GB2263874A

GB2263874A - Filter for printing machine

Info

Publication number: GB2263874A
Application number: GB9202416A
Authority: GB
Inventors: Stephen Ward
Original assignee: M G ELECTRIC
Current assignee: M G ELECTRIC
Priority date: 1992-02-05
Filing date: 1992-02-05
Publication date: 1993-08-11
Anticipated expiration: 2012-02-05
Also published as: GB9202416D0; GB2263874B

Abstract

Fountain solution being returned through pipe 11 to reservoir 10 of the dampening system of a printing machine passes through filter 14. Filter 14 is in the form of a bag with multi-layer walls consisting of an inner layer of felt, an intermediate layer of sponge foam or low density fibrous material and an outer layer also of felt. The upper half of the bag is above the liquid level 12 in the reservoir so that at least the outer layer thereof remains relatively dry. Bubbles in the returning liquid separate therefrom as the liquid passes through the bag wall. <IMAGE>

Description

"FILTER FOR PRINTING EQUIPMENT DAMPENING SYSTEM" This invention relates to a filter for the dampening system of printing equipment.

In printing equipment such as, for example, for offset printing, a socalled "fountain solution" is circulated to rollers which apply it in a thin film to the printing plate. The solution is drawn from a reservoir tank, in which it may be chilled, to a trough in which a press roller rotates to pick up the solution which is then taken by other rollers to the printing plate. Surplus solution passes over a wier at the opposite end of the trough to its inlet end and is carried by the circulating pump back to the tank. liquid in the tank is normally maintained at a level such that the tank is about one third full by occasionally "topping up" the returned liquid with more fountain solution, water, acid, alcohol and other additives.

A convenient way to return the fountain solution to the tank is by the use of a suction system, but this gives rise to the problem that air is entrained in the returned fountain solution to the extent that undesirable quantities of foam are produced in the tank. If foam reaches the printing plate it can have adverse consequences. Filters have been interposed between the interior of the tank and the inlet for returned fountain solution but these have not been fully effective in preventing the generation of foam as the aerated solution is reintroduced into the tank.

A principal object of the present invention is to provide an improved filter which will prevent, or substantially reduce, the generation of foam in the reservoir tank.

In accordance with the present invention there is provided a filter for filtering fountain solution returned to the reservoir tank of the dampening system of a printing machine, the filter comprising a hollow structure to be interposed between an inlet of the tank for said returned solution and the tank interior, said structure having at a location such that it will be at least partly exposed to atmosphere above the level of solution in the tank, in use, a wall area which is both liquid and air pervious and of a iuilti-layer construction comprising at least an inner layer of relatively high density fibrous material, an intermediate layer of relatively low density fibrous material or of relatively high porosity and an outer layer of fibrous material of a density similar to that of the inner layer, the fibre-density and/or porosity of the layers being such that, in use of the filter, at least the greater part of liquid which has passed through the inner layer above the level of solution in the tank outside the structure will drop through the material of the intermediate layer before passing through the outer layer and such that at least the outer surface of the outer layer above the level of liquid in the tank outside the structure will remain non-saturated.

The said structure may be in the form of a bag substantially wholly of said nalti-layer construction. When the the inlet is in the form of a pipe depending into and terminating short of the bottom of the tank the bag may have a mouth whereby the bag is located relative to the inlet pipe loosely to surround the outlet orifice of the latter.

The intermediate layer may be of a sponge-like material and may be approximately 10 mm thick. It may be of a resilient plastics foam, and may have a porosity of approximately 80 pores per 2.5 Cm.

The inner and outer layers are preferably of felt and each is preferably approximately 4 mm thick. Polyester felt may be used.

The effectiveness of the filter of the invention is believed to result from the following combination of factors: Bubbles forming inside the bag are burst by the inner layer of felt as they are forced through it. The interinediate layer returns the liquid emerging from the inner layer to the tank without permitting the reformation of bubbles. Any liquid which does emerge from the outer surface of the intermediate layer encounters the outer layer, which again prevents the formation of bubbles and since the outer surface of the outer layer remains substantially dry no foam forms where the filter is exposed to surrounding air. Air above the liquid level can thus escape from the interior of the filter without causing the re-formation of bubbles outside the filter structure.

A preferred embodiment of the invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: Figure 1 schematically illustrates in sectional elevation the reservoir tank of the dampening system of a printing machine, Figure 2 is a cross sectional view on an enlarged scale of the filter, taken generally on the line Il-Il of Figure 1, and Figure 3 illustrates the area III of the filter of Figure 2 on a larger scale.

A fountain solution reservoir tank 10 of the dampening system of a printing machine has extending into it from above an inlet pipe 11 whereby fountain solution is returned to the tank 10 by suction equipment (not shown) such as a Venturi after passing to and back from the printing machine (not shown). The tank 10 is approximately one third full of fountain solution to the level 12, the solution being primarily water with the admixture of fountain solution, acid, alcohol and other minor additives.

For clarity of illustration the outlet of the tank 10, whereby solution is pumped to a trough of the printing machine, is not shown.

Surrounding the inlet pipe 11 is the mouth 13 of a filter bag 14, so that the bag 14 is partially immersed in the solution in the tank 10 but is suspended above the bottom of tank 10 with a greater part of its surface area exposed to atmosphere. Because of resistance of the filter bag 14 to the outflow through it of the incoming solution from pipe 11 the level 15 of solution within the bag, in use, is slightly above the level 12 of solution outside the bag and the air in bag 14 above the liquid level 15 will be at a pressure slightly above atmospheric. This also serves to keep the bag in an expanded condition with an internal space 16 between its two sides 17 and 18. As shown, each of these sides 17 and 19 is generally rectangular and the two sides are joined together to form the bag e.g. by stitching around their edges.Of course, any one of the edges of the bag may be formed by folding a single piece of wall material of the bag to provide both sides, or two separate side pieces may be joined all round all four edges except where the mouth 13 is provided.

Each side 17 and 18 of the bag 14 consists of an inner layer 19 of polyester felt approximately 4 urn thick, an intermediate layer 20 of sponge foam approximately 10 urn thick and with a porosity of approximately 80 pores per 2.5 cm and an outer layer 21, again of polyester felt approximately 4 urn thick.

Solution entering the bag 14 from inlet 11 will be aerated and foam will form above the liquid inside the bag in use. The bag 14 inhibits the passage of foam to the interior of tank 10 outside the bag in that bubbles are burst by the inner layer 19 as they attempt to pass through it and the liquid from which they are formed is returned to the liquid in tank 10 by falling through the sponge layer 20 without the re-formation of bubbles.

Abcze the liquid level 12 the outer surface of the outer layer 21 of felt is substantially dry, so that air passing out of the bag 14 above the liquid level cannot form new bubbles.

Instead of being of sponge-like material the intermediate layer 20 may also be of a loose, fibrous material but of considerably lower fibre density than the fibrous material of the two layers 19 and 21 such that the intermediate layer 20 is "free draining (which is to say that it offers negligible resistance to liquid dropping through it).

It will be appreciated that in another modified construction it is not essential that the whole surface area of the filter should consist of the imilti-layer material. A hollow structure surrounding the inlet 11 may have one or more "windows" or wall areas consisting of the mdlti-layer material.

Claims

CLAIMS:

1. A filter for filtering fountain solution returned to the reservoir tank of the dampening system of a printing machine, the filter comprising a hollow structure to be interposed between an inlet of the tank for said returned solution and the tank interior, said structure having at a location such that it will be at least partly exposed to atmosphere above the level of solution in the tank, in use, a wall area which is both liquid and air pervious and of a rrollti-layer construction comprising at least an inner layer of relatively high density fibrous material, an intermediate layer of relatively low density fibrous material or of relatively high porosity and an outer layer of fibrous material of a density similar to that of the inner layer, the fibre-density and/or porosity of the layers being such that, in use of the filter, at least the greater part of liquid which has passed through the inner layer above the level of solution in the tank outside the structure will drop through the material of the intermediate layer before passing through the outer layer and such that at least the outer surface of the outer layer above the level of liquid in the tank outside the structure will remain non-saturated.

2. A filter as claimed in claim 1 wherein said structure is in the form of a bag substantially wholly of said multi-layer construction.

3. A filter as claimed in claim 2, wherein the inlet is in the form of a pipe depending into and terminating short of the bottom of the tank and wherein the bag has a mouth whereby it is located relative to the inlet pipe loosely to surround the outlet orifice of the latter.

4. A filter as claimed in any one of the preceding claims, wherein the intermediate layer is of a sponge-like material and is approximately 10 nan thick.

5. A filter as claimed in claim 4, wherein the sponge layer is of a resilient plastics foam.

6. A filter as claimed in claim 4 or claim 5, wherein the sponge layer has a porosity of approximately 80 pores per 2.5 cm.

7. A filter as claimed in any one of the preceding claims, wherein the inner and outer layers are of felt and are each approximately 4 mm thick.

8. A filter as claimed in claim 7, wherein the inner and outer layers are of polyester felt

9. A filter for filtering fountain solution returned to the reservoir tank of the dampening system of a printing machine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.