JPH09234783A - Measuring method for drawdown of molten parison in direct blow molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure simply and with high accuracy the status of generation of drawdown by photographing with time the status of dropping of a molten parison to be extruded from a die in the vertical direction and measuring the status of generation of drawdown of the molten parison based on a photographing data. SOLUTION: A molten parison 3 is extruded out of an extruder 1, and the molten parison 3 are cut off on the position of a die outlet at the time of the state of being extruded normally. The extrusion is continued, and a camera 4 is started to operate from the time that the end of the molten parison 3 is passed through a measurement start point and the photographing time of the molten parisons 3 is recorded. The dropping speed and the acceleration speed of respective timings of the parisons 3 are computed by an image formed by the camera 4 based on the data of the length of the parison 3 or the data of end positions at respective photographing times processed and found by an image processing device 7. At what points of time the drawdown is generated and how the drawdown is developed can be grasped accurately by the arrangement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for accurately measuring drawdown of a molten parison in direct blow molding. The occurrence of drawdown is one of the difficult problems in direct blow molding.
Accurate measurement of drawdown occurrence is important for setting molding conditions in direct blow molding.

[0002]

2. Description of the Related Art Direct blow molding, as is well known,
In this molding method, a molten parison extruded vertically downward from a die of an extruder is housed in a mold, and then a gas is blown into the molten parison to manufacture a hollow container. One of the difficult problems in this molding method is the occurrence of drawdown. Drawdown is a phenomenon in which a molten parison extruded from a die of an extruder hangs down by its own weight. When drawdown occurs, the total length of the parison becomes longer than the extrusion length,
In addition, the thickness of the parison locally changes, which greatly affects the quality of the obtained product. Therefore, in direct blow molding, it is necessary to measure the occurrence of drawdown in advance and take measures against it.

Conventionally, measurement of the situation of occurrence of drawdown is
A scale is provided behind the molten parison extruded vertically downward from the extruder die, and the observer visually observes that the tip of the molten parison passes between the upper and lower gauges provided on the scale. , It was done by measuring the required time. That is, if such measurement is carried out for some reference points at different distances from the nozzle, based on the obtained measurement data, the tip of the molten parison leaves the nozzle at the tip at each time point. The descent speed and acceleration can be calculated.

[0004]

However, the method of visually observing by the measurer is low in the accuracy of measurement depending on the difference between the measurer and the visual position. Usually, the measurement is repeated to improve the accuracy, but the accuracy is not improved so much. Therefore, the present invention is intended to provide a method capable of accurately and easily measuring the situation of occurrence of drawdown.

[0005]

According to the present invention, the descending state of a molten parison extruded vertically downward from a die of an extruder is photographed with a camera over time, and the molten parison is analyzed based on the photographed data. It is possible to easily measure the occurrence of drawdown by obtaining how much the die is descending from the die at the time point, and then obtaining the descending speed due to the weight of the molten parison and the descending acceleration based on this data.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail. In the present invention, instead of visually observing the descending state of the molten parison, images are taken with a camera over time. Therefore, it is possible to easily obtain data at short time intervals. The image data obtained by photographing is processed by the image processing device to calculate the amount of fall of the parison at each photographing time point (the distance from the die of the extruder or the distance from the previous photographing time). Normally, the entire length of the parison is photographed and the amount of descent is calculated, but it is also possible to install a scale plate behind the parison and measure where the tip of the parison corresponds to the scale plate. For the shooting, we installed a board with a different reflectance from the parison behind the parison, for example, a matte black plate,
It can be performed with a normal CCD camera. If desired, the parison can be colored to distinguish it from the surroundings. Also, since the parison is hotter than the surroundings, it can be taken with an infrared camera. The descent speed and descent acceleration at each time point of the parison are automatically calculated by a computer based on a group of data relating to the shooting time point thus obtained and the parison descent amount at that time point. Usually, since the molten parison is extruded from the extruder at a constant speed, the descending speed due to its own weight is obtained by subtracting the extruding speed from the descending speed of the molten parison. By tracking the change in the descending speed due to its own weight over time, the occurrence of drawdown can be grasped. The details of drawdown can be grasped by examining the descent acceleration.

An example of an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 is an extruder, 2 is an extruder die, 3 is a descending molten parison, and 4 is a descending of the molten parison. A camera for photographing the situation, 5 is a black backboard for preventing harmful light that becomes noise from entering the camera (4), 6 is an image processing device, 7 is a monitor TV, and 8 is a printer. . First, the molten parison is extruded from the extruder, and when it reaches a state of being constantly extruded, the molten parison is separated at the position of the die exit. Then, the extrusion is continued, and the camera is operated from the time when the tip of the molten parison passes the measurement starting point to photograph the molten parison and record the photographing time. Shooting continues until the tip of the molten parison passes the measurement end point. Note that, as described above, the photographing is normally started from the position where the molten parison is lowered from the die exit by a certain distance, but the measurement may be started from the time when the molten parison appears at the die exit. The image obtained by the camera is processed by the image processing device 7, and the length or the tip position of the molten parison at each image capturing time is obtained. Calculating the descent rate and the descent acceleration at each time of the melting parison based on the data of the length or the tip position of the melting parison at the time of this shooting and at that time, and at what time the drawdown occurs, and how You can know exactly how to proceed.

For example, FIG. 2 shows an intrinsic viscosity of 1,130 (dl
/ G) polyethylene terephthalate is extruded from the same extruder at screw rotation speeds of 10, 20, 30 rpm, and the molten parison that descends is photographed with a CCD camera over time by the method of the present invention, and the obtained image is subjected to image processing. hand,
The relationship between the descent distance and the descent acceleration at that time is calculated. From this figure, the acceleration of descent is 10m
If the parison is housed in the mold at m / sec ^2, the parison length becomes 375 mm when extruded at 10 rpm or 20 rpm, but it becomes only 330 mm when extruded at 30 rpm. It In addition, the set temperature of the extruder is 23 in the case of 10 rpm.
The temperature is 243 ° C. at 4 ° C. and 20 rpm, and 248 ° C. at 30 rpm. As described above, according to the present invention, since it is possible to accurately measure how the drawdown progresses, it is possible to set appropriate molding conditions.

[Brief description of drawings]

FIG. 1 schematically shows an example of an embodiment for carrying out the method of the present invention.

FIG. 2 is a graph showing an example of the relationship between the descent distance and the descent acceleration of the molten parison obtained by the method of the present invention.

[Explanation of symbols]

 1 Extruder 2 Die 3 Melting parison 4 Camera 5 Backboard 6 Image processing device 7 Monitor TV 8 Printer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayoshi Shimada, 370 Yenzo, Chigasaki City, Kanagawa Prefecture Mitsubishi Kasei Engineering Co., Ltd. Shonan Technology Development Center (72) Inventor, Koji Yuba, 370 Yenzo, Chigasaki City, Kanagawa Mitsubishi Kasei Engineering Co., Ltd. Company Shonan Technology Development Center (72) Inventor Takeshi Kawakami 370 Enzo, Chigasaki City, Kanagawa Prefecture Mitsubishi Chemical Co., Ltd. Chigasaki Plant

Claims (4)

[Claims] 1. A method in which a descending state of a molten parison extruded vertically downward from an extruder die is photographed with a camera over time, and a drawdown occurrence state of the molten parison is measured based on the photographed data. How to measure drawdown. 2. A molten parison extruded vertically downward from an extruder die is photographed with a camera over time to determine the amount of molten parison fall at each time point, and from this data the descent rate of the molten parison at each time point is determined. A method for measuring drawdown, which comprises: 3. A molten parison extruded vertically downward from an extruder die is photographed with a camera over time to obtain the amount of molten parison drop at each time point, and from this data, the molten parison drop at each time point is calculated. A drawdown measuring method characterized by calculating an acceleration. 4. The drawdown according to claim 2 or 3, wherein the amount of fall of the molten parison is calculated based on data obtained by image-processing an image of the parison obtained by photographing. Measuring method.