Electrostatic deposition

Details Electrostatic deposition Electrostatic deposition

1999-05-14

2001-06-12

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S031270, C106S031300, C106S031310, C106S031410, C106S031570, C106S031580, C106S031600, C106S031610, C106S031620, C106S031850, C106S031860, C106S031880

Reexamination Certificate

active

06245139

ABSTRACT:

TECHNICAL FIELD
This invention relates to deposition of materials by electrostatic means and particularly by droplet deposition.
BACKGROUND ART
Patent Co-operation Treaty publication No. WO93/11866 discloses an apparatus and method for deposition of droplets, for instance for printing, using a high resistivity carrier and chargeable particles in the carrier. The particles agglomerate during droplet formation and can be ejected from an ejection location on demand.
Deposition materials or inks for such equipment are disclosed in Patent Co-operation Treaty publication Nos. WO95/011414 and WO96/10058. All of these deposition materials or inks have particles of insoluble material which are agglomerated in the ejection apparatus using electrostatic forces.
It is now surprisingly been found that it is possible to prepare deposition materials, such as inks, which do not contain insoluble particles but which contain active or desired ingredients in solution which may also be ejected as droplets on demand from an apparatus of the type as discussed above.
It is an object of this invention therefore to provide inks which do not contain particles but which can be ejected from the apparatus discussed above.
DISCLOSURE OF THE INVENTION
In one form therefore the invention is said to reside in a deposition material for an electrostatic deposition apparatus, the material comprising a carrier liquid having insulative properties, a charging agent which is soluble in the carrier liquid, and a charge augmenting additive which is soluble in the carrier liquid.
In an alternate form the invention is said to reside in an ink for an electrostatic ink jet printer comprising a carrier liquid having insulative properties, a charging agent which is soluble in the carrier liquid, and a charge augmenting additive which is soluble in the carrier liquid and a toning agent.
These deposition materials or inks may be described as particle-less inks and they generally contain materials which are completely soluble in the chosen insulative carrier media and which appear to undergo some degree of ionisation in the solvent thus creating a charge carrier in the ink. These inks are made to eject from the apparatus discussed above on application of an electric field. Furthermore drop ejection is controllable by voltage modulation (pulsing) such that the ejection is of a drop-on-demand type.
The particle-less deposition materials or inks of the present invention may be useful for delivering, printing or applying any material that is soluble in the insulative solvent of the ink. Possible applications include printing using soluble dyes such as for the printing of fabrics, platemaking for printing processes where resin solutions for instance can be printed, varnishing for instance applying a gloss overcoat on prints using resin solutions, pharmaceutical dosage because of the ability to control the number of drops and security printing such as printing UV fluorescent dyes.
In a particular application the printing ink of the present invention can be used in combination with a colour printing process to provide a impermeable coating over a picture being printed.
In one preferred embodiment, the carrier liquid may comprise the active or desired ingredient in the printing process or there may be further included a further active ingredient which is also soluble in the carrier liquid. An example of a carrier liquid which is itself the desired active ingredient may be a resin which can be polymerised after deposition.
Where there is an added active ingredient the active ingredient may be those materials to be printed for a given application. Materials may be added to the carrier liquid to impart some feature to the printed ink deposit such as colour, adhesion, gloss, durability, electrical resistance and pharmacology. Examples include colour dyestuffs, fluorescent dyes, resins, adhesives, optical brighteners and pharmaceuticals.
One theory to which the applicants do not wish to be bound by which it is suggested that the present invention operates is that the charge augmenting additive enhances the kinetics of dissociation of the charging agent. Charging agents are added to the carrier liquid to introduce ionic species to the non-aqueous ink carrier liquid thereby increasing the mobility of the ink under the influence of an applied electric field and it has been found experimentally that the addition of a charge augmenting additive increases the degree of ionisation.
For instance, in the case of the preferred “metal soap” charging agents, the mechanism of charging appears to involve the formation of structures known as inverse micelles. These inverse micelles can undergo ionic dissociation whereby pairs of oppositely charged inverse micelles are formed, thereby forming ionic species within the carrier liquid. It has been found that the level of inverse micelle dissociation is dramatically increased in the presence of charge augmenting additives. The exact mechanism for this charge enhancement is unclear, however, it is thought that these additives introduce active sites whereby the kinetics of inverse micelle dissociation are significantly improved.
The carrier liquid may be any suitable liquid with the characteristics of a high resistivity and in which the charging agent and charge augmented additive as well as any active ingredient is soluble. The carrier liquid may include aliphatic hydrocarbons such as hexane, cyclohexane, iso-decane, Isopar (manufactured by Exxon) and Shellsol T (manufactured by Shell); aromatic hydrocarbons such as xylene, toluene and Solvesso 100 (manufactured by Exxon); chlorinated solvents such as diethylene chloride and chloroform; silicone oils such as dimethyl polysiloxane such as DC 200 (manufactured by Dow Corning) and the cyclic dimethyl polysiloxane such as DC 345 (manufactured by Dow Corning); monomer liquids such as esters of acrylic acid, esters of methacrylic acid and vinyl acetate and vegetable oils such as olive, safflower, sunflower, soya and linseed oil.
The charging agent may be any material that is soluble in the carrier liquid and that is capable of undergoing dissociation in non-aqueous media to form ionic species. Examples of such agents include metal salts such as lithium, cadmium, calcium, manganese and magnesium salts of heptanoic acid as well as zirconium, aluminium, cobalt and magnesium salts of 2-ethyl hexanoic acid.
The charge augmenting additives are carrier soluble materials that assist in the dissociation of the charging agent. A common feature of these charge augmenting additives is that they usually contain nitrogen groups (e.g. amine functionality).
Examples of these materials have been found to be:
Acryloid 958, Acryloid 917. These are polymeric oil additives made by Rohm and Haas.
OLOA 1200. This is a low molecular weight polyisobutylene succinimide made by Chevron Chemical Company.
Antaron V220, Antaron V216. These are alkylated poly vinyl pyrrolidones made by Gaf Chemicals.
Soy Lecithin. This is an oil soluble lecithin made by ICI Chemicals.
FOA-2. This is a petroleum additive made by Du Pont Chemicals and Pigments and consists of a methacrylate polymer.
There may be further included in the deposition material or ink formulation according to this invention further compounds such as property modifying agents. Such materials can be used to modify the physical properties of the deposition material or ink, including surface tension and viscosity, such that ink print performance is enhanced. Examples of suitable materials are: resins and polymers such as modified rosin esters, acrylic resins, vinyl resins and hydrocarbon resins; waxes such as polyethylene wax, hydrogenated castor oil, ester wax and paraffin wax; surface active agents including detergents, wetting agents and emulsifiers. Preservatives may also be included in the deposition material or ink.
This then generally explains the invention but to assist with understanding reference will now be made to a number of examples of formulation of deposition materials or inks.


REFERENCES:
patent: 5453121 (1995-09-01), Nic

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