US3334047A - Liquid dispersible toner for electrophotography - Google Patents

Description

United States Patent 3,334,047 LIQUID DISPERSIBLE TONER FOR ELECTROPHOTOGRAPHY Josef Matkan, Malvern, South Australia, Australia, as-

signor to Research Laboratories of Australia Limited, North Adelaide, South Australia, Australia No Drawing. Filed May 8, 1963, Ser. No. 278,981 Claims priority, application Australia, May 16, 1962,

1 Claim. ((31. 25262.1)

This invention relates to reproduction by electrophotography, and particularly to the reproduction of colour by electrophotography in such form as to be substantially similar in hue, balance and intensity to that produced by lithographic and other mechanical printing methods and colour photography.

It is known that electrophotographic images can be produced in any desired colour by one skilled in the art, and toner formulations capable of producing images of various colours are known. It is also known to produce such images in a multiplicity of colours by the use of repetition exposure and development procedures on the same electrophotographic sheet.

Colour printing by xerographic methods usually involves the use of a photo-sensitive material on a relatively conducting backing or supporting layer such as a paper or metal sheet or film, the photo-sensitive film comprising a particulate photoconductor such as zinc oxide or the like in a resin binder, such coating resin being sufiiciently hardened or polymerised so that its electrical properties are not affected by environmental changes during production of the print. Such a sheet is first sensitised by subjecting it to a corona discharge from a series of wires or points held at a relatively high DC. potential above the base upon which the sheet is placed, the polarity being such as to impart a negative potential to the photo-layer in case such photo-layer is composed of zinc oxide which is not capable of supporting a positive electrostatic charge. The sheet is then subjected to a light pattern corresponding to the requirements of the first colour to be applied, and after this exposure the sheet is developed in a dish or bath or by means of some other device containing the liquid toner dispersion of the appropriate colour. It is preferable to dry the sheet after this development step as this allows the first deposited image to become sufiiciently adherent to the photo-surface to enable it to remain in position during subsequent handling.

Subsequent colours are deposited in turn by repetition of the charge, expose, develop and dry cycle, the exposure step in each instance imposing the correct light pattern corresponding with the particular colour being reproduced at that time. Provided the successive images are placed in register with each other using a balanced set of com patible, overprinting toners, the resultantimage will be substantially similar to that which would be produced by a mechanical printing using the same separations and inks corresponding in hue to the toners used.

One of the problems in overprinting xerographically is that the developers tend to afiect the charging characteristic and bleeding away of the charge on the photoconductor surface and therefore while the first colour can be put down in the normal manner, this colour can then modify the charge which different areas can take when preparing the photoconductor for the application of the second colour, the position being intensified when an attempt is made to charge through the first two colours in preparation for the application of a third colour.

The problem which is thus raised is that while overprinting by mechanical means is a simple matter as each block applies the ink in proportion to the ink carried by the block surface, in xerography the electrostatic pattern itself is varied by the application of the colours and therefore unless complete overprinting is obtained, the result is not a true representation of the image which is projected on to the surface in each of the succeeding stages.

To obtain complete over-printing the image areas must contain an insulating component either within the image forming pigment structure or as a layer over the image such component being capable of supporting an electrostatic charge in case the surface is re-charged for the subsequent colour step. This is especially the case with pigments which are so much conductive that the photoconductive layer beneath them cannot become charged. In such cases the said insulating component is the only medium capable of supporting a charge if the image is recharged with the purpose of depositing another colour which has to overlap the previous colour.

In the prior art process of over-printing by electrophotographic methods it was customary to incorporate insulating resins into the developers or toners such resins being capable of supporting an electrostatic charge when co-deposited with conductive pigments on to image areas. The quantity of such insulating resin required to be present for charge holding purposes is generally so high that it may prevent intense colour deposition or result in changes in the colour value of the system. This large quantity ofinsulating resin is required because such resin being essentially fully or partially soluble in the liquid developer vehicle it will dissolve or soften to a greater or lesser extent during the process of developing any subsequent colours even if the liquid vehicle used for each subsequent colour is progressively weaker in solvent power than the liquid vehicle from which the previous image or colour containing the insulating resin has been deposited. An improved approach was to introduce the insulating resin into the image areas in the form of a film over the image forming pigment or other particulate matter and such film forming resin being applied from solution in the developer liquid during the process of developing or such insulating resin being deposited as an overall film by dipping the print containing the conductive image in a weak solution of such resin. An extremely exact viscosity control of the resin solution is necessary in order to obtain a uniform film deposit.

It has been further proposed to use a wax or waxy substance absorbed on the surface of a pigment or pigmented particle, such wax or waxy substance being capable of supporting an electrostatic charge and thus rendering the deposited pigment or pigmented particle amenable to over-printing. Waxy materials are generally opaque and certain waxes are at least slightly yellow, which results in formulation adjustments being necessary to provide toners of the hue and intensity necessary to simulate the results of lithographic printing and the like.

In accordance with the present invention there are provided method of and means for producing developers or toners suitable for dispersion in appropriate liquid vehicles such toners being capable of developing an electrostatic image in any desired colour and such developed images containing sufiicient insulating matter so as to be capable of supporting an electrostatic charge upon subsequent and repeated subjecting to a corona discharge and furthermore such insulating matter being deposited on to the image areas in such form that it will not be readily removed or effected by repeated immersions in the developer vehicle and thereby rendering images containing such insulating matter capable of being overprinted by other colours in the process of repeated and subsequent developing in liquid vehicles containing toners of other colours.

Accordingly, an object of this invention is to provide improved method of and means for the production of toners of various colours which are capable of being over-printed by one or more colours in the electrophotographic process using liquid toner vehicles.

A further object of this invention is to provide method of and means for the production and use of toners of various colours capable of simulating the hue, intensity, transparency and over-printing characteristics of lithographic, gravure and letterpress inks and capable of reproducing multi-colour images produced by colour photography when such toners are used under controlled conditions as hereafter defined.

Another object of this invention is to provide method of and means for the production of a four colour system of toners capable of simulating the hue, intensity, transparency and over-printing characteristics of standard lithographic four colour ink systems.

Yet another object of this invention is to provide a system of toners in various colours all of which contain insulating matter for over-printing purposes and such insulating matter being sufliciently resistant to solvent action after deposition on to image areas whereby it becomes possible to use one and the same type of liquid vehicle for developing of each colour without the necessity of progressively decreasing the solvent power of successive vehicle fluids.

A further object of this invention is to provide as an insulating coating on the pigment or pigmented particles a layer which is substantially transparent and colourless so that the colour hue and intensity of the pigments or pigmented particles are not modified by the addition of this layer.

Yet another object of this invention is to provide an insulating coating on the pigment or pigmented particles, such coating having such chemical and electrical characteristics that the dispersed toner does not suffer electrical or chemical deterioration in the dispersed form due to reaction between such coating and the dispersion medium.

A further object of this invention is to provide as a transparent colourless insulating coating around the pigment or pigmented particles, a layer of material dispersible in the preferred carrier liquids in such form that the image deposit derived from such dispersions, upon drying of the excess liquid, forms a self fixing image.

I have found that thermoplastic polymers of ethyl, methyl, n-butyl and isobutyl methacrylate esters can be incorporated with toners to provide the insulating matter in image areas for overprinting purposes, and that the poly-acrylic layer so formed on each pigment or pigmented particle is clear and transparent, maintains its insulating properties when dispersed in a highly diluted form in a liquid toner dispersion, and due to the nonreactive nature of this layer the toner suspension retains electrical and chemical stability for long periods.

In one embodiment of the invention I propose to introduce the high polymer acrylic resin into the liquid developer system by first dispersing the pigment or other particulate matter in a solution of the poly-acrylic resin such solution being obtained by dissolving the resin in an aromatic hydrocarbon such as toluene and then to suspend such dispersion in the developer vehicle fluid.

In the second embodiment of this invention it is proposed to grind or mill the pigment or other particulate matter with a wetting agent as known in the prior art processes and then to disperse such pre-wetted pigment or other particulate matter in a solution of the polyacrylic resin and then to suspend such dispersion in the developer vehicle fluid.

In the third embodiment of this invention it is proposed to introduce the insulating poly-acrylic resin substance into the liquid developer system by first grinding or milling a liquid developer or toner concentrate such as known in the prior art and comprised of a pigment or other particulate matter dispersed in oil or resin or oleoresinous varnish with the solution of the poly-acrylic resin, such solution being prepared by dissolving the polyacrylic resin in an aromatic hydrocarbon liquid such as toluene and then suspending such developer or toner concentrate blended with the solution of the poly-acrylic substance in the developer vehicle fluid.

In the fourth embodiment of this invention it is proposed to introduce the insulating poly-acrylic resin into the liquid development system by dispersing the polyacrylic resin in the developer vehicle fluid itself by first dissolving the poly-acrylic resin in an appropriate quantity of solvent miscible with the vehicle fluid and sufficient to give a stable suspension of the poly-acrylic resin at ambient temperatures and then dispersing such solution or suspension of poly-acrylic matter in the bulk of the developer vehicle fluid into which pure pigment or other particulate matter or pre-wetted pigment or developer or toner concentrates such as known in the prior art is dispersed either prior to or after the addition of the poly-acrylic suspension or solution.

The following examples containing detailed descriptions of the method of and means for producing liquid developers or toners containing poly-acrylic insulating matter in accordance with the above embodiments of the invention together with the examples of developer or toner formulations will give a better understanding of this invention and its advantages and it will be realised that this invention is not limited to the materials and to the combinations and proportioning thereof as cited in the following examples and that therefore one skilled in the art of preparing liquid developers or toners for electrostatic printing processes will be in the position to adapt the teachings of this invention to particular requirements depending from case to case on the characteristics of pigments or other particulate matter or oils or resins or oleoresinous varnishes or other matter or the developer fluid which may be desired to be used in a particular liquid developer system and to select and proportion suitable poly-acrylic resin substances for incorporation into liquid developer systems as insulating matter for over-printing purposes in accordance with this invention and it will also be realised that more than one polyacrylic resin substance can be used in conjunction as may be preferred for the end result from case to case.

The photoconductive material which can be used in the following examples can be a relatively conducting backing or support such as paper or metal sheet or film upon which is deposited a coating comprising a particulate photoconductor capable of supporting a negative electrostatic charge such as zinc oxide or the like in a resin binder and such resin binder being capable of attaining a degree of hardness suflicient to prevent the resin from being attacked or softened during contact with the carrier fluid. The following photoconductive coating can be used in the liquid developer process:

Grams Zinc oxide Durham Special Z 900 Rhodene M8/50 600 Toluol 200 Manganese naphthenate (4%) 2.5 Cobalt naphthenate (3%) 2.5

The ingredients can be milled together, diluted if required, and then deposited on a relatively conducting support by any known coating method. An alternative to this formulation is the following:

Grams Zinc oxide Durham Special Z 750 DYAL XOR 36 416 Toluol 250 Lead naphthenate (15%) 8.5 Manganese naphthenate (4%) 3.5

Here again, the ingredients can be milled together, diluted if required, and deposited on to a support by any known coating method. The photo-conductive material thus prepared and sufliciently hardened can be now sensitised by subjecting it to a corona discharge from a series of wires or points held at a relatively high direct current potential such as 500-10000 volts above the base plate upon which the material is placed, the polarity being such as to impart a negative electrostatic blanket charge to the photoconductive layer. The material is then subjected to a light or X-ray pattern whereby non image areas are rendered conductive and permit the charge to dissipate into the relatively conducting support or backing whereas under the shielded image areas a latent image consisting of the remaining negative charge is formed.

This latent image can now be rendered visible by developing it in any one of the liquid developers hereafter described. The developing step can be performed by immersing the photo-conductive material in a vessel containing the liquid developer, or by mechanical means such as wet roller and squeegee, or cascading and the like.

It should be noted that an image developed by any one of the toners described in the following examples dispersed in the particular developed vehicle fluid as stipulated for such particular toner can be over-printed with one or more images in any colour by using any of the other toners as defined in the following examples wherever it is stipulated that such toner is dispersible in the same developer vehicle fluid as used for the preceding toner.

Example 1 Grams Lucite 46, 22% solution in toluol 100 Microlith Blue 4 GT 11 These components are mixed together by grinding such as for instance in a ball mill or roller mill or by the use of a high speed rotary mixer such as a food mixer and the resulting toner concentrate dispersed in the carrier liquid in the proportion of 0.5-5 grams toner concentrate/ 100 m1. carrier liquid. Over-printing and self fixing characteristics are achieved with this toner dispersed in each of the carrier liquids n-heptane, n-hexane, cyclohexane, solvent X55, solvent X4, and Solvesso 100.

Example 2 For the Lucite 46 of Example 1 is substituted n-butyl methacrylate polymer, such as for example Lucite 44, the resultant toner concentrate being suitable for dispersion in cyclohexane, n-heptane, n-hexane, solvent X55 and solvent X4.

Example 3 Grams Lucite 46, 25% solution in toluol 100 Permanent Red FRR 11 These components are milled together by grinding in a ball mill or roller mill and the resulting toner concentrate is dispersed in the carrier liquid in the proportion 0.5-5 grams toner concentrate/100 ml. carrier liquid. Suitable carrier liquids are nheptane, n-hexane, cyclohexane, solvent X55 and solvent X4.

Example 4 Grams Microlith Black CT 10 Microlith Blue 4GT 5 Lucite 46, 25 solution in toluol 40 The components are milled or mixed together as in Example 1 and the resultant concentrate dispersed in carrier liquid in the proportions 0.2-5 grams concentrate/100 ml. carrier liquid. Suitable carrier liquids are solvent X55, n-heptane and cyclohexane.

Example 5 Grams Permanent Yellow GG 40 Polymerised Linseed Oil No. 160

These components are milled together in a ball mill or roller mill and 0.5- grams of the resultant paste dispersed in 5-10 m]. of a 25% solution of Lucite 46 in toluol. The resultant cream is dispersed in m1. carrier liquid such as n-hexane, n-heptane, cyclohexane, solvent X55 or solvent X4.

Example 6 The Lucite 46 of Example 5 is replaced with n-butyl methacrylate polymer, such as Lucite 44.

Example 7 Grams Brillfast Rose Red pigment No. 4444 20 Brillfast Geranium pigment No. 3543 20 Calcium resinate varnish in bodied linseed oil (25% resin) 50 These components are milled together in a roller mill and 10 grams of the resultant concentrate mixed with 4 grams of a 25% solution of Lucite 46 in toluene. The resultant toner cream is dispersed in carrier liquid in the proportion 0.2-2 grams concentrate/100 ml. carrier liquid. Suitable carrier liquids are n-hexane, n-heptane, cyclohexane, and solvent X4, solvent X55.

Example 8 Grams Microlith Blue 4 GT 180 Superbeckosol 1352 360 Bodied linseed oil These components are milled together in a roller mill or similar and 30 grams of the resultant concentrate are mixed with 14 grams of a 25 solution of Lucite 46 in toluene, and the resultant cream dispersed in the carrier liquid in the ratio 0.2-5 grams toner concentrate/100 ml. carrier liquid. Suitable carrier liquids are n-heptane, cyclohexane, and solvent X4, solvent X55.

Example 9 A 25% solution of an isobutyl methacrylate polymer, such as Lucite 45 is dispersed in cyclohexane and added to the carrier liquid so that 100 ml. carrier liquid contains 0.5-10 grams Lucite 45. Microlith Blue pigment 4 GT is then stirred into the dispersion in the proportion 0.1-1 gram pigment/100 m1. carrier liquid. Suitable carrier liquids are n-heptane, n-hexane, cyclohexane, solvent X55, solvent X4, and Solvesso 100.

Example 10 For the Microlith Blue 4 GT pigment of Example 9 is substituted an equal weight of the magenta pigment B-rillfast Rose Red 4444.

Example 11 A 20% solution of a high polymer methyl methacrylate such as Lucite 41 in toluene is substituted for the Lucite 45 of Example 9. This toner is suitable for use in the carrier liquid containing high proportions of aromatic hydrocarbons such as Solvesso 100 or mineral turpentine.

Example 12 A 20% solution of a high polymer ethyl methacrylate such as Lucite 42 in toluene is substituted for the Lucite 45 of Example 9. This polymer is suitable for use in conjunction with the carrier liquids perchloroethylene, carbon tetrachloride, trichlorotrifluoroethane, n-hexane, solvent X55, and Solvesso 100.

Trade names of materials mentioned in the above examples are as follows:

Rhodene M8/50an isophthalic short oil alkyd by Polymer Corp.

DYAL XOR 36an ether resin by Sherwin Williams Co.

Lucite 41a very high molecular weight polymethyl methacrylate, sp. gr. 1.19, dielectric constant 3.6, manufactured by E. I. du Pont de Nemours & Co. Inc.

Lucite 42-a very high molecular weight polymethyl methacrylate, sp. gr. 1.12, dielectric constant 3.5, manufactured by E. I. du Pont de Nemours & Co. Inc.

Lucite 44a high molecular weight polymer of n-butyl methacrylate, sp. gr. 1.06, dielectric constant 3.2. manufactured by E. I. du Pont de Nemours & Co. Inc.

Lucite 45-a high molecular weight polymer of isobutyl methacrylate, sp. gr. 1.05, dielectric constant 2.7, manufactured by E. I. du Pont de Nemours & Co. Inc.

Lucite 46a high molecular weight 50/50 co-polymer of n-butyl and iso-butyl methacrylate, sp. gr. 1.05, dielectric constant 2.7 manufactured by E. I. du Pont de Nemours & Co. Inc.

Microlith Blue 4 GT-a green shade phthalocyanine blue pigment manufactured by Ciba Ltd., Switzerland.

Microlith Black CTa processed carbon black manufactured by Ciba Ltd., Switzerland.

Permanent Yellow GG-a transparent disazo pigment manufactured by Farbwerke Hoechst Ag., Germany.

Permanent Red FRR-A monoazo pigment manufac tured by Farbwerke Hoechst Ag., Germany.

Brillfast Rose Red 4444-a phospho-tungsto-molybdic acid toner of basic dyes, manufactured by J. W. & T. A. Smith Ltd., UK.

Brillfast Geranium 3543--a yellow shade red pigment manufactured by I. W. & T. A. Smith Ltd., U.K.

Superbeckosol 1352an isophthalic alkyd resin, acid no 3-6, oil length 60% type of oil-semi-drying, Sp. Gr. 0.940 manufactured by Reichhold Chemical Inc. U.S.A.

Solvesso 100a high aromatic hydrocarbon solvent, flash point 46 C., Kauri Butanol value 92, Sp. Gr. 0.8756 manufactured by Esso Oil Co.

Solvent X55-a substantially aliphatic hydrocarbon solvent, Kauri-Butanol value 40, Sp. Gr. 0.720 manufactured by Shell Chemical (Aust) Pty. Ltd.

Solvent X4-a substantially aliphatic hydrocarbon solvent, Kauri-Butanol value 30, Sp. Gr. 0.670 manufactured by Shell Chemical (Aust) Pty. Ltd.

What I claim is:

A method of providing a liquid toner for electrophotography comprising intimately dispersing pigment particles and a substantially transparent polyacrylic resin in an hydrocarbon carrier liquid that is not a solvent for said resin and until a uniform suspension is obtained, said carrier liquid being selected from the group consisting of n-heptane, n-hexane, and cyclohexane, said pigment being present in the amount of at least about ten percent by weight based on the weight of said resin, and said pigment and resin in combination comprising between about 0.2 to 5 grams per milliliters of carrier liquid, the pigment particles being first coated with linseed oil and then mixed with a solution of said resin prior to dispersing the pigment particles and the resin in said carrier liquid.

References Cited UNITED STATES PATENTS 2,891,911 6/ 1959 Mayer et al. 25262.1 2,907,674 10/1959 Metcalfe et al. 25262.1 XR 3,076,722 5/1963 Greig 25262.1

LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, Examiner.

I. D. WELSH, Assistant Examiner.