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,...
Utility Patent
1999-02-22
2001-01-02
Derrington, James (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,...
C264S435000, C264S436000, C264S618000, C264S645000, C264S678000, C264S328200
Utility Patent
active
06168746
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of injection molding of ferroelectric materials and more particularly to low and medium pressure injection molding of particulate piezoelectric, its composites, and other particulate ceramics for manufacture of low cost, high precision, and complex shaped articles such as ink jet heads.
BACKGROUND OF THE INVENTION
Experience indicates that manufacture of complex shaped devices from ferroelectric and more particularly, piezoelectric materials involve a series of complicated processing steps. Ferroelectric materials, particularly the piezoelectric materials are suitable candidates for actuators, transducers, resonators, and sensors. Because of high piezoelectric coefficients of lead based piezoelectric materials, these materials are suitable candidates for high precision ink jet heads. Unfortunately, the manufacturing processes for these piezoelectric ceramics are difficult and are very costly, primarily because of labor intensive machining processes to produce high precision complex shaped articles. Injection molding, however, is a technique which can be successfully utilized to manufacture large volumes of complex shaped articles in a cost effective way. Injection molding of inorganic powders with very fine particulate size, such as ferroelectric lead based piezoelectric materials, and a wide variation in particle size such as in composites of these ferroelectric materials, pose a multitude of manufacturing problems.
An ink jet printhead made from a piezoelectric material is 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 channels and energy pulses are used to actuate the printhead channels causing the droplets of ink to be ejected on demand or continuously, through orifices in a plate in an orifice structure.
In one representative configuration, a piezoelectric ink jet printing system includes a body of piezoelectric material defining an array of parallel open topped channels separated by walls. In the typical case of such an array, the channels are micro-sized and are arranged such that the spacing between the adjacent channels 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 channels. An orifice structure comprising at least one orifice plate defining the orifices through which the ink droplets are ejected, is bonded to the open end of the channels. In operation of piezoelectric printheads, ink is directed to and resides in the channels 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. Operation of piezoelectric ink jet printheads is 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. The piezoelectric materials forms a special class of ferroelectric materials, wherein the ferroelectric materials develop an electric field when subjected to pressure forces, or conversely, exhibit a mechanical deformation when subjected to an electric field. 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.
Under previous methods of making piezoelectric ink jet printheads, a block of piezoelectric ceramic such as PZT in which channels are to be formed is poled, to make the material piezoelectrically deflectable or “active”, by imparting a predetermined voltage widthwise across the piezoelectric ceramic block 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 therein. These grooves are generally formed by sawing, laser cutting or etching process. This current process of poling a bulk ceramic and later fabricating micro-sized channels by sawing or other processes is discussed in details in U.S. Pat. Nos. 5,227,813, and 5,028,937, and EP Patent 827833. This process of forming channels is not only time consuming and expensive, but also is amenable to many defects generated during cutting the channels 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.
In order to produce a lead based piezoelectric material, such as lead-zirconate-titanate (PZT), pure zirconium and titanium need to be alloyed with lead. Lead zirconate and lead titanate are crushed and mixed in appropriate proportion and calcined at a high temperature to form a piezoelectric material of requisite piezoelectric coefficient. In the powder form of the piezoelectric material, the crystallite size needs to be maintained at a submicron level, preferably at or below 0.3 &mgr;m for the ease of processing and development of uniform grain structure in the manufactured components.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method for manufacturing of ferroelectric articles of complex shapes and more particularly, of piezoelectric articles of complex shapes, such as ink jet printheads.
It is also an object of the present invention to provide a method of making piezoelectric ceramic ink jet printhead which will eliminate time consuming and costly processes of cutting channels.
Almost all the prior art in the field of injection molding fails to teach the molding process which is effective either at ambient temperature or at low temperature (<100° C.) Generally, any manufacturing process at ambient temperature/low temperatures provide a multitude of advantages wherein close control of temperature dependent variables, such as injection pressure and viscosity of the injected materials is not warranted.
This object is achieved in a method for injection molding fine particulate ceramic ferroelectric materials to form an article such as ink jet printhead comprising the steps of:
(a) spray drying fine particulate ceramic ferroelectric material to form agglomerate material;
(b) mixing the spray dried fine particulate agglomerate ceramic ferroelectric material with a binder system including materials selected from the group consisting of wax having wax components of different molecular weight, magnesium-X silicate, agaroid gel forming material, and agaroid gel forming material mixed with magnesium-X silicate to form a compounded material;
(c) injecting the compounded material at a selected pressure into a mold to form a green article;
(d) debinding or drying the green article;
(e) sintering the debinded or dried green article to form the final molded article;
(f) poling the final molded article to align the electrical dipoles within the piezoelectric material;
(g) forming a coating of conductive material over the top and bottom surfaces of the final molded article and then cutting grooves through conductive coating into the top surface in the valleys of the final molded article to form a channel member; and
(h) providing an orifice plate over top surface of the channel member and a substrate over the bottom surface of the channel member.
The present invention is directed to injection molding of fine part
Chatterjee Dilip K.
Ghosh Syamal K.
Lee James K.
Derrington James
Eastman Kodak Company
Owens Raymond L.
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