1. Field of the Invention
This invention relates to laminar electrical heaters.
2. Introduction to the Invention
Laminar electrical heaters, including those which comprise a laminar resistive heating element composed of a conductive polymer, are known. Some of these heaters comprise a pair of laminar electrodes, e.g. of metal foil or pierced metal sheet, with the heating element sandwiched between them. The heating element preferably exhibits PTC behavior, thus rendering the heater self-regulating. It is also known to make such heaters which are heat-recoverable or which are deformable so that they can be atached to heat-recoverable articles and will not prevent heat-recovery thereof. Reference may be made for example to U.S. Pat. Nos. 4,085,286, 4,177,376, 4,177,446, 4,223,209, and 4,318,220, and copending and commonly assigned patent application Ser. Nos. 818,711 and 254,352, published as European Application No. 63,440. For further details concerning conductive polymers and electrical devices concerning them, reference may be made to U.S. Pat. Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,861,029, 4,017,715, 4,072,848, 4,117,312, 4,177,446, 4,188,276, 4,237,441, 4,242,573, 4,246,468, 4,250,400, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,315,237, 4,317,027, 4,318,881 and 4,330,704, 4,388,607 and 4,426,633; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 (Moyer), now abandoned, published as German OLS No. 2,634,999; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz); 141,984 (Gotcher et al.), published as European Application No. 38718; 141,987 (Middleman et al.), now Pat. No. 4,413,301, published as European Application No. 38715, 141,988 (Fouts et al.), also published as European Application No. 38718, 141,989 (Evans ), published as European Application No. 38713, 141,991 (Fouts et al.), published as European Application No. 38714, 142,053 (Middleman et al.), now Pat. No. 4,352,083 published as European Application No. 38716, 150,909 (Sopory) and 150,910 (Sopory), U.S. Pat. No. 4,334,351 published as UK Application No. 2076106 A, 184,647 (Lutz), 250,491 (Jacobs et al.) 273,525 (Walty), now Pat. No. 4,398,084 274,010 (Walty et al.), 272,854 (Stewart et al.), 300,709 (van Konynenburg et al.), 369,309 (Midgley et al.), 380,400 (Kamath) and 418,354 (Gurevich) now U.S. Pat. No. 4,435,639. The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.
For a number of uses of laminar heaters, it is desirable to make use of a heater having an irregular shape. For example, when such a heater is used as part of a heat-recoverable article, e.g. to cover a telephone splice case, recovery of only certain parts of the article may be desired or necessary. Alternatively, if recovery of parts of the article is all that is needed, then even if recovery of the whole article is not harmful, limitations on the available power supply (e.g. a battery) may make it necessary or desirable to restrict heating to those parts of the article which need to recover (and/or provide other thermal response such as melting of a hot melt adhesive).