Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-02-13
2003-09-02
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108700, C430S137170
Reexamination Certificate
active
06613489
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing toner and the toner produced therefrom. More specifically, the present invention relates to surface treating toner with silicate and the toner produced therefrom.
BACKGROUND OF THE INVENTION
Toners which contain hydrophilic functional groups on the toner surface, such as the sodio-sulfonated polyester emulsion aggregation (“EA”) toners, have the disadvantage of having high humidity sensitivity. Although these toners have exhibited satisfactory charging in the low-humidity zone (≦20% relative humidity (“RH”), also known as the C-zone) and excellent fusing properties with wide fusing latitude, the tribocharge levels in the high humidity zone (≦80% RH, also known as the A-zone) are low consequently leading to large RH sensitivity ratios (20% RH to 80% RH). Previous attempts toward improving the RH ratio of polyester toners included forming a hydrophobic fluoropolymer shell by seed polymerization on the toner particle surface; however, the fusing characteristics were adversely affected due to increasing the crease minimum fusing temperature (“MFT”) value 5-10° C. to the level of styrene-based EA toner MFT.
Another recent surface treatment approach used cationic tetra-alkylated phosphonium and ammonium salts to complex chemoselectively with the toner's surface sulfonate groups thereby rendering the particle surface more hydrophobic and allowing a 2-fold reduction in the tribocharging RH sensitivity. Cationic tetra-alkylated phosphonium or ammonium salts, such as stearyltributyl-phosphonium bromide (“STBP”), which complexes chemoselectively at the sites of surface-bound sulfonate groups was used to treat the toner surface at the end of the EA process.
SUMMARY OF THE INVENTION
A toner in accordance with one embodiment includes a resin, colorant, and a silicate component bound to the toner surface.
A method in accordance with another embodiment includes preparing a colloidal solution of a sulfonated polyester resin by heating water, adding a sulfonated polyester resin to the heated water, and cooling. A colorant is added to the colloidal solution, followed by heating the resulting mixture to a temperature equal to or higher than the resin glass transition temperature. An aqueous solution of either an alkaline earth metal (II) salt or a transition metal salt is added to the heated colloidal solution whereby the coalescence and ionic complexation of sulfonated polyester colloid, colorant, and metal cation occur until the particle size of the composite is about 3 to about 10 microns in volume-average diameter having a geometric distribution of from about 1.13 to about 1.23. An aqueous slurry of the toner particle composite is heated to a temperature of from about 25° C. to about 60° C. The toner particles are chemically treated in the heated aqueous slurry with an aqueous solution containing a water-soluble silicate component.
DETAILED DESCRIPTION OF THE INVENTION
This invention in embodiments thereof describes a process for chemoselective, optionally, in situ, surface treatment of sulfonated polyester EA toners dispersed in aqueous slurry. The toner particles are rendered more hydrophobic in nature with a reduced RH sensitivity ratio for tribocharging while maintaining the excellent fusing characteristics of the parent untreated toner. The silicate reagent functions as a tribocharge enhancer and flow aid. The present toners are suitable for known electrophotographic imaging methods, printing processes, including color processes, digital methods, and lithography.
Water-soluble silicates that include the cationic complexes of tetraalkylammonium and/or tetraalkylphosphonium, such as tetraethylammonium silicate (“TEASi”), tetramethylammonium silicate (“TMASi”), tetrabutylammonium silicate (“TBASi”) and tetrabutylphosphonium silicate (“TBPSi”), selectively attach to the surface sulfonate groups on these toners by ion exchange. This chemical surface treatment selectively targets the anionic sulfonate moieties on the toner surface by causing cation exchange of the complexed sodium cation (or other metal cation) for the tetraalkylammonium (“TAA”) or tetraalkylphosphonium cation (“TAP”). The silicate portion of the molecule is also incorporated onto the toner's surface providing good toner flow upon drying. The present invention in embodiments thereof provides enhanced triboelectric performance and reduced RH sensitivity of surface treated polyester EA toner particles, which is suitable for an in situ chemical surface treatment, using water-soluble silicates that include large organic cations such as tetraalkylammonium and/or tetraalkylphosphonium. The organic cations are optionally substituted with C
1
to C
20
alkyl substituents, for example, methyl, ethyl, propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, lauryl, tridecyl, tetradecyl, myristyl, pentadecyl, hexadecyl, cetyl, heptadecyl, octadecyl, stearyl, nonadecyl, cicosyl groups, and the like; aryl groups, for example, phenyl, benzyl, 2-phenyethyl, naphthyl, anthracenyl, phenanthrenyl, and the like; and mixtures thereof. The present toner material is suitable for color and black-white systems, electrophotographic imaging and printing systems, xerographic copiers and printers, including digital copiers, and the like.
Chemoselective treatment of the toner's surface-bound sulfonate groups can be accomplished with water-soluble silicates that include the cationic complexes of tetraalkylammonium and/or tetraalkylphosphonium, such as tetraethylammonium silicate, tetramethylammonium silicate, tetrabutylammonium silicate and tetrabutylphosphonium silicate. Tetramethylammonium silicate as shown in Formula 1 is available as an about 10% (as SiO
2
) aqueous solution (SaChem, Austin, Tex.) with a pH of from about 11 to about 13. Silica dissolves above about pH 10.7 to about 11.0 and can therefore be prepared with organic bases such as TMA, which have dissociation constants greater that about 10
−3
. As well, these quaternary ammonium ions are most likely absorbed on the surface of the silica which is rendered hydrophobic when covered with this organic base. See, ller, Ralph K. 1979
. The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry
. John Wiley & Sons, Inc. (New York), p. 150, 427, the disclosure of which is incorporated herein by reference in its entirety.
The quaternary ammonium cation, e.g. tetramethylammonium (“TMA”), ion exchanges with the complexed sodium cation (or other metal cation) for the sulfonate moieties on the toner surface, thereby creating a hydrophobic toner surface. Criteria in choosing a candidate compound for polyester EA toner surface treatment include: 1) cost-effectiveness and commercially availability; 2) water solubility for in situ chemical surface treatment in aqueous media; 3) selective reactivity with the surface-bound sulfonate groups only; 4) efficacy in enhancing A-zone tribocharge level and/or reducing the C-zone tribocharge level and thereby reducing RH sensitivity ratio at least about 2-fold; and 5) chemical stability in the final surface-treated toner, without adversely affecting other toner properties such as fusing and color performance. It has been found that TMASi fits the criteria #1 through to #4; results are in progress for evaluation of toner fusing and color performance (i.e., #5).
This method includes chemoselective surface treatment of surface-bound sulfonate groups on EA polyester toners using water-soluble silicates that include the cationic complexes of tetraalkylammonium and/or tetraalkylphosphonium. The intent of the surface treatment method is to alter the toner particle surface chemistry by masking the sulfonate moiety, which is hydrophilic in nature, with a hydrophobic additive. This in turn will not alter the toner's overall morphology or effect it's fusing characteristics. Instead the toner will demonstrate enhanced negative tribocharging
Goodrow John
Xerox Corporation
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