Method for pretreating a printing material for ink jet printing

Abstract

A method pretreats a printing material used for ink printing to influence the spreading of ink print dots on the printing material. The spreading behavior is influenced in such a way that the ink print dots spread in an anisotropic way. The anisotropic spreading advantageously allows undesired quality losses in the print that are caused by a failed ink nozzle to be reduced or avoided. The influencing of the spreading behavior may be achieved by an anisotropic application of a liquid, in particular a primer or varnish, to the printing material, or by an anisotropic embossment or print on the printing material or by an anisotropic treatment of the printing material with charged particles, in particular by a plasma or a corona, or with electromagnetic radiation, in particular laser radiation.

Claims

1. A method for pretreating a printing material used in ink jet printing to influence a spreading of ink print dots on the printing material, which comprises the step of: influencing a spreading behavior such that the ink print dots spread in an anisotropic way.

2. The method according to claim 1, which further comprises influencing the spreading behavior by an anisotropic application of a liquid to the printing material.

3. The method according to claim 2, which further comprises selecting the liquid from the group consisting of a primer and a varnish.

4. The method according to claim 1, which further comprises influencing the spreading behavior by an anisotropic embossment or print on the printing material.

5. The method according to claim 1, which further comprises influencing the spreading behavior by performing an anisotropic treatment of the printing material with charged particles or with electromagnetic radiation.

6. The method according to claim 1, which further comprises influencing the spreading behavior such that a transverse spreading behavior in a direction perpendicular to a side edge of the printing material is increased relative to a longitudinal spreading behavior in a direction parallel to the side edge.

7. The method according to claim 6, which further comprises aligning the side edge to be parallel to a direction of transport of the printing material.

8. The method according to claim 1, which further comprises influencing the spreading behavior such that a transverse spreading behavior in a direction perpendicular to a side edge of the printing material is reduced relative to a longitudinal spreading behavior in a direction parallel to the side edge.

9. The method according to claim 1, which further comprises influencing the spreading behavior such that a longitudinal spreading behavior in a direction parallel to a side edge of the printing material is increased relative to a transverse spreading behavior in a direction perpendicular to the side edge.

10. The method according to claim 1, which further comprises influencing the spreading behavior such that a longitudinal spreading behavior in a direction parallel to a side edge of the printing material is reduced relative to a transverse spreading behavior in a direction perpendicular to the side edge.

11. The method according to claim 1, which further comprises achieving an influencing of the spreading behavior by an anisotropic embossment or a flexographic print on the printing material.

12. The method according to claim 1, which further comprises achieving an influencing of the spreading behavior by performing an anisotropic treatment of the printing material with charged particles with a plasma or corona, or with laser radiation.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is an illustration of an exemplary embodiment of a method of the invention and a device for carrying out the method of the invention; and

(2) FIGS. 2A to 2C are illustration showing anisotropic patterns for influencing a spreading behavior in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a preferred exemplary embodiment of a method of the invention. At the same time, FIG. 1 illustrates a preferred exemplary embodiment of a preferred device carrying out the method of the invention.

(4) 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.

(5) 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.

(6) 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.

(7) The printing material 1 shown in FIG. 1 has a first region 1a and a second region 1b. In the first region, the element 8 is inactive; consequently, the spreading behavior is not influenced. In the second region, the device 8 is active; consequently, the spreading behavior is influenced in such a way that the ink print dots spread in an anisotropic way. The two regions are shown to be next to one another (solely for understanding the invention) to visualize the effect of the method of the invention. Under production conditions, the element 8 will preferably treat the entire surface of the printing material 1 instead.

(8) As shown in FIG. 1, the element 8 creates an anisotropic structure 10 in the second region 1b, in particular lines of a specific width and spacing. The anisotropic structure is preferably created by a liquid 11 applied by the element 8/8a. Alternatively, the anisotropic structure 10 may be created as an embossment/print/plasma/corona/laser structure 12, i.e. as a structure that is created by embossing, printing, plasma treatment, corona treatment, and/or laser treatment.

(9) 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.

(10) 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.

(11) 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.

(12) 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.

(13) 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 FIG. 1 is not shown as a completely closed or covered line to illustrate the closing of the line and the position thereof. In a preferred case, the transverse spreading behavior is influenced in such a way, however, that the entire line 16 is covered and no longer visible as a white line, for instance.

(14) The top of the two regions 1a and 1b (“top” with respect to FIG. 1) illustrates drops applied to create print dots 13/15 spaced apart from one another in a longitudinal direction. This illustration is only used to explain the invention and to show how individual print dots (without direct neighbors) behave with and without the influencing of the spreading behavior in accordance with the invention. The print dots shown in region 1a have a size (average diameter) of approximately 40 μm. The anisotropic structures (lines) shown in regions 1a and 1b have a line width of preferably between approximately 10 μm and approximately 20 μm and are spaced apart (from center to center) by approximately 40 μm.

(15) 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.

(16) FIGS. 2A and 2C illustrate anisotropic patterns for influencing the spreading behavior in accordance with the invention. Such patterns may be made available to the device 8 in a way similar to a print image. If the device 8 is a print head 8a, the print head 8a may apply the respective pattern to the printing material as an anisotropic structure 10.

(17) FIG. 2A illustrates an anisotropic pattern composed of parallel lines, preferably lines of equal width and equal spacing. The line spacing (from line center to line center) may in particular be approximately 5 μm.

(18) FIGS. 2B and 2C illustrate patterns that are the result of additionally superposing white noise to the pattern of FIG. 2A. The white noise hides the anisotropy of the patter, preferably preventing any anisotropic structures visible to the naked eye from being created on the printing material. The pattern may for instance be created as a bitmap with arbitrary numbers between 0 and 255, to which a cosine of a wavelength of 2 bitmap lines is added, for example (corresponds to the anisotropy). To conclude, a threshold operator may be applied to the bitmap, resulting in a bitmap containing only zeros or ones: Zeros for a cell value between 0 and 127 and ones for a cell value between 128 and 256.

(19) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 printing material 1a first region 1b second region 2 side edges 3 direction of transport 4 transverse direction 5 longitudinal direction 6 ink print head 7 nozzles 7a nozzles that are printing 7b failed nozzles 7a nozzles that are printing 7b failed nozzles 8 device for pretreating the printing material 8a print head for treatment liquid 8b embossing or printing device 8c plasma/corona device or laser 9 nozzles 10 anisotropic structure 11 liquid 12 embossed/printed/plasma/corona/laser structure 13 ink print dots 14 white line 15 ink print dots 16 closed white line 17 computer 18 conduit 20a-20c anisotropic pattern