CH682381A5 - A method for producing a foraminous plastic film. - Google Patents

Abstract

A process for manufacturing a plastic film with openings is characterized in that a film made of a crystalline or partly crystalline plastic is slit, and the slit film is stretched in one direction to several times its initial dimension. The plastic is a polyolefin. The resultant process for obtaining a plastic film with openings can be used to manufacture a high-strength, possibly even thinner packaging film. In a process for packaging goods with this packaging film, the film is wrapped under tension and extension around the goods to be packaged. At least one layer of the film is wrapped around the goods to be packaged, and curved ridges of the top layer project from the plane of the film and engage in equally curved ridges of the underlying layer of film.

Description

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CH 682 381 A5

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description

The invention relates to a method for producing an opening plastic film.

Plastic films with openings have been known for a long time. These openings can e.g. can be obtained by punching holes.

From CH-A 387 285 a method is known in which a film is slit by means of slitting knives and the film is stretched in one direction after slitting. This results in a film that has openings and a larger area than the starting film. The weight of the film in relation to the area has been significantly reduced. However, such a slit and stretched film has the major disadvantage that the film, especially if it is damaged in one place, the damage spreads over the film when pulled lightly, ie this stretched film has a very poor tear behavior . Such a film has e.g. a basis weight of 20-50 g / m2.

Sheets of low density polyethylene with a linear structure (LLD-PE) have recently become known which are very stretchable. If these foils are stretched with an increase in area, the weight of the foil in relation to the area is also significantly reduced. This material shows very good tear propagation behavior. This low-density polyethylene with a linear structure (LLDPE) is very difficult to machine. For example, special knives with carbide or alloy-reinforced blades are necessary to trim such foils. Also, when cutting the film, the cutting knife should expediently be heated to 100 ° C. to 300 ° C. and the knife edge must be guided at a certain angle with respect to the film.

These low-density polyethylene films with a linear structure (LLDPE films) have thicknesses of 0.025 mm and very good tear resistance.

Plastic nets are also known in many different forms. It is known, for example, to cross plastic threads at their points of intersection with one another, e.g. to connect by gluing or welding. According to another proposal, these threads can also be extruded together.

It has also been proposed to shrink a slotted plastic film in order to obtain a net (CH-A 515 109).

These plastic nets are also used to package goods. Full-surface plastic films are also used to pack goods.

However, all of these known nets do not always have sufficient strength properties.

The invention has for its object to provide a generic method by which a high-strength, mesh-like plastic film can be produced.

This object is achieved by the method characterized in the claims.

In the process for producing a plastic film with openings, a film consisting of a crystalline or a partially crystalline plastic is slit and the slotted film is stretched to a multiple of its starting mass in at least one direction. A polyofin is preferably used as the plastic. The film can consist of a low-density polyethylene with a linear structure (LLDPE), a polypropylene, a fiber raw material polyamide or polyester.

Plastics such as low-pressure polyethylene, polyolefins with appropriate crystalline fractions are also suitable.

Such a plastic film having openings is particularly tear-resistant compared to the known films. Such a film can also have a very low weight.

The slots are preferably arranged in rows parallel to one another and the slots in adjacent rows are offset from one another.

According to a special embodiment of the method, the slotted film web is shrunk while opening the slits and thickening the remaining webs before stretching the film.

Alternatively or additionally, the plastic film can be pulled out by opening the slots. This stretching or stretching of the plastic film is carried out at room temperature.

Preferably, the webs located between the slots bulge out when they are pulled out of the plane of the plastic film.

According to one embodiment, the plastic film is cut into webs. A e.g. shrunk mesh is cut to a width of 1 to 10 cm, preferably 2 to 5 cm. This gives you a packaging tape. If the film material is adhesive, an adhesive strip is obtained.

A shrunk network is preferably stretched in the longitudinal direction of the web by a factor of 3 to 8, in particular 4 to 6. As a result, in addition to an increase in the strength of the openings in the plastic film, the weight of the film per unit area can be reduced.

According to a special embodiment of the method, the one end of a shrunk net web is fixed to an object to be packed and the net web, which rolls off a roll in particular, is only stretched while the object is wrapped.

The process produces a new type of packaging film. Such a packaging film is preferably placed under tension and stretch around the goods to be packaged. The film can be placed at least in one layer around the goods to be packaged, and webs of the top layer that bulge out of the plane of the film can snap into webs that bulge out of the layer of the film underneath.

In the method according to the invention

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CH 682 381 A5

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Provide a film web made of a crystalline plastic with slits, shrink this slotted film web while opening the slits and thickening the remaining webs and stretching the shrunk film web.

When shrinking, the film thickens in the area of the webs remaining between the slots, while the slots open. The webs merge into one another homogeneously, which is why the stability of the mesh shrunk from a slotted film is much more stable than the stability of a cross made of and connected threads.

These webs now have a sufficiently large material thickness that allows the shrunk net to be stretched many times its length. According to one embodiment of the invention, the network is to be stretched by a factor of 3 to 8, preferably 4 to 6. Essentially, only the webs of the network are stretched many times over. This stretching of the webs can be compared to the stretching of plastic fibers, although the latter are endless.

The slots in the plastic film can have a length of 1 to 10 mm, the distance between the slots in the longitudinal direction being approximately equal to the slot length. The rows of slots can be spaced apart by a distance equal to or slightly greater than the slot length. The dimensions in this regard depend essentially on the plastic used and the maximum desired stretch of the film. The degree of tear resistance should be kept low by suitable design of the slots.

While in the known packaging networks the final dimensions of the network are already determined during the direct network production, the packaging material according to the invention is only stretched during packaging. The film with stretched openings tries to contract again against the applied tensile stress.

Since the webs formed between the slots bulge out of the plane during stretching, layers of the film lying one above the other can be held by webs of two layers which snap into one another.

This film has great elasticity in the transverse direction due to the mesh slits, while the longitudinal strength increases the strength in the longitudinal direction.

A tape cut out of the film in the form of a strip can be used as a normal net packing tape, etc. Through the choice of material according to the invention, the user can increase the strength of this band as a whole or at individual points by stretching. It makes it much thinner. Such stretching can e.g. to 5 times the length.

The slots can be arranged in different ways. This also depends on the desired result. With longer slots, narrower webs are formed, which are monofilament-like after stretching.

A stretchable, cut from a film

Band should have a width of, for example, 1 to 5 cm so that this band e.g. can be stretched evenly by hand.

Claims (14)

Claims I. Process for the production of a plastic film having openings, characterized in that a film consisting of a crystalline or a partially crystalline plastic is slit and the slotted plastic film is stretched at least in one direction to a multiple of its initial mass. 2. The method according to the preceding claim, characterized in that the plastic film consists of a polyolefin. 3. The method according to any one of the preceding claims, characterized in that the plastic film consists of a low-density polyethylene with a linear structure (LLDPE), a polypropylene, a fiber raw material polyamide or polyester. 4. The method according to any one of the preceding claims, characterized in that the slots are arranged in rows parallel to each other and the slots of adjacent rows are offset from one another. 5. The method according to any one of the preceding claims, characterized in that the slotted film web is shrunk to a network while opening the slots and thickening the remaining webs before stretching the plastic film. 6. The method according to any one of claims 1 to 4, characterized in that the plastic film is drawn while opening the slots. 7. The method according to any one of the preceding claims, characterized in that the plastic film is stretched or stretched at room temperature. 8. The method according to any one of the preceding claims, characterized in that the webs located between the slots bulge when they are pulled out of the plane of the plastic film. 9. The method according to any one of the preceding claims, characterized in that the plastic film is cut into webs. 10. The method according to claim 5, characterized in that the shrunk network is stretched in the longitudinal direction of the web by a factor of 3 to 8, in particular 4 to 6. II. Method according to one of claims 5, 9 or 10, characterized in that the one end of a shrunk net web is fixed to an object to be packaged and the net web, in particular rolling off a roll, is stretched during the wrapping of the object. 12. The method according to any one of claims 5 or 9, characterized in that the shrunk mesh sheet is cut to a width of 1 to 10 cm, preferably 2 to 5 cm. 13. The method according to any one of the preceding claims, characterized in that the 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd 5 CH 682 381 A5 slotted plastic film is placed under tension and stretch around the goods to be packed. 14. The method according to any one of the preceding claims, characterized in that the plastic film is placed at least in one layer around the goods to be packaged and from the plane of the plastic film arched webs of the top layer in equally arched webs of the underlying layer of plastic - Snap the film into place. 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 4th