JP2007223150A - Air ring for forming inflation film and inflation film forming apparatus equipped with the air ring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the generation of white streaks by eliminating a part lacking in cooling of a bubble by the measures of forming a gap through which the air flows to each other between adjoining air supply passages, mutually diverting part of the air between the adjoining partitions by the formed connecting passage of the air to make distributary in this gap, and solving the lack of the air flow quantity between the blow-off openings of the adjoining partitions. <P>SOLUTION: By forming the gap 57 through which the air flows to each other between the adjoining air supply passages 52 and by the formed connecting passage of the air that makes distributary in this gap 57, a thin-film cooling air layer is formed over the whole circumference of the bubble in the connecting passage and, therefore, the areas lack in the air quantity in the positions between the adjoining air supply passages 52 are eliminated. Further, by a large quantity of the cooling air sent, adjacently to the cooling air layer over the whole circumference of the bubble, from the each partitioned air supply passage 52, the surface of the bubble facing oppositely to the blow-off opening 50 is cooled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  As a means for forming a synthetic resin into a film, an inflation method is often used. This method has the advantage of being advantageous in terms of cost since it can be produced with relatively simple equipment. In this method, the thickness unevenness of the film is adjusted by adjusting the gap of the die lip. However, this adjustment requires skill, and even if the adjustment is performed over a long time, the thickness accuracy is limited.

  Many attempts have been made as means for solving such problems. For example, there is a method in which the thickness of the film extruded and solidified is measured over the entire circumference, and the die lip gap is automatically adjusted based on the data. However, this method has a problem that the mechanism for adjusting the gap of the die lip is complicated and expensive, and further, a mechanism for adjusting the gap of the die lip needs to be provided directly on the circular die, so that the apparatus is large. There was a problem of becoming.

  On the other hand, as described above, there is a method in which the thickness of the film extruded and solidified in a tube shape is measured over the entire circumference, and then the temperature of the cooling air flow blown from the air ring is adjusted based on the data. . In this method, when cooling air is blown onto the molten resin discharged from the die lip in the form of a tube, if the temperature of the cooling air is lowered, the synthetic resin in the part solidifies faster and the thickness becomes thicker. If the height is increased, the portion of the portion uses the phenomenon that the solidification of the synthetic resin is delayed and the blow-up progresses, resulting in a decrease in the thickness, which is effective in improving the thickness accuracy. However, this method directly controls the temperature of the cooling air blown from the air ring, which is the main means for cooling the molten resin. Therefore, the temperature of the cooling air blown to the molten resin extruded into a tube shape is controlled at each location, and from the state where a tubular film with good thickness accuracy is obtained, the increase and decrease of the extrusion amount, the increase and decrease of the take-up speed, If the total amount of cooling air supplied from the air ring is increased / decreased due to changes in manufacturing conditions such as increase / decrease in blow ratio, the well-controlled state will collapse, and it will take a considerable amount of time to stabilize control again. There was a problem of requiring. Therefore, these methods are not suitable for use in situations where production conditions change. Further, in these methods, the air ring bears most of the ability to cool the molten resin, and the cooling ability of the air ring is directly controlled, so that the control fluctuation tends to be large. there were.

In the latest prior art, as the conventional improved version shown in FIG. 5, the air supply passage 52 'of the air ring is divided into at least 80 in the circumferential direction, and the air supply passage 52' divided by the partition wall 53 'is used. The amount of cooling air blown out in response to the variation in thickness is determined by an output signal from a central processing system that receives the thickness deviation of the film as an electrical signal from a thickness measuring device located downstream of the air ring. (See FIG. 1 of Patent Document 1).
European Patent No. 0476641

  However, even if the latest prior art is used, the cause of the white streak is not clearly clarified at the position of the adjacent air supply path 52 ′, but near the wall surface of each divided air supply path 52. It is conceivable that the air volume or the wind speed differs from the central portion of each air supply path 52 due to the influence of fluid friction. As a result, the cooling air is not uniformly blown to the outer peripheral surface of the bubble, and the adjacent air The amount of cooling air in the vicinity of the boundary of the supply path 52 tends to be insufficient, and the number of white streaks that are considered to be cooling segments along the film take-up direction during molding, that is, the longitudinal direction, corresponds to the number of divisions of the air ring. It has been found that there is a phenomenon that occurs, which is undesirable in terms of product quality. In order to eliminate this white streak, the present inventor tried and errored, and improved the air supply passage 52 between the adjacent sections to solve the above-mentioned problem so that the air volume near the wall surface of each passage does not decrease. did.

In order to solve the above-mentioned problem, in the present invention, in the air ring for forming an inflation film having an annular blowout port that is concentric with this die in the vicinity of the annular discharge port of the inflation film forming die,
The lower annular outlet near the annular outlet is formed by an inner lip and an intermediate lip, and the upper annular outlet is formed in a trumpet shape by the intermediate lip and the outer lip,
The air supply passages connected to the upper annular air outlet are formed as a plurality of air supply passages extending radially from the center of the upper annular air outlet, and the adjacent air supply passages are substantially vertical partition walls, respectively. Each partition wall is in the form of an elongated triangular cross section whose thickness is gradually reduced toward the outlet, and one of the lower and upper surfaces of the partition walls is the bottom ceiling surface of the air supply path. It is an air ring for forming an inflation film characterized in that it is slightly spaced from one side, a gap is formed between the adjacent air supply paths, in which air flows mutually, and an air communication path that divides the air is formed in this gap. .

  Further, in order to solve the above-mentioned problems, the related invention relates to the thickness of the air ring and the tubular film formed by cooling and solidifying the bubble discharged from the annular discharge port of the inflation film forming die in a tube shape. A thickness measuring device for measuring the entire circumference of the tube, and a flow rate or temperature of cooling air blown out from a plurality of air supply paths in the air ring based on the thickness data of the tubular film obtained by the thickness measuring device. Is provided with a control device that controls each air supply path independently.

In the air ring configured as described above, a gap in which air flows between adjacent air supply paths is formed, and an air communication path that divides the air is formed between the adjacent air supply paths. A part of the air is connected to each other without being divided, and the air flow shortage near the wall of the adjacent divided air flow is solved, and accordingly, the insufficient cooling of the bubble is eliminated, and the occurrence of the white stripe is eliminated. The thickness of the film can be made uniform. In other words, a gap for air to flow between adjacent air supply paths is formed, and a communication path for air to be shunted by this gap is formed, so that a cooling air layer of a thin film over the entire circumference of the bubble in the connection path Therefore, a region where the air volume is insufficient at a part of the air outlet is eliminated, and further, the cooling air layer over the entire circumference of the bubble is contacted and sent from each divided air supply path. By cooling the surface of the bubble with a large amount of cooling air, it is possible to cool the bubble still in the molten state below the frost line as in the conventional case, and along the film drawing direction during molding, that is, along the longitudinal direction. This eliminates the phenomenon that white stripes, which are considered to be cooling groups, occur in a number corresponding to the number of divisions of the air ring.
Further, if proved in detail, the cooling air flowing through the adjacent air supply path is compared with the conventional air ring having the air supply path 52 ′ shown in FIG. The parts communicate with each other, and even when blown on the bubble side, a continuous cooling air layer can exist between adjacent air supply paths, and the air volume or wind speed distribution of the cooling air discharged from each air supply path is a parabola. The cooling air that is drawn and discharged from the divided air supply passages draws a waveform curve that connects the parabolas, but the cooling air layer that discharges through the gap between the adjacent air supply passages continues for 360 degrees. Therefore, it is possible to increase the thickness of the trough portion of the corrugated curve, that is, the trough portion of the cooling air layer corresponding to the apex of the adjacent air supply path, and reduce the bubble cooling effect less. And the lack of cooling can be resolved. As a result, it is possible to eliminate the phenomenon in which the number of white streaks corresponding to the number of divisions of the air supply path occurs.

  This embodiment shows a typical embodiment of the invention described in claims 1 to 5, and will be described together with a typical embodiment of the related invention described in claim 6.

In FIG. 1, reference numeral 10 denotes an inflation film forming air ring, which has two upper and lower annular air outlets 40, 50 concentric with the die 20 in the vicinity of the annular discharge port 30 of the inflation film forming die 20.
The lower annular outlet 40 near the annular outlet 30 is formed by an inner lip 60 and an intermediate lip 70, and the tip of the inner lip 60 follows the bubble in the flow direction of the bubble discharged from the annular outlet 30. And inclined outward. The upper annular outlet 50 is formed in a trumpet shape by the intermediate lip 70 and the outer lip 80.
The air supply path 52 upstream of the upper annular outlet 50 is divided into, for example, 80 pieces in the circumferential direction of the air ring, and the air supply path 52 connected to the outlet 50 is connected to the upper annular outlet 50. Formed as a plurality of air supply paths extending radially from the center, adjacent air supply paths 52 are partitioned by a substantially vertical partition wall 53, and air is passed between the adjacent air supply paths 52. A gap 57 of a size flowing in the air is formed, and air is blown in the gap 57 portion without being divided.
The partition wall 53 has a thin and thin triangular cross-sectional shape in which the thickness of the partition wall 53 gradually decreases toward the air outlet 50 side, that is, the bubble side, and the apex 54 is located on the side of all bubbles. A gap 57 is formed between the adjacent air supply paths 52, which is slightly spaced from the bottom surface 56 of the supply path 52, and an air communication path is formed in the gap 57.

  The size of the gap 57 is about 1 to 5 millimeters. The lower annular air outlet 40 is connected to an annular air passage 41 that communicates 360 degrees in the circumferential direction, and the amount of air blown from the lower annular air outlet 40 is blown from the upper annular air outlet 50. It is about half of the air volume. In addition, this air volume may be made equivalent.

The lower annular blower outlet 40 and the upper annular blower outlet 50 are arranged in communication with the secondary side of a common blower.
Preferably, the upper ends of the intermediate lip 70 and the inner lip 60 are substantially horizontal and located in the same plane, the lower annular outlet 40 faces upward substantially perpendicularly, and the outer lip 80 of the upper annular outlet 50 faces upward. The vicinity of the connection point with the air supply path 52 is formed as a reduced diameter portion projecting inward, and the diameter and height of the upper end of the intermediate lip 70 of the outlet 51 and the upper end of the outer lip 80 thereof are greatly different. A trumpet-shaped lip that is continuous with the reduced diameter portion is formed.
By forming in this way, the air outlet 51 in a state in which the cooling air layer of the thin film covering the entire circumference of the bubble in the communication path and the large amount of cooling air layer sent from each divided air supply path 52 are substantially laminated. It is blown toward the surface of the bubble facing from the bubble to cool the bubble. As a result, the decrease in the air volume due to the wall resistance of each partition wall 53 is alleviated and does not appear as a clear temperature change, and bubbles that are still in the molten state below the frost line are overcooled and undercooled all around. Cools uniformly without any spots, and eliminates the phenomenon that the number of white streaks that seem to be a cooling section along the longitudinal direction of the film during molding, that is, the number of air rings, is generated. .
The air ring 10 is optimal for forming a five-layer film having a polyethylene layer as an outermost layer.

A thickness measuring device that measures the thickness of the tubular film formed by cooling and solidifying the bubble discharged from the annular ring outlet 30 of the air ring 10 and the inflation film forming die 20 over the entire circumference. 90 and the amount of cooling air blown from the plurality of air supply paths 52 in the air ring 10 based on the thickness data of the tubular film obtained by the thickness measuring device 90 for each air supply path 52. The inflation film forming apparatus 101 includes a control apparatus 100 that controls each independently.
In the above embodiment, the lower surface 55 of the partition wall 53 is slightly separated from the bottom surface 56 of the air supply path 52 to form a gap 57 through which air flows between the adjacent air supply paths 52. Even if the upper surface of the partition wall 53 is slightly separated from the ceiling surface of the air supply path 52 and a gap 57 through which air flows between the adjacent air supply paths 52 is formed, it is within the technical scope of the present invention. Further, the temperature may be adjusted instead of the air volume of the cooling air.

It is a schematic longitudinal cross-sectional view of the air ring of embodiment. It is a partial division longitudinal cross-sectional view of the air supply path in FIG. FIG. 3 is a schematic cross-sectional view of FIG. 2. It is the schematic of an inflation film forming apparatus provided with the air ring in FIG. It is partial section sectional drawing of the air supply path of the air ring of a prior art example.

Explanation of symbols

10 Inflation film forming air ring 20 Inflation film forming die 30 Annular discharge port 40 Lower annular outlet 50 Upper annular outlet 52, 52 'Air supply path 53, 53' Partition walls 56, 56 'Bottom surface 57 Gap

Claims (6)

In the air ring for forming an inflation film, which has an annular blowout port that is concentric with this die in the vicinity of the annular discharge port of the inflation film forming die,
The lower annular outlet near the annular outlet is formed by an inner lip and an intermediate lip, and the upper annular outlet is formed in a trumpet shape by the intermediate lip and the outer lip,
The air supply passages connected to the upper annular air outlet are formed as a plurality of air supply passages extending radially from the center of the upper annular air outlet, and the adjacent air supply passages are substantially vertical partition walls, respectively. Each partition wall is in the form of an elongated triangular cross section whose thickness is gradually reduced toward the outlet, and one of the lower and upper surfaces of the partition walls is the bottom ceiling surface of the air supply path. An airfoil for forming an inflation film, characterized in that a gap is formed between the adjacent air supply passages so that air flows between the adjacent air supply passages, and an air communication passage is formed in the gap. 2. An air ring for forming an inflation film according to claim 1, wherein the size of the gap is about 1 to 5 millimeters. The lower annular air outlet is connected to an annular air passage that communicates 360 degrees in the circumferential direction. The amount of air blown from the lower annular air outlet is approximately 1 of the amount of air blown from the upper annular air outlet. The air ring for forming an inflation film according to claim 1 or 2, wherein: The lower annular blower outlet and the upper annular blower outlet are provided in communication with the secondary side of a common blower, and the upper ends of the intermediate lip and the inner lip are substantially horizontal and located in the same plane. The outlet is substantially vertically upward, and the vicinity of the root of the outer lip in the upper annular outlet is formed as a reduced diameter portion projecting inward, and the diameter of the upper end of the intermediate lip of the outlet and the upper end of the outer lip and 4. The air ring for forming an inflation film according to claim 1, wherein the height is greatly different, and a trumpet-shaped lip that is continuous with the reduced diameter portion of the outer lip is formed. The air ring is for forming a multi-layer film, and each partition wall has a plane elongated triangular cross-sectional shape whose thickness gradually decreases as the apexes are located on the entire bubble side, and its lower surface is the bottom surface of the air supply path A gap is formed between the adjacent air supply passages so as to allow air to flow between the adjacent air supply passages, and an air communication passage for shunting the gaps is formed. Inflation film forming air ring as described. The air ring according to claim 1, 2, 3, 4 or 5, and the thickness of the tubular film formed by cooling and solidifying the bubble discharged from the annular discharge port of the inflation film forming die into a tube shape, Based on the thickness measurement device that measures the entire circumference, and the thickness data of the tubular film obtained by the thickness measurement device, the flow rate or temperature of cooling air blown out from a plurality of air supply paths in the air ring is determined. An inflation film forming apparatus comprising: a control device that controls each air supply path independently.

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