EP0712726A2

EP0712726A2 - Coated nozzle plate for ink jet printing

Info

Publication number: EP0712726A2
Application number: EP95308310A
Authority: EP
Inventors: Ashok Murthy; Gary Raymond Williams
Original assignee: Lexmark International Inc
Current assignee: Lexmark International Inc
Priority date: 1994-11-21
Filing date: 1995-11-21
Publication date: 1996-05-22
Also published as: JPH08224878A; EP0712726A3

Abstract

A nozzle plate for an ink jet head which has nozzle holes in which both the outside of the plate and the inside of the holes are coated with a low surface energy polymer.

Description

FIELD OF THE INVENTION

The present invention is concerned with nozzle plates for ink jet printing. The plates are coated to improve properties.

BACKGROUND OF THE INVENTION

It has been believed that although the outside surface of a nozzle plate used in ink jet printing has to have a low surface energy, the inside surface of the nozzle holes needs to have a high surface energy. This has been considered desirable because the high surface energy causes the ink to wick up into the firing chamber faster, thereby allowing a higher firing rate and also controlling the drop mass of the ejected drop. This belief is true in the sense that a higher surface energy does cause the ink to wick up and fill the firing cavity, but the higher surface energy also causes the ink meniscus to come close to the nozzle hole surface, making it possible for the ink to creep out along the outer surface of the nozzle plate. This causes "drooling," which results in a number of problems, such as no ink jetting, misdirected jetting, cross-contamination and variations in velocity and mass of the ejected drop.
In order to attempt to compensate for some of these problems, the machine print algorithm has to include a high frequency of maintenance cycles wherein the printhead has to be serviced. Excessive maintenancy results in higher cost and lower print speed.

DISCLOSURE OF THE INVENTION

According to the present invention, a low surface energy coating is applied to both the inside surfaces of the nozzle holes and an outside surface of the nozzle plate. This reduced surface energy causes the ink meniscus to be lower in the ink cavity, i. e., recessed away from the nozzle surface. This results in the following effects:

a) The ink tends not to come out on the outer nozzle plate surface, hence there is little or no 'flooding';
b) Since there is no flooding, there is a lesser incidence of misdirected or missing nozzle fires;
c) The drop mass is lower since there is less ink in the firing chamber. This reduces the amount of satellites and results in a cleaner, crisper printed image;
d) Since there is a smaller drop mass, there is less splatter and therefore a cleaner print;
e) The pocket of stagnant air above the ink meniscus reduces the amount of drying of the ink with the result that the cartridge can be kept out for extended periods of time with no clogging or misdirection of ink drops;
f) Maintenance frequency is somewhat to greatly reduced, improving the throughput and page count of the printer and printhead.

The low energy surface coating is a polymer. This polymer may include a polyolefin, a poly-(halogenated olefin) or a polyxylylene. The preferred materials are the poly-(para-xylylenes). The most preferred polymer is poly-(monochloro-para-xylylene), which is commercially available under the trademark Parylene-C from Specialty Coating Systems, a former division of Union Carbide. The term "pristine" as an adjective to "polymer" is used in this application to designate a polymer which is substantially undegraded and not oxidized. Such pristine polymers are preferably used in the invention. Polyxylylenes which have been significantly ashed by treatment with a plasma are not pristine.
It is difficult to coat the inside surfaces of the holes in the nozzle plate because they are so small. It is necessary that the coating be uniform and smooth and not clog any of the holes. To obtain the desired uniform coating, the most preferred way is by a vapor deposition technique. Parylene-C is particularly suitable for chemical vapor deposition, and is the most preferred coating for this reason among others. Chemical vapor deposition, as used herein, refers to a process by which a monomer gas heterogeneously nucleates and forms a polymer film on any and all surfaces it comes in contact with. The term "vacuum deposition" is also used for this process by providers of Parylene-C.
Parylene C, when applied by chemical vapor deposition, yields none of the shape distortions typical of liquid based deposition techniques. In addition, the material is extremely inert chemically, and can withstand the high temperatures used in chip, nozzle plate, and cartridge assembly. Furthermore, this polymer has high hydrolytic stability, low moisture absorbence and low diffusion rates for moisture and oxygen. It is thus an excellent barrier material for preventing corrosion in the underlying base metal, usually nickel.
It is preferred that the inside surfaces of the nozzle holes and the ink exit side of the nozzle plate are coated with the low surface energy polymer. It is also preferred that the opposite side of the nozzle plate (the side attached to the ink jet cartridge, for example to a heater substrate) is not coated with said polymer, and this side can be masked in the deposition step.
While it is not necessary for the nozzle plate to function, it is essential for the durability of the nozzle plate that the polymer coating adhere to it. This is accomplished by the use of an adhesion promoter, many of which are commercially available. The preferred type of adhesion promoter for use in the present invention is a silane. One such is Z6032, available from Dow Corning.

BEST MODE OF THE INVENTION

The following is the preferred method of making a coated nozzle plate of the present invention. It should not be interpreted as a limitation on the invention.
A nickel nozzle sheet is dipped into 0.1 M HCl for 15 minutes. It is then rinsed with deionized water, and then with ethanol. The nozzle sheet is dipped in a .25% to 1% solution of the silane adhesion promoter Z6032 for 15 minutes, and hung up to dry in quiescent air. When dry, the sheet is placed in a Parylene coating vacuum chamber and coated with Parylene C to a thickness of about 1.5 microns. (This coating step is conventional, and is described in detail in the equipment manual from Specialty Coating Systems, the manufacturer of the coater, and the side of the plate opposite to the ink exit side can be masked during the coating step). The nozzle plate sheet is then ready for the usual assembly steps.
The thickness of the polymer coating is not a critical feature of the invention. A thickness of less than a micron is sufficient to work, but in general it is preferred that, for the sake of durability, the thickness be somewhere up to five microns.
In summary, the present invention advances the art by providing nozzle plates which have less leaking, need less maintenance, give better print quality, have good wear resistance, and cost less than those of the prior art.

Claims

A nozzle plate for an ink jet print head, said nozzle plate including nozzle holes and being characterized by having a coating of a low surface energy polymer, said coating extending to the inside surfaces of said nozzle holes.
A nozzle plate as claimed in claim 1 in which the polymer is bonded to the nozzle plate by means of an adhesion promoter.
A nozzle plate as claimed in claim 2 in which the adhesion promoter is a silane.
A nozzle plate as claimed in claim 1 in which the low surface energy polymer is a polyolefin, a poly(halogenated olefin), or a polyxylylene.
A nozzle plate as claimed in claim 4 in which the polymer is a poly-(para-xylylene).
A nozzle plate as claimed in claim 5 wherein the polymer is poly-(monochloro-para-xylylene).
A nozzle plate as claimed in claim 5 wherein the polymer has been deposited on the nozzle head by means of chemical vapor deposition.
A nozzle plate for an ink jet print head, said nozzle plate including nozzle holes and being characterized by a coating of poly-(monochloro-paraxylylene) covering the plate and extending to the inside surfaces of said nozzle holes.
A nozzle plate as claimed in claim 8 in which the coating is bonded to the nozzle plate by a silane adhesion promoter.
A nozzle plate as claimed in claim 8 in which the coating has been deposited on the nozzle plate by chemical vapor deposition.
A nozzle plate for an ink jet print head said nozzle plate including nozzle holes and an outside surface to be attached in an ink jet cartridge and being characterized by the surfaces of said nozzle holes having a coating of a low surface energy pristine polymer and said outside surface not being a low surface energy polymer.
A nozzle plate as in claim 11 for an ink jet head in which the polymer is bonded to the nozzle plate by means of an adhesion promoter.
A nozzle plate as in claim 12 in which the adhesion promoter is a silane.
A nozzle plate as in claim 11 in which the low surface energy polymer is a polyolefin, a poly(halogenated olefin), or a polyxylene.
A nozzle plate as in claim 14 in which the polymer is a poly-(para-xylylene).
A nozzle plate as in claim 15 in which the polymer is a poly-(monochloropara-xylylene).
The nozzle plate as in claim 16 in the polymer is bonded to the nozzle head by means of a silane adhesion promoter.
A nozzle plate as in claim 15 in which the polymer is bonded to the nozzle head by means of a silane adhesion promoter.