JPH0576413B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to the thickness in the width direction of a plastic sheet or film (hereinafter simply referred to as a sheet) formed by an extrusion molding machine using a T-die at the extrusion port. The present invention relates to a control method, and particularly to a control method for assigning and setting die bolt position numbers corresponding to measurement points of sheet profile data measured with a scanning thickness gauge.

[Conventional technology]

In general, two known methods for controlling the average thickness of this type of sheet are thickness control in the sheet delivery direction (referred to as MD control) and thickness control in the width direction of the sheet (referred to as CD profile control). There is. These MD control and CD profile control are performed simultaneously using a sensor (scanning thickness gauge). In the process of forming this type of sheet, one of the causes of uneven thickness of the extruded sheet is that the sheet extruded from the extrusion port of a mold (called a T-die) reaches the forming roll. The so-called net-in phenomenon, in which both ends of the sheet shrink, is known. This net-in phenomenon occurs due to the viscoelasticity of the plastic material, and the net-in amount, which is the amount of sheet contraction, or its streamline pattern are determined by the type of material and molding conditions [e.g., resin temperature, draw ratio (take-up speed and outflow velocity ratio), air gap, roll temperature, etc.]
It varies depending on the situation. Therefore, in extrusion molding machines for plastic sheets, etc., the die that forms the extrusion port is divided into a fixed lip and a movable lip, and these are placed facing each other in order to use a T die that can adjust the thickness unevenness in the width direction of the sheet. The gap between the two lips forms the opening gap of the extrusion port, and the thickness of the plastic sheet to be extruded is determined by the gap between the opening gaps. Die bolts are arranged, and by adjusting the die bolts and moving the movable lip along the sliding surface of the movable die, the interval between the opening gaps is adjusted, and the thickness of the sheet extruded from this gap is adjusted. There are known configurations that allow this. In order to properly adjust the lip gap of such a T-die, the measuring head of a scanning thickness gauge is moved back and forth in the width direction of the plastic sheet being extruded to measure the thickness, and based on this measurement value, the thickness is measured. An automatic profile control system is employed in which the die bolt is operated by a servo motor or the like to set the lip gap of the T-die at an appropriate interval.

[Problem that the invention seeks to solve]

However, in such an automatic profile control system, in order to form a sheet with high precision by adjusting the die bolt, it is necessary to obtain sheet profile measurement data, such as how far the measuring head has moved from one end of the extrusion port. If it is not clear from the data that there is an abnormality in the sheet thickness which die bolt corresponding to this measurement point should be adjusted, it will not be possible to correct the sheet thickness appropriately. Therefore, it is necessary to allocate die bolt positions. In recent years, computer-based profile monitoring and control systems have been developed, but even in this case, the accuracy of allocation of corresponding die bolts has a large effect on the control accuracy of sheet thickness. This means that the measurement point of the sheet profile data is in the flowing fluid.
Easily adapts to frequently changing netuquin amounts,
This is because a simple and accurate method for allocating die bolts has not yet been established. Usually, the actual situation is that a fixed die bolt allocation pattern is applied to all conditions or is determined based on human skill and experience. In addition, attempts have been made to testly operate several die bolts and measure the change in thickness with a thickness gauge in order to determine the correspondence relationship precisely, but this method is not only complicated to operate, but also complicated. , which is not practical as it requires a lot of time and effort.

From this perspective, the present inventors repeatedly and carefully measured and analyzed the netquin phenomenon, and were able to elucidate the following general characteristics.

A: The amount of shrinkage in the sheet width due to the net-in amount is significantly large on both sides, gradually decreases toward the inside, and becomes so small that it can be practically ignored inside a specific position.

B. The range width that causes a relatively large sheet width contraction is approximately proportional to the amount of net-in, and in most cases is about 2 to 4 times the amount of net-in in the lip coordinates.

C. The most important thing in profile control is the predetermined width at both ends of the sheet, and if the correspondence within this range is properly set, a product of fairly good quality can be obtained.

Based on the above characteristics, the applicant first derived a theoretical algorithm based on the correspondence between the sheet thickness measurement pitch and the die bolt setting pitch using a method that expresses the net-in ratio using a linear equation. Patent application was made in 1984 by finding out that the problem could be solved.
A patent application was filed as No. 125147. However, subsequent test research has revealed that there are various patterns for the net-in ratio, and the most practical pattern is the exponential formula.This method further improves accuracy through die bolt adjustment and produces high-quality sheets. It has become clear that it is possible to mold

Therefore, an object of the present invention is to express the net-in ratio by an exponential function f(x) regarding profile control, and to correctly assign and set die bolt positions corresponding to measurement points using a thickness gauge using the minimum necessary information. An object of the present invention is to provide a method for controlling the profile of a plastic sheet, etc.

[Means for solving problems]

The profile control method for plastic sheets, etc. according to the present invention involves continuous production of plastic sheets, etc. from an extrusion molding machine equipped with a plurality of die bolts in the width direction of the mold extrusion openings, which can adjust the opening gap of the mold extrusion openings. In a method for controlling the profile of a plastic sheet, etc., in which the thickness of the sheet, etc. is controlled by extrusion molding and reciprocating the measuring head of a thickness meter in the width direction of the sheet, etc., the thickness of the sheet, etc. is controlled by extrusion molding. In addition to measuring the net-in influence area of the sheet, etc., an exponential relationship of the sheet pitch based on a predetermined net-in ratio corresponding to the pitch between the die bolts provided at the mold extrusion port of the extrusion molding machine in this net-in influence area is established. The present invention is characterized in that, when an abnormality in the thickness is detected by the thickness gauge, the allocation setting or correction of die bolt positions corresponding to the measurement points of the measurement head of the thickness gauge is performed.

[Effect]

According to the profile control method according to the present invention,
When the measuring head of the thickness gauge detects an abnormality in thickness at measuring point S _i on the measuring line of a plastic sheet, etc. extruded from the mold extrusion port of an extrusion molding machine, the data is immediately transferred to measuring point S. The sheet thickness at the measurement point S _i is corrected with high precision by controlling the die bolt at the die bolt position x _i corresponding to _i . In addition, if the netquin amount B changes for some reason, by using an exponential formula for the netquin ratio function f(x), the following formula 1-e ^-k

Claims (1)

[Scope of Claims] 1. Continuously extruding a plastic sheet or the like using an extrusion molding machine equipped with a plurality of die bolts that can adjust the opening distance of the mold extrusion ports in the width direction of the mold extrusion ports, In a method for controlling the profile of a plastic sheet, etc., in which the thickness of the sheet, etc. is controlled by reciprocating the measuring head of a thickness meter in the width direction of the sheet, etc., the amount of neck-in of the sheet, etc. is measured, and the The net-in-affected portion of the sheet, etc. is set, and the exponential relationship of the sheet pitch based on a predetermined net-in ratio corresponding to the pitch between the die bolts provided at the mold extrusion port of the extrusion molding machine in this net-in-affected portion is calculated, and the above-mentioned thickness is calculated. 1. A method for controlling a profile of a plastic sheet, etc., characterized in that, when an abnormality in thickness is detected by a thickness gauge, assignment setting or correction of die bolt positions corresponding to measurement points of a measuring head of the thickness gauge is performed.