CN112078264A - Printing method using compensated printing image for balancing inkjet printing defects - Google Patents

Abstract

The invention relates to a printing method for producing a printed product, in which inhomogeneities of the inkjet ink during inkjet printing, in particular by the substrate to be printed, are equalized by means of a compensating printing image printed before inkjet printing. Wetting behavior and/or optical defects caused by defective inkjet printing nozzles.

Description

Printing method using compensating printed image for equalizing inkjet printing defects

technical field

The present invention relates to a method for producing a printed article and a printed article obtained by the method according to the present invention.

Background technique

In the case of printing substrates, such as sheet-like or web-like substrates, such as paper, cardboard or plastic, defective print results can partly occur during inkjet printing. That is to say, the printed image in the prepress stage and the finished printed image on the substrate deviate from each other in an undesired manner. In this case, the substrate, for example, has too much or too little ink in certain areas. The cause of defective print results can be traced to the substrate, the inkjet system (especially the inkjet printhead), or both.

A known problem in the production of printed articles is that the substrates used do not have homogeneous, ideal surface properties, but rather have an inhomogene surface. Such surfaces may, for example, have a non-homogeneous wetting behavior for inkjet inks. Sometimes the substrates used in printing all have the same non-homogeneous surface. When printing such substrates by means of ink jet printing, as long as no special measures are taken, prints are obtained which all exhibit the same altered printed image, the same altered printed image Has the same flawed optical appearance.

Another known problem in the manufacture of printed articles is traced back to the ink jet print heads of ink jet printers, which partly have faulty ink jet printing nozzles. These faulty inkjet printing nozzles then in particular do not print on the substrate parallel to the adjacent inkjet printing nozzles, but rather at an angle. As a result, defective printed images on the substrate can also be caused by inkjet printheads with inkjet printing nozzles that are printed at an angle.

To deal with defective printed images, different approaches have been suggested. For example, it is known in principle to optically evaluate the substrate before printing by means of a camera system and to modify the print image in the prepress phase based on this evaluation in such a way that the desired error-free print image is obtained on the substrate as a result.

基于这种光学探测来生成用于补偿印刷图像的校正数据。DE 43 34 712 A1 describes a reproduction system comprising a printing press, in which distortion of the printed image is detected by means of a camera

Correction data for compensating the printed image is generated based on this optical detection.

WO 2005/092613 A2 describes a printing press with an optical detection device which, on the basis of the detected printing image data, judges the quality of such printing and, if necessary, changes the parameters of the printing press based on this.

The methods known from the prior art are relatively complex. These methods typically require analytical evaluation of each individual substrate prior to the original printing process.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method by means of which a printed image that is as defect-free as possible is obtained during inkjet printing. The method should be simple to implement with conventional printing presses and should not require a complex image analysis for each individual substrate. The method should in particular also be suitable for continuously compensating for recurring non-homogeneous surfaces on successively printed sheets or webs.

It has been found that a defect-free printed image can be obtained in a simple manner by means of inkjet printing if a suitable compensation printing image is applied to the substrate prior to inkjet printing. These compensating printed images are preferably colorless or have substantially the same color as the substrate, so that an observer of the finished printed article ideally cannot recognize such compensating printed images with the naked eye, but is obtained after inkjet printing in Optically flawless printed images. These offset printing images or intermediate images can be applied to the substrate simply by means of printing methods known in principle, such as offset printing, flexographic printing or screen printing.

Accordingly, the invention relates to a method for producing a printed product, wherein a substrate is printed by means of at least one inkjet print head, wherein the substrate and/or the at least one inkjet print head have a At least one defect of a defective printed image on the substrate, characterized in that the substrate is equalized by imprinting an intermediate image on the substrate before printing by means of the at least one inkjet print head and/or at least one defect of the at least one inkjet print head, thereby obtaining a substantially defect-free printed image on the substrate.

In a preferred embodiment, a substrate having a non-homogeneous surface is used, and the properties of the intermediate image are selected such that the intermediate image substantially compensates for the non-homogeneous surface of the substrate. Particular preference is given to using a substrate which has a non-homogeneous wetting behavior for the inkjet ink of the at least one inkjet print head. This is to be understood in particular as substrates which do not have a uniform wetting behavior for inkjet inks, in particular aqueous inkjet inks, over the entire surface of the substrate. The surface of the substrate can accordingly be easily wetted with the aqueous inkjet ink in one area, for example, and difficult to wet with the aqueous inkjet ink in another area.

In another preferred embodiment, the at least one inkjet print head has a non-ideal image generation performance. Such non-ideal image production behavior of the at least one inkjet printhead can be traced only to the at least one inkjet printhead or to other components of the overall inkjet system (in particular the electronic drive or ink supply system). An example of non-ideal image production performance for the at least one inkjet print head is the presence of inkjet printing nozzles that exhibit deviating performance from most inkjet printing nozzles and that The printing nozzles in particular apply the inkjet ink obliquely to the substrate. Thus, the inkjet print head in this preferred embodiment in particular comprises one or more inkjet printing nozzles with non-ideal printing performance.

In another preferred embodiment, the intermediate image is a dot/raster. A periodic grid is particularly preferred. As a periodic grating, a grating capable of compensating for the anisotropic properties of the substrate is particularly preferred. As a result, the best possible isotropy for the final printed image is obtained on the substrate. For example, the substrate may have, as an anisotropic property, a preferential ink flow direction at an angle of about 90° with respect to the reference line. Then, as an intermediate image, a periodic grid is usually chosen which compensates for the preferential ink flow direction within the substrate in such a way that the final obtained printed image no longer has a preferential direction, that is to say is ultimately isotropic of. In particular, the substrate, such as a sheet of paper, may have a preferential ink flow direction that results in a pattern of stripes being printed parallel to the sheet edges if there is no intermediate image. But it is desirable that the stripe pattern does not appear. In this case, an intermediate image is usually selected which has a grid of strips oriented perpendicular to the edges of the sheet. In this way, the anisotropy of the intermediate image compensates for the anisotropy of the substrate and as a whole an error-free (in this case isotropic) printed image is obtained.

In the method according to the invention, an intermediate image is printed on the substrate. Preferred printing methods for imprinting the intermediate image are selected from form-dependent/formgebundenes printing methods, in particular: offset printing methods, flexographic printing methods, screen printing methods and combinations thereof.

As printing media in the printing process for applying the intermediate image to the substrate, in principle all printing media (in particular printing pigments and printing varnishes) which can be used in the respective printing process used are considered in principle. In a preferred embodiment, the at least one print medium is colorless. In another preferred embodiment, the at least one print medium has substantially the same color as the substrate. Printing media with different colors can also be used, especially when the substrates are of different colors.

A preferred print medium that can be used to make the intermediate image is water repellent. Particular preference is given to oil-based offset printing pigments. The substrate is partially encapsulated by printing the intermediate image by means of this or a similar printing medium. This has the additional advantage when using especially water-based inkjet inks that the water-based inkjet ink printed onto such partially enclosed areas will stay on the surface of the substrate longer without bleeding into the base. Thereby, thermal drying of the inkjet ink in the printing press can be achieved more easily. Another effect is that there is less deformation of the substrate due to penetrating water when using paper or cardboard as the substrate.

The substrate can be used in the method according to the invention in different forms, preferably in the form of sheets or webs. If the substrate is in the form of a web, one or more cutting devices can be provided before or after the printing method for cutting the printed web into individual sheets.

In principle, all types of printing substrates that can be processed in a printing press are considered as substrates for the method according to the invention. This can be, for example, plastic (especially plastic film), metal (especially metal film), paper or cardboard. In a preferred embodiment, the substrate is selected from paper, cardboard and plastic.

The printed articles obtained by the method according to the invention are also the subject of the invention.

The method according to the invention is also suitable for continuously compensating for repeated non-homogeneous surfaces on sheet-like or web-like substrates. In this case, such a sheet-like or web-like substrate preferably has the same non-homogeneous surface on each printed section. Here, for example, it may be a stack of paper sheets in which all the individual sheets have the same non-homogeneous wetting behavior for the inkjet ink.

Description of drawings

FIG. 1 : exemplarily illustrates the method according to the invention;

Figure 2: Illustratively shows an intermediate image that can be used to compensate for a non-homogeneous surface of a substrate.

Detailed ways

Figure 1 should further illustrate the method according to the invention. The path on the left shows a method according to the invention, the path on the right shows a method not according to the invention for comparison purposes. The starting point of the present invention is a substrate (1) with a non-homogeneous surface, such as a paper sheet, which on its own side exhibits a non-homogeneous wetting behavior for aqueous inkjet inks. According to the invention, the paper sheet is printed with an intermediate image ( 2 ), ie a substrate ( 1 ) having a non-homogeneous surface, which is structured in the form of a periodic grid (all directions opposite sex) (shown only schematically). This printing is carried out in an offset printing press (not shown) by means of offset printing in offset printing colors. Then, a circular image is printed as a print image (3) on the intermediate image (2) with an aqueous inkjet ink by means of an inkjet print head (5). The intermediate image (2) compensates for the non-homogeneous surface (anisotropy) of the substrate (1). As a result, a circular optical image, ie a substantially defect-free printed image (3), is obtained on the substrate (1). The anisotropy of the substrate and the anisotropy of the intermediate image balance each other. In contrast, if a circular image is printed directly onto a substrate (1) with a non-homogeneous surface without passing through the inkjet print head (5) with aqueous inkjet printing in the middle of the intermediate image (2) step, then a distorted circular image, ie a defective printed image (4), is obtained.

Figure 2 exemplarily shows an intermediate image (2) that can be used to compensate for a non-homogeneous surface of a substrate (1). Such printed images can be printed in an offset printing press simply by means of offset printing.

List of reference signs

1 base

2 Intermediate images

3 Substantially defect-free printed images

4 Defective printed images

5 Inkjet print head

Claims (10)

1. A method for manufacturing a printed article of manufacture,

wherein the substrate (1) is printed by means of at least one inkjet print head (5),

wherein the substrate (1) and/or the at least one inkjet printing head (5) have at least one defect which leads to a defective printed image (4) on the substrate (1),

it is characterized in that the preparation method is characterized in that,

-compensating for said at least one defect of said substrate (1) and/or said at least one inkjet print head (5) by printing an intermediate image (2) on said substrate (1) prior to printing by means of said at least one inkjet print head (5), thereby obtaining a substantially defect-free printed image (3) on said substrate (1).

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein a substrate (1) having a non-homogeneous surface is used, and

the characteristics of the intermediate image (2) are selected such that the intermediate image (2) substantially compensates for a non-homogenous surface of the substrate (1).

3. The method of claim 2, wherein the first and second light sources are selected from the group consisting of,

wherein the substrate (1) having a non-homogenous surface has a non-homogenous wetting behaviour with respect to the inkjet ink of the at least one inkjet print head (5).

4. The method according to any one of the preceding claims,

wherein the at least one inkjet print head (5) has a non-ideal image producing appearance.

5. The method of claim 4, wherein the first and second light sources are selected from the group consisting of,

wherein the at least one inkjet print head (5) has one or more inkjet printing nozzles with a non-ideal printing behaviour.

6. The method according to any one of the preceding claims,

wherein the intermediate image (2) is a periodic grid.

7. The method according to any one of the preceding claims,

wherein the intermediate image (2) is applied by a form-dependent printing method, in particular an offset printing method, a flexographic printing method or a screen printing method.

8. The method according to any one of the preceding claims,

wherein the intermediate image (2) is colorless or has substantially the same color as the substrate (1).

9. The method according to any one of the preceding claims,

wherein the substrate (1) is in the form of a sheet or web and is selected from: paper, cardboard and plastic.

10. A printed article obtained by the method according to any one of claims 1 to 9.

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