Coloring pigment

Details Coloring pigment Coloring pigment

2002-04-24

2003-11-18

Koslow, C. Melissa (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C406S150000

Reexamination Certificate

active

06648959

ABSTRACT:

This invention relates to a method for preparing a coloring pigment. This invention further relates to a coloring pigment and the use thereof for coloring substrates.
In the context of the invention, a coloring pigment is understood to mean a substance which can give a particular, desired color to a substrate of another material. In addition to color, a coloring pigment gives coverage and it improves the durability of the substrate, in that a part of the incident light is absorbed and/or reflected. According to the invention, a coloring pigment is therefore distinct from a dye. Although a dye is capable of giving coloring to a substrate, it does not have the other properties mentioned, Which a coloring pigment does have.
Polymeric materials are normally colored with inorganic pigments. These provide a good color stability to light, oxygen and heat. As regards color and color intensity, however, these pigments have their limitations. In addition, inorganic pigments are less desirable for environmental reasons. Many inorganic pigments, for instance, contain heavy metals.
Organic pigments not only offer a wider range of color possibilities with higher intensities, but are also broken down faster and better in the environment, for instance under the influence of oxygen. A major disadvantage of organic dyes, however, is that they have a relatively low temperature and UV stability. Moreover, these substances exhibit the tendency to leach out when substrates colored with them are wed.
In the literature, attempts to combine the advantages of the known inorganic and organic pigments have already been described. U.S. Pat. No. 3,950,180 discloses a composite material which is based on an organic, basic dye and a mineral, viz. a zeolite or montmorillonite. It has been found, however, that the dye is not very homogeneously distributed over the mineral. Nor can a substrate be colored sufficiently homogeneously with such a composite material.
The international patent application 92/00366 describes a coloring pigment based on a layered double hydroxide and a water-soluble, anionic dye. According to a first possibility, this coloring pigment is prepared by calcination of the layered double hydroxide, so that carbonate ions between the clay sheets are driven out, and subsequent subjection to ion exchange with the dye. According to a second possibility, the layered double hydroxide is formed in situ in the presence of the dye. In the coloring pigment which is obtained according to one of the two possibilities, the dye is also not homogeneously distributed over the clay (the layered double hydroxide). With this coloring pigment, too, a substrate cannot be colored sufficiently homogeneously.
In the international patent application 89/09804, a coloring pigment is described which is based on a combination of a mineral material and an organic pigment. Although the mineral material is broadly defined, the document in fact only shows the use of hectorite. A hectorite slurry is prepared which is heated with stirring for half an hour to 80° C., whereafter an organic pigment is the form of an aqueous solution is added. What is described is that the thus obtained coloring pigment can be used for coloring a variety of materials, such as plastic and rubber composition. In the examples, only the coloring of polypropylene is shown.
Presently, it has been found that for the coloring of particular materials, such as non-polar materials (polymers) or polar materials (polymers). The coloring pigment described in WO-A-89/09804 is not sufficiently suitable. The coloring pigment proves difficult or impossible to distribute homogeneously in the material to be colored, which results in an unsatisfactory color quality.
It is an object of the invention to provide a coloring pigment which combines the advantages of the known organic pigments with those of the known inorganic coloring pigments; and with which polymeric materials can be colored in an efficient, homogeneous manner. Contemplated is a class of coloring pigments with which a large number of diverse colors of high intensity can be given to a polymer substrate, which coloring pigments can be broken down properly and fast in the environment. Further, the coloring pigment should be stable under the influence of light, oxygen and but. It is another object of the invention to provide a coloring pigment which can be incorporated in a homogeneous manner in a large variety of materials to be colored, so that a colored material with an intense color in an optimum color quality is obtained.
Surprisingly, it has presently been found that the stated objects can be achieved by preparing a coloring pigment in a specific manner from as organic dye and a day. Accordingly, the invention relates to a method for preparing a coloring pigment, wherein an anionic or cationic clay, which clay contains substantially no agglomerates of day sheets, is subjected to an ion exchange with an organic dye.
It has been found that the present method leads to a coloring pigment with a very high intensity. In other words, to obtain the same color intensity as with a coloring pigment from the prior art, a much smaller quantity of coloring pigment can suffice. Further, any color shade can be achieved that can also be created with known organic pigments. Another great advantage of the invention is that the coloring pigment can be incorporated into substrates very well. A very homogeneous color effect is obtained, while substantially no individual coloring pigment particles are perceptible. Leaching out of the coloring pigment does not occur, at least occurs to a much lesser extent than in the known organic pigments. Further, the present coloring pigment is very stable, in comparison with organic dyes, under the influences of light, oxygen and heat, and does not yield any, or hardly any, environmental hazard.
The clay which is used in the present method is an anionic or a cationic clay. In principle, any anionic or cationic clay obtained synthetically or from a natural source can be used. Suitable examples can be selected from the classes of smectites, hydrotalcites and layered double hydroxides. Particularly preferred are cationic clays, such as sodium or hydrogen montmorillonite, and hydrotalcites.
As already indicated hereinabove, it is an important aspect of the invention that the clay contains substantially no agglomerates of clay sheets. All clay types consist of a sheet structure. Under normal conditions, these sheets form agglomerates, whereby the clay sheets stack onto each other. According to the invention, these agglomerates are to be substantially broken, so that the relative distance between the clay sheets is at least 50 Å, preferably at least 75 Å, and still more preferably at least 100 Å. This distance can be suitably determined using x-ray diffraction techniques.
An example of a suitable procedure for breaking the agglomerates in the clay, i.e., for deagglomeration, is a method whereby the clay is dispersed in, preferably, water that is substantially free of ions. This water preferably has a temperature of 20-40° C. Preferably, the amount of clay is not more than 10% by weight, based on the dispersion, so that the viscosity remains low. This has a positive effect on the processability of the dispersion. Thereafter, the clay is allowed to swell for a period between half an hour and a few hours. Other methods to break the agglomerates in the clay are known to those skilled in the art.
Under certain circumstances, in particular when the coloring pigment to be prepared is to be used for coloring non-polar materials (polymers), it may be desirable to modify the clay and/or the finished coloring pigment.
In this connection, it is noted that according to the invention the classification of a material to be colored into the group of polar or non-polar materials is based on a solubility parameter. This is a parameter in which dispersive and polar properties, as well as the presence of hydrogen bridges, of a material are expressed. According to the invention, when the solubil

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