WO1999025562A1

WO1999025562A1 - Laser marking method and material

Info

Publication number: WO1999025562A1
Application number: PCT/US1998/024135
Authority: WO
Inventors: Enos Ayres Axtell, Iii; David C. Kapp; Timothy A. Knell; Miroslav Novotny; George Emil Sakoske; Daniel Russell Swiler
Original assignee: Cerdec Corporation
Priority date: 1997-11-14
Filing date: 1998-11-12
Publication date: 1999-05-27
Also published as: AU1402299A

Abstract

A method of laser marking substrates such as glass, ceramic, metal and plastic is disclosed. A marking material is applied to the surface of the substrate, followed by removal of a portion of the marking material with a laser. The remaining portion of the marking material is then adhered to the substrate by heating or the like. The marking material may comprise a marking component such as glass frit or precursors thereof, inorganic pigments or precursors thereof, silicates, metal oxides, sulfides, nitrides and carbides, organometallic materials or metal powders. In addition to the marking component, the marking material preferably includes a removable medium which facilitates removal of the material from the substrate upon laser irradiation. The marking method is highly versatile, can be performed quickly, and produces permanent marks of high resolution and contrast with minimal or no damage to the substrate.

Description

- 1 - PATENT

LASER MARKING METHOD AND MATERIAL

FIELD OF THE INVENTION The present invention relates to laser marking, and more particularly relates to a method and material for marking substrates such as glasses, ceramics, metals and plastics.

BACKGROUND INFORMATION

Laser marking methods have recently been developed for marking metals, plastics, ceramics and glasses. Laser marking of metals typically involves a vaporization process, wherein a laser is used to remove or ablate metal from the surface along the travel path of the laser. The resultant marking comprises engraved or indented portions which provide three-dimensional contrast to the surface of the metal. Alternatively, laser marking of metals may be achieved by annealing a selected portion of the metal surface to provide areas of contrasting color. In this case, instead of removing metal from the surface, the laser is used to heat the surface of the metal to an annealing temperature which typically results in darkening of the annealed regions. Plastics are typically laser marked by either changing the color of the plastic or engraving the surface of the plastic along the travel path of the laser. The color of the plastic is typically changed by localized melting and re-solidification of the plastic. In contrast, engraving is achieved by vaporization and removal of the plastic. Plastic laser engraving methods can be used to remove a surface layer of the plastic to reveal an underlying layer of contrasting color. Such a process is disclosed in U.S. Patent No. 5,061,341 to Kildal et al.

Laser marking of ceramics and glasses has also been investigated, as a replacement for conventional etching, engraving and glazing techniques. For example, laser marking of glass has been achieved by ablation techniques as disclosed in U.S. Patents No. 4,327.283 to Heyman et al. and U.S. Patent No. 4,515,867 to Bleacher et al. In the disclosed methods, two coating layers are applied to a glass substrate, and the top layer is removed by the laser to reveal the contrasting underlayer. Another technique for laser marking ceramics and glasses is disclosed in

U.S. Patent No. 4,769,310 to Gugger et al. and U.S. Patent No. 5,030,551 to Herren et al. In this technique, a glaze having a radiation-sensitive additive comprising an inorganic pigment or titanium dioxide is deposited and fired on the surface of a ceramic or glass substrate. A laser beam is then used to irradiate the fired surface layer to thereby change the color of the surface layer in the areas of irradiation.

Each of the patents cited above is incorporated herein by reference. Despite the above-noted marking techniques, a need still exists for a method of marking substrates such as metals, ceramics, glasses and plastics which is versatile and can be performed quickly, and which produces permanent marks of high resolution and contrast with minimal or no damage to the substrate.

SUMMARY OF THE INVENTION

The present invention provides a method of laser marking substrates such as glass, ceramic, metal and plastic. A marking material is applied to the surface of the substrate, a portion of the marking material is removed from the substrate with a laser beam or other source of focused electromagnetic energy, and the remaining portion of the marking material is adhered to the substrate to form a permanent marking. The marking material preferably comprises glass frit or precursors thereof, inorganic pigments or precursors thereof, silicates, metal oxides, sulfides, nitrides and carbides, organometallic materials, metal powders and the like, as well as combinations thereof. To achieve favorable marking resolution, the marking material may also comprise a removable medium which can be removed from the substrate or decomposed by the focused electromagnetic energy. The marking method produces permanent marks of high resolution and contrast, or texturing of the surface with a desired pattern, with minimal or no damage to the substrate. An object of the present invention is to provide a method of marking a surface of a substrate. The method includes the steps of applying a marking material to the surface of the substrate, removing a portion of the marking material from the substrate with a beam, and adhering the remaining portion of the marking material to the substrate to form a permanent marking thereon.

Another object of the present invention is to provide a marking material for marking a surface of a substrate. The marking material comprises a marking component and a sufficient amount of a removable medium which facilitates removal of the marking material from a substrate upon irradiation by a laser beam.

These and other objects of the present invention will be more apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic cross-section perspective view of a substrate that has been marked by a conventional laser ablation process.

Fig. 2 is a schematic cross-section perspective view of a substrate that has been marked by a conventional laser annealing or color changing process. Figs. 3a-3c are schematic cross-section views of a substrate, illustrating a laser marking method in accordance with an embodiment of the present invention.

Figs. 4a-4c are schematic cross-section views of a substrate, illustrating a laser marking method in accordance with another embodiment of the present invention.

Figs. 5a-5c are schematic cross-section views of a substrate, illustrating a laser marking method in accordance with a further embodiment of the present invention.

Figs. 6a-6c are schematic cross-section views of a substrate, illustrating a laser marking method in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 schematically illustrates a substrate 10 which has been ablated by a laser to form an engraved groove 12. In such conventional ablation processes, the laser is used to vaporize and remove a portion of the substrate 10. The resultant groove 12 provides a three-dimensional mark which typically has very low contrast.

Fig. 2 schematically illustrates another substrate 20 which has been irradiated by a laser to form a mark 22 of contrasting color. In this conventional process, laser marking is achieved by changing the visual characteristics of the irradiated substrate material. For example, a metal substrate such as aluminum, copper or steel may be anodized or heat treated by the laser to change the color or reflectivity of the metal in the treated region. Alternatively, a plastic substrate such as ABS, polycarbonate or PVC may be locally melted and resolidified in order to change its color in the treated area.

Figs. 3a-3c illustrate a laser marking method in accordance with an embodiment of the present invention. In Fig. 3a, a substrate 30 has a layer of marking material 32 applied thereto. Fig. 3b illustrates the substrate 30 and marking material 32 after a portion of the marking material has been removed by a laser beam (not shown) which preferably travels across the upper surface of the substrate 30 to form a groove 34 in the marking material 32. While the entire thickness of the portion of marking material is removed to form the groove 34 in Fig. 3b, partial removal is possible wherein a layer of the marking material remains at the bottom of the groove. The remaining marking material 32 shown in Fig. 3b is then converted to a permanent marking 36 as shown in Fig. 3c. The adhered layer 36 and groove 34 shown in Fig. 3c provide a permanent marking on the substrate 30.

Figs. 4a-4c illustrate a laser marking method in accordance with another embodiment of the present invention. In Fig. 4a, a substrate 40 has a marking material applied thereto comprising a marking component layer 42 and an inner layer 43. The layer 42 may include a marking component alone, or in combination with a removable medium. The inner layer 43 may comprise a removable medium, or may comprise a layer of burnable filler, non-marking compound or a combination thereof, e.g., organic polycarbonate resin or inorganic synthetic clay, which facilitates adhesion of the marking component layer 42 to the substrate 40. Fig. 4b illustrates the substrate 40 and marking material layers 42 and 43 after a portion of the layers 42 and 43 have been removed by a laser beam (not shown) to form a groove 44. The remaining marking component layer 42 shown in Fig. 4b is then converted to a permanent marking 46 as shown in Fig. 4c. During the conversion process, the remaining portion of the inner layer 43 is typically burned out or otherwise removed from the substrate by heating or the like. The inner layer 43 of marking material shown in Fig. 4a may be useful in modifying the surface of the substrate 40 to enhance both the application and removal processes. The inner layer 43 may act in the manner of a primer in which the porosity of the substrate, the wettability of the substrate 40, or the adhesion of the overlying layer 42 is modified. Alternatively, the inner layer 43 can aid the removal process by acting as a physical barrier between the substrate 40 and the overlying layer 42, by reducing the adhesion of the layer 42 to the substrate 40 and/or by acting as a laser sensitive vaporizable material to aid in the ablation of the overlying layer 42.

Figs. 5a-5c show another laser marking method in accordance with the present invention. In Fig. 5a, a substrate 50 has a layer of marking material 52 applied thereto. An outer layer 53 covers the marking material layer 52. In this embodiment, the layer of marking material 52 may include a marking component alone, or in combination with a removable medium. The outer layer 53 may comprise a removable medium, or may comprise a protective layer or film of UV curable material, lacquer or the like which may increase the mechanical durability of the layer 52 and/or prevent reattachment of ablated particles that may settle back onto the workpiece during the marking operation. Fig. 5b shows the substrate 50 and marking material layer 52 after a portion of the marking material has been removed by a laser beam (not shown) to form a groove 54. The remaining marking material 52 shown in Fig. 5b is then converted to a permanent marking 56 as shown in Fig. 5c. During the conversion process, the remaining outer layer 53 is typically removed by burning off, evaporation or the like. Figs. 6a-6c illustrate a laser marking method in accordance with a further embodiment of the present invention. In Fig. 6a, a substrate 60 has layers of marking material 61 and 62 applied thereto, with an intermediate layer 63 separating the marking material layers. The marking material layers 61 and 62 may be of the same or different composition. The intermediate layer 63 preferably provides a barrier between the marking material layers 61 and 62 in order to prevent unwanted diffusion or intermixing at the interface between the marking material layers. The intermediate layer 63 also preferably reduces or eliminates ablation of the underlying marking material layer 61 during the marking process. Suitable intermediate layer 63 compositions include burnable fillers, non-marking compounds and the like, such as organic polycarbonate resins and inorganic synthetic clays. Fig. 6b illustrates the substrate 60 and marking material layers 61 and 62 after a portion of the overlying marking material 62 has been removed by a laser beam (not shown) to form a groove 64. At least a portion of the intermediate layer 63 that is located along the laser marking path may remain after the marking operation, as shown in Fig. 6b. Alternatively, the intermediate layer 63 may be removed in the region of laser treatment. The remaining marking material layers 61 and 62 are then converted to permanent marking layers 65 and 66 as shown in Fig. 6c, thereby forming a permanent marking on the substrate 60. The marking layers 65 and 66 may be the same or different colors. For example, the outer marking layer 66 may be black or any other desired color, while the inner marking layer 65 may be white or any other contrasting color.

In accordance with the present invention, many substrates may be coated for functional or decorative reasons with various coatings. By selectively removing portions of the coating with a laser beam, the substrate can be marked, decorated, serialized or patterned with a simple operation. For example, automotive glass windshields, backlights and side windshields are routinely decorated around their perimeter for functional and decorative reasons with a band of black enamel. A portion of the black enamel may be selectively removed with a laser beam, allowing serialization of each piece of glass prior to firing. Similarly, glass containers are commonly decorated with glass enamels. Marking by selective removal of enamel with a laser prior to firing may be used to enhance the decoration as well as to include barcoding or serialization on the container. The same process can be used to mark metals, ceramics, plastics, papers, transfer decals and other components.

In accordance with the present invention, various substrate materials can be marked. For example, the present method may be used to mark glass, ceramic, brick, stone, metal, composite and plastic substrates.

Exemplary glass substrate compositions include lead as well as lead-free glasses such as soda lime silicates, borosilicates, aluminum silicates, fused silica and the like. Typical ceramic substrates include tiles, sanitary ware, stoneware bodies, porcelain bodies and bricks, as well as electronic quality ceramic substrates such as silica, alumina, aluminum nitride, etc. Stone substrates include marble, granite, slate, limestone and the like. Suitable metal substrates include steel, brass, copper, aluminum, tin, zinc and the like. Typical plastic substrates include PVC, polyamides, polyolefins, polyethylenes, polycarbonates and polytetrafluoroethylene. Combinations of the above substrate materials may also be used, such as porcelain enamelled steel substrates, glass coated ceramic bodies and glass enamelled bodies.

Substrates that may be marked in accordance with the present invention include automotive parts, automotive glass, aerospace parts, medical devices, electronic devices, tooling, consumer products, packaging, glass bottles, metal cans, metal tags, bricks, tiles, plumbing, electrical, construction supplies, lighting and the like.

The marking material may comprise a single layer as shown in Fig. 3a, in which case any removable medium is mixed together with the marking component. Alternatively, the marking material may comprise multiple layers as shown in Figs. 4a, 5a and 6a. In Fig. 4a, the marking material comprises an inner layer 43 between the marking component layer 42 and the substrate 40. In the embodiment shown in Fig. 5a, the marking material comprises a layer 52 of the marking component and an overlying outer layer 53. In Fig. 6a, the marking material comprises marking component layers 61 and 62 separated by the intermediate layer 63. In accordance with the present invention, a marking material is applied to the surface of the substrate. As used herein, the term "marking material" means a material capable of being removed from a substrate upon impingement by a laser beam or other source of focused energy. The marking material preferably comprises a marking component which is used to form a permanent marking on the substrate and a removable medium which is used to facilitate removal of a portion of marking material from the substrate upon irradiation. The marking component typically comprises from about 10 to 100 weight percent of the marking material, preferably from about 40 to about 99 weight percent, and more preferably from about 60 to about 90 weight percent. The removal medium typically comprises from 0 to about 90 weight percent of the marking material, preferably from about 1 to about 60 weight percent, and more preferably from about 10 to about 40 weight percent.

The marking component of the applied marking material may comprise glass frit such as lead or lead-free frit. Finely ground glass substrate may also be suitable for marking glass substrates. As used herein, the term "glass frit" means pre- fused glass material which is typically produced by rapid solidification of molten material followed by grinding or milling to the desired powder size. Preferred glass frits may comprise from 0 to about 75 weight percent lead oxide, from 0 to about 75 weight percent bismuth oxide, from 0 to about 75 weight percent silica, from 0 to about 50 weight percent zinc oxide, from 0 to about 40 weight percent boron oxide, from 0 to about 15 weight percent aluminum oxide, from 0 to about 15 weight percent zirconium oxide, from 0 to about 8 weight percent titanium oxide, from 0 to about 20 weight percent phosphorous oxide, from 0 to about 15 weight percent calcium oxide, from 0 to about 10 weight percent manganese oxide, from 0 to about 7 weight percent copper oxide, from 0 to about 5 weight percent cobalt oxide, from 0 to about 15 weight percent iron oxide, from 0 to about 20 weight percent sodium oxide, from 0 to about 20 weight percent potassium oxide, from 0 to about 15 weight percent lithium oxide and from 0 to about 7 weight percent fluoride, as well as other oxides conventionally used in glass frit compositions.

In addition to glass frit, precursors of such glass frit materials may be used as the marking component. Examples of glass frit precursors include metal oxides with glass formers, such as silica, zinc oxide, bismuth oxide, sodium borate, sodium carbonate, feldspars, fluorides, and the like.

Inorganic pigments such as spinels, zircons, rutiles, garnets, hematites, ultramarines and the like may also be used as the marking component. In addition to inorganic pigments, precursors thereof are useful in forming high quality marks. For example, a light green colored mixture of titanium dioxide, antimony trioxide and chrome oxide, which is the precursor to Cr-Sb-Ti buff, may be used. Such a precursor mixture may be dispersed in a removable medium, coated on a substrate, and partially removed therefrom with a laser beam. The remaining portion of the marking material is then fired to give a buff colored mark. The marking component may also comprise alkali and other silicates such as water glass solution and colloidal silicates.

Metal oxides, sulfides, nitrides, carbides and salts are also suitable marking components. For example, cobalt oxide, copper oxide, iron oxide, praseodymium oxide, copper sulfide, iron sulfide, nickel sulfide, aluminum nitride, titanium nitride, chrome carbide and tungsten carbide may be used.

Organometallic materials of various metals such as cobalt, copper, iron, etc. , for example, sold under the designation CERADYE. or organometallic materials that can be prepared by reacting metal salts or metal oxides with various organic ligands such as acetyl acetonate, or with various organic acids, such as citric, acetic, naphthenic or octanoic acid may be used as marking components.

Furthermore, metal powders such as iron, copper, nickel, silver, chromium and the like, may be used.

The above-noted marking components may be used alone or in various combinations in accordance with the present invention. For example, a combination of metal oxides with glass frit, metal oxides with metal sulfides or inorganic pigments with glass frits may be used.

Table 1 lists marking components suitable for use in accordance with the present invention.

Table 1

Marking Components

Glass frits Lead-containing frits^*

E-1313 E-1538 E-1549 E-1640 E-1733 E-1800 E-1936 E-1937 E-2141

Lead-free frits^*

CA-1410

E-8007

E-8008

E-8009

E-8010

E-8012

E-8015

E-8016

E-8017

E-8018

E-8023

E-8027

GAL- 10004 Table 1 (continued)

GAL- 10048 RD-2051 RD-2060 RD-2070

Glass Frits Precursors alumina alumina hydrate antimony oxide barium carbonate barium sulfate bismuth oxide sodium borate boric acid boric oxide cadmium oxide calcium carbonate cerium oxide sodium aluminum fluoride silica calcium fluoride lead oxide lead bisilicate lithium carbonate potassium carbonate sodium carbonate sodium fluoride sodium nitrate sodium silica fluoride sodium sulfate titania vanadium oxide calcium silicate zinc oxide zirconia zirconium silicate manganese oxide copper carbonate copper oxide iron oxide magnesium oxide feldspar strontium carbonate calcium phosphate nepheline syenite Table 1 (continued)

Inorganic pigments zirconium vanadium yellow baddeleyite chrome alumina pink corundum manganese alumina pink corundum iron brown hematite cobalt silicate blue olivine cobalt nickel grey periclase lead antimonate yellow pyrochlore nickel antimony titanium yellow rutile chrome antimony titanium buff rutile chrome niobium titanium buff rutile chrome tungsten titanium buff rutile manganese antimony titanium buff rutile chrome tin pink sphene cobalt aluminate blue spinel cobalt chromite green spinel cobalt titanate green spinel iron chromite brown spinel zinc ferrite brown spinel copper chromite black spinel manganese ferrite black spinel chrome iron nickel black spinel zirconium vanadium blue zircon zirconium praseodymium yellow zircon zirconium iron pink zircon

Precursors of inorganic pigments titanium oxide, titanium hydroxide, titanium sulfate cobalt oxide, cobalt metal chromium oxide nickel oxide, nickel carbonate zirconium dioxide or zirconium hydroxide vanadium oxide or ammonium vanadate red iron oxide, yellow hydrated iron oxide, black iron oxide silica manganese dioxide, manganese (II. Ill) oxide, manganese carbonate alumina, aluminum hydrate lead oxide antimony trioxide tungsten pentoxide niobium pentoxide zinc oxide copper oxide praseodymium oxide Table 1 (continued)

Silicates colloidal silicates potassium silicates sodium silicates lithium silicates hydrous sodium lithium magnesium silicate common clays

Metal oxides cobalt oxide copper oxide iron oxide praseodymium oxide neodymium oxide Metal sulfides copper sulfide iron sulfide nickel sulfide cadmium sulfide cadmium sulfide selenide

Metal nitrides aluminum nitride titanium nitride

Metal carbides chrome carbide tungsten carbide

Organometallic materials citrate and ammonium citrate salts of manganese, cobalt, iron, and vanadium acetylacetonates and fluorinated acetylacetonates of transition metals metal carboxylates such as the transition metal and rare earth salts of napthenic,

2-ethyl hexanoic, and neodecanoic acids ethylene diamine tetraacetic acid and nitrilotriacetic acid salts of transition and rare earth metals Table 1 (continued) metal complex dyes and pigments such as copper phthalocyanine blues and greens and dyes organosilicates, e.g. , tetra-ethyl -ortho silane Metal powders iron copper nickel silver chromium zinc gold lead tin Inorganic metal salts tin chloride copper nitrate cobalt nitrate cobalt carbonate ferric sulfate nickel sulfate

Commercially available from Cerdec Corporation

In accordance with an embodiment of the present invention, the marking material may include removable media such as those listed in Table 2, and the like. Table 2

Removable Media Water

Alcohols methanol ethanol n-propanol iso-propanol butanol and its isomers lauryl alcohol myristyl alcohol Table 2 continued stearyl alcohol Texanol

Polyols ethylene glycol propylene glycol di- and tri- propylene glycols glycerines polyethylene propylene glycols

Chlorinated solvents methylene chloride 1 ,1, 1 trichloroethane perchloroethylene trichloroethylene

Amines triethanolamine diethanolamine

Esters ethylene glycol monomethyl ether acetate propylene glycol monomethyl ether acetate diethylene glycol monomethyl ether acetate diethylene glycol monobutyl ether acetate lactates propionates

Glycol ethers ethylene glycol methyl ether diethylene glycol methyl ether ethylene glycol n-butyl ether diethylene glycol n-butyl ether propylene glycol methyl ether dipropylene glycol methyl ether tripropylene glycol methyl ether Table 2 continued

Ketones methyl ethyl ketone acetone methyl isobutyl ketone methyl amyl ketone tetrahydrofuran diacetone alcohol C-l l ketone glycol dimethyl ether diglycol dimethyl ether

Terpenes turpentines alpha pinene dipentene alpha terpineol terpineol pine oil citrus extracts Petroleum naphthas kerosene heptanes hexanes mineral spirits naphthas mineral oil

Aromatic hydrocarbons toluene, xylenes aromatic hydrocarbon blends

Natural oils soya oil vegetable oil corn oil palm oil coconut oil Other suitable removable media include furans, isoparaffins, N,N dimethylformamide. dimethylsulfoxide and tributylphosphine. In addition to the marking component and removable medium, the marking materials of the present invention may comprise small amounts of binder materials to improve green strength or package stability. Additions may include epoxies, polyesters, acrylics, cellulosics, vinyls, natural proteins, styrenes, polyalkyls, carbonates, rosins, rosin esthers, alkyls, drying oils, and polysaccharides such as starches, guar, extrins and alginates, and the like. The marking materials may optionally include additives generally known in the art to improve dispersability, wetting, flow and rheology, and to relieve surface defects. Energy absorption of the laser beam can be optimized if necessary by the addition of carbon black, titanium dioxide and/or iron oxide and the like to the marking material. Such energy absorbing materials may be mixed with the marking material or added to the surface thereof.

The marking material is typically applied to the surface of the substrate with a total thickness of at least 0.1 micron, preferably from about 1 micron to about 1 mm, more preferably from about 5 to 200 microns, and most preferably from about 10 to about 100 microns.

Various methods may be used to apply the marking material to the surface of the substrate. The substrate surface can be coated with powders of marking material or, preferably, it can be coated with a dispersion of the powders in a suitable media. Water based media are preferred because of their minimal environmental impact, but solvent based media can also be used to control drying rate, dispersion or moisture sensitivity of certain marking materials. In accordance with one embodiment, sol gel materials may be used to apply the marking material to the substrate. Where dispersions are used, the deposited layer can be dried prior to the irradiation step, however this is not necessary. The marking material in a water or solvent dispersion can be applied onto the substrate surface by various methods such as screen printing, brushing, spraying, roll coating, dipping, flow coating, electrostatic application and doctor blading. The marking material may be applied as a single layer, or may be applied as two or more layers. Marking materials can also be dispersed in high temperature waxes or polymers and applied to a substrate surface from a hot melt or by rubbing the surface of the substrate with such a material. Alternatively, the layer of marking material may be applied in the form of a tape, sticker or decal.

After the marking material is applied to the surface of the substrate, a portion of the marking material is removed from the substrate with a beam. Removal of the material may be achieved, for example, by vaporization, evaporation, thermal decomposition or sublimation of the material upon irradiation by the beam. Removal may alternatively be achieved by physically altering a portion of the marking material with the beam, followed by subsequent vacuuming, brushing, blowing off or the like to complete the removal step. A laser is preferably used to selectively remove the marking material. However, other forms of focused energy may be used in accordance with the present invention. Removal may be achieved by moving a laser beam over a stationary substrate using conventional beam steering methods, by moving the substrate in relation to the laser beam and/or by masking the substrate. Laser removal is typically achieved by directing the beam directly against the layer of marking material, but may also be achieved by directing the beam through a sufficiently transparent substrate. The laser beam may be directed perpendicularly with respect to the substrate, or at any other suitable angle which facilitates removal of the marking material from the substrate.

Suitable lasers for use in accordance with the present invention include neodymium: yttrium aluminum garnet (Nd:YAG) lasers, carbon dioxide (C0₂) lasers, diode lasers, excimer lasers and the like.

Typical YAG lasers emit light in the near-infrared spectrum at a wavelength of 1064 nm. Such lasers typically have continuous power outputs of from about 1 to about 50 watts, and can be operated in a pulsed mode at peak powers of from about 1 watt to about 45 kilowatts. For pulsed mode operation, frequencies of from about 1 to about 64,000 pulses/second may be used.

Typical CO₂ lasers emit light in the far- infrared region of the spectrum, with intensity spikes at wavelengths of 9.8 and 10.6 microns. Such CO₂ lasers typically operate at a continuous output power of from about 1 to about 40 watts.

In contrast with laser marking methods that use a laser beam to fuse or adhere the irradiated portion of a material to a substrate, the present method uses a laser beam to remove or ablate material from a portion of the substrate. In accordance with the preferred embodiment, pulsed mode laser operation is used to promote removal of the marking material. While continuous wave laser operation provides a steady stream of heat energy to the material, pulsing laser operation is believed to provide discontinuous bursts of energy which facilitate removal of the material from the substrate in the irradiated areas. Preferred pulse rates are from about 10 to about 64,000 pulses/second or higher, more preferably from about 500 to about 20,000 pulses/second. In accordance with the present invention, the size of the laser spot that impinges the marking material is typically greater than 0.1 micron in diameter, preferably from about 40 to about 500 microns, and more preferably from about 50 to about 125 microns. The speed at which the laser beam travels across the surface of the marking material preferably ranges from 0 to about 100 inches/second (up to about 250 cm/second), more preferably from about 1 or 2 to about 20 inches/second (about 2.5 or 5 to 50 cm/second) for most thicknesses and compositions of marking material. The laser beam may be projected with a seam overlap of 0 to 100 percent, preferably from about 10 to about 90 percent for many applications. The laser parameters are controlled in order to provide sufficient localized removal of the marking material while avoiding unwanted damage to the substrate.

For many laser marking operations, a Lumonics LightWriter SPe YAG laser operating under the following parameters is suitable. Typically, marks on a glass substrate may be made using pulse rates of from about 10 to about 64,000 pulses/second or higher, lamp currents from about 28 to about 38 amps, marking speeds from about 1 to about 20 inches/second (about 2.5 to 50 cm/second), laser dot sizes from about 0.002 to about 0.01 inches (about 50 and 250 microns), and seam overlaps from about 25 to about 50 percent. Laser marking is typically performed with the beam in focus, but may also be carried out with the beam out of focus. Pulse rates of from about 1 ,000 to about 10,000 pulses/second, lamp currents of from about 28.5 to about 30 amps and writing speeds of from about 2 to about 5 inches/second (about 5 to 12.7 cm/second) are particularly advantageous for many applications.

The laser beam, the movement of which can be controlled by a computer, may be used to create discrete symbols or designs or, alternatively, may be serially indexed across the surface of the marking material to create multiple symbols or designs at the same time. For example, a word may be created by separately making each letter of the word with the laser, or by rastering the laser across the entire word to form all of the letters at the same time. A single laser beam may be used for removal of the marking material in accordance with the present invention. Alternatively, two or more laser beams may be used.

In accordance with a preferred embodiment, substrate surface damage caused by the laser marking process may be minimized or eliminated. While not intending to be bound by any particular theory, it is believed that the heat generated by the laser beam may be consumed by ablating the marking material from the surface rather than overheating the substrate and creating surface damage such as micro-cracks. During the removal and adhering steps, the surface of the substrate may be exposed to any desired type of atmosphere. For example, the atmosphere may comprise air at atmospheric, sub-atmospheric or super- atmospheric pressures. Furthermore, the atmosphere may comprise an inert gas such as nitrogen, argon or carbon dioxide, an oxidizing atmosphere such as air or oxygen, a reducing atmosphere such as hydrogen or carbon monoxide, or a vacuum. Oxidizing or reducing gases can be used in a combination with inert gases. It is also possible to control the atmosphere on the surface of the substrate through the type of media the marking component is dispersed in. The atmosphere to which the surface of the substrate is exposed may affect the color and the quality of the mark.

In accordance with the present invention, after a portion of the marking material has been removed from the substrate, the remaining portion of the marking material is permanently adhered to the substrate. As used herein, the term "adhere" is used to designate any permanent means of attachment of the remaining marking material to the substrate. For example, the remaining marking material may be adhered to the substrate by sintering the marking material to the substrate, fusing the marking material to the surface of the substrate, diffusing the marking material into the substrate, reacting the marking material with the substrate and the like.

The remaining marking material may be adhered by heating the material and substrate in a furnace or the like. Alternatively, heating can be achieved by microwaving, by a laser, or by any other suitable form of electromagnetic radiation. For laser heating, the laser beam may be de-focused and/or directed over a relatively large surface area or travel path in order to adhere the marking material to the substrate. Typical heating times of from about 10 seconds to about 3 hours may be used for many marking materials, more preferably from about 1 to about 30 minutes. Material temperatures of from about 100 to about 1 ,500 °C may typically be used for many marking materials, more preferably from about 100 to about 250 °C for many plastics and from about 400 to about 700 °C for many glass frits and enamels. In addition to or in place of heating, the remaining marking material may be adhered to the substrate by polymerizing or curing, using such techniques as UV curing, infrared curing and thermosetting.

As used herein, the term "permanent marking" means a non-temporary marking which, for example, possesses relatively high wear resistance, corrosion resistance and/or fading resistance. The permanent markings produced in accordance with the present invention preferably have a thickness of from 0 to about 1 mm as measured from the surface of the substrate, preferably from about 0.05 to about 200 microns. In some embodiments, the permanent marking may comprise an indentation or groove which extends into the surface of the substrate. Many different types of permanent marking compositions may be achieved in accordance with the present invention. Examples of permanent marking compositions include colored or colorless sintered glass frit, inorganic chromophores fused into the surface of the glass or metal substrate, a combination of the two, and metal oxide fused into the glass or metal surface or reacted with the substrate material. Because of the interaction with the marking material, the composition of the marking or indentation may depend on the composition of the substrate.

Various types of marks may be produced in accordance with the present invention. For example, the marks may comprise alphanumeric symbols, graphics, logos, designs, decorations, serializations, bar codes, two dimensional matrices and the like. In addition, the markings may comprise three-dimensional lines forming patterns suitable for use in plasma display TV screens, fresnel lenses, polarizing filters, conductive circuits and the like.

In accordance with the present invention, permanent markings are formed with high contrast and high resolution. Resolution of the mark is determined by the size of the laser beam and the particle size of the marking material. Contrast/color of the mark is typically determined by the laser beam energy, marking material and atmosphere in which the marking is carried out. In addition, the present markings have favorable wear, corrosion and fade resistance properties that are determined by the marking material and marking parameters. For example, marks created with glass frits have wear, corrosion and fade resistance properties similar to the resistance of the glass from which the frit was made. Furthermore, by using conventional laser controlled hardware and software, the markings of the present invention may be quickly varied from operation to operation for applications such as serialization, bars codes, manufacturing quality control and automated manufacturing.

Example 1 A paste of spreadable viscosity was mixed by combining white ceramic enamel sold under the designation Cerdec 20-1015 white and a water-based medium. The water-based medium consists of 7 percent hydroxypropylcellulose in water. The paste was applied at a thickness of 3 mils wet on a green glass beer bottle. The bottle was then placed in a 90 °C oven until dry. A YAG laser sold by Lumonics under the designation LightWriter SPe was operated in a pulsed mode. A large fill font was written on the bottle to test the feasibility of scribing artwork, logos, etc. The following laser parameters were employed: beam current 30 amps; pulse rate 500 pulses/second; writing speed 2.0 inches/ second (about 5 cm/second); dot size 0.002 inches (about 50 microns); seam overlap 25 percent. The bottle was placed on its side and the laser was focused perpendicular to the side surface of the bottle. A ten-letter message was written on the bottle in 3/8 inch high letters on the bottle. The mark took 348 seconds to write, and resulted in no damage to the glass substrate. The bottle was then fired with a temperature program of 1, 150 °F for 15 minutes to form a permanent marking.

Example 2 Example 1 was repeated, except another paste was made by combining

122.5g of white ceramic enamel sold under the designation Cerdec 20-1015 white and 35g of a solvent-based screen print medium sold under the designation Cerdec 1588. The white paste was screen printed on the bottle, dried, laser marked and fired as in Example 1 to form a permanent marking on the bottle. Example 3 Example 1 was repeated, except single stroke fonts were used. The following laser parameters were used: beam current 32 amps; pulse rate 2,000 pulses/second; writing speed 10.0 inches/second (about 25 cm/second); dot size 0.002 inches (about 50 microns); and seam overlap 25 percent. The message " 1234567890" was written in 0.7 seconds. After firing, a permanent marking was formed on the bottle.

Example 4 Example 2 was repeated, except single stroke fonts were used. The following laser parameters were used: beam current 32 amps; pulse rate 2,000 pulses/second; writing speed 10.0 inches/second (about 25 cm/second); dot size 0.002 inches (about 50 microns); and seam overlap 25 percent. The message "1234567890" was written in 0.7 seconds. After firing, a permanent marking was formed on the bottle. Example 5

Samples were made by combining 6.1 grams of screenprint medium sold under the designation Cerdec 175 and 12.5 grams of unpigmented zinc-based frit sold under the designation Cerdec E-8007. The samples were milled into a paste and screen printed onto glass with a 200 mesh screen. One print was dried to remove solvent before exposure to the laser and the other print was not dried. Fifteen different sets of laser parameters were used to write marks on the glass: beam current 30 amps; pulse rates 100, 500 and 1,000 pulses/second; marking speeds 0.5, 0.8, 1 , 2, 5, 10 and 20 inches/second (about 1.25, 2.0, 2.5, 5, 12.5, 25 and 50 cm/second); dot sizes 0.005 and 0.002 inches (about 125 and 50 microns); and seam overlap 25 percent. The marks consisted of 10 parallel lines, and the laser made one pass per line. The coating material was ablated where the laser passed. The wet sample was more sensitive to lower power levels than the dried sample. The vaporizing solvent appears to assist in the ablation of the solids from the surface. The samples were then fired with a temperature profile of 1 ,270 °F for 15 minutes to form permanent markings on the glass substrates. Example 6 Samples were made by combining 6.1 grams of Cerdec 175 screen print medium, 0.35 grams of C.I. solvent black 28 solvent soluble dye, and 12.5 grams unpigmented zinc -based frit sold under the designation Cerdec E-8007. The sample was milled into a paste and screen printed onto glass with a 200 mesh screen. One print was dried to remove solvent before exposure to the laser and the other print was not dried. Fifteen different sets of laser parameters were used to write marks on the glass: beam current 30 amps; pulse rates 100, 500 and 1,000 pulses/second; marking speeds 0.5, 0.8, 1, 2, 5, 10 and 20 inches/second second (about 1.25, 2.0, 2.5, 5, 12.5, 25 and 50 cm/second); dot sizes 0.005 and 0.002 inches (about 125 and 50 microns); and seam overlap 25 percent. The marks consisted of 10 parallel lines, and the laser made one pass per line. The coating material was ablated where the laser passed. The black dye appeared to assist the ablation of the laser energy without adversely effecting the appearance of the resulting mark. The wet sample was more sensitive to lower power levels than the dried sample. The vaporizing solvent appears to assist in the ablation of the solids from the surface. The samples were then fired with a temperature profile of 1,270 °F for 15 minutes to form permanent markings on the glass substrates. Compared with the marks of Example 5, these marks were of higher definition. The small amount of black dye may assist the ablation by increasing the absorption of the laser energy.

Example 7

Samples were made by combining commercially available Cerdec RD- 2094 lead based white enamel with 1326 oil in approximately a 5: 1 ratio. The materials were mixed together in a muller to make a screen printable paste. The paste was screen printed to a soda-lime silica glass substrate using a 200 mesh screen and dried on a hot plate to remove solvent. Sixty different laser parameters were used over ranges of: beam currents 30 to 34 amps; pulse rates 100 to 20,000 pulses/sec; marking speeds 0.5 to 40 inches/second (about 1.25 to 100 cm/second); laser dot sizes 0.002 to 0.005 inches (about 50 to 125 microns); and seam overlap 25 percent. The material was ablated from the samples in parallel lines with one pass per line, leaving a distinct line where the laser beam had passed. The samples were fired in a furnace pre-set at 1,200 °F

(684 °C) for 3 minutes to form permanent markings. Favorable ablation was observed with laser parameters of: 30 amp beam current; pulse rates 500 to 20,000 pulses/second; marking speeds 1.0 to 20.0 inches/second (about 2.5 to 50 cm/second); laser dot size 0.005 inch (about 125 microns); and seam overlap 25 percent.

Example 8 Samples were made by combining a powder consisting of 60 percent zinc borosilicate frit, 26 percent copper chrome spinel pigment, and 14 percent zinc borate material with 1326 oil in approximately a 4: 1 ratio. Such a black glass-ceramic enamel exhibits typical firing characteristics of black enamels used for automotive glass periphery bands. The materials were mixed together in a muller to make a screen printable paste. The paste was screen printed to a soda-lime silica glass substrate using a 200 mesh screen. One half of the samples were dried on a hot plate to remove solvent and one half the samples were allowed to remain wet. Sixty different laser parameters were used over the ranges of: beam currents 30 to 34 amps; pulse rates 100 to 20,000 pulses/second; marking speeds 0.5 to 40 inches/ second (about 1.25 to 100 cm/second); laser dot sizes 0.002 to 0.005 inches (about 50 to 125 microns); and seam overlap 25 percent. The material was ablated from the samples in parallel lines with one pass per line, leaving a distinct line where the laser beam had passed. The samples were fired in a furnace pre-set at 1,250 °F (712 °C) for 3 minutes, which is typical of an automotive press-bend type fire schedule, to form permanent markings. Favorable ablation was observed with wet enamels containing solvents with laser parameters of: 30 amp beam current; pulse rates 500 to 20,000 pulses/second; marking speeds 1.0 to 20.0 inches/second (about 2.5 to 50 cm/second); laser dot size 0.005 inch (about 125 microns); and seam overlap 25 percent.

Example 9 A paste containing 8 grams of -325 mesh copper metal, 0.3 grams of commercially available Cerdec E-8017 glass frit, and 1.7 grams of commercially available Cerdec 1326 screen print medium was applied with a 200 mesh silk screen to a 4 x 5 inch (10.1 x 12.7 cm) pane of window glass. The pane was dried on a hot plate to remove the solvent. The laser was operated in a pulsing mode, where the pulse rate was 10,000 pulses/second. The beam current was 34 amps. A writing speed of 10 inches/second (25 cm/second) and a dot size of 0.005 inches (125 microns) were used. A series of lines was drawn, with the lines 20 mils (500 microns) wide and 60 mils (1.5 mm) apart. The copper metal was ablated were the laser beam passed, without damaging the substrate. The plates are fired in an inert or reducing atmosphere, e.g. , nitrogen or hydrogen, to form permanent copper lines on the substrate.

Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method of marking a surface of a substrate comprising: applying a marking material to the surface of the substrate; substantially removing a portion of the marking material from the substrate with a beam; and adhering the remaining portion of the marking material to the substrate to form a permanent marking thereon.

2. The method of Claim 1, wherein the marking material comprises from about 10 to 100 weight percent of a marking component and from 0 to about 90 weight percent of a removable medium.

3. The method of Claim 2, wherein the marking material comprises from about 40 to about 99 weight percent of the marking component and from about 1 to about 60 weight percent of the removable medium.

4. The method of Claim 2, wherein the marking component comprises at least one material selected from the group consisting of glass frit, precursors of glass frit, inorganic pigments, precursors of inorganic pigments, silicates, metal oxides, metal sulfides, metal nitrides, metal carbides, organometallic materials, metal powders and inorganic metal salts.

5. The method of Claim 2, wherein the marking component comprises glass frit selected from the group consisting of lead oxide, bismuth oxide, silicon oxide, zinc oxide, boron oxide, aluminum oxide, zirconium oxide, titanium oxide, phosphorous oxide, calcium oxide, manganese oxide, copper oxide, cobalt oxide, iron oxide, sodium oxide, potassium oxide, lithium oxide, fluoride and combinations thereof.

6. The method of Claim 2, wherein the marking component comprises glass frit precursors selected from the group consisting of alumina, alumina hydrate, antimony oxide, barium carbonate, barium sulfate, bismuth oxide, sodium borate, boric acid, boric oxide, cadmium oxide, calcium carbonate, cerium oxide, sodium aluminum fluoride, silica, calcium fluoride, lead oxide, lead bisilicate, lithium carbonate, potassium carbonate, sodium carbonate, sodium fluoride, sodium nitrate, sodium silica fluoride, sodium sulfate, titania, vanadium oxide, calcium silicate, zinc oxide, zirconia, zirconium silicate, manganese oxide, copper carbonate, copper oxide, iron oxide, magnesium oxide, feldspar, strontium carbonate, calcium phosphate, nepheline syenite and combinations thereof.

7. The method of Claim 2, wherein the marking component comprises an inorganic pigment selected from the group consisting of metal oxides, sulfides, selenides and combinations thereof.

8. The method of Claim 2, wherein the marking component comprises an inorganic pigment precursor selected from the group consisting of titanium oxide, titanium hydroxide, titanium sulfate, cobalt oxide, cobalt metal, chromium oxide, nickel oxide, nickel carbonate, zirconium dioxide or zirconium hydroxide, vanadium oxide or ammonium vanadate, red iron oxide, yellow hydrated iron oxide, black iron oxide, silica, manganese dioxide, manganese (II, III) oxide, manganese carbonate, alumina, aluminum hydrate, lead oxide, antimony trioxide, tungsten pentoxide, niobium pentoxide, zinc oxide, copper oxide, praseodymium oxide and combinations thereof.

9. The method of Claim 2, wherein the marking component comprises at least one silicate selected from the group consisting of colloidal silicate, sodium silicate, potassium silicate, lithium silicate and hydrous sodium lithium magnesium silicate.

10. The method of Claim 2, wherein the marking component comprises at least one material selected from the group consisting of cobalt oxide, copper oxide, iron oxide, praseodymium oxide, copper sulfide, iron sulfide, nickel sulfide, cadmium sulfide, cadmium sulfide selenide, aluminum nitride, titanium nitride, chrome carbide, tungsten carbide, tin chloride, copper nitrate, cobalt nitrate, cobalt carbonate, ferric sulfate and nickel sulfate.

11. The method of Claim 2, wherein the marking component comprises an organometallic material including at least one metal or metal compound selected from the group consisting of cobalt, copper, iron, silica, zircon, titania and phosphorous.

12. The method of Claim 2, wherein the marking component comprises at least one metal powder selected from the group consisting of iron, copper, nickel, silver, chromium, zinc, gold, lead and tin.

13. The method of Claim 2, wherein the marking component comprises at least two materials selected from the group consisting of glass frit, precursors of glass frit, inorganic pigments, precursors of inorganic pigments, silicates, metal oxides, metal sulfides, metal nitrides, metal carbides, organometallic materials, metal powders and inorganic metal salts.

14. The method of Claim 2, wherein the removable medium comprises at least one material selected from the group consisting of water, alcohols, polyols, chlorinated solvents, amines, esters, glycol esters, ketones, terpenes, petroleum naphthas, aromatic hydrocarbons and natural oils.

15. The method of Claim 2, wherein the marking material is a single layer.

16. The method of Claim 15, wherein the marking material comprises a mixture of the marking component and the removable medium.

17. The method of Claim 2, wherein the marking material comprises multiple layers.

18. The method of Claim 17, wherein one of the layers comprises the marking component and another one of the layers comprises the removable medium.

19. The method of Claim 18, wherein the removable medium layer is adjacent the substrate.

20. The method of Claim 18, wherein the marking component layer is adjacent the substrate.

21. The method of Claim 17, wherein at least two of the layers comprise a marking component.

22. The method of Claim 21 , wherein the marking component layers are of different compositions.

23. The method of Claim 21, wherein the marking component layers are separated by an intermediate layer.

24. The method of Claim 1, wherein the marking material is applied to the surface of the substrate with a total thickness of from about 0.1 micron to about

1 mm.

25. The method of Claim 1 , wherein the portion of the marking material is removed with a laser.

26. The method of Claim 25, wherein the laser is pulsed.

27. The method of Claim 26, wherein the laser is pulsed at a frequency of from about 10 to about 64,000 pulses/second.

28. The method of Claim 25, wherein the laser beam impinges on the substrate at a marking speed of from 0 to about 100 inches/ second.

29. The method of Claim 25, wherein the laser beam has a spot size of from about 0.1 to about 500 microns in diameter.

30. The method of Claim 25, wherein the laser beam is projected with a seam overlap of from 0 to about 90 percent.

31. The method of Claim 25, wherein the laser is a YAG laser operating at a lamp current of from about 28 to about 38 amps.

32. The method of Claim 1, wherein the remaining portion of the marking material is adhered to the substrate by heating.

33. The method of Claim 32, wherein the remaining portion of the material is heated to a temperature of from about 100 to about 1,500 ┬░C for a time of from about 10 seconds to about 3 hours.

34. The method of Claim 32, wherein the remaining marking material is heated in a furnace.

35. The method of Claim 32, wherein the remaining marking material is heated by a laser.

36. The method of Claim 1, wherein the remaining portion of the marking material is adhered to the substrate by curing.

37. The method of Claim 36, wherein the remaining portion of the marking material is cured by radiant energy.

38. The method of Claim 1 , wherein the permanent marking has a thickness of from 0 to about 1 mm measured from the surface of the substrate.

39. The method of Claim 1 , wherein the permanent marking comprises a cured, melted or fused material.

40. The method of Claim 1 , wherein the permanent marking comprises sintered glass frit.

41. The method of Claim 1, wherein the substrate comprises at least one material selected from the group consisting of glass, ceramic, brick, stone, metal, composites and plastic.

42. A laser marking material comprising a marking component and a removable medium.

43. The laser marking material of Claim 42, wherein the removal medium comprises at least about 1 weight percent of the marking material.

44. The laser marking material of Claim 43, wherein the marking component comprises from about 10 to about 99 weight percent of the marking material, and the removable medium comprises from about 1 to about 90 weight percent of the marking material.

45. The laser marking material of Claim 43, wherein the marking component comprises from about 60 to about 90 weight percent of the marking material, and the removable medium comprises from about 10 to about 40 weight percent of the marking material.

46. The laser marking material of Claim 42, wherein the marking component comprises at least one material selected from the group consisting of glass frit, precursors of glass frit, inorganic pigments, precursors of inorganic pigments, silicates, metal oxides, metal sulfides, metal nitrides, metal carbides, organometallic materials, metal powders and inorganic metal salts.

47. The laser marking material of Claim 42, wherein the removable medium comprises at least one material selected from the group consisting of water, alcohols, polyols, chlorinated solvents, amines, esters, glycol esters, ketones, terpenes, petroleum naphthas, aromatic hydrocarbons and natural oils.