JP3283564B2 - Method for producing polyvinyl alcohol-based film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyvinyl alcohol film used for forming a polarizing film . More specifically, the present invention relates to a method for efficiently producing a polyvinyl alcohol-based film used for producing a polarizing film having excellent polarization performance and durability.

[0002]

2. Description of the Related Art Conventionally, a polyvinyl alcohol film is usually prepared 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 of having 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 from small devices such as calculators and watches in the early days to high quality and high reliability such as laptop personal computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, and liquid crystal televisions. Equipment. Under these circumstances, there is a demand for a polarizing film having both more excellent polarization characteristics and durability than conventional polarizing films. Therefore, in order to meet such demands, for example, a method using a special dye, a method for producing a polyvinyl alcohol film as a base material by forming a gel from an organic solvent solution, and the like have been proposed. However, these methods have drawbacks such as difficulty in producing dyes, and the use of an organic solvent inevitably increases costs in terms of safety and equipment maintenance.

[0003]

SUMMARY OF THE INVENTION Under the above circumstances, the present invention provides a method for efficiently producing a polyvinyl alcohol-based film used for producing a polarizing film having excellent polarization characteristics and durability. It was made for the purpose of providing.

[0004]

Means for Solving the Problems The present inventor has conducted intensive studies to achieve the above object, and as a result, has found a single-sided drying type drying apparatus composed of one rotating body and a heat treatment apparatus directly connected thereto. Using a film forming machine having a film, a polyvinyl alcohol-based resin aqueous solution film is subjected to a drying treatment until a constant moisture content is obtained, and then subjected to a heat treatment at a higher temperature, whereby the product of the hot water cutting temperature and the weight swelling degree is obtained. A polyvinyl alcohol-based film having a certain value or more was obtained, and it was found that 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, the present invention uses a film forming machine having a one-sided drying type drying device composed of one rotating body and a heat treatment device directly connected to the drying device to convert a polyvinyl alcohol-based resin aqueous solution film into a polyvinyl alcohol-based film. Wherein the film is transferred from a drying step to a heat treatment step when the moisture content of the film reaches 2 to 15% by weight, and is subjected to a heat treatment at a temperature higher than the drying temperature. (° C) and weight swelling degree W
(%) And the product T × W (° C.%) are 13,000 or more
An object of the present invention is to provide a method for producing a polyvinyl alcohol-based film used for producing a polarizing film .

The polyvinyl alcohol-based film obtained by the method of the present invention (hereinafter, polyvinyl alcohol is referred to as PV
A, a polyvinyl alcohol-based film is abbreviated as a PVA-based film), the product T × W (° C.%) of the hot water cutting temperature T (° C.) and the degree of weight swelling W (%) is 13,000 or more, preferably 14000. It is necessary to be at least 15,000 . The value of this T × W 1300
If it is less than 0, high polarization characteristics and / or high durability or both characteristics may not be sufficiently exhibited when a polarizing film is formed. The method of measuring the degree of weight swelling W (%) is as follows. That is, 3 g of a sample film was cut into a width of about 3 mm, immersed in warm water of 30 ° C. for 15 minutes, and centrifuged and dehydrated at 300 rpm for 5 minutes to obtain a sample weight of (W1).
Assuming that the sample weight after drying at 05 ° C. for 16 hours is (W2), the weight swelling degree W (%) is obtained by the following equation. Weight swelling degree W (%) = (W1) / (W2) × 100
(I) The method of measuring the hot water cutting temperature T (° C.) is as follows. That is, a sample having a width of 5 mm and a length of 15 cm is attached with a weight of 0.5 g / 10 μm and suspended in water at a temperature of 40 ° C., and then the water temperature is raised at a rate of 3 ° C./min. Hot water temperature, hot water cutting temperature T
(° C).

[0007] In the method of the present invention, the PVA-based film is prepared by using a PVA-based resin aqueous solution by using a film-forming machine having a single-side drying type drying apparatus composed of one rotating body and a heat treatment apparatus directly connected thereto. When a PVA-based film is formed from the film, the film is transferred from the drying step to the heat treatment step when the water content of the film reaches 2 to 15% by weight, preferably 3 to 10% by weight, and Obtained by heat treatment at a high temperature. In the present invention, a single-sided drying type constituted by one rotating body is used as a drying device. Specifically, a rotary heating drum, a rotary heating belt (or a roll), or the like can be used. In these drying devices, drying of the PVA-based resin aqueous solution film is not performed on the drum side (drum surface), but is performed on the opposite side of the drum. It only takes place on the free side. When 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 in combination, the drying efficiency is advantageously improved. The present invention requires a heat treatment device directly connected to a drying device, and a heat roll or a hot blast stove 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,
Preferably it is 70-120 degreeC. Also, 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 depending on various situations, but is usually from 80 to 140 ° C., preferably from 100 to 1 ° C.
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 apparatus 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, a metal rotary heating drum surface. The PVA-based resin aqueous solution film immediately enters a drying process, and drying of the free surface side (the opposite side to the drum) of the aqueous solution film is preceded. Drying proceeds, and the average moisture content of the entire film is 2 to 15% by weight, preferably 3 to 10%.
When the weight% is reached, the process proceeds to a heat treatment step. 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. After the heat treatment step, the PVA-based film usually reaches an absolutely dry state.
A base film is obtained.

[0009] P when transferring from the drying step to the heat treatment step
When the moisture content of the VA-based film is less than 2% by weight or more than 15% by weight, a film having high polarization and high durability cannot be obtained, and the object of the present invention cannot be achieved. The reason why the thus obtained PVA-based film exhibits high polarization characteristics is presumed as follows. That is, the PVA
When the system film moves from the drying step to the heat treatment step, the moisture content of the entire film (average of the total thickness) is 2 to 15% by weight, but differs in the position in the thickness direction. 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 having a high moisture content proceeds, but crystallization on the free surface side having little moisture hardly progresses. As a result, the film has one surface (free surface side) having low crystallinity and therefore a high degree of weight swelling, and the other surface (drum surface side) having high crystallinity and high hot water cutting temperature. As a result, it is estimated that the product of the degree of weight swelling of the PVA-based film and the hot water cutting temperature was increased.
In addition, when a polarizing film is prepared from this film, high dyeing properties and orientation during stretching are combined with excellent hot water resistance, that is, excellent high temperature stretchability on one side, resulting in high polarization. It is estimated that characteristics and high durability are exhibited.

[0010] The PVA-based fill-time obtained in this way
In order to manufacture a polarizing film by using a known method, for example, P
A method in which a VA-based film is dyed, stretched, treated with a boric acid compound, and then dried to form a polarizing film can be used. Dyeing may be performed before, during or after uniaxial stretching, and as a dye,
For example, iodine-potassium iodide or a dichroic dye can be used. The stretching may be performed in warm water or the film after water absorption may be performed in the air. The stretching temperature is usually 30 ° C. or higher, preferably 40 ° C. or higher, more preferably 50 ° C. or higher. Further, in the boric acid compound treatment, an iodine compound may be mixed in the boric acid compound bath. The polarizing film thus obtained is usually laminated with various supports, for example, cellulose triacetate, on both outer surfaces thereof.

The raw material PVA-based resin usable in the present invention is a so-called ordinary PVA produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate.
A modified polyvinyl alcohol copolymerized with an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, and the like, in an amount of less than about 15 mol%, or polyvinyl formal or polyvinyl acetoacetal And polyvinyl acetal such as polyvinyl butyral, and an ethylene-vinyl alcohol copolymer 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 suitable because they have excellent polarization characteristics and durability. In addition, the degree of saponification of the PVA-based resin is preferably at least 90 mol%, more preferably at least 95 mol%, more preferably at least 98 mol%, because it is excellent in durability and desirable. As the solvent for preparing the PVA-based film in the present invention, any of water, an organic solvent and a mixture thereof can be used. However, the present invention relates to a water-only solvent-based PVA having high polarization characteristics and high durability. A characteristic feature is that a base film can be obtained. 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 150 μm.
It is selected in the range of 100 μm. Further, to the PVA-based film, various polyol-based plasticizers such as glycerin, and additional components such as nonionic, anionic and cationic surfactants may be appropriately added as required.

[0013]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. In Examples and Comparative Examples, the moisture content of the film was determined by the weight (G) of the film sample before drying.
1) Assuming that the weight after vacuum drying at 50 ° C. for 16 hours is (G2), the moisture content (%) of the film can be obtained by the following equation: (G1−G2) / G1 × 100 (II) Common manufacturing conditions in the polarizing film manufacturing process are as follows. That is, the dye concentration of the dyeing bath is fixed at a weight ratio of iodine / potassium iodide of 1/10, and the iodine concentration is appropriately selected within a range of 1 to 20 g / liter to obtain a polarizing film having a single transmittance of about 43%. Collected. The concentration of boric acid in the boric acid bath was 4% by weight, and boric acid was added to the stretching bath so as to have a concentration of 4% by weight. Drying is 5
The test was performed with hot air at 0 ° C.

In the present invention, the dichroic ratio is used to express the polarization performance. The dichroic ratio is calculated from the light transmittance (single transmittance) Ts (%) of the polarizing film and the degree of polarization P (%) using the formula: dichroic ratio = log (Ts / 100-Ts × P / 10000) / log ( Ts / 100 + Ts × P / 10000) ··· Determined in (III). The durability was evaluated by bonding a polarizing plate obtained by bonding a 80 μm-thick cellulose triacetate to both surfaces of a polarizing film using a PVA-based adhesive at a temperature of 60 ° C. and a relative humidity (RH) of 90%. The measurement was performed by measuring the single transmittance and the degree of polarization after being left for 200 hours.

EXAMPLE 1 A rotary heating metal drum was formed by using a film forming machine comprising a single rotary heating metal drum covered with an extruder, a die and a hot stove and a hot stove type heat treatment apparatus. Temperature 7
5 ° C, hot air temperature 75 ° C, heat air temperature of heat treatment equipment 12
It was set to 0 ° C. A pellet composed of 41 parts by weight of PVA having a degree of polymerization of 1700 and a saponification degree 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, dried and heat-treated continuously, and a 75 μm-thick P
A VA film was made. The obtained film had a weight swelling degree of 210% and a hot water cutting temperature of 65 ° C., and therefore, the product of the weight swelling degree and the hot water cutting temperature was 13650. The moisture content of the film collected 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. Upper limit water temperature at which stretching is possible (hereinafter abbreviated as upper limit water temperature during stretching)
The film was uniaxially stretched under the conditions of 35 ° C. and 5.3 times the maximum stretch ratio at which stretching was possible (hereinafter abbreviated as the upper limit stretch ratio). The obtained polarizing film has a single transmittance of 43.3%, a degree of polarization of 98.8%,
The dichroic ratio was 35.1, indicating excellent 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 temperature of hot air was set to 90 ° C., and the temperature of hot air of the heat treatment apparatus was set to 120 ° C. Degree of saponification with polymerization degree of 4000
A pellet composed of 35 parts by weight of PVA of 6 mol%, 60 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, and a film thickness of 7% was obtained.
A 5 μm PVA film was made. The weight swelling degree of the obtained film was 215%, the hot water cutting temperature was 70 ° C., and the product of the weight swelling degree and the hot water cutting temperature was 15050. The moisture content of the film collected between the drying device and the heat treatment device was 8.5% by weight.

Application Example 2 The film obtained in Example 2 was sequentially subjected to dyeing, stretching, boric acid treatment and drying to form a polarizing film. Uniaxial stretching was performed under the conditions of an upper limit water temperature of 50 ° C. and an upper limit stretch ratio of 5.0 at the time of stretching. The polarizing film obtained had a single transmittance of 43.2%, a degree of polarization of 99.7%, and a dichroic ratio of 45.0, showing excellent polarizing performance. After the durability test, the polarizing film had a single transmittance of 47.3%, a degree of polarization of 93.6%, and a dichroic ratio of 39.7, indicating excellent durability.

Comparative Example 1 Using the same film forming machine as in Example 1, the temperature of the rotary heating metal drum was set at 70 ° C., the temperature of hot air was set at 70 ° C., and the temperature of hot air of the heat treatment apparatus was set at 150 ° C. The same pellets as in Example 1 were cast on a rotary heating metal drum, and drying and heat treatment were continuously performed to form a PVA film having a thickness of 75 μm. The degree of weight swelling 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 moisture content of the film collected between the drying device and the heat treatment device was 4.4% by weight.
Next, the film was sequentially dyed, stretched, treated with boric acid, and dried to form a polarizing film. Maximum water temperature during stretching 50
The film was uniaxially stretched under the conditions of ° C and an upper limit stretching ratio of 4.4 times. The obtained polarizing film had a single transmittance of 42.6% and a degree of polarization of 94.6.
%, The dichroic ratio was 20.1, indicating poor polarization performance.

Comparative Example 2 Using the same film forming machine as in Example 1, the temperature of the rotary heating metal drum was set to 85 ° C., the temperature of hot air was set to 85 ° C., and the temperature of hot air of the heat treatment apparatus was set to 120 ° C. The same pellets as in Example 1 were cast on a rotary heating metal drum, and drying and heat treatment were continuously performed to form a PVA film having a thickness of 75 μm. The weight swelling degree of the obtained film was 205%, and the hot water cutting temperature was 62 ° C. Therefore, the product of the weight swelling degree and the hot water cutting temperature was 12,710. The moisture content of the film collected between the drying device and the heat treatment device was 0.8% by weight.
Next, the film was sequentially dyed, stretched, treated with boric acid, and dried to form a polarizing film. Maximum water temperature during stretching 30
The film was uniaxially stretched at a temperature of 4.5 ° C. and an upper limit of 4.5 times. The obtained polarizing film has a single transmittance of 43.0% and a degree of polarization of 92.6.
%, And the dichroic ratio was 18.3, indicating poor polarization performance.

Comparative Example 3 Using the same film forming machine as in Example 1, the temperature of the rotary heating metal drum was set to 50 ° C., the temperature of hot air was set to 50 ° C., and the temperature of hot air of the heat treatment apparatus was set to 120 ° C. The same pellets as in Example 1 were cast on a rotary heating metal drum, and drying and heat treatment were continuously performed to form a PVA film having a thickness of 75 μm. The weight swelling degree of the obtained film was 180%, the hot water cutting temperature was 67 ° C., and the product of the weight swelling degree and the hot water cutting temperature was 12060. The moisture content of the film collected between the drying device and the heat treatment device was 20.6% by weight. Next, the film was sequentially dyed, stretched, treated with boric acid, and dried 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 at the time of stretching.
The obtained polarizing film has a single transmittance of 44.3% and a degree of polarization of 93.
The dichroic ratio was 83.6% and the polarization performance was inferior.

Comparative Example 4 Using the same film forming machine as in Example 1, the temperature of the rotary heating metal drum was set to 90 ° C., the temperature of the hot air was set to 90 ° C., and the same pellets as in Example 2 were cast. Go to film thickness 7
A 5 μm unheated PVA film was obtained. The moisture content of this film was 8.5% by weight. After leaving this film roll for one day, it was subjected to heat treatment using the same heat treatment apparatus as in Example 1 to obtain a heat-treated PVA film. The weight swelling degree of the obtained film was 177%, and the hot water cutting temperature was 71%.
° C, thus the product of the degree of weight swelling and the hot water cutting temperature is 12
567. Next, the film was sequentially dyed, stretched, treated with boric acid, and dried to form a polarizing film. Uniaxial stretching was performed under the conditions of an upper limit water temperature of 50 ° C. and an upper limit stretching ratio of 4.4 times during stretching. The single transmittance of the obtained polarizing film is 43.6%,
The degree of polarization 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, good PVA-based film can be easily obtained in the creation of an extremely excellent polarization film of the polarization property and durability. The polarizing film obtained from the PVA-based film can be sufficiently applied to the LCD field, for example, for a personal computer, a word processor, a television, and the like, which requires more characteristics than conventional polarizing films.

Claims (1)

(57) [Claims] 1. A method for producing 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 constituted by one rotating body and a heat treatment device directly connected thereto. 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 heat treatment is performed at a temperature higher than the drying temperature. Product T × W with weight swelling degree W (%)
(° C.%) is 13000 or more, for making polarizing film
Method for producing a polyvinyl alcohol film which are.