Apparatus for washing out photopolymer printing plates by means of solvents, drying the printing plates and recovering the solvents

An apparatus for washing out photopolymer printing plates by means of solvents, drying the printing plates and recovering the solvents, a conventional washout station and a conventional drying station being connected to a solvent recovery means integrated in the drying station, which consists of the following parts: PA1 a hermetically sealing drying chamber for the printing plates, having an adjustable hood (15) and stationary panel (16), with panel heaters (18a, 18b) inserted in the hood and panel, PA1 a system which is connected to the interior space formed when the drying chamber is closed and which consists of a heat exchanger (25) for cooling the solvent vapor/air mixture, formed by drying the printing plates in the drying chamber, and condensation of the solvents, PA1 a solvent separator (26) for separating off the liquefied solvents, PA1 a vacuum pump (27) and a buffer vessel (33) for sucking up the solvent vapor/air mixture and compressing the solvent vapor/air mixture, PA1 a heat exchanger (28) for increasing the temperature of the air circulating in the system, two three-way valves (31, 32) and connecting pipelines from the drying chamber via the individual units and back to the drying chamber.

The present invention relates to an apparatus for washing out photopolymer 
printing plates by means of solvents, drying the printing plates and 
recovering the solvents using a conventional washout station and a 
conventional drying station having an apparatus for recovering the 
solvents, consisting of a drying chamber for the printing plates, having 
an adjustable hood and stationary panel. 
The apparatus described above is used predominantly for recovering solvents 
which are used for washing out photopolymer printing plates (referred to 
below as printing plates) using known processing apparatuses, for example 
combined washers and driers. The solvents used are predominantly mixtures 
of chlorinated hydrocarbons (referred to below as hydrocarbons) and 
alcohols. These solvents are present in intermolecular form or as surface 
moisture during washing out of the printing plates and as readily volatile 
vapors during drying. 
In the prior art, the solvent-containing vapors obtained during drying of 
the printing plates are passed directly from the combined apparatuses 
through pipelines into the atmosphere, without subjecting these vapors 
beforehand to a waste air treatment. 
According to the new West German Clean Air Act of Feb. 1986, this procedure 
will no longer be possible after a transition period to 1991; the waste 
air containing the readily volatile hydrocarbons may no longer be passed 
into the atmosphere. 
Attempts are currently being made to recover the hydrocarbons by means of a 
waste air treatment plant. Such a plant is familiar in process 
engineering. There, the waste air enriched with solvent vapor is passed 
through a layer of an absorbent (active carbon or a molecular sieve). This 
solvent is in the form of layer is bound by the adsorbent, so that 
solvent-free, treated waste air leaves the adsorbent layer and passes into 
the atmosphere. 
However, this procedure requires very expensive apparatus since the 
adsorbent, which becomes saturated after a certain adsorption time, must 
be desorbed using hot air. This is circulated, ie. after passing the 
adsorbent the air is cooled until the solvent condenses and can be 
separated off; the air is reheated and is passed through the adsorbent 
layer. After the desorption step, the adsorbent layer has to be cooled 
again with cool air. Since the heat capacity of the apparatus, the pipes 
and the adsorbent is relatively large and air is a poor heat-transfer 
medium, the process is very energy-consumptive and time-consuming. 
Furthermore, DE-A-3 503 974 describes an apparatus for washing out and 
drying plates in a continuous procedure. The objects of this apparatus is 
to ensure better washout of these plates and at the same time to increase 
the throughput speed. 
These processes are thereof unsuitable for solving the problem encountered. 
It is an object of the present invention to combine the processing 
apparatuses in which solvent vapors are formed, ie. the washer and dryer, 
into a closed system without exit of waste air, the said system having 
only one sealable input slot for the exposed printing plate still to be 
washed out and a sealable output apparatus from which the ready, dried 
printing plate is removed.

DETAILED DESCRIPTION OF THE INVENTION 
We have found that this object is achieved, according to the invention, by 
the defining clause of claim 1. 
Further features of the novel apparatus are described in the subclaims. 
An embodiment of the invention having the essential inventive features is 
shown in the drawing and is described in detail below with reference to 
various FIGS. 
FIG. 1 shows a schematic structure of the apparatus. 
The compact apparatus is divided into a conventional washout station 1 and 
the novel drying station 2, having the integrated means for solvent 
recovery, by a bulkhead partition 3 which has only one slot 4 to allow the 
washed out printing plate 5 to pass. 
The previously exposed printing plate is connected in a conventional manner 
to the driver bar 6 and suspended at the intake slot 7 in the two 
revolving transport chains 8. The transport chains move parallel at a 
distance apart corresponding to the driver bar, on both sides of the 
washout area. To prevent solvent vapors escaping from the intake slot, a 
flexible, thin antiadhesive apron 9 made of glass fiber-reinforced teflon 
cloth of excessive length is mounted so that it either slides on the 
printing plate or rests on the plate table. The arrangement of the plate 
table, which is not shown for the sake of clarity, corresponds to the path 
of the transport chains 8 and 10. 
The printing plate 5 is thus drawing continuously through the washout 
station and is first treated with spent solvent, which is sprayed through 
the nozzles 11, and then with fresh solvent from the nozzles 12. To 
improve the subsequent washing effect, the printing plate is transported 
obliquely upward in the region of the nozzles 12. By means of a fan 13 and 
a slot nozzle 14, the solvent is blown as completely as possible out of 
the indentations in the printing plate relief. The extracted air 
originates from the washout stations; it is thus virtually saturated with 
solvent vapor and circulates internally. 
The distance from the slot nozzle to the slot 4 in the bulkhead partition 
corresponds to the greatest possible printing plate length. When the 
driver bar passes through the slot, the printing plate is transferred to a 
second pair of transport chains 10 and moved at high speed into the drying 
chamber, which si formed by the upper flat hood 15 and the lower 
stationary panel 16. 
Instead of the second pair of chains 10, transport of the printing plate 
and loading of the drying chamber could be effected using a double fork 
which moves in a linear manner and grips the two ends of the driver bar 6. 
The hood can be raised or lowered by the lifting means 17. The drying 
chamber consists of a hood and a panel, each of which has a panel heater 
18a or 18b, which corresponds to the dimensions of the largest possible 
printing plate. The lower heater 18a i sunk flush in the panel 16. 
The hood 15 has a peripheral seal 19, which ensures a hermetic seal in the 
closed, ie. lowered, state. Furthermore, the frame of the hood is designed 
so that two distribution channels 20 and 21 are formed in the closed 
state, the said channels each being connected via a gap to the interior of 
the chamber. The gaps occur between the shortened inner walls 24 of the 
panel and the panel 16. In the closed state, the lines 22 and 23 are thus 
connected to the interior of the chamber via the distribution channels 20 
and 21 and via the two gaps. 
The line 22 leads from the drying chamber to the heat exchanger 25, solvent 
separator 26, vacuum pump 27 and heat exchanger 28, and via line 23 to the 
distribution channels 21, and back to the drying chamber via the gap. 
The heat exchangers 25, 28 and 29 are part of the heat pump 30: 
The heat removed from the heat exchanger 25 and the power of the 
refrigeration unit of the heat pump 30 are mainly fed to the heat 
exchanger 28. 
The residual heat in the refrigerant circulation is released in heat 
exchanger 29. 
The three-way valves 31 and 32 in conjunction with the buffer vessel 33 
permit the following possibilities for drying the printing plate. 
FIG. 2 shows a possible procedure. 
The procedure described below is preferable for sensitive printing plates 
which tend to form bubbles at the relief surface below a certain reduced 
pressure. This type of drying also functions in a normal atmosphere. 
After the printing plate 5 to be dried has been automatically inserted into 
the preheated drying chamber 15/16 with the aid of the driver bar 6 and 
the said chamber has been sealed, the vacuum pump 27 begins to reduce the 
pressure partially in the entire drying chamber and pipe system. The 
three-way valve 31 is switched so that the air sucked in is compressed in 
buffer vessel 33. 
The three-way valve 32 is then switched to that the air is circulated via 
the closed drying chamber with the aid of the vacuum pump 27. 
The solvent vapor/air mixture sucked out of the drying chamber first passes 
into the heat exchanger 25, in which the solvent vapor is virtually 
completely liquefied by removal of heat. 
The solvent separated in the downstream separator 26 is transported to the 
washout station 1 for reuse, while the cooled air passes through the 
vacuum pump 27, the two valves 31 and 32 and the heat exchanger 28, in 
which the air is reheated before it is fed again to the drying chamber. 
The drying effect is thus based not so much on the boiling point of the 
solvent, which is depressed due to the reduced pressure, as on the ability 
of the air to take up the solvent as a function of temperature. 
Intensive and very uniform flow around the printing plate 5 is therefore of 
great importance, this being achieved by means of the distribution 
channels 20 and 21 and the gaps formed by the inner walls 24 and the panel 
16. Considered in the opposite way, if there were no exchange of air at a 
point in the drying chamber, the printing plate could not give up any 
solvent to the stationary saturated air at that point. For this reason, it 
has been possible to achieve somewhat shorter drying times in an 
experiment with a metal fabric between the heating panel 18a and the 
printing plate 5. 
The following optimum values for a sensitive multilayer plate having a 
length of 750 mm, a width of 450 mm, a total thickness of 2.75 mm and a 
relief height of 0.7 mm have been determined by experiments: 
______________________________________ 
Drying chamber temperature: 
60-65.degree. C. 
Drying chamber pressure: 
800-900 mbar 
Temperature in heat -15.degree. C. 
exchanger (25) 
Temperature in heat +70.degree. C. 
exchanger (28) 
Mean flow rate in the drying 
0.1 m/s 
chamber: 
Solvent used 89% by weight of Per 
11% by weight of 
butanol 
Solvent absorption: at 60.degree. C. 750 g/m.sup.3 of 
air 
at -15.degree. C. 18 g/m.sup.3 of 
air 
Drying time: 14 min 
Residual solvent content: 
13 g 
(determined by subsequent 
drying in a heating oven) 
______________________________________ 
FIG. 3 shows an alternative procedure. 
This procedure is suitable predominantly for single-layer printing plates 
in which reduced pressure does not cause any reduction in quality. 
In order to avoid having to give the buffer vessel 33 unnecessarily large 
dimensions at the relatively low pressures desired, the buffer vessel is 
preevacuated with the hood 15 raised. The hood is then lowered, ie. 
hermetically sealed. During the drying time, the vacuum pump 27 delivers 
into the buffer vessel 33. As in the procedure shown in FIG. 2, the 
solvent vapors are limited in the heat exchanger 25 by removal of heat, 
and the liquid solvent is fed via the separator 26 to the solvent 
container 36. 
The quantity of heat removed by the heat pump 30 is released into the 
atmosphere exclusively via the heat exchanger 29. 
Air circulation is dispensed with. All that is important is that the heat 
required for evaporating the solvent is supplied uniformly to the printing 
plate 5 to be dried, in the required time, partly by heat conduction by 
the panel heater 18a and partly by heat radiation by the panel heater 18b. 
The following have proven optimum values for a single-layer plate having a 
length of 750 mm, a width of 450 mm, a total thickness of 2.84 mm and a 
relief height of 1.2 mm; 
______________________________________ 
Drying chamber temperature: top 
60-65.degree. C. 
bottom about 120.degree. C. 
(radiant heat) 
Drying chamber pressure: 
20-50 mbar 
Boiling point at this pressure: 
22-40.degree. C. 
Temperature in heat exchanger (25): 
-20.degree. C. 
Solvent used: 89% by weight of 
Per 
11% by weight of 
butanol 
Drying time: 10 min 
Residual solvent content: 
11 g 
______________________________________ 
The advantages obtained with the invention primarily relate to occupational 
safety, since the operator of the processing apparatuses virtually no 
longer comes into contact with the solvent. In the past, he was exposed to 
the solvent vapors, considered physiologically unacceptable, during 
transport of the printing plates from the washout apparatus to the drying 
oven and during operation of the drying oven. 
The same applies to environmental protection: the solvent emission is 
negligibly small and is well below the limits set by the new West German 
Clean Air Act. 
Furthermore, the production time for the printing plate is substantially 
reduced since the hour-long drying in the heating oven is dispensed with. 
Compared with the alternatives undergoing trials (active carbon or 
molecular sieve), the novel apparatus entails substantially lower capital 
costs and operating costs. 
The drying station of the novel apparatus is also suitable as a separate 
apparatus for replacing the heating oven as a temporary compromise in 
existing plants, so that, in conjunction with changes to the continuous 
washers on the market, emission values which meet the legal requirements 
are achieved.