ES2390984T3 - Laser marking procedure of a document, showing the document a fixed color in an environment with a color shift effect - Google Patents

Abstract

Laser marking procedure of a document, in which a document comprising a coating containing at least one kind of effect pigment showing different colors at different viewing angles and at least one kind of laser sensitive pigment is treated in at least a part of the area covered with a laser beam that operates in OC mode at a speed of 500 mm / s that uses a power of 90%, calculated based on a laser that has an average power of 12 W, and a marking is obtained by laser having a fixed color, in which said fixed color is one of the different colors shown at different viewing angles by the effect pigment.

Description

Laser marking procedure of a document, the document showing a fixed color in an environment with a color shift effect 5 Background of the invention

1. Field of the invention

The present invention relates to a process for the manufacture of laser-marked documents, preferably security documents, such as banknotes, passports, checkbooks, etc., which show a fixed color in an environment with a displacement effect of color.

2. Description of the related technique

15 The use of self-authentication security features to produce documents serves to protect against unauthorized reproduction by counterfeiters. This is necessary, in particular, for securities, such as banknotes, checks, traveler's checks, stocks, etc. There is also a need for security documents that do not have a direct monetary value, such as identification documents, passports, etc., against the non-copy

20 authorized.

In particular, in the case of daily circulating values, for example, banknotes, a counterfeiter can succeed in copying the contents of the optically recorded document, for example, the printed optical image of the bills, in a deceptively accurate manner. A protection against this is the mark of authenticity contained in the security document, used for the elaboration of the documents, as a result of the structure imparted to the security document during manufacture whose authenticity characteristic cannot be copied supposedly by a forger with the means at your disposal. In addition, the application of watermarks or the introduction of a security thread in the paper is known. However, these conventional measures can no longer be considered totally satisfactory taking into account the progress of the work environment

30 employees per counterfeiters.

One possible way to overcome this problem can be seen in the use of pearl luster coatings, since the angle-dependent optical effects obtained from pearl luster pigments cannot be easily copied with photocopying machines or photographic techniques making counterfeiting much more complicated. Y

35 face.

In addition, interactions between coated substrates (paper, boards, film, laminate) and laser radiation are also known. It is possible to mark a coated substrate by ablation of the laser sensitive layer of the substrate or create marks within the coating layer by means of a suitable laser. The laser beam penetration into the

The coated substrate becomes larger with the increase in laser energy so that the substrate obtains a certain touch sensitivity or becomes finer until the laser beam finally perforates the substrate.

For security applications, such as applications on banknotes or other security documents, special paper types are used in this context. These documents are often made of matter cotton

45 natural premium or contain cotton fibers. Depending on the wavelength of the laser, the pulse rate and the laser energy, the laser beam can generate the following characteristics in these coated or uncoated special papers:

Ablation marks of coating layers 50

•

 Printing ink ablation [Bank of England, document DE 2836526]

•

Color layer / polymer layer ablation [OPS, US 4,740,269]

55 Markings by laser effects on the coating layers

•

Fine line marks on optically variable layers [G&D, document DE 19544130]

•

Laser markings on laser marking paper or paper coatings [Merck, document DE 19704478,

document DE 19732860]

•

Visible marks on the laser sensitive layer that are created through a transparent optically variable layer

for the laser [G&D, document DE 10008851] 5

•

Dark or black marks on coated paper [G&D, document DE 4243987]

•

Laser markings on paper or a paper coating containing multivalent metal oxyanions

[Sherwood, WO 02/074548] 10

• Marks due to the laser marking composition for coating paper containing pigment (multivalent metal compound) and conductive polymer [Sherwood, WO 2005/012442]

Marks for laser treatment of the substrate 15

•

 Change of paper fiber structure [PAHO, US 4,740,269]

•

Touch marks on paper or paper coating [G&D, document DE 10232786, document DE 10247591]

20 • Touch sensitivity due to a surface structure similar to an embossed pattern without removing from the surface layer [J.A. Ramos de Campos, ECB, EP 1658992]

• Reduction and bleaching of paper thickness by laser engraving [Karel Schell, US 6,395,191].

25 US 2006/0141391 A1 describes a laser mark in a value document, which comprises at least one printing ink or a layer of printing ink on a substrate, wherein the at least one printing ink

or printing ink layer comprises a laser sensitive component, and in which the printing ink in at least one area of the at least one printing ink is selectively removed by a laser, and a micro-inscription / image is produced optically the laser in a selectively removed area, and in the case where

30 otherwise the complete removal of the printing ink from the brand is performed, said micro-registration / image is produced in the brand.

According to this application, the laser sensitive component used can be any material that absorbs the energy of the laser light sufficiently in the indicated wavelength range and converts it into thermal energy. However, pigments such as mica flakes coated with one or more metal oxides are particularly preferred. The metal oxides used herein are both colorless, metal oxides of a high refractive index, such as, in particular, titanium dioxide, antimony (III) oxide, zinc oxide, tin oxide and / or zirconium dioxide, and also colored metal oxides, such as, for example, chromium oxide, nickel oxide, copper oxide, cobalt oxide and, in particular, iron oxide (Fe2O3, Fe3O4). The laser sensitive component used is

In particular, preferably antimony (III) oxide, alone or in combination with tin oxide.

As for the preparation of laser markings, the document does not specify the parameters to be used in detail, but indicates that "the parameters of the laser used depend on the particular application and can be easily determined by one skilled in the art. in the individual case. " The only example describes the use of a

45 Nd vanadate laser (1064 nm), whose power ranges from 30 to 80% in 10% steps at a speed of 500 mm / s and a frequency of 40 to 60 kHz in pulsed operation. However, the contrast and color shift effect of the laser marks that can be obtained under such conditions are comparatively low and difficult to identify.

50 DE 10 2006 057507 refers to a document having a variable optical security feature comprising effect pigments, which show different colors at different viewing angles and laser sensitive pigments, in which said document also comprises a mark laser in at least part of said coating having one of the different colors of the effect pigment set in an environment with a color shift effect.

Document WO 2005/108110 refers to a value document, particularly a banknote, comprising a sequence of layers in which visually and / or mechanically recognizable markings are introduced in the form of patterns, letters, numbers or images with The effect of laser radiation. According to the application, the layer sequence includes a labeling layer that is composed of a mixture of inks comprising a component that absorbs laser radiation and a component that is transparent to laser radiation. The marks can be recognized visually and / or mechanically as a result of an irreversible change in the optical characteristics of the mixture of inks, said irreversible change being caused by laser radiation.

5 Summary of the invention

The main objective of the present invention is to provide a process for the production of a more flexible and reliable security means for documents, especially security documents that have improved counterfeit-proof properties. Therefore, it is desirable that the security means can be authenticated from

10 an easy way and show optically striking features. At the same time, the security medium will be highly flexible with respect to its design, small in thickness in comparison and highly durable.

In the embodiment of these and other objects of the present invention there is provided a method for laser marking a document, in which a document comprising a coating containing at least one class of

15 effect pigment that shows different colors at different viewing angles and at least one class of laser sensitive pigment is treated in at least part of the area covered with a laser beam that operates in an OC mode at a speed of 500 mm / s using a power of 90%, calculated on the basis of a laser that has an average power of 12 W, and a laser mark having a fixed color is obtained, in which said fixed color is one of the different colors that They are shown at different viewing angles by the effect pigment.

20 Therefore, a highly flexible and reliable evident security means is offered for documents that have improved counterfeit-proof properties and can be identified in a very simple way, showing a striking optical appearance.

25 In particular, the document's security means allows it to easily verify its authenticity by visual inspection from different viewing angles.

Furthermore, the present invention overcomes the limitations of size, flexibility and durability of conventional security means. The document of the present invention is extremely thin, preferably more

30 fine of 100 μm. In addition, the security document of the present invention shows very high flexibility, and very high durability.

Especially suitable variables of the process for laser marking of a document of the present invention are described in the process dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the present invention. It provides a procedure for laser marking of a document, preferably a security document. The term "document", as used in this document, refers to a limited physical representation of a body of information designed with the ability (and usually the intention) to communicate. A document may manifest symbolic, diagrammatic or sensory representation information and will be understood as a paper artifact, which contains information in the form of ink marks. The term "security document", as used in this document, refers to all types of documents that contain at least one feature that can be used to avoid

45 forgery providing authentication, identification or classification of the document. In particular, they include banknotes, passports, checkbooks, identification cards, credit cards and / or debit cards.

From a technical point of view, said document may comprise various substrates, such as, for example, paper, cardboard, boards, plastics, plastic films and laminates. They are particularly suitable for applications

50 security papers containing annual plant fibers, such as cotton (for example, cotton vellum paper) or combinations of cotton fibers or mixtures of cotton fibers with plastic fibers, which may have a mono- or multilayer structure.

In accordance with the present invention, a document comprising a coating containing at least one

The class of effect pigments is treated with a laser beam under specific conditions. In this context, the expression "effect pigment" comprises all types of pigments that show different colors at different viewing angles and includes pigments with a pearl luster effect, with an iridescent interference effect and with a color shift effect.

Pearl or pearly shine pigments are well known in the art and have become very popular in creating gloss effects on coatings. The pearl luster effect is produced by the specular reflection of light from various platelet surfaces with a parallel orientation at various depths in the coating film. The light hitting the platelets is partially reflected and is partially transmitted through the

5 platelets A pearl luster effect is produced by the dependence of the reflection on a viewing angle, and the sense of depth is created by the reflection of many layers. Platelets must be extremely uniform to maximize reflected light and any surface roughness lessens the bright effect. Particles or pigments that are not thin with rough edges can also adversely affect the bright appearance.

10 Pearl shine pigments show iridescence, that is, an optical phenomenon characterized as the property of the surfaces on which changes in hue can be observed according to the angle from which the surface is seen as can be seen in soap bubbles and wings of the butterflies. Iridescence is caused by multiple reflections from multilayer, semi-transparent or transparent surfaces in which the displacement

Phase 15 and the interference of the reflections modulates the incident light by amplifying or attenuating some frequencies more than others. This procedure is the functional analogue of selective wavelength attenuation as observed with the Fabry-Perot interferometer.

The special attraction of the pearl effect pigments is the smooth and smooth color displacement effect, which is

20 unique in the art. They are very useful for security applications, since the obvious color shift feature cannot be duplicated by a copy machine.

Pearl shine pigments show optical effects, such as directed reflection, multiple reflection, interference and smooth color path (angle-dependent optical effects), which generate their optical appeal due to the

25 ability to easily orient a multitude of platelet-like particles in parallel.

In addition, several advantages derive from the use of pearl luster pigments. The first is the optical illusion of depth, which is created by the arrangement of a multiplicity of platelet-like particles of a pearl luster pigment. The impression achieved is the result of the reflection of the light at the different interfaces between the pigment and the

30 binder and in the boundary layers of the effect pigment itself. Such an effect is especially strong when large areas are outlined.

Another advantage, which can be achieved with multilayer pearl luster pigments, is the striking effect of subtle to surprising an angle-dependent color. The multilayer pigments that show such a surprising effect

35 are also called optically variable pigments.

Therefore, according to a preferred embodiment of the present invention, optically variable pigments (or optically variable effect pigments) are used as said effect pigments. Optically variable pigments are pigments that have at least two and at most four optically separated colors clearly distinguishable at least two different lighting or viewing angles, but preferably have two separate optically distinguishable colors clearly at two viewing or lighting angles. different or three optically distinct colors clearly distinguishable at three different lighting or viewing angles. In each case, the separate shades are preferably present and not the intermediate shades, that is, a clear change from one color to another is evident when tilting the security element (or the substrate coated in it

45 case) comprising optically variable pigments.

Particularly suitable effect pigments for the present invention comprise a transparent or semi-transparent platelet-shaped dielectric carrier material coated with at least one layer of a metal oxide, preferably selected from the group consisting of SiO2, Al2O3, TiO2, SnO2 , Fe2O3, Fe3O4, 50 chromium oxides, silicon hydroxide, aluminum hydroxide or magnesium fluoride. Accordingly, the dielectric carrier material is preferably selected from the group consisting of platelet-shaped silicates, such as synthetic or natural mica, talc, kaolin, glass plates, alumina flakes and SiO2 platelets. Particularly preferred are the effect pigments in which the platelet-shaped vehicle is coated with a multilayer coating comprising layers of different metal oxides having different refractive indices. More useful are the sequences of layers comprising the alternation of layers of low refraction and layers of high refraction. Accordingly, the materials mentioned above are preferably used for the metal oxide layers. In especially preferred pigments, the outer layer that has optical activity is a high refractive layer. Materials with high refractive indices are materials that have refractive indices that are equal to or greater than 1.8 at 25 ° C, while materials with indexes

Low refractions show refractive indices that are lower than 1.8 at 25 ° C. The former are represented by TiO2, SnO2, Fe2O3, Fe3O4 and chromium oxides, the latter by SiO2, Al2O3, silicon hydroxide, aluminum hydroxide and magnesium fluoride, to name just a few. With these multilayer pigments, eye-catching color effects can be achieved. The increase in refractive index is preferably greater.

5 of 0.1.

In addition to the effect pigments, the security document coating also comprises at least one class of laser sensitive pigments. In this context, the expression "laser sensitive pigments" refers to all types of pigments, which are capable of absorbing laser energy and causing reactions in the layers of

10 substrate coating. Preferably, the laser sensitive pigments are capable of absorbing more laser energy than the effect pigments.

Examples of particularly suitable laser sensitive pigments include

15 • metal compounds, especially antimony oxide (III) and / or tin oxide, zinc oxide, tin oxide and / or zirconium oxide, iron oxides, copper hydroxyphosphate, copper diphosphate, molybdenum disulfide, oxychloride of bismuth, indium tin oxide, Sn (Sb) O2, TiO2,

• anthracene, 20

•

 IR absorption materials (780 nm - 1 mm), especially perylene / rylene, pentaerythrite, carbon black and / or graphite; Y

•

 plate-shaped materials, especially transparent or semi-transparent pigments based on silicates,

Talc, kaolin, glass plates and SiO2 plates, in which the plate-shaped pigments are preferably coated with at least one oxide, selected from the group consisting of SiO2, TiO2, Sn (Sb) O2, Fe2O3 and Fe3O4.

Such laser sensitive pigments may be present together with the effect pigments in a single layer or

30 in separate layers. Preferably, at least one type of laser sensitive pigments and at least one type of the effect pigments mentioned above are present in a single layer.

The weight ratio of the effect pigments with respect to the laser sensitive pigments is preferably between 4: 1 and 1: 2.

The document can be coated in a usual way. Suitable inks containing the effect pigments and laser sensitive pigments are preferably printed on suitable substrates by usual printing or coating techniques such as embossing, gravure printing, flexographic printing, direct offset printing, indirect offset printing, pad printing, printing on low relief, printing

40 screen printing, paper coating, K coating or application with scraper blades. In addition, it is possible to apply the ink by means of varnishing in line or partially or totally out of line.

The concentration of the effect pigments in the ink is preferably between 5% by weight and 33% by weight, most preferably between 10% by weight and 20% by weight. The concentration of laser sensitive pigments

In the ink it is preferably between 5% by weight and 33% by weight, most preferably between 10% by weight and 20% by weight.

Suitable binders for inks, which will be used favorably, are:

50 a) for aqueous systems:

acrylates, methacrylates, polyesters, polyurethanes, polyvinyl alcohols, polyvinyl pyrrolidones and copolymers of said substances

55 b) for solvent based systems:

nitrocellulose, ethyl cellulose, polyamides, PVC-PVA copolymers, polyvinylbutyral, polyisobutylene, chlorinated rubber, phenolic resins modified with rosin, maleic resins, calcium / zinc resinates, EHEC, acrylates and copolymers of said substances

c) radiation curing systems (UV, EB):

epoxy acrylates, polyurethane acrylates, polyester acrylates, polyether acrylates 5 d) oil based systems:

rosin-modified phenolic resins, maleic acid modified phenolic resins, alkyd resins (eg, flaxseed oil alkyd resin), hydrocarbon resins. The binder content is preferably 10-50% by weight, based on the total weight of the liquid system.

Suitable solvents and cosolvents for inks, which will be used favorably, are:

15 a) for aqueous systems:

water, water / alcohol mixtures

b) for systems containing solvent:

Ethyl alcohol, isopropyl alcohol, n-propyl alcohol, acetone, ethyl acetate, isopropyl acetate, npropyl acetate, methoxypropanol, ethoxypropanol, toluene, aliphatic hydrocarbons, and mixtures of such solvents

c) for radiation curing systems (reactive diluents):

25 hexanediol diacrylate, di / tripropylene glycol diacrylate, trimethylpropane triacrylate, trimethylolpropane ethoxytriarylate

d) for oil-based systems: 30 mineral oils, vegetable oils and mixtures of the two classes of substance.

The solvent content is preferably 30% by weight to 70% by weight, based on the liquid system.

In accordance with the present invention, at least a part of the coating of the document containing effect pigments is treated with a laser beam. A laser is a device that emits light through a specific mechanism, so the term laser is an acronym for its acronym in English: Light amplification by stimulated emission of radiation. The laser creates a coherent and monochromatic light with low divergence.

40 A laser consists of an active medium inside an optical cavity, with a means for supplying energy to the active medium. The active medium is a material (gas, liquid, solid or free electrons) with appropriate optical properties. In its simplest form, a cavity consists of two mirrors arranged in such a way that the light bounces back and forth, each time it passes through the active medium. Typically, one of the two mirrors, the

45 output coupler, is partially transparent. The beam of the output laser is emitted through this mirror.

Light of a specific wavelength that passes through the active medium is amplified (increases in power); Surrounding mirrors ensure that most of the light passes through the active medium. Some of the light that is between the mirrors (that is, it is in the cavity) passes through the partially transparent mirror and a beam of light appears as 50. The process of supplying the energy required for amplification is called pumping and the energy is typically supplied as an electric current or as light at a different wavelength. In the latter case, the light source may be a flashing lamp or another laser. The most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

The laser used in the present invention preferably has a wavelength within the range of 157 nm to 10.6 μm, most preferably within the range of 355 nm to 10.6 μm. Particularly suitable lasers contain diode lasers (808-980 nm), Nd: YAG lasers and Nd: YVO4 lasers (355, 534 and 1064 nm) and CO2 lasers (10.6 μm). The average power of the laser is 12 W.

In accordance with the present invention, the laser operates in OC mode. In the continuous wave (OC) mode of operation, the laser output is relatively consistent with respect to time. The population inversion necessary for stimulated excitation is continuously maintained by a constant pump source.

5 In the present invention, a speed of 500 mm / s is used.

The laser power is 90%.

In the same laser radiation, the laser effect pigments interact with the laser beam. Due,

10 a laser mark is formed in which one color of the effect pigments with color shift effect is fixed in the laser radiation and the color shift effect is no longer observed after laser treatment. The fixing of a color of the effect pigment anywhere in the substrate, preferably in an environment with an unaltered color shift effect, is a unique feature, which cannot be done by printing techniques.

In the present invention, the effect pigments are only gradually removed from the laser mark, if it occurs. Preferably, more than 50% of the original amount of the effect pigments remain in the label after laser treatment, more preferably more than 80%.

The actual size of the laser mark is of minor importance in the present invention. It is possible to create both fine lines and larger areas, in which the optical effect can be observed in all marking sizes, especially when the environment is set optically variable.

The authenticity of the document of the present invention can easily be checked by visual inspection from different viewing angles.

The present invention will be further illustrated by the following examples. However, it should be noted that these examples are for illustrative purposes only and will not limit the desired scope of protection defined by the present claims.

Example

Laser marking of a layer made of ink containing laser sensitive pigments and effect pigments with fixed color effect

35 g of a plaque-effect pigment with a red-to-gold color effect (multilayer pigment based on mica) and 15 g of a laser sensitive pigment containing copper hydroxyphosphate are added to 70 g of screen printing binder MZ-varnish 093 (Proll, WeilJenburg). The mixture is homogenized and adjusted to the correct viscosity. The ink is printed on a banknote paper by screen printing on

40 silk

The laser experiments are performed with solid-state or diode lasers (wavelength range of 355 nm, 532 nm, 980 nm 1064 nm) and a gas laser, for example, CO2 laser (10.6 μm), preferably with an Nd: YAG laser and an Nd: YVO4 laser.

45 Marked areas are obtained (for example, a 5 x 5 mm rectangle) with a high contrast and a fixed red color with the following laser parameter of a Nd laser: YVO4 (1064 nm, average power of 12 W) in the OC mode. These parameters are exemplary, but are not limited to this laser system alone. For evaluation purposes, the following classification was applied.

50 1: very intense color with high brightness

Table 1: Marked areas (5 x 5 mm rectangle)

55 Marking lines with high contrast and a fixed red color are obtained with the following laser parameter of an Nd laser: YVO4 (1064 nm) in OC mode.

Table 2: Marking lines

Claims (6)

1. Laser marking procedure of a document, in which a document comprising a coating containing at least one kind of effect pigment showing different colors in different 5 viewing angles and at least one kind of laser sensitive pigment is treated in at least a part of the area covered with a laser beam that operates in OC mode at a speed of 500 mm / s using a power of 90%, calculated on the basis of a laser that has an average power of 12 W, and a laser marking that has a fixed color is obtained, in which said fixed color is one of the different colors shown at different viewing angles by the effect pigment

2.

Method according to claim 1, characterized in that said effect pigments comprise optically variable pigments.

3.

Method according to claim 1 or 2, characterized in that said pigments of

The effect comprises a transparent or semi-transparent dielectric carrier material coated with a layer of at least one oxide, wherein said dielectric carrier material is selected from the group consisting of platelet-shaped silicates, glass plates, alumina flakes and SiO2 platelets, and wherein said oxide is selected from the group consisting of SiO2, Al2O3, TiO2, SnO2, Fe2O3, Fe3O4, chromium oxides, silicon hydroxide or aluminum hydroxide.

Four.

Method according to claim 3, wherein said dielectric vehicle is selected from the group consisting of natural or synthetic mica, talc, kaolin.

5.

Method according to at least one of the preceding claims, characterized in that

Said laser sensitive pigments comprise antimony oxide (III) and / or tin oxide, zinc oxide, tin oxide and / or zirconium oxide, iron oxides, copper hydroxyphosphate, copper diphosphate, molybdenum disulfide, bismuth oxychloride, indium tin oxide, Sn (Sb) O2 and / or TiO2. 6. Method according to at least one of the preceding claims, characterized in that The weight ratio of said effect pigments with respect to said laser sensitive pigments is in the range of 4: 1 to 1: 2.