film made of a polyvinyl alcohol polymer, and may be abbreviated as PVA film hereinafter), and both polarizing films. The outer surface has a structure in which a supporting plate such as a cellulose triacetate (TAC) film is attached. Since the polarizing film is uniaxially stretched, the dimensional stability is poor, and the dimensional stability is not sufficient even in a polarizing plate to which a TAC film is attached. The poor dimensional stability of this polarizing plate is due to the fact that when the polarizing plate is attached to an LCD glass substrate with an adhesive and used, the polarizing plate may peel off from the glass substrate or the attachment position may shift over time. This causes a problem of significantly impairing the display performance of the LCD. Therefore, in order to improve the dimensional stability of the polarizing plate, it is required to improve the dimensional stability of the polarizing film.

A conventional polarizing film is produced by uniaxially stretching a PVA film using iodine or a dichroic dye to dye it, or dyeing it and then uniaxially stretching it and then fixing it with a boron compound. In order to obtain high polarization, the uniaxial stretching ratio is about 4 times or more. However, as the stretching ratio is increased, the polarizing performance of the polarizing film obtained is improved, but the dimensional stability of the polarizing film is lowered, and a polarizing film having both properties at the same time has not been obtained. Further, as a method for obtaining high polarization, a polymerization degree of 2600
Although it has been proposed to use the above-mentioned high polymerization degree PVA, there is a problem that the use of such a high polymerization degree PVA further deteriorates the dimensional stability of the polarizing film obtained by uniaxial stretching.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied, in the following order, a method of improving the dimensional stability of a polarizing film made of PVA film while maintaining high polarization. First, in order to grasp the present situation, a polarizing film is produced by a conventional manufacturing method using an unstretched PVA film made of a polyvinyl alcohol polymer (PVA) having a polymerization degree of around 1750, which has been generally used conventionally. Was prepared, and the polarization performance and dimensional stability of the obtained polarizing film were investigated. As a result, a polarizing film having a high dichroic property with a dichroic ratio of 40 or more can be obtained even when the stretching ratio is increased even under the conventional manufacturing conditions of the polarizing film, but the dimensional retention of this polarizing film is 0. It was 5 to 0.65 and the dimensional stability was poor.

Here, the dichroic ratio is an index for evaluating the polarization performance of the polarizing film. The dichroic ratio of the obtained polarizing film is the Japan Electronic Machinery Manufacturers Association Standard (EIAJ) LD-
According to 201-1983, the transmittance Ts (%) obtained by measuring and calculating in a C light source and a 2 degree visual field using a spectrophotometer.
And the degree of polarization P (%), it is calculated by the formula (I). Dichroic ratio = log (Ts / 100-Ts × P / 10000) / log (Ts / 100 + Ts × P / 10000) (I) In addition, dimensional retention rate evaluates dimensional stability This dimensional retention is an index, and the dimensional retention is obtained by taking a sample of 4 cm in length × 4 cm in width with the uniaxially stretched direction of the polarizing film as the vertical direction, and sandwiching one end with a clip at no load, at a temperature of 60 ° C. and a relative humidity (R
H) Suspended in a 90% constant temperature and humidity chamber for 10 days and free-shrinked in the longitudinal direction (B) to the longitudinal direction before free shrinkage (A), the formula (II) is obtained. Required by. Dimensional retention rate = (B) / (A) ... (II)

Further, the inventor of the present invention has made the raw material PVA film,
As a result of various studies on uniaxial stretching conditions, dyeing conditions, fixing treatment conditions, and dimensional stabilization treatment conditions, the stretching ratio was increased to 3 times or more, and by using a polyvalent aldehyde as a cross-linking agent, two-color It has been found that a polarizing film having a high sex ratio and a significantly improved dimensional stability can be obtained. The present invention has been completed based on such findings. That is, the present invention provides a polyvinyl alcohol-based polarizing film, which is crosslinked with a polyhydric aldehyde. Further, the present invention provides that when a polyvinyl alcohol film is dyed, uniaxially stretched and fixed to produce a polarizing film, it is uniaxially stretched by 3 times or more, and is crosslinked with a polyvalent aldehyde. The present invention provides a method for producing a characteristic polyvinyl alcohol-based polarizing film.

The polarizing film of the present invention comprises a polyvinyl alcohol polymer (PVA) as a raw material and is cross-linked with a polyhydric aldehyde. The cross-linking treatment with the polyvalent aldehyde is based on insolubilization of PVA due to partial cross-linking and contributes to dimensional stabilization. The degree of insolubilization is not particularly limited, but in order to provide excellent dimensional stability without impairing the polarization performance, the insoluble residue in hot water at 100 ° C. is preferably 0.01 to 5% by weight, 0.1
˜2 wt% is more preferred. When the undissolved residue is less than 0.01% by weight, the effect of the crosslinking treatment is low and the dimensional stabilization effect is not sufficient. On the other hand, if the undissolved residue is 5% by weight or more, the polarizing performance will be deteriorated, which is not suitable for the purpose of the present invention.

Examples of the polyhydric aldehyde used in the present invention include glyoxal, glutaraldehyde and aldehydated starch. Among them, dialdehyde is preferable, and glyoxal is more preferable. These polyhydric aldehydes are used alone or as a mixture. The PVA used as the material of the polarizing film of the present invention is PVA produced by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester such as vinyl acetate. The degree of polymerization of this PVA is not particularly limited, but usually 5
00 or more, preferably 2400 or more, more preferably 4000 or more is suitable in that a polarizing film having high polarization performance can be obtained. On the other hand, the degree of saponification of PVA may be appropriately selected, but is usually 90 mol% or more, preferably 95 mol% or more, more preferably 98 mol% or more, because a polarizing film having more excellent dimensional stability can be obtained. Is suitable for. In addition to these PVA, unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, modified polyvinyl alcohol obtained by copolymerizing less than about 15 mol% of α-olefins having 2 to 30 carbon atoms; polyvinyl formal, polyvinyl Polyvinyl acetals such as acetoacetal and polyvinyl butyral; ethylene-vinyl alcohol copolymers having an ethylene unit content of 20 mol% or more can also be used.

To produce a PVA film from the above PVA, for example, a PVA solution obtained by dissolving the raw material PVA in water, an organic solvent or a mixed solution of water and an organic solvent is placed on a resin film, a drying drum or On the drying belt,
It may be formed by a cast casting method or a die casting method and dried. Here, if necessary, a plasticizer, a surfactant, iodine, an iodine compound, a dichroic dye, or the like can be added to the PVA solution. The thickness of the raw material film may be 5 to 150 μm, preferably 30.
˜100 μm.

The weight swelling degree of the PVA film used for the polarizing film of the present invention is extremely important for the dimensional stability of the film. The degree of swelling of the raw material film used in the present invention is not particularly limited, but it is generally preferable that the degree of swelling by weight is high, specifically, 190% or more is preferable and 200% is particularly preferable. The upper limit of the degree of weight swelling is not particularly limited and may be set appropriately, but is usually 270% or less. By using such a PVA film having a high degree of weight swelling, it becomes easy to impart a high polarization property with a dichroic ratio of 40 or more, and the crosslinking effect by the polyvalent aldehyde can be further enhanced. Here, the weight swelling degree W is determined by cutting 3 g of the sample film into a width of about 3 mm, and
Sample weight (W1) after immersion in warm water at 0 ° C for 15 minutes and centrifugal dehydration at 3000 rpm for 5 minutes
It is determined by the following formula (III) from the sample weight (W2) after drying for 16 hours. Weight swelling degree W (%) = (W1) / (W2) × 100 (III) In order to obtain a PVA film having such a high weight swelling degree, drying at the time of film production is performed. It is preferable to keep the temperature low and the preferred drying temperature is 60-90 ° C. When performing hot air drying such as belt hot air drying method or combined method of drum drying and hot air drying, hot air drying temperature is generally 130 ° C or higher, so be careful not to raise the drying temperature too high. is necessary. Also, when heat treatment is performed, it is preferably 130 ° C. or lower.

In the polarizing film of the present invention, the dichroic ratio calculated by the above formula (I) is preferably 40 or more, more preferably 50 or more. Further, the polarizing film of the present invention has such high polarization performance, and it is preferable that the dimension retention rate obtained by the above formula (II) is larger than 0.65.
0.7 or more is more preferable, and 0.8 or more is even more preferable. The polarizing film of the present invention is usually used by attaching a support film such as a TAC film to both outer surfaces of the polarizing film.

Various methods are conceivable for producing the polarizing film of the present invention having such a high polarization performance and dimensional stability at the same time. According to the production method of the present invention,
Moreover, a high-performance polarizing film can be obtained. A known method such as a wet stretching method or a dry stretching method can be used for producing a polarizing film from a raw material PVA film, and a polarizing film can be obtained after dyeing, uniaxial stretching treatment, fixing treatment and crosslinking treatment, and if necessary, drying treatment. Manufactured. Dyeing can be performed before stretching, during stretching, and after stretching. As the dye used for this dyeing, iodine-potassium iodide or a dichroic dye can be used. The uniaxial stretching treatment may be performed in warm water, or may be performed in air using the film after absorbing water. The stretching temperature is not particularly limited, but when stretching in warm water, it is 30
-80 ° C is preferable, and 50 to 15 in the case of dry heat drawing.
0 ° C is preferred. The treatment bath in the fixed treatment is usually
Boric acid and boron compounds are added. An iodine compound may be mixed in the fixing treatment bath.

In the production method of the present invention, the stretching ratio of uniaxial stretching is 3 times or more, preferably 3.5 times or more. The upper limit of the stretching ratio is not particularly limited, but it is preferably 7.0 times or less from the viewpoint that uniform stretching can be obtained. If the draw ratio is less than 3 times, it will be difficult to obtain a dichroic ratio of 40 or more in the obtained polarizing film, and the desired highly polarizing polarizing film cannot be obtained. In the production method of the present invention, the timing of adding the polyvalent aldehyde is not particularly limited, but the polyvalent aldehyde is preferably added as a crosslinking agent to the crosslinking treatment bath after the fixing treatment. It is also effective to omit the crosslinking treatment bath and add the polyvalent aldehyde to the fixed treatment bath, or to add the polyvalent aldehyde to the fixed treatment bath and the polyvalent aldehyde to the crosslinking treatment bath. In the present invention, by using a polyvalent aldehyde as a cross-linking agent, a polarizing film having high polarization and excellent dimensional stability can be obtained. Further, the cross-linking agent in the cross-linking treatment bath or the fixing treatment bath is used. The addition concentration of 0.01 to 20% by weight, especially 0.05 to 5% by weight
Is preferred. As a result, the undissolved residue of the polarizing film was 0.0
The amount can be adjusted to 1 to 5% by weight, particularly 0.1 to 2.0% by weight, and the high polarization property and dimensional stability are improved.

[0015]

The present invention will be described in more detail with reference to the following examples. Example 1 Degree of polymerization 1750, degree of saponification 9 using a drum dry film forming machine.
A solution prepared by dissolving 100 parts by weight of 9.9 mol% PVA and 5 parts by weight of glycerin in 1000 parts by weight of water was cast on the drum to form a film, which was dried at 70 ° C. and then 120 in a hot air oven.
Heat treatment at ℃, film thickness 75μm, weight swelling degree 210% P
A VA film was created. Next, this film was dyed, uniaxially stretched, fixed, crosslinked and dried in this order to form a polarizing film. At this time, the concentration of iodine in the dyeing bath water was 0.5 g / liter, and the concentration of potassium iodide was 50 g / liter.
Liter, the draw ratio of uniaxial stretching is 5.0 times, the concentration of boric acid in the drawing bath water is 4% by weight, the concentration of boric acid in the fixing treatment bath water is 4% by weight, the concentration of potassium iodide is 4% by weight, and the dimensions are The concentration of glyoxal in the stabilizing bath water was 0.2% by weight. The water temperature of the dyeing bath, the drawing bath, the fixing treatment bath, and the dimension stabilizing treatment bath were all set to 40 ° C. The subsequent drying was performed with hot air at 50 ° C. The obtained polarizing film has a thickness of 27 μm,
Transmittance 44.3%, degree of polarization 99.8%, dichroic ratio 57.
It was 6. The polarizing film was boiled and dissolved in hot water at 100 ° C. for 10 minutes, and the dry weight (insoluble residue) of the residue obtained by filtration with a paper filter was 0.2 weight with respect to the weight of the original polarizing film. %Met. This polarizing film has a temperature of 60 ° C and a relative humidity of 90%.
The dimension retention rate after leaving it in the constant temperature and humidity chamber for 10 days was 0.85.

Example 2 Using the same apparatus as in Example 1, a solution obtained by dissolving 80 parts by weight of PVA having a polymerization degree of 4400 and a saponification degree of 99.7 mol% and 5 parts by weight of glycerin in 1000 parts by weight of water is used. PVA having a film thickness of 75 μm and a weight swelling degree of 220% is formed by casting a film on the top, drying at a temperature of 80 ° C., and heat-treating at a hot air temperature of 120 ° C.
I made a film. Next, a polarizing film was prepared by dyeing, uniaxially stretching, fixing, crosslinking and drying under the same conditions as in Example 1 except that the uniaxially stretching ratio of the film was 4.5 times. The obtained polarizing film has a thickness of 30 μm and a transmittance of 4
The degree of polarization was 4.0%, the degree of polarization was 99.9%, and the dichroic ratio was 60.2. For this polarizing film, the insoluble residue determined in the same manner as in Example 1 was 0.3% by weight.
The dimensional retention rate after standing for 10 days in a thermo-hygrostat at 0 ° C. and a relative humidity of 90% RH was 0.82.

Comparative Example 1 A polarizing film was prepared under the same conditions as in Example 2 except that the PVA film obtained in Example 2 was not cross-linked. The obtained polarizing film has a thickness of 30 μm and a transmittance of 4
The degree of polarization was 3.8%, the degree of polarization was 99.9%, and the dichroic ratio was 58.2. With respect to this polarizing film, the insoluble residue determined in the same manner as in Example 1 was 0%, and the polarizing film was completely dissolved. The dimension retention of this polarizing film was 0.58 when it was left for 10 days in a thermo-hygrostat having a temperature of 60 ° C. and a relative humidity of 90% RH.

[0018]

INDUSTRIAL APPLICABILITY The polarizing film of the present invention has extremely excellent polarization characteristics and dimensional stability, and is useful as a polarizing plate for vehicle-mounted LCDs, such as LCD navigation systems or LCD TVs, which undergo large temperature and humidity changes.

Claims (2)

[Claims] 1. A polyvinyl alcohol-based polarizing film, which is crosslinked with a polyhydric aldehyde. 2. A polyvinyl alcohol film is dyed, uniaxially stretched and fixed to produce a polarizing film, which is uniaxially stretched by 3 times or more and crosslinked with a polyhydric aldehyde. And a method for producing a polyvinyl alcohol-based polarizing film.