EP3409495B1 - Genuine colour image, thermal transfer foil for producing a genuine colour image and method for producing a genuine colour image - Google Patents

Description

The invention relates to a thermal transfer film for producing a true color image and a method for producing a true color image and a true color image.

It is known to coat substrates with effect pigments which provide a viewer with particularly brilliant colors and color effects, in particular optically variable effects that depend on the viewing and / or lighting angle. This is because effect pigments can act as a type of spectral filter when irradiated with white light and only reflect and / or transmit part of the spectrum of the incident white light. This creates brilliant color impressions. See for example US2012 / 0225775 .

The problem here is the printing of paints containing effect pigments by means of digital printing processes such as, for example, electrophotography processes or inkjet printing processes. This is problematic because the relatively large diameter of the effect pigments to be printed leads to the supply lines of the corresponding printing devices becoming clogged. This leads to production losses and the associated high financial burdens. The tendency of the effect pigments to settle in the storage containers and the supply lines of the corresponding printer must also be taken into account. Depending on the type and geometry of the effect pigments used, the corresponding printing device must be on the the expected tendency of the effect pigments to settle, so that this results in a high and incalculable development effort.

The present invention is based on the object of providing an improved method for producing a true color image, as well as a thermal transfer film that can be used for this purpose and a true color image provided thereby.

This object is achieved by a thermal transfer film according to claim 6.

This object is also achieved by a method for producing a true color image according to claim 1.

This object is also achieved by a true color image according to claim 15.

Such a thermal transfer film for producing a true color image is characterized in that the thermal transfer film has at least one effect pigment layer and a carrier film, the effect pigment layer comprising first effect pigments in one or more first areas.

Such a method for producing a true color image is characterized in that partial areas of an effect pigment layer of a thermal transfer film formed as raster dots by means of a thermal transfer print head or partial areas of effect pigment layers formed as raster points by means of a thermal transfer print head or several thermal print heads of two or more different thermal transfer foils on a first surface of a substrate for formation of the true color image are applied.

Such a true color image is characterized in that the true color image comprises a multiplicity of raster points applied to a first surface of a substrate, the raster points of partial areas of an effect pigment layer Thermal transfer foils or partial areas of effect pigment layers of two or more different thermal transfer foils are formed.

This provides a true color image which offers advantages in terms of production technology and a brilliant color impression for a viewer, in particular a brilliant optically variable color impression that depends on the viewing and / or illumination angle. Thus, the invention makes it possible to individualize very finely formed halftone dots containing effect pigments and to use them directly on the basis of an electronically or digitally available printing template without a fixed and specially produced printing form such as a printing roller, a printing screen or a printing blanket, ie using "dieless printing "or" plateless printing "on a substrate and to avoid the disadvantages outlined at the beginning. This means that the thermal transfer print head is controlled directly on the basis of the print template available electronically or digitally, which enables the digital printing of effect pigment layers.

It has also been shown, surprisingly, that the size of the individual raster points can be selected essentially independently of the size of the effect pigments used.

Studies have also shown that this can also achieve a wide variety of other advantages over the application of paints containing effect pigments by means of a printing process, such as inkjet printing in particular: It is possible to control the distribution of the pigments within the raster dot and also the alignment of the Design effect pigments or the distribution of the orientation of the effect pigments in a predefined manner and differently from raster point to raster point, which is not possible when applied in a liquid medium. This enables numerous new optical effects to be achieved.

Furthermore, it has also been shown that by appropriate application of such raster points containing different effect pigments, different distributions of effect pigments and / or different orientations of effect pigments by corresponding additive and subtractive color mixtures and optical superimposition of the effects complex, optically variable, multicolored images let generate.

Advantageous refinements of the invention are specified in the subclaims.

The first region of the effect pigment layer preferably comprises at least 90% of the area of the effect pigment layer and / or the area of the carrier film. This is particularly advantageous if the thermal transfer film is used in a thermal printing process which is aimed at a high throughput. In such methods it is advantageous if several thermal transfer foils are used and the individual thermal transfer foils each show a uniform optical effect over their entire surface. In this regard, it can also be possible and advantageous if the first region of the effect pigment layer occupies the entire area of the effect pigment layer and / or the area of the carrier film. In this context, however, it is also possible for the first area of the effect pigment layer to have partial areas in which the first effect pigments are arranged in different particle surface densities and / or orientations, and which are thus distinguished by a different optical effect.

According to a further embodiment variant, the effect pigment layer can comprise second effect pigments in one or more second regions and / or comprise third effect pigments in one or more third regions and / or comprise fourth effect pigments in one or more fourth regions. The first, second, third and / or fourth effect pigments can differ with regard to their optical effect, in particular with regard to their color effect and / or orientation. The first, second, third and / or fourth regions can be in relation to the plane spanned by the effect pigment layer be arranged side by side. Side by side can mean here that the first, second, third and / or fourth areas can be arranged directly adjacent to one another or also with a spacing or gap between them. It is possible for the first, second, third and / or fourth regions to be arranged in an iterative sequence with respect to the longitudinal extension of the effect pigment layer. For example, an effect pigment layer can have first, second and third regions lying next to one another, which are repeated in this sequence along one direction.

Such transfer foils bring advantages, in particular when using thermal transfer printing processes, which are designed for a low printing throughput. It is thus possible to achieve large color spaces and diverse optically variable effects by using one or only a few thermal transfer foils and thus also to produce individual images or small series of an individual image very cost-effectively.

The total area of the first, second, third and / or fourth areas each comprises at least 25% of the area of the effect pigment layer and / or the area of the carrier film.

The particle surface density of the first, second, third and / or fourth effect pigments is preferably essentially constant over the respective first, second, third and fourth regions. This has the advantage that the real-color image produced by thermal transfer printing reproduces the print template particularly true to the original, i.e. the homogeneous or constant properties of the effect pigments that are achieved in this way enable an equally homogeneous or constant quality of the optical effects to be achieved.

"Particle surface density" is the number of first, second, third and / or fourth effect pigments or the number of pigments per unit area in a flat area which can have a certain layer thickness, Roger that. The particle surface density of the respective effect pigments can also have statistical fluctuations over the respective first, second, third and / or fourth areas. A substantially constant particle surface density is thus also understood to mean a particle surface density distribution in the respective area which is present with a standard deviation of less than 30%, in particular less than 20%, more preferably less than 10%.

The particle surface density of the first, second, third and / or fourth effect pigments in the first, second, third and fourth regions is between 30% and 100%, in particular between 50% and 100%, preferably between 70% and 100%.

It is also possible here for the particle surface density in which the effect pigments are present in the respective first, second, third and fourth regions to be different. For example, the first region or the first regions have a first particle surface density, the second region or the second regions have a second particle surface density, etc., which is selected individually so that, for example, the first particle surface density differs from the second particle surface density.

The orientation of the first, second, third and / or fourth effect pigments is preferably essentially constant over the respective first, second, third or fourth regions or else, in particular, exhibits a statistical variation around an essentially constant mean orientation. In this case, both the mean alignment and the distribution of the alignment are preferably essentially constant over the respective first, second, third and fourth areas. This has the advantage that replicas of an original image can be produced that are particularly true to the original, that is, with a homogeneous or constant quality of the optical effects, and that a large number of optically variable effects can also be realized by means of thermal transfer printing.

The orientation of an effect pigment is to be understood as the surface normal on the sectional plane through the effect pigment, which is distinguished from the other sectional planes of the effect pigment by the maximum surface size. In the case of flake-form effect pigments, this cutting plane is thus determined by the cutting plane parallel to the main surfaces of the flake.

A substantially constant orientation is to be understood as an orientation in which the orientation of the respective effect pigments varies over the respective area by no more than 30 °, preferably no more than 20 °, more preferably no more than 10 °.

A substantially constant mean orientation is to be understood as an orientation in which the respective orientations of the effect pigments of a surface area by no more than 15 °, in particular by no more than 10 °, preferably by no more than 5 °, based on the corresponding mean Vary the orientation of the effect pigments of the surface area.

An essentially constant orientation can also be understood to mean an orientation in which the statistical distribution of the orientation around a mean orientation has a standard deviation of less than 15%, preferably of less than 10%, more preferably of less than 5%.

An essentially constant statistical variation of the alignment around a mean alignment is understood to mean a statistical variation, the standard deviations of which do not differ by more than 10%.

It is also advantageous if the orientation, the mean orientation and / or the distribution of the orientation of the effect pigments in the first, second and third and / or fourth regions differs, preferably by more than 15%. This makes it possible to use interesting optically variable effects To realize thermal transfer printing because the slightly different alignment of the effect pigments to one another can lead to a different optical appearance or to a different optical effect for each differently aligned effect pigment, which can be advantageous for special optical effects such as a slight glitter effect.

The carrier film is preferably made of PET (PET = polyethylene terephthalate). The carrier film preferably has a layer thickness between 3 μm and 30 μm, in particular between 3 μm and 15 μm. For example, the layer thickness of the carrier film can be 5.7 μm. Such a carrier film is particularly flexible. It is also conceivable that the carrier film is stretchable and / or can be rolled up. The layer thickness and / or the material of the carrier film are preferably set such that the carrier film conducts sufficient heat sufficiently quickly during thermal transfer printing from the thermal transfer print head to the layers to be transferred to the substrate.

The effect pigment layer is preferably produced on the carrier film by means of a decorative lacquer using a coating process such as gravure printing, flexographic printing or screen printing. The decorative lacquer preferably has one or more binders from the following classes of substances: polyacrylate, polyurethane, polyvinyl chloride, polyvinyl acetate, polyester, polystyrene and copolymers of the aforementioned classes of substances. Furthermore, the decorative lacquer consists of one or more solvents in which the binders are dissolved. These can be, for example, ketones such as acetone, cyclohexanone or methyl ethyl ketone. Furthermore, these solvents can be esters, such as, for example, ethyl acetate, butyl acetate and others. Furthermore, the solvents can be hydrocarbons such as. B. toluene, mineral spirits, etc. Alcohols are also conceivable, such as ethanol, 2-propanol, 1-propanol or 1-butanol. The use of an aqueous dispersion or emulsion is also conceivable. The first, second, third and / or fourth effect pigments are preferably embedded in the corresponding binder. In particular, there are up to 80 percent by weight (percent by weight = proportion of the Weight in percent of the total weight) of the solid body of the effect pigment layer composed of the respective first, second, third and / or fourth effect pigments or mixtures thereof. In such a case, it is also said that the degree of filling of the effect pigments in the solid present as an effect pigment layer is up to 80 percent by weight. A rheology additive can be provided as a further component of the effect pigment layer.

The rheology additive can in particular consist of a sheet silicate, for example a bentonite. The rheology additive can dampen or prevent the deposition and / or the settling and / or the compacting of the effect pigments. In this context, one also speaks of sedimentation of the effect pigments, which is dampened or suppressed by the rheology additive.

The sedimentation of effect pigments in a liquid medium, such as a solution of the above binders in the above-mentioned solvents, is a frequently encountered and important technical problem that must be solved by a suitable formulation, i.e. a suitable composition, of decorative lacquers in order to to prevent clogging of decorative paint supply lines or decorative paint storage containers. The size and / or shape and / or the high density of the effect pigments as solids in the liquid binders, especially compared to the above binders, leads to rapid settling and / or rapid sedimentation in relation to the dwell time of the decorative lacquer in the corresponding supply lines or storage containers. The problem of settling and / or sedimentation is, for example, with white pigments, which can have a spherical shape and / or a diameter of less than 5 μm, in particular less than 1 μm, in contrast to the first, second, third and / or fourth effect pigments as components of the decorative lacquer of the effect pigment layer not very pronounced.

The settling rate of effect pigments contained in the decorative lacquer can depend not only on the size, shape and / or density but also or exclusively on the viscosity and / or polarity of the binder and / or the rheology additive. The settling time of the effect pigments can range from a few days to a few hours. Another solution to this problem is to keep the decorative lacquer in motion by stirring and / or shaking so that the effect pigments contained therein do not settle. A combination of shaking and / or stirring the decorative lacquer and adding one or more of the above rheology additives, in particular phyllosilicates and / or bentonites, is also conceivable. Layered silicates and / or bentonites are particularly advantageous rheology additives, since they keep a possible precipitate of the effect pigments soft and in a voluminous form, so that such an effect pigment precipitate can be dissolved again by stirring and / or shaking.

It is particularly advantageous if the effect pigment layer also performs the functions of a primer layer and / or an adhesive layer. As a result, on the one hand, it is no longer necessary for the thermal transfer film to have a corresponding additional primer layer or adhesive layer which ensures that the effect pigment layer adheres after application to the substrate. Furthermore, it has also been shown that an appropriate design of the effect pigment layer can result in an improved optical result (and also the protection against forgery can be improved, since detachment of the applied raster points is made more difficult without loss of optical information.

In order to enable this dual function of the effect pigment layer, it has proven advantageous to add corresponding binders to the effect pigment layer which can be activated and / or cured by heat and / or UV radiation. It is possible that the activation in particular also generates or initiates a crosslinking reaction in the binder of the effect pigment layer. The adhesive layer formed in this way by the effect pigment layer thus represents represents an adhesive layer which, in particular, can be activated by heat and / or UV radiation (UV radiation = electromagnetic radiation from the ultraviolet part of the spectrum of electromagnetic radiation or from one or more sub-areas from the ultraviolet part of the spectrum of electromagnetic radiation) and / or curable adhesive layer. Additional curing of the binder of the effect pigment layer by means of UV radiation can preferably take place in a process step (postcuring) that takes place after the activation by heat.

Furthermore, the effect pigment layer can additionally have one or more primer and / or adhesive layers on the side of the effect pigment layer facing away from the carrier film.

The decorative lacquer for forming the effect pigment layer on the carrier film of the thermal transfer film is preferably applied to the carrier film by means of a printing process, in particular by means of a gravure printing, screen printing, flexographic printing, offset printing or pad printing process. The decorative lacquer can in particular have an organic solvent or binder or be water-based.

Furthermore, a release layer can be arranged between the effect pigment layer and the carrier film of the thermal transfer film, wherein the release layer can be applied to the carrier film by means of a printing process, in particular by means of a gravure printing, screen printing, offset printing or pad printing process. The release layer consists in particular completely or partially of a resin, preferably a silicone resin, and at least one binder, in particular an acrylate, and / or of one or more waxes. The layer thickness of the release layer is preferably in a range between 0.1 μm and 3 μm, in particular between 0.25 μm and 0.75 μm.

The layer thickness of the effect pigment layer is between 0.5 μm and 5 μm, in particular between 1 μm and 3 μm, preferably between 1.5 μm and 2.5 μm. The effect pigment layer can be provided, for example, with a layer thickness of 2 μm, the above layer thickness in particular providing an optimum with regard to a desired decorative effect of the effect pigment layer and the print cleanliness. Larger layer thicknesses of the effect pigment layer of more than 2.5 µm have a visually more brilliant and / or result in a stronger color effect or color change effect that can be perceived by an observer than effect pigment layers with layer thicknesses of less than 1.0 µm, but are more unclean during application the effect pigment layer during the subsequent thermal transfer printing, in particular in the form of raster points.

Furthermore, the effect pigment layer can additionally have absorbing inorganic and / or organic dyes and / or pigments, each of which provides the color of the dyes or pigments by absorbing a partial spectrum of the incident light. The proportion by weight of absorbent pigments in the total amount of pigments is preferably below 20%, in particular below 5%, preferably below 1%.

An effect pigment is preferably understood to be an interference pigment of any shape, which is preferably transparent and platelet-shaped and in particular has at least one interference layer.

A body is referred to as “platelet-shaped”, the two largest surfaces of which are arranged essentially parallel to one another. Thus, a flake-form effect pigment can be distinguished in particular by the fact that the two largest opposing surfaces of an effect pigment are aligned parallel to one another.

In the case of a transparent effect pigment, a first part of the light incident on an effect pigment is reflected by the effect pigment and a second part is reflected by the effect pigment incident light is transmitted through the effect pigment, with preferably only a negligible part of the incident light being absorbed.

Here, “transparent” is preferably understood to mean a transmission in the visible wavelength range of more than 50%, preferably of more than 80%, and more preferably of more than 90%.

However, one or more layers or components of the effect pigment can also be semitransparent. In particular, a portion of the incident radiation or of the incident light that cannot be neglected is absorbed.

In this context, “semitransparent” is understood to mean a transmissivity in the visible wavelength range between 10% and 70%, more preferably between 10% and 50%.

“Interference pigment” is understood here to mean a pigment which generates optical effects by means of interference from the light that strikes the pigment and is reflected and / or transmitted again. For example, interference pigments can act as interference color filters and generate one or more, in particular different colors in transmission and / or reflection. Particularly preferably, the interference pigments generate a color shift effect in the visible wavelength range that is dependent on the viewing angle or the angle of incidence of light.

Non-transparent effect pigments are, for example, effect pigments which have non-transparent layers, in particular metal layers, for example made of aluminum or of opaque color pigments. Metal effect pigments in particular have strong interference effects or color effects, but are not transparent in this case.

One or more or all of the first, second, third and / or fourth effect pigments are preferably transparent or semitransparent.

Furthermore, effect pigments preferably have an auxiliary carrier, in particular a platelet-shaped auxiliary carrier. Here, the subcarrier has at least one interference layer on at least one side. The auxiliary carrier is preferably comprehensively surrounded by one or more interference layers, it being possible for the interference layers to be arranged next to one another and / or one above the other. At least one first auxiliary layer can be arranged on the interface between the auxiliary carrier and one or more of the interference layers. The one or more sides and / or surfaces on the one or more sides and / or surfaces facing away from the auxiliary carrier preferably have at least one second auxiliary layer.

The layer thickness, in particular the mean layer thickness, of the at least one auxiliary carrier is between 100 nm and 2000 nm, in particular between 300 nm and 700 nm. The auxiliary carrier, which increases the mechanical strength of the corresponding effect pigment, preferably consists of one or more of the substances: Natural Mica, synthetic mica, aluminum oxide Al ₂ O ₃ , silicon dioxide SiO ₂ , borosilicate glass, nickel, cobalt. The at least one first auxiliary layer preferably consists of tin oxide SnO ₂ and acts in particular as a crystallization aid in the formation of the metal oxide layer or the interference layer. The at least one second auxiliary layer acts as a protective layer against chemical and / or physical interactions with the surroundings of the respective first, second, third and / or fourth effect pigment.

The layer thickness of the at least one interference layer is between 50 nm and 500 nm, in particular between 70 nm and 250 nm, the interference layer preferably consisting of one or more metal oxides, metal halides or metal sulfides, etc. Here, for example, iron oxide Fe ₂ O ₃ , zinc sulfide ZnS, silicon oxide SiO ₂ , titanium dioxide TiO ₂ , in particular in the Rutile modification, but also in the anatase modification or in the brookite modification, and / or magnesium fluoride MgF ₂ can be selected.

One or more of the interference layers of an effect pigment can provide interference effects, such as, for example, color change effects, when light is incident. These interference effects are generated here by the path differences for the incident light provided by the one or more interference layers. In particular, the color change effects based on interferences at the metal oxide / binder and / or auxiliary carrier / metal oxide boundary layers are dependent on the viewing angle and / or illumination angle of the incident light. Part of the spectrum of the incident light is extinguished by destructive interference and another part of the spectrum of the incident light is amplified by constructive interference. This effect provides an observer with a color effect when the incident light is reflected on the interference layer of the corresponding effect pigment. For such color effects or color change effects, preference is given to using materials for forming the interference layers of the effect pigments, which in particular have a higher refractive index n _D than air. One or more of the following materials are preferably used here: MgF ₂ (n _D = 1.38), SiO ₂ (n _D = 1.42 to 1.47), rutile or TiO ₂ (n _D = 2.6 to 2.9). The interference layer in particular has a refractive index between 1.2 and 4.0, in particular between 1.38 and 2.9.

One or more or all of the first, second, third and / or fourth effect pigments can be selected from: red interference pigments, green interference pigments, blue interference pigments, white interference pigments, white effect pigments, black effect pigments. "Red", "green", "blue", "white" and "black" denote the color effects of the correspondingly assigned effect pigments or interference pigments with incident light, in particular white light, for the average human eye of an observer.

Furthermore, one or more or all of the first, second, third and / or fourth effect pigments can have a spherical, platelet-like, cubic, cuboid, toroidal, disc-shaped, clod-shaped or irregular shape, the white effect pigments in particular having a spherical shape with a diameter of preferably less than 5 µm, in particular less than 1 µm. Here, one or more or all of the first, second, third and / or fourth effect pigments have a smallest diameter, in particular a mean smallest diameter, which is in particular less than 5 μm, preferably less than 2 μm.

One or more or all of the first, second, third and / or fourth effect pigments can have a largest diameter, in particular a mean largest diameter, which is between 2 μm and 200 μm, in particular between 5 μm and 35 μm. In the case of an ellipsoid-shaped effect pigment which has three semiaxes a, b, c of different sizes, so that, for example, a> b> c, the semiaxis a would correspond to the largest diameter of the effect pigment and the semiaxis c to the smallest diameter of the effect pigment.

The use of transparent or semi-transparent effect pigments has proven to be advantageous here, since particularly brilliant colors and color mixing effects can be achieved due to the low absorption or lack of absorption of the incident light and the optical effects also occurring in transmission. This is also done using both effects, namely the optical effect in reflection and transmission.

The size of the first, second, third and / or fourth effect pigments in the respective first, second and / or third regions is preferably essentially constant or has an essentially constant effect pigment size distribution.

The effect pigment size distribution of the effect pigments of the effect pigment layer and in particular in the first, second, third and / or fourth areas is preferably selected as follows:
The value of the 50% quantile of the effect pigment size distribution divides the effect pigment size distribution in such a way that 50% of the values of the effect pigment size distribution are below the value of the 50% quantile and the remaining 50% of the values of the effect pigment size distribution are above the value of the 50% quantile. Instead of a 50% quantile, any desired quantile can be selected, such as the 90% quantile or the 10% quantile. The 50% quantile is also often referred to as D ₅₀ . D ₅₀ can also indicate the mean effect pigment size. D ₅₀ means that 50% of the effect pigment sizes are smaller than the specified value. Other important parameters are D ₁₀ as a measure of the smallest effect pigment sizes (10% of the particles are smaller than the specified value) and D ₉₀ (90% of the particles are smaller than the specified value). The closer D ₁₀ and D _{90 are} together, the narrower the effect pigment size distribution, and vice versa.

The 90% quantile of the effect pigment size distribution is preferably less than 35 μm and / or the 50% quantile of the effect pigment size distribution is preferably less than 20 μm and / or the 10% quantile of the effect pigment size distribution is preferably less than 12 μm. 35% to 45% of the effect pigment sizes are preferably in a range between 6 μm and 20 μm, in particular between 10 μm and 18 μm.

Investigations have shown that the above-mentioned choice of the effect pigment sizes and their distribution make the optical effect of the applied raster points particularly effective.

One or more or all of the first, second, third and / or fourth effect pigments can advantageously be used in incident light, in particular in incident light with white Light, have a first color impression and, in particular in transmitted light, provide a different color impression, for example a second color impression that is complementary to the first color impression. The complementary color impression in transmitted light is produced in that the effect pigment reflects a certain part or area of the spectrum of the incident light at the air / interference layer and / or interference layer / auxiliary carrier interfaces and this part of the spectrum cannot transmit through the effect pigment. In the case of several interference layers, the incident light can also be reflected at the interfaces interference layer / interference layer, the number of interfaces interference layer / interference layer being the number of interference layers minus one.

For example, an effect pigment in reflected light with incident white light in reflection can extinguish all colors or spectral components of the spectrum of the incident white light except for the color green, so that a viewer perceives an effect pigment of green color in reflected light. If the viewer looks at the effect pigment in transmitted light, the viewer will perceive the complementary color, i.e. red to magenta. The remaining wavelength ranges of the originally white light are extinguished by destructive interference within the layer structure of the effect pigment.

Furthermore, the side and / or surface of the carrier film facing away from the effect pigment layer can have a back coating, in particular a slidable back coating, since the surface or surfaces of the carrier film often do not have sufficient slidability to allow the thermal transfer print head to slide over the carrier film.

The backside coating can be applied to the carrier film or to the side and / or surface of the film facing away from the effect pigment layer by means of a printing process, in particular by means of a gravure printing, screen printing, flexographic printing, offset printing, inkjet printing or pad printing process Carrier film are applied. The back coating preferably has one or more polyester resins or consists of one or more polyester resins. In addition to the components listed, the rear-side coating can also have one or more solvents, for example organic solvents, which evaporate after the coating. Furthermore, it is also possible for the back coating to be a water-based coating. The rear side coating can in particular have one or more layers of identical or different lacquers. The back coating preferably has one or more polyester resins or consists of one or more polyester resins. The layer thickness of the rear side coating is preferably in a range from greater than or equal to 0.05 μm to less than or equal to 3 μm, in particular from greater than or equal to 0.2 μm to less than or equal to 0.8 μm, and the application weight of the rear side coating is preferably in a range from greater than or equal to 0.05 g / m ² to less than or equal to 3 g / m ² , preferably from greater than or equal to 0.2 g / m ² to less than or equal to 0.8 g / m ² .

The true-color image can consist of a large number of true-color areas which, when illuminated in reflected-light observation and / or transmitted-light observation, show an assigned true color.

True color is to be understood here as a color which can be formed in particular by color mixing from one or more spectral colors. A true color image and a true color area show at least one true color when illuminated.

The true color areas of the true color image here preferably have lateral dimensions between 400 μm and 50 μm. Both lateral dimensions are preferably selected in the range between 300 μm and 50 μm and are in particular 300 μm, 250 μm or 200 μm. The size of the color area is preferably selected so that the color area is at the resolution limit of the human eye lies at the selected viewing distance and thus the color area is perceived by the human observer as a color or color area that cannot be further resolved.

Preferably, in at least 10% of the real color areas, preferably in more than 40% of the real color areas, two or more raster points are applied by means of the thermal transfer print head or the thermal print heads. These two or more raster points are formed here by partial areas of effect pigment layers which differ with regard to the optical effect and / or orientation of their effect pigments. In this case, these raster points are applied in such a way that the assigned real color is generated by additive and / or subtractive color mixing of these raster points applied in the respective real color area during illumination.

In each of the true color areas, two or more of the raster points are preferably applied next to one another and / or one above the other and / or overlapping one another on the first surface of the substrate. The true color image thus preferably has color areas in which two or more raster points are applied next to one another and / or partially and / or completely one above the other and / or overlapping. In this case, these raster points can be formed by partial areas of one and the same effect pigment layer of a thermal transfer film and / or by partial areas of effect pigment layers of different thermal transfer foils. Furthermore, these raster points can be formed by partial areas of one or different effect pigment layers which have different effect pigments, a different orientation of the effect pigments and / or a different surface density of effect pigments. A correspondingly individualized integrative optical effect for the human observer is preferably brought about by the corresponding arrangement of two or more raster points in the respective true color area due to the optical superimposition of the optical effects generated by the raster points in the respective true color area. Depending on the used Effect pigments, their alignment and surface density, as well as the type of application on top of one another, next to one another or overlapping, occur on the one hand additive and / or subtractive color mixing effects and also a specific appearance dependent on the viewing angle. With this embodiment, real-color images can thus be built from such real-color areas which, on the one hand, cover a broad color space and, furthermore, also have an individual, complexly selected, optically variable appearance.

The grid points preferably have at least one lateral dimension in the range between 40 μm and 100 μm, the lateral dimensions of the grid points preferably being between twice and five times the lateral dimension of the effect pigments.

Investigations have shown that when choosing such a grid point size, a good compromise is achieved between the fineness of the grid point and the brilliance of the optical effect generated by the respective grid point.

The following steps are preferably carried out to produce the true color image:
First, a preferably opaque motif, in particular in digital form, is provided.

The motif to be implemented as a true color image can be shaped as desired. The process can be used for both multicolored and single-colored motifs. A single-colored or multicolored motif or one or more parts of a single-colored or multicolored motif can in particular be composed of photos, images, alphanumeric characters, logos, micro-texts, portraits and / or pictograms. Any digital templates can be selected for one or more motifs. For example, a template for a motif can be used as an image file in PNG format (PNG = Portable Network Graphics) or JPEG format (JPEG = Joint Photographic Expert Group) or FITS format (FITS = Flexible Image Transport System) or TIFF format (TIFF = Tagged Image File Format). It is advantageous here that the template for a motif has at least the same resolution as the motif printed as a true color image. A better quality of the true color image can be provided if the resolution of the original of a motif is greater, in particular twice as large, than the motif printed as a true color motif.

Two or more color channels are then selected in the digital template of the motif and the gray-scale image assigned to the respective color channels is determined. For example, a first grayscale image associated with a red color channel, a second grayscale image associated with a green color channel, and a third gray scale image associated with a blue color channel are determined.

A “grayscale image” is to be understood here as an image which assigns the respective color value in the form of a corresponding gray value or brightness value of the assigned color channel to the respective image points of the motif.

The division into the color channels or the choice of color channels takes place depending on the effect pigments provided in the effect pigment layer or effect pigment layers of the thermal transfer foils or thermal transfer foil and their effect in reflection or in transmission, i.e. whether here a color mixture through additive color mixing, subtractive color mixing, as well as additive and subtractive color mixing should be achieved.

Furthermore, it is also possible for two or more color channels to be determined for different spatial areas of the observation area of the color image become. This is particularly advantageous when areas are provided in the effect pigment layer or layers in which the effect pigments have a different spatial orientation or distribution of orientation and thus have correspondingly different optical effects in the selected spatial areas.

The respective grayscale images are then converted into a respective raster image consisting of a large number of raster points using appropriate algorithms and calculation methods, for example with the aid of a specially designed RIP (RIP = Raster Image Processor). This, preferably based on a frequency-modulated grid and / or a period- or amplitude-modulated grid.

The thermal transfer print head or the thermal transfer print heads are then controlled in such a way that the partial areas of the effect pigment layer formed as raster dots are transferred to the first surface of the substrate in accordance with the size and arrangement of the raster dots of the raster images.

In this case, each of the gray-scale images or color channels is preferably assigned a thermal transfer film or an area of a thermal transfer film, for example a first gray-scale image of the first and / or the first areas, the second gray-scale image of the second or second areas, the third gray-scale image of the third or third areas and / or the fourth grayscale image of the fourth area or areas, as specified above.

The raster images are preferably provided based on a periodic rasterization with two or more different screen angles and / or two or more different screen dot shapes.

The grid point shapes are preferably selected from: point-shaped, diamond-shaped, cross-shaped. However, it is also possible to use differently shaped halftone dot shapes.

The grid width of the grid is preferably selected in the range between 35 lpi and 70 lpi.

A thermoplastic substrate such as PVC, PET, PP, PE, PA, PEN is advantageously used for thermal transfer printing. Papers and cardboard boxes are also advantageous substrates for the thermal transfer printing described here. The use of fabrics with synthetic, natural or mixed fibers for the substrate has also proven to be advantageous. The composition of the substrate is selected such that the thermal transfer film adheres to the substrate after application, in particular by means of thermal transfer printing.

The substrate can be provided as a transparent substrate so that incident light can transmit through the substrate, the transparent substrate in particular being applied with the surface opposite the first surface on a dark or black background, in particular on a colored background.

Furthermore, it is also possible for the thermal transfer printing to take place in a mirror-inverted manner on the transparent substrate. A preferably black / dark background is then applied to the printed side of the transparent substrate. As a result, the transparent substrate protects the print provided between the transparent substrate and the black background.

It has proven advantageous to use a black and / or dark and / or opaque substrate and / or a surface of a black and / or dark one and / or opaque substrate to be printed in particular by means of thermal transfer printing with a thermal transfer film. "Opaque" is understood here in particular to mean that no light or only a negligible amount of light is transmitted through an opaque material.

It has been found that in particular highly reflective, in particular light and / or white substrates, which are printed with the thermal transfer film containing first, second, third and / or fourth effect pigments, reduce the color effect of the effect pigments. This means that the color effects and / or color shift effects of the effect pigments printed on a white and / or light substrate are more difficult to detect for a viewer than if a black and / or dark and / or opaque substrate is used.

Furthermore, one or more protective layers can be applied to the first surface and / or to the surface of the substrate opposite the first surface, wherein one or more of the protective layers can be selected exclusively and / or in combinations from: transparent overprint, laminate, plastic pane, glass pane .

Furthermore, the substrate can have a base on a second surface of the substrate opposite the first surface of the substrate, the base being formed from at least one colored lacquer layer. The color value of the visible intrinsic color of the at least one color lacquer layer can be spanned in a color space, in particular a CIELAB color space, in a range of L * greater than or equal to 0 in a color space spanned by the coordinate axes a * and b * specifying the opposite colors and the coordinate axis L * specifying the brightness of the hue and less than or equal to 90 are provided.

The colored lacquer layer can advantageously have one or more dyes and / or one or more pigments, in particular one or more different colored pigments, one or more of the pigments in particular are selected from: optically variable pigments, in particular pigments containing thin film layers and / or liquid crystal layers that generate a viewing or lighting angle dependent color shift effect, organic pigments, inorganic pigments, luminescent additives, UV fluorescent additives, UV phosphorescent additives, IR phosphorescent additives, IR Upconverter, thermochromic additives. As an IR upconverter, additives are preferably chosen which, in particular, glow in the visible wavelength range of light when they are exposed to infrared radiation.

wobei gilt:

mp

= Masse eines Pigments in der Farblackschicht in Gramm,

mBM

= vorzugsweise konstant; Masse eines Bindemittels in der Farblackschicht in Gramm,

mA

= vorzugsweise konstant; Masse Festkörper der Additive in der Farblackschicht in Gramm,

ÖZ

= Ölzahl eines Pigments, insbesondere nach DIN 53199,

d

= Dichte eines Pigments, insbesondere nach DIN 53193,

x

= Laufvariable, entsprechend der Anzahl an unterschiedlichen Pigmenten in der Farblackschicht.

When using pigments in the at least one colored lacquer layer, it has proven useful to determine the pigmentation by a pigmentation number PZ, which is preferably in a range greater than ^{or equal to 1.5 cm 3} / g and less than or equal to 120 cm ³ / g, in particular greater than or equal to 5 cm ³ / g and less than or equal to 120 cm ³ / g. The pigmentation number can be defined using the following equations: $$\mathrm{PZ}={\displaystyle \sum _1^x\frac{{\left(m_{\mathrm{P.}}\times f\right)}_x}{\left(m_{\mathit{BM}}+m_{\mathrm{A.}}\right)}\mathrm{and}\mathrm{f}=\frac{\mathit{ÖZ}}{d}},$$

where:

mp

= Mass of a pigment in the colored lacquer layer in grams,

mBM

= preferably constant; Mass of a binding agent in the colored lacquer layer in grams,

mA

= preferably constant; Mass of solids of the additives in the colored lacquer layer in grams,

ÖZ

= Oil number of a pigment, in particular according to DIN 53199,

d

= Density of a pigment, especially according to DIN 53193,

x

= Run variable, corresponding to the number of different pigments in the colored lacquer layer.

In particular, it is also possible to apply further layers or layer sequences to the substrate before and / or after applying the true color image to the substrate Apply substrate, which in particular together with the motif of the true color image represent an overall motif. The other layers or layer sequences can also be applied to the substrate by means of thermal transfer foils or also by means of other methods such as, for example, gravure printing, flexographic printing, screen printing, pad printing, inkjet printing, hot stamping, cold stamping or other known methods.

The further layers or layer sequences can be, for example, transparent and / or translucent and / or opaque colored layers, transparent and / or translucent and / or opaque metallic layers (vapor-deposited and / or sputtered and / or printed), an open or embedded replication layer with diffractive and / or refractive relief structures, in particular with a transparent and / or translucent and / or opaque reflective layer arranged thereon as a thin metal layer and / or as an HRI layer with a high refractive index (HRI = High Refractive Index) and / or as an LRI layer with a Low refractive index (LRI = Low Refractive Index), a volume hologram, a transparent and / or translucent and / or opaque thin-film structure, in particular according to Fabry-Perot, with an absorption layer, spacer layer and reflective layer or other known layers or layer sequences.

For example, by means of such layers applied before and / or after the application of the effect pigment layer, individual subregions of the true color image can be accentuated or also weakened. For example, contours or partial areas of the true color image can be designed differently in this way. For example, the true color image can be embedded or inserted into an overall motif and / or into an overall pattern by means of such previously and / or subsequently applied layers, so that the true color image is arranged adjacent to the previously and / or subsequently applied layers.

The register tolerance in a first and / or in a second direction, preferably the feed direction of the thermal transfer film and / or the substrate and / or a direction perpendicular to the feed direction, between the true color image and the further layers or layer sequences is here approximately ± 0, 15 mm, preferably in the range ± 0.05 mm to ± 0.5 mm.

Aspects of various embodiments are specified in the claims.

Fig. 1

zeigt eine schematische Darstellung einer Thermotransferfolie

Fig. 2

zeigt eine schematische Darstellung von Thermotransferfolien

Fig. 3

zeigt eine schematische Darstellung einer Thermotransferfolie

Fig. 4

zeigt eine schematische Darstellung eines Effektpigments

Fig. 5

zeigt eine schematische Darstellung eines Farbraumes

Fig. 6

zeigt eine schematische Darstellung einer Thermotransferdruckvorrichtung

Fig. 7

zeigt eine schematische Darstellung einer Rasterung

Fig. 8

zeigt eine schematische Darstellung einer Rasterung

Fig. 9

zeigt eine schematische Darstellung einer Rasterung

In the following, the invention is explained by way of example on the basis of several exemplary embodiments.

Fig. 1

shows a schematic representation of a thermal transfer film

Fig. 2

shows a schematic representation of thermal transfer foils

Fig. 3

shows a schematic representation of a thermal transfer film

Fig. 4

shows a schematic representation of an effect pigment

Fig. 5

shows a schematic representation of a color space

Fig. 6

shows a schematic representation of a thermal transfer printing device

Fig. 7

shows a schematic representation of a grid

Fig. 8

shows a schematic representation of a grid

Fig. 9

shows a schematic representation of a grid

Fig. 1 shows the basic layer structure of a thermal transfer film 1.

The thermal transfer film 1 has a carrier film 12 and an effect pigment layer 11. With regard to its layer structure and the design of the individual layers, the thermal transfer film 1 is designed in such a way that the effect pigment layer 11 by means of a thermal transfer process and in particular can be applied in areas to a surface of a substrate by means of a thermal transfer print head. For this purpose, it is necessary that areas of the effect pigment layer 11 can be detached from the carrier film 12 with the local introduction of heat by means of a thermal transfer print head and, mediated by the heat, adhere accordingly to the surface of the substrate.

For this purpose, the thermal transfer film 1 is preferably designed as described below:
In addition to the carrier film 12, the thermal transfer film 1 preferably has a back coating 14, a release layer 13 and an adhesive layer 15.

The carrier film 12 preferably consists of a plastic film in a layer thickness between 3 μm and 30 μm. It has proven particularly useful to use a PET film for the carrier film 12, and in particular to use a PET film with a layer thickness of between 3 and 15 μm, for example 5.7 μm. This choice of the layer thickness of the carrier film 12 ensures that sufficient heat can be transported from the print head through the carrier film 12 to enable the subsequent layer to be transferred to the surface of the substrate.

The use of the rear-side coating 14 is also particularly advantageous here, since the surface of conventional plastic carrier films is often too rough or too dull to slide sufficiently well over the print head of the thermal transfer printer. The rear-side coating 14 thus preferably consists of a lubricious lacquer, which is preferably applied to the carrier film 12 with a layer thickness of between 0.05 μm and 3 μm, in particular approximately 0.3 μm. The rear-side coating 14 is preferably applied here by means of gravure printing. The back coating 14 preferably comprises one or more polyester resins or consists of one or more polyester resins.

The optionally provided release layer 13 improves the release property of the effect pigment layer 11 from the carrier film 12 during thermal transfer printing. The release layer 13 preferably has a layer thickness between 0.1 μm and 3 μm, more preferably between 0.25 μm and 0.75 μm. The release layer 13 here preferably consists of a resin, in particular a silicone resin, with a binder, in particular an acrylate. Furthermore, the release layer 13 can also consist of a wax or one or more waxes can be added to the release layer 13. The release layer 13 is preferably applied to the carrier film 12 by means of a printing process, in particular by means of gravure printing, screen printing, flexographic printing, offset printing, inkjet printing or pad printing.

The effect pigment layer 11 has effect pigments which are preferably embedded in a binder matrix. The effect pigment layer 11 preferably has a layer thickness between 0.5 μm and 5 μm, in particular between 1 μm and 3 μm, more preferably between 1.5 μm and 2.5 μm.

As already stated above, in addition to the effect pigments, the effect pigment layer preferably has one or more binders from the following classes of substances: polyacrylate, polyurethane, polyvinyl chloride, polyvinyl acetate, polyester, polystyrene and copolymers of the aforementioned classes of substances. Furthermore, additives, in particular rheology additives, in particular a layered silicate, preferably one or more bentonites, are preferably added to the effect pigment layer 11.

The effect pigment layer 11 preferably has a high degree of filling of effect pigments, in particular a degree of filling of more than 30 percent by weight, preferably between 50 percent and 70 percent by weight, for example 60 percent by weight, in the solid.

The addition of the rheology additive listed above is of particular importance here for the formulation of the decorative lacquer, by means of which the effect pigment layer 11 is formed on the release layer 13 by means of a coating process. In addition to the components listed, this decorative lacquer also has one or more solvents, for example organic solvents, which evaporate after the coating. It is also possible that the decorative lacquer is a water-based decorative lacquer. A printing process, in particular gravure printing, screen printing, flexographic printing, offset printing, has proven particularly useful as the coating method.

The addition of the rheology additive to the decorative varnish reduces sedimentation of the effect pigments in the decorative varnish. In contrast to absorption pigments commonly used in printing inks, such as white pigments, which have an approximately spherical shape with a diameter smaller than 5 μm, in particular smaller than 1 μm, effect pigments are usually quite large, clod-like structures. Due to the size and high density of the material, the pigments settle relatively quickly and this precipitate compacts. The settling speed depends on the one hand on the shape of the particles and on the other hand on the properties of the medium in terms of viscosity, density, polarity, etc. and can range from a few days to a few hours. As long as the print medium is kept in motion, by shaking or shaking, the dispersion is mostly retained. On the other hand, in a stationary paintwork, settling cannot usually be avoided over the long term. If such a precipitate occurs, the decisive factor is whether it is a soft, voluminous precipitate, which can be broken up again, for example, by gently stirring or shaking, or whether the precipitate is so compacted that the forces between the particles do not readily occur can be broken open by stirring or shaking. Such a compact one Print media should be avoided in any case, as further use is then hardly or not at all possible.

In order to obtain the precipitate in a soft and voluminous form, the addition of the rheology additives listed above has proven to be advantageous. These additives are preferably added to the decorative lacquer in a percentage by weight of 1 to 10, preferably 2 to 8, more preferably 3 to 5. Through the appropriate addition of this additive and also, if necessary, also appropriate accompanying measures when feeding the decorative lacquer to the printing unit, it is possible to improve the settling behavior of the effect pigments and thereby also the particle surface density within the effect pigment layer 11 as well as the alignment of the effect pigments of the effect pigment layer 11 by applying the decorative layer accordingly.

Furthermore, it is also possible for the effect pigment layer 11 to also have absorbent inorganic and / or organic dyes and / or pigments in addition to the effect pigments. These dyes or pigments preferably absorb a partial spectrum of the incident visible light and thereby generate the color of the respective dye or pigment. Furthermore, phosphorescent or fluorescent pigments and / or dyes can also be added to the effect pigment layer 11.

The proportion of absorbent pigments in the total amount of pigments is preferably below 20%, in particular below 5%, more preferably below 1%.

It has also proven useful if the composition of the effect pigment layer 11 is selected in such a way that the effect pigment layer 11 simultaneously performs the function of an adhesive layer. This makes it possible to dispense with the adhesive layer 15. This can be achieved in particular by using a binder which can be thermally activated, for example via thermoplastics, as the binder or binder component of the effect pigment layer 11 Has properties or can be crosslinked by heat and / or UV radiation. It is possible that the activation in particular also generates or initiates a crosslinking reaction in the binder of the effect pigment layer 11. Additional curing of the binder of the effect pigment layer 11 by means of UV radiation can preferably take place in a process step (postcuring) that takes place after the activation by heat.

The effect pigments used in the effect pigment layer 11 are preferably transparent, platelet-shaped interference layer pigments. As already stated above, with such transparent interference layer pigments, on the one hand, part of the incident light is preferably reflected at several interfaces of the interference layer pigment and another part of the light is transmitted through the pigment. The transmitted portion of the light is then preferably absorbed and / or reflected by the background. Such transparent interference layer pigments preferably have a transparency of more than 30%, preferably of more than 50%, in the visible spectral range.

A schematic representation of such an effect pigment is for example in Fig. 4 shown:
Fig. 4 shows an effect pigment 2 which has an interference layer 22, an auxiliary carrier 20, a first auxiliary layer 21 and a second auxiliary layer 23. The effect pigment 2 also has a platelet-like shape, the effect pigment 2 having a diameter c and a thickness or height d. The interference layer 22 also has a layer thickness a and the auxiliary carrier 20 has a layer thickness b.

The auxiliary carrier 20 essentially serves to increase the mechanical load-bearing capacity of the pigment. The auxiliary carrier 20 is preferably made of natural or synthetic mica, aluminum oxide, silicon dioxide, borosilicate glass or nickel or cobalt. The layer thickness d of the auxiliary carrier 20 is preferably in a range between 100 nm and 1000 nm.

The interference layer 22 preferably consists of iron oxide, zinc sulfide, silicon dioxide, titanium dioxide, both in the rutile and in the anatase and brookite modification, or magnesium fluoride.

The layer thickness a of the interference layer 22 is preferably selected such that interference effects occur in the visible wavelength range. For this purpose, the optical thickness of the interference layer 22 is preferably selected such that it fulfills the λ / 2 or λ / 4 condition for a wavelength λ in the range of visible light.

Optical thickness is to be understood as the product of the physical thickness and the refractive index of the layer. This means that layers with a higher refractive index have to be correspondingly less thick in order to produce the same optical thickness as a layer with a lower refractive index.

The λ / 2 or λ / 4 condition is to be understood as the path difference, i.e. the path difference (path difference) of two or more coherent waves of the incident light. This path difference is decisive for the occurrence of interference phenomena. If the path difference between two waves of the same wavelength λ and the same amplitude is exactly half a wavelength (plus any integral multiple of the wavelength), the two partial waves cancel each other out. This weakening of the intensity is called destructive interference. If it is an integral multiple of the wavelength, the amplitudes of the two partial waves add up. In this case, there is constructive interference. With values in between there is a partial cancellation.

Depending on the refractive index of the material used for the interference layer 22, the layer thickness a is therefore preferably in a range between 50 nm and 500 nm . transmitted. This also preferably results in a more or less pronounced color change as a function of the angle of incidence of the light. This color change is particularly pronounced when substances with a low refractive index are selected for the interference layer 22, whereas it is only weakly pronounced for substances with a high refractive index.

The optional first auxiliary layer 21 preferably serves as a crystallization aid in order to produce the metal oxide layer in a particularly advantageous crystal modification and can for example consist of tin dioxide.

The optional second auxiliary layer 23 can be provided in order to protect the effect pigment 2 from environmental influences. In particular, this layer ensures that a chemical and / or physical interaction of the effect pigment with the surrounding binder matrix is prevented or minimized. Furthermore, it is also possible for a colored metal oxide to be used as the second auxiliary layer 23 in order to modify the color of the effect pigment in a suitable manner.

As already stated above, the effect pigment 2 is preferably designed in platelet form. In this context, “platelet-shaped” is preferably to be understood as meaning that the upper and lower sides of the effect pigment 2 are aligned approximately parallel to one another. Furthermore, the height or thickness d of the effect pigment 2 is further significantly smaller than its diameter c. The height d of the effect pigment 2 is preferably less than 1 μm, whereas the diameter c is between 2 μm and 200 μm, preferably between 5 μm and 35 μm. In addition to a disk-shaped configuration of the platelet-shaped effect pigments, in particular the effect pigment 2, any other shape, in particular an irregular shape, an angular shape or an elliptical shape of the platelet-shaped effect pigments, is possible.

The color impression of such effect pigments is based - in contrast to absorbent pigments - essentially on interference phenomena. These are brought about by multiple reflections at interfaces of the effect pigments, for example the interface on the front and the back of the interference layer 22. It is also possible for the effect pigment 2 to have not only one interference layer 22, but an even or odd number of interference layers with different refractive indices , whereby the filter effect of the effect pigment can be adjusted correspondingly narrower.

By choosing the layer thickness of the interference layer 22, as explained above, part of the irradiated white light, which contains all wavelengths of the visible spectrum, is extinguished by destructive interference, and another part is amplified by constructive interference, which creates a corresponding color impression in reflection . A corresponding, complementary color impression then arises in transmission.

Because the effect pigments of the effect pigment layer 11 are designed as transparent effect pigments, a large part of the irradiated spectrum can be transmitted through the respective effect pigments and interact with the background or also adjacent effect pigments of the effect pigment layer. This also ensures that even if the raster points overlap on the substrate, an optical superimposition of the optical effects provided by the effect pigments of different raster points occurs.

In order to ensure this effect, it is also advantageous that the binder of the effect pigment layer 11 is also chosen such that it is transparent or largely transparent in the visible wavelength range, and in particular a transmissivity of more than 30%, more preferably of, in the visible wavelength range has more than 50%, more preferably more than 80%, based on a formation in the layer thickness of the effect pigment layer 11.

The size distribution of the effect pigments is preferably selected such that the effect pigments have a lateral dimension between approximately 1 μm to 35 μm based on the longest dimension of the effect pigment. It has also been shown that, as already stated above, the D _x value of the distributor is another important variable, where x stands for the percentage of the particles that are smaller than the specified value. The preferred range of the particles is in particular D ₉₀ 35 μm, D ₅₀ <20 μm, D ₁₀ <12 μm. This means that only a very small proportion of the effect pigments is larger than 35 µm, while 40% are in the middle range between 12 µm and 20 µm. This enables a particularly good compromise between gloss and hiding power of the effect pigment layer 11 as well as sufficient applicability of the halftone dots by means of a thermal transfer print head.

The effect pigments offered by Merck under the brand names Iriodin, Spectraval or Pyrisma can be used as effect pigments.

Several thermal transfer foils, or just one specially designed thermal transfer foil, can be used to produce the true color images.

The thermal transfer foils used can in principle on the one hand be designed in such a way that they have one or more first regions which comprise first effect pigments. The first area can preferably encompass at least 90% of the area of the effect pigment layer of the thermal transfer film and / or the area of the carrier film or also encompass the entire area of the effect pigment layer of the carrier film.

Such an embodiment is shown in FIG Fig. 2 shown:
Fig. 2 shows an example of several thermal transfer films, namely a first thermal transfer film 1a, a second thermal transfer film 1b and a third Thermal transfer film 1c. The thermal transfer foils 1a, 1b and 1c are, as in relation to the exemplary embodiment according to FIG Fig. 1 and each have an effect pigment layer 11 with first, second and third effect pigments 211, 212 and 213, respectively. The feed direction 100 of the thermal transfer foils 1a, 1b, 1c is indicated by an arrow, which preferably also provides the direction of the longitudinal extension of the thermal transfer foils 1a, 1b, 1c.

The effect pigment layer 11 of the thermal transfer film 1 a is formed identically over the entire area or at least 90% of the area of the effect pigment layer 11 or the carrier film 12 and in this area forms, for example, a first area 111 which comprises the first effect pigments 211. The thermal transfer films 1b and 1c are designed accordingly, so that their effect pigment layer 11 forms a second area 112 or a third area 113 in which the second effect pigments 212 or third effect pigments 213 are provided.

In the simplest case, the effect pigment layer 11 of the thermal transfer film 1a thus has only one type of color pigment, namely the first effect pigments 211. The second thermal transfer film 1b likewise only has only a single type of effect pigments, namely the second effect pigments 212. In the simplest case, the thermal transfer film 1c likewise has only one type of effect pigment, namely the effect pigments 213.

The first effect pigments 211, second effect pigments 212 and third effect pigments 213 preferably differ with regard to their optical effect, in particular with regard to their color effect and / or orientation. In a preferred embodiment, for example, the first effect pigments 211 are formed by interference pigments with a reddish color impression, the second effect pigments 212 by interference pigments with a greenish color impression and the third effect pigments 213 by interference pigments with a bluish color impression.

Furthermore, it is also possible that the areas 111, 112 and 113 each comprise not just one effect pigment, but a mixture of two or more different effect pigments and thus the effect pigment layers of the thermal transfer film 1a, 1b and 1c each contain a mixture of two or more effect pigments . The mixture of the corresponding effect pigments is preferably selected here such that the areas 111, 112 and 113 differ with regard to their optical effect, in particular with regard to their color effect. For example, the respective mixture of the effect pigments in the areas 111, 112 and 113 can be selected such that the areas 111 generate a red color impression, the areas 112 a green color impression and the areas 113 a blue color impression in a given viewing / lighting situation .

Furthermore, it is also possible for a thermal transfer film to encompass not just one area, but several of the areas shown above, and thus include several areas, each with a different optical effect.

For example, the embodiment shown in FIG Fig. 3 a section of a thermal transfer film 1d, which like the thermal transfer film according to Fig. 1 is constructed. This transfer film has a plurality of first regions 111, second regions 112, third regions 113, which are provided in particular in an iterative arrangement on the thermal transfer film 1d. In each of the areas 111, 112 and 113, the effect pigment layer generates a correspondingly assigned optical effect, the optical effect of the first areas 111 differing from that of the second areas 112 and the third areas 113. Correspondingly, the effect pigment layer 11 is mutually different in the areas 111, 112 and 113. The feed direction 100 of the thermal transfer film 1d is identified by an arrow, which preferably also provides the direction of the longitudinal extension of the thermal transfer film 1d.

This was preferably achieved by providing different effect pigments and / or different mixtures of effect pigments in the areas 111, 112 and 113.

By using different effect pigments or different mixtures of effect pigments in areas 111, 112 and 113, in particular a different optical color effect of the effect pigment layer is brought about in these areas, as already mentioned above with reference to FIG Fig. 2 explained.

Furthermore, it is also possible that the particle surface density of the effect pigments differs in the areas 111, 112 and 113 and / or that the orientation of the effect pigments in the areas 111, 112 and 113 is selected differently.

In particular, due to the different alignment of the effect pigments in the areas 111, 112 and 113, further interesting optical effects can be achieved in the real color image produced with the thermal transfer film 1d or the thermal transfer films 1a, 1b and 1c:
For example, it is possible that the orientation of the effect pigments in areas 111, 112 and 113 differs in that the orientation in each case has a different angle to the plane spanned by the thermal transfer film or the mean orientation of the effect pigments has a correspondingly different angle. This can lead to the effect pigments having a correspondingly different optically variable appearance and thus, for example, making special color effects and / or other optical effects in different spatial areas visible to the viewer.

Furthermore, it is also possible for the orientation of the effect pigments to have a different statistical distribution around a mean orientation in the Areas 111, 112 and 113 has. This means that, for example, the solid angle range in which the respective color effects are visible differs. Furthermore, through a correspondingly selected statistical distribution, on the one hand, special glitter effects and the like and, on the other hand, intensive color shift effects in the areas 111, 112 and 113 through a correspondingly parallel alignment.

The different orientation of the effect pigments in the areas 111, 112 and 113 can be achieved here by applying these partial areas accordingly using different printing units and further, if necessary, by appropriately influencing the orientation of the effect pigments using mechanical tools, in particular embossing tools and / or using electrical and / or magnetic fields be effected, which are applied accordingly during the printing process or during the curing of the decorative lacquer on the carrier film.

The Figure 3a shows an effect pigment layer 11 with a layer thickness e comprising an effect pigment 2 with an effect pigment size c or a largest diameter c. The effect pigment 2 is arranged tilted by an angle α with respect to the surface or plane spanned by the effect pigment layer. The effect pigment 2 lies against the first surface of the effect pigment layer 11a and the second surface of the effect pigment layer 11b. The distance between the first surface of the effect pigment layer 11a and the second surface of the effect pigment layer 11b preferably corresponds to the layer thickness e of the effect pigment layer 11. The angle γ corresponds to the angle between the surface spanned by the effect pigment layer 11 and the normal to the surface spanned by the effect pigment layer 11 .

When using effect pigments with effect pigment sizes of 1 µm to 35 µm, the D ₉₀ value (90% quantile) of the corresponding effect pigment size distribution is, for example, between 26 µm and 32 µm, the D ₅₀ value (50% quantile) is between 14 µm and 19 µm and the D ₁₀ value (10% quantile) is between 7 µm and 11 µm. Most of the effect pigment sizes are preferably between 10 μm and 30 μm. The layer thickness of the lacquer layer e, in particular the dry lacquer layer, is, for example, between 2 μm and 5 μm. Depending on the effect pigment sizes, an orientation of the effect pigments parallel to the area spanned by the substrate is preferably specified if the layer thickness of the lacquer layer e is less than or less than or equal to the effect pigment sizes of the effect pigments.

The angle α results from the sine law with $$\frac{\mathrm{e}}{\sin \left(\mathrm{\alpha }\right)}=\frac{\mathrm{c}}{\sin \left(\mathrm{\gamma }\right)}.$$

The angle α is, for example, a maximum of 3.8 ° if the angle γ = 90 °, the layer thickness e = 2 μm and the effect pigment size c = 30 μm. The angle α is, for example, a maximum of 9.6 ° if the angle γ = 90 °, the layer thickness e = 5 μm and the effect pigment size c = 30 μm. The angle α is, for example, a maximum of 11.5 ° if the angle γ = 90 °, the layer thickness e = 2 μm and the effect pigment size c = 10 μm. The angle α is, for example, a maximum of 30 ° if the angle γ = 90 °, the layer thickness e = 5 μm and the effect pigment size c = 10 μm.

The maximum angle α can provide a measure of the tilting of one or more effect pigments 2 contained in an effect pigment layer 11. The maximum possible tilting of the respective effect pigments 2 is limited by the layer thickness e of the effect pigment layer 11 and / or the effect pigment size c.

The orientation of the effect pigments 2 in the effect pigment layer 11 takes place statistically and the maximum value of the angle α is preferably the maximum Disorientation of a single pigment along a spatial axis. This value can drop further due to the influence of neighboring pigments.

An almost plane-parallel alignment, in particular a plane-parallel alignment, of the effect pigments 2 parallel to the surface spanned by the effect pigment layer 11 is preferred. An almost plane-parallel or plane-parallel alignment of the effect pigments 2 in the effect pigment layer 11 is advantageous for the most photorealistic reproduction of images possible, in particular avoiding a change in the color impression on the observer as a function of the viewing angle.

The alignment of the effect pigments 2 in the effect pigment layer 11 can be specified particularly advantageously by the production process with predetermined parameters, the use of predetermined substrates in combination with an effect pigment layer 11 that is as thin as possible.

90% of the effect pigments 2 preferably have an angle α of less than 10 ° and / or 50% of the effect pigments 2 have an angle α of less than 5 °.

Furthermore, it is also possible that the thermal transfer foils used in the method for producing the true color image include both the in Fig. 2 shown thermal transfer foils as well as thermal transfer foils Fig. 3 include, and that further also the in Fig. 2 Thermal transfer foils shown have a different orientation or particle surface density in some areas as in the case of the thermal transfer foil Fig. 3 have described.

It is particularly advantageous if the particle surface density of the effect pigments in the respective area 111, 112, 113 is essentially constant as seen over the area of the respective area. In particular, it is preferred for this purpose that the standard deviation of the particle surface density over the area of these respective regions is less than 30%, preferably less than 20%, more preferably than less 10% is. This also applies accordingly to the orientation of the effect pigments in the respective areas 111, 112 and 113 and / or with regard to the distribution of the orientation of the effect pigments in the areas 111, 112 and 113. This ensures that in the respective areas 111, 112 and 113 a similar, constant optical impression is generated in each case and the advantages already explained above are achieved in the process as a result.

As above, especially according to the figures FIGS. 1 to 4 formed thermal transfer foils are preferably used to produce a true color image. Here, partial areas of the effect pigment layer of the thermal transfer film formed as raster points using a thermal transfer print head or partial areas of effect pigment layers formed as raster points using one or more thermal transfer print heads are applied to the surface of a substrate to form the true color image. For example, one or more of the transfer foils 1a, 1b, 1c and 1d are used to produce the true color image using a thermal transfer printer which has one or more thermal transfer print heads.

The basic structure of a thermal transfer printer that can be used for this purpose is exemplified in Fig. 6 shown.

Fig. 6 shows the thermal transfer printer 3 with the thermal transfer print head 35, the heating element 35a, the counter pressure roller 36, the thermal transfer ribbon winding 37, the deflection roller 34 and the thermal transfer ribbon unwinding 32. FIG Fig. 6 the thermal transfer film 1 is shown, which is unwound from the thermal transfer film winding 32 and is fed to the print head 35 via the deflection roller 34, and is then wound up again on the thermal transfer film winding 37. Next shows Fig. 6 a substrate 31. The substrate 31 is unwound from the substrate development 30 and then fed to the gap between the counterpressure roller 36 and the print head 35 or heating element 35a. The thermal transfer ribbon handling 32, the Thermal transfer film winding 37, the counter pressure roller 36 and / or the substrate winding 30 and the print head 35 are not in Fig. 6 The control device shown is controlled in such a way that partial areas of the effect pigment layer 11 of the thermal transfer film 1 formed as raster dots are transferred to the surface of the substrate 31 facing the print head 35 by means of the print head 35 or the heating element 35a.

The print head 35 is preferably designed as a "flat head" print head. The position of the heating elements 35a (thermocouples) of the print head 35 at which the partial areas of the effect pigment layer are applied to the substrate 31 is preferably between 5 mm and 10 mm from the edge of an in particular ceramic carrier plate. The heating elements 35a are designed in particular as a heating strip on which the heating elements 35a are arranged in a line close to one another. The carrier film 12 of the thermal transfer film 1 with the remaining effect pigment layer 11 that has not been applied is preferably over an additional, in Fig. 6 Additional deflection plate (not shown) and / or an additional roller guided away from the substrate 36 upwards. The separation between the carrier film 12 and the substrate 31 takes place with a certain temporal and spatial delay after the heat has been released via the print head 35. The temporal and spatial delay can be advantageous so that the effect pigment layer 11 applied to the substrate 31 has a longer time span Can build up adhesion and only then is the carrier film 12 removed from the applied effect pigment layer 11.

It is also possible for the thermal transfer printer to use a "near-edge" thermal transfer printing process. In this printing process, the position of the heating elements 35a (thermocouples) of the print head 35 is very close to the edge of the carrier plate. The heating elements 35a are also designed here in particular as a heating strip on which the heating elements 35a are arranged in a line close to one another. The carrier film 12 of the thermal transfer film 1 with the unapplied remaining effect pigment layer 11 is without additional Deflection at a sharp angle upwards away from the substrate 31, as shown in FIG Fig. 6 is shown. The separation of the carrier film 12 from the substrate 31 therefore takes place immediately after the transfer of the partial areas of the effect pigment layer 11 from the carrier film 12 to the substrate 31 by means of the partial heating of the thermal transfer film 1 by the print head 35. The advantage of this variant is that this results in higher printing speeds let reach.

The layers of the thermal transfer film 1, in particular the effect pigment layer 11 and the optionally provided release layer 13 or adhesive layer 15, are preferably set as follows with regard to the interlayer adhesion or adhesive force to the substrate 31:
The partial heating of the thermal transfer film 1 by the heating elements 35a of the print head 35 used in the respective method causes a change in the behavior of this layer system: In the areas in which the transfer film 1 in contact with the substrate 31 is not affected by the heating elements 35a of the print head 35 is heated, the interlayer adhesion between the effect pigment layer 11 and the carrier film 12 is higher than the adhesive force between the effect pigment layer 11 and the substrate 31. In the areas in which the thermal transfer film 1 in contact with the substrate 31 is removed from the heating elements 35a of the print head 35 is heated, the corresponding activity of the thermally activated adhesive layer 15 and / or the thermally activated effect pigment layer 11 brings about an increase in the adhesive force between the effect pigment layer 11 and the substrate 31, and possibly a reduction in the adhesive force between the effect pigment layer 11 and the like nd the carrier film 12 caused by the reduced adhesive force of these two layers to one another, for example by melting on the release layer 13.

The increase in the adhesive force between the effect pigment layer 11 and the substrate 31 is set here in such a way that in these areas the adhesive force between the effect pigment layer 11 and the substrate 31 is higher than between the Effect pigment layer 11 and the carrier film 12 is. In this way, the partial areas of the effect pigment layer 11 to which heat is applied by means of the heating elements 35a of the print head 35 are applied to the substrate 31. It is also possible here for the effect pigment layer and / or the adhesive layer 15 to melt for a short time and thus to be able to enter into a particularly intimate connection with the substrate 31.

By adjusting the adhesive force of the layers of the thermal transfer film 1, as described above, this also has the effect that when the thermal transfer film 1 is peeled off from the substrate 31, the partial areas of the effect pigment layer 11 heated by the heating elements 35a of the print head 35 remain on the substrate 31 and the remaining partial areas the effect pigment layer 11 with the carrier film 12 are detached from the substrate 31.

As already stated above, the thermal transfer printer 3 can have not only one print head 35, but also several print heads 35. It is also possible here for a thermal transfer film from a number of thermal transfer films used to be assigned to each of these multiple print heads 35, or for the same thermal transfer film to be fed to multiple print heads 35.

This one or more print heads 35, the feeding of the one or more thermal transfer foils 1 and the feeding of the substrate 31 are controlled as follows depending on the thermal transfer foils used and the real color image to be produced:
During the print preparation, the print template, which, as shown above, is preferably a single or multi-colored motif to be displayed as a true-color image, is first broken down into its color channels.

As already explained above, the color channels are based on the one or more thermal transfer foils used to produce the true color image. So will A color channel is preferably assigned to each of the available areas of the one or more transfer foils, which have a different optical effect.

These color channels can thus represent both color channels of a customary color model, for example RGB, that is to say a red color channel, a green color channel and a blue color channel. As a result, the respective color of the respective color channel is generated from the respective area of the thermal transfer film through the effect pigments provided there.

Furthermore, however, it is also possible and advantageous to define and provide corresponding color channels that take into account the optical color effect in a predefined viewing angle range or additional optical effects in addition to the color effect, for example glitter effects, etc. For example, several color channels can be assigned to one and the same color, For example, a first color channel with a corresponding color effect in a first viewing angle range, a second color channel with the same color effect in another viewing angle range, and a third color channel with a corresponding color effect, but superimposed, for example, by a glitter effect, also in a special viewing angle range.

The corresponding breakdown of the motif into the color channels can also be based on further information on the desired optically variable effects of the motif or, if appropriate, based on a three-dimensional representation of the motif.

For each of the color channels, an assigned grayscale image is determined in the digital template of the motif and the information that may still be available. In a preferred case, there is thus a first gray-scale image for a red color channel, a second gray-scale image for a green color channel, and a third gray-scale image for a blue color channel.

The respective grayscale images are then converted into a respective raster image consisting of a large number of raster points using appropriate algorithms and calculation methods, for example with the aid of a specially designed RIP (RIP = Raster Image Processor). The size of these raster points preferably corresponds to the size of the individual pixels which can be resolved by the print head used. Such a raster image can consist of a binary black-and-white bitmap, for example.

In this conversion, the grayscale image is preferably divided into halftone cells. Each grid cell comprises a certain number of binary pixels, namely the grid points. The gray level or color level of the respective color channel is simulated by the grid points provided in the respective grid cell.

The conversion of the grayscale image into the respective raster image can be implemented using various raster methods.

For example, with the amplitude-modulated screening with screen cells of a fixed size and with a fixed raster width, i. H. Period, successive grid cells rasterized. The individual raster points thus comprise one or more of the individual pixels that can be converted by the print head 35. The respective gray level is simulated within the grid cell by means of a variable size of the individual grid points. The grid points are varied in size and can also have different shapes (for example point shape, diamond shape, cross shape). The size of the grid determines the area occupied by the grid points within the grid cells and thus the color gradation or gray gradation of the grid.

Another method is frequency-modulated rasterization with fixed, predetermined raster point sizes, but with a varying spacing of the raster points in the x and y directions and / or in the feed direction and perpendicular to the feed direction of the Substrate. In this case, the size of the raster points preferably corresponds to the size of the individual pixels that can be converted by the print head 35. This results in a quasi-random distribution of the distances between the raster points, which is why this rasterization can also be referred to as stochastic rasterization.

When determining the parameters of the rasterization, it is necessary to consider on the one hand what fineness the representation should have, in particular is necessary for fine image details, and on the other hand how graduated the respective color should be. The finer the screen ruling, the better the display of fine image details. The finer the selected grid width, the smaller the grid cells generated and the fewer pixels available for varying the grid points in the respective grid cell. Since the respective gray level or color gradation of the color channel is to be simulated within the respective raster cell, it is advantageous that as many pixels as possible are available for simulating as many fine gray gradations as possible. The fewer pixels there are in the grid cell, the fewer color gradations can be simulated in the grid cell. The fewer color gradations are available, the less realistic or natural the real color image appears, in particular due to sound separation effects (so-called posterization or posteration).

If, for example, the real color image is to be executed with a resolution of 300 dpi (dpi = dots per inch, pixels per inch), it has proven useful to rasterize the color channels with a screen ruling of 35 lpi to 70 lpi (lpi = lines per inch, Lines per inch), especially amplitude modulated. This results in raster cells with sizes between 8 x 8 pixels (35 lpi) and approx. 4 x 4 pixels (70 lpi). With 8 x 8 pixels, 64 shades of gray can be displayed per color channel. With 4 x 4 pixels per color channel, 16 color gradations can be displayed per color channel.

In Fig. 8 a section from a raster image is now illustrated, which by means of the method of amplitude-modulated rasterization outlined above from a surface has been determined with 50% gray gradation or color gradation for one of the color channels:
Thus, a representation 5 shows such a surface section of the raster image, a representation 50 a section of the representation 5 enlarged by 500% and a representation 500 a section from the representation 5 enlarged by 500% with the representation of a single raster cell 502. This is based on the the examples given above with a screen ruling of 70 lpi. The representation 500 here exemplifies the raster cell 502, which comprises 4 × 4 pixels and has the raster point 501, which is formed by the area of the pixels designed in white.

Fig. 9 illustrates the corresponding section from the raster image for the screen ruling of 35 lpi set out above. Representation 5 shows the section from the raster image. The representation 50 shows a section enlarged by 500% and the representation 500 shows a section enlarged from this by a further 500% with the raster cell 502, which comprises 8 × 8 pixels, and has the raster point 501.

It is also possible to use other raster methods for determining the raster image. For example, a frequency-modulated screen can be used which has no fixed screen cells. In this case, the rasterization follows only on the basis of the print resolution 300 dpi with correspondingly free positioning of the individual pixels or raster points.

Fig. 7 shows an example of a representation 4 of such a section of a raster image screened by means of frequency-modulated screening, also called “diffusion dither”, corresponding to a gray gradation or color gradation of 50%. The representation 40 shows a section thereof enlarged by 500%, with the individual raster points or individual pixels 501.

A resolution of 600 x 600 dpi corresponds in particular to a pixel size of 42 µm x 42 µm and a resolution of 300 x 300 dpi corresponds in particular to a pixel size of 84 µm x 84 µm. If the mean largest diameter of the effect pigments is, for example, between 1 µm to 35 µm, then it is advantageous that within a pixel several effect pigments can be arranged partially or completely as well as one above the other and / or next to one another in order to achieve the most brilliant possible optical effect per pixel ( and thus per color channel). The smaller the effect pigments used, the more effect pigments can be arranged, in particular, within a pixel, and the lower the typical pearlescent effect that can be generated is preferably. The larger the effect pigments, the stronger the pearlescent effect, in particular, and the fewer effect pigments that can preferably be arranged within a pixel. For example, about 1 to about 7000 effect pigments, preferably about 10 to about 1000 effect pigments, particularly preferably about 10 to about 500 effect pigments, can be arranged partially or completely and one above the other and / or next to one another within a pixel.

To generate the true color image on the substrate from the raster image of the color channels, the color channels must be combined with one another by applying the raster points accordingly on the substrate so that the true color image is created through additive and / or subtractive color mixing of the raster points, and in particular the selected true color image or motif arises. This is implemented in that the print heads or feed device are controlled in such a way that the raster images assigned to the color channels and thus raster points are applied to the substrate in a correspondingly accurate register with one another. In such a way that a corresponding local color mixing can take place.

Register or register or register accuracy or register accuracy is understood to mean a positional accuracy of two or more elements and / or layers relative to one another. The register accuracy should move within a specified tolerance and at the same time be as low as possible. At the same time, the register accuracy of several elements and / or layers to one another is an important feature in order to increase process reliability. The positionally accurate positioning can take place in particular by means of sensory, preferably optically detectable, register marks or register marks. These registration marks or register marks can either represent special separate elements and / or areas and / or layers or can themselves be part of the elements and / or areas and / or layers to be positioned.

The corresponding activation takes place in particular in such a way that the real color image has a multiplicity of real color areas which, when illuminated in reflected light observation and / or transmitted light observation, show an assigned real color to the human observer. This true color is generated in each case in particular by additive and / or subtractive color mixing of the raster points applied in the respective true color area during illumination.

With the above-described grid cells consisting of 8 x 8 pixels per color channel and 64 color gradations per color channel, for example, with three color channels 64 x 64 x 64 = 262144 color tones are created. With the above-described grid cells of 4 x 4 pixels per color channel and 16 color gradations per color channel, with three color channels 16 x 16 x 16 = 4096 color tones are available, which are available for a respective true color image. With this large number of color tones, realistic and natural-looking true-color images can be generated.

Furthermore, it has proven to be advantageous not to choose the rasterization too fine, in particular to choose the rasterization in the above-described areas between 35 lpi and 70 lpi. It has been shown that if the pixels or raster points are too fine, the reproduction of details is reduced and the individual pixels are inaccurate, which falsifies the color reproduction.

The methods described above are preferably carried out by means of a corresponding image processing software which can be carried out on the controller of the printer 3 or separately on an external computer.

Based on the specific raster images for the individual color channels as set out above, the printer 3 can be controlled to carry out the method as described below:
If the printer 3 has only one print head 35 which is arranged transversely to the feed direction, ie the print line transversely to the feed direction, the following procedure is recommended:
On the one hand, it is possible to use different thermal transfer foils, each of which is coated over the entire surface with an effect pigment layer which has a uniform optical appearance. Each of these thermal transfer foils is assigned to one of the color channels. In the case of these thermal transfer foils, for example, it can be based on Fig. 2 the thermal transfer foils 1a, 1b and 1c explained.

In a preferred embodiment, the effect pigment layer of a first film when illuminated (and at a predetermined angle) shows the color impression red, a second of the thermal transfer foils shows the color impression green and a third of the thermal transfer foils shows the color impression blue.

First, the raster image assigned to the color channel of the first thermal transfer film, for example the color channel red, is sent to the control of the printer. This controls the printhead 35 in such a way that the raster dots assigned to this raster image, consisting of partial areas of the effect pigment layer of the first thermal transfer film (for color channel red), are applied to the substrate 31, in particular to a black substrate 31, by means of the printhead 35. After the application, the first thermal transfer film is against the second Thermal transfer foil (for color channel green) replaced. The substrate 31 is moved back to the starting position. The raster image, which is assigned to the second color channel, for example the green color channel, is then sent to the control of the printer. The assigned raster points are then applied in the same way by means of the print head 35 by appropriate application of partial areas of the effect pigment layer of the second thermal transfer film. This is repeated in the same way in a third step with the third thermal transfer film and the third color channel, for example for the blue color channel.

The positioning of the substrate 31 at the starting position is preferably carried out by means of a stepping motor which controls the substrate advance. Two variants have proven themselves here:
In the first variant, the substrate 31 has a perforation in at least one edge area into which corresponding retaining lugs engage. The substrate 31 is then moved forwards and backwards via this mechanical toothing.

In the second variant, the substrate 31 has no perforation. It is clamped mechanically between two rollers and fixed there during the entire forward and backward advance so that the forward path is known and can be moved back again accordingly.

The register tolerance in the feed direction and / or perpendicular to the feed direction is approximately ± 0.15 mm, preferably in the range ± 0.05 mm to ± 0.5 mm.

Furthermore, it is also possible to use only a single thermal transfer film in such a printer, which film has several areas with different optical effects, in particular color effects. This thermal transfer film can, for example, like the thermal transfer film 1d according to Fig. 3 be trained. So If this thermal transfer film has, for example, an iterative arrangement of areas 111, 112 and 113, which are each assigned to a different one of the color channels and, for example, reproduce the color red, green or blue when illuminated. The size of the areas is preferably based on the length of the image to be printed or the motif to be printed. This single thermal transfer film can also have additional areas, for example for an additional color white or black or another bright color or an optically variable color or optically variable layer sequences or for a protective lacquer that is applied over the real color image partially or over the entire surface after the real color image has been applied becomes.

The individual color channels are printed one after the other in the same way as described above by corresponding transmission of the respectively assigned raster image to the control of the printer and, after each printing of a color channel, the substrate 31 is moved back to the starting position. There is no need to change the thermal transfer film due to the special design of the thermal transfer film, as described above.

It is also advantageous if the printer has a plurality of separate print heads 35, each with an assigned transfer film. A print head 35 with an associated thermal transfer film 1 is preferably provided here for each of the color channels. The print heads 35 are positioned here one after the other, so that the raster points of the individual color channels are applied one after the other to the substrate 35 without the substrate 35 having to be moved back to the starting position. The distance between the print heads 35 in the printer is preferably known and fixed here and is taken into account accordingly during printing. The register tolerance in the feed direction and / or perpendicular to the feed direction is around ± 0.1 mm, preferably in the range between ± 0.05 mm to ± 0.5 mm.

Furthermore, it is also possible for the printer to have a print head 35 which is arranged along the feed direction, ie the print line along the feed direction.

With such an arrangement it is advantageous to use several different thermal transfer foils. An assigned thermal transfer film is preferably used for each of the color channels, each of which, as already described above, is formed over the entire surface with an effect pigment layer which exhibits an optical effect assigned to the respective color channel. The print head 35 prints a corresponding strip of the substrate 35 corresponding to the print head width, here preferably with all color channels. The substrate 31 remains positioned until all of the color channels have been printed. Thereafter, the substrate 31 is shifted by a predetermined amount (print head width). The thermal transfer film is preferably changed automatically. The register tolerance in the feed direction and / or perpendicular to the feed direction is approximately ± 0.1 mm, preferably between ± 0.05 mm to ± 0.5 mm.

As already explained above, the optical appearance of the true color image is also determined by the substrate 31. With regard to the substrate used, in particular the substrate 31, there are in particular the following advantageous design variants:
It is thus possible for the substrate 31 to be made black or dark and / or to be applied to a black or dark surface. Due to the black or dark background thus formed by the substrate, the light not reflected by the effect pigments is absorbed or to a large extent absorbed. As a result, essentially only the part of the spectrum reflected by the effect pigments can be seen in reflection, as a result of which a very pure and intense color impression is produced.

Furthermore, it is also possible for the substrate to have a highly reflective property, for example to have a metal layer or a white colored layer or white colored area. This has the effect that part of the light transmitted through the effect pigments of the raster points is reflected on this background. This allows interesting color effects realize. This is because when using transparent effect pigments, as explained above, the color spectrum differs in terms of transmission and reflection and so the color generated by the effect pigments in transmission or in reflection becomes visible as a function of the angle.

Furthermore, it is also possible for the substrate to form a colored background or to have colored areas which, for example, only reflect part of the irradiated spectrum. In this way, in combination with the overlying effect pigments provided in the raster points, it is possible to change the color impression in a targeted manner.

Thus, the substrate preferably has at least one colored lacquer layer, which can be provided over the entire surface or in the form of a pattern on the substrate. The lightness L * of the at least one colored lacquer layer is preferably in the range from 0 to 90. The lightness L * is preferably measured according to the CIELAB form L * a * b * under the following conditions:
According to geometry: Diffuse / 8 degrees according to DIN 5033 and ISO 2496 Diameter of the measuring opening: 26 mm Spectral range 360 nm to 700 nm according to DIN 6174, standard illuminant: D65.

The Figure 5 shows in the upper part of the Figure 5 a two-dimensional coordinate system spanned by the coordinate axes a * and b *, which is referred to here as "a *, b * chromaticity diagram". The color values on the axis a * range from green ("green") in the negative area to red ("red") in the positive area of the possible values of a *. Furthermore, the color values on the b * axis range from blue (“blue”) in the negative area to yellow (“yellow”) in the positive area of the possible values of b *.

Next shows the Figure 5 in the lower part of the Figure 5 a three-dimensional one spanned by the coordinate axes L *, a * and b * Coordinate system, which also includes the two-dimensional coordinate system spanned by the axes a * and b *. The color values on the axis a * range from green ("green") in the negative area to red ("red") in the positive area of the possible values of a *. Furthermore, the color values on the b * axis range from blue (“blue”) in the negative area to yellow (“yellow”) in the positive area of the possible values of b *. Furthermore, the brightness values on the L * axis range from black in the negative area to white in the positive area of the possible values of L *.

The individual colored lacquer layers can be colored with dyes and / or pigments. Pigments are to be preferred to dyes because of their usually higher hiding power.

For coloring the pigments, it is advantageous if the pigmentation of the at least one colored lacquer layer is selected so that a pigmentation number PZ in the range from 1.5 cm ³ / g to 120 cm ³ / g, in particular from 5 cm ³ / g to 120 cm ³ / g. The pigmentation number PZ is calculated here as already explained above.

As already explained above, it is advantageous with regard to the color effect of the true color image if the substrate is made black or dark or has a correspondingly black or dark layer.

However, it is also possible to combine the above-described alternative embodiments of the substrates with one another. For example, a substrate can be provided which is made black or dark in areas, is heavily reflected in areas or is white in areas and is provided with differently colored lacquer layers in areas. The corresponding design or the preprinting of the substrate can further influence the visual appearance of the true color image and thereby generate further optically variable effects which can only be imitated with difficulty by other methods.

In particular, it is also possible to apply further layers or layer sequences to the substrate 31 before and / or after applying the true color image to the substrate, which together with the motif of the true color image represent an overall motif. The further layers or layer sequences can also be applied to the substrate 31 by means of thermal transfer foils or also by means of other methods such as, for example, gravure printing, flexographic printing, screen printing, pad printing, inkjet printing, hot stamping, cold stamping or other known methods.

The further layers or layer sequences can be, for example, transparent and / or translucent and / or opaque colored layers, transparent and / or translucent and / or opaque metallic layers (vapor-deposited and / or sputtered and / or printed), an open or embedded replication layer with diffractive and / or refractive relief structures, in particular with a transparent and / or translucent and / or opaque reflective layer arranged thereon as a thin metal layer and / or as an HRI layer with a high refractive index (HRI = High Refractive Index) and / or as an LRI layer with a Low refractive index (LRI = Low Refractive Index), a volume hologram, a transparent and / or translucent and / or opaque thin-film structure, in particular according to Fabry-Perot, with an absorption layer, spacer layer and reflective layer or other known layers or layer sequences.

For example, by means of such layers applied before and / or afterwards, individual partial areas of the true color image can be accentuated or also weakened. For example, contours or partial areas of the true color image can be designed differently in this way. For example, the real color image can be embedded or inserted into an overall motif and / or into an overall pattern by means of such previously and / or subsequently applied layers, so that the true color image can be arranged adjacent to the layers applied before and / or afterwards.

For example, functional layers can also be applied subsequently to the true color image by means of such previously or subsequently applied layers, for example in the form of a transparent protective lacquer to seal the true color image, in particular by means of thermal transfer printing, hot stamping or cold stamping. It is also possible to apply an adhesion promoter layer or primer layer to the substrate before the true color image is applied.

The register tolerance in the feed direction and / or perpendicular to the feed direction between the true color image and the further layers or layer sequences is approximately ± 0.15 mm, preferably in the range ± 0.05 mm to ± 0.5 mm.

Furthermore, it is also possible and advantageous if, in addition to the above-described transfer films with an effect pigment layer, one or more thermal transfer films are used which have a transfer color layer which does not contain any effect pigments. For example, it is possible, by means of the printer, to additionally apply raster points to the substrate which have dyes and / or pigments which are based on absorption of the incident light. For example, it is possible to additionally use a thermal transfer film which has a transfer layer formed by a white lacquer layer.

Furthermore, it is also possible for further processing steps to be carried out to produce the true-color image after the substrate has been printed.

It is thus possible, for example, for the substrate to be a transparent substrate, the front side of which is printed with the printer 3. Then the substrate is applied with the back on a preferably black / dark background and the back in another Process printed, in particular to provide a multicolored background, as set out above.

Furthermore, it is also possible for the printing with the printer 3 to be mirror-inverted on the transparent substrate. A preferably black / dark background is then applied to the printed side of the transparent substrate. As a result, the transparent substrate protects the print provided between the transparent substrate and the black background.

To improve the resistance, the substrate printed with the printer 3 can also be protected on one or both sides with additional transparent overprints, laminates, plastic or glass panes.

List of reference symbols

1

Thermal transfer foil

1a

First thermal transfer film

1b

Second thermal transfer film

1c

Third thermal transfer film

1d

Fourth thermal transfer ribbon

11

Effect pigment layer

11a

First surface of the effect pigment layer

11b

Second surface of the effect pigment layer

12th

Carrier film

13th

Release layer

14th

Back coating

15th

Adhesive layer

100

Feed direction

111

First area

112

Second area

113

Third area

114

Fourth area

2

Effect pigment

20th

Auxiliary carrier

21

First auxiliary layer

22nd

Interference layer

23

Second auxiliary layer

211

First effect pigments

212

Second effect pigments

213

Third effect pigments

214

Fourth effect pigments

3

Thermal transfer printer

30th

Substrate processing

31

Substrate

32

Thermal transfer ribbon handling

34

Pulley

35

Thermal transfer print head

35a

Heating element

36

Counter pressure roller

37

Thermal transfer ribbon rewind

Claims (15)

1. Method for producing a true-colour image,
   wherein, by means of a thermal transfer printing head (35a), partial surfaces, formed as grid points, of an effect pigment layer (11) of a thermal transfer film (1) or, by means of one or more thermal transfer printing heads (35a), partial surfaces, formed as grid points, of effect pigment layers of two or more different thermal transfer films are applied onto a first surface of a substrate (31) to form the true-colour image, wherein the true-colour image consists of a plurality of true-colour areas which show an assigned true colour when illuminated in incident light observation and/or transmitted light observation, characterised in that,
   in at least 10% of the true-colour areas, two or more grid points are applied by means of the thermal transfer printing head or the thermal printing heads, which grid points are formed by partial surfaces of effect pigment layers (11) which comprise effect pigments (2) which differ with respect to their optical effect and/or orientation in such a way that the assigned true colour is generated by additive and/or subtractive colour mixing of these grid points applied in the respective true-colour area when illuminated, and wherein the thermal transfer film or the thermal transfer films has/have at least one effect pigment layer (11) and a carrier film (12), and wherein the effect pigment layer (11) comprises first effect pigments (211) in one or more first regions (111).
2. Method according to claim 1,
   characterised in that,
   in particular in each of the true-colour areas, two or more of the grid points are applied adjacently to one another and/or on top of one another and/or overlapping one another on the first surface of the substrate (31).
3. Method according to one of claims 1 to 2,
   characterised in that
   the grid points have at least a lateral dimension in the range of between 40µm and 100µm, wherein the lateral dimensions of the grid points are preferably between twice and five times the lateral dimensions of the effect pigments (2).
4. Method according to one of claims 1 to 3,
   characterised in that
   the register tolerance in the advance direction (100) and/or perpendicular to the advance direction (100) between at least two regions, which are each transferred or printed onto the substrate from different thermal transfer films (1), is greater than or equal to -0.5mm and less than or equal to +0.5mm, in particular greater than or equal to -0.15mm and less than or equal to +0.15mm, preferably greater than or equal to - 0.1mm and less than or equal to +0.1mm, particularly preferably greater than or equal to -0.05mm and less than or equal to +0.05mm.
5. Method according to one of claims 1 to 4,
   characterised in that
   a first of the thermal transfer films (1) has a red effect pigment layer (11), a second of the thermal transfer films (1) has a green effect pigment layer (11), and a third of the thermal transfer films (1) has a blue effect pigment layer (11).
6. Thermal transfer film (1) for producing a true-colour image in accordance with a method according to claim 1,
   wherein the thermal transfer film (1) has at least one effect pigment layer (11) and a carrier film (12), wherein the effect pigment layer (11) comprises first effect pigments (211) in one or more first regions (111).
7. Thermal transfer film (1) according to claim 6,
   characterised in that
   the effect pigment layer (11) comprises second effect pigments (212) in one or more second regions (112), and/or the effect pigment layer (11) comprises third effect pigments (213) in one or more third regions (113), and/or wherein the effect pigment layer (11) comprises fourth effect pigments (214) in one or more fourth regions (114), the first, second, third and/or fourth effect pigments (211, 212, 213, 214) differ with regard to their optical effect, in particular with regard to their colour effect and/or orientation, and the first, second, third and/or regions (111, 112, 113, 114) are arranged adjacently to one another with regard to the plane spanned by the effect pigment layer (11), and in particular are arranged in an iterative sequence in relation to the longitudinal extension of the effect pigment layer (11).
8. Thermal transfer film (1) according to one of the preceding claims 6-7,
   characterised in that
   the side of the carrier film (12) facing away from the effect pigment layer (11) has a reverse side coating (14), in particular a slidable reverse side coating.
9. Thermal transfer film (1) according to one of the preceding claims 6-8,
   characterised in that,
   to form the effect pigment layer (11) on the carrier film (12), a decorative coating is applied onto the carrier film (12) by means of a printing process, in particular by means of a gravure printing, screen printing, flexographic printing, offset printing, inkjet printing or pad printing process, wherein the decorative coating in particular has an organic solvent or is water-based.
10. Thermal transfer film (1) according to one of the preceding claims 6-9,
    characterised in that
    the effect pigment layer has a binder system consisting of one or more of the following substance classes: polyacrylate, polyurethane, polyvinylchloride, polyvinyl acetate, polyester, polystyrene and copolymers of the aforementioned substance classes, in which the first, second, third and/or fourth effect pigments (211, 212, 213, 214) are embedded, and further preferably has a rheology additive, in particular a layer silicate, preferably one or more bentonites, in particular have a proportion of between 1 percent by weight and 10 percent by weight, preferably a proportion of from 2 percent by weight to 8 percent by weight, and particularly preferably a proportion of from 3 percent by weight to 5 percent by weight, of the dry mass, and/or the effect pigment layer (11) additionally has absorbent inorganic and/or organic dyes and/or pigments, which the respective colour of the dyes or pigments provides by absorbing a partial spectrum of the incident light.
11. Thermal transfer film (1) according to one of the preceding claims 6-10,
    characterised in that
    the proportion of the absorbent pigments in the total amount of the pigments is under 20%, in particular under 5%, preferably under 1%.
12. Thermal transfer film (1) according to one of the preceding claims 6-11,
    characterised in that
    the effect pigment layer (11) is a priming layer and/or adhesive layer (15), in particular an adhesive layer which can be hardened by heat.
13. Thermal transfer film (1) according to one of the preceding claims 6-12,
    characterised in that
    the first, second, third and/or fourth effect pigments (211, 212, 213, 214) are selected from: red interference pigments, green interference pigments, blue interference pigments, white interference pigments, white effect pigments, black effect pigments.
14. Thermal transfer film (1) according to one of the preceding claims 6-13,
    characterised in that
    one or more or all of the first, second, third and/or fourth effect pigments (211, 212, 213, 214) have a spherical, platelet-like, cubic, cuboid, torus-shaped, disc-shaped or irregular shape, wherein the white effect pigments in particular have a spherical shape with a diameter of preferably less than 5µm, in particular less than 1µm, and/or one or more or all first, second, third and/or fourth effect pigments (211, 212, 213, 214) have a largest diameter, in particular an average largest diameter, wherein the largest diameter, in particular the average largest diameter, is between 2µm and 200µm, in particular between 5µm and 35µm, and/or one or more or all of the first, second, third and/or fourth effect pigments (211, 212, 213, 214) have an effect pigment size distribution, wherein the 90%-quantile of the effect pigment size distribution in particular is less than 35µm, and/or the 50%-quantile of the effect pigment size distribution is in particular less than 20µm, and/or the 10%-quantile of the effect pigment size distribution is in particular less than 12µm, wherein preferably 35% to 45% of the effect pigment sizes are between 6µm and 20µm, in particular between 10µm and 18µm, and/or
    one or more or all of the first, second, third and/or fourth effect pigments (211, 212, 213, 214) are designed to be transparent or semi-transparent, wherein the effect pigments (2) are transparent in particular for light from more than 30%, preferably more than 50%, of the visible spectral range, and/or
    one or more or all of the first, second, third and/or fourth effect pigments (211, 212, 213, 214) have a first colour impression in incident light, in particular in incident light with white light, and provide a second colour impression which is complementary to the first colour impression in particular in transmitted light, and/or
    one or more or all of the first, second, third and/or fourth effect pigments (211, 212, 213, 214) have at least one auxiliary carrier (20), in particular at least one platelet-shaped auxiliary carrier (20), wherein the respective auxiliary carrier (20) is surrounded by at least one interference layer (22) on at least one side, wherein, in particular, at least one first auxiliary layer (21) is arranged on the interface between the respective auxiliary carrier (20) and the at least one interference layer (22), and wherein the surfaces of the at least one interference layer (22) facing away from the respective auxiliary carrier (20) in particular have at least one second auxiliary layer (23).
15. True-colour image produced according to one of the preceding claims 1 to 5,
    characterised in that
    the true-colour image comprises a plurality of grid points applied on a first surface of a substrate (31), wherein the grid points are formed by partial surfaces of an effect pigment layer (11) of a thermal transfer film (1) or by partial surfaces of effect pigment layers of two or more different thermal transfer films,
    preferably one grid point comprises 1 to 7000 effect pigments (2), which are arranged partially or completely on top of one another and/or adjacently to one another.

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