GB1602979A

GB1602979A - Method of and an apparatus for drying a substance on or in print carrier

Info

Publication number: GB1602979A
Application number: GB2381178A
Authority: GB
Original assignee: Reinhard Mohn GmbH
Current assignee: Reinhard Mohn GmbH
Priority date: 1977-06-10
Filing date: 1978-05-30
Publication date: 1981-11-18
Also published as: DE2726222B2; LU79785A1; NL7805658A; FR2394046A1; FR2394046B1; DE2726222A1; CH638408A5

Abstract

The paper web (9) is passed through a drying tunnel (1). Piping (7) and ducts (4, 5) are employed to feed the drying medium to the paper web. The drying medium used is pure superheated steam at from 100 to 180 DEG C at 1 bar. The residence time of the paper web in the zone of exposure to the drying medium is approximately 1 second. The velocity of the drying-medium flow is from 25 to 30 m/s. In the dryer there is a reduced pressure of from 1 to 5 mm water column. The temperature of the drying medium is from 50 to 100 DEG C below the boiling point of the solvent to be driven off. Owing to the temperature gradient with respect to the drying medium, a water condensate film forms on the paper web. This condensate prevents the paper from being overdried. <IMAGE>

Description

(54) A METHOD OF AND AN APPARATUS FOR DRYING A SUBSTANCE ON OR IN A PRINT CARRIER (71) We, REINHARD MOHN GmbH, of Carl-Bertelsmann-Strasse 161, 4830 Güter- sloh 1, Federal Republic of Germany, a Limited Liability Company organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method of and an apparatus for drying a substance, such as inks, lacquers, glues or the like containing solvents, on or in a print carrier.

The print carrier may be paper or cardboard in the form of webs or sheets with a flowing drying medium.

Known devices for the drying of printing inks on paper webs operate with air circulation and feed of hot air. The hot air is brought into contact with the surface of the printed web so that the solvent evaporates and is conducted away with the hot air.

However, not only the ink of the printed product, but also the print carrier, the paper, is heated up by the hot air and moisture is withdrawn from the paper by reason of the low water vapour partial pressure in the atmosphere of the drier. The paper, which at the inlet of the drier displays a normal moisture content of about 5 to 6% by weight, shrinks during the drying and gives off so much moisture that the content at the outlet of the drier amounts to only 0.5 to 1.5% by weight. During the storage at a room temperature of 20 to 30"C and normal relative air humidity of 50 to 60%, the paper adsorbs moisture from the atmosphere until the equilibrium moisture of 5 to 6% by weight is nearly again attained. In that case, the paper swells, i.e. it grows out as the expert says. The giving-off and the taking-up of water is a reversible process with unprinted papers.

With printed papers, the water withdrawal during the drying with hot air however takes place zonally differently and is dependent on the strength of the ink application. Ink-free zones dry out more than ink-covered zones and, in the case of the latter, the zones with thin ink application again dry out more than zones with thick ink application. The water take-up of the printed product from the atmosphere after the drying therefore generate wave formation and reduced the quality of the printed product appreciably. The excess drying can also occur with other print carriers as for paper and lead to the same or similar disadvantages.

According to one aspect of the present invention there is provided a method of drying a substance on or in a print carrier, comprising the steps of disposing the carrier in a drying chamber, feeding steam to the drying chamber, so subjecting the print carrier to the steam in the drying chamber as to effect substantially 50 to 100 C below the boiling temperature of the solvent to be expelled from the substance, and removing the steam from the drying chamber by means comprising a blower.

The substance may comprise ink, glue, lacquer or the like. The print carrier may comprise paper or cardboard.

According to another aspect of the present invention there is provided apparatus for drying a substance on or in a print carrier, the apparatus comprising a drying chamber, means to feed steam into the drying chamber, a channel system disposed in the chamber and comprising a plurality of channels provided with outlet slots to feed steam to such substance in such a manner as to, in use, subject the print carrier to steam at a temperature substantially 50 to 100 C below the boiling point of the solvent to be expelled from the substance, a blower disposed within the chamber and operable to extract steam together with entrained evaporated components of the substance from the chamber, and circuit means for conducting extracted steam for return to the feed means and channel system of the blower.

Advantageously, an excess drying of the print carrier may be avoided and the drying process may be accelerated.

Preferably, pure steam of 100 to 1 80do, for preference 150 to 170 C at one atmosphere, is used, for which the dwell time of the print carrier in the region of influence of the drying medium may amount to 0.5 to 3 seconds, preferably 1 second. Preferably, a water condensate film in thin layer may be caused to precipitate on the print carrier after the first contact with the drying medium by reason of the temperature gradient to the drying medium.

The condensate may prevent an excess drying of the paper and at the same time provide a particularly good heat transfer from the drying medium to the substance in or in the print carrier. Furthermore, it has been discovered, rather surprisingly, that the solvent evaporation, evidently catalytically influenced by the water vapour condensate film, may occur very much more rapidly and thereby the drying may take place unusually fast. This may be due to a distillation effect whereby the substance transfer solvent-condensate-atmosphere is accelerated.

Expediently, the condensate may evaporate again with increasing heat transfer and increasing temperature rise in the ink, lacquer or glue layer and may be completely evaporated at the output of the drier or after termination of the drying. The ink, lacquer to glue is dried and the print carrier in all regions preferably has the desired equilibrium moisture of 5 to 6% by weight in the case where normal types of paper are used as the print carrier, because the condensate film in conjunction with the steam prevents excess drying, during which a disequilibrium temporarily arises. The use of steam for drying was in no way obvious. Rather, it seems illogical to want to expel solvents, which inter alia can contain water, out of the ink, lacquer or glue more rapidly through increasing the water content in the drying medium and thereby reduction of the water take-up capacity of the drying medium.

In the drying of printed paper webs in the rotary offset process, advantageously, the paper web may be exposed to a drying medium current at a speed of 25 to 30 metres per second, and an underpressure of 1 to 5, preferably 2 to 3, millimetres of water column may be maintained in the drier. In this case, the paper web runs into the drier at a temperature of about 20 to 30"C and remains in the region of the influence of the drying medium until the ink, lacquer or glue layer has reached the desired temperature and the solvent has been completely expelled. The optimum conditions with respect to tetnperature and water content of the paper web during feed into the drier, the temperature and steam content of the drying medium, the underpressure and the speed of flow as well as dwell time and outlet temperature of the paper web may be determined empirically in a simple manner. In each case, -the drying of the ink, lacquer or glue may be terminated before the drying-out of the paper starts.

Advantageously, a method embodying the invention is suitable for the conditioning of paper webs in the case of excess drying, wherein the dry paper webs, printed or unprinted, are briefly exposed to a steam current.

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawing, which is a schematic elevation of drying apparatus embodying the invention.

Referring to the drawing, the apparatus comprises a drying tunnel 1, a blower 2, a channel system 3 provided with channels 4 and 5 having slots 6, a pipe duct 7 for the feed and discharge of the drying medium, and a heat exchanger 8.

A paper web 9 is conducted through the drier by conventional transport means (not illustrated). A drying medium jet 10 is directed through the by way slots 6 onto the paper web 9.

The drying medium is guided in a circuit, wherein the drying medium loaded with solvent vapours is sucked out of the dryer by the fan 2 and fed to a condenser 11. The solvents are precipitated in the condenser 11 and removed through a duct 12, while the water vapour remains in the drying medium.

In place of the condenser 11, a by-pass system 14 may be used, by which a part of the drying medium is guided out of the circuit in order to reduce the concentration of the solvent content in the drying medium.

The drying medium then enters the heat exchanger 8 to bring it to the desired temperature and in a given case, enriched with water vapour through a duct 13. Thereafter, it is fed to the channel system 3 and guided through the channels 4 or 5 to the paper web. For paper webs printed on both sides, a symmetrically arranged channel system (not illustrated) with corresponding pipe ducts is disposed underneath the paper web 9. The channel shape 5 is suitable for the beaming of the drying medium into a jet.

The condensate film on the paper web very probably has the effect that the paper web briefly takes up moisture which after the evaporation of the solvent and the condensate film is again withdrawn so that the paper web contains the usual moisture at the dryer outlet. This is attained particularly through a rapid heating-up of the paper web to about 100 C, for which the condensate film serves to cause a brief over heating up to about 130"C and a subsequent relatively slow cooling-down of the paper web. The temperature guidance in the drying medium is set in correspondence with the temperature guidance in the paper web, for which, advantageously, temperature differences of 20 to 60"C at running speeds of the paper web of 30 to 150 metres per minute may be chosen.

WHAT WE CLAIM IS: 1. A method of drying a substance on or in a print carrier, comprising the steps of disposing the carrier in a drying chamber, feeding steam to the drying chamber, so subjecting the print carrier to the steam in the drying chamber as to effect drying, the temperature of the steam during the step of subjecting being substantially 50 to 100 C below the boiling temperature of the solvent to be expelled from the substance, and removing the steam for the drying chamber by means comprising a blower.

2. A method as claimed in claim 1, wherein the substance comprises ink.

3. A method as claimed in claim 1, wherein the substance comprises a glue.

4. A method as claimed in claim 1, wherein the substance comprises a lacquer.

5. A method as claimed in any one of the preceding claims, wherein the print carrier comprises paper.

6. A method as claimed in any one of claims 1 to 4, wherein the print carrier comprises cardboard.

7. A method as claimed in any one of the preceding claims, wherein the steam is at a pressure of substantially one atmosphere.

8. A method as claimed in any one of the preceding claims, wherein the steam fed to the drying chamber is at a temperature of 100 to 180 C.

9. A method as claimed in any one of the preceding claims, wherein the steam fed to the drying chamber is at a temperature of 150 to 170 C.

10. A method as claimed in any one of the preceding claims, wherein the step of subjecting is for a duration of between 0.5 to 3 seconds.

11. A method as claimed in claim 10, wherein the step of subjecting is for a duration of substantially 1 second.

12. A method as claimed in any one of the preceding claims, wherein the step of subjecting is so controlled as to controlled as to cause the precipitation of a thin layer of a water film on the print carrier on an initial contact between steam and print carrier, the water condensate film evaporating with increase of heat transfer end of temperature in the substance.

13. A method as claimed in any one of the preceding claims, wherein the print carrier is exposed to a current of steam at a speed of between 25 to 30 metres per second during the step of subjecting.

14. A method as claimed in any one of the preceding claims, wherein the step of subjecting is effected at a pressure between 1 to 5 millimetres of a water column below normal atmospheric pressure.

15. A method as claimed in claim 14, wherein the step of subjecting is effected at a pressure of between 3 to 5 millimetres of the water column below normal atmospheric pressure.

16. A method as claimed in any one of the preceding claims, wherein the print carrier is arranged to be at a temperature of between 20 to 30"C at the start of the step of subjecting.

17. A method as claimed in any one of the preceding claims, wherein the step of subjecting is effected to condition a printed paper web.

18. A method as claimed in any one of claims 1 to 16, wherein the step of subjecting is effected to condition an unprinted paper web.

19. A method of drying a substance on or in a print carrier, substantially as hereinbefore described with reference to the accompanying drawing.

20. Apparatus for drying a substance on or in a print carrier, the apparatus comprising a drying chamber, means to feed steam into the drying chamber, a channel system disposed in the chamber and comprising a plurality of channels provided with outlet slots to feed steam to such substance in such a manner as to, in use, subject the print carrier to steam at a temperature substantially 50 to 100 C below the boiling point of the solvent to be expelled from the substance, a blower disposed within the chamber and operable to extract steam together with entrained evaporated components of the substance from the chamber, and circuit means for conducting extracted steam for return to the feed means and channel system by the blower.

21. Apparatus as claimed in claim 20, comprising duct means to convey steam to the channel system, and a heat exchanger connected to the duct means.

22. Apparatus as claimed in claim 21, comprising another duct means to convey water vapour to the heat exchanger.

23. Apparatus as claimed in any one of claims 20 to 22, comprising a bypass system to convey the extracted steam.

24. Apparatus as claimed in any one of claims 20 to 22, comprising a condenser and further duct means to convey the extracted steam.

25. Apparatus for drying a substance on or in a print carrier, the apparatus being substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 130"C and a subsequent relatively slow cooling-down of the paper web. The temperature guidance in the drying medium is set in correspondence with the temperature guidance in the paper web, for which, advantageously, temperature differences of 20 to 60"C at running speeds of the paper web of 30 to 150 metres per minute may be chosen. WHAT WE CLAIM IS:

1. A method of drying a substance on or in a print carrier, comprising the steps of disposing the carrier in a drying chamber, feeding steam to the drying chamber, so subjecting the print carrier to the steam in the drying chamber as to effect drying, the temperature of the steam during the step of subjecting being substantially 50 to 100 C below the boiling temperature of the solvent to be expelled from the substance, and removing the steam for the drying chamber by means comprising a blower.

2. A method as claimed in claim 1, wherein the substance comprises ink.

3. A method as claimed in claim 1, wherein the substance comprises a glue.

4. A method as claimed in claim 1, wherein the substance comprises a lacquer.