WO2007141123A2

WO2007141123A2 - Polymeric particles and their preparation

Info

Publication number: WO2007141123A2
Application number: PCT/EP2007/054814
Authority: WO
Inventors: Bryan Grey; Kishor Mistry; Paul Dymond
Original assignee: Ciba Holding Inc.
Priority date: 2006-06-09
Filing date: 2007-05-18
Publication date: 2007-12-13
Also published as: GB0611422D0; WO2007141123A3

Abstract

Invention relates to polymeric particles containing microcapsules distributed throughout the polymeric particles, wherein an amphipathic stabiliser is located at the surface of the polymeric particles. Also encompassed by present invention is a process of producing polymeric particles containing microcapsules distributed throughout the polymeric particles, comprising the steps: i) providing a water immiscible liquid containing an amphipathic stabiliser, ii) providing a dispersion of microcapsules in an aqueous liquid, iii) dispersing the dispersion into the water immiscible liquid and agitating to form a water in oil emulsion or a water in oil suspension, iv) subjecting the water in oil emulsion or water in oil suspension to dehydration by dis tillation to form a dispersion of polymeric particles in the water immiscible liquid and, v ) recovering the polymeric particles. The particles of invention are particularly useful for heat storage compositions in which the microcapsules contained therein have in their core a phase change material.

Description

Polymeric Particles And Their Preparation

The present invention relates to polymeric particles containing microcapsules distributed throughout and their manufacture. The microcapsules may contain any variety of active ingredients including UV absorbers, thermal storage substances such as phase change materials, flame retardants etc. The particles may be used in a variety of applications including textiles and in the construction industry.

There are many instances where it would be desirable to provide capsules comprising a shell surrounding a core material. For instance, the core may comprise an active ingredient which is released slowly, such as fragrances, pesticides, medicaments and the like. In other instances it may be desirable for the core material encapsulated within the shell to remain substantially intact either permanently or at least until a suitable trigger induces the core to be released. There are instances where it is important that the core material is not released from the capsules. This includes, for example, encapsulated ultra violet light absorbers for use in sunscreens and articles of clothing.

Another important application includes encapsulated phase change materials which can be used as thermal energy storage products. Such products include fabrics and especially clothing. Particles comprising encapsulated phase change hydrocarbon material may be applied to fabrics or incorporated into fibres that form the fabrics.

In the field of thermal energy storage it is known to use phase change materials. Energy is stored in such materials as latent heat achieved by the material changing phase, for instance changing from solid to liquid. Energy is released when the material reverts to the previous phase, for instance when the liquid phase solidifies. Phase change materials may be used in a variety of physical forms when used in thermal energy storage applications. A particularly desirable product includes micro encapsulated phase change materials, in which the phase change material is held in the core surrounded by a shell wall. Conventionally, microencapsulated phase change materials tend to have weight average particle sizes no greater than 50 microns.

Various methods for making capsules have been proposed in the literature. For instance it is known to encapsulate hydrophobic liquids by dispersing the hydrophobic liquid into an aqueous medium containing a melamine formaldehyde pre-condensate and then reducing the pH resulting in an impervious aminoplast resin shell wall surrounding the hydrophobic liquid. Variations of this type of process are described in GB-A-2073132, AU-A- 27028/88 and GB-A-1507739, in which the capsules are preferably used to provide encapsulated inks for use in pressure sensitive carbonless copy paper.

GB 1529231 describes an opacifying agent consisting of substantially spherical particles having a spherical discontinuous shell formed from agglomerated discrete, secondary particles in which this shell surrounds a substantially spherical hollow core.

WO-A-01 /54809 provides acrylic capsules which can easily be incorporated into fibres. The capsules contain a polymeric shell which is formed from a monomer blend comprising A) 30 to 90% by weight methacrylic acid, B) 10 to 70% by weight alkyl ester of (meth)acrylic acid which is capable of forming a homopolymer of glass transition temperature in excess of 6O⁰C and C) 0 to 40% by weight other ethylenically unsaturated monomer.

WO-A-9924525 describes microcapsules containing as a core a lipophilic latent heat storage material with a phase transition at -20 to 12O⁰C. The capsules are formed by polymerising 30 to 100 wt. % C 1-24 alkyl ester of (meth)acrylic acid, up to 80 wt. % of a di- or multifunctional monomer and up to 40 wt. % of other monomers. The microcapsules are said to be used in mineral molded articles. Microencapsulated products tend to have a weight average particle size diameter of no greater than 50 microns. These products may be provided as dispersions, for instance water continuous slurries, particularly where the particle size is below 20 or 30 microns, but may be provided as a solid particulate products or for example as wet cakes containing up to 60 or 70% by weight of the solid product. However, there are a number applications where it will be desirable to use the products in a solid particulate form larger than 50 microns. It would also be desirable to provide a solid product that has improved flow properties and handleability properties. This would be particularly true for microencapsulated phase change materials used in the textiles industry. It would also be desirable to provide products for use in textiles exhibiting longer term thermal regulation. However, the microcapsules of up to 50 microns provided in solid form tend to suffer handleability problems, such as dusting especially when they are below 20 or 30 microns. Such larger encapsulated products would have the advantage of having the potential for inclusion of a larger amount of active ingredient, for instance phase change material in energy storage products. It would therefore be desirable to provide encapsulated products in a solid form having weight average particle size diameters in excess of 50 microns. However, in many applications, such as the textile processing, larger capsules tend to be prone to damage. Therefore, a further objective is to produce such larger sized particles containing encapsulated active material that are stronger and able to withstand processing in an industrial application, for instance textile applications.

It is generally difficult to produce capsules of weight average particle size diameter greater than 50 microns by direct means. Furthermore, we have found that attempts to produce capsules of larger sizes often result in instability and result in a certain amount of agglomeration of the capsules. Such uncontrolled agglomeration may lead to inferior products which are more difficult to process and furthermore the agglomerates may form deposits on the inside of the reactors and other equipment used to produce the capsules, necessitating the interruption of production in order to remove the unwanted agglomerates.

Another approach would be to prepare conventional microcapsules, typically of particle size below 50 microns, and convert these to macrocapsules of particle size greater than 50 microns.

However, such a conversion risks damage to the microcapsules resulting in release of the core material.

US 6835334 and US 6703127 each describe macrocapsules prepared by a process of encapsulating microcapsules by adding a slurry of said microcapsules suspended in a gelling agent to a cross-linking solution such that the gel cross-links to form discrete gel droplets containing a plurality of microcapsules which are then rinsed, dried and separated. However, careful condition of the additives would be required in order to prevent uncontrolled gelation. Hence this method requires a high degree of precision in controlling the process which may make large scale production more difficult.

WO 2006 018130 describes the course particle microcapsule preparation in which the particles have a size between 200 microns and 5 cm in which the capsule wall contain a duroplastic polymer and at least one polymer binding agent having thermoplastic properties and film forming properties. A granulator is used in the processing. However, the resultant preparation consists of coarse particles which tend to have a broad distribution of particle sizes.

The objective of the present invention is to provide large particles containing encapsulated material and a method for preparing them that overcomes the aforementioned disadvantages. It would also be desirable to provide a method that avoids any damage to the capsules or microcapsules which would otherwise result in loss of the core material.

The present invention provides polymeric particles containing microcapsules distributed throughout the polymeric particles, wherein an amphipathic stabiliser is located at the surface of the polymeric particles.

The particles exhibit and high degree of resilience to damage and so they can be used in many industrial applications. We have found that the particles of the invention do not easily fracture or disintegrate and will retain the constituent microcapsules. Generally the particles may be substantially spherical and be in the form of beads. When the products are in the form of beads, they tend to exhibit improved flow properties, which is important for the transfer of the products, especially through small diameter conduits or small diameter exit points on holding vessels. The particles of the present invention containing therein microcapsules may be regarded as macrocapsules. Furthermore, they may be regarded as multicomponent macrocapsules containing a plurality of microcapsules.

Typically the microcapsules contained in the particles of the invention will have a core shell configuration. The core material may comprise an active ingredient selected from the group consisting of UV absorbers, UV reflectors, flame retardants, active dye tracer materials, pigments, dyes, colorants, enzymes, detergent builders and fragrances. Generally within the context of the present invention it would be unnecessary for the active ingredient to be released. For instance encapsulated pigments may be used in pigmented articles, such as ceramics, where it would be important for the pigment not to be released. There is also an application for encapsulated colorants, i.e. dyes and pigments for many other applications, for instance in preparing textile products. Thus the particles comprising a pigment or dye can be incorporated into or adhered to a fibre or textile article. The colour would be held by the particle and there would be no risk of colour leaching. Alternatively the encapsulated colorant may be applied to packaging materials, for instance food packaging. Thus shaded paper or board used in food packaging may be prepared by including the encapsulated pigments or dyes into the paper making process. Typically the colorants can be C.I. Pigment Violet 19, C.I. Pigment Blue 15, C.I. Pigment Blue 60, C.I. Pigment Red 177 as described in WO-A-00/61689

Alternative applications of encapsulated pigments includes cosmetics, for instance as described in US-A-5,382,433, US-A-5,320,835 or WO-A-98/50002. Typically the colorants can be mica, talc, D&C Red 7 Calcium Lake, D&C Red 6 Barium Lake, Iron Oxide Red, Iron Oxide Yellow, D&C Red 6 Barfum Lake, Timiron MP-1001 , Mineral (Carnation White), Helindon Pink, Red 218, Japan Blue No.1 Al lake, Polysiloxane-treated Titanium mica.

Suitable ultra violet light absorbers of the present invention include naphthalene- methylenemalonic diesters, for instance as mentioned in US-A- 5508025 or compositions comprising mixtures of benzotriazoles and 2-hydroxy benzophenones as claimed by US-A-5498345.

When the core material is a phase change substance it may be for instance any known hydrocarbon that melts at a temperature of between -30 and 15O⁰C. Generally the substance is a wax or an oil and preferably has a melting point at between 20 and 8O⁰C, often around 4O⁰C.

Preferably the phase change material is selected from the group consisting of paraffin hydrocarbons, natural waxes, fatty alcohols, fatty acids, fatty esters and fatty amides. Desirably the phase change substance may be a Cs_-4O alkane or may be a cycloalkane. Suitable phase change materials includes all isomers of the alkanes or cycloalkanes. In addition it may also be desirable to use mixtures of these alkanes or cycloalkanes. The phase change material may be for instance any of the compounds selected from n-octadecane, n-tetradecane, n- pentadecance, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, n- eicosane, n-uncosane, n-docosane, n-tricosane, n-tetracosane, n-pentacosane, n-hexacosane, n-heptacosane, cyclohexane, cyclooctane, cyclodecane and also isomers and/or mixtures thereof. Examples of suitable matter waxes for use as phase change materials include beeswax, Candelilla wax, Carnauba wax, palm wax, beatle wax. Typical fatty acids for use as phase change materials include any carboxylic acid having between 8 and 40 carbon atoms. Preferred examples of fatty acids include lauric acid, oleic acid stearic acid, other fatty acids having between 13 and 27 carbon atoms. Suitable fatty alcohols may be any alkanol that has between 8 and 40 carbon atoms, especially lauryl alcohol, stearyl alcohol and other fatty alcohols having between 13 and 27 carbon atoms. Fatty esters that can be used for this application include esters having between 8 and 40 carbon atoms, suitably methyl stearate, methyl cinnamate, methyl laurate, methyl oleate and other fatty esters having fatty acid moieties between 8 and 39 carbon atoms and lower alkyl alcohol moieties e.g. between 1 and 5 carbon atoms or alternatively fatty esters having fatty alcohol moieties between 8 and 39 carbon atoms and lower alkanoate moieties having between 1 and 5 carbon atoms. Suitable fatty amides include amides having between 8 and 40 carbon atoms and preferably stearamide, lauramide, oleamide and other amides having between 13 and 27 carbon atoms.

In a preferred form of the invention the core consists essentially of a hydrophobic substance, for instance at least 90%, which is a non-polymeric material, for instance an oil or wax, in particular a phase change material. Although the preferred hydrophobic substance is a phase change material which is essentially non-polymeric, it is within the scope of the present invention for a smaller amounts of polymeric additives to be included within the phase change non-polymeric material. Usually this will be in amounts of less than 10% by total weight of core and often will be less than 5, for instance 0.5 to 1.5 or 2% by weight. A particularly desirable polymeric additive is a substance that will modify the properties of the phase change material. For instance it is known that the temperature at which a phase change material melts on absorbing heat can be significantly different from the temperature at which it solidifies when losing heat. Thus a particularly desirable polymeric additive would be a substance which will bring the melting and solidifying temperatures closer together. This minimisation of the shift in melting/freezing point of the phase change material may be important in various domestic applications or for garments.

Alternatively the phase change material comprised in the core could be a substance other than a hydrocarbon. The phase change material could be an inorganic substance that aborbs and desorbs latent heat during a liquifying and solidifying phase transition. The inorganic substance may be a compound which releases or absorbs heat during a dissolving / crystallisation transition. Such inorganic compounds include for instance sodium sulphate decahydrate or calcium chloride hexahydrate. Thus the inorganic phase change material may be any inorganic substance that can absorb or desorb thermal energy during a transition at a particular temperature. The inorganic phase change material may be in the form of finely dispersed crystals which are dispersed throughout the core matrix which comprises a hydrophobic substance.

Various methods for making microcapsules have been proposed in the literature. Microencapsulation processes involving the entrapment of active ingredients in a matrix are described in general for instance in EP-A-356,240, EP-A-356,239, US 5,744,152 and WO 97/24178. Typical techniques for forming a polymer shell around a core are described in, for instance, GB 1 ,275,712, 1 ,475,229 and 1 ,507,739, DE 3,545,803 and US 3,591 ,090.

Microcapsules of core shell configuration may be formed from a number of different types of materials including aminoplast materials, particularly using melamine and urea e.g. melamine-formaldehyde, urea-formaldehyde and urea- melamine-formaldehyde, gelatin, epoxy materials, phenolic, polyurethane, polyester, acrylic, vinyl or allylic polymers etc. WO01 /54809 discloses microcapsules with acrylic polymer shell material formed from acrylic monomers. Whilst microcapsules prepared with such acrylic shells and also aminoplast shells have been found to be very suitable, it is likely that other materials will also be suitable to produce microencapsulated phase change materials of this invention.

It is known to encapsulate hydrophobic liquids by dispersing the hydrophobic liquid into an aqueous medium containing a melamine formaldehyde pre- condensate and then reducing the pH resulting in an impervious aminoplast resin shell wall surrounding the hydrophobic liquid. Variations of this type of process are described in GB-A-2073132, AU-A-27028/88 and GB-A-1507739, in which the capsules are preferably used to provide encapsulated inks for use in pressure sensitive carbonless copy paper. Such techniques are known to be suitable for the manufacture of microcapsules containing phase change material. U.S. 5456852 referred to above describes microencapsulation of phase change material in a melamine formaldehyde resin shell.

Other techniques for manufacturing microcapsules containing phase change material are described in WO-A-9924525 which reveals microcapsules containing as a core a lipophilic latent heat storage material with a phase transition at -20 to 12O⁰C. The microcapsules are formed by polymerizing 30 to 100 wt. % Ci_-24 alkyl ester of (meth)acrylic acid, up to 80 weight % of a di- or multifunctional monomer and up to 40 weight % of other monomers.

WO-A-01/54809 provides capsules which can easily be incorporated into fibres without suffering the loss of an active core material during the spinning process. The capsules contain a polymeric shell which is formed from a monomer blend comprising A) 30 to 90% by weight methacrylic acid, B) 10 to 70% by weight alkyl ester of (meth)acrylic acid which is capable of forming a homopolymer of glass transition temperature in excess of 6O⁰C and C) 0 to 40% by weight other ethylenically unsaturated monomer.

A preferred microencapsulation process involves the in situ formation of a polymeric shell around emulsified or dispersed droplets of the primary phase change material/paraffinic nucleating material, resulting in a dispersion of microcapsules in water. More preferably this would be prepared according to the process described in British patent application 0520831.9 (internal attorney docket number EP/3-22375) unpublished at the date of filing the present application.

A process for making phase change microcapsules is described in International application WO 2005 105291. This process is also useful for making microcapsules used according to the present invention.

When the active material held within the microcapsules is a phase change material, it may be desirable to additionally include coadditives. Typically this may include flame retardants in order to increase the fire resistance. Furthermore, the graphite and/or metallic particles, such as aluminium powder, may also be included in order to increase thermal conductivity. In may also be desirable to include other polymers and/or cross-linkers in order to increase the robustness and shatter resistance of the particles of the invention.

The amphipathic stabiliser will generally be a compound that is polymeric and has an affinity for both aqueous phases and non aqueous phases. Typically the amphipathic stabiliser may be a polymer comprising monomeric repeating units of ethylenically unsaturated carboxylic acids and/or esters of ethylenically unsaturated carboxylic acids. Preferably the ethylenically unsaturated carboxylic esters will be alkyl (meth) acrylates and alkyl esters of other ethylenically unsaturated carboxylic acid such as maleic acid, fumaric acid and itaconic acid. More preferably the acrylic esters include C₈ to 40 alkyl acrylates and C₈ to 40 alkyl methacrylates. Particularly preferred acrylic esters include Ci₆ to 22 alkyl acrylates and Ci6to22 alkyl methacrylates such as stearyl acrylate, cetostearyl acrylate, stearyl methacrylate and cetostearyl methacrylate. It may be desirable to include other monomers, for instance styrene, methyl methacrylate, vinyl acetate etc. Preferably the ethylenically unsaturated carboxylic acid component of stabiliser include monomers such as acrylic acid, methacrylic acid, maleic acid, fumaric acid or itaconic acid. More preferably the ethnic unsaturated carboxylic acid is selected from acrylic acid and methacrylic acid.

Other materials that would work include oil-soluble polymers composed of potentially anionic monomers, i.e. monomers that would become anionic in a high pH environment, and also potentially cationic monomers, i.e. monomers that would become cationic in a low pH environment, such as an amine-type molecule. Anionic monomers include acrylic acid, methacrylic acid, maleic anhydride, ethacrylic acid, fumaric acid, maleic acid, maleic anhydride, itaconic acid, itaconic acid anhydride, crotonic acid, vinyl acetic acid, (meth) allyl sulfonic acid, vinyl sulfonic acid and 2-acrylamido-2-methyl propane sulfonic acid. Preferred anionic monomers are carboxylic acids or acid anhydrides. Particularly preferred amphipathic stabilisers include those outlined in WO-

2005-123009, page 15, lines 17 to 22 and WO-2005-123796, page 20, lines 19 to 26.

Preferably the amphipathic stabiliser should have an HLB (hydrophilic lipophilic balance) of below 10, usually in the range of 1 to 8. Typically the ratio hydrophilic monomers i.e. carboxylic acid monomers to lipophilic monomers i.e. carboxylic esters should preferably be such the polymer exhibits an HLB in the above ranges. Preferably the amphipathic stabiliser comprises 1 to 99% by weight ethylenically unsaturated carboxylic ester, preferably acrylic ester, 1 to 99% by weight ethylenically unsaturated carboxylic acid and 0 to 40% by weight other ethylenically unsaturated monomer. One desirable group of amphipathic stabilisers are formed from 25 to 99% by weight ethylenically unsaturated carboxylic ester, preferably acrylic ester, 1 to 75% by weight ethylenically unsaturated carboxylic acid especially acrylic acid or methacrylic acid and 0 to 40% by weight other ethylenically unsaturated monomer. One more preferred group of amphipathic stabilisers are formed from 1 to 75% by weight ethylenically unsaturated carboxylic ester, preferably acrylic ester, 25 to 99% by weight ethylenically unsaturated carboxylic acid especially acrylic acid or methacrylic acid and 0 to 40% by weight other ethylenically unsaturated monomer. Particularly preferred amphipathic stabilisers are polymers, which may be hydrophobic, prepared from monomers having Tg (glass transition) values between about -110⁰C and 20⁰C or mixtures thereof, for example d- C3oalkyl acrylates such as methyl acrylate (Tg 9°C), ethyl acrylate (Tg -23°C), propyl acrylate, butyl acrylate (Tg -49°C), etc., as well as others including but not limited to stearyl methacrylate (Tg -100⁰C). By referring to the glass transition temperature of monomers we mean a homopolymer formed from the specific monomer. Especially preferred amphipathic stabilisers comprised stearyl methacrylate between 30 and 60% by weight and methacrylic acid between 40 and 70% by weight.

Alternative preferred forms of the amphipathic stabiliser include a polymer formed from a monomer blend comprising alkyl(meth)acrylate(s) to carboxylic acid functional monomer ratio may be between 95:5 to 50:50 on a weight basis, preferably between 95:5 and 70:30, and most preferably between 90:10 and 75:25 on a weight basis.

Tg values are found for example in Polymer Handbook (3rd Edition), Ed. Brandrup & immergut, Pub : Wiley lnterscience , 1989 ISBN : 0-471-81244-7

Desirably the amphipathic stabiliser is a polymer of weight average molecular weight below 500,000 and preferably below 200,000. The stabiliser is particularly effective when the molecular weight is below 150,000, especially in the range of 100 to 100,000, more especially from 500 to 50,000 and more particularly between 8000 and 25,000, such as between 10,000 and 20,000.

The amphipathic stabiliser may be as a solution in an organic solvent produced by conventional means described in the literature. Typically the monomers may be dissolved in a suitable organic solvent, especially in volatile paraffin solvent such as Exxsol D40 and lsopar G. Typically the amphipathic stabiliser may be prepared by use of redox or thermal initiators.

By volatile solvent we mean a solvent whose distillation point is below 200⁰C when tested using ASTM D86-05 "" Standard Test Method for Distillation of Petroleum Products at Atmospheric Pressure" ASTM International, (lsopar M which is used as a common non-volatile solvent has an upper value of 225).

A preferred type of the polymeric amphipathic stabilizer is a copolymer of an alkyl(meth)acrylate and a carboxylic functional monomer which may be prepared as follows:

The alkyl(meth)acrylate, carboxylic functional monomer and a suitable oil soluble thermal initiator, for example 2,2'-azobis(2-methylbutyronitrile), are dissolved in an inert solvent, for example an aliphatic or aromatic hydrocarbon solvent such as ISOPAR G^®. This mixture is fed into a vessel containing further solvent and thermal initiator over a period of 2 to 6 hours at reaction temperatures of 80 to 90⁰C. The reaction is maintained at this temperature for a further two hours before being cooled and discharged.

The amphipathic stabiliser will promote stability during the preparation of the particles of the present invention and indeed enable the particles to remain intact and resilient to disintegration, thereby preventing the unwanted release of microcapsules. Generally the amphipathic stabiliser will at least partially cover the surface of the particles. By this we mean that generally the amphipathic stabiliser will at least partially cover the constituent microcapsules. Nevertheless it is preferred that the amphipathic stabiliser forms a coherent coating and more preferably forms a complete coating of the particles such that none of the constituent microcapsules are exposed.

Preferably the polymer particles of the invention will have a weight average particles sized diameter of greater than 50 microns. Typically the polymer particles may have a weight average particles sized diameter of up to 5000 microns. Suitably the particles will have a size at least 100 microns and up to 2000 or 3000 microns. More preferably the particles are in the size range of from 150 or 200 microns to 2000 microns and even more preferably between 500 microns and 1500 microns.

The microcapsules will in general have a weight average particles sized diameter of below 50 microns. Typically this may be between 0.1 and below 50 microns. The preferred particle sizes are between 0.5 and 10 microns especially between 0.6 and 5 microns. More preferably the microcapsules have average diameters between 0.75 and 1 or 2 microns.

Desirably the particles of the invention comprise a high proportion of the microcapsules. Thus the particles preferably contain greater than 50% by weight of the microcapsules. The amount of microcapsules containing in the particles may be as much as 95 or 99% by weight. Nevertheless, it is especially preferred that the particles constitute between 75 and 90% by weight microcapsules. It is possible that other materials additional to the microcapsules and amphipathic stabiliser may be used as previously stated, for instance flame retardants, graphite particles, metallic particles other polymers and cross-linkers. The other polymers and cross-linkers may for instance be used to help the bind together the microcapsules. However, it is not normally necessary for such additional microcapsules binding materials, since the amphipathic stabiliser and microcapsules themselves tend to form coherent and stable particles.

In a further aspect, the present invention also provides a process of producing polymeric particles containing microcapsules distributed throughout the polymeric particles, comprising the steps: i) providing a water immiscible liquid containing an amphipathic stabiliser, ii) providing a dispersion of microcapsules in an aqueous liquid, iii) dispersing the dispersion into the water immiscible liquid and agitating to form a water in oil emulsion, iv) subjecting the water in oil emulsion to dehydration by distillation to form a dispersion of polymeric particles in the water immiscible liquid and, v) recovering the polymeric particles.

In general the amphipathic stabiliser will tend to be located at the interface between the dispersed aqueous phase and continuous organic phase. Therefore the amphipathic stabiliser tends to be located at surface of formed particles.

Preferably the particles resulting from the process may include any of the aforementioned specific and/or preferred features concerning the polymeric particles of the invention.

Desirably the water immiscible liquid is a suitable organic liquid suitable for the dissolving the amphipathic stabiliser and dispersing droplets of an aqueous medium. Preferably the organic liquid is a volatile paraffin. By volatile paraffin we mean a paraffin whose distillation point is below 200°C when tested using ASTM D86-05 "" Standard Test Method for Distillation of Petroleum Products at Atmospheric Pressure" ASTM International. (Isopar M which is used as a common non-volatile solvent has an upper value of 225).. Preferred examples of organic liquids include Exxsol D40 and lsopar G.

In the preparation of the dispersion of microcapsules in the aqueous liquid is may for instance be the an aqueous suspension of microcapsules resulting for instance from any of the aforementioned processes of preparing microcapsules. Such a suspension of microcapsules may already contain suitable suspending agents to ensure that the microcapsules do not settle. Nevertheless it may be desirable to add further suspending agents. Such a suspension of microcapsules may be used directly in the present process or alternatively may be diluted with water or other aqueous medium. On diluting the suspension of microcapsules in may be necessary to add further stabilising or suspending agents to ensure that the microcapsules do not settle. Alternatively the microcapsules may be prevented from settling by constant agitation until they are used in the present process.

Optionally the dispersion of microcapsules may be prepared by dispersing the separated particulate microcapsules into an aqueous medium, that optionally contains a stabilising or suspending agent. Typically the dispersion of microcapsules will contain at least 20% by weight and often between 40 and 60% by weight microcapsules in the aqueous medium.

The aqueous dispersion of microcapsules is then dispersed into the water immiscible liquid. Generally, the aqueous phase is added at a rate conventionally used in the formation of for instance suspensions in reverse phase suspension or emulsion polymerisations. Usually the aqueous dispersion is added to the water immiscible liquid under constant agitation. The amount of agitation given depends upon the particular size and shape of impeller that is used to bring about agitation, the size and shape of the vessel and the volume of liquid to be dispersed. Generally this will be synonymous to conditions used in conventional reverse phase suspension or emulsion polymerisation. Typically the conditions chosen will be sufficient to form a water in oil emulsion or water in oil suspension. The formation of a water in oil emulsion will require vigorous agitation and optionally passing the aqueous phase through a screen to result in emulsification. Once and emulsion has been formed this needs only to be stirred or agitated gently. In the case of a water in oil suspension the suspension of aqueous droplets requires less agitation to be formed but a constant rate of agitation needs to be maintained in order to be the droplets buoyant in the water immiscible liquid.

The dispersed phase droplet size will generally correspond to the particle size of the polymeric particles that are eventually formed in a process.

The water in oil emulsion or the water in oil suspension thus formed is then subjected to a dehydration step. It is normally achieved by distillation to form a dispersion of polymeric particles dispersed or suspended in the water immiscible liquid. Distillation may be achieved by employing an elevated temperature and/or subjecting the emulsion or suspension to reduced pressure, for instance vacuum distillation. Preferably vacuum distillation is employed using a temperature of at least 40°C and more preferably using a temperature in the range of 50 to 70⁰C. It may be desirable and in some cases necessary to ensure that the emulsion or suspension is agitated sufficiently during the dehydration step to prevent any settling of the dispersed phase.

The polymeric particles may then be recovered by use of conventional techniques. This may be achieved by filtration and air drying using for instance a fluid bed drier. Such methods of extraction are conventional and described in the literature.

The invention also concerns polymeric particles obtainable by the above described process. The following examples are an illustration of the invention.

Example 1 :

An aqueous phase is prepared from 330 g of an approximately 45% dispersion of a microencapsulated phase change material. An oil phase is prepared by mixing 60Og of hydrocarbon solvent (Isopar G, ex Multisol, Chester UK) and 35g of 25% amphipathic polymeric stabiliser hydrocarbon solution. The amphipathic stabiliser is a copolymer of stearyl methacrylate and methacrylic acid (90/10 on a weight basis) exhibiting a molecular weight of about 20,000. This oil phase is transferred into a set of apparatus equipped for distillation A water-in-oil suspension is formed by pouring the aqueous phase into the oil phase, under continuous agitation. This dispersion is dehydrated using vacuum distillation and heating (maximum temperature 100⁰C). Once dehydration is complete, the reaction mass is cooled to 25°C and filtered to recover the beads of dehydrated mPCM (microcapsules containing phase change material), average particle size D₅₀ 300 to 500 μm. Finally the beads are air dried to yield a granular product.

Example 2:

An aqueous phase is prepared by mixing 150 g of an approximately 45% dispersion of a microencapsulated phase change material (adjusted to pH 8 using sodium hydroxide / acetic acid as needed), 50 g of a 25% solution of an aqueous copolymer of styrene/acrylic acid - ammonium salt (65/35 wt/wt ratio, molecular weight ~ 30,000) and 10g zinc oxide . An oil phase is prepared by mixing 60Og of hydrocarbon solvent (Isopar G, ex Multisol, Chester UK) and 35g of 25% amphipathic polymeric stabiliser hydrocarbon solution. The amphipathic stabiliser is a copolymer of stearyl methacrylate and methacrylic acid (90/10 on a weight basis) exhibiting a molecular weight of about 20,000. This oil phase is transferred into a set of apparatus equipped for distillation

A water-in-oil suspension is formed by pouring the aqueous phase into the oil phase, under continuous agitation. This dispersion is dehydrated using vacuum distillation and heating (maximum temperature 100°C). Once dehydration is complete, the reaction mass is cooled to 25°C and filtered to recover the beads of dehydrated mPCM (microcapsules containing phase change material), styrene based copolymer and zinc oxide, are recovered by filtration, average particle size D50 300 to 500 μm. Finally the beads are air dried to yield a granular product.

Analysis

All of the prepared samples and the base material have been analysed by thermo gravimetric analysis (Perkin Elmer DSC 7) - Table 1

Table 1 Thermo gravimetric analysis results

¹ Mass loss @ 250°C: this is the amount of material lost (expressed as a percentage) from the sample between the starting condition, 110°C, and 25CPC.

² Mass loss @ 300°C: this is the amount of material lost (expressed as a percentage) from the sample between the starting condition, 110°C, and 30CPC.

³ Half height: this is the half-height of the decay curve. ³ Melamine- formaldehyde shell chemistry: these are samples of commercial product Encapsulence PC 140 (trade mark) available from Ciba Specialty Chemicals.

⁴ Acrylic shell chemistry: Microcapsules made in accordance with WO 2005 105291

The results show that

1. Subjecting the melamine formaldehyde based mPCM (microcapsules containing phase change material) to the exemplified processes does not detrimentally changed the mass loss at up to 300°. In fact it actually improved the robustness of the capsules by this measure.

2. Subjecting the acrylic shell based mPCM (microcapsules containing phase change material) to the exemplified processes does not detrimentally change the mass loss at up to 300⁰C

Claims

1. Polymeric particles containing microcapsules distributed throughout the polymeric particles, wherein an amphipathic stabiliser is located at the surface of the polymeric particles.

2. Polymeric particles according to claim 1 in which the microcapsules have a core shell configuration wherein the core contains a phase change material.

3. Polymeric particles according to claim 2 in which the phase change material is selected from the group consisting of paraffin hydrocarbons, natural waxes, fatty alcohols, fatty acids and fatty amides.

4. Polymeric particles according to any preceding claims in which the microcapsules have a core shell configuration and in which the shell comprises an acrylic polymer or a melamine formaldehyde resin.

5. Polymeric particles according to any preceding claims, which particles additionally contain additives selected from the group consisting of flame retardants, graphite, and metallic particles.

6. Polymeric particles according to any preceding claims in which the amphipathic stabiliser is a polymer comprising monomeric repeating units of alkyl (meth) acrylates and/or (meth) acrylic acid.

7. Polymeric particles according to any preceding claims, which particles have a weight average particle size diameter of greater than 50 microns and in which the microcapsules exhibit a weight average particle size diameter of below 50 microns.

8. Polymeric particles according to any preceding claims in which the microcapsules have a weight average particle size diameter of between 0.1 and below 50 microns, preferably 0.5 to 10 microns.

9. Polymeric particles according to any preceding claims, which particles have a weight average particle size diameter of between greater than 50 microns and up to 5000 microns.

10. Polymeric particles according to any preceding claims, which particles comprise greater than 50% by weight the microcapsules, preferably between 75 and 90% by weight microcapsules.

11. A process of producing polymeric particles containing microcapsules distributed throughout the polymeric particles, comprising the steps: i) providing a water immiscible liquid containing an amphipathic stabiliser, ii) providing a dispersion of microcapsules in an aqueous liquid, iii) dispersing the dispersion into the water immiscible liquid and agitating to form a water in oil emulsion or a water in oil suspension, iv) subjecting the water in oil emulsion or water in oil suspension to dehydration by distillation to form a dispersion of polymeric particles in the water immiscible liquid and, v) recovering the polymeric particles.

12. A process according to claim 11 in which the amphipathic stabiliser is located at the surface of the recovered polymeric particles.

13. A process according to claim 11 or claim 12 including any of the features recited in any of claims 2 to 10.

14. A process according to any of claims 11 to 13 in which the water immiscible liquid is an organic liquid, preferably a volatile paraffin.

15. A process according to any of claims 11 to 14 in which dehydration is affected by subjecting the emulsion or suspension to vacuum distillation.

16. A process according to claim 15 in which the vacuum distillation at a temperature of at least 40⁰C, preferably at a temperature in the range 50 to 70⁰C.

17. Polymeric particles containing microcapsules distributed throughout the polymeric particles obtainable by a process defined by any of claims 11 to 16.