Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1998-12-21
2001-07-31
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S401000, C106S461000, C106S466000
Reexamination Certificate
active
06267811
ABSTRACT:
BACKGROUND OF THE INVENTION
The present application relates to talc slurries that exhibit minimal foaming.
Talc is a mineral used in the paper making and coating arts. More specifically, talc has been used as a filler in base sheets, and as a pigment in enamel coating of papers. It is advantageous to the paper maker to receive talc in the form of a pumpable, aqueous slurry, in that it greatly simplifies the handling of the mineral.
In conventional practice the mineral processor mines the talc and suspends it in water. Talc pigment is highly hydrophobic with a surface energy of 68-70 j/cm
2
. This low surface energy makes talc difficult to disperse in water. Relatively large amounts of nonionic polymers must be used as wetting agents in combination with other dispersing agents to adequately disperse the talc. The relatively large amounts of these surface active agents present in the talc slurry disadvantageously lead to excessive foaming of the slurry. Foaming clogs screening, coating application mechanisms, and otherwise makes the handling of the slurry very difficult and impractical.
Accordingly, there is an unresolved need for a talc slurry that does not foam excessively.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a talc slurry that is resistant to foaming, and a method for making the same.
It is a further object of the invention to provide a stable talc slurry and a method for stabilizing a slurry so as to maintain talc particles in suspension for extended periods of time.
SUMMARY OF THE INVENTION
The present invention generally comprises an aqueous talc slurry with a carboxymethyl cellulose (CMC) wetting agent. The present invention further comprises a method of making a talc slurry using CMC as a wetting agent. Use of CMC as a wetting agent eliminates the foaming problems associated with prior art slurries.
A preferred embodiment of the aqueous talc slurry of the invention comprises between approximately 0.5 and 0.8 parts CMC wetting agent by weight per 100 parts dry talc. The preferred slurry further comprises at least one dispersing agent, preferably between 0.15 and 0.25 parts sodium polyacrylate by weight per 100 parts dry talc. The pH of the slurry is preferably adjusted to between 9 and 11 prior to addition of the dispersing agent; between 0.03 and 0.06 parts NaOH per 100 parts dry talc will result in this pH level. The solids content of the slurry is between approximately 55% and 65%, and the slurry viscosity is less than 100 centipoise.
The slurry of the invention has been found to have an entrained air content of less than 4% after mixing during its preparation; and preferably of less than 1%. Entrained air content will be even less should the slurry be allowed to de-aerate. Such a low entrained air content results in minimal foaming, thereby allowing for the slurry of the invention to be easily screened and otherwise processed. The slurry of the invention may also advantageously be used in the wet end of paper making machine without significantly affecting the wet end charge balance.
Aqueous talc slurries are subject to quickly settling out. For prolonged stability, the talc slurry of the invention may further comprise a stabilizing agent. A small amount of xanthan gum has been found to extend the stability of the preferred slurry of the invention from a few days time to 3-4 weeks. A preferred concentration is between 0.03 and 0.08 parts by weight xanthan gum per 100 parts dry talc.
The present invention further comprises a method of preparing an aqueous talc slurry. The preferred method comprises the steps of first mixing between approximately 0.5 and 0.8 parts by weight CMC with 167 parts water with mixing at low shear for at least approximately 30 minutes. Between approximately 0.03 and 0.06 parts NaOH is next added to bring the pH to a level of about 10. This pH level has been found to benefit the wetting of the talc pigment. The next step comprises the addition of between approximately 0.15 and 0.25 parts sodium polyacrylate dispersing agent, followed by the step of dispersing approximately 100 parts dry talc into the mixture while at low shear mixing. After completing addition of the talc, the mixing rate is increased to high shear for at least approximately 30 minutes.
To prolong the stability of the slurry, the preferred method of preparation further comprises adding between approximately 0.03 and 0.08 parts xanthan gum stabilizing agent by weight per 100 parts dry talc.
The preferred method of preparation of an aqueous talc slurry of the invention results in a slurry having an entrained air content of less than 1% after mixing during preparation. Such a low content insures minimal foaming, so that the slurry prepared by the method of the invention can be readily screened and otherwise processed.
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description and examples that follow may be better understood, and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the examples of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the compositions and methods set forth in the following description. The present invention is capable of other embodiments and of being practiced and carried out in various ways, as will be appreciated by those skilled in the art. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.
DETAILED DESCRIPTION
The aqueous talc slurry of the invention comprises carboxymethyl cellulose (CMC) wetting agent. A CMC wetting agent has been found to eliminate the foaming problem associated with aqueous talc slurries that has been heretofor unresolved.
Not all CMC's are useful as wetting agents. High molecular weight CMC yields less surface area per unit weight but is effective in separating the individual talc particles, resulting in generally good dispersant properties but bad wetting properties. A slurry prepared with CMC of too high a molecular weight will be overly viscous. Lower molecular weight CMC is very effective in wetting the talc, but is less effective as a dispersant. A slurry prepared with a CMC of too low a molecular weight will result in a slurry of poor talc suspension. A preferred molecular weight range of CMC for the slurry of the present invention has been found to be between approximately 50,000 and 150,000. A most preferred CMC molecular weight is approximately 80,000; CMC of this weight is commercially available under a Finnfix-30 trade name from Metsa Specialty Chemicals OY, Aonekoski, Finland. A useful composition range for CMC in the talc slurry of the invention is between 0.2 and 2 parts by weight per 100 parts dry talc, with a preferred concentration range of 0.5 to 0.8 parts. The most preferred composition is 0.7 parts by weight per 100 parts dry talc.
The preferred slurry of the invention further comprises NaOH for its effect on the pH of the slurry. NaOH is added to adjust the pH of the slurry to a value of about 10 prior to addition of a dispersing agent. A useful concentration range for the slurry of the invention is between approximately 0.01 to 1 part by weight per 100 parts dry talc. In the preferred slurry, between 0.03 and 0.06 parts NaOH is present by weight per 100 parts talc, with a most preferred concentration of 0.05 parts. It is noted that NaOH presence is not required in the slurry of the invention; the presence of the talc alone, for instance, is known to result in an alkaline solution. Also, alkaline materials other than NaOH as are known in the art may be used to adjust the pH to the desired level.
The slurry of the invention also preferably comprises a dispersing agent to aid in the distribution of the talc. Any commercially available anion
Bell Mark L.
DiVerdi Michael J.
Greer Burns & Crain Ltd.
Stora Enso North America Corp.
LandOfFree
Talc slurry dispersion does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Talc slurry dispersion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Talc slurry dispersion will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2502401