JP2002355883A - Method for manufacturing polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyester film while preventing the adhesion of foreign matter to a die lip or the accumulation and growth thereof on the die lip even in long-time operation without lowering the quality and film forming properties of the polyester. SOLUTION: In manufacturing the polyester film by extruding a polyester resin from a die in a molten state to cool and solidify the same on a cooling medium in a close contact state, moist air is supplied to the periphery of the die lip to control humidification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester film. More specifically, the present invention relates to a method for extruding a molten resin from a lip (die lip) outlet of a die such as a T die or an I die of an extruder. The present invention relates to a method for producing a polyester film which prevents adhesion and deposition of foreign substances (aggregates of low molecular weight substances such as oligomers and oxides thereof) generated by separation.

[0002]

2. Description of the Related Art After a polyester resin is melted by an extruder, the molten resin is extruded from a die, and is tightly cooled and fixed on a cooling medium to produce a cast film. A gasified substance of molecular weight is generated. At this time, these gasified substances may solidify and adhere to the tip of the die lip, and may be deposited as foreign matter on the tip of the die lip.

When such foreign matter accumulates, streaks in the flow direction of irregularities (commonly referred to as die streaks and die lines) are formed on the cast film surface which has contacted with the molten resin extruded from the die and cooled and solidified. This causes unevenness in thickness and causes deterioration in quality of the final product (for example, in the case of a printer ribbon, the applied ink becomes streak-like unevenness, resulting in uneven shading during printing). Further, if the foreign matter itself falls off and rides on the molten resin, it becomes a spot-shaped convex defect or breaks from the foreign matter as a starting point, which is a serious cause of deterioration in film quality and yield. Therefore, when the solidified material adheres and grows on the die lip portion, the film formation is stopped, the lip portion is cleaned, and an operation of removing the foreign matter is performed, which also causes a reduction in yield.

Conventionally, various techniques have been proposed in order to prevent the deposit of foreign matter as described above. These proposals can be broadly divided into two types. One is an attempt to make it difficult for foreign matter to adhere to the die lip portion by the shape, material, and surface treatment of the die lip portion. Another proposal is to remove the generated gas outside the die lip without solidifying it around the die lip by suctioning the generated gas causing foreign matter or injecting an inert gas or steam into the die lip outlet.

[0005]

In the above-mentioned conventional proposal, in the prevention method using the shape, material, and surface treatment of the die lip portion, the initial adhesion can be suppressed, but the solidified material does not adhere during a long operation. Therefore, once the solidified material adheres, it is difficult to suppress the subsequent growth.

Further, in the method of removing generated gas by suctioning or injecting an inert gas or steam to the outside, the air flow around the die lip is disturbed. In the field of films, which are becoming increasingly thinner in recent years (for example, for magnetic recording materials such as video tapes and data recording, and for OA equipment such as printer ribbons and stencils), cast films also become thinner, so cooling from die lip parts If the air flow is turbulent in the space above the medium, the molten resin film between them will fluctuate, causing a fatal cause such as a decrease in quality due to thickness unevenness and a decrease in film formability due to cast unevenness. Therefore, installation of a suction / spray device that disturbs airflow should be avoided as much as possible.

It is an object of the present invention to provide a method for producing a polyester film which prevents foreign matter from adhering to the die lip portion and prevents the growth of the film even during long-time operation without deteriorating the quality or film forming property.

[0008]

Means for Solving the Problems In view of the above-mentioned problems, the present inventors have conducted intensive studies and as a result, have found that there is a significant difference in the adhesion and deposition growth of foreign substances due to environmental changes around the die lip. We paid attention to absolute humidity (moisture content in air) as a factor of. The inventors have found that the above-mentioned problems can be solved by controlling the absolute humidity of the die lip portion, and have reached the present invention.

That is, in the method for producing a polyester film according to the present invention, in a method for producing a cast film by melting a polyester resin, extruding it from a die, and tightly cooling and solidifying it on a cooling medium, heating steam is supplied around the die lip. Then, when controlling the humidification to the absolute humidity of 0.010 kg / kg or more, the position of the supply port of the heating steam is set as in the following equations (1) and (2), and (1) A ≧ h ≧ (B -500) (2) 3000 ≧ d ≧ 500 h: Supply port height [unit: mm] d: Horizontal distance from die lip outlet to supply port [unit:
mm] A: Height of die lip surface [unit: mm] B: Height of cooling medium for cooling and solidifying molten resin [unit: m]
m] The method for producing a polyester film, characterized in that the heated steam is supplied so as not to be directly blown to a molten resin and a die lip outlet from which the molten resin is discharged.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for producing a polyester film of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a positional relationship between a heating steam supply port, a die, and a cooling medium.

In FIG. 1, a polyester resin melted at 280 ° C. by an extruder (not shown) is extruded from a die 1 into a sheet, and a cast drum 2 cooled to 25 ° C. with water as a cooling medium is used. After being cooled and solidified, it is separated from the cast roll by the separating roll 3 to obtain an unstretched polyester film. The obtained unstretched polyester film is subjected to uniaxial stretching or biaxial stretching as required to produce a desired polyester film.

According to the present invention, in a method of manufacturing a cast film by melting a polyester resin, extruding it from a die 1, and tightly cooling and solidifying it on a cast drum 2, a heating steam supply port 5 is provided around a die lip 4 through a heating steam supply port 5. To control the humidification to an absolute humidity of 0.010 kg / kg or more. At this time, it is important to supply the heated steam from the heated steam supply port 5 so as not to directly blow the molten resin and the die lip outlet 6 from which the molten resin is discharged. Therefore, in the present invention, the supply port height h [unit: mm], the horizontal distance d from the die lip outlet to the supply port d [unit: mm], the die lip surface height A [unit: m]
m], and a cooling medium height B for cooling and solidifying the molten resin.
[Unit: mm] is set as in the following equations (1) and (2). (1) A ≧ h ≧ (B−500) (2) 3000 ≧ d ≧ 500 h: Supply port height [unit: mm] d: Horizontal distance from die lip outlet to supply port [unit:
mm] A: Height of die lip surface [unit: mm] B: Height of cooling medium for cooling and solidifying molten resin [unit: m]
m] The moist air supplied around the die lip in the present invention is heated steam. The heating steam referred to in the present invention is preferably 60
C. or higher, more preferably 70C to 100C.
Of steam. The moist air of the ultrasonic humidifier flows downward due to the low temperature, and is not suitable because the moisture cannot sufficiently diffuse to the exit portion of the die lip.

It is necessary to set the position of the supply port for supplying the heating steam as shown in the following equations (1) and (2). (1) A ≧ h ≧ (B−500) (2) 3000 ≧ d ≧ 500 h: Height of supply port [unit: mm] d: Horizontal distance from die lip outlet to supply port [unit:
mm] A: Height of die lip surface [unit: mm] B: Height of cooling medium for cooling and solidifying molten resin [unit: m]
m] The height of the die lip, the height of the supply port, and the height of the cooling medium for cooling and solidifying the molten resin are in a relationship of A ≧ h ≧ (B-500).

Since the temperature of the heated steam is high, the heated steam diffuses to the surroundings while rising upward. At this time, h <(B-5)
In the case of (00), high-humidity air comes into contact with a cooling medium (usually a cast drum) for cooling and solidifying the molten resin, causing dew condensation to cause various problems in casting film formation. In addition, a humidity distribution occurs in which the lower part has a low humidity and the upper part has a high humidity with the height of the heating steam supply port as a boundary. In the case of A <h, before the surrounding area of the die lip, which is the target, is sufficiently humidified, the vicinity of the ceiling becomes highly humid and dew condensation occurs on the ceiling. Causes various problems.

Therefore, when A ≧ h ≧ (B-500), it is possible to control the surroundings of the die lip as a target at a high humidity without affecting the quality and the film forming property most.

The position of the supply port in the horizontal direction with respect to the die lip outlet is 3000 ≧ d ≧ 500. When the horizontal position of the supply port with respect to the die lip outlet is d> 3000, most of the moisture diffuses to the periphery of the target die lip, so that a large amount of heated steam is required for sufficient humidification. That is, the air flow around the die lip is disturbed, and the thickness unevenness occurs.

On the other hand, if 500> d, interference with the electrostatic application device and other peripheral devices will occur, and workability such as thickness adjustment will be impaired.

Further, in the present invention, it is necessary to prevent the heated steam from being directly blown to the molten resin and the die lip outlet from which the molten resin is discharged. If heated steam is blown directly to the die lip outlet and the molten resin, the molten resin will fluctuate, causing the landing point on the cooling medium to fluctuate, causing thickness unevenness, and lowering the film forming property. is there. In the present invention, preferably, the supply port is installed in the vicinity of 2 m in the horizontal direction from the die lip outlet, for example, about 1.5 to 2.0 m, and the wind speed is 2 m / sec or less, for example, about 0.
At 5 to 1.5 m / sec, the heated steam is supplied at an angle such that the wind direction does not become the exit of the molten resin and the die lip.

The absolute humidity around the die lip outlet controlled by the present invention needs to be 0.010 (kg / kg) or more. It is preferably at least 0.012 (kg / kg), more preferably at least 0.016 (kg / kg). If the absolute humidity is less than 0.010 (kg / kg), streaks that are unacceptable as a product will occur in about 24 to 48 hours. Although there is no particular upper limit for the absolute humidity, it is usually about 0.050 (kg / kg). this is,
Since the die is hot and the relative humidity is not so high, there is no condensation around the die lip.However, condensation forms on the surrounding ceiling, causing water droplets to fall and causing various problems in quality and film forming properties. That's why. Further, if the ambient temperature is increased to reduce the relative humidity to prevent dew condensation, the environmental level substantially exceeds the level at which the operator can work.

In the present invention, when referring to the periphery of the die lip, a space formed when the bottom of the die having a die lip surface for extruding the molten resin in a sheet shape is lowered to a height at which the molten resin lands on a cast drum as a cooling medium. Used as a pointed word. In other words, it is used as a term that refers to the space represented by (die depth) x (die width) x (distance from the height of the die lip surface to the height at which the molten resin lands on the cast drum that is the cooling medium). . The periphery of the die lip is shown, for example, in FIG.

As means for controlling the humidification, a process portion for producing the cast film is surrounded by a partition or a film curtain, and a constant flow is supplied so that the accompanying flow when the film moves to the next process or leakage to the periphery is replenished. There is a method of supplying an amount of heated steam, a method of measuring the humidity at the die lip outlet portion by a humidity sensor, and feeding back the measurement result to the supplied amount of heated steam.

The cooling medium used in the present invention may be any as long as it can be cooled and solidified. Generally, it is a cast drum cooled by water. In addition, cooling may be performed by blowing air using a chamber, and this may be used in combination with a cast drum.

The polyester resin used in the present invention is a well-known polyester comprising an acid component and an alcohol component, and may be any polyester resin capable of forming a uniaxially or biaxially stretched film. As an acid component,
Terephthalic acid, isophthalic acid, phthalic acid, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, resin dicarboxylic acids such as decanedicarboxylic acid, alicyclic dicarboxylic acids such as cyclohexanecarboxylic acid, and more Can be used tricarboxylic acids such as trimellitic acid, etc.Alcohol components include ethylene glycol, diethylene glycol, polyethylene glycol, 1,4-butanediol, neopentyl glycol, cyclohexanedimethanol, polytetramethylene glycol, etc. Can be used.
In addition, other monomers or prepolymers may be copolymerized as long as they do not impair the film-forming properties, or may be blended with various polymers.

As the ester exchange catalyst for the polyester resin as described above, Ca, Li, Mn, Zn or T
i or the like can be used. Alternatively, terephthalic acid may be directly transesterified. Sb ₂ O ₃ , germanium oxide, or the like can be used as the polymerization catalyst.

If necessary, known additives such as stabilizers, viscosity modifiers, antioxidants and antistatic agents can be added to the polyester.

The polyester film obtained by the present invention can be used for magnetic recording materials such as video tapes and data recording, OA equipment such as printer ribbons and stencil paper, and diffusion films, transmission films and antireflection films used for personal computers and the like. For optical applications and release applications such as release films for ceramic capacitors, stamping films and label release films.

[0027]

EXAMPLES The absolute humidity was measured and calculated as follows. That is, the temperature T and the relative humidity φ were measured using a Crimomaster anemometer (Nippon Kanomax Co., Ltd.), and the absolute humidity was calculated according to the following equation. (Absolute humidity) = 0.622 e / (P-e) e: Temperature T, partial pressure of water vapor at relative humidity φ P: Total pressure of humid air (Example 1) Polyethylene terephthalate (PET) resin is extruded at 290 ° C. , And extruded in a sheet form from a T-die at a die lip surface height position (A) of 1850 mm, and cooled with a cast drum at a height position (B) of 1820 mm. Around the T die lip, the height of the supply port (h)
Is 1820 mm at the same height as the cast drum and heated steam is supplied from a position where the horizontal distance (d) from the exit of the die lip is 1500 mm, and the absolute humidity is 0.022 (kg / k).
g).

Using a roll stretching apparatus, a stretching temperature of 125
The film was roll-stretched in the longitudinal direction at a temperature of 6.0 ° C. and a draw ratio of 6.0.
Next, the obtained longitudinally stretched film is stretched in the transverse direction by a known transverse stretching apparatus (stenter) under the conditions of a stretching temperature of 110 ° C. and a stretching ratio of 4.0 times, and is subjected to a usual heat fixing treatment to have a thickness of 5 μm. Was obtained. As a result of observing the surface state of the obtained film, no base streaks were observed on the film surface, and the film was in an extremely good state. Table 1 shows the results.

(Example 2) The height (h) of the heating steam supply port was 1520 mm, the horizontal distance from the die lip outlet was 2000 mm, and the absolute humidity around the T-die was 0.017 (kg / kg). Example 1 except that
In the same manner as in the above, a polyester film having a thickness of 5 μm was obtained. As a result, as in Example 1, the film surface was in a good state. Table 1 shows the results.

(Embodiment 3) The absolute humidity around the T-die was set to 0.
A polyester film having a thickness of 5 μm was obtained in the same manner as in Example 1 except that the film thickness was changed to 012 (kg / kg). Observation of the sheet cooled by the cast drum
Although a very thin ferrule was observed, the strength of the ferrule was 0.2 μm in the film after biaxial stretching. Table 1 shows the results.

(Comparative Example 1) In order to control the absolute humidity around the T-die, moist air was generated by an ultrasonic humidifier. However, the generated steam has a temperature of about room temperature (3.
The test was abandoned because it was cold moist air (0 to 40 ° C.) and, unlike heated steam, flowed downward from the supply port and could not sufficiently diffuse into the space, and did not rise to the desired absolute humidity. Table 1 shows the results.

COMPARATIVE EXAMPLE 2 Except that the height (h) of the heating steam supply port was set to 820 mm and the absolute humidity around the T-die was set to 0.025 (kg / kg). A film was formed in the same manner as in Example 1. As a result, the test was abandoned because the cast drum was dewed and the film was cracked due to the blocking of the drum and the sheet. Table 1 shows the results.

(Comparative Example 3) The height of the heating steam supply port was 2
Example 1 except that the height was 050 mm above and the absolute humidity around the T-die was 0.012 (kg / kg).
A film was formed in the same manner as described above. As a result, the test was abandoned because the area around the ceiling was in a high humidity state, and water droplets condensed from the ceiling fell on the cast drum and the sheet, causing a defect of the film and causing the film to break due to blocking of the drum and the sheet. Table 1 shows the results. (Comparative Example 4)
Except that the heating steam supply port height was 1520 mm, the distance from the die lip outlet was 3500 mm, and the absolute humidity around the T-die was 0.012 (kg / kg),
A film was formed in the same manner as in Example 1. As a result, the test was abandoned because the wind speed increased to supply a large amount of heated steam to achieve the target absolute humidity, the air flow around the die lip was disturbed, and the fluctuation of the molten resin became large. Table 1 shows the results.

(Comparative Example 5) The absolute humidity around the T-die was set to 0.
A polyester film having a thickness of 5 μm was obtained in the same manner as in Example 1 except that the film thickness was changed to 008 (kg / kg). The result is that the strength of the base streak is 0.4 μm, and the number is 5 / m,
Three lines / m were measured at 0.2 μm. Table 1 shows the results.

[0035]

[Table 1]

[0036]

According to the present invention, in a method for producing a polyester film, foreign matter (such as oligomers and other low molecular weight substances) separated from a molten resin is formed at the lip exit of a die such as a T-die or an I-die of an extruder. Aggregates and their oxides) can be prevented from adhering and accumulating, and a film having no cap streaks can be formed for a long time, which is of great industrial value.

[Brief description of the drawings]

FIG. 1 is a diagram showing a positional relationship between a heating steam supply port, a die, and a cooling medium.

[Description of Signs] 1: Die 2: Cast drum 3: Separating roll 4: Around die lip 5: Supply port of heated steam 6: Die outlet h: Supply port height d: Horizontal distance from die lip exit to supply port A: Die lip surface height B: Cooling medium height for cooling and solidifying molten resin

Claims (1)

[Claims] 1. A method for manufacturing a cast film by melting a polyester resin, extruding the same from a die, and cooling and solidifying the polyester resin on a cooling medium. In controlling the humidification to at least kg, the position of the supply port of the heated steam is set according to the following formulas (1) and (2), and (1) A ≧ h ≧ (B−500) (2) 3000 ≧ d ≧ 500 h: Supply port height [unit: mm] d: Horizontal distance from die lip outlet to supply port [unit:
mm] A: Height of die lip surface [unit: mm] B: Height of cooling medium for cooling and solidifying molten resin [unit: m]
m] A method for producing a polyester film, characterized in that the heated steam is supplied so as not to be directly blown to a molten resin and a die lip outlet from which the molten resin is discharged.