The invention relates to a method for producing a paper machine clothing, comprising the following steps: a) providing a film-like substrate having an upper side and a lower side opposite the upper side and b) introducing a pattern of holes into the substrate by boring a multiplicity of holes connecting the upper side to the lower side into the substrate by means of at least one laser light source.
The term “paper machine clothing” is intended to mean a clothing for a machine for producing or refining a fibrous material web, in particular a paper, cardboard or tissue web. For example, this clothing may be used in the forming part or the pressing part or the drying part of a paper machine. Traditionally, such clothings are currently still substantially produced by weaving methods, that is to say a method in which warp and weft threads are woven together. However, an alternative production method for such paper machine clothings has already been known for a relatively long time. In this method, film-like substrates are perforated by means of a laser. The term “film-like substrates” is in this case intended to mean thin, flat articles which are generally formed by extrusion of plastic. The substrates may in this case be monolithically constructed or formed as a laminate of a plurality of layers. The individual layers may differ from one another in respect of their properties, for example material or thickness. The substrate, or individual layers of the substrate, may also be provided with particles, fibers or yarns in order to impart desired properties to the substrate, particularly in respect of strength. Furthermore, substances, for example a staple fiber layer, may also be applied onto the substrate in order to produce the finished paper machine clothing.
Patent specification U.S. Pat. No. 4,446,187 describes a method of the generic type for perforating a film-like substrate for the purpose of producing a paper machine clothing. As is represented in
Particularly when the paper machine clothing is used as a forming screen, a very large number of very small holes arranged close to one another need to be introduced into the film-like substrate in order to allow maximally uniform and marking-free dewatering of the fibrous material web during the paper production. Depending on the size of the forming screen, the number of holes in the substrate may be in the six or even seven figure range. In the case of the above-described method known from the prior art, it is disadvantageous that a considerable manufacturing time is required for the introduction of so many holes. Although pulsed lasers can nowadays be operated without problems with a very high working frequency, the risk arises that by excessively high energy input into the substrate locally in a short time the material will not only be sublimed where the holes are intended to be introduced, but will also be damaged, in particular melted and/or vaporized, beyond this. This applies particularly to the turning points at the side edges of the substrate.
It is an object of the present invention to eliminate or at least minimize the above-described problem with the method from the prior art.
This object is achieved according to the invention in that, in the method described in the introduction, a bore hole strategy is applied which ensures that, chronologically between the introduction of a first hole and a second hole immediately adjacent to the first hole in the pattern of holes, at least one further hole, which is not immediately adjacent to the first hole or the second hole in the pattern of holes, of the pattern of holes is introduced into the substrate. This prevents an excessively high amount of energy being introduced into the film-like substrate locally in too short a time, despite a very high working frequency of the laser light source. The manufacturing time during the laser perforation of the film-like substrate can therefore be reduced significantly in comparison with the prior art, without unacceptable damage to the substrate occurring.
The term “not immediately adjacent” is in this case to be understood as meaning that at least one further hole of the pattern of holes is provided between the two holes which are not immediately adjacent. Thus, if for example the midpoints or midaxes of the two holes which are not immediately adjacent are joined to one another with a line, this line therefore extends through at least one further hole of the pattern of holes.
So that unacceptable damage does not occur anywhere in the film-like substrate, and the entire manufacturing process can nevertheless be carried out with a high speed, it is advantageous for the bore hole strategy to be applied to the majority of the holes, preferably to all the holes, of the pattern of holes. If it is applied to all the holes of the pattern of holes, this means that spatially immediately adjacent holes are not introduced chronologically in direct succession into the substrate by means of the laser light source.
In one refinement of the invention, the bore hole strategy provides, chronologically between the introduction of the first hole and the second hole immediately adjacent to the first hole of the pattern of holes, the introduction of at least two further holes, preferably at least three further holes, more preferably at least four further holes into the substrate, all of which are not immediately adjacent to the first hole or the second hole. Preferably, these additionally introduced holes are also not immediately adjacent to one another. In this way, the time spacing between the introduction of two immediately adjacent holes of the pattern of holes may be increased for an equal pulse frequency of the laser light source, or the pulse frequency of the laser light source may be increased without reducing the time spacing between the introduction of two immediately adjacent holes of the pattern of holes.
As an alternative or in addition, for the same reasons, it is proposed for the spatial distance between two holes introduced chronologically in direct succession into the substrate to be at least two times as great, preferably at least three times as great, more preferably at least four times as great as the smallest spatial distance between two immediately adjacent holes in the pattern of holes.
According to one variant for carrying out the bore hole strategy according to the invention, scanner optics, by means of which a laser beam from the laser light source can be displaced in jumps on the substrate, are used, the scanner optics preferably comprising at least one movable mirror. In this way, the manufacturing speed is not limited by the maximum speed with which the laser light source can be moved relative to the film-like substrate. Scanner optics are capable of guiding the laser beam in a fraction of a second from one location on the film-like substrate —within certain spatial limits—onto another location, without the laser light source having to be moved relative to the film-like substrate for this purpose.
Nevertheless, for a further increase in the working speed, it may be advantageous for the laser light source to be moved relative to the substrate during the method. This relative movement may in this case be carried out either substantially discontinuously or substantially continuously. In the first case, the laser light source is kept stationary over the film-like substrate until a predetermined surface region of the film-like substrate, which may for example be reached by means of scanner optics, is provided with holes, before the laser light source is moved relative to the film-like substrate to a further predetermined surface region. In the second case, the laser light source is moved relative to the film-like material while the laser light source introduces holes into the film-like substrate, for example by means of scanner optics. This further increases the working speed in comparison with the first case. For both the continuous and the discontinuous relative movement, it is for example possible for the substrate, which may be tensioned by means of two rollers having axes aligned substantially parallel to one another, to be moved in the machine direction of the future clothing, for example by the rollers being rotated, while the laser light source is moved slowly in the machine transverse direction of the future clothing. In this way, a helical track of holes is obtained on the substrate.
In order to further increase the working speed, more than one laser light source may be used simultaneously in order to introduce holes into the substrate. In this case, each laser light source may be assigned its own scanner optics. The greater the number of laser light sources which are used in parallel is, the greater the working speed is. When using a plurality of laser light sources operating chronologically in parallel, it is also advantageous to apply the bore hole strategy according to the present invention for each individual laser light source.
Two exemplary embodiments of the method according to the invention will be described in more detail below with the aid of
The chronological order with which the holes 1-8 of the pattern of holes are introduced into the film-like substrate is represented by the arrows and the numbering in
On the other hand, the effect of the method according to the second embodiment example is that the hole spacing in the edge region of the film-like substrate 10 (on the left in
By the method according to the invention, it is possible to perforate the film-like substrate 10 much more rapidly than with the method described in the introduction from the prior art, since the individual holes can be introduced more rapidly in succession without the substrate 10 locally experiencing a critical energy input and being damaged.
Number | Date | Country | Kind |
---|---|---|---|
102019103107.9 | Feb 2019 | DE | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP2020/050661 | 1/13/2020 | WO |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2020/160873 | 8/13/2020 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4446187 | Eklund | May 1984 | A |
5837102 | Graf | Nov 1998 | A |
Number | Date | Country |
---|---|---|
102012210768 | Jan 2014 | DE |
0 103 376 | Mar 1984 | EP |
2008049398 | Mar 2008 | JP |
WO 2014001217 | Jan 2014 | WO |
Entry |
---|
WO 2014/001217, Derwent English Language Abstract (Year: 2014). |
Number | Date | Country | |
---|---|---|---|
20220081837 A1 | Mar 2022 | US |