Toning method and member for electrostatography

A toning method and member for electrostatography wherein a recording member containing information on its image bearing surface in the form of electrostatic latent images of one polarity is toned by attracting to such latent images toner material of opposite polarity including providing a carrier or toning member according to the invention containing on at least one surface thereof a dry pre-toner coating; activating such pre-toner coating with an insulative solvent to thereby solvate and confer opposite polarity to such pre-toner coating contained thereon while rendering such pre-toner coating releasable from the carrier member; establishing virtual contact between the activated and releasable pre-toner coating on the carrier member and the image bearing surface of the recording member; transferring the pre-toner coating in image configuration onto the recording member by attraction to the latent images to form toner deposits thereon; and separating the carrier member from the recording member.

FIELD OF THE INVENTION 
This invention relates generally to electrostatography, and, more 
particularly, to a method of toning electrostatic latent images by means 
of a novel toning member. 
BACKGROUND OF THE INVENTION 
Electrophotography and electrostatic printing are well known image 
reproduction methods as is the reproduction of color images by these 
methods, for instance, in color copiers, color printers and color 
proofers. 
In electrophotographic color copiers, the color original is projected onto 
a photoconductor sequentially through several color separation filters, 
such as blue, green and red. These filters separate the yellow, magenta 
and cyan color components of the original, respectively. Such color 
components then are sequentially toned on the photoconductor with toners 
of appropriate colors. The toner deposits then are sequentially 
transferred to a receptor to reproduce the original. In many instances, a 
black color also is used to enhance contrast. 
The main difference between electrophotographic color printers and color 
copiers is that in color printers, the color original is scanned, the 
separated color components are electronically processed, digitized and 
stored if so desired. Such electronic data then is used to expose the 
photoconductor by means of a laser scanner. 
In electrophotographic color proofing, the photoconductor is exposed 
sequentially to color separation films and toned sequentially with toners 
of appropriate colors. The color toner deposits then are transferred 
sequentially to a receptor, such as printing stock paper. Such pre-press 
color proofing processes are disclosed, for example, in U.S. Pat. Nos. 
3,809,555 and 3,862,848. An apparatus for the production of 
electrophotographic pre-press proofs is described, for example, in U.S. 
Pat. Nos. 4,556,309 and 4,557,583. 
It is known that for high image quality in electrophotographic color 
reproduction processes it is necessary to use fine particle size liquid 
toners. In certain such processes, for instance in color proofing, it is 
essential to have very uniformly filled in solid image areas. 
Additionally, the density of the image areas must be within narrow 
tolerances as specifically required over each proof and from proof to 
proof. 
With liquid toners, however, it is necessary to operate at slow toning 
speeds in order to obtain uniform fill-in of solid images without any 
appreciable variation in the required image density. Variations in fill-in 
and density, at least in part, are caused by liquid toners being very 
sensitive to minor surface voltage or charge density variations on the 
photoconductor. These variations are common and result in differences in 
the rate of toner attraction. 
Slow toning appears to compensate for such differences or variations, 
provided they are not more than about 5 to 7 percent of the nominal 
surface voltage. Slow toning, however, slows down the throughput and, for 
economic reasons, there is an obvious need for fast throughput. 
The method of the invention provides virtually instantaneous liquid toning 
whereby complete fill-in of solid image areas at any required density can 
be obtained. Such toning virtually provides no variations in image density 
which can be caused by surface voltage variations on the photoconductor, 
even where such voltage variations can be 10 or even 20 percent of the 
nominal surface voltage. The method of the invention particularly is 
applicable to color proofers, color copiers, color printers and the like, 
henceforth referred to in general as color printers. The method, however, 
also is applicable to black and white or single color processes. 
SUMMARY OF THE INVENTION 
This invention provides a toning method and member for electrostatography 
wherein a recording member containing information on its image bearing 
surface in the form of electrostatic latent images of one polarity is 
toned by attracting to such latent images toner material of opposite 
polarity including providing a carrier or toning member according to the 
invention containing on at least one surface thereof a dry pre-toner 
coating; activating such pre-toner coating with an insulative solvent to 
thereby solvate and confer opposite polarity to such pre-toner coating 
while rendering such pre-toner coating releasable from the carrier member; 
establishing virtual contact between the activated and releasable 
pre-toner coating on the carrier member and the image bearing surface of 
the recording member; transferring the pre-toner coating in image 
configuration onto the recording member by attraction to the latent images 
to form toner deposits thereon; and separating the carrier member from the 
recording member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the method of this invention there is provided a toning member 
including a disposable carrier member, for example, paper or the like. The 
paper is coated on at least one surface thereof with a composition of 
matter henceforth referred to as "pre-toner". The pre-toner coating can be 
dried on the carrier member and subsequently, reactivated to function as a 
liquid toner. The specific method of practicing this invention includes 
the steps of: 
applying pre-toner coating compositions of desired colors to carrier 
members, the coating compositions and/or thicknesses being selected to 
give specific final image densities in a given process; 
drying the coatings; 
rolling up the carrier members to form rolls or cutting the carrier members 
into sheets and stacking the carrier members or using the carrier members 
in individual form; 
inserting carrier rolls, or stacks of carrier sheets or individual carrier 
sheets of the required colors into a color printer operating with a 
photoconductor on a conductive support and preferably having program 
actuated means to guide sequentially the appropriate color carriers to the 
toning position; 
placing a roller adjacent the uncoated side of the carrier member; 
activating the dry pre-toner coating on the carrier member by wetting it 
and/or the surface of the charged and exposed photoconductor with an 
insulative liquid prior to toning; 
establishing virtual contact between the photoconductor surface and the 
activated coating on the carrier member for toning by moving the roller 
positioned behind the carrier member toward the photoconductor and rolling 
the carrier member over the entire surface of the photoconductor; 
simultaneously while the carrier member is being rolled over the 
photoconductor surface, applying an appropriate so-called bias voltage of 
appropriate polarity between the conductive support of the photoconductor 
and the roller behind the carrier member to tone the photoconductor by 
transfer to the charged image areas thereon of activated toner from the 
carrier member; 
separating the carrier member from the photoconductor; and 
disposing of the used carrier member. 
In those instances where the photoconductor is in the form of a flat plate, 
contact with the carrier member for toning can be made, for instance, by 
rolling the roller behind the carrier member along the photoconductor 
plate and having the carrier member wrapped around part of the roller 
circumference. Toning thereby occurs substantially along a line since the 
carrier member touches the photoconductor simultaneously with the 
traversing roller and is separated from the photoconductor immediately 
behind the roller. 
In those instances where the photoconductor is in the form of a cylinder 
which is rotating while being toned, contact with the carrier member can 
be made, for instance, by moving the roller behind the carrier member 
toward the cylinder and rotating it at the circumferential speed of the 
cylinder to thereby cause the carrier member to pass therebetween. 
The application of appropriate bias voltage is well known in this art. The 
terms "appropriate bias voltage" and "appropriate polarity" also cover, of 
course, those conditions where no voltage is applied or where both the 
conductive support of the photoconductor and the roller behind the carrier 
member are grounded or are at the same potential. Instead of applying the 
bias voltage between the conductive support of the photoconductor and the 
roller behind the carrier member, it can be applied between the conductive 
support of the photoconductor and the carrier member itself, provided the 
carrier member is conductive or semiconductive, or has a conductive or 
semiconductive coating on its side nearest the roller. 
The insulative liquid utilized to activate the pretoner coating on the 
carrier member can be an isoparaffinic hydrocarbon of the type used in 
office copiers operating with liquid toners. 
The toning method of this invention can be referred to as transfer toning 
where a toner deposit is transferred under the influence of an electrical 
field from one surface to another. Such transfer toning virtually is 
instantaneous, unlike liquid toning where individual toner particles 
migrate under the influence of the field due to electrophoresis, which is 
a relatively slow process. 
At high toning speed, this invention provides uniform fill-in of solid 
image areas and virtually no density variation over a print or from print 
to print. This is because the thickness and/or composition of the 
pre-toner layer on the carrier member is selected to produce, upon 
virtually complete transfer to the photoconductor, final images of 
specific colors and specific densities. Also, the pre-toner composition 
and/or bias voltage during toning can be selected to effect virtually 
complete transfer at specific surface voltages to suit various 
photoconductors. Furthermore, such selection can be made to effect 
virtually complete transfer at a surface voltage which, for instance, can 
be 10 or even 20 percent lower than the nominal surface voltage of a 
specific photoconductor. These surface voltages above such minimum are of 
no significance because they can not attract any more toner. Thus, density 
uniformity of the final image depends solely on the coating uniformity of 
the pre-toner on the carrier member, rather than on process or 
photoconductor related inconsistencies. 
It should be noted, however, that in some processes there is a need for 
both virtually complete transfer and only partial transfer of the toner 
layer. Such processes are, for example, color proofing involving halftone 
imagery, where solid and screened image areas have the same density and 
virtually complete transfer of the activated toner layer to the 
photoconductor is needed, and in certain other processes involving 
continuous tone or grayscale reproduction where the image densities vary 
and depend on the surface voltage on the exposed photoconductor. This 
invention is equally applicable in such processes since, by appropriate 
formulation of the pre-toner coating and/or selection of appropriate bias 
voltage for toning, it is possible readily to transfer the toner layer 
virtually completely or to transfer only a part thereof, where the 
thickness of the layer transferred is determined by the surface voltage on 
the photoconductor. 
The carrier member of the invention preferably is flexible so that it can 
be rolled up if so desired and wrapped around part of the circumference of 
the roller effecting contact with the photoconductor during toning. 
Suitable materials for the carrier member can include, for example, coated 
and uncoated paper with and without a conductive coating at least on one 
side thereof, aluminum foil with and without a paper or plastic backing, 
and plastic sheet with and without a conductive layer. The surface of the 
carrier member to be coated preferably is smooth to allow good release of 
the activated layer for transfer toning and to ensure that the final image 
has a smooth appearance. 
The pre-toner coating of the invention preferably is a composition of 
matter which can be applied as a coating in the form of a liquid 
resembling paint or printing ink to form a layer on the carrier member. 
The coating then can be dried to become solid, and some time later, upon 
activation by wetting with an insulative liquid, can become responsive to 
attraction by surface charges of a certain polarity. The coating also can 
produce, by transfer toning, high quality and high resolution imagery 
identical to that produced by conventional liquid toners in 
electrophoretic toning. 
The main requirements for the pre-toner layer preferably are that it must 
dry to a smooth finish without shrinkage cracks and that the dry layer 
must be sufficiently flexible so that it does not crack when the carrier 
member is rolled up and then sometime later unrolled and when the carrier 
member is wrapped around part of the roller circumference effecting 
contact with the photoconductor during toning. Also, the dry layer must be 
sufficiently firm to withstand rolling up or stacking of the carrier 
member without being disturbed or damaged by the pressure and shear 
involved. 
It has been determined that many types of transferable liquid toner 
compositions can be used by incorporation therein of certain substances to 
meet the requirements for the pre-toner material of the invention. 
To produce a pre-toner layer which dries to a smooth finish which is 
sufficiently flexible yet firm, a plasticizer can be incorporated into the 
toner composition. The plasticizer preferably is an acrylic copolymer of 
the film forming so-called convertible or re-solvatable type. Such 
materials form a flexible film which is non-tacky upon drying and is 
instantly soluble in an aliphatic or isoparaffinic hydrocarbon. Such 
acrylic copolymers, in addition to plasticizing or rendering flexible the 
dry pre-toner layer, also effect adhesion of the layer to the carrier 
member. They also impart internal cohesiveness to the layer by binding 
together the toner particles which may be coated with or attached to other 
materials in the toner composition. Upon activation of the dry pre-toner 
layer by wetting, such binder becomes instantly solvated whereby adhesion 
to the carrier member ceases and the internal cohesion of the layer 
becomes very weak, allowing virtually complete transfer of the toner layer 
at high resolution. 
Response of the activated toner layer to attraction by surface charges on 
the photoconductor depends mainly on the viscosity or cohesiveness of the 
wetted layer and on its conductivity. Viscosity and cohesiveness can be 
adjusted as desired by the type and/or proportioning of the above 
disclosed acrylic copolymer binder. The conductivity of the layer 
conveniently can be adjusted by incorporation therein of charge directors 
or polarity control agents, such as, for instance, metallic soaps and the 
like. It was determined that an increase in conductivity reduces the 
sensitivity which means in general that for photoconductors having low 
surface voltages the conductivity of the layer should be low. The charge 
director or polarity control agent is selected to be of the type which 
confers the desired polarity to the toner layer. 
The desired density of the final image produced by a virtually completely 
transferred toner layer in accordance with the method of this invention is 
obtained by coating the pre-toner layer to the appropriate thickness 
and/or incorporating in the pre-toner composition the pigment or coloring 
material in the appropriate proportion. 
In those instances where virtually complete transfer of the toner layer to 
the photoconductor is needed, such as in halftone imagery, it is 
preferable to apply a release coating to the carrier member prior to 
coating it with pretoner. Such a release coating may comprise, for 
instance, a silicone compound or a fine dispersion of silica with a small 
proportion of a binder material in alcohol, and the like. 
As stated above, uniformity of the final image density produced in 
accordance with this invention depends on the uniformity of the pre-toner 
layer on the carrier member. Therefore, it is essential to coat the 
carrier member with the pre-toner material by methods which can be 
precisely controlled. Since the viscosity of the pre-toner material 
readily can be adjusted, for instance by the proportion of the solvent 
used for the acrylic copolymer plasticizer/ binder, various known and 
precisely controllable coating methods can be used. These methods can 
include reverse roll, knife and dip coating, electrostatic deposition, as 
well as gravure, flexographic and offset printing and the like. 
The pre-toner composition comprising coloring matter, binder, plasticizer, 
charge control agent and solvent can be prepared by blending these 
materials and then placing the thus formed mixture into a dispersing 
device, such as a ball mill, high speed mixer, attritor, roll mill, and 
the like. 
The coloring matter may include organic and inorganic pigments and organic 
dyes. 
The binder may include acrylic polymers and copolymers, styrene polymers 
and copolymers, natural resins, esters of rosin, synthetic rubber, and the 
like. 
The plasticizer may include formaldehyde resins, abietates, ether resins, 
acrylic polymers and copolymers, alkyd resins, vinyl resins, and the like. 
It should be noted that both the binder and plasticizer material should be 
compatible with each other in the dissolved state and they should be so 
selected that they form a pre-toner coating which upon drying is 
non-tacky, flexible, cohesively relatively weak and instantly solvated or 
loosened upon activation or wetting with the chosen insulating liquid. 
The charge control agent can be of the type well known in the art, such as 
for instance a metallic soap for imparting positive polarity to the 
pre-toner composition. 
The solvent is selected with regard to the solubility of the binder and 
plasticizer used and may include aliphatic and aromatic hydrocarbons, 
ketones, halogenated solvents, alcohols, and the like. 
In general the ratio of the binder/plasticizer to coloring matter can be in 
the range from about 1:2.5 to 9:1 by weight. The exact ratio will depend 
on the nature of the materials used, including, for instance, the color 
strength or hiding power of the coloring matter and the final image 
density required. 
The proportion of solvent used will depend mainly on the viscosity required 
for a specific coating method chosen and the thickness of the wet coating 
which is to be applied. It was determined that by the reverse roller 
coating method, for instance, very uniform dry coatings in the thickness 
range of 2 to 8 microns could be obtained with a corresponding wet coating 
thickness in the range of about 10 to 50 microns, the proportion of 
solvent to the other materials in the pre-toner coating being in the range 
1.5:1 to 9:1 by weight. 
The following Examples are included to further illustrate this invention. 
Example 1 
A cyan color pre-toner coating was prepared with the following composition: 
______________________________________ 
Phthalocyanine pigment, Pigment Blue 15.3 
100 grams 
Vinyl toluene methacrylate copolymer (binder) 
50 grams 
Toluene sulphonamide formaldehyde resin 
5 grams 
(plasticizer) 
Manganese naphthenate, 4% metal, 
5 grams 
(positive charge control agent) 
Toluene (solvent) 500 grams 
______________________________________ 
The above materials were blended, placed in a one liter ball jar and milled 
for 48 hours. 
The carrier member for the pre-toner comprised smooth clay coated art 
paper, 80 grams per square meter (gsm) weight, coated on one side to 
approximately 0.5 gsm weight with a silicone polymer release agent Dow 
Corning 30 (TM) manufactured by Dow Corning Corporation, Michigan, U.S.A. 
The milled composition was reverse roller coated onto the side of the 
carrier member containing the release layer to a wet coating thickness of 
about 25 microns, which upon drying resulted in a dry pre-toner coating 
having a thickness of about 5 microns. 
A commercially available zinc oxide/binder photoconductor coated copier 
type paper was used as the recording member. The photoconductor was 
electrostatically charged negatively and exposed to a light pattern, after 
which the surface voltage was measured and was determined to be in the 
range of 380-420 Volts negative in the latent image areas corresponding to 
solid density. 
The latent image bearing surface of the recording member was wetted with 
Isopar G (TM). It was then brought into contact with the pre-toner coating 
on the carrier member and the thus formed sandwich was passed at a speed 
of 12cm/second between a pair of rollers set at a light pressure just 
sufficient to maintain uniform virtual contact between the recording 
member and the carrier member. 
Each roller comprised a metal shaft coated with conductive rubber. The 
roller located behind the recording member was grounded, whereas the 
roller behind the pre-toner coated carrier had a forward bias voltage of 
150 Volts positive applied thereto to assist transfer of the pre-toner 
coating having positive polarity upon activation. 
Immediately upon emergence from the rollers, the recording member was 
separated from the pre-toner carrier member and it was determined that the 
pre-toner coating had transferred virtually completely to the latent image 
areas on the recording member forming toner deposits thereon. 
Such toner deposits on the recording member were measured upon drying with 
a Macbeth reflection densitometer and showed remarkably uniform density in 
the range 1.60 to 1.62 ODU (optical density units), despite the relatively 
large variation in the surface voltage. 
Example 2 
A yellow color pre-toner coating was prepared with the following 
composition: 
______________________________________ 
Diaryl pigment, Pigment Yellow 83 
50 grams 
Alpha methyl styrene polymer (binder) 
100 grams 
Methyl abietate (plasticizer) 
15 grams 
Zirconium octoate, 12% metal 
10 grams 
(positive charge control agent) 
Isopar G .TM. (solvent) 
500 grams 
______________________________________ 
The materials were blended, milled and coated onto a carrier member as in 
Example 1. The thickness of the wet coating was about 70 microns, which 
upon drying resulted in a dry pre-toner coating having a thickness of 
about 6 microns. 
The carrier member with the pre-toner coating was used as in Example 1. 
The density of the dry yellow deposits on the recording member was in the 
remarkably narrow range of 1.62 to l.65 ODU. 
Example 3 
A magenta color pre-toner coating was prepared with the following 
composition: 
______________________________________ 
Calcium 4B pigment, Pigment Red 57.1 
50 grams 
Glycerol ester of hydrogenated rosin 
25 grams 
(binder) 
Polyvinyl ethyl ether (plasticizer) 
5 grams 
Cupric naphthenate, 4% metal 
5 grams 
(positive charge control agent) 
Toluene (solvent) 500 grams 
______________________________________ 
The materials were blended, milled and coated onto a carrier member as in 
Example 1. The thickness of the wet coating was about 60 microns, which 
upon drying resulted in a dry pre-toner coating having a thickness of 
about 3 microns. 
The carrier member with the pre-toner coating was used as in Example 1. 
The density of the dry magenta deposits on the recording member was in the 
narrow range of 1.56 to 1.59 ODU. 
Example 4 
Example 1 was repeated with the exception that the thickness of the wet 
pre-toner coating was about 15 microns, which resulted in a dry coating 
thickness of about 3 microns. 
The density of the dry cyan toner deposits on the recording member was in 
the narrow range of 1.30 to 1.33 ODU. 
Example 5 
Example 2 was repeated with the exception that the thickness of the wet 
pre-toner coating was about 40 microns, which resulted in a dry coating 
thickness of about 4 microns. 
The density of the dry yellow toner deposits on the recording member was in 
the narrow range of 1.42 to 1.44 ODU. 
Example 6 
Example 3 was repeated with the exception that the thickness of the wet 
pre-toner coating was about 30 microns, which resulted in a dry coating 
thickness of about 2 microns. 
The density of the dry magenta toner deposits on the recording member was 
in the narrow range of 1.25 to 1.28 ODU. 
Example 7 
Example 1 was repeated with the exception that the quantity of the 
Phthalocyanine pigment was reduced from 100 grams to 80 grams. 
The thicknesses of the wet and dry pre-toner coatings were substantially 
the same as in Example 1. 
The density of the dry cyan toner deposits on the recording member was in 
the narrow range of 1.45 to 1.47 ODU. 
Example 8 
Example 2 was repeated with the exception that the quantity of the Diaryl 
pigment was reduced from 50 grams to 40 grams. 
The thicknesses of the wet and dry pre-toner coatings were substantially 
the same as in Example 2. 
The density o.+-.the dry yellow toner deposits on the recording member was 
in the narrow range of 1.15 to 1.17 ODU. 
Example 9 
Example 3 was repeated with the exception that the quantity of the Calcium 
4B pigment was reduced from 50 grams to 40 grams. 
The thicknesses of the wet and dry pre-toner coatings were substantially 
the same as in Example 3. 
The density of the dry magenta toner deposits on the recording member was 
in the narrow range of 1.28 to 1.31 ODU. 
Examples 10-18. 
Examples 1- 9 were repeated with the exception that the toner deposits 
formed on the recording member were not dried but were transferred 
therefrom by the well known electrostatic transfer method onto a receptor 
comprising a sheet of clay coated art paper. 
Upon drying on the receptor, the densities of the toner deposits were 
measured with the Macbeth reflection densitometer. 
The cyan toner deposits of Examples 1, 4 and 7 and the magenta toner 
deposits of Examples 3, 6 and 9 showed a density decrease of about 0.04 
ODU caused by a slight residue remaining on the recording member, whereas 
the yellow toner deposits of Examples 2, 5 and 8 showed a decrease of only 
about 0.02 ODU. Uniformity was excellent, same as in Examples 1-9. 
Examples 19-21. 
Examples 1-3 were repeated with the exception that when passing the 
sandwich through the pair of rollers both rollers were held at ground 
potential. 
Transfer of pre-toner coating to the latent image areas on the recording 
member was not complete and residues in the range of 0.12 to 0.20 ODU were 
measured on the carrier member. 
The densities of the toner deposits transferred onto the recording member 
were proportionally decreased. Also, uniformity was slightly decreased 
since the density ranges as given in Examples 1, 2 and 3 were determined 
to have widened by about 0.02 ODU average in each case. 
Examples 22-24 
Examples 1-3 were repeated with the exception that the art paper carrier 
member for the pre-toner coating did not contain a release layer. 
Transfer of pre-toner coating to the latent image areas on the recording 
member was not complete and residues of about 0.15 ODU average were 
measured on the carrier member. 
The densities of the toner deposits transferred onto the recording member 
were proportionally decreased. Also, uniformity was decreased since the 
density ranges as given in Examples 1, 2 and 3 were determined to have 
widened by about 0.05 ODU average in each case. 
Isopar G (TM) in the above Examples is an isoparaffinic hydrocarbon, 
boiling range 155-173 deg.C, manufactured by the Exxon Corporation, USA. 
Toluene in the above Examples is an aromatic hydrocarbon, boiling range 
110-111 deg. C. 
It should be noted that throughout the above Examples for simplicity of 
comparison we have used commercially available zinc oxide/binder 
photoconductor coated paper as the recording member. Equally uniform toner 
deposits, however, were produced with the compositions and methods given 
in the Examples on other recording members, such as organic 
photoconductors, selenium, cadmium sulphide, amorphous silicon, and the 
like. Such results also were produced on recording members comprising 
commercially available dielectric paper as used in plotters operating with 
liquid toners where the latent image is formed by charging the dielectric 
paper in image configuration by styli or other corona or ion generating 
means. 
For the same reason, throughout all of the above Examples the carrier 
member for the pre-toner coating comprised smooth clay coated art paper 
and it will be realized that other materials having a smooth surface are 
equally suitable as carrier members. As has been stated earlier, such 
materials include plain paper, paper or plastic film with a conductive 
coating, aluminum foil preferably laminated onto paper or plastic film, 
and the like. The bias voltage applied between the recording member and 
the pre-toner carrier member will have to be optimized from case to case 
as it will depend not only on the surface voltage of the recording member 
in latent image areas and on the pre-toner composition, but also on the 
nature of the pre-toner carrier member, mainly in relation to the 
thickness and electrical conductivity thereof. 
Furthermore, again for simplicity of comparison, in Examples 10-18 the 
toner deposits formed on the recording member were transferred therefrom 
onto the receptor by electrostatic methods. Other methods of transfer, 
however, such as by means of heat and/or pressure are equally applicable. 
It should be realized that the method of this invention also can provide an 
image reversal process, that is, production of a positive image from a 
negative film or negative color separation film. This is because if a 
negative film is used to expose the photoconductor, the toner transferred 
to the photoconductor will form a negative image thereon, while the 
residue on the carrier member will form a positive image. The thus formed 
positive image then can be transferred from the carrier member to a 
receptor, and, if residues of appropriate colors are sequentially 
transferred from the respective carriers to a printing stock paper 
receptor, a positive color proof can be produced from negative color 
separation films. 
There has been disclosed a novel method of very fast toning whereby high 
quality imagery can be produced with virtually no density variation caused 
by photoconductor or process related inconsistencies. The method is 
particularly applicable to electrostatographic color printing. The 
description given herein of the method as carried out and of the materials 
useful in the method is intended to be construed in an illustrative sense 
without restricting the scope of this invention.