JP2002096371A - Method for manufacturing sheet and apparatus for controlling thickness of sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a sheet and an apparatus for controlling thickness of the sheet by which the thickness in the width direction of the sheet can be uniformly and stably controlled over the whole width. SOLUTION: The apparatus for controlling used for a manufacturing process of the sheet in which a polymer is extruded by using a die with a plurality of thickness adjusting means arranged in the width direction and is molded to prepare the sheet with a required thickness and the thickness distribution in the width direction of the sheet is measured and based on the measured values, amount of operation added to the thickness adjusting means is controlled by means of a controlling apparatus is provided and the apparatus is characterized by a constitution in which by using a process model wherein a relation between amount of operation of the thickness adjusting means and the thickness of the sheet is respectively different at the corresponding parts at the end parts and the central part in the width direction of the sheet, the amount of operation is added to the thickness adjusting means in such a way that the thickness distribution in the width direction of the sheet is made to be the target thickness distribution set in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sheet such as a plastic film and a sheet thickness control apparatus suitably used for the method.

[0002]

2. Description of the Related Art Raw materials discharged from a base as a sheet,
For example, the molten resin is continuously passed through a sheet forming process, for example, a stretching process, and the thickness of the sheet after passing through the sheet forming process is measured as a distribution in the sheet width direction by a thickness measuring device, and the sheet width direction of the die is measured. Various sheet manufacturing methods are known in which the thickness adjusting means is controlled based on the measured thickness values at the measurement positions corresponding to a large number of sheet thickness adjusting means provided in the apparatus. As control means,
Well-known proportional (P), proportional integral (PI) or proportional integral derivative (PI
D) Control is widely used. In recent years, however, control systems using computers have been developed.
As described in JP-A-527, JP-A-2000-94497, etc., a method of determining an operation amount to be applied to the thickness adjusting unit using a process model representing a mathematical relationship between the operation amount to be applied to the thickness adjusting unit and a sheet thickness is proposed. Have been.

[0003]

However, process characteristics related to control in the process model, such as process gain and interference phenomena, are non-uniform in the film width direction, and are affected by neck-in phenomena and polymer flow at edges. At the end of the product part, the actual process characteristics do not always match the process model at the center, so if the control means is determined based on the same process model in the sheet width direction as in the conventional method, the control stability Was a problem.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a sheet thickness control apparatus and a sheet thickness control apparatus capable of controlling the thickness in the sheet width direction uniformly and stably over the entire width. It is to provide a manufacturing method.

[0005]

According to the present invention, there is provided a sheet manufacturing method for discharging a raw material using a die having a plurality of thickness adjusting means arranged in a width direction.
In forming the sheet to a desired thickness, the relationship between the operation amount of the thickness adjusting means and the sheet thickness is determined by using different process models at portions corresponding to the edge and the center in the sheet width direction. The thickness adjusting means is controlled so that the thickness distribution in the width direction becomes a predetermined target thickness distribution.

A preferred embodiment of the sheet manufacturing method according to the present invention includes a process gain and an interference factor as parameters, and at least one of the two uses a different process model between the film edge and the center. It is a feature.

Further, the sheet thickness control apparatus of the present invention for solving the above-mentioned problems discharges a raw material using a die having a plurality of thickness adjusting means arranged in the width direction, forms the raw material, and forms the desired thickness. The control device used in a sheet manufacturing process for measuring the thickness distribution in the width direction of the sheet and controlling the operation amount applied to the thickness adjusting means based on the measured value by the control device. ,
The relationship between the amount of operation of the thickness adjusting means and the sheet thickness is such that the width direction thickness distribution of the sheet is changed to a preset target thickness distribution using different process models at portions corresponding to the end portion and the center portion in the sheet width direction. And an output means for outputting the obtained operation amount to the thickness adjusting means.

Further, in the computer-readable storage medium according to the present invention, the step of inputting a measured value of the thickness distribution of each portion in the width direction of the sheet, and the relationship between the operation amount of the thickness adjusting means and the sheet thickness is determined. A step of calculating an operation amount so that a target thickness distribution is obtained using a different process model in a portion corresponding to an end portion and a center portion in the direction, and a step of outputting the obtained operation amount to thickness adjusting means. The program is characterized by storing a program to be executed by a computer.

According to the present invention, the control stability of the end of the product portion can be improved, and the uniformity of the thickness in the width direction can be improved. Further, by improving the stability of the end portion, sheet breakage is reduced, and the yield can be increased.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a plastic film manufacturing method according to an embodiment of the present invention.

FIG. 2 is a diagram showing the general schematic configuration of a general sheet manufacturing facility, and FIG. 3 is an enlarged perspective view of a main part of the base 4 shown in FIG.

The sheet manufacturing equipment includes an extruder 3 for extruding a polymer, a die 4 for forming the extruded polymer into a sheet, and cooling the sheet-shaped polymer (hereinafter referred to as a sheet 1). A stretching roll 2 for stretching the sheet 1 in the vertical and horizontal directions, and a winding machine 6 for winding the stretched sheet 1. The base 4 includes a number of thickness adjusting means 10 arranged in the width direction of the sheet 1 (a direction orthogonal to the plane of the drawing) and a gap 11 for discharging the polymer.
Further, the sheet manufacturing equipment includes a thickness measuring device 8 for measuring the thickness distribution in the width direction of the sheet, and a control means (thickness control device) 9 for controlling the thickness adjusting means based on the thickness distribution.
It has.

As the thickness measuring device 8, an arbitrary thickness measuring device such as a device using a β-ray, an X-ray, an ultraviolet ray, or an optical interference type can be used. It is desirable to measure at intervals.

As shown in FIG. 4, the control means 9 feeds back the sheet thickness 24, which is the output of the sheet manufacturing process 26, to obtain a deviation 25 from the target value, and calculates the operation amount 23 by the operation amount calculating means 21. And the obtained operation amount 23
For example, the operation amount output unit 22 performs processing such as multiplying by a process gain (the amount by which the sheet changes per unit of operation amount), and adds the result to the thickness adjustment unit 10 of the sheet manufacturing process 26.

Various methods such as modern control using a mathematical model and PID control can be applied to the method of calculating the manipulated variable.

A plurality of thickness adjusting means 10 are arranged at equal intervals in the width direction of the base 4. As a means for adjusting the thickness of the sheet, heat bolts are used for the thickness adjusting means 10 and the gaps 11 of the base 4 are adjusted by changing the temperature of these bolts to thermally expand and contract the bolts. The thickness of the sheet 1 is adjusted by using a lip heater as the thickness adjusting means 10 and changing the temperature of the polymer to change the discharge amount of the polymer discharged from the base 4 by changing the viscosity of the polymer. A viscosity method, or a method of adjusting the gap 11 using a motor or the like can be used.

In such a sheet manufacturing process, when the sheet is stretched in the width direction, the stretching conditions can be regarded as substantially constant in the width direction at the center of the sheet, but the end of the sheet product portion is shown in FIG. As shown, immediately after the raw material is discharged from the die 4, the sheet width is narrower than at the time of discharge, and the material is easily affected by the polymer flow at the edge portion, and the end portion is stretched under different conditions from the center portion. Is done.
As described above, since the end portion is greatly affected by the process conditions as compared with the center portion, when designing the sheet thickness control means, as shown in FIG. 1, the portions corresponding to the end portion and the center portion in the sheet width direction, respectively, are used. Process model with different settings, preferably parameters involved in the control means determination,
For example, it is necessary to separately set the process gain and the interference rate.

The process gain is a value representing the ratio of the control amount change to the operation amount change. That is, it is a value indicating how much the sheet thickness changes when the operation amount input to the sheet thickness adjusting means is changed by a unit amount.

The interference ratio is defined as the change in the sheet thickness at the sheet thickness measuring position corresponding to the thickness adjusting means when a certain thickness adjusting means is operated, and the sheet thickness at the measuring position corresponding to the adjacent thickness adjusting means. Is a value indicating how much changes are made. That is, when a certain thickness adjusting means is operated, the sheet thickness changes not only at the operation position but also at the peripheral portion with a certain spread due to the influence of the rigidity of the die and the stretching process. At this time, the rate of change in the sheet thickness at the measurement position corresponding to the thickness adjusting means adjacent to the operated thickness adjusting means is an interference rate, and for example, 1.0% at the operating position. Whereas, at the position corresponding to the immediately next adjusting means, it is expressed as 0.6, at the position corresponding to the adjusting means two distances away, 0.2, and so on.

The method for determining the boundary between the central portion and the end portion is determined based on film forming conditions such as the stretching ratio in the sheet width direction and the sheet thickness, and the distribution of the dispersion of the sheet thickness in the sheet width direction. You may. During stable film formation,
The width of the central portion is 70 to 80% and the remaining portion is the end portion. During the initial stage of film formation, when the sheet thickness in the width direction is not stable, the ratio of the central portion is set to 60% or less. It is also preferred to change the ratio.

Regarding the process gain, it is preferable that the process gain at the end is set smaller than the process gain at the center. This is because even if the sheet thickness adjusting means changes the amount of operation to the sheet thickness adjusting means by a certain amount due to the structural limitation of the base and the buffering effect of the polymer at the edge at the sheet end, FIG. This is because, as shown in the thickness distribution, the sheet thickness may not change as much as the center. That is, since the outermost end of the base is fixed, or some thickness adjusting means is fixed from the outermost part, the sheet thickness adjusting means may be adjusted so that the sheet thickness at the end is reduced. Even if the operation amount is added, the actual operation amount of the thickness adjusting means may be small, and the actual sheet thickness does not become thinner than the center portion due to a part of the flow of the polymer at the edge portion flowing in. This is because there are cases. Similarly, even if the operation amount is added to the sheet thickness adjusting means so that the sheet thickness of the end portion becomes thicker,
In some cases, the actual thickness of the sheet does not become as large as the center part because the amount by which the thickness adjusting means actually operates is small or a part of the polymer flows into the edge part.

Further, as for the interference ratio, it is preferable that the interference ratio at the position corresponding to the adjacent adjusting means is larger at the end portion than at the center portion. This is due to the same reason as described for the above process gain.Because the end portion of the base is fixed at the end portion or some thickness adjusting means is fixed from the end portion in some cases. In addition, when an operation amount is added to the thickness adjusting means of the sheet at the end, the difference from the actual operation amount at the position of the adjacent thickness adjusting means may be small, and the flow of the polymer at the edge is buffered. This is because the difference in the actual sheet thickness between the operation position and the position corresponding to the adjacent thickness adjustment device may become small in order to cause the action.

Further, for the above-mentioned reason, the interference ratio at the end portion may not be symmetrical with respect to the operation position, but may be large at the end portion and small at the center portion.

Further, both the process gain and the interference rate
The settings may be different on the left and right end sides in the seat traveling direction.

In order to determine the process gain and the interference rate of the central portion and the end portion used for expressing these process models, it is preferable to actually measure the step response of the thickness adjusting means. That is, an operation amount that changes in a stepwise manner is added to the position of the thickness adjusting means representing the end and the thickness adjusting means representing the center, and the process gain or interference between the end and the center is determined from the change in the sheet thickness at this time. The rate can be measured.

Next, a method of designing the control means 9 based on the process gain and the interference rate determined by the above method will be described.

When designing the control means, control parameters are determined by the method shown in FIG. The control parameters to be determined depend on the design method. First, a process model is created based on the process gain and the interference rate determined by the method of the present invention. Since the process gain is smaller at the end of the film than at the center, the control parameters are adjusted so that the control gain is larger than at the center, and the sheet thickness variation is simulated using the process model. If the control performance, such as control accuracy and responsiveness, obtained by simulation is better than a preset reference value, the design parameters at this time are adopted. If the control performance is not satisfied, the operation of adjusting the control parameters again and executing the simulation is repeated to determine the optimal control parameters.

As described above, when the control parameter of the control means is determined by simulating the variation of the sheet thickness using the process model created by the present invention, the control parameter can be determined by trial and error while forming the film. Since it can be avoided, the sheet can be manufactured efficiently.

As described above, instead of performing the same control over the entire sheet width direction, the central part and the end part are controlled by using appropriate process models, whereby the neck-in phenomenon and the polymer of the edge part are controlled. The sheet thickness can be accurately and stably controlled with respect to the sheet edge, which is easily affected by the flow and is likely to be unstable in control.

Each operation of the control means in the above embodiment is realized by a computer and a program for operating the computer. Such programs and data of various storage means are distributed through computer-readable tangible media such as floppy disks, MOs, and CD-ROMs, and transmission means such as a wired or wireless network.

[0031]

EXAMPLE A 2.7 .mu.m thick polyester film was manufactured using the sheet manufacturing equipment shown in FIG. 2 described above. The thickness adjusting means 10 uses a heat bolt method in which the gap 11 is adjusted by thermally expanding and contracting a bolt having a built-in cartridge heater. The number of heat bolts used for thickness control is 45, and each bolt has a 20 mm pitch. It is arranged in. As the thickness measuring device 8, an optical interference type thickness meter utilizing an optical interference phenomenon was used. The film formation width is 3.
5 m, and the film forming speed is 175 m / min in the product section.

In this embodiment, according to the control means determination flow of FIG. 5, first, in order to create a process model, an operation amount of an arbitrary heat bolt is changed stepwise to measure a change in thickness. Tested. The step response test was performed at the end and the center to measure the change in thickness. (1) The process gain was smaller at the end than at the center. (2) The interference rate was different between the end and the center. (3) It became clear that it is preferable to make the central part 70% of the entire width and the both ends 1.5% each.

The measured values were as shown in Table 1.

[0034]

[Table 1]

Here, the process gain indicates the rate of change in the sheet thickness when the amount of operation on the heat bolt is changed. The operation amount of the heat bolt is represented by a percentage of a time for supplying constant power to the heat bolt in a certain time (10 seconds). Therefore, the unit of the process gain is μm /%.

On the other hand, the interference rate is expressed as a ratio of the change in the sheet thickness at the operation position, the position where one heat bolt is separated and the position where two heat bolts are separated when a certain heat bolt is operated, and the change at the operation position is set to 1. It was done.

According to the results of the step response test, in this embodiment, a process model in which two types of process characteristics, that is, a process gain and an interference were different between an end portion and a center portion was prepared.

That is, the central part of the static relational expression between the thickness change Yi at the corresponding position of the heat bolt and the operation amount change Ui applied to the heat bolt is represented by: Yi = 0.05 * (0.2Ui-2 + 0.6Ui-1 + Ui + 0.6Ui + (1 + 0.2 Ui + 2) (1) The end was expressed as Yi = 0.03 * (0.3 Ui-2 + 0.7 Ui-1 + Ui + 0.7 Ui + 1 + 0.3 Ui + 2) (2) Here, Ui: change in the operation amount of the heat bolt at the i-th position [%] Yi: change in the thickness at the corresponding position [μm] Further, observing the influence after operating the heat bolt involves a time constant and a dead time. Therefore, it is assumed that a time constant T and a dead time Td exist as dynamic characteristics of the process model. The time constant T and the dead time Td were identified from the above-described step response test. In the present embodiment, as shown in Table 1, equal values were obtained at the end and the center.

In this embodiment, a well-known PID control is adopted as the control calculation method. For the tuning of the PID parameters, a control simulation was performed using the process model obtained according to the flow of FIG.
The ID parameters have been optimized. As a result, it is possible to avoid searching for the optimum value of the PID parameter by trial and error while actually forming a film, and it is possible to efficiently determine the PID parameter.

FIG. 6 shows the control result of the sheet thickness when the PID controller determined as described above is used and the plastic film is stabilized for a sufficient time after the production starts. Control range from 11th volt to 52
No. bolt (corresponding to a position 310 mm from the position 600 mm from the end of the product film), and the center part was in the range of No. 18 bolt to No. 45 bolt. As shown in the figure, the thickness became uniform over the entire width, and a film was formed stably.

On the other hand, FIG. 7 shows a PID controller determined using a process model in which Yi = 0.05 * (0.2 Ui-2 + 0.6 Ui-1 + Ui + 0.6 Ui + 1 + 0.2 Ui + 2) (3) in the entire width. This shows the result of controlling the sheet thickness when a plastic film was manufactured. The actual gain at the end was small, but the gain of the control system was adjusted to the center, so the overall gain was Was insufficient, the stability of thickness control was poor, and thickness unevenness remained even after sufficient time.

[0042]

As described above, in the present invention, since the process model in which the conventional process characteristics are uniform in the film width direction, the actual process characteristics do not match the model at the end of the product portion, and the control stability is reduced. However, the film thickness can be controlled uniformly and stably over the entire width, and the yield can be improved and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between thickness adjusting means and sheet thickness measurement according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a general film production facility.

FIG. 3 is an enlarged perspective view of a main part of the base shown in FIG. 2;

FIG. 4 is a diagram showing a basic configuration of thickness control.

FIG. 5 is a flowchart of a control means designing method.

FIG. 6 is a diagram showing the distribution of the film thickness when the film thickness is controlled using the method of the present invention.

FIG. 7 is a diagram showing a distribution of film thickness when the film thickness is controlled using a conventional method.

[Explanation of symbols]

 1: Sheet 2: Stretching machine 3: Extruder 4: Cylinder 5: Cooling roll 6: Winding machine 7: Conveying roll 8: Thickness measuring device 9: Control means 10: Thickness adjusting means 11: Gap 21: Operation amount calculation Means 22: manipulated variable output means 23: manipulated variable 24: measured thickness value 25: deviation data 26: sheet manufacturing process

Continued on the front page F term (reference) 4F207 AA24 AG01 AK01 AP11 AQ01 AR12 KA01 KA17 KL76 KL84 KM05 KM15 KW41

Claims (5)

[Claims] 1. A method in which a raw material is discharged by using a die having a plurality of thickness adjusting means arranged in a width direction and the sheet is formed to have a desired thickness. The thickness adjusting means is controlled so that the thickness distribution in the width direction of the sheet becomes a predetermined target thickness distribution by using different process models at portions corresponding to the end portion and the center portion in the sheet width direction. A method for manufacturing a sheet, comprising: 2. The film according to claim 1, wherein a process gain and an interference rate are included as parameters, and at least one of the parameters uses a different process model between an end portion and a center portion of the film. Production method. 3. A material having a desired thickness is discharged by using a die having a plurality of thickness adjusting means arranged in the width direction and formed into a sheet having a desired thickness, and the thickness distribution of the sheet in the width direction is measured. The control device used in a sheet manufacturing process in which a control device controls an operation amount applied to the thickness adjusting unit based on a measured value, wherein a relationship between the operation amount of the thickness adjusting unit and the sheet thickness is in a sheet width direction. Calculating means for calculating an operation amount such that the thickness distribution in the sheet width direction becomes a preset target thickness distribution using different process models at portions corresponding to the end portion and the center portion of the sheet, and the obtained operation Output means for outputting the amount to the thickness adjusting means. 4. A step of inputting a measured value of a thickness distribution of each portion in the width direction of the sheet, and a portion in which a relationship between an operation amount of the thickness adjusting means and the sheet thickness corresponds to an end portion and a center portion in the sheet width direction. A program for causing a computer to execute a step of calculating an operation amount so as to achieve a target thickness distribution using a different process model and a step of outputting the obtained operation amount to thickness adjustment means is stored.
Computer readable storage medium. 5. A sheet manufactured by the sheet manufacturing method according to claim 1.