DE102010034085A1 - Embossing tools for microstructure elements - Google Patents

Abstract

The invention relates to a method for producing embossing tools which consist of a substrate, in whose surface embossed structures for microstructure elements, such as holograms, nanostructures or the like, are introduced. According to the invention, the embossed structures for the microstructure elements are introduced into the surface of the substrate by means of ultra-short laser pulses composed of polarized electromagnetic waves or polarized electromagnetic radiation. A surface structuring method is thus used to manufacture embossing tools for microstructure elements. This means that the original structure can be transferred directly to the surface of an embossing tool and foil prints can be made from it.

Description

The invention relates to a method for producing embossing tools, which consist of a substrate, in the surface of which embossed structures for microstructure elements, such as holograms, nanostructures or the like, are introduced.

The manufacturing method of the prior art, are produced with the embossing tools for microstructure elements, involves a relatively long process chain. First, a so-called original is produced in a photolithographic process, wherein an electron beam from an electron accelerator, a so-called e-beam system, removes material from the surface of a hardened metallic sheet of nickel. Here, a homogeneous grid is preferably written with the e-beam system and etched in quartz. Of these, copies are molded into a substrate of an inorganic-organic hybrid polymer. These copies are then processed in a photolithographic process with the laserwriter to make a lateral structuring.

The original is then copied several times galvanically to make a stamp for the production of the embossing tool. Finally, with this stamp, the motif of the original is multiplied in a recombination plant to fill the entire surface of a stamping tool. Ultimately, the embossing tool is produced as a galvanic impression of this duplicated impression.

However, this manufacturing process is very labor-intensive, time-consuming and cost-intensive. Furthermore, high investments are required for the construction of manufacturing facilities for this manufacturing process.

The invention is therefore the object of developing a generic security element such that the disadvantages of the prior art are eliminated.

This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, the embossed structures for the microstructure elements are introduced into the surface of the substrate by means of ultrashort laser pulses of polarized electromagnetic waves or polarized electromagnetic radiation. Thus, a method of surface structuring is used to produce embossing tools for microstructure elements. Thus, the original structure can be transferred directly to the surface of an embossing tool and made of it slide prints.

In the production method according to the invention, the original structure can be introduced directly into the surface of a hardened metallic sheet, so that particularly advantageously the nanostructures can be introduced directly into the surface of a stamping cylinder. The photolithographic process steps of the original production and the subsequent galvanic replication are thus eliminated in the production process according to the invention.

The period of the resulting microstructure elements depends on the wavelength of the pulsed laser radiation, but also on the pulse duration and the number of pulses of the laser radiation. The homogeneity of the quasigitter structure, the so-called ripples, is limited by the homogeneity of the focused laser beam at the surface. For example, a typical laser beam has a diameter of about 20 μm, with a larger diameter reducing the intensity at the surface of the substrate.

The resulting microstructure elements preferably have a period of about 500 nm and a depth of a few hundred nm. However, finer structures with a period of less than 300 nm are also possible.

The exact formation process of the microstructure elements or quasigitter structure is currently not fully understood. According to the current scientific opinion, it is a mixture of a self-assembly process that is triggered on the surface of the substrate by the high energy input, and the interacting order by the electromagnetic radiation of the laser light. The result is a lattice structure that shows some irregularities.

The substrate is subjected to ultrashort laser pulses so that nanostructures are formed on the substrate. In a preferred embodiment, a separating layer, for example a Trichlorosilane compound, applied to the surface of the embossing tool and finally molded the relief structure in a UV varnish on a plastic film.

The laser pulses preferably have a pulse duration of less than 50 picoseconds, ie less than 50 × 10 ^-12 seconds, preferably less than 1 picosecond, ie less than 1 × 10 ^-12 seconds, and particularly preferably about 150 femtoseconds, ie approximately 150 × 10 ^-15 seconds.

Preferably, the electromagnetic waves of the laser pulses are linearly polarized, resulting in a lattice structure whose grating lines are aligned perpendicular to the direction vector of the electromagnetic wave, the so-called E-vector, the incident laser radiation. As is known, the directional vector of the electromagnetic field of a wave is always perpendicular to its propagation direction and defines the direction of polarization of the wave. If two regions each having a different linear polarization direction are patterned and the two polarization directions are preferably perpendicular to one another, these two regions show maximum color contrast.

Alternatively, the electromagnetic waves of the laser pulses are elliptically polarized, resulting in a lattice structure whose grating lines are aligned perpendicular to the major axis of the E vector of the incident laser radiation. Here, the preferred direction of the ripple structures compared to the case of the linear polarization direction varies more and the structure appears dull.

A special case of elliptical polarization represents the circular polarization of the electromagnetic waves, resulting in a grid structure whose grid lines are aligned about 45 ° for left circular polarized and about -45 ° for right circularly polarized laser radiation, based on the plane of incidence of the laser beam.

When such structures are molded in UV varnish on a foil and as in DE 10 2009 058 243 respectively. DE 10 2009 056 933 described are coated with a multi-layer structure, the structured areas appear in different colors. The matting of the colors can be adjusted by the ripple assembly according to the invention.

Particularly preferably, the substrate consists at least on its surface of a hardened metal, in particular hardened nickel or a hardened nickel alloy, a dielectric or a ceramic.

Preferably, the embossing tools consist of a substrate which, at least on its surface, has a Vickers hardness of at least 100 HV-5 and preferably of at least 150 HV-5. The following table lists some materials and the associated Vickers hardness in HV-10: Galvanic gloss nickel 450-600 HV-10 Galvanic Matt Nickel 300-400 HV-10 titanium 300-400 HV-10 Martensite (stainless steel) 700-1200 HV-10 Chromed stainless steel 1100-2000 HV-10 Titanium nitride layer 1800-2000 HV-10 ceramics 1400-1900 HV-10 sapphire 1800-2200 HV-10

These values were determined using a stationary tester according to DIN EN ISO 6507-1: 2005 to -4: 2005 at a test load of 5 kiloponds (HV-5) and 10 kiloponds (HV-10) determined.

Microstructure elements that are produced with an embossing tool according to the invention are particularly preferably used for security elements to increase the protection against forgery of security documents, such as banknotes, securities, identity cards, credit cards, debit cards or the like. That is, with the inventive method embossing tools are produced, which in turn security elements to increase the protection against counterfeiting of security documents, such as banknotes, securities, ID cards, credit cards, debit cards or the like, or the trademark protection are produced. The protection against counterfeiting is essentially based on the fact that it is visually simple and clearly recognizable optically variable effect of the microstructures of reproduction equipment, such as color copiers, is not or insufficiently reproduced.

Reference to the following embodiments and the additional figures, the advantages of the invention will be explained. The embodiments represent preferred embodiments, to which, however, the invention should not be limited in any way. Furthermore, the representations in the figures of better understanding are highly schematized and do not reflect the realities. In particular, the proportions shown in the figures do not correspond to the conditions present in reality and serve exclusively to improve the clarity. Furthermore, the embodiments described in the following exemplary embodiments are reduced to the essential core information for the sake of clarity. In the practical implementation much more complex patterns or images can be used.

In detail, show schematically:

1 a scanning electron micrograph of a lattice structure generated by femtosecond laser pulses,

2 a device for introducing microstructures into a substrate with a laser,

3 a microstructure according to the invention in sheet steel and in this case in 3a at vertical angle of incidence the entire microstructure and in 3b a detailed view of it as well as in 3c at oblique angle of incidence the entire microstructure and in 3d a detailed view of it,

4 a cross section through a vaporized film deduction of the microstructure 3 ,

1 shows a scanning electron micrograph of a lattice structure generated by femtosecond laser pulses. It can be seen that the structure produced by femtosecond laser pulses does not have the same regularity as a photolithographically or interferometrically produced grid. Due to the relatively small spot size of the laser pulse edge effects play a major role. Therefore, the period and profile shape of the generated grating varies slightly. Profiles with a sharp rectangular shape can not be created. This affects the visual appearance. The colors are therefore duller than the color appearance of conventional grids. The first diffraction order is scattered by the fluctuation of the azimuth and period in a cone of light.

Nevertheless, high-contrast fine structures with dimensions of up to 10 μm can be produced. As a result, a hologram-like character can be reproduced. Such patterns can be molded in UV varnish on plastic films and then steamed.

• • Pulsdauer: 150 fs,
• • Wellenlänge: 800 nm,
• • Wiederholrate: 5 kHz,
• • Strahldurchmesser ca. 20 μm,
• • Energie 0,2 J/cm²–2 J/cm² (12,5 mW–140 mW),
• • linear polarisierte Strahlung,

wobei der Effekt der Oberflächenstrukturierung bereits ab Pulslängen im Bereich von Pikosekunden erfolgen kann. Eine Mehrzahl von einzelnen Laserpulsen wirkt dabei solange auf einen Bereich des Substrats ein, bis sich die gewünschte Oberflächenstrukturierung eingestellt hat.The lattice structure off 1 was generated by means of an ultrashort pulse laser, for example a Ti: sapphire laser with the following parameters:

• • pulse duration: 150 fs,
• Wavelength: 800 nm,
• • repetition rate: 5 kHz,
• • beam diameter approx. 20 μm,
• Energy 0.2 J / cm ² -2 J / cm ² (12.5 mW-140 mW),
• • linearly polarized radiation,

wherein the effect of the surface structuring can already take place from pulse lengths in the range of picoseconds. A plurality of individual laser pulses acts on a region of the substrate until the desired surface structuring has been established.

Depending on the material, a certain transfer of energy to the substrate is necessary in order to shape out the surface structuring. However, this energy input is lower than with laser ablation. Because the material is temporarily transferred to the liquid state of aggregation. Due to the electromagnetic interaction of the electron gas with the incident laser radiation, the quasiperiodic surface structure is characterized. In the laser ablation process, on the other hand, material is removed from the substrate surface by evaporation.

For processing various areas of a substrate can according to 2 the substrate 3 respectively. 3 ' relative to the laser beam of a laser 1 be moved, the laser beam by a respective deflection mirror 2 respectively. 2 ' on the substrate 3 respectively. 3 ' is steered. For a cylindrical substrate 3 For example, the relative movement can take place by rotation of the substrate in the circumferential direction. Alternatively, the relative motion may be on a planar substrate 3 ' for example, by means of a displacement table in the x and y directions. Alternatively or additionally, the laser beam may be provided by movable deflection mirrors 2 respectively. 2 ' be deflected, for example, with a scanning device, as in 2 through the double arrows on the axes of rotation of the deflecting mirror 2 respectively. 2 ' indicated.

3 shows a pattern according to the invention in the form of the lettering "PL" and a star in a substrate made of a stainless steel foil, wherein the lettering or the star have a total length of about 30 mm. The structuring of the entire surface required a time in the range of a few minutes, the laser pulses had a pulse length in the range of femtoseconds.

3a shows the entire microstructure when viewed vertically, 3c at a viewing angle of about 20 ° with respect to the normal to the substrate surface. The associated detail shots in 3b respectively. 3d show a section of the dot-shaped pattern. The visual appearance varies at different viewing angles. Thus, when viewed vertically, the lettering or the star appears dark against a light background and at the viewing angle of 20 ° with respect to the perpendicular to the substrate surface bright against a dark background.

4 shows a cross section through a film deduction of the microstructure or of the original 3 , This is an embossing stamp 4 with a release agent 5 coated, for example, a trichlorosilane compound. Subsequently, it is an impression in a UV varnish 5 on a PET film 7 generated. These UV varnish prints are metallized and finally laminated with a cover foil.

For example, the film print was vapor-deposited with a 10 nm thick aluminum layer, a 200 nm thick layer of silicon dioxide and a 10 nm thick aluminum layer. In reflection, the lettering or star appears almost black on a golden background, while in transmission the background is blue. When viewed obliquely, the lettering or star appears in green.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009058243 [0017]
• DE 102009056933 [0017]

Cited non-patent literature

• DIN EN ISO 6507-1: 2005 to -4: 2005 [0020]

Claims (8)

A method for producing embossing tools, which consist of a substrate, in the surface of which embossed structures for microstructure elements, such as holograms, nanostructures or the like are introduced, characterized in that the embossed structures for the microstructure elements in the surface of the substrate by means of ultrashort laser pulses of polarized electromagnetic waves be introduced. A method according to claim 1, characterized in that the embossing tools consist of a substrate which has a Vickers hardness of at least 100 HV-5 and preferably of at least 150 HV-5 at least on its surface. A method according to claim 2, characterized in that the substrate consists of a hardened metal, in particular hardened nickel or a hardened nickel alloy, a dielectric or a ceramic. Method according to at least one of the preceding claims, characterized in that the laser pulses have a pulse duration of less than 50 picoseconds, preferably less than 1 picosecond, and more preferably of about 150 femtoseconds. Method according to at least one of the preceding claims, characterized in that the electromagnetic waves of the laser pulses are linearly polarized, resulting in a lattice structure whose grating lines are aligned perpendicular to the E-vector of the incident laser radiation. Method according to at least one of claims 1 to 4, characterized in that the electromagnetic waves of the laser pulses are elliptically polarized, resulting in a lattice structure whose grating lines are aligned perpendicular to the major axis of the E vector of the incident laser radiation. Method according to at least one of claims 1 to 4, characterized in that the electromagnetic waves of the laser pulses are circularly polarized, resulting in a lattice structure whose grating lines are aligned about 45 ° for left circularly polarized and about -45 ° for right circularly polarized laser radiation related on the plane of incidence of the laser beam. Method according to one of the preceding claims, characterized in that the microstructure elements which are produced with the embossing tool for security elements to increase the protection against counterfeiting of security documents, such as banknotes, securities, ID cards, credit cards, debit cards or the like can be used.

Images