Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1995-10-11
1998-02-10
Merriam, Andrew E. C.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524922, 524377, 524378, 524394, 210734, 525187, 525530, C02F 152, C02F 156
Patent
active
057170231
DESCRIPTION:
BRIEF SUMMARY
This invention relates to solid products which comprise water soluble or water swellable polymeric particles.
In order to utilise the polymeric material in such particles, for instance as viscosifier or flocculant, it is usual practice first to expose the particles to water under conditions that allow full hydration of the particles either to form a solution of the polymeric material or to form a suspension of highly swollen particles in water. Various problems can arise in handling the polymer particles prior to and during the exposure to the water.
For instance the particles may tend to acquire a gel layer upon initial exposure, which gel layer may inhibit access of water and cause aggregation, thus interfering with dissolution or swelling of the particles. This problem can be minimised in many instances by appropriate selection of the exposure conditions but in some instances it is not possible to optimise these. It is known to apply coatings of various materials to the particles in order to try to minimise this problem. These problems arise even when the polymer particles are relatively coarse (e.g. 100 .mu.m to 800 .mu.m).
Particular problems arise in the handling and exposure to dissolution water of polymer particles which are fines, below 100 .mu.m and often below 70 .mu.m.
Conventional methods for making dry water soluble or water swellable polymer particles as a powder (for instance gel polymerisation followed by comminution and drying or reverse phase bead polymerisation) tend to result in a product that contains some of these fines. Handling a powder product which consists of or contains a significant amount of such fines is undesirable since they can impart undesirable environmental, flow and dissolution effects. Accordingly it is conventional to separate unwanted fines from the coarser particles, and it is then necessary to find a use for them. Commonly they are recycled into the process, often after aggregation by contact with moisture, and various proposals have been made for bonding them into aggregates using a small amount of a bonding agent (see for instance EP-A-326382 and EP-A-401044). It is also known that coating the particles can facilitate dispersion into water.
In U.S. Pat. No. 3,839,500 polymer particles are coated with 0.1 to 20%, usually 0.1 to 10%, by weight polyalkylene glycol. It is mentioned that the process results in reducing the proportion of fines by agglomeration to form larger particles. The glycol is generally applied from a solution but it is mentioned that the coating can be achieved by mixing the particles with solid granulated polyalkylene glycol in a rotating drum or blender at a temperature sufficient to melt the glycol, the blended product is then cooled while mixing, and the cooled product is discharged from the blender.
In U.S. Pat. No. 4,389,506 fines in a polyvinyl alcohol powder are agglomerated by contacting the powder with 0.5 to 4% molten polyethylene glycol. Other processes of coating or agglomerating polymer particles are described in DE-A2616639, JP-A-57049643 and JP-A-57162610. In U.S. Pat. No. 3,891,592 polyalkylene glycol is included in the aqueous phase of an oil-in-water polymerisation emulsion so as to agglomerate the emulsion particles.
Although it is conventional practice to dissolve water soluble particulate polymeric flocculant in water to form a dilute aqueous solution of the polymer and then to add this solution to the suspension that is to be flocculated, other ways of administering the polymeric flocculant to the suspension are known. In particular, it is known to place blocks containing flocculant in a flowing stream so as to allow the block to be eroded with resultant entrainment of the flocculant from the block. For instance it is known to flow the suspension past a block formed from a blend of particulate polymeric flocculant and a salt such as sodium carbonate. In JP-B-4726584 (JP-A-44102922) a foamed block is formed from a polyacrylic ester polymer, alginate polymer, aluminium sulphate, water and a foam-forming material. In EP-A-2
REFERENCES:
patent: 3839500 (1974-10-01), Dexter
patent: 3891592 (1975-06-01), Chauvel et al.
patent: 3960584 (1976-06-01), Savage
patent: 4389506 (1983-06-01), Hassell, Jr.
patent: 4438015 (1984-03-01), Huber
patent: 5171781 (1992-12-01), Farrar et al.
Allen Adrian Swinburn
Batty Norman Stewart
Moody Gillian Mary
Whitley Martin William
Allied Colloids Limited
Merriam Andrew E. C.
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