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

Definitions

• the invention relates to a method for laser marking of colored or uncolored films with at least one top layer and one base layer.
• the labeling of production and consumer goods is becoming increasingly important. Compared to conventional labeling techniques such as printing, embossing and labeling, the non-contact marking of packaging foils or moldings with the help of lasers is becoming more and more important because it can easily be used in ongoing production processes.
• thermoplastics especially the polyolefins, polystyrene and polyamides
• lasers with low energies there is either no labeling or only labeling with poor contrast.
• lasers with correspondingly higher energies the polymeric material generally decomposes, which leads to blackening.
• the labeling of foils in particular, is very difficult since, when using laser radiation with high energies, undesired carbonization of the foil occurs, which can lead to the destruction of the foil in the irradiated areas.
• polyolefins cannot be inscribed with the usual laser inscription systems for plastics, or only insufficiently, because on the one hand they do not absorb the wavelength of the laser light in certain areas and on the other hand the necessary sharpness of the marking is not achieved by light scattering.
• This disadvantage means that polyolefins, which, due to their appearance and properties, are ideal for packaging purposes, can only be insufficiently labeled with laser technology. The reason for this is that the polyolefin matrix does not absorb laser beams in the typical wavelengths of standard lasers used, such as 284, 351, 532, 1064 nm, or only little. For other polymers that absorb more, thermal damage to the polymer is generated at these wavelengths, causing the material to be engraved and blackened. The following labeling processes are essentially based on this effect.
• DE AI 39 17 294.5 describes laser-inscribable polyolefins. These materials contain 0.2 to 4.5% by weight of copper (II) hydroxide phosphate or 0.2 to 2.5% by weight of molybdenum (VI) oxide as an additive.
• a neodymium-YAG laser at a wavelength of 1064 nm or an excimer laser at wavelengths of 308 or 351 nm is preferably used as the laser. With this process, black inscriptions with good contrast are achieved on polymer injection molded parts.
• thermoplastic molding compositions with laser-sensitive pigmentation which contain 0.001 to 0.199% by weight of copper (II) hydroxide phosphate as an additive.
• polyolefins are used as thermoplastics.
• the laser marking is carried out with the aid of a neodymium-YAG solid-state laser with a wavelength of 1060 nm. A black marking was obtained on molded articles made of polypropylene.
• EP-Bl 0 190 997 describes a method for laser marking pigmented colored polyolefins.
• plastics such as polyethylene and polypropylene are first colored with inorganic or organic pigments or polymer-soluble dyes, these colorants preferably absorbing in the near UV and / or visible or near IR range.
• these thermoplastic molding must be labeled with laser radiation, the laser light having a wavelength in the UV range (0.25 and 0.38 ⁇ m) and / or in the visible range and / or in the IR range (0.78 and 2 ⁇ m).
• the process creates black labels for polyolefins.
• EP-AI 0 111 357 describes a method for laser marking molded articles made of polyolefins by irradiation with a TEA-CO 2 laser.
• the intensity of the laser pulse is 333 kW / cm 2 .
• the polyolefin contains calcium metasilicate, aluminum silicate or kaolin. The procedure produces black lettering.
• the polyolefins is added as an additive from about 0.1% by weight of a mica pigment, sold under the name Iriodin ®: is commercially available (manufactured by Merck, Darmstadt).
• Iriodin ® is commercially available (manufactured by Merck, Darmstadt).
• the flat mica flakes are coated with a thin layer of a metal oxide with a high refractive index.
• the pigment flakes are oriented parallel to the surface. If a laser beam hits the pigment platelets, part of the light is reflected on the pigments, the rest is transmitted. Due to the geometry of the platelets, the incident and the reflecting light beam are close together, so that in the area of the laser light beam the available energy density is increased and a surface layer of the plastic is carbonized. This results in a high-contrast black marking.
• the smooth surface of the film is adversely changed in laser marking, and these changes result in numerous disadvantages for the use of the films.
• the foaming or the engraving mechanically weaken the film. It becomes more brittle and loses its mechanical properties. Since the foaming or engraving of the surface of the film also causes roughening, there is a tendency for the surface of the film to become dirty at these points, which means that the labels become illegible over time and lose their contrast.
• the packaging area there is also the great disadvantage that bacteria can also nest in this rough surface layer, which are undesirable particularly in the packaging of foodstuffs.
• Multi-layer films are known from the prior art. They can be equipped in various ways depending on the intended use and can be produced by coextrusion.
• the cover layer consists of polymers or copolymers of polyethylene, polypropylene, polybutene-1, polyisobutylene, poly-4-methylpentene-1, polyacetylene or polyamide.
• the carrier layer preferably consists of a polyolefin and contains 0.05 to 10% by weight of an additive selected from the group consisting of silicates and silicon dioxide with a particle size of 0.01 to 100 ⁇ .
• the additive for the base layer is selected from the group consisting of silicon dioxide in crystalline or amorphous form, mica, feldspar, calcined kaolin, kaolin, nepheline syenite, talc, calcium silicate hydrate, silica, pyrogenic or precipitated silica, cristobalite, diatomaceous earth , Diatomaceous earth, micro-glass balls or mixtures thereof.
• Excimer lasers have wavelengths in the UV range from 193 to 351 nm, for example 196, 248, 308 and 351 nm.
• Neodymium YAG lasers are used in the visible and in the near IR range, for example at wavelengths of 532 and 1064 nm.
• the use of pulsed lasers with pulse durations of 1 to 1000 ns is particularly preferred.
• the energy densities used are preferably between 1 and 20 J / cm.
• Inorganic or organic pigments or polymer-soluble dyes are preferably used for coloring the film.
• the additive for the base layer can also be used in a mixture with polyolefin as a masterbatch.
• a CO 2 laser at wavelengths of 10,600 or 9,300 nm is preferably used for laser marking.
• the foils can have an energy density of 1 to 10 J / cm 2 ,
• FIG. 1 shows an SEM image of the cross section of a brittle fracture of a multilayer film which was produced by the method according to the invention.
• FIG. 2 shows a SEM image of a brittle fracture of a laser-inscribed film of the prior art in supervision.
• FIG. 3 shows an SEM image of the cross section of a brittle fracture of a laser-inscribed film of the prior art.
• the polyolefins used for the support layer are preferably those derived from alkenes having 2 to 10 carbon atoms.
• Homopolymers or copolymers of ethylene, propylene or butylene are preferably used.
• Polyethylenes can be manufactured using the high, medium or low pressure process. Ren. Copolymers of ethylene with phenyl esters, acrylic esters or with propylene can also be used. In a particularly preferred manner, high-density polyethylene or linear low-density polyethylene are used.
• Polyethylenes which contain conventional fillers, stabilizers and antiblocking agents can also be used.
• polypropylene Another polyolefin that can be used in a preferred manner is polypropylene, which is used, for example, according to the gas phase process using Ziegler-Natta
• Catalysts can be made. Also to be mentioned are copolymers of propylene which consist, for example, of propylene homopolymer and polypropylene copolymer with copolymerized C2 to CIO-alk-1-enes. Ethylene, butene-1, pentene-1, hexene-1 or octene-1 or mixtures thereof are used, for example, as polymerized C2 to cin-alkenes. Ethylene and butene-1 are preferred.
• propylene copolymers are prepared by polymerization using Ziegler-Natta catalysts, preferably in the gas phase using the polymerization reactors customary in the art. Processes for the production of polyolefins are generally known and are described in "Ullmann's Encyclopedia of Industrial Chemistry", 4th edition, volume 19, pages 167 to 226.
• the polyolefin suitable for laser marking can also contain conventional additives or pigments.
• inorganic pigments that cause discoloration are white pigments, such as titanium oxide, zinc oxide, antimony trioxide, zinc sulfide, lithopone, basic lead carbonate, basic lead sulfate or basic lead silicate, and also metal oxide, such as iron oxides, chromium oxides, nickel antimony titanate, chromium antimony titanate, manganese blue, manganese violet , Cobalt blue, cobalt chrome blue, cobalt nickel gray or ultramarine blue, Berlin blue, lead chromates, lead sulfochromates, molybdate orange, molybdate red, metal sulfides such as cadmium sulfide, arsenic disulfide, antimony tri sulfide or Cadmiu sulfoselenide, zirconium silicates such as zirconium vanadium blue and zirconium praseodymium
• organic pigments examples include azo, azomethine, methine, anthraquinone, indanthrone, pyranthrone, flavonthrone, benzanthrone, phthalocyanine, perylene, dioxazine, thioindigo, isoindoline, isoindolinone, quinacridone, Pyrrolopyrrole or quinophthalone pigments and metal complexes of azo, azomethine, methine, anthraquinone, indanthrone, pyranthrone, flavonthrone, benzanthrone, phthalocyanine, perylene, dioxazine, thioindigo, isoindoline, isoindolinone, quinacridone, Pyrrolopyrrole or quinophthalone pigments and metal complexes of azo, azomethine, methine, anthraquinone, indanthrone, pyranthro
• the polyolefins can also contain fillers, such as kaolin, mica, feldspar, wollastonite, aluminum sili
• the polyolefin for the carrier layer can also be produced as a concentrate (masterbatch). It then has correspondingly higher additions of the additive according to the invention, in the range from 20 to customary for masterbatch
• This masterbatch is then mixed with a polyolefin before the production of films, so that the necessary concentrations of the additive of 0.05 to 10% by weight in the total amount are achieved.
• the energy radiation of the laser used is preferably in the range of a wavelength in the far IR. In preferred
• the energy radiation of the laser used is at a wavelength of 9,300 or 10,600 nm.
• a laser with pulsed light is particularly preferably used, with
• Polymer material is preferably carried out via an optical system consisting of a mirror, mask and lens.
• the polyolefins can also be colored with various customary pigments or dyes.
• the dye is generally brightened, the degree of brightening of which can be influenced by the energy density of the laser radiation used.
• the process according to the invention has the advantage that there is no change in the surface of the laser-marked film when irradiated through the cover layer of the multilayer film, and thus the disadvantages of the prior art processes mentioned at the outset are completely avoided become.
• the inscriptions produced using the method according to the invention are considerably more wear-resistant and can also be used without problems for packaging in the food sector, since this does not roughen the surface of the films.
• the markings achieved are also high-contrast, sharp, abrasion-resistant and solvent-resistant.
• the use for the labeling method according to the invention is intended for film packaging made of polyolefins, in particular for food packaging, for example films which are used for meat packaging.
• the laser marking method according to the invention can also print, for example, packaging data, expiry dates, bar codes and other data on running filling lines in the filling cycle. Since the additives according to the invention have no color-imparting influence in visible light, foils equipped with them can be over-colored with colorants as desired, whereby the color intensity can easily be graded by adding the colorant.
• FIG. 1 shows an SEM image of the cross section of a brittle fracture of a multilayer film which was produced by the method according to the invention. It can be seen on the picture that the surfaces of the film are unchanged and only in the middle part, where the laser-inscribable base layer is located, can foaming be seen.
• FIG. 2 shows an SEM image of a brittle fracture of a laser-inscribed film of the prior art in a top view.
• FIG. 3 shows a SEM image of a brittle fracture of the same film of the prior art in cross section. It can be clearly seen here that foaming and roughening occur on the surface of the layer, so that dirt particles or bacteria can penetrate into the film surface.
• a single-layer film made of polyethylene (Escorene "LD-100 BW was produced on a film casting machine from Leistritz, Nuremberg. Cristobalite flour in the form of a masterbatch (50% filler degrees) distributed homogeneously in the film.
• the labeling was carried out using a C02 laser, type Almark AL 861K from Alltech GmbH & Co KG, Luebeck, at a wavelength of 9300 nm. Energy densities of 3.5 J / cm " 4 resulted in clear white labeling.
• REM 2 and 3 show recordings on a film cross section, the writing being recognizable as an open-pore foam structure on the film surface. The surface is foamed and rough.
• a film with at least three layers was produced from polyethylene (Escorene ® LD-100 BW) as a test specimen on a multi-layer film casting system from Leistritz, Nuremberg.
• the film was constructed as follows: top and bottom cover layers each 20 ⁇ m thick without additive; in the middle layer, also 20 ⁇ m thick, 2% cristobalite flour in the form of a masterbatch (50% filling degree) was homogeneously distributed as an additive.
• the labeling was carried out using the CO 2 laser according to Comparative Example 1. The energy density of 3.5 J / cm gave clear labeling.
• the SEM image of the film cross section is shown in FIG. 1. The position of the lettering as a foam structure in the middle layer can be seen. The other two layers, especially the surface of the foils, were not foamed and not rough.
• a film was produced as in Example 1.
• a surface-treated mica was (Iriodin 100 ® from Merck, Darmstadt) incorporated as a laser-sensitive additive. Labeling was carried out as in Comparative Example 1. The typeface was created in the middle layer without foaming the surface.

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• 1996
  • 1996-07-27 DE DE19630478A patent/DE19630478A1/de not_active Withdrawn
• 1997
  • 1997-07-14 DE DE59705289T patent/DE59705289D1/de not_active Expired - Fee Related
  • 1997-07-14 WO PCT/EP1997/003757 patent/WO1998004417A1/fr active IP Right Grant
  • 1997-07-14 JP JP10508438A patent/JP2000501670A/ja active Pending
  • 1997-07-14 ES ES97934462T patent/ES2167763T3/es not_active Expired - Lifetime
  • 1997-07-14 AT AT97934462T patent/ATE208280T1/de not_active IP Right Cessation
  • 1997-07-14 EP EP97934462A patent/EP0914257B1/fr not_active Expired - Lifetime

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