Stock material or miscellaneous articles – Composite – Of polyamide
Patent
1995-06-30
1997-09-16
Glass, Margaret W.
Stock material or miscellaneous articles
Composite
Of polyamide
4284744, B32B 706, B32B 708
Patent
active
056679009
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an improved aramid paper with satisfactory surface smoothness and reduced fuzzing. In particular, the present invention concerns an especially thin aramid paper suitable for use as electrical insulation paper, heat-resistant labelling paper, and heat resistant paper.
BACKGROUND TECHNOLOGY
Aramid paper is synthetic paper composed of aromatic polyamides. Because of its heat resistance, electrical insulating properties, and flexibility, said paper has been used as electrical insulation paper. Of these materials, Nomex.RTM. of Du Pont (U.S.A.) is manufactured by mixing poly(metaphenylene isophthalamide) flocks and fibrids and then subjecting the mixture to hot-press calendering, and is known as electrical insulation paper with excellent electrical insulation papers and with strength which remains high even at high temperatures.
Not only has Nomex.RTM. paper, due to its resistance to radiation, been used in electrical equipment designed for nuclear power plants and highly radioactive environments, but its use in high-temperature labels, in which the heat resistance of this type of paper can be utilized, has also been the subject of investigations in recent years. [Such paper,] however, contains highly crystalline poly(metaphenylene isophthalamide) flocks (as has been described above), and these flocks hardly change their shape even when subjected to hot-press treatment. The result is not only that it is impossible to ensure high smoothness of the sheet surface, but also that fuzzing of the surface flocks inevitably occurs, and this impairs the printing properties [of the paper] and limits its applicability as labelling paper. In particular, the paper must have a higher level of surface smoothness than does conventional aramid paper when bar codes are to be printed on such high-temperature labels.
In addition, high-voltage (500,000 V) power transmission has recently been utilized, and the utilization of ultrahigh-voltage (1,000,000 V or higher) power transmission (UHV power transmission) is expected in the near future. Electrical insulation paper to be used in transformers for such high-voltage and ultrahigh-voltage power transmission must have high resistance to fuzzing because even microscopic fuzz fibers (about 50 .mu.m) may cause a local insulation puncture.
Japanese Laid-Open Patent Application 4-6708 discloses an electrical insulation paper whose fuzzing is reduced by the hot pressing of a two-layer structure obtained by laminating synthetic paper; said paper is composed of 100% of poly(metaphenylene isophthalamide) pulp and weighs 10 g/m.sup.2 or more. The application also describes synthetic paper which is composed of poly(metaphenylene isophthalamide) pulp and poly(metaphenylene isophthalamide) staple fibers.
However, poly(metaphenylene isophthalamide) fibrids retain water extremely well and drain water poorly, so an increase in the weight of 100% fibrid paper impairs its paper-making properties. In addition, because the synthetic paper thus manufactured is characterized by low tear strength and appreciable thermal contraction, an increase in the proportion of this paper during its lamination and manufacture into electrical insulation paper lowers the tear strength, renders thermal contraction more pronounced, produces sheets which curl readily, and causes other practical problems, which become more evident with a decrease in the weight of the aramid paper as a whole.
When only one side of laminated paper is composed of the above-mentioned 100% fibrid layer, the danger that fuzzing will occur on the other side still remains, limiting the scope of applications. When attempts are made to overcome this drawback by using the above-mentioned 100% fibrid layers on both sides, it becomes difficult to control not only the drawbacks described above, but also the treatment conditions maintained during hot rolling. Specifically, a 100% fibrid layer such as the one described above is less permeable to gases than the above-mentioned layer composed of a mixture of flocks and fibrids,
REFERENCES:
patent: 4255817 (1981-03-01), Heim
patent: 4392315 (1983-07-01), Irving et al.
patent: 4482603 (1984-11-01), Yoshida et al.
patent: 4515656 (1985-05-01), Memeger, Jr.
patent: 5094794 (1992-03-01), Croman et al.
patent: 5393601 (1995-02-01), Heinrich et al.
Hesler Lee James
Kato Ippei
Kimura Yuji
E. I. Du Pont de Nemours and Company
Glass Margaret W.
Mishima Paper Ltd.
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