US3108893A

US3108893A - Applying printed patterns electrostatically

Info

Publication number: US3108893A
Application number: US851150A
Authority: US
Inventors: Oliphant Keith Meredith
Original assignee: Research Laboratories of Australia Pty Ltd
Current assignee: Research Laboratories of Australia Pty Ltd
Priority date: 1958-11-07
Filing date: 1959-11-05
Publication date: 1963-10-29
Anticipated expiration: 1980-10-29
Also published as: FR1245790A; CH390961A; GB897227A

Description

Oct. 29, 1963 K. M. OLlPHANT 3,108,893

APPLYING PRINTED PATTERNS ELECTROSTATICALLY Filed Nov. 5, 1959 United States Patent 3,1il8,893 APPLYHJG PRENTED PATTERNS ELECTROTATICALLY Keith Meredith Oiiphant, Westbourne Park, South Aus tralia, Australia, assignor, by mesne assignments, to Research Laboratories oi Australia Limited, North Adelaide, South Australia, Australia, a corporation of South Australia, Australia Filed Nov. 5, 1959, Ser. No. 851,150 Claims priority, application Australia Nov. 7, 1958 4 (Iiaims. (Cl. 1171fi) This invention relates to a method and means for applying printed patterns electrostatically, with particular reference to patterns in paint, printing ink, lacquers, resins and dyes, such patterns being obtained after a uniform coating has been applied.

Previously patterns have been applied to surfaces by controlling the application of paint, printing ink and the like by the use of a mask, shield or grid of the desired shape or by means of a printing block or mat which ensures that the paint or ink is deposited only in desired areas and not elsewhere. Devices to control the pattern include printing blocks, silk screens, cut-out masks, type metal characters, lithographic plates and the like. The application of the paint or ink has been carried out by the use of brushes, knife coating, spray guns, air blushes, electrostatically assisted spray guns and jets, and electrocoating of surfaces from baths containing liquids of high electrical resistivity.

Difliculties arise in masking off the areas Where it is desired to avoid coating and in printing great care has to be exercised to put the ink only on the desired areas. To cover a surface completely with paint or the like it is known to assist the deposition of paint from a spray gun by means of a strong electric field initiated by about 100,000 volts. In another variation of this process an electrostatic field is used to drive liquid paint from an edge .through the air in the form of globules onto an object to be coated. Electrostatic painting therefore is already well known, according to which the paint particles are charged and carried to their site by an electrostatic field. It is also known to deposit particles by electrostatic means in developing electrostatic images.

The present invention differs in that the deposition of the paint particles by electrostatic means is not involved but said invention relates to the placing of paint particles by lateral movement according to an electrostatic pattern after the pigment particles have been applied.

The object of the present invention of course is to allow pigment or dye particles and binders to be applied in greater thicknesses and under eifective control, and to allow more normally painted surfaces to be patterned, this being achieved by locating and moving paint particles to specific areas after application of the pigment or dye particles has already taken place but before the particles and binders have been fixed in position by drying, polymerisation or chemical reaction.

The invention therefore consists in pie-coating a member or web which is to have a pigment dye or resin pattern applied to it, and while the coating is in an unset stage subjecting the coating to a pattern forming electric or magnetic field which will move the said pigment particles, dye, resin or the like to a required site in whole or in part.

The invention can be carried out simply by treating the means to be pigmented with a suitable paint, dye or ink or other medium and while still in the unset or fluid or plastic stage placing the medium between electrodes which are arranged to apply an electric field having the required potential and pattern, whereupon it will be found that the pigment particles or dye or the like already on the mate rial will be relocated and when the desired pattern has been obtained the material can be fixed in position according to any of the usual methods such as by the application of heat or other drying factor :for the pigment, resin or dye.

The invention depends for its operation on the effects of electric fields on insulating materials, pigments and the like wherein, if pigment particles are suspended in an insulating base which is of such a nature that the particles can move, the particles will acquire or possess a basic charge which will depend on the particles themselves or on coatings on the particles and such particles can then be moved depending on the direction of the field in relation to the magnitude and polarity of the charge on the particles.

A further effect and a contributing effect in some cases is the alteration of surface tension of a fluid such as an insulating liquid or combination of liquids or solution of solid in a liquid when an electrostatic stress is applied. It is found that a manifold increase in the wettability of the liquid for the surface occurs and further that a gross change in topography of the liquid surface occurs at po sitions of sharp changes of potential across the surface. The net result is to push the liquid from the electrified areas and concentrate it in an area not electrified.

It has been found for instance that a paint can be applied to a cloth web or other permeable material and the particles or paint layer constituting the paint mixture can then be moved or segregated according to a pattern.

In this connection it is possible to incorporate different pigment colours in the paint mixture and to separate these according to their colour by using the particles charge effect which may differ with colour to cause the particles of different colour to move to different localities depending on the electric field induced in pattern form to produce the pattern.

It has been found for example that by incorporating various coloured particles or dyes in a suitable insulating vehicle or carrier and applying to a material, by introducing electrostatic fields, some of the colours may move away from the charged areas while other colourswill be attracted to the charged areas so that while the initial application of the paint or dye to the material may give an initial overall uniform colour, this colour is then split into negatively and positively charged component parts with the result that the differently inherently charged particles move to different localities and thus produce coloured patterns.

'In another modification of the invention one uniform coating of one colour may first be applied and allowed to fix partially, following which another uniform coating of a second colour may be applied but this one is then subjected to electric stress in pattern form whereupon the second material is moved according to the pattern from some areas to expose the fixed or partly fixed first coating in the desired areas.

The first stage of the process therefore comprises vcoat ing the chosen backing material, which may for example be sheet metal, wood, plastic, cloth, paper, hardbo-ard, or (the like, with a uniform coating of fluid or semi-fluid coating composition such as a paint or printing ink or dye solution, characterised in that it is itself, or is disbursed in, an insulating vehicle such as a resin or hydrocarbon solvent or the like. The application of the coating can be effected by any known means such as spray painting, dip coating, knife or doctor blade coating, electrostatic spray painting, brush coating, roller coating or the like, characterised in that the coating remains fluid, mobile or plastic, ready for the second step of applying an electric field or stress.

An electric stress is applied for example by establishing a high potential and consequently high electric field strength between the backing that has been coated and a suitable point array which has a predetermined pattern. For example the points may be arranged in a geometrical pattern of lines, polygonal figures, or irregular figures and an electric field of 10,000 volts per inch field stren 1 applied between the points and the backing. Under the influence of the electric field an intense corona discharge is set up from the points which moves the particles of the coating in the desired pattern. The stage of the invention comprises drying or curing the coating to fix the pattern so obtained either during or after the application of the electric field, depending on the result desired.

Curing may be delayed if desired and the process repeated with a second coating or more coatings, or the process can be carried out after drying and curing of the first coating or other coatings. In this way the process can be used for printing and over-printing of patterns.

As stated above, the patterns are produced by the configuration of the points, wires or other electrodes from which the corona discharge or electric field is applied. In another modification of the invention a grid or other pattern is interpolated between the points or wires and held at a desired potential equal to or less than that of the original points or Wires and the pattern or the coating is accordingly modified.

From the foregoing it will be realised that the basic feature of the invention consists in first applying a pigment, dy paint, ink or the like to the means on which a pad En is to be produced and then moving the particles or dyes according to the initial electrical pattern, such particles or dyes moving to selected areas or portions which will correspond to the electrical pattern produced through the material or web.

The present invention uses as coatings paints, inks, pigments, dyes, lacquers, waxes, resins, gums, oils, adhesives, or solutions, characterised in that in the fluid or plastic state they have an electrical resistivity greater than ohms per cubic centimeter to obtain a substantial eifect with very small currents.

Selection of the coating depends on the use intended and the photographic, electrical, mechanical or chemical characteristics required. Normally the coating will be a filmdorrning material or vehicle selected from a large number of substances which will give the desired flexibility, colour and hiding power. Suitable vehicles include the following: natural gums and resins such as shellac, synthetic resins such as the thermosetting resins of the phenolic amino (urea), protein (casein), alkyd (Glyptals), styrenated alkyds, allyl (petroleum plastics), silicone plastics and the thermoplastic resins, cellulose, cellulose esters such as cellulose acetate and cellulose nitrate, and the ethenoid plastics such as the ethylene derivatives, ethylene polymers, vinyl polymers, styrene polymers, and polymethyl methacrylate. The following are also suitable in some applications: waxes such as paraifin wax, carnauba wax, beeswax, and such as dammar, dragons blood, copal and the like, dispersed in suitable solvents for these materials.

As in the manufacture of paints, varnishes, inks and the like, the pigment or dye may be suspended in the vehicle in many ways. For example:

(a) The vehicle is thinned with a solvent and mixed with the powdered pigment,

(b) The vehicle is melted and mixed with the pigment by mechanical means,

(c) The plastic vehicle is blended with the pigment in a pug mill, ball mill, rod mill or other mechanical mixer,

(d) The vehicle is co-precipitated or coated with the pigment by electrostatic coating means.

The proportions of the pigment in relation to the vehicle or binder may be varied widely as in most paint compositions and formulations, and will depend more on the end use of the coating than on the present process. Any number of coatings of normal paint and ink thicknesses may be applied, such as two or three coatings the FIG. 1 illustrates the base sheet with a coating in'the fluid condition,

FIG. 2 illustrates the charging principle,

FIG. 3 illustrates the exposure to the charge or electric field, but using a modulating grid,

FIG. 4 illustrates the patterned sheet after curing,

FIG. 5 illustrates a second step in which a further coating is applied, and

FIG. 6 illustrates the patterned sheet after the application of a second pattern.

In FIG. 1 there is shown the layer of backing material 2 with a uniform coating of fluid paint designated 1.

In FIG. 2 the composite layer (2,1) is shown in relationship to a charging array comprising a holding frame 3 with embedded needles 4 and a second electrode 3' connected to a power pack 5 which can supply up to 20,000 volts DC. potential when required. The corona discharge is designated 6, and movement of the paint is indicated. In FIG. 3 the charging array 3, 4 is associated with an earthed grid 8 to set up a modified electric stress and movement in the coating 1 on the backing sheet or layer 2.

In FIG. 4 is shown the patterned coating 1 of FIG. 2 which is now patterned both in terms of thickness and area after fixing by drying, curing or both.

In FIG. 5 is shown a further coating 7 applied over the top of the now patterned coating 1, preparatory to forming a further pattern.

In FIG. 6 is shown the coating 7 after application of a further electrical pattern forming step similar to that in FIG. 3, and the consequent pattern 7 superimposed on the pattern 1.

It will be appreciated that the pattern 1 can be of such a nature as regards conducting or insulating properties that it exercies an effect on coating 7 if desired.

For the better understanding of the invention, the following examples are given, but the scope of the invention is not limited to these. 7 (a) Base material:

(l) Aluminium,

plate, (2) Art paper, kraft paper, lithographic paper or other paper, (3) Cloth or other textile, (4) Hardboard, plasters, Wood and the like. (b) Coating material:

(1) Alkyd resin base paints, (2) Polyvinyl chloride base coatings, (3) Phenolic resin coating formulations, (4) Polymethylmethacrylate formulations, (5) Polystyrene base formulations, (6) Silicone resin paints, (7) Epoxy resin coating formulations,

(8) Printing ink compositions. (c) Pigments and dyes for (b):

(1) Inorganic pigments such as iron oxides, lead chromate, chromium oxides and the like, (2) Organic pigments such as Monolite Red,

Monolite Yellow, and the like, (3) Organic dyestufis, (4) Spirit and oil soluble dyes such as Waxoline Red, Waxoline Yellow, and the like. (d) Sealers:

(1) Alkyd resin base paints, (2) Polyvinyl chloride base coatings, (3) Phenolic resin coating formulations, (4) Polymethylmethacrylate formulations, (5) Polystyrene base formulations, (6) Silicone resin paints,

brass, steel or other metal or alloy R.C.I. 5035 Toluidine Red 67 P-78650 Beckosol 134 Xylol 100 This was ground in a ball mill and then the following added:

Parts by weight P-786-50 Beckosol 429 Xylol 61 Cobalt Nuodox 2.5

Before the roller coated coating was dry, it was placed under an array of needle points such as shown in FIG. 3 of the drawings and spaced on half inch centers and in rows a half inch apart and about one inch from the pattern. An electric field of 10,000 volts per inch was ap plied and a pattern corresponding to the array was produced on the painted surface in well defined oval zones. The coating was then dried, giving a finished pattern as shown in FIG. 4 of the drawings.

(2) A backing material, in this case art paper, was coated with an alkyd resin coating material made up in the following manner similar to printing ink:

Grams Rhodene L9/50 resin 100 Iron oxide 120 Waxoline nigrosine 20 4% cobalt naphthenate 0.5 4% manganese naphthenate 0.5 Toluene 100 These materials were milled together in a ball mill for eight hours.

This composition was diluted to suit spraying purposes and sprayed onto the art paper. While it was still plastic or fluid it was subjected to an electric field in pattern form from a wire grid having 9% inch openings activated by an electric field of 15,000 volts per inch strength at a distance of one inch.

A pattern corresponding to the wire grid was produced in the paint which was then fixed by drying and heating.

(3) A hardboard backing material was coated by brush coating with a non-permanent coating of the following type:

Grams Rhodene L9/5O resin 200 Carbon black (gas black) 120 Waxoline nigrosine 20 Castor oil 20 These materials were milled together in a ball mill for for four hours before being applied by brush coating.

This coating was then subjected to an electric field in pattern form produced by putting an earthed metal mask or semi-conductor mask between the charging points earlier described and the coating so that the mask shielded the coating from the electric stress in selected areas. Such a metal mask can be in the form of lettering or other characters.

It was found also that this non-hardening coating could be transferred easily to another surface. This is also true of the coatings produced in Examples 1 and 2 if they are transferred while still wet or plastic, for example by pressing them into contact with some other surface.

It will be seen that the patterned painted surface can be used and re-used and so constitutes a means of printing substantid thicknesses of paint, ink and the like, for example 1, 2 or 3 mgm. per square centimetre, to some other surface such as paper, wood, plastic or cloth. The process can of course be continuous and in colour, the

novel feature being that the coated pattern is independent of the actual coating process. This is unlike electro-development processes where the pigment is carried to the site, the pigment being first applied in the desired thickness and being subsequently moved to produce the pattern.

In this specification the following trademarks have been referred to:

R.'C.I. 5 035 Toluidine Red is a red pigment.

P-786*50 Beckosol is a synthetic resin epoxy ester acid value 3, specific gravity 0.9 50-.96, type of oil dehydrated castor.

Cobalt Nuodex is a registered trademark for cobalt naphthenate.

Rhodene L9/50 is a trademark of a linseed oil modified alkyd resin, oxidising typeoil length 40%, acid value 2535, specific gravity at 20 C.- 0.980.99'.

Waxoline Nigrosine is a trademark of I.C.I. and is a wax soluble dye.

I claim:

1. The method of producing a pattern on a solid surface characterised by:

forming a paint by suspending a pigment and binding medium in a fluid insulating vehicle whereby said pigment develops an electrical charge in relation to said insulating vehicle,

applying said paint to a base,

placing said base on a first electrode,

placing a second electrode, which is shaped to produce an electrical pattern of configuration corresponding to the placement required for the pigment of the paint, over said base but spaced therefrom,

and while said paint is still wet applying an electrical potential between said first and said second electrodes and maintaining said potential until said pigment particles of said paint are moved laterally on said base to define the said pattern,

and evaporating the said fluid insulating medium to dry said paint and fix the pigment to said base.

2. The method of producing a pattern on a solid surface characterised by:

forming a paint by suspending a pigment and binding medium in a rfluid insulating vehicle whereby said pigment develops an electrical charge in relation to said insulating vehicle,

applying said paint to a base,

placing said base between a first electrode and a second electrode,

placing a grid which is shaped to produce an electrical pattern of configuration corresponding to the placement required for the pigment of the paint, between said base and one said electrode but spaced there from and while said paint is still wet applying an electrical potential between said first and said second electrodes and maintaining said potential until said pigment particles of said paint are moved laterally on said base to define the said pattern,

3. The method of producing a pattern on a solid surface characterised by:

forming a paint by suspending two pigments of diflerent colour and binding medium in a fluid insulating vehicle whereby one said pigment develops a posiitive electrical charge in relation to said insulating vehicle and said other pigment develops a negative electrical charge in relation to said insulating vehicle, applying said paint to a base,

placing said base on a first electrode,

and while said paint is still wet applying an electrical potential between said first and said second electrodes and maintaining said potential until said pigment particles of said paint are moved laterally on said base according to their charge to define the said pattern, in two colors,

4; The method of producing a pattern on a solid surface characterised by:

forming a paint of one color by suspending a pigment and binding medium in a fluid insulating vehicle whereby said pigment develops an electrical charge in relation to said insulating vehicle,

I applying a paint of another color to a base and drying same,

applying said paint of the first said color to said base,

placing said base on a first electrode,

References Cited in the file of this patent UNITED STATES PATENTS Pollock et a1. July 14,

Great Britain Sept. 15,

Claims

4. THE METHOD OF PRODUCING A PATTERN ON A SOLID SURFACE CHARACTERISED BY: FORMING A PAINT OF ONE COLOR BY SUSPENDING A PIGMENT AND BINDING MEDIUM IN A FLUID INSULATING VEHICLE WHEREBY SAID PIGMENT DEVELOPS AN ELECTRICAL CHARGE IN RELATION TO SAID INSULATING VEHICLE, APPLYING A PAINT OF ANOTHER COLOR TO A BASE AND DRYING SAME, APPLYING SAID PAINT OF THE FIRST SAID COLOR TO SAID BASE, PLACING SAID BAE ON A FIRST ELECTRODE, PLACING A SECOND ELECTRODE, WHICH IS SHAPED TO PRODUCE AN ELECTRICAL PATTERN OF CONFIGURATION CORRESPONDING TO THE PLACEMENT REQUIRED FOR THEPIGMENT OF THE PAINT, OVER SAID BASE BUT SPACED THEREFROM, AND WHILE SAID PAINT IS STILL WET APPLYING AN ELECTRICAL POTENTIAL BETWEEN SAID FIRST AND SAID SECOND ELECTRODES AND MAINTAINING SAID POTENTIAL UNTIO SAID PIGMENT PARTICLES OF SAID PAINT ARE MOVED LATERALLY ON SAID BASE TO DEFINE THE SAID PATTERN, AND EVAPORATING THE SAID FLUID INSULATING MEDIUM TO DRY SAID PAINT AND FIX THE PIGMENT TO SAID BASE.