Method and apparatus for drying printed or inked webs by means of heat

In a method of and apparatus for heat-drying of webs, especially printed or inked webs, the web is first subjected to a contactless heat shock treatment, for example by hot air at about 300.degree. C. It is then heated by a contact process at a lower temperature, for example by heated rollers at about 230.degree. C., after which it is cooled by a contact process in a third step. Each of the heated rollers may have associated therewith a roller for applying a film of a buffer agent and also a cleaning roller. Energy expended in the processes is recovered by the use of heat exchangers. The apparatus may comprise a closed housing divided into separate chambers within which the sequence of steps is carried out.

BACKGROUND OF THE INVENTION 
The invention relates to the drying of printed or inked webs by means of 
heat. 
In known driers the web to be dried is guided through a tunnel in which the 
web has hot air blown on to it on both sides and therefore has to be 
guided in a free-floating manner. However, with such a contactless drying 
process the heat transfer is very small, so that the drying tunnel has to 
be made comparatively long. A further disadvantage of known driers is 
that, because of the high expenditure of energy, the efficiency is 
extremely low. In the manufacture of paper it is already known to guide 
the damp web over heated rollers, with the result that the moisture 
contained in the paper web is evaporated by the hot contact. Although this 
method is suitable for the drying of damp paper webs, it is not suitable 
for the drying of printed webs, since the fresh ink would be deposited on 
the rollers and the ink would be smudged. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and an 
apparatus by means of which the difficulties previously encountered in the 
drying of printed or inked webs in particular are overcome. 
It is a particular object of the invention to provide a method and an 
apparatus which permit a drying of printed or inked webs in a relatively 
short path length without the ink being smudged. 
A further object of the invention is to provide a method and an apparatus 
which make possible the drying of printed or inked webs without the 
expenditure of the amount of energy previously considered necessary for 
this purpose. 
In accordance with the present invention there is provided a method in 
which the web, in a first step, is subjected to a contactless heat shock 
treatment, in a second step is heated by a contact process at a lower 
temperature than in the first step, and, following that, in a third step, 
is cooled by a contact process. 
Also, in accordance with the invention, there is provided an apparatus 
comprising a housing divided into at least three chambers through which 
the web is arranged to pass sequentially, a source of hot air for heat 
shock treatment of the web being provided in a first of the chambers, at 
least one pair of rotatable heated rollers for contact heating of the web 
in a second of the chambers, and at least one pair of rotatable cooling 
rollers for contact cooling of the web in the third of the chambers. 
The heat shock treatment of the web in the first step is preferably carried 
out by the use of a gaseous medium at a temperature of about 300.degree. 
C., while the temperature of the heated rollers in the second step or 
chamber is about 230.degree. C. The temperature of the cooling rollers in 
the third step or chamber may be about 25.degree. C. 
One advantage of the method of the present invention lies in the fact inter 
alia that the web to be dried only needs to be subjected to hot air over a 
very short path length. In the first heat treatment step the upper surface 
of the web is only slightly dried, so that in the second heat treatment 
step in which there is contact drying by means of heated rollers, the web 
does not stick to the heated rollers, so that the ink is not smudged. 
Since the drying of the web is a contact drying process, correspondingly 
little energy needs to be used. 
A further advantage of the invention lies in the fact that a drying 
apparatus operating according to the method only needs to be of short 
structural length. An advantage of the closed chamber arrangement which is 
used is that the applied energy is not lost but can be recovered by the 
use of heat exchangers. In order to prevent smudging of the ink and thus a 
contamination of the heated rollers or a build-up of ink on the heated 
rollers, each of the heated rollers preferably has associated therewith 
both an application roller for a buffer agent and also a cleaning roller. 
Further means are also preferably provided in order to recover the energy 
expended for the heating and cooling processes.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 1 and 2 show a substantially closed housing 1 which is divided into a 
number of chambers 2 through 8. A printed or inked web 9 runs sequentially 
through chambers 2, 3 and 5 for the purpose of drying the web. The web 
enters chamber 2 through an entry slot 10 and is guided out from the 
apparatus, out of chamber 5, through an exit slot 11. A wall 12 separating 
chamber 2 from chamber 3 is provided with a communicating slot 15 through 
which the web passes, and, in like manner, a separating wall 13 associated 
with chamber 5 is provided with a communicating slot 14 for the web. 
The web 9 which first passes through chamber 2 is subjected in that chamber 
to a heat shock treatment. For this purpose hot air, for example at a 
temperature of about 300.degree. C., is blown into chamber 2 by means of a 
blower 16 which is provided in chamber 8. The hot air is directed on to 
the surface of the web 9 in a targeted manner by the use of deflector 
plates 17. After the heat shock treatment, as a result of which the inked 
surface of the web gains a thin skin, the web 9 is guided in chamber 3 
along an S-shaped path over and around a pair of heated rollers 19 and 18, 
thereby being subjected to contact drying. The temperature of the heated 
rollers 18, and 19 may be about 230.degree. C. Although only one pair of 
heated rollers 18, and 19 is shown, one could alternatively provide a 
greater number of such rollers, as determined by the need. By looping the 
web in an S-shaped path around the heated rollers 18 and 19 one ensures 
that the upper and lower surfaces of the web are uniformly heated, and 
consequently that the ink is uniformly dried. After this contact drying 
process the web 9 passes into chamber 5 where it is cooled for example to 
about 25.degree. C. or room temperature. For this purpose a pair of 
cooling rollers 21 and 20 are provided in chamber 5 around which the web 
is again looped in an S-shaped path. Instead of a pair of cooling rollers 
one could alternatively provide a greater number of cooling rollers, as 
desired. After the cooling process the web leaves the chamber 5 through 
the exit slot 11. 
As mentioned above, a heated gaseous medium, and one is referring here in 
particular to hot air, is blown into the first chamber 2. In order to 
prevent the hot air escaping from the closed housing 1 through the entry 
slot 10, the entry slot 10 is made as narrow as possible, and can, if 
desired, comprise an appropriate sealing means, for example a labyrinth 
seal. 
The communicating slot 15 in the dividing wall 12 between chamber 2 and 
chamber 3 is on the other hand comparatively large, so that the hot air 
blown into chamber 2 can pass through the communicating slot 15 into 
chamber 3. From chamber 3 the hot air is then blown by means of a blower 
22 into a further chamber 4, and is preferably blown directly on to a 
liquid extractor 23 located therein. The extractor 23 comprises plates 24 
through which a cooling medium such as cold water flows, so that a solvent 
contained in the hot exhaust air from chamber 3 condenses and can thus be 
recovered. The condensate runs down into a collecting tank 24' which is 
positioned below the extractor 23. The cooled air can be guided out of the 
housing through a filter (not shown) filled for example with activated 
carbon. 
Within a suitable part of the housing, for example beneath chamber 5, there 
is provided a further chamber 6 in which is located a refrigerator or a 
compressor 25. A refrigerating medium heated by the refrigerator 25 flows 
through a pipe 26 to a heat exchanger 27 which is arranged in a chamber 7 
also provided within the housing 1, in order to give off the heat to the 
ambient air. Associated with the heat exchanger 27 is a fan 28 which sucks 
in cold air from the outside through slots (not shown) provided in the 
sides of the housing 1 and which blows this cold air under pressure 
through the fins 28' of the heat exchanger 27. The air which is preheated 
in this way up to for example about 100.degree. to 120.degree. C. serves 
as combustion air for a heating device in the form for example of a hot 
blower 30 which likewise is provided in chamber 7. The hot blower 30 acts 
on a heat transfer medium or a heat transfer liquid in a heat exchanger 31 
to heat this medium. From the heat exchanger 31 the heat transfer medium 
flows partly by means of a pump 32 and a pipe 34 to the heated rollers 18 
and 19 in chamber 3 and partly by means of a pump 33 to a heat exchanger 
35 in chamber 8. Associated with the heat exchanger 35 in chamber 8 is a 
fan 36 which sucks in air from the outside through air intake slots (not 
shown) in the housing 1 and which directs this air through the fins 36' of 
the heat exchanger 35. 
The air heated to for example about 300.degree. C. by the heat exchanger 35 
is then blown by the blower 16, preferably directly into chamber 2, in 
order to carry out in this chamber 2 the first-mentioned short-term 
contactless heat drying process on the web 9. Both the heated rollers 18 
and 19 and also the blower 16 preferably have heat sensors associated with 
them, by means of which the periods of time that the pumps 32 and 33 are 
switched on can be controlled, so that pump 32 only supplies heated heat 
transfer medium to the heated rollers 18 and 19 until the associated 
temperature sensors indicate a preset temperature of for example 
230.degree. C., while heat exchanger 35 is supplied by pump 33 with the 
heat transfer medium only until the temperature sensor associated with the 
blower 16 indicates that a desired predetermined temperature of the hot 
air of for example 300.degree. C. has been reached. The return of the heat 
transfer medium after it has passed through the heated rollers 18 and 19 
and through the heat exchanger 35 is effected by passing it through return 
pipes 37 and 38. 
The refrigerating medium heated in the compressor 25 is supplied to heat 
exchanger 27. After passing through the heat exchanger 27 the cooled 
refrigerating medium passes through a pipe 40 into a heat exchanger 41 and 
from there by way of a pipe 42 back to the compressor 25. In heat 
exchanger 41 the refrigerating medium of the compressor 25 is heated 
again, so that no energy has to be supplied by the compressor 25 for the 
heating of the refrigerating medium. 
For the cooling of the plates 24 of the extractor 23 through which the 
cooling medium flows, and for the cooling of the cooling rollers 20, and 
21, there is provided a cooling medium circulating system which is 
independent of the refrigerating medium circulating system (which consists 
of the compressor 25 and the heat exchanger 27), as can be seen from FIG. 
1. The cooling medium, for example cold water, heated in the extractor 23 
and in the cooling rollers 20 and 21 flows through a pipe 44 into heat 
exchanger 41 where a heat transfer with the refrigerating medium of the 
compressor 25 flowing through the pipe 45 takes place. By this means the 
cooling medium for the extractor 23 and for the cooling rollers 20, and 21 
is cooled. 
The cooled cooling medium is fed back through a pipe 46 fitted with a pump 
47, back again to the extractor 23 and to the cooling rollers 20, and 21. 
As shown, the housing 1 is screened from the environment and internally is 
divided hermetically by the chambers 2 through 8. In this way a 
substantially closed energy circuit is created so that the efficiency and 
consequently the saving in energy as compared with conventional drying 
systems is considerably increased and can amount for example to about a 
60% saving. 
As will be seen from FIG. 1, each heated roller 18, and 19 has associated 
therewith a cleaning roller 48, and 49 and an application roller 50, and 
51 for a buffer agent. Since the cleaning and application rollers are 
identical in form, there is shown in FIG. 3 just one of the heated rollers 
in combination with an application roller 51 and a cleaning roller 49. The 
application roller 51 is for the purpose of continuously applying to the 
heated roller a thin film of a buffer agent, for example a 
silicon-containing liquid, in order to prevent the fresh ink which is to 
be dried from being deposited on the roller. The cleaning roller 49 
associated with the application roller 51 is for the purpose of wiping off 
the film of buffer agent laid down by the application roller 51 after one 
revolution of the heated roller. By this means one ensures that there is 
always a fresh film of buffer agent present between the web 9 which is to 
be dried and the heated roller 19. The rotational speed of the heated 
roller 19 is greater than the rotational speed of the cleaning roller 49 
and of the application roller 51, with the result that the direction of 
rotation of the cleaning roller 49 is in the opposite direction to the 
direction of rotation of the heated roller 19. 
The applied thickness both of the film of buffer agent and also of the 
cleaning agent can be adjusted appropriately by stepless variation of the 
speed of rotation and/or by changing the pressure of the buffer agent or 
cleaning agent. Since the rollers 48 and 51 are identical in form, FIG. 4 
is a perspective view of just one of these rollers, in this case the 
application roller 51. This comprises a tubular body 52 which can be 
driven by a motor, for example a pneumatic motor 53, mounted on a flange 
at one end of the body. At the other end of the tubular body 52 there is 
provided a rotary coupling 54 by means of which the buffer agent can be 
pumped into the interior of the tubular body 52. The buffer agent flows to 
the outside of the tubular body 52 by way of a number of holes 54' which 
are provided through the tubular body. Additionally, as shown, a wire 55 
can be wound helically around the tubular body 52. Rings 56 of a fibrous 
or felt-type material are arranged on the wire coil to lie tightly against 
one another. The felt rings 56 are thus soaked uniformly with the buffer 
agent. The felt rings 56 then moisten the heated roller 19 with a very 
thin film of buffer agent. After one revolution of the heated roller 19 
the buffer agent applied by the application roller 51 comes into contact 
with the cleaning roller 49, from the felt rings 56 of which there comes 
continuously a cleaning agent which forms a thin film on the heating 
roller. Because of the relative speed difference between the heated roller 
19 and the cleaning roller 49 the film of buffer agent laid down by the 
application roller 51 and which is perhaps slightly dirty is cleaned off. 
The buffer agent which is cleaned off then flows away through a discharge 
pipe 57. Since the outer surfaces of the rollers 49 and 51 are porous and 
the buffer agent and cleaning agent are each forced from the inside 
outwardly, a continuous self-cleaning action takes place. The discharge 
pipe 57 is connected to a tank 58 which encloses both the cleaning roller 
49 and also the application roller 51, as is shown in FIG. 3. Preferably, 
a guide device extends between the discharge pipe 57 and the application 
roller 51 over the whole length of the latter, in order to guide away the 
dirty buffer agent cleaned off from the heated roller 19 by the cleaning 
roller 49. 
From FIG. 1 it can be seen that the heat exchanger 41, in which a heat 
exchange takes place between the refrigerating medium of the refrigerating 
medium circulating system and the cooling medium of the cooling medium 
circulating system, is arranged in chamber 6, together with the compressor 
25. The heat exchanger 27 of the refrigerating medium circulating system, 
the hot blower 30 and the heat exchanger 31 of the circulating system for 
the heat transfer medium are all located in chamber 7. The heat exchanger 
35 for the hot air to be supplied to chamber 2 is provided in chamber 8, 
together with the hot air blower 16. 
The refrigerating medium of the refrigerating medium circulating system 
which includes the compressor 25 flows through heat exchanger 27 and heats 
up the combustion air for the hot blower 30. The cooled refrigerating 
medium flowing back from heat exchanger 27 flows into heat exchanger 41 in 
order to cool the cooling medium of the cooling medium circulating system. 
The cooled cooling medium passes to the extractor 23 and to the cooling 
rollers 20, and 21, in order then to flow back to heat exchanger 41. The 
liquid heat transfer medium heated in heat exchanger 31 by means of the 
hot blower 30 flows partly to the heated rollers 18, and 19 and partly to 
heat exchanger 35 in chamber 8. Associated with heat exchanger 31 in 
chamber 7, as shown schematically in FIG. 1, there may be an exhaust flue 
for leading the waste combustion gases from the hot blower 30 to the 
outside of the housing. Chambers 6, 7 and 8 are preferably hermetically 
separated from one another. 
The invention has been described above in relation to a preferred 
embodiment. However, the present invention may be embodied in other 
specific forms without departing from the spirit or essential attributes 
thereof, and, accordingly, reference should be made to the appended 
claims, in addition to the foregoing specification, as indicating the 
scope of the invention.