EP0542190A2 - Relief printing and application therefore - Google Patents

Abstract

In a process for applying binder systems, in particular printing ink, to web material by the relief printing technique, a solvent-free binder system is applied to the relief printing form of an applicator roll by means of an engraved roller which has engraved cells of a cell depth of </= 15 mu m. The applicator device has an impression cylinder and one or more applicator rolls which are each supplied with a binder system, preferably printing ink, via a binder application system with an engraved roller, which has engraved cells of a cell depth of </= 15 mu m.

Description

When printing web-shaped printing material, e.g. B. paper, plastic or the like, this runs over an impression cylinder and is printed by means of a printing roller, which is inked with an inking unit with printing ink. In the high-pressure process, the cliché is raised on the printing roller, and in the case of the flexographic printing process, the cliché consists of a plastic material with elastomeric properties. Solvent-based printing inks with a solids content of approximately 30% by weight and a solvent content of approximately 70% by weight are used exclusively for high pressure, in particular flexographic printing. Organic solvents and / or water serve as solvents (diluents).

Surprisingly, it has now been found that the high-pressure process can be carried out using solvent-free (ie 100% solids) printing inks or binder systems if a specially designed anilox roller is used for the inking or coating of the printing or application roller.

The invention thus relates to a method for applying binder systems, in particular printing inks, to web material using high-pressure technology, the application of the binder system to the high-pressure form of an application roller being carried out by means of an anilox roller, which is characterized in that a solvent-free binder system is applied by means of an anilox roller , which has a well grid with a well depth of ≦ 15 µm.

The invention further relates to a printing device for carrying out the aforementioned method, with an impression cylinder and one or more Application rollers, each of which is supplied via a binder application unit with an anilox roller with a binder system, in particular printing ink, which is characterized in that the anilox roller has a cell grid with a cell depth of ≦ 15 µm.

Finally, the invention relates to an anilox roller with a cell grid for carrying out the aforementioned method, which is characterized in that the average cell depth is ≦ 15 µm.

In principle, all solvent-free binder systems are suitable for carrying out the method of the invention, which, according to their application properties, e.g. B. be referred to as printing inks, varnishes or adhesives.

Preferred solvent-free printing inks are radiation-curing printing inks, with UV-curing printing inks based on acrylate or methacrylate or epoxy resin being particularly preferred. Such printing inks are commercially available under the name UVAFLEX (Zeller & Gmelin GmbH, Eislingen), UVA-temp (Hostmann-Steinberg, Celle) or SUNCURE (Sun Chemical, Brussels).

Examples of suitable solvent-free adhesives are radiation-curable hot-melt adhesives based on acrylate or methacrylate or on epoxy resin. These serve e.g. B. for the production of composite films.

Compared to the known flexographic printing processes which work with solvent-containing printing inks with a solvent content of 70% by weight, the process of the invention offers various advantages. Since conventional printing inks have to release the solvent as part of the drying process, complex changes such as shrinkage, porosity, pigment changes or "knocking away" of the binders are inevitable. In contrast, solvent-free systems are much more stable in the period from application to hardening. Only the shrinkage behavior of radiation-curable systems is currently known; here the shrinkage during curing can be minimized by a suitable molecular weight distribution. Since the printing ink contains no solvents, no drying occurs, ie the thickness of the wet film is equal to the thickness of the dry film. Since no solvents escape, no special effort is required for vacuuming and, if necessary, the recovery of solvents, and the solvent-free printing inks are largely odorless; both mean an improvement in occupational hygiene. Due to the lack of solvent evaporation, special fire protection measures are also unnecessary, and finally the printing inks do not contain any raw materials that are on a negative list of the Federal Health Office or the Federal Drug Administration, which is important for the printing of food packaging. The Draize value is below 1, ie the skin irritation factor corresponds to conventional solvent-based printing inks.

The use of solvent-free printing inks with a solid content of 100% gives an excellent printout. The grid points are optimal, i. H. with the correct design of the printing cylinder parameters, such as plate material or substructure, and in particular the anilox roller configuration, good tonal value increase conditions are observed. While solvent-based printing inks show a strong increase in viscosity in accordance with solvent evaporation, the printing inks or binders used according to the invention are viscosity-stable, the viscosity being able to be regulated in a defined range via the temperature. In contrast to solvent-based printing inks, there is also no drying out in the machine, even after a long standstill, e.g. B. at the weekend. With UV-curing systems, it is of course important to ensure that all UV exposure is kept away.

The processing of the solvent-free binder systems used according to the invention, e.g. B. printing inks or hot melt adhesive can be done at room temperature, ie 20 - 25 ° C. However, problems can easily arise here because the viscosity of the binder is too high, and certain binders cannot be processed at all at room temperature in practice. It is therefore preferable to work with solvent-containing printing inks which are 5 to 60 ° C higher than the processing temperatures. Based on the room temperature given above, this means a processing range of 25 - 85 ° C, preferably 30 - 65 ° C. Temperatures of 35-45 ° C. are particularly preferred, temperatures of around 40 ° C. having proven particularly useful in practical implementation.

Depending on the selected working temperature, it is necessary to ensure a uniform printing process, temperature control over the entire application of an application device, for. B. pressure device to perform, where appropriate, the impression cylinder and the high pressure rollers are to be heated.

In general, binder systems can be processed which have viscosities (at shear rates of 25-400 s⁻¹) of 0.01-2 Pa · s. At the preferred processing temperatures of around 40 ° C. for printing inks, the printing ink viscosities are generally in the range from 0.02-0.5, preferably 0.05-0.15, with viscosities from 0.08-0.12 being particularly preferred . In the case of printing inks, the pigment content generally bears 20-50% by weight. In the case of adhesives, the processing temperatures and the viscosities are generally higher.

A particular advantage of the radiation-curable binder systems is that - due to the lack of solvent - no drying is required and, moreover, the curing (crosslinking) of the binder takes place so quickly that multi-color printing can be carried out without problems. Difficulties sometimes arise in the known processes using solvent-containing systems because of incomplete drying and / or incomplete cross-linking, color smearing occurs.

The cleaning of the cylinders, clichés, cleaning cloths, dirty clothes, etc. can, for. B. with aqueous, surfactant-containing, alkaline solutions or using solvents. The UV-hardened printing inks are also extremely resistant, with chemical, temperature, scratch, wrinkle and adhesive resistance.

Overall, the printability according to the invention is much easier than with the known methods using solvent-containing systems. UV-curing solvent-free printing inks are considerably more expensive than the known solvent-based printing inks. However, the comparison is based on the solids content or the amount of printed products cost-neutral, with the above-mentioned advantages when working with solvent-free printing inks.

With the method of the invention, numerous substrates, e.g. B. from polyethylene, polypropylene, polyamides, polyesters, paper or steel / aluminum (painted or unpainted) with good adhesion and high fastness properties. Different ink systems often have to be used for conventional printing inks. In the case of printed plastic webs, a particular advantage of UV-curable printing inks is that they can be sealed and laminated without discoloration. Finally, there is a further advantage that when using UV-curing printing inks, the printed material (possibly also from the inside!) Is sterile due to the UV action, which offers advantages when used for medical purposes.

In a further particular embodiment of the method of the invention, a radiation-curable laminating adhesive is applied to a first web material as a solvent-free binder system, and a second web material is fed in and laminated. Depending on the adhesive system, a reaction (hardening) by radiation (UV light or electron beams) can be used both before and after lamination. An advantage of this method is that the adhesive is already cured immediately after the lamination process, so that the composite material roll can be cut immediately, while the curing takes 3 to 10 days in the prior art processes.

In a further embodiment of the method of the invention, the adhesive is applied only in the area of the panel, so that after the panel has been punched out, the adhesive-free film residues can be reused. An important application for this is the recovery of composite film waste, e.g. B. leadframe recycling.

The method according to the invention is preferably carried out with an application device with a counter-pressure cylinder and one or more application rollers, each of which is supplied with the binder system, preferably the printing ink, via a binder application unit with an anilox roller, the anilox roller having a cup screen with one compared to the usual anilox rollers (40 µm) significantly reduced well depth of ≦ 15 µm. The depth of the cells is preferably in the range from 1 to 10 μm and particularly preferably in the range from 5 to 8 μm. The geometry of the cells can be the same as in the known anilox rollers with a larger cell depth. The cups are preferably designed geometrically as a cylinder, spherical cap or truncated pyramid. In addition, well geometries with a high loss of scooping, ie only a small well emptying occurs during the printing process, have proven to be particularly advantageous.

An important parameter for anilox rollers is the so-called raster width (L / cm), which indicates the number of cells measured in a line of 1 cm. A screen width of 100 L / cm (a screen size common for conventional screen rollers) means e.g. B. that there are 100 cells per cm or 10,000 cells per cm². The screen rollers according to the invention have considerably larger screen widths, generally in the range from 170-280, preferably 180-240 and in particular 190-200 L / cm, the screen width of 200 L / cm corresponding to 40,000 cells / cm 2.

Another practically important parameter of anilox rollers is the well / web ratio (N / S ratio), which, like the raster width, is measured in the line (cf. FIG. 2). According to the invention, the N / S ratios are 8: 1-1: 1, preferably 5: 1-2: 1 and in particular 3: 1-2: 1. The measurement in line with the N / S ratio means that with the same N / S ratio, the area of the webs in relation to the area of the well openings is larger for round wells than for square ones. This difference would have to be taken into account if necessary, since printing or laminating is always carried out in terms of area.

In a special embodiment of a grid, the web surfaces between the wells are partially recessed, but the depths are smaller than in the wells, e.g. B. only 5 microns deep with a well depth of 10 microns. The partial deepening of the web surfaces may, based on the entire web surface, only go so far that there is still sufficient contact surface for the squeegee, otherwise the anilox roller can no longer be properly supplied with printing ink or binder. The partial deepening of the web surfaces offers an advantage in full-area printing, because the better area flow means that better area filling and thus better printed products are obtained.

In a special embodiment of the application device, one or more devices for emitting high-energy radiation to the printed web material are located on the outer circumference of the impression cylinder. These radiation devices are preferably designed as UV lamps. Because of the high energy density of the UV lamps (about 150 W / cm), the lamps are preferably water-cooled, a water-cooled housing having proven particularly useful. Here, in a further preferred embodiment, movably mounted, water-cooled reflectors are provided in the interior of the housing, which automatically slide between the radiation source and the impression cylinder in the event of faults, in particular when the vehicle is at a standstill, so that overheating of printing material and system parts is avoided. At the same time, the radiator output is reduced to a minimum of e.g. B. reduced about 40 W / cm. When the substrate throughput speed changes, the lamp output is continuously adjusted.

In a further particular embodiment, the application unit for supplying the anilox roller with a binder system or printing ink has a chamber doctor blade with a binder level regulator, the chamber doctor blade being fed and emptied by a binder container which is connected to the chamber doctor blade via a fore / back pump via a single line is. The line preferably opens into the chamber doctor blade at the lowest point of the binder filling, so that the fresh binder is fed in from below.

In a further preferred embodiment, the chambered doctor blade is designed as a heatable doctor blade with elastic sealing profiles on both sides as well as inlets and outlets. In contrast to solvent-based printing inks, it is not possible to control the viscosity via the solvent content in solvent-free printing inks. A desired lowering of the viscosity can therefore only be achieved by increasing the temperature. The heated chamber doctor blade is used to reach the higher temperature and to keep the desired temperature constant. The adjustment and fixing of the doctor arms can, for. B. done via steel springs. The side sealing profiles are preferred made of an elastomeric material, e.g. B. from swell-resistant rubber. The chambered doctor blade can be easily cleaned by pulling off the side sealing profiles.

In a further particular embodiment, the chambered doctor blade contains one or more further sealing profiles at a distance from the lateral sealing profiles, the chambers formed thereby having their own printing ink feed and a level regulator. This makes it possible to feed the individual chambers with different printing inks, so that printing can be carried out in multiple colors at the same time.

In a further particular embodiment, in the application device of the invention according to patent application P 41 08 883.2, the impression cylinder and / or the binder application unit are divided in the axial direction into a plurality of thermal zones which have individually controllable temperature control devices. In the case of the solvent-free binders, the viscosity of which depends on the temperature, this embodiment makes it possible to carry out specific changes or measurements of the amounts of binder or paint applied.

In a further particular embodiment, a corona treatment according to patent application P 39 35 013 is carried out on the printing material, the corona electrodes being heated outside their operating position to an operating temperature at which they work without ozone and then brought into the operating position. This heated electrode technology can also only be used when working with solvent-free binder systems (explosion protection).

The anilox roller according to the invention consists, for. B. made of steel and has a surface made of ceramic or titanium nitride. The engraving (generation of the grid geometry) can be carried out using laser beams.

Figur 1

eine perspektivische Darstellung einer erfindungsgemäßen Auftragsvorrichtung,

Figur 2A-E

stark vergrößerte Teildarstellungen (II der Rasterwalze 13 von Fig. 1) verschiedener Oberflächenstrukturen einer erfindungsgemäßen Rasterwalze,

Figur 3

eine perspektivische Darstellung eines beheizbaren Kammerrakels,

Figur 4

einen Schnitt durch ein Kammerrakel mit Farbbehälter und Pumpe

Figur 5

eine schematische Darstellung einer Auftragsvorrichtung im Zusammenhang mit einer Kaschiereinrichtung, und

Figur 6

einen Schnitt durch einen UV-Strahler mit beweglichen Reflektoren.

The invention is described below with reference to the drawings. Show it:

Figure 1

a perspective view of an application device according to the invention,

Figure 2A-E

greatly enlarged partial representations (II of the anilox roller 13 of FIG. 1) of various surface structures of an anilox roller according to the invention,

Figure 3

2 shows a perspective illustration of a heatable doctor blade,

Figure 4

a section through a doctor blade with ink tank and pump

Figure 5

a schematic representation of an application device in connection with a laminating device, and

Figure 6

a section through a UV lamp with movable reflectors.

In the application device shown in FIG. 1, a web material (polyethylene film of 20 μm thickness) runs at a web speed of 300 m / min over an impression cylinder 11 and is printed on by means of a high-pressure roller 12. The high-pressure roller 12 is supplied via an inking unit 17, which comprises an anilox roller 13 with a doctor blade 14 and an inking roller 15 with an ink pan 16. The anilox roller 13 has a well depth t of 6 ± 1 μm (see FIG. 2). The anilox roller 13 has a geometry according to FIG. 2A with a raster width of 180 L / cm corresponding to 32,400 cells / cm 2, and an N / S ratio of approximately 2: 1. A solvent-free (100% solid) UV-curable acrylate printing ink with a pigment content of 20% by weight is used. This has a viscosity of 0.1 Pa · s at 40 ° C. The high-pressure roller 12 is a conventional high-pressure cliché. It is printed with an application thickness of 1.5 µm, whereby there is practically no difference between wet and dry film thickness. Immediately after the printing ink has been applied to the web material 10 by means of a high-pressure roller 12, the curing of the printing ink takes place by means of two UV lamps mounted on the outer circumference of the impression cylinder 11 (for a detailed description, see FIG. 6).

FIG. 2 shows details of the surface properties of the anilox roller 13, specifically FIGS. 2A, 2B, 2C and 2D show, in the order mentioned, cup geometries in the form of domes, truncated pyramids, pyramids and cylinders, the cup-web ratio being approximately 2: 1 (Figure 2A) to about 3: 1 (Figure 2D). FIG. 2E shows (in a top view) a variant of FIG. 2B with partial web recess. At a depth t of the well N of 10 μm, there are partial depressions P of 5 μm depth in the web surfaces S, so that on the one hand the wells N through the partial depressions P are connected to each other, but on the other hand there is still enough web surface S available as a contact surface for the ink doctor blade. With the embodiment according to FIG. 2E, a better surface profile and thus a better surface filling can be achieved with full surface printing, which means an increase in print quality.

FIG. 3 shows a perspective view of a heatable chamber doctor blade 52 which is closed on both sides by elastic sealing profiles 32, 32 '. The chamber doctor blade 52 is subdivided into three separate chambers 35, 35 ', 35' 'by further sealing profiles 32' ', 32' '', each of which has its own ink supply 56, 56 ', 56' 'and its own ink level controller 53 , 53 ', 53' '. The subdivision of the chamber doctor blade makes it possible to feed the separate chambers with different printing inks, so that printing can be carried out in multiple colors at the same time. The viscosity of the individual printing inks can be influenced by different temperature control in the axial direction by means of individually controllable temperature control devices (not shown), so that specific changes or measurements of the ink application quantities can be carried out. The adjustment and fixing of doctor arms 36, 36 'is carried out by steel springs (not shown). The side and inner sealing profiles are made of swell-resistant rubber. The chambered doctor blade can be easily cleaned by pulling off the lateral sealing profiles 32, 32 'or moving the middle sealing profiles 32' ', 32' ''.

FIG. 4 shows a section through the chambered doctor blade 52 of FIG. 3, fed via an ink container 58, which is connected to the chambered doctor blade 52 via a fore / back pump 57 via a single ink line 56. The ink line 56 opens into the chamber doctor blade 52 at the lowest point of the ink filling 65 ', so that the fresh ink is always fed from below. The ink container 58 is supplied via a feed line 59. The homogeneity of the ink 65 is maintained by an agitator 60. The chambered doctor blade 52 has ventilation devices 66 to prevent bubbles from forming in the ink filling 65 '. Both the printing ink container 58 and the chamber doctor blade 52 can be heated by means of temperature control devices 69 and 67, the temperature being kept constant via control devices 70 and 68, respectively.

5 shows a schematic representation of an application device according to the invention in connection with a laminating device. A web material 10 (polyethylene, 20 μm) is drawn off from a roll 21 and fed to a counter-pressure cylinder 11 via a deflection roll 22. A UV-curable laminating adhesive is applied to the web material 10 by means of a high-pressure roller 12. The high-pressure roller 12 is supplied with laminating adhesive by means of an anilox roller 13 with a heated chamber doctor blade 52. A further web material 20 (polyamide, 60 μm) is then applied to the web material 10 coated with the reaction laminating adhesive, which is pulled off a roll 23 and by means of a Laminating roller 24 is applied to the adhesive-coated web material 10. The laminated composite material is then taken up on a roller 26 via a deflection roller 25. UV lamps 18, 18 'are provided on the outer circumference of the impression cylinder 11 for curing the reaction laminating adhesive. Before the second web of material 20 is applied, the UV lamp 18 pre-hardens the reaction adhesive, care being taken to ensure that there is still sufficient tack when applying the second web material 20 to achieve adhesive bonding. After the second web material 20 has been fed in, post-curing is then carried out by means of the UV lamp 18 '. It works with a web speed of the impression cylinder 11 of 150 m / min. A solvent-free UV-curable laminating adhesive based on epoxy resin with a viscosity at the working temperature of 60 ° C of 0.6 Pa · s is used. The application takes place over the entire area in an amount of 3 g / m², which corresponds to an application thickness of approximately 3 µm. An anilox roller 13 with a geometry according to FIG. 2E is used, with a raster width of 170 and an N / S ratio of 3: 1 (here the web depressions are calculated as a web). The entire system is kept at a working temperature of 60 ° C by appropriate temperature control devices.

6 shows details of such a UV lamp. Such a UV lamp 61 has a UV radiation source 63 with an energy density of 150 W / cm (axial), which is accommodated in a water-cooled housing 62. Movable, also water-cooled reflectors 64, 64 'are provided in the interior of the housing, which automatically slide between the radiation source 63 and the impression cylinder 11 (see FIG. 5) in the event of faults, in particular when the system is at a standstill, so that the web material 10 overheats or 10 and 20 (cf. Figure 5) is avoided. In addition, a control device (not shown) is provided which, when the web speed of the counterpressure cylinder 11 changes, automatically adjusts the radiation power.

Claims (22)

Process for applying binder systems, in particular printing ink to web material according to the high-pressure technique, the application of the binder system to the high-pressure form of an application roller being carried out by means of an anilox roller, characterized in that a solvent-free binder system is applied by means of an anilox roller, which has a cell grid with a cell depth of ≦ 15 µm. A method according to claim 1, characterized in that a radiation-curable printing ink is used. Process according to Claim 1, characterized in that a UV-curable printing ink is used. Process according to Claim 3, characterized in that an acrylate or methacrylate-based printing ink is used. Process according to Claim 4, characterized in that a printing ink with a pigment content of 20 to 50% by weight and a viscosity at 40 ° C of 0.08 to 0.12 Pa.s is used, and this at a temperature of 40 - 60 ° C processed. Process according to Claim 1, characterized in that a radiation-curable laminating adhesive is used as the solvent-free binder, a second material web being laminated onto the web material provided with the adhesive and the radiation curing of the adhesive taking place before and / or after the laminating process. Application device with an impression cylinder (11) and one or more application rollers (12), each with a binder application unit (17) an anilox roller (13) can be supplied with a binder system, preferably printing ink, characterized in that the anilox roller (13) has a cell grid with a cell depth (t) of ≦ 15 µm. Applicator according to claim 7, characterized in that the well depth (t) of the anilox roller (13) is 1 - 10 µm. Applicator according to claim 8, characterized in that the depth of the cells (t) of the anilox roller (13) is 5-8 µm. Applicator according to one of claims 7 to 9, characterized in that the anilox roller (13) has a cell / web ratio of 3: 1 to 2: 1. Applicator according to one of claims 7 to 10, characterized in that the screen width of the screen roller (13) is 180-240 L / cm. Applicator device according to one of Claims 7 to 11, characterized in that one or more devices (18) for emitting high-energy radiation to a web material (10) are attached to the outer circumference of the impression cylinder (11). Applicator device according to claim 12, characterized in that the devices (18) are designed as UV lamps (61). Application device according to claim 13, characterized in that the UV lamps (61) are cooled. Applicator according to claim 14, characterized in that the UV lamps (61) are equipped with a water-cooled housing (62) and movable, water-cooled reflectors (64, 64 '). Application device according to one of claims 7 to 15, characterized in that the application unit (17) for supplying the anilox roller (13) with binder has a chamber doctor blade (52) with binder level controller (53), fed and emptied by a container (58) which is connected to the chambered doctor blade (52) via a forward / return pump (57) via a single binding agent line (56). Application device according to claim 16, characterized in that the binder line (56) opens into the chamber doctor blade (52) at the lowest point of the binder filling. Applicator device according to claim 16 or 17, characterized in that the chambered doctor blade is designed as a heatable doctor blade with elastic sealing profiles (32, 32 ') on both sides as well as inlets and outlets (56). Applicator device according to claim 18, characterized in that the chambered doctor blade (52) has one or more further sealing profiles (32 '', 32 '' ') at a distance from the lateral sealing profiles (32, 32'), the chambers (35 , 35 ', 35' 'each) have their own binder feed (56, 56', 56 '') and their own level controller (53, 53 ', 53' '). Applicator according to one of claims 16 to 19, characterized in that the chambered doctor blade (52) has ventilation devices (66, 66 ', 66' ') to prevent bubbles from forming in the binder. Anilox roller with cell grid for carrying out the method according to one of claims 1 to 6, characterized in that the cell depth (t) of the anilox roller (13) is ≦ 15 µm. Anilox roller according to claim 21, characterized by the features according to one of claims 8 to 11.

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