JP2002187196A - Method for controlling film thickness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling a film thickness which gives a film having a good film profile by combining a control of a short period and a control of a long period. SOLUTION: A method for manufacturing a film roll comprises the steps of measuring a widthwise thickness distribution of a film roll composed of an extended film wound in a roll shape, controlling a short period and a long period based on the accumulated data and accumulating these outputs and outputting them to give a film having a good thickness profile.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a film thickness, and more particularly, to a film having a good thickness distribution by optimizing a feedback amount in controlling a film in a film forming process. The present invention relates to a method for controlling a film thickness.

[0002]

2. Description of the Related Art In the process of manufacturing a film made of a thermoplastic resin such as polyester, polyamide, or polypropylene, it is required to control the thickness in the width direction of the film to a predetermined profile, for example, a uniform thickness over the entire width. The thickness of the film is adjusted by a group of thickness adjusting means arranged over the entire width of a wide die for extruding the molten polymer. The thickness adjusting means group includes elements such as a heater group for controlling a wide die temperature and a gap adjusting tool group for adjusting the discharge gap of the molten polymer.

The thickness adjusting means including the heater, the gap adjusting tool, and the like are arranged in fixed sections over the entire width of the wide die. Therefore,
The thickness of the film is adjusted by controlling each of the thickness adjusting means groups based on the thickness of the product film (normally, the film after biaxial stretching) measured at each measurement point on the downstream side. Generally, multipoint thickness control means is used to adjust the amount of each polymer discharged over the entire width of the die to control the film thickness to a desired value.

The method of controlling the film thickness profile by the above-mentioned multi-point thickness control means is to biaxially stretch a wide polymer discharged from a die into, for example, a biaxially stretched film, and then to form a biaxially stretched film. Is controlled so as to approach the target thickness profile. However, even if the film thickness after biaxial stretching is controlled within the control value, in the case of a film that has been laminated and wound up in a roll shape, the thickness of the film is multiplied by the lamination, thereby causing a problem that the thickness unevenness is accumulated. Occurs.

[0005] Further, even if the film thickness at the control point has sufficiently reached the target value, there is a problem that the film thickness is accumulated when the film thicknesses are laminated due to a thin spot between control points. When the accumulation of such thick and thin spots occurs, there arises a problem that a bump and a wrinkle which cannot be controlled by the above-mentioned multi-point thickness control means occur at a specific location in the width direction of the wound roll.

[0006] Therefore, the thickness profile of the biaxially stretched film is measured for a certain period of time, and the measured data are integrated to obtain each thickness profile in the width direction of the film wound into a roll. It is conceivable to predict and control bumps and wrinkles. However, since the measured thickness profile data is superimposed with the statistical fluctuation of the thickness gauge and the measurement error due to the measurement state of the film, an accurate profile cannot be obtained with short-cycle control and the control is not performed correctly. However, there is a problem in that the control of the long cycle cannot correct the variation in thickness in the short cycle.

For this reason, the measured data is disclosed in Japanese Patent Laid-Open No. 1-12828.
By adding processing by the method described in Japanese Patent Application Publication No. 92-92, a measurement error can be reduced even in a short-cycle control. However, processing data causes loss of control responsiveness, and lack of data volume results in incorrect thickness profile data, which in turn results in contradiction that fine control cannot be performed. Was not obtained.

Further, as described in Japanese Patent Application Laid-Open No. Hei 7-108586, a method in which an output is applied only to a specific portion has a disadvantage that the profile around the specific portion is disturbed. Further, as described in Japanese Patent Application Laid-Open No. 8-276491, in a method of changing a target value of a specific portion, a target value is different from a profile originally desired, so that a target value is set for each brand, There is a risk that the target value will diverge, and there is a possibility that the situation will deviate from the original control state.

[0009] When the stretched film is wound into a roll, poor winding shapes such as bumps and wrinkles are caused, for example, by coating unevenness when applying a magnetic layer when used as a support for a magnetic recording medium. There is a problem that an error occurs at the time of magnetic recording / reproducing, or that when a slit is formed after the magnetic layer is applied, there is a difference in a longitudinal direction in a width direction, so that it is not possible to wind up cleanly.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method for controlling a film thickness capable of obtaining a film profile which can obtain a good rolled shape without bumps and wrinkles. It is intended to provide.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for dividing a die into which a molten thermoplastic resin is discharged in the form of a film into a plurality of sections. The thickness of the stretched film formed by stretching the molten resin discharged from the die is measured, and the thickness distribution in the width direction of the stretched film is measured based on each thickness measurement value of the stretched film. In the method of controlling each discharge amount of the molten resin discharged from the die and controlling the thickness distribution in the width direction of the film to a predetermined profile, in the width direction of the film roll composed of the stretched film wound into a roll shape, This is achieved by a film thickness control method characterized by measuring a thickness profile two or more times and combining a short cycle control and a long cycle control output.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. Here, FIG. 1 is a schematic process diagram schematically illustrating a film forming process for implementing the present invention.

In FIG. 1, reference numeral 1 denotes a thermoplastic resin (hereinafter, referred to as a thermoplastic resin).
A die for discharging a film-like polymer), adjusting means for adjusting the discharge amount of the thermoplastic resin, a cooling drum 3, a film stretching device 5 in the running direction of the film, A width stretching device for a film, 6 is a thickness gauge for a stretched film, 7 is a film roll, 8 is a control means, and 9 is a film (in the present invention, an unstretched film is 9a and a stretched film is 9b. Are shown separately).

In the manufacturing process of the film of the present invention configured as described above, the thermoplastic resin for a film is melt-extruded from an extruder (not shown) and supplied to the die 1. Note that an adjusting means 2 for adjusting the discharge amount of the polymer divided into a plurality of sections in a predetermined width section is provided over the entire width of the die 1 for discharging the molten polymer. By operating the adjusting means 2, the discharge amount of the polymer discharged from the die 1 can be adjusted for each section,
The discharge amount distribution of the polymer can be adjusted over the entire width of the die 1. As a result, the thickness profile of the film 9 (thickness distribution in the width direction of the film) can be finally adjusted to the initial desired thickness profile.

The division over the entire width of the die 1 is divided by a controller capable of adjusting the discharge amount of the resin. The number of divisions differs depending on the die width and the installation interval of the controller. It is preferable because it becomes possible. It is preferable that the width of each section is substantially the same, but the sections at both ends may be wider than the other sections.

The adjusting means 2 includes a die 1
There is no particular limitation as long as the polymer discharge amount can be adjusted according to the operation amount output for each section. However, in terms of operability, maintainability, and simplification of the structure of the die 1, the flow rate of the polymer is changed by changing the lip temperature of the die 1 by using a heater group capable of adjusting the heat transfer amount for each section. A temperature control method is preferred.

As described above, the molten polymer is discharged in the form of a film from the die 1 while the discharge amount is controlled for each section by the adjusting means 2, cooled and solidified by the cooling drum 3, and 9a. Thereafter, the unstretched film 9a that has been cooled and solidified is biaxially stretched in the running direction and the width direction by the stretching devices 4 and 5, to become a stretched film 9b, and finally as a film roll 7 as a winding device (not shown). Is wound up.

The film 9 may be a single-layer film or a multilayer film in which two or more films are laminated. In this case, if the film 9 has two or more layers, the polymers forming the films of the respective layers may be formed by being merged upstream of the die 1 and then extruded from the die 1. Also, JP-A-63-
A plurality of polymer passages are formed in a die 1 and a plurality of polymers are merged into the passages and guided to an opening as in the prior art proposed in Japanese Patent No. 120629 or the like. Then, a composite die configured to extrude the composite die may be used.

As described above, the unstretched film 9a
Is stretched by the stretching device 5 to obtain a stretched film 9b. At this time, the thickness of the stretched film 9b is determined at least for each stretched portion corresponding to each section where the polymer discharge rate is adjusted. It is measured by a total of 6. The discharge amount of the polymer from the die 1 is adjusted by the adjusting means 2 so that each measured thickness value thus measured matches a preset target stretch thickness value. At this time, the thickness gauge 6 for a stretched film is scanned in the width direction of the stretched film 9b. By this scanning, the thickness profile of the stretched film 9b is measured for each stretch thickness measurement site to be measured. The thickness gauge 6 for a stretched film is not particularly limited as long as the thickness of the stretched film 9b can be accurately measured with required accuracy.
As such a thickness gauge 6 for a stretched film, it is preferable to use, for example, a radiation transmission type thickness meter from the viewpoint of on-line measurement accuracy.

The scanning of the thickness gauge 6 is performed throughout the film formation, and the thickness profile data for each measurement site is appropriately integrated in a control cycle.

Assuming that the integration number of the short cycle control is nA and the integration number of the long cycle control is nB, the control output is calculated by the control means 8 based on the thickness profile data integrated nA times.
It is output to the adjusting means 2 of the die 1. It is preferable that the control cycle at this time is set to a value obtained by adding a time constant and a waiting time that can confirm a change in the profile due to a change in the output. Although the control method is not particularly limited, it is preferable to use PID control in terms of parameter adjustment and control accuracy.

The short-period control is for correcting the fluctuation of a short-period profile. Therefore, if the number of profile integration is too large when obtaining a deviation by the control,
It took time, I could n’t catch the change,
Not suitable. The control means 8 performs integration for performing long-period control while performing short-period control. Normally, the data of the thickness gauge 6 has statistical fluctuations, and the data actually measured because the film is running is measured in the form including the profile fluctuations in the running direction, so it shows a correct value. Not. Therefore, control is performed based on the integrated data. The larger the number of integrations, the more an average profile in the width direction can be captured.

Therefore, the control cycle of the long-period control is sufficiently longer than the short-period control cycle and more than twice the short-period control. More preferably, the control cycle is set based on the time required to finish winding one roll.

In the long-period control, the control gain is large because an average profile in the width direction is well captured. In the short-period control, statistical variation and profile data in the running direction are often included in the integrated data of the thickness profile data. Therefore, the control gain is set to be small and small. As a result, a film sheet having a more stable profile can be obtained.

The long-period control output thus calculated is:
In order not to adversely affect the short-period control, it is added to the short-period control output and output at the same timing.

[0026]

The present invention will be further described with reference to the following examples. Various characteristic values in the present invention were measured as follows. Note that the present invention is not limited to the following examples unless it exceeds the gist.

(1) Thickness of Biaxially Oriented Film A β-ray thickness gauge was used as a radiation transmission type thickness gauge.

(2) Outer Diameter of Film Roll The outer diameter of the film roll was continuously measured in the width direction using a bulk shape measuring device manufactured by Kitano Planning Co., Ltd. still,
The roll outer diameter is measured at three locations at 120-degree intervals in the circumferential direction, and is represented by an average value thereof.

Example 1 Polyethylene-2 containing 0.02% by weight of calcium carbonate particles having an average particle diameter of 0.6 μm and 0.2% by weight of silica particles having an average particle diameter of 0.1 μm;
After 6-naphthalate was dried at 180 ° C. for 5 hours, it was supplied to an extruder hopper, melted at 300 ° C., extruded using a T-shaped extrusion die (a die having a total width of 81 sections), and finished with a surface finish of 0. 3S, quenched and solidified on a casting drum maintained at a surface temperature of 60 ° C. to obtain an unstretched film.

The unstretched film is preheated at 75 ° C.
830 ° C above 14mm between low and high speed rolls
The film was stretched to 5.1 times by heating with an infrared heater having a surface temperature of, cooled rapidly, and then supplied to a stenter and stretched 4.8 times in the transverse direction at 125 ° C. Followed by 240
After heat setting at 10 ° C. for 10 seconds, 1.
After a relaxation treatment of 0%, a biaxially oriented film having a thickness of 4.5 μm was obtained.

At this time, the time from the output to the adjusting means 2 until the thickness change appears on the thickness gauge 6 (time constant +
The dead time was 10 minutes, and the time until the change was completed was 12 minutes. Since it takes one minute for the thickness gauge 6 to scan once, the integration of the short cycle was set to four times, and the integration was started after the thickness change appeared, and the control calculation was performed. The control gain for the deviation was set to 0.3.

When a film is manufactured under the conventional control state without the control of the long cycle and only the control of the short cycle, the maximum thickness and the minimum thickness in the average thickness profile when one film roll 7 is manufactured. Was 0.6%. The difference between the maximum outer diameter and the minimum outer diameter in the width direction of the film roll was as large as 780 μm, and wrinkles were formed at a portion where the outer diameter difference was relatively large in the width direction, which was not preferable as a product.

Since three times the short period is set as the long period control, the number of integrations used for the control can be 42 times, which is ten times or more that of the short period control. Therefore, it is considered that the statistical fluctuation is suppressed to 1/3 or less. The control gain of the long-period control was set to 0.7, and output was performed together with the short-period control.

At this time, the difference between the maximum thickness and the minimum thickness in the average thickness profile when one film roll 7 is manufactured is 0.4%, and the variation in the profile in the width direction is smaller than that in the case of the short cycle control. I could get rid of it.
Further, the difference between the maximum outer diameter and the minimum outer diameter in the width direction of the film roll was greatly improved to 370 μm, and a roll having a beautiful winding shape without wrinkles could be obtained.

The polymer discharge flow rate of each section of the die was adjusted by a temperature adjustment method in which the temperature of each die lip was changed.

[0036]

According to the present invention, it is possible to produce a film having a good profile, which has been difficult only by conventional thickness control. Overall productivity is also improved. As described above, the present invention greatly contributes to improving the quality of a product in a film forming process of manufacturing a film by extruding a molten polymer into a film, and has a great effect.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 2 Adjusting means 3 Cooling drum 4 Running direction stretching device 5 Width direction stretching device 6 Thickness gauge for stretched film 7 Film roll 8 Control means 9 Film 9a Unstretched film 9b Stretched film

Claims (4)

[Claims] 1. The entire width of a die from which a molten thermoplastic resin is discharged in the form of a film is divided into a plurality of sections, and the discharge amount of the resin is adjusted for each of the divided sections. Measuring the thickness distribution in the width direction of a stretched film formed by stretching the molten resin, and controlling each discharge amount of the molten resin discharged from the die based on each thickness measurement value of the stretched film. In a method of controlling a thickness distribution in a width direction of a film to a predetermined profile, a thickness profile in a width direction of a film roll composed of a stretched film wound up in a roll shape is measured twice or more, and a short cycle control and a long cycle A film thickness control method characterized by combining control outputs of the above. 2. The method according to claim 1, wherein the long-term control gain is larger than the short-term control gain. 3. The method of controlling a film thickness according to claim 1, wherein the long-period control cycle is at least twice the short-period control cycle. 4. The method according to claim 1, wherein the combination of the short-period control output and the long-period control output is a summation.