GB1575686A

GB1575686A - Offset printing machine

Info

Publication number: GB1575686A
Application number: GB2774577A
Authority: GB
Original assignee: NRG Manufacturing Ltd
Current assignee: NRG Manufacturing Ltd
Priority date: 1977-07-01
Filing date: 1977-07-01
Publication date: 1980-09-24
Also published as: DE7819446U1; DE2828454A1

Description

(54) OFFSET PRINTING MACHINE (71) We, GESTETNER LIMITED, a British Company, of Fawley Road, Tottenham, London N17 9LT, Enguand, 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 the application of solvent to the surface of a blanket cylinder in offset printing apparatus, for cleaning the surface of the image transfer blanket on the cylinder.

According to one aspect of the present invention we provide an offset printing machine including a blanket wash unit comprising a blanket wash solvent applicator member, a removable tank forming a reservoir for blanket wash solvent, a feed line for blanket wash solvent connecting said tank to said applicator member, a return line for recycling to said tank used blanket wash solvent from said applicator member and/or the image transfer blanket, and a cap through which said feed line and said return line pass, wherein said tank has a neck which is adapted to receive said cap in sealing manner to connect the interior of said tank with the feed line for wash solvent to the applicator member and the return line for wash solvent from the applicator member and/or image transfer blanket.

The wash solvent tank is preferably of shallow, flat construction so as to provide a considerable flow area onto which the ink residue from used wash solvent can settle i!l the form of a sludge, leaving the blanket wash solvent above the sludge relatively clean.

More preferably the tank includes a removable cap adapted to be sealed in airtight manner on a neck of the tank, said cap being provided with a pressurising air inlet, a main feed pipe to pass solvent to the applicator member, and a return pipe from a "dry sump" trough under the blanket wash roller. Conveniently the main supply pipe dips into the tank well below the top wall of the tank thereby defining a minimum liquid level in the settling tank which is just above the intended maximum sludge level. A transit cover may be provided, again adapted to fit on the neck of the tank, to allow the tank to be used as a container for supply of fresh blanket wash solvent and for disposal of sludge and contaminated blanket wash solvent.

According to another aspect of the present invention we provide a method of operating an offset printing machine comprising removing the transport closure from the tank, attaching said cap to the tank to connect the blanket wash tank to the blanket wash unit, carrying out blanket washing operations as required from time to time until the build-up of sludge in said tank reaches or nearly reaches the bottom of said feed line, and then exchanging said tank for a fresh one and disposing of the first mentioned tank after attachment of the transit closure thereto.

In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which: Figure 1 is a side elevational, partly sectional view of the blanket cylinder and blanket wash applicator of a blanket cleaning system in accordance with the present invention; Figure 2 is a view in the direction of arrow II of Figure 1 but showing the blanket wash solvent distribution duct, the blanket wash roller and its drive system, and the settling tank and pressurising pump; and Figure 3 is a sectional view from the same direction as Figure 1 and illustrating the drive mechanism to the pressurising pump and the applicator roller.

As shown in the side view of Figure 1, which shows the blanket cleaning system in vertical section and the blanket in side elevation, the blanket cleaning system uses a trough 1 surrounding the lower part of a blanket cleaning roller 2 which has a cellular plastics jacket 2a forming an absorbent outer covering to the blanket wash solvent applicator roller 2.

At the upper part of the roller 2 is a pair of links 3 each of which is spring-urged by means of a spring cartridge 4 towards the surface of the applicator roller 2 so that two pressure rollers 5 rotatably mounted on the links 3 can be pressed downwardly onto the adsorbent jacket 2a to squeeze surplus blanket wash solvent from the jacket before the squeezed jacket comes into contact with the blanket surface. Only one link 3 and one spring cartridge 4 can be seen in Figure 1.

Each spring cartridge 4 is, as indicated above, pivotally mounted on the end wall la of the trough, at 4a, so that the two pressure rollers 5 can readily be moved to an out-of-the-way position simply by pivoting the spring cartridge 4 in the clockwise sense until its spring-loaded ball 4b is released from the arcuate notch 3a of the associated link 3 which is then free to pivot in the anti-clockwise sense about its axis of rotation 3b. This allows the blanket wash solvent applicator roller 2 to be removed for maintenance or replacement.

Although not shown in Figure 1, the spring-loaded ball 4b is captive in the cylinder of the spring cartridge 4 so that when the spring detent unit is swung to its "outof-the-way" position the ball 4b will still be retained in place.

Extending between the two links 3 is a blanket wash solvent distribution duct 6 with an array of spray holes 6a through which blanket wash solvent is to be poured onto the rising portions of the blanket wash solvent applicator roller 2 to soak the jacket 2a of the roller. The distribution duct 6 is supplied from a main supply tube 7 which, as will be described later with reference to Figure 2, communicates the distribution duct 6 with a location near the bottom of a settling tank.

This settling tank is also connected to the blanket wash solvent return pipe 8 which opens into the bottom of the trough 1 to collect all surplus blanket wash solvent wrung from the jacket 2a by the pressure rollers 5 to recycle it back to the settling tank.

In order that the applicator roller 2a may have a rest position which can be attained without the need for any lateral shifting of the axis of rotation of the spindle 2b of the cleaning roller, the roller 2 has a recess into which the absorbent jacket 2a fits and which is closed by a filler segment 9 which supports the pressure rollers 5 in the inoperative position of the blanket wash applicator roller 2.

The filler segment 9 has a smaller overall radius than does the absorbent jacket 2a covering the remainder of the surface of the roller 2, and thus in the inoperative position illustrated in Figure 1, the filler segment 9 will be out of contact with the blanket surface and during normal printing operation the blanket cylinder 19 will therefore be free to rotate without any marring of the image by contact with the blanket wash solvent applicator roller 2.

Figure 2 shows that the spindle 2b of the blanket wash solvent applicator roller carries a main drive sprocket 10 chain-driven to rotate the spindle 2b during a blanket wash cycle. The drive to the sprocket 2b will be described later with reference to Figure 3.

At the bottom of Figure 2 there is shown the settling tank 11 which has a neck 1 1a to which is sealingly fitted a cap 12 carrying both the main blanket wash solvent supply line 7 and the recycle line 8. The recycle line 8 can be seen to terminate at a flap valve 13 which is arranged to close off the bottom of the recycle line 8 when an overpressure exists in the air space above the maximum liquid level in the tank 11. This over-pressure will be generated during each blanket wash cycle by means of a deformable chamber pump, in this case a bellows pump.

The settling tank 11 may be made of seamed construction from tinplate or, more preferably, may be a blow-moulded plastics container. The flat configuration of the settling tank is important in order to provide a considerable floor area on which a large quantity of residue may build up with only a shallow thickness of the residue layer spread over the tank. This allows the most economical use of the blanket wash solvent, as the lower end of the main supply pipe 7 may be very close to the bottom of the settling tank so that when eventually the level of the blanket wash solvent drops so low that air is entrained through the pipe 7, the quantity of blanket wash solvent mixed with the sludge is only a very small proportion of the total volume of solvent initially in the settling tank 11.

The settling tank 11 is provided with a separate transit closure which is secured to the neck of the settling tank 11 when the tank is first supplied and can be re-attached to the tank when the contents are spent, i.e.

when the blanket wash solvent has become contaminated and a layer of ink residue sludge has built up in the bottom of the settling tank, so that the settling tank 11 can be used as a container to assist in disposing of the waste.

This disposal may either involve returning the sealed settling tank 11 to the supplier for recovery of the ink residue and for cleaning of the settling tank and refilling with fresh blanket wash solvent, or else the tank 11 may be disposed of in any other safe way.

In this way the operator has no need to touch the blanket wash solvent or to inhale the fumes of the solvent as has been the case in the past where it has been necessary for periodic replacement of the quantity of blanket wash solvent in a reservoir trough.

The air pump includes a bellows 14 of any suitable flexible material, open at one end to a pipe 18 which runs to the settling tank cap 12 for communicating the pressure within the bellows 14 with the air space above the liquid level in the tank 11, and closed at the other end where it carries a reinforcing plate 14a secured to a tab 15a at the bottom end of a push-rod 15. The push rod has a slot 15b extending along it at its upper end and this slot receives the spindle 2b so that the push rod 15 can reciprocate vertically while this slot moves laterally of the spindle 2b.

The motion of the push rod results from a cam 16, keyed to the spindle 2b, and cooperating with a cam follower roller 15c carried by the push-rod 15. The spindle 15d of the cam follower roller 15e has one end of a helical tension spring 21 hooked on it, the other end of the spring being hooked over the end of the spindle 2b to leavee the spindle free to rotate while the spring 21 slides thereon.

The side frame 17 of the machine carries a bearing 17a which rotatably supports the spindle 2b, there being another similar bearing on the opposite side frame of the machine. The side frame 17 also carries a bracket 20 to which the lower, open end of the bellows 14 is secured. In this way the lower end of the bellows 14 will be held stationary while the upper end is driven for vertical motion by virtue of the connection between the tab 15a of push-rod 15 and the reinforcing plate 14a of the bellows 14.

During each revolution of the blanket wash solvent applicator roller 2, the pushrod 15 will descend to compress the bellows 14, thereby compressing the air in the pressure supply pipe 18 and the air space above the liquid level in the settling tank 11, and urging flow of blanket wash solvent from above the sludge level in the tank 11 through the main supply pipe 7 and the distribution duct 6 to be sprayed onto the absorbent jacket 2a of the solvent applicator roller 2.

For this purpose the lower end of the main blanket wash solvent supply pipe 7 opens into the settling tank at a level near the bottom so that this will define both the maximum sludge level to be tolerated and the minimum liquid level.

If, during a blanket wash cycle, the level of solvent falls below the lower end of the main blanket wash solvent supply pipe 7 then air will be expelled through the pipe 7 and this will defeat the pumping action of the bellows pump. Thus it will be clear to the printing machine operator that the blanket wash solvent flow is partially interrupted and he or she will be aware that the settling tank 11 needs attention, either topping up or replacement. If desired, some other warning system may be incorporated, for example a liquid level switch may be provided at the level of the lower end of the main blanket wash solvent supply pipe 7.

The drive system of the bellows pump and also the blanket wash solvent applicator roller 2 can best be appreciated from Figure 3 which shows a side elevational view in schematic form.

Coaxially with the blanket cylinder 19 is a clutch ring 22 having a notch 22a for receiving a tooth 23a of a clutch pawl 23. The clutch pawl 23 is pivotally mounted on a stub-spindle 23b carried by one end of the blanket cylinder 19 and is spring-urged for clockwise pivoting by means of a helical tension spring 35 extending between a hooked end of the pawl 23 and a stud 27a on an eccentric cam 27 carried by the blanket cylinder 19. Rotation of the blanket cylinder 19 about its axis 19a turns the eccentric cam 27 which is arranged to be engaged by a cam follower roller 26a of a bellcrank 26. The bellcrank 26 is mounted for pivoting movement about the axis of a spindle 28a of a timing ratchet wheel 28.

The bellcrank 26 has, at the end of its other limb, a toe 26b arranged to be received within a notch 24a of a latch lever 24 which in turn is pivotally connected at 24b to the the armature of a solenoid 25. The same latch lever 24 also engages the clutch pawl 23 to hold the toe 23a of the clutch pawl out of engagement with the notch 22a of the clutch ring 22 when the latch lever 24 is in its "blanket wash disengaged" position in which it also holds the bellcrank 26 against clockwise movement.

The bellcrank 26 serves to drive the timing ratchet wheel 28 by virtue of a driving pawl 32 which engages with the teeth of the timing ratchet wheel 28 to drive the ratchet wheel in the anticlockwise sense as the eccentric cam 27 carried by the blanket cylinder 19 drives the cam follower roller 26a in the downward direction. The return stroke of the bellcrank 27 is derived by way of a helical tension spring 31 extending between a point 31a on the bellcrank 26 and a point 31b on the machine frame.

A stop switch is carried by the machine frame and arranged to be engaged by a projection 34 carried by the timing ratchet wheel 28 so that once the timing ratchet wheel 28 has executed one complete revolution the switch 33 is tripped to de-energise the solenoid 25 allowing the latch lever 24 to be spring-urged downwardly towards its Figure 3 position.

The left-hand end of Figure 3 shows the push-rod 15 with its cam follower roller 15c riding on the surface of the eccentric cam 16, in this case an eccentric circular cam, causing the push-rod 15 to oscillate in a generally upward and downward direction.

The outer periphery of the clutch ring 22 has sprocket teeth 29, and an idler sprocket 30 is mounted coaxially with but rotatable with respect to the timing ratchet wheel 28 such that an endless drive chain 36 passing around the sprocket 10 and over the sprocket teeth 29 of the clutch ring 22 is capable of linking the sprockets 10 and 29 to give clockwise rotation of the sprocket 10 when the sprocket 29 rotates in the anti-clockwise sense once it is linked to the blanket cylinder 19 by inter-engagement of the toe 23a of the clutch pawl with the notch 22a of the clutch ring.

By way of further explanation, the operation of the printing apparatus incorporating this blanket cleaning system will now be described.

To prepare the printing apparatus for use, a settling tank 11 full of fresh blanket wash solvent is placed in position in the appropriate space within the machine casing, for example in the lower part of the machine below the paper feed, and the transit closure (not shown) of the settling tank 11 is replaced by the cap 12 shown in Figure 2.

This automatically connects the air supply pipe 18, the main blanket wash solvent supply pipe 7 and the recycle pipe 8 to the settling tank 11 in air-tight sealed manner.

During the printing operation, the plate cylinder and the blanket cylinder 19 will be in rolling contact and the blanket cylinder will be rotating in the anti-clockwise direction but with the clutch pawl 23 held in the Figure 3 position by engagement with the free end of the latch lever 24. Thus there will be no operation of the blanket wash system at this time.

At the end of the printing operation a suitable automatic signal will be given, triggered either by a counter indicating the number of copies needed, or by some other machine function such as operation of a plate eject mechanism, and this signal will energise the solenoid 25 to pull the latch lever 24 upwardly (rotating it in the clockwise direction from the position shown in Figure 3).

This will both release bellcrank 26 to allow the tension spring 31 to pull the bellcrank in the clockwise direction while the drive pawl 32 clicks over the teeth of timing ratchet wheel 28, and also releases the clutch pawl 23 so that the helical tension spring 35 pulls the pawl 23 for clockwise rotation to drive the toe 23a of the clutch pawl against the inner periphery of the clutch 22 whereby the pawl toe 23a will rise into the notch 22a of the clutch ring when next the toe 23a and notch 22a come into alignment.

Once the toe 23a and notch 22a are in engagement, the continued anti-clockwise rotation of the blanket cylinder 19 will drive the sprocket teeth 29 on the clutch ring 22 for anti-clockwise rotation thereby circulating the chain to rotate the idler sprocket 30 and the driving sprocket 10 in the clockwise sense. The blanket wash solvent applicator roller 22 will thus embark on a clockwise rotation from the rest position shown in Figure 1. Simultaneously, the cam 16 will begin to rotate to depress the cam follower roller 15c and the push rod 15 to compress the bellows 14 and begin to impose an overpressure on the air space above the liquid level in the settling tank 11. This overpressure causes the flap valve 13 to close off the bottom of the return pipe to prevent air leakage up the pipe 8.

Thus the start of rotation of the blanket wash solvent applicator roller 2 will be accompanied by the beginning of a pumping action bringing blanket wash solvent up through the pipe 7 and distribution duct 6 to spray onto the blanket wash solvent applicator roller 2. As indicated above with reference to Figure 1, the spray of solvent will flush the rising part of the absorbent jacket 2a on the blanket wash solvent applicator roller 2 and the surplus solvent held by the absorbent jacket will be wrung out by the pressure rollers 5 so that a clean and moist (but not soaking wet) portion of the jacket 2a will come into contact with the blanket surface to exert a washing and wiping action thereon.

Once the spindle 2b has executed 1800 of rotation, the cam follower roller 1 sic will have passed the lobe of the cam 16 and from there on the bellows 14 will begin to expand causing a cessation of the pumping flow of blanket wash solvent through the spray holes 6a of the distribution duct 6, and eventually even a slight suction effect (because of the need to fill with air the volume previously occupied by the displaced solvent) allowing the valve 13 to open to drain the recycled solvent into the tank 11.

During this further rotation the blanket wash solvent applicator roller 2 will continue through the second half of its rotational cycle while the flow of blanket wash solvent will have stopped.

The subsequent revolutions of the applicator roller 2 will be accompanied by further strokes of the pump and consequently by further spurts of solvent from the duct 6.

Throughout this rotation of the blanket wash solvent applicator roller 2 the rotation of the cam 27 carried by the blanket cylinder will now be causing oscillatory pivoting of the bellcrank 26 since the toe 26b is no longer constrained in the Figure 3 position by the notch 24 so the spring 31 will in each case pull the bellcrank 26 in the clockwise direction, after the cam follower roller 26a has mounted the lobe of the cam 27, driving it for a return stroke in the anticlockwise sense. This oscillatory pivoting motion of the bellcrank 26 will result in an intermittent anti-clockwise movement of the timing ratchet wheel 28 until such time as the projection 34 comes into contact with the switch 33 at the completion of one revolution, when the solenoid 25 will be de-energised. The electric circuitry connecting the switch 33 and the solenoid 25 will be readily apparent to the expert in the art and does not need detailed illustration or discussion in this Application.

Once the solenoid 25 has been de-energised, the armature will spring back to the Figure 3 position bringing the latch lever 24 down onto the toe 26b of the bellcrank 26.

When the cam follower roller 26a at the other end of the bellcrank next arrives at the lobe of cam 27 the toe 26b will have come into register with the notch 24a of the latch lever, allowing the latch lever to continue its anti-clockwise movement until the toe 26b is fully home in the notch 24a. At the same time, the free end of the latch lever 24 will then be in a position to engage the toe 23a of the clutch pawl 23 when it next passes under the free end of the latch lever 24, thereby knocking the toe 23a out of engagement with the notch 22a of the clutch ring 22 and disengaging rotational drive to the sprocket teeth 29 of the clutch ring, thereby stopping the rotational drive to the sprocket 10, spindle 2b and the blanket wash solvent applicator roller 2 in the "rest" position of the roller 2. At this point the spring 31 will be fully stretched but return movement of the bellcrank in the clockwise direction will be prevented by engagement of the toe 36b and the notch 24a.

The pressure in the air space above the blanket wash solvent in the tank 11 will then have returned to the starting value and the blanket wash mechanism will remain inactive until the next time the automatic "blanket washing" signal is given.

Many hundreds of such blanket wash cycles may proceed until such time as the liquid level in the settling tank 11 drops to expose the bottom end of the main supply pipe 7, or until such time as the sludge level rises to meet the bottom end of the pipe 7 in which case the blanket wash solvent issuing from the spray holes 6b in the distribution duct 6 will be seen to be contaminated.

At this stage, the cap 12 must be removed from the settling tank 11 and the tank 11 then fitted with its transit closure and removed from the machine and replaced by another settling tank 11 already filled with fresh blanket wash solvent.

Tests have shown that the most advantageous blanket washing effect is achieved if the peripheral speeds of the blanket surface and the jacket 2a on the blanket wash solvent applicator roller are in the ratio 9:1. With the relative dimensions illustrated in the accompanying drawings, this is equivalent to a ratio of approximately six revolutions of the blanket wash roller for one revolution of the timing ratchet wheel 28. Thus the blanket wash roller will have carried out six consecutive washing phases, each separated from the next by a rest phase in which the filler segment 9 passes the blanket surface. Throughout this cycle of several successive phases the timing ratchet wheel 28 will be executing a single revolution.

In a preferred embodiment, the settling tank 11 had a total volume of 2.5 litres (including air space) with a fluid depth (when full) of 76 mm and the inlet tube 7 disposed 10 mm above the tank floor. Sludge has been found to accumulate on the floor of the tank to a depth of approximately 3 mm maximum by the time the amount of blanket wash solvent loss is such that the supply to the spray bar 6 becomes interrupted. With this arrangement the usable solvent occupies 83 % of the total available volume, the waste fluid occupies 13% and the sludge deposit 4%, approximately.

However, these various values are given purely by way of example and it will be understood that different materials and dimensions may be employed with different cleaning characteristics, as desired.

WHAT WE CLAIM IS:- 1. An offset printing machine including a blanket wash unit comprising a blanket wash solvent applicator member, a removable tank forming a reservoir for blanket wash solvent, a feed line for blanket wash solvent connecting said tank to said applicator member, a return line for recycling to said tank used blanket wash solvent from said applicator member and/or the image tranfer blanket, and a cap through which said feed line and said return line pass, wherein said tank has a neck which is adapted to receive said cap in sealing manner to connect the interior of tank with the feed line for wash solvent to the applicator member and the return line for wash solvent from the applicator member and/or image transfer blanket.

2. A printing machine according to claim 1, wherein said tank is provided with a transport closure for facilitating disposal of the tank after use.

3. A printing machine according to claim 1 or 2, and including an air line for pressurising air space at the top of said tank to urge wash solvent along said feed line to the applicator member, and further including a non-return valve in said return line to allow flow of wash solvent only in a direction towards said tank.

4. A printing machine according to any one of claims 1 to 3, wherein the positioning

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. intermittent anti-clockwise movement of the timing ratchet wheel 28 until such time as the projection 34 comes into contact with the switch 33 at the completion of one revolution, when the solenoid 25 will be de-energised. The electric circuitry connecting the switch 33 and the solenoid 25 will be readily apparent to the expert in the art and does not need detailed illustration or discussion in this Application. Once the solenoid 25 has been de-energised, the armature will spring back to the Figure 3 position bringing the latch lever 24 down onto the toe 26b of the bellcrank 26. When the cam follower roller 26a at the other end of the bellcrank next arrives at the lobe of cam 27 the toe 26b will have come into register with the notch 24a of the latch lever, allowing the latch lever to continue its anti-clockwise movement until the toe 26b is fully home in the notch 24a. At the same time, the free end of the latch lever 24 will then be in a position to engage the toe 23a of the clutch pawl 23 when it next passes under the free end of the latch lever 24, thereby knocking the toe 23a out of engagement with the notch 22a of the clutch ring 22 and disengaging rotational drive to the sprocket teeth 29 of the clutch ring, thereby stopping the rotational drive to the sprocket 10, spindle 2b and the blanket wash solvent applicator roller 2 in the "rest" position of the roller 2. At this point the spring 31 will be fully stretched but return movement of the bellcrank in the clockwise direction will be prevented by engagement of the toe 36b and the notch 24a. The pressure in the air space above the blanket wash solvent in the tank 11 will then have returned to the starting value and the blanket wash mechanism will remain inactive until the next time the automatic "blanket washing" signal is given. Many hundreds of such blanket wash cycles may proceed until such time as the liquid level in the settling tank 11 drops to expose the bottom end of the main supply pipe 7, or until such time as the sludge level rises to meet the bottom end of the pipe 7 in which case the blanket wash solvent issuing from the spray holes 6b in the distribution duct 6 will be seen to be contaminated. At this stage, the cap 12 must be removed from the settling tank 11 and the tank 11 then fitted with its transit closure and removed from the machine and replaced by another settling tank 11 already filled with fresh blanket wash solvent. Tests have shown that the most advantageous blanket washing effect is achieved if the peripheral speeds of the blanket surface and the jacket 2a on the blanket wash solvent applicator roller are in the ratio 9:1. With the relative dimensions illustrated in the accompanying drawings, this is equivalent to a ratio of approximately six revolutions of the blanket wash roller for one revolution of the timing ratchet wheel 28. Thus the blanket wash roller will have carried out six consecutive washing phases, each separated from the next by a rest phase in which the filler segment 9 passes the blanket surface. Throughout this cycle of several successive phases the timing ratchet wheel 28 will be executing a single revolution. In a preferred embodiment, the settling tank 11 had a total volume of 2.5 litres (including air space) with a fluid depth (when full) of 76 mm and the inlet tube 7 disposed 10 mm above the tank floor. Sludge has been found to accumulate on the floor of the tank to a depth of approximately 3 mm maximum by the time the amount of blanket wash solvent loss is such that the supply to the spray bar 6 becomes interrupted. With this arrangement the usable solvent occupies 83 % of the total available volume, the waste fluid occupies 13% and the sludge deposit 4%, approximately. However, these various values are given purely by way of example and it will be understood that different materials and dimensions may be employed with different cleaning characteristics, as desired. WHAT WE CLAIM IS:-

1. An offset printing machine including a blanket wash unit comprising a blanket wash solvent applicator member, a removable tank forming a reservoir for blanket wash solvent, a feed line for blanket wash solvent connecting said tank to said applicator member, a return line for recycling to said tank used blanket wash solvent from said applicator member and/or the image tranfer blanket, and a cap through which said feed line and said return line pass, wherein said tank has a neck which is adapted to receive said cap in sealing manner to connect the interior of tank with the feed line for wash solvent to the applicator member and the return line for wash solvent from the applicator member and/or image transfer blanket.

of said cap on the feed line is such as to ensure that when the cap is connected on the tank the opening at the bottom of said feed. line is in the lower half of the tank at a location above the floor of the tank.

5. A printing machine according to claims 3 and 4 taken together, wherein in addition to said connections to said return line for used wash solvent and to said feed line for wash solvent, said cap includes a third connection to said air line, said third connection including a stub pipe projecting downwardly into said tank from said cap through a distance which will cause the stub pipe to terminate just short of the floor of the tank; and wherein said non-return valve in the return line is carried by the cap.

6. A printing machine according to claim 5, wherein said tank has a flat floor, a flat roof, and a neck projecting upwardly from said roof.

7. A printing machine according to any one of the preceding claims wherein said feed line includes: an expansible chamber pump effective to transfer wash solvent from said tank to said applicator member.

8. A printing machine according to claim 7, wherein said expansible chamber pump is a diaphragm pump.

9. A printing machine according to claim 7, wherein said expansible chamber pump is a bellows pump.

10. A printing machine according to claim 9, wherein the return line for recycling used wash solvent from the applicator member and/or the blanket to said tank includes a non-return valve, and said bellows pump is connected to one end of an air line whose other end is connected to the top of said tank whereby compression of the bellows will pressurise an air space in said tank to urge wash solvent along said wash solvent feed line to the applicator member and expansion of said bellows will remove the pressurising effect to end the feed flow of wash solvent and to allow return of spent solvent along the return line by way of the non-return valve.

11. A printing machine according to claim 9 or 10, wherein said bellows pump is driven by a mechanical linkage to a rotating shaft of the printing machine.

12. A printing machine according to claim 11, wherein said rotating shaft carries an eccentric cam and the bellows of said pump is driven by a slide on which a cam follower roller is mounted, said cam follower roller being positioned to engage the cam profile of said cam for the purposes of inducing reciprocation of said slide during rotation of said eccentric cam.

13. A printing machine according to claim 11 or 12, wherein the applicator member is a rotatable roller having a solventabsorbent cylindrical outer surface, and is mounted on said shaft for rotation therewith, said shaft being driven from the printing machine main drive.

14. A printing machine according to claim 12, wherein said feed line terminates at a spray bar positioned just above said blanket cleaning roller to spray solvent onto the roller during rotation of the roller in a direction which will transfer the blanket wash solvent to the surface of said blanket.

15. A printing machine substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

16. A method of operating an offset printing machine according to claim 2, comprising removing the transport closure from the tank, attaching said cap to the tank to connect the blanket wash tank to the blanket wash unit, carrying out blanket washing operations as required from time to time until the build-up of sludge in said tank reaches or nearly reaches the bottom of said feed line, and then exchanging said tank for a fresh one and disposing of the first mentioned tank after attachment of the transit closure thereto.

17. A method of operating an offset printing machine substantially as hereinbefore described with reference to the accompanying drawings.