GB2310166A - An apparatus for washing printing plates - Google Patents

Description

"An apparatus for washina printing plates" The invention relates to an apparatus for washing printing plates of the flexible or flexographic type.

Generally speaking, printing plants which use such plates must store a large number of plates for use according to customer orders. There may be a considerable time delay between uses of particular plates and it is therefore very important that they are comprehensively washed after use to avoid build-up of ink and dirt.

PCT Patent Specification No. WO 92/01568 (Container Graphics Corporation) describes an apparatus for washing printing plates. This apparatus comprises a washing enclosure within which is mounted a rotatable drum for supporting a plate, a rotary brush for brushing a plate on the drum and a sprayer bar for spraying water on the plate. The plate is connected to the drum by inserting a reversedly bent edge portion of the plate into a drum slot and then connecting another edge to the drum by use of straps.

It appears that some problems would arise with such an apparatus. For example, it appears that the task of securing a printing plate to the drum would be quite timeconsuming. Further, because an edge of the plate must be bent over on itself, it appears that such an edge would become distorted over time and further, there would be non-uniform washing of the plate. It also appears to be quite difficult to connect a number of different plates of different sizes to the drum.

The invention is directed towards providing an improved apparatus which provides for simpler and more versatile connection of a plate to a drum, and which provides more versatility in operation. Another object of the invention is to improve the effectiveness of a washing cycle.

According to the invention, there is provided an apparatus for washing printing plates, the apparatus comprising : a controller; a washing enclosure within which is mounted a rotatable drum for supporting a plate, a rotary brush for brushing a plate and a spray bar for spraying water on the plate; and a pump system connected to the spray bar for supplying washing water, wherein the drum comprises a cylinder within which is mounted a plate clamp extending along the cylinder for clamping a plate at a leading edge against the surface of the cylinder.

In one embodiment, the clamp terminates in an operator handle at an end wall of the cylinder.

Preferably, the handle comprises a catch for holding the clamp at an outer, inoperative position to allow fitting of a plate to the drum.

In another embodiment, the handle comprises an arm pivotally connected to the cylinder at the end wall, the arm engaging the clamp at a floating pivot connector.

Preferably, the catch comprises a spring-biased knob on the handle.

In a further embodiment, the pump system comprises recirculation water and fresh water sub-systems connected to a main pump, and means for directing re-circulated water from a sump of the enclosure to the spray bar for a washing stage of a wash cycle, and means for directing fresh water to the spray bar for initial fill and a rinsing stages of the wash cycle. Preferably, the fresh water sub-system comprises a fresh water reservoir.

Ideally, the reservoir comprises a heating means.

In one embodiment, the pump system comprises a detergent dosing pump. Preferably the detergent dosing pump is connected to an inlet of the main pump.

In a further embodiment, the re-circulation sub-system comprises, in sequence, a sump valve, a filter, and a recirculation tank connected between the sump and the main pump.

Preferably, the re-circulation tank includes a level sensor connected to the controller, and the controller comprises means for directing start of a washing stage only after the level in the re-circulation tank has reached a pre-set value.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which : Fig. 1 is a perspective view of a printing plate washing apparatus of the invention; Fig. 2 is a diagrammatic side view of the apparatus; Fig. 3 is a schematic representation of a pump system of the apparatus; and Fig. 4 is a side view of a drum of the apparatus.

Referring to the drawings, there is shown an apparatus 1 for washing flexible printing plates. The apparatus 1 comprises a support frame 2 on castors 3. The frame 2 forms a washing enclosure 4 having a hinged cover 5. A plate-supporting drum 6 is mounted within the enclosure 4.

At one end of the frame 2, there is a control section 10, on a face of which there is a control panel 11.

The apparatus 1 also comprises an upper rotary brush 20 and a lower rotary brush 21 mounted above and below the drum 6. The two brushes 20 and 21 and the drum 6 are driven by a common drive chain 22, which is driven by a motor 23. The motor 23 is connected to a programmed controller 24, which is in turn connected to the control panel 11. A spray bar 30 extends across the enclosure 4 above the drum 6 at an orientation whereby nozzles are directed downwardly onto the drum 6 to provide a flat spray jet at a pressure of 8 bar onto a plate on the drum 6. An air bar 31 is also mounted within the enclosure 4 and this also comprises nozzles which are directed towards the drum 6. The air bar 31 is connected to a pneumatic supply via a solenoid-controlled valve connected to the controller 24.

The spray bar 30 is supplied by a pump system 32, illustrated in schematic form in Fig. 3. The pump system 32 comprises a fresh water reservoir 35 in which there is a heating element 36 controlled by a thermostat, not shown, and connected to an electrical supply 37. A level sensor 38 is connected to a level detector circuit 39.

The reservoir 35 is connected at its outlet to a fresh water valve 40, which is in turn connected to a main pump 41 which supplies water to the spray bar 30. A detergent dosing system comprising a detergent tank 45 and a dosing pump 46 is connected to an inlet duct 47 for the main pump 41.

The pump system 32 also comprises a re-circulation subsystem comprising a sump 50 in the base of the enclosure 4 connected to a sump valve 51. The sump valve 51 has a drain outlet 52 and a re-circulation outlet connected to a gauze filter 53. The filter 53 is in turn connected to a re-circulation tank 54 which has a float sensor 55 connected to the level detector circuit 39. The recirculation tank is in turn connected to the inlet 47 of the main pump 41.

Referring now to Fig. 4, construction of the drum 6 is now described in more detail. The drum 6 comprises a cylinder 58 having an end wall 59 and a central sleeve 60 for connection with a drive shaft. The drum 60 also comprises a pair of diagrammatically opposed clamps 61. Each clamp 61 has a lip 62 which extends substantially tangentially and an inwardly-extending shank which terminates in a pin 64 which engages within a slot 65 in a handle 66. The handle 66 is pivotally connected at a pin 68 to the end wall 59 of the cylinder 58 and terminates in a springbiased knob 67. The inner end of the handle 66 is biased in the anti-clockwise direction as viewed in Fig. 4 by a bias spring 69. The end wall 59 includes a recess 70 for engagement with the spring-biased knob 67.

In use, a flexographic printing plate is mounted on the drum 6. Referring in particular to Fig. 4, this is achieved by an operator grasping the knob 67 and rotating the handle 66 in the clockwise direction until a position is reached where the knob may be released for engagement within the recess 70 in the end wall 59. This is the position shown for the lower clamp 61 shown in Fig. 4.

Engagement of the knob within the recess 70 holds the clamp 61 at an outer position at which the lip 62 is spaced-apart from the surface of the cylinder 58. In this position, the operator may place one or more printing plates against the surface of the cylinder 58 and engage a leading edge of the plate under the lip 62. Any desired number of plates may be connected in this fashion along the length of the drum. When all plates are in position, the knob 67 is released and the clamp 61 is plunged downwardly by action of the spring 69 so that the leading edge of the printing plates are clamped against the surface of the cylinder 58 by the lip 62. If the length of a printing plate does not exceed half of the circumference of the drum 6, an additional printing plate may be mounted on the opposite clamp 61. There may of course be additional plates mounted side-by-side. This provides the possibility of washing several printing plates at the one time for more efficient washing. The printing plates will have a natural curvature around the drum and there is therefore no need to secure them to the drum at the trailing edge. Further, during washing the water helps to create a vacuum for adhesion of the plates to the drum. It has been found that clamping of the plates to the drum 6 in this manner is extremely efficient as very little operator time is required and further it is very effective because of the positive clamping action.

Another advantage is that there is no need to distort the printing plate at the edges and this provides for a relatively long life of the printing plate and for uniform washing. This in turn leads to a better printing quality.

Once the plates have been mounted, the cover 5 is closed to seal the enclosure and the operator then inputs instructions at the control panel 11. The controller 24 is programmed to direct a number of different wash cycles including short, medium and long wash cycles depending on the nature of the plate being washed. All cycles have the sequential stages of filling, washing with the circulating water, rinsing, drying, and drainage. To achieve this, the controller 24 operates the various parts of the pump system 32, the electrical signal connections being indicated by interrupted lines. Before the fill stage, the controller directs operation of the heating element 36 to heat the water to a desired temperature. The desired temperature depends on the nature of the printing plate and the inks which have been used. When the pre-set temperature has been reached, the valve 40 is opened and the main pump 41 draws water from the reservoir 35 and directs it to the spray bar 30 at a pressure of 8 bar.

The controller 24 also directs operation of the dosing pump 46 to inject a quantity of detergent at a predetermined flow rate, again depending on the nature of the plates and inks. Because the detergent is injected before the pump 41, there is a thorough mixing of the detergent with the fresh water, resulting in an effective cleaning action. As fresh water is drawn from the reservoir 34, the controller 24 monitors levels of water in the recirculation tank 54. When the level reaches a pre-set value, the controller closes the fresh water valve 40 and opens the re-circulation valve 42. The controller 24 had previously directed the valve 51 to provide a recirculation output to the filter 53. The controller 24 then directs a washing stage for a duration which has been inputted by the operator at the control panel 11.

During washing, the spray bar 30 is used to output a pressure spray of re-circulated water onto the drum. The two brushes and the drum 6 rotate in the same direction and accordingly, the relative motions at the points of contact are opposed. These motions provide for comprehensive washing of the plates and the brushes also help to keep the plates in place against the drum at the trailing edges. Unless a leak occurs in the system, there will be sufficient water in the pump system for the recirculation stage, this quantity being set by the level of the re-circulation tank 54 which triggers the start of the re-circulation stage.

At the end of the re-circulation washing stage, the valve 42 is closed and the fresh water valve 40 is again opened to direct rinsing water without detergent onto the drum 6.

This rinses the drum and the brushes.

For the drying stage of the wash cycle, both of the valves 40 and 42 are closed and the pump 41 is not operated. The controller 24 opens the solenoid connected to the air bar 31 so that air at high pressure impinges upon the drum as it rotates. It has been found that this assists in drying of the plate in a relatively short time period. In another embodiment the brushes may be moved away a further distance from the drum to assist drying.

Finally, the controller 24 directs switching of the valve 51 so that the contents of the sump 50 are directed out at the drain outlet 52. After this stage, both the sump 50 and the pump system 52 are empty, with the exception of the fresh water reservoir 35, which is kept topped up.

It has been found that the apparatus 1 of the invention provides for very simple connection of printing plates and allows several plates to be washed at any one time. It also helps to ensure that plates are not damaged after a large number of wash cycles.

Further, it has been found that the invention provides for very effective washing of the plates because of use of a fresh water reservoir which is heated, and injection of detergent in dosed amounts at the inlet of the pump. It has also been found that the system is very reliable because of the construction- of the re-circulation subsystem. For example, provision of a filter before the main pump 41 helps to ensure that the pump 41 is not damaged and, further, provision of a buffer tank 54 between the sump 50 and the pump 41 helps to ensure that there is always sufficient re-circulation water in the system. While many of these features are very simple, it has been found that they provide for very effective and reliable washing of printing plates.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (13)

1. An apparatus for washing printing plates, the apparatus comprising a controller; a washing enclosure within which is mounted a rotatable drum for supporting a plate, a rotary brush for brushing a plate and a spray bar for spraying water on the plate; and a pump system connected to the spray bar for supplying washing water, wherein the drum comprises a cylinder within which is mounted a plate clamp extending along the cylinder for clamping a plate at a leading edge against the surface of the cylinder.

2. An apparatus as claimed in claim 1, wherein the clamp terminates in an operator handle at an end wall of the cylinder.

3. An apparatus as claimed in claim 2, wherein the handle comprises a catch for holding the clamp at an outer, inoperative position to allow fitting of a plate to the drum.

4. An apparatus as claimed in claims 2 or 3, wherein the handle comprises an arm pivotally connected to the cylinder at the end wall, the arm engaging the clamp at a floating pivot connector.

5. An apparatus as claimed in claims 3 or 4, wherein the catch comprises a spring-biased knob on the handle.

6. An apparatus as claimed in any preceding claim, wherein the pump system comprises re-circulation water and fresh water sub-systems connected to a main pump, and means for directing re-circulated water from a sump of the enclosure to the spray bar for a washing stage of a wash cycle, and means for directing fresh water to the spray bar for initial fill and a rinsing stages of the wash cycle.

7. An apparatus as claimed in claim 6, wherein the fresh water sub-system comprises a fresh water reservoir.

8. An apparatus as claimed in claim 7, wherein the reservoir comprises a heating means.

9. An apparatus as claimed in any preceding claim, wherein the pump system comprises a detergent dosing pump.

10. An apparatus as claimed in any of claims 6 to 9, wherein the detergent dosing pump is connected to an inlet of the main pump.

11. An apparatus as claimed in any of claims 6 to 10, wherein the re-circulation sub-system comprises, in sequence, a sump valve, a filter, and a re circulation tank connected between the sump and the main pump.

12. An apparatus as claimed in claim 11, wherein the re-circulation tank includes a level sensor connected to the controller, and the controller comprises means for directing start of a washing stage only after the level in the re-circulation tank has reached a pre-set value.

13. An apparatus substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.