METHOD OF PRODUCING PRINTED PRODUCTS

Abstract

A printed product is produced by applying at least one colored and water-containing ink to image regions on a printing material in a drop-on-demand process, applying a substantially colorless and water-containing liquid a) to non-image regions and/or b) to image regions that have little ink in a drop-on-demand process and drying the printing material. In this case, the printing material has a coating with at least one acid. After applying ink and applying the liquid, a water-containing further liquid is applied both to image regions and to non-image regions of the printing material. The first-mentioned liquid and/or the further liquid contains at least one substance for at least partly neutralizing the acid. The undesired formation of crease waves or curls and glossiness fluctuations between varnished image areas and varnished non-image areas is thus advantageously avoided.

Claims

1. A method of producing a printed product, the method comprising: providing a printing material substrate with a coating containing an acid; applying at least one colored and water-containing ink to image regions on said coating in a drop-on-demand process; applying a substantially colorless and water-containing liquid in a drop-on-demand process to one or both of the following: a) non-image regions on the coating; and/or b) image regions on the coating that carry only a small amount of ink; applying a water-containing further liquid both to the image regions and to the non-image regions on the printing material; and wherein at least one of the water-containing liquid or the water-containing further liquid contains a substance for at least partly neutralizing the acid; and drying the printing material.

2. The method according to claim 1, wherein the water-containing liquid is a colorless, water-based ink that is substantially free of binding agents.

3. The method according to claim 1, wherein the water-containing liquid is a non-pigmented or colorant-free liquid.

4. The method according to claim 1, wherein a concentration of the substance for at least partly neutralizing the acid substantially corresponds to a defined concentration value and the defined concentration value depends on a concentration of the acid in the coating.

5. The method according to claim 4, which comprises selecting the defined concentration value so as to achieve a substantially complete neutralization of the acid.

6. The method according to claim 1, wherein the drying step comprises irradiating the printing material and wherein the water-containing liquid contains an IR absorber.

7. The method according to claim 6, wherein the water-containing liquid contains an optical whitener.

8. The method according to claim 1, wherein the water-containing liquid is applied to a) the non-image regions on the coating and an average of an amount of liquid applied per unit area on the printing material is substantially equal to an average amount of ink applied per unit area on the printing material.

9. The method according to claim 1, wherein the substance for at least partly neutralizing the acid is a base.

10. The method according to claim 9, wherein the substance for at least partly neutralizing the acid is an amine, 2-Amino-2-methyl-1-propanol, and an alkali hydroxide.

11. The method according to claim 10, wherein the amine is a water-soluble amine.

12. The method according to claim 10, wherein the alkali hydroxide is NaOH or KOH.

13. The method according to claim 1, wherein the water-containing further liquid is a colorless liquid.

14. The method according to claim 13, wherein the water-containing further liquid is a water-based varnish.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0035] The sole FIGURE of the drawing contains a flow chart of a preferred exemplary embodiment of the method of the invention and a side-by-side illustration of device-related measures for implementing the method.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Referring now to the FIGURE of the drawing in detail there is shown a schematic illustration of steps A to E and E′, respectively, of a preferred embodiment of the method of the invention, in the form of a flow chart. Next to every step, the FIGURE also schematically shows the respective device-related measures that may be taken and how the printed product may successively be produced.

[0037] Step A is to provide a printing material substrate 10 having a surface 10′. The printing substrate may be a sheet or a web. The printing substrate may be made of paper, cardboard, or plastic. A coating 11 comprising an acid 11a is applied to the printing substrate. The coating may for instance be applied by means of a roller 13. As an alternative to the illustrated step A, a printing substrate may be provided that has already been coated with an acid. The expression “providing a substrate with a coating,” therefore, may relate to either alternative.

[0038] In step B, a water-based ink 21 is printed onto the printing material 10 or rather the surface 10′ thereof, i.e. an ink layer 21 is created. The image region may for instance represent a pattern, image, or text. To create the ink layer 21, ink droplets 22 are transferred to the printing material, i.e. the surface thereof, in a contact-free way by way of a print head 23. In this process, the print head is controlled in a known way, making use of the print data required for the image. In general, this process requires a relative movement between the print head and the printing material to be generated. It is possible to print more than one ink, e.g. four (CMYK) or more than four (CMYK plus spot color/s). The ink may contain pigments or colorants to give it color.

[0039] In step C, a liquid 31 is applied to a non-image region and/or a liquid layer 31 is created. The liquid contains at least one substance 31a for neutralizing the acid 11a, preferably a base such as NaOH or KOH. In addition, the liquid may contain a second substance 31b, preferably an IR absorber. In addition, the liquid may contain a third substance 31c, preferably an optical whitener. In the non-image areas of the surface 10′ of the printing substrate 10, the acid 11a is neutralized by the application of the liquid 31 and the neutralizing substance 31a contained therein. The application of the liquid 31 is achieved by transferring liquid droplets 32 to the surface of the printing substrate by means of a further print head 33 in a contact-free way. The use of a print head makes it easy to control the amount of liquid that is applied.

[0040] In step D, a further liquid 41 is applied to the printing material 10, i.e. the surface 10′ thereof, and/or a further liquid layer 41 is created. The application may for instance be achieved by means of a roller 43. The further liquid may be a colorless or transparent water-based varnish. Such a layer of varnish may essentially cover the entire surface of the printing material, i.e. both the image areas 20 and the non-image areas 30. In accordance with the invention, the neutralized acid has no (chemical) effect or only a minor (chemical) effect on the varnish layer, which thus globally (over the entire printing material, i.e. in image regions and non-image regions) exhibits a substantially homogeneous glossiness.

[0041] In step E, the printing material 10 or rather the surface 10′ thereof and in particular the ink 21 and liquids 31 and 41 applied thereto are dried, preferably thermally. For this purpose, IR radiation 52 may be generated and directed towards the printing material surface by means of an IR drier 53, e.g. an LED drier or an LED laser drier. This process may likewise require a relative movement between the drier and the printing material to be carried out. The intensity of the radiation may be controlled.

[0042] An alternative to step E is to carry out a drying step E′, which preferably occurs after step C and before step D. Another alternative is to carry out both drying steps E and E′.

[0043] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0044] 1 printed product [0045] 10 printing material [0046] 10′ surface [0047] 11 coating [0048] 11a acid [0049] 13 roller [0050] 20 image region [0051] 21 ink/ink layer [0052] 22 ink drops [0053] 23 print head [0054] 30 non-image region [0055] 31 liquid/liquid layer [0056] 31a neutralizing substance/base [0057] 31b second substance/IR absorber [0058] 31c third substance/optical whitener [0059] 32 drops of liquid [0060] 33 further print head [0061] 41 further liquids/further liquid layer/varnish layer [0062] 43 roller [0063] 52 IR radiation [0064] 53 IR drier [0065] A providing a printing substrate with a coating [0066] B applying ink [0067] C applying liquid [0068] C applying further liquid/varnish [0069] E, E′ IR drying