CN109562629B

CN109562629B - Method for producing an optically variable printing pattern

Info

Publication number: CN109562629B
Application number: CN201780046672.8A
Authority: CN
Inventors: P·克劳特; K·罗登哈乌泽
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2016-08-04
Filing date: 2017-08-02
Publication date: 2021-02-02
Anticipated expiration: 2037-08-02
Also published as: WO2018024760A1; DE112017003883A5; CN109562629A

Abstract

The invention relates to a method for printing optically variable printed patterns in the RGB mode, wherein interference pigments are used in combination with absorption pigments or combination pigments for the purpose of colorizing the printing inks, to printed articles produced with such a method and to the use thereof in decorative, artistic or security products.

Description

Method for producing an optically variable printing pattern

The invention relates to a method for printing optically variable printed patterns in the RGB mode, wherein interference pigments are used in combination with absorption pigments or combination pigments for colorizing the printing inks in a chromatic manner, and also to printed articles produced by means of such a method and to the use thereof in decorative, artistic or security products.

In conventional printing processes, such as offset, gravure or screen printing, multicolored printing patterns are printed by printing dots or printing surfaces which are arranged next to one another and overlap one another, onto a generally white or light-colored printing material by the primary colors (cyan, magenta, yellow and optionally also black (CMYK)) customary for analog printing processes. Each of the printing inks is pigmented with a classical absorption color, which is subtractive in color mixing in terms of visual perception. From the appropriate combination of the primary colors, a number of desired hues on the color wheel can be generated. However, if equal amounts of cyan, magenta and yellow pigmented printing inks are applied on top of each other on a single planar unit, the colour perceived from the viewer's perspective is black. Furthermore, the writing of a black surface or a printing ink additionally pigmented with black is enhanced in the actual printing application. Modern digital methods, such as inkjet printing or toner-based electrophotography, are also based on already well-developed CMYK systems, since the printing of images is associated as before with the presence of coloured absorbing pigments or absorbing dyes in the printing inks, although digital photographs themselves are not stored in CMYK systems but in RGB mode.

Digital displays of different types of displays (LCD, LED, OLED, plasma) use light beams of the primary colors red, green and blue, which are combined in different combinations with each other into a light spot, which can take any color position in the color wheel. In contrast to the CMYK color system, the colored light beams in the RGB mode are mixed in a color-additive manner, that is, the RGB light beams overlapping each other with appropriate intensities are mixed to white in visual perception. Digital photographing of optical or film cameras is also done in RGB mode so that these photographs can be visualized on digital displays without major matching problems, whereas printing digital photographs on a typical printer (e.g. an inkjet printer) requires converting image data obtained in RGB mode into mechanically printable images for use in CMYK systems.

In addition to the use of absorption pigments or absorption dyes, interference pigments with different optical properties (pure interference color, interference color combined with absorption color, gloss and sparkle effect, optically visible effect) for highlighting details, achieving a particular additional gloss or sparkle or in general for optically improving the overall impression of the printed article have also been used more frequently in recent years in printing processes which support CMYK. However, such printed products are inconvenient to produce and achieve only moderate effects due to the interference pigment usage which is only possible in a small range. In addition, it is becoming increasingly difficult to find interference pigments which are very particularly capable of producing effects which attract attention in professional circles.

The optical effect of interference pigments is based on the difference in the refractive index of materials which are arranged one above the other in the form of thin layers in the pigment and reflect, transmit and in some cases also absorb incident light in different ways depending on the refractive index of the respective layer and of the medium surrounding the interference pigment. By the difference in refractive index between adjacent layers, an optical path difference is generated in the reflected light beams so that the former overlap and wavelength-selective light of a specific wavelength is enhanced or attenuated. The reflected light beam in the visible wavelength range enhanced in this way is perceived by the observer as a visible interference color under suitable conditions. If all layers of the interference pigments consist of transparent, colorless materials, only the interference color and not the bulk color of the interference pigments can be perceived.

The interference color of an interference pigment without an absorption color optically behaves like a colored light beam, i.e. a self-hyperchromic combination. A transparent filler of interference pigments which is colorless as a separate pigment (present at suitable mixing ratios of the red, blue and green interference pigments, i.e. the interference colors of red, green or blue are displayed in the application medium) should therefore theoretically produce a visually perceptible overall impression of white, but in practice usually deviate therefrom, so that a whitish, grayish hue is perceived.

The individual interference pigments usually consist of a flake-form carrier material and of one or more or less transparent layers by means of which the flake-form carrier is coated. However, the uniform layer thickness of the carrier and the individual layers, the uniformity of the composition of the individual layers and the surface quality of the carrier and the individual layers and the size and size distribution of the pigments determine, in particular, how far the optical behavior of the respective interference pigment deviates from the ideal phase of the material used in practice. Thus, the production conditions of interference pigments have a large influence on their optical behavior. It is thus also explained that interference pigments having the same formal hue (for example red) and the same formal layer structure (for example a titanium dioxide layer on mica platelets) are very different in terms of optical behavior (for example expressed by saturation, brightness or color angle) depending on the manufacturer and the production process employed, and in fact sometimes themselves also depending on the respective feed.

In practice, therefore, until recently it has not been successful to develop a simulated printing process which allows the production of multicoloured printed images whose colour formation is based solely on the optical effect of the pure interference colour produced by the interference pigments.

Interference pigments which have an absorption color in addition to the interference color are referred to as combination pigments. The optical effect of such pigments consists of the corresponding interference color and absorption color, wherein the absorption color (also referred to as bulk color) produces the main color impression of the pigment, which is enhanced or completely coated by the interference effect. Since it is not uncommon to use multicolored colors as absorption colors in combination pigments in order to supplement the relatively weakly colored interference effects in an attractive manner, combination pigments are used in printing inks with body colors in the cyan, magenta or yellow range or with multicolored body colors deviating from the colors in order to achieve special optical effects. The use of combination pigments in conventional printing processes is however limited to the achievement of special effects and always only takes place in mixtures with the usual colored absorption pigments in the color positions cyan, magenta and yellow.

In contrast, combination pigments which exhibit a black bulk color and at the same time a weaker interference color are always used in the application medium as an alternative or complement to classical black pigments.

As a printing method alternative to the classical CMYK printing method, a theoretical concept is proposed in US 2006/0082844 a1, by means of which interference pigments should be possible for printing multicolored printed images. This concept, which is referred to as R 'G' B 'Y', is based on the use of four printing inks, comprising interference pigments of red, green, blue and yellow (gold) respectively, wherein four so-called bytes are required to produce a printed dot (pixel). This concept is based on the following recognition or assumption: the interference pigments of red and green, unlike the light of red and green, do not mix into yellow, but rather into gray. In this concept, therefore, in order to obtain a yellow pixel color, a self-yellow or gold color mark (farbsbur) must be generated. It follows that, in order to produce a white color impression, red, green, blue and yellow printing inks are required, which are colored with interference pigments of the respective interference colors. The concepts described herein remain only theoretically. Thus, neither the information actually available can be obtained by the interference pigments to be employed, nor can a printing pattern be deduced from the disclosure which may actually realize this concept.

The applicant has however succeeded shortly before in developing a practical and in industry-wide interest-oriented printing process based on the use of only three colored printing inks, which are colored only with interference dyes (PCT/EP 2016/000120). The printing method is a printing method in the RGB mode, by means of which a brightly colored print image can be produced in all colors of a color wheel of printing inks, which are colored in color only with interference pigments in red, green or blue, respectively. However, the method preferably exhibits its full effect on black or dark substrates, since the substrates provide sufficient contrast for the interference color of interference pigments, which are known to be significantly weaker in optical perception than usual colored absorption pigments.

However, in addition, there is also a need for printed articles which generate an optically unusual attention, which can be produced on different types of substrates conventionally used for printing processes, white, light-colored or even colorless transparent, and which have optical effects which have hitherto been unknown.

The object of the present invention is to provide a practically implementable printing method of the RGB model, by means of which optically appealing printed images can be produced on variable, preferably colorless transparent, white or light-colored substrates, wherein the printing inks are colored in color with interference pigments, but not with colored absorption pigments, and wherein printed images can be produced with as small amounts as possible of different printing inks, which have a hue in the entire color space, and wherein the printing method can be variably adapted to common analog and digital printing methods.

It is a further object of the present invention to provide printed articles having multicolored printed images with additional special optical effects and to demonstrate the use thereof.

The object of the invention is achieved by a method for printing optically variable printed images in an RGB-mode, in which three colored printing inks are applied to a substrate in succession to one another in the form of printing surface units and are fixed, and in which the printing inks each consist of a printing ink carrier which is formed from a printing ink carrier

a) Coloring with red, green or blue interference pigments and black absorption pigments, respectively, wherein the printing ink carrier additionally contains no further coloring pigments, or

b) Colored only with combination pigments, wherein the printing inks have red, green or blue combination pigments, respectively, which have red, green or blue interference colors and additionally have black absorption colors, respectively,

and wherein the three colored printing inks form printing surface elements which are arranged next to one another and/or overlap one another and which, at least at a first viewing angle, produce a multicolored overall printed image which differs from a second overall printed image which appears at least one second viewing angle.

The object of the invention is likewise achieved by a printed article prepared according to the above-described method and its use in decorative or artistic products or in security articles.

The printing method of the invention is based on the RGB scheme known per se, but as mentioned before, with the exception of the display in PCT/EP2016/000120, the RGB scheme is only practically applied to methods not yet disclosed, so far only for the combination of different colored light beams in a display or similar technical equipment. However, the inventors have now surprisingly been able to provide a further printing process in which it is sufficient to print only three combination pigments of only three printing inks colored with interference pigments or colors one after the other to obtain an optically variable print, which, at a constant illumination angle, shows a multicolored overall print with hues which can reach the entire color space at least one viewing angle, while at least one second viewing angle the following overall print is visible: the overall printed image differs significantly from the first overall printed image in terms of its color formation and is preferably not multicolored or colored.

A red, green or blue printing ink is understood hereinafter as a printing ink which is colored only with interference pigments or with combination pigments which have a red, green or blue interference color, respectively.

The presence of interference colors is here, as is common in the art, obtained on the basis of reflection of interference pigments in a transparent, colorless medium, typically a coating on a substrate.

The black absorption pigments (having no interference colors other than the black absorption color) added according to the invention to the red, green and blue interference pigments in the respective printing inks are not regarded according to the invention and according to the general public perception in contrast as colored pigments or colored pigmented pigments, since "black" is in the color theory just like "white" and not a color.

All measurements in the present invention were carried out with the aid of the samples described hereinafter using a Multiangle Color Spectrophotometer MA 68/II, Inc., of U.S. A.X-Rite, Inc. For determining the interference color of the interference pigments, directional reflection at the sample and spectrally resolved analysis of the reflected light are used here. In all data used in this specification, the measurement conditions were an illumination angle of 45 ° and an observation angle of as25 ° (non-specular 25 °, representing the spacing between the observation angle and the grazing angle).

In each case, the red interference pigment has an enhanced reflection in the wavelength range of 600 to 750nm, the green interference pigment has an enhanced reflection in the wavelength range of 490 to 550nm and the blue interference pigment has an enhanced reflection in the wavelength range of 400 to 490 nm. The more prominent and narrower the corresponding reflection maxima are, the more clearly the monochromatic and saturated interference colors can be visually perceived.

The wavelength ranges given for the corresponding reflection maxima also apply to combination pigments which, in addition to the respective interference colors of red, green and blue, also have an absorption color of black. The latter represents the visible bulk color of these pigments, i.e. the corresponding pigment powder appears black or dark gray and is colorless or whitish, as is the case in red, green and blue interference pigments which do not have an absorption color.

Only when a yellow printing surface unit is applied to a substrate by applying a printing ink containing a red interference pigment and a printing ink containing a green interference pigment one after the other on the same printing surface unit, a multicolored overall print (visible as a result of the invention at least one viewing angle and possibly with a color spectrum up to the entire color space) can be produced under the conditions of the invention with the aid of only three colored printing inks.

For this purpose, the red printing ink and the green printing ink must contain interference pigments of red or green color which satisfy certain conditions. Therefore, according to the invention, it is necessary to produce a yellow printing surface unit such that the red interference pigments in the red printing ink have a hue angle h in the CIELUV (1976) color space system in the range from 0 ° to 25 °, in particular from 0 ° to 20 °, and very particularly in the range from 0 ° to 10 °_u'v'And the green interference pigment in the green printing ink has a hue angle h in the range from 100 ° to 180 °, in particular from 100 ° to 150 °, and very particularly in the range from 100 ° to 130 °_u'v'Wherein the hue angle of the red interference pigment is not 0 ° when the hue angle of the green interference pigment is 180 °, and vice versa (see fig. 1; hue angle at 45 °/as25 ° in the CIELUV (1976) color space system, determined in a separate, overall coating layer formed on a black substrate by the respective colored printing ink, see below for a more detailed description).

(definition and determination of hue Angle see Richter, M., Einf ü hrung in die Farbmeter, 2. Aflage, de Gruyter,1981, pp.118-122.)

The application-dependent color properties of interference pigments (in whatever color space system) can only be determined in one application form, and not at individual particles. For this reason, all color data used in the present invention relate to coatings consisting of commercially available liquid printing ink vehicles and the corresponding interference pigments at a concentration of 23% by weight relative to the finished coating composition and are applied to a black substrate and fixed in the intaglio printing on the whole.

30 parts by weight of pigment and 70 parts by weight of gravure binder (e.g. Siegwerk5036 blend NC TOF) were intimately mixed and the viscosity was adjusted with 30 parts by weight of an ethanol/ethyl acetate (3:1) mixture to be ready for printing before printing. The printing inks containing the corresponding red, blue or green interference pigments are then applied individually to a Black-pigmented substrate (for example Fedrigonin SPX Black) in each case in full using a gravure printing unit (60L/cm, 120 °, E-Gravur) and dried. The obtained printed substrate was divided into suitably sized pieces and optically measured, see below.

Color data was measured using a Multiangle Color Spectrophotometer MA 68/II, Inc., of U.S. X-Rite, Inc. From the spectral data obtained, the corresponding color coordinates L u ', v' of the CIELUV (1976) color space system under given boundary conditions (2 ° or 10 ° for normal observers and a light source of D65) were calculated.

When the hue angle h of the red interference pigment_u'v'Hue angle h with green interference pigments_u'v'The process according to the invention can be carried out particularly advantageously with a spacing of 90 to 160 degrees and preferably in the range from 105 to 140 degrees and in particular in the range from 110 to 130 degrees. This applies in the same way also to the corresponding hue angle spacings between the green and blue interference pigments and between the blue and red interference pigments. That is to say, the hue angle h of the green interference pigment_u'v'Hue angle h with blue interference pigments_u'v'And the hue angle h of the blue interference pigment_u'v'Hue angle h with red interference pigments_u'v'The distance between them should advantageously be in the range of 90 to 160 degrees, preferably 105 to 140 degrees and in particular 110 to 130 degrees, respectively.

In the case of interference pigments of the red and green colors, in particular, with regard to the amount of printing ink, the surface elements printed on the substrate with the red printing ink and the green printing ink in a predefined succession one above the other can have a color tone which is visually perceived as yellow, with a particular proportion of the printing ink amount and with a defined pigment content. Here, each of the applied printing layers may be fixed separately or a composite made of a printing layer formed of red printing ink and a printing layer formed of green printing ink overlapping with the first layer may be fixed together.

Hue angle h of blue interference pigments_u'v'Can be selected relatively freely, but preferably points in the range of the previously specified pitch of the hue angles and advantageously lies in the range from 210 ° to 280 °.

Maintaining the conditions previously described, in particular for the red and green interference pigments, enables: a printing process with only three printing inks (RGB) colored with interference pigments is sufficient to obtain a multicoloured printed image in a colour variation over the entire colour space at least one viewing angle. Here, the color intensity and the lightness of the printed image depend, of course, on other conditions.

Including, inter alia, high color saturation and high chroma (chroma). Therefore, advantageous according to the invention are embodiments of the invention in which the respective interference pigments used have as high a color saturation as possible, i.e. are particularly strongly colored, and exhibit a high chroma. Corresponding details and particularly suitable interference pigments are explained in detail in the already mentioned patent application PCT/EP 2016/000120. The patent applications mentioned are hereby expressly incorporated by reference.

However, if no yellow printing surface is provided or required for the optically variable print produced using the method according to the invention and if the loss in the range of the color space to be achieved (full range) is acceptable, the red, green or blue interference pigments used for the respective printing inks can also deviate from the abovementioned range of hue angles in terms of their hue angle, so that other interference hues of red, green and blue can be used, which can even be produced individually from mixtures of different interference pigments. It is however also very advantageous in terms of saturation and chroma of the interference pigments to select for the process of the invention the interference pigment with the respectively highest available value.

The interference pigments used in the printing process according to the invention exhibit interference colors of red or blue or green in the application medium. They consist of a sheet-like support which is coated with one or more layers of a material having a different refractive index than the material of the support, this applying at least to the material of the first layer located on the support and, as long as there are a plurality of layers on the support, there are refractive indices which differ from one another between the layers located directly above one another.

According to the invention, interference pigments consisting of transparent, colorless, flake-form carriers coated with one or more layers of transparent, colorless materials are used as red, green or blue interference pigments.

The interference pigments themselves likewise exist in flake form.

Although it is theoretically possible in the printing process of the invention to use interference pigments of red, green and blue color at all available particle diameters (typically in the range from 1 to 250 μm for the length or width of the pigment flakes and for values of 0.1 to 5 μm for their thickness), in order to achieve a high surface coverage of the printing substrate and thus a high color intensity of the multicolored printed image, it is very advantageous for the particle diameters of the red, green and blue interference pigments used according to the invention to be in the range from 1 to 45 μm, with a particle diameter in the range from 1 to 45 μm<40 μm, especially<D of 35 μm₉₀The value is obtained. It is preferred to use d thereof₅₀Has a value of<20 μm, especially<18 μm and d thereof₁₀The value is preferably<Interference pigments of 12 μm. The particle diameters are each the principal axis of the pigment, i.e. the longest dimension of the respective pigment particle.

In order to obtain absolute values of particle size based on extensive statistical analysis, the particle size values in the present invention are based on individual analysis in a light microscope with automated image analysis functionality. Since the interference pigments canIn the form of flakes and oriented with their major axes parallel to the light source, specific particle surfaces and shape factors can be measured separately by this method. Number weighted distribution of spindle lengths through d₁₀、d₅₀、d₉₀And optionally d₉₅Values (corresponding to the percentage of particles smaller than a given value). Over 1000 pigment particles were analyzed separately. Analysis according to [ a]ISO13322-1: 2014-particle size analysis-image analysis method-part 1: a static image analysis method; [ b ] a]ASTM E1617-09(2014) reports standard practice for particle size standard data; or [ c]Powder sampling and Particle size determination, T.Allen, Elsevier 2003.

The values obtained with the aid of these individual analyses in the light microscope enable the most practical overview of the particle size and particle size distribution of the flake-form pigments. However, other conventional methods can also be used to obtain the particle size of the interference pigment.

The interference pigments used according to the invention generally possess an aspect ratio (ratio of mean diameter to mean particle thickness) of from 3:1 to 1000:1 and especially from 6:1 to 250: 1.

From the values stated above, the red, blue and green interference pigments preferably used according to the invention advantageously have a minimal proportion of coarse particles. Furthermore, it is particularly preferred that they also have a high average fine particle proportion, wherein at most 40% of the pigment particles have a particle diameter in the range from 12 to 20 μm.

As red, blue and green interference pigments, interference pigments of different manufacturers can be used in the printing process according to the invention, for example under the name Merck KGaA

And

the commercially available interference pigments provided below, also under the name BASF SE

And a pigment of

The Royal series of pigments and also other commercially available interference pigments from other manufacturers. When these pigments meet the previously stated requirements with regard to color angle, saturation, chroma and particle size, high-quality, multicolored prints can be obtained by the printing process according to the invention at least one viewing angle, which prints can have a photo-realistic optical impression if desired.

Under the name of

And interference pigments commercially available under Spectraval, in particular

And Spectraval_TMA series of interference pigments has proven to be particularly suitable.

In a first embodiment of the present invention, these interference pigments are used according to the invention together with black absorbing pigments in the corresponding printing inks. The black absorbing pigment may be particulate Fe₃O₄Based on granular Fe₃O₄The pigment of (a), particulate graphite, particulate carbon black or also the combination pigments with black absorption colors described hereinafter.

If it is granular Fe₃O₄Based on granular Fe₃O₄The corresponding materials are commercially available in different particle sizes and are known, for example, under the designations c.i. pigment Black 7, c.i. pigment Black 11, c.i. pigment Black28, c.i. pigment Black 30 or c.i. pigment Black 33. The corresponding particle diameters are used here for the printing method used, since different printing methods also apply to the particle diameters of the particulate material contained in the printing inkGenerally very different requirements are set forth. In particular, the granular material is not allowed to block the mat of the printing mould, does not hinder or prevent its emptying or leads to a build-up on the printing mould. In general, the black absorption pigments have a particle size in the range from 0.01 to 100 μm, in particular from 0.01 to 20 μm. The black absorbing pigments can be used individually or in mixtures in the corresponding printing inks. However, carbon blacks, in particular finely divided colored carbon blacks, which are generally used under the designation c.i. pigment Black 7 in conventional CMYK printing processes, are particularly advantageously used.

According to the invention, the proportion by weight of the black absorbing pigment in the respective printing ink is from 0.001 to 1.5% by weight, in particular from 0.02 to 0.75% by weight, relative to the total weight of the printing ink. And particularly preferably 0.03 to 0.40% by weight.

However, it is also possible according to the invention to use the combination pigments described below as black absorbing pigments having a black absorbing color. They have, in addition to the black absorption color, an interference color of red, green or blue and are used correspondingly in connection with the interference pigments of red, green or blue. Thereby enhancing the interference effect in the respective printing ink. Since the combined pigment of the black absorption color has a flake shape and a particle diameter similar to that of the interference pigment, less sedimentation or demixing of the two components can occur in the pre-pigment mixture formed from these two components or also in the finished printing ink than in the case of granular components of different shapes and sizes.

If a combination pigment with a black absorption color as black absorption pigment is used according to the first embodiment of the invention, the proportion thereof in the respective printing ink is 5 to 30 wt.%, in particular 10 to 25 wt.%, relative to the total weight formed by the interference pigment and the combination pigment, i.e. relative to the total pigment content in the respective printing ink.

The corresponding commercially available products are further explained below.

The proportion of the respective red, green or blue interference pigment in the respective printing ink is generally between 1 and 40 percent by weight and preferably between 5 and 35 percent by weight, in particular between 10 and 30 percent by weight, relative to the total weight of the respective printing ink. It is self-evident here that the pigment concentration is in each case selected such that the printing method according to the invention can be carried out without problems with available equipment. Depending on the printing apparatus used, the pigment concentration in the printing ink is furthermore selected such that a processable pigment proportion is preferably selected as high as possible in order to be able to achieve the desired surface coverage of the printing surface unit to be printed. When desired, the pigment concentrations in the red, blue and green printing inks may be selected to be different from each other. It is also preferred, however, to use a corresponding pigment concentration in each of the three printing inks also in the case of the same printing apparatus for each printing step.

In a second embodiment of the invention, the red, green and blue printing inks are colored only with a red, green or blue combination pigment which, in addition to the black absorption color, also has a red, green or blue interference color.

Such composite pigments are based on flake-form supports and have at least one interference layer on the support, the support or the at least one interference layer or both being made of Fe₃O₄Or graphite or containing Fe alone or in mixtures₃O₄Graphite or carbon black.

Pigments based, for example, on graphite flakes and at the same time having interference colors are likewise commercially available, as are the so-called carbon-containing pigments (which have incorporated carbon in the support material and/or in a layer located on the support). In addition, there may be other interference layers, typically consisting of metal oxides.

Preferably, the red, green and blue combined pigment is a flake-form pigment having a flake-form support made of natural or synthetic mica, SiO, and an interference layer on the support₂、Al₂O₃Or glass, the interference layer containing Fe₃O₄. Optionally one or more further interference layers may be included.

As non-limiting examples of suitable combination pigments, mention may be made here of the combination pigments provided by Merck KGaA

The Blacks tar series, i.e. Rona

Blackstar Red，Rona

Blackstar Green and Rona

Blackstar Blue. These are based on having Fe content on a flake-form support₃O₄Mica flakes of the layer of (a).

The particle size of the combined pigments used is from 1 to 250 μm, in particular from 5 to 100 μm and preferably from 10 to 60 μm, the thickness of the pigment flakes being in the range from 0.1 to 5 μm. The particularly fine particle size distribution in the interference pigment used as in the first embodiment does not result in an improved printed article in the second embodiment of the invention, but may be advantageous when a combination pigment is used as the black absorbing pigment in the first embodiment of the invention.

According to a second embodiment of the invention, the printing inks of red, green and blue are each colored only with the combination pigment, wherein the colors are obtained here only by the corresponding interference colors.

The concentration of the combination pigment in the respective printing ink is between 1 and 40 weight percent and preferably between 5 and 35 weight percent, in particular between 10 and 20 weight percent, relative to the total weight of the respective printing ink. The concentration of the combined pigments in each of the three printing inks may be the same or may also be set to values different from each other as needed.

Since the combination pigments have, in part, a very strong black absorption and thus a bulk color, concentrations of not more than 15% by weight and advantageously in the range from 1 to 10% by weight, relative to the total weight of the printing ink, are also required in several cases.

The three printing inks are applied to the respective substrate (printing material) in succession to one another, both in the first embodiment and also in the second embodiment of the method according to the invention.

The respective three printing inks here each consist of a printing ink carrier, the corresponding interference pigment and the black absorption pigment (first embodiment) or of a printing ink carrier and the corresponding combination pigment (second embodiment).

As printing ink vehicle, commercially available or generally used printing ink vehicles can be used, which comprise at least one binder or binder system and usually also a solvent, as long as the binder system is not radiation-curable.

As binders there may be used binders or binder systems which are customarily used in printing processes, for example aqueous or solvent-containing cellulose nitrate-based, polyamide-based, acryl-based, polyvinyl butyral-based, PVC-based, PUR-based binders or mixtures thereof. It is important for carrying out the printing process according to the invention that the corresponding binder or binder system is cured transparently and colorless, in order not to impede or distort the optical effect of the interference pigment in cooperation with the black absorption pigment or combination pigment.

In addition to water, it is also possible to use organic solvents, for example branched or unbranched alcohols, aromatics or alkyl esters, such as ethanol, 1-methoxy-propanol, 1-ethoxy-2-propanol, ethyl acetate, butyl acetate, toluene or mixtures comprising these. However, when using radiation-curable binder systems (e.g. UV-curable binder systems), the corresponding colored printing inks may also contain little or no solvent.

In addition to the binder or binder system and optionally the solvent, the printing ink vehicle may also comprise different auxiliaries and/or additives in addition to the corresponding interference pigments in a mixture with the black-absorbing pigment or the combination pigment.

Possible additives are UV stabilizers, inhibitors, flame retardants, slip agents, dispersants, redispersing agents, defoamers, leveling agents, film formers, adhesion agents, drying accelerators, drying retarders, photoinitiators, etc. Preferably, the respective printing ink vehicle comprises all necessary auxiliaries in liquid form, so that the optical effect of the interference pigments is not impaired or otherwise adversely affected by further solids. For this reason, it is preferred that in the finished colored printing ink, neither (soluble) dyes nor other colored pigments or solid fillers are contained, apart from the red, blue or green interference pigments required according to the invention in combination with the black absorbing pigment or the red, green and blue combination pigments.

The abovementioned red, blue and green interference pigments are present in the colored printing inks used according to the invention individually or in the form of mixtures of two or more. This means that, for example, a red printing ink either contains only one type of red interference pigment or may also contain a plurality (plurality of types) of different red interference pigments, which may have the same, similar or mutually different layer structures on the same carrier material or on different carrier materials, but which, as a mixture, satisfy the requirement of a color angle h of a mixture of_u'v'Aspects and preferably the above requirements in terms of saturation values and chroma. The process of the invention can be carried out successfully as long as the stated conditions are maintained and the interference pigments used as particles have a high transparency and are preferably colorless. The described composition of the interference pigments in the respective colored printing inks is of course also applicable to blue or green printing inks in the same way as the red printing inks described above.

In the printing process according to the invention, the red, blue and green printing inks (colored with red, blue or green interference pigments mixed with black-absorbing pigments or with red, green or blue combination pigments, respectively) are applied to the substrate in succession in the form of printing surface units and fixed. The printing surface unit here consists of a printing layer formed from one printing ink or of a plurality of printing layers formed from two or three printing inks. Each of the individual colored print layers can be fixed separately or two or three print layers on a print surface unit can be applied one after the other and fixed together in a single method step.

According to the invention, the substrate can be virtually any substrate that can be printed by conventional printing methods, i.e. paper of different composition, cardboard, wallpaper, plastic film, plastic body, metal foil, textile, different forms of ceramics and glass, wood or a composite material comprising at least one of the aforementioned materials. Here, according to the present invention, even a colorless transparent substrate, for example, a colorless transparent plastic film, may be printed in addition to a substrate having an opaque surface.

The opaque substrate may itself have a light or white color or may have a base or gloss coating having a light or white color. Such light-colored or pre-coated substrates, unlike the process described in PCT/EP2016/000120, are particularly suitable for use in the process of the present invention, as they form a sufficient contrast with respect to the grey scale constituted by the black absorbing pigment or the black absorbing color of the combined pigments, as will be explained below. They are commercially available in a wide variety of forms, since they are here printing materials which are generally used in common printing processes.

The opaque substrate preferably has an L in the range of 60 to 100^*White or light color of value (CIELUV). Such coloration of the substrate can be obtained, depending on the substrate material used and the intended purpose of use of the finished product, by dyeing the substance of the substrate material (for example in the case of plastic films) or by means of coating the substrate with a white or light-colored coating. The latter may be applied instead of or in addition to a primer layer or a gloss layer. Said layer can be obtained by adding common color agents to the corresponding coating composition, for example adding white pigments, such as TiO₂、BaSO₄Or ZnO. Preferably all surfaces of the opaque substrate to be printed are white or light-colored or provided with such whiteA colored or light-colored coating, but also white or light-colored and transparent surface portions on the substrate or the substrate may be completely transparent.

The order of application of the individual colored printing inks also has an effect on the color composition of the print image that can be achieved. It is therefore particularly preferred according to the invention that the order of the printing inks to be applied on the substrate is as follows:

a first printing layer: a red printing ink with a red interference pigment or a red combination pigment,

a second printing layer: green printing inks with green interference pigments or green combination pigments, and

a third printing layer: blue printing ink with blue interference pigment or blue combined pigment

(sequential RGB).

In the printing method according to the invention, the three colored printing inks are applied to the substrate to be printed in the form of printing surface units, wherein the printing surface units which are respectively printed with the individual colored printing inks are arranged next to one another or partially or completely above one another, i.e. overlapping one another. Only in the case of partially or completely overlapping printing surface units for the individual printing inks, mixed colors are present in the resulting printed image, which are formed by a combination of red, blue and green interference pigments and black absorption pigments or by differently composed red, green and blue combination pigments.

The printing surface unit is understood to be a printing dot or a printing surface depending on the printing die to be used, which may take various sizes and forms depending on whether the method is a grid printing method or a printing method that can directly print a large surface unit.

The printing method of the invention can be applied in general to very different conventional printing methods and can therefore also be carried out with common printing tools. The method can therefore be carried out as a conventional analog printing method, for example as a flat printing method, a gravure printing method, a letterpress printing method or a print-through method, or as a digital printing method.

A lithographic printing method is understood here to mean, in particular, a conventional or UV-curing lithographic printing method or also a dry lithographic printing method which is carried out without wetting agent. Mention may be made, as intaglio printing methods, for example, of packaging intaglio printing, display intaglio printing, decoration intaglio printing or also intaglio printing (embroidery intaglio). Letterpress printing methods are understood to mean book printing methods, indirect letterpress printing methods (such as letterpress printing) or the customary flexographic printing methods. One known print-through method is screen printing. Known as digital methods are ink-jet printing, toner-based electrophotographic methods or thermal transfer.

All of these conventional printing methods typically work with four color printing according to CMYK color decomposition. Instead of this, the printing method according to the invention can now be applied to all the described printing methods, instead of the usual cyan, magenta, yellow and black-pigmented printing inks, red, blue and green printing inks pigmented only with interference pigments and black-absorbing pigments or so-called combination pigments are printed one after the other.

This results in different color combinations, especially when mixtures of pure interference pigments with black absorption pigments are used, i.e. printed images of the same yellow, cyan or magenta color, especially in combinations of red/green-yellow, green/blue-cyan and blue/red-magenta.

Each of the above printing methods allows for a maximum layer thickness of the dry printed layer produced in a single printing process. This maximum layer thickness varies greatly depending on the printing method. Correspondingly, the layer thickness of the individual printing layers in the printing method of the invention is 0.2 to 250 μm. However, it is understood that, with a very small layer thickness of the individual printing layers, only very little pigment can be applied to the respective printing surface unit. The printing step of transferring the individual color printing inks to the substrate can thus optionally be repeated one or more times in these cases in order to adjust a high degree of area coverage. The printing layer thickness (dry layer thickness) of the individual printing inks is therefore preferably in the range from 0.4 to 80 μm, particularly preferably in the range from 0.6 to 10 μm and in particular in the range from 1.0 to 5.0. mu.m.

The high area coverage of the individual printing surface units with the color pigments used according to the invention can additionally be promoted by the choice of the absorption volume of the printing tool, for example by the grid of the printing cylinder and/or the mat, for the printing forme. However, such measures are within the expertise of the person skilled in the art of printing and therefore need not be explained in detail here.

The printing method according to the invention is preferably carried out in such a way that each of the different printing inks is applied by means of the respectively identical printing method (i.e. by means of the same type of printing tool). Although it is theoretically possible to use different printing tools for the different printing steps, respectively, the printing process is thereby unnecessarily more complicated and more expensive.

The printing method of the invention can be adapted to most common analog and digital printing methods and can therefore be carried out with common printing tools. By means of only three colored printing inks colored with a mixture of interference pigments and black absorbing pigments or with a combination pigment (having a black absorbing color), an optically variable printed image can be produced in RGB mode, which printed image, at least one viewing angle, can cover a palette over the entire available color space and, at another viewing angle, produces a second printed image which is completely different from the first printed image in terms of its color effect.

Furthermore, the printing method of the present aspect may also be combined with common printing methods in CMYK mode, so that on the same substrate a surface portion or a print pattern portion may be printed in common CMYK color sorting mode and several other captured or different print surface portions or print pattern portions of said surface portion or print pattern portion may be printed in RGB mode of the present invention. New, hitherto unrealizable possibilities and effects are thus provided for the design of coloured surfaces in printing processes.

The invention also relates to printed articles which exhibit optically variable prints on a preferably white, light-coloured or colourless transparent substrate and which have been produced according to the above-described method.

Optically variable means that the printed article has a distinctly different color and/or gloss appearance at different viewing and/or illumination angles.

The inventive printed image and therefore the printed product containing said printed image show a very weakly colored representation or preferably a non-colored representation on a dark background with a half-tone quality (i.e. different grey levels) at a steep viewing angle (e.g. when viewed in the normal direction) at a constant illumination angle.

A corresponding printed image in the range of grazing angle ± 30 degrees (grazing angle corresponds to the angle of incidence of the light beam at the imaginary 90 ° line) has a clearly improved hue with increased gloss, but in a saturated, dark hue (second embodiment) or an impressively distinct, hiding, colorful under light color (including possibly yellow face parts and strong gloss (first embodiment)). Since the optical effect in the first embodiment eventually becomes so surprisingly apparent and excellent, this embodiment of the method of the invention is clearly preferred. The multi-color printed image according to the first embodiment of the invention, which appears at and around glancing angles, optically behaves like a printed image printed with a hiding flake-like effect pigment having a strong gloss (for example with a colored metallic effect pigment), but with a much greater color diversity than the latter (if it is likewise prepared with only three different printing inks). In addition, such a comparative printed image is likewise colored when viewed under normal conditions, whereas the printed image according to the invention has a very pronounced color and gloss difference between different viewing angles and in each case as an effect of printing with different printing inks, i.e. as a multicolored gloss pigment having only black pigments of halftone quality at least one (preferably steeper) viewing angle and having a large color diversity and a high covering power at and around glancing angles.

Furthermore, the use of the above-mentioned printed articles in decorative or artistic products and especially also in security products is also the subject of the present invention. The above-mentioned optical properties of the printed article of the invention determine its use in all types of decorative products, which themselves consist of or comprise the printed article of the invention (e.g. advertising and commercial prints) or (e.g. packaging for very different products and in very different embodiments). Since the printed articles according to the invention have optical properties which have hitherto not been obtainable in printing processes, they are also suitable for use in the art sector, for example for wallpaper, advertising prints, collages, calendars, textile coatings and many more.

However, it is also proposed to use the printed products according to the invention in very different types of security products, since this novel method produces optically variable printed images which are very often used in security documents in the hitherto known form (respectively exhibiting different multicolored colors in at least two viewing angles), but are virtually unknown in the form producible in this context and are therefore also difficult or completely impossible to counterfeit.

Security articles in which the optically variable printed article according to the invention may be applied are for example banknotes, cheques, passports, passage authorization documents, certificates, document authentication, tax banderoles, credit cards and other payment carriers, admission cards, lottery tickets, gift voucher cards, stamps, tokens or logos (to mention just a few).

The printed articles prepared according to the invention have attractive optical properties which are hitherto not available on the market in the field and thus make a valuable contribution to the expansion of the palette of decorative and artistic products and possibly security features for security products.

FIG. 1: showing a CIELUV color space (1976) with a neutral or achromatic point E and a structure for determining the color angle in this color space

The invention is illustrated below with the aid of examples, to which, however, the invention is not restricted.

Example 1:

1a：

red, green and blue printing inks were prepared from a commercially available printing ink vehicle for screen printing (Follmann Aquascreen FS10-931) by adding the interference pigments mentioned below to the printing ink vehicle in respective concentrations each having 0.1 part by weight of Black printing ink (Follmann Aquascreen FS-801; c.i. pigment Black 7 corresponding to about 0.025% by weight in the printing ink) and intimately mixing all the components with one another:

t30-21 Red 15 parts by weight

T30-24 Green 12 weight portions

T30-23 Blue 9 parts by weight

(all numerical values are relative to 100 parts by weight of the printing ink prepared, respectively)

The patterns broken down into these printing inks were printed on white cardboard coated on both sides (Invercoat Creato from Iggesund) successively in a red-green-blue sequence one after the other with a conventional screen (90L/cm, 40PW, mesh width 68 μm).

A printed pattern is obtained with a display image of good contrast (grey halftone values) which is uncolored at steep viewing angles under a constant illumination angle and with a brightly colored, hiding, bright-colored, colorful display image (including a yellow printed surface) at glancing angle deflection.

1b：

Example 1a was repeated with the following changes: black printing inks were added to the respective printing inks in amounts of 0.5 parts by weight (corresponding to about 0.125% by weight of c.i. pigment Black 7 in the printing inks).

A printed pattern is obtained with a very high contrast display (grey halftone value) uncolored at steep viewing angles under a constant illumination angle and with a contrast-rich, brightly colored, hiding, colored, highly glossy, color-rich full-color display (including yellow printed side) at grazing angle deflection.

Example 2:

red, green and blue printing inks were prepared from a commercially available printing ink vehicle for screen printing (Follmann Aquascreen FS10-931) by adding the combination pigments mentioned below to the printing ink vehicle in the corresponding concentrations and intimately mixing all the components with one another:

15 parts by weight of Black tar Red

15 parts of black tar Green

15 parts of Black tar Blue

The patterns from examples 1a and 1b, which had been decomposed into these printing inks, were printed on white cardboard coated on both sides (Invercoat creator from Iggesund) successively in red-green-blue order one after the other with a conventional screen (90L/cm, 40PW, mesh width 68 μm).

A printed motif is obtained with a black display with good contrast against a dark background at steep viewing angles under a constant illumination angle and with a color-evident, hiding, black-gloss, dark-colored display at glancing angle deflection. No yellow print was observed.

Claims

1. Method for producing optically variable printing patterns in the RGB mode, in which three colored printing inks are applied successively in the form of printing surface units to a substrate and fixed, characterized in that the printing inks each consist of a printing ink carrier body

a) Coloring with a red interference pigment, a green interference pigment or a blue interference pigment, respectively, and a black absorption pigment, wherein the printing ink carrier furthermore contains no further coloring pigments,

or

2. The method according to claim 1, characterized in that the multicolored overall print has yellow printing surface units which are formed by applying a printing ink comprising red interference pigments and a printing ink comprising green interference pigments to the substrate one after the other.

3. Method according to claim 1 or 2, characterized in that the combined red, green or blue pigments are respectively flake-like pigments having a flake-like carrier and at least one interference layer on the carrier, wherein the carrier or the at least one interference layer or both consist of Fe₃O₄Or graphite or containing Fe alone or in mixtures₃O₄Graphite or carbon black.

4. The method of claim 3,the red, green or blue combined pigment is a flake-like pigment having a flake-like carrier made of natural or synthetic mica, SiO, and an interference layer on the carrier₂、Al₂O₃Or made of glass, the interference layer containing Fe₃O₄。

5. A method according to claim 1 or 2, characterised in that the black absorbing pigment is particulate Fe₃O₄Based on granular Fe₃O₄The pigment of (a), particulate graphite, particulate carbon black or a combination pigment having a black absorption color.

6. The method according to claim 5, characterized in that the particulate carbon black is a colored carbon black.

7. A method according to claim 5, characterized in that the black absorbing pigment is particulate Fe₃O₄Based on granular Fe₃O₄And the weight proportion of the black-absorbing pigment in the colored printing ink pigmented with red, green or blue interference pigments is in each case from 0.001 to 1.5% by weight, based on the weight of the respective printing ink.

8. A method according to claim 5, characterised in that the black absorbing pigment is a combination pigment having a black absorbing colour and the weight proportion of the black absorbing pigment in the coloured printing ink coloured with red, green or blue interference pigments is 5 to 30% by weight, respectively, based on the total weight of interference pigments and combination pigment.

9. The method according to claim 1 or 2, characterized in that the red, green or blue interference pigments respectively consist of a transparent, colorless, flake-like carrier which is coated with one or more layers made of a transparent, colorless material.

10. The method according to claim 1 or 2, characterized in that the red, blue and green interference pigments have a particle size in the range of 1 to 45 μm and<d of 40 μm₉₀The value is obtained.

11. The method according to claim 1 or 2, wherein the substrate is a transparent, colorless substrate or is an opaque substrate having a surface with an L in the CIELUV color space system in the range of 60 to 100^*The value is obtained.

12. The method of claim 11, wherein the substrate is a plastic body, glass, ceramic, paper, cardboard, wallpaper, foil, textile, wood, or a composite material comprising at least one of the foregoing materials.

13. The method of claim 12, wherein the plastic body comprises a plastic film.

14. A method according to claim 1 or 2, wherein the overall printed image appearing at the at least one second viewing angle is an uncoloured halftone printed image.

15. A method according to claim 1 or 2, wherein the first viewing angle is an angle in the range of a grazing angle ± 30 °.

16. The method according to claim 1 or 2, characterized in that the red interference pigment has a hue angle h_u'v'The hue angle is relative to the hue angle h of the green interference pigment_u'v'Having a pitch in the range from 90 to 160 DEG, wherein the hue angles are respectively measured at 45 DEG/as 25 DEG from printing inks colored only with the corresponding interference pigments by separate overall coatings on black substratesTo be determined.

17. The method according to claim 1 or 2, characterized in that the method is a flat printing method, a gravure printing method, a letterpress printing method, a print-through method or a digital printing method.

18. The method according to claim 1 or 2, characterized in that each of the printing inks is applied in a dry layer thickness in the range of 0.2 to 250 μ ι η.

19. A printed article prepared according to the method of any one of claims 1 to 18.

20. Use of the printed article according to claim 19 in decorative or artistic products or in security articles.