JP2002028966A - Method for molding polyester sheet and film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding polyester sheet and film by which the sheet or the film with an excellent surface smoothness and high quality can be produced at a high speed. SOLUTION: In a method for molding the sheet by which a molten sheet of a polyester in which terephthalic acid is a main acid ingredient is extruded from an orifice-like die and is tightly stuck on a cooling roll by means of electrostatic sticking and is solidified, the method of the polyester sheet is characterized by a specific resistance of the polyester under a molten condition being 3×106-1×108 Ω.cm and the cooling roll being such a cooling roll that has a microcrack surface and the molding speed of the sheet being 65-250 m/min and the method for molding the polyester film is characterized by biaxially drawing the molded sheet in both the longitudinal and the transverse directions.

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 polyester sheet or film, and more particularly to a method for producing a polyester sheet or film having excellent smoothness and good quality at high speed for a long time. The present invention relates to a method for forming a polyester sheet and a film.

[0002]

2. Description of the Related Art As a method of forming a polymer sheet at a high speed, a molten sheet of a polymer is extruded from an orifice-shaped die and is brought into close contact with a cooling roll surface and solidified (cast).
Methods are conventionally known. In order to promote the adhesion of the molten sheet to the cooling roll by this method, various proposals have been made to use an electrostatic adhesion method together.

[0003] As a method for producing a film, a molten sheet of a polymer is extruded from an orifice-shaped die, and is adhered to a cooling roll and solidified (cast) to form an unstretched sheet. A method of stretching a film in a direction to form a biaxially stretched film is also conventionally known.

In these forming methods, a cooling roll having a smooth finished surface (mirror finish) is usually used. When a molten sheet of a polymer is brought into close contact with the cooling roll surface, the cooling roll surface is used. It is necessary to discharge air interposed between the sheet and the molten sheet. However, the discharge of air becomes more difficult as the casting speed increases, resulting in various problems. For example, when the casting speed is increased, the intervening air remains in the form of bubbles, which causes a defect on the sheet surface and causes a problem that the smoothness of the sheet is reduced. The sheet surface defects also have an adverse effect on the surface smoothness of a film obtained by stretching the sheet. For this reason, the sheet forming method by the conventional electrostatic contact method has a limit in the sheet forming speed.

[0005] Various methods have been proposed to improve the forming speed limit in forming a sheet by the electrostatic adhesion method. For example, polymers such as alkali metals, alkaline earth metals, Mg,
A method for improving the adhesion between the molten sheet and the cooling roll by blending P or a compound thereof and reducing the specific resistance of the molten polymer or increasing the initial accumulated charge amount (for example, Japanese Patent Publication No. 53-40231). JP, JP-B-56-15730, JP-B-59-62
627, JP-A-62-187724, JP-A-62-189133, etc.).

In these methods, however, it is necessary to contain a large amount of a metal compound in order to increase the molding speed limit. However, the added metal compound precipitates as a simple metal or a metal salt in the polymer, There is a problem that this becomes a foreign substance in a sheet or a film. The deposited metal (salt) becomes a foreign substance and forms coarse projections on the surface. When the film is used as a base film of a magnetic recording material, this causes a dropout of a magnetic recording signal. When the film is used for optical applications, foreign matter causes a problem in uniform light transmission. In addition, since the thermal stability of the polymer is reduced, there is a problem that the polymer is colored in the melting step and a problem that the viscosity is significantly reduced. Therefore, in the method of adding a metal compound to a polymer, the amount of addition is limited, and it is difficult to greatly improve the production speed of a sheet or a film.

Further, by forming a sheet by an electrostatic adhesion method,
Other methods have been proposed to improve the molding speed limit. For example, Japanese Patent Application Laid-Open No. 46-439 proposes a method in which the surface of a roll is roughened and the discharge of air interposed between the sheet and the cooling roll surface is promoted through the connected gap. However, in order to enhance the effect of discharging the intervening air by this method, it is necessary to roughen the surface of the cooling roll, but as a result, the concave and convex pattern on the surface of the cooling roll is transferred as a replica to the sheet surface, Orange skin-like defects occur. This drawback causes surface defects of the film obtained by stretching the sheet. In the method in which the surface of the roll is roughened by sandblasting, since the connected passage serving as an air discharge passage is shallow and narrow, a low-molecular compound sublimating from the molten sheet adheres and accumulates on the surface of the passage to discharge air. There is a disadvantage that the road is easily blocked, and as a result, the effect of improving the molding speed is reduced in a short time.

As another proposal for improving the molding speed limit in forming a sheet by the electrostatic adhesion method, a method using a cooling roll on the surface of a micro crack (Japanese Patent Laid-Open No. 58-183220)
Publication). According to this method, since the air interposed between the molten sheet and the cooling roll is dissipated through the grooves of the microcracks, the molding speed can be significantly increased.

The surface of the microcrack has a structure in which fine grooves are provided on a flat surface, and there is a groove having a groove depth larger than the groove width. Discharge path can be secured. Also, clogging of the air discharge path due to sublimation of the low molecular compound can be significantly reduced, and transfer defects to the sheet or stretched film surface can be improved.

However, in recent years, it has become necessary to greatly increase the forming speed of a sheet or a film compared with the conventional one.
Further, as the demands for the quality of sheets and films have become more and more advanced, new problems arise in order to achieve this even with the use of a cooling roll on the surface of microcracks. In other words, it is necessary to dissipate the air interposed between the molten sheet and the cooling roll more quickly to increase the speed, but for this purpose, it is necessary to use a cooling roll with a micro crack surface having a wide groove width. Become. However, in such a microcrack, the shape of the groove is transferred to the sheet surface to cause a network pattern defect, and an orange-skin-like defect occurs in a film obtained by biaxially stretching the sheet. This defect leads to insufficient uniformity of the light transmittance of the film in optical applications, and in magnetic recording applications (for example, high-density recording in which an ultrathin film having a thickness of Angstrom level such as a vacuum deposited thin film is used as a recording layer). The surface smoothness of the base film becomes insufficient.

As described above, in spite of the increasingly demanding user's demands for film quality such as optical uniformity and surface smoothness, improvement of film productivity (higher speed and higher operation rate) has been required. This is an important issue for film makers.

[0012]

SUMMARY OF THE INVENTION The present inventor has solved the above problems and has achieved excellent optical uniformity and surface smoothness.
In other words, as a result of examining a method of producing a sheet or a stretched film at a high speed with a weak transfer defect of a microcrack groove, a polyester having a specific resistance in a molten state in a specific range is cooled at a specific molding speed at a specific molding speed. The present invention has been found that the transfer strength of microcracks decreases as the forming speed of the sheet increases when the forming is performed using a roll.

[0013]

That is, the present invention relates to a sheet forming method in which a molten sheet of polyester containing terephthalic acid as a main acid component is extruded from an orifice-shaped die and is adhered to a cooling roll by an electrostatic adhesion method to be solidified. ,
The specific resistance of the polyester in the molten state is 3 × 10 ⁶ to 1
× 10 ⁸ Ω · cm, wherein the cooling roll is a cooling roll on the surface of a microcrack, and the forming speed of the sheet is 65 to 250 m / min.

In the present invention, a molten sheet of polyester containing terephthalic acid as a main acid component is extruded from a die, and is adhered to a cooling roll by an electrostatic adhesion method to be solidified to form a sheet. In a method for forming a film to be biaxially stretched in the direction, the specific resistance of the polyester in a molten state is 3 × 10 ⁶ to 1 × 10 ⁸ Ω · cm, and the cooling roll is a cooling roll on a microcrack surface, And a sheet forming speed of 65 to 250 m / min.

Further, according to a preferred embodiment of the present invention, the micro-crack groove width of the cooling roll on the micro-crack surface is in the range of 0.2 to 20 μm, and the ventilation resistance of the cooling roll surface measured by a vacuum leak method is reduced. 500
0 seconds or less.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION [Polyester] In the present invention, a polyester is a thermoplastic polyester comprising an acid component and a glycol component. At least 50 mol% of the acid component is terephthalic acid. 3 × 10 ⁶ ~
1 × 10 ⁸ Ω · cm polyester.

Examples of the glycol component of the polyester include ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, and 1,6-hexane. Examples thereof include diol, cyclohexane dimethanol, polyethylene glycol, and polytetramethylene glycol. Among them, ethylene glycol, 1,3-propanediol, and 1,4-butanediol are preferable. It is preferable because it has excellent characteristics and thermal characteristics.

Preferred examples of the polyester in the present invention include polyethylene terephthalate. The polyethylene terephthalate may be one in which components other than terephthalic acid and ethylene glycol are copolymerized at a ratio of 50 mol% or less, particularly 20 mol% or less. Examples of the copolymerization component include acid components such as 2,6-naphthalene dicarboxylic acid, isophthalic acid, hexahydroterephthalic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid. The glycol component is diethylene glycol,
Propylene glycol, 1,3-propanediol,
1,4-butanediol, neopentyl glycol,
Examples thereof include 1,5-pentanediol, 1,6-hexanediol, cyclohexanedimethanol, polyethylene glycol, and polytetramethylene glycol.

Also, polyethylene terephthalate has 5
Another polymer, for example, polyethylene-2,6-naphthalate, may be mixed at a ratio of 0% by weight or less.

The polyester in the present invention has a specific resistance in a molten state of 3 × 10 ⁶ to 1 × 10 ⁸ Ω · cm. The lower limit of this specific resistance is 5 × 10 ⁶ Ω
cm, and the upper limit is 5 × 10 ⁷ Ω · cm
It is preferred that When the specific resistance is less than 3 × 10 ⁶ Ω · cm, there is a problem that the number of coarse particles and foreign substances in the film increases, or a problem occurs such that the thermal stability of the polymer is insufficient and the film is colored yellow. . On the other hand, if the specific resistance exceeds 1 × 10 ⁸ Ω · cm, a high-speed effect cannot be obtained by molding by the electrostatic adhesion method.

The polyester whose specific resistance in the molten state falls within the range of the present invention is obtained by mixing at least one of these metal compounds such as alkali metal, alkaline earth metal, Mg, P or a compound thereof with the above polyester. Can be adjusted. Among these metal compounds, Mg compounds (for example, magnesium acetate) are preferable, and it is particularly preferable to use them together with P compounds.

The compounding ratio of the metal compound is, for example, preferably 20 to 2000 ppm as a metal atom in the polyester, more preferably 50 to 1000 ppm, and particularly preferably 100 to 1000 ppm.
Preferably it is ~ 600 ppm.

[Specific Resistance] In the present invention, the specific resistance in the molten state is determined by the British Journal of Applied Physics (Brit. J. Appl. Phys.).
s. ) Vol. 17, pp. 1149-1154 (1966)
Year)). However, the melting temperature of the polymer was 290 ° C., and the value immediately after the application of a DC voltage of 1000 V was defined as the specific resistance of the polyester in the molten state.

[Cooling Roll] In the present invention, a cooling roll having microcracks on its surface (a cooling roll on the microcrack surface) is used. The microcrack surface has a structure in which a large number of fine and disordered grooves (cracks) are provided on a flat surface, and the cracks themselves are formed from a flat surface to a deep portion. The number of cracks intersecting at least one direction of the scanning line 10 mm on the surface of the chill roll is at least five, and 70% or more of the cracks have an opening width of 0.2 to 20 μm. It is preferable that the sum of the widths of all the cracks intersecting the scanning line of 10 mm is 5 mm or less. Since the transfer strength of the microcracks depends on the groove width, the average groove width of the microcracks is 15 μm or less, preferably 1 μm, in order to reduce the transfer strength.
It is preferably 0 μm or less. When the molten sheet comes into close contact with the surface of the cooling roll, air entrained in the meantime is discharged through the crack.

Although the microcracks are formed irregularly, the formation state is such that the ventilation resistance on the surface of the cooling roll measured by a vacuum leak method described later is 5000 seconds or less.
Further, it is preferable that the time is 3000 seconds or less, particularly 1000 seconds or less. The most preferable range of the ventilation resistance is 2 to 500 seconds. If the ventilation resistance exceeds 5000 seconds, no improvement in casting speed can be expected.

[Airflow resistance] In the present invention, airflow resistance means that a sealed space having a specific volume is provided on the surface of a rough surface, and after this space is evacuated to a predetermined degree of vacuum, air is introduced through a groove of the rough surface. Means the time required for the degree of vacuum 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. Although air flows into the vacuum system through the grooves on the rough surface of the suction cup portion, the degree of vacuum is reduced. At this time, the degree of vacuum is changed 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.

[Casting Method] In the present invention, a molten sheet of a polymer is extruded from an orifice-shaped die, and is adhered to a cooling roll on the surface of a microcrack together with an electrostatic adhesion method, solidified and cast to form a sheet. I do.
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. The electrostatic adhesion method is a method in which an electrostatic charge is applied to an extruded molten sheet and the molten sheet is brought into close contact with a cooling roll surface by Coulomb force.

The object of the present invention is to improve the transfer defects caused by the transfer of irregularities on the surface of the cooling roll and to produce a sheet at a high speed. Is achieved by using a cooling roll on the surface of a microcrack and simultaneously using an electrostatic adhesion method at a high speed.

The transfer strength of the microcrack shape is also related to the sheet forming speed. If the temperature of the molten sheet or the surface temperature of the cooling roll near the landing point where the molten sheet first contacts the cooling roll is constant, The transfer strength tends to decrease as the sheet forming speed increases. Although the reason is not clear, in the method using the electrostatic adhesion method in order to adhere the molten sheet to the cooling roll, the charge density on the sheet becomes thinner as the molding speed becomes faster, and the Coulomb force, that is, the adhesion force is reduced. It is presumed to be due to this.

When the surface of the cooling roll is a mirror surface, if the electrostatic adhesion is reduced, the intervening air remains, resulting in a bubble-like defect in the sheet. However, when the surface is a microcrack, the intervening air causes the microcrack. It is estimated that the decrease in adhesion due to the increase in molding speed will effectively reduce the transfer strength of microcracks without causing a bubble-like defect because it dissipates through the groove, and the surface smoothness will be reduced. Excellent high quality sheets can be produced at high speed.

In the present invention, the sheet forming speed is 65
２５０250 m / min is required, and preferably 80-200 m / min. Molding speed is 65
If it is less than m / min, the high-speed effect aimed at by the present invention is poor, and in addition, the transfer strength of microcracks may increase. If it exceeds 250 m / min, a defect similar to a bubble-like defect may occur.

In the present invention, the surface temperature of the molten sheet ranges from Tm of the polyester to Tm + 40 ° C. (T
m: the melting point of the polyester), and the surface temperature of the cooling roll near the landing point where the molten sheet first comes into contact with the cooling roll is from Tg-70 ° C. of the polyester to T
By maintaining the temperature in the range of g, particularly in the range of Tg-60 ° C. to Tg-20 ° C. (Tg: glass transition temperature of polyester), the adhesive strength of the molten sheet to the cooling roll becomes appropriate, and the micro crack sheet This is preferable because the transfer strength to the toner can be reduced.

The surface temperature of the molten sheet is a surface temperature of the sheet in a section before the molten sheet leaves the die and comes into contact with at least the cooling roll. This temperature is a non-contact type temperature such as a radiation thermometer. It can be measured with a measuring instrument.
Further, the surface temperature of the cooling roll is measured by a heat flow rate sensor (for example, a roll temperature measuring device T of Teijin Engineering Co., Ltd.).
It can be measured in a non-contact manner by LR-1).

In the present invention, the thickness of the sheet is 30.
It is preferably from 400 to 400 μm.

[Biaxially stretched film] In the present invention, a polyester film obtained by biaxially stretching an unstretched sheet cast by an electrostatic adhesion method using a cooling roll on the surface of a microcrack in a machine direction and a transverse direction. Molding. By this method, the transfer of microcracks to the surface of the biaxially stretched film can be greatly reduced.

In the present invention, the biaxial stretching means that the unstretched sheet is preheated, stretched in the machine direction and then stretched in the transverse direction, or the stretch is performed simultaneously in the machine direction and the transverse direction. 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-A-8672 and JP-A-54-8672 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.

[0038]

EXAMPLES The present invention will be further described below with reference to examples. The physical property values in the present invention are measured and defined as follows.

(1) Specific Resistance The specific resistance in the molten state is determined by the British Journal.
Of Applied Physics (Brit. J. Ap)
pl. Phys. ), Vol. 17, pages 1149-1154 (1966). However, the melting temperature of the polymer is 290 ° C.
The value immediately after the application of the voltage of 00 V was defined as the specific resistance of the polyester in the molten state.

(2) Sheet and Film Thickness Ten points were measured with a micrometer, and the average value was determined to be the thickness of the sheet or film.

(3) Glass transition temperature (Tg) A sample (10 mg) was set in a DSC device (differential scanning calorimeter) manufactured by PerkinElmer, and the sample was heated at a temperature of 300 ° C. for 5 minutes.
After melting for 1 minute, the sample was quenched in liquid nitrogen, and the quenched sample was heated at a rate of 10 ° C./min to measure a glass transition temperature (Tg).

(4) Melting Point (Tm) A sample (10 mg) was set in a DSC device (differential scanning calorimeter) manufactured by PerkinElmer, and the sample was heated at a temperature of 300 ° C. for 5 minutes.
After melting for 1 minute, the sample was quenched in liquid nitrogen, and the quenched sample was heated at a rate of 10 ° C./minute to measure the melting point (Tm).

(5) Mixing ratio of metal compound X-ray fluorescence (Rigaku Electric Industry Co., Ltd. X-ray fluorescence type 3270)
The amount of metal in the polymer (unit pp)
m) was measured.

Example 1 Magnesium compound (90p
pm), a phosphorus compound (30 ppm) and an antimony compound (330 ppm), and the specific resistance at the time of melting is 7 × 10
⁶ Ω · cm polyethylene terephthalate (Tg: 79
C., Tm: 253 ° C.) was extruded from a die into a sheet having a thickness of 180 μm, and was adhered to a cooling roll on the surface of the microcrack together with an electrostatic adhesion method to be solidified to obtain an unstretched sheet. The surface temperature of the molten sheet was 292 ° C., the surface temperature of the cooling roll near the landing point of the molten sheet was 48 ° C., and the maximum speed of sheet forming was 130 m / min. This unstretched 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.

The cooling roll used for casting was a roll on the surface of a microcrack, having an average ventilation resistance of 65 seconds measured by a vacuum leak method on the surface, and a scanning line of 10 mm on the surface.
The average number of cracks intersecting with the scanning line is 105, and the average opening width of all the cracks intersecting with the scanning line 10 mm is 7 μm.

Although the transfer pattern of micro cracks was very weak in the obtained molded sheet, the orange-skin-like defect was not found in the biaxially stretched film, there was no coarse foreign matter, and the surface smoothness of the film was poor. It met the quality standards as a base material for magnetic recording materials for video.

[Comparative Example 1] Using the same apparatus and polymer as in Example 1, the sheet was formed at a speed of 10 m / min according to Example 1 by adjusting the surface temperature of the sheet material and the cooling roll.
Subsequently, biaxial stretching was performed. A transfer pattern of microcracks was clearly observed in the obtained molded sheet, and an orange skin-like defect was observed in the biaxially stretched film.

[0048]

According to the present invention, polyethylene terephthalate having a specific resistance at the time of melting in a specific range is formed by high-speed molding using a cooling roll on the surface of a microcrack by an electrostatic adhesion method, whereby excellent surface smoothness is obtained. High quality sheet or film can be produced at high speed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring a ventilation resistance of a micro crack.

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 (4)

[Claims] 1. A method for forming a sheet in which a molten sheet of polyester containing terephthalic acid as a main acid component is extruded from an orifice-shaped die and is adhered to a cooling roll by an electrostatic adhesion method to be solidified. A polyester sheet having a resistance of 3 × 10 ⁶ to 1 × 10 ⁸ Ω · cm, the cooling roll being a cooling roll on a microcrack surface, and a sheet forming speed of 65 to 250 m / min. Molding method. 2. The method for forming a polyester sheet according to claim 1, wherein the average value of the microcrack groove width on the surface of the cooling roll is in the range of 0.2 to 20 μm. 3. The method for forming a polyester sheet according to claim 1, wherein the ventilation resistance of the cooling roll surface measured by a vacuum leak method is 5,000 seconds or less. 4. A molten sheet of polyester containing terephthalic acid as a main acid component is extruded from a die, is adhered to a cooling roll by an electrostatic adhesion method, and is solidified to form a sheet. In the method for forming a film to be axially stretched, the specific resistance of the polyester in a molten state is 3 × 10 ⁶ to 1 × 10 ⁸ Ω · cm, the cooling roll is a cooling roll on a microcrack surface, and A method for forming a polyester film, wherein the forming speed is 65 to 250 m / min.