Ink Jet Ink Formulation for Reduced Start-Up Problems

This invention relates to ink jet ink formulations, and more particularly to an ink jet ink and methods of eliminating or at least reducing problems associated with start-up when an ink jet apparatus is initially discharged.

The problems associated with ink jet start-up are legion and notorious. Start-up problems include: (1) misfiring or non-firing of the initial ink droplets; and (2) slower initial ink droplet velocities.

Poor start-up is generally believed to be a result of evaporation of the ink in the nozzle of the ink jet during an idle period between firings.

Heretofore, such problems have been always addressed in a mechanical or electrical sense, i.e. added pulses or signals were used to discharge the initial drop of ink in order to prevent misfiring, and to accelerate the ink drop to normal operating speed.

To the best of our knowledge and belief, no one has ever tried to formulate an ink which would prevent or substantially reduce start-up problems.

To the best of our knowledge and belief, no one has ever realized that a blending of ink fluid components could eleviate problems associated with ink jet start-up.

The present invention was discovered quite by accident during the scientific and engineering research of formulating ink jet compositions using oleic acid, as taught in our U.S. patent application Ser. No. 248,551, filed: Mar. 27, 1981; now U.S. Pat. No. 4,361,843, issued Nov. 30, 1982.

During the aforementioned research, it was noted that one particular formulation always started properly during initial discharge of the ink jet. This formulation comprised by approximate weight: 30 percent oleic acid; 20 percent Typophor Black (30% weight of Nigrosine and 70% weight of oleic acid); and 50 percent benzyl ether.

Analysis of this formulation revealed that the oleic acid and benzyl ether had similar boiling points and low vapour pressures. It was then decided to formulate other ink compositions with components having matching boiling points and/or vapour pressures to see whether they too would exhibit a freedom from start-up problems. It was indeed observed that these new compositions were also free from start-up problems.

The chemistry is not yet fully understood regarding all the parameters which enter into the method of blending ink components to reduce start-up problems. Other factors, such as viscosity, may play a part in properly matching ink fluid components. At this time, however, it is safe to state that the matching of vapour pressures and/or boiling points of the components reduces to a significant degree the aforesaid problem.

It is believed that the matching of vapour pressures and/or boiling points produces an ink whose components evaporate at substantially similar or equal rates, thus providing an ink that maintains its initial formulation percentages despite evaporation. It is believed that this phenomenon results in the elimination of the problems associated with start-up.

It should also be obvious in view of the above discovery, that components having a lower vapour pressure, such as oleic acid, would be most desirable for use in the invention.

The invention pertains to ink jet formulations and a method for eliminating or substantially reducing start-up problems when an ink jet apparatus is initially discharged. The ink jet ink is formulated to comprise at least two fluid components. The components are matched with respect to either or both of their vapour pressures and/or boiling points. These parameters are matched to provide an ink whose components have substantially similar evaporation rates. Thus, the initial ink formulator will be maintained despite evaporation of each component from the ink.

When an ink jet ink is so formulated, the tendency for the ink jet apparatus to improperly discharge during initial start-up will be substantially reduced or eliminated.

Non-aqueous, oil-based ink components with low evaporation rates are preferred in the invention, such as oleic acid, castor oil, etc.

Matching components for such oil-based components can be aromatic ethers or high molecular weight alcohols.

Another component of such an ink formulation may by a pyrrolidone.

Naturally, such ink formulations must contain a dye component.

The ink jet ink is preferred to have a surface tension of at least approximately 35 dynes/cm at operating temperature.

The invention can be utilized with a wide variety of apparatuses, and the inventive formulations are not limited to any specific types or classes of fluid components, in so far as they are each matched to provide the benefits and purposes of the described invention.

It is an object of this invention to provide an ink jet ink and method for substantially eliminating or at least reducing the tendency of an ink jet apparatus to improperly discharge during initial start-up.

The above object and other such objects will be better understood and will become more apparent with reference to the following detailed description.

Generally speaking the invention features ink jet ink formulations and a method for substantially eliminating or at least reducing some or all of the problems associated with improper discharge of the ink jet apparatus during initial start-up.

Each fluid component of the ink is matched with other components of the ink with respect to its vapour pressure and/or boiling point. This will provide an ink whose components all evaporate at substantially the same rate.

The following typical ink jet inks in Table I below, have been formulated to substantially reduce or eliminate start-up problems. Each formulation has components that are matched to provide similar evaporation rates.

Having thus described the invention, what is desired to be protected by Letters Patent is presented by the following appended claims.