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Controlled color laser marking of plastics

  • US 5,977,514 A
  • Filed: 06/13/1997
  • Issued: 11/02/1999
  • Est. Priority Date: 06/13/1997
  • Status: Expired due to Term
First Claim
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1. A method for obtaining both light and dark laser marks on a colored plastic article, comprising the steps of:

  • providing a plastic article suitable for laser marking and having a composition comprising (i) a thermoplastic resin that foams when heated, (ii) about 0.4% to about 0.7% by weight of a mica-based laser energy absorbing additive, and (iii) a coloring agent comprising one or more colorants selected from the group consisting of an organic pigment, an inorganic pigment, a polymer-soluble dye, and mixtures thereof;

    providing a laser having a principal wave length, a preselectable beam aperture and scanning velocity, and at least two variable laser parameters selectable from the group consisting essentially of an amperage from a range of amperages, a pulse frequency from a range of pulse frequencies, and a pulse duration from a range of pulse durations, wherein each individual selection of two or more of an amperage, a pulse frequency or a pulse duration comprises a laser setting that provides a laser beam having an individual laser energy characteristic;

    selecting a first laser setting comprising an amperage, a pulse frequency and a pulse duration to provide a first laser beam having an energy characteristic which causes the resin to foam;

    irradiating a first portion of the plastic article with the first laser beam to produce a laser mark having a light shade;

    selecting a second laser setting different than the first laser setting and comprising an amperage, a pulse frequency and a pulse duration to provide a second laser beam having an energy characteristic which causes at least the resin to carbonize; and

    irradiating a second portion of the plastic article with the second laser beam to produce a laser mark having a dark shade.

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