Method for the formation of narrow, metal-free strips in a metal layer on plastic sheets

A method for forming metal-free strips on a plastic sheet provided with a thin layer of vaporizable metal from which to manufacture electrical capacitors, comprising the steps of:

• moving the metallized plastic sheet at a feed rate relative to an n number of laser beams arranged parallel to one another in a plane parallel to the direction of said sheet movement, said n number of laser beams being greater than one;
• pulsing said n number of laser beams with a predetermined frequency;
• vaporizing one area of the metal layer at each laser pulse for each laser beam due to the duration and intensity of the individual pulses, said one areas each having a center and a length in the direction of said sheet movement and a width substantially transverse of said length;
• determining a clock spacing of centers of said one areas depending on said feed rate of the metallized plastic sheet and said predetermined frequency of the laser pulses, said clock spacing of two successive ones of said one areas vaporized being equal at least to an n multiple of half of said length and at most to an n multiple of said length shortened by half said width;
• providing a cooling distance between said centers of said one areas vaporized by neighboring ones of said laser beams, said cooling distance being a distance greater by an n.sup.th part of said clock spacing than a whole multiple of said clock spacing of successive ones of said one areas vaporized by the same laser beam.