Self-sealing filter module for inkjet printing

A filter module (38) for a continuous inkjet printer (10) comprising a filter housing (40) and a filter medium (42) fixed within the housing (40). The filter housing (40) further includes an inlet portal (44) through which ink flows into the housing under pressure and a first self-sealing valve assembly (54) disposed within the inlet portal. In addition, housing includes an outlet portal (46) through which ink flows out of the housing (40) under pressure and a second self-sealing valve assembly (56) disposed within the outlet portal (46). The first and second valve assemblies (54, 56) open when mechanically connected to an ink flow path (34) from an ink tank (18) to a print head (14), and the first and second valve assemblies (54, 56) seal closed when mechanically disconnected from the ink flow path (34).

FIELD OF INVENTION

The present disclosure relates to ink jet printing and more particularly to filtration of ink supplied to a print head of a continuous ink jet printer.

BACKGROUND

In ink jet printing systems the print is made up of individual droplets of ink generated at a nozzle and propelled towards a substrate. There are two principal systems: drop on demand where ink droplets for printing are generated as and when required; and continuous ink jet printing in which droplets are continuously produced and only selected ones are directed towards the substrate, the others being recirculated to an ink supply.

Continuous ink jet printers supply pressurized ink to a print head drop generator where a continuous stream of ink emanating from a nozzle is broken up into individual regular drops by, for example, an oscillating piezoelectric element. The drops are directed past a charge electrode where they are selectively and separately given a predetermined charge before passing through a transverse electric field provided across a pair of deflection plates. Each charged drop is deflected by the field by an amount that is dependent on its charge magnitude before impinging on the substrate whereas the uncharged drops proceed without deflection and are collected at a gutter from where they are recirculated to the ink supply for reuse. The charged drops bypass the gutter and hit the substrate at a position determined by the charge on the drop and the position of the substrate relative to the print head. Typically the substrate is moved relative to the print head in one direction and the drops are deflected in a direction generally perpendicular thereto, although the deflection plates may be oriented at an inclination to the perpendicular to compensate for the speed of the substrate (the movement of the substrate relative to the print head between drops arriving means that a line of drops would otherwise not quite extend perpendicularly to the direction of movement of the substrate).

In continuous ink jet printing a character is printed from a matrix including a regular array of potential drop positions. Each matrix comprises a plurality of columns (strokes), each being defined by a line including a plurality of potential drop positions (e.g., seven) determined by the charge applied to the drops. Thus each usable drop is charged according to its intended position in the stroke. If a particular drop is not to be used then the drop is not charged and it is captured at the gutter for recirculation. This cycle repeats for all strokes in a matrix and then starts again for the next character matrix.

Ink is delivered under pressure to the print head by an ink supply system that is generally housed within a compartment of a cabinet that includes a separate compartment for control circuitry and a user interface panel. The system includes a main pump that draws the ink from a reservoir or tank and delivers it under pressure to the print head. As ink is consumed the reservoir is refilled as necessary from a replaceable ink cartridge that is releasably connected to the reservoir by a supply conduit. The ink is fed from the reservoir via a flexible delivery conduit to the print head. The unused ink drops captured by the gutter are recirculated to the reservoir via a return conduit by a pump or venturi. The flow of ink in each of the conduits is generally controlled by solenoid valves and/or other like components.

Filtration of the ink is provided to capture or limit the amount of particulate in the ink that is delivered to the print head for printing. More specifically, a filter module provides a filter medium in the ink flow path from an ink source to the print head. Filters used in these printing systems have a known effective life span, so the replacement of the filters is performed at timed service intervals. The replacement of the filters can be time consuming, which means the continuous ink jet printer is not operating, which is not desirable for production line printing and marking. Moreover, when a filter module is replaced it often contains an amount of ink such that it is regarded as HAZMAT waste and special precautions must be taken to dispose of the filter module.

BRIEF SUMMARY

The present disclosure provides a filter module with self-sealing valve assemblies, that is configured to leave a minimal amount of printing fluid in the module after use.

In one aspect, a filter module for a continuous inkjet printer includes a filter housing, a filter medium fixed within the housing, and an inlet portal through which ink flows into the housing under pressure. A first self-sealing valve assembly is disposed within the inlet portal. Ink flows out of the housing under pressure through an outlet portal. A second self-sealing valve assembly is disposed within the outlet portal. The first and second valve assemblies open when mechanically connected to an ink flow path from an ink tank to a print head, and the first and second valve assemblies seal closed when mechanically disconnected from the ink flow path.

In another aspect, a continuous inkjet printer includes an ink tank for holding ink, a print head in fluid communication with the ink tank and the print head having an ink nozzle for ejecting ink droplets onto a substrate to print an image, an ink flow path providing fluid communication from the ink tank to the print head, and a pump disposed in the ink flow path and in fluid communication with the ink tank and print head for delivering ink from the ink tank to the print head under pressure. A filter module is disposed in the ink flow path between the pump and the print head.

The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF INVENTION

The inventors have recognized that during servicing a continuous inkjet printer, filter modules that are to be replaced often contain a sufficient volume of ink such that the component is regarded as HAZMAT, thereby requiring certain precautions in terms of disposing of the filter module. Filter modules sometimes have a tendency to leak when being replaced thereby fouling the work area and parts of the printer. In addition, the removal of filter modules is oftentimes a relatively complicated task that can be time consuming and messy. Accordingly, the inventors have developed a “self-sealing” filter module that minimizes or eliminates ink leakage upon removal from a continuous inkjet ink flow path. To that end, the filter is adapted to maximize the emptying of ink from the filter module when pressure in ink lines and the filter module is removed. Accordingly, the filter module in accordance with embodiments of the invention is provided that empties ink from the filter module so there is less than a certain amount (e.g., 30 mL) that avoids the necessity of HAZMAT precautions for disposal.

Now in reference toFIG. 1, an ink flow circuit for a continuous ink jet printer10is illustrated. The printer10includes a fluid system12, a print head14, and a condenser16. The fluid system12includes an ink or mixer tank18for holding ink, a makeup tank20for holding solvent and an ink source22. The ink source22and makeup tank20provide fluids to mixer tank18. Solvent is added to the ink or mixer tank18during operation of the printer to replace solvent loss due to evaporation and to properly control the ink viscosity. Inks for continuous ink jet printers are typically complex mixtures of many substances, with a large proportion of volatile organic solvents. Typical organic solvents include methyl ethyl ketone (MEK), acetone, and ethanol. The print head14includes a nozzle26in fluid communication with the ink tank18for ejecting ink droplets and a gutter30for receiving, through an ink-receiving inlet thereof, ink droplets which are not used for printing. A gutter flow path32starts at the ink-receiving inlet or orifice of the gutter30and provides fluid communication to the ink tank, for ink and air that has entered the gutter30through the ink-receiving inlet. A return line (not shown) may be placed in fluid communication with the gutter30for conveying air from the condenser16to the gutter30and to enter the gutter flow path32, which returns ink to the mixer tank18.

Ink is supplied to the print module or print head14via an ink flow path34. A pump36is provided in the ink flow path34to deliver ink to the print head14under pressure for printing. In addition, a filter module38is provided in the ink flow path34between the pump36and the print head14to filter particulates from the ink before it reaches the print head14. The filter module38is shown in more detail inFIGS. 2 and 3, and includes a housing40with a top40A and bottom40B. A filter medium42is mounted within the housing40to filter ink supplied to the module38under pressure. The filter may be a 5μ polypropylene filter capable of filtering ink supplied to the module at a pressure of about 2.5 barr to about 3.5 barr.

The module38includes an inlet port44and outlet port46, on the bottom40B of the module38, and through which ink enters and exits the module38. A second outlet port48may also be provided for returning ink in the module38to the mixer tank18via a return line52. In order to maintain pressure in the module38at a desired level or within a desired range, some ink in the module38is periodically vented through the second outlet port48by operation of venturi pump51and returned to the mixer tank18, while ink continues to flow to the print head14. In addition, or alternatively, the second outlet port48and/or additional ports may be incorporated in the module38to circulate pigmented ink to through the module (and not necessarily through the filter medium42) so that pigment of the ink does not collect or settle in the ink tank18.

The module may be provided with an electronic data storage device such as a memory chip45with surface-mounted electrical contacts for connection to corresponding contacts provided on the printer. The memory chip45may be any suitable electronic storage device, may be supported on any suitable substrate and may be connected to suitable electrical contacts (or contact) in any convenient manner, providing those contacts are accessible for connection to the printer when the filter module38is inserted in the printer. The memory chip45includes at least Read Only Memory (ROM). The data on the memory chip can be any suitable data and would typically include such information as filter module serial number, production date, model number, expiration date, and the like. The memory chip may include security data so that only suitable or recognized filter modules can be used with the printer. Other data on the memory chip45could include fluid type (such as solvent, ink type, or dye-based or pigmented ink), service life, and the like. The memory chip may also include a writable data portion. The printer may write to the memory chip to indicate that the filter module has reached the end of its service life, so that the filter module can no longer be used in the printer or any other printer.

Self-sealing valve assemblies54,56are mounted within the inlet port44and outlet port46, respectively. A similar valve assembly may also be mounted in the second outlet port48. Since the valve assemblies54,56are identical in structure and function, the below description of valve assembly54applies to the valve assemblies54,56of both outlet ports46,48. These self-sealing valve assemblies54,56allow for the mechanical connection of the module38to the ink flow path, and when disconnecting the module38from the ink flow path, minimize or eliminate ink leakage.

With respect toFIGS. 4 and 5, the valve assembly54is illustrated in more detail and includes a valve housing60having a top end62and first opening64at the bottom of the assembly54distal to the top end62. In particular, the valve assembly is depicted engaging an ink flow pin70that is mounted to a top of an ink tank. The ink tank may include at least two of the ink flow pins70to engage or open valve assemblies54,56. As shown inFIG. 4, a biasing mechanism76, such as a spring, biases a ball66toward the second opening64and against a seal71, when in a closed position. When the filter module38is fixed to an ink tank, the ink flow pin70extends through the first opening64and the seal71to move the ball66toward the top end62of the valve housing60. More specifically, and as shown inFIG. 5, when the valve assemblies54,56, or filter module38, is mechanically connected to the ink flow path and ink container, the pin(s)70force the ball66toward the top end62to open the valve assemblies54,56. The ink flow pin70includes a conduit72and apertures74through which ink flows into the module38through side openings82in the valve assembly54. When the module38is connected to ink flow path33the valve assemblies54,56automatically open for ink flow through the module38, filter medium42and to the print head14. The terms “mechanically connected” and “mechanically disconnected” refer to the mechanical interaction between the components of the filter module38and parts and/or components connected to the ink path or ink tank of the printer, where the mechanical interaction serves to open and close valves to control ink flow through the filter module.

As further shown inFIGS. 4 and 5, in an embodiment of the invention, the ink flow pin70comprises a contoured outer surface including an upper shoulder84that tapers inward relative to a shaft88of the pin70. In addition, an internal surface84of the seal71is contoured as well generally corresponding to the shape of the pin70at the shoulder84. Accordingly, when the valve assembly54and filter module38are fixed on the ink tank an inclined surface84of the seal71abuts the shoulder81of the pin70. This sealed interface between the pin70and seal71prevents any back flow of ink leaking out of the valve assembly54during operation of the print system10. To that end, given that valve assembly56is configured identical to valve assembly54, the similar sealed interface at valve assembly56prevents ink that is flowing out of the filter module38from leaking out of the filter module38and valve assembly56. The seal71is further configured and dimensioned at the first opening64and within a base86of housing60to provide a seal against the shaft88to further prevent ink from leaking from the valve assembly54and also support the filter module38on the ink tank. Again in reference toFIG. 2, flanges90with bolt holes92may be provided at toward the bottom of the housing60to affix the module38to an ink tank with bolts or other fasteners.

When servicing the printer10, the ink pump36is deactivated removing pressure from within the internal volume of the module38, and the ink vents through the second outlet port48via the return line52and venturi pump51, and is returned to the ink tank22. However, as the valve assemblies54,56, and the similar valve assembly of the second outlet port48, remain open, the ink flow pin70abuts the seal71, as described above, preventing or minimizing ink leakage. When the module38is disconnected from the ink flow path33, the biasing mechanism76forces the ball66against seal71, automatically closing the valve assemblies54,56so that any remaining ink in the module38does not escape.

While embodiments of the invention described herein show the valve assemblies54,56depending from a bottom40B of the housing40, the invention is not so limited to such a configuration. For example, the valve assemblies54,56could be could be disposed entirely within the housing40such that second opening64is generally flush with a bottom of housing40or is disposed entirely within the housing40.

In the embodiment illustrated inFIG. 3, the module38may also comprise an ink flow pressure damper58that is used to control or minimize pressure fluctuations in the ink flow path33. As will be described in more detail below, the damper58may also assist in evacuation of ink from the module38. The damper comprises a diaphragm78operatively connected to the top40A of the housing40and that is suspended within the module38and an inner circumference of the filter medium42. A biasing mechanism80, such as a helical coil spring, is also operatively connected to the top40A of the housing40and is positioned within the diaphragm78to bias the diaphragm78toward the bottom40B of the housing40and valve assemblies54,56.

When ink is supplied to the module38under pressure, the ink flow forces the biasing mechanism80and diaphragm78toward the top40A of the housing40. The biasing member80and diaphragm78apply a counter force against the pressurized ink flow to thereby absorb pressure fluctuations in the ink flow. When pressure is removed from the module38by deactivating the pump36, the biasing mechanism80forces the diaphragm toward the valve assemblies54,56and the valve assembly of the second outlet portal48thereby forcing ink to evacuate from the chamber of the module38. In this manner, when the module38is disconnected from ink flow path33only a nominal amount of ink remains and the module38can be discarded in the normal waste stream without the need to take precautions for disposing of a toxic waste. Preferably, after being used and then removed from the printer, the spent module includes less than 30 mL, less than 20 mL, or less than 10 mL of printing liquid.