JPS5850173B2 - Manufacturing method of polyester film - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a polyester film.

More specifically, a film is manufactured by closely solidifying a thin film-like melt extrudate of thermoplastic polyester on the surface of a rotating cooling roll. The present invention aims to provide a method for producing a homogeneous film by preventing air from being entrained in the film and uniformly cooling the film.

Conventionally, when manufacturing a film by melt-extruding a thermoplastic polymer into a thin film and solidifying it on the surface of a cooling roll, this was done to prevent air from being trapped between the cooling roll and the film and causing uneven thickness of the film. , a method is known in which the film is brought into close contact with a cooling roll due to an electrostatic charge, but this method increases the production speed of the film (for example, about 30 m/am).
(above), there is a drawback that air cannot be prevented from being trapped between the film and the cooling roll.

A method has also been proposed in which the film is cast on the cooling roll surface and another roll is used to bring the film into close contact with the cooling roll surface, but the film extruded from the die lip tends to be thicker at both ends. However, it is difficult to provide a pressure roll that matches the thickness of the film in the width direction, and the film surface is easily scratched if the film is forcibly pressed.

Various methods have also been proposed in which the thin film is brought into close contact with the cooling roll surface using an air knife.

Although these methods do not entrap air and can be performed at higher speeds than the electrostatic adhesion method, they have many unsatisfactory points when producing polyester films.

For example, the melt viscosity when forming a polyester film is significantly lower than that of polypropylene, etc., and if the distance between the extrusion die lip and the cooling roll is large, it is not only difficult to accurately control the width of the thin film, but also Since the shrinkage in the width direction is not uniform, the thickness of the thin film becomes non-uniform, and the flatness of the obtained film is significantly impaired.

In order to improve this problem, when trying to bring the die lip and the cooling roll closer together, airflow is blown from the air knife even though the molten polymer thin film is still in a flowable state, causing vibrations due to the airflow of the molten material. However, it has the disadvantage that it causes significant periodic fluctuations in thickness and width, especially at both ends of the thin film, reducing the value of the product.

In order to improve these drawbacks, Japanese Patent Publication No. 4119706 discloses that after casting a molten film on a cooling roll, it is fixed by blowing an air stream to both ends of the film, and then air stream is applied to the entire width of the film using an air knife. A method of spraying has been proposed.

This method can reduce shrinkage in the width direction of the film, but
Because the thickness is significantly different between the ends and the center of the film, and because the molten film is vibrated by the airflow that first blows on both ends, the unevenness of the film's thickness cannot be improved much, and the smoothness of the ends of the film cannot be improved. Sex isn't good either.

Furthermore, in Japanese Utility Model Application Publication No. 50-117173, in order to prevent part of the air blown from the air knife from flowing to the die lip side and causing the film to vibrate, it is proposed that the air knife be separated from the molten film between the extrusion die and the air knife, and An air knife has been proposed that is provided with a seal plate that covers the gold mine of the molten film.

However, with this method, there is an air current flowing at high speed around both ends of the seal plate toward the die lip, and the molten film vibrates little by little between the die lip and the cooling roll.
The thickness unevenness and smoothness of the film are not improved much.

Japanese Patent Publication No. 49-30694 d discloses that in order to suppress film vibration and aspirate effect caused by high-speed gas flow,
At a position above the normal frost point where the extruded film comes into contact with the mirror roll circumference, a high-speed gas flow is injected at a downward angle to the mirror roll circumference, and a spray nozzle is directed downward to the mirror roll circumference. A method has been proposed in which the atmospheric pressure in the vicinity is made somewhat higher than atmospheric pressure.

This method can prevent the film from floating on the mirror roll due to the aspirate effect and reduce the uneven thickness of the film in the width direction. During a certain period of time, the film is forcibly pressed against the cooling roll by the jet stream, causing the film to vibrate, resulting in periodic thickness unevenness in the direction in which the film is taken.

Furthermore, Japanese Utility Model Publication No. 44-19914 discloses that the opening degree of the air outlet of the air knife can be adjusted, and of the two lips constituting the outlet, the lip on the side farther from the extrusion die protrudes from the opposite lip. An air knife with a structure has been proposed.

However, when this air knife is applied to polyester film formation, the film width tends to decrease due to the low melt viscosity of polyester during film formation.
In order to prevent this, it is necessary to accelerate solidification by spraying this gas before it is sufficiently solidified. The gas jet that impinged on the film also flows toward the extrusion die, bounces off the die, and disturbs the air flow around the die and air knife, causing the unsolidified film to vibrate, resulting in the resulting film Unevenness in thickness and poor smoothness cannot be sufficiently improved.

In recent years, there has been a strong trend toward wider and faster film production equipment, and as a result, these drawbacks tend to become more prominent.Therefore, there is a strong demand for film production methods that do not have these drawbacks. There is.

The present inventor has developed a film forming method that does not have such drawbacks (as a result of intensive research). The length of the protruding part of the lip is the length of the side near the extrusion die l, keeping the tip of the lip of the air knife in a certain relationship, and
The point at which the thin film in a molten state starts contacting the cooling roll surface (hereinafter, this point is referred to as point F).

) is maintained in a specific relationship with t, and the gas is blown at a position where the thin film in a molten state naturally starts contacting the cooling roll, these drawbacks can be improved. We have discovered that this is the case, and have arrived at the present invention.

That is, the present invention involves manufacturing a film by melt-extruding thermoplastic polyester into a thin film onto the surface of a rotating cooling roll and solidifying the thin film in close contact with the cooling roll surface using gas injected from an air knife. (a) The shortest distance between the extrusion die slit tip and the cooling roll surface is maintained at 10 mm or more and 30 plates or less, (b) The point at which the thin film in a molten state starts contacting with the cooling roll surface (
(c) inject the gas from the air knife so that the point F) does not substantially vary between when the gas is injected from the air knife and when the gas is not injected; The length of the protruding part of the lip is determined by setting the length of the side closest to the extrusion die E as a dog, the opening degree t (unit: mm) of the gas outlet, and the length of the protruding part of the two lips forming the gas outlet. Length difference △l (unit: h), shortest distance h between point F and lip tip (unit: m)
7IL), and "a straight line connecting the tip of the gas-injecting side (inside) of the lip that is close to the cooling roll out of the two lips that form the air outlet and point F" and "a straight line that connects point F with the tip of the lip that is close to the cooling roll" The value θ (unit: degrees) measured in the direction of the extrusion die based on the normal line is calculated by the following formula tζ△l 5t (Formula 1) 2≦h
≦8t ・・・・・・・・・(Formula 2) Oo<θ×35°
This is a method for producing a polyester film characterized by providing an air knife and forming the film so as to satisfy (Formula 3).

The thermoplastic polyester used in the method of the present invention is preferably one in which 90 mol% or more of the dicarboxylic acid component is an aromatic dicarboxylic acid component.

Moreover, it is preferable that 90 mol% or more of the diol component is an aliphatic glycol component.

In particular, its dicarboxylic acid component and diol component are each 9
0 mol% or more is a single component (for example, in the dicarboxylic acid component, the terephthalic acid component, or naphthalene-2,
Among diol components such as 6-dicarboxylic acid components, those occupied by ethylene glycol components, tetramethylene glycol components, etc. are preferred.

Preferably used polyesters include polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate,
Examples include polytetramethylene-2,6-naphthalene dicarboxylate.

The thermoplastic polyester may be used alone or in combination of two or more.

Blends in which the thermoplastic polyester accounts for 90% by weight or more and the other polymers account for 10% by weight or less are also included in the thermoplastic polyester I used in the process of the present invention.

In the method of the present invention, the shortest distance between the extrusion die slit tip and the cooling roll surface is maintained at 101nrIL or more and 30rIL1rL or less.

If the distance is less than 10 minutes, it is undesirable because if the film wraps around the cooling roll, it will easily fuse to the extrusion die and it will take a long time to return to a stable production state. .

Furthermore, if the distance is greater than 30 mm, the width of the melt-extruded thin film will be significantly reduced, which is not preferable.

The distance is particularly preferably 12 plates or more and 20 r/1 rIL or less.

In addition, in the method of the present invention, the point at which the thin film in a molten state starts contacting the cooling roll surface (point F) does not substantially change between when gas is injected from the air knife and when no gas is injected. Injects gas from an air knife.

Point F changes due to gas injection compared to when no gas is injected (this means that point F approaches the die lip side due to gas injection.

), when the gas is not injected, the gas jet blows onto at least a part of the part where the molten thin film is still in the space between the die and the cooling roll surface, forcing the thin film onto the cooling roll surface. This is because the thin film vibrates when it is pressed.
This is not preferable because periodic thickness unevenness occurs in the direction in which the obtained film is taken.

It is preferable to inject the gas toward point F as much as possible without moving point F from the position when no gas is injected.

In the method of the present invention, Δl is made to satisfy Equation 1 above.

If Δl is smaller than t, the gas injected from the nozzle will also flow toward the die lip, which is undesirable because the thin film between the die and the cooling roll surface will vibrate.

If Δl is larger than 5t, it is necessary to significantly increase the gas flow velocity in order to bring the thin film into close contact with the cooling roll surface, and in this case, a large amount of high-speed gas flows toward the non-protruding lip of the air knife. Because of the flow, the thin film that is in the middle of cooling and solidifying on the cooling roll surface is likely to float and vibrate, which is undesirable.

A preferable range of Δl is from 2 to 3.

In the method of the present invention, h is made to satisfy Expression 2 above.

If h is less than 2 plates, it is not preferable because if the thin film sticks to the cooling roll, it will be caught between the air knife and the cooling roll and will be difficult to remove.

Furthermore, if h is thicker than 8t, it is necessary to significantly increase the gas flow velocity to bring the thin film into close contact with the cooling roll surface, and in this case, a large amount of high-speed gas flows toward the non-protruding lip of the air knife. This is not preferable because the thin film that is in the middle of being cooled and solidified on the cooling roll surface tends to vibrate.

The preferred range of h is 2 (tomo) or more and 4 or less.

In addition, in the method of the present invention, θ is rubbed so that it satisfies the above formula 3.

If θ is smaller than 35°, an aspirate effect will occur and the thin film will float more easily, which is undesirable. If it is smaller than Oo, air will flow toward the die, causing the thin film between the die and the cooling roll surface to This is not desirable because it causes vibration.

A preferable range of θ is 00 or more and 20° or less.

In order to obtain a film of uniform quality, the lip spacing t of the air knife outlet should be 0.3 to 1.5 mm, especially 0.5 to 1.5 mm.
It is preferable to have 0 dishes.

Further, in order to bring the thin film into close contact with the cooling roll surface, it is preferable to blow out gas at a wind speed of 10 to 60 m/sec through the lip portion l of the air knife outlet.

If other manufacturing conditions are the same, as the film forming speed increases, the smoothness of the obtained film tends to improve as the gas jet speed increases.

In the method of the present invention, it is preferable to inject gas at a higher speed at both ends of the air knife outlet than at the center because the film can be brought into close contact with the roll surface without any undesirable side effects.

In that case, it is preferable to provide a partition wall at a distance of 10 to 30 degrees from both ends of the air outlet f of the air knife to divide the gas flow path and thereby provide a difference in the gas injection speed.

And the injection speed is 5m/5eC0~10m for the injection from both ends than for the injection from the center.
It is preferable to increase the speed by /5eC0.

According to the method of the present invention, 1) A uniform film can be easily produced at high speed, where methods such as electrostatic adhesion methods trap air between the film and the cooling roll and cannot obtain a uniform film. sell.

2) Thickness unevenness and film width fluctuations caused by vibrations at both ends of the film can be eliminated.

3) If the film to be cast is thin (approximately 30
When the film is extruded from a die with a thickness of 0μ or less, both ends are particularly thick (approximately 1.5 to 3 times the thickness of the center). High-speed gas blowing I can thus be suppressed.

4) Since the positions of the gas outlet of the Daito air knife and the cooling roll can be brought closer to each other, reduction in film width can be suppressed.

5) Precipitation of white powder on the cooling roll can be reduced.

There are advantages such as

Next, some examples of embodiments of the present invention will be described with reference to the drawings.

1-4 are schematic diagrams of examples of embodiments of the invention.

Moreover, FIG. 5 is a schematic diagram showing an example of the gas supply part and the blowing part of the air knife, and FIG. 6 is a schematic diagram showing the mutual positional relationship of the extrusion die, the cooling roll, and the air knife lip.

In these drawings, 1 is a sheet extrusion die, 2 is a cooling roll, 3 is a film, 4 is an air knife, 5 is a gas outlet lip, 6 is a sealing material, 7 is a heat insulating material, 8 is a gas supply pipe, and 9 is a Both ends are gas supply pipes, 10 is a flow path partition plate, 11 is a uniform thickness tube, and 12 is a hole for measuring gas static pressure.

The molten resin film discharged from the extrusion die 1 comes into contact with the cooling roll 2, and is further firmly adhered to the cooling roll by a gas jet blown from between the lips 5 of the air knife, and at the same time is cooled and solidified.

In an embodiment of the invention, the lip 5 of the air knife protrudes in such a way that the side closer to the extrusion die is in each case closer to the film 3t to be tightly adhered to the cooling roll than the lip on the opposite side.

3 and 4 1 is a structure for filling the space between the air knife lip and the die, and this structure is used to further reduce the vibration of the molten film between the die and the cooling roll. belongs to.

Preferably, the portion of the structure 6 facing the molten film 3 is coated with a heat-resistant material, such as a material mainly composed of polytetrafluoroethylene.

By carrying out such a treatment, even if the molten film sticks to the surface of the film 6, the stickiness can be easily removed.

In FIG. 5, air flowing from the gas supply pipe 8 is made uniform in the barrels 11 and 4, bundled together in the flow path, and blown out from between the lips 5.

Further, the gas flowing in from the gas supply pipe 9 enters both ends of the barrel 4 and is ejected from a triangular outlet surrounded by a lip 5 and a lip 10.

The length of this triangular air outlet is 10 mm from the end of the air knife.
It is best to set it to ~20 mm.

The speed of the jet from both ends of the blow-off port may be adjusted depending on the thickness of both ends of the film, but it is generally preferable to set it higher than that at the center.

The one shown in FIG. 4 is a combination of an air knife and an extrusion die, but the air knife 4 and die 1 are separated by a heat insulating material 7.

I prevents heat transfer from the die to the air knife and prevents the gas temperature from rising.

Below, methods for measuring main measurement values in the present invention are shown.

Air velocity) Create a beat tube using an ultra-thin stainless steel tube (1,0+ymφ) and position it extremely close to the lip.
The dynamic pressure and static pressure of the jet were measured to determine the differential pressure.

The relationship between differential pressure and wind speed was determined in advance by measuring the wind speed with an anemometer (Anemo Master Nippon Kagaku Kogyo Co., Ltd.).

Wind speed was determined by actually measuring the differential pressure.

Thickness variation rate of film) Samples were taken in the length direction 1 and 2 m, and the thickness was measured with a micrometer at intervals of 10cII1, and was determined from the following formula.

(Film width variation) Classification was done as follows.

There was almost no variation in the width of the first grade, and both ends of the film were transparent.

Grade 2: Both edges of the film were whitened and sawtoothed (the width varied).

Grade 3: Both ends of the film become white, the width of the serrations fluctuates,
Due to this variation in width, the rate of variation in thickness at the center of the film also increased.

Grade 4: It was difficult to increase the number of continuous films.

Examples 1 to 7 and Comparative Examples 1 to 5 Polyethylene terephthalate having an intrinsic viscosity (measured at 25°C using 0-tetrachlorophenol as a solvent) of 0.640 was melted by heating at 300°C in an extruder, and a 410 mm wide polyethylene terephthalate was melted in an extruder. It was extruded from an extrusion die, rapidly cooled on the surface of a cooling roll (diameter 634 mm) with a surface temperature of 65°C, and was heated to about 10% under the conditions shown in Table 1.
The 0μ film was taken off.

At this time, an air knife of the type shown in FIG. 2 was used so that air was blown out at a uniform velocity over the entire width of the outlet.

As a result, the uniformity of the thickness and width of the obtained film was as shown in Table 1.

In the case of Examples 1 to 7, films with clearly good uniformity were obtained.

On the other hand, in the method shown in the comparative example, a film with desired uniformity could not be obtained.

The amount of white powder deposited on the cooling roll was extremely small except for Comparative Examples 2, 4, and 5.

Example 8 The molten film was extruded onto a chill roll under the same conditions as in Example 5.

At this time, the air knife was used to blow a jet stream at both ends of the film at a higher speed than at the center.

The velocity of the jet at the air outlet is 45 m at both ends.
/sec, and 30 m/sec in the wide central part as in Example 5.

The variation rate of the film thickness thus obtained was 2.7%, the variation of the film width was first grade, and the uniformity of the film was significantly improved.

[Brief explanation of drawings]

1-4 are schematic diagrams of examples of embodiments of the invention. FIG. 5 is a schematic diagram showing an example of the gas supply section and blowout section of the air knife. FIG. 6 is a schematic diagram showing the mutual positional relationship of the extrusion die, cooling roll, and air knife lip.

Claims (1)

[Claims] 1. A film is produced by melt-extruding thermoplastic polyester into a thin film on the surface of a rotating cooling roll, and solidifying the thin film on the cooling roll surface with gas injected from an air knife. (a) The shortest distance between the extrusion die slit tip and the cooling roll surface should be 10 mm or more.
(b) The point at which the thin film in the molten state starts contacting the cooling roll surface (point F) does not substantially vary between when gas is injected from the air knife and when no gas is injected. (c) The length of the protruding portion of the two lips forming the gas outlet of the air knife is set so that the length of the side closer to the extrusion die is larger, and the length of the protruding part of the two lips forming the gas outlet of the air knife is increased. Opening degree t (unit: mO1) Difference between the lengths of the protruding parts of the two lips forming the gas outlet △l (unit: mO1)
The shortest distance h (unit: h) between the molF point and the tip of the lip, and the tip of the lip on the side (inside) that injects the gas of the two lips that form the air outlet, which is close to the cooling roll, and F.
The value θ (unit: degree) measured in the direction of the extrusion die using the normal line as a reference l is the angle formed by the straight line connecting the point F and the normal line of the cooling drum that passes through point F. A method for producing a polyester film, characterized in that the film is formed using an air knife so as to satisfy %. 2. The method according to claim 1, wherein the gas is injected at both ends of the air knife outlet at a higher speed than at the center. 3 The air knife outlet l is 10 mm from both ends.
A partition wall is provided between the plates and 30 m or less to divide the gas flow path, and the speed of the gas injected from both ends is 5 m/5ec0 or more 10 m/
The method according to claim 1, characterized in that Sec is increased.