DE102019204966A1 - Method of printing a substrate with ink - Google Patents

Abstract

A method according to the invention is a method of printing a substrate with ink, wherein ink drops (3) on the substrate (1) generate pixels (11) and the pixels on the substrate dot dots (11a), wherein a transition area (12) is printed between a first area (6) of the substrate, which is printed with the ink (7) such that at least partially merging raster points are generated and a second area (8) of the substrate, which prints unprinted or with a different fluid from the ink (9) or coated, and wherein the average ink volume of the ink drop generated pixels in the transition region is reduced from the average ink volume of the pixels produced by the ink drops in the first region. The invention advantageously makes it possible to reduce or even prevent disturbances in the transition area of printed areas.

Description

The invention relates to a method for printing a substrate with ink having the features of claim 1.

Technical field and state of the art

The invention is in the technical field of the graphic arts industry and in particular in the field of industrial inkjet printing (inkjet) on flat substrates, i. H. the application and optionally the drying / hardening / pinning of liquid ink on sheet or web-shaped substrates, preferably of paper, cardboard, cardboard, plastic or composite material.

Printing by inkjet printing can cause problems at the edges of printed areas.

The JP 2005 / 041041A already discloses a method in which smaller drops are printed in an edge region in order to produce a closed edge without so-called pixel gaps.

It has been recognized that besides such pixel gaps, other types of problems may also arise in the periphery of printed areas. For example, the edge area may have perceptible interference with the eye, as this z. B. as streaks in 8th are shown.

task

It is therefore an object of the invention to provide an improvement over the prior art, which in particular makes it possible to reduce disturbances in the edge region of printed areas or even prevent.

Inventive solution

This object is achieved by a method according to claim 1. Advantageous and therefore preferred developments of the invention will become apparent from the dependent claims and from the description and the drawings.

A method according to the invention is a method for printing a substrate with ink, wherein ink droplets on the substrate generate dots and the pixels on the substrate generate dots, wherein a transition region is printed between a first region of the substrate which is printed with the ink such that at least partially overlapping halftone dots are produced and a second region of the substrate which is blank or printed or coated with a fluid, pasty or solid other than the ink, and wherein the average ink volume of the ink drop generated pixels in the transition region is opposite the average ink volume is reduced by the ink droplets generated in the first area.

The invention advantageously makes it possible to reduce or even prevent disturbances in the transition area of printed areas.

According to the invention, the average volume of ink in the transition area is reduced. As a result, in particular such disorders, such as those in 8th are shown as streaks, reduced or even prevented. Extensive research has shown that unwanted irregularities or streaks visible to the naked eye occur at the edges of printed areas. It has also been recognized that these irregularities can be reduced or even prevented by reducing the ink volume in the transition area according to the invention. It was also recognized that as a result of the ink reduction, the performance during drying and / or curing, in particular during pinning (partial curing), can be reduced and that higher gloss values can be achieved thereby.

The method according to the invention can be carried out in all transition regions of the image to be printed. Alternatively, the method may be limited to those transition areas which are considered critical by the use of digital image processing, i. potentially disturbing (potentially forming streaks or the like). For this purpose, test prints with varying test fields (for example varying ink volumes and / or rasters) can be printed, evaluated and "critical" transition areas can be stored for later comparison.

Further developments of the invention

• - dass der Übergangsbereich eine Breite b mit b ≥ 10*h und b ≤ 50*h aufweist, wobei h die mittlere Dicke einer von der Tinte erzeugten Tintenschicht im ersten Bereich ist.
• - dass die mittlere Dicke h der Tintenschicht zwischen 5 und 10 Mikrometer beträgt und der Übergangsbereich eine Breite b von etwa 100 bis etwa 500 Mikrometern aufweist.
• - dass der Übergangsbereich eine Breite b von mehr als 2 Pixel, mehr als 5 Pixel oder mehr als 10 Pixel aufweist.
• - dass der Übergangsbereich eine Länge 1 aufweist, wobei 1 ≥ 2 Millimeter, 1 ≥ 3 Millimeter oder 1 ≥ 10 Millimeter.
• - dass der Übergangsbereich einen offenen Rand umfasst.
• - dass der Übergangsbereich einen geschlossenen Rand umfasst.
• - dass das mittlere Tintenvolumen auf weniger als 90%, weniger als 80%, weniger als 75%, weniger als 70%, weniger als 60% oder weniger als 50% reduziert wird.
• - dass das Reduzieren des mittleren Tintenvolumens abgestuft mit wenigstens einer Stufe erfolgt.
• - dass das Reduzieren des mittleren Tintenvolumens kontinuierlich oder quasi-kontinuierlich erfolgt.
• - dass das mittlere Tintenvolumen von etwa 4 Pikoliter auf etwa 3 Pikoliter reduziert wird.
• - dass die Tinte im ersten Bereich eine geschlossene Tintenschicht bildet.
• - dass der erste Bereich eine Breite B von mehr als 10 Pixeln aufweist.
• - dass der fluide, pastöse oder feste Stoff im ersten Bereich unter der Tinte durch Drucken oder Beschichten aufgebracht wird.
• - dass der fluide, pastöse oder feste Stoff im ersten Bereich über der Tinte durch Drucken oder Beschichten aufgebracht wird.
• - dass das Verringern des mittleren Tintenvolumens der von den Tintentropfen erzeugten Pixel durch ein Verändern von Bilddaten des Übergangsbereichs vor einem digitalen Rastern der Bilddaten des Übergangsbereichs erfolgt.
• - dass die Tinte wenigstens im Übergangsbereich mit geringerer Leistung gepinnt wird.
• - dass der fluide, pastöse oder feste Stoff ein Reinstoff oder ein Stoffgemisch ist, insbesondere eine von der Tinte verschieden zusammengesetzte und/oder verschieden farbige Tinte, eine Druckfarbe, z.B. eine Offsetfarbe oder eine Flexofarbe, ein Lack, ein Kaltfolientransfermaterial, ein (Flüssig- oder Trocken-) Toner, eine Grundierung, ein Primer (Haftvermittler) oder ein Precoat (z.B. eine Säure enthaltende Flüssigkeit für den Einsatz beim Drucken mit wasserbasierten Tinten) ist.
• - dass das Substrat aus Papier, Karton oder Kunststoff ist.

Preferred developments of the invention can be characterized as follows:

• - That the transition area has a width b with b ≥ 10 * h and b ≦ 50 * h, where h is the average thickness of an ink layer formed by the ink in the first region.
• - that the average thickness H the ink layer is between 5 and 10 microns and the transition region is one width b from about 100 to about 500 microns.
• - That the transition area has a width b of more than 2 pixels, more than 5 pixels or more than 10 pixels.
• - that the transition area is a length 1 wherein 1 ≥ 2 millimeters, 1 ≥ 3 millimeters or 1 ≥ 10 millimeters.
• - That the transition area includes an open border.
• - That the transition area includes a closed edge.
• - that the average volume of ink is reduced to less than 90%, less than 80%, less than 75%, less than 70%, less than 60% or less than 50%.
• - That reducing the average volume of ink graded with at least one stage takes place.
• - That reducing the average volume of ink is continuous or quasi-continuous.
• - The average volume of ink is reduced from about 4 picoliters to about 3 picoliters.
• - That the ink forms a closed ink layer in the first area.
• - that the first area has a width B of more than 10 pixels.
• - That the fluid, pasty or solid material in the first area under the ink by printing or coating is applied.
• - That the fluid, pasty or solid material in the first area over the ink by printing or coating is applied.
• - Reducing the average ink volume of the pixels produced by the ink drops by changing image data of the transition region before digitally rasterizing the image data of the transition region.
• - That the ink is pinned at least in the transition area with lower power.
• that the fluid, pasty or solid substance is a pure substance or a mixture of substances, in particular a differently composed and / or differently colored ink, an ink, eg an offset ink or a flexo ink, a lacquer, a cold foil transfer material, a liquid or dry) toner, a primer, a primer or a precoat (eg, an acid-containing liquid for use in printing with water-based inks).
• - That the substrate is made of paper, cardboard or plastic.

Embodiments of the invention

The invention and its preferred developments are described below with reference to the drawings with reference to preferred embodiments. Corresponding features are provided in the figures with the same reference numerals.

The drawings show in the 1 to 8th Representations of preferred embodiments of the method according to the invention, as well as its details.

1 shows the implementation of a preferred embodiment of a method according to the invention and at the same time a plan view of a printed product produced according to the invention. This becomes a substrate 1 (or a portion of the substrate), e.g. As labels or sheets or webs of paper, cardboard or plastic film, by means of an ink jet print head 2 printed, ie there are drops of ink 3 or ink 7 transferred to the substrate. The printhead may be a piezo-controlled drop-on-demand printhead. It can also be provided several heads, z. For producing multi-color prints. The ink is preferably a UV ink. The method can also be used when printing 3D objects or their arbitrarily shaped surfaces.

It is a control device 4 , z. As a computer, provided, which the image data 4a stores the image to be printed and processed, for. Example by means of a raster image processor (RIP), and the data to the printhead 2 transmitted. The image data can be changed by the computer prior to processing by the RIP (that is, before the so-called rasterization) such that the average volume of ink is reduced according to the invention. It is also a dryer 5 , z. B. a UV dryer or a hot air dryer is provided, which is the substrate 1 with radiation or hot air 5a acts on. The dryer can be used for pre-drying, ie it can increase the viscosity of the ink. The dryer may in particular be provided for pinning, ie for curing the ink (ie only for partial curing). The final curing can be done with another dryer.

In 1 a first area is visible (eg the letter " A "), In which ink 7 is transferred to the substrate. The applied drops of ink produce 3 on the substrate pixels 11 in ink, and these pixels in turn prefer halftone dots 11a from ink (see also 2 ). The pixels or the grid points flow at least partially into each other and thus generate an ink layer in the first area 7a , preferably a closed ink layer. The first area can be very small (micrometer range to millimeter range), z. B. a letter of a printed text in the usual font size. But it can also be larger, z. As a printed area in the size range of a few millimeters to centimeters or decimeters to dimensions in the size range of the format of the substrate 1 , eg several decimeters.

The edge 10 can be an open border 10a be, z. B. an outer contour of a letter (as shown, for example) or any other enclosed first area 6 within a second area 8th , He can also have a closed edge 10b be, z. A "gap" in a letter, or any other enclosed second area 8th within a first range 6 ,

In 1 is also a second area 8th recognizable, which to the first area 6 at least on one edge 10 of the first area adjacent. This second area can be unprinted or it can be made with a fluid, pasty or solid material 9 , preferably a fluid 9 , printed or coated, which of the ink 7 is different, for. As a differently composed ink, a different colored ink, a paint, a primer, a primer or a so-called Precoat. In the following, the use of a fluid 9 is described (without limitation of generality). The fluid can be a fluid layer 9a , preferably a closed layer, forming. The second area may be generated before, during or after the first area.

The mean volume of ink from the ink drops 3 generated pixels 11 in the transition area 12 is according to the invention opposite (ie, relative to or relative to) the average ink volume of the ink drops 3 generated pixels 11 in the first area 6 reduced. In each case an averaging over the transition region 12 or first area 6 respectively. It may preferably be reduced to about 75%, e.g. On average from about 4 picoliters to about 3 picoliters per ink drop. For example, the average volume of ink can also be reduced by printing drops of different volumes of ink alternately in space, e.g. B. alternately medium and small drops of ink.

The reduction can be ink-dependent, ie the degree of reduction (eg 75%) and / or the amount of width b of the transition region is determined or qualified for various inks before carrying out the method according to the invention, for. B. by printing test fields and their evaluation. The respective measure can be stored in the computer. During evaluation, it can be determined with the aid of digital image processing under which conditions (eg average ink volume) annoying streaks or the like are avoided in an advantageous manner.

The measure of reduction and width b may also depend on the material of the substrate 1 or the (average) area coverage. Other parameters that can be considered are, for. B. the (average) printing speed and the (average) pinning performance. On the other hand, the method is preferably independent of the type of printheads used. A detection of appropriate test prints and the storage of the measurements need not be made in each production of printing according to the invention, ie the inventive method is at given and stored dimensions without a constant detection from.

The in the following 2 to 7 embodiments shown or the prints shown there are by the in 1 shown radiation 5a pinned, ie the applied ink is cured or only partially cured. It is in the transition area 12 preferably pinned with less power. Reducing the pinning performance is compared to a conventional pinning performance. Such a reduction of the pinning performance has the advantage that higher gloss levels can be produced

In 2 is the in 1 as a circle shown detail II shown enlarged. There are (left) the first area 6 , (in the middle) the transition area 12 and the edge 10 and (right) the second area 8th recognizable. The transition area 12 has a width b , in the example shown (one letter in typical font size) of about 10 pixels, ie in the range below one millimeter. The first area has a width B , in the example shown, more than 10 pixels. The width B can be measured in about the same direction, in which also the width b the transition area is measured, ie z. B. substantially perpendicular to the edge 10 , The transition area has a length 1 , preferably a multiple of the width b So in the range over a millimeter.

In the transition area 12 can z. B. edge-parallel and offset to each other with gaps lines to reduce the volume of ink in the transition region. Instead, a pattern can be printed, for. B. a checkerboard pattern. Alternatively, a line pattern could be perpendicular to the edge.

The 3 to 7 each show the implementation of a preferred embodiment of a method according to the invention and at the same time in each case a sectional view through a printed product produced according to the invention.

This in 3 The method shown includes reducing the average volume of ink with a step 13 , which is preferably in the transition region 12 located. In the first area 6 is the average thickness of the ink layer H , The mean thickness of the ink layer in the transition region 12 In contrast, is reduced stepwise. In the example shown, one stage is used. Alternatively, several stages could be used. In 3 is also recognizable that the second area 8th unprinted and uncoated. Thus, ink application in this embodiment is directly on the substrate 1 or its surface.

4 shows an embodiment in which the average volume of ink in the transition area 12 is continuously reduced. In practice, as a result of the application of the drops, the rastering, the intertwining and the drying or hardening, the transition often will not be continuous (as illustrated), but rather quasi-continuous, ie essentially continuous and with imperceptible disturbances.

In 5 an embodiment is shown in which the substrate 1 with a fluid 9 (as a fluid layer 9a) provided, z. B. is coated. The fluid 9 is in the second area 8th , in the transition area 12 and also under the ink 7 in the first area.

6 shows an embodiment in which the fluid 9 as a fluid layer 9a only in the second area 8th is applied.

7 Finally, shows an embodiment in which the fluid layer 9a in the second area 8th and also in the first area 6 over the ink 7 or the ink layer 7a is applied (and also in the transition area 12 over the ink applied there). The thickness of the fluid layer 9a may be as shown so that together with the ink 7 or the ink layer 7a a substantially uniform layer thickness is formed.

Alternatively, the thickness of the fluid layer 9a be substantially constant (dashed line).

In 8th a pressure is shown, which was made in part without application of the method according to the invention. On the left edge of the printed area streaks or waves in the ink are noticeable, which disturb the visual impression. Such streaks were detected in extensive tests mostly on edges of printing areas, but sometimes also in the area. At the edges, ink seems to accumulate and thereby form the streaks and their surveys. As a result, there are perceptible and therefore disturbing density fluctuations. This was observed especially with black ink. At the top, instead, an inventive transition region was created. It was by lowering the transition area 12 amount of ink effectively prevents the aforementioned streaking or disruptive formation of microstructures.

LIST OF REFERENCE NUMBERS

1

substratum

2

printhead

3

ink drops

4

control device

4a

image data

4b

Raster Image Processor (RIP)

5

dryer

5a

Radiation / convection

6

first area

7

ink

7a

ink layer

8th

second area

9

Fluider, pasty or solid material, in particular fluid

8a

fluid layer

10

edge

10a

open border

10b

closed edge

11

pixel

11a

dots

12

Transition area

13

stepped transition area / step

14

continuous or quasi-continuous transition region

b

Width of the transition area

l

Length of transition area

H

average thickness of the ink layer

B

Width of the first area

II

neckline

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2005041041 A [0004]

Claims (19)

Method for printing a substrate with ink, wherein ink drops (3) on the substrate (1) generate pixels (11) and the pixels on the substrate generate dots (11a), wherein a transition area (12) is printed between a first area (6) the substrate which is imprinted with the ink (7) in such a way that at least partially intermeshing raster dots are produced, and a second region (8) of the substrate which is unprinted or with a fluid, pasty or solid substance (9) other than the ink printed or coated, and wherein the average ink volume of the pixels produced by the ink droplets in the transition region is reduced from the mean ink volume of the pixels produced by the ink droplets in the first region. Method according to Claim 1 , characterized in that the transition region (12) has a width b with b ≥ 10 * h and b ≤ 50 * h, where h is the average thickness of an ink layer (7a) produced by the ink in the first region. Method according to Claim 2 , characterized in that the mean thickness h of the ink layer (7a) is between 5 and 10 microns and the transition region (12) has a width b of about 100 to about 500 microns. Method according to Claim 3 , characterized in that the transition region (12) has a width b of more than 2 pixels, more than 5 pixels or more than 10 pixels. Method according to one of the preceding claims, characterized in that the transition region (12) has a length 1, wherein 1 ≥ 2 millimeters, 1 ≥ 3 millimeters or 1 ≥ 10 millimeters. Method according to one of the preceding claims. characterized in that the transition region (12) comprises an open edge (10, 10a). Method according to one of the preceding Claims 1 to 6 , characterized in that the transition region (12) comprises a closed edge (10, 10b). Method according to one of the preceding claims, characterized in that the average volume of ink is reduced to less than 90%, less than 80%, less than 75%, less than 70%, less than 60% or less than 50%. Method according to Claim 8 , characterized in that reducing the average volume of ink is graded with at least one stage (13). Method according to Claim 8 , characterized in that reducing the average volume of ink is continuous or quasi-continuous (14). Method according to one of the preceding Claims 8 to 10 , characterized in that the average volume of ink is reduced from about 4 picoliters to about 3 picoliters. Method according to one of the preceding claims, characterized in that the ink (7) in the first region (6) forms a closed ink layer (7a). Method according to one of the preceding claims, characterized in that the first region (6) has a width B of more than 10 pixels. Method according to one of the preceding claims, characterized in that the fluid, pasty or solid substance (9) is in the first region (6) of the ink (7) is applied by printing or coating. Method according to one of the preceding Claims 1 to 13 , characterized in that the fluid, pasty or solid substance (9) in the first region (6) is applied over the ink (7) by printing or coating. Method according to one of the preceding claims, characterized in that the reduction of the average ink volume of the pixels (11) produced by the ink drops by changing image data (4a) of the transition region (12) before a digital screening (4b) of the image data of the transition region , Method according to one of the preceding claims, characterized in that the ink (7) is pinned (5a) at least in the transition region (12) with lower power. Method according to one of the preceding claims, characterized in that the fluid, pasty or solid substance (9) of the ink (7) differently composed and / or differently colored ink, an ink, an offset ink, a flexo, a lacquer, a Cold foil transfer material, a toner, a primer, a primer or a precoat. Method according to one of the preceding claims, characterized in that the substrate (1) made of paper, cardboard or plastic.

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