Organic compounds -- part of the class 532-570 series – Organic compounds – Azo
Reexamination Certificate
2000-03-30
2001-04-03
Powers, Fiona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Azo
C534S867000, C534S876000, C548S306400
Reexamination Certificate
active
06211347
ABSTRACT:
The present invention relates to pigment dispersions, to a process for preparing them, and to the pigment dispersions obtainable by this process and their use for pigmenting high molecular mass material.
Recent pigment applications are placing stringent requirements on the coloristic and processing properties of pigments. The pigments are required to possess clean, strong and bright shades to allow the opening-up of a large color area. Furthermore, they should be able to be used not only as an individual pigment but also as an element for combination in, say, trichromatic pigmentations. In terms of technical application it proves advantageous to apply the pigment as a dispersion, since it is then possible to avoid laborious mixing and milling operations which represent an additional hygiene burden. Moreover, the dispersions make the pigmentation process more reproducible, since there is a more homogeneous distribution of the pigment particles than in the powder form. On economic grounds it is particularly desirable to employ concentrated, stable dispersions which require little space on transportation or storage and at the same time possess good stability.
From U.S. Pat. No. 4,597,794 and 5,085,698 it is known to prepare fine pigment dispersions having an average particle size distribution of 0.015-0.5 micrometers, which are obtained with the addition of stabilizing copolymers by mechanical comminution and subsequent selection techniques, such as filtration or centrifuging, in order to remove coarse particles. A disadvantage of these processes is the extremely time-consuming and energy-intensive milling process, which may last for several days and requires high frictional energy. The milled product has a broad particle size distribution and rough surfaces owing to the mechanical stress. Excessively large pigment particles, or those with a roughened surface, lead to a loss of transparency. Smaller particles, on the other hand, tend to form aggregates which in the course of the dispersion process are broken up by known techniques, by means of high energy input in the form, for example, of ultrasound. One consequence of the propensity of smaller particles to aggregate is their flocculation tendency, and so these dispersions are inherently unstable.
The disadvantages described can be alleviated only in part by other techniques, such as evaporation methods (see U.S. Pat. Nos. 5,030,669 and 5,106,533) or the preparation of fine dispersions under high pressure (WO 96/14925). Moreover, these techniques require special apparatus for their application. The problem of providing pigments having the high transparency required, in particular, for the preparation of inks from pigment dispersions, in order to achieve the correct coloring properties in accordance with the precise specifications, has still not been satisfactorily solved.
Compositions of polymers and latent pigments are known from EP-A 654 711, as are chemical, thermal or photolytic methods by means of which it is possible to generate pigment particles by known processes, in pre-structured layers consisting of polymers and soluble pigment precursors.
In the text below, the use of the word polymer signifies polymer and/or copolymer.
The object of the present invention is therefore to provide pigment dispersions which possess high stability and good transparency, and a process for preparing them.
The present invention accordingly provides a process for preparing pigment dispersions comprising a pigment and a polymer, which comprises
a1) subjecting a mixture A comprising a latent pigment and a polymer to thermal, chemical or photolytic treatment and
b) then adding a solvent, or
a2) subjecting a mixture B comprising a latent pigment, a polymer and a solvent to thermal, chemical or photolytic treatment.
In general, the weight ratio of latent pigment to polymer in the mixtures A and B is chosen from the range from 1:1 to 1:20, preferably from 1:1.5 to 1:10 and, with particular preference, from 1:1.5 to 1:5.
By means of the thermal, chemical or photolytic treatment, which can be conducted in analogy to EP-A 654 711 or EP-A-742 255, the pigments are prepared from the soluble pigment precursors, the latent pigments.
Normally, the mixture A or B is treated thermally. In general, the mixture is heated within the temperature range from 100 to 200° C. for from one minute to 36 hours, with particular preference in the temperature range from 120 to 150° C. for from 10 minutes to 24 hours.
In a preferred embodiment of the process of the invention, thermal treatment is conducted under pressure. In general, this pressure is chosen to be in the range from 70 kPa to 10 MPa, preferably from 90 kPa to 5 MPa; atmospheric pressure is particularly preferred.
The mixtures A and B can in general be prepared by generally known mixing methods, such as by stirring, kneading or fluidizing for from one minute to 36 hours, preferably for from 10 minutes to 24 hours.
In a particular embodiment of the process of the invention, mixing and the thermal treatment of the mixture A are carried out in an extruder. Depending on the reactants employed, latent pigment or polymer, it may be appropriate to undertake prior mixing in accordance with generally known methods of mixing. The process steps in the extruder can be carried out continuously or batchwise. In general it is possible to use any kind of extruder, such as twin-screw extruders or kneading extruders; co-rotating twin-screw extruders are particularly preferred. Operation with an extruder is common knowledge and is described, for example, in “The Canadian Journal of Chemical Engineering”, 71, June 1993 and U.S. Pat. No. 3,637,545.
Therefore, a further embodiment of the process of the invention relates to preparation in an extruder, with the mixture A being subjected to thermal treatment in an extruder.
The mixtures A or B are preferably homogeneous mixtures. It is particularly preferred for the mixture B to be a solution, and with very particular preference a homogeneous solution in which the components are distributed uniformly. The term “homogeneous” here is restricted to “macroscopically uniform” and in this sense is the opposite of the term “heterogeneous”; since homogeneous does not mean the same as “pure, unmixed”, it is also possible for mixtures to be homogeneous, such as, for example, powders, salt solution, wine, milk chocolate (Römpp, 1997, p. 1795).
If desired, the mixture A can be prepared by mixing the latent pigment and the polymer with a solvent and then removing the solvent by generally known methods. Use is made in particular of solvents in which the latent pigment and/or the polymer, with particular preference both latent pigment and polymer, are present in dissolved form.
In general, the solvent-containing mixtures A or B are prepared from latent pigment and polymer by stirring, preferably intensive stirring.
In general, the mixtures comprising latent pigment, polymer and solvent are prepared by preparing separately two mixtures, one comprising latent pigment and solvent and one comprising polymer and solvent, and generally mixing them with one another for from one minute to 24 hours, preferably for from 10 minutes to 12 hours. An alternative option if desired is first to mix a latent pigment and polymer and then to add a solvent to this mixture.
In the present invention, the term solvent represents water-free organic and/or aqueous solvents, which may comprise organic solvents and/or solvent mixtures thereof.
Organic solvents or solvent mixtures commonly chosen are polar, aprotic solvents, such as aliphatic C
1
-C
4
alcohols, such as methanol, ethanol, 1- or 2-propanol, 1- or 2-isopropanol, n-butanol, sec-butanol, tert-butanol, and also polyols, Cellosolves and carbitols, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, propylene gylcol [sic], diacetone alcohols, such as 4-hydroxy-4-methyl-2-pentanone, or ether alcohols, such as bis(2-hydroxyethyl) ether, bis(2-hydroxyproplyl) [sic] ether or bis(2-hydroxybutyl) ether, ethylene glycol monomethyl o
Hall-Goulle Veronique
Sieber Werner
Ciba Specialty Chemicals Corporation
Crichton David R.
Powers Fiona T.
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