KR910000497B1 - Method and apparatus for producing mesh film - Google Patents

Abstract

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Description

Method and apparatus for manufacturing mesh film

1 is a side view of a first aspect of the present invention with a portion cut away.

2 is a side view of a second aspect of the present invention with a portion cut away.

3 is a side view of a third aspect of the present invention with a portion cut away.

The present invention relates to a method and apparatus for producing a mesh film tube, which is a thermoplastic synthetic resin material, and more particularly, to a method and apparatus for producing a tube of various diameters.

Many different techniques have been used to form extrudable thermoplastic resin compositions into films. Such films have been found to be useful in many applications, such as, for example, packaging materials, garbage bags and the like. It has been found that the tear resistance of such films is significantly increased by forming ridges in the film, which increase the thickness of the film, thereby producing a product sometimes called a mesh film. Ridges can be formed in a variety of patterns, including parallel lines, crosses, and combinations thereof.

Havens, U.S. Patent No. 4,265,853 (May 5, 1981), describes an apparatus for forming ridges on an extruded film by differentially cooling the film during the stretching process. The film is extruded through a tubular die and stretched away from the die. Multiple nozzles spaced around the tubular film increase the thickness by cooling the film to form multiple thin lines while rotating around the film while the film is stretched, resulting in a pronounced ridge effect. Two pairs of nozzles rotating in opposite directions around the film may be used to form a cross ridge. In Harbens' device, the tubular film extends to the desired diameter and then passes around the outer surface of the cylindrical cooling mandrel. The tubular film is then divided into two film pieces and collected for subsequent processing.

Harbens's device provides a good quality reinforcement film product, while being limited to being able to produce only tubular films of specific diameters. Thus, there is a need for a method and apparatus for producing mesh films of varying selected diameters without changing the apparatus.

This need is met by an apparatus for producing a mesh film according to the invention comprising a die for extruding a thermoplastic resin film tube and a first cooling means for cooling the inner surface of the tube and located in the center of the extruded tube. The outer diameter of the first cooling means is approximately equal to the inner diameter of the extruded tube. The plurality of cooling nozzles disposed radially outwardly from the first cooling means inject a plurality of cooling gas strips to the outer surface of the extruded tube. The annular gas bearing is axially spaced from the first cooling means such that the extruded tube passes through the annular gas bearing after passing through the first cooling means. This causes bubbles trapped inside the extruded tube to actually increase the diameter of the extruded tube.

The first cooling means may consist of a generally cylindrical cooling mandrel and a pair of gas bearings positioned on both sides of the mandrel and arranged axially and generally cylindrical. In addition, the first cooling means may comprise a conventional gas bearing. At least some of the plurality of cooling nozzles may circulate around the extruded tube.

The apparatus of the invention may further comprise second cooling means for cooling the tube when the diameter of the tube is expanded after the tube has passed through the annular gas bearing.

The apparatus of the present invention may also further comprise third cooling means for cooling the tube when the tube is separated from the die. The third cooling means may comprise means for injecting cooling gas towards the outer surface of the extruded tube as soon as the tube is separated from the die.

The apparatus of the present invention further comprises a fourth cooling means located in the inner center of the extruded tube for cooling the inner surface of the tube after the tube is separated from the annular gas bearing. The outer diameter of the fourth cooling means is substantially larger than the inner diameter of the annular gas bearing. The fourth cooling means may consist of a cooled mandrel and a gas bearing connected thereto.

The extrusion die can extrude a tube of film that is a thermoplastic resin material of relatively large diameter. The second annular gas bearing is located adjacent to the extrusion die and arranged coaxially to the die for receiving the tube from the extrusion die. The inner diameter of the second annular gas bearing is smaller than the diameter of the tube after detaching from the die and is approximately equal to the outer diameter of the first cooling means.

In particular, the present invention relates to a method for producing a mesh film, characterized by the following steps; a) extruding a film that is a thermoplastic synthetic resin material to form a film tube; b) cooling the inner surface of the tube by injecting a plurality of cooling gas streams on the outer surface of the tube, passing the film tube through a centrally located common cooling means; c) passing the tube through an annular gas bearing whose inner diameter is approximately equal to the outer diameter of the cooling means, and d) increasing the diameter of the tube using bubbles trapped inside the tube.

The cooling means may consist of a generally cylindrical cooling mandrel and a pair of gas bearings positioned axially and positioned on both sides of the mandrel. The cooling means may also comprise a generally cylindrical gas bearing. At least a portion of the cooling gas stream may move around the extruded tube.

The method also includes cooling the tube by injecting cooling gas to the outer surface of the tube as the diameter of the tube increases. The method also includes cooling the tube by injecting a cooling gas to the outer surface of the tube immediately after the tube is extruded. In addition, the method may further comprise cooling the tube using a cooling mandrel located in the tube and a gas bearing connected thereto after the diameter of the tube is increased.

The extruding of the tube of the film may include extruding a tube of relatively large diameter and then stretching the tube axially to reduce the diameter of the tube of relatively large diameter.

It is therefore an object of the present invention to provide a method and apparatus for producing a mesh film into extruded tubes of varying diameters; The tube's outer diameter is approximately equal to the inner diameter of the tube and passes around the cooling means with a plurality of cooling nozzles arranged radially outward, the tube passes through the annular gas bearing, and then the tube's expansion Providing a method and apparatus facilitated by trapped bubbles; Providing a method and an apparatus wherein the cooling means comprises a generally cylindrical cooling mandrel and a generally cylindrical gas bearing positioned axially on both sides of the mandrel; Providing a method and apparatus in which a cooling means for cooling the inner surface of the tube is located in the center of the extruded tube after the tube has been separated from the annular gas bearing; An extrusion die extrudes a tube of relatively large diameter and a second annular gas bearing receives the tube from the extrusion die to reduce the diameter of the tube to approximately the diameter of the cooling means; It is also to provide a method and apparatus which can provide additional cooling means at various points along the path of the extruded tube.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

FIG. 1 illustrates a first aspect of the apparatus of the present invention for producing a mesh film, wherein the extrusion die 10 extrudes a tube 12 of thermoplastic synthetic resin material, such as polyethylene. As shown in FIG. 1, the extruded tube 12 generally moves upwards and is positioned in the inner center of the extruded film tube 12 to cool the inner surface of the tube 12. Pass through the cooling means (14). The outer diameter of the first cooling means 14 is approximately equal to the inner diameter of the extruded tube 12.

The plurality of cooling nozzles 16 and 18 are arranged radially outwardly and in opposition to the first cooling means 14 and inject a plurality of cooling gas streams to the outer surface of the extruded tube. The cooling nozzles are annularly arranged around the tube 12 and radially inward from the annular members 20 and 24 defining the air passages 22 and 26. The support ring 28 surrounds the annular member while allowing the annular members 20 and 24 to rotate freely. The support ring 28 receives pressurized air through conduits 30 and 32 and an opening (not shown in the drawings) in the annular members 20 and 24 through an internal air passage (not shown). The air is supplied to the air passages 22 and 26 via e). The annular members 20 and 24 can freely rotate around the tube 12 in the same way or in opposite directions.

The first cooling means 14 comprises a generally cylindrical water-cooled mandrel 34 and a pair of generally cylindrical gas bearings 36 and 38 which are located on both sides of the mandrel 34 and are axially arranged with the mandrel. do. Gas bearings 36 and 38 of conventional type provide a thin air cushion that allows the tube 12 to pass through without any obstacle.

It can be seen that by selectively contacting the surface of the extruded tube 12 with air ejected from the nozzles 16 and 18, a number of fine lines can be formed in the portion where the film is cooled. As can be appreciated, by selectively cooling, the melt tension of the material in the cooled portion increases, so that while continuing to stretch the film, the film is not stretched as much as the film in the adjacent warmer portion. Due to this high melt tension, distinct ridges are formed in the film. When nozzles 16 and 18 rotate in opposite directions around tube 12, cross-shaped ridges are formed to provide substantially increased mechanical film strength. A suitable motor drive (not shown in the figure) of conventional type may optionally rotate the annular members 20-24.

Expansion and stretching of the tube 12 is carried out after the tube has passed through an annular gas bearing 40 spaced axially away from the first cooling means 14. With this operation, the diameter of the extruded tube 12 continues to increase, due to the trapped bubbles typically present in the interior 42 of the expanded face 44 of the extruded tube, and the nozzles 16 and 18 and cooling. The tube 12 is held in an appropriate position between the means 14. As described, the tube can be expanded at the site 44 to form various desired diameters. This expansion process is carried out in a conventional manner.

Second cooling means 46 may be provided for cooling the tube 12 after the tube 12 passes through the annular gas bearing 40. Such cooling means may comprise means for injecting cooling gas towards the outer surface of the extruded tube when the tube is expanded. In a similar manner, a third cooling means 48 may provide for injecting cooling gas to the outer surface of the extruded tube after the tube has been separated from the die. The second cooling means 46 and the third cooling means 48 preferably inject air towards the surface or portion 14 of the tube 12 so that the film is not cooled differently.

The outer gas bearing 40 can inflate the tube 12 extruded from the portion 44 over the bearing 40 to various desired diameters, as indicated by the dashed line and solid line of the portion 44. Thus, using a die 10 that provides an extruded film tube 12 of particular diameter, the tube 12 can be expanded at the site 44, for example, at a ratio of 1.5: 1 to 3: 1 and more. Can be. Of course, the expansion ratio chosen will depend on a number of factors including the particular film material used and the method of application for producing the film.

As can be seen from FIG. 1, the water cooled mandrel 34 is slightly smaller in diameter than the gas bearings 36 and 38. However, in the drawings, these differences are slightly exaggerated for clarity. The mandrel 34 preferably has a low friction of the outer surface. The air from the nozzles 16 and 18 makes the tube 12 very close to the surface of the mandrel 34, thereby improving the cooling of the surface portion of the film tube with which the air is in contact, thereby increasing the formation of distinct ridges and the rate of extrusion. .

A second aspect of the present invention will be described with reference to FIG. Since the apparatus shown in FIG. 2 is similar in many respects to the apparatus of FIG. 1, similar constructions have used corresponding numbers and will not be described again. The aspect of FIG. 2 is located in the center of the extruded tube 12 and in particular the area 44 of the expanded or expanded tube for cooling the inner surface of the tube after the tube has been separated from the annular gas bearing 40. The point of including the 4th cooling means 50 differs from the aspect of FIG. As can be seen from the figure, the outer diameter of the fourth cooling means 50 is substantially larger than the inner diameter of the annular gas bearing 40.

The fourth cooling means 50 consists of a mandrel 52 which can be water cooled and a bearing 54 connected to the mandrel. The mandrel 52 is used when manufacturing the smallest tube portion 44 with a solid line together with a larger tube that is not cooled by the mandrel 52 with a dotted line. This makes it possible to produce larger mesh film tubes. In some cases, when the smallest tube is manufactured to move the tube relative to the mandrel 52, an air box (not shown in the figure) may be provided around the mandrel 52. This air box consists of two semicircle areas for easy removal when large mesh film tubes are produced. In addition, the fourth cooling means 50 may be constituted by the gas bearing 54 alone without the mandrel 52 connected to the bearing 54.

3 illustrates a third aspect of the present invention. Many parts are similar to those shown in FIGS. 1 and 2 and corresponding numbers are used. The aspect of FIG. 3 differs from the aspect of FIG. 1 and FIG. 2 in that the extrusion die 55 manufactures a tube with a relatively large diameter made of a film made of a thermoplastic synthetic resin material. The extrusion die further includes a second annular gas bearing 58 adjacent to and arranged coaxially with the die 55. The second annular gas bearing 58 receives the tube 56 from the extrusion die 55. The inner diameter of the bearing 58 is smaller than the diameter of the tube 56 separated from the die 55 and is approximately equal to the outer diameter of the first cooling means 14. The diameter of the tube 56 decreases as the tube is stretched between the die 55 and the gas bearing 58.

Indeed, the use of larger dies 55 results in the treatment of the film material at a specific extrusion rate at lower pressures and lower melting temperatures than in the case of the embodiments described above. As a result, the form of FIG. 3 is more productive. In some cases, additional cooling means similar to the means 48 shown in FIG. 1 may be provided adjacent to the die 55. By varying the amount of cooling, the amount of film material whose orientation is maintained in the extrusion direction can be varied to exhibit optimal properties for the material used. The outer air box can be positioned around the tube 56 to minimize the pressure difference between the inside and outside of the tube 56.

In some instances, it may be desirable to simplify the apparatus of FIGS. 1 through 3 by replacing the mandrel 34 and gas bearings 36 and 38 connected thereto with a single gas bearing of approximately the same length and larger. However, this will result in a decrease in cooling power and a corresponding reduction in the obtainable extrusion rate. In addition, many other changes may be made to the apparatus of FIGS. 1 to 3 within the scope of the present invention. For example, the fourth cooling means 50 shown in FIG. 2 may optionally be connected to the apparatus of FIGS. 1 and 3. The apparatus and method of the present invention may employ synthetic resin materials that are thermoplastic and extrudable into a film.

By referring to the detailed description of the invention and its preferred embodiments, it will be apparent that modifications and variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims (13)

An extrusion die for extruding a tubular film of thermoplastic resin material, the first cooling being located at the center of the extruded tubular film and having an outer diameter smaller than the inner diameter of the tubular film so as to pass through the tubular film and cooling the inner surface of the tubular film Means, a plurality of cooling nozzles arranged radially outwardly from the first cooling means and injecting a plurality of cooling gas streams on the outer surface of the tubular film after being separated from the first cooling means For passing through a gas bearing, the diameter of the tubular film is arranged to continue to increase by bubbles trapped therein, and for producing a mesh film comprising an annular gas bearing spaced axially away from the first cooling means. Device. The device of claim 1, wherein the first cooling means comprises a cylindrical cooling mandrel or gas bearing and a pair of gas bearings positioned on both sides of the mandrel and axially arranged with the mandrel. The apparatus of claim 1, wherein at least a portion of the plurality of cooling nozzles can circle around the tubular film. 4. The second cooling means according to claim 1, 2 or 3, which injects cooling gas toward the outer surface of the tubular film when the diameter of the tubular film expands after the tubular film passes through the annular gas bearing. Device comprising a. 5. An apparatus according to claim 4, comprising third cooling means for injecting cooling gas towards the outer surface of the tubular film immediately after the tubular film is separated from the extrusion die. 6. The apparatus of claim 5, further comprising fourth cooling means located in the center of the tubular film and having an outer diameter greater than the inner diameter of the annular gas bearing and cooling the inner surface of the film after the tubular film is separated from the annular gas bearing. Device. 2. An extrusion die according to claim 1, arranged coaxially with them adjacent to the extrusion die and having an inner diameter smaller than the diameter when the tubular film is separated from the extrusion die, the same as the outer diameter of the first cooling means and from the extrusion die. And a second annular gas bearing for receiving the tubular film passed through. Extruding the thermoplastic synthetic resin material to form a tubular film, passing the tubular film through a first cylindrical means for cooling centrally while injecting a plurality of cooling gas streams towards the outer surface of the tubular film, the inner surface of the tubular film Cooling the tube, passing the tubular film through an annular gas bearing whose inner diameter is equal to the outer diameter of the cooling means, and increasing the diameter of the tubular film using bubbles trapped inside the tubular film. Method for producing a mesh film, characterized in that. The method of claim 8, wherein at least a portion of the cooling gas stream is circularly moved around the extruded tubular film. 10. The method of claim 8 or 9, comprising a relationship of cooling the tubular film by injecting a cooling gas towards the outer surface of the tubular film as the diameter of the tubular film increases. The method of claim 8 including cooling the tubular film by spraying cooling gas towards the outer surface of the tubular film immediately after the tubular film is extruded. The method of claim 8, wherein the first chiller comprises a cylindrical cooling mandrel or gas bearing and a pair of cylindrically arranged gas bearings axially arranged on both sides of the mandrel. The method of claim 8 including extruding a relatively large diameter tubular film and reducing the diameter by axially stretching the tubular film.

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