Abstract:
An orifice plate for a jet drop recorder is fabricated by plating techniques. It is formed throughout of a single, homogenous material, such as nickel, for compatibility with the recorder ink, and is of sufficient thickness to provide adequate strength. The orifices are open on both sides for easy cleaning.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of U.S. application Ser. No. 861,852, filed Dec. 19, 1977, now U.S. Pat. No. 4,184,925. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to jet drop recorders of the general type disclosed in U.S. Pat. Nos. 3,577,198, 3,701,476, 3,701,998, 3,709,432, 3,739,393, 3,882,508, 3,970,222 and 4,031,561, all assigned to the assignee of the present invention. Such jet drop recorders comprise a series of electric and fluidic components, including an orifice plate and a charge plate, for generating one or more rows of jets of ink and selectively charging the ink droplets as they form from the jets. Typically, there may be several hundred jets formed in each such row, and each jet may be stimulated to produce drops of ink at a rate of about 400 kHz. All such drops fall through an electrical deflection field, and those which are charged are deflected into a catcher. Uncharged drops are deposited on a moving web transported below the recording head. 
     One of the critical requirements in such a jet drop recorder is an orifice plate which will produce several hundred jets of ink which are precisely positioned, precisely parallel, and precisely uniform. The orifice plate must also be compatible with the ink compositions used, and must be resistant to erosion by the ink. In addition, the regions around the orifices should be sufficiently open to provide for cleaning ink and dirt deposits from the orifices for maintaining proper operation. 
     One method for producing such an orifice plate is to etch a suitable substrate, which can be done using well-known photoresist techniques. A difficulty with this method, however, is the requirement of virtually absolute uniformity among all the orifices. When a metallic substrate is etched, for example, great care must be taken to achieve the required accuracy. 
     Some success in the forming of etched orifice plates has been achieved through the use of selective etching of crystalline substrates along particular planes of the crystal. See, for example, U.S. Pat. Nos. 3,921,916, 3,949,410, and 4,007,464. However, the preferred crystalline material (silicon) does not have as much resistance to erosion by the ink as would be desirable, sometimes requiring an erosion resistant coating as shown in several of these references. Such crystalline orifice plates are thus expensive (being made of a single crystal), difficult and expensive to fabricate, and not always of the desired strength or durability. 
     A need thus remains for an orifice plate which meets the above noted requirements in an inexpensive, easily fabricated, strong, durable, and reliable configuration. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention meets the above-noted needs while overcoming the difficulties of prior art configurations with a solid, homogeneous orifice plate formed of a single material. In the preferred embodiment the orifice plate is formed of nickel metal, which is compatible with inks used in jet drop recorders, and is resistant to erosion. The method for fabricating the orifice plate provides extreme uniformity among the orifices. Further, recesses and cavities on both sides of the orifice are provided which are open and accessible. There are no enclosed cavities so that the orifice plate and orifices are easy to keep clean for proper operation. 
     The orifice plate itself is formed entirely by plating techniques. No drilling or etching of the orifice plate (as distinguished from its substrate) is involved. This provides good control of the various orifice and plate dimensions throughout the fabrication thereof. 
     In forming the orifice plates, a suitable flat substrate (such as a sheet of stainless steel) is coated with a suitable photoresist material. The photoresist is then exposed through a suitable mask and developed so that there are round, preferably cylindrical, photoresist peg areas on the substrate corresponding to the orifices which are to be formed. The orifice plate material, such as nickel, is then plated (preferably by electroplating) onto the substrate. Plating continues until the nickel has grown up beyond the height of the pegs, at which time the nickel begins to plate inwardly over the edges of each peg as well as upwardly from the substrate. This progressively covers the edges of the pegs with the nickel, and is continued until orifices of exactly the desired size are formed over the photoresist pegs on the substrate. The volumes occupied by the resist pegs will eventually be orifice recesses in the final orifice plate, each having an effective diameter larger than the orifice itself. 
     Next a larger and much thicker plug is formed over each orifice on the sides of the orifices opposite the pegs (that is, opposite the recesses). The plugs are also formed of photoresist material, by suitable coating, masking, and developing procedures, using either a separate mask, or using the orifice plate itself, at this stage, as a mask. The latter eliminates the problems associated with aligning a separate mask with the orifices. Each plug is preferably much larger than the orifice diameter, so that the cavity which it ultimately will form will likewise be much larger. The plating is then continued so that the nickel builds up to the top level of the resist plugs. 
     At this point an orifice plate has been fabricated on the substrate. The photoresist is removed by conventional techniques (such as chemically dissolving the photoresist), and the substrate may be removed (a by mechanically peeling the orifice plate from the substrate), yielding a solid, homogeneous, metallic orifice plate. 
     It is therefore an object of the present invention to provide a solid orifice plate for use in a jet drop recorder; an orifice plate formed throughout of a single homogeneous material such as nickel; an orifice plate which may be formed by plating the material around resist pegs on a substrate to form orifices around the pegs, and then forming resist plugs over the orifices and further plating the orifice plate material around the sides of the plugs to thicken the orifice plate, following which the resist is removed; which provides such an orifice plate in an inexpensive yet highly reliable configuration in which the orifices are uniform and highly resistant to erosion, easy to clean, and in which the orifice plate may readily be fabricated in the thickness necessary to provide sufficient strength for the application at hand. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a solid orifice plate fabricated according to the present invention; 
     FIG. 2 shows a portion of a substrate having resist pegs formed thereon as the first step in one method for preparing the orifice plate shown in FIG. 1; 
     FIG. 3 illustrates the next step, in which the orifice plate material has been plated onto the substrate to form the orifice plate nozzles; 
     FIG. 4 shows the step following FIG. 3, in which resist plugs have been formed over the orifices; 
     FIG. 5 illustrates the step following FIG. 4, in which additional material has been plated to the tops of the plugs; 
     FIG. 6 illustrates the two completed orifice plates following removal of the substrate and resist in FIG. 5; 
     FIG. 7 is a fragmentary, partially broken away view of the orifice plate showing details of one of the orifices; 
     FIG. 8 is an early step, analogous to that of FIG. 3, in another method for preparing an orifice plate such as shown in FIGS. 1 and 7; 
     FIG. 9 illustrates the step following FIG. 8, in which the substrate has been etched away in the region adjacent the recess; 
     FIG. 10 shows the step following FIG. 9, in which a photoresist has been applied to the surface of the plated metal; 
     FIG. 11 illustrates the step following FIG. 10 in which the photoresist is exposed to light by shining the light through the orifice and reflecting it back; 
     FIG. 12 shows the next step in preparing the exposed resist, plate, and substrate for developing the photoresist; 
     FIG. 13 illustrates the photoresist after it has been developed; 
     FIG. 14 illustrates the step following FIG. 13 in which additional material has been plated to the top of the developed resist plug; 
     FIG. 15 shows the completed orifice plate structure; and 
     FIG. 16 illustrates the optional removal of the substrate from the completed orifice plate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In one embodiment, the orifice plate 10 (FIG. 1) is formed by first preparing a suitable substrate 12, such as a plate of stainless steel. The stainless steel plate may be as thick as necessary to be sure it will remain flat and true. This is then coated in known fashion by a photoresist material, which is exposed through suitable masks to form a series of cylindrical pegs 14 on each side of the substrate 12. The resist pegs 14 remain on the substrate 12 after the photoresist is developed to remove the unexposed resist. 
     The substrate 12 is then plated with nickel 16, as illustrated in FIG. 3. Nickel is preferred since it provides adequate strength and is compatible with current ink compositions used in jet drop recorders, reducing erosion of the orifices to a minimum. The plating may be done, for example, by electroplating the substrate 12 in a suitable solution. During such an electroplating process, the nickel 16 is formed on the areas of the substrate which are conductive. Thus, no nickel plates onto the pegs 14. As the nickel plate 16 reaches and plates above the tops of the pegs 14, the plating begins to creep inwardly across the top edges of the pegs, since the nickel around the edges of the pegs is conductive, inducing plating in a radial direction across the tops of the pegs as well as in the outward direction away from the substrate. The plating is continued until the openings over the pegs 14 have been closed by the nickel to the exact diameters desired for forming and defining orifices 15 for the orifice plate 10. 
     Next the orifice plate is thickened to provide the desired physical strength for use in a jet drop recorder. As will be seen, when the orifice plate is so thickened, enlarged cavities are also formed opposite each orifice 15 to provide open access to the orifices for cleaning and for reducing the likelihood that deposits will accumulate. FIGS. 4 and 5 illustrate these steps. First, again using a suitable photoresist and mask, a cylindrical plug 17 of a greater diameter and a substantially greater thickness than the pegs 14 is formed on the side of each orifice 15 opposite the pegs 14, and substantially in line therewith (FIG. 4). Plating of the nickel is then resumed up the sides of the plugs 17 to the outer surface of the plugs. 
     Next the resist and substrate are removed. The nickel material which remains from each side of the substrate is an orifice plate. The areas previously occupied by each of the pegs 14 define orifice recesses 21 larger in effective diameter than the orifices themselves, and the regions occupied by the plugs 17 are now even larger cavities 22, with the orifices 15 disposed between their respective recesses and cavities. The orifice plate itself is of a thickness to provide the strength necessary for use in the jet drop recorder. The recesses and cavities 21 and 22 provide open and easy access to the orifices 15 for cleaning, and for reducing the likelihood that dirt or other deposits will accumulate. 
     In a typical embodiment, when the nickel is first plated (FIG. 3), it is plated to a thickness of approximately 1.5 mils. The cylindrical plugs 17 (FIG. 4) are approximately 10 mils in diameter and 6 mils thick, so that the final orifice plate is 7.5 mils thick. 
     FIGS. 8-16 illustrate another embodiment of the invention which eliminates the need to align a second mask with the substrate and with the partially formed orifice plate, shown in FIG. 3, in order to form the plugs 17. Instead, the orifices themselves are used as a mask for forming the plugs, thus assuring proper alignment. 
     More particularly, a substrate 32 corresponding to substrate 12 has pegs 34, corresponding to pegs 14, formed on one side thereof. These are plated around and partially over with nickel 36, as in FIG. 3, to form orifices 35, as shown in FIG. 8. Next the pegs 34 are removed so that the areas previously occupied by them define orifice recesses 41. The substrate 32 is then etched through the orifices 35 to provide access to the recesses 41 from the substrate side of the plated nickel 36. 
     Next a photoresist 38 is applied to the surface of the nickel plating 36 opposite the substrate 32, over the orifices 35, and opposite the recesses 41 (FIG. 10). A mirror 40 is positioned opposite the photoresist 38, at a distance d from the side of the photoresist opposite the nickel plating 36 (FIG. 11). Then, since the substrate has been etched away in the region adjacent the recesses 41, a light 39 may be used to expose the photoresist 38 by shining it through the orifices 35 from the recess and substrate side and onto the photoresist 38 itself. Further, the light actually shines through the photoresist and onto the mirror 40, which reflects the light back onto the photoresist itself. As shown in FIG. 11, the light diverges as it passes through the orifices 35, and continues to diverge as it is reflected back to the photoresist from the mirror 40. Therefore, by suitably adjusting the distance d (FIG. 11), the diameters of the regions in the photoresist which are exposed to the light may be readily adjusted. The greater the distance d, the larger will be the diameters of the exposed areas, and the exposed areas will be greater in diameter than those exposed to the light shining only through the orifices 35. 
     The exposed resist is then developed as illustrated in FIGS. 12 and 13. First a developing mask 43 is attached to the back side of the etched substrate 32. This protects the exposed resist at the orifice itself, since, even though the resist in that area has been cross-linked by the light; it may still be attacked by the developing solution, albeit much more slowly. Mask 43 thus assures that the exposed portions of the resist 38 will not receive any developing action from the back or orifice side. If mask 43 is made of a transparent material, it may be applied at an earlier suitable time. After development, nearly cylindrical resist plugs 37 are left over the orifice 35. As will be appreciated, the resist plugs 37 are thus automatically aligned with the orifices 35, greatly simplifying the formation of the plugs 37. Also, by properly adjusting the distance d, the plugs 37 and cavities 42, in the preferred embodiment, are made larger than the pegs 34 and the recesses 41, as in the embodiment shown in FIGS. 2-6. 
     As in FIG. 5, the FIG. 13 structure then receives further plating of nickel around the sides of plugs 37 to thicken the orifice plate 30 and form the cavity 42 (FIG. 14). Finally, the photoresist plugs 37 and developing mask 43 are removed (FIG. 15) to leave the orifice plate 30 having the orifices 35 disposed between the recesses 41 and the cavities 42. 
     FIG. 15 shows the orifice plate 30 still attached to the etched substrate 32, and according to the particular needs and applications at hand, the orifice plate may be left attached to the substrate in that manner. Alternatively, the orifice plate may be stripped or otherwise removed from the substrate, as shown in FIG. 16. 
     As may be seen, therefore, the present invention has numerous advantages. It is formed of relatively inexpensive material by a relatively inexpensive and uncomplicated procedure. The results are uniform, and such uniformity is easier to obtain than with etching or drilling. In contrast to crystal orifice plates, the present invention starts with an inexpensive metal substrate rather than an expensive, fragile, single crystal which must be prepared with a specific orientation. Standard photoresist materials are used, following by standard, inexpensive electroplating of the desired metal onto the substrate. The plugs 17 may be of any suitable thickness to provide the strength necessary in the orifice plate 10. The final orifice plates are extremely uniform, compatible with the inks used in the jet drop recorder, and the orifices are readily accessible for cleaning. In fact, due to the open access to the orifices, they can be given protective coatings if, for example, a particular ink might be used under circumstances where such a coating would be desirable. 
     While the methods and articles herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited thereto, and that changes may be made therein without departing from the scope of the invention.