Methods of making crystalline-coated polymeric materials

Details Methods of making crystalline-coated polymeric materials Methods of making crystalline-coated polymeric materials

1993-01-15

1994-11-08

Szekely, Peter

Coating processes

Particles, flakes, or granules coated or encapsulated

Resin base

428407, 523204, 523205, 523207, 523210, B05D 702, B32B 2706, C08K 902, C08K 910

Patent

active

053625170

DESCRIPTION:

BRIEF SUMMARY
This invention relates to particulate compositions of water soluble or water swellable polymeric material, and their preparation and use, wherein the compositions are particularly designed to distribute very rapidly and easily into water or other aqueous medium.
It is well known that when particles of water soluble or water swellable polymeric material are mixed with water there is a tendency for the particles to agglomerate into sticky lumps. Initial contact of the water with the polymer particles tends to form a sticky gel around the surfaces of the particles. The presence of this gel layer tends to reduce ingress of water into the particles, thus reducing the rate of dissolution or swelling of the polymer. Because the particles are sticky, they tend to agglomerate, thus reducing still further the ingress of water into the particles. This problem increases as the molecular weight of the polymer increases and as the particle size decreases. Thus, although small particles ought to dissolve or swell more quickly (because in theory they have a larger surface area exposed to water) in practice the presence of "fines" tends to lead to agglomeration problems.
It is therefore necessary to try to keep the particles apart during the initial dissolution stages, so as to prevent agglomeration.
One standard technique is to wet the particles with an organic solvent such as acetone before admixture with water, but the use of organic solvent is inconvenient on an industrial scale.
Various forms of mixing apparatus are known but many of them do not really solve the problem since they tend to apply turbulence after the formation of sticky aggregates, rather than prevent the formation of sticky aggregates. One successful apparatus involves entraining the particles in air and passing this stream through a mist of water droplets, so that initial swelling and dissolution starts while the particles are entrained in air. This is successful, but it would be desirable to provide the composition in a form that could easily be dissolved or distributed into water merely by mixing.
Numerous proposals have therefore been made for providing the polymer particles in compositions which have the property of promoting distribution in water.
One known method comprises providing cross linking at the surface of the particles, for example by spraying powdered particles of sodium polyacrylate homopolymer or copolymer with a polyvalent metal compound or by including such a compound in an oil phase in which the particles are made by reverse phase polymerisation.
This technique can be adequate when the particles are relatively large (e.g., above 100 .mu.m) and when the polymer is a swellable cross linked polymer. It can be less satisfatory when the polymer is intended to be wholly soluble, since the cross linking can produce some insolubility. The process can be inconvenient and uneconomic to operate on a large scale and tends to give incomplete surface treatment. Thus, when spraying, parts of the polymer surfaces are liable to remain untreated. In particular, the process is inadequate for the treatment of polymer fines. If sufficient is applied for treating fines and/or minimising the risk of an incomplete coating, the risk of insolubility increases.
It is also known to provide pellets of polymeric particles that are pressed together in admixture with diluents and fillers, that may be a variety of particulate materials that can be soluble or insoluble and can be organic or inorganic. When the filler is a particulate inorganic material, the pellet consists of the polymer particles in side by side relationship with the filler particles. If the filler is easily water soluble, it may promote the permeation of water into the pellet and accelerate the initial disintegration of the pellet. However once permeation of water and disintegration of the pellet starts, the surfaces of the particles will be exposed to each other and to water, and so again gel blocking is likely to occur, especially in view of the close proximity of the water soluble particles a

REFERENCES:
patent: 3657182 (1972-04-01), Jolly
patent: 3766120 (1973-10-01), Gershberg
patent: 4010135 (1977-03-01), Tutein
patent: 4012354 (1977-03-01), Paul
patent: 4105827 (1978-08-01), Brichard et al.
patent: 4409353 (1983-10-01), Umekawa et al.
patent: 4880870 (1989-11-01), Zimmermann et al.

Affiliated with

Also associated with

Rating

Methods of making crystalline-coated polymeric materials does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Methods of making crystalline-coated polymeric materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods of making crystalline-coated polymeric materials will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1780726