JPH05245858A - Production of polyvinyl alcohol type film - Google Patents

Abstract

PURPOSE:To efficiently produce a polyvinyl alcohol type film suitable for the formation of a polarizing film excellent in physical properties capable of being subjected to various uses and especially excellent in both of polarizing characteristics and durability. CONSTITUTION:When a polyvinyl alcohol type film is formed from a polyvinyl alcohol type resin solution film using a film forming machine having a single surface drying type dryer constituted of one rotary body and the heat treatment device directly connecting said dryer, the film is transferred from a drying process to a heat treatment process at the point of time when the moisture content of the film reaches 2-15wt.% and heated at temp. higher than drying temp. to produce a polyvinyl alcohol type film wherein a product of hot water cutting temp. and a wt. swelling degree is 13000 or more.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polyvinyl alcohol film. More specifically, the present invention is a method for efficiently producing a polyvinyl alcohol-based film having excellent physical properties that can be used in various applications, particularly a polyvinyl alcohol-based film suitable for producing a polarizing film having excellent polarization performance and durability. Regarding

[0002]

2. Description of the Related Art Conventionally, a polyvinyl alcohol film is usually produced by using a metal heating roll and drying it substantially completely. The film obtained by such a method is used as a polyvinyl alcohol film having excellent shape stability in many applications because it has uniform physical properties over the entire thickness, and one of the applications is a polarizing film. It has been known. The polarizing film has a function of transmitting and blocking light and is used as a basic component of a liquid crystal display (LCD) together with a liquid crystal having a function of switching light. In recent years, LCDs have been required to have high quality and high reliability such as laptop personal computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, and liquid crystal TVs from small devices such as calculators and watches in the early days. It is expanding to other devices. Under such circumstances, there is a demand for a polarizing film having both excellent polarization characteristics and durability that are far superior to those of conventional polarizing films. Therefore, in order to meet such a demand, for example, a method using a special dye, a method of forming a gel film of an organic solvent solution to produce a polyvinyl alcohol film as a base material, and the like have been proposed. However, these methods have drawbacks such that it is difficult to prepare a dye, and when an organic solvent is used, costs are inevitably increased in terms of safety and facility maintenance.

[0003]

Under these circumstances, the present invention provides a polyvinyl alcohol film having excellent physical properties which can be used in various applications, and more particularly a polarizing film having both excellent polarization characteristics and durability. The present invention has been made for the purpose of providing a method for efficiently producing a polyvinyl alcohol film suitable for forming a film.

[0004]

As a result of intensive studies to achieve the above-mentioned object, the present inventor has found that a single-sided drying type drying device constituted by one rotating body and a heat treatment device directly connected thereto are provided. By using a film forming machine having the same, the polyvinyl alcohol-based resin aqueous solution film is subjected to a drying treatment until a certain moisture content is obtained, and then subjected to a heat treatment at a higher temperature, so that the product of the hot water cutting temperature and the weight swelling degree is It was found that a polyvinyl alcohol film having a certain value or more was obtained, and this film was suitable for producing a polarizing film having excellent polarization characteristics and durability. The present invention has been completed based on such findings.

That is, according to the present invention, a polyvinyl alcohol-based resin aqueous solution film is changed to a polyvinyl alcohol-based film using a film-forming machine having a single-sided drying type drying device composed of one rotating body and a heat treatment device directly connected thereto. In the production of the above, when the water content of the film reaches 2 to 15% by weight, the film is transferred from the drying step to the heat treatment step, and the film is heat treated at a temperature higher than the drying temperature. (° C) and weight swelling degree W
A method for producing a polyvinyl alcohol-based film having a product T × W (° C.%) of (%) of 13,000 or more is provided.

A polyvinyl alcohol film obtained by the method of the present invention (hereinafter, polyvinyl alcohol is referred to as PV
A, a polyvinyl alcohol film is abbreviated as PVA film) has a product T × W (° C.%) of hot water cutting temperature T (° C.) and weight swelling degree W (%) of 13000 or more, preferably 14000. As described above, more preferably 15000 or more. The value of this T × W is 13
If it is less than 000, it may not be possible to sufficiently exhibit the high polarization property and / or the high durability or both of them when used as a polarizing film. The method of measuring the weight swelling degree W (%) here is as follows. That is, 3 g of the sample film was cut into a width of about 3 mm, immersed in warm water at 30 ° C. for 15 minutes, and then cut at 300 rp.
The sample weight after spin-drying at m for 5 minutes (W1) and the sample weight after drying it at 105 ° C for 16 hours (W2)
Then, the weight swelling degree W (%) is calculated by the following equation. Weight swelling degree W (%) = (W1) / (W2) × 100 (I) Further, the method for measuring the hot water cutting temperature T (° C.) is as follows. That is, 0.5 g for a sample with a width of 5 mm and a length of 15 cm.
A weight of / 10 μm is attached and suspended in water at a temperature of 40 ° C., then the water temperature is raised at a rate of 3 ° C./minute, and the hot water temperature when the sample is cut is taken as the hot water cutting temperature T (° C.). Ask.

In the method of the present invention, the PVA-based film is prepared by using a film-forming machine having a single-sided drying type drying device composed of one rotating body and a heat treatment device directly connected to the drying device. When a PVA-based film is formed from the film, when the moisture content of the film reaches 2 to 15% by weight, preferably 3 to 10% by weight, the film is transferred from a drying step to a heat treatment step, and It is obtained by heat treatment at a high temperature. In the present invention, as the drying device, a one-sided drying type constituted by one rotating body is used. Specifically, a rotary heating drum, a rotary heating belt (or roll), or the like can be used. In these drying devices, the PVA-based resin aqueous solution film is not dried on the drum side (drum surface) and is opposite to the drum. Will be done only on the free side of. It is advantageous that the rotary heating drum or the periphery of the rotary heating drum is covered with a hot air chamber and hot air heating is used together, so that the drying efficiency is improved. The present invention requires a heat treatment device directly connected to the drying device, and a heating roll or a hot air oven can be used for this heat treatment device. The drying temperature in the above-mentioned drying step is not particularly limited, but is usually 60 to 140 ° C,
It is preferably 70 to 120 ° C. The heat treatment in the heat treatment step is not particularly limited as long as it is higher than the drying temperature, and may be appropriately selected according to various situations, but is usually 80 to 140 ° C., preferably 100 to 1
It is 30 ° C.

Next, an example of a preferred embodiment for producing a PVA-based film by the method of the present invention will be described. First, a PVA-based resin aqueous solution is dried in a drying device by a known method such as a casting method or an extrusion casting method. A PVA-based resin aqueous solution film is formed by casting on a surface, for example, the surface of a metal rotary heating drum. The PVA-based resin aqueous solution film immediately enters a drying process, and the free surface side (the surface opposite to the drum) of the aqueous solution film is dried first. As the drying proceeds, the average moisture content of the entire film is 2 to 15% by weight, preferably 3 to 10%.
When the weight% is reached, the heat treatment step is performed. It is necessary to set the heating temperature during the heat treatment so that the PVA-based film temperature in the heat treatment step is higher than the PVA-based film temperature in the drying step. Since the PVA-based film usually reaches the absolute dryness after the heat treatment process, the PVA film to which the desired water content has been imparted is subjected to the humidity conditioning treatment thereafter.
A system film is obtained.

P when transferring from the drying step to the heat treatment step
When the water content of the VA-based film is less than 2% by weight or more than 15% by weight, neither of them has high polarization and high durability, and the object of the present invention cannot be achieved. The reason why the PVA film thus obtained exhibits high polarization characteristics is presumed as follows. That is, the PVA
When the film is transferred from the drying process to the heat treatment process, the water content (total thickness average) of the entire film is 2 to 15% by weight, but it differs depending on the position in the thickness direction, and the dryness progresses on the free surface side. There is almost no water, and much water is unevenly distributed on the drum surface side. When such a film enters the heat treatment step, crystallization on the drum surface side, which has a high moisture content, progresses, but crystallization on the free surface side, which has almost no moisture, progresses little. As a result, the film has low crystallinity and therefore has one side with high weight swelling (free side) and the other side with high crystallinity and high hot water cutting temperature (drum side). As a result, it is estimated that the product of the weight swelling degree of the PVA-based film and the hot water cutting temperature was increased.
In addition, when a polarizing film is formed from this film, excellent dyeing properties on one side, orientation at the time of stretching, and excellent hot water resistance on the other side, that is, excellent high-temperature stretchability, are combined, resulting in high polarization. It is presumed that the characteristics and high durability are exhibited.

The PVA-based film thus obtained is suitable for various uses, and is most suitable for a polarizing film. To produce a polarizing film using this PVA-based film, a known method, for example, dyeing with a PVA-based film,
It is possible to use a method of producing a polarizing film by performing stretching, treatment with a boric acid compound, etc., and then drying. The dyeing may be performed before, during or after the uniaxial stretching, and as the dye, for example, iodine-potassium iodide or a dichroic dye may be used. The stretching may be carried out in warm water, or the film after absorbing water may be carried out in air, and the stretching temperature is usually 30 ° C. or higher, preferably 40 ° C. or higher, more preferably 50 ° C. or higher. Furthermore, in the boric acid compound treatment,
You may mix an iodine compound in a boric acid compound bath. The polarizing film thus obtained is usually laminated with various supports such as cellulose triacetate on both outer surfaces thereof.

The raw material PVA resin that can be used in the present invention is a so-called ordinary PVA produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate.
In addition, unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, modified polyvinyl alcohol copolymerized with less than about 15 mol% of α-olefin having 2 to 30 carbon atoms, or polyvinyl formal or polyvinyl acetoacetal Examples thereof include polyvinyl acetals such as polyvinyl butyral and ethylene-vinyl alcohol copolymers having an ethylene unit content of 20 mol% or more.

As the PVA-based resin in the present invention, those having a degree of polymerization of 500 or more, preferably 2400 or more, more preferably 4000 or more are preferable because they have excellent polarization characteristics and durability. The degree of saponification of the PVA-based resin is 90 mol% or more, preferably 95 mol% or more, more preferably 98 mol% or more, which is excellent in durability and desirable. As the solvent for producing the PVA-based film in the present invention, water, an organic solvent, or a mixture thereof can be used. However, the present invention is a water-only solvent system having high polarization characteristics and high durability. The feature is that a system film can be obtained, and naturally, it is advantageous to use a water solvent which is excellent in safety and economy. The thickness of the PVA-based film of the present invention is usually 5 to 150 μm, preferably 30 to
It is selected in the range of 100 μm. In addition, various polyol plasticizers such as glycerin and additive components such as nonionic, anionic and cationic surfactants may be appropriately added to the PVA-based film, if desired.

[0013]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. In addition, in Examples and Comparative Examples, the moisture content of the film is the weight of the film sample before drying (G
1) When the weight after vacuum drying at 50 ° C. for 16 hours is (G2), the moisture content of the film (%) = (G1−G2) / G1 × 100 ... (II). Further, common manufacturing conditions in the polarizing film manufacturing process are as follows. That is, the dye concentration of the dyeing bath was fixed at an iodine / potassium iodide weight ratio of 1/10, and the iodine concentration was appropriately selected within the range of 1 to 20 g / liter to prepare a polarizing film having a single transmittance of about 43%. It was collected. The boric acid concentration in the boric acid bath was set to 4% by weight, and boric acid was added to the drawing bath so that the concentration was 4% by weight. Dry 5
It was performed with hot air at 0 ° C.

In the present invention, the dichroic ratio is used to express the polarization performance. This dichroic ratio is calculated from the light transmittance (single transmittance) Ts (%) of the polarizing film and the polarization degree P (%) according to the formula: dichroic ratio = log (Ts / 100-Ts × P / 10000) / log ( Ts / 100 + Ts × P / 10000) ・ ・ ・ (III) Further, the durability was evaluated by using a polarizing plate obtained by adhering cellulose triacetate having a thickness of 80 μm on both sides of a polarizing film using a PVA adhesive, in an atmosphere of a temperature of 60 ° C. and a relative humidity (RH) of 90%. It was performed by measuring the single-body transmittance and the degree of polarization after standing for 200 hours underneath.

Example 1 A rotary heating metal drum was prepared by using a film-forming machine comprising an extruder, a die, a single rotary heating metal drum whose periphery is covered with a hot air oven, and a hot air oven type heat treatment device. Temperature 7
5 ℃, hot air temperature 75 ℃, heat treatment equipment hot air temperature 12
It was set to 0 ° C. A pellet consisting of 41 parts by weight of PVA having a degree of polymerization of 1700 and a degree of saponification of 99.9 mol%, 54 parts by weight of water and 5 parts by weight of glycerin was cast on a rotary heating metal drum and dried and heat-treated continuously to obtain a P film having a thickness of 75 μm.
A VA film was created. The weight swelling degree of the obtained film was 210% and the hot water cutting temperature was 65 ° C., and therefore the product of the weight swelling degree and the hot water cutting temperature was 13650. The water content of the film taken between the drying device and the heat treatment device was 4.2% by weight.

Application Example 1 The film obtained in Example 1 was sequentially subjected to dyeing, stretching, boric acid treatment and drying to form a polarizing film. Maximum water temperature at which stretching is possible (hereinafter abbreviated as maximum water temperature during stretching)
The film was uniaxially stretched under the conditions of 35 ° C. and the upper limit of draw ratio (hereinafter abbreviated as upper limit draw ratio) of 5.3 times. The obtained polarizing film has a single transmittance of 43.3% and a polarization degree of 98.8%.
The dichroic ratio was 35.1, which was excellent in polarization performance.

Example 2 Using the same film forming machine as in Example 1, the temperature of the rotary heating metal drum was set to 90 ° C., the hot air temperature was set to 90 ° C., and the hot air temperature of the heat treatment apparatus was set to 120 ° C. Saponification degree of polymerization degree 4000 9.
Pellet consisting of 35 parts by weight of 6 mol% PVA, 60 parts by weight of water and 5 parts by weight of glycerin was cast on a rotating heated metal drum, dried and heat-treated continuously to give a film thickness of 7
A 5 μm PVA film was created. The weight swelling degree of the obtained film was 215%, the hot water cutting temperature was 70 ° C., and therefore the product of the weight swelling degree and the hot water cutting temperature was 15050. The water content of the film taken between the drying device and the heat treatment device was 8.5% by weight.

Application Example 2 The film obtained in Example 2 was dyed, stretched, treated with boric acid and dried in order to prepare a polarizing film. The film was uniaxially stretched under the conditions of an upper limit water temperature of 50 ° C. and an upper limit draw ratio of 5.0 times. The obtained polarizing film had a simple transmittance of 43.2%, a polarization degree of 99.7%, and a dichroic ratio of 45.0, and had excellent polarization performance. After the durability test of this polarizing film, the single transmittance was 47.3%, the degree of polarization was 93.6%, and the dichroic ratio was 39.7, showing excellent durability.

Comparative Example 1 Using the same film forming machine as in Example 1, the rotary heating metal drum temperature was set to 70 ° C., the hot air temperature was set to 70 ° C., and the hot air temperature of the heat treatment device was set to 150 ° C. The same pellets as in Example 1 were cast on a rotary heating metal drum, and dried and heat-treated continuously to prepare a PVA film having a film thickness of 75 μm. The weight swelling degree of the obtained film was 163%, the hot water cutting temperature was 74 ° C., and therefore the product of the weight swelling degree and the hot water cutting temperature was 12062. The water content of the film taken between the drying device and the heat treatment device was 4.4% by weight.
Next, this film was sequentially subjected to dyeing, stretching, boric acid treatment and drying to form a polarizing film. Maximum water temperature during stretching 50
The film was uniaxially stretched under conditions of a temperature of ℃ and a maximum draw ratio of 4.4 times. The obtained polarizing film has a single transmittance of 42.6% and a polarization degree of 94.6.
%, The dichroic ratio was 20.1, and the polarization performance was poor.

Comparative Example 2 Using the same film forming machine as in Example 1, the rotating heating metal drum temperature was set to 85 ° C., the hot air temperature was set to 85 ° C., and the hot air temperature of the heat treatment device was set to 120 ° C. The same pellets as in Example 1 were cast on a rotary heating metal drum, and dried and heat-treated continuously to prepare a PVA film having a film thickness of 75 μm. The weight swelling degree of the obtained film was 205%, the hot water cutting temperature was 62 ° C., and therefore the product of the weight swelling degree and the hot water cutting temperature was 12710. The water content of the film taken between the drying device and the heat treatment device was 0.8% by weight.
Next, this film was sequentially subjected to dyeing, stretching, boric acid treatment and drying to form a polarizing film. Maximum water temperature during stretching 30
The film was uniaxially stretched at a temperature of ℃ and a maximum draw ratio of 4.5. The obtained polarizing film has a single transmittance of 43.0% and a polarization degree of 92.6.
%, The dichroic ratio was 18.3, and the polarization performance was inferior.

Comparative Example 3 Using the same film forming machine as in Example 1, the rotary heating metal drum temperature was set to 50 ° C., the hot air temperature was set to 50 ° C., and the hot air temperature of the heat treatment device was set to 120 ° C. The same pellets as in Example 1 were cast on a rotary heating metal drum, and dried and heat-treated continuously to prepare a PVA film having a film thickness of 75 μm. The weight swelling degree of the obtained film was 180%, the hot water cutting temperature was 67 ° C., and therefore the product of the weight swelling degree and the hot water cutting temperature was 12060. The water content of the film taken between the drying device and the heat treatment device was 20.6% by weight. Next, this film was sequentially subjected to dyeing, stretching, boric acid treatment and drying to form a polarizing film. The film was uniaxially stretched under the conditions of an upper limit water temperature of 35 ° C. and an upper limit stretch ratio of 4.5 times.
The resulting polarizing film has a single transmittance of 44.3% and a polarization degree of 93.
The dichroic ratio was 8%, and the dichroic ratio was 23.6, which was inferior in polarization performance.

Comparative Example 4 Using the same film forming machine as in Example 1, the rotary heating metal drum temperature was set to 90 ° C. and the hot air temperature was set to 90 ° C., the same pellets as in Example 2 were used for casting, and only drying was performed. Go to 7
An unheated PVA film of 5 μm was obtained. The water content of this film was 8.5% by weight. After leaving this film roll for 1 day, it was heat-treated using the same heat-treatment device as in Example 1 to obtain a heat-treated PVA film. The obtained film had a weight swelling degree of 177% and a hot water cutting temperature of 71.
℃, therefore the product of the weight swelling degree and the hot water cutting temperature is 12
It was 567. Next, this film was sequentially subjected to dyeing, stretching, boric acid treatment and drying to form a polarizing film. The film was uniaxially stretched under the conditions of the upper limit water temperature of 50 ° C. and the upper limit stretch ratio of 4.4 times. The single transmittance of the obtained polarizing film is 43.6%,
The polarization degree was 94.0% and the dichroic ratio was 21.7, which was inferior to the polarization performance.

[0023]

According to the method of the present invention, a PVA-based film having various excellent physical properties, particularly a PVA-based film excellent in the production of a polarizing film having extremely excellent polarization characteristics and durability, can be easily obtained. The polarizing film obtained from this PVA-based film can be sufficiently applied to the LCD field for which characteristics higher than those of the conventional polarizing film are required, such as those for personal computers, word processors, and televisions.

Claims (1)

[Claims] 1. When manufacturing a polyvinyl alcohol-based film from a polyvinyl alcohol-based resin aqueous solution film using a film-forming machine having a single-sided drying type drying device composed of one rotating body and a heat treatment device directly connected to the drying device. A hot water cutting temperature T (° C.), characterized in that the film is transferred from the drying step to the heat treatment step when the moisture content of the film reaches 2 to 15% by weight, and heat treatment is performed at a temperature higher than the drying temperature. Product T × W with the degree of weight swelling W (%)
A method for producing a polyvinyl alcohol-based film having a (° C ·%) of 13,000 or more.