JP2002001796A - Method for molding polyester sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can control the transfer of the micro- cracks of the surface of a cooling roll to the surface of a polyester sheet and can produce the polyester sheet excellent in smoothness and good in quality stably at a high speed for a long time in a method for molding the polyester sheet using the cooling roll having a micro-crack surface. SOLUTION: In the method for molding the sheet in which the molten sheet of the polyester in which 2,6-nephthalene dicarboxylic acid is used as a main acid component is extruded from an orifice-shaped nozzle, contacted closely with the cooling roll having the micro-crack surface, and solidified, the surface temperature of the cooling roll in the neighbourhood of a point where the molten sheet contacts the cooling roll is kept at 5-100 deg.C.

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 using a cooling roll on the surface of a microcrack, and more particularly, it is possible to suppress the transfer of the shape of the microcrack to the sheet surface, and to provide excellent smoothness. The present invention relates to a method for forming a polyester sheet capable of stably producing a high quality polyester sheet at a high speed for a long time.

[0002]

2. Description of the Related Art As a method for forming a polymer sheet, there has been conventionally known a method in which a molten sheet of a polymer is extruded from an orifice-shaped die, and is adhered to a cooling roll and solidified (cast). In this method, in order to promote the adhesion of the molten sheet to the cooling roll, an electrostatic adhesion method, a reduced pressure adhesion method, a gas pressing method and the like are usually used in combination. At this time, if the sheet is cast in a state where a part of the air entrapped between the cooling roll and the molten sheet remains, a defect occurs on the surface of the sheet, so that the molding is performed under the condition that the air is sufficiently discharged. It is necessary.

For forming a sheet, a cooling roll having a smooth surface (mirror finish) is usually used. In the case of casting using the mirror-finished cooling roll, discharge of air interposed between the molten sheet and the cooling roll becomes insufficient as the casting speed increases. In particular, when the electrostatic adhesion method is used in combination, the remaining air causes a remarkable foam-like defect on the sheet surface, so that the surface smoothness is reduced.

As a measure for solving such a drawback, Japanese Patent Application Laid-Open No. 46-439 proposes a sheet forming method using a cooling roll whose surface is roughened by sandblasting or the like. According to this method, since the gap between the molten sheet and the cooling roll can be secured by roughening the roll surface, the air can be easily discharged.
However, in order to make the air discharge effect remarkable by this method, it is necessary to make the mat roughness of the cooling roll surface rough, and as a result, the unevenness of the roll surface is transferred as if it were replicated on the sheet surface. Then, an orange-skinned or pear-skinned defect occurs on the sheet. This defect remains as a surface defect in a stretched film obtained by further stretching the sheet.

On the other hand, if the unevenness (matte roughness) of the roll surface is reduced to such an extent that transfer defects do not occur by this method, the gap from which air is discharged becomes narrow, and the sublimation from the molten sheet occurs. There is a disadvantage that the casting speed is reduced in a short time because the material adheres and accumulates in the gap as the production progresses and closes the discharge passage.

Another solution is disclosed in Japanese Patent Application Laid-Open No. 58-1 / 1983.
No. 83220 proposes a method using a cooling roll having a number of fine microcracks formed on the surface thereof (microcrack surface cooling roll). In this method, since a cooling roll having microcracks with a very fine groove width formed on a flat surface is used, the winding is performed without lowering the smoothness as compared with a method using a cooling roll roughened by sandblasting or the like. There is an advantage that a discharge path for the intake air can be secured.

However, even in this method, in order to increase the speed of sheet production, it is necessary to increase the cross-sectional area of the microcrack groove to increase the dissipation speed of the trapped air. However, it is difficult to arbitrarily control the ratio between the groove width and the groove depth in the process of processing the microcracks on the cooling roll surface. It will be wide. When a sheet is produced using a microcrack-shaped cooling roll having a large groove width, the groove shape is also transferred to the sheet surface, and a net pattern defect clearly appears on the sheet surface. When the sheet is subsequently stretched to form a biaxially stretched film, the orange skin-like defect on the film surface becomes remarkable.

For this reason, in order to produce a high-quality film having no transfer defects, a micro-cracked cooling roll having a narrow groove width is used. Another problem arises in that sublimates from the sheet clog the air outlet and reduce productivity.

In order to solve this problem, Japanese Patent Application Laid-Open No. 62-196
Japanese Patent Publication No. 118 proposes a method using a cooling roll having a surface on which microcracks having a shape narrower than a ventilation groove inside a cross section having an opening connected to the opening are formed.
This method narrows the opening of the microcrack, which is the main cause of the transfer defect of the sheet, to secure a wide width of the ventilation groove inside the cross section which is a dominant element of the speed-up effect.
However, the process of narrowing the opening of the micro crack is
In the process of processing, there is a problem that the opening is closed, or when the surface is polished, the opening ends are missing and the opening is widened. We have not yet reached a satisfactory level.

As other measures, a method of increasing the depth of the groove without increasing the groove width of the microcrack, or a method of improving the shape of the microcrack by connecting one groove to a plurality of grooves are considered. However, a technique for arbitrarily controlling the basic characteristics of microcracks such as groove width, groove density, and airflow resistance has not yet been realized. In particular, it is extremely difficult to form optimal microcracks uniformly on a wide surface of a large cooling roll.

In recent years, the accuracy required for film quality has become more and more advanced, and a film having a surface defect as described above cannot satisfy the requirement for uniformity of light transmittance in, for example, optical applications. Further, in magnetic recording applications, particularly in high-density recording in which an extremely thin film having a thickness of Angstrom level such as a vacuum deposited thin film is used as a recording layer, the surface smoothness requirement as a base film cannot be satisfied. As described above, while demands for film quality such as optical uniformity and surface smoothness are becoming more and more advanced, improvement of productivity (higher speed and improvement of operation rate) is an important issue in film production.

[0012]

SUMMARY OF THE INVENTION The present inventor has solved the above-mentioned problems and has succeeded in reducing the transfer to a sheet or a stretched film without improving the shape of microcracks on the surface of a cooling roll, and has a long production time. As a result of studying measures to maintain the time, the inventors have found that the problem can be solved by maintaining the surface temperature of the cooling roll in a specific range, and have reached the present invention.

[0013]

SUMMARY OF THE INVENTION The object of the present invention is to provide a method comprising:
In a method for forming a sheet in which a molten sheet of polyester containing naphthalene dicarboxylic acid as a main acid component is extruded from an orifice-shaped die and is adhered to a cooling roll on the surface of a microcrack to be solidified, the vicinity of a point where the molten sheet lands on the cooling roll The surface temperature of the cooling roll is 5 ° C to 1 ° C.
It can be attained by a method for forming a polyester sheet, which is maintained at a temperature of 00 ° C.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[Polyester] In the present invention, a polyester is a thermoplastic resin polyester comprising an acid component and a glycol component, wherein at least 50 mol% of the acid component is a polyester comprising 2,6-naphthalene dicarboxylic acid. 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, 1,6-hexanediol, and cyclohexane. Examples thereof include dimethanol, polyethylene glycol, and polytetramethylene glycol. Among them, ethylene glycol, 1,3-propanediol, and 1,4-butanediol are preferable. Is preferred because of its excellent mechanical properties and the like.

Preferred examples of the polyester in the present invention include polyethylene-2,6-naphthalate. Polyethylene-2,6-naphthalate is 2,6-naphthalate in a proportion of 50 mol% or less, particularly 20 mol%.
A component other than naphthalene dicarboxylic acid and ethylene glycol may be copolymerized. Examples of the copolymerization component include terephthalic acid, isophthalic acid, hexahydroterephthalic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid in the acid component, and diethylene glycol and propylene in the glycol component. Glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanedimethanol, polyethylene glycol, polytetramethylene glycol, and the like. it can.

The polyethylene-2,6-naphthalate may be mixed with another polymer such as polyethylene terephthalate at a ratio of 50% by weight or less.

The polyester in the present invention preferably has a melt viscosity of 300 to 3000 Pa · s. When the melt viscosity is less than 300 Pa · s, a transfer defect of microcrack strength may occur in the obtained sheet. On the other hand, when the melt viscosity exceeds 3000 Pa · s, uniform adhesion of the molten sheet to a cooling roll is achieved. Is not preferable because it may be difficult.

[Cooling Roll] In the present invention, a cooling roll having a microcrack 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 cracks existing on the surface of the cooling roll have at least five cracks intersecting at least one direction of the scanning line 10 mm on the surface, and 70% or more of the cracks have an opening width of 0.3 μm or more. Therefore, it is preferable that the total width of all the cracks intersecting the scanning line 10 mm is 5 mm 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 of the surface of the cooling roll measured by a vacuum leakage method described later is 10,000 seconds or less, further 5000 seconds or less, particularly 1000 seconds or less. It is preferable that The most preferable range of the ventilation resistance is 2 to 500 seconds. If the ventilation resistance exceeds 10,000 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, the air flows through a groove of the rough surface. The time required for the degree of vacuum in the space 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 to connect a vacuum pump 4 to one end of a vacuum vessel 1 having a vacuum gauge 2 via a vacuum cock 3 as schematically shown in FIG. 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 polyester is extruded from an orifice-shaped die, is adhered to a cooling roll on the surface of a microcrack, and is solidified to form a sheet. 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, when the molten sheet is brought into close contact with the cooling roll, it is preferable to use an electrostatic adhesion method, a reduced pressure adhesion method and / or a gas pressing method together. Here, the electrostatic adhesion method is a method in which an electrostatic charge is applied to a molten sheet and the molten sheet is brought into close contact with a cooling roll surface by the Coulomb force. The reduced pressure adhesion method is to reduce the pressure on the cooling roll side of the molten sheet. The gas pressing method is a method in which a static pressure of a gas mainly composed of gas pressurized air is applied to a molten sheet and pressed against the cooling roll surface.

In the present invention, the surface temperature of the cooling roll near the point where the molten sheet lands on the cooling roll is 5 ° C to 1 ° C.
It is necessary to keep it in the range of 00 ° C. The cooling roll surface temperature near the point where the molten sheet lands on the cooling roll is defined as at least one cooling roll in a section from the position where the molten sheet coming out of the die lands on the cooling roll surface to 200 mm in the upstream direction of the roll. The surface temperature (hereinafter, may be simply abbreviated as “cooling roll surface temperature”). At the position where the molten sheet lands on the cooling roll, the measurement space between the molten sheet and the cooling roll is narrow, and it is often difficult to insert a sensor for temperature measurement. Is the temperature of at least one point in a 150 mm section from 50 mm upstream to 200 mm from the landing point. This temperature depends on the thin film thermistor,
A method in which a temperature sensor such as a thermocouple is brought into contact with the surface of a cooling roll, or a non-contact measurement with a heat flow sensor (for example,
Teijin Engineering Limited Roll temperature measurement device TL
R-1) can be conveniently used.

In the present invention, the surface temperature of the cooling roll is set to 5 ° C.
By keeping the temperature in the range of 100 ° C., it is possible to obtain a polyester sheet in which transfer defects of microcracks are improved. In the cooling process of the sheet in casting, the highest flowability of the molten sheet is at the moment when the molten sheet comes into contact with the cooling roll. The surface temperature of the contact surface is quenched, and it is estimated that the transfer strength decreases because the fluidity of the polymer decreases rapidly.If the surface temperature of the cooling roll is high, the transfer strength decreases because the fluidity of the polymer gradually decreases. It is estimated to be larger.

When the cooling roll surface temperature is less than 5 ° C.,
Condensation occurs at the side end of the cooling roll where the sheet is not in contact, and the condensed water droplets contact the sheet to cause defects on the sheet. The lower limit of the cooling roll surface temperature is preferably 10
° C, more preferably 13 ° C. On the other hand, when the cooling roll surface temperature exceeds 100 ° C., transfer of microcracks becomes remarkable depending on the type of polyester and the viscosity of the molten sheet. Further, sublimates accumulate inside the microcracks, and a portion having high airflow resistance is locally formed, so that a defect occurs in the film in that portion. This drawback causes film cutting, especially in the process of further stretching the sheet. The upper limit of the cooling roll surface temperature is preferably 90 ° C., and more preferably 80 ° C., because microcrack transfer defects are further suppressed and the stability of the film forming process is improved.

By keeping the surface temperature of the cooling roll within the range of the present invention, the rate of diffusion of the polyester sublimate from the molten sheet is reduced, and the rate of sublimation from the surface is also reduced, so that deposition on the microcrack surface is prevented. Can be suppressed. Further, since the temporal change of the ventilation resistance of the crack groove can be suppressed, the casting speed can be maintained at a high level for a long time.

Generally, the microcrack surface has a variation in groove width and crack density depending on the portion, and it is difficult to avoid the variation in airflow resistance due to the portion. Yes, if a portion with high airflow resistance occurs locally, it will cause a defect in the film at that portion, and the defect may cause cutting in the subsequent stretching process and also affect the stability of the film forming process There is.

In the present invention, the thickness of the sheet is 5 to 200.
μm is preferred. Further, the casting speed in the present invention is preferably 30 m / min or more at the peripheral speed of the cooling roll. There is no particular upper limit, but 200 m /
min is preferred. The sheet formed by the present invention can be stretched favorably in the subsequent biaxial stretching step.

[0031]

The present invention will be further described with reference to the following examples. Incidentally, the melt viscosity of the polymer in the examples (Pa · s)
Uses a Koka type flow tester (manufactured by Shimadzu Corporation) in accordance with JIS K7210 to reduce the amount of the molten polymer to 30.
After maintaining at 0 ° C. for 60 seconds, the measurement was performed at a load of 30 MPa using a nozzle having a length of 10 mm and a diameter of 1 mm.

Example 1 Melt viscosity was 1200 Pa · s
Of polyethylene 2,6-naphthalate of width 40
Extruded from a 0 mm die into a 120 μm thick sheet,
An unstretched sheet was obtained by casting with a cooling roll at a speed of 55 m / min while using the electrostatic adhesion method. Subsequently, the unstretched sheet was biaxially stretched 3.9 times in the longitudinal direction and then 4.1 times in the transverse direction, and further heat-treated at a temperature of 225 ° C. to obtain a biaxially stretched film.

The cooling roll has a microcrack surface having an average of 29 seconds of ventilation resistance measured by a vacuum leak method (the number of cracks crossing a scanning line of 10 mm on the surface is 75 on average, and the number of cracks crossing the scanning line of 10 mm is 10 mm). On the other hand, those having an average opening width of all the intersecting cracks of 12 μm) were used. Also, during the casting, 100
The surface temperature (measured by the roll temperature measuring device TLR-1) of the cooling roll upstream of 55 mm was 55 ° C.

Although a very weak transfer pattern of microcracks was observed in the obtained unstretched sheet, no orange-skin-like defect was observed in the biaxially stretched film. The material met the quality standards as a base material. Although the height of the mountains of the transfer pattern of the unstretched sheet was about 0.05 μm, the height of the transfer pattern of the biaxially stretched film was 0.01 μm.
Could not be detected with the detection accuracy of

Comparative Example 1 An unstretched sheet was cast in the same manner as in Example 1 except that the surface temperature of the cooling roll 100 mm upstream from the point at which the sheet material lands was 110 ° C.
Further, a biaxially stretched film was obtained.

The obtained unstretched sheet has a very clear transfer pattern of microcracks, and a clear orange-skin-like defect is also observed in the biaxially stretched film. However, it did not meet the criteria for a low-rank magnetic recording material for audio. In addition, the height of the mountain range of the transfer pattern of the unstretched sheet reaches about 0.7 to 0.9 μm, and the height of the transfer pattern in the biaxially stretched film is 0.06 to 0.09 μm, which is obtained by the present invention. The surface smoothness was much lower than that of the film.

[0037]

According to the present invention, when a polyester containing 2,6-nalephthalenedicarboxylic acid as a main acid component is cast by a cooling roll on the surface of a microcrack, the transfer of microcrack irregularities to a cast sheet is low. Level, and high-quality film can be produced stably 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 (3)

[Claims] 1. A method for forming a sheet comprising extruding a molten sheet of polyester containing 2,6-naphthalene dicarboxylic acid as a main acid component from an orifice-shaped die and adhering it to a cooling roll on the surface of a microcrack to solidify the molten sheet. A surface temperature of the cooling roll near a point where the rubber sheet lands on the cooling roll is kept in a range of 5 ° C to 100 ° C. 2. A polyester having a melt viscosity of 300 to 30.
The method for forming a polyester sheet according to claim 1, wherein the range is 00 Pa · s. 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 leakage method is 10,000 seconds or less.