METHOD AND APPARATUS FOR TESTING THE CONTINUITY OF AN ELECTRICALLY CONDUCTIVE WEB OR COATING

1294457 Detecting flaws electrically EASTMAN KODAK CO 4 Dec 1969 [9 Dec 1968] 59238/69 Headings G1N; G1U [Also in Division D1] Discontinuities in an electrically conductive coating applied to a web 22 are detected by initially electrostatically charging the web and detecting the presence of any charged areas remaining on the coating thereby indicating a break in the coating. As shown, a polyethylene terephthalate film base 22 is charged triboelectrically, and is coated with an aqueous gel subcoat 26 which is levelled by air-knife 30 and, before drying by lamps 32 is tested for discontinuities by three field detectors 34, 36, 38, Fig. 3 (not shown) each connected to a respective alarm device as shown. Alternatively, all detectors may be connected to a single alarm device. Discontinuities in an electrically conductive web are also detected by applying an electric field to one side of the web and detecting, on the other side of the web, the presence of any areas where the field has penetrated the web, Fig. 1 (not shown).