JP2002187195A - Method for molding polymer sheet and polymer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a polymer sheet and a polymer film which can produce a quality polymer sheet or film excellent in smoothness over a long time in high productivity. SOLUTION: In the method in which the molten polymer sheet is extruded from a nozzle, charge radiated from a tape-shaped discharge electrode is applied to the molten sheet, and the sheet is adhered to a cooling roll by an electrostatic adhesion method and solidified, the surface of the cooling roll is hydrophilic. In the method for molding the polymer film, the polymer sheet is biaxially stretched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a polymer sheet and a polymer film, and more particularly to a polymer sheet and a polymer capable of stably producing high-quality sheets and films having excellent smoothness at a high speed. The present invention relates to a method for forming a film.

[0002]

2. Description of the Related Art As a method of forming a thin sheet at a high speed, a molten polymer is extruded into a sheet form from an orifice-shaped die, and a high voltage is applied to a thin-line electrode provided so as to cross the sheet. A method of forming a sheet by discharging the sheet, depositing the electric charge on the sheet, and firmly contacting the sheet with a cooling roll surface by Coulomb force (electrostatic adhesion method) is known (Japanese Patent Publication No. 37-6142). When forming on a mirror-shaped cooling roll surface, it is difficult to discharge the entrained air between the sheet-like material and the cooling roll surface as the molding speed is increased. Is a foam-like defect, and the smoothness of the sheet surface is reduced, and the conventional electrostatic adhesion method has a limitation in the molding speed.

For the purpose of raising the limit of the molding speed, for example, Japanese Patent Application Laid-Open No. 1-69324 proposes to increase the amount of charge dissipation by making the line of the discharge electrode thinner. There is a problem that the tensile strength decreases. Japanese Patent Publication No. 63-20688 and Japanese Patent Application Laid-Open No. 1-1520
No. 31, JP-A-10-323881, JP-A-10-323881 discloses a thin tape-shaped electrode having a rectangular cross section to increase the amount of charge emission, and to narrow the charge emission area to deposit on the sheet. A method has been proposed in which the charge density is increased to increase the adhesion, but the tape-shaped electrode has a narrow charge emission area, so the relative positions of the electrode, the sheet, and the cooling roll are important. Position adjustment is indispensable. Further, since the charge density on the sheet is increased in the tape-shaped electrode, if the limit of the molding speed is greatly increased by the method, there is a problem that the sheet is easily broken down due to the high charge applied. .

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for stably producing a sheet or film at a high speed by eliminating the need for delicate position adjustment of a tape-shaped electrode and making the position adjustment easy. The purpose is to:

A second object of the present invention is to provide a method for producing a sheet and a film capable of stably producing a high-quality product sheet or film for a long time by reducing the dielectric breakdown of the sheet. .

[0006] As a result of studying the effect of the surface properties of the cooling roll to solve the problems of the present invention, the present inventors have found that the above problems can be improved by casting with a cooling roll having a hydrophilic surface. .

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to extrude a molten sheet of a polymer from a die, apply a charge radiated from a discharge electrode in the form of a tape to the molten sheet, and apply a charge to a cooling roll by an electrostatic adhesion method. The method for forming a sheet to be adhered and solidified can be achieved by a method for forming a polymer sheet, wherein the surface of the cooling roll is a hydrophilic surface.

Another object of the present invention is to extrude a molten sheet of a polymer from a die, apply a charge radiated from a discharge electrode in the form of a tape to the molten sheet, and adhere to a cooling roll by an electrostatic adhesion method to solidify. In the method for producing a stretched film by biaxially stretching the unstretched sheet in the machine direction and the transverse direction, a method for forming a polymer film, wherein the cooling roll surface is a hydrophilic surface, Can be achieved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION [Polymer] In the present invention, a polymer is an aromatic polyester such as polyethylene terephthalate, polyethylene-2,6-naphthalate, or a copolymer containing these as a main component, or a polypropylene. Thermoplastic polymers such as polyolefins, polyvinyls such as polystyrene, polyamides such as nylon, and polycarbonates. Among them, aromatic polyesters are particularly preferable.

[Casting Method] In the present invention, a molten sheet of a polymer is extruded from an orifice-shaped die, is adhered to a cooling roll having a hydrophilic surface, is solidified, and is cast to form a sheet. The sheet is stretched to form a biaxially stretched film. The orifice-shaped base is, for example, a base having a linear opening, such as a T die, a fish tail die, and an I die.

In the present invention, the tape-shaped discharge electrode used for bringing the molten sheet into close contact with the cooling roll is a conductive tape having a rectangular or elliptical cross-section, and usually has a thickness of 10 mm.
A metal tape having a uniform shape in the length direction of about 100 μm and a width of 0.2 to 20 mm is used.

The tape-shaped discharge electrode traverses the molten sheet extruded from the die, and near the point where the sheet is attached to the cooling roll, the major axis of the cross section of the tape-shaped electrode is substantially perpendicular to the surface of the cooling roll. It is installed so that it becomes. When a high voltage is applied to the electrode, charges are radiated from the edge of the tape-shaped electrode facing the cooling roll surface toward the molten sheet, and the sheet is charged and adheres to the cooling roll.

The characteristics of the tape-shaped electrode with respect to the linear electrode are as follows.
The tensile strength of the electrode is ensured, and the discharge-emitting portion of the electrode can be made thinner or sharper to increase the amount of discharge charge. Charges can be efficiently concentrated into a portion most suitable for electrostatic adhesion. As a result, the charge density of the sheet is increased, the Coulomb force is increased, and the adhesion of the sheet is increased, so that even with a mirror-finished cooling roll, it is thought that the casting upper limit speed of the conventional linear electrode can be greatly exceeded. Can be

However, in order to effectively exhibit the above-described characteristics of the tape-shaped electrode, it is necessary to accurately adjust the electrode to a specific position having a very narrow allowable range. The optimal electrode position is strongly related to the point at which the molten sheet is attached to the cooling roll.If the width of the molten sheet is large, there is variation in the thickness in the width direction of the sheet, and variation in the melt viscosity. The landing point on the cooling roll is hard to be straight, and it is more difficult to adjust the position optimally. In addition, since the thermal history of the polymer from the extruder to the die changes slightly with time, the melt viscosity of the sheet extruded from the die also changes with time. Will be attracted. Therefore, even if the electrode can be adjusted to the optimum position first, the position may not be the optimum position as time elapses, and a defect due to poor adhesion of the sheet occurs in the solidified sheet. In the case of the tape-shaped electrode, since the charge density of the sheet is increased, when the sheet is deviated from the optimum position and a defect of poor adhesion occurs, the sheet is likely to cause dielectric breakdown with a high-density charge.

However, when the cooling roll is changed from a conventional mirror roll to a roll having a hydrophilic surface proposed in the present invention,
It has been found that the problem in the case of the mirror roll is improved. Although the cause is not clear, the optimal position of the tape-shaped electrode may change from a specific position with a narrow tolerance range to a wide area that is enlarged when the surface of the cooling roll is changed from a mirror surface to a hydrophilic surface. understood. As a result, it is easier to adjust the electrode to the optimum position, slight dispersion of the landing point of the molten sheet does not matter, casting of a wide sheet is possible, and the melt viscosity generated over time Small changes were acceptable. As a result, the dielectric breakdown of the sheet has been greatly reduced, and a wide sheet can be stably produced at a high speed.

In the present invention, the thickness of the unstretched sheet is 40
５００500 μm is preferred. The casting speed is preferably 60 m / min or more at the peripheral speed of the cooling roll. The upper limit is not particularly limited, but is preferably 200 m / min.

[Cooling Roll] In the present invention, a cooling roll having a hydrophilic surface is used. In the present invention, the hydrophilic surface is
A surface having a wetting index of 40 mN / m or more and a centerline average roughness of 0.01 to 0.35 μm, and the wetting index is used as a scale that quantitatively indicates the degree of hydrophilicity of the roll surface. JIS K6768, "Method for Wetting Test of Polyethylene and Polypropylene Films", which can be conveniently diverted as a method for evaluating the wetting characteristics of metal surfaces in the present invention. That is,
In this method, the surface tension (mN / m) is represented by a numerical value, and this numerical value is called a wetting index. This wetting index is referred to as "critical surface tension".
nsion) is also known in the area of surface science. However, the JIS specifies a wettability index in the range of 30 to 56 mN / m, and evaluation beyond this range cannot be made.

Generally, the surface of a smooth and smooth chromium plating has a wetting index of about 35 mN / m, and a thin (about 1 μm) water coating on such a surface has high water repellency and cannot exist stably. Has a metal surface wetting index of at least 4
Above 0 mN / m, a thin water coating can be stably present.

The hydrophilic surface is the same as the surface introduced in Japanese Patent Application Laid-Open No. 58-63415, which discloses a method in which a molten sheet extruded from a die is coated on a hydrophilic roll surface with a thin water film. The present invention relates to a device for bringing into close contact.

On the other hand, the present application relates to a method in which a molten sheet extruded from a die is electrostatically adhered directly to the surface of a hydrophilic roll without passing through a water coating, and the phenomenon that the upper limit speed of sheet forming increases as the wetting index increases. In order to increase the forming speed of the sheet, the wetting index of the surface of the cooling roll is at least 40 mN / m or more, desirably 45 mN / m or more, and particularly preferably 48 mN / m or more.

A hydrophilic surface having a high wetting index can be produced, for example, by the following method. That is, the first method is a method of chemically etching the surface layer portion of the chromium plating once formed, or a method of electrochemically slightly etching, etc.
A hydrophilic chromium plating surface having a wetting index of 40 mN / m or more or 50 mN / m or more can be formed.

The center line average roughness of the cooling roll surface in the present invention is preferably 0.01 to 0.3 μm. If the average roughness is less than 0.01 μm, it may not be possible to produce a desired high-quality sheet at high speed. On the other hand, if the average roughness exceeds 0.3 μm, the plating becomes brittle and, in addition, transfer defects occur on the sheet, which is not preferable. The upper limit of the center line average roughness of the cooling roll surface is 0.27 μm, particularly 0.2
It is preferably 4 μm, and the lower limit is preferably 0.2 μm, particularly preferably 0.18 μm.

It is not clear why the upper limit speed of sheet forming increases when the surface of the cooling roll is made hydrophilic by the above-mentioned etching treatment. However, when the hydrophilic surface is observed, the following phenomenon occurs. That is, the surface is very thin and milky white with respect to the mirror surface chromium plating, and is roughened. According to the surface microscopic observation, in addition to the surface roughening, the channel sometimes has a very narrow groove width (about 0.2 μm). Although a type microcrack may be recognized, a microcrack similar to this is often observed even with mirror-surface chromium plating, and it is difficult to think that the microcracks increase hydrophilicity. However, there is a peculiar phenomenon on the surface of the hydrophilic roll of the present invention, and there is a phenomenon that a large number of small bubbles rise from the roll surface when water is applied, and when the etching treatment is excessively performed so that the wetting index increases. In addition, there are phenomena such that the plating is easily broken by an impact to cause partial chipping.

It is assumed that an increase in the wetting index means an increase in the water retention volume on the roll surface. Considering these phenomena, it is estimated that the inside of the plating layer has a porous structure. Based on this inference, the entrapped air generated when the molten sheet is electrostatically brought into contact with the porous structure inside the plating layer is temporarily absorbed or diffused and discharged through the porous structure. As a result, it is estimated that the upper limit speed of sheet forming increases.

[Ventilation Resistance] The surface of the cooling roll of the present invention has a ventilation resistance of 5 as measured by a vacuum leak method.
00 to 10000 seconds, preferably 600 to 8 seconds.
Especially preferred is 000 seconds. 500 ventilation resistance
If it is less than seconds, there is a problem that an undesirable microcrack-like defect sometimes exists, and there is a problem that the plating is easily broken.

In the present invention, the ventilation resistance means that a sealed space of a specific volume is provided on the surface of a rough surface, and after this space is evacuated to a predetermined degree of vacuum, the degree of vacuum of the space is reduced by air flowing through a groove of the rough surface. It refers to the time required to decrease to a predetermined degree of vacuum. That is, after the air in the sealed space having the specific volume is exhausted by a vacuum pump or the like to form a vacuum area of a predetermined degree of vacuum, the discharge of the air is stopped, and the degree of vacuum of the space is reduced to a predetermined level by the air flowing through the rough groove. The time required to decrease to the value of is measured.

A specific method of measuring the ventilation resistance is as shown in a schematic diagram of FIG. 1, in which a vacuum pump 4 is connected to one end of a vacuum vessel 1 equipped with a vacuum gauge 2 via a vacuum cock 3. A rubber suction cup 6 (for example, FPM. PFYK-40 manufactured by Myotoku Corporation) is attached to the other end via a vacuum hose 5. As shown in the enlarged schematic cross-sectional view of FIG.
A 0 mm suction cup (6, 12) is pressed against the chill roll surface 14, and a 30 mm diameter porous sheet (for example, Naslon low density baking manufactured by Nippon Seisen Co., Ltd.) so that the outer peripheral surface of the suction cup is in close contact with the rough surface. The body 8-L-500) 13 is placed at the center of the suction cup and pressed. At this time, the space volume from the vacuum cock 3 to the suction cup 6 is adjusted to be 100 cc. Next, the degree of vacuum in the space of 100 cc was -93.
Vacuum pump 4 until 1 kPa (-700 mmHg)
After the air in the space is exhausted, the vacuum cock 3 is closed and the time measurement is immediately started. The degree of vacuum is reduced because air flows into the vacuum system through the grooves on the rough surface of the suction cup portion. At this time, the degree of vacuum falls from -93.1 kPa to -86.45 kPa.
The time required to decrease from (−700 mmHg to −650 mmHg) is measured, and this required time is defined as the ventilation resistance. In order to check the vacuum leak of the measuring instrument before the measurement of the ventilation resistance, it is confirmed that the ventilation resistance of the polished glass plate is 20,000 seconds or more.

[Biaxially stretched film] In the present invention, an unstretched sheet cast by an electrostatic adhesion method using a discharge electrode in the form of a tape using a cooling roll having a hydrophilic surface is biaxially stretched in the longitudinal and transverse directions. To form a polymer film. By this method, a high-quality biaxially stretched film having no defects can be stably produced at a high speed.

In the present invention, the biaxial stretching means that the unstretched sheet is preheated, stretched in the longitudinal direction, and then stretched in the transverse direction, or biaxial stretching is performed sequentially, or stretching in the longitudinal and transverse directions is performed simultaneously. This is to perform simultaneous biaxial stretching. Particularly in the case of sequential biaxial stretching, various known stretching methods, for example,
The stretching method proposed in JP-8672-A can be conveniently applied. For example, an unstretched sheet is stretched in multiple stages in the longitudinal direction so that the total magnification in the longitudinal direction is 2 to 8 times by repeating heating and stretching in a plurality of sections, and between the plurality of longitudinal stretching sections, and A method of stretching the film so that the total magnification in the horizontal direction is 2 to 8 times following the longitudinal stretching step to make the product of the vertical and horizontal stretching magnifications 4 to 64 times can also be used in the present invention.

[0030]

The present invention will be further described with reference to the following examples.

[Example 1] The cooling roll used for casting was a roll having a hydrophilic surface, having a surface roughness of 0.07 µm, a wetting index of 502 mN / m, and a ventilation resistance of 4500 seconds. Electrostatically contacted. The maximum speed of sheet forming was 125 m / min. The sheet was once wound, then biaxially stretched 3.6 times in the longitudinal direction and 3.9 times in the transverse direction, and heat-treated at 215 ° C. No transfer pattern on the hydrophilic surface was observed in the obtained molded sheet, no orange-skin-like defects were observed on the biaxially stretched film, and there was no coarse foreign substance. The quality standard as a base material was met.

At this time, at a casting speed of 100 m / min, the allowable movement width of the tape-shaped electrode for stably producing a high-quality sheet without defects is 1.5 mm, and the allowable movement width of this electrode is stable. It remained unchanged after 24 hours. In addition, the sheet does not show any orange skin-like defects,
The surface smoothness was good. The sheet that has been cast and wound up in this manner is then 3.6 mm in the longitudinal direction.
It was biaxially stretched 3.9 times in the transverse direction and heat-treated at 215 ° C. The obtained biaxially stretched film did not show any orange skin-like defects, and satisfied the quality standard as a base material of a high-grade video magnetic recording material with respect to the surface smoothness of the film.

Comparative Example 1 A film was formed by the same apparatus and method as in Example 1 except that a cooling roll having a mirror-finished surface was used as the cooling roll. As a result, the maximum casting speed is 71 m / min. At this time, the optimum position of the tape-shaped electrode is a dot having an allowable movement width of 0.5 mm or less. Sometimes, the sheet broke due to dielectric breakdown.

[0034]

According to the present invention, a high quality product sheet or film having no surface defects can be manufactured with high productivity over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for measuring a ventilation resistance on a cooling roll surface.

FIG. 2 is a schematic diagram showing an enlarged cross section of a suction cup portion of the ventilation resistance measuring device.

[Explanation of symbols]

 1: vacuum container 2: vacuum gauge 3: vacuum cock 4: vacuum pump 5, 11: vacuum hose 6, 12: suction cup 13: porous sheet 14: cooling roll surface

Claims (5)

[Claims] 1. A molten sheet of a polymer is extruded from a die,
A method for forming a sheet in which a charge radiated from a tape-shaped discharge electrode is applied to the molten sheet and solidified by being adhered to a cooling roll by an electrostatic adhesion method, wherein the cooling roll surface is a hydrophilic surface. A method for forming a polymer sheet. 2. The cooling roll surface has a wetting index of 40 mN /
m or more, and the center line average roughness is 0.01 to 0.35 μm
The method for forming a polymer sheet according to claim 1, wherein m is m. 3. The method for forming a polymer sheet according to claim 1, wherein a ventilation resistance of the cooling roll surface measured by a vacuum leak method is 500 to 10,000 seconds. 4. The method for forming a polymer sheet according to claim 1, wherein the surface of the cooling roll is manufactured by chemically or electrochemically etching chromium plating. 5. Extruding a molten sheet of polymer from a die,
The electric charge radiated from the tape-shaped discharge electrode is applied to the molten sheet, adhered to a cooling roll by an electrostatic adhesion method and solidified to form an unstretched sheet, and then the unstretched sheet is biaxially stretched in the longitudinal and transverse directions. A method for forming a polymer film, wherein the surface of the cooling roll is a hydrophilic surface.