阅读说明：本技术 用于印刷及干燥的方法 (Method for printing and drying ) 是由 W·舍恩贝格尔 P·哈赫曼 C·希布 R·米勒 M·绍尔 于 2019-07-03 设计创作，主要内容包括：本发明涉及一种用于印刷及干燥的方法,其中,在油墨印刷方法中在基底上印刷包含水分及保湿剂的油墨,由此增加所述基底的湿度,和其中,首先在第一干燥步骤(3a)期间基本上完全蒸发所印刷的油墨的水分和接下来在第二干燥步骤(3b)期间蒸发所述保湿剂。本发明能够最佳地干燥用油墨印刷的基底并避免可能由保湿剂在基底上引发的问题。(The invention relates to a method for printing and drying, wherein in an ink printing method an ink comprising moisture and humectant is printed on a substrate, thereby increasing the humidity of the substrate, and wherein first the moisture of the printed ink is substantially completely evaporated during a first drying step (3a) and subsequently the humectant is evaporated during a second drying step (3 b). The present invention is capable of optimally drying substrates printed with inks and avoiding problems that may be caused by humectants on the substrates.)

1. A method for printing and drying a substrate,

wherein an ink comprising moisture and humectant is printed onto a substrate in an ink printing process, thereby increasing the humidity of the substrate, and

wherein the moisture of the printed ink is first allowed to evaporate substantially completely during the first drying step (3a) and subsequently the humectant is allowed to evaporate during the second drying step (3 b).

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

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

the evaporation (3a) of the water takes place during a first predetermined time interval (t1) by means of hot air (10a) or by means of radiation (10a) which is coupled predominantly to water molecules or to pigments contained in the ink.

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

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

the evaporation of the moisture (3a) takes place i) by means of hot air or ii) by means of hot air and infrared radiation or iii) by means of ultraviolet radiation, by means of high-frequency radiation or by means of microwave radiation.

4. The method according to claim 2 or 3,

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

the duration of the first predefined time interval (t1) is in the range from 1 second to 5 seconds.

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

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

the evaporation (3b) of the humectant takes place during a second predefined time interval (t2) by means of hot air (11a) and/or by means of radiation (11a) which is coupled predominantly to the humectant or to a pigment contained in the ink.

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

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

the evaporation (3b) of the humectant takes place by means of hot air and/or by means of ultraviolet radiation.

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

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

the evaporation (3b) of the humectant takes place by means of hot air and/or by means of ultraviolet radiation having at least one wavelength in the range from 365 nm to 405 nm or having at least one wavelength in the range from 365 nm to 395 nm or having a wavelength of 385 nm.

8. The method according to any one of claims 5 to 7,

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

the duration of the second predefined time interval (t2) is in the range of 0.1 seconds to 0.5 seconds.

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

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

the first drying step (3a) is carried out at a temperature in the range of 50 ℃ to 100 ℃.

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

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

the second drying step (3b) is carried out at a temperature in the range of 150 ℃ to 250 ℃.

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

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

after the second drying step (3b), the substrate is cooled by means of blowing air.

Technical Field

The invention relates to a method having the features of claim 1.

Background

The technical field to which the invention pertains is that of the graphic industry and here in particular that of printing and drying inks comprising moisture and humectants, thus belonging to the so-called ink-jet printing field.

Inks are known which contain a humectant (or evaporation resist or "Humectants" in the english language) which serves to keep the ink from drying out completely on the ink printhead (or its nozzle face). Such humectants can reach the substrate (e.g., paper) in an undesirable manner with the ink when printed.

From the two documents EP 3012110 a1 and EP 3034309 a1, respectively, an inkjet printer with a dryer is known, wherein a treatment means in combination of high frequency and infrared (or hot air) is disclosed, with the aim of: the printed and unprinted areas of the substrate are dried uniformly (i.e., without tension on the substrate). However, problems may arise here: the humectant remains on the substrate and interferes with the post-processing of the substrate (such as gloss oil application).

Disclosure of Invention

The object of the present invention is therefore to provide an improved solution in relation to the prior art, which enables in particular optimal drying of substrates printed with ink, i.e. in particular avoids the problems which can be caused by the retention of humectants on the substrates.

This object is achieved according to the invention by a method having the features of claim 1. Advantageous and preferred developments of the invention result from the dependent claims as well as from the description and the drawings. The features of the invention, the improvements of the invention and the embodiments of the invention in combination with one another also form advantageous improvements of the invention.

Within the extensive survey of printing experiments to solve this task, it was found that: the optimum drying is carried out in two steps, wherein the water is evaporated first and the humectant is evaporated afterwards.

The invention relates to a method for printing and drying, wherein an ink containing moisture and a humectant is printed onto a substrate in an ink printing method, wherein the humidity of the substrate is increased, wherein the moisture of the printed ink is first evaporated substantially completely during a first drying step and the humectant is subsequently evaporated during a second drying step.

The invention advantageously achieves optimum drying of substrates printed with ink. Problems that may be caused by the humectant remaining on the substrate can be avoided.

The second drying step may preferably be performed as a brief hot bump (Hitzesto β) that substantially completely removes the humectant from the substrate surface while protecting the substrate.

The substrate may be an absorbent substrate (such as paper or paperboard); moisture from the ink can reach such substrates and subsequently enter the substrate. Further, the substrate may be a laminated substrate (such as laminated paper or laminated paperboard); such substrates may already contain moisture.

A preferred refinement of the invention may be characterized in that the evaporation of the moisture takes place during a first predetermined time interval by means of hot air and/or by means of radiation which is coupled predominantly to water molecules or to pigments contained in the ink.

A preferred development of the invention can be characterized in that the evaporation of the moisture takes place i) by means of hot air or ii) by means of hot air and infrared radiation or iii) by means of ultraviolet radiation, by means of high-frequency radiation or by means of microwave radiation.

A preferred refinement of the invention may be characterized in that the duration of the first predefined time interval lies in the range from 1 second to 5 seconds.

A preferred refinement of the invention may be characterized in that the evaporation of the humectant takes place during a second predetermined time interval by means of hot air and/or by means of radiation which is coupled predominantly to the humectant or to a pigment contained in the ink.

A preferred development of the invention can be characterized in that the evaporation of the humectant takes place by means of hot air and/or by means of uv radiation.

A preferred development of the invention can be characterized in that the evaporation of the humectant takes place by means of hot air and/or by means of uv radiation having at least one wavelength in the range from 365 nm to 405 nm or at least one wavelength in the range from 365 nm to 395 nm or a wavelength of 385 nm.

A preferred refinement of the invention may be characterized in that the duration of the second predefined time interval lies in the range from 0.1 seconds to 0.5 seconds.

A preferred development of the invention can be characterized in that the first drying step is carried out at a temperature in the range from 50 ℃ to 100 ℃, preferably at a temperature slightly below 100 ℃.

A preferred development of the invention can be characterized in that the second drying step is carried out at a temperature in the range from 150 ℃ to 250 ℃.

A preferred development of the invention can be characterized in that after the second drying step the substrate is cooled by means of blowing air (preferably by means of drawn-in ambient air and particularly preferably by means of cooled ambient air). In this way, it is advantageously possible to prevent undesired heat from penetrating into the substrate (or into deeper layers of the substrate) by thermal conduction, and thus to prevent the center temperature of the substrate from rising undesirably.

Drawings

The invention and its preferred modifications will now be described further on the basis of preferred embodiments with reference to the accompanying figures 1 to 3. Here, mutually corresponding elements are denoted by the same reference numerals.

The figures show:

FIG. 1: a flow chart of a preferred embodiment of the method according to the invention;

FIG. 2: temperature characteristic curves in a preferred embodiment of the method according to the invention; and

FIG. 3: an ink printer when carrying out a preferred embodiment of the method according to the invention.

Detailed Description

Fig. 1 shows a flow chart of a preferred embodiment of the method according to the invention, showing the following steps:

method step 1 (preparation): a substrate and an ink to be printed on the substrate are prepared for carrying out the method according to the invention, in particular in a printing press. The substrate may be paper, cardboard, kraft paper or corrugated paper. The ink was a water-based ink, i.e.: the ink contains water as a solvent. In addition, the ink contains at least one humectant.

Method step 2 (printing): the prepared ink is applied to the prepared substrate in an ink printing process by delivering ink drops in an imagewise fashion. Here, the moisture and the humectant also reach the substrate along with the ink. The humidity of the substrate (or its moisture content) is increased by the moisture.

Method step 3 (drying) and in particular 3a (first drying step): first, the moisture of the printed ink is allowed to evaporate substantially completely. This evaporation is preferably by loading: i) hot air or ii) hot air and infrared radiation, or iii) ultraviolet radiation, high frequency radiation or microwave radiation.

Method step 4a (predefined first predefined time interval): a first predefined time interval t1 for the duration of the drying 3 (i.e. the first drying step 3a) is predefined. This predetermination can be carried out by the computer of the printing press and the corresponding control of the dryer and/or the printing press (or its transport speed). For example, the drying section can be controlled in a dryer that can be switched in a stepwise manner. Alternatively, the conveyance speed of the substrate may be controlled. Another alternative is: a dryer is provided with a fixed drying section which corresponds to the time interval t1 with a fixed conveying speed.

Method step 3 (drying), in particular the second drying step (3 b): the humectant is evaporated after process step 3 a. This evaporation is preferably carried out by applying hot air and/or ultraviolet radiation.

Method step 4b (predefined second predefined time interval): a second predefined time interval t2 for the duration of the drying 3 (i.e. the second drying step 3b) is predefined. This predetermination can be made in accordance with step 4a and the alternatives described therein.

The temperature characteristic shown in fig. 2 is described next. The graph has a time axis and a temperature axis with respect to the time axis.

The graph in fig. 2 shows the surface temperature (temperature characteristic curve 5) and the center temperature (temperature characteristic curve 6) of the substrate 8 during the drying process. In a first phase during time interval t1, the substrate 8 is continuously supplied with energy. This phase preferably lasts about 1 to 2 seconds. During this time, the surface temperature rises significantly. Due to the heat conduction of the substrate 8, the temperature in the deeper layers of the substrate 8 likewise rises and the central temperature rises with a time lag.

As the temperature rises, the evaporation of water increases exponentially. Particularly in the last part of the first phase, the amount of evaporated moisture is maximal when the target temperature T1 (about 90 ℃) for evaporating moisture is exceeded. In this first phase, energy cannot be supplied at any rate, otherwise the substrate would burst due to water vapor formed inside. There is a relatively long drying time of 1 to 2 seconds. At the end of this first phase, the moisture transferred to the substrate 8 is substantially completely evaporated.

If one were to continue further in the manner of a uniform energy supply (curve 5, dashed section in phase t 3), the temperature would rise faster. Since no more water evaporates, there is also no cooling effect (enthalpy of evaporation). This process continues until the target temperature T4 (about 130 ℃) for evaporating the humectant is sufficiently exceeded to allow sufficient evaporation of the evaporation resist (verdunsthengshemmer) during the time when the surface temperature is high. The temperature in the center of the substrate (curve 6, dashed section in phase t 3) likewise rises. The substrate loses a significant amount of its natural moisture. The substrate will dry and become brittle. In particular in the case of thick substrates, a large amount of energy is injected in this way, only to heat the uppermost layer of the substrate.

Even better (and provided according to the invention) is the so-called "hot bump" in the second stage t 2. The drying energy still required is introduced in as short a time as possible. Here, there is no fear of paper bursting (as in stage t 3), since almost no more vapour formations can enter, since the substrate is already dry. The phase t2 is preferably only a few tenths of a second long. The surface temperature (curve 5) rises so rapidly that the central temperature (curve 6) rises only slightly with it due to the limited heat transfer capacity of the substrate. Preferably, the uppermost layer is heated only briefly, with deeper layers in the substrate warming less. Accordingly, surface temperatureThe degree also drops abruptly after the stage t2, since it is cooled by the deeper layers of the substrate. Overall, less energy is also introduced into the substrate during this time. Especially on thick substrates (e.g. 200 g/cm)²To 800g/cm²) The drying process according to the invention saves a lot of energy. In order to allow as much humectant to evaporate in the steeper and shorter temperature peak as in the slower process corresponding to stage t3, the peak temperature is then preferably somewhat higher.

The "thermal impingement" can be performed by either a selective drying process or a uniform drying process. In an alternative method, energy is coupled only to the locations where ink has been applied. This may be, for example, ultraviolet radiation having a wavelength of 385 nm. The plurality of UV radiators can be arranged in such a way that they focus the light onto one point. Alternatively, the light of the plurality of UV radiators may be focused by means of suitable lenses or mirrors.

In the case of a uniform drying process, energy is coupled in at all points (that is to say also at the unprinted places). However, thorough drying out of the unprinted areas is not desirable. However, since only the uppermost layer is heated substantially during the "hot-blast" process, this thorough drying out also occurs only in the uppermost layer. For example, hot air may be blown onto the sheet. This air is preferably between 200 ℃ and 500 ℃ hot. Preferably, a large volume of air is blown onto the paper with small nozzles (diameter <5mm) and at small intervals (less than 20 mm). Because of the high air velocity, a good heat transfer coefficient is thereby obtained. At the same time, because of the high air temperature, the required energy can thus be introduced in a few tenths of a second.

T2 shows the center peak temperature with thermal shock in fig. 2, and T3 shows the center peak temperature with conventional heating.

The ink printer shown in fig. 3 is described next.

Fig. 3 shows a printing press 14 with a feeder 7 for a sheet-form substrate 8. After the water-based inkjet ink is applied by the print head 9a in the printing mechanism 9, drying is performed by a plurality of first dryers 10 (first drying step 3 a). These first dryers 10 can preferably be operated with hot air (combined infrared and hot air), or with ultraviolet, or microwave, or high frequency domain. These dryers are arranged on a drum. Next, drying (second drying step 3b) is effected by means of a second dryer 11 for thermal impingement (preferably directly after the last first dryer, with the sheet still hot). After the dryer 11, a cooling device 11a (or cooler 11a) can be arranged, preferably for blowing air or cooling air onto the substrate 8.

Alternatively, the sheet can also be guided on a conveyor belt or in a linearly guided gripper. Further alternatively, the web form substrate may be dried.

List of reference numerals

1 preparation (substrate, ink)

2 printing

3 drying

3a first drying step/Evaporation of Water

3b second drying step/Evaporation of humectant

4a predetermining a first predetermining time interval

4b predetermining a second predetermining time interval

Time temperature characteristic curve of 5 surface temperatures

Time temperature characteristic curve of 6 center temperature

7 feeder

8 base

9 printing mechanism

9a print head

10 first dryers

10a hot air and/or radiation

11 second dryer

11a cooler

12 material collector

13 computer

14 printing machine

t1 first predetermined time interval/first phase

t2 second predetermined time interval/second phase

t3 third time Interval/third phase

Temperature T1-T4