OR MAGNETOGRAPHICALLY DEVELOPING

A COMPOSITE COLORED IMAGE

The present invention relates to a process for electrostatographically or magnetographically developing a composite color image onto a receiver substrate such as paper. More particularly, the present invention relates to a process for electrostatographically or magneto¬ graphically developing a composite color image onto a receiver substrate using more than one colored magnetic toner composition.

There are three general classes of magnetic toner/developer compositions used in electrostatographical and magnetographical printing processes: mono-component, two-component, and hybrid toners/developers. In a mono-component toner/developer, a magnetic material having the same approximate particle size as the other toner/developer ingredients is incorporated into the toner/developer. In a two-component toner/developer system, a toner formulation is mixed with relatively large size magnetic material called a carrier. A hybrid toner generally contains two magnetic materials; a magnetic material in a toner formulation as well as a magnetic carrier.

Mono-component powdered toners/developers have several advantages over two-component systems since the magnetic core is part of the transferred toner particle.

Mono-component toner/developers are generally simpler to use and have greater longevity than two-component developers and equipment using mono-component toner/developers is easier to design and is simpler to service. However, because the magnetic materials used in mono-component toners are black or another dark, color and are usually about 40% by weight of the toner, the resulting toners can only be used to develop black or very dark colors. The addition of bright color pigments (e.g., yellow, cyan, and magenta) are generally precluded in mono-component toners since the pigments would be severely "muddied" by the dark colored magnetic material. In addition, these prior art mono-component toners do not form transparent images. Therefore, they could not be used to form multiple transparent colored images that may be overlaid with each other or used adjacent to each other.

U.S. Patent No. 4,758,490 describes a transparent, mono-component magnetic toner made by dispersing approximately 40% by weight of a very small magnetic particle (<200 angstroms) along with a coloring agent (e.g., a pigment) in a methacrylate/styrene or acrylate/styrene copolymer resin system. This patent does not teach that combinations of such magnetic mono- component toners may be used together. It is believed the approximate 40% by weight loading of magnetic material in this reference's toners would preclude the use of combinations of more than one colored toner to produce a composite colored image over the full spectrum of colors. Accordingly, the present invention is directed to a process of electrostatographically or magnetographically developing a composite colored image on a receiver substrate comprising the steps of:

(1) providing an electrostatographic or magnetographic imaging member having a recording surface;

(2) forming an electrostatic or magnetographic color separation latent image on said

5 recording surface;

(3) contacting said electrostatic or magnetographic color separation latent image with a first particulate colored toner composition comprising:

10 (a) magnetic particles having a mean diameter of less than about 750 angstroms;

(b) a coloring agent; and

(c) a resin matrix for binding said magnetic particles and said coloring agent; said

15 magnetic particles comprising from about

0.5% to about 10% by weight of said toner composition and said toner particles having a mean diameter from about 4 to about 30 microns; 20 whereby said toner composition is attracted to and deposited on said recording surface in conformance with said electrostatic latent image;

(4) transferring said deposited toner composition 25 from said recording surface to a receiving substrate, whereby a colored image is formed in conformance with said electrostatic or magnetographic color separation latent image;

(5) repeating the sequence of steps (1), (2), 30 (3), and (4), at least once wherein a different electrostatic or magnetographic

color separation latent image is employed for each repeated sequence and wherein said particulate colored toner composition employed for each repeated sequence comprising: (a) magnetic particles having a diameter of less than about 750 angstroms;

(b) a coloring agent; and

(c) a resin matrix for binding said magnetic particles and said coloring agent, said magnetic particles comprising from about

0.5% to about 10% by weight of said toner composition, said coloring agent having a different color than the coloring agents of said other colored toner compositions employed herein and said toner particles having a mean diameter from about 4 to about 30 microns; said steps thereby forming a composite colored image on said receiving substrate. The present process of the present invention may use any conventional electrostatographic or magnetographic printing equipment which uses either a mono-component or two-component or toner/developer or a hybrid toner/ developer. Preferably, the machine should use an organic photoconductor for a recording surface. Also, preferably, the machine should have heat and pressure fusing stations with a silicone oil supply to a roller contacting the receiver substrate.

The electrostatic or magnetostatic color separation latent image may be formed by any conventional means including analog and digital means.

The equipment may contain any conventional developing station in order to contact the electrostatic or magnetographic color separation latent image with the particulate colored toners used in the present process. Each of the toners used in the process of the present invention have three critical ingredients: magnetic particles, a colorant agent, and a resin matrix. Other optional ingredients may also be added to these toners. The magnetic particles are preferably magnetites, ferrites, and mixtures thereof. The most preferred magnetic particle is doped (e.g., cobalt and titanium) and undoped barium hexaferrite. Preferably, the magnetic particles have a mean diameter of less than about 100 to about 600 angstroms and constitute from about 2% to about 7% by weight of each toner composition.

The term colorant agent, as used in the present invention, may mean any colorant material except opaque black, including dyes and pigments. Preferably, the colorant agent for each particulate colored toner is a primary process color pigment or dye. A primary process color means yellow, cyan, and magenta. The most preferred colorant agents are diarylide yellow (Pigment Yellow 12); lithol rubine (Pigment Red 57); and copper phthalocyanine blue (Pigment 15:3). Preferably, the colorant agents of each particulate colored toner have a mean diameter of less than 1 micron and constitute from about 5% to about 30% by weight of said toner composition.

It is preferred that the present process be carried out wherein said first particulate colored toner has a yellow pigment or dye as said colorant agent; the second particulate colored toner has a magenta pigment or dye as said colorant agent; and the third particulate

colored toner has a cyan pigment or dye for the colorant agent. This combination of the three primary process colors allows for a composite colored image having the full spectrum of colors to be produced on the receiving substrate. The resin matrix may be any suitable resin material capable of binding the magnetic particles and coloring agent and suitable for use in a toner/developer formulation. Preferred resin matrix include maleic modified rosin ester, acrylate/styrene copolymers, methacrylate/styrene copolymers, polyesters, polyamides, and polyvinylchlorides . Preferably, the resin matrix constitutes from about 35% to about 93% by weight of each toner composition.

Optional ingredients for each toner composition include plasticizers and flow enhancers. Preferred plasticizers are polyethylene glycol, polypropylene glycol, metal stearates, and polyolefins. Plasticizers may constitute from about 0% to about 25% by weight of each toner composition. The preferred flow enhancer is fumed silica. Each particular colored toner may contain from about 0% to about 5% by weight of a flow enhancer.

Preferably, each particulate colored toner composition has toner particles having a mean diameter from about 5 to 20 microns. The step of transferring the deposited toner composition from said recording surface to the receiving substrate may be carried out by electrostatic means, magnetic means or simply by direct contact of the two surfaces . Since the present process requires a repetition of the same process steps, this process repetition may be carried out on a series of machine modules outfitted with

supply means for different particulate color toners. Alternatively, one machine may be used with a replaceable developer station having different particulate colored toners in each station. In the latter case, it may be necessary to clean the recording surface after each colored print image-producing sequence. The preferred cleaning means would be a rotating, soft synthetic or natural fur brush.

In order to make a colored print image having the full spectrum of colors, it would be necessary only to pass the same receiving substrate (e.g., a paper sheet) through the machine three times; one time each for each of the primary process colors— ellow, cyan, and magenta. Said composite color image on the receiving substrate may be made by overlaying each deposited toner image over the previous deposited toner image or depositing each toner image adjacent to the previous deposited toner image. To make an improved quality full color spectrum print image on the same receiving substrate, it may also be desirable to develop the receiving print with an opaque black toner after developing the same receiving substrate with the three primary colors.

In order to more fully explain the present invention, the following Example is provided. All parts and percentages are by weight unless otherwise explicitly stated.

EXAMPLE A. Formulation Preparation

The following ingredients were thoroughly mixed together in a plastic container containing the indicated parts by weight:

Ingredient Parts bv Weight

Magenta pigment (l) 10

Maleic-modified rosin ester (2) 77

Polyethylene glycol (M.W. 8,000) (3) 8

Cobalt and titanium-doped Barium Hexaferrite

^{(Ba Co} 0.9 ^Ti 0.9 ^Fe 10.2 °19> © —a

100

The mixture was added to a Baker-Perkin Twin

Screw Extruder (Machine No. 51591) and compounded at 80°C and 200 rpm and at approximately 3,000 Newton-Meters back pressure. Three passes were made through this extruder.

The doped barium hexaferrite has a mean number particle size of about 600 angstroms.

1 Lithol Rubine C.I. Pigment Red 57 available from BASF Corp. of Parsippany, NJ.

2 UNIREZ 709 available from Union Camp of Wayne, NJ.

3 Available from Aldrich Chemical of Milwaukee, WI .

4 Available from Olin Corp. and made according to the process disclosed in U.S. Patent No. 4,781,852 which is incorporated herein by reference in its entirety.

After the third pass, the compounded material was cooled to room temperature and then coarsely ground through a Fitz mill fitted with 0.1 millimeter screen to form about 100 to 200 micron particles. The coarsely

ground material was immediately micronized in a Trost mill to form about 10 micron mean diameter particles.

The magnetic properties of the above-formed reddish-colored mono-component toner were measured as follows:

Saturation Moment 6.135 EMU/g Retentivity 1.414 EMU/gm

Coercivity -655 Oersteds

B. Transparency Application Testing The above-noted toner (40 grams) was combined with Aerosil R972 fumed silica (available from DeGussa Corp. of Teterboro, NJ) (0.04 grams). The silica provides the toner with enhanced flow properties. This mixture was processed in a high shear disperser for five seconds. This modified toner composition was then combined with 30 grams of FCA nickel/zinc ferrite carrier (available from Indiana General Company—now known as Titan Advanced Products, Inc.) to form a hybrid developer composition. The ferrite material was about 110 microns in average particle size. The developer was a hybrid developer because it contained two magnetic materials, the magnetic barium hexaferrite mono-component and the magnetic ferrite carrier.

The primary purpose of the magnetic ferrite carrier in this application was to break up agglomerates of the mono-component toner to permit better flow.

This hybrid developer was tested in a NEC LC800 Laser Printer which normally uses a hybrid developer containing an opaque black mono-component toner. Both bond paper and polyester transparencies were used as the receiving substrate. Prints which were made were of acceptable density with some residual background in the non-imaged areas.

When the magenta colored image was printed onto the polyester substrate and then that printed substrate was placed on top of a preprinted yellow sheet. The perceived composite image was an orange hue. This indicated that the magenta mono-component toner was transparent. C. Four Color. Half-Tone Imaging Testing

The magenta colored mono-component toner made above may be tested in a four color, half-tone imaging process along with the three other process colors (i.e., cyan, yellow, and black) . The toners containing the cyan and yellow color pigments would be very similar to the above-made magenta colored toner. That is, they would also contain less than 10% by weight of very small magnetic particles, preferably barium hexaferrite particles, having a mean number diameter of less than 750 angstroms. These other two toners would also contain corresponding amounts of appropriate color pigment, resin matrix, and optionally a plasticizer such as polyethylene glycol.

The critical characteristics of such cyan and yellow toners will be that they also contain less than about 10% by weight magnetic particles (which are very small in size—mean number diameter of less than 750 angstroms) and their toner particles would be in the range of about 5-20 microns in size.

The black colored toners could be of similar composition or contain much more magnetic particles or black pigment/carbon black or both. These four toner compositions may be used to produce a half-tone print using a NEC LC800 Laser Printer by the following method:

First, a yellow colored half-tone print of various dot sizes would be produced and fused onto a receiver substrate, preferably a paper print by the laser printer. Next, a magenta colored half-tone print of different dot sizes would be produced and fused onto the same receiver substrate in an offset fashion. Third, a cyan colored half-tone print of different dot sizes would be produced and fused onto the same receiver substrate in another offset fashion. Finally, a black colored half-tone print of different dot sizes would be produced and fused onto the same receiver substrate in still another offset fashion. Therefore, the receiver substrate would have four offset, adjacent, and overlapping colored prints would would show a full spectrum of colors. That showing of the full spectrum of colors would indicate that the yellow, magenta, and cyan toners are transparent in nature.

D. Liquid Magnetic Ink Character Recognition (MICR) Application Liquid magnetic colored toners (i.e., yellow, cyan, and magenta colored) in both aqueous and nonaqueous solvents could be prepared wherein the magnetic particles have the critical particle sizes mentioned above and the amount of magnetic particles in each toner are low enough (i.e., no greater than about 10% by weight) to produce transparent images which are also magnetic.