Patent Publication Number: US-5898451-A

Title: Method for ink-jet printing using a collapsible ink reservoir structure and printer ink cartridge

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of application Ser. No. 08/240,297, filed May 9, 1994, which in turn is a file wrapper continuing application of application Ser. No. 07/929,615, filed Aug. 12, 1992. 
    
    
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     The present invention relates generally to ink cartridges for high speed computer driven printers such as inkjet printers and plotters. In such printers the ink reservoir is ordinarily maintained under a sub-atmospheric or negative pressure so that ink will not leak or drool from the printhead. Various types of ink reservoirs may be used including refillable ink reservoir cartridges which are mounted on the moveable printer carriage, throwaway replaceable cartridges which are mounted on the printer carriage and remote or offboard ink reservoirs from which ink is drawn to the print head by tubing. In the onboard refillable or throwaway cartridges, a polymer foam is ordinarily provided in the ink reservoir so that the capillary action of the foam will prevent ink from drooling from the printhead. Polymeric foams of the type typically used for this purpose are non-biodegradable and thus cause environmental problems whenever a previously used cartridge is emptied and thrown away. In addition, the use of industrial foam in the ink reservoir restricts the operating pressure range of the ink cartridge and such foams ordinarily leave a chemical residue which is incompatible with and/or reacts adversely with printer ink. Similarly, the relatively long tubing used to convey ink from an offboard pressure reservoir to a printing head does not lend itself well for different printing pressure ranges. 
     It is accordingly an object of the present invention to provide a collapsible ink reservoir structure and a printer ink cartridge containing it which is easy to construct and which obviates the above difficulties. 
     SUMMARY OF THE INVENTION 
     The present invention accordingly provides an ink reservoir structure for a printer ink cartridge in which ink is to be maintained under negative pressure and an ink print head in fluid communication with said reservoir structure, said structure comprising: 
     a) a rigid frame having a pair of peripherally extending edges on opposite sides thereof and an ink discharge port; 
     b) a pair of flexible impervious membranes sealingly joined to said edges of said frame to form, with said frame, said ink reservoir structure. 
     The present invention further provides a printer ink cartridge comprising: a rigid housing containing an ink reservoir structure in which ink is to be maintained under negative pressure and an ink print head in fluid communication with said reservoir structure, said structure comprising: 
     a) a rigid frame having a pair of peripherally extending edges on opposite sides thereof and an ink discharge port; 
     b) a pair of flexible impervious membranes sealingly joined to said edges of said frame to form, with said frame, said ink reservoir structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a replaceable or throwaway ink cartridge for a thermal inkjet printer containing a collapsible ink reservoir structure. 
     FIG. 2 is a vertical cross section of the cartridge of FIG. 1. 
     FIG. 3 is a cross sectional plan view of the cartridge of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A replaceable ink cartridge is seen in FIG. 1 to comprise a rigid outer housing 10 having a pair of spaced cover plates 12, 14 intended to be affixed as by cementing to opposite sides of a plastic peripheral wall section 16. Snout portion 13 of the cartridge has an ink discharge aperture in its lowermost end wall (as seen in FIG. 1) to which is affixed an electrically driven print head, not shown. 
     A reservoir structure unit comprised of a relatively rigid inner plastic frame 20 and flexible ink bag membranes 22, 24 attached thereto is mounted in the outer housing 10. Alternatively, inner frame 20 can be formed integrally with the outer housing 10 in an injection molding process. Preferably, frame 20 is formed of a softer and lower melting point plastic than housing 10 to permit heat bonding of the membranes 22 thereto. Such can be accomplished in a two-step molding process as is well within the skill of a person skilled in the art. 
     Frame 20 may be constructed with some flexibility to assist in mounting it in the housing 10 but is rigid relative to the flexible membranes described below. The frame 20 has a pair of opposite side edges 21 to which a pair of flexible membranes 22, 24 are respectively joined as by heat welding at their peripheral edges to form the reservoir structure 25. The reservoir structure 25 preferably contains a pressure regulator 30 which in turn is comprised of a pair of spaced substantially parallel plates 40, 50 urged apart by a spring 60 into engagement with the flexible membranes 22, 24. The assembled reservoir structure including the inner frame 20, membranes 22, 24 and pressure regulator 30 is then mounted inside of wall section 16 of the cartridge and side walls 12, 14 are then affixed to the cartridge housing peripheral wall 16. The snout portion 13 of housing 10 also contains an ink filter 18 which is placed in fluid communication with the flexible ink bag reservoir. The filter 18 may be mounted inside the reservoir structure or the it can be positioned outside of the reservoir structure but inside outer housing 10 with minor porting and seal modifications to ensure fluid communication from the ink reservoir to the filter 18. The lowermost portion of the peripheral outer housing wall 16 (as viewed in FIG. 1) is provided with an ink discharge aperture 19 (FIG. 2) through which ink is downwardly discharged from the filter 18 to the print head, not shown. 
     The pressure regulator side plates 40, 50, best seen in FIG. 3, are of generally rectangular configuration with rounded corners to avoid damaging the flexible bag membranes 22, 24. Prior to or simultaneous with attachment of the membranes 22, 24 to the sides of inner frame 20, the regulator 30 is placed in the inner frame 20 by collapsing it partially against the spring force such that it initially occupies a prestressed condition inside the ink bag formed by the inner frame 25 and membranes 22, 24. The amount of this prestressing is readily controllable by the designer by selecting the desired degree of compression of the spring 60. 
     The flexible membranes 22, 24 and the pressure regulator sideplates 40, 50 gradually move towards each other as the reservoir is evacuated of ink. The membranes 22, 24 are sized with enough extra membrane material near their edges of attachment to the inner frame 20 such that they are freely moveable with the side plates between full and empty positions as best indicated in FIG. 3. This permits most of the ink in the reservoir structure 25 to be used before the cartridge is discarded or refilled, as the case may be. 
     Ideally, both sideplates 40, 50 and the spring 60 are made of a non-corrosive sheet metal such as stainless steel and the inner frame 20 and bag membranes 22, 24 are made of inert plastics which do not react with print ink. 
     Persons skilled in the art will readily appreciate that various modifications can be made from the preferred embodiment of the invention disclosed herein and that the scope of protection is intended to be defined only by the limitations of the appended claims.