Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-02-17
2001-05-01
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C264S004330, C264S004700, C424S405000, C424S408000, C424S417000, C424S490000, C428S423100, C428S474400, C523S200000, C525S902000
Reexamination Certificate
active
06225372
ABSTRACT:
This invention relates to condensation polymers and their production and in particular to membranes, especially capsule walls, formed of such polymers. In particular, the invention relates to the production of particles which have a core of core material encapsulated within a polymeric shell, including the production of such particles as a substantially stable dispersion in a liquid.
Various methods are known for forming capsules having a shell core configuration. One method involves coacervation of a polymer around the core. Methods of forming a coacervate coating from a polymer solution around an aqueous core, and which are suitable for the manufacturer of micro capsules that can be included in a liquid detergent concentrate, are described in, for instance, the EP356239 and WO92/20771. It is difficult to obtain by this technique a product in which the enzyme is retained satisfactorily in the particles while in the concentrate but is reliably released from the particles when the concentrate is diluted into wash water.
Another known method for making the shell of capsules having a shell core configuration is interfacial polymerisation in which one or more monomers polymerise at the interface between a dispersed phase and a continuous phase to form a shell around the dispersed phase. One particular type of interfacial polymerisation is interfacial condensation (IFC) polymerisation. The polymer shell forms at the interface between an oil phase and an aqueous phase as a result of reaction between a water soluble IFC reactant (in the aqueous phase) and an oil soluble IFC reactant (in the oil phase).
IFC polymerisation has been applied for encapsulating a hydrophobic or oil core by forming an oil- in-water dispersion and causing IFC polymerisation around each dispersed oil droplet. Methods for performing this reaction have been developed to allow reasonably satisfactory encapsulation. However these methods are of no value when the core material is aqueous or hydrophilic and, instead, it is then necessary to conduct the IFC polymerisation in a water-in-oil dispersion, i.e. in a dispersion in which the aqueous or hydrophilic core material is dispersed in a continuous oil phase.
Although it is suggested in some patent examples, e.g., in JP-A-63-137996 that the water-in-oil process is satisfactorily operable, we have found that in practice it is not easy to obtain satisfactory results using environmentally acceptable materials. For instance there is a risk that a substantial amount of the product may be a sediment or not encapsulated, and the process may require the use of a halogenated hydrocarbon. This may have good properties for the IFC polymerisation but is now considered environmentally undesirable. The process can be particularly difficult when it is desired to achieve a small particle size (e.g. at least 90% by weight below 30 &mgr;m) and a product in which substantially all the core material is enclosed within such particles and the particles are substantially stably dispersed in a liquid.
It might be thought that the formation of a fine dispersion, i.e. an emulsion, would be promoted by the use of a water-in-oil emulsifier. However we have found that if we use a conventional water-in-oil emulsifier such as Span 85 (trade mark) it is difficult to obtain a dispersion of satisfactory encapsulated particles in oil, especially when the amount of dispersed phase is reasonably high. Increasing the amount or effectiveness of a conventional type of water-in-oil emulsification system does not improve the result. Instead, it seems to tend to reduce satisfactory shell formation and to increase the risk of non-uniformity in the shell.
In EP-A-0671206, an IFC process is described for making the shell of microcapsules having a size below 1 &mgr;m and is characterised by the use of a block copolymer as a protective colloid. A mixture of one of the IFC reactants with the core material is dispersed in a water immiscible liquid and the other IFC reactant is dripped into this. In each of the examples, the core material is a non-aqueous core based on polyethylene glycol and the stabiliser is selected from polysiloxane polyalkylene oxide block polymers, block polymers of lauryl methacrylate and polyhydroxyethyl acrylate, together with a graft polymer of methyl methacrylate, cetyl methacrylate and an ethylene oxide adduct of hydroxyethyl methacrylate. These stabiliser systems will be somewhat similar to water-in-oil emulsifiers because of their very pronounced physically separate hydrophilic moieties (i.e., the hydrophilic block) and hydrophobic moieties (i.e., the hydrophobic block). These systems tend to give unsatisfactory results when used in the manner described in EP 671206.
Accordingly there remains a need for IFC products and processes which can be conducted in convenient manner using convenient and environmentally acceptable materials to give a satisfactory wall structure and a product of satisfactory and predetermined particle size.
According to the invention, we provide a particulate composition comprising particles having a hydrophilic core within a shell comprising a membrane comprising an association product of (a) an IFC condensation product formed by reaction between a first IFC reactant having at least two first condensation groups and a second IFC reactant having at least two second condensation groups, and (b) an amphipathic polymeric stabiliser which will concentrate at the interface between oil and water and which has recurring hydrophobic groups and recurring reactive hydrophilic groups which associate with the second condensation groups.
The association may comprise a condensation reaction between the reactive hydrophilic groups and the second condensation groups. For instance when, as is preferred, the reactive hydrophilic groups comprise carboxylic acid groups and the second condensation groups are amino, the association may involve the formation of an amide condensate linkage between the stabiliser and the IFC condensation product. This is thought to occur particularly when the stabiliser is a copolymer of an ethylenically unsaturated carboxylic anhydride, such as maleic anhydride.
However the association can be any other type of association that results in attraction between the stabiliser and the second reactant (and thus also the IFC condensation product). The association often comprises ionic association, for instance as a result of the formation of an ionic salt between carboxylic groups and groups which will form a salt with them. For instance the polymeric stabiliser may have carboxylic groups and a salt forming amine IFC reactant will then form a salt with them. It is then preferred that the amine should have been introduced in free base form, so as to minimise competition between the carboxylic groups and other acid moieties in the reaction mixture.
Best results seem to be achieved when the polymeric stabiliser is a copolymer of ethylenically unsaturated polycarboxylic acid (including dicarboxylic acid and the anhydrides) such as maleic acid or maleic anhydride, and the second reactant is a polyamine (including diamines, triamines and tetra amines) preferably having two to six carbon atoms between the amine groups. It appears that this configuration of adjacent carboxylic groups and diamine or higher groups is particularly conducive to the formation of strong association between the amine and the stabiliser, probably due to the formation of an internal, ring-formed, salt between the adjacent carboxylic groups and the diamine groups.
The invention also provides various processes for making particles having hydrophilic core within a shell formed by IFC polymerisation of a substantially oil soluble first IFC reactant having at least two first condensation groups with a substantially water soluble second IFC reactant having at least two second condensation groups. These processes all comprise forming a water-in-oil emulsion of an aqueous core composition comprising core material and a second reactant in a water immiscible liquid which contains an oil soluble or oil s
Lykke Mads
Mistry Kishor Kumar
Simonsen Ole
Symes Kenneth Charles
Ciba Speciality Chemicals Water Treatments Limited
Niland Patrick D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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