Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1997-05-29
2000-05-09
Le, Hoa T.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
428407, 210728, 25217423, 526335, 526910, 526911, 526916, B32B 516
Patent
active
060601647
DESCRIPTION:
BRIEF SUMMARY
This invention relates to polymers which can be used as flocculants or viscosifiers and, in particular, to ways of providing such polymers in powder form while retaining known advantages of polymers which commercially have previously been provided in liquid form.
BACKGROUND OF THE INVENTION
Polymers which are to serve as flocculants or viscosifiers tend to provide a high aqueous solution viscosity with the result that it is not practicable to supply such polymers to the user in the form of aqueous compositions. Usually the polymers are supplied as powders or reverse phase emulsions.
The powders are usually made by gel polymerisation followed by comminution and drying or by reverse phase bead polymerisation followed by drying, filtration and, if desired, comminution. The reverse phase emulsions are made by reverse phase emulsion polymerisation to form an emulsion of small (below 10 .mu.m) aqueous polymer droplets in a non-aqueous liquid. Frequently, the user is supplied with this emulsion of aqueous polymer particles. It is, also, known to subject the emulsion to distillation so as to form an emulsion of substantially non-aqueous polymer particles in the non-aqueous liquid, and then supply the user with this. However it is also known to recover powder from the emulsion.
A typical process for this recovery is described in U.S. Pat. No. 3,284,393 and involves diluting the emulsion of aqueous polymer particles with non-aqueous liquid and then flocculating the particles with acetone, filtering them from the emulsion and drying under vacuum.
However this has not proved to be commercially successful. One of the reasons for this is probably that it is difficult to control the agglomeration or precipitation of the emulsion so as to form aggregates of controlled size in an economic manner.
Another way which has been proposed in the literature for recovering water soluble dry, polymer from a reverse phase polymer emulsion is by spray drying. An example of such a disclosure is in U.S. Pat. No. 4,035,317. However spray drying processes also have not proved to be of any significant technical value in the recovery of powder from reverse phase emulsions and, so far as we are aware, there is no commercial production of spray dried granules of water soluble polymer made by reverse phase emulsion polymerisation.
Instead, the present state of the technology is that viscosifier or flocculant polymers which are required in powder form are made by gel or bead polymerisation and they are only made by reverse phase emulsion polymerisation if they are going to be supplied in the form of reverse phase emulsions.
One disadvantage of putting the polymers into powder form by any of these techniques is that it is necessary to put them into the form of a homogeneous aqueous composition before use as viscosifier or flocculant. Thus the water soluble powder is dissolved in water to make a homogeneous solution. It is well known that the contact between particles of water soluble high molecular weight polymer in the presence of water is liable to lead to the formation of gelatinous agglomerates which can take a long time to dissolve. Accordingly special techniques and apparatus have been developed for minimising the accidental formation of these agglomerates during the dissolution of the soluble polymer. As a result, provided that reasonable care is taken, the soluble polymer can be put into true homogeneous solution irrespective of whether it is provided as particles of regular or irregular size and irrespective of whether the particles have been made by gel polymerisation, bead polymerisation or some other technique.
When a water soluble, reverse phase emulsion, polymer is being used in liquid form, the normal process for "activating" the emulsion comprises mixing the reverse phase emulsion with water in the presence of an oil-in-water emulsifier. Again, suitable procedures for achieving a homogeneous solution by such activation procedures are well known and can result in rapid activation of the individual polymer particles, substantial
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Field John Rodney
Green Michael
Hawe Malcolm
Ciba Specialty Chemicals Water Treatments Limited
Crichton David R.
Le Hoa T.
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