Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Producing or treating inorganic material – not as pigments,...
Reexamination Certificate
1999-07-16
2001-07-03
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Producing or treating inorganic material, not as pigments,...
C264S619000, C264S678000, C029S025350
Reexamination Certificate
active
06254819
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of making channel members for ink jet printheads.
BACKGROUND OF THE INVENTION
Ink jet printheads made from a piezoelectric material are used to selectively eject ink droplets onto a receiver to form an image. Within the printhead, the ink may be contained in a plurality of channel members and energy pulses are used to actuate the printhead channel members causing the droplets, which form the reservoirs of ink to be ejected on demand or continuously, through an orifice plate over the channel member.
In one representative configuration, a piezoelectric ink jet printing system includes a body of piezoelectric material defining an array of parallel open topped channel members separated by walls. In the typical case of such an array, the channel members are micro-sized and are arranged such that the spacing between the adjacent channel members is relatively small. The channel walls have metal electrodes on opposite sides thereof to form shear mode actuators for causing droplets to expel from the channel members. An orifice defining structure includes at least one orifice plate defining the orifice through which the ink droplets are ejected, and is bonded to the open end of the channel members. In operation of piezoelectric printheads, ink is directed to and resides in the channel members until selectively ejected therefrom. To eject an ink droplet through one of the selected orifices, the electrodes on the two side wall portions of the channel in operative relationship with the selected orifice are electrically energized causing the side walls of the channel to deflect into the channel and return to their normal undeflected positions when the applied voltage is withdrawn. The driven inward deflection of the opposite channel wall portions reduces the effective volume of the channel thereby increasing the pressure of the ink confined within the channel to force few ink droplets, 1 to 100 pico-liters in volume, outwardly through the orifice. Piezoelectric ink jet printheads are described in detail in U.S. Pat. Nos. 5,598,196; 5,311,218; 5,365,645, 5,688,391, 5,600,357, and 5,248,998.
The use of piezoelectric materials in ink jet printheads is well known. Most commonly used piezoelectric material is lead-zirconate-titanate (PZT) ceramic, which is used as a transducer by which electrical energy is converted into mechanical energy by applying an electric field across the material, thereby causing the piezoelectric ceramic to deform. The degree of deformation of the piezoelectric materials depend on several factors, including chemical composition, grain size of the material, and the electrode configuration of the transducers.
Under previous methods of making piezoelectric ink jet printheads, a dense sintered slab of piezoelectric ceramic such as PZT in which channel members/grooves are to be formed is poled. Poling makes the material piezoelectrically deflectable or “active”, by imparting a pre-determined voltage widthwise across the piezoelectric ceramic slab in a selected poling direction of the internal channel side wall sections later to be created in the poled ceramic body section by forming a spaced series of parallel grooves in channel members. These grooves in the channel members are generally formed by sawing, laser cutting or etching process. This current process of poling a bulk piezoelectric ceramic material and later fabricating micro-sized channel members by sawing or other processes is discussed in detail in U.S. Pat. Nos. 5,227,813 and 5,028,937, and in EP 827833. This process of forming channel members is not only time consuming and expensive, but also is amenable to many defects generated during cutting the channel members or forming the channel members thereby reducing the throughput and increasing the unit manufacturing cost. Furthermore, mechanical damages caused during sawing or laser cutting also are detrimental to the piezoelectric characteristics of the material.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of making piezoelectric ceramic ink jet printhead forming channel members, which will eliminate time consuming and costly processes of making channel members/cavities which form ink reservoirs.
These objects are achieved in a method of making an ink jet printer channel member for use in ink delivery comprising the steps of:
(a) molding piezoelectric ceramic powders into a slab in the green state having top and bottom surfaces;
(b) machining the top and bottom surfaces of the green state slab to form alternating grooves on the top and bottom surfaces of the green state slab which provide peaks and valleys in opposite sides of the green state slab, wherein the valleys in the top surface are disposed in an offset relationship to the peaks in the bottom surface;
(c) sintering and polling the grooved green state slab;
(d) forming electrically conductive surfaces on the exposed top and bottom surfaces of the sintered green state slab;
(e) cutting a slot through the top conductive layer in each of the valleys in the top surface of grooved sintered green state slab; and
(f) positioning an orifice plate over the conductive surface on the top peak surfaces of the slotted sintered slab and a substrate on the conductive surface on the bottom peak surfaces to produce the ink jet printer channel member.
ADVANTAGES
Forming green machined slabs for print head application has numerous advantages. The diamond sawing, which is essential for forming channel members in sintered, dense materials, particularly ceramics, causes defects, such as chipping and unevenness of the channel member walls. In the conventional method of channel member formation in piezoelectric materials, the poled materials are subjected to diamond sawing. This produces a heat-affected zone on the channel member walls, where the composition of the material changes due to heat generated by sawing. The dipole characteristics of this heat-affected zone will be different than that of the interior, producing a different and variable piezoelectric coefficient. This invention facilitates the poling of the piezoelectric channel members. It also eliminates time consuming and batch saw processing.
REFERENCES:
patent: 5028937 (1991-07-01), Khuri-Yakub et al.
patent: 5227813 (1993-07-01), Pies et al.
patent: 5248998 (1993-09-01), Ochiai et al.
patent: 5311218 (1994-05-01), Ochiai et al.
patent: 5365645 (1994-11-01), Walker et al.
patent: 5598196 (1997-01-01), Braun
patent: 5600357 (1997-02-01), Usui et al.
patent: 5680163 (1997-10-01), Sugahara
patent: 5688391 (1997-11-01), Hayes
patent: 5704105 (1998-01-01), Venkataramani et al.
patent: 5725825 (1998-03-01), Hotomi et al.
patent: 5758396 (1998-06-01), Jeon et al.
patent: 0 827 833 (1998-03-01), None
Carlton Donn B.
Chatterjee Dilip K.
Ghosh Syamal K.
Sime David L.
Eastman Kodak Company
Fiorilla Christopher A.
Owens Raymond L.
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