EP1260360B1 - Process for applying printing inks to a printable substrate - Google Patents

Abstract

For printing, a plate surface is prepared with zones which accept and reject ink. The inking zones have set ink acceptance characteristics. The ink is applied to the surface as particles, where the ink molecules and/or pigments are structured to match the characteristics of the ink acceptors and cling to them. The ink is transferred from their zones to the surface to be printed, giving the required printing. The ink acceptance zones are formed by electromagnetic rays and especially by a laser or an ultra violet mask, or other light source with a short wavelength. Or a layer on the printing plate (20) is removed where ink is to be accepted. The zones are indexed (42-45) to attract and hold the ink colors (42'-45').

Description

The invention relates to a method for applying printing inks to a printing substrate.

The lithographic printing is based on utilizing the immiscibility of oil and water on a printing form, whereby the lipophilic solution or the ink or ink is captured by the image-forming areas and the water or hydrophilic solution by the non-image forming areas of the printing area. When the suitably prepared print area is wetted with hydrophilic and lipophilic substance or solution, especially water and ink or paint, the non-image areas preferentially retain the hydrophilic substance or solution and repel the lipophilic substances while the imagewise areas repel the lipophilic ones Take solution or ink or paint and repel the hydrophilic substances. As a result, the lipophilic substance is then suitably transferred to the surface of a material on which the image is to be fixed, for example, paper, cloth, polymers and the like.

For many years, aluminum has been used as a substrate for printing plates. Usually, the aluminum is first subjected to a graining process and then a subsequent anodization process. The anodization serves to provide an anodic oxide layer whose adhesion is improved by the grain. Graining enhances the hydrophilic properties of the background of the printing plate. In the anodization process, a strong acid such as sulfuric or phosphoric acid is usually used to subsequently make the surface hydrophilic by another method such as a thermal silicization method or so-called electrosilication.

For producing a printing plate as described above, a large number of radiation-sensitive materials are known which are suitable for generating images in the use of the lithographic printing method, in that they provide an image area used for printing after exposure and optionally required development and fixing can be. For example, photopolymerizable substances can be used for this purpose.

The above-described arrangement is subjected to imagewise exposure by selectively supplying energy. This can be done for example by means of the exposure through a mask with UV light or by direct writing with a laser.

The lithographic printing plates of the type described above are usually treated with a developing solution, which is typically an aqueous alkaline solution with organic additives. The need to use and dispose of significant amounts of these substances has long been a particular problem in the use of printing processes.

For this reason, efforts have been made for some time to produce printing plates, which can be dispensed to produce the image on a wet-chemical development process. For this purpose, oxide ceramics, which are present for example in the form of coatings on a printing plate, are used.

In the EP 0 911 154 A1 is proposed as a material for the plate surface TiO ₂ and ZnO ₂ , which may be present in ceramic form both pure and with other metallic additives in different mixing ratios. This surface is hydrophobic when unexcited and can be rendered hydrophilic by irradiation with ultraviolet light. Imaging is now done by illuminating the entire surface of the plate with ultraviolet light and masking areas of ink which are to be printed.

In order to be able to produce a color print image on a printing substrate, it is necessary to print the colors cyan, magenta and yellow as well as to improve the contrast also black (CMYK) each with the help of its own printing form on the substrate one above the other. This procedure requires, especially in offset printing machines, in which the respective color is transferred in a separate inking unit on the substrate, a high registration accuracy when transporting the printing material from one inking unit to another. Only then can it be avoided that unwanted register fluctuations lead to a blur in the color image. In such high-precision printing presses, the individual inking units are arranged in series construction one behind the other, which makes the machine very long. All the more so, if in addition to the front side, the back to be printed or if additional special colors or paints to be printed on the substrate. Such a printing press is for example from the DE 42 34 928 known. In order to counteract at least the problem of extended longitudinal design of the printing press, is in the EP 0 512 549 have already been proposed a printing machine in so-called satellite construction, in which the individual inking units are arranged around a central blanket cylinder, such as satellites. Although this significantly reduces the length of the printing press, the individual printing inks must still be applied in individual inking units. In addition, it is not possible with this machine to print on the back of the substrate.

From the US 6,096,386 In addition, a stamp printing method is known in which printing ink is transferred from the raised areas to a substrate by means of a stamp having raised and recessed areas. For this purpose, this stamp over its entire surface, ie provided on the raised and non-raised areas with a so-called activated surface, which is then provided by means of a masking process with so-called orientation materials. These orientation materials may differ depending on the masking in the individual mask areas. If the plunger is then immersed in a suitable liquid, suitable counterparts can be arranged on the orienting materials. To transfer of these counterparts on a receiving surface, this receiving surface is immersed in a liquid and pressed the plunger within this liquid on the receiving surface. Thus, the counterparts deposited on the punch at the raised areas can be transferred to the receiving surface. The auxiliary liquid in which the transfer to the receiving surface, serves to provide the stamp surface immediately after transfer immediately with orientation materials. This is achieved by mixing the auxiliary liquid with orientation substances. After transferring the counterparts to the receiving surface, the receiving surface may be used to form an etch mask or sensor.

Against the background of this prior art, the object of the present invention is to propose a simplified printing method, which also allows a shorter design of the printing press.

This object is achieved by a method for printing with the features of claim 1.

In the method proposed according to the invention, therefore, the surface of a printing plate is pretreated in accordance with the ink to be applied in the individual regions of the surface in such a way that these regions are suitable for accepting a particular printing ink. This can be achieved with specifically designed printing inks that attach only certain color particles, such as dyes, pigments, color molecules or colored particles to the correspondingly pretreated areas of the printing plate. In concrete terms, this means that in the planographic printing process in question, in particular the offset printing process, in a first process step, the surface of the planographic printing plate pretreated, that is marked so that only the ink corresponding to the marking can attach to defined areas. For example, on a single printing form, a mark for cyan, a mark for magenta, one for yellow and one for black be applied. If the printing form is then brought into contact with a mixture containing the color particles cyan, magenta, yellow or black corresponding to the markings, the color particles associated with the markings are deposited at the corresponding points of the printing plate and can be used in a further method step be transferred directly or indirectly to the substrate.

Although it is possible with this method to give up the previously required in planographic separation of the printing plate for color separations in individual inking, can be provided to improve the resolution or the coverage of ink more printing plates and inking units in a printing press, each of a certain subset of aufzudruckenden Have information. On the one hand, this can contain markings separate from printing inks or mixtures of different markings for different printing inks.

In the production of the markings on the printing form, it is particularly possible to treat the printing form with a laser beam and thereby produce geometric markings on the printing plate, which allow that in the so marked areas of the printing form can arrange only those color particles, in turn have the corresponding geometric properties. This approach to marking the printing plates can also be referred to as a "key lock principle", wherein on the printing form a "lock" is applied, which can be occupied only with such a color particle having a matching key.

In addition to the geometrical characterization of the printing form, it is also possible to use a so-called functional key-lock principle, in which on the printing forme the areas to be occupied by a specific printing ink are occupied by functional groups, for example functional molecules. In this case, the printing inks corresponding to the markings must each have the molecules or molecular parts corresponding to the functional molecule. This will ensure that selected inks then hit the marked area be attached when a colorant corresponding to the marking is associated with the printing forme in the area of the marking.

The printing method proposed according to the invention has the advantage that, in contrast to the conventional technology in the planographic printing method, it becomes possible for the first time to accommodate different color separations on a single printing form and thus significantly reduce the number of inking units required in a printing press. This reduces the technical effort required for printing considerably while at the same time a reduction in the cost of the printing press can be achieved by omitting inking unit components.

Further advantages and advantageous embodiments of the invention are the subject of the following figures and their parts of the description, in the representation of which has been omitted in favor of clarity to a true to scale reproduction.

Figur 1

einen schematisierten Ablaufplan des erfindungsgemäße Verfahrens,

Figur 2

eine Prinzipdarstellung des Druckes sowie zur Erzeugung einer Druckformoberfläche mit Hilfe eines Laserstrahls,

Figur 3

eine Prinzipdarstellung zum Aufbringen geometrischer Kennzeichnungen auf die Druckformoberfläche,

Figur 4

eine Prinzipdarstellung zum Aufbringen funktioneller Kennzeichnungen auf die Druckformoberfläche,

Figur 5

eine Druckformoberfläche mit einer Beschichtung zur Erzeugung der Kennzeichnungen,

Figur 6

eine Druckform mit einer Beschichtung und in der Beschichtung liegenden Kennzeichnungen.

They show in detail:

FIG. 1

a schematic flowchart of the method according to the invention,

FIG. 2

a schematic representation of the pressure and for generating a printing form surface by means of a laser beam,

FIG. 3

a schematic diagram for applying geometric markings on the printing plate surface,

FIG. 4

a schematic diagram for applying functional markings on the printing plate surface,

FIG. 5

a printing form surface with a coating for producing the markings,

FIG. 6

a printing form with a coating and lying in the coating markings.

In FIG. 1 is schematically illustrated the inventively provided process flow. In a first method step 10, a marking is initially introduced into a surface of a printing form which corresponds to a color to be printed in a certain area of the printing form. Thus, on the surface of a printing form, a plurality of areas with fixed color acceptor properties are produced. In a further method step 12, the surface of the printing form is then brought into contact with color particles, the color particles having properties which correspond to the markings on the printing form, ie, to the color acceptor properties of the areas applied to the printing plate. This makes it possible to attach certain so marked color particles at defined locations on the printing plate. In order to bring the printing form with the color particles in connection, the printing for example, as is already common practice, be designed as a rotating offset printing cylinder, wherein the printing cylinder is occupied in a already used today, conventional inking with color. However, the ink used in the inking unit has color particles which have properties that correspond to the markings applied on the surface of the printing cylinder, so that the individual color particles can be deposited precisely at the marked locations of the printing surface. After the desired color particles have been deposited on the intended areas on the printing plate surface, in a further method step 14, the color image applied to the printing plate can be transferred directly or indirectly to a printing material. For indirect transfer, the print image z. B. initially transferred to a blanket cylinder and printed thereon on the substrate. However, the direct transfer of the print image on the substrate is also possible. If necessary, prior to method step 14, the printing plate surface can be cleaned of unwanted color particles not deposited on the markings of the printing plate. Before method step 14, in a further method step 16, the printing form can be freed of unwanted or unnecessary color particles, which is preferably done with the aid of a physical wiping or doctor blade operation can be performed. This step may be necessary in particular if the colors are not transported in a conventional inking unit but are transferred to the plate by means of an immersion bath or a spraying technique. Of course, it is also possible to provide the printing plate following the cleaning in an optional method step 18 with new or the same markings in order to continue the printing process with changed information or the same information can.

In FIG. 2 is a schematic diagram and shown using the example of a short inking unit, a use of a printing form. In this case, a printing form cylinder 20 is provided which forms a printing gap 21 together with an impression cylinder 22, through which a printing material 24, such as a paper sheet or a paper web, is transported therethrough. Furthermore, a component 25 for applying the printing ink to the printing form cylinder 20 is provided, which consists in the present example of an applicator roller 26, an anilox roller 28 and a paint container 30. From the ink container 30, a mixture of different printing inks containing the required colorant particles is transferred to the anilox roller 28. The color particles are designed so that they are recorded at the locations of the printing forme cylinder 20, which corresponds to their color acceptor property. For example, a mixture of the colors cyan, magenta, yellow and black can be provided in the ink container 30, the respective individual colors being assigned different surface acceptor properties corresponding to the color acceptor properties of the printing form cylinder 20.

As already stated, in the present invention, the basic principle of offset printing with hydrophilic and hydrophobic regions can remain unaffected as color-leading or color-repelling regions. Alternatively, however, electrostatic or other forces could act or act in addition. However, the color or pigment particles are in a common mixture. As soon as this color mixture is brought into contact with a correspondingly prepared printing plate 20, the color particles self-locate and seek their surface-accepting properties corresponding surface areas with the corresponding color acceptor properties. In other words, this means that the respective dyes or pigments are attached to their associated identification points of the printing form. As in FIG. 2 1, the surface of the printing form 20 inside or outside a printing press can be pretreated by means of a laser 32 emitting a laser beam 34 in such a way that the surface properties corresponding to the color particles used are generated.

How out FIG. 3 It can be seen, for example, a geometric marking of the printing plate 20 can be used for this purpose. In this form of marking, a plurality of markings 35, 36, 37, 38 is applied to the printing form 20. The different markings 35, 36, 37, 38 represent a respective different geometric marking of the printing plate 20, which allows that at these locations only one particular ink, namely attached to the respective marking 35, 36, 37, 38 attached can be. Thus, for example, the marking 38 may represent the color cyan, the mark 37 yellow, the mark 36 the color magenta and the mark 38 black, which means that only the corresponding dye can be attached to the respective mark. The geometric markings 35, 36, 37, 38 in turn consist of individual points 40, which can be applied by means of the laser 32. The characteristic features of the geometric marking can be made two-dimensional or three-dimensional. When waterless offset can be realized on the printing plate 20, for example, with a laser system with 10 micron resolution shapes with a diameter of about 30 microns. For this purpose, for example, a diode laser with a laser wavelength of 860 nm can be used. This corresponds to a resolution of one dot / μm a point on the printing plate and thus about 30 microns. Thus, a resolution of about 600 dpi can be achieved. In FIG. 3 this resolution is characterized by the distance d. Of course, it is possible by the use of already known microtechnologies using, for example, UV or X-ray radiation to further increase the resolution in any desired ranges. This will also be the Possibilities of finest screenings accessible. For example, cyclodextrin molecules can be used for the geometric identification of the color particles according to the invention. Cyklodextrins are sugar molecules with characteristic shape and size. They also have the advantage that they are biodegradable, toxicologically safe and can be produced by enzymatic degradation of starch on a large scale inexpensively and in any purity.

Under the formation of complex and / or covalent bonds z. B. azo dyes are attached and thereby the geometrically characteristic molecules are provided with desired hues. Since cyclodextrins have a hydrophobic cavity, this can also be used to store or store color particles. In addition to the use as geometric identification molecule on the color particles, it is also conceivable to use cyclodextrins as geometric or functional identification molecules in the printing form.

Another class of materials for geometric identification color particles are pieces of fiber, complex forming Supramolekülgruppen or macromolecules in a suitable shape and size, to which then the dyes, pigments or other color particles, eg. As the Cyklodextrinmoleküle described above, are attached, in which case, in particular, the cyclotriveratrylenes should be noted. With these supramolecular components, it is possible to complex the pigment particles used today, so that the pigment production would hardly have to be changed compared to conventional paints. In addition, functional groups can be coupled to such supramolecular components, so that the molecules can be selectively produced (molecular design).

Very promising are the technical possibilities by Polyelektrolytkapseln with characteristic geometric shape. Polyelectrolyte capsules can be chemically functionalized and combined with coloring groups. They can also serve as dye containers. A very important advantage is that polyelectrolyte capsules in Sizes from a few nm to a few hundred microns can be produced. It is thereby possible to adapt the "color production" to the respective technical approaches in the production of the markings on the printing plate. In particular, it is intended here at different spatial resolutions when using different exposure wavelengths.

As in FIG. 4 but it is also possible, the printing plate 20 functionally, ie to identify by the provision of certain chemical groups at certain points of the printing plate 20. These markings 42, 43, 44, 45 are different from each other and allow the attachment of dyes or pigments having the corresponding markings 42 ', 43', 44 ', 45'. In FIG. 4 this possibility of attachment by the addition arrows a is shown. The markings 42, 43, 44, 45 on the pressure plate 20 can be, for example, molecular chains with correspondingly functional groups which can be coated with the corresponding markings of the dyes or pigments 42 ', 43', 44 '45'. In the selection of the markings 42, 43, 44, 45 of the printing plate 20 and the correpondierenden markings 42 ', 43', 44 ', 45' of the dyes or pigments, for example, can be made of molecules having a coupling process, analogous to the the base sequences in a DNA chain is to be considered.

In FIG. 5 is shown a way to apply the markings on the surface of a printing plate 20. In this case, the printing form 20 is produced so that a plurality of layers are applied to a base 46, which already contain the respective markings 42, 43, 44, 45. With the help of in FIG. 1 shown laser radiation, it is now possible to remove the top layer of the printing form 20 so far that each of the desired marking is located on the surface of the printing plate 20. This makes it possible to attach different color molecules at the points 48, 50 and 52, which correspond to the particular marking present there.

Another possibility for generating the marking on the printing form 20 is in FIG. 6 shown. The printing plate 20 is hereby made so that on a base 46 a additional layer 54 is applied. This layer 54 includes capsules 56 that are tightly packed in layer 54 and that contain the various indicia 42, 43, 44, 45 required for the printing process. For example, in one operation where electromagnetic radiation such as a laser or an electric field is applied, the capsules 56 may be selectively broken so that the tag may surface. Since the markings 42, 43, 44, 45 are each housed in capsules 56 which have different properties, in particular different wall properties, it is possible to selectively control only by controlling the intensity of the laser beam or wavelength and by controlling the applied field Break capsules so that selectively certain labels can escape from the capsules.

If a conventional or a short inking unit is used for the application of ink to the printing plate, then the self-assembly of the color particles on the printing plate takes place by splitting the color layer several times back and forth. Analogous to today's standard offset method, the effective forces resulting from the surface energy and the rheology of the color are adjusted so that no toning and no "color toning" occurs. So that means that at the non-image areas can not hold any color particles, so no cloning occurs, and can hold only the appropriate color particles at the corresponding marked image locations, which is referred to as color tones.

If alternative techniques for the application of paint to the printing plate are used, such as a dipping bath or spraying techniques, the ink particles in the ink must not adhere to one another and should be able to diffuse easily to the identification points in order to ensure a self-alignment. The color should then be as thin as possible. In particular, in the waterless offset, therefore, a job using a paint spray can be very well implemented. In a subsequent wiping operation, it is possible to easily remove the unnecessary paint, wherein the forces must be designed so that the binding forces to the markings are greater than the wiping force.

In particular, in indirect printing, ie when transferring the color to a blanket, there may be problems in transferring the color, for example, due to high capillary forces or excessive adhesion forces of the color particles at the identification points. In a further advantageous embodiment of the invention, therefore, electrically charged color particles are used, wherein in addition a workable electric field is used on the printing plate. This means that the color molecules are electrically attracted when applied to the plate and are electrically repelled from the plate when transferred to the blanket as soon as the electric field is reversed.

LIST OF REFERENCE NUMBERS

10

Process step marking

12

Process step Creation of printing ink

14

Process step Print

16

Process step doctoring

18

Process step Mark

20

printing form

21

nip

22

Impression cylinder

24

substrate

25

Component for applying the printing ink

26

application roller

28

anilox roller

30

paint container

32

laser

34

laser beam

35, 36, 37, 38

markings

40

Points

42, 43, 44, 45

markings

46

Base layer

48, 50

Points

d

diameter

52

Points

54

layer

56

capsules

Claims (9)

1. A method for applying printing ink to a printing material, which comprises producing a plurality of ink-conducting areas (35-38, 42-45) with defined color acceptor properties for printing inks of various colors on a surface of a flat printing form (20); bringing the surface into contact with color particles (42'-45') from a container (30) with a mixture of differently colored printing inks, wherein the color particles (42'-45'), possessing surface acceptor properties corresponding to the color acceptor properties, are deposited on the corresponding areas (35-38, 42-45); and transferring the deposited color particles (42'-45') from the surface to the printing material (24).
2. Method according to claim 1, characterized in that the color acceptor properties on the surface are produced with the aid of electromagnetic radiation.
3. Method according to claim 1, characterized in that the color acceptor properties on the surface are provided as geometric shapes, wherein geometric markings are provided on the surface, allowing color particles possessing corresponding geometric properties to be deposited.
4. Method according to claim 1, characterized in that the color acceptor properties on the surface are provided as functional chemical groups, wherein printing inks (42'-45') with corresponding functional groups are used.
5. Method according to claim 4, characterized in that the color acceptor properties on the printing form (20) are produced by at least partial removal of a coating.
6. Method according to claim 4, characterized in that the color acceptor properties on said printing form (20) are produced by breaking open capsules (56).
7. Method according to claim 6, characterized in that a laser (32, 34) with a different wavelength and/or pulse intensity is operated in order to produce different color acceptor properties.
8. Method according to claim 6, characterized in that an electric field is applied in order to produce the color acceptor properties on the printing form (20).
9. Method as claimed in any one of claims 1 to 8, characterized in that the deposition of the color particles on said printing form (20) is assisted by applying a reversible electric field.

Images