KR101257377B1 - Polyvinyl alcohol-based polymeric film and method for preparing same using ir heater - Google Patents

Abstract

Supplying a polyvinyl alcohol raw material solution through a die onto a casting drum, predrying and stripping using a stripper roll, and then passing through several drying rolls, between the die and the casting drum, between the stripper roll and the drying roll, And a method of manufacturing a polyvinyl alcohol-based polymer film further including mounting and operating an IR heater at at least one position of the drying roll passing section, which is excellent in drying efficiency and can be increased in line speed and width. It is possible to produce films with uniform directional thickness and very small retardation.

Description

POLYVINYL ALCOHOL-BASED POLYMERIC FILM AND METHOD FOR PREPARING SAME USING IR HEATER}

The present invention relates to a polyvinyl alcohol-based polymer film minimized retardation, a manufacturing method thereof, and a polarizing film using the same.

Conventional polyvinyl alcohol (PVA) films generally cast a film raw material containing a solution or molten polyvinyl alcohol onto a drum (casting drum) or belt through a die and then heat the drum or belt or air chamber The moisture content (water content) was adjusted by secondary drying using a multi-stage drying roll and a floating dryer, followed by primary drying using a multistage drying roll and the like (Korea Patent Publication Nos. 2010-123801 and 2007-83925).

However, in the method of controlling the moisture content of the polyvinyl alcohol film, a widthwise necking phenomenon due to the stretching stress occurs (see FIG. 2) until the resin discharged from the die is seated on the casting drum. Thickening the end caused a difference in the widthwise physical properties and caused a decrease in the end use rate.

In addition, conventional methods require large diameter casting drums and a large number of dry rolls. However, there is a disadvantage in that it is difficult to manufacture industrially large casting drums in addition to the high facility cost when the size of the casting drum increases. In addition, when the number of dry rolls increases, in addition to the process price problem, the adhesive surface of the film and the roll increases, so that scratches may occur on the surface of the film or non-uniform widthwise shrinkage may occur, thereby increasing the width retardation.

Republic of Korea Patent Publication No. 2010-123801 Republic of Korea Patent Publication No. 2007-83925

Therefore, an object of the present invention is to solve the conventional problems as described above and to produce a polyvinyl alcohol polymer film having a low retardation, a polyvinyl alcohol polymer film produced by such a method, and a polarizing film using the same To provide.

In order to achieve the above object, the present invention comprises the steps of: a) supplying a polyvinyl alcohol raw material solution through an extruder and a die on a casting drum and predrying; b) peeling the pre-dried film from the casting drum using a stripper roll and then transferring to the drying roll; And c) multistage drying the conveyed film while passing through several drying rolls, wherein between the die of the step a) and the casting drum (A), between the stripper roll of the step b) and the drying roll (B) And an IR heater mounted at at least one position in the drying roll passing section (C) of step c), and operating under the temperature condition of the following Equations 1 to 3, of the polyvinyl alcohol-based polymer film Provide the manufacturing method:

Equation 1: 30 + 50 x s <Ta <150 + 50 x s;

Equation 2: 50 × s ≦ Tb ≦ 100 + 50 × s; And

Equation 3: 50 x s ≤ Tc ≤ 50 + 50 x s,

In Equations 1 to 3, Ta, Tb, and Tc are the temperatures (° C.) of the heater operated at the A, B, and C positions, respectively, and s is the line speed (m / min) in steps a) to c). And 0.5 ≦ s ≦ 4.

The present invention also provides a polyvinyl alcohol-based polymer film prepared by the above method, and a polarizing film obtained by dyeing and stretching the same and then drying the same.

According to the method of the present invention, it is possible to obtain a film having a uniform thickness in the width direction by reducing necking phenomenon, thereby increasing the end use ratio and reducing the width property difference. In addition, when the film is dried, the temperature difference in the thickness direction decreases, so that the drying variation in the thickness direction is reduced, so that the physical properties of the film can be uniform, and the drying efficiency is increased, thereby reducing the width of the casting drum or the number of drying rolls. The speed is increased to increase the production rate. As a result, according to the method of the present invention, a film having a very low in-plane retardation and thickness direction retardation can be produced.

1 is a process schematic showing one embodiment of the process of the invention (A to C: IR heater running section, 10: extruder, 20: die, 30: casting drum, 40: air chamber, 50: stripper roll, 60 : Drying roll, 70: floating dryer, 80: cooling roll, 90: winding roll).
2 illustrates a necking phenomenon that may occur during the film manufacturing process.

One embodiment of the process of the invention is shown in FIG. 1 as a process schematic.

The manufacturing method of the polyvinyl alcohol polymer film of the present invention

a) A raw material solution composed of polyvinyl alcohol, a plasticizer, a releasing agent and a solvent having a saponification degree of 99 mol% or more and a polymerization degree of 1700 or more is supplied onto the casting drum 30 through the extruder 10 and the die 20 and the air chamber 40 Pre-drying with and forming a film;

b) peeling the film from the casting drum 30 using the stripper roll 50 and then transferring to the drying roll 60; And

c) performing a step of drying the transferred film while passing through several drying rolls 60,

(A) between the die 20 of the step a) and the casting drum 30,

(B) between the stripper roll 50 and the drying roll 60 of step b), and

In the drying roll 60 passing section (C) of the step c), the IR heater is operated at at least one position.

In this case, in the A position, the IR heater may be mounted on one side or both sides of the sheet-shaped raw material solution discharged from the die, and in the B and C positions, the IR heater may be mounted on the top, bottom, or of the film. The upper and lower parts may be mounted respectively.

IR heaters mounted at the A, B, and C positions are operated under the temperature conditions of the following Equations 1 to 3:

Equation 1: 30 + 50 x s <Ta <150 + 50 x s;

Equation 2: 50 × s ≦ Tb ≦ 100 + 50 × s; And

Equation 3: 50 x s ≤ Tc ≤ 50 + 50 x s,

In Equations 1 to 3, Ta, Tb, and Tc are temperatures (° C.) of heaters mounted at positions A, B, and C, respectively, and s is line speed (m / min) in steps a) to c). And 0.5 ≦ s ≦ 4. Here, the line speed means the speed at which the raw material or the film under manufacture is transferred to the next step in the film manufacturing process. Increasing the drying capacity of the plant can result in faster line speeds.

When the temperature of each IR heater is lower than the above range, drying of the film may not be sufficient, and the thickness deviation and phase difference may be large. Also, when the temperature of each IR heater is higher than the above range, the moisture content becomes too small so that the film may Sticking can occur and as a result staining can occur.

Preferably, the IR heater may be operated at a temperature of 80 to 200 ° C. for a length section of 10 to 20 mm in the A position, and 50 to 150 ° C. for a length section of 200 to 1000 mm in the B position. The IR heater may be operated at a temperature, and the IR heater at a temperature of 50 to 100 ° C. may be operated for a length section of 200 to 1500 mm in the C position.

The IR heater at the A position serves as a preheater before the resin discharged from the die is seated on the casting roll. As a result, necking can be reduced by giving heat to the raw material solution discharged from the die, and a film having a more uniform thickness in the width direction can be obtained, thereby increasing the end use ratio and decreasing the width property difference. Can be obtained. The important point at this location is to apply excess calories so that the moisture on the surface of the sheet does not boil. Therefore, an appropriate value should be selected in the above-described temperature range according to the experimental atmosphere. In addition, when the gap between the die and the casting roll is widened, physical properties such as retardation of the produced film may be deteriorated, so it is preferable to use only one IR heater in the A position to have a gap of about 10 to 20 mm.

The IR heater mounted at the B position serves to prevent a phenomenon that the film passing through the stripper roll 50 is cooled in the air before reaching the drying roll (C position) to decrease the drying efficiency. If the temperature of the initial drying roll is 50 ~ 70 ℃ about the film passed through the stripper roll is cooled in the air may cause a difference in physical properties in the thickness direction when it reaches the initial drying roll can be prevented. At this time, when drying the upper and lower parts of the film can be uniform drying in the film thickness direction. In addition, it is possible to reduce the moisture content of 1 to 3% at position B, thereby reducing the total number of dry rolls required.

Finally, the IR heater in the C position is to assist the role of the drying roll, because the surface contacting the film is limited when using only the drying roll occurs a slight temperature difference in the thickness direction, the temperature difference in the thickness direction by using an IR heater By decreasing the shrinkage difference (drying deviation) in the thickness direction, the physical properties of the film can be made uniform. The film passed through the drying roll has a water content of about 12-16% and can then be produced through a floating dryer to produce a film having a water content of about 2-5%. The film entering the drying roll with a water content of about 18 to 23% has a water content of 12 to 16% while passing through the drying roll. By using an IR heater, the number of drying rolls and the process length can be reduced. Moreover, the phenomenon which the film which enters the floating dryer which has a temperature condition of 80-120 degreeC receives high heat, and changes temperature rapidly from the surface can also be prevented.

In this way, by operating the IR heater in the A to C position, it is possible to reduce the width of the casting drum or the number of dry rolls and increase the line speed can be expected to increase the production rate.

The polyvinyl alcohol used in the present invention preferably has a saponification degree of 99 mol% or more, more preferably 99.90 mol% or more, in particular 99.95 mol% or more, and a polymerization degree of 1700 or more, more preferably 1700 to May be 5000. If the polyvinyl alcohol has a saponification degree of less than 99 mol%, the durability of the polarizing plate obtained by dyeing and stretching polyvinyl alcohol may be lowered. If the polyvinyl alcohol has a degree of polymerization of less than 1700, an extending process for manufacturing the polarizing plate is performed. In this case, sufficient stretching may not be possible and optical properties may be degraded.

The polyvinyl alcohol-containing raw material solution used in the present invention includes a plasticizer, a releasing agent and a solvent in addition to polyvinyl alcohol. Specifically, it is obtained by dissolving polyvinyl alcohol in a solvent, adding a plasticizer and a releasing agent, These are further kneaded in an extruder.

The polyvinyl alcohol may be used in an amount of 10 to 60% by weight, preferably 20 to 50% by weight, in consideration of uniform solubility.

As the solvent, dimethylsulfoxide, dimethylformamide, water, tetraethylene glycol, diethyltriamine or a mixture thereof may be used, and it may be used in an amount suitable for achieving uniform dissolution of polyvinyl alcohol .

The plasticizer serves to weaken hydrogen bonds in film formation to improve processability, and polyhydric alcohol compounds such as glycerin, ethylene glycol, polyethylene glycol, and mixtures thereof may be used as the plasticizer. In particular, it is preferable to use glycerin which has a good affinity for polyvinyl alcohol and can minimize the occurrence of optical deviation. The plasticizer may be used in an amount of 5 to 20 parts by weight based on 100 parts by weight of polyvinyl alcohol.

The release agent serves to improve the peelability at the time of peeling with the supporting film before winding the final dried film, and cationic surfactants, nonionic surfactants or mixtures thereof can be used as the release agent. Specific examples of the cationic surfactant include bisimidazolium methyl sulfate, dodecyl benzyl dimethyl ammonium chloride, tetradecyl methyl ammonium chloride, alkyltrimethyl ammonium methyl chloride, and mixtures thereof, and specific examples of the nonionic surfactant Alkyl ether types such as polyoxyethylene lauryl ether and polyoxyethylene oleyl ether; Alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine types such as polyoxyethylene lauryl amino ether; Alkylamide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; Alkanoylamide types such as lauric acid diethanolamide and oleic acid diethanolamide; Allyl phenyl ether types such as polyoxyethylene allyl phenyl ether; And mixtures thereof. The release agent may be used in an amount of 0.01 to 1 parts by weight based on 100 parts by weight of polyvinyl alcohol.

The plasticizer and the exfoliating agent that can be added to the solution are preferably added at the same temperature as the solution in consideration of the uniform dissolution and saponification degree of the polyvinyl alcohol required in the present invention. Do.

According to the method of the present invention, the polyvinyl alcohol-containing raw material solution of the above-described composition is extruded through an extruder 10, in particular a twin extruder, to completely remove bubbles generated during the dissolution process, and a casting drum ( 30) Prior to feeding on, the extrudate of the polyvinyl alcohol-containing stock solution may be passed through a filter, preferably for removing debris (not shown in FIG. 1). The temperature of the extruder may be between 95 and 100 &lt; 0 &gt; C.

Subsequently, an extrudate of the polyvinyl alcohol-containing raw material solution is supplied onto the casting drum 30 for coating or sheeting, wherein the raw material solution extrudate is placed on the casting drum heated to about 80 to 100 ° C. It can be fed or coated or sheeted by conventional methods. The casting drum 30 used in the present invention may have a diameter of 1 to 5 m, and may be made of a metal material selected from nickel, chromium, copper, stainless steel, and alloys thereof.

The polyvinyl alcohol-containing raw material solution coating layer formed on the casting drum 30 is pre-dried on the casting drum 30, whereby an air chamber 40 surrounding the casting drum may be installed and operated to help pre-drying. The resulting polyvinyl alcohol-based polymer film may be gently peeled from the casting drum 30 using the stripper roll 50, and then dried in a temperature of 90 ° C. or lower while passing through several drying rolls 60. . The dried polymer film is further dried in a floating dryer 70 and then wound by a winding roll 90 via a cooling roll 80 to obtain a desired final polyvinyl alcohol polymer film.

The polyvinyl alcohol polymer film of the present invention prepared as described above may have an average thickness of 30 to 200 μm, and a thickness variation ((maximum thickness min. Thickness) / average thickness x 100) of 1 to 11%, 2 It may have a water content of from 5%. In addition, it may have a very low phase difference in the range corresponding to the in-plane phase difference of 0 to 50 and the thickness direction phase difference of 0 to 50.

In addition, the present invention can produce a polarizing film from the polyvinyl alcohol-based polymer film by a conventional method such as dyeing, stretching and drying the polyvinyl alcohol-based polymer film. At this time, the dyeing and stretching may be performed in any order or at the same time.

The polarizing film of the present invention thus obtained has a very uniform and excellent polarization performance.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments for better understanding of the present invention. However, the following examples are intended to illustrate the present invention, but the scope of the present invention is not limited to or by the following examples.

Examples 1-7 and Comparative Examples 1-4

Step a)

Polyvinyl alcohol having a saponification degree of 99.99 mol% and a polymerization degree of 3000 was dissolved in water, followed by glycerin plasticizer and nonionic surfactant. A release agent was added and mixed to prepare a polyvinyl alcohol-containing raw material solution. At this time, polyvinyl alcohol was used in an amount of 30% by weight in the solution, and a plasticizer and a release agent were used in amounts of 12 parts by weight and 0.1 parts by weight, respectively, based on 100 parts by weight of polyvinyl alcohol.

The raw material solution was extruded at 130 ° C. through a twin screw extruder and then the extrudate passed through a filter and then heated to 95 ° C. 1,000 mm And hard chrome coating A die (1000 mm in width) was supplied onto the casting drum of the material, and the air chambers were operated together and pre-dried on the casting drum to form a film.

Step b)

The polyvinyl alcohol-based polymer film pre-dried on the casting drum was gently peeled from the casting drum using a stripper roll and then transferred to a drying roll.

Step c)

The polyvinyl alcohol polymer film of 75 micrometers in average thickness was obtained by carrying out several drying rolls, and drying and winding up at the temperature of 50-70 degreeC.

 In the above steps a) to c), the line speed on the film production process was adjusted as described in Table 1 below.

In addition, IR heaters (14,000 W, model name: short wave IR, manufacturer: Heraeus Noblelight) were installed at positions A to C below, and these were operated by drying at the temperature conditions as summarized in Table 1 below. In Table 1 below, X means that the IR heater is not operated at the corresponding position).

A. Between the die and the casting drum (dry section: 15 mm)

B. Between the stripper roll and the drying roll (dry section: 500mm)

C. Upper and lower parts of the drying roll (dry section: 1200mm)

Test Example

For the films prepared in Examples 1 to 7 and Comparative Examples 1 to 4, the width of the casting drum and the final film obtained, the dry roll back end moisture content, the film thickness variation, the in-plane retardation, the thickness retardation and the widthwise stain (MD Mura) was measured and shown in Table 1 below.

(1) In-plane phase difference

In a birefringence measuring instrument (trade name: KOBRA-WPR, manufactured by Oji Scientific Instrument), light having a wavelength of 40 nm was measured by being incident in the film normal direction.

(2) Dry Roll Backward Moisture Content

The moisture content measurement of the back end of a dry roll was measured using the moisture content meter (heat source: ceramic IR heater, model name: MA45, manufacturer: Sartorius) by taking the film immediately after passing a dry roll in the Example process.

(3) Film thickness variation (%)

The thickness of the film was measured using an X-ray thickness meter (Model: MKG-5010HT, manufacturer: MEK), and calculated using the following equation:

Thickness Deviation (%) = (Max Thickness-Min Thickness) / Average Thickness x 100

(4) widthwise staining

The number of stains per meter of width was evaluated by counting:

X: 6 or more, Δ: 3 to 6, ○: 3 or less, ◎: no stain

IR heater
(℃) Average film
thickness
(Μm) line
speed
(m / min) Back end of casting roll
Film width
(mm) Dry roll
Trailing
Moisture content
(%) Film thickness
Deviation
(%) In-plane phase difference
(Unit: nm) Width direction
stain A B C Example 1 150 X X 75 One 984 14.8 9.3 26 △ Example 2 X 10O X 75 One 979 14.4 10.7 110 ○ Example 3 X X 8O 75 One 979 13.6 8.0 46 △ Example 4 15O 10O X 75 One 984 14.3 9.3 15 ○ Example 5 15O X 8O 75 One 984 13.6 6.7 12 ○ Example 6 X 10O 8O 75 One 979 13.4 8.0 42 ○ Example 7 15O 100 8O 75 One 984 13.4 4.0 11 ◎ Example 8 20O 15O 13O 75 2 961 14.0 6.7 23 ○ Comparative Example 1 X X X 75 One 979 14.9 16.0 125 △ Comparative Example 2 20O 15O 13O 75 One 985 12.9 17.3 109 X Comparative Example 3 X X X 75 2 956 17.8 20.0 161 X Comparative Example 4 15O 10O 8O 75 2 961 15.6 16.0 94 △

From the results in Table 1, the polyvinyl alcohol-based polymer films of Examples 1 to 7 prepared according to the method of the present invention have a low water content, low film thickness deviation and low in-plane retardation, and dry rolls, transmittance, haze, and the like. It can be seen that excellent physical properties in all respects.

On the other hand, the film of Comparative Example 1, which was not subjected to IR drying, showed a large film thickness variation and a high in-plane retardation.

In addition, as shown in Comparative Example 2, when the temperature of each IR heater was increased, a lower moisture content could be expected, but the thickness variation and the in-plane retardation showed high values. Sticking phenomenon occurred. Therefore, it was confirmed that a lot of widthwise staining occurs.

In addition, as shown in Comparative Examples 3 and 4, when the line speed was increased, it did not sufficiently dry and showed a high water content.

Claims (10)

a) feeding the polyvinyl alcohol raw material solution onto the casting drum through an extruder and a die and predrying;
b) peeling the pre-dried film from the casting drum using a stripper roll and then transferring to the drying roll; And
c) drying the conveyed film in several stages while passing through several drying rolls,
Between the die of the step a) and the casting drum (A),
(B) between the stripper roll and the dry roll of step b), and
In the drying roll passing section (C) of step c)
Mounting the IR heater at two or more positions, characterized in that for operating under the temperature conditions of the following formula 1 to 3, a method for producing a polyvinyl alcohol-based polymer film:
Equation 1: 30 + 50 xs &lt; Ta &lt; 150 + 50 xs;
Equation 2: 50 × s ≦ Tb ≦ 100 + 50 × s; And
Equation 3: 50 xs ≤ Tc ≤ 50 + 50 xs,
In Equations 1 to 3, Ta, Tb, and Tc are the temperatures (° C.) of the heater operated at the A, B, and C positions, respectively, and s is the line speed (m / min) in steps a) to c). And 0.5 ≦ s ≦ 4.
The method of claim 1,
IR heaters of the B and C position is mounted to the upper, lower or upper and lower portions of the film, respectively, characterized in that the operation of the polyvinyl alcohol-based polymer film production method. The method of claim 1,
Method for producing a polyvinyl alcohol-based polymer film, characterized in that for operating the IR heater at a temperature of 80 to 200 ℃ for a length section of 10 to 20 mm in the A position. The method of claim 1,
Method for producing a polyvinyl alcohol-based polymer film, characterized in that for operating the IR heater at a temperature of 50 to 150 ℃ for the length section of 200 to 1000 mm in the B position. The method of claim 1,
Method for producing a polyvinyl alcohol-based polymer film, characterized in that for operating the IR heater at a temperature of 50 to 100 ℃ for a length section of 200 to 1500 mm in the C position. The method of claim 1,
The polyvinyl alcohol raw material solution is polyvinyl alcohol, a plasticizer, a releasing agent and a solvent having a degree of saponification of 99 mol% or more and a polymerization degree of 1700 or more. The polyvinyl alcohol polymer film manufactured by the method of any one of Claims 1-6. The method of claim 7, wherein
Polyvinyl alcohol-based polymer film, characterized in that the thickness variation ((maximum thickness-minimum thickness) / average thickness x 100) of the film is 1 to 11%. The method of claim 7, wherein
Polyvinyl alcohol-based polymer film, characterized in that the film has an in-plane retardation of 0 to 50. A polarizing film obtained by dyeing and stretching the polyvinyl alcohol polymer film of claim 7 and then drying.

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