Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-11-23
2001-06-26
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109500
Reexamination Certificate
active
06251553
ABSTRACT:
The present invention relates to the use of novel mixed-crystal pigments in electrophotographic toners and developers, powder coating materials and inkjet inks.
DESCRIPTION OF THE RELATED ART
In electrophotographic recording techniques a “latent charge image” is produced on a photoconductor. This latent charge image is developed by applying an electrostatically charged toner which is then transferred, for example, to paper, textiles, foils or plastic and is fixed by means, for example, of pressure, radiation, heat, or the action of a solvent. Typical toners are one- or two-component powder toners (also called one- or two-component developers); furthermore, special toners are employed, examples being magnetic or liquid toners, latex toners and polymerization toners.
One measure of the quality of a toner is its specific charge q/m (charge per unit mass). In addition to the sign and level of the electrostatic charge, the rapid attainment of the desired charge level and the constancy of this charge over a prolonged activation period, in particular, is a decisive quality criterion. Moreover, the insensitivity of the toner to climatic effects such as temperature and atmospheric humidity is another important criterion for its suitability.
Both positively and negatively chargeable toners are used in photocopiers, laser printers, LEDs (light-emitting diodes), LCS (liquid crystal shutter) printers or other digital printers based on electrophotography, depending on the type of process and type of equipment.
In order to obtain electrophotographic toners or developers with either a positive or a negative charge it is common to add charge control agents. As the color-imparting component in color toners, use is typically made of organic color pigments. As compared with dyes, color pigments have considerable advantages on account of their insolubility in the application medium, such as improved thermal stability and lighffastness, for example.
On the basis of the principle of substractive color mixing it is possible, with the aid of the three primary colors yellow, cyan and magenta, to reproduce the entire spectrum of colors visible to the human eye. Exact color reproduction is only possible if the particular primary color satisfies the precisely defined color requirements. If this is not the case, some shades cannot be reproduced and the color contrast is inadequate.
In the case of full color toners, the three toners yellow, cyan and magenta must not only meet the precisely defined color requirements but must also be matched exactly to one another in their triboelectric properties, since they are transferred one after another in the same device.
It is known that colorants may have a long-term effect in some cases on the triboelectric charging of toners. Because of the different triboelectric effects of colorants and, as a result, their sometimes highly pronounced effect on toner chargeability, it is not possible simply to add the colorants to a toner base formulation once prepared. It may instead be necessary to prepare a specific formulation for each colorant, with the nature and amount of the required charge control agent being tailored specifically. This approach is, correspondingly, laborious and in the case of color toners for process color is just another difficulty to add to those already described above.
Furthermore, it is important for practical use that the colorants possess high thermal stability and good dispersibility. Typical temperatures for incorporation of colorants into the toner resins are between 100° C. and 200° C. when using compounders or extruders. Accordingly, a thermal stability of 200° C., or even better 250° C., is a great advantage. It is also important that the thermal stability is maintained over a prolonged period (about 30 minutes) and in different binder systems. Typical toner binders are resins formed by addition polymerization, polyaddition and poly-condensation, such as styrene, styrene-acrylate, styrene-butadiene, acrylate, polyester and phenol-epoxy resins, polysulfones and polyurethanes, individually or in combination.
Fundamentally there is a need for color pigments possessing a very high degree of transparency, good dispersibility and a low inherent electrostatic effect: as far as possible a neutral inherent triboelectric effect. Neutral inherent triboelectric effect means that the pigment has very little or no effect on the inherent electrostatic charging of the resin and readily follows a defined charge established by means, for example, of charge control agents.
Transparency is of essential importance since, in the case of full color copies or in printing, the colors yellow, cyan and magenta are copied or printed over one another, the sequence of colors depending on the device. Consequently, if an overlying color is not sufficiently transparent, then the underlying color is unable to show through to a sufficient extent and the color reproduction is distorted. In the case of copying or printing on sheets for overhead projection use, transparency is even more important, since in this case a lack of transparency even in just one color makes the whole of the projected image gray.
The object of the present invention is to provide color pigments satisfying the above requirements for use in electrophotographic toners and developers, powder coating materials, inkjet inks, color filters, and electret fibers.
This object has surprisingly been achieved by the use of quinacridone mixed crystals defined hereinbelow.
SUMMARY OF THE INVENTION
The present invention provides for the use of mixed-crystal pigments of the quinacridone series, consisting of
a) from 85 to 99% by weight, in particular from 87 to 95% by weight, of unsubstituted &bgr;-phase quinacridone of the formula (I)
in which R
1
and R
2
are hydrogen atoms, and
b) from 1 to 15% by weight, in particular from 5 to 13% by weight of one or more substituted quinacridones of the formula (I) in which the substituents R
1
and
R
2
are identical or different and are chlorine, bromine or fluorine atoms or C
1
-C
4
-alkyl, C
1
-C
4
-alkoxy or carboxamido groups, which can be substituted by C
1
-C
6
-alkyl groups, and R
1
can additionally be hydrogen,
as colorants in electrophotographic toners and developers, powder coating materials, inkjet inks, electret fibers, and color filters.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Quinacridone mixtures comprising from 85 to 99% by weight of unsubstituted &bgr;-phase quinacridone and from 1 to 15% by weight of one or more, especially 1 or 2, differently substituted quinacridones under certain conditions form mixed crystals, also referred to as solid solutions. By mixed crystals are meant systems in which one or more components added—usually in a nonstoichiometric ratio—to a crystal phase crystallize together with the host compound in one and the same lattice. The X-ray diffraction diagram of a mixed crystal shows only the reflections of the (in many cases expanded) crystal lattice of the host compound or else of a similar or else of a markedly different crystal lattice, whereas the reflections of all the components appear in the X-ray diffraction diagram of the corresponding mechanical mixture.
In the mixed-crystal pigments used in accordance with the invention, preference is given to substituted quinacridones (b) of the formula (I) in which R
1
is hydrogen, chlorine atoms, methyl groups or carboxamido groups and R
2
is chlorine atoms, methyl or carboxamido groups.
The color properties of the mixed-crystal pigments of the invention differ considerably from those of the corresponding mechanical mixtures of the individual components. In particular, they possess cleaner hues and have higher color strengths. Furthermore, the hues obtained cannot be established using the individual components or the prior art mixed crystals, especially in the red-violet region. The fastness properties are excellent.
The mixed-crystal pigments described above can be prepared by cyclizing the 2,5-dianilinoterephthalic acid on which the compound a) is based and the substituted terephthal
Baur Ruediger
Boehmer Martin
Macholdt Hans-Tobias
Schnaitmann Dieter
Urban Manfred
Clariant GmbH
Goodrow John
Hanf Scott E.
Jackson Susan S.
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