Method and apparatus for applying coatings to ink jet printheads or printhead dies

Abstract: A method and apparatus for applying a coating to a front face of an ink jet print head die (18) or print head die comprise positioning a die (18) in a cut out (13) in a top surface of a block (12) such that the die (18) extends from the top surface of the block (12). An applicator such as a roller or flat blade is used to apply the coating to at least an upper surface of the die (18) as the applicator rides along the upper surface of the die (18). When a roller is used as the applicator, the roller has a recess corresponding to the extension of the die from the top surface of the block (12). The roller recess contains a piece of elastomeric material which extends to an outer portion of the roller adjacent to said roller recess. The method and apparatus facilitate transfer of a thin, uniform film of coating to an ink jet printer print head die (18) or a completed ink jet printer print head.

Description: The present invention relates to a method and apparatus for applying a front face coating to ink jet printheads or ink jet printhead dies and, more particularly, to a method and apparatus for applying a long- lasting hydrophobic coating to the front face of ink jet printer printheads or dies. In ink jet printing, a printhead is provided, the printhead having at least one ink-filled channel for communication with an ink supply chamber at one end of the ink-filled channel. An opposite end of the ink-filled channel has a nozzle opening from which droplets of ink are ejected onto a recording medium. In accordance with the ink droplet ejection, the printhead forms an image on the recording medium. The ink droplets are formed as an ink meniscus at each nozzle opening experiences the momentum of the expanding bubble formed in the respective channel as a direct result of the voltage pulse applied across the heater in the channel. After a droplet is ejected, additional ink surges to the nozzle opening to re-form the meniscus. The direction of the ink jet determines the accuracy of placement of the droplet which, in turn, determines the quality of printing performed by the printer. Accordingly, precise jet directionality is an important characteristic of a high quality printhead. Precise jet directionality ensures that ink droplets will be placed precisely where desired on the printed document. Poor jet directionality results in the generation of deformed characters and visually objectionable banding in half-tone pictorial images, particularly so with the newer generation of ink jet printers which enable printing at at least 300 dots per inch. In these high resolution printers the improved print quality demanded by the customer can only be provided if drop directionality were maintained over the entire useful life of the printhead. Currently available ink jet printers provide accurate placement of ink droplets on a page for only a very limited period of time. The current printers do not maintain high print quality by maintaining the directionality of the ink jet throughout the entire printing lifetime of the printhead. A major source of jet misdirection is associated with wetting of the front face of the printhead containing at least one nozzle opening. One factor which adversely affects jet directionality accuracy is the interaction of ink previously accumulated on the front face of the print head with the exiting droplets. This accumulation is a direct consequence of the forces of surface tension between the ink and the polar front face of the printhead, the accumulation becoming progressively severe with aging due to oxidation of the front face of the printhead. Ink may accumulate on the printhead front face due to either overflow during the refill surge of ink or the splatter of small droplets resulting from the process of ejecting droplets from the printhead or both. When ink accumulated on the front face of the print head makes contact with the ink meniscus at the nozzle orifice, the meniscus distorts, resulting in an imbalance of forces acting on the ejected droplet. This distortion leads to ink jet misdirection. This wetting phenomenon becomes more troublesome after extensive use of the printhead as the front face either oxidizes or becomes covered with dried ink film. As a result, gradual deterioration of the generated image quality occurs. One way of avoiding these problems is to control the wetting characteristics of the printhead front face so that no accumulation of ink occurs on the front face even after extensive printing. Thus, in order to provide accurate directionality for the exiting jet of ink, wetting of the front face of the printhead ought to be suppressed. This can be achieved by rendering the print head front face hydrophobic. A European patent application filed concurrently herewith and corresponding to U.S. Patent Application Serial No. 874,865, and published as EP-A-568 249, discloses a novel hydrophobic coating for the front face of a printhead in an ink jet printer. The coating controls the wetting characteristics of the front face to prevent ink accumulation on the front face. The coating comprises an epoxy adhesive (i.e., resin+curing agent) doped with a silicone rubber compound. The coating can be provided in the form of a 24% solution of the epoxy adhesive (resin+curing agent) and a 30:70 mixture of xylene and methyl iso-butyl ketone by weight doped with 1% by weight of the silicone rubber compound. The proportions of the components of the epoxy mix and the concentration of the epoxy mix in the solvent can be varied to suit a particular method of application. The coating enables the directionality of an ink jet to be maintained for the printing lifetime of the printer. The application of such a long-lasting hydrophobic coating to the front face of an ink jet print head is extremely crucial to the maintenance of good print quality over the life of the ink jet printer. JP-A-2 048 953 discloses a method of applying a coating to a recording head by riding an applicator having the coating on a surface thereof along the surface of the recording head and discloses an apparatus therefore, according to the preambles of claims 1 and 3. An object of the present invention is to provide a method and apparatus for applying a front face coating to an ink jet printhead or printhead die without requiring a considerable amount of effort. Accordingly, there is provided a method and apparatus for applying a coating to the front face of an ink jet printhead or printhead die according to any one of the appended claims. In one embodiment a block is provided which has a cut out in a top surface thereof. A die is positioned in the cut out such that the die extends from the top surface of the block. A roller is used to apply the coating to at least one surface of the die as the applicator rides along the surface of the die. The roller has a recess corresponding to the extension of the die from the top surface of the block. The roller recess preferably contains a piece of elastomeric material which extends to an outer portion of the roller adjacent to the roller recess. The method and apparatus facilitate transfer of a thin uniform film of coating to an ink jet print head die or a front face of an ink jet printer print head. In one embodiment the roller recess contains substantially a 8-9mm thick piece of said elastomeric material, an outer portion of said roller adjacent said roller recess being ground such that said roller recess is substantially 1-3mm deeper than said outer portion of said roller. In another embodiment the outer portion of said roller has a diameter which is substantially 1-3mm larger than a diameter of an innter portion of said roller. In one embodiment the die extends in a range substantially 1-3mm above the top surface of the block. In another embodiment the cut out has a width in a range of substantially 4-5mm. The invention will be described in detail further with reference to the following figures in which like reference numerals refer to like elements and wherein: Figure 1 is a schematic view of the apparatus according to an embodiment of the present invention; and Figure 2 provides a schematic illustration of the device for transfer of the hydrophobic coating. Referring now to the figures and more particularly to Figure 1 thereof, an apparatus 10 according to the present invention is described. Apparatus 10 comprises an block 12 of, for example, aluminum having a cut-out 13 located in a top surface thereof. Aluminum block 12 can be mounted on a stand 14 by way of isolators 16. Cut-out 13 of aluminum block 12 has a width of approximately 4-5mm. Cut-out 13 of aluminum block 12 receives a die 18; die 18 extending approximately 1 to 3 mm above the top surface of block 12. Accordingly, cut-out 13 must be sufficiently deep to accommodate die 18 such that the approximate 1 to 3 mm portion of die 18 extends above the top surface. Coating transfer is preferably performed at approximately 65°C, although formulations facilitating room temperature transfer can also be transferred using this apparatus. To effect the coating transfer at a temperature higher than room temperature, aluminum block 12 has a heater 26 located therein. Heater 26, which is controlled by a temperature controller 28 and a thermistor such as an RTD sensor located next to the heater, maintains the temperature of aluminum block 12 at approximately 65 ± 1°C. Cut-out 13 has two parts which are joined together via screw 30. Screw 30 allows one to adjust the distance between the two faces of the cut-out , which , in turn , allows one to hold the die firmly in place or release the same simply by turning the screw one way or the other. Figure 2 illustrates the application of a coating to at least a top surface of die 18. A roller 20 is used for application of the coating. Roller 20 is approximately 50-60mm wide. Roller 20 has a recess which is substantially 10-12mm deep in a middle portion thereof. The roller recess 24 can be filled with an elastomeric material 22 such as a thick piece of neoprene rubber having a thickness of approximately 8-9 mm. The elastomeric material 22 wraps completely around roller 20. Roller 20 has an outer portion. The diameter of the outer portion of roller 20 is approximately 1-3mm larger than the inner portion of the roller. The outer portion can be ground to provide the recess in the roller. Such an arrangement allows for smoother motion of the roller , and a more intimate contact between the die and the roller during transfer. The hydrophobic coating is applied to at least the top surface of die 18 by moving roller 20 smoothly across at least the top surface of die 18 over the aluminum block 12. Alternatively, a film of the coating material could be spun onto a mylar disk. Subsequently, the side with the film is pressed against either the printhead or the printhead die and simply either by rolling the roller or moving the flat blade over the other side of the mylar disk, a thin film of the coating material is transferred to either the printhead or the die. Using the above-described arrangements, a very thin, uniform film of the hydrophobic front face coating formulation can be easily transferred to either a die or a completed printhead. This manner of applying a hydrophobic coating provides a long-lasting coating which is extremely crucial to the maintenance of good print quality over the life of the printer. The advantage of this manner of application is the ease of application of a water resistant coating to the front face of either a die or a completed printhead at any stage including the restoration of printheads in the field. The characteristics of this manner of application include favorable adhesion and favorable advancing and receding contact angles against water and various inks. While the invention has been described with reference to particular preferred embodiments, the invention is not limited to specific examples described above. It is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative not limiting. Various changes may be made without departing from the scope of the invention as defined in the following claims.

Claims: A method of applying a coating to an ink jet print head die (18) or a front face of an ink jet printer print head, including: positioning a die (18) or a printhead and applying a coating to an upper surface of said die (18) or printhead by riding an applicator (20) having said coating on a surface thereof along said upper surface of said die (18) or printhead, characterised in that the die (18) or the printhead is positioned into a cut out (13) in a surface of a block (12) such that said die (18) extends above, i.e. past said surface of said block (12); and wherein said applicator (20) is a roller having a recess (24) into which said die (18) extends and said applying comprises riding said roller (20) along at least said upper surface of said die (18). A method according to claim 1, including positioning a heater (26) in said block (12) to control a temperature of said block (12) at substantially 65 ± 1°C and controlling said heater (26) by a temperature controller (28) and a thermistor. An apparatus (10) for applying a coating to an ink jet printhead die (18) or a front face of an ink jet printer printhead, including: an applicator (20) for riding along at least an upper surface of said die (18) or printhead for applying a coating to at least said upper surface of said die (18) or printhead, characterised by a block (12) having a cut out (13) located in a surface thereof for receiving the die (18) or printhead with said die (18) or printhead extending above, i.e. past said cut out (13); and wherein said applicator is a roller (20), having a recess (24) into which said die (18) or printhead extends. An apparatus according to claim 3, wherein said roller (20) is covered with an elastomeric material (22). An apparatus according to claim 3 or claim 4, wherein a heater (26) is located in said block (12), said heater (26) for maintaining said block (12) at a temperature of substantially 65 ± 1°C, said heater (26) being controlled by a temperature controller (28) and a thermistor. An apparatus according to any one of claims 3 to 5, wherein a screw (30) is provided in an upper portion of said block (12), said screw (30) holding together areas of said block (12) adjacent said cut out (13).

Inventors: HAROLD ROBERT A SR, NARANG RAM S, POND STEPHEN F, HAROLD, ROBERT A., SR., NARANG, RAM S., POND, STEPHEN F.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1993
Main classification: B41J2
IPC codes: B05D1, B41J2, B05C1