Non Aqueous Dispersion Ink With Improved Shelf Life, Tack and Flow

Great demands have been made upon printing systems and materials therefor in light of the need of faster printing, in conjunction with the computer age, and the seeking of lower toxicity to comply with governmental environmental regulations. In high speed printing, a problem has been encountered with paper dust which is generated during paper transport and the impact of a printing element on the paper. This is particularly true of the printing on envelopes which are made of paper with loose fibers.

One of the components of the printing system that has required extensive modification is the ink. In most printing applications, a pad or roller made of a porous material is supplied with ink for the purpose of transferring the ink to a printhead. The printing pad may be one which is self contained or it may be one that is periodically supplied with ink from a reservoir. The problems in producing a satisfactory fluorescent ink are compounded because a plurality of dyes and pigments are required for achieving good color, fill in, edge acuity and the other qualities required from an ink. One of the major problems associated with inks is aging which results in printing that has a change in color and intensity with the passing of the time the ink is stored. An ink that overcomes the aging problem and shows low environmental sensitivity (high humidity and low and high temperatures), low tackiness and flow properties, material compatibility and paper dust resistance would be advantageous. Another consideration is that the ink pad must function in an open environment without drying for at least six months; therefore, the ink solvents should be non volatile.

Non aqueous dispersion ink formulations have been discovered that are nontoxic and have flow properties which substantially reduce the tendency of the ink to cause plugging in an inking pad. Ink pad life has a variability caused mainly by the inherent properties of the ink with which it is used. The inking pad may be assembled with two layers of foam, the first layer serving as an ink reservoir layer and the second layer serving as a metering layer which contacts the print head. Because of its high density and smaller pore size, the metering layer can act as a filter as a consequence of the ink concentrating at the interface of the two layers. As a result, plugging tends to occur. Of course, what is meant by plugging is the fact that particles of the ink are captured within the pores of the inking member and thus prevent the flow of ink.

It has been found that the plugging onset can be delayed with the ink formulations of the instant invention because of decreased dissolved resin concentration, thereby decreasing the viscosity, even though the size of the pigments can vary from 0.1.mu. to 0.5.mu..

The ink formulation of the instant invention is based on organic pigments dispersed in rosin esters or a combination of organic pigments dispersed in rosin esters and amino formaldehyde resin dispersed in an alkyd resin. The resulting color of these inks can be red, blue, green or black. It has been found that these ink formulations reduce the effects of paper dust accumulations because the solvents of the instant ink formulations are non drying on the printing elements and maintains printing elements in a wet state. Preferably the solvent has emollient properties. This wet state causes the flushing of elements resulting in paper dust being carried away. Lower concentrations of dissolved resin produces a lower tack ink which results in less paper dust attraction in the ink.

The ink formulations of the instant invention have low environmental sensitivity due to small variation of the viscosity in the operating temperature range of 5.degree. to 45.degree. C. and the low hygroscopicity of the solvents.

The preferred embodiment of the invention is the inclusion of an emollient solvent in the ink formulation. Use of this type of solvent has been found to be compatible with the pigments used to produce the ink, provides low toxicity, ease of fabrication of the ink, is inert to materials in the inking system and provides a non-drying ink. Another advantage to the inclusion of an emollient solvent is that it is non-volatile and consequently results in the inking pad not drying.

The formulations of the instant invention provide inks with improved print quality, are inert to materials used in a printer such as inker foams and rubber, low tack, good shelf life stability, and good flow through porous foam materials.

It has been found that the inks of the instant invention have an acceptable shelf life. The aged samples show no settling after two weeks of accelerated testing. The aging of the inks by temperature shock shows no settling for the inks during two weeks of accelerated testing that simulated one year-of aging by varying the temperature between 70.degree. C. to -2.degree. C., every four hours of the working day.

The dual inker foam described above that is used in high speed flat bed systems is made of a polychloroprene foam bottom layer. The top layer is made of polyethylene sintered foam. The rubber used in the printing elements is made of polybutadiene acrylonitrile rubber, which is plasticized with dibutyl phthalate. The solvents used in the instant ink formulations are inert to all these materials. The print head should be usable for ten million prints, or ten years, and the pad materials should be compatible with the inks for six months.

The pigment dispersion used in the ink formulation is stabilized by using easily dispersible pigments predispersed in a vehicle such as a rosin ester carrier, soy bean oil alkyds, non-ionic surfactants and other type of alkyds. An example of such a pigment dispersion is triazine aryl sulphonamide paraformaldehyde resin dispersed in linseed oil alkyd raisin. The non aqueous pigment dispersion used in the ink formulation is stabilized by using easily dispersible non fluorescent organic pigments predispersed in a vehicle such as rosin ester carrier, linseed oil alkyds, or other type of alkyds. The rosin ester dispersants are preferable because of the wide range of compatibility with solvents and resins. The non-fluorescent pigments also can be predispersed in a non-ionic surfactant such as oleyl alcohol ethoxylate and the like.

The solvent system is preferably of the emollient solvent type. The solvent system can be composed of a mixture of low molecular weight polypropylene glycol, 10 to 30%, polyoxypropylene stearyl ether (the emollient solvent), 70 to 90%, and nonyl phenoxy polyoxyethylene ethanol, up to 0.5%. All percentages in this disclosure and the accompanying claims are in weight percent. Other solvents that can be used are polyoxypropylene (10) cetyl ether, castor oil, soy bean oil and oleic acid.

The pigment dispersion can be further stabilized with a neoalkoxy titanate coupling agent and emulsifiers such as nonyl phenoxy polyethoxylated alcohols, which emulsifiers have an HLB (hydrophylic lipophylic balance) value from 2 to 15. The solvent system is inert to the materials used in the printer, such as ink foams, print elements, pumps, tubing, print pads, and the like.

The formulation of the instant invention involves unique color combinations based on mixtures of organic pigments such as the phthalocyanines and results in strong colors with high purity. Other organic pigments that can be used are given in the General Composition table hereinafter.

The selection of the phthalocyanines for the blue ink is based on their dichroic properties. They reflect highly in the red region of the spectrum where the transmitted color is much greener.

The organic pigments such as the phthalocyanines can be used in different forms such as powder or chips or predispersed pigments in rosin esters and organic pigments flushed with non-ionic surfactants such as oleyl alcohol ethoxylates. The average particle size of the organic pigments is between 0.1 and 0.4.mu. for at least 98% of the particles.

Another component that may be included as an additive to the ink formulations is fumed silica with grafted polysiloxane groups. This additive controls the thioxtrophy of the ink, reduces surface tension and flattens the variation of the viscosity at different temperatures. At the same time, it reduces the hygroscopicity of the ink.

The present invention provides a new class of inks that are compatible with the polymeric materials used in contemporary printers. Examples of such inks are as follows:

It will be appreciated that the above are given by way of example only and one skilled in the art will recognize that other components having similar properties can be used in the practice of the invention.

The above embodiments have been given by way of illustration only, and other embodiments of the instant invention will be apparent to those skilled in the art from consideration of the detailed description. Accordingly, limitations on the instant invention are to be found only in the claims.