Claims
- 1. Toner for incorporation into an electrophotographic liquid developer composition comprising (a) a charge control agent comprising a metal salt and (b) particles comprising a colored resinous phase having specific surface ion exchange sites available for complexation with the metal salt, said sites being comprised of a monomeric compound physically admixed in said resinous phase, and wherein the ion exchange sites are selected relative to the charge control agent so that the equilibrium of complexation therebetween is such that virtually all of the charge control agent is associated with the particles.
- 2. A composition as in claim 1 and wherein said metal salt is divalent, trivalent or tetravalent.
- 3. A composition as in claim 2 and wherein said metal salt is a trivalent metal salt of an ortho-hydroxy aromatic acid.
- 4. A composition as in claim 3 and wherein said metal salt is aluminum.
- 5. A composition as in claim 3 and wherein said charge control agent has the formula (RO.sup.-).sub.x M.sup.+n (AA.sup.-).sub.y in which:
- M is a metal atom;
- AA.sup.- represents an ortho-hydroxy aromatic acid anion
- R is selected from the group consisting of R'CO--, C.sub.1 -C.sub.15 alkyl, and a 1-3 ring aryl moiety optionally substituted with 1-6 lower alkyl substituents, where R' is C.sub.1 -C.sub.14 alkyl;
- n is 2, 3, or 4; and
- x and y are integers the sum of which is equal to n.
- 6. The composition as in claim 5 and wherein M is aluminum, AA.sup.- is diisopropyl salicylate, R is C.sub.10 H.sub.21 CO--, n is 3, x is 1 or 2 and y is 1 or 2.
- 7. A composition as in claim 1 and wherein said ion exchange sites comprise the hydroxy and carboxy moieties of a first ortho-hydroxy aromatic acid.
- 8. A composition as in claim 7 and wherein said first ortho-hydroxy aromatic acid is monomeric.
- 9. A composition as in claim 8 and wherein said metal salt is divalent, trivalent or tetravalent.
- 10. A composition as in claim 8 and wherein said charge control agent comprises a metal salt of a second ortho-hydroxy aromatic acid.
- 11. A composition as in claim 10 and wherein said charge control agent has the formula (RO.sup.-).sub.x M.sup.+n (AA.sup.-).sub.y in which:
- M is a metal atom;
- AA.sup.- represents an ortho-hydroxy aromatic acid anion
- R is selected from the group consisting of R'CO--, C.sub.1-C.sub.15 alkyl, and a 1-3 ring aryl moiety optionally substituted with 1-6 lower alkyl substituents, where R' is C.sub.1-C.sub.14 alkyl;
- n is 2, 3, or 4; and
- x and y are integers the sum of which is equal to n.
- 12. The composition as in claim 11 and wherein M is aluminum, AA.sup.- is diisopropyl salicylate, R is C.sub.10 H.sub.21 CO--, n is 3, x is 1 or 2 and y is 1 or 2.
- 13. A composition as in claim 10 and wherein the first and the second ortho-hydroxy aromatic acids are independently selected from the group consisting of salicylic acid and derivatives thereof.
- 14. A composition as in claim 13 and including therein an antistain agent.
- 15. A composition as in claim 14 and wherein said particles additionally contain an incompatible phase.
- 16. A composition as in claim 7 and including therein an antistain agent substantially insoluble in said insulating carrier and in said resin phase.
- 17. A composition as in claim 16 and including therein an antistain agent selected from the group consisting of (a) ethoxylated derivatives of fatty acids, alcohols and amides; (b) alkyl phosphates and phosphonates and metal salts thereof; (c) homopolymers of ethylene oxide; and (d) copolymers of ethylene and propylene oxide.
- 18. A composition as in claim 17 and wherein said particles additionally contain an incompatible phase comprising wax.
- 19. A composition as in claim 1 and wherein said resinous phase is oleophobic and is prepared by admixing a resin with said compound at temperature in the range of about 100.degree. C. and 200.degree. C. followed by comminuting the admixture.
- 20. A composition as in claim 13 and wherein said resinous phase is oleophobic and is prepared by admixing a resin with said compound at temperature in the range of about 100.degree. C. and 200.degree. C. followed by comminuting the admixture.
- 21. A process for preparing toner particles for incorporation into an electrophotographic liquid developer composition comprising:
- (a) admixing, at a temperature in the range of about 100.degree. C. and 200.degree. C., colorant, resin and ionizable monomeric metal salt effective to associate with said toner particles and to provide said particles with surface ion exchange sites, whereby an admixture is provided;
- (b) comminuting the admixture provided in step (a), without addition of liquid, to give intermediate particles; and
- (c) subjecting said intermediate particles to liquid attrition in a selected attrition liquid to provide particles of said toner.
- 22. A process as in claim 21 and wherein said metal salt is a trivalent metal salt of an ortho-hydroxy aromatic acid.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a division of U.S. application Ser. No. 08/016,660, filed Feb. 10, 1993 now U.S. Pat. No. 5,411,833, which, in turn, is a continuation of U.S. application Ser. No. 07/780,526, filed Oct. 18, 1991 now abandoned, which, in turn, is a continuation of U.S. application Ser. No. 7/464,896, filed Jan. 16, 1990, now abandoned which, in turn, is a continuation-in-part of U.S. applications Ser. No. 07/356,264, filed May 23, 1989, now U.S. Pat. No. 5,069,995 Ser. No. 07/355,484, filed May 23, 1989, now abandoned and Ser. No. 07/398,460, filed Aug. 25, 1989, now U.S. Pat. No. 5,045,425.
The present invention relates to the field of color electrophotography, and more particularly relates to novel toner and developer compositions for use in color electrophotographic processes and to processes of their manufacture. The invention additionally relates to consecutive multicolor image development processes utilizing the novel compositions, which processes give rise to color prints of exceptionally high quality, i.e., having superior image density and resolution with virtually no background or image staining.
Preparation of printed images by electrophotographic, or "xerographic", processes involves coating a selected substrate, or xerographic plate (typically comprised of metal, glass or plastic), with a photoconductive insulating material such as selenium, and then providing an electrostatic charge on the photoconductive surface, e.g., by ionization from a corona discharge. A light image is then focused onto the charged surface, which discharges or lowers the potential of the irradiated areas, while leaving the remainder of the surface charged. The electrostatic image so formed is then made visible by application of a suitable developing composition, which may be in either dry or liquid form.
Conventional liquid developer compositions comprise a dispersion of pigment particles in an insulating carrier liquid. Application of such a composition to the substrate carrying the electrostatic image results in migration of charged pigment particles to the substrate surface and deposition thereon in conformance with the electrostatic image. The developed image is then transferred to another substrate such as paper. (In some cases, it is desirable to eliminate the intermediate step of image transfer, i.e., so that the developed image is directly produced upon the final surface; see, e.g., U.S. Pat. No. 3,052,539 to Greig.)
Liquid developers for use in multicolor image development are relatively recent, and are comprised of colorant embedded in a thermoplastic resin core. These "toner" particles are then dispersed in an insulating carrier medium as above. Like compositions used in black-and-white electrophotography, these developer compositions additionally contain charge control agents to control the charge acquired by the toner particles in the insulating liquid.
When a color image is to be produced electrophotographically, the above-described charging, exposure, and development steps are carried out separately in succession for each of the constituent colors of the image using a correspondingly colored toner. In some color printing processes, each of the color images is transferred from the electrophotographic member to a print substrate after development and prior to formation of the next color image. This process, however, requires extremely accurate registration of the successive color images on the substrate to which they are transferred in order to obtain a high-quality composite image.
Another color printing process, and the process currently in use commercially, is a four-color liquid electrophotographic process known as "consecutive color toning" or "consecutive multicolor image development". This process involves: (1) charging a photoconductive (pc) surface; (2) impressing a first latent image on the surface by exposure through a colored transparency; (3) developing the image by contacting the pc with a liquid developer composition of a first color, typically yellow; and (4) discharging the pc surface. The steps are then repeated in sequence, typically using magenta, cyan, and black developer compositions, i.e., the cyclic process is repeated until the colored image is complete.
A significant problem which has been encountered in consecutive color toning is "image" or "character" staining, that is to say, where a second process color overtones the first image in regions where portions of the first image should have been discharged but were not. See, for additional explanation of the problem, R. M. Schaffert, Electrophotography (London: Focal Press, 1975), at pp. 184--186.
Many schemes have been advanced to overcome this difficulty. In U.S. Pat. No. 4,701,387 to Alexandrovich et al., for example, the problem of residual toner is discussed. The inventors propose a solution wherein the developed surface is rinsed with a polar liquid after each development step. It is suggested that application of a polar rinse liquid neutralizes and solvates residual counterions deriving from charge control agents and stabilizers present in the liquid developer.
While the Alexandrovich et al. method may be effective in reducing the staining problem, such a multiple washing procedure is time-consuming and unwieldy (it is recommended in the '387 patent that "after each development step and before the next developer is applied, the developed image is rinsed. . . . After rinsing, the rinse liquid is removed from the photoconductive element by drying, wiping or other method . . . ", see col. 2, lines 62--67).
U.S. Pat. No. 2,986,521 to Wielicki proposes the use of photoconductive toner particles to permit dissipation of charge applied to a toner layer during exposure of a second or subsequent color image to avoid charge retention in those areas. Such developers, however, may also be sufficiently conductive in the dark to dissipate the charge where it is intended to be retained during a subsequent imaging process, thereby preventing the subsequent image from being developed in those areas. U.S. Pat. No. 3,687,661 to Sato et al. seeks to overcome the problem resulting from retained charge by applying a reverse-polarity charge which neutralizes any charge retained in previously developed regions of the electrophotographic member. Such additional steps, however, not only prolong the processing time required to produce a composite color image, but also add to the complexity of the electrophotographic apparatus.
Other problems frequently encountered in electrophotographic color processes include: background staining, i.e., the appearance of toner in uncharged, non-image areas (a problem which is ubiquitous in zinc oxide and other positive toner systems); poor image resolution (i.e., poor edge acuity); poor image density resulting from insufficient deposition of toner particles in intended image regions; and colorant exposure, in which colorant contained within the resinous toner particles is exposed to the developer solution (as well as to the substrate) and thus affects the chemistry of the particular developer composition.
The invention herein now provides compositions and processes which address and overcome each of the aforementioned problems. First with respect to image staining in multicolor image development, the present toner and developer compositions substantially eliminate the cause of the problem and avoid the time-consuming, multi-step procedures of the prior art. The presently disclosed compositions and processes also enable preparation of a final electrophotographic print of unexpectedly high quality, with respect to both image density and edge acuity. The problems of colorant exposure and background staining are also virtually eliminated as will be described in detail below.
R. M. Schaffert, Electrophotography (London: Focal Press, 1975), provides a comprehensive overview of electrophotographic processes and techniques. Representative references which relate to the field of color electrophotography, specifically, include U.S. Pat. No. 3,060,021 to Greig, U.S. Pat. No. 3,253,913 to Smith et al., U.S. Pat. No. 3,285,837 to Neber, U.S. Pat. No. 3,337,340 to Matkan, U.S. Pat. No. 3,553,093 to Putnam et al., U.S. Pat. No. 3,672,887 to Matsumoto et al., U.S. Pat. No. 3,687,661 to Sato et al., and U.S. Pat. No. 3,849,165 to Stahly et al. References which describe electrophotographic toners and developers include U.S. Pat. No. 4,659,640 to Santilli (which describes a developer composition containing dispersed wax), U.S. Pat. No. 2,986,521 to Wielicki, U.S. Pat. No. 3,345,293 to Bartoszewicz et al., U.S. Pat. No. 3,406,062 to Michalchik, U.S. Pat. No. 3,779,924 to Chechak, and U.S. Pat. No. 3,788,995 to Stahly et al.
References which relate to charge control agents, also sometimes referred in this and related applications as "charge directors", include U.S. Pat. No. 3,012,969 to van der Minne et al. (polyvalent metal organic salts in combination with an oxygen-containing organic compound), 3,411,936 to Rotsman et al. (metallic soaps), 3,417,019 to Beyer (metallic soaps and organic surface active agents), 3,788,995 to Stahly et al. (various polymeric agents), 4,170,563 to Merrill et al. (phosphonates), 4,229,513 (quaternary ammonium polymers), 4,762,764 to Ng (polybutene succinimide, lecithin, basic barium petroleum sulfonates, and mixtures thereof), and Research Disclosure, May 1973, at page 66.
U.S. Pat. No. 4,701,387 to Alexandrovich et al., discussed in the preceding section, and U.S. Pat. No. 3,337,340 to Matkan, are relevant insofar as each of these references relates to the problem of image staining in consecutive color toning.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
5045425 |
Swidler |
Sep 1991 |
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5393635 |
Russell et al. |
Feb 1995 |
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Related Publications (2)
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355484 |
May 1989 |
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398460 |
Aug 1989 |
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Divisions (1)
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16660 |
Feb 1993 |
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Continuations (2)
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780526 |
Oct 1991 |
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Parent |
464896 |
Jan 1990 |
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Continuation in Parts (1)
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356264 |
May 1989 |
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