DE19613383C1 - Security hologram die made of plastic hardening while retaining flexibility - Google Patents

Abstract

A die applies micro-structures especially flat surface holograms, diffractive structures or holographic optical elements to an object. The die material is a plastic which hardens after processing while retaining flexibility. The plastic shrinks by no more than 5%, preferably 1%, and retains a surface tension of less than 0.03 N/m, preferably 0.02 N/m. The die is translucent and incorporates a transmission window for light in the UV-IR range. The plastic is a condensation-networked or addition-networked silicon polyurethane hardened by radiation. Also claimed is a process to apply the micro-structure to the die.

Description

The invention relates to an impression stamp for applying Microstructures, especially surface holograms, diffractive tive structures or holographic optical elements an object, as well as a suitable method.

Microstructures of the type mentioned, in particular surfaces holograms are widely used today. You find yourself for example on many check cards or on soft goods as proof of authenticity. Such a microstructure doors have a grid spacing of approx. 1 µm and a structure Door depth of about 0.1 to 0.2 microns, which is a printing technology Point density of 5000 to 10,000 pts / cm corresponds.

There are two types of holograms, Volume holograms and surface holograms. With volume holo the microstructure forming the hologram is internal half an optically transparent layer of thickness arranged which is much larger than the wavelength of the incident light. The microstructure thus imagines three-dimensional grid on which the light is diffracted. The Surfaces of such volume holograms are usually smooth. Surface holograms, however, and only these are of interest here as part of the present invention, who through a single microstructure level in the form of micro scopic indentations on the surface of a body educated. The body itself does not necessarily have to do this be transparent. The diffraction efficiency of surface holo gram is less than that of volume holograms, however surface holograms can be made using an impression system Duplicate pels easily.

For the perfect application of a microstructure that can be a surface hologram, for example  The object must be the impression stamp used in a series of Requirements met. Nowadays are used as impression stamps mostly so-called nickel shims used by a primal or Master hologram are generated galvanically. These nickel shims have a very stiff surface so they can Ideally, microstructure under pressure 1: 1 on the object transferred, they also have a high image quality and are therefore well able to transfer the data to be transferred Microstructure to be able to record yourself first, and you have a long service life, so that many copies without Qua loss of quality can be produced.

The materials on which microstructures use such ab stamps can be transferred are plastic films, for example polyester films, but also surface sheer papers, which under heat a plastic behavior ten show so that by means of the impression stamp the latter existing microstructure under pressure and / or tem temperature in the plastic or the laminated paper can be shaped. Radiation-curing lacquers are also included suitable to record microstructures. The impression stamp is doing so in the unpolymerized or polymerized paint layer pressed and the paint then hardens in contact with the Impression stamp. After curing, the impression stamp away. Especially with the widespread impression The impression stamp must be extremely high in foils and papers Show flatness, otherwise the differences in contact pressure become too large over the surface of the impression stamp, from which an uneven and therefore much worse impression results.

From the requirements of the known impression described above there are limitations both in terms of the procedure Materials as well as the objects on the microstructures can be applied.

The object of the invention is to achieve this to provide a solution that limits the conventional cher impression process overcomes and the impression of Mi Crostructures allowed on objects and materials that  so far could not be provided with microstructures. Un ter the term "microstructures" are intended here in particular Surface holograms, diffractive structures or hologra phical optical elements can be understood.

To achieve this object, the invention makes an impression stamp ready made from a curable and after the Cure flexible plastic, its volume shrinkage during curing is at most about 5% and which has a surface tension of less than 0.03 N / m having. This makes it possible not only to build microstructures flat objects, but also objects with a curved, three-dimensional surface. Furthermore, by using a flexible art Fabric impression stamp microstructures applied to materials be brought, for example on chocolate, on the Microstructures using conventional impression stamps are not had to be brought up.

Basically, plastic is used to manufacture the inventions appropriate impression stamp suitable for any material that is pourable, which can mold at the molecular level, d. H., which has the ability to have an extremely fine microstructure record it yourself or take it, which is flexible but dimensionally stable body is curable, that when the curing has only a small volume shrinkage, and that one has low surface tension. Such a, more flexible Impression stamp can due to its elasticity and flexibility After the impression process, there is no risk of breakage Chen materials are subtracted so that without further notice both sensitive materials and uneven surfaces as well as three-dimensional objects with microstructures verse can be hen. Due to the low surface tension there are no residues left in the impression stamp Quality of the next, reproduced by the impression stamp microstructure. The low volu Shrinking is a prerequisite for a good takeover of the Master surface hologram on the impression stamp. Preferential  the volume shrinkage for the production of Impression stamp used plastic therefore only about 1% or less and the surface tension of the plastic be carries less than 0.02 N / m.

The following is briefly the manufacture of a fiction Impression stamp used according to the method explained in the selected example, the duplication of a surface hologram should enable. The manufacturing method below does not differ at first from the production of conventional ones Nickel impression stamp. So first it is conventional In a photographic silver halide emulsion which applied to a glass plate or a plastic carrier the desired hologram is imprinted. The holographi The information then lies inside the photoemulsion as Phase or absorption grid before and is therefore not for Impression suitable. Therefore, in a second step optically a copy of the first hologram formed in a photoconductive, thermoplastic layer. To the photoconductive, thermoplastic layer is first on a conductive support, e.g. B. a metal plate and then static charge by a suitable method applied to the surface of the photoconductor. In a subsequent exposure, the charged surface of the Photoconductor with the hologram created from the beginning going diffraction pattern and an additional reference beam irradiation of the same wavelength. The interference of both Wave fields on the surface of the photoconductor lead to Be range with high and with low light intensity. To the The electrical guide increases in places of high light intensity of the photoconductor, so that at these points a charge recombination with the  are at a reference voltage or at ground potential Metal carrier takes place. In places of low light however, the original charge distribution remains largely preserved. After the exposure is finished, the Surface of the photoconductor on the holographic information containing latent charge carrier image. Because of of locally different charge concentrations prevail also locally different electrical field strengths. The thermo plastic photoconductor is now over its softening point heated. The locally different electrical field strengths result in corresponding electrostatic forces that cause the now plastic surface to change accordingly the force locally acting on them plastically deforms itself forms a surface relief. By cooling the thermoplas table photoconductor, this surface relief, which already represents the desired surface hologram. The surface hologram created in this way is also used as a master's degree surface hologram (or original hologram).

Conventionally, galvanic growth of A nickel impression on this master surface hologram stamp made. In contrast, it is used to manufacture of a plastic impression stamp according to the invention first of all Prepared plastic. The plastic used it is usually a mix of at least two compos nenten, namely binders and hardeners, immediately before Use. Alternatively, a photopolymeri sierbare plastic, the z. B. cures under UV light, ver be applied. This pourable, viscous mass can be used in a rough vacuum degassed to give a more homogeneous impression material. in the Following this, the unpolymerized mass is transferred to the Master surface hologram poured on and hardens depending on the chosen binder / hardener combination within a few Minutes or even several hours to a dimensionally stable, flexible plastic impression stamp made by the master surface hologram is subtracted.  

Particularly suitable as a plastic for the production of the inventions Impression stamp used according to the method has a Series of silicones, such as those found in dentists area. These silicones consist of two components that crosslink at room temperature. One under differentiates between condensation and addition cross-linking Guys. Both are for the purposes of the present invention well suited. Silicones of this type are subject to during their Crosslinking or curing process of only a very small amount Volume shrinkage of about 1%. These silicones also have a low surface tension and polarity are stable against cleaning agents such as soapy water and alcohols mechanically resilient and temperature resistant. The hardness (Shore hardness) of these silicones in the hardened state can between A 12 (extremely soft) and A 75 (very hard) and therefore good be adapted to the special application. Another, good suitable plastic materials are polyurethanes.

Plastic impression stamps of this type enable connection with the method according to the invention the application of micro structures on materials or objects, on the microstructure Do not apply with conventional impression stamps can. So it is for example with the invention Process possible, microstructures on edible objects or Apply materials. Examples include gelatin (in Shape of a film, as a coating or as a shaped body), fats (vegetable and animal in hardened, partially hardened or uncured form), non or slightly hygroscopic sugar, Starch (in the form of an emulsion, as a coating or as a form body), fruit gums and fruit gum mixtures, gum arabic (as a coating) and combinations of the aforementioned materials called. Only the grain size of the respective mate has a limiting effect rials, d. H. the material on which a microstructure is applied should be, with its grain size in the molecular Be move richly to absorb the microstructure. Self  if there is a coarser grit, however, a micro structure can be applied to the material if - as with Food is often the case - at least the binder (Fats, starch, sugar, emulsions, etc.) a sufficiently fine one Grain size and the coarser grit as complete as possible encloses so that the microstructure to be molded in the first Line is taken up by the binder. For a high stock Ensure the accuracy of the molded microstructures also make sure that the material on which the microstructure has been applied, not or only slightly hygroscopically is otherwise swelling of the upper due to water absorption surface layer occurs, whereby the microstructure is destroyed. Of course, materials are allowed on the microstructures have been applied, also not to be heated too much, because softening or melting of the material the microstructure also destroyed.

To protect against moisture and for increased resistance ability against mechanical influences is determined according to a preferred embodiment of the method according to the invention brought microstructure covered with a protective layer. As Protective layer is suitable for example gum arabic or also a thin layer of fat. For non-edible objects a clear coat, for example, is suitable as a protective layer Depending on the application, also flexible or particularly scratch-resistant can be.

The method according to the invention is extremely suitable for for example to apply microstructures to chocolate load. As tests in the run-up to the invention have shown, Microstructures with conventional impression stamps not on lap cola transferred because either the chocolate material breaks when the impression is pressed on, or when the chocolate mass is poured onto the impression stamp was broken when removed from the impression stamp. Furthermore  Chocolate residues adhering to the impression stamp make the impression Stamp for a subsequent subsequent, new embossing bar. The flexibility and low surface tension of the erfin plastic impression stamp according to the invention provides a remedy and allows the application of microstructures even on three dimensions sional chocolate items such as B. Easter bunnies, Easter eggs, Chocolates and the like.

To increase the luminosity of the applied microstructure this is according to an embodiment of the invention Process vapor-deposited with a thin layer of gold. The Evaporation with gold (layer thickness approx. 10 to 20 nm) is suitable both for transparent materials (e.g. gelatin) and for opaque materials (e.g. chocolate) because the thin Gold layer follows the embossed microstructure almost ideally and not covering them. Gold is also in life released medium-sized industry for use, so that micro structures on edible materials with a gold layer can be steamed. Alternatively, the one applied Microstructure with a gold or gold approved Silver paint with very fine grain (<20 nm) coated will. The color and the reflective contained in it Particles also shape the microstructure. The relative thick layer of paint, however, causes the microstructure is covered and therefore no longer from the order side is visible. Brushing with gold or silver paint is suitable therefore only for transparent microstructure carrier materials, where the luminosity of the microstructure is increased viewed from behind through the transparent support can. It is advantageous that the sensitive microstructure this alternative protected between the transparent support and the gold or silver color is.

This is made possible by the flexible plastic impression stamp The inventive method also, microstructures directly at Applying the manufacturing process of an object to this.  

So the flexible plastic impression stamp can be part of a Form blow, mold or injection mold, so that for example Plastic body (bottle, can, etc.) already in its manufacture is provided on the surface with the microstructure. It offers, for example, a company logo or another Identifying a company in this way any plastic give product to this company. Especially with smaller ones The plastic impression stamp can also cover objects Represent the mold or its lining.

Basically, with the method according to the invention shape all materials that are molecular molding by Heat and / or pressure are plastically deformable in contact are curable with the impression die and which are low Show shrinkage. Removal of the impression stamp is due the low surface tension of the plastics used and easily possible due to the flexibility of the impression stamp.

The following are a number of application examples of the given method according to the invention.

example 1

A child's lollipop made of colored but transparent material should be provided with a surface hologram that is possible should be visible as long as possible. For this, the lollipop body made of two halves, one half using the Method according to the invention with a surface hologram has been provided. The other half of the lollipop body will then connected to the first half in such a way that it serves as protection for the surface hologram is used, d. H. that the surface holo gram is inside the lollipop body. Due to the Transparency of the lollipop material is still possible To look at the hologram from the outside until the core the lollipop is destroyed by the sucking process. In a alternative embodiment, both can face each other  Provide surfaces of the lollipop halves with surface holograms be. When looking at the lollipop from different Different holograms can then be viewed from different angles will. The surface holograms are expediently on the faces of the lollipop halves facing each other somewhat into the appropriate surface sunk into it, so that damage of the holograms when the two halves of lollipop are joined together is avoided.

Example 2

A chocolate body is by means of the Ver drive with a surface hologram. To protect the Surface hologram is a on the chocolate body Layer of transparent sugar paste applied. Before that, if desired, the surface hologram can be gold-coated, to increase its brilliance.

Example 3

Chocolate bars are said to have a surface hologram be provided. For this, the mold of the chocolate bar chens or part of it through the flexible plastic impression stamp formed according to the invention. The liquid chocolate mass is poured into this form, taking care that that the temperature difference between the casting temperature and the Solidification temperature is not too high. Otherwise, can by the different expansion behavior of the impression stamp and Chocolate destroys the molded hologram in the cooling phase will. There is a temperature difference of about 10 ° C to 20 ° C but usually not critical. When filling the chocolates chocolate mass and impression stamp should be about the same have the same temperature to avoid a solidification shock the one that affects the exact impression of the surface hologram can be pregnant.  

Example 4

Gelatin is provided with surface holograms in a rotary embossing process (see FIG. 1). For this purpose, a gelatin film web 10 is guided through the nip of two rollers 12 , 14 rotating in opposite directions. The upper roller 12 carries the impression die, which here has the shape of a flexible embossing cylinder 16 . Immediately before passing through the nip, the gelatin film web 10 is slightly moistened on its upper side, onto which the surface holograms are to be embossed. This slight addition of moisture - sufficient water vapor condensing on the surface of the film web - causes the uppermost gelatin layer to soften somewhat, which favors the embossing of the surface holograms.

The above in connection with the production of gelatin foils described example can be made with minor modifications transferred the production of plastic films.

Alternatively, a gelatin foil sheet can be provided with surface holograms already during its manufacture (see FIG. 2). Liquid gelatin mass is applied to a roller 12 'via a gap-doctor system with a constant thickness, the structure of which corresponds to the roller 12 shown in FIG. 1. The applied gelatin mass hardens on the flexible embossing cylinder 16 'and is then drawn off and processed with the aid of a take-off roller 18 from the roller 12 '.

Example 5

By means of an injection mold 20 (see FIG. 3), a plastic container is to be produced, which is provided on the outside with a surface hologram. For this purpose, the flexible plastic impression die 25 is inserted into the outer mold 22 of the injection mold 20 at the desired location in such a way that the surface hologram to be molded comes into contact with the plastic 26 injected between the inner mold 24 and the outer mold 22, thus drawing the surface hologram on the outer surface of the bottle. Due to the flexible nature of the impression die 25 , the latter can also be attached in a curved region of the outer shape 22 .

Example 6

The visible surface of cathode ray tubes 30 (see FIG. 4) is to be anti-reflective. For this purpose, a transparent, curable lacquer 34 is applied to the glass surface 32 . This paint can be a two-component paint or a radiation-curing paint. The application to the mostly curved screen surface 32 can be carried out by spinning, knife coating, brushing or the like. On the not yet hardened lacquer 34 , a flexible impression die 36 adapted to the shape of the picture tube 30 is pressed in, which impresses a microstructure in the lacquer 34 , which produces destructive interference. The paint hardens in contact with the impression die 36 either by itself (in the case of a two-component paint) or by supplying suitable radiation (for example UV radiation 37 in the case of a UV-curing paint). In the latter case, the impression stamp 36 must be sufficiently transparent to the radiation used. The material for the impression die 36 is then, for example, transparent silicone. Preferably, the material of the impression die 36 is also UV-stable in order not to lose its flexibility in the context of UV radiation. After the hardening of the lacquer 34 , the impression stamp 36 is removed and is available for a further impression process.

Alternatively, in the example described last, the lacquer 34 can also be applied first to the impression stamp 36 , and then the impression stamp 36 with the lacquer 34 can be pressed onto the screen surface 32 .

Finally, the term "destructive interference" is closer explained. This is the case with "normal" surface holograms lateral distance of two neighboring wave crests in size order of about 1 µm, while the amplitude, i.e. H. the maximum extension perpendicular to the surface, about 0.1 µm is up to 0.3 µm. In so-called zero order diffraction gratings however, the lateral distance is so small that a Beu generated generated constructive interference no longer take place can. Such structures are also called "Moth eyes" known. This is based on the lattice equation

n · λ = g · sin (ϕ)

explained, in which n is the atomic number of the diffraction, λ the use the wavelength (visible range: λ = 400 nm to 750 nm), g the lateral distance, and ϕ corresponds to the angle at which the constructive interference is of the nth order. If n = 1 (first diffraction) and the color green (λ = 555 nm) results in at a distance g <555 nm there is no longer any constructive interference, since the angle ϕ no longer exists. However, it occurs destructive Interference because there are not integer multiples overlap the wavelength (1 λ, 2 λ, 3 λ,...), but 0.5 λ, 1.5 λ 2.5 λ,. . . With such structures, the reflections grade of, for example, glass plates from 4% to less than 0.5% decorate without affecting the transparency of the glass.

Claims (18)

1. Impression stamp for applying microstructures, in particular special surface holograms, diffractive structures or holographic optical elements, to an object, characterized in that the impression stamp consists of a hardenable and flexible after curing, the volume shrinkage during curing is at most about 5 % and which has a surface tension of less than about 0.03 N / m. 2. Impression stamp according to claim 1, characterized in that the volume shrinkage of art is about 1% or less. 3. Impression stamp according to claim 1 or 2, characterized in that the plastic has a surface has a tension of less than 0.02 N / m. 4. Impression stamp according to one of claims 1 to 3, characterized in that it is translucent and before preferably a transmission window for light in the range of UV to IR. 5. impression stamp according to claim 4, characterized in that the plastic is UV stable. 6. Impression stamp according to one of claims 1 to 5, characterized in that the plastic is a condensation cross-linking or addition-cross-linking silicone. 7. Impression stamp according to one of claims 1 to 6, characterized in that the plastic is radiation-hard plastic is tender.   8. Impression stamp according to one of claims 1 to 7, characterized in that the plastic is a polyurethane is. 9. A method for applying microstructures, in particular surface holograms, diffractive structures or holographic optical elements, on an in particular non-planar surface of an object, with the steps:

• Providing an impression stamp according to one of the preceding claims, the stamp surface of which is provided with the microstructure to be applied,
• - Contacting this impression stamp with the surface of the object such that the microstructure is molded on the upper surface of the object, and
• - Separation of the impression stamp from the surface of the object.

10. The method according to claim 9, characterized in that the impression stamp is a blowing, Cast or injection mold or part of such for Formation of the object forms on which the microstructure is applied. 11. The method according to claim 9 or 10, characterized in that the object to which the Mi crostructure is applied, consists of a plastic, which is hard or rubbery flexible after hardening. 12. The method according to claim 9 or 10, characterized in that the object to which the Microstructure is applied, is edible. 13. The method according to claim 12, characterized in that the surface of the object from gelatin, fat, sugar, starch, fruit gums, gum ara bicum or a combination of the aforementioned substances.   14. The method according to claim 12, characterized in that the object at least partially chocolate. 15. The method according to any one of claims 12 to 14, characterized in that after the application of the micro structure on the object the microstructure with an edba Ren protective layer is coated, especially rubber arabic or fat. 16. The method according to any one of claims 9 to 14, characterized in that after the application of the micro structure on the object the microstructure with a thin layer of gold is deposited. 17. The method according to any one of claims 9 to 16, characterized in that the applied microstructure zero order interference (destructive interference) generated. 18. edible object, characterized by a microstructure by a ver drive according to one of claims 9 to 17 has been applied is.