EP1440133B1 - Method for producing a laser-printable film - Google Patents

Description

The invention relates to a method for producing a laser-writable film.

For identification of parts on vehicles, machinery, electrical and electronic equipment, etc., increasingly technical labels are used, e.g. as nameplates, as control labels for process sequences or as warranty and inspection labels.

In order to label such signs or labels, powerful controllable lasers are widely used, with the help of markings such as fonts, encodings and the like are "burned". High demands are placed on the material to be inscribed. So the labeling should be fast, the resolution should be high, the application should be simple and the material should have a high resistance to mechanical, physical and chemical influences. Common materials such as printed paper, anodized or painted aluminum or PVC films do not meet all these requirements.

Applicant produces a multilayer label which is self-supporting, has a thin, opaque pigmented lacquer layer over a thick lacquer layer and is made of an electron beam cured, solventless lacquer. Such a label is in the DE 81 30 861 U1 described. The label is labeled by using a laser to engrave the thinner lacquer layer by removing the layer so that the lower thicker lacquer layer becomes visible. The film material has high durability due to its chemical structure and electron beam curing.

Processing by means of a laser (preferably a Nd: YAG laser or a CO ₂ laser) requires that the top coat layer serving as a contrast layer be rather thin (less than 15 μm) and must have a high layer thickness constancy. This is realized in the production by using a precision application unit (multi-roll system) to apply the thin lacquer layer. For this purpose, the thin lacquer layer is first applied to a process foil or support carrier foil (polyester foil) and then the thick lacquer layer is knife-coated. Both layers of paint are polymerized in one operation by electron irradiation (80 kGy, 350 kV) to form a highly crosslinked polymer. This laser lacquer film is still equipped with a self-adhesive and decalcified in the final assembly of the support carrier film.

In the production of the prior art laser-writable film, the application of the first lacquer coating is a cost-intensive and sensitive process step. For example, the precision application unit limits the working width, the choice of paint colors is limited, the color design of the thin lacquer layer is less flexible, and sufficient coating quality can only be achieved with a relatively low coating speed.

Furthermore, there is a desire in fields of application for an individualization of the labels, which should already be present before the inscription by means of a laser. Such individualization could e.g. a custom design included. This would serve in the context of a controlled distribution channel of the still unlabeled, but customized individualized labels of tamper evidence, because a counterfeiting of labeled labels would then be almost impossible.

It is an object of the invention to provide a method for producing a laser-writable film, which can be carried out more cost-effectively than the previously known method and allows greater variability in the design of the laser-inscribable film, up to the customization.

This object is achieved by a method for producing a laser-inscribable film with the features of claim 1. Advantageous embodiments of the method emerge from the subclaims. Claim 19 relates to a multilayer label produced by such a method.

In the method according to the invention for producing a laser-inscribable film, an engraving layer which has a UV-curable lacquer is printed on a support carrier film. Over the engraving layer, a base layer is applied, which has an electron beam curable lacquer. Hardening takes place by means of electron irradiation.

In the terminology chosen here, which is based on the manufacturing process, the backing sheet is "down". In the finished film, however, the engraving layer is exposed, ie it is "up". Similar to the previously known multilayer label, the film produced by means of the method according to the invention can be labeled with a laser by removing the engraving layer at the desired locations.

According to the invention, the engraving layer is printed, preferably with a UV flexographic printing process. Printing processes allow a variety of possibilities with regard to the design of geometries, colors and color arrangements. Thus, the UV flexographic printing process can also be used to apply the engraving layer to web-like materials and, despite the low price, provides good print quality. This allows considerably larger working widths than the previously described prior art method.

Preferably, the engraving layer is cured prior to application of the base layer by means of UV irradiation. Later, when the base layer (or an optional interlayer, see below) is cured by electron beam irradiation, a firm bond of the UV cured lacquer to the electron beam cured lacquer results at high interlaminar adhesion.

The properties of the laser writable film, e.g. a high resistance to mechanical, physical and chemical influences are similar to the conventional laser films. However, a complicated coating process with a multi-roll system is not required in contrast to the production of the multiple label described above. Instead of the UV flexographic printing process, other common printing techniques can be used to apply the engraving layer to the backing film.

In an advantageous embodiment of the invention, the engraving layer is printed over the entire surface. In this case, the engraving layer can be monochrome, wherein preferably a strong color contrast to the color of the base layer or an intermediate layer (see below) is provided. In this case, the laser-writable film is made similar to the conventional multilayer label. The film can be labeled by means of a laser (eg an Nd: YAG or a CO ₂ laser) by locally removing the engraving layer; if there is a strong color contrast between the engraving layer and the underlying layer, then the lettering is particularly easy to read.

However, the engraving layer can also be printed over the entire surface and in this case multicolored, since the printing techniques for applying the engraving layer can be handled flexibly. Thus, e.g. two or more than two contrasting colors can be provided, which extend in the longitudinal direction of the laser-writable film, ie in the direction in which the engraving layer is printed. Another example is different contrast colors, which are printed in the transverse direction of the film as a repeat at a predetermined distance. In this way, within a label set, which is cut from the laser-writable film, different colored labels are produced. In principle, other color muffles of the engraving layer are also possible, down to individualizing markings according to customer requirements, such as e.g. Logos or specific labels provided in the engraving layer. In this case, the laser inscription can be done by removing the engraving layer as in a monochrome engraving layer. In the conventional multilayer labels a multi-colored design is possible only with great effort.

In a further advantageous embodiment of the invention, the engraving layer is printed over part of the area. An example is an individualizing logo, which is printed in a predetermined color (preferably in strong color contrast to the base layer or intermediate layer) at predetermined intervals on the support carrier film. This is technically easier and less expensive than when the engraving layer is printed over the entire surface and a different-colored lacquer must be provided at the points between the individual logos.

This variant of the method is particularly suitable for an embodiment in which, after printing the engraving layer and before applying the base layer, an intermediate layer is applied, which preferably has a pigmented, electron-beam-curable lacquer. The intermediate layer is preferably in color contrast to the base layer. As long as the film is not labeled, the base layer of the Intermediate layer hidden, and a partially printed on engraving layer stands out visually from the intermediate layer. For labeling with the aid of a laser, the intermediate layer is removed locally, if appropriate together with parts of the engraving layer which are located at the relevant point. The base layer becomes visible.

The electron beam curable coating is preferably cured in one operation and crosslinked with the engraving layer, both in embodiments in which only a base layer is provided, as well as in embodiments in which a base layer and an intermediate layer are applied. The energy dose of electron irradiation is preferably in the range from 50 kGy to 150 kGy, and the electron energy preferably in the range from 200 keV to 500 keV. The base layer and / or the optional intermediate layer may be applied prior to curing by knife coating.

In an advantageous embodiment of the invention, the engraving layer has at least one originality feature that allows for additional individualization and increases the security against forgery of the laser-inscribable film or of a multilayer label cut therefrom. Preferably, such originality features are not directly visible, but require a more or less large amount of equipment in order to be recognized and thus to provide the proof of originality. For example, the engraving layer may contain fluorescent dyes in ultraviolet light which become visible when illuminated by a UV lamp. Another example is thermochromic dyes that change color upon heating. It is also conceivable to dope the varnish of the engraving layer with other detectable substances which can provide a proof of originality, for example with substances such as "biocode" or "microtaggent". Biocode markets under the brand name "Biocode" a system with agent, marker and receptor that allows specific detection of biological samples. "Microtaggent" is a brand of the company Microtrace Inc. for a multi-layered pigment, which only allows a customized color code to be detected when viewed microscopically. These originality features are known as such and available in different embodiments. They can be used on both sides for the clear identification and labeling of products.

The engraving layer may comprise a cationic UV lacquer, which is preferably printed in a low thickness, for example in the range of 1 to 20 g / m ² and more preferably in the range of 3 to 6 g / m ² . (At a material density of 1 g / cm ³ , 1 g / m ² corresponds to a thickness of 1 μm.)

The base layer and / or the optional intermediate layer preferably comprises a pigmented electron beam curable polyurethane acrylate lacquer. The thickness of the engraving layer may be in the range of 20 to 500 g / m ² , preferably in the range of 100 to 160 g / m ² . An optional interlayer is typically thinner than the engraving layer.

The backing sheet may have a polyester film whose thickness is preferably in the range of 10 to 200 μm.

In a preferred embodiment of the invention, an adhesive is applied over the base layer, e.g. a pressure-sensitive adhesive having a layer thickness in the range of 5 to 70 microns, preferably 10 to 30 microns. This adhesive may be covered with a protective layer (e.g., a silicone paper).

The laser-writable film can be produced by the method according to the invention in tracks. From these labels can be cut to the sizes required for the usual applications. The support carrier film can already be decalcified during the production process, preferably in a final process step. But it is also conceivable that the backing sheet is removed only by the customer before the label in question is labeled by means of a laser. If the base layer is provided with an adhesive, the customer can easily attach the label in the designated place.

Figur 1

einen schematischen Längsschnitt durch eine gemäß einer ersten Ausführungsform des erfindungsgemäßen Verfahrens hergestellte laserbeschriftbaren Folie, die sich noch auf einer Stützträgerfolie befindet,

Figur 2

einen schematischen Längsschnitt durch ein Etikett aus einer Folie gemäß Figur 1 während eines mit Hilfe eines Lasers durchgeführten Beschriftungsvorgangs,

Figur 3

eine Draufsicht auf das beschriftete Etikett gemäß Figur 2,

Figur 4

einen schematischen Längsschnitt durch eine gemäß einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens hergestellte laserbeschriftbare Folie, die hier wie in Figur 2 orientiert ist, und

Figur 5

eine Draufsicht auf ein beschriftetes Etikett aus einer Folie gemäß Figur 4.

In the following the invention will be further explained by means of exemplary embodiments. The drawings show in

FIG. 1

3 shows a schematic longitudinal section through a laser-inscribable film produced according to a first embodiment of the method according to the invention, which is still located on a support carrier film,

FIG. 2

1 is a schematic longitudinal section through a label made of a film according to FIG. 1 during a marking process carried out with the aid of a laser;

FIG. 3

a top view of the labeled label according to Figure 2,

FIG. 4

a schematic longitudinal section through a laser-inscribable film produced according to a second embodiment of the method according to the invention, which is oriented here as in Figure 2, and

FIG. 5

a top view of a labeled label of a film according to Figure 4.

FIG. 1 shows how a laser-inscribable film 1 according to a first exemplary embodiment is produced.

The carrier used is a support carrier film 10, for which in the exemplary embodiment a polyester film with a thickness of 50 μm (Hostaphan film RN 50, Mitsubishi) is used. On the support carrier film 10, a cationic UV varnish is printed over the entire surface using a UV flexographic printing process. In the exemplary embodiment, the engraving layer 11 formed in this way contains a paint quantity of 3 to 6 g / m ² , ie the thickness of the engraving layer is approximately 3 to 6 μm. In the embodiment this paint is darkly pigmented. After printing, the engraving layer 11 is irradiated with ultraviolet light for curing.

Thereafter, a base layer 14 of an electron-beam-hardenable lacquer (in the exemplary embodiment, a white-pigmented polyurethane acrylate lacquer) is applied to the cured engraving layer 11. The preferred amount of paint is in the range of 100 to 160 g / m ² , corresponding to a layer thickness of about 100 to 160 microns followed by irradiation of the base layer 14 with electrons, wherein in the embodiment, the acceleration voltage of the electrons 350 kV and the absorbed dose is 80 kGy. In this case, the electron-beam-hardening lacquer of the base layer 14 is crosslinked, wherein at the same time chemical bonds to the engraving layer 11 are formed. The result is a mechanically high-quality and chemically very resistant material with firmly interconnected layers.

In a further step, an adhesive is applied to the base layer 14 using a conventional coating method, so that an adhesive layer 16 is formed. In the exemplary embodiment, the adhesive layer 16 is covered with a silicone paper serving as a protective layer 17.

In general, the laser-writable film 1 is so large that it can be cut from a number of multi-layer labels. The support carrier film 10 can be decalcified before cutting, but also after cutting, so that the engraving layer 11 is freely accessible.

FIG. 2 shows a multilayer label composed of the laser-writable film 1 after the support carrier film 10 has been peeled off. In the illustration according to FIG. 2, the engraving layer 11 is oriented upwards and the protective layer 17 is removed, since the label is glued onto an object not shown in FIG. The adhesive layer 16 sticks preferably so strong that the film 1 can not be detached from the object nondestructively.

With the aid of an indicated in Figure 2 by an arrow laser beam, which is preferably generated with a Nd: YAG laser or a CO ₂ laser, the film 1 can be labeled. In this case, the engraving layer 11 is removed, so that the underlying base layer 14 is exposed. In this way, an engraved lettering 19 is produced, which is particularly clearly visible when the color contrast between the engraving layer 11 (dark in the exemplary embodiment) and the base layer 14 (white in the exemplary embodiment) is large.

In Figure 3, the film 1 is shown after labeling in plan view. In the color choice of the embodiment, therefore, the engraved lettering 19 appears as white writing in front of a dark background, which is formed by the non-eroded part of the engraving layer 11.

Reference to the figures 4 and 5, a second embodiment of a method for producing a laser-writable film will be described. The film is designated 2 here. As in the first embodiment, a polyester film of 50 microns thickness (Hostaphan RN 50, Mitsubishi) is used as a support carrier film, are successively applied and cured several layers. Finally, the backing sheet is decalcified. FIG. 4 shows the laser-writable film 2 designed as a multilayer label after removal of the support carrier film in an orientation similar to that in FIG. 2. The individual method steps are explained in more detail below.

First, the backing sheet is partially printed with a cationic UV-curable lacquer over a UV flexographic printing process. In this way, a partial area engraving layer 21 is formed, which can be seen in the upper area of FIG. In the exemplary embodiment, the UV-curable lacquer is pigmented dark green and in the form of recurring at regular intervals Logos 28 are applied, see also Figure 5. The amount of paint is (based on a full-surface imprint) in the range of 3 to 6 g / m ² . After printing, the engraving layer 21 is irradiated with ultraviolet light for curing.

Subsequently, an intermediate layer 22 is applied with a doctor blade, which in the exemplary embodiment consists of a black-pigmented electron-beam-curable polyurethane acrylate lacquer (lacquer amount about 13 g / m ² ). In this case, the material of the intermediate layer 22 surrounds the parts of the engraving layer 21, which protrude from the support carrier film, so that a substantially planar surface 23 is formed ("in-mold-embossed" method). The engraving layer 21 is therefore virtually cast in the intermediate layer 22, see FIG. 4.

Before an electron beam hardening is carried out, a further layer of an electron-beam-hardening lacquer is spread on, namely the base layer 24. In the exemplary embodiment, it consists again of polyurethane acrylate lacquer and is pigmented in white. The amount of paint is preferably in the range of 100 to 160 g / m ² . Subsequently, the base layer 24, the intermediate layer 22 and the engraving layer 21 are irradiated from the side of the base layer 24 with electrons (in the embodiment, 80 kGy absorbed dose at 350 kV). In this case, the base layer 24 and the intermediate layer 22 are cured and the intermediate layer 22 is crosslinked with the engraving layer 21.

As in the first embodiment, an adhesive layer 26 is finally applied (in the embodiment, a pressure-sensitive adhesive with a layer thickness of 20 microns) and with a protective layer (which is not shown in Figure 4) covered. After the support carrier film has been peeled off and the laser-inscribable film 2 is optionally cut into pieces of the desired size, the state shown in FIG. 4 results. Figure 4 is (as well as Figures 1 and 2) not to scale.

FIG. 5 shows the laser-inscribable film 2 (or a section thereof) in plan view. The engraving layer 21 is configured as a pattern of logos 28 which appear dark green on the black background formed by the intermediate layer 22. The film 2 is individualized by the logos 28.

In order to label the film 2, the intermediate layer 22 is removed locally with the aid of a laser until the white base layer 24 appears underneath. If a part of a logo 28 is located at a position detected by the laser beam, this area of the engraving layer 21 is likewise removed. In this way, an engraved inscription 29, as shown in Figure 5 (not in the embodiment corresponding color reproduction).

Claims (19)

1. Process for producing a laser-inscribable film, using the steps:

   - applying, by printing, an engraving layer (11; 21), which comprises a UV-curable lacquer, to a supportive backing film (10),

   - applying, over the engraving layer (11; 21), a base layer (14; 24), which comprises an electron-beam-curable lacquer,

   - curing by means of irradiation with electrons.
2. Process according to Claim 1, characterized in that the UV flexographic printing process is used to apply the engraving layer (11; 21) by printing.
3. Process according to Claim 1 or 2, characterized in that the engraving layer (11; 21) is cured by means of UV irradiation prior to the application of the base layer (14; 24).
4. Process according to any of Claims 1 to 3, characterized in that the engraving layer (11) is applied by printing over the entire surface.
5. Process according to any of Claims 1 to 3, characterized in that the engraving layer (21) is applied by printing over part of the surface.
6. Process according to any of Claims 1 to 5, characterized in that the engraving layer is applied by printing in two or more colors.
7. Process according to any of Claims 1 to 6, characterized in that, after the engraving layer (21) has been applied by printing, and before the base layer (24) has been applied, an intermediate layer (22) is applied, and preferably comprises a pigmented electron-beam-curable lacquer.
8. Process according to any of Claims 1 to 7, characterized in that the electron-beam-curable lacquer is cured in a single operation and is thus crosslinked with the engraving layer (11; 21), the energy dose from the irradiation with electrons preferably being in the range from 50 kGy to 150 kGy, and the energy of the electrons preferably being in the range from 200 keV to 500 keV.
9. Process according to any of Claims 1 to 8, characterized in that a doctor is used to apply the base layer (14; 24) and/or the optional intermediate layer (22).
10. Process according to any of Claims 1 to 9, characterized in that the engraving layer comprises at least one anti-counterfeiting feature which has preferably been selected from the following group: dyes that fluoresce in UV light, thermochromic dyes, substances comprising a detection system specific to biological specimens, multilayer color pigments.
11. Process according to any of Claims 1 to 10, characterized in that the engraving layer (11; 21) comprises a cationic UV lacquer.
12. Process according to any of Claims 1 to 11, characterized in that the engraving layer (11; 21) is applied by printing at a thickness in the range from 1 to 20 g/m², preferably in the range from 3 to 6 g/m².
13. Process according to any of Claims 1 to 12, characterized in that the base layer (14; 24) and/or the optional intermediate layer (22) comprises a pigmented electron-beam-curable polyurethane-acrylate lacquer.
14. Process according to any of Claims 1 to 13, characterized in that the base layer (14; 24) is applied at a thickness in the range from 20 to 500 g/m², preferably in the range from 100 to 160 g/m².
15. Process according to any of Claims 1 to 14, characterized in that the supportive backing film (10) comprises a polyester film whose thickness is preferably in the range from 10 to 200 µm.
16. Process according to any of Claims 1 to 15, characterized in that, over the base layer (14; 24), an adhesive mass (16; 26) is applied, and is preferably protectively covered by a protective layer (17).
17. Process according to any of Claims 1 to 16, characterized in that the laser-inscribable film (1; 2) is cut to size.
18. Process according to any of Claims 1 to 17, characterized in that the supportive backing film (10) is peeled away, preferably in a final step of the process.
19. Multilayer label, produced by a process according to any of Claims 1 to 18.

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