JPH10323881A - Formation of thermoplastic resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thermoplastic resin sheet of superior thickness uniformity, and scarcely having surface defects at high speed. SOLUTION: In a method for forming a sheet by extruding molten thermoplastic resin in the sheet shape from a mouthpiece and bonding and solidifying the resin on a cooling drum by the electrostatic applying method, a conductive tape having a rectangular section and the uniform shape in the longitudinal direction and the relation of thickness (X) and width (Y) satisfies the formula of 50<=Y/X<=1000 is used as an electrode, and also the tensile strength of 10 to 90% of the breaking strength is applied to the conductive tape.

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 thermoplastic resin sheet, and more particularly, to a method for forming a thermoplastic resin sheet having excellent thickness uniformity and less surface defects at a high speed. It is about the method.

[0002]

2. Description of the Related Art As a molding method of a thermoplastic resin sheet,
An electrode is provided between the die and the cooling drum so as to cross the molten resin extruded in a sheet shape from the slit of the die, a high voltage is applied to the electrode to apply static electricity to the molten resin, and the molten resin is discharged. A method of solidifying the resin onto a cooling drum is widely known (for example, Japanese Patent Publication No. 37-6142 and Japanese Patent Publication No. 49-55759). This method is generally called an electrostatic application method.

[0003]

However, there is a limit to the above-mentioned method. For example, if the rotation speed of the cooling drum is increased to increase the molding amount of the thermoplastic resin sheet, the space between the thermoplastic resin sheet and the cooling drum is increased. The accompanying airflow is caught in the resin, and uniform molding of the thermoplastic resin sheet is hindered. Even if it does not reach that point, the vibration will become severe until the molten resin coming out of the die lands on the cooling drum, and the landing point will fluctuate in the circumferential direction of the cooling drum, and the thickness unevenness will worsen. In many cases. In addition, when the adhesion between the molten resin and the cooling drum is weakened, the cooling of the molten resin is not performed smoothly, and depending on the type of the thermoplastic resin, the resin sheet is crystallized, and the transparency is impaired, or the stretch is performed. In many cases, problems such as deterioration of performance occur.

[0004] In order to obtain a uniform sheet without these inconveniences by the electrostatic application method, the upper limit is a molding speed of 50 to 60 m / min, depending on the type of the thermoplastic resin.

[0005] The object of the present invention is to solve the above problems,
An object of the present invention is to form a thermoplastic resin sheet having excellent thickness uniformity and having few surface defects at a higher speed.

[0006]

In order to solve the above-mentioned problems, a method for forming a thermoplastic resin sheet according to the present invention comprises extruding a molten thermoplastic resin from a die into a sheet shape, and applying the molten thermoplastic resin onto a cooling drum by an electrostatic application method. In a method of forming a sheet by tightly adhering it to a sheet, the cross section is rectangular, and the relationship between the thickness (X) and the width (Y) satisfies 50 ≦ Y / X ≦ 1000. The method is characterized in that a conductive tape is used as an electrode and a tensile stress of 10% or more and 90% or less of the breaking strength is applied to the conductive tape.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
As the thermoplastic resin in the present invention, polyethylene terephthalate, polyethylene isophthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, poly-1,4-cyclohexane dimethylene terephthalate, polyethylene α, β-bis (2-chlorophenoxy) ) Polyesters such as ethane 4,4-dicarboxylate, polyolefins such as polyethylene, polypropylene, polybutene and poly-4-methylpentene-1, polyamides such as nylon 6, nylon 66 and nylon 12, polyimides and polysulfones , Polystyrenes, polyvinyls, polyester ethers, polycarbonates, polyester carbonates, polyether sulfones, polyether imides, polyphenylene sulfides Which can be applied. These resins may be used alone, or may be a copolymer or a mixture. Of course, these thermoplastic resins may contain other additives such as an antistatic agent, a weathering agent, a lubricant composed of inorganic particles, organic particles, and wax, a pigment, and the like.

The present invention is effective when the thermoplastic resin is, among the above-mentioned ones, polyesters, particularly mainly polyethylene terephthalate, polyethylene isophthalate and polyethylene-2,6-naphthalate. Here, “mainly” means that the polyester
It indicates that it contains at least mol%. The polyester may be a single polyester, a copolymer, or a simple mixture of other components at a ratio of less than 30 mol%.

The molten resin sheet extruded from the die may be a single layer or a multilayer of the above thermoplastic resin.

A means for melting the thermoplastic resin in the present invention,
A well-known base can be used. For example, as a melting means, chips are supplied to a single-screw or twin-screw extruder, melted, and extruded. Depending on the type of thermoplastic resin such as polyester and polyamide, it is necessary to sufficiently dry the chips before supplying them to the extruder. The melted and extruded thermoplastic resin is filtered by a filter and measured by a gear pump, then sent to a die and extruded. A die having a slit, such as a T die, a coat hanger die, and a fish tail die, can be used.

Conventionally, as a means for forming a thermoplastic resin sheet at a high speed by an electrostatic application method, a method of bringing an electrode close to a molten thermoplastic resin sheet or increasing an applied voltage is generally used. However, if these methods are performed excessively, spark discharge is generated from the electrode to the molten thermoplastic resin, and in severe cases, the spark may penetrate the sheet, and the sheet and the cooling drum may be damaged. Even before spark discharge does not occur, the surface of the thermoplastic resin sheet on the electrode side is damaged, and the surface is entirely or partially roughened into a fogged glass, so that the quality of the product can no longer be maintained. .

It is also common to adjust the position of the electrode in the circumferential direction of the cooling drum. If the position of the electrode is too close to the anti-rotation direction of the cooling drum from the landing point of the molten sheet,
The molten sheet vibrates by being electrically repelled from the electrodes.
Conversely, if the position of the electrode is too close in the rotational direction from the landing point, the entrainment of the accompanying airflow cannot be completely eliminated. Since all of these hinder smooth application, it is preferable to position the electrode near the landing point of the molten sheet for speeding up. Conventionally, a wire electrode having a circular cross section is generally used as an electrode, but the upper limit of the forming speed of the electrode is 50 to 60 m / min, regardless of which means is used.

As a result of intensive studies, the present inventors have found that the use of an electrode having a specific shape enables further high-speed molding. That is, the electrode according to the present invention has a rectangular cross section, and has a relation between thickness (X) and width (Y) satisfying 50 ≦ Y / X ≦ 1000. It is necessary to be. If Y / X is less than 50, the application becomes unstable, and a slight change such as a voltage applied to the electrode or a discharge of a thermoplastic resin easily causes a spark discharge from the electrode. On the other hand, if Y / X is larger than 1000, the applied force becomes weak, and the molding speed cannot be increased. Y / X is preferably 70 ≦
Y / X ≦ 800, more preferably 10
0 ≦ Y / X ≦ 500.

In the present invention, it is necessary to apply a tensile stress of 10% to 90% of the breaking strength to the conductive tape. If the tensile stress is less than 10% of the rupture strength, the vibration of the electrode becomes severe, and smooth application cannot be performed. Furthermore, when the conductive tape is used as an electrode for electrostatic application for a long period of time, the electrode surface microscopically changes due to corrosion of the electrode or adhesion of a monomer or oligomer sublimating from the molten thermoplastic resin, and the entire or partial electrode There is a disadvantage that the glow discharge that emits purple light continues to be generated.
The present inventors have investigated these phenomena in detail, and found that this continuous glow discharge is caused by microscopic, total or partial vibration of the electrode, and to prevent them, It has been found that it is necessary to apply a tensile stress of 10% or more of the breaking strength to the conductive tape.
Conversely, if the tensile stress is greater than 90% of the breaking strength, the electrode will be partially or entirely deformed remarkably, not only not being able to apply smoothly but also possibly cutting the electrode. The tensile stress is preferably in a range from 15% to 80% of the breaking strength, and more preferably in a range from 20% to 70% of the breaking strength.

The electrodes of the conductive tape having a uniform shape in the longitudinal direction in the present invention include stainless steel, titanium,
Beryllium copper, palladium, permalloy, tantalum,
Metals such as gold, platinum, silver, copper, brass, iron, tin, phosphor bronze, copper, nickel silver, aluminum, aluminum alloy, nickel, niobium, zinc, molybdenum, and tungsten, and carbon can be used. For the electrode, these materials may be used as they are, or in some cases, these materials may be polished, or the surface may be subjected to a treatment such as plating, vapor deposition, or sputtering.

The conductive tape of the present invention is arranged so that one edge of the conductive tape faces the thermoplastic resin side. That is, by effectively using the sharp edge portion of the conductive tape, the electric field around the electrode is increased, and a strong applied force can be obtained. The angle between the normal direction of the cooling drum and the side surface of the conductive tape is preferably set to an angle of 0 ° or more and 45 ° or less. The distance between the thermoplastic resin and the lower edge of the electrode is preferably 20 mm or less in order to obtain a strong applied force.

The conductive tape of the present invention has a thickness of 0.01
It is preferable that the thickness is not less than 0.5 mm and not more than 0.50 mm. When the thickness of the conductive tape is less than 0.01 mm, not only is spark discharge easily generated, but also the electrode is easily cut due to corrosion when used as an electrode, which is not preferable. Conversely, if the thickness of the conductive tape is greater than 0.50 mm, a high applied force cannot be obtained, and high-speed molding of a thermoplastic resin film cannot be achieved, which is not preferable. Note that the thickness of the conductive tape is more preferably 0.015 mm or more and 0.3
0 mm or less, more preferably 0.02 m
m and 0.10 mm or less.

The width of the conductive tape of the present invention is preferably as narrow as 1 mm or more and 20 mm or less. If the width of the conductive tape is smaller than 1 mm, a high applied force cannot be obtained,
It is not preferable because not only high-speed molding of the thermoplastic resin film cannot be achieved, but also twisting of the electrode cannot be ignored and non-uniform application occurs in the width direction. Conversely, if the width of the conductive tape is larger than 20 mm, the application becomes unstable, and spark discharge occurs due to a slight change, which is not preferable. The width of the conductive tape is more preferably in a range from 2 mm to 17 mm, and further preferably in a range from 3 mm to 15 mm.

The thickness unevenness of the conductive tape of the present invention is 30%.
The following is preferred. If the thickness unevenness of the conductive tape exceeds 30%, the thermoplastic resin sheet partially discharges at a thin portion of the electrode, which causes a surface defect or a hole in some cases, which is not preferable. The thickness unevenness of the conductive tape is more preferably 25% or less, and further preferably 20% or less.

The conductive tape of the present invention is preferably moved continuously in the longitudinal direction in order to prevent the occurrence of glow discharge when the thermoplastic resin sheet is formed.
The moving speed (Vt) is equal to the rotational speed (V
In the case of d), it is preferable that Vt ≧ Vd / 50,000 because glow discharge can be suppressed. It is considered that the reason for this is that the continuous movement can suppress the whole or partial fine vibration of the electrode. The continuous movement of the conductive tape is also desirable from the viewpoint of eliminating the cause of spark discharge due to electrode corrosion and adhesion of monomers and oligomers. Vt is more preferably Vt ≧ Vd / 30000, and still more preferably Vt ≧ Vd / 10000.

As a method for moving the conductive tape, for example, a reel on which an electrode is wound is torque-controlled by, for example, a perma torque manufactured by Shin Nippon Material Co., Ltd. or a hysteresis clutch / brake manufactured by Shinko Electric Co., Ltd. However, a method of winding and moving the other reel with a motor or the like can be specifically applied.

The voltage applied to the conductive tape of the present invention is preferably a positive voltage from the viewpoint of application stability. When the applied voltage is a negative DC voltage, spark discharge easily occurs due to minute scratches, burrs, corrosion, etc. on the end face of the conductive tape. Also, in the case of an AC voltage, the same phenomenon occurs when the electrode has a negative polarity, which is not preferable.

The thickness of the thermoplastic resin sheet obtained in the present invention is preferably 0.05 mm or more and 2 mm or less. If the thickness of the thermoplastic resin sheet is less than 0.05 mm, spark discharge is likely to occur, and if it is more than 2 mm, sufficient adhesion to the cooling drum cannot be obtained, which is not preferable. The thickness of the thermoplastic resin sheet is more preferably in the range of 0.07 mm or more and 1 mm or less, and further preferably in the range of 0.1 mm or more and 0.5 mm or less.

It is also preferable to subject the thermoplastic resin sheet obtained in the present invention to biaxial stretching and heat treatment to form a biaxially oriented film. The method of biaxial stretching and heat treatment is not particularly limited, but as a typical method, a thermoplastic resin is heated to a temperature equal to or higher than a glass transition temperature, and is stretched in one or more stages between stretching rolls having a low speed and a high speed difference. After stretching in the direction, the longitudinally stretched film obtained by cooling is subjected to transverse stretching and heat treatment, which is a so-called sequential biaxial stretching, in which a tenter of a type that grips and runs the film end portion with a clip and performs heat treatment can be applied. .

[Evaluation Method of Physical Property Value and Evaluation Method of Effect] (1) Breaking strength of conductive tape The conductive tape was cut into a sample length of 150 mm, and the distance between the chucks was 100 mm, and the tensile speed was 300 mm / min. Pull with a universal tensile tester of the type. The breaking strength is determined from the obtained stress-strain curve.

(2) Stress of the conductive tape The central part of the conductive tape having the length L (mm) is pushed in a direction perpendicular to the direction in which the conductive tape is stretched.
Pull a certain length x (mm) with a pull, read the load F at that time, and obtain the tension T (N) from the following equation. T = FL / 4x The obtained tension is divided by the cross-sectional area of the conductive tape, and is converted into the tension per unit cross-sectional area (MPa).

(3) Uneven thickness of conductive tape and thermoplastic resin sheet Film Thickness Tester KG601A manufactured by Anritsu Corporation
And using an electronic micrometer K306C, the thickness is continuously 10 m in the longitudinal direction (maximum value Ta, minimum value Tb,
The average value Tc) is measured, and the thickness unevenness (%) is calculated from the following equation. Uneven thickness = (Ta−Tb) / Tc × 100

(4) Measurement of melting specific resistance A sufficiently dried pellet is melted at 280 ° C. in a nitrogen atmosphere, a pair of electrodes are inserted, and an applied voltage V (V) when a voltage is applied by a DC high voltage generator. From the following equation, the melting specific resistance (Ω · cm) is calculated from the measured current I (A), the distance D (cm) between the electrodes, and the area S (cm ² ) of the electrodes. Melting specific resistance = V × S / (I × D)

(5) Upper limit molding speed of thermoplastic resin sheet Obtained thermoplastic resin sheet or molded state is observed and classified into the following four ranks. A: There is no defect on the film surface. ：: A thin spot-like defect partially occurs on the film surface. Δ: A spot defect occurs on the entire surface. X: Large air is trapped between the thermoplastic resin and the cooling drum, and the flatness of the sheet is extremely deteriorated. The rotation speed of the cooling drum is increased from a low speed, and the upper limit speed capable of maintaining the range of ◎ to ○ is defined as the upper limit molding speed of the thermoplastic resin sheet. At this time, the electrode is moved in the circumferential direction of the cooling drum before and after the thermoplastic resin is applied, and the position is adjusted so that the number of defects is minimized.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Examples 1 to 11 Polyethylene terephthalate (PET) pellets having a melting specific resistance of 5 × 10 ⁸ Ω · cm were dried at 180 ° C. in a vacuum for 4 hours, supplied to an extruder and melted at 280 ° C. After passing through, it was discharged from a T-die and cast on a cooling drum having a surface temperature of 25 ° C. and a diameter of 1200 mmφ under the following conditions by an electrostatic application method to obtain a sheet. (1) Electrode for electrostatic application Material: SUS304H B. Shape: tape-shaped cross section as shown in Table 1 C. Breaking strength: as shown in Table 1. Uneven thickness: as shown in Table 1 (2) Electrostatic application conditions B. Applied voltage: + DC voltage 14 kV Electrode tensile stress: as shown in Table 1. Electrode moving speed: as shown in Table 1. Distance between the molten thermoplastic resin and the lower surface of the electrode: 5 mm

The upper limit molding speed determined while adjusting the extrusion amount of the thermoplastic resin so that the average thickness of the obtained sheet is 200 μm is as shown in Table 1. In each case, the high speed was achieved. In addition, the thickness unevenness of the thermoplastic resin sheets thus obtained was small and good.

COMPARATIVE EXAMPLES 1 AND 2 Using the same thermoplastic resin and molding apparatus as in the examples, a sheet was cast by the electrostatic application method under the following conditions. (1) Electrode for electrostatic application Material: Tungsten C. Breaking strength: as shown in Table 2 (2) Electrostatic application conditions B. Applied voltage: + DC voltage 14 kV Electrode tensile stress: as shown in Table 2. Electrode moving speed: as shown in Table 2. Distance between the molten thermoplastic resin and the lower surface of the electrode: 5 mm

The upper limit molding speed obtained while adjusting the extrusion amount of the thermoplastic resin so that the average thickness of the obtained sheet becomes 200 μm is as shown in Table 2, and the high speed could not be achieved. Further, the thickness unevenness of the thermoplastic resin sheets thus obtained was all large.

Comparative Examples 3 to 10 Using the same thermoplastic resin and molding apparatus as in the examples, the sheets were cast by the electrostatic application method under the following conditions. (1) Electrode for electrostatic application Material: SUS304H B. Shape: Tape-shaped section with rectangular shape as shown in Table 2. Breaking strength: as shown in Table 2. Uneven thickness: as shown in Table 2 (2) Electrostatic application conditions B. Applied voltage: + DC voltage 14 kV Electrode tensile stress: as shown in Table 2. Electrode moving speed: as shown in Table 2. Distance between the molten thermoplastic resin and the lower surface of the electrode: 5 mm

The upper limit molding speed determined while adjusting the extrusion amount of the thermoplastic resin so that the average thickness of the obtained sheet is 200 μm is as shown in Table 2, and the higher speed could not be achieved. Further, the thickness unevenness of the thermoplastic resin sheets thus obtained was all large.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

According to the present invention, there is provided a method for forming a sheet by extruding a molten thermoplastic resin from a die into a sheet shape, and solidifying the molten thermoplastic resin on a cooling drum by an electrostatic application method.
A conductive tape having a uniform shape in the longitudinal direction and having a relation between the thickness (X) and the width (Y) satisfying 50 ≦ Y / X ≦ 1000 is used as an electrode; By applying a tensile stress of 10% or more and 90% or less of the breaking strength to the conductive tape, a thermoplastic resin sheet excellent in thickness uniformity and having few surface defects can be formed at a high speed.

Claims (9)

[Claims] 1. A method in which a molten thermoplastic resin is extruded from a die into a sheet shape, and is tightly solidified on a cooling drum by an electrostatic application method to form a sheet. A conductive tape having a uniform shape in the longitudinal direction, which satisfies 50 ≦ Y / X ≦ 1000 with respect to (Y), is used as an electrode, and the conductive tape has a breaking strength of 10% to 90%. % Of a thermoplastic resin sheet, wherein a tensile stress of not more than 10% is applied. 2. The conductive tape having a thickness (X) of 0.01
The method of forming a thermoplastic resin sheet according to claim 1, wherein the thickness is not less than 0.5 mm and not more than 0.50 mm. 3. The method for forming a thermoplastic resin sheet according to claim 1, wherein the width (Y) of the conductive tape is 1 mm or more and 20 mm or less. 4. The method for forming a thermoplastic resin sheet according to claim 1, wherein the thickness unevenness of the conductive tape is 30% or less. 5. The conductive tape is continuously moved in the longitudinal direction, and the moving speed (Vt) and the rotation speed (V
The method for forming a thermoplastic resin sheet according to any one of claims 1 to 4, wherein the relationship with d) satisfies Vt≥Vd / 50,000. 6. A positive DC voltage is applied to the conductive tape,
The method for forming a thermoplastic resin sheet according to any one of claims 1 to 5, wherein the cooling drum is grounded. 7. The thermoplastic resin sheet has a thickness of 0.05 m.
The method for forming a thermoplastic resin sheet according to any one of claims 1 to 6, wherein the length is not less than m and not more than 2 mm. 8. The method for forming a thermoplastic resin sheet according to claim 1, wherein the thermoplastic resin is a polyester. 9. A biaxially oriented film obtained by subjecting a thermoplastic resin sheet to biaxial stretching and heat treatment.
A method for molding a thermoplastic resin sheet according to any one of claims 1 to 8.