EP1914071B1 - Rotary printing press - Google Patents

Description

The invention relates to a rotary printing machine with electrostatic printing aids.

In a rotary printing press, the printing cylinder (also called "printing form cylinder") and the impression cylinder (also called "impression roller") roll in opposite directions. A distinction is made between roller and sheet-fed presses, depending on whether a web-shaped or sheet-shaped substrate is being processed. In web-fed printing presses, the web-shaped substrate is pulled off a supply reel and, after printing, either wound up on a take-up reel or cut by a punch into web sections or blanks, and the web sections or blanks are stacked. The wound, web-shaped substrate is optionally later cut into sections or blanks. In rotogravure, the impression cylinder picks up ink from a paint pan in cells on its surface. The excess is shredded off. The ink is transferred to the substrate passing through the printing cylinder and impression cylinder.

Electrostatic printing aids improve the ink transfer from the printing cylinder to the substrate and thus increase the print quality. For this purpose, an electric field is generated in the region of the printing gap between the printing cylinder and impression cylinder, which exerts a force on the ink in the cells of the printing cylinder, which intensifies the transition of the ink to the printing material and increases the print quality.

In known electrostatic printing aids, the printing cylinder is made of an electrically conductive material (e.g., a metal) to ground. The impression cylinder or impression roller has on the circumference a (semi-) conductive layer to which a high voltage is transmitted, which generally has a negative polarity. The layer on the circumference is mostly semi-conductive to minimize electrical currents and to avoid the generation of sparks that could cause explosion / ignition when working with solvent paints. Especially when working with watercolors, it is also possible to work with a conductive or highly conductive layer on the circumference of the impression roller.

A semiconducting layer is understood as meaning a layer with a high electrical resistance, which greatly reduces the electrical current but still allows a certain electrical current to pass through. The electrical resistance of the layer is measured, for example, with a measuring device having two parallel forks each holding a moistened leather strip about 8 cm long and about 1 cm wide, so that the two parallel leather strips are about 10 cm apart. The two parallel leather strips are looped to a length of 8 cm around the outside of the layer. A measuring voltage of 1,000 volts is applied. With this measuring arrangement, resistances in the range from about 1 MΩ to 20 MΩ are measured for semiconducting layers which are particularly suitable for the present purpose. In the case of conductive layers, the resistances measured with this measuring arrangement are significantly lower and in the case of highly conductive layers they are much lower.

To transfer the high voltage to the impression roller, for example, charging electrodes which are directed onto the circumference of the impression roller and serve the charge deliver the (semi-) conductive layer on the circumference of the impression roller, which sits on an insulating layer (so-called "top-loading"). In this case, the resistance of the insulating layer is preferably selected so that it allows a slow discharge of the impression roller after switching off the printing press. Particularly suitable insulating layers have a resistance in the range of about one to two gigaohms as measured by a device of the type discussed above.

Other charging electrodes are directed onto at least one end face of the impression roller and deliver the charge to a conductive or highly conductive layer below a (semi) conductive layer which is exposed at an end face of the impression roller (so-called "side charging"). Furthermore, arranged on the front side charging electrodes are known, which cooperate with a conductive board on the front side of the impression roller, which is electrically connected to a (highly) conductive layer. The (highly) conductive layer below the (semi) conductive layer ensures a uniform distribution of the charge over the length of the impression roller.

Further known are devices for transmitting the high voltage on a front side of the impression, working on the transformer principle. At the front side a fixed primary coil is arranged and this is associated with a fixed on the front side of the impression roller, co-rotating secondary coil.

A "direct charging" takes place, for example, via wiper contacts or brushes on the circumference or an end face of the impression roller or via electrically conductive roller bearings which support a shaft of the impression roller or via which the impression roller is mounted on an axle. Preferably, the impression roller here consists of a metallic, electrically conductive material (for example steel) with a semiconducting layer on the circumference.

The (semi-) conductive layer on the circumference of the impression roller is made, for example, of rubber or polyurethane with embedded electrically conductive particles (eg graphite). A (high) conductive layer can also be made of rubber or polyurethane with a correspondingly higher proportion of electrically conductive particles. This can also be a metallic layer. An insulating layer will For example, also made of rubber or polyurethane, but with a correspondingly low number of electrically conductive particles or without electrically conductive particles.

Rotary printing machines usually have several successively arranged printing units in order to apply different colors to the substrate. A disadvantage of these rotary printing presses is that as a result of the electrostatic charging by electrostatic printing aids, the printing substrate can assume very high charges, which impair subsequent processing. For example, when transporting or cutting a roll comprising the printed substrate, flashovers can occur which adversely affect the print shop workers. When the sheet substrate is being cut and when working with sheets, the high loads may cause problems stacking the blanks or sheets and removing individual blanks from the stacks, as well as flashovers that affect the print shop workers. This is observed when using paper as a substrate and reinforced when using plastic film and composites comprising, for example, plastic, paper and aluminum foils.

The US 5,205,212 A. describes a rotary printing press that is used to print paper. Four color printing units are used: yellow (Y), magenta (M), cyan (C) and black (B). After printing, the paper is cut into sheets or sheets and stacked on top of each other. The thereby occurring adhesion of the papers to each other should be overcome.

The web material is printed on both sides and turned over for this purpose. The electrical charge of the paper sheets is based on the fact that when printed on the underside of the electrostatic printing aid electrically charges dried ink on the top of the paper.

The electric charge of the dried paint is neutralized by applying an electric field of reverse polarity. For the colors yellow, magenta and cyan, a positive potential electrostatic printer does not work well. Therefore, the printing units for yellow, magenta and cyan are operated with a printing aid of negative polarity, and only the printing unit for the color black with an electrostatic printing aid of positive polarity.

The WO 98/03049 A describes an electrostatic printing aid with a provided with an electrically (semi-) conductive outer layer of the impression roller.

The invention has for its object to provide a rotary web printing machine for packaging films available, which reduces unwanted charges of the wound to a roll substrate.

The object is achieved by a rotary printing machine with the features of claim 1. Advantageous embodiments of the rotary printing press are specified in the subclaims.

The rotary web press according to the invention comprises a plastic film or a composite film comprising a plastic film as a substrate on a take-off roll from which the printing material is guided to at least four printing units arranged one behind the other in the direction of passage of the printing material, each having a printing cylinder and an electrostatic printing aid associated therewith, the electrostatic printing aids having different polarities in the direction of passage of the printing stock of successive printing units and / or the electrostatic printing aids having different polarities in the direction of passage of the printing stock of successive groups of printing units and a take-up roll to which the printing material is guided behind the printing units.

The rotary printing machine according to the invention comprises for the first time electrostatic printing aids of different polarity, so that at least one electrostatic printing aid with negative and at least one electrostatic printing aid with positive polarity is present. This will cause excessive charging of the substrate counteracted. Unwanted discharges of the printed substrate and impairments of the printing workers are avoided as a result. The handling or further processing of the printed substrate is favored.

The rotary printing press is e.g. a high-pressure, planographic or screen printing machine. Preferably, it is a gravure printing machine. Furthermore, it is a web-fed printing machine.

Depending on the design of the electrostatic printing aid, the charge can be introduced to the printing gap in various ways. For example, it is possible to place a charging electrode in the vicinity of the printing nip, which is connected to a high voltage source. According to one embodiment, the electrostatic printing aid comprises a pressure roller provided with at least one electrically (semi-) conductive outer layer, a device for transferring electrical charge to the outer layer of the impression roller and a high voltage source with a specific polarity connected to a device for transmitting electrical charge. In this embodiment, the electrostatic printing aid applies the charge to the printing nip via a impression roller. The impression roller may consist altogether of electrically conductive and / or semiconductive material, to which the outer layer also belongs. Furthermore, the impression roller can only have an electrically (semi-) conductive outer layer, which is arranged on an insulating core. In particular, the impression rollers described above can be used. The means for transmitting electrical charge transfers the electrical charge from the high voltage source to the outer layer. In this case, in particular the devices described in the introduction for transmitting electrical charge can be used (top-loading, side-charging or direct-charging systems). From the outer layer, the electrical charge reaches the pressure gap.

Various assignments of the electrostatic printing aids of different polarities to the successive printing units are possible. According to a variant of the invention, the electrostatic printing aids have different polarities in the direction of passage of the printing material of successive printing units. Consequently Change from printing unit to printing the polarities of the electrostatic printing aids from negative to positive or vice versa. Accordingly, positive or negative charges are supplied to the nip.

According to another variant of the invention, the electrostatic printing aids have different polarities in the direction of passage of the printing material of successive groups of printing units. Thus, in the direction of passage to a group of printing units with electrostatic printing aids of a specific polarity, a group of printing units with electrostatic printing aids of opposite polarity follows. Gravure printing machines are also included in the invention, in which a part of the successive printing units in the passage direction electrostatic printing aids have different polarities and in which another part in the direction of passage of successive groups of printing units have different polarities.

Included are electrostatic printing aids, where the high voltage sources provide constant high voltages. According to a further embodiment, the electrostatic printing aids at least partially high voltage sources with adjustable high voltages and / or adjustable polarities. This makes it possible to optimize the high voltage or the polarity for each printing unit. In addition, adjustment depending on the selected substrate and / or environmental conditions (e.g., humidity) is possible.

According to one embodiment, the electrostatic printing aids have high voltages of at least a few 100 volts. According to a further embodiment, the high voltage is at least 1,000 volts. According to another embodiment, the high voltages are at least 5,000 volts. According to another embodiment, they are at least 10,000 volts.

Several printing units arranged one behind the other allow, in particular, gravure printing with different colors. The rotary printing press comprises at least four printing units arranged one behind the other. This allows, for example, a printing of the substrate with the primary colors blue, red, yellow and black. According to In another embodiment, the rotary printing press comprises at least six printing units arranged one behind the other. This allows, for example, an additional printing of the substrate with the two metal colors silver and gold.

According to a further embodiment, the rotary printing press has at least twelve printing units arranged one behind the other. This allows in particular the additional printing of the substrate with special colors and / or gloss colors.

The invention will be explained in more detail with reference to the accompanying drawing of an embodiment which shows a rotary printing machine with electrostatic printing aids in a rough schematic view.

The gravure printing machine comprises twelve successively arranged printing units 1.1 to 1.12. Each printing unit 1.1 to 1.12 has a metallic, electrically conductive printing cylinder 2.1 to 2.12, which rests on electrically conductive bearings to ground. Furthermore, each printing unit 1.1 to 1.12 has an electrostatic printing aid 3.1 to 3.12.

Each electrostatic printing aid 3.1 to 3.12 has a impression roller 4.1 to 4.12, which is an impression cylinder, which rolls on the printing cylinder 2.1 to 2.12. Furthermore, each electrostatic printing aid 3.1 to 3.12 has a high voltage source 5.1 to 5.12. The high voltage of each high voltage source 5.1 to 5.12 is adjustable.

Each high voltage source 5.1 to 5.12 is grounded. Furthermore, each high-voltage source 5.1 to 5.12 is provided with a device for transferring electrical charge 6.1 to 6.12 on a impression roller 4.1 to 4.12. The device for transmitting electrical charge 6.1 to 6.12 is, for example, a charging electrode.

From a take-off roll 7, a printing material 8 between the printing cylinders 2.1 to 2.12 and impression rollers 4.1 to 4.12 successive printing units 1.1 to 1.12 passed. In this case, deflecting and compensating rollers 9.1 to 9.11 are present between the printing units 1.1 to 1.12, over which the printing material 8 is carried away. Behind the printing units 1.1 to 1.12, the printing material 8 is guided on a take-up reel 10.

The printing material 8 is unwound from the unwinding roller 7, passed through the printing units 1.1 to 1.12 and wound onto the take-up reel 10. In the printing units 1.1 to 1.12 it is printed with different colors. In the printing units 1.1 to 1.4 it is e.g. printed with the four primary colors blue, red, yellow and black. In the printing units 1.5 and 1.6 he is e.g. printed with the two metal colors silver and gold. In the printing units 1.7 to 1.12 he is e.g. printed with special colors and glossy colors.

The polarity of the high voltage sources 5.1 to 5.12 changes in the direction of passage of the printing material 8 of printing unit 1.1 to 1.12 to printing unit from negative to positive and vice versa. Accordingly, alternately charges of different polarity (minus or plus) are fed to the pressure gaps between the impression rollers 4.1 to 4.12 and the pressure cylinders 2.1 to 2.12 via the means for transferring electrical charge 6.1 to 6.12 and the impression rollers 4.1 to 4.12 in the passage direction.

By supplying the electric charges, the quality of the gravure printing is improved, since the ink is almost completely taken out of the cups of the printing cylinders 2.1 to 2.12. As a result of the alternating polarity, however, there is no appreciable charging of the printing material 8 when it is wound onto the take-up reel 10 at the end of the gravure printing machine. As a result, the handling, transport and further processing of the wound, printed substrate 8 is facilitated.

Claims (7)

1. A rotary printing press with a plastic film or a compound film comprising a plastic film as a print substrate (8) on an supply roll (7), from which the print substrate (8) is guided to at least four printing units (1) which are arranged one behind the other in the machine direction of the printing substrate (8), each of them comprising a gravure cylinder (2) and an electrostatic printing assist (3, 4, 5, 6) associated to it, wherein the electrostatic printing assists (3, 4, 5, 6) have different polarities in the machine direction of the printing substrate (8) of consecutive printing units (1), and/or wherein the electrostatic printing assists (3, 4, 5, 6) have different polarities in the machine direction of the printing substrate (8) of consecutive groups of printing units (1), and with a take-up reel (10) to which the printing substrate is fed after the printing units (8).
2. The rotary printing press according to claim 1, wherein each of the electrostatic printing assists (3, 4, 5, 6) has an impression roller (4), provided with at least one electrically (semi-) conductive outer layer, a device for transferring electrical charge (6) to the outer layer of the impression roller, and a high voltage source (5) connected to the device for transferring electrical charge (6) and having a certain polarity.
3. A rotary printing press according to claim 1 or 2, wherein the electrostatic printing assists (3, 4, 5, 6) have high voltage sources (3) with adjustable high voltage and/or adjustable polarities.
4. A rotary printing press according to any one of claims 1 to 3, wherein the electrostatic printing assists (3, 4, 5, 6) have high voltages of at least some 100 Volts.
5. A rotary printing press according to any one of claims 1 to 4, with at least six printing units (1) that are disposed one after the other.
6. A rotary printing press according to any one of claims 1 to 5, with at least twelve printing units (1) that are disposed one after the other.
7. A rotary printing press according to any one of claims 1 to 6, which is a rotogravure web fed press.

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