Device and method for printing and drying plastic films

Abstract

A device and method for printing and drying a plastic film web is provided, especially a device and method for printing and drying a polypropylene, polystyrene or polyethylene film web. The device can include several offset printing mechanisms for printing the film web with different ink applications and at least one flame drying station, characterized by a drawing roller, which is arranged between a last printing mechanism and the at least one flame drying station, and which can contact the unprinted surface of the film web, and apply tension to the film web.

Claims

1. A device for printing and drying a polypropylene, polystyrene or polyethylene film web, the device comprising a plurality of offset printing mechanisms for printing the film web with different ink applications, at least one flame drying station for flame drying a printed side of the film web, and a drawing roller arranged between a last printing mechanism and the at least one flame drying station, wherein the drawing roller acts on an unprinted surface of the film web and applies tension to the film web, so that a web tension in a flame drying area is reduced compared with a web tension in a printing area, wherein a cooling tunnel is arranged between the at least one flame drying station and a rear deflecting roller, wherein a cooling mechanism is arranged after the rear deflecting roller, and wherein the cooling mechanism comprises polytetrafluoroethylene-coated cooling rollers.

2. The device according to claim 1, wherein the drawing roller is a driven vacuum roller provided with a plurality of openings formed on its lateral surface, and wherein the vacuum roller is configured to apply negative pressure to the film web through its openings.

3. The device according to claim 1, comprising a deflecting roller aligned at about 45 to a web feed direction, and a rear deflecting roller aligned at about 45 to the web feed direction, wherein the deflecting roller is arranged between the last printing mechanism and the at least one flame drying station, and wherein the rear deflecting roller is arranged in the web feed direction after the at least one flame drying station.

4. The device according to claim 3, wherein the deflecting roller and the rear deflecting roller are configured as stationary air cushion rollers which, as a result of openings formed in a lateral surface, are suitable for applying an air cushion to the film web.

5. The device according to claim 1, wherein a portion of the at least one flame drying station is configured to maintain a distance of 0.5 to 4 cm from the film web.

6. The device according to claim 5, wherein an extraction station for gases formed during flame drying is provided above the at least one flame drying station.

7. The device according to claim 1, 2, 3, 4, 5, or 6, wherein cooled rollers arranged in a region of the at least one flame drying station below the film web are provided, which cooled rollers serve as support rollers for the film web.

8. A method for printing and drying a polypropylene, polystyrene or polyethylene film web, the method comprising: printing the film web with different ink applications; subjecting the film web to flame drying on a printed side using at least one flame drying station; and applying tension to the film web on an unprinted side thereof after printing and before flame drying, so that a web tension in a flame drying area is reduced compared with a web tension in a printing area, wherein a cooling tunnel is arranged between the at least one flame drying station and a rear deflecting roller, wherein a cooling mechanism is arranged after the rear deflecting roller, and wherein the cooling mechanism comprises polytetrafluoroethylene-coated cooling rollers.

9. The method according to claim 8, comprising: deflecting the film web by approximately 90 after printing and before flame drying; and deflecting the film web by approximately 90 in a web feed direction after the flame drying.

10. The method according to claim 9, wherein the film web is guided by an air cushion while being deflected.

11. The method according to claim 8, wherein a width of a flame during the flame drying is adjustable.

12. The method according to claim 8, wherein gases formed during the flame drying are extracted.

13. The method according to claim 8, wherein the film web is cooled between flame drying and rear deflection and after the rear deflection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic view of an embodiment of the invention comprising a device for printing and drying plastic films; and

(2) FIGS. 2-6 depict aspects of the embodiment of FIG. 1 consistent with the description and claims.

DETAILED DESCRIPTION OF THE INVENTION

(3) In FIG. 1 a plurality of printing mechanisms 10, 12, 14 and 16 arranged successively at a distance from one another in the web feed direction are provided, which mechanisms provide an approximately 300-600 thick PP (polypropylene) film with applications of different ink. The printing mechanisms are suitable for withdrawing the film web from the roll and, with the aid of an infeed device, conveying and printing at a speed of 180 m/min. The PP film webs are printed in the roll offset process. The offset printing mechanisms are identified with the reference numbers 10, 12, 14, 16, the last printing mechanism being identified with reference number 16. Located after the last offset printing mechanism 16 in the web feed direction is a driven drawing roller 24 at negative pressure, which forms the termination of the printing area. The drawing roller 24 is provided with approximately 3 to 5 mm openings on its lateral surface (FIG. 2), through which the negative pressure formed in the interior of the vacuum roller is transferred to the film web so that this is pressed onto the drawing roller 24. The drawing roller 24 is a so-called unilaterally acting drawing roller, where the drawing speed and the web tension can be adjusted depending on the infeed set in the printing mechanisms by adjusting the rotational speed of the roller and the intensity of the vacuum. The drawing roller 24 designated as vacuum roller is provided with its own motor for producing negative pressure and has a stationary extraction region inside the driven roller which extends over at least 180 of the cylinder segment. This ensures that a sufficient area of the extracted film web is forcibly conveyed by the vacuum roller. The vacuum roller forms the termination of the printing area and separates the printing area from the flame drying area. In the prior art these areas were not separated so that at high web tension the film was overstretched in the flame drying area and possibly destroyed.

(4) Provided after the vacuum roller or drawing roller 24 in the web feed direction is a non-driven, stationary microporous deflecting roller 26, which is disposed at an angle of 45 to the web and which is provided with a plurality of openings on its lateral surface, through which an air flow conveyed in the interior is applied to the lateral surface so that it can form an air cushion or an air film there. The openings have a size in the range of 1-3 My. The air film or the air cushion provides for disturbance-free turning of the film web through 90 on its unprinted surface. Without an air film or an air cushion, there would be the risk of the rear side of the film web being damaged. A stationary arrangement of the deflecting roller 26 is preferred since as a result of a possible rotation of the roller, the web guidance could be influenced, which is important to avoid. It is provided that a pressure of 6 to 10 bar is applied to each roller. As a result of the air film formed on the surface, the film does not rest on the lateral surface but as a result of the air cushion formed, is at a distance of several micron from the lateral surface of the deflecting roller.

(5) The film web deflected by 90 with respect to the original web feed direction is initially passed over a roller 29 and then guided over a roller 31 into a drying station 18 which is formed from a group of three successively arranged flame drying devices or gas nozzles, each having three rows. Each flame drying device extends over a length of 780 to 820 mm but as a result of the closure devices (not shown) attached at the ends, can be shortened to a free opening length of 600 mm. The flame drying devices are water-cooled, a heating power of 150 kW being provided for one three-row burner. The nozzles of the flame drying devices maintain a distance of preferably 1 to 3 cm, particularly preferably 1.5 to 2.5 cm from the surface of the film web. (FIG. 3.) Cooled rollers 38 in the form of support rollers looping the film web are provided underneath the flame drying devices to prevent any deformation of the film web. The cooled rollers 38 provide a gentle looping of the film web so that the rollers can be driven by the film with the result that the water-cooled rollers also cool the film.

(6) Located after the flame drying station 18 is a cooling tunnel 32 which extracts an air flow and guides it past cooling fins onto the film web 2 so that the web is cooled with an approximately 15 C. cold air flow.

(7) Gas extraction station 30 is depicted above flame drying station 18.

(8) Located in the web feed direction after the rear microporous deflecting roller 28 is a first cooling mechanism comprising cooling rollers 48 cooled to about 20 C. which are temperature rollers are suitable for cooling the film web of about 70 C. to about 40 C. (FIGS. 4-6.) The cooling rollers 48 are preferably coated with TEFLON tape to avoid attachment of the film web or adhesion.

(9) Located in the web feed direction after the rear microporous deflecting roller 28 is a first (not shown) cooling mechanism comprising cooling rollers cooled to about 20 C. which are suitable for cooling the film web from a temperature of about 70 C. to about 40 C. The cooling rollers are preferably coated with Teflon tape to avoid attachment of the film web or adhesion.

(10) Located after the first cooling mechanism is a painting mechanism (not shown) which applies a dispersion paint exclusively to the printed side of the film web.

(11) Located after the painting mechanism in the web feed direction is a hot air drying device with approximately 80 C. hot air, which is suitable for taking up any solvent residues still present and drying the printing side of the film web.

(12) Located after the hot air drying station in the web feed direction is a second cooling mechanism which also comprises 20 C. cooled cooling rollers which are suitable for lowering the film temperature to a temperature of 25 to 28 C.

(13) Located after the second cooling mechanism is a rolling mechanism by which means the printed and sufficiently dried film web is wound, the speed of the winding roller and the web tension being reduced as the radius of the winding increases so that a continuous winding process at constant conveying speed can be ensured. The device according to the invention and the method according to the invention thus enable a decoupling of the printing area from the flame drying area by the unilaterally acting drawing roller, which appreciably reduces the risk of damage to the film in the non-decoupled flame drying phase according to the prior art. Furthermore, due to the deflecting rollers disposed before and after the flame drying station, a considerable space saving can be achieved by displacing the drying process perpendicular to the original print feed direction. The loss of quality hitherto accepted in the prior art is eliminated and the waste reduced. The risk of doubling (inaccurate matching of points between successive ink mechanisms) is also reduced.

(14) An alternative to the unilaterally acting drawing roller or vacuum roller would be bilateral rollers where the upper roller merely acts in the area of the printed side of the film free from the printing design. Such an arrangement is preferred under specific conditions.