EP1409263B1 - Continuous-tone image produced by printing - Google Patents

Abstract

Half-tone image, made by printing on a substrate, consists of not less than 2 types of dots of different colors in a raster, which give each required color by color mixing of the dots. The novelty is that the dots consist of printing inks containing pigments fluorescing in a particular color when stimulated with electromagnetic radiation.

Description

The invention is concerned with printing produced on a substrate Halftone images consisting of at least two types of grid-like arranged Pixels of different colors, whereby by color mixing of the colors Pixels the respectively desired color is generated and on the substrate on the one hand fluorescent pixels of when excited with a certain electromagnetic colors containing fluorescent pigments printing inks and on the other hand non-fluorescent pixels of colored, upon excitation with the certain electromagnetic radiation non-fluorescent pigments containing printing inks are present.

In in conventional printing processes, for example, offset printing, gravure or Thermal transfer printing produced colored halftone prints creates the color impression by subtractive color mixing of four basic colors (generally cyan, yellow, magenta and black). In such halftone prints, the pigments absorb the Inks from the incoming white light the respective Komplementäranteil. The unabsorbed corresponding color component of the white light is reflected, reaches the eye of the beholder and calls there a corresponding color impression out. Each of the primary colors thus reflects only a fraction of the striking one Light. The brightness of halftone prints generated in this way depends on the background which the basic colors are printed. The lighter the background, the lighter Games can be achieved with the halftone image.

On a television tube or a movie screen on the other hand, images through additive color mixing produced. It represents virtually every point on the canvas or TV tube is a small light source that shines in a special color. Be it three, as is the case with the TV tube, for example selected areas of the visible spectrum as colored light sources, for example, red, green and blue-violet, covering the entire area of the visible spectrum are distributed and the corresponding It is thus possible to stimulate color receptors in the eye by means of additive Color mixing to create color images with realistic color position.

After prerequisite for additive color mixing the presence is corresponding luminous pixels, so far one has to use the need to dispense with additive color mixing in printed halftone images.

JP-A-10 278 407 describes a print produced on a substrate Halftone image consisting of at least two types arranged in a grid fluorescent pixels of different colors, where by color mixing the colors of the pixels the respectively desired color is generated.

The invention is an object of the invention to propose a way, how halftone images can be produced by a printing process on a substrate, which compared to the previous halftone images by high brilliance and the Possibility to distinguish realistic color production.

To solve this problem is proposed according to the invention, a by Print generated halftone image of the type mentioned in such a way that the fluorescent pixels on the one hand and the non-fluorescent pixels On the other hand, nested on the substrate are provided.

Printed halftone images according to the invention thus differ from the hitherto customary, printed colored halftone pictures in that the respective Colors are only recognizable if contained in the individual printing inks Pigments excited by electromagnetic radiation of appropriate wavelength and then fluoresce. Once the pigments are excited, you then get but a very bright, strong color halftone image. In this context, let noted that the term "printing inks" of course in the broadest Meaning is understood and includes all kinds of paints or varnishes that are suitable are to create a print or raster image on a substrate. Especially are "inks" within the meaning of the invention, for example, the paint or Sublimation layers of thermal transfer or thermal printing films.

Special and for security purposes very valuable effects can be achieve that on the one hand fluorescent pixels of fluorescent upon excitation with a given electromagnetic radiation Pigments-containing inks and on the other hand non-fluorescent Pixels of colored, at excitation with the specific electromagnetic Radiation non-fluorescent pigments containing inks are present. It is not generally understood by "non-fluorescent pixels" that the printing inks used to produce these pixels are absolutely not fluoresce. In the context of the present invention may be also act around pixels that consist of printing inks, their pigments though fluoresce upon excitation with certain electromagnetic radiation, not however, upon excitation with the particular electromagnetic radiation that the brings fluorescent pixels to fluoresce. If a halftone image like that composed of fluorescent and non-fluorescent pixels, Depending on the irradiation results in each case a different effect, since at Irradiation with the excitation of the fluorescent pixels causing electromagnetic radiation corresponding to the fluorescent pixels light up and create a halftone color image while irradiated with different radiation the so-called non-fluorescent pigments the Create halftone color image. It can be achieved, for example, that at Irradiation with UV light is due to the effect of the fluorescent pigments first color impression results, while under illumination with daylight and correspondingly low UV component, a different color impression established.

If then according to the invention the fluorescent pixels on the one hand and the On the other hand, non-fluorescent pixels intermesh on the substrate nested, face up to the same, both fluorescent as well as non-fluorescent pixels having surface area of Substrates each dependent on the lighting, different effects.

It is further provided that the fluorescent pixels are a first image and the non-fluorescent pixels represent a second image. For example, would be In this way it is possible to duplicate a personal document with the Portrait of the document holder, with the first document as normal halftone image by mixing the colors cyan, magenta and yellow (as well possibly black), while the second portrait by additive Color mixing, e.g. under UV light, fluorescent pigmented inks is generated. In this way, the security of a personal document can be increase significantly and you get at the same time a simple method to Authenticity test, namely, that only has to be checked, whether by Subtractive color mixing generated portrait of the document owner with the Lighting with very specific electromagnetic radiation in appearance passing, resulting from positive color mixing of fluorescent colors Portrait coincides. The production of such images from normal, a subtractive color mixing effect pigments and fluorescent, one For example, additive color mixing pigments can be easily prepared by means of Thermal transfer printers happen, which then have to be able to correspondingly to provide many colors for the pressure points.

A very special feature of the halftone images according to the invention is to see that the desired color or color can only be observed if the halftone image with electromagnetic radiation corresponding Wavelength is irradiated. This has the consequence that the color or color position of the halftone image changes when irradiation with light of different Wavelength, for example, on the one hand with visible light, on the other hand with ultraviolet light. This effect can be exploited, for example To represent a substrate different structures, depending on the wavelength or Frequency of the electromagnetic radiation used for lighting are alternately visible.

Halftone images according to the invention are preferably produced in such a way that fluorescent pixels are provided from three different printing inks, wherein the pigments of the different printing inks each in one of three Primary colors (for example red, green and blue-violet) for additive color mixing Fluorescent, because then by appropriate combination of pixels of individual, each different fluorescent pigments almost all Colors of the visible spectrum can be generated.

To stimulate the fluorescent pigments, the most diverse types be provided electromagnetic radiation. In practice, however, it will be in the be generally useful when using pigments under Influence of UV radiation fluoresce.

It is further provided according to the invention that the pixels on black Subsurface are arranged. The black background can be either from be formed directly to the substrate. It would also be conceivable, however, the black one To form the background by means of a corresponding printing ink, wherein the Substrate forming ink then over the entire surface or even only in Intermediate spaces between the colored fluorescent pixels may be arranged can.

Special effects can be achieved according to the invention if at least one of the pigments used in a printing ink is selected so that it Influence of radiation of different frequencies in different colors fluoresce. Depends on the one used to illuminate the halftone image Radiation then gives a different result, depending on which one Color the corresponding pigment just fluoresces, with both color change, as well as changes in the motif, depending on the one used for the irradiation Frequency, can be achieved.

It is particularly advantageous if according to the invention the dimensions of the - Halftone image - - pixels are chosen so that this with the unarmed eye are not resolvable, which will be achieved in any case if, according to the invention, the dimensions of the pixels are less than 0.3 mm are selected. In this case, for the viewer, the mix of the individual pixels come colored light rays and it arises as it were the impression of a continuous, correspondingly colored surface.

Halftone images according to the invention can be used for a variety of purposes use. Particularly advantageous and subject of the invention However, the use of a corresponding halftone image as security or Guarantee element for valuables, documents, in particular securities, Banknotes and identity cards, or for correspondingly valuable items. For example, it is conceivable to use a banknote, a check or another Securities with a corresponding halftone printing to provide, in which case only when lighting with appropriate radiation of the desired color effect occurs. For example, one could achieve that on a banknote or one the same existing security element only upon irradiation of the banknote with UV light of a certain frequency shows a special color effect, while at Irradiation with normal light only a slight gray shimmer available is without the outlines or the like of the actual printed Halftone image would be recognizable in this type of lighting. If you have the according to fluorescent pigments and possibly in addition It is, for example, non-fluorescent pigments to the printing inks also possible, one when lighting with normal light white or gray appearing halftone image, which is more special when illuminated with light Wavelength, especially UV light, then due to the fluorescence occurring shows strong colors. This effect (change between black and white representation and colored representation) is an easily recognizable security element excellent.

Special securing effects can be achieved if, as explained above, on the document or the like. Two images are combined, the first image a normal halftone color image, while the second image is due to fluorescence only more special when illuminated with light or electromagnetic radiation Wavelength is perfectly recognizable, with the special fuse effect in the possibility to see two basically matching images provide, which can then be compared with each other accordingly.

To apply appropriate security elements to valuables facilitate, it is advantageous if the halftone image of the on the secured Object transferred decorative layer of a transfer film, in particular hot stamping or Thermal transfer film is formed. Halftone images can be part of it Of transfer films easily produce in conventional printing process and then in shape label-like stains, streaks, etc. in a simple manner to the Transfer securing objects. This has the advantage that the user corresponding security elements relate this more or less finished can and then only a relatively simple device for transmitting the Security element of the transfer film on the object to be secured needed.

Finally, it is within the scope of the invention that when using corresponding halftone images as a security element for objects the halftone image is combined with an optically active element, for example one Lattice structure, a hologram, a high-gloss reflective surface, a purposefully frosted area or a color change or different transparency causing thin film arrangement.

Alone the halftones according to the invention are difficult imitate, because it is difficult to find the exact combination between Pigments, paint vehicle and essential wavelength of the to find out electromagnetic radiation. But the fake is then even more difficult if the principle already considered hard to falsify known optically active elements are additionally present. This is true in particular, when a colored halftone image according to the invention and an optical immediately adjacent effective structure in a single security element or even nested inside each other. Here manufacturing processes are required which make imitation practically impossible. In addition, the Backup and verification options further improved. It would be e.g. conceivable, with the halftone image on the one hand and the optically active element on the other hand, to present matching or complementary patterns, what additional testing options, be it with normal lighting, is it opens when lighting with light of special wavelength, these being Review options can certainly be designed so that they even for an untrained observer are easily detectable.

As can be seen above, halftone images are according to the Invention extremely versatile. For example, it would also be conceivable relatively large-format halftone prints on large-format printers in one To produce embodiment according to the invention, so large, For example, to produce UV-fluorescent prints that are suitable for special effects, e.g. in the advertising industry, can be used. It would be, for example conceivable, advertising posters produced in discotheques according to the invention od. Like. whose contents are then exposed only when irradiated with appropriate light, e.g. UV radiation, it can be seen, with such advertising posters from previously known, under UV radiation fluorescent elements characterized distinguish that one actually receives halftone color images and thus extremely versatile design options are given. Despite the created Possibilities are the production costs for such advertising media but comparatively low.

Below are some principles and examples of half-tone prints explained in more detail according to the invention.

Is a halftone print on a dark, preferably black, background printed using inks with fluorescent pigments and In this case, the pigments are selected so that they with appropriate Irradiation in the colors red, green and blue light, so you can enter Create a halftone image that basically in terms of its properties corresponds to a TV picture tube generated image, in addition to the individual pixels of the halftone image should be so small that this from the Eye can not be resolved individually. This condition is under consideration of the halftone image from normal reading distance, if the pixels have a Diameter of less than 0.3 mm, preferably even less than 0.1 mm. In addition, if the pixels of the halftone image so densely printed are that the dark, preferably black, underground anymore translucent, halftone images can be printed, the different Have properties. If one assumes that UV fluorescent Pigments are not used when irradiated with normal daylight light up a special color, one achieves that the halftone images at Illumination with normal daylight as pale black and white images appear (due to the inherent color of the fluorescent pigments). If, on the other hand, the halftone image is illuminated with appropriate UV radiation, the pigments fluoresce in the respective colors, taking the pigments expediently in the sense of additive color mixing, preferably so should light up in red, green and blue. Depending on which each assigned to individual colors at a specific location of the Halftone image are present and in what density, can then be - similar to in a television picture tube - generate a corresponding color image, wherein the dark or black background ensures that even dark parts of the picture Although it is possible to do so by means of additive color mixing is to produce the color white, but not the color black.

As already mentioned, special effects can be achieved, if at least used for an ink pigments, not just at one wavelength in the fluoresce for her characteristic color, but also at a second Wavelength are excitable, in which case fluorescence in a second color occurs. For example, pigments could be used which fluorescently UV are, on the one hand at the wavelength 365 nm and on the other hand, at the wavelength of 254 nm.

The halftone images can be printed using appropriate inks in the customary printing method are generated, expediently offset printing (Digital offset) or thermal transfer printing can be used. The usage This printing process has the advantage that in this process each image associated image information (usually as red, green and blue color separation) can be used directly.

BF11 (rot):

bifluoreszierendes Pigment (rot bei 254 nm, blauweiss bei 365 nm)

Hersteller:

Specimen Document Security Division, Budapest

CD 120 (rot):

monofluoreszierendes Pigment (orangerot bei 254 nm, rot bei 365 nm)

Hersteller:

Allied Signal Special Chemicals Riedel De Haen

CD 130 (orangegelb):

monofluoreszierendes Pigment (orange bei 254 nm und 365 nm)

Hersteller:

Allied Signal Special Chemicals Riedel De Haen

CD 397 (gelbgrün):

monofluoreszierendes Pigment (gelb-grün bei 254 nm und 365 nm)

Hersteller:

Allied Signal Special Chemicals Riedel De Haen

MF 1 (grün):

monofluoreszierendes Pigment (grün bei 254 nm und 365 nm)

Hersteller:

Specimen Document Security Divison, Budapest

MF 40 (blau):

monofluoreszierendes Pigment (blau bei 254 nm und 365 nm)

Hersteller:

Specimen Document Security Division, Budapest

MF 50 (blau):

monofluoreszierendes Pigment (fahlblau bei 254 nm, keine Fluoreszenz bei 365 nm)

Hersteller:

Specimen Document Security Division, Budapest

Examples of different pigment combinations in printing inks for producing corresponding halftone images are explained below, in which case, for example, the following pigments are used:

BF11 (red):

bifluorescent pigment (red at 254 nm, blue-white at 365 nm)

Manufacturer:

Specimen Document Security Division, Budapest

CD 120 (red):

monofluorescent pigment (orange red at 254 nm, red at 365 nm)

Manufacturer:

Allied Signal Special Chemicals Riedel De Haen

CD 130 (orange yellow):

monofluorescent pigment (orange at 254 nm and 365 nm)

Manufacturer:

Allied Signal Special Chemicals Riedel De Haen

CD 397 (yellow-green):

monofluorescent pigment (yellow-green at 254 nm and 365 nm)

Manufacturer:

Allied Signal Special Chemicals Riedel De Haen

MF 1 (green):

monofluorescent pigment (green at 254 nm and 365 nm)

Manufacturer:

Specimen Document Security Division, Budapest

MF 40 (blue):

monofluorescent pigment (blue at 254 nm and 365 nm)

Manufacturer:

Specimen Document Security Division, Budapest

MF 50 (blue):

monofluorescent pigment (pale blue at 254 nm, no fluorescence at 365 nm)

Manufacturer:

Specimen Document Security Division, Budapest

Using appropriate pigments, offset inks were used 10 to 40 weight percent of the UV fluorescent produced in a conventional manner Pigments with an oxidatively drying offset varnish grated and used immediately.

If a corresponding thermal transfer film with color layers with accordingly fluorescent pigments are prepared, it is known in per se Make a thin PET carrier coated with a lacquer layer into which each desired fluorescent pigments are incorporated.

Using the above-mentioned pigments, the following halftone prints were obtained created:

Example 1:

Halftone print in red-green-blue technique on black, excitable at 365 nm CD 120 (red) MF 1 (green) MF 40 (blue)

With uniform distribution or intensity of the three pigments used is obtained by irradiation with UV light of a wavelength of 365 nm additive color mixing white. When irradiated with UV light of a wavelength of 254 nm results in a pale orange, because the pigment CD 120 at This wavelength is not red but orange fluoresces.

Example 2:

Halftone print in red-green-blue technique on black excitable at 254 nm BF 11 (red) CD 397 (yellow-green) MF 50 (blue)

With uniform distribution results when irradiated with UV light of 254 nm Wavelength due to additive color mixing, the color white when irradiated with UV light of a wavelength of 365 nm, however, the color green-white, and indeed because the pigment BF 11 only fluoresces red at 254 nm, at 365 nm against blue-white. However, this means that in interpretation of the Halftone image on the irradiation with UV light with a wavelength of 254 nm performs a conventional three-color halftone print while irradiated with 365 nm, the combination according to Example 2 only for a kind of black and white printing suitable is.

Example 3:

Halftone print with black and white on black, excitable at 365 nm BF 11 (blue White) CD 130 (Orange-yellow)

In accordance with uniform distribution and intensity of the individual Pigmented printing inks obtained when irradiated with UV light a Wavelength of 365 nm the color white, while when irradiated with UV light the wavelength 254 nm gives the color red. This is due to, that the bifluorescent pigment BF 11 is used. Halftone prints according to Example 3 therefore appear when irradiated with UV light of wavelength 365 nm as black and white prints (the two color pigments complement each other too white), while on irradiation with UV light of wavelength 254 nm a red image observed on a black background.

As can be seen from the above examples, it is using the Basic idea of the invention, namely the additive color mixing over fluorescent pigments, possible to achieve a variety of color effects, wherein, in particular, color changes upon irradiation with light differ Wavelength particularly noticeable and therefore especially good as light detectable security features are suitable. Also can be generate machine-readable security elements according to the invention which are then perfectly evaluated only by means of devices that the special, required for the excitation of the pigments electromagnetic radiation generate, which differs considerably from the radiation of normal daylight can differentiate.

Example 4:

Using the pigments BF 11 (red, fluorescent at 254 nm), MF 1 (green, fluorescent at 254 nm) and MF 40 (blue, fluorescent at 254 nm) creates a halftone image of a portrait on a substrate, with the distance the individual pixels is chosen sufficiently large that in the Interspaces further pixels can be inserted. Size and Distance of the pixels must be such that the individual pixels with the unaided eye at a normal viewing distance of about 30 cm can not be resolved individually.

In the spaces between the fluorescent pixels from the Pigments BF 11, MF 1 and MF 40 become colored pressure points accordingly imprinted small size, where these pressure points to Pressure points in the four primary colors for subtractive color mixing (in general cyan, yellow, magenta and black).

If, according to the above proposal with six (or seven at Use of black) colors may be required Provision should be made that there is no overlay or moiree formation comes in pressure. This can be achieved, for example, by the fact that the different representations of fluorescent pixels on the one hand and normal-colored pressure points on the other hand in different screening (e.g., 48 and 60 grid). An other possibility would be to use frequency modulated rasters instead of amplitude modulated rasters, as is already common in a variety of digital printers today.

Both the pressure points with the fluorescent pigments and the Pressure points of normal printing inks are each arranged so that a Halftone image results, e.g. the portrait of a person in both pictures can be shown. The selection of colors to create the halftone image is then made such that under normal illumination, e.g. with daily or Artificial light, the subtractive color mixing causing pressure points the first Halftone color image of the person pose while the fluorescent Pressure points when illuminated with suitable radiation, e.g. UV radiation, an im reproduce a substantially consistent picture. The examination of Correspondence of the two images is a suitable means for checking the authenticity.

Claims (11)

1. Continuous-tone image produced on a substrate by printing, comprising at least two types of image points of different colours arranged in the manner of a grid, the respectively desired colour being produced by means of colour mixing of the colours of the image points, and there being on the substrate, firstly, fluorescent image points of printing inks containing pigments that fluoresce when excited with a specific electromagnetic radiation and, secondly, non-fluorescent image points of coloured printing inks containing pigments that do not fluoresce when excited with a specific electromagnetic radiation, characterized in that the fluorescent image points, firstly, and the non-fluorescent image points, secondly, are provided nested in one another on the substrate.
2. Continuous-tone image according to Claim 1, characterized in that the fluorescent image points represent a first image and the non-fluorescent image points represent a second image.
3. Continuous-tone image according to Claim 1 or 2, characterized in that fluorescent image points of three different printing inks are provided, the pigments of the various printing inks in each case fluorescing in one of three primary colours (for example red, green and blue-violet) for additive colour mixing.
4. Continuous-tone image according to one of the preceding claims, characterized in that the pigments are UV-fluorescing pigments.
5. Continuous-tone image according to one of the preceding claims, characterized in that the image points are arranged on a black background.
6. Continuous-tone image according to one of the preceding claims, characterized in that at least one of the fluorescent pigments fluoresces in different colours under the action of radiation of different frequency.
7. Continuous-tone image according to one of the preceding claims, characterized in that the dimensions of the image points are selected such that these cannot be resolved by the naked eye.
8. Continuous-tone image according to Claim 7, characterized in that the dimensions of the image points are selected to be smaller than 0.3 mm.
9. Use of a continuous-tone image according to one of Claims 1 to 8 as a security or guarantee element for items of value, documents, in particular valuable papers, banknotes, identity papers or objects.
10. Use according to Claim 9, characterized in that the continuous-tone image is formed by the decorative layer of a hot embossing film that is transferred to the object to be protected.
11. Use according to Claim 9 or 10, characterized in that the continuous-tone image is combined with an optically active element.