Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/267—Marking of plastic artifacts, e.g. with laser
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/146—Laser beam
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/165—Thermal imaging composition

Definitions

• the present invention relates to a method for laser marking plastic objects in any shape per se with special effects, and the material so marked.
• the laser marking of plastic objects with a contrast marking at the irradiated areas of the plastic is known.
• a laser-sensitive additive is often added to the material to be inscribed, the additive discoloring, fading, decomposing or causing discoloration due to the absorption of the laser energy, so that a contrast marking is generated at the irradiated areas (see, for example, EP patent applications No. 0036680 and No. 0190997 and U.S. Patent No. 4307047).
• the additive e.g. a mixture of different dyes has been proposed, only one component of the mixture being discolored or bleached during irradiation, so that a color contrast is produced at the irradiated areas (see, for example, JP patent applications No. 58-210937 or No. 60-155493) .
• Soot and graphite have also been proposed as an additive in the laser marking of plastics.
• U.S. Patent No. 4391764 e.g. mixed with the plastic as filler carbon black or graphite in such a concentration that the absorption of the energy radiation triggers a local decomposition (a melting-gassing process) in the plastic and therefore causes a mostly black and white contrast marking.
• a laser marking process has now been found which leads to effect markings which, depending on the angle of illumination and observation, appear clearly visible or completely invisible and also have perfect general properties, such as abrasion and scratch resistance, and good resistance to chemicals, light and weather.
• the new process allows so-called subcutaneous labeling of the material without the surface of the object being visibly damaged.
• the present subject matter of the invention accordingly relates to a method for laser marking plastic objects in any desired form, according to which the object to be labeled contains a radiation-sensitive additive which causes a change in light reflection and is exposed to a laser with pulsed light in such a way that the laser beam corresponds to the shape the marking to be applied is shaped by means of a mask or is guided over the surface of the object to be marked, so that a visual effect marking is produced at the irradiated areas of the object without the surface of the labeled object being visibly damaged by the eye, characterized in that Molybdenum disulphide additive is used and the laser parameters wavelength, pulse energy density and pulse width are selected in such a way that an effect marking is generated, the contrast of which changes visually depending on the angle of illumination and observation rt.
• the effect is peculiar in that the marking becomes visible at certain lighting and observation angles, but invisible at other angles.
• the marking is black at larger observation angles, for example at angles of 60 ° -90 °.
• the dark marking disappears, that is to say no contrast can be seen.
• the method according to the invention allows a marking with an additional effect, in that the marking appears dark in the top view, but appears light and almost transparent in the view.
• Plastic can e.g. are modified natural substances, for example cellulose derivatives, such as cellulose esters or cellulose ethers, and in particular fully synthetic organic polyplastics, that is to say plastics which are produced by polymerization, polycondensation or polyaddition.
• cellulose derivatives such as cellulose esters or cellulose ethers
• fully synthetic organic polyplastics that is to say plastics which are produced by polymerization, polycondensation or polyaddition.
• polyolefins such as polyethylene, polypropylene, polybutylene or polyisobutylene, furthermore polystyrene, polyvinyl chloride, polyvinylidene chloride, the fluorine-containing polymers, such as polytetrafluoroethylene, furthermore polyvinyl acetals, polyacrylonitrile, polyacrylic acid and polymethacrylic acid esters or polybutadiene, and copolymerisate thereof , especially ABS or EVA; Polyesters, especially high molecular esters of aromatic polycarboxylic acids with polyfunctional alcohols; Polyamides, polyimides, polycarbonates, polyurethanes, polyethers, such as polyphenylene oxide, also polyacetals, the condensation products of formaldehyde with phenols, the so-called phenoplasts, and the condensation products of formaldehyde with urea, thiourea or melamine, the so-
• Diols or polyphenols and also the unsaturated polyesters used as coating resins, such as maleate resins.
• coating resins such as maleate resins.
• Plastics in dissolved form as film formers or binders for paints or printing inks are also possible, e.g. Linseed oil varnish, nitrocellulose, alkyd resins, phenolic resins, melamine resins, acrylic resins and urea-formaldehyde resins, it being possible for the films obtained therefrom to be labeled in accordance with the invention.
• Plastics which are particularly suitable for the process according to the invention are polyvinyl chloride, polyvinyl esters, such as polyvinyl acetals, furthermore polyacrylic acid and polymethacrylic acid esters, polyesters, polyamides, polyimides, polycarbonates, polyurethanes, polyethers, in particular polyphenylene oxides, furthermore polyacetals, phenoplasts, aminoplasts, epoxy resins and very particularly polyolefins, such as Polyethylene and polypropylene.
• polyvinyl chloride polyvinyl esters, such as polyvinyl acetals, furthermore polyacrylic acid and polymethacrylic acid esters
• polyesters polyamides, polyimides, polycarbonates, polyurethanes, polyethers, in particular polyphenylene oxides, furthermore polyacetals, phenoplasts, aminoplasts, epoxy resins and very particularly polyolefins, such as Polyethylene and polypropylene.
• molybdenum disulfide in flake or platelet form with a particle diameter of less than 100 ⁇ m, but very particularly with a particle diameter of 0.1 to 25 ⁇ m and a thickness of up to 4 ⁇ m.
• molybdenum disulfide in the preferred particle composition can be obtained in a known manner, for example by grinding in air jet, sand or ball mills.
• a grinding device which contains metal, glass or porcelain balls, plastic granules or sand grains as grinding media.
• These grinding media are set in motion, for example, by rotating the vessel or by vibrators or stirrers.
• the optimal effect markings can be determined by varying the amount of molybdenum disulfide within the range specified below.
• preference is given to using from 1.0 to 15.0% by weight, in particular from 1.0 to 10% by weight, of molybdenum disulfide, based on the dry paint or printing ink layer.
• preference is given to using from 0.01 to 5.0% by weight, in particular from 0.05 to 1% by weight, of molybdenum disulfide, based on the plastic material.
• flaky or platelet-shaped molybdenum disulfide with 60-95% by weight of the particles which have a median value of 1-12 ⁇ m. They expediently have a diameter of 0.1 to 25 ⁇ m.
• the colorant or mixture thereof may only be present in the plastic in such a concentration that the effect marking produced according to the invention is not impaired or covered.
• the concentration is expediently 0.01 to 0.5% by weight or 0.5 to 5% by weight.
• Inorganic or organic pigments and polymer-soluble dyes are suitable as additional colorants, especially those which absorb in the visible range.
• inorganic pigments are white pigments, such as titanium dioxide (anatase, rutile), zinc oxide, antimony trioxide, zinc sulfide, lithopone, basic lead carbonate, basic lead sulfate or basic lead silicate, and also colored pigments, such as iron oxides, nickel-antimony-titanate, chromium-antimony-titanate, Manganese blue, manganese violet, cobalt blue, Cobalt chromium blue, cobalt nickel gray, or ultramarine blue, Berlin blue, lead chromate, lead sulfochromates, molybdate orange, molybdate red, cadmium sulfides, cadmium, antimony, zirconium silicates such as Zirkonvanadiumblau and Zirkonpraseodymgelb, as well as carbon black or graphite in a low
• organic pigments examples include azo, azomethine, methine, anthraquinone, indanthrone, pyranthrone, flavanthrone, benzanthrone, phthalocyanine, perinone, perylene, dioxazine, thioindigo, isoindoline, isoindolinone and quinacridone -, Pyrrolopyrrole or quinophthalone pigments, furthermore metal complexes of, for example Azo, azomethine or methine dyes, or metal salts of azo compounds and also platelet-shaped organic pigments.
• Suitable polymer-soluble dyes are, for example, disperse dyes, such as those of the anthraquinone series, for example hydroxyl, amino, alkylamino, cyclohexylamino, arylamino, hydroxylamino or phenylmercaptoanthraquinones, and also metal complexes of azo dyes, in particular 1: 2 chromium or - Cobalt complexes of monoazo dyes and also fluorescent dyes, such as those from the coumarin, naphthalimide, pyrazoline, acridine, xanthene, thioxanthene, oxazine, thiazine or benzothiazole series.
• disperse dyes such as those of the anthraquinone series, for example hydroxyl, amino, alkylamino, cyclohexylamino, arylamino, hydroxylamino or phenylmercaptoanthraquino
• the inorganic and organic pigments or polymer-soluble dyes can be used individually or as mixtures, optionally together with pigment additives.
• Suitable pigment additives are, for example, fatty acids with at least 12 carbon atoms, such as stearic acid or behenic acid, their amides, salts or esters, such as magnesium stearate, zinc stearate, aluminum stearate or magnesium behenate, and also quaternary ammonium compounds, such as tri (C1-C4) alkylbenzylammonium salts, waxes, such as polyolefin waxes, for example polyethylene wax, also resin acids, such as abietic acid, rosin soap, hydrogenated or dimerized rosin, C12-C18 paraffin disulfonic acid or alkyl phenols, alcohols, such as ®TCD alcohol M, or vicinal aliphatic 1,2-diols.
• fatty acids with at least 12 carbon atoms such as stearic acid or behenic acid, their amides, salts or esters, such as magnesium stearate, zinc stearate, aluminum stearate
• the plastic objects are produced by methods known per se, for example in such a way that the required color components (molybdenum disulfide and, if appropriate, an additional colorant) are optionally in the form of masterbatches, the plastic material and the customary additives using extruders, rolling mills, mixing or grinders.
• the mixture obtained is then brought into the desired final shape by methods known per se, such as calendering, pressing, extrusion, brushing, centrifuging, casting, extruding, blowing or by injection molding.
• plasticizers can be incorporated into the polymers before or after incorporation of the coloring components that are possible according to the invention.
• plastic material such as fillers such as kaolin, mica, feldspar, wollastonite, aluminum silicate, quartz or glass powder, barium sulfate, calcium sulfate, chalk, talc, calcite and dolomite, as well as light stabilizers, antioxidants, Flame retardants, heat stabilizers, glass fibers or processing aids, which are common in the processing of plastics and are known to the person skilled in the art.
• fillers such as kaolin, mica, feldspar, wollastonite, aluminum silicate, quartz or glass powder, barium sulfate, calcium sulfate, chalk, talc, calcite and dolomite, as well as light stabilizers, antioxidants, Flame retardants, heat stabilizers, glass fibers or processing aids, which are common in the processing of plastics and are known to the person skilled in the art.
• the plastic material, the molybdenum disulfide and, if appropriate, an additional colorant, together with further paint and printing ink additives are finely dispersed or dissolved in water or a common organic solvent or solvent mixture. You can do this by dispersing or dissolving the individual components for yourself or several together, and only then bringing all the components together.
• the homogenized paint or the printing ink is then applied to a substrate by methods known per se and baked or dried, and the coating or printing ink film obtained is then labeled according to the invention.
• High-energy pulsed laser sources are used to label the plastic objects that are suitable according to the invention.
• the energy radiation according to the shape of the marking to be applied expediently at a steep angle, directed at the surface of the material to be marked, optionally focused, an effect marking being formed at the irradiated points without the surface of the labeled material being visibly damaged.
• laser sources are solid-state pulse lasers, such as ruby lasers or frequency-multiplied Nd: YAG lasers, pulsed lasers with additional devices, such as pulsed dye lasers or Raman shifters, and continuous wave lasers with pulse modifications (Q-Switch, Mode-Locker), for example based on CW Nd: YAG lasers with a frequency multiplier, or CW ion lasers (Ar, Kr), also pulsed metal vapor lasers, such as Cu vapor lasers or Au vapor lasers, or possibly powerful pulsed semiconductor lasers that emit visible light directly or by frequency doubling , also pulsed gas lasers, such as excimer and nitrogen lasers.
• solid-state pulse lasers such as ruby lasers or frequency-multiplied Nd: YAG lasers
• pulsed lasers with additional devices such as pulsed dye lasers or Raman shifters
• continuous wave lasers with pulse modifications Q-Switch, Mode-Locker
• CW Nd YAG lasers with a frequency
• pulse energy densities up to a few joules per cm2 power densities up to terawatts per cm2
• pulse widths from femto-seconds to micro-seconds and repetition rates up to gigahertz are possible.
• Pulse energy densities from millijoules to one kilojoule per cm2 and pulse widths from micro seconds to pico seconds are advantageously used. This corresponds to power densities from kilowatts per cm2 to megawatts per cm2 and repetition rates from a few hertz to 50 kilohertz.
• Pulsed or pulse-modified, frequency-doubled Nd YAG lasers or metal vapor lasers, such as Au or in particular Cu vapor lasers, and excimer lasers are preferably used.
• a pulsed frequency-doubled Nd: YAG laser between 0.05 and 1 joule per cm2 of pulse energy density, about 4 kilowatts peak power, 6-8 nano-seconds pulse width and 30 Hertz repetition rate (model Quanta Ray DCR-2 A from Spectra Physics, Mountain View, California).
• exposure is, for example, to 250 millijoules per cm2 of pulse energy density, about 10 kilowatts of peak power, 30 nano-seconds pulse width and 6 kilohertz repetition rate.
• Lasers with good adjustability of their laser parameters allow optimal adaptation to the needs of the materials to be labeled.
• the optimum wavelength to be selected for irradiation is the one at which the radiation-sensitive MoS2 and possibly the additional colorant absorb the most, but the plastic to be labeled does not absorb much.
• Laser light with a wavelength in the near UV and / or visible and / or near IR range is expediently used, but preferably with a wavelength in the visible range.
• the visible range is the range between 0.38 ⁇ m and 0.78 ⁇ m
• the near IR range is the range between 0.78 ⁇ m and 2 ⁇ m
• the near UV range is between 0.25 and 0.38 ⁇ m .
• the mask method There are generally three different methods for labeling with lasers: the mask method, the linear labeling and the dot-matrix method.
• the laser is preferably coupled to a laser labeling system, so that the plastic can be labeled with any numbers, letters and special characters programmed in a computer, for example.
• the choice of the laser system with regard to power and repetition rate is basically based on the labeling method used. High performance and low repetition rate, as with the solid-state pulse laser and excimer laser, are preferred for mask exposures. Medium to low power and fast repetition rates for pulsed metal vapor lasers or for continuous wave lasers with pulse modifications are preferred for labels that require dynamic beam guidance.
• the beam deflection can take place, for example, acousto-optically, holographically, with galvo mirrors or polygon scanners.
• the dynamic beam guidance enables extremely flexible labeling or marking, since the characters can be generated electronically.
• a wide variety of types of marking and labeling can be obtained by the method according to the invention. Examples of this are: Variable text programming of numeric characters using text input via a keyboard, text program of standard characters or special characters, such as names, further initials and dedications, identity cards, signs or frequently repeated data, consecutive numbering of pieces, input of measurement quantities, input of stored programs, Line lettering or graphics and decorations, as well as security documents such as checks, traveler checks, banknotes, lottery tickets, credit cards, passports with data from computer programs, graphic data records or templates that can be read in with digitizing devices or scanners.
• plastic objects such as molded plastic bodies or foils, and paint and printing ink films.
• plastic objects such as tapes, sheets, tubes and profiles, buttons, buttons and plastic-covered electronic components or parts with different colors that are manufactured using the two-phase injection molding process.
• the markings obtained according to the invention are corrosion-resistant, dimensionally stable, deformation-free, light, heat and weather resistant. They have a clean edge zone and are easily readable by the naked eye in the area described at the beginning, without, for example. Need to use IR or UV readers. Furthermore, the mechanical and physical properties of the material so labeled are practically unaffected, such as the mechanical strength and chemical resistance. The depth of penetration of the marking depends on the labeled plastic. It is usually less than 1 mm. The plastic material is largely protected. Inscriptions are therefore possible that do not cause any loss of surface gloss that can be seen by the eye and do not impair the strength properties of the workpiece.
• a change in reflection with a variable contrast occurs at the irradiated points of the material under laser irradiation. Most of the time there is a color change to black or dark gray in the top view, bright markings in the see-through and the markings disappear when the viewing angle is narrow or reduced. Depending on the laser system, it is also possible to generate a contrast marking which, when viewed under a microscope, also has a clearly recognizable fine structure.
• the mixture is then extruded in two passages on a single-screw extruder, and the granules obtained in this way are injected into plates on the injection molding machine (Allround Aarburg 200) at 220 ° C., which are then pressed at 180 ° C. for 5 minutes.
• the press plates have a homogeneous metallic gray shimmering color.
• the press plates obtained in this way are labeled with a laser beam deflected via two orthogonally movable mirrors in accordance with the shape of the marking to be applied (in the present case the inscription "GRETAG"; height and width of the letters 6 mm; font width 0.1 mm).
• An Nd: YAG pulse laser (®Quanta Ray DCR 2, Spectra Physics) with frequency doubler (harmonic generator) and frequency filter (harmonic separator) is used as the laser.
• the laser is adjusted and attenuated with neutral filters so that the beam focused on a lens (focal length 200 mm) on the surface of the plate reaches a pulse energy of 0.2 mJ with a pulse width of 10 nano-seconds.
• the deflection unit with the orthogonally movable mirrors is part of a ®GRETAG 6210 laser marking system (GRETAG AG, Switzerland) and is mounted vertically above the sample plate.
• the labeling achieved in this way is dark (black on the gray underlay with approximately vertical supervision) and stands out clearly from the unmarked metallic gray shimmering colored article. Depending on the incidence of light and the angle of observation, the marking is clearly recognizable or disappears completely.
• the plastic granulate is mixed with the molybdenum disulfide pigment described in Example 1 and injected into flakes of size 55 ⁇ 45 ⁇ 1.5 mm in accordance with the information in the list below.
• the samples thus produced are labeled according to Example 1 using the device described there; Instead of the 'GRETAG' lettering, two markings are made in the form of an arc (3/4 circle) and a rectangle (9x9 mm).
• the labeled plates all show the effect that the markings are only visible under certain lighting and viewing angles, but practically disappear when the lighting is flat.
• a platelet-shaped molybdenum IV disulfide pigment with a particle fraction of 80-90%, a size of 4-25 micrometers and a median value of 9.5 micrometers (measured on granulometer 715E598 from CILAS, F-91460, Marcoussis / FR), 7.3 ml of dioctyl phthalate and 13.3 g of stabilized polyvinyl chloride are mixed well in a beaker with a glass rod and then processed on a roller mill at 160 ° C. for 5 minutes to form a thin film.
• the film thus obtained is labeled with a laser beam in accordance with Example 1.
• the inscriptions obtained are dark (black on the gray surface) when viewed from a vertical angle, but they appear light when viewed through with a pronounced fine structure.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
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• 1990
  • 1990-08-09 DE DE59008746T patent/DE59008746D1/de not_active Expired - Fee Related
  • 1990-08-09 EP EP90810601A patent/EP0413664B1/fr not_active Expired - Lifetime
  • 1990-08-10 US US07/565,768 patent/US5075195A/en not_active Expired - Fee Related
  • 1990-08-17 JP JP2215945A patent/JPH03106944A/ja active Pending

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