Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1991-09-19
1992-11-17
Bell, James J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
428280, 428287, 428300, B32B 502
Patent
active
051642514
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to paper machine felts. In a paper making machine, a slurry of paper making constituents referred to as "furnish" is deposited on a fabric or "wire" and the liquid constituent is drawn or extracted therethrough to produce a self-cohesive sheet which is then passed to the pressing and drying sections of a paper making machine. In the pressing section, the paper sheet is transported by a felt to a pair of rollers where the felt and paper sheet pass between the nip of the rollers to dewater and to initiate drying of the paper sheet. The paper sheet itself may contain all types of chemical additives and in particular contains a considerable amount of residual bleach or peroxide which were added in the pulping process to whiten or enhance the whiteness of the final paper produced. The paper sheet, at the same time, will be subjected to elevated temperatures to aid the dewatering and drying thereof; the paper making felt together with its sheet tend, therefore, to be subjected to immense pressure at elevated temperatures in a rigorous chemical environment.
Polyamide 6 and polyamide 6,6 (PA-6, PA-6,6) have been used extensively in the manufacture of paper machine felts. These polymers are readily formable as fibres and their fibre characteristics can be controlled to make acceptable felts. Many prior art proposals for the use of polyamide materials in sheet and felt materials in general have been proposed. In British Patent Specification No. 1304732, for example, there is a reference to the use of polyamides such as nylon 6, nylon 6-6, nylon 6-10, nylon 7, nylon 8, nylon 9, nylon 11 and nylon 12. The specification is concerned with the manufacture of a fibre sheet material and is not specifically concerned with paper machine clothing.
British Patent Specification No. 1329132 again relates to a non-woven fabric for use, for example, as an inter-lining. Again, there is reference to the use of polyamides such as nylon 6, nylon 11, nylon 12 and copolyamides such as nylon 6/66 and copolymers of nylon 6 and nylon 66 with nylon 11 or nylon 12. British Patent Specification No. 1585632 has been concerned with the manufacture of artificial leather and like materials and again, the use of nylon 6, nylon 6-6, nylon 10, nylon 11 and nylon 12 are disclosed together with various copolymers of different variations and combinations thereof.
In each of these cases referred to the nylon materials are used primarily for their inherent strength in a cloth or decorative assembly and would not be subjected to the aggressive physical and chemical environment of a paper making machine.
European Patent Specification No. 0070708 relates to a paper making felt comprising a woven heat set belt in the machine and in the transverse direction of thermoplastic filaments in which the filaments in at least one of the machine and transverse directions are co-extruded and monofilaments having a core of a polymer selected from nylon 6-6, polyethylene terephthalate and a terpolymer of a tere- or isophthalic acid and a sheet of a copolymer selected from nylon 11, nylon 12, nylon 6, nylon 6,10, nylon 6,12, polybutylene terephthalate and a large number of other materials.
In European Patent Specification No. 0070708 the materials are employed principally for their well known properties of strength and abrasion resistance.
At the present time industry standard felts are produced from both polyamide-6 and 6,6 material. Such materials have been found over the years to produce consistent results. As the papermaking process becomes more efficient, the process requires the presence of increasing amounts of hydrogen peroxide or chlorine, particularly when the paper concerned has a proportion of re-cycled pulp. These aggressive chemicals subject the polyamide material to extreme degradation with a result that the life of the felt correspondingly decreases. Thus, improvements in process efficiency are counterbalanced by shorter felt life.
Papermaking felts are generally produced by needling batt fibre to a woven backing which t
REFERENCES:
patent: 4874660 (1989-10-01), Davis et al.
Barlow Sandra K.
Davis Robert B.
Kramer Charles E.
Albany International Corp.
Bell James J.
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