JPH05232316A - Polarizing film - Google Patents

Abstract

PURPOSE:To obtain a polarizing film having high polarizing property and high durability and especially having high transmittance for light and high polarizing property by using a PVA film as the raw material and satisfying specified conditions. CONSTITUTION:This polarizing film consists of a polyvinylalcohol (PVA) film and has >=30 dichroism ratio and dimensional ratio of (A)/(B)>=1.5, wherein (A) is the longitudinal length of the film before free contraction and (B) is the longitudinal length after free contraction by leaving the film in dried air at 140 deg.C for 30sec. As for the raw material PVA used, usual PVA obtd. by oxidization of polyvinyl acetate obtd. by polymn. of vinyl acetate is used. Further, modified polyvinyl alcohols containing <15mol% of unsatd. carboxylic acid or its deriv., unsatd. sulfonic acid or its deriv., alpha-olefin of 2-30 carbon number, etc., or polyvinyl acetals such as polyvinylformal and polyvinylacetoacetal can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing film having excellent polarization performance and durability.

[0002]

2. Description of the Related Art A polarizing plate having a light transmitting function and a light shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. In the field of application of this LCD, high-quality and high-reliability is demanded from small devices such as calculators and watches in the early days to laptops, personal computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal TVs, etc. It has been expanded to the equipment that is used. Under such circumstances, the polarizing film is required to have more excellent polarization characteristics and durability than ever before. Especially a personal computer,
Since a word processor requires screen brightness, a polarizing film having a high degree of polarization at a single transmittance of 43% or more is desired. In general, a polarizing film is likely to have high polarization performance when the single transmittance is low, but as the single transmittance increases, the polarization property decreases, and only a low dichroic ratio can be obtained. This tendency was particularly remarkable in a conventional polarizing film using a polyvinyl alcohol (hereinafter abbreviated as PVA) film formed by using water as a solvent.

As a method of improving the polarization property, there have been proposed some polarizing films using a PVA film formed by using an organic solvent instead of water as a solvent. For example, JP-A-1-105204 discloses that PV having a degree of polymerization of 2500 or more.
It has been proposed to stretch and dye a film prepared using an organic solvent solution having a concentration of A of 2 to 35% by weight.
Since this method uses an organic solvent, explosion-proof type equipment is required from the viewpoint of safety, and rust-proof type equipment is required from the viewpoint of maintenance, resulting in a large equipment cost. In addition, the release of the solvent to the atmosphere leads to environmental pollution, and on the other hand, there is a problem in that the recovery of the solvent imposes a large burden of equipment cost. Further, in JP-A-64-84203, the degree of polymerization is 260
It has been proposed to stretch and dye a film prepared by using an organic solvent solution having a PVA concentration of 0 or more and 4 to 10% by weight. In this method as well, it is safe to use an organic solvent as in the above proposal. In addition, there are problems in terms of maintenance and solvent recovery.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a polarizing film made of a PVA-based film as a raw material, which has high polarization and durability.
In particular, the invention provides a polarizing film having a high light transmittance and a high polarization property.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have diligently studied a polarizing film made of a PVA film (hereinafter referred to as a PVA film) as a raw material for improving its polarizing property and durability. First, the inventors of the present invention have used unstretched P using PVA as a raw material, which is generally used for the purpose of further testing the current situation.
When the relationship between the various manufacturing conditions of the polarizing film and the polarization characteristics was examined using the VA film, the stretching temperature of the PVA film produced by the conventional method was 35 ° C., and the stretching temperature was 40 ° C. or higher. Makes uniform stretching difficult,
As a result, it was found that variations in thickness and polarization performance occur. On the other hand, as a result of intensive studies by the present inventors, if the uniaxial stretching temperature of the PVA film can be increased and the PVA film can be uniformly stretched, it is possible to improve the polarization characteristics and the durability at a high single transmittance. I got the prospect.

That is, the present invention is composed of a PVA film, and has a longitudinal dimension (A) before free shrinking and a longitudinal dimension (B) after free shrinking by being left in dry air at 140 ° C. for 30 seconds. And a dichroic ratio of 30 or more. Further, the present invention has a weight swelling degree of 200 to
A 270% PVA film is uniaxially stretched at a temperature of 40 ° C. or more, and is allowed to shrink freely by allowing it to stand in dry air at 140 ° C. for 30 seconds and the longitudinal dimension (A) before free shrinking. The ratio (A) / (B) with respect to the vertical dimension (B) is 1.5 or more, and the dichroic ratio is 3
The present invention provides a method for producing a polarizing film of 0 or more.

The polarizing film of the present invention has a free shrinkage ratio (A) /
(B) is 1.5 or more, preferably 2.0 or more, more preferably 2.5 or more, and the dichroic ratio is 30 or more,
The dichroic ratio is preferably 35 or more, more preferably the dichroic ratio at a single transmittance of 43% is 30 or more, and even more preferably the dichroic ratio at a single transmittance of 43% is 35 or more.

Here, the free shrinkage ratio is the size of the polarizing film 4c.
The m-square sample was left in a hot air drying oven at 140 ° C for 30 seconds, and the polarizing film was freely shrunk in the vertical dimension (A) before free shrinking and the longitudinal direction after free shrinking. It is a value obtained by the following formula from the dimension (B). Free shrinkage ratio = (A) / (B) In the present invention, the dichroic ratio is used to specify the polarization performance. The dichroic ratio is the light transmittance (single transmittance: Ts) of the polarizing film. (%)) And the degree of polarization (P (%)).

[Equation 1] When the free shrinkage ratio (A) / (B) is less than 1.5, both polarization characteristics and durability are poor. It is presumed that when the free shrinkage ratio (A) / (B) is less than 1.5, both the orientation of the polymer and the dye becomes insufficient, and as a result, high polarization and high durability cannot be exhibited. It

As the polarizing film having such high polarization performance, a PVA film having a weight swelling degree of 200 to 270%, preferably 210 to 250% is 40 ° C. or higher, preferably 50 ° C. or higher,
More preferably, by uniaxially stretching at 60 ° C or higher,
You can get it for the first time. Here, the degree of weight swelling was determined by cutting 3 g of the sample film into a width of about 3 mm and immersing it in warm water at 40 ° C.
After immersion for 300 minutes, 300 r. p. The sample weight after centrifugal dehydration at m for 5 minutes (W ₁ ) and the sample weight after drying at 105 ° C. for 16 hours (W ₂ ) are determined by the following formula. Weight swell degree (%) = (W ₁ / W ₂ ) × 100 The weight swell degree of the PVA film of the present invention is 200%.
When it is less than 1, a polarizing film with high polarization performance cannot be obtained. When the weight swelling degree of the PVA film is larger than 270%, a polarizing film having high polarization and high durability cannot be obtained.

PVA films include optical films such as polarizing films and retardation films, as well as bags for packaging textile products,
It is widely used for agricultural films, unsaturated polyester release films, etc., but these have a polymerization degree of 1200-
It uses 1700 PVA and its weight swelling degree is 2
It is less than 00%, and most is 160 to 180%. In particular, using PVA with a higher degree of polymerization than conventional PVA,
When a PVA film is produced under conventional conditions, the degree of weight swelling of PVA is further lowered, and a PVA film suitable for producing the highly polarizing and highly durable polarizing film of the present invention cannot be obtained.

The present inventors have studied the production conditions of a PVA film having a target weight swelling degree, and as a result,
It was found that the PVA concentration and the drying temperature of the film are extremely important in the film formation from the aqueous solution. The PVA concentration of the film-forming stock solution needs to be 25% by weight or more, preferably 30% by weight or more, and more preferably 35% by weight or more. If the PVA concentration is less than 25% by weight, the weight swelling degree of the PVA film does not fall within the target range. Especially in the case of high degree of polymerization PVA, the target degree of weight swelling is obtained by adopting a high concentration solution. This is presumed to be the result of restraining the crystal growth by restraining the molecular arrangement by adopting a high concentration solution. The upper limit of the PVA concentration is preferably 50% by weight or less from the viewpoints of maintaining the kneading property of the undiluted solution and the film-forming stability, maintaining the uniformity of the film thickness, and preventing the occurrence of defects such as gel.

It is also important to control the film temperature during drying during the production of the PVA film of the present invention. In particular, it is preferable to keep the film temperature as constant as possible until the end of drying. Specifically, the film temperature during drying is 60 to 13
The temperature is 0 ° C, preferably 70 to 110 ° C. When the film temperature during drying is less than 60 ° C., the degree of weight swelling becomes too high, and the target free shrinkage ratio and dichroic ratio cannot be achieved. On the other hand, when the film temperature exceeds 130 ° C., the degree of weight swelling becomes too low, and the target high polarization property cannot be obtained. When using a high degree of polymerization PVA, the degree of weight swelling tends to be low, so care must be taken not to raise the film temperature too much in the latter half of drying.

The raw material PVA used in the present invention includes:
In addition to ordinary PVA produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, α-olefin having 2 to 30 carbon atoms, etc. It is also possible to use a modified polyvinyl alcohol obtained by copolymerizing less than about 15 mol% of polyvinyl alcohol, polyvinyl formal, polyvinyl acetoacetal, polyvinyl acetal such as polyvinyl butyral, and the like.
The degree of saponification of PVA in the present invention is preferably 90 mol% or more, preferably 95 mol% or more, more preferably 98 mol% or more from the viewpoint of durability. The degree of polymerization of PVA is preferably 500 or more from the viewpoint of polarization characteristics and durability,
2400 or more is more preferable, and 4000 or more is even more preferable.

Water, an organic solvent, or a mixture thereof can be used as a solvent for preparing the raw material film in the present invention, but the greatest feature of the present invention is that it is a water-only solvent system having high polarization and high durability. It is recommended to use a water-only solvent system which is characterized in that it can be obtained, and is naturally superior in safety and economy. As a method for forming the raw material film, a metal drum, a metal belt, a resin belt, a casting method on a resin film or a glass plate, an extrusion casting method or various coating methods can be used. As the method for drying the PVA film, heat transfer drying, hot air drying, static drying, etc. can be used. As a practical drying method, a heat medium circulating metal drum, hot air drying, or a combination of both is generally used. The temperature of the heat medium circulating metal drum is close to the film temperature and is relatively easy to manage. In the case of hot air drying, the hot air temperature is often much higher than the film temperature, and care must be taken not to raise the film temperature too much. That is, when drying progresses and the moisture content of the film is 10% by weight or less, the film temperature is likely to rise, so care must be taken not to take an excessive difference between the hot air temperature and the film temperature.

The raw material film may have a thickness of 5 to 150 μm, preferably 30 to 100 μm. Various polyol plasticizers such as glycerin, nonionic, anionic and cationic surfactants can be appropriately added to the raw material film of the present invention. Dyeing raw PVA film ・ 1
Axial stretching, boric acid compound treatment, and drying are performed to form a polarizing film. Cellulose triacetate is usually laminated as a support on both outer surfaces of the polarizing film. Before dyeing, during dyeing,
Either after stretching is possible. As the dye, iodine-potassium iodide or a dichroic dye can be used. PVA
The uniaxial stretching of the film may be carried out in warm water, or the film after absorbing water may be uniaxially stretched in the air. You may mix an iodine compound in the bath at the time of a boric acid compound process.

[0016]

EXAMPLES In the following examples and comparative examples, common manufacturing conditions and the like in the polarizing film manufacturing process are as follows.
The dye concentration in the dye bath is iodine / potassium iodide weight ratio of 1
The iodine concentration was fixed at / 10 and the transmittance of the polarizing film was 4 per unit.
Appropriately 4-6 levels were chosen between 1 and 20 g / l so as to cover 3%. Boric acid concentration of boric acid bath is 4
% By weight, and 4% by weight of boric acid was added to the drawing bath. Drying was performed with hot air at 50 ° C. Regarding the obtained polarizing film,
The dichroic ratio was calculated by measuring the simple substance transmittance and the degree of polarization. In addition, the polarizing plate obtained by laminating 80 μm thick cellulose triacetate on both sides of the polarizing film with a PVA adhesive was used for 60 hours at 90 ° C. and 90% RH for 200 hours. It measured and evaluated durability.

Example 1 Pellets of 35 parts by weight of PVA having a polymerization degree of 4000 and a saponification degree of 99.9 mol%, 61 parts by weight of water and 4 parts by weight of glycerin were discharged onto a metal drum at 90 ° C. by extrusion die casting, and 90 Combined with hot air drying at ℃, film thickness 75
A μ PVA film was prepared. The weight swelling degree of the obtained film was 225%. Next, this film was dyed, stretched, treated with boric acid and dried in order to form a polarizing film. The water temperature at the time of stretching was set to 50 ° C., and the film was uniaxially stretched up to a stretchable upper limit draw ratio of 5.2 times. The free shrinkage ratio (A) / (B) of the obtained polarizing film is 2.7, and the single transmittance is 4
The polarization degree at 3.5% is 99.6% and the dichroism is 45.
It was 0, indicating excellent polarization performance. After the durability test of this polarizing film, the single transmittance was 46.9% and the polarization degree was 93.
The durability was 7% and the dichroic ratio was 36.7, showing excellent durability.

Example 2 Pellets comprising 26 parts by weight of PVA having a degree of polymerization of 8000 and a degree of saponification of 99.9 mol%, 71 parts by weight of water and 3 parts by weight of glycerin were discharged onto a metal drum at 90 ° C. by extrusion die casting, and 90 Combined with hot air drying at ℃, film thickness 75
A μ PVA film was prepared. The weight swelling degree of the obtained film was 215%. Next, this film was treated in the same manner as in Example 1 to prepare a polarizing film. The water temperature during stretching was set to 55 ° C, and the film was uniaxially stretched up to a stretchable upper limit of 5.5 times. Free shrinkage (A) of the obtained polarizing film
/ (B) was 3.5, the degree of polarization was 99.9% and the dichroism was 50.2 when the single substance transmittance was 43.3%, showing excellent polarization performance. After the durability test of this polarizing film, the single transmittance was 45.4%, the polarization degree was 96.7%, and the dichroic ratio was 3%.
It was 7.1, showing excellent durability.

Example 3 Pellets comprising 40 parts by weight of PVA having a degree of polymerization of 2500 and a degree of saponification of 99.9 mol%, 53 parts by weight of water and 7 parts by weight of glycerin were discharged onto a metal drum at 90 ° C. by extrusion die casting, and 90 Combined with hot air drying at ℃, film thickness 75
A μ PVA film was prepared. The weight swelling degree of the obtained film was 245%. Next, this film was treated in the same manner as in Example 1 to prepare a polarizing film. The water temperature during stretching was set to 45 ° C., and the film was uniaxially stretched up to a stretchable upper limit of 5.5 ×. The free shrinkage ratio (A) / (B) of the obtained polarizing film was 2.0, the degree of polarization was 99.5% and the dichroism was 37.8 at a unit transmittance of 42.6%.

Comparative Example 1 Example 1 using the PVA film obtained in Example 1
A polarizing film was prepared by the same process as above. The water temperature during stretching is 35
Change to ℃, and draw up to a maximum draw ratio of 4.5 times 1
Axial stretched. Free shrinkage ratio (A) / of the obtained polarizing film
(B) was 2.6, the degree of polarization was 96.2% and the dichroic ratio was 26.6 at a single transmittance of 43.7%.

Comparative Example 2 Using the same pellets and the same equipment as in Example 1, the temperature of the metal drum and the temperature of the dry hot air were both set to 50 ° C. to prepare a PVA film having a thickness of 75 μm. The weight swelling degree of the obtained film was 290%. Using this film, a polarizing film was prepared by the same process as in Example 1. The water temperature during stretching was set to 45 ° C., and the film was uniaxially stretched up to a stretchable upper limit stretch ratio of 6.5 times. The free shrinkage ratio (A) / (B) of the obtained polarizing film is 1.2, and the single transmittance is 42.8%.
The degree of polarization was 92.6%, and the dichroic ratio was 17.9. Further, stretching unevenness was observed in the obtained polarizing film.

Comparative Example 3 Using the same pellets and the same equipment as in Example 1, only the hot air temperature was changed to 150 ° C. to prepare a PVA film having a film thickness of 75 μ. The weight swelling degree of the obtained film is 170.
%Met. Using this film, a polarizing film was prepared in the same process as in Example 1. Set the water temperature during stretching to 55 ° C,
The film was uniaxially stretched up to a stretchable upper limit of 4.5 times.
Free shrinkage ratio (A) / (B) of the obtained polarizing film 2.8,
At a single transmittance of 44.0%, the degree of polarization was 92.7 and the dichroic ratio was 20.8.

[0023]

EFFECTS OF THE INVENTION The polarizing film obtained by the present invention is excellent in polarization performance, particularly polarization performance at a high single transmittance, and has high durability. Therefore, a bright screen for personal computers, word processors, televisions, etc. It is useful as a polarizing film suitable for LCDs and the like that require.

Claims (5)

[Claims] 1. A longitudinal direction dimension (A) of 140 ° C., which is made of a polyvinyl alcohol-based film before free shrinking.
The ratio (A) / (B) to the longitudinal dimension (B) after free contraction by leaving it in dry air for 30 seconds is 1.5 or more, and the dichroic ratio is 30 or more. Is a polarizing film. 2. A polyvinyl alcohol film having a degree of polymerization of 2400 or more, which has a longitudinal dimension (A) before free shrinking and a vertical length after free shrinking by being left in dry air at 140 ° C. for 30 seconds. A polarizing film having a ratio (A) / (B) to the dimension (B) in the direction of 1.5 or more and a dichroic ratio of 30 or more. 3. A longitudinal direction dimension (A) before free shrinkage and 140 ° C., which is characterized in that a polyvinyl alcohol film having a weight swelling degree of 200 to 270% is uniaxially stretched at a temperature of 40 ° C. or higher. The ratio (A) / (B) to the longitudinal dimension (B) after free contraction by leaving it in dry air for 30 seconds is 1.5 or more, and the dichroic ratio is 3
The manufacturing method of the polarizing film which is 5 or more. 4. A longitudinal dimension before free shrinkage (A) characterized by uniaxially stretching a polyvinyl alcohol film having a degree of weight swelling of 200 to 270% and a degree of polymerization of 2400 or more at a temperature of 40 ° C. or more (A). ) And the longitudinal dimension (B) after free contraction by leaving it in dry air at 140 ° C for 30 seconds, the ratio (A) / (B) is 1.5 or more, and dichroism A method for producing a polarizing film having a ratio of 35 or more. 5. A longitudinal dimension before free shrinkage (A) in which a polyvinyl alcohol film having a weight swelling degree of 200 to 270% and a polymerization degree of 2400 or more is uniaxially stretched at a temperature of 50 ° C. or more (A). ) And the longitudinal dimension (B) after free contraction by leaving it in dry air at 140 ° C for 30 seconds, the ratio (A) / (B) is 1.5 or more, and dichroism A method for producing a polarizing film having a ratio of 35 or more.