EP0911786B1 - Laserlabels and their use - Google Patents

Description

Technical labels are used in many areas for high quality applications, as type plates for vehicles, machines, electrical and electronic devices, as control labels for process flows as well as guarantee and test badges. frequently these applications inherently involve the need for a more or less pronounced level of security against counterfeiting. This security against counterfeiting applies primarily for the period of attachment and the entire useful life on the part to be marked: removal or manipulation is only to be done with destruction or visible, irreversible change. In particularly sensitive fields of application a security level must also apply to the manufacture of the labels: too easy procurement and labeling of such labels and production Plagiarism would prevent unauthorized persons from distributing articles enable.

For the rational and variable production of high-quality labels, especially in technical-industrial applications, the laser marking of suitable base material is becoming increasingly popular. DE G 81 30 861.2 describes a multi-layer label in which a different colored cover layer is removed by the laser beam and thus the color contrast to the next layer enables labels of high quality and legibility. This label is a type of engraving, which eliminates the possibility of manipulation as with traditional printing with colors and inks. In DE G 81 30 861.2 the label film is so brittle due to the raw materials used and the manufacturing process that removal of the bonded labels from the adhesive substrates is only possible with destruction.

An additional security level is given in the single-layer laser label according to DE G 94 21 868: in addition to the advantageous properties of DE G 81 30 861.2 the inscription is not here by engraving in the cover layer, but by a Color change in the plastic layer itself causes subsequent manipulations the labels largely prevented.

The only potential gap in the security chain is that such Single and multilayer labels for laser marking are freely accessible - for accordingly High quality goods could thus be sourced from the labels and lettering to be regarded as possible and worthwhile even with expensive laser units.

In order to remedy this, the aim of the development was to develop the label material for the later labeling so that it can be used as authentic original material at any time can be identified with little effort and non-destructively. For those already subsequent identification is in principle also possible, however with unacceptable analytical effort and not non-destructive.

Known for particularly security-related goods such as banknotes, checks, checks and Personal identification cards etc. are various procedures to prevent counterfeiting to ensure. In addition to watermarks, printing with filigree patterns, application Holograms also occasionally use "invisible" markings.

JP 08/328474 describes a textile clothing label which is printed on the top side with a transparent, fluorescent color, the woven design and printed image being said to be approximately congruent. A similar superficial printing with UV-active, photochromic inks is described in WO 8801288; however, an additional protective layer against oxygen and water is necessary to protect the chemicals in this colored layer.

In FR 2734655 , security marking for checks is achieved in that the printing under an only IR-permeable layer is invisible in the visible wavelength range, but is machine-readable / identifiable with special IR light.

In EP 727316 , hidden protection against forgery is achieved in that two reactive components are present in an extra layer , especially on paper, which give rise to a color reaction under pressure - this is, however, irreversible.

The use of electrically conductive or magnetic inks for printing on the surface are described in JP 08/054825 and CN 1088239 . Such systems can only be used to a very limited extent for label applications on complex metal parts such as, for example, vehicle and machine parts.

The ink ribbons described in JP 07/164 760 with fluorescent particles that can be excited by IR are transferred by heat using thermal transfer printers. Although the prints contain a concealed tamper-evident designation, the printing is applied superficially both with solvents, heat and mechanically removable or changeable.

DE 4231800 describes labels which, for security against counterfeiting , leave indelible traces on the adhesive substrates by means of sublimation dyes or corrosive substances - however, the traces can only be identified after the label has been removed, which is often undesirable or impossible.

EP 453131 describes for highly secured papers such as passports, shares, bank notes etc. that fluorescent, especially UV-fluorescent indicators are incorporated into an intermediate layer between two permanently bonded layers of paper, which are only detectable when light of suitable wavelength is transmitted through the laminate, but not through reflection in reflected light. This system is unsuitable for applications in which a transmission of light through the glued label is not possible, as well as for the completely opaque laser labels.

DE 195 09 505 C discloses a multi-layer label, the backing layer of which contains an additive which shows a color change under laser irradiation, that is to say changes irreversibly.

All of these methods are applied superficially or are superficially effective and therefore not or only to a very limited extent for the known laser labels, because here for e.g. Nameplate applications optically high quality and extremely resistant Surface would change and deteriorate. Would be particularly annoying such a modification in the as a technical standard for type plates viewable two-layer labels with high-gloss black top layer and white base layer. Also include those known in the art Subsequent superficial counterfeit security, the potential, mechanical or manipulations using heat, chemicals, etc.

The object of the present invention was therefore to provide a largely "invisible" additional Install security level in the label stock, so that with as possible verification of originality is carried out quickly and non-destructively with little effort can be. This invention became an example of the laser-inscribable labels carried out, but is for the specialist for problems similar to printed labels, self-adhesive tapes, etc. available.

This task is solved by a laser label, as detailed in the claims is characterized in more detail.

As both technically favorable and inexpensive solutions to problems the possibility that stands out from the prior art in that neither the high quality surface quality of the top layer nor the top layer itself is changed; minor interventions only take place in the base layer. Consequently neither the overall optical impression nor that for mechanical, chemical and physical resistance of the label changed the top layer. Furthermore, a customer-specific marking can be easily created manufacture what the unauthorized procurement and use of labels in addition difficult.

In the case of two-layer and multi-layer labels, the one that is decisive for the font is thus Base layer an additive suitable for reversible optical identification, the Additive by means of electron beams, X-rays, in particular by visible light, especially recognizable by IR or UV rays, in particular made visible is, or a suitable for reversible magnetic or electrical labeling Additively incorporated. The top layer itself for e.g. high-gloss nameplates remains unchanged, the base layer is only partially attached to the laser engraving The labeling is exposed. Are in the example here white Base layer color pigments, color particles, colored fibers, etc., so these are attached to the engraved areas visible. Become the recipe of the base layer different particles (different in color, shape and / or size) in defined Such relationships can be added and distributed homogeneously serve in the label base layer as a "fingerprint" that is custom made and can be distributed. The coloring particles can be fine Color pigments are or preferably visible particles of the order of magnitude from 0.1 - 5 mm. When using finely ground color pigments, a slight change in color of the lettering created with the visible particles characteristic color mosaic. When using daylight fluorescent colors is without aids the "fingerprint" to recognize what is often undesirable. To be favoured therefore color pigments or particles used in the range of visible light do not absorb and are therefore normally invisible - only when the label is illuminated the color pigments are excited with a lamp of a suitable wavelength and shine characteristic. In addition to color pigments excited by IR radiation mainly UV-active systems. In principle, are also suitable Phosphors that are emitted by electron beams, X-rays, etc. be excited as well thermochromic pigments that change color reversibly when the temperature changes - however In these cases, it is practical to carry out identification on the glued label cumbersome and more complex than visualization using light of a suitable wavelength. When selecting the color pigments, care must be taken that they are used in the manufacturing process the labels (film production, adhesive coating) are sufficiently stable and do not become irreversible in the process conditions (possibly thermal drying, electron beam or UV curing, etc.) change. Advantageous for permanent label applications is that these mostly sensitive phosphors are embedded in a polymer matrix and are additionally protected by the cover layer. Further measures against mechanical abrasion and protection against direct contact with oxygen and water unnecessary.

For the application according to the invention, different color pigments and substances are used. Long afterglow are the most common (phosphorescent) or fluorescent pigments that are only or predominantly by UV radiation are excited and emit in the visible region of the spectrum (as Overview see e.g. Ullmann's Encyclopedia of Technical Chemistry, 4th edition, 1979, publisher Chemistry). However, IR-active luminescent pigments are also known. Examples of systems with UV fluorescence are xanthenes, coumarins, naphthalimides etc., some of which are below the generic term 'organic phosphors' or 'optical brighteners' in the literature become. The addition of a few percent of the phosphors in question is sufficient the integration into a solid polymer matrix is particularly favorable in relation on luminosity and stability. For example, recipes can be used with RADGLO® pigments from Radiant Color N.V./Holland or Lumilux® CD pigments by Riedel-de-Haen. Inorganic phosphors are also suitable; as long afterglow Fabrics, especially those with light emission in the yellow area, have been found Metal sulfides and oxides, usually in combination with suitable activators, as cheap proved. These are, for example, under the trade name Lumilux® N or as Stability, luminosity and afterglow duration improved luminous pigments the trade name LumiNova® from Nemoto / Japan.

These dyes / pigments listed as examples are included in the formulation of the base layer in amounts of 0.1-50%, preferably incorporated and coated with 1-25%. After the final adhesive coating of the base layer and, if necessary, covering with Release paper or release film is the label material for customer-specific use in front. After punching / laser cutting the desired label geometries as well the final inscription using a laser beam with lettering, barcodes, logos etc. the label is in its final form. When incorporating e.g. afterglow After appropriate stimulation, the label assigns pigments to the base layer Luminous pigments a characteristic afterglow in the area of laser marking and on the edges on what an easy and quick identification as an original label allowed. In addition to the special light source and, if necessary, a privacy screen against disturbing Ambient light does not require any additional complex equipment - after the test the label remains unchanged.

Such labels, the phosphors in the base layer, especially those only after UV or IR excitation in the visible wavelength range, are suitable also for precise registration (printing, punching, application, etc.). Instead of of separately applied pressure or control marks can be used during processing the light emission of the base layer can be used for this: especially after Labeling and cutting the labels using a laser beam made from uncut punched material can be located in a downstream control unit at a defined point in the Labels the excitation and emission with suitable equipment as a tax stamp for further processing steps or for the production of the next label can be used.

An alternative to the use of phosphors is the incorporation of substances into the Base layer that can be detected magnetically or electrically. magnetic field changes as with alarm labels for e.g. Garments are possible in principle, but for the fields of application (marking of machine and auto parts mainly from Metal) not predestined. In contrast, there is a hidden security level, in which Add base layer substances that lead to an electrical conductivity of the layer to lead. With suitable measuring devices, which are portable, easy to use and inexpensive are available, and suitable electrodes can be attached to the adhesive label the conductivity of the base layer can be determined directly. The electrodes are on two stopped different points A and B of the base layer and applied a voltage. If there is a continuous electrical conductivity between A and B a current flow can be measured, depending on the type and amount of the used Additive can have a characteristic value. Because even when using the Labels directly on metals the base layer through the electrically insulating adhesive layer separated from the conductive metal are not erroneous measurements to fear.

Counterfeiting through subsequent manipulation is particularly ruled out if that the conductivity measurement not only from edge to edge of the labels, but between any points exposed by lasering: so here If a conductivity can be detected, the entire base layer must be continuous be three-dimensionally conductive, which is only possible in the context of the original manufacturing process can guarantee. Such a laser-inscribable label can be produced by adding electrically conductive substances to the formulation of the base layer; this can be in addition to the previous pigments or at least partially in the replacement of the existing pigments happen to the good processing properties to maintain the paint pastes. In principle, conductive additives are electrical conductive metallic, organic, polymeric and inorganic substances suitable, the use of metals is preferred. Especially for white or light base layers the inherent color of the conductive additive must be taken into account for the selection. Conductive carbon black is also suitable, but only for black or dark base layers.

To ensure good conductivity, a minimum limit concentration should be set Additively ensure that sufficient particles are present in the base layer are to touch and to have contact with each other. When falling below this Limit concentration is a conductive one in the three-dimensional structure of the base layer No longer ensured from A to B. Metallic particles are therefore preferred used, fibers with a high length to cross-section ratio preferred because with lower concentrations there is a three-dimensional conductivity can be ensured than with spherical particles; besides, the falls Color change of the base layer with the fibers from less. Preferred metals are preferred for cost-benefit considerations copper, iron, aluminum and steel and their Alloys used, but also expensive, highly conductive metals such as silver, Suitable for gold. The fiber dimensions are 0.1 - 50 mm in length and cross sections with 1 - 100 microns, preferably metal fibers with a diameter of 2 - 20 microns at a Cross-sectional to length ratio of approx. 1: 100 to 1: 1000 are used. Fibers of this type are incorporated into the known formulation at 0.5-25%, preferably at 2-10% homogeneously incorporated and acc. DE G 81 30 861.2 coated and cured. To Adhesive coating and covering with release paper are available label material, which can be labeled with a laser beam. By removing the top In the area of laser marking, the lettering of the base layer becomes the top layer exposed - when a voltage is applied to two different ones via suitable electrode contacts Locations A and B of these logos are measured for conductivity is characteristic of the base layer and i.a. by amount and type of conductive Additive is determined. There is thus the possibility of customer-specific using defined recipes Manufacture label stock.

Both alternative options mentioned, the base layer of a two- or multi-layer label Modify to provide additional counterfeit protection in the label stock can also be used in a modified form for a single-layer label are, however, the advantages of the invention are not in part to the full extent Come wear.

Example A

As described in detail in DE G 81 30 861.2, a patented two-layer laser label consists, for example, of a thin black cover layer and a thick white base layer. The basic formulation for the respective paint paste consists of 90% of a commercially available aliphatic polyurethane acrylate and 10% hexanediol acrylate. The black paste is made with soot, as is known, the white paste with titanium dioxide as a color pigment. Black paste 10% carbon black, viscosity approx. 15 dPas. White paste 20% titanium dioxide,
10% pigment Lumilux® ROT CD 105 FF from Riedel de Haen with an additional 10% reactive thinner to adjust a suitable processing viscosity.

The black paste is spread evenly with 13 g / m ² onto a high-gloss, biaxially stretched polyester film of 50 µm and crosslinked with EB radiation [4 kGy]; after coating with the white paste on the black top layer with 100 g / m ² , the complete crosslinking takes place with 80 kGy. Coating with a polyacrylate PSA of 25 g / m ² and covering with a commercially available silicone paper result in the label material for further customer-specific uses.

After lasering the two-layer label with logos, lettering, barcodes etc. normal daylight no change compared to the previous label, only when the label is irradiated with a strong light source in the near UV range [Wavelength maximum at approx. 360 nm] the lasered writing area and the Edges of the label in the area of the white base layer red-violet. Helpful for one Clear detection is provided by a privacy screen to darken the label area Ambient light.

Example B

Analogous to example A, but instead of the luminophore Luminlux CD, the white paste is used the long-afterglow pigment Luninova® G 300 M from Nemoto / Japan 20% incorporated.

After suitable darkening against ambient light, a characteristic becomes here Afterglow in the color yellow on the one hand by one as described in example A. UV lamp achieved, but also by a strong, in the visible wavelength range emitting light source. In contrast to A, this light is not switched off the light source disappeared, but remains recognizable for minutes.

Claims (9)

1. Laser label comprising at least one polymer layer which is coated on one side with a self-adhesive composition, which is in turn optionally covered with a release paper or a release film, characterized in that an additive for reversible optical labelling, the additive being made recognizable, and especially visible, by means of electron beams, X-rays, in particular by visible light and, very particularly by IR or UV radiation, or an additive suitable for reversible magnetic or electrical labelling has been incorporated into the polymer.
2. Laser label according to Claim 1, characterized in that the additive consists of colour pigments, ink particles and/or coloured fibres.
3. Laser label according to Claim 1, characterized in that the additive is arranged in the form of various particles in defined proportions as patterns or the like in the polymer, as in the form of a fingerprint.
4. Laser label according to Claim 1, characterized in that the additive consists of colour pigments having particle sizes of 0.1 - 5 mm.
5. Laser label according to Claim 1, characterized in that the additive is present in the polymer in amounts of 0.1 - 50% by weight, in particular 1 - 25% by weight.
6. Laser label according to Claim 1, characterized in that the polymer comprises a further additive which shows a reversal of colour under laser irradiation.
7. Laser label according to Claim 1, characterized in that electrically conductive substances are present in the polymer.
8. Laser label according to Claim 1, characterized in that on that side of the polymer facing away from the self-adhesive composition there has been applied a further polymer layer which is partially removable by means of laser radiation, said further layer consisting in particular of an electron-beam-cured coating film whose thickness is 1 - 20 µm and whose colour contrasts with that of the underlying layer.
9. Use of a laser label according to one of Claims 1 - 8 for anti-counterfeit marking.