FI72919B - FOERBAETTRING AV FOER BLAOSFORMING AV PLASTFILM AVSEDD ANORDNING. - Google Patents

Description

7291 9 IMPROVEMENT IN PLASTIC MOLDING EQUIPMENT FOR PLASTIC FILM. -FÖRBSlTRING AV FÖR BLÄSPOPMING AV PLASTFHM AVSEDD ANORDNING.

The invention relates to a method and apparatus for producing a biaxially oriented synthetic thin plastic film, the so-called puhallusmenetelmäliä.

In the blowing method, the plastic is extruded through the nozzle of the extruder into the shape of a molten tube. The tube is pulled along the cooling mandrel, whereupon the material solidifies and crystallizes. This results in a continuous, moving, cooled and solidified tubular product which is pulled upwards by means of a pair of traction rollers. Above the draw rolls, the tube is reheated in a heating furnace. The tubular product reaches a certain orientation temperature in the oven. At this temperature, the preform is blown by means of a blow tube biaxially into a bubble of large diameter and thin wall thickness. The bubble is flattened evenly, keeping the perimeter of the bubble constant, and the bubble is closed at one end by means of two compression rollers between which the product is drawn. Finally, the product is usually split in half, heat treated and wound on rolls for storage for further processing.

In the known method, the blow pipe is also inside the bubble at the pulling point of the hose, in which case the pulling roller pair must have an opening formed by the ring grooves to enable the situation. In this case, the surface of the traction roller pair touches the hose unevenly, whereby uneven contact of the rollers causes cooling disturbances in the hose. The rollers either cool or heat the hose surface depending on the running parameters. The cooling effect of the rollers causes the orientation to result in thicker points in the film at the point of contact of the rollers. In addition, the drive rollers shape and compress the hose unevenly as it is pulled from the cooling mandrel.

Uneven mechanical modification of the matter caused a point of interference that causes the film to leak and thickness variations of 2 7291 9 mm. bag-like spots that appear in the middle of the final product path, degrading the quality of the film. Spillage is caused by the buckling of the hose at the edges of the flattening points.

In addition, the blow tube inside the hose scratches the inner surface of the hose by rubbing, so that the abrasion residues are also visible in the finished film. Abrasion points must be directed to the edges of the track and to the wreck, as they impair the electrical properties.

The effects of the above disturbances are visible in the finished product and increase the amount of waste, especially in thin films, from 6 to 10.

Cooling defects, even a 1 to 3 ° C temperature change, adversely affect quality due to the sensitivity of the cooling effect.

The object of the invention is to eliminate the disadvantages of the known method and to eliminate the disturbances caused by the known method on the heat-sensitive material, to improve the quality of the product, in particular the uniformity, and to reduce the amount of scrap.

The method according to the invention is characterized by the features mentioned in the characterizing part of claim 1 and the apparatus according to the invention is characterized by the features mentioned in the characterizing part of claim 5.

In the following, the invention and its advantages will be described in more detail with reference to the figures of the accompanying drawings, in which

Fig. 1 shows a schematic view of the equipment conventionally used in the blowing method 3,72919

Figure 2 shows a conventional pair of traction rollers from above

Figures 3a and 3b show a side view of a known pair of traction rollers and in particular the disturbances they cause to the hose

Figures 4a, 4b and 4c show an apparatus with a double nip according to the invention in different stages of blowing

Figure 5 shows a top view of a second pair of rollers according to the invention.

Figure 1 shows the equipment conventionally used in the blow molding process. Upon reaching the cooling mandrel 3, the mass begins to crystallize into a tubular primary hose 4 »with a thickness of about 300 to 700 μm. The primary hose is conveyed upwards through a first pair of traction rollers 5 which pull the hose at a certain speed v 1. After passing the first traction roller pair 5, the primary hose 4 is reheated by means of a suitable heating device 6. Compressed air is blown into the reheated hose through the blow pipe 7. Blowing causes the formation of a controlled bubble 8. The thickness of the bubble 8 is about 5 to 30 microns. The bubble 8 is flattened by a pair of upper traction rollers 9, the speed V2 of which is initially equal to v1 and during the actual work n.

5xv- | . The hose is flattened in a controlled manner and fed to the splitting device 11, after which the obtained product 12, 12 'is heat-treated 13 »13" and directed to the storage rolls 14, 14' to await further processing.

The blowing of the bubble 8 is carried out through a blowing pipe 7 passing through the first pair of traction rollers 5. The first pair of traction rollers 5 for the blow pipe 7 is provided with an opening 15 »between the rollers, as shown in Fig. 2. Figures 3a and 3b show the passage of the primary hose 4 through the pair of traction rollers 4 7291 9 5 viewed from different sides. Figure 2 and Figure 3b show the uneven contact of the lower traction roller pair 5 with the hose 4 * Figure 3b also shows the disturbance caused by the uneven contact of the traction roller pair 5 with the hose 4.

Figures 4a, 4b and 4c show schematically a part of an apparatus according to the invention for producing a biaxially oriented synthetic thin plastic film. According to the invention po. in the manufacture of the product, the hot raw material extruded from the extruder nozzle 2 is passed over a conventional cooling mandrel 3. The resulting primary hose 4 is passed through a lower pair of drawing rollers 16 with a cavity for a blowpipe. The primary hose passing through the pair of draw rolls 16 is introduced into the reheating device 6 and directed to pass through the latter pair of rollers 9, Fig. 4a.

Once the primary hose in the reheater 6 has been heated to the correct orientation temperature of about 130-150 ° C, blowing is started (to about 100-300 ° C, preferably about 200 ° C) with heated or room temperature compressed air to form a bubble 8. Compressed air lifts the telescopic blow tube 17 according to the invention upwards through the opening in the first pair of traction rollers 16, to the situation according to Fig. 4b. The blowing of compressed air is continued until the bubble 8 has reached its suitable working dimension. During blowing, the diameter of the primary hose increases, in which case the hose has increased approximately 7-8 times with respect to the direction of travel of the track.

When the bubble 8 has reached a suitable size, the blowing is stopped and the blowing pipe 17 falls down. In this case, the second pair of traction rollers 18 according to the invention is closed around the hose 4. The first pair of rollers 16 with an opening opens and the second pair of rollers 18 acts as a lower pair of traction rollers, Fig. 4c. The second lower traction roller pair 18 includes smooth wide traction rollers.

5 7291 9

The drive roller pair 18 does not require a recess for the blowpipe. In this case, the hose 4 is in even contact between the rollers. The effect of smooth punchless rollers on temperature and the effect on the surface of the hose is uniform; and there is no interference from temperature fluctuations caused by the cavity. The abrasion mark caused by the blowpipe is also not generated when using the apparatus according to the invention.

The use of the apparatus according to the invention eliminates the sharp variations in thickness and bag taste caused by stretching, which were typically visible as track curvature. At the upper end of the hose in the flattening phase, the flattening trace caused by buckling is easy to direct to the edges of the tracks.

Polypropylene is often used as a raw material in the blow molding process, especially when making a film for electrical insulation purposes. However, other plastic materials (LLDPE, PB, PA) can be used as raw material in the blowing process.

The invention may be modified within the scope of the following claims.

Claims (4)

6 PATENT CLAIMS 72 91 9 A method of manufacturing a biaxially oriented synthetic plastic film by a blow molding method, wherein the hose (4) coming from the nozzle (2) is cooled and drawn by a pair of rollers up to a heating space. for storage rollers (13), characterized in that the compressed air! for feeding the hose, the method uses two lower pairs of traction rollers (16, 18), the first of which is provided with an annular groove (15) to pull the hose when compressed air blows the hose into a bubble (8) and the second smooth surface pair of rollers (18) to pull the hose during . Method according to Claim 1, characterized in that the blowing is carried out by means of a telescopic tube (17) which, under the action of compressed air, rises during the blowing phase and falls down at the end of the blowing phase. Apparatus for use in the method of claim 1, comprising a pair of annular traction roller rollers (16) for pulling a cooled hose and a blowing device for introducing compressed air into the hose to produce a large diameter, thin wall thickness bubble, characterized in that the apparatus alternatively comprises a Pull roller (16). another, smooth pair of rollers (18). Apparatus according to claim 2, characterized in that said blowing device is formed by a telescopic tube (17).