DK2428359T3

DK2428359T3 - Printer and method of printing on flat materials.

Info

Publication number: DK2428359T3
Application number: DK10405223.8T
Authority: DK
Inventors: Guntmar Michael Ludin; Michael Wagner
Original assignee: Hoffmann Neopac Ag
Priority date: 2010-09-14
Filing date: 2010-11-22
Publication date: 2017-04-24
Also published as: CH703704A1; EP2428359A1; EP2428359B1

Description

Specification [0001 ] The subject matter of the invention is a printer and a method for printing on flat materials according to the preamble of Claims 1 and 4.

[0002] Tinplate is used as a semi-finished product in various industries including the packaging industry for manufacturing containers such as tin cans. The standard commercial forms are sheets or rectangular blanks and coils or rolls. The plate can be reshaped into the desired form by means of mechanical post-processing steps such as punching, deep-drawing, embossing and crimping. In addition, containers or other objects manufactured in such a way can be lacquered and/or printed on with one or more inks by means of different printing techniques such as offset printing or silk screen printing. In the case of relatively small quantities, the plate is not printed, on as a general rule, until after it has been reshaped. In the case of larger quantities, on the other hand, it is more economical to print on the plate in sheet form and only then reshape it into the desired form.

[0003] Tinplate sheets comprise a cold-rolled steel plate which is elect roly tically covered with a thin tin layer. The tinplate surface can additionally be coated with a Cr6+-containing passivation layer or alternatively with a chromate-free passivation layer and can be greased e.g. with dioctyl sebacate (DOS) or acetyltributylcitrate (ATBC). As a result, the oxidation resistance of the coated steel sheet is, on the one hand, increased and, on the other hand, the friction coefficient thereof is decreased, so that the plate can be better processed mechanically. Tinplate sheets treated in this way have a low interfacial tension or surface tension and cannot therefore be easily wetted. Prior to printing on such tinplate sheets with printing inks, an adhesive agent (adhesive lacquer or powder, also called “primer”, e.g. an epoxy lacquer) is conventionally first applied to the surface of each sheet. Any solvents are evaporated in a drying furnace, and the lacquer is cured by the action of temperature. Compared to the unlacquered surface of the tinplate, the lacquer used has a substantially higher surface tension and, thus, better adhesion properties. Printing inks can therefore be applied to the lacquer, the surface tensions of which printing inks are also relatively high. The surface tensions of solution inks are, as a general rule, greater than approximately 40mN/m, those of UV (ultraviolet) drying inks are greater than approximately 55mN/m and those of water-based inks are greater than approximately 70mN/m. A prerequisite for a secure adhesion of such inks to the lacquer surface is that the surface tension of the lacquer or of the holding primer is greater than the surface tension of the respective inks.

[0004] One method used during the manufacture of plastic films to increase the surface tension is corona treatment. During this process, a film web is generally subjected to an electrical high-voltage discharge at the end of the production process.

This occurs between a grounded, polished roller made of steel or aluminum and a close-fitting insulated electrode. The film thereby rests on the polished roller, so that only the side facing the electrode is treated. The electrode is supplied with an AC voltage by a high-frequency generator. Electrical discharges lead to ionization of the air and the local formation of ozone. Furthermore, the electrical discharges also cause an increase in the surface tension of such films. Corona treatments can be difficult to control. The uneven distribution of the discharges result in nonuniformities in the surface tension and, therefore, in inhomogeneities of the adhesion of printing inks. High discharge currents and the strong ozone formation pose a risk to humans and require elaborate safety measures. The ozone-charged air has to be sucked off in the discharge area.

[0005] A printer for printing on metal sheets is known from WO03/089244. This printer comprises one or more printing units for applying one or more printing inks. When viewed in the process direction, the printer comprises, mounted upstream of the printing units, a first printing device for applying a primer, a second printing device for applying white lacquer and a drying unit for drying a primer and/or white lacquer layer applied to the flat material, before the flat material which is treated in this way is supplied to the additional printing units for application of the printing inks.

[0006] A printing device having at least one sheet guiding cylinder and having sheet retaining means for transporting the sheets is known from WO2010/060788, wherein waste heat arising in said printing device is fed by at least one heat source into the at least one sheet guiding cylinder.

[0007] One object of the present invention is to create a printer and a printing method, with which flat materials in the form of tinplate sheets, the surface tension of which is less than the surface tension of a printing ink which is to be applied, can be printed on with at least one printing ink without the prior application of a holding primer and without prior corona treatment.

[0008] This object is achieved by a printer and by a method for printing on flat materials in accordance with the features of Claims 1 and 4. Advantageous configurations of the device and the method are indicated in the subordinate claims.

[0009] As a general rule, printing systems comprise multiple printing units arranged one behind the other for printing on a printing substrate with multiple inks. A drying unit for drying the applied inks is arranged downstream after the last of these printing units. Downstream of one or more of these printing units, UV intermediate dryers can in addition be optionally arranged between adjacent printing units. UV-curable printing inks can be at least partially dried or cured with such intermediate dryers following application, before further printing inks are applied in one or more subsequent printing units. The high-energy UV light causes polymerization with such inks and, thus, a curing or drying of the applied printing inks.

[0010] Depending on the number of inks to be printed, one, multiple or all of these printing units can be activated for printing on the flat material in systems having multiple printing units arranged one behind the other in the process direction. Those printing units, which are not required for a specific printing process, can be configured as simple throughfeed units or can be disconnected. These printing units will henceforth also be referred to as inactive printing units. The flat material is transported further in these printing units, but is not printed on.

[0011] Those printing units, which are configured to print printing ink on the flat material, will henceforth also be referred to as active printing units. The printing units are preferably configured as active or inactive printing units by an overriding control device. Intermediate dryers, with which UV-curable printing inks can be dried following application to the flat material in the active printing unit(s), can optionally be arranged downstream of one or more of the active printing units. Such intermediate dryers are generally configured as UV intermediate dryers having an elongated UV gas-discharge tube. They can either be arranged on the printing system in a fixed or interchangeable form. As a general rule, each intermediate dryer comprises its own dryer control device, with which the radiated power can be controlled or preferably regulated. Intermediate dryers, which are indeed arranged in the printing system but which remain switched off during printing, are designated as inactive intermediate dryers in connection with this patent application, whilst those which emit UV light during printing are designated as active intermediate dryers. Conventionally, active intermediate dryers are only arranged downstream or after an active printing unit in the process sequence.

[0012] According to the invention, at least one active UV intermediate dryer or another electromagnetic radiation source is arranged upstream of the first active printing unit in the process sequence. Intermediate dryers are preferably provided between all of the printing units, of which intermediate dryers all those which are arranged upstream of the first active printing unit are configured as active intermediate dryers. If the first printing unit is already used as an active printing unit, an intermediate dryer or another suitable electromagnetic radiation source is arranged before this first printing unit.

[0013] A flat material which is to be printed on in the form of a tinplate sheet therefore passes through one or more irradiation zones before the first active printing unit and is irradiated there with high-energy electromagnetic radiation. As a result, the surface is activated such that the surface tension of the flat material increases. Following the application of a first printing ink in the first active inking unit, additional printing inks can optionally be applied to the flat material in one or more additional inking units. The printing is carried out wet-on-wet, i.e. no intermediate drying is carried out following the printing of the first printing ink or prior to the printing of additional printing inks. The last active printing unit is preferably also simultaneously the last printing unit of the printer, so that the flat material, after passing through said last active printing unit, can be supplied directly to the end dryer. The printing units are thus preferably configured such that, when viewed in the process direction, the flat material to be printed on first passes through the inactive printing units and then active printing units.

[0014] Such a printer is suitable for directly printing on metal sheets in the form of tinplate sheets. The invention will be described in more detail below with reference to two figures, wherein:

Figure 1 shows a schematically represented conventional printer,

Figure 2 shows a schematically represented exemplary embodiment of a printer according to the invention.

[0015] Figure 1 shows a conventional printer 1a for printing on flat materials such as sheets of paper or other materials having a good holding primer or having good adhesion properties. The printer 1a comprises a control device 3, five printing units 5, 5a, 5b, 5c, 5d, 5e arranged one behind the other in the process direction (arrow P), a lacquering unit 7 arranged downstream or in the process direction after the last printing unit 5e, a drying unit 9 arranged at the end of the process chain having one or more dryers (not shown) as well as a supplying unit 11 arranged on the inlet side for supplying the printing substrate or the flat materials to be printed on. The printing device 1a is configured for printing on flat materials with up to five UV-curable printing inks with the printing units 5a, 5b, 5c, 5d, 5e. An intermediate dryer 13 having one or more UV radiation sources is arranged before the lacquering unit 7. Usually, elongated gas-discharge tubes having a power of approx. 160 to 200 W/cm, which extend over the entire width of the flat material to be irradiated, are used as radiation sources. Such UV intermediate dryers 13 are, for example, offered by multiple companies. Usually, such intermediate dryers are controlled by an autonomous dryer control device 15. Alternatively, a dryer control device 15 can also be partially or completely integrated into the control device 3 of the printer 1a (not shown). One, multiple or all of the printing units 5, 5a, 5b, 5c, 5d, 5e can each be equipped with one printing ink in order to print on the flat material. In the case of the printer 1a shown by way of example in Figure 1, the printing units 5a, 5b, 5c marked with a cross 17 are configured by the control device 3 as active printing units 5a, 5b, 5c for printing on the flat material.

[0016] Figure 2 schematically shows a printer 1b which is configured according to the invention. Unlike the printer 1a according to Figure 1, one electromagnetic irradiation unit 19, 19a, 19c, 19d, 19e is arranged upstream of each of the printing units 5, 5a, 5b, 5c, 5d, 5e. Each of these irradiation units 19, 19a, 19b, 19d, 19e preferably comprises one UV intermediate dryer 13 each with the associated dryer control device 15. Alternatively or additionally, the irradiation unit 19, 19a, 19b, 19c, 19d, 19e could also comprise other radiation sources such as infrared heaters, lasers or a magnetron. In addition, further energy sources such as a hot-air fan can also be provided. In the exemplary arrangement according to Figure 2, only the last two printing units 5d and 5e are configured as active printing units 5d, 5e for printing on the flat material and are accordingly marked with a cross 17. Similarly to the markings of the active printing units 5, those irradiation units 19 marked with a cross 17 are active irradiation units 19, which irradiate the flat material with energy-intensive electromagnetic radiation when said flat material is conveyed in the process direction P through the printer 1b. In the case of the printer 1b shown by way of example, the three irradiation units 19b, 19c and 19d arranged upstream next to the first active printing unit 5d are configured as active irradiation units 19b, 19c and 19d and are accordingly marked with crosses 17. Prior to being printed on in the first active printing unit 5d, the flat material in the form of a tinplate sheet having a low surface tension is activated by irradiation with energy-intensive UV light by the irradiation units 19b, 19c and 19d. The elongated UV gas-discharge tubes have a lamp wattage of approximately 120 W/cm to approximately 200 or 240 W/cm per length unit of the lamp. The distance between the gas-discharge tube and the surface to be irradiated is preferably in the order of approximately 60mm to approximately 120mm.

[0017] After being irradiated with UV light and printed on in the first active printing unit 5d, a second printing ink is printed on the flat material in the last printing unit 5e without an additional drying step. Then, after all of the printing inks have been applied, these UV-curable printing inks are dried, prior to entry into the lacquering unit 7, by the intermediate dryer 13 arranged there. After passing through the lacquering unit 7, the flat material is supplied to the drying unit 9 where the printing inks and the lacquer are completely dried. The pre-treatment of the flat material prior to the application of the first printing ink in the first active printing unit— this is printing unit 5d in the case of the embodiment according to Figure 2—can be carried out by one or more irradiation units 19a, 19b, 19c, 19d arranged upstream of this active printing unit 5d.

Claims

A printer (1b) for printing on flat materials in the form of tinplate sheets having at least one ink, whereby the surface tension of these flat materials is less than the surface tension of the ink, which printer comprises at least one printer unit (5, 5e) operable, and a drying unit (9) disposed on the downstream side of this at least one printer unit (5, 5e) operable which dryer unit is provided to dry the ink applied to the flat material of the at least one printer unit (5). 5e) which can be activated, characterized in that at least one irradiation unit (19a, 19b, 19c, 19d, 19e) is provided upstream of the first printer unit (5, 5e) which can be activated in the process sequence. one electromagnetic radiation source, each configured to irradiate and increase the surface voltage of the flat material prior to its delivery to the first operable printer unit (5, 5e), and the radiation source is an elongated UV gas discharge tube or an elongated infrared heater.

The printer (1b) of claim 1, comprising a plurality of printer units (5, 5a, 5b, 5c, 5d, 5e) arranged one after the other, each of these printer units (5, 5a, 5b, 5c, 5d) 5e) of a control apparatus (3) can be configured to print a ink on the flat material as an active printer unit (5, 5a, 5b, 5c, 5d, 5e) or alternatively as a transit unit without a printing function, characterized in that upstream, starting from the last printer unit (5e), one or more printer units (5a, 5b, 5c, 5d) can be configured to pair in color so that they print in color and the irradiation unit (19a, 19b) , 19c, 19d, 19e) comprise one or more radiation sources located upstream of the activatable and configured for printable printer units (5, 5a, 5b, 5c, 5d, 5e).

Printer (1b) according to any one of claims 1 or 2, characterized in that at least one of the irradiation units (19a, 19b 19c, 19d, 19e) comprises a UV-based intermediate dryer.

Method for printing on flat materials in the form of tinplate sheets, which can be realized with a printer (1b) according to any one of claims 1 to 3, characterized in that before printing in the first active printer unit (5a, 5b) , 5c, 5d, 5e) with a first ink, irradiation of the flat materials to be printed is effected by electromagnetic radiation by means of the radiation source on the at least one radiation unit (19a, 19b, 19c, 19d, 19e) disposed upstream of the first printer unit (5a, 5b, 5c, 5d, 5e) and that the surface tension of these flat materials is increased due to the irradiation.

Process according to claim 6, characterized in that, after coating the flat material with a first ink, coating is carried out with at least one additional ink in at least one additional printing unit (5a, 5b, 5c, 5d).

Process according to any one of claims 4 or 5, characterized in that, after the application of the ink or inks, a drying step is realized to dry the ink and the ink in an intermediate dryer (13).