Patent Grant
11529815
This application claims the priority, under 35 U.S.C. § 119, of German application DE 10 2017 212 015.0, filed Jul. 13, 2017; the prior application is herewith incorporated by reference in its entirety.
The present invention relates to a method for pretreating a printing material for ink jet printing to influence the spreading of ink print dots on the printing material.
The technical field of the invention is the field of the graphic arts industry and in particular the field of industrial ink jet printing on flat substrates, i.e. the field of applying liquid ink to sheet-shaped or web-shaped printing materials, preferably made of paper, cardboard, or plastic.
In the known DOD (drop-on-demand) ink printing methods, liquid ink is applied and a print is created on a flat printing substrate by an ink printing head (in short: head) with individually controllable nozzles that generate tiny ink droplets, preferably in a picoliter range, and transfer them to the printing substrate in a touch-free way as print dots in accordance with the image to be printed. The nozzles may be actuated by piezoelectric actuators.
In general, every head has a plurality of individually controllable nozzles. In general, the nozzles are disposed in one or more rows of nozzles that are parallel to (or slightly inclined relative to) the direction of transport of the printing material. When actuated, every nozzle generates an ink drop. When a nozzle is continuously actuated, it prints a visible line in the color of the ink onto the printing material.
On the other hand, a visible line may occur if a nozzle does not work properly, for instance because its nozzle opening is blocked by solidified ink. As the failed nozzle consistently does not produce any ink drops, the printing material color, usually white, will become visible as a white line in the print. Such undesired stripes (also referred to as “missing nozzle” or “missing line”) affect the quality of the print and thus the quality of the printed product.
Published, European patent applications EP1955858 A1 (corresponding to U.S. Pat. No. 8,541,063) and EP1958782 A1 (corresponding to U.S. patent publication No. 2008/019962) describe liquids that are applied to the entire surface of the substrate before ink is applied; they have an influence on the spreading behavior of the ink drops on the substrate. U.S. patent publication No. 2010053236 A1 discloses the application of an aqueous precoat over the entire surface to influence the spreading behavior.
Against this background, an object of the present invention is to provide a method that overcomes the disadvantages of the prior art and improves the quality of a print to be created and thus of the printed product and in particular reduces or avoids the formation of undesired stripes caused by failed nozzles.
In accordance with the invention, this object is attained by a device as recited in the main claim. Advantageous and thus preferred further developments of the present invention will become apparent from the dependent claims as well as from the description and drawings.
The invention relates to a method for pretreating a printing material for ink printing wherein the spreading behavior of ink print dots on the printing material is influenced. The method is characterized in that the spreading behavior is influenced in such a way that the ink print dots spread in an anisotropic way.
The invention advantageously allows the quality of the printed image and thus of the printed product to be improved, in particular to reduce or avoid the formation of undesired stripes caused by failed nozzles.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced by an anisotropic application of a liquid, in particular a primer or varnish, to the printing material. The application may be achieved by at least one print head (similar to or identical with an ink print head). The varnish may be a UV varnish and may be pinned, in particular if UV-curable inks are used. The primer may be what is referred to as a precoat (containing water and an acid), in particular if water-based inks are used.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced by an anisotropic embossment or print on the printing material. The embossment or print may be created by an anisotropic embossing or printing plate, in particular a flexographic printing plate (or a lithographic offset or gravure plate). The embossment may in particular be a micro-embossment, i.e. an embossment of structures in an order of magnitude of between 0.1 μm and 10 μm, in particular structures of approximately 1 μm in terms of size (e.g. line width) and spacing. The anisotropic spreading influenced by the embossment may, for instance, be attained by a capillary effect of the embossment structures on the ink. In flexographic printing, line widths and spacings of approximately 6 μm may be created.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced by an anisotropic treatment of the printing material with charged particles, in particular with a plasma or a corona, or with electromagnetic radiation, in particular laser radiation. By laser radiation, line widths and spacings of approximately 1 μm or less may be created.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced in such a way that the transverse spreading behavior in a direction essentially perpendicular to a side edge of the printing material is increased relative to the longitudinal spreading behavior in a direction essentially parallel to the side edge. Advantageously, a provision may be made for the increased transverse spreading to be factored in as early as at a preprint stage when print data are generated for the ink print heads inasmuch as the widening of the print dots (and thus of longitudinal lines, for instance) correlated with the transverse spreading is compensated for. Advantageously, a provision may be made for print dots to be printed closer together in a longitudinal direction (or to reduce the printing material transport speed in a corresponding way) to counteract undesired (“white”) transverse lines that may occur as a result of the transverse spreading.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced in such a way that the transverse spreading behavior in a direction essentially perpendicular to a side edge of the printing material is reduced relative to the longitudinal spreading behavior in a direction essentially parallel to the side edge.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced in such a way that the longitudinal spreading behavior in a direction essentially parallel to a side edge of the printing material is increased relative to the transverse spreading behavior in a direction essentially perpendicular to the side edge.
A preferred further development of the invention may be characterized in that the spreading behavior is influenced in such a way that the longitudinal spreading behavior in a direction essentially parallel to a side edge of the printing material is reduced relative to the transverse spreading behavior in a direction essentially perpendicular to the side edge.
A preferred further development of the invention may be characterized in that the side edge is aligned to be parallel to a direction of transport of the printing material.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for pretreating a printing material for ink jet printing, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly to
A printing material 1, e.g. paper, cardboard, or a foil, has side edges 2. The printing material is conveyed along a device in a direction of transport 3. The device may be part of an ink printing machine and may comprise at least one transport element for transporting the printing material, in particular a transport cylinder or a transport belt. A transverse direction 4 is perpendicular to the side edges 2; a longitudinal direction 5 is parallel to the side edges 2.
The device suitable for implementing the method of the invention contains an ink print head 6 with a row of individually controllable nozzles 7 (disposed to be essentially parallel to the transverse direction). The ink print head may be configured as an assembly of multiple neighboring heads as what is known as a print bar, and may in particular extend over the width of the printing material 1 (measured in the transverse direction 4); in short, it may be as wide as a page. For a better understanding of the invention, individual nozzles 7a to 7d of the head 6 are shown at an enlarged scale.
The device further contains an element 8 for pretreating the printing material 1. The element 8 may for instance be a print head 8a for treatment liquid or an embossing or printing device 8b (or a plasma or corona device or a laser 8c). Like the print head 6, the device 8 may be as wide as a page. The preferred embodiment including a print head 8a will be described below. In a way similar to print head 6, such a print head 8a includes individually controllable nozzles 9 disposed in a row. The treatment liquid may be ink, in particular colorless or white ink, or a primer (e.g. what is known as a “precoat”), in particular a varnish or a liquid containing water and an acid for reacting with the ink.
The printing material 1 shown in
As shown in
As shown in the first region 1a, the nozzles 7a are actuated to create ink drops and consequently ink print dots 13 on the printing material 1. Additionally, it can be seen that the ink print dots of adjacent nozzles 7a run together on the printing material 1 to form a continuous ink surface due to the spreading of the ink.
Nozzle 7b is likewise actuated separately, but it is an example of a defective nozzle or one that has been blocked by solidified ink. Thus nozzle 7b creates no ink drop and thus no ink print dot 13. The failure of nozzle 7b results in a visible white line 14 extending in a longitudinal direction 5. If black ink is printed onto white paper, for instance, a white line 13 would be visible in a black environment. This is an undesired phenomenon. Without limiting the invention in any way, please note that the exemplary embodiment assumes that a white printing material is used, resulting in a potentially visible white line.
In the second region 1b, it is shown that nozzles 7c are actuated to create ink drops and ink print dots 15 on the printing material 1. In addition, it is visible that the ink print dots of adjacent nozzles 7c run into one another on the printing material 1 to form a continuous ink surface due to the spreading of the ink.
In the second region 1b, the spreading behavior of the ink print dots 15 is influenced by the anisotropic structure 10 that has been created. The ink print dots spread in an anisotropic way; for instance, their spreading behavior in the longitudinal direction 5 differs from that in the transverse direction 4 (in the illustrated example, the print dots become essentially elliptical). In the illustrated example, the transverse spreading behavior of the ink print dots 15 is increased relative to the longitudinal spreading behavior. This increase may be caused, for instance, by a liquid 11 that is applied by the device 8 in an anisotropic way to attain increased transverse spreading.
Nozzle 7d in the second region 1b is an example of a missing nozzle that does not create any print dot 15. However, it can be seen that the white line 16 is closed because of the increased transverse spreading behavior. Line 16 in
The top of the two regions 1a and 1b (“top” with respect to
A computer 17, which is connected to the print head 6 and the device 8 by lines 18, controls the two units 6, 8. The print head 6 is actuated in accordance with the image to be printed or in accordance with corresponding data. The device 8 is preferably actuated with data or patterns that exhibit anisotropy or create anisotropy as they are processed.
The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017212015.0 | Jul 2017 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6649249 | Engle et al. | Nov 2003 | B1 |
| 8541063 | Kawakami et al. | Sep 2013 | B2 |
| 8789925 | Thompson | Jul 2014 | B1 |
| 9376582 | Dannhauser | Jun 2016 | B1 |
| 9662889 | Zhang et al. | May 2017 | B2 |
| 20040191688 | Mizushima | Sep 2004 | A1 |
| 20080199631 | Makuta et al. | Aug 2008 | A1 |
| 20090133169 | Mirkin et al. | May 2009 | A1 |
| 20090237442 | Yamanobe | Sep 2009 | A1 |
| 20100053236 | Ooishi et al. | Mar 2010 | A1 |
| 20160052302 | Willems | Feb 2016 | A1 |
| 20180147871 | Landa | May 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 1353647 | Jun 2002 | CN |
| 1538423 | Oct 2004 | CN |
| 104417064 | Mar 2015 | CN |
| 102014201050 | Aug 2014 | DE |
| 1955858 | Aug 2008 | EP |
| 1958782 | Aug 2008 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20190016157 A1 | Jan 2019 | US |
