Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Scrim – Nonwoven scrim
Patent
1995-08-14
1998-07-21
Weisberger, Rich
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Scrim
Nonwoven scrim
442 58, 442193, 442199, 442200, 442201, 162358, 162900, 162907, D21F 708
Patent
active
057835012
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates in particular to postcondensed paper machine felts comprising a polyamide base fabric and a polyamide coating needled thereon.
The invention further relates to a method of increasing the molecular weight of the aforementioned paper machine felts.
Paper machine felts generally comprise a base fabric on which preneedled web material has been needled. Basically, it is also possible to use spunbonded webs in place of dried web materials.
DE-A-4,027,063 discloses a process for preparing particularly high-weight polyamide fibers by postcondensation. Such postcondensed fibers have the drawback of poor processability because they are very rigid due to their high molecular weight.
Therefore, more energy is needed for carding and needling, and this increased energy enhances the risk of fiber damage during processing.
Another factor to be considered is that postcondensed fibers in the felt can hardly be heat set, that is to say that tension that builds up in the fiber during processing cannot be fully eliminated. This promotes fiber shedding, that is the removal of major fiber fragments or even entire fibers from the felt.
In addition, postcondensed fibers exhibit virtually no thermal shrinkage. The felts are no longer precompressed during the setting process necessary for the base fabric. As a result, fiber bonding may not be optimal.
It is therefore the object of the invention to provide paper machine felts having a high resistance to chemicals, high air permeability and improved wear resistance.
This object is achieved by the postcondensed paper machine felts defined in claim 1 and by the method defined in claim 6. The subclaims contain advantageous embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the method by which the felts used in the comparative experiments described in the present application were made.
FIG. 2 is a schematic view of the pressure test procedures utilized in the comparative examples described in the present application. examples described in the present application.
DETAILED DESCRIPTION OF THE INVENTION
It is not a matter-of-course for someone skilled in the-art that there is a difference in quality between paper machine felts comprising postcondensed fibers as known in the state of the art and postcondensed paper machine felts as defined in the present invention.
Yet, simultaneous postcondensation of the base fabric comprising monofilaments and/or multifilaments is expected to result-in a certain advantage. In general, however, the resistance of the base fabric is not problematic.
However, it has been found that, surprisingly, tests conducted on felt testing presses (see also Table 1 below) revealed significant differences between standard felts and postcondensed paper machine felts as defined in the present invention. When compared to felts comprising postcondensed fibers, the postcondensed felts of the present invention showed a clearly lower change in air permeability, with the final values for both felts being similar, however. This is advantageous in the manufacture of paper because it causes the startup time to be shorter and the felt properties to undergo only slight changes during the startup time.
It has also been a surprising finding that the two felts considerably differed with respect to fiber loss.
On the whole, it has been found that, surprisingly, postcondensed paper machine felts as defined in the present invention will have the required good resistance to chemicals and abrasion if they have a solution viscosity of 5 or more as determined in sulfuric acid at 20.degree. C. (in accordance with the DIN 53,727 standard).
The polyamide fibers of the paper machine felts postcondensed by using the methods of the present invention comprise in particular aliphatic or partly aromatic polyamides or copolyamides, the aliphatic polyamides or copolyamides being based on m-amino carboxylic acids, lactams or aliphatic diamines and aliphatic dicarboxylic acids having 4 to 12 carbon atoms, and
Schuetze Gustav
Spindler Jurgen
Ems-Inventa AG
Weisberger Rich
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