Stock material or miscellaneous articles – Structurally defined web or sheet – Nonplanar uniform thickness material
Patent
1991-04-04
1992-12-08
Hastings, Karen M.
Stock material or miscellaneous articles
Structurally defined web or sheet
Nonplanar uniform thickness material
162358, 162DIG1, 428234, 428287, D21F 708, D01F 662
Patent
active
051694999
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to paper machine clothing suitable for use in the forming, pressing or drying sections of a paper making machine and has particular reference to paper making machine clothing used in the dryer section of a paper making machine, such as through air drying fabrics, and dryer screens.
In paper making machines, a slurry of paper making constituents referred to as "furnish" is deposited on a fabric or "wire" and the liquid constituent of the furnish is drawn or extracted through the fabric or wire to produce a self-cohesive sheet. This cohesive sheet is passed to a pressing and drying section of a paper making machine. In the pressing section of the machine, the paper sheet is transported by a felt to a pair of rollers where the felt and paper sheet are passed between the nip of the rollers to dewater and dry the paper sheet. The paper sheet itself may contain all types of chemical finishes and will be at the same time, subjected to an elevated temperature in order to aid the dewatering and drying thereof.
After pressing the paper sheet passes to the drying section of the machine where it is dried at an elevated temperature. The fabric in the drying section of the machine together with its sheet of paper tends to be subjected to elevated temperatures in a rigorous chemical environment. Dryer fabrics or "dryer screens" employed in the paper making industry have, traditionally, been formed from a variety of materials such as poly(ethylene terephthalate), polyphenylene sulfide and polypropylene. Each material has different properties and pricing, which affects its relative position in the marketplace. An important property for any material used as a drier screen in a paper making machine is that the material should have good hydrolytic stability and good dimensional stability.
Polypropylene is the cheapest material presently available; it has excellent hydrolytic stability, but poor dimensional stability at elevated temperature, and as a result it has only limited use.
Poly(ethylene terephthalate) (PET) is moderately priced, has exceptional dimensional stability and reasonable hydrolytic stability. Poly(ethylene terephthalate) is the predominant material currently used in the marketplace and in most cases, the hydrolytic stability of poly(ethylene terephthalate) can be improved by the addition of carbodiimide stabilisers. Polyphenylene sulfide has excellent dimensional and hydrolytic stability, but suffers from the disadvantage that it is extremely highly priced, is more difficult to work, and tends to suffer from brittle fracture problems in the crystalline state due to normal flexing experienced on the paper machine.
According to one aspect of the present invention, there is provided an article of paper making machine clothing suitable for use in the forming, pressing or drying sections of a paper making machine which article includes a fibre structure characterised in that the fibres of said structure comprise a polyester material having a hintered carboxyl group and in that said fibres have a melting point greater than 260.degree. C. The fibres may have a creep extension of less than 10% at 1.1 grams per denier.
For the purposes of this specification fibre refers to a shaped polymeric body of high aspect ratio capable of being formed into two or three dimensional articles as in woven or nonwoven fabrics. Fibre further refers to staple, multifilament or monofilament forms. Melting point is defined in this context as the temperature of the highest peak on the endotherm of the plot produced via Differential Scanning Calorimetry. By way of example of how melting point is determined FIG. 1 (hereinafter referred to) is a graph of a Differential Scanning Calorimetry response of a commercial polyester with a melting point of 255.degree. C.
In another aspect of the present invention, the fibres may additionally have an initial modulus greater than 25 grams per denier, an elongation at break of greater than 15% and a tenacity of greater than 2 grams per denier.
In a further aspect of
Ditaranto Francis
Eagles Dana B.
Leon Jeanne A.
Albany International Corp.
Hastings Karen M.
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