Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-06-03
2001-05-22
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06234623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an improved integral ink filter for an ink jet printhead that has decreased flow resistance and minimal machine cost to implement. The integral ink filter includes both a first filter portion patterned in a silicon channel plate of the printhead and a second filter portion patterned in a polyimide layer located between the channel plate and a heater plate.
2. Description of Related Art Integral ink filters for inkjet printheads are known. Examples of such are U.S. Pat. No. 4,639,748 to Drake et al., U.S. Pat. No. 5,124,717 to Campanelli et al., U.S. Pat. No. 5,141,596 to Hawkins et al., and U.S. Pat. No. 5,204,690 to Lorenze, Jr. et al.
Of these, only U.S. Pat. No. 4,639,748 includes an integral, internal ink filter positioned within the channel plate before the individual ink channel nozzes. However, while its ink filter fabrication costs are small, it suffers an undesirable problem in that the filter pore open area is on the same order as the channel array density. Accordingly, such an ink filter induces significant ink flow resistance, which is detrimental to ink refill frequency.
The other cited references include a membrane filter fabricated over an ink fill opening between an ink supply cartridge and the ink manifold of the printhead (i.e., external to the channel plate and affixed to an outer face thereof). As such, these latter patents require additional fabrication costs and time to pattern and implement the ink filter assembly. Further, such a filter is quite removed from the nozzes.
Another known ink filter is the integral filter provided on the Hewlett Packard HP722 color printhead.
As technology moves towards smaller drop capability and thus increased resolution, there is a need for a better integral ink filter that can be fabricated with only minimal impact on manufacturing costs, while achieving a desired small pore size and decreased flow resistance.
SUMMARY OF THE INVENTION
In ink jet printers, very small nozzles having correspondingly small flow areas are required to produce small ink droplets for printing. Current ink jet trends are requiring smaller and smaller ink droplets. This necessitates the use of a very fine filtration system to prevent contaminating particles from clogging the small printhead nozzles. To maximize effectiveness, the filtration system should be located close to the nozzles so as to not restrict ink flow. However, as pore sizes decrease, flow rates of ink to the nozzles accordingly decrease.
The present invention overcomes the above problems by providing an integral ink filter having two separate filter portions fabricated on separate elements of an ink jet printhead. In particular, the invention in exemplary embodiments provides a first filter array portion formed in a channel plate of the printhead and a second filter array portion patterned and formed in an insulating layer sandwiched between the channel plate and a heater plate of the printhead. The filter arrays have a pore size equal to or smaller than the width of the individual ink channels.
Applicants have found that the additional filtering, in addition to the filtering achieved by an internal filter as used in U.S. Pat. No. 4,639,748, can be achieved by creating filtration pores in the already existing thick film structure interposed between the channel plate and the heater plate. Moreover, as this thick film structure already requires photolithographic patterning, such as to remove portions over heating elements and between the ink manifold and the nozzle channels, there is no additional processing steps necessary. As such, the present invention achieves improved filtration, while retaining a small pore size corresponding to a channel size of the nozzles, by doubling the filtration rate and maintaining a desired ink flow to the nozzles.
In a first exemplary embodiment of the invention, a plurality of ink jet printheads with integral, internal ink filters are fabricated from two separate substrates, such as silicon (
100
) wafers. The printheads are preferably of the thermal, drop-on-demand type and adapted for carriage printing. However, the invention is applicable to other ink jet printheads.
A plurality of sets of heating elements and their individual addressing electrodes are formed on a surface of one of the wafers (i.e., heater wafer) and a corresponding plurality of sets of parallel channels are etched in a surface of the other wafer (i.e., channel wafer), with each channel communicating with a recessed manifold through a first integral filter array formed in the channel wafer between the manifold and channels. A fill hole and alignment openings are etched in the other surface of the channel wafer. The heating elements and channels are aligned and bonded together with a thick film organic structure, such as polyimide, interposed therebetween. Prior to bonding, the thick film organic structure is patterned and etched to form a second filter array. A plurality of individual printheads are obtained by dicing the two bonded wafers.
Each printhead is fixedly positioned on a daughterboard with the manifold fill hole exposed so that the channel nozzles are parallel to the daughterboard edge. The printhead and daughterboard are mounted on an ink supply cartridge so that the printhead fill hole is coincident with an aperture in the cartridge to fill and maintain ink in the printhead manifold and associated ink channels.
The printhead and cartridge may be mounted on a carriage of an ink jet printer adapted for reciprocation across the surface of a recording medium, such as paper. Current pulses are selectively applied to the heating elements in each channel from a controller in the printer in response to receipt of data signals by a controller in a known fashion. In a pagewidth configuration, the printhead array can be fixed and oriented perpendicular to a direction of movement of the recording medium. During the printing operation, the recording medium continually moves at a constant velocity in a known fashion.
The current pulses cause the heating elements to transfer thermal energy to the ink, vaporizing the ink as known in the art to produce a bubble. The heating element cools after the passage of the current and the bubble collapses. This bubble formation forms an ink droplet and propels it towards the recording medium.
REFERENCES:
patent: 4639748 (1987-01-01), Drake et al.
patent: 4774530 (1988-09-01), Hawkins
patent: 5124717 (1992-06-01), Campanelli et al.
patent: 5141596 (1992-08-01), Hawkins et al.
patent: 5204690 (1993-04-01), Lorenze, Jr. et al.
patent: 5489930 (1996-02-01), Anderson
Le N.
Nghiem Michael
Oliff & Berridg,e PLC
Xerox Corporation
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