WO1993017868A1

WO1993017868A1 - Recovery system

Info

Publication number: WO1993017868A1
Application number: PCT/GB1993/000519
Authority: WO
Inventors: Mark Smith
Original assignee: Willett International Limited
Priority date: 1992-03-12
Filing date: 1993-03-12
Publication date: 1993-09-16
Also published as: GB9205330D0

Abstract

The present invention provides a method for reducing the amount of solvent lost from an ink jet printer in air vented from the ink system of the printer, characterized in that at least part of the solvent vapour in the air is condensed out of the air by contacting the air with a Peltier effect device so as to reduce the temperature of the air to below its dew point. The invention also provides apparatus for use in the method of the invention and an ink jet printer incorporating such apparatus.

Description

TITLE: RECOVERY SYSTEM

The present invention relates to a recovery system, notably for use with an ink jet printer.

BACKGROUND TO THE INVENTION:

In continuous ink jet printers, ink is fed under pressure by a circulation pump from a reservoir to a print head where it is ejected as a jet of ink from a nozzle orifice. The jet of ink is broken up into a series of substantially uniformly sized and spaced apart droplets by the application of vibration and/or pressure pulses to the ink and/or the nozzle assembly, for example by means of a piezoelectric crystal acting directly on the ink or through a wall of the ink chamber immediately upstream of the nozzle orifice. The flight path of the droplets is controlled by charging the jet of ink so as to form charged droplets which then pass through a deflecting electric field. By varying the charge on the droplets and/or the strength of the deflecting field, the droplets are diverted to varying extents from their straight line flight to deposit at the desired position on a substrate. Those droplets which are not to be printed are not deflected and are collected in a gutter or other catching means and the ink is then re-cycled to the reservoir, usually by means of a venturi or other pump in the re-cycle line. For convenience, the term continuous jet ink jet printer will be used herein to denote such printers.

Typically, the inks for use in an ink jet printer are in the form of solutions or dispersions of a dyestuff in an aqueous or organic solvent or carrier medium. For convenience, the invention will be described hereinafter in terms of an ink comprising a dyestuff dissolved in a volatile organic solvent mediu .

During their flight from the nozzle orifice to the gutter or the substrate on which they are printed, the droplets of ink lose part of their solvent or carrier medium due to evaporation, so that an atmosphere rich in solvent vapour is formed around the gutter. Due to partial condensation of some of the solvent values from the air stream, part of the solvent values in the air stream may be present in the air stream as droplets or mist rather than as true vapour. For convenience the term vapour will be used herein to encompass the case where part of the solvent values are present as droplets or mist as well as the case where all the solvent values are present as evaporated solvent.

This solvent vapour-laden air is sucked into the re-cycle line by the suction of the venturi or other pump used to re-cycle ink from the gutter to the reservoir. Hitherto, this solvent vapour-laden air passes with the re-cycled ink into the reservoir and the air is vented to waste. Since the vented air is saturated with solvent vapours, this represents a loss of valuable solvent values from the system, which must be made up by adding fresh solvent to maintain the desired viscosity of the ink. The venting of the solvent vapour-saturated air can also pose health and fire hazards.

We have now devised a system by which the amount of solvent in the air which is vented can be reduced.

SUMMARY OF THE INVENTION:

Accordingly, the present invention provides a method for reducing the amount of solvent lost from an ink jet printer in air vented from the ink system of the printer, characterised in that at least part of the solvent vapour in the air is condensed out of the air by contacting the air with a Peltier effect device so as to reduce the temperature of the air to below its dew point. Preferably, at least part of the solvent which condenses out from the air is recovered and returned to the solvent make up εystem of the ink jet printer^"for re-use. The invention also provides an ink jet printer through which ink is to flow, preferably one in which the ink is be circulated within the ink flow system of the printer, and from which a solvent vapour-laden air is to be vented, characterised in that a Peltier effect device is provided in thermal contact with the air flow path so as to extract heat from the air so as to cause cooling of the air.

The invention can be applied to any form of ink jet printer in which a solvent vapour-laden air stream is formed and from which stream it is desired to recover at least part of the solvent values. However, the invention is of especial application in continuous ink jet printers to recover solvent values from the air vented from the ink flow system. For convenience, the invention will be described hereinafter in terms of this preferred application.

In the method of the invention heat is extracted from the solvent laden air stream at any suitable point in the air flow path by the Peltier device, which acts as a heat pump to reduce the temperature of the air stream to below its dew point and thus condense out at least part of the solvent values in the air stream. Preferably, the Peltier device is located at the point at which the air stream is vented from the ink system, which is usually at the ink reservoir. It will also be preferred to cool the air stream by a sufficient amount to recover at least 50% of the solvent values from the air stream. Typically, the air stream will have a temperature of from 15 to 35°C and it will be desired to cool the air stream to from 0 to 10°C. The optimum cooling is a balance between the amount of the solvent which can be recovered and its cost and the cost of operating the Peltier device and can be readily determined by simple trial and error tests in any given case.

The Peltier heat pump device can be of any suitable type which extracts heat from the air stream. However, it is preferred that the heat pump is of the thermoelectric type and can take a wide range of forms of such heat pumps, for example a solid state crystalline semi-conductor heat pump, such as one made from a quaternary alloy of bismuth, tellurium, selenium and antimony. Many forms of suitable heat pump are available commercially and may be selected depending upon the physical shape and size requirements as well as the heat load they are to handle.

The heat pump can be of any suitable construction, for example one having* a tubular operating element which is fitted around a duct through which the air stream flows in indirect thermal communication with the element via the duct wall. However, it is preferred that the operating element of the heat pump be in direct thermal contact with the air stream to optimise heat transfer between the air stream and the heat pump.

In a particularly preferred embodiment of the invention, the heat pump is in the form of a planar operating element and this forms one wall of a thermally insulated chamber through which the air stream flows to provide a simple add-on component which can be inserted into any suitable point in the air flow path, for example at the air vent to the ink reservoir, of an existing ink jet printer ink flow system. In such a component, the heat pump is typically provided by a Peltier effect sheet, for example a sheet of a suitable solid state semi-conductor alloy and the cooling effect is achieved by passing an electric current through that sheet. The amount of heat extracted from the air stream will depend upon the area of the heat pump element and the current passed through the element and the optimum current and area can readily be determined for any given case.

As indicated above, the operative element of the heat pump forms one or more walls of an insulated chamber through which at least part of the air stream flows. Alternatively, the heat pump element can be incorporated into a split sleeve or other device which is clamped onto a suitable duct in the air flow system and acts indirectly on the air flow through the duct via the duct wall, the duct then acting as the chamber for the air flow.

It is preferred to provide one or more heat sinks in thermal contact with the operative element of the heat pump to assist removal of heat from the heat pump when it is cooling the air passing through the chamber. Typically, such heat sinks are provided with fins or the like over which air is passed by a fan or other means to aid removal of heat from the heat pump element of the chamber in which it is located.

Where the heat pump element forms part of a chamber through which the air stream flows, the chamber is provided with one or more outlets for the condensed solvent which can be re-cycled to the container from which the make up solvent is drawn to adjust the solvent content of the ink circulating in the ink jet printer.

The control of the flow of electrical current through the operative element of the heat pump and the operation of the fan or other means for removing heat from the heat pump element can be regulated in response to a conventional temperature sensor in the air stream to achieve the required drop in temperature in the air stream using conventional techniques and equipment.

Thus, in a preferred embodiment of the invention, the solvent vapour-laden air stream flows through a device comprising: a. a rectangular, tubular or other shaped housing formed from a thermally insulating material, such as an aluminium or other metal sheet having a thermally insulating outer surface, or a thermally insulating plastic; and b. one or more Peltier effect heat pump operative elements incorporated into at least one wall of the housing; the housing defining a chamber having an air inlet, an air outlet and a condensed solvent outlet, which may also serve as the air outlet, through which chamber the air stream is adapted to flow in thermal contact with the heat pump element(s); the heat pump element being adapted to be connected to an electric current supply so as to cause the heat pump element,to cool the air stream to below its dew point and thus condense out at least part of the solvent values contained in the air stream.

If desired, two or more heat pumps may be used at different points in the air flow path or in parallel or series at the same point in the flow path.

The invention thus provides a means by which at least part of the solvent values in the air stream can be recovered for re¬ use by means of a simple device which can readily be inserted into the air flow system of an existing ink jet printer or as part of the air flow system during the manufacture of new printers.

DESCRIPTION OF THE DRAWING:

The invention will now be described by way of illustration only with respect to a preferred form thereof as shown in the accompanying drawing, which is a diagrammatic part exploded view of a device incorporating the heat pump element for insertion into the air discharge from the ink reservoir of an ink jet printer.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

The device comprises a generally rectangular housing 1 defining an internal chamber having an air inlet 2 and an air/condensate outlet 3. The chamber walls are typically made from a metal inner wall having an outer foamed plastic or other thermally insulating layer, or may be made from a thermally insulating plastic, so as to reduce incidental heat gains through the walls of the chamber.

One wall of the chamber is provided with a Peltier effect heat pump element 4 which is removably mounted on the housing^" so that one face of the heat pump is in thermal contact with the interior of the chamber. Preferably, as shown, the housing 1 is formed with one open face 5 and the heat pump element 4 is mounted on the housing to form a wall of the chamber at that face. The heat pump element 4 is in direct thermal contact with air within the chamber. The element 4 preferably is a sheet of a solid state semi-conductor alloy.

The above device is mounted in the air vent outlet to the reservoir in the ink system of the printer and condensed solvent vapour is returned from outlet 3 to the make up solvent container, not shown, by a suitable gravity feed line.

In operation, solvent vapour-laden air is sucked into the ink return line to the reservoir by the action of the venturi pump sucking ink caught in the gutter of the printer. A temperature sensor, not shown, monitors the temperature of the air stream. This regulates the flow of an electric current through the heat pump element 4 to cool the internal, chamber side, face of the element and thus extract heat from the air flowing through the chamber. The current flowing through element 4 may have a fixed value so that the element 4 extracts heat at a constant rate from the air stream. Alternatively, the amplitude of the current may be varied by a control means, not shown, so that the amount of heat extracted is related to the amount of solvent vapour in the air stream, which in turn is related to the temperature of the air stream. As the air^' stream is cooled, solvent vapour condenses out and drains through outlet 3. The air stream exiting the chamber will typically have its solvent content reduced by from 50 to 85% and can be discharged to waste.

Air from a fan, not shown, is blown over a finned heat sink, not shown, attached to the outer face of the heat pump element 4 to aid dissipation of heat from the face of the element. The heat pump thus provides a simple means without any moving parts for cooling the air stream to recover at least part of the solvent values therein. Furthermore, since the element 4 can be designed to operate at low voltages and can be totally sealed within the wall of the housing 1, the device presents a low fire risk and can be used with air streams containing flammable solvents.

Claims

CLAIMS :

1. A method for reducing the amount of solvent lost from an ink jet printer in air vented from the ink system of the printer, characterised in that at least part of the solvent vapour in the air is condensed out of the air by contacting the air with a Peltier effect device so as to reduce the temperature of the air to below its dew point.

2. A method as claimed in claim 1, characterised in that at least part of the solvent which condenses out from the air is recovered and returned to the solvent make up system of the ink jet printer for re-use.

3. A method as claimed in either of claims 1 or 2, characterised in that at least 50% of the solvent values in the air are condensed out by the cooling of the air by the Peltier effect device.

4. A method as claimed in any one of the preceding claims, characterised in that the air has a temperature of from 15 to 35°C and is cooled to from 0 to 10°C.

5. A method as claimed in any one of the preceding claims, characterised in that the air is the air stream which is vented from the ink reservoir of the ink jet printer.

6. A method as claimed in any one of the preceding claims, characterised in that the air flows through a chamber having one wall formed by the operative element of a Peltier effect device.

7. A method as claimed in any one of the preceding claims, characterised in that one or more heat sinks are provided in thermal contact with the Peltier effect device to aid dissipation of heat removed from the air.

8. A method according to claim 1, substantially as hereinbefore described with respect to the accompanying drawing.

9. Apparatus suitable for use in condensing out at least part of the solvent values from an air stream in the method of claim 1, which apparatus comprises: a. a rectangular, tubular or other shaped housing formed from a thermally insulating material; and b. one or more Peltier effect heat pump operative elements incorporated into at least one wall of the housing; the housing defining a chamber having an air inlet, an air outlet and a condensed solvent outlet, which may also serve as the air outlet, through which chamber the air stream is adapted to flow in thermal contact with the heat pump element(s); the heat pump element(s) being adapted to be connected to an electric current supply so as to cause the heat pump element(s) to cool the air stream to below its dew point and thus condense out at least part of the solvent values contained in the air stream.

10. Apparatus as claimed in claim 9, substantially as hereinbefore described with respect to the accompanying drawing.

11. A method as claimed in claim 1, characterised in that the air flows through apparatus according to claim 9.

12. An ink jet printer through which ink is to flow and from which a solvent vapour-laden air stream is to be vented, characterised in that a Peltier effect device is provided in thermal contact with the air flow path so as to extract heat from the air so as to cause cooling of the air.

13. An ink jet printer as claimed in claim 12, characterised in that the Peltier effect device is provided by an apparatus as claimed in claim 9.