Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-11-24
2001-03-27
Edwards, Newton (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S374000, C428S370000, C428S221000, C139S3830AA
Reexamination Certificate
active
06207276
ABSTRACT:
TECHNICAL AREA
This invention relates to the area of synthetic fibers of the kind usually employed to manufacture paper machine felt, in particular of paper machine felt for use in the press area of paper machines. It relates to a sheath-core bicomponent fiber, significant parts of which consist of polyamide. It also relates to the use of such a fiber for manufacturing paper machine felt.
PRIOR ART
Press felts are used in paper machines to support the paper pulp and take water out of the paper pulp during the pressing procedure. This usually happens in the paper manufacturing process immediately after the headbox and Fourdrinier wire part, and before the sheet in the reeling end is completely dried.
To increase the dewatering performance in the pressing procedure, the temperatures in the press area of paper machines have in past years been continuously increased (B. Wahlstrom, “Pressing-the state of the art and future possibilities”, Paper technology, February 1991, pp. 18-27). New developments such as “Hot Pressing” or “Impulse Pressing” (e.g., see D. Orloff et al., TAPPI Journal Vol. 81 (07/1998), pp. 113-116 and H. Larsson et al., TAPPI Journal Vol. 81 (07/1998), pp. 117-122) use in part very high temperatures. The high temperatures (at times over 200° C. in impulse pressing) lead to an advantageous reduction in water viscosity on the one hand, but place an enormous demand on the fibers processed in the press felts on the other. The high temperatures make in particular synthetic fibers soft in the jacket region, which can result in increased compaction and felt abrasion. Given an increase compaction, the fibers become conglutinated, the gaps in the felt get smaller, and hence the felt loses some of its capacity to take water out and away from the paper.
To ensure high felt run times, and hence the lowest possible machine downtimes, a high abrasion resistance and low compaction represents a very important criterion for the usability of fibers for press felts. For this reason, press felts today consist almost exclusively of polyamide 6 (PA 6) or PA 66) fibers and monofilaments, although the literature also describes felts made out of PA 11 fibers (EP 0 372 769), and PA 12 fibers (EP 0 287 297), etc.
PEEK (polyetheretherketone) fibers (EP 0 473 430) or PTFE (polytetrafluoroethylene) fibers (WO 9210607) have also been tested for use in paper machine felts, for example. While they proved suitable in terms of temperature resistance, their low abrasion resistance does not enable any acceptable felt run times.
The use of fibers as partially aromatic polyamides, along with a buildup of fibers as bicomponent fibers consisting of two components arranged side to side has been proposed (EP 529 506), but sufficient abrasion resistances have also yet to be achieved with such fibers.
Compaction was to be prevented by coating fibers with layer silicates, e.g., by manufacturing layer silicate-containing fibers and monofilaments (WO 97/27356; EP 0 070 709). The disadvantage to Incorporating layer silicates into the fiber polymer is that fiber strength is greatly diminished, however.
EP 0 741 204 describes the use of sheath-core bicomponent adhesive fibers for press felts that are primarily designed to improve the surface quality, run characteristics of the felt, recovery and dewatering. This is accomplished with bonds that are generated by melting on the sheath component.
DESCRIPTION OF THE INVENTION
The object of the invention is therefore to provide a fiber that, for example when processed into a paper machine felt, exhibits a sufficient abrasion resistance and simultaneously withstands high temperatures, in particular under the conditions that arise during impulse pressing, without becoming significantly compacted and conglutinated.
This task is achieved in a fiber of the kind mentioned at the outset by designing the fiber as a sheath-core bicomponent fiber that exhibits a core and a sheath that at least partially envelops the core, and by having the sheath consist of 45-98% w/w of a first polyamide having a melting point exceeding 280° C., and 2-20% w/w of a layer silicate. In addition, the core consists of a second polyamide. The sheath also contains up to 35% w/w of this second polyamide. The core of the invention is therefore to build up the fibers as a sheath-core bicomponent fiber, and to use a layer silicate-containing and high-melting point sheath both to prevent compacting and achieve a high abrasion resistance, but to prevent the reduction in fiber strength caused by the incorporation of silicates by having a solid core be present. The fact that the core consists of a second polyamide and the sheath also contains up to 35% w/w of this second polyamide ensures an intimate bond between the core material and sheath material.
The feature of one preferred embodiment is that at least the core or the sheath or both parts contain up to 1% w/w of heat stabilizers, and that in particular these heat stabilizers are inhibited phenols, phosphonic acid derivatives, phosphates or combinations of these stabilizers. This is another effective measure for increasing heat stability, and hence for preventing the two-component fiber from compacting.
In addition, the invention claims the use of such a fiber according to the invention for manufacturing a paper machine felt, in particular a needled paper machine felt, which continuous to be preferably geared toward use in the pressing area, in particular in impulse pressing or hot pressing.
Additional embodiments of the sheath-core bicomponent fiber and the application of the latter arise from the dependent claims.
PERFORMANCE OF THE INVENTION
In describing the manufacture of a fiber according to the invention out of two components designed as the core and sheath, the composition of the core followed by that of the sheath will first be discussed.
The core is preferably manufactured out of PA 6 or PA 66 with a relative solution viscosity of 2.4-5.0 (1 g polymer per 100 ml of 96% sulfuric acid at 25° C.) or mixtures of the corresponding PA 6 and PA 66 qualities in a 1:99 to 99:1 ratio. Polyamide types PA 11, PA 12, PA 69, PA 610, PA 612 or PA 1212 with a relative solution viscosity of 1.6-2.8 can also be used for the core (0.5 g of polymer per 100 ml of m-cresol at 25° C.). In addition, the core should preferably contain 0-1% 2/2 of heat stabilizers, e.g., based on sterically inhibited phenols, phosphonic acid derivatives or phosphites or combinations of these stabilizers. The core hence ensures the necessary strength of the fibers, for example when they are processed to felts.
The sheath must consist of a polyamide with a melting point of at least 280° C., and it must contain an additional 2-20% w/w of layer silicates (e.g., MICROMICA® MK 100 from the company CO-OP Chemical CO., LTD, Japan) and 0-35% w/w of the polyamide type used to build up the core. Suitable polyamides with a melting point of at least 280° C. include
PA 46 hompolymers based on tetramethylenediamine and adipic acid;
PA 46/4T copolymers based on tetramethylenediamine, adipic acid, and terephthalic
PA 66/6T copolymers based on hexamethylenediamine, adipic acid, and terephthalic acid;
PA 6T/6I copolymers based on hexamethylenediamine, terephthalic acid, and isophthalic acid;
PA 9T homopolymers based on nonanediamine and terephthalic acid;
PA 10T homopolymers based on decanediamine and terephthalic acid;
PA 12T homopolymers based on dodecanediamine and terephthalic acid; and
PA MPMD T/6I copolymers based on 2-methyl-1,5-pentanediamine, hexamethylenediamine, terephthalic acid and isophthalic acid.
The above listed polyamides can contain up to 20% w/w of additional monomers such as caprolactam or laurinlactam. The sheath also contains 0-1% w/w heat stabilizers, e.g.; based on sterically inhibited phenols, phosphonic acid derivatives or phosphates or combinations of these stabilizers. The layer silicates can either be incorporated into the polymer through compounding with a two-screw extruder or, during the polymerization of one of the PA components, be added at the beginning of polymerizatio
Schäch Gunther
Spindler Jurgen
Sutter Simon
Weller Thomas
Edwards Newton
Ems-Chemie AG
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
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