GB2312396A

GB2312396A - Producing structured sheeting using corona discharge

Info

Publication number: GB2312396A
Application number: GB9708076A
Authority: GB
Inventors: Walter Kramer
Original assignee: Reifenhaeuser GmbH and Co KG Maschinenenfabrik
Current assignee: Reifenhaeuser GmbH and Co KG Maschinenenfabrik
Priority date: 1996-04-24
Filing date: 1997-04-22
Publication date: 1997-10-29
Anticipated expiration: 2017-04-22
Also published as: FR2747957A1; ITMI970941A1; JPH1052853A; FR2747957B1; IT1291635B1; ITMI970941A0; DE19616331C1; GB9708076D0; GB2312396B

Description

1 2312396 "A process for producing structured sheeting from synthetic

thermoplastic material" This invention relates to a process for producing structured sheeting from synthetic thermoplastic material, wherein a virgin fused length is produced with the aid of an extruder and a sheet die and is fed in the plastic state on to a structure-forming roll which is driven in rotation and which has a negative surface structure with respect to the structure of the sheeting, which negative surface structure is copied positively and three-dimensionally in the structured sheeting.

The fused length is already in the shape of sheeting, but is still in a state which is substantially similar to that of a melt.

In the process which is known in practice and from which the present invention stems, the structure-forming roll which is driven in rotation is an embossing roll in a calendering machine. It forms part of a pair of rolls, the second roll of which acts against the structure forming roll as a backing roll. The backing roll has a coating or cladding of elastically deformable material, for example of rubber. The surface of the structureforming roll can be pressed into this elastically deformable material. The fused length is introduced, without any pretreatment, into the roll gap between the structure-forming roll and the backing roll. The structures of the structure-forming roll are produced by mechanical embossing. After it has cooled sufficiently, the structured sheeting can be stripped from the structure-forming roll. These known measures are costly. The structured sheeting may be subjected to mechanical damage during embossing, e.g. tears maybe formed at the edges of the negative surface structure of the structure-forming roll. This applies in particular when these known measures are carried out at a high output.

2 A basic object of the present invention is to produce structured sheeting in a very simple manner, even at high output, and with the avoidance of a mechanical embossing operation which can give rise to the disadvantages described above.

According to the present invention, there is provided a process for producing structured sheeting from synthetic thermoplastic material, wherein a virgin fused length is produced with the aid of an extruder and a sheet die and is fed in the plastic state on to a structure-forming roll which is driven in rotation and which has a negative surface structure with respect to the structure of the sheeting, characterised in that in the region of feeding on to the structure-forming roll the fused length is electrostatically charged, on its side remote from the roll, with the aid of a corona discharge treatment device, that the structure-forming roll is connected as a counterelectrode with respect to the corona discharge treatment device, that positive copying of the negative surface structure of the structure-forming roll is effected in the fused length by electrostatic forces of attraction, and that the structured sheeting, which is positively structured in accordance with the negative surface structure, is formed on the structure-forming roll by cooling and is thereafter stripped from the roll.

The electrostatic forces of attraction act between the fused length, which has been subjected to treatment with the corona discharge treatment device, and the structure-forming roll.

The structure-forming roll can be negatively charged. It can also be earthed, however.

The corona discharge treatment of synthetic material sheeting which is in a sufficiently plastic state is known in principle (EP 0 546 988 A1). These known measures have contributed nothing to the solution of technical problems such as those described above during the production of structured sheeting.

In detail, numerous possibilities exist within the scope of the present invention for the 3 further development of the process according to the invention. Thus the fused length, which is positively structured geometrically in accordance with the negative surface structure of the structure-forming roll, can be cooled by a flowing cooling gas to form structured sheeting, on the structure-forming roll in fact. However, it also fails within the scope of the invention to cool the structure-forming roll.

Me invention stems from the recognition that by corona discharge treatment of the fused length in the course of producing structured sheeting, mechanical embossing, with its mechanical constraints which frequently produce defects, particularly at a high production rate, can be dispensed with, and can be replaced by moulding the fused length gently and electrostatically, as it were, into the negative surface structure of the structure-forming roll. The disadvantages described at the outset are completely avoided, and a high production rate can be employed. The backing roll which is necessary within the scope of the known measures is dispensed with.

The invention is described in more detail below with reference to the drawings, which merely illustrate an example of an embodiment, and where:

is Figure 1 is a schematic illustration, in side view, of an installation for carrying out the process according to the invention; and Figure 2 shows area A from the subject of Figure 1, on a considerably enlarged scale.

Figure 1 shows a device for producing structured sheeting 1 from synthetic thermoplastic material. The synthetic thermoplastic material is processed in an extruder and enters a die disposed downstream of the extruder. This is a sheet die 2 which produces a fused length 3, the width of which corresponds fairly accurately to the width of the structured sheeting 1 to be produced.

4 An examination of Figures 1 and 2 shows that the fused length 3 is fed in a plastic state to a structure-forming roll 4 which is driven in rotation. The latter has a negative surface structure 6 with respect to the structure 5 of the structured sheeting 1 to be produced. In the region of feeding on to the structure-fonning roll 4, the fused length 3 is electrostatically charged, on its surface remote from the roll 4, with the aid of a corona discharge treatment device 7. The structure-forming roll 4 is connected as a counterelectrode with respect to the corona discharge treatment device 7. Positive copying of the negative surface structure 6 of the structure-forming roll 4 is effected in the fused length 3 by electrostatic forces of attraction. The arrangement is effected so that the structure 5 of the structured sheeting 1, which is positive in accordance with the negative surface structure 6 of the structure-forming roll 4, is formed on the structure-forming roll 4 by cooling and can thereafter be stripped from the roll 4. The structure forming roll 4 can be negatively charge or earthed, for example. The cooling measures described above can be carried out in addition.

Claims

1. A process for producing structured sheeting from synthetic thermoplastic material, wherein a virgin fused length is produced with the aid of an extruder and a sheet die and is fed in the plastic state on to a structure-forming roll which is driven in rotation and which has a negative surface structure with respect to the structure of the sheeting, characterised in that in the region of feeding on to the structure-forming roll the fused length is electrostatically charged, on its side remote from the roll, with the aid of a corona discharge treatment device, that the structure-forming roll is connected as a counterelectrode with respect to the corona discharge treatment device, that positive copying of the negative surface structure of the structure-forming roll is effected in the fused length by electrostatic forces of attraction, and that the structured sheeting, which is positively structured in accordance with the negative surface structure, is formed on the structure-forming roll by cooling and is thereafter stripped from the roll.

2. A process according to claim 1, characterised in that the structureforming roll is negatively charged.

3. A process according to claim 1, characterised in that the structureforming roll, which consists of metal, is earthed.

4. A process according to any one of claims 1 to 3, characterised in that the fused length, which is positively structured in accordance with the negative surface structure of the structure-forming roll, is cooled by a flowing cooling gas to form structured sheeting.

5. A process according to any one of Claims 1 to 4, characterised in that the structure forming roll is cooled.

6

6. A process for producing structured sheeting from synthetic thermoplastic material substantially as hereinbefore described with reference to the accompanying drawings.