Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-06-04
2001-01-09
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031890, C106S031860, C106S472000
Reexamination Certificate
active
06171382
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to aqueous carbon black dispersions, a method of their production and use.
BACKGROUND OF THE INVENTION
Aqueous carbon black dispersions are used in producing printing inks and are also used directly as inks, e.g., in ink-jet printers.
The ink-jet printing process is a known duplicating technology in which the printing ink is transferred in a contactless manner, that is, without contact of the printing head with the print medium. Ink drops are sprayed from a jet onto a receiving material, during which their deflection can be electronically controlled. This technology, also designated as contactless printing, is particularly suited for printing products with irregular surfaces and packages because there is a certain distance between the printing head and the matter to be printed.
The printing process is very flexible and relatively economical and is therefore also used in computer printing, e.g., in a workplace printer. The ink-jet printing process is also being increasingly used in the industrial area, e.g., in outdoor advertising. In outdoor advertising the ink must meet special requirements of resistance to light and to water. In addition, the ink components must be very finely divided so that the printer jets do not become clogged. Dyes, colorants, and, recently, even pigments are being used as color-causing substances.
Pigments have the advantage over dyes that their resistance to light is very high and that they are water-resistant. Pigments have a disadvantage compared to dyes in that they form stable dispersions with a high storage stability only by means of treatment with surface-active substances (surfactants). Pigment particles are not present in the form of primary particles but rather in the form of aggregates. Pigment aggregates are larger than soluble dyes. If pigment aggregates are not sufficiently finely dispersed they clog the jets of the printing head. In addition, large aggregates alter the light-absorption properties of the pigment black. A graying of the printing and a loss of covering power and opacity results.
A description of pigment blacks in ink-jet printer inks are found in U.S. Pat. No. 5,085,698 and U.S. Pat. No. 5,320,668. These patents describe the use of water-soluble acrylates for pigment stabilization.
The production of aqueous carbon black dispersions with carbon black having an average primary particle size of not greater than 30 nm and a DBP number of at least 75 ml/100 g is known (U.S. Pat. No. 5,538,548).
The production of aqueous carbon black dispersions using water-soluble, organic solvent and water-soluble acrylic resins is also known (U.S. Pat. No. 5,609,671).
The known aqueous carbon black dispersions have the following disadvantages:
The obtainable optical densities are comparatively low.
The abrasion resistance is poor (see reference examples A, B and C).
Therefore, the object of the invention is to produce carbon black dispersions which do not have these disadvantages.
SUMMARY OF THE INVENTION
The invention provides aqueous carbon black dispersions containing the following components in addition to water:
Carbon Black: 1 to 40% by weight, preferably 3 to 20% by weight,
Surfactant: 1 to 30% by weight, preferably 2 to 15% by weight.
Nonionic and/or anionic wetting agents can be used as surfactants.
The following are suitable nonionic surfactants: cross-linked polyoxyethylene acrylic acid (e.g. HYPERMER CG 6), fatty alcohol ethoxylate with 30 units of ethylene glycol (e.g. LUTENSOL AO 30).
Lignin sulfonates, alkyl benzene sulfonates, naphthalenesulfonic acid derivatives, etc. can be used as anionic surfactants.
In a preferred embodiment the dispersion can contain a combination of two nonionic wetting agents.
In a preferred embodiment of the invention, a combination of
a) a cross-linked polyoxyethylene acrylic acid, and
b) an alkoxyethylate, preferably a fatty acid ethoxylate, especially a fatty alcohol ethoxylate with 30 ethylene glycol units,
can be used as surfactant, in which the ratio of the surfactants b : a can be 1:2 to 1:10.
An increase in the rise of the viscosity of the dispersions during storage can be prevented by the further addition of an anionic wetting agent such as, e.g., lignin sulfonates, alkyl benzene sulfonates or naphthalenesulfonic acid derivatives. The carbon black dispersions can contain an anionic wetting agent, preferably a lignin sulfonate and/or a cationic wetting agent in addition to the nonionic wetting agents.
Pigment blacks with an average primary particle diameter of 8 to 80 nm, preferably 10 to 35 nm, and a DBP number of 40 to 200 ml/100 g, preferably 60 to 150 ml/100 g, can be used as the carbon black. In a preferred embodiment of the invention, gas blacks with an average primary particle diameter of 8 to 30 nm, preferably 10 to 25 nm, canbe used.
The invention further includes a method of producing an aqueous carbon black dispersion in which bead mills, ultrasonic mills and/or an ultra-turrax are used for dispersing the carbon black. The carbon black dispersion can be centrifuged following the dispersal.
The pH of the dispersions constituting the subject matter of this invention is in the basic range, preferably in a range of 8-10.
The dispersions in accordance with the invention have a very high flocculation stability and therewith a high storage stability. The aggregate size does not exceed 160 nm. The average particle size of the carbon black aggregates present in the dispersion is approximately 60-100 nm. TEM photographs show that this aggregate size remains the same even after drying. This is not the case in reference examples A, B and C. Rather, a distinct agglomeration occurs. The agglomerates do not allow the pigment black to develop its full covering power. The printing therefore has low optical density and a distinct gray tone. In contrast thereto, the dispersions in accordance with the invention display a high covering power which stems from the small aggregate sizes. The carbon black dispersions of the invention improve the printing quality and the water resistance of ink-jet inks produced using these dispersions. Printing using ink-jet inks containing dispersions made with gas black in accordance with the invention display especially high optical densities without gray tone and are therefore particularly suited for being used in ink-jet inks or in writing inks. The black dispersions of the invention advantageously display a higher optical density than known black dispersions.
As a result of the higher optical density, the printed image in four-color printing becomes more brilliant and sharper. The written image and, therefore, the legibility is improved in black-and-white printing by virtue of the higher contrast.
The aqueous black dispersions of the invention can be used to produce printing inks, ink-jet inks and writing inks.
REFERENCES:
patent: 4530961 (1985-07-01), Nguyen et al.
patent: 5538548 (1996-07-01), Yamazaki
patent: 5542969 (1996-08-01), Hirasa et al.
patent: 5736606 (1998-04-01), Yanagi et al.
patent: 196 54 752 A1 (1997-07-01), None
patent: 0 704 503 A1 (1996-04-01), None
patent: 0 805 191 A2 (1997-11-01), None
patent: 0 805 191 A3 (1997-11-01), None
Karl Alfons
Kleinhenz Horst
Leimann J{umlaut over (u)}rgen
St{umlaut over (u)}bbe Andreas
Bell Mark L.
Degussa-Huls AG
Faison Veronica F.
Pillsbury Madison & Sutro LLP
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