JPS6227983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film forming method and apparatus using an inflation method, and particularly relates to bubble expansion and cooling solidification during high speed (high discharge rate, high take-up speed) forming. It is.

In order to improve productivity, high discharge volume and high speed take-up are required, and there is a desire to improve the efficiency of thick film forming, especially for packaging bags for grains, fertilizers, feed, etc. However, conventionally known methods and equipment Therefore, when molding is performed by high discharge rate and high speed take-off, molding becomes impossible, or even if molding is possible, a high quality film cannot be obtained.

In other words, when the withdrawal speed increases, the frost line (the boundary line between the expanding part and the solidifying part) moves away from or approaches the die significantly due to insufficient cooling, causing a so-called breathing phenomenon, and eventually the bubbles meander and the tube collapses. The diameter becomes uneven, causing wrinkles and uneven thickness.

In addition, if the frost line separates significantly and the bubble is held between the nip rolls without being sufficiently cooled, the inner surfaces of the film will fuse together and the bag will no longer function as a bag after the bag-making process. Furthermore, if the film is wound up onto a nip roll before it has been cooled sufficiently, there is a risk that the film will break, making subsequent film molding impossible. Therefore, the maximum take-up speed was 30 to 50 m/min.

Next, even in the case of thick film molding, the film thickness is limited to 50 to 60μ, and if it is made thicker than that, a high discharge rate is required, but if the bubble becomes thick, frost lines will be formed on the outside. However, the inner part of the bubble may not be completely cooled and solidified, and it may not be possible to form a flat tube by the time the bubble is clamped by the nip rolls. In other words, since the cooling and solidification of the inside is caused by the temperature difference between the outside surface of the bubble and the outside surface of the bubble, high-speed molding is impossible unless the outside surface of the bubble is cooled to as low a temperature as possible.

In short, stabilizing the frost line is the key to improving productivity in both cases of high discharge volume and high speed take-up.

Therefore, in order to increase the ability to cool the bubble,
When the external cooling air volume is increased, the frost line approaches the die, but the wind speed at the cooling air outlet increases, causing the molten bubbles just discharged from the annular die slit to vibrate or rock. In young cases, haze and gloss deteriorate due to cooling spots caused by high-speed wind blowing, and therefore there is a limit to increasing the amount of cooling air.

In order to further lower the temperature of the cooling air, some methods use refrigerators or incorporate cooling devices inside the bubble to directly cool the inner surface of the bubble, but the equipment and utility costs are enormous. Moreover, maintenance management is also troublesome, which increases the cost of the entire device and increases power consumption, which is not commensurate with the improvement in productivity.

Utility Model Publication No. 52-12791 and Japanese Patent Publication No. 53-8339 have already proposed a system in which the lower part of the bubble cooling air guide tube is opened to the outside to let in secondary air in order to improve cooling efficiency. However, this invention improves the cooling effect by bringing cooling air into contact with the expanding bubbles without introducing secondary air, and also stabilizes the frost line by promoting and stabilizing the expansion of the film. The present invention is a method and apparatus for metering, high discharge volume, or high-speed withdrawal.

This invention is an inflation film forming method in which bubbles discharged from a die slit are expanded by internal pressure, and a tapered outer ring is positioned closely along the outside of the tapered portion of the bubble during the expansion process. Further, a cylindrical guide cylinder is provided outside the equal diameter portion that connects to the tapered portion immediately after the expansion is completed, and is connected to the upper end of the tapered outer ring, so that the ring can be inserted between the bubble in the expansion process and the outer ring. This is a plastic film forming method characterized by blowing out cooling air in the direction of bubble migration.

In another invention, an annular cooling air outlet is provided between inner and outer rings provided on the outside of the die slit, and an inner ring forming an inner edge of the air outlet is provided on the die outside of the die slit. It is provided in close contact directly or indirectly, and its axial length is approximately the same as the expansion deformation start line of the bubble discharged from the die slit, and the outer ring constituting the outer edge of the outlet is The mouth edge is larger than the inner circumferential edge of the inner ring, and the inner circumferential surface of the outer ring connected to the mouth edge is tapered such that the inner diameter increases as the distance from the mouth edge increases, and the large diameter end of the outer ring There is also a cylindrical guide tube that runs along the bubble cylindrical part,
The plastic film forming apparatus is characterized in that the outer ring and the cylindrical guide tube are movable and fixed in position in the axial direction with respect to the inner ring.

First, typical embodiments of the device invention will be described. In the figure, reference numerals 10 and 11 denote dies having an inner and outer side, and an annular die slit 12 is formed between the pair of dies for discharging the molten plastic into a tube. An annular cooling air outlet 13 is formed surrounding the die slit 12, and an inner ring 14 constituting an inner edge of the cooling air outlet 13 is connected to the outer die 1.
1 is closely equipped. The length of the inner ring 14 in the axial direction is approximately the line at which the molded bubble A starts to expand, and is 20 to 40 cm in the embodiment, but is not necessarily limited to this value. The lower end of the outer ring 15 constituting the outer edge of the cooling air outlet 13 is larger than the inner circumferential circle of the inner ring 14, and there is a gap of 10 mm between the outer ring 15 and the inner ring 14.
A cooling air outlet 13 is formed with an annular gap of 50 mm to 50 mm. The aforementioned outer ring 1
5 has a tapered inner circumferential surface 16 whose diameter becomes larger as the distance from the air outlet 13 increases, and this taper angle (angle of inclination from the axis) is formed to be 15° to 50°, preferably 20° to 40°. The length in the axial direction should be approximately the same as the position where bubble A finishes expanding. Reference numeral 17 is a cylindrical guide tube having an inner diameter that substantially matches the inner diameter of the large diameter portion of the outer ring 15, and has a length of about 0.8 to twice the inner diameter. There is no difference in the present invention even if the outer ring 15 and the cylindrical guide tube 16 are provided as separate members so that they can be coupled and separated, or if they are integrally molded. The aforementioned outer ring 15 is
When screwed into the casing of the cold air blower 18, the outer ring 15 and the cylindrical guide tube 17 approach the dies 11 and 12 together, and when rotated in the opposite direction, they move away from the dies 11 and 12.

The method invention of this invention will be explained using the above-mentioned apparatus.

First, molten plastic is discharged from the die slit 12 in the shape of a tube, air is introduced into the tube, the plastic is held between nip rolls (not shown), and air is blown from the expansion air inlet in the center of the inner die 10. Cooling air is blown out from the cooling outlet 13, and the internal pressure is adjusted so that the bubble completes expansion in the outer ring 15 to a predetermined size.Then, the vertical position of the outer ring 15 is adjusted to form a tapered circle. The circumferential surface 16 is made to approach the outer circumferential surface of the bubble.

In this way, when cooling air is blown between the bubble and the outer ring from the cooling outlet, the cooling air passes through the gap between the two, expands in a tapered shape, and then passes between the cylindrical bubble and the guide tube, and then passes through the bubble surface. It rises while coming into contact with.

In the method of the present invention, when the cooling air passes through the narrow gap between the bubble A and the outer ring 15, it becomes a high-speed airflow, and since the airflow passes through this narrow portion, the airflow effectively contacts the bubbles. However, the effect of cooling the bubble A in this portion is significant, and has the effect of stabilizing the frost line substantially in this portion. Also, due to the increased speed of the airflow, the pressure in this area decreases, creating a pressure difference with the inside of the bubble and promoting the expansion of the bubble. Furthermore, in this method, cooling air is blown onto bubbles that are still at a high temperature while they are expanding, so the temperature difference between the bubbles and the cooling air is large, and the cooling effect is significant.

Moreover, this method does not require a large air volume, so the bubbles do not vibrate or oscillate, making it possible to perform high discharge volume and high-speed take-up molding, which significantly improves productivity. Molding over 50m per minute,
It is also possible to mold thick films exceeding 60μ.

In addition, in the above-described device invention, the above-described method can be carried out, and by adjusting the outer ring 15 by moving it up and down, the tapered inner circumferential surface 16 is brought closer to the bubble, and by this approach, the bubble is removed. The speed of the cooling air can be increased at this point, improving the cooling effect and stabilizing the frost line.The increased speed also has the effect of promoting bubble expansion due to the reduced pressure. Together with the guidance of surface 16, the bubble is vibrated,
Stable molding can be performed without shaking, increasing productivity.

In addition, in the method of the embodiment in which the blowing direction of the cooling air is parallel to the blowing direction of the bubbles or parallel to the circumferential surface of the outer ring, no swirl is generated in the cooling air and no vibration is given to the bubbles. The outer ring 15 has a taper angle of 15° to 50°,
When the length is 40 to 100 mm, it is possible to handle a fairly wide range of bubble diameters, and especially when the length is increased to nearly 10 mm, most of the work on the molding machine can be done without replacing the outer ring 15. becomes possible.

In addition, as long as the die slit 12 of the die used in this invention is annular, there is no particular limitation on the shape of the internal resin path, and the amount of air flow etc. can of course be adjusted with the external air control, and the properties of the plastic , select according to the thickness, diameter, and forming speed of the formed film.

Example Die slit diameter is 100mm, inner ring 14
outer diameter d = 140 to 200 mm, lower end inner diameter of outer ring 15 is d + (30 to 100 mm), taper angle α = 30°,
The length of the outer ring 15 is 60 mm, the length of the guide cylinder is the same as its diameter, and the blowing angle of the cooling air is 0 to 60 mm with respect to the axis.
The range was 15°.

This results in a drawing speed of 80 to 100 m/min or a thickness of 100 m/min.
Even in molding of ~120μ, a good film with the above effects was obtained.

[Brief explanation of the drawing]

The drawing is a longitudinal sectional side view of the entire device showing a typical embodiment of the device of the present invention. In the figure, 10, 11...Inner and outer dies, 12...Die slits, 13...Cooling air outlet, 14...Inner ring, 15...Outer ring, 16...Tapered inner peripheral surface, 17...Cylindrical guide cylinder , A...bubble.

Claims (1)

[Claims] 1. In an inflation film forming method in which bubbles discharged from a die slit are expanded by internal pressure, a tapered outer ring is brought close along the outside of the tapered portion of the bubble during the expansion process. Further, a cylindrical guide cylinder connected to the upper end of the tapered outer ring is provided on the outside of the equal diameter part connected to the tapered part immediately after the expansion is completed, so as to prevent the bubble during the expansion process and the outer ring. A plastic film forming method characterized by blowing out a ring-shaped cooling air from the gap in the direction of bubble migration. 2. The plastic film molding method according to claim 1, wherein the blowing direction of the cooling air is parallel to the blowing direction of the bubbles or parallel to the inner circumferential surface of the outer ring. 3. An annular cooling air outlet is provided between the inner and outer rings provided on the outside of the die slit, and the inner ring forming the inner edge of the air outlet is directly or indirectly connected to the outer die of the die slit. The outer ring constituting the outer edge of the outlet has an axial length approximately equal to the expansion deformation start line of the bubble discharged from the die slit. The inner circumferential surface of the outer ring, which is larger than the inner circumferential edge of the inner ring and is connected to the mouth edge, has a tapered shape in which the inner diameter increases as the distance from the mouth edge increases;
The large diameter end of this outer ring is further connected with a cylindrical guide tube along the bubble cylindrical portion, and the outer ring and the cylindrical guide tube are fixed in position while being movable in the axial direction relative to the inner ring. A plastic film forming device characterized by being freely equipped. 4 The angle of the taper of the inner peripheral surface of the outer ring is 15° to 50°.
4. The plastic film forming apparatus according to claim 3, wherein the plastic film forming apparatus has an axial length of 40 to 100 mm.