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

• Current Assignee: Polyone Corporation (Avient Corp.)
• Original Assignee: M.A. Hannacolor
• Inventors: Harris, Ronald M., Feng, Ke, Burgess, Alan R.
• Primary Examiner(s): Evans, Geoffrey S.
• Application Number:
  US08/874,401
• Time in Patent Office: 872 Days
• Field of Search: 264/400, 264/409, 427/554, 427/555, 427/596, 219/121.61, 219/121.62, 219/121.68, 219/121.69, 219/121.83, 524/417
• US Class Current: 219/121.69
• CPC Class Codes: B41M 5/267 Marking of plastic artifacts, e.g. with laser
• CPC Class Codes: B41M 5/34 Multicolour thermography
• CPC Class Codes: C08K 7/00 Use of ingredients characterised by shape
• CPC Class Codes: Y10T 428/24901 including coloring matter

Abstract

A method for obtaining both light and dark laser marks on a colored plastic article by using a composition with (i) a thermoplastic resin that foams when heated, (ii) about 0.4% to 0.7% by weight of a mica based laser energy absorbing additive and (iii) a coloring agent with one or more colorants selected from the group of pigments, dyes, and mixtures of pigments and dyes. Using a laser at certain settings results in charring of the resin to produce dark laser marks. At other selected laser settings, the resin foams to produce a light mark on a colored background. By varying the laser energy settings, various degrees of both foaming and charring can be achieved on a single plastic article, having a single resin composition, resulting in a multicolored laser image produced by various shades of light and/or dark marks against the background color.

Claims

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.

2. The method according to claim 1, further comprising the steps of:

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

(b) irradiating a third portion of the plastic article with the third laser beam to produce another laser mark having a different light shade or a different dark shade on the plastic article; and

(c) repeating steps (a) and (b) a desired number of times to produce a plurality of different shades of light and dark laser marks on the plastic article.

3. The method according to claim 1, wherein the composition comprises about 50% to 98% by weight of a polyolefin resin, and about 0.7% to 1% by weight of the coloring agent.

4. The method according to claim 3, wherein the laser energy absorbing additive comprises mica in flake, platelet or pearl form having a particle size of less than 15 μ

m.

5. The method according to claim 1, wherein the laser has a wavelength in the near infrared range, the visible range or the near ultraviolet range.

6. The method according to claim 5, wherein the laser is a Nd:

YAG laser or a frequency doubled Nd;

YAG laser or a metal vapor laser or an excimer laser.

7. The method according to claim 1, wherein the laser is a Nd:

YAG laser with a Q-switch, and the variable laser parameters comprise the amperage and the pulse frequency.

8. The method according to claim 1, wherein the laser settings comprise amperages ranging from 1 to about 20 amperes and pulse frequencies ranging from 1 to about 15 kHz.

9. The method according to claim 1, wherein at least one colorant vaporizes or becomes colorless when exposed to the laser energy.

10. The method according to claim 1, wherein the resin comprises a polyolefin.

11. A method for obtaining a multi-color laser image having preselected tones of a color on a plastic article, comprising the steps of:

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;

providing a plastic article suitable for laser marking comprising (i) a thermoplastic resin, (ii) a coloring agent comprising two or more colorants selected from the group consisting essentially of (a) an organic pigment, a polymer-soluble dye, and mixtures thereof, (b) an inorganic pigment, a polymer-soluble dye, and mixtures thereof, and (c) an organic pigment and an inorganic pigment having a different color, wherein at least one of the colorants is thermostable, and (iii) a laser energy absorbing additive,

wherein the laser energy absorbing additive or at least one colorant other than the thermostable colorant masks the color of the thermostable colorant prior to exposure to laser energy and decomposes or vaporizes when exposed to laser energy thereby exposing the color of the thermostable colorant;

selecting a plurality of different laser settings, each setting comprising an amperage, a pulse frequency and a pulse duration to provide a plurality of laser beams, each beam having a different energy characteristic;

irradiating a plurality of portions of the plastic article with the plurality of laser beams to obtain a plurality of laser marks each having a different light or dark tone of the color of the thermostable colorant, to obtain a plastic article having a plurality of light and dark color tones;

selecting at least two color tones from the plurality of light and dark color tones;

selecting a first laser setting to produce a first laser beam having an energy characteristic for obtaining one of the selected color tones;

irradiating a portion of a second plastic article having the same composition as the first plastic article with the selected laser beam;

selecting a second laser setting to produce a second laser beam having an energy characteristic for obtaining another of the selected color tones;

irradiating another portion of the second plastic article with the second laser beam; and

repeating the selecting of the laser setting and the irradiating of an another portion of the second plastic article a desired number of times to obtain a multi-colored laser image having preselected color tones of a color.

12. The method according to claim 11, wherein the resin is selected from the group consisting essentially of polyesters, polyethylene, polypropylene, polyisobutylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetals, polyacrylonitrile, polyacrylates, polymethacrylates, polybutadiene, acrylonitrile butadiene styrene, ethylene vinyl acetate, polyamides, polyimides, polyoxymethylene, polysulfones, polyphenylene sulfide, polycarbonates, polyurethanes, polyethers, polyether sulfones, polyacetals, phenolics, polycarbonate, polyester carbonate, polyethylene terephthalate, polybutylene terephthalate, polyarylates, polyarylene sulfides, polyether ketones, and mixtures and copolymers thereof.

13. The method according to claim 11, wherein the composition comprises a resin selected from the group consisting essentially of acrylonitrile butadiene styrene, polycarbonate, polyethylene, high density polyethylene, polypropylene, and mixtures and copolymers thereof.

14. The method according to claim 11, wherein the laser energy absorbing additive comprises carbon black.

15. The method according to claim 14, wherein the ratio of the coloring agent to the carbon black is about 10:

1 to about 1;

1.

16. A method for obtaining a laser mark having the same color hue on two or more differently colored plastic articles, comprising the steps of:

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;

providing a first and a second plastic article suitable for laser marking, each of said articles comprising (i) a thermoplastic resin, (ii) a coloring agent comprising one or more colorants selected from the group consisting essentially of an organic pigment, an inorganic pigment, a polymer-soluble dye, and mixtures thereof, wherein the selection of the coloring agent is such that the first and second articles are differently colored, and (iii) a non-carbon black laser energy absorbing additive;

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

irradiating the first plastic article with the first laser beam to produce a laser mark having a first color hue;

selecting a second laser setting comprising an amperage, a pulse frequency and a pulse duration to provide a second laser beam having an energy characteristic that is the same or different than the first energy characteristic;

irradiating the second plastic article with the second laser beam to produce a laser mark having a second color hue;

obtaining a measurement of the color intensity of the first color hue;

obtaining a measurement of the color intensity of the second color hue;

comparing the measurements and obtaining a numerical value, Δ

E, for the color variance between the two color hues; and

assigning an allowable tolerance range for the Δ

E of 0 to about 5,

wherein if the value of Δ

E falls outside of the allowable tolerance range, the method further comprises the step of modifying the first or the second laser setting to obtain a value of Δ

E that is within the allowable tolerance range.

17. The method according to claim 16, wherein the measurements are obtained with a spectrophotometer.

18. A method for obtaining laser marks having two different colors on a single plastic article, comprising the steps of:

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;

providing a plastic article suitable for laser marking having a composition comprising (i) a thermoplastic resin, (ii) a color pigment that is capable of chemically and irreversibly changing its original color to a second color at higher than a predetermined temperature, (iii) a second color pigment that vaporizes or becomes colorless when exposed to laser energy and that masks the original color of the color pigment prior to exposure to laser energy, and (iv) a laser energy absorbing additive;

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 second color pigment to vaporize or become colorless thereby exposing the original color of the pigment in the composition;

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

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 changes the color of the color pigment to the second color; and

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

19. A method for obtaining two or more laser marks having color hues of the same color intensity on plastic articles, comprising the steps of:

providing a first and second plastic article, the first article comprising a first laser mark having a color hue with a color intensity and the second article comprising a second laser mark having a color hue presumed to be of the same color intensity as the first laser mark;

obtaining a measurement of the color intensity of the color hue of the first laser mark;

obtaining a measurement of the color intensity of the second color hue;

comparing the measurements and obtaining a numerical value, Δ

E, for the color variance between the two color hues; and

assigning an allowable tolerance range for the Δ

E of 0 to about 5,

wherein if the value of Δ

E falls outside of the allowable tolerance range, the method further comprises the step of modifying the first or the second laser setting to obtain a value of Δ

E that is within the allowable tolerance range.

20. The method according to claim 19, wherein the measurements are obtained with a spectrophotometer.