INK JET PRINT HEAD AND NOZZLE PLATE THEREFOR

Abstract: The deposition and drying out of ink on the front surface of a print head nozzle plate adversely affects the ejection of the ink droplets. The nozzle plate (12) of ink wettable material carries a coating (30) on its front surface on non-wetting material. Such arrangement provides a stable meniscus of the ink column in each nozzle (24) and prevents ink from depositing at the front surface around the nozzle orifice. The principal use is in an ink jet printer.

Description: INK JET PRINT HEAD AND NOZZLE PLATE THEREFOR Technical Field The invention relates to an ink jet print head and to a nozzle plate therefor. Background Art In the field of non-impact printing, one of the most common type of printers has been the ink jet printer. Ink jet printers are provided with a single or multiple nozzle print head usually movable in the direc- tion of the line of printing and arranged to eject drop¬ lets of ink onto record media spaced therefrom. The number of ink nozzles in the face of a print head may range from a single nozzle up to nine nozzles in align¬ ment, for example, in a vertical direction to provide for dot matrix printing. A convenient way of producing the ink nozzle of multiple nozzle print heads is to form the nozzles through a nozzle plate which is then fixed to the body of the print head. A print head of such construction is well known and is disclosed e.g. in the DE-OS 27 28 657. By reason of the fluid characteristics of the ink and the high speed of the driven ink droplets, cer¬ tain problems and trouble areas can and do exist in the ink jet printing operation. The absence* of one or more intended spots on the record material may indicate that a nozzle or several nozzles of the nozzle plate became clogged and that the print head requires cleaning or rinsing. The actual position of the ink mark may be different from the desired position which may be due to incorrect speed of the ink droplets relative to the speed of the moving print head. Another problem may be that the actual size of the ink spot on paper does not corres¬ pond with the desired ink spot size which again may be due to a partial blockage of a nozzle. Disclosure of Invention It is the object of the invention-to provide an improved ink jet print head and a nozzle therefor which produce ink droplets with high accuracy and re- liability, in which the ink column within the nozzles is maintained in a more stable condition, and in which ink is prevented from depositing and drying out on the front surface of the nozzle plate around the nozzle orifices. Thus according to the invention, there is pro- • vided an ink jet print head for ejecting ink in droplet form, having a body portion-' and a nozzle plate which is fixed to said body portion and which has a plurality of equally spaced nozzles formed therethrough, character¬ ized in that said nozzle plate is of ink wettable mater- ial and carries a layer of ink resistant material on the side thereof distal from said body portion at least adjacent the orifice of each nozzle to prevent particles of ink from adhering therearound. -•According ' to another aspect of the invention, there is provided a nozzle plate for an ink jet- print head and having a substrate with a plurality of nozzles formed therethrough and equally spaced from one another, characterized in that said substrate is of ink wettable material and carries a layer of ink resistant material on one major surface thereof at least adjacent the ori¬ fice of each nozzle to prevent particles of ink from adhering therearound. In accordance with one embodiment of the present invention, a glass nozzle plate is provided and the nozzles are produced by means of a photo-etching process to maintain uniformity of the nozzles and maintain narrow tolerances along with an economic means of manufacturing. The nozzles are substantially cylin¬ drical in shape by the formation thereof during the etching process. The glass has a good wetting property for water and aqueous inks and the meniscus of the ink column within the nozzle is better stabilized in regard -3- to movement of the print head. The front side of the nozzle plate is coated with an ink-repellent material such as chromium, nickel or an ink-repellent plastic material. The meniscus of the ink column extends only 5 to the inner diameter of the nozzle and the outer surface remains free from ink. Brief Description of the Drawing One embodiment of the invention will be now described, by way of example, with reference to the 10 accompanying drawing, in which Fig. 1 is a side elevational view of a print head according to the present invention; ~ Fig. 2 is a front view of the nozzle plate shown in Fig. 1; 15 Fig. 3 is an enlarged sectional view taken • along .the plane 3-3 of Fig. 2; and Fig. 4 is a greatly enlarged view of one of the nozzles in the plate. * Best Mode of Carrying Out the Invention 20 Figs. 1 and 2 show a side elevational view and a front view of an ink jet print head 10 having on the face thereof a nozzle plate 12 and a leaf spring 14 for securing the plate to the print head. The nozzle plate 12 is secured by studs 16 and 18 to the head 10 and the- 25 leaf spring 14 is secured to the head in overlying fash¬ ion by screws 20 and 22. The nozzle plate 12 includes the substrate material with, for example, nine nozzles 24 therethrough and the leaf spring has an opening or window 25 therein for the nozzles. 30 Fig. 3 shows an enlarged side view of the nozzle plate 12 with the nozzles therein. The inner surface 26 or the left side of the plate is smooth glass and is easily wettable for ink adherence, whereas the outer surface 28 is polished and is resistant to wetting. 35 The nozzle plate 12 is made of glass and the nozzles 24 are produced by a photoetching process with the result¬ ant nozzles being circular, sharp edged and" substantial¬ ly cylindrical in form. The glass nozzle plate results in the high accuracy of printed characters and a high reliability. The glass structure of the nozzle plate has a good wetting property for water and aqueous inks and is extremely beneficial for this feature from the inner surface 26 and through the nozzle 24 so that the meniscus of the ink column within the nozzle has a good stability which makes the print head relatively insen¬ sitive to movement and vibrations. Fig. 4 shows a greatly enlarged one of the nozzles 24 of the glass plate 12 and is identified with the inner surface 26 and the outer surface 28. The nozzle 24 is shown as being cylindrical therethrough, however it may be slightly cone shaped for certain applications. The outer surface 28 is preferably coated with a non-wetting material 30 relative to the character¬ istics of the aqueous ink. Suitable ' materials for the non-wetting layer or coating 30 are water-repellent metals such as chromium or nickel, or water-repellent plastic materials, such as "Teflon" or certain of the silicon based materials. The non-wetting or water- repellent layer or coating 30 prevents deposits of ink at the front surface around the orifice of the nozzle 24. The presence of such ink deposits would adversely affect the ejection of ink droplets from the nozzle 24. The depositing of the non-wetting material 30 such as chromium onto the glass plate 12 may be per— formed by means of a vacuum type process. If the depositing of the material is carried out in a vertical direction with respect to the plate to be coated, the orifice of the nozzle 24 need not be protected. In the case of cylindrical construction, the walls of the nozzles 24 extend in parallel manner with the direction of de¬ positing of the non-wetting material 30. Additionally, where the walls of the nozzles 24 form a small negative angle, with respect to the direction of depositing of the material 30, the chromium or other metallic par¬ ticles will not reach and settle on the walls of the nozzle. It should be noted that known nozzle plates of single or of multiple nozzle print heads may consist of steel, silicon or nickel materials. Additionally, known methods for producing the nozzles within plates made of the above materials include mechanical drilling, laser beam boring, electron beam boring, material depositing, spark erosion and etching. Since certain requirements are set for the nozzles in an ink jet printer, such as, for example, " ' reliable and proper functioning, uniformity of all the nozzles, the maintaining of close tolerances ' and an economical process of manufacture, it has been found that the above materials and the noted manufacturing processes do not always satisfy these requirements. The present embodiment provides that the nozzle plate material of glass, together with the photo- etching process of forming the nozzles and the coating on the outer surface of the plate, result in a higher accuracy of the individual nozzles and also in a higher print quality of the print head. If a non-aqueous ink is used ' in the printing, other suitable materials may be selected for finishing the nozzle plate 12 so that the inner face 26 of the plate and the nozzle orifice itself is easily wettable whereas the outer face 28 of the nozzle plate is non- wettable. y .. ' ■< -- A ,

Claims: CLAIMS : 1. Ink jet print head for ejecting ink in droplet form, ha ing a body portion and a nozzle plate which is fixed to said body portion and which has a plurality of equally spaced nozzles formed therethrough, characterized in that said nozzle plate (12) is of ink wettable material and carries a layer (30) of ink resis¬ tant material on the side thereof distal from said body portion (10) at least adjacent the orifice of each nozzle (24) to prevent particles of ink from adhering therearound. 2. Ink jet print head according to claim 1, characterized in that said nozzle plate (12) is of glass. 3. Ink jet print head according to claim 2, characterized in that said layer (30) of ink resistant material is of chromium. 4. Ink jet print head according to claim 2, characterized in that said layer (30) of ink resistant material is of nickel. 5. Ink jet print head according to claim 2, characterized in that said layer (30) of ink resistant material is of plastic material. 6. Ink jet- print head according to claim 2, characterized in that the nozzles (24) of " said nozzle plate (12) are produced by photo-etching. 7. Ink jet print head according to claim 2, characterized in that said layer (30) of ink resistant material is formed on said side of the nozzle plate (12) by vacuum deposition. -7- 8. Ink jet print "head according to, either claim 1 or 2, characterized in that the nozzles (24) are substantially cylindrical in shape. 9. Ink jet print head according to claim 1, characterized by spring means (14) for fixing said noz¬ zle plate (12) to said body portion (10). 10. Nozzle plate for an ink jet print head and having a substrate with a plurality of nozzles formed therethrough and equally spaced from one another, char¬ acterized in that said substrate (12) is of ink wettable material and carries a layer (30) of ink resistant __. material on one major surface thereof at least adjacent the orifice of each nozzle (24) to prevent deposits of ink from adhering therearound.

Inventors: BADER LEONHARD, GIESSNER FRANK, ROMBACH FRIEDRICH B, WINTER HERMANN
Applicants: NCR CO, NCR CORP
Application year: 1981
Main classification: G01D15
IPC codes: B41J2