WO2023244936A1 - Transparent biaxially oriented film overlay for marking coated metal tags - Google Patents

Abstract

A plurality of metal tags having a breakable metal connection between each adjacent metal tag. Each tag has a front and a back face. A laser markable coating covers the tag front faces. A coating overlays the laser markable coating applied to the tag front faces. The overlaid coating is less than completely transparent to a laser beam effective for marking the laser markable coating. The overlaid coating is capable of holding each adjacent tag together in the presence of broken metal connections between each adjacent metal tag for rolling up the plurality of metal tags or laser printing of the laser markable coating through the overlaid coating. The overlaid coating exhibits a transmissivity of 95% or greater. The metal tag back face may be coated with an adhesive followed by a release liner being placed over the adhesive coated back of tag back faces.

Description

TRANSPARENT BIAXIALLY ORIENTED FILM OVERLAY FOR MARKING COATED METAL TAGS

[1] CROSS-REFERENCE TO RELATED APPLICATIONS

[2] This application claims benefit of U.S. 63/366,414 filed on June 15, 2022.

[3] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[4] Not applicable.

[5] THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

[6] Not applicable.

[7] REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM

[8] Not applicable.

[9] STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR

[10] Not applicable.

[11] BACKGROUND OF THE INVENTION

[12] The present disclosure relates to metal identification tags or other surfaces and more particularly to their marking. The use of a laser to mark surfaces coated with silicone resins has been taught in US 5,855,969. This method is well known and useful in the creation of identification and tracking methods for use in harsh environments that often include high temperatures. The usefulness of identification indicia produced with these coatings has been limited in certain areas, such as described in U.S. Publication No. 2015/017 0551 , which teaches a method for protecting the silicone-coated surface from obscuration by paint by providing a cover laminate after the identification indicia have been applied to a laser reactive coating. US 6,764,016 teaches the use of a temporary film to protect indentification indicia from chemical attack during galvanizing pre-treatment.

[13] In both cases, application of the protective laminate or film occurs after the silicone-coated surface has been imaged with a laser to produce the desired identification indicia, creating an additional, time-consuming step for the enduser. Automatic lamination devices, such as described in US 6,764,016, are sensitive to dust, dirt and temperature extremes often found in industrial facilities, leading to increased maintenance requirements when operated at the final point-of-use for the finished laminated tag. The speed of lamination with such an automatic device is often mismatched with the speed of laser printing, creating additional inefficiencies for the end-user.

[14] When the silicone-coated surface to be marked takes the form of a connected series of metal tags joined by a breakable metal junction between the tags, and the protective over-laminate takes the form of a continuous film, such as a tearresistant adhesive tape, covering more than one tag, the presence of the film at the breakable metal junction can impede the ability to create a clean separation when breaking the connected series of metal tags into individual metal tags to be used in their intended application.

[15] EP0732678 teaches a laser-permeable film covering for a plastic base layer, but does not create a solution for silicone coatings requiring higher laser power capable of melting or ignititing plastics. Similarly, U.S. Patent No. 5,340,628 teaches a transparent top sheet to prevent release of particles from a thermally sensitive base sheet, but does not teach a solution for higher powered lasers capable of burning through the base sheet. Neither teaching addresses the requirement to cleanly separate individually marked tags or labels from a continuous strip.

[16] Protective films also are useful in shielding rough or porous surfaces, such as silicone-coated metal identification tags, from the accumulation of dirt and other environmental pollutants, extending their useful life before cleaning or possible replacement is required. Protective films sufficiently resistent to UV radiation have been shown to be effective substitutes for directly applied liquid protectants, on laser-markable surfaces such as, for example, anodized micro- pore aluminum tags that are prone to sun-induced UV fading and environmental degradation. See, for example, US 6,451 ,421 which discloses a durable abrasion-resistant asset tag, but which requires additional protection after laser marking for outdoor applications. Heretofor, such protective films could only be applied after the completion of laser marking, requiring an undesired additional operation step typically performed by the end-user rather than the tag manufacturer.

[17] Needed, then, is a method to (1) mark a silicone-coated surface with identification indicia, (2) protect said surface and indicia markings from chemical and/or environmental attack, and (3) optionally facilitate the separation of a continuously connected strip of marked and protected tags into two or more marked and protected tags, all in a single step. Such a method is described herein.

[18] BRIEF SUMMARY OF THE INVENTION

[19] Metal identification tags are coated with a silicone resin-based coating engineered to produce a color change under the action of a laser beam of sufficient power at a specific wavelength. Although commonly white, the silicone-based coating may optionally be tinted or colored with suitable pigments. A variety of metal tag aspect ratios are suitable for use in the present invention, including a single continuous unbroken strip of multiple tags joined by a thin breakable metal neck or junction separating each tag from the next, or said continuous strip without such junctions from which tags may be created through a slitting, cutting, shearing or punching action.

[20] A protective film or tape semi-transparent to the laser at the specific wavelength suitable for marking is applied over the coated metal tag, advantageously by the tag manufacturer before the tags are packaged, for example in coils or stacks, for efficient shipping to and handling by a user. The protective film may be colorless or it may be tinted with a suitable colorant.

[21] Identification indicia, then, are created on the silicone-based surface by action of the laser of specific wavelength at which the film is semi-transparent, through the film, at a power level or output power (watts) sufficient for producing the desired color change on the underneath layer, but less than the level at which the semi-transparent film would melt, burn, ignite, or otherwise be disrupted or compromised to or beyond the point of failure. Advantageously, all markings are produced after the semi-transparent protective film has been applied to the metal identification tag, but those skilled in the art will recognize that certain preliminary markings produced by lasers or other suitable methods may be created on the silicone-based surface prior to application of the laminate, without affecting the utility of the disclosed inventive process.

[22] Common methods for controlling the power of the laser beam of specific wavelength, on a unit-area and/or unit-time basis, include, but are not limited to, controlling the incident laser spot size through focusing and defocusing techniques; and/or controlling the pulse duty cycle of a pulsed laser beam; and/or changing the traversing rate of the laser beam across the surface to be marked.

[23] When the form of the surface with protective film to be marked includes a metal or other sufficiently heat conductive substrate under the silicone-based coating, the effective power of the laser beam also may be controlled by changing the method of pattern generation between continuously drawn arcs, also referred to as x-y or always-on vector marking, and raster scanning, also referred to as matrix or on-off marking, as taught in US 5,855,969. By design and for cycle time efficiency, the vector technique marks adjacent dots or pixels in rapid succession, resulting in increased heat loading on both the silicone based coating and the protective film, whereas the raster technique marks individual dots or pixels interspersed with unmarked white space in a less efficient manner, allowing the residual heat from laser marking to be absorbed by the heat conductive metal substrate before the next adjacent dot or pixel is marked on a later raster pass. Excessive heat loading during vector-type laser marking will compromise the integrity of the protective film at lower power levels compared to raster-type laser marking. Resulting discontinuities in the protective film provide a ready pathway for chemical attack on the identification indicia and/or the underlying silicone-based coating. [24] An advantage of the raster technique is that higher laser power may be used to mark identification indicia on the silicone-based surface without disrupting the protective film, resulting in reduced overall cycle time and/or higher contrast identification indicia.

[25] At chosen points during the marking cycle, the power of the laser beam of specific wavelength may be increased sufficiently to partially or totally disrupt the protective film in one or more desired areas, without disrupting the protective film in other areas where protection is desired. The protective overcoat can be severed between adjacent metal tags thereby.

[26] When the form of the silicone-based surface with protective film is at least one metal tag containing one or more open features such as holes or slots, such as for facilitating the attachment of the tag to fabricated metal using wire, clips, studs or other suitable devices, the laser beam of specific wavelength may be directed to the interior of the open feature to partially or totally disrupt the protective film, thus facilitating the insertion of the attachment device through the open feature. The lack of the metal or other suitably heat conductive substrate under the protective film in interior of the open feature is often sufficient to enable selective disruption of the film without further control of the power of the laser beam.

[27] When the form of the silicone-based surface with protective film is a connected series of metal tags, each tag joined to the next by a breakable junction, the power of the laser beam of specific wavelength may be increased sufficiently to partially or totally disrupt the protective film along the area of the tag defined by the breakable junction, thus facilitating the subsequent separation of individual tags from the continuous series of tags by breaking the breakable junction.

[28] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[29] For a fuller understanding of the nature and advantages of the present method and process, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

[30] FIG. 1 is a side sectional view through the disclosed tag; [31] FIG. 2 is the tag of Fig. 1 showing the laser heat being transferred to the underlying metal substrate;

[32] FIG. 3 is the foregoing tag of Fig. 2 being laser marked;

[33] FIG. 4 is an enlarged view of the tag of Fig. 2 showing the heat being transferred through the overlay and striking the underlaying metal;

[34] FIG. 5 is an isometric view of two adjacent connected tags with the continuous overlay;

[35] FIG. 6 is spectra chart of absorbance (AU) versus wavelength for the preferred BOPP overlay film;

[36] FIG. 7 is an isometric view of a roll of the disclosed tags; and

[37] FIG. 8 shows a plurality of tags of different dimensions with their back sides adhered to an adhesive sheet with an intended release liner not shown.

[38] The drawings will be described in greater detail below.

[39] DETAILED DESCRIPTION OF THE INVENTION

[40] Silicone coatings produced from siloxane resins on a metal carrier or substrate are extremely useful for high-temperature applications such as, for example, identification and traceability in primary metals production, processing and fabrication. See, for example, U.S. Patents Nos. 5,714,234 and 5,855,969. Such coatings, even though capable of withstanding temperatures in excess of 900°C, are less resistant to chemical attack, such as, for example, from caustics or bases. See, for example, U.S. Patent No. 6,764,016.

[41] Heretofore, plastic films have been used to protect thermal paper, but were ineffective on silicone coatings designed for laser marking, unless the protective film was applied after marking. The incompatibility is due to the specific wavelength and power level required to produce the desired color change in the silicone coating. The laser energy required to darken a silicone- based coating is significantly higher than the energy needed to darken direct thermal coatings on paper or plastic and well beyond the melting point of common plastic films and laminates.

[42] In the preferred embodiment of the disclosed inventive method, a semicrystalline thermoplastic, such as, for example, biaxially oriented polypropylene (“BOPP”), semi-transparent to the specific wavelength effective for producing the desired color change in the silicone-based coating, is used as the protective film or laminate. BOPP has been observed to pass >97% of laser energy at a wavelength of 10.6pm, 21 , in FIG. 6, limiting disruption of the laminate caused by direct absorbtion of laser energy. A wavelength of 10.2 m, 20, is near optimum for vaporizing BOPP in free space and has been observed to melt and distort the BOPP overlaid on the silicone-coated surface without creating the desired color change in the silicone-based coating.

[43] The protective film also creates a barrier between the silicone coated surface and the external oxygen-laden atmosphere, limiting the intensity and extent of heat generation as carbon is released from organics in the silicone-based coating during laser marking, reducing the heat load on the protective film and further limiting its disruption.

[44] The skilled artisan will appreciate that lasers of other wavelengths, in combination with films sufficiently transparent to lasers of the chosen wavelength, may be used to advantage in accordance with the present disclosure, as may laser-markable coatings other than the disclosed silicone coatings.

[45] In the presently disclosed method, the metal substrate below the silicone coating also acts as a heatsink to lessen the duration of the heat affected zone created during the desired laser-induced color change in the silicone coating underneath the protective laminate, further limiting disruption of the laminate by the laser at power levels (wattage) and duty cycles sufficient for marking. The same power level often cuts through the laminate in areas without the underlying metal substrate, such as, for example, in the interior of holes or slots punched through the substrate, being useful as an aid for inserting attachment hardware, such as, for example, wire clips or nails, through the laminated hole or slot.

[46] An adhesive, such as, for example, a synthetic rubber adhesive, sufficiently transparent to the specific laser wavelength suitable for effecting a color change in the silicone coating, can be applied to the BOPP film to aid in intercoat adhesion and consistent intimate contact between the protective film and the silicone coated surface.

[47] When the aforementioned series of metal tags with protective film joined by breakable junctions has said junctions pre-broken after application of the protective film, the protective film holds adjacent tags in sequence, allowing, for example, the continuous strip of separated tags to be rolled into a coil for ease of handling, and/or, for example, facilitating the feeding of said tags into a printing device. At a chosen point during the marking cycle, the power of the laser beam of specific wavelength may be increased to sever the protective film along the area of the broken junction between tags, thus producing an individually separated tag with no further action required. As an alternative to first creating and then breaking the junctions to create individual tags, those skilled in the art will recognize that other forms of individual tags, such as produced by die cutting, may be connected in sequence by the same protective film. The skilled artisan also will recognize that the disruption in the film caused by the laser may be less than total severance, yet still sufficient to simplify later separation of individual tags with minimal effort and without requiring the use of an additional cutting device.

[48] In an advantageous embodiment illustrated in FIGS. 1-5, the surface of a metal or other heat conductive surface, 3, advantageously a rigid metal substrate, is coated with a silicone-based high-temperature resistant coating, 2, engineered to produce a color change under the action of laser beam, 6, advantageously of 10.6pm wavelength, from a laser, 5, advantageously a CO2 laser. A protective film, 1, semi-transparent to laser beam, 6, advantageously of biaxially oriented polypropylene (BOPP), is overlaid atop the surface of silicone layer, 2, to protect the silicone surface from chemical and/or environmental attack in further process operations. Laser beam, 6, passes through the semitransparent film, 1 , with desireably at least 95% transmittance at the wavelength laser beam, 6, with advantageously at least 97% transmittance, but with less than 100% transmittance, and strikes silicone-based coating, 2, to produce a specific spot size, 7, suitable for creating identification indicia, as illustrated at location 8 in FIG. 4 for marked silicon coating 4. Protective film, 1, can be severed along junction line, 9, in FIG. 5, by an increase in intensity (wattage) of laser beam, 6, emitted from from laser, 5, advantageously performed subsequent to the marking of all indentification indicia.

[49] Rolls of labels or tags, such as roll 10 in FIG. 7, advantageously of rigid metal construction, find advantage in the commercial market. Adjacent tags have perforations or scores forming a thin, breakable neck or junction, 9, therebetween for easy separation of tags by tearing or bending at the junction, 9. Advantageously, labels or tags may also contain one or more openings, such as hole, 11 , so each individual tag can be hung, if necessary, desireable, and/or convenient. Protective film, 1 , advantageously of BOPP and further advantageously in continuous form, is applied to metal surface 3 of roll, 10. Later disruption of the protective film, 1 , by laser beam, 6, along junction, 9, restores the utility of original breakable junction between tags.

[50] A plurality of tags of the same or different dimensions, such as, for example, tags 12, 14, and 16 in FIG. 8, may be placed with their backsides in contact with the top side of an adhesive, 18, such as a pressure sensitive adhesive (PSA), with the bottom side of the adhesive in contact with a release liner (not shown). Protective film, 1 , then is overlaid on top of the assembly of tags and adhesive, permitting, for example, the assmbly to be rolled into a coil for ease of handling. Laser beam, 6, then may be used to cut around the circumference of a tag with a power level suitable for cutting through the protective film overlay, 1 , and adhesive, 18, without cutting through the release liner (not shown).

[51] While the apparatus, system, and method have been described with reference to various embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope and essence of the disclosure. In addition, many modifications may be made to adapt a particular situation or material in accordance with the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that the disclosure will include all embodiments falling within the scope of the appended claims. In this application all units are in the metric system and all amounts and percentages are by weight, unless otherwise expressly indicated. Also, all citations referred herein are expressly incorporated herein by reference.

Claims

CLAIMS:

1 . A method for producing laser marked metal tags comprising the steps of:

(a) providing a plurality of metal tags, each metal tag being connected to an adjacent metal tag by a breakable junction, each metal tag having a front face and a back face;

(b) coating each metal tag on at least a portion of its front face with a laser markable coating;

(c) overlaying at least a portion of the laser markable coating with an overlay coating that is less than completely transparent to a laser beam; and

(d) presenting each overlayed coated tag front face to a laser beam effective to create images within the laser markable coating without compromising the overlay coating covering the images.

2. The method of Claim 1 for a single metal tag without connection to an adjacent metal tag.

3. The method of Claim 1 , wherein the breakable junction between each metal tag of the plurality of metal tags is broken either before step (d) or after step

(d).

4. The method of Claim 1 , wherein each metal tag of the plurality of metal tags contains an opening penetrating therethrough and which includes the step of:

(e) controlling the laser beam to sever or weaken at least a portion of the overlay coating at each metal tag opening.

5. The method of Claim 1 , which includes the step of:

(f) controlling the laser beam to sever or weaken at least a portion of the overlay coating at the tag breakable junction.

6. The method of Claim 1 , which includes the step of: (g) breaking the breakable junction between at least two adjacent tags, the overlay coating holding the two adjacent broken breakable junction tags together; and

(h) controlling the laser beam to sever at least a portion of the overlay coating holding the two adjacent broken breakable junction tags together. The method of Claim 4, which includes the step of:

(i) controlling the laser beam to sever or weaken at least a portion of the overlay coating between at least two adjacent tags. The method of Claim 1 , wherein the overlaid coating in step (c) exhibits a transmittance of at least about 95% to the laser wavelength used for marking the laser markable coating. The method of Claim 8, wherein the overlay coating in step (c) exhibits a transmittance of at least about 97% at a laser wavelength of 10.6pm. The method of Claim 1 , wherein each metal tag of the plurality of metal tags has a width and the overlaid coating in step (c) the covers less than the width of the tag front face A metal tag produced by the method of Claim 1 . The metal tag of Claim 11 produced by the method of Claim 3. The metal tag of Claim 11 produced by the method of Claim 4. The metal tag of Claim 11 produced by the method of Claim 5. The metal tag of Claim 11 produced by the method of Claim 6.

16. The metal tag of Claim 11 produced by the method of Claim 7.

17. An array of the metal tags of Claim 11. 18. An array of the metal tags of Claim 13.

19. An array of the metal tags of Claim 14.

20. An array of the metal tags of Claim 15.