GB2487794A

GB2487794A - Microparticles

Info

Publication number: GB2487794A
Application number: GB201102072A
Authority: GB
Inventors: Juan Esteban Diaz Gomez; Ignacio Gonzalez Loscertales; Jose Garcia Miralles; Ciaran Bernard Mcardle; David Farrell; Michael Doherty; Peter Joseph Wrobel
Original assignee: Henkel Ireland Ltd Dublin
Current assignee: Henkel Ireland Ltd Dublin
Priority date: 2011-02-07
Filing date: 2011-02-07
Publication date: 2012-08-08
Anticipated expiration: 2031-02-07
Also published as: GB2487794B; GB201102072D0

Abstract

A friable micro-particle comprises a solid matrix and at least one additional solid material dispersed with the solid matrix, wherein the additional solid material is releasable form, or exposable from within the solid matrix to initiate or boost cure of a curable material. A micro-particle comprising a solid matrix in which at least one reactive component of a cure system for a curable composition is held in solid solution in the matrix as well as a curable composition, a method of bonding and methods for making the micro-particles are also disclosed. The additional material may be one or more metal salts, onium salts, nucleophic amines, a cure catalyst or a cure accelerator. The solid matrix may be comprised of polysaccharide, polyvinyl alcohol, polyethylene, polypropylene or combinations thereof.

Description

Micro pa rticles

Field of the Invention

[0001] The present invention relates to microencapsulation and the preparation of novel materials thereby. In particular novel solid microparticu late materials with a second solid dispersed therein are disclosed. Such materials may find use in adhesives. The invention further relates to methods of preparing the novel microparticles.

Background to the Invention

[0002] Encapsulation represents one of the most attractive methods of isolating a reactive species from its surroundings so as to achieve timed delivery of the reactive core into the surroundings. The capsule may be designed to release all the reactive material into the surroundings on rupturing, or alternatively, the capsule may be designed to achieve sustained release of the encapsulated reactive material from the capsule core to the surroundings. Some of the most common applications for encapsulated materials include flavou rings, pharmaceuticals and adhesives.

[0003] Microencapsulation has enabled traditionally 2-part adhesive compositions to essentially become pseudo 1-part compositions, wherein a cure catalyst is isolated within a rupturable microparticle, the microparticle being in turn suspended within curable resin. A stimulus sufficient to break the particle, for example mechanical shear, results in the cure catalyst being released into and permeating within the curable resin, ultimately resulting in cure of the resin. Thus, microencapsulation of a reactive component of the adhesive composition enables all the components of a curable composition to be formulated within the same composition. For example, U.S. Patent No. 4,252,708 discloses pseudo 1-part cationically curable compositions formulated alongside a microencapsulated Lewis acid (to. the cure catalyst). Application of a mechanical force to the pseudo 1-part system releases the Lewis acid catalyst into a cationically curable resin, thus initiating cure thereof.

[0004] A number of conventional processes for encapsulating materials exist.

Interfacial polymerisation is an in-situ encapsulation technique wherein reactive components meet at an interface resulting in the formation of polymer walls at the interface of the reactants thereby encapsulating one the reactants in a polymer shell.

U.S. Patent No. 4,252,708 describes microcapsules (for an adhesive composition) in which the shell walls are the interfacial reaction product of an aromatic polyisocyante, glycerol and a cycloaliphatic polyepoxide. Matrix polymerisation or spray-drying comprises dissolving or suspending a reactive material in a solution of a polymer and subsequently evaporating off the solvent to yield a dried particle. Spray-drying is a common technique utilised in the preparation of microparticles from a liquid or slurry by rapidly drying with a hot gas.

[0005] Photocu ring provides a further option for the preparation of (micro)capsules.

Photocu ring generally comprises dispersing a reactive material in a UV polymerisable monomer such that exposure to UV light will result in cure of the polymerisable monomer around the reactive material. The preparation of microcapsules via photocuring is discussed in U.S. Patent Nos. 4,588,639; 5,397,812; and 7,503,979.

[0006] Typically, the microencapsulation techniques involve creating a particle in which liquid material is encapsulated. Solid shell, liquid core microcapsules produced for adhesive applications by the methods discussed above can often exhibit relatively rapid diffusion of the cure catalyst from within the capsule core. Thus, pseudo 1-part adhesive compositions comprising a cure catalyst within a microcapsule often exhibit poor shelf lives and may have to be prepared directly prior to use. In effect, such systems may offer little advantage in terms of convenience over storage stable 2-part compositions.

[0007] Notwithstanding the state of the art it would still be desirable to provide for microparticles, and methods of production thereof, that mitigate and/or remedy the problems discussed.

Summary of the Invention

[0008] The present invention provides for inventive microparticles comprising a solid envelope and solid core with a further solid reactive material (i.e., not the same as the envelope or core) dispersed within the solid core. The solid envelope and core may be comprised of the same polymeric material and may comprise a matrix. As used herein the microparticle refers to a particulate material such as a powder which may be of any shape such as a sphere, a rod, etc. or it may be a material of irregular, non-discernable shape.

[0009] Accordingly, in a first aspect the present invention may provide for a friable microparticle comprising: a solid matrix; and at least one additional solid material dispersed within the solid matrix, the additional solid material being different from the solid matrix, where the additional solid material is dispersed within the solid matrix and is releasable from or exposable from within the solid matrix to initiate or boost cure of a curable material.

[0010] The solid matrix and the at least one additional solid material dispersed therein may be considered to be in a host-guest type relationship. The solid matrix may act as a host to: a single type of additional solid material (or guest); or a number of different types of additional solid materials (or guests). Such guests are releasable from the host matrix upon the application of a force, for example a mechanical or shear force, to initiate cure of a curable material.

[0011] When ruptured, the microparticle may initiate or boost cure of a curable material. As used herein the term initiate covers direct initiation (for example, release of a Lewis acid in a cationically curable formulation or amine in an anionically curable formulation) or indirect initiation (for example, via release of a Cu(ll) salt and acetylphenylhydrazine which interact with a peroxide to generate free radicals which in turn initiate cure of a radically curable formulation, such as an acrylate formulation).

[0012] Similarly, the additional solid material or (different) solid materials dispersed within the solid matrix may be releasable from or exposable from within the solid matrix of the microparticles to boost (or augment) the rate of an existing cure reaction. For example, anaerobic adhesives may exhibit a slow rate of underlying cure.

Microparticles of the present invention may be ruptured to release a metal salt (e.g. a copper salt) or a combination of a metal salt and a solid accelerator (e.g. a copper salt and acetylphenylhydrazine) thereby boosting (or augmenting) the rate of cure of the anaerobic adhesive. The microparlicles (when ruptured) may be utilised to boost rates of cure in adhesives applied to low surface energy substrates.

[0013] The at least one additional solid material dispersed in the microparticle matrix may comprise at least one reactive component of a cure system for a curable adhesive composition. As used herein the term reactive component of a cure system refers to a component that may be directly or indirectly involved in the cure process. The reactive component may be suitable for one of a radically curable formulation, a cation ically curable formulation or an anionically curable formulation. The at least one reactive component of a cure system may be selected from one or more metal salts, onium salts, nucleophilic amines, a cure catalyst, or a cure accelerator. The at least one reactive component of a cure system may be a nucleophilic phosphine.

[00141 For utility in radically curable (anaerobic) compositions, the at least one additional solid material dispersed in the microparticle matrix may comprise a cure catalyst, a cure accelerator and combinations thereof. The cure catalyst is a component that increases the rate of cure of the anaerobic/radically curable adhesive and is regenerated, for example by a RedOx process. The cure catalyst may be an ionic solid or salt. The cure catalyst may be one or more metal salts. The metal salts may be transition metal salts. Suitable transition metal salts may be selected from the group consisting of Cu, Fe, Co, Ag, Mn, Zn, and combinations thereof. The cure catalyst may be a copper salt, a zinc salt, and combinations thereof. The cure catalyst may be a copper salt.

[0015] The microparticle may comprise a number of different components of a cure system dispersed within the solid matrix [provided no issues of compatibility between the different components arise]. The microparticle may also comprise an accelerator for an anaerobic adhesive. For example, the microparticle may comprise a cure catalyst and an accelerator within the polymer matrix. Suitable accelerators may be selected from amines (cyclic and acyclic), imides (cyclic and acyclic), hydrazines, saccharin, toluidines and maleic acid.

[0016] Suitable amines include tertiary amines, polyamines, arylamines, amine oxides, sulfonamides and triazines. Suitable hydrazines include ethyl carbazate, N-amino rhodanine, acetylphenylhydrazine, para-nitrophenylhydrazine and para- tolylsulfonylhydrazide. Suitable toluidines include N,N-diethyl-p-toluidine and N,N-dimethyl-o-toluidine.

[0017] Where the microparticle of the present invention has two or more different additional solid materials dispersed in the solid matrix, desirably, such materials will combine (upon release) to produce a synergistic effect on the rate of cure of an adhesive composition. For anaerobic or radically curable adhesive formulations release of a metal salt [such as a Cu(ll) salt] and an accelerator (such as acetylphenylhydrazine [APH]) will provide for electron transfer from the accelerator to the metal salt. The reduced metal salt will in turn transfer an electron to a radical generating component to liberate free radicals thereby promoting cure of the radically curable component. Thus, the metal salt and the accelerator may act synergistically to increase the rate of cure of the radically curable component.

[0018] In a further aspect the present invention provides for a microparticle comprising a solid matrix in which at least one reactive component of a cure system for a curable composition is held in solid solution in the solid matrix.

[0019] As used herein the term solid solution is utilised to indicate that the reactive cure component is fixed within or immovably suspended within the solid matrix such that diffusion of the reactive cure component from the solid matrix is minimised.

[0020] The reactive component may be suitable for one of a radically curable formulation, a cationically curable formulation or an anionically curable formulation.

The at least one reactive component of a cure system may be selected from one or more metal salts, onium salts, nucleophilic amines, a cure catalyst, or a cure accelerator.

[0021] For utility in radically curable (anaerobic) compositions, the at least one reactive component dispersed in the microparticle matrix may comprise a cure catalyst, a cure accelerator and combinations thereof. The cure catalyst may be an ionic solid or salt.

The cure catalyst may be one or more metal salts. The metal salts may be transition metal salts. Suitable transition metal salts may be selected from the group consisting of Cu, Fe, Co, Ag, Mn, Zn, and combinations thereof. The cure catalyst may be a copper salt, a zinc salt, and combinations thereof. The cure catalyst may be a copper salt.

[0022] The microparticle may comprise a cure catalyst and an accelerator (i.e. two reactive components) within the polymer matrix. This may be particularly advantageous for utility in radically curable/anaerobic adhesives. The accelerator may be the same as those defined above.

[0023] In yet a further aspect, the present invention provides for a cure system for a curable composition in which at least one reactive component of the cure system is held in solid solution in a microparticle, where the microparticle comprises a solid matrix.

[0024] The reactive component may be suitable for one of a radically curable formulation, a cation ically curable formulation or an anionically curable formulation.

The at least one reactive component of a cure system may be selected from one or more metal salts, onium salts, nucleophilic amines, a cure catalyst, or a cure accelerator. The at least one reactive component of a cure system may be a nucleophilic phosphine.

[0025] For utility in radically curable (anaerobic) compositions, the at least one reactive component dispersed in the microparticle matrix may comprise a cure catalyst, a cure accelerator and combinations thereof. The cure catalyst may be an ionic solid or salt.

[0026] The cure system may comprise a cure catalyst and an accelerator (Le. two reactive components) within the solid matrix of the microparticle. This may be particularly advantageous for utility in radically curable/anaerobic adhesives. The accelerator may be the same as those defined above.

[0027] Advantageously, a microparticle comprising a solid matrix having an additional solid material dispersed therein may limit the extent of diffusion of the second solid material from the matrix of the microparticle (on account of the density of the solid matrix). Prior art microcapsules comprising a liquid material within a polymeric solid shell often exhibit rapid diffusion of the liquid material through the solid shell.

[0028] As used herein the term dispersed within the solid matrix, indicates that the additional solid material is trapped or sequestered within the solid matrix. The additional solid material may be dispersed as large clusters within the solid matrix of the microparticle. The additional solid material may be discretely or finely dispersed throughout the solid matrix of the microparticle. That is, the additional solid material does not form clusters and individual units of the second solid material are interspersed within the solid matrix of the microparticle. Preferably, the additional solid material is discretely or finely dispersed throughout the solid matrix of the microparticle.

[0029] Thus, the microparticle differs from two or more solids merely mixed together in that the one or more additional solid materials is suspended through and embedded within the solid matrix and is generally immovable therefrom. A mechanical force is required to release the one or more solid materials from or expose the second solid material from within the solid matrix.

[0030] As used herein the term friable simply refers to a microparticle that disintegrates under an external stimulus. Such a stimulus may be a mechanical force such as a shearing force or a crushing force.

[0031] The microparticle may be rupturable under a mechanical force to release the additional solid material from the microparticle. Alternatively, the application of a mechanical force may result in exposure of the additional solid material on the surface of the microparticle. For example, the microparticle may fragment to expose the additional solid material on the surface of a microparticle fragment. Advantageously, when the microparticle ruptures or breaks or fragments the surface area of the particle exposable to a curable composition greatly increases. Thus, a larger concentration of the additional solid material or cure catalyst or reactive component of a cure system dispersed within the particle is exposed when the microparticle breaks. This may help to initiate or boost cure of a curable material.

[0032] Microparticles according to the present invention may be mechanically friable or rupturable at low pressures. The microparticles of the present invention may rupture at pressures between 0.05 MPa to 1.0 MPa, for example 0.08 MPa to 0.3 MPa, such as 0.1 MPa to 0.2 MPa.

[0033] The solid matrix of the friable microparticle may be comprised of a polymeric material. The solid matrix may be composed of a plurality of polymeric subunits. As a component of the solid matrix the plurality of polymeric subunits are desirably substantially insoluble in organic media. The polymeric subunits will not swell in organic media. Consequently, swelling and or gelling of the solid matrix can be minimised or avoided when the microparticle of the present invention is formulated as part of a liquid composition. Suitably, the solid matrix will be a powder.

[0034] The polymeric subunits may be comprised of polysaccharides, polyvinyl alcohol, polyethylene, polypropylene or combinations thereof. The polymeric subunits may be comprised of polysaccharides. The polysaccharide may be maltodextrin, dextran, cyclodextrin, alginate, alginate-poly(L-lysine), alginate-chitosan.

Advantageously, maltodextrin, dextran, cyclodextrin, alginate, alginate-poly(L-lysine), alginate-chitosan are non-toxic, readily available natural products often used in food stuffs.

[0035] Microparticles prepared according to the present invention may be between I to 300 micrometres in diameter. As used herein diameter refers to the longest straight line distance between any two points on a microparticle surface. For example, in a batch of microparticles according to the present invention, at least 70% of microparticles produced may be between 36 to 100 micrometres in diameter. At least 50% of microparticles produced according to the present invention may be approximately 50 to 100 micrometres in diameter.

[0036] In a further aspect, the present invention provides for a curable composition comprising: (i) a curable component; and (ii) a plurality of microparticles according to the present invention; or (iii) a plurality of cure systems according to the present invention.

[0037] For example, the present invention may provide for a curable composition comprising: (i) a curable component; and (ii) at least one microparticle comprising a solid matrix in which at least one reactive component of a cure system for a curable composition is held in solid solution in the solid matrix.

[0038] References to the reactive component of a cure system are to be construed as per the definitions given previously in this specification.

[0039] The microparticles or cure systems may be dispersed within the curable component. Sufficient microparticles or cure systems with sufficient loading of reactive component must be physically broken up into smaller fragments to effect cure.

[0040] Desirably, the curable component comprises non-solid matter and the microparticles are suspended or dispersed within the non-solid matter. The curable component may a liquid, a gel or combinations thereof. The curable compositions may be one or two-part compositions.

[0041] lt will be appreciated by a person skilled in the art that the curable compositions of the present invention may additionally comprise conventional additives such as fillers, pigments, stabilisers, moisture scavengers, etc., subject to said additives not interfering with effective curing of the compositions.

[0042] The curable component may be radically curable. The curable component may be a radically curable material. Where the curable component is a radically curable material the composition may further comprise a radical generating component. The radical generating component may be selected from the group consisting of peroxides, hydroperoxides, hydroperoxide precursors, persulfates and combinations thereof.

Suitable materials comprise Cumene Hydroperoxide, tert-Butyl hydroperoxide, Hydrogen peroxide, 2-Butanone peroxide, Di-tert-Butyl peroxide, Dicumyl peroxide, Lauroyl peroxide, 2,4-Pentanedione peroxide, pentamethyl-trioxepane [such as that sold under the band name Trigonox® 311], Benzoyl Peroxide and combinations thereof.

[0043] Suitable radically curable materials may have at least one functional group selected from the group consisting of acrylates, methacrylates, thiolenes, siloxanes, vinyls and combinations thereof.

[0044] In embodiments where the curable component comprises a radically curable material the additional solid material dispersed within the solid matrix of the microparticle of the present invention may be a cure catalyst (for example a metal salt), an accelerator and combinations thereof. Desirably the metal salt comprises a transition metal cation. Suitable transition metal salts may be selected from the group consisting of Cu, Fe, Co, Ag, Mn, Zn, and combinations thereof. The cure catalyst may be a copper salt, a zinc salt, and combinations thereof. The cure catalyst may be a copper salt. The metal salt may be substituted with a ligand. Desirably, the metal salt counterion is chosen from naphthenate, ethylhexanoate, benzoate, nitrate, chloride, acetylacetonate, C104, BF4, PF6, SbF6, AsF6, (C6F5)4B, (C6F5)4Ga, Carborane, triflimide, bis-triflimide, anions based thereon and combinations thereof. Further desirably the metal salt counterion is chosen from naphthenate, ethylhexanoate, benzoate, nitrate, chloride, acetylacetonate, C104, BF[, PF6, SbF6 and combinations thereof. Preferably, the metal salt counterion is chosen from the group consisting of SbF6, BF4 and combinations thereof.

[0045] The curable component may be cationically curable. The curable component may be a cationically curable material. Suitable cationically curable components including monomers may have at least one functional group selected from the group consisting of epoxy, vinyl, vinyl ether, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene and combinations thereof.

[0046] In embodiments where the curable component comprises a cationically curable material the additional solid material dispersed within the solid matrix of the microparticle of the present invention may be selected from the group consisting of onium salts, metal salts, and combinations thereof. Desirably, the additional solid is a metal salt and the metal salt comprises a transition metal cation. Suitable metals include silver, copper, and combinations thereof. The metal salt may be substituted with a ligand. The metal salt counterions may be chosen from C104, BF4, PF6, SbF6 AsF6, (C6F5)4B anion, (C6F5)4Ga anion, Carborane anion, triflimide (trifluoromethanesulfonate) anion, bis-triflimide anion, anions based thereon and combinations thereof. Further desirably, the metal salt counterions may be chosen from C1O[, BF4, PF6, SbF6 and combinations thereof.

[0047] The curable component may be anionically curable. The anionically curable component may be a cyanoacrylate. In embodiments where the curable component comprises an anionically curable material the additional solid material dispersed within the solid matrix of the microparticle of the present invention may be a nucleophilic amine or phosphine. The additional solid material dispersed within the solid matrix of the microparticle of the present invention may be a nucleophilic amine.

[0048] For embodiments where at least one additional solid, for example a cure catalyst and an accelerator, is dispersed within the microparticle matrix, surface level cure catalyst and accelerator on the microparticle may come into contact with the curable component at the interface of the microparticle and the curable monomer resulting in Iocalised cure. Low concentrations of the cure catalyst can result in localised cure of the curable component at the microparticle-curable monomer interface. Thus, providing a polymerised barrier such as in the form of a layer or skin around the microparticle surface. Localised cure does not effect bulk cure as the curable component is not exposed to sufficient reactive cure component.

[0049] With reference to anaerobic adhesive compositions, by passing air through/aerating the anaerobically curable adhesive moderation of cure is achieved, i.e. cure can be suppressed. Thus, the presence of air may further help in localising cure of the anaerobic adhesive around the microparticle to provide a polymeric layer on the outersurface of the microparticles without promoting bulk cure.

[0050] Within a curable composition, the microparticle of the present invention may thus comprise a polymeric (or passivated) layer on the outersurface thereof. The polymeric layer may comprise a polymerised layer of the curable monomer. The polymeric layer may further aid in preventing unwanted diffusion of the component of a cure system from the microparticle matrix into the surrounding curable component.

Furthermore, the polymeric layer may aid in preventing diffusion of a liquid curable component (monomer) into the microparticle.

[0051] In such cases bulk cure (that is cure through a substantial portion of the curable component) will only arise when a sufficient number of particles have been physically broken to release or expose quantities of a reactive cure component to effect bulk cure.

So, there may be two distinct cases of cure -localised cure at the particle surface and bulk cure through the curable component. The latter only occurs when the composition is subjected to a deliberate mechanical force.

[0052] In a further aspect the present invention provides for a method of bonding comprising: i) applying a curable composition according to the present invention to a first substrate; ii) mating the first substrate with a second substrate; and iii) breaking the microparticles or the cure systems according to the present invention to initiate or boost cure of the curable composition.

[0053] In yet a further aspect the present invention provides for a pack comprising: a) a closeable container; and b) a radically curable composition according to the present invention held within the container; the container being air permeable.

[0054] Microparticles according to the present invention may be prepared by spray-drying or (micro)emulsion-evaporation techniques.

[00551 Moreover, the microparticles of the present invention may be prepared by microfluidic techniques such as electrostatic atomisation (also known as electrospray), electro-coaxial extrusion or electro-emulsion. In addition, the microparticles according to the present invention may be prepared by hydrodynamic focussing.

[0056] In a further aspect the present invention provides for a method of preparing a microparticle according to the present invention comprising the steps of: i) providing a solution of the solid matrix and the least one additional solid material in a first liquid; ii) providing a second liquid, wherein the first and second liquids are immiscible; and iii) adding the solution to the second liquid, where the second liquid is heated to a temperature greater than the boiling point of the first liquid such that the first liquid evaporates to provide the microparticles.

[0057] As will be appreciated by a person skilled in the art, there is no temporal limitation to the step of heating. For example, the second liquid may be heated prior to the addition of the solution thereto, or alternatively, the second liquid may be heated subsequent to the addition of the solution thereto. Preferably, the second liquid is heated prior to the addition of the solution to the second liquid.

[0058] Desirably, the solution is added to the second liquid dropwise. The solution may be added dropwise to the second liquid at a specific flow rate. Advantageously, this may allow for a small standard deviation from the mean particle size.

[0059] The first liquid may be water. The second liquid may be an oil, such as sunflower oil. The solution of the solid matrix and the second solid material in the first liquid may further comprise a surfactant.

[0060] The method for preparing a microparticle according to the present invention may further comprise the steps of: iv) filtering the microparticles from the second liquid; and v) washing the microparticles in a C6-C20 organic solvent.

[0061] The 06-020 organic solvent may be selected from the group consisting of hexane and isomers thereof, heptane and isomers thereof, octance and isomers thereof, and combinations thereof.

[0062] Preferably, microparticles of the present invention will be manufactured by spray-drying. Spray-drying is a common technique utilised in the preparation of microparticles from a liquid or slurry by rapidly drying with a hot gas. Accordingly, the invention further provides for a method of preparing a microparticle according the present invention comprising the steps of: i) providing a solution or slurry of the solid matrix and the least one additional solid material in a liquid; ii) dispersing the solution or slurry into a plurality of droplets; and iii) drying the droplets with a hot gas to provide a plurality of microparticles.

[0063] Where suitable, it will be appreciated that all optional features of one embodiment of the invention may be combined with optional features of another/other embodiment(s) of the invention.

Brief Description of the Drawings

[0064] Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the invention and from the drawings in which: [0065] Figure 1 illustrates a Scanning Electron Microscope Micrograph (SEM) of microparticles according to the present invention; [0066] Figure 2 illustrates a SEM of ruptured microparticles in accordance with the present invention; [0067] Figure 3 illustrates the stability of microparticles according to the present invention comprising differing concentrations of copper salts; [0068] Figure 4 illustrates the relative stability of microparticles containing two different copper salts; [0069] Figure 5 illustrates the bond strength of an anaerobically curable composition containing microparticles according to the present invention; [0070] Figure 6 illustrates the bond strength of an anaerobically curable composition containing microparticles according to the present invention; [0071] Figure 7 illustrates the presence of a cured polymeric outer shell on the surface of the microparticles according to the present invention; and [0072] Figure 8 illustrates the size distribution profile of microparticles according to the present invention prepared by spray drying.

Detailed Description of the Invention

[0073] It should be readily apparent to one of ordinary skill in the art that the examples disclosed herein below represent generalised examples only, and that other arrangements and methods capable of reproducing the invention are possible and are embraced by the present invention.

Examples

PREPARATION of MALTODEXTRIN PARTICLES CONTAINING MICROENTRAINED Cu(BF4)2 [0074] The methodology disclosed below for the preparation of microparticles is not intended to be limiting. Other methodologies such as spray drying and electrospray are also embraced by the present invention.

Required Equipment -500 ml jacketed reactor -JULABO MC 12 Heating bath circulator -IKA T 50 basic ULTRA-TURRAX -Disperser -1 50 -G45M -Dispersing unit -Fill-Master Pump Type 311 -Delta Scientific material -IKA overhead stirrer -Standard hot plate Solution A [0075] Solution A is an aqueous solution containing catalyst and accelerator. The concentrations of the individual components are provided in the table below: Component %wt.

P1 -Water 30.3 P2 -Maltodextrin 60.6 P3 -Copper II tetrafluoroborate 6.06 P4 -1-Acetyl-2-phenylhydrazine 3.03 P3 -Copper (II) tetrafluoroborate hydrate sourced from Sigma Aldrich. P2 - Maltodextrin 16.5-19.5 dextrose equivalent sourced from Sigma Aldrich. P4 -1-acetyl-2-phenylhydrazine »= 98% sourced from Sigma Aldrich.

Preparation of Solution A [00761 Water was charged into the mixture and the mixer was started at low speed.

Copper (II) tetrafluoroborate was added and then 1-acetyl-2-phenylhydrazine was added whilst increasing the mixer speed to give good circulation. The colour of the solution should changed from blue to green. Maltodextrin was added in small lots. The suspension was mixed until all products were completely dissolved.

HOT BATH WATER-IN-OIL (WIO) MICROEMULSION PROCESS _____________ %wt P5 -Sunflower oil 89.27 P6-Span8O 1.79 P7 -Solution A 8.93 P6 -Sorbitan oleate surfactant sourced from Sigma Ad rich.

[0077] Sunflower oil and Span 80 were charged into a jacketed reactor. The mixer (IKA T50) was started at a low speed. The oil was pre-heated to Ga. 112 °C by setting the heating bath circulator temperature accordingly. (Tbath = 115°C).

[0078] The mixer speed was increased to ensure enough turbulent mixing (it is important to induce enough turbulence to the fluid so no dead zones are formed.

Solution A was added slowly using a feeding pump in order to have proper control over the feeding rate (flow rate 13.3 mI/mm). The flow was broken into small drops in the dispersion unit (mixer shaft). The water in solution A evaporates off as steam leaving the solid particles containing catalyst and accelerator in the oil.

[0079] When evaporation of the water as steam ceased the contents of the mixer were transferred into a beaker. When the temperature of the oil fell below 90 °C, n-heptane was added to the beaker and the solid particles were filtered off. The filtered particles were washed in n-heptane for 3 mm to remove all the excess oil and then filtered to obtain the final product.

[0080] Figure 1 illustrates a SEM of the solid microparticles prepared by the water-in-oil (WIO) microemulsion procedure described above. A scale bar of 100 pm can be found at the bottom right of the figure. The particles illustrated are predominately spherical in shape, however, other shapes (both geometric and irregular shapes) are contemplated and within the scope of the present invention.

[0081] Figure 2 provides a SEM of the solid microparticles prepared by the water-in-oil (W/O) microemulsion procedure after they have been rupture between two glass slides.

A scale bar of 100 pm can be found at the bottom right of the figure.

ADHESIVE FORMULATiON [0082] A typical anaerobic formulation containing encapsulated catalyst would be as follows: 93.52% wt. -Loctite 2701; 2.34% wt. -Maltodextrin particles containing Cu(BF4)2as prepared above; 3.74% wt. -Hydrophobic fumed silica [Cab-o-sil T5720]; and 0.40% wt. -3.5% wt Na4EDTA in propylene glycol.

[0083] Loctite 2701 is a commercially available product and consists of a mixture of different methacrylate monomers. It is based on redox-initiated radical polymerization system. Loctite 2701 also contains small quantities of stabilizers/inhibitors.

[0084] Using an overhead stirrer, the hydrophobic fumed silica was added to 2701.

Keep stirring until homogeneous distribution. Then the appropriate quantity of 3435-15 Stock Solution was added and mixed for several minutes. The maltodextrin particles were slowly added and the blend was kept stirring for I day. The mixture was stirred sufficiently such that the whole mixture is constantly moving and no dead zones are created.

[0085] Figure 3 graphically illustrates the stability [over timel of Loctite 2701 formulations containing Cu(N03)2/maltodextrin microparticles according to the present invention. The stability of the Loctite 2701, Cu(N03)2/maltodextrin microparticle formulation is proportional to the fixture times shown. Loctite 2701 formulations containing 2.5%, 5% and 7% wt of Cu(N03)2/maltodextrin microparticles are shown.

[0086] As is evident from Figure 3, in the absence of any force to rupture the particles, the formulations end up being inactive due diffusion of Cu into the bulk adhesive.

Logically, formulations containing a greater percentage weight of the Cu(N03)2/maltodextrin microparticles are less stable and exhibit faster fixture times, in the absence of any force to rupture the particles. Thus, such formulations are less

stable.

[0087] Similar results were observed for Loctite 2701 formulations containing Cu(gluconate)2/maltodextrin microparticles.

[0088] Figure 4 illustrates the improved stability of Loctite 2701 formulations containing Cu(B F4)2tmaltodextrin microparticles of the present invention.

Microparticles containing Cu salts with highly acidic counter anions appear to illustrate improved stability. For example, when compared to a Loctite 2701, Cu(N03)2/maltodextrin microparticle formulation the Loctite 2701, Cu(BF4)2/maltodextrin microparticle formulation of equivalent concentration illustrated superior shelf-life. No signs of cure were observed even after a 30 day period. Whereas, the corresponding Cu(N03)2 microparticle formulation started to cure after approximately 19 days.

[0089] Table I provides stability data on a plurality of different Loctite 2701 formulations containing Cu(BF4)2/maltodextrin microparticles of the present invention containing a number of different additives.

[0090] The abbreviation SPP in Table I corresponds to a metal salt system of 1:1 Cu(BF4)2:Zn(BF4)2 and up to 2.5% wt APH (1-acetyl-2-phenylhydrazine -as an accelerator for the redox polymerisation).

____ _______ ________ _________ 16 ______ _________ _______ _______ 82 C Ma. Bottle Formulation Particles Stabilizer! %wt 5i02!%wt Fixture t!min RT stability stability 1 lOmi 3435-12 2.5% Cu(BF4)2 --15 6÷ months - 2 SOmI 3435-16B1 2.5% Cu(BF4)2 0.025% Na4EDTA -20-25 9+ months - 3 3435-16B2 2.5% Cu(BF4)2 0.01% Na4EDTA -15 9+ months - 4 3435-26A 2.5% SPP system 0.01% Na4EDTA -not tested 7+ months - 3435-26B 2.5% SPP system 0.01% Na4EDTA 2% hphobic 15 7+ months - 6 3435-26C 2.5% SPP system 0.01% Na4EDTA 2% hphilte 15 7÷ months - 7 250m1 3435-14-1 2.5% Cu(BF4)2 0.02% Na4EDTA -not tested 7+ months - 8 3435-14-2 2.5% Cu(BF4)2 1% Premix 17 -not tested 7+ months - 9 3435-25 2.5%Cu(BF4)2 0.015% Na4EDTA 2% hphobic 15 4+ months 2.5-3 h 3435-29 2.5% Cu(BF4)2 0.015% Na4EDTA 4% hphobic I mm 3-'-months 2.5-3 h 11 3435.37 3%(BF4)2 0.015% Na4EDTA 4% hphobic 1 mm 2+ months 2 h CONTROL Loetite 2701 --4h 1 year 5 h

Table I

* Fixture time test always tested on Alelad.

Stability Testing [0091] The formulations listed in Table I were tested by a "Standard Stability Test". In the Standard Stability Test, a standard 1 cm diameter test tube is half filled with the blend (adhesive + microcapsules); the tube is then suspended in a constant temperature bath maintained at a specified temperature. The length of time from the placing of the test tube in the bath to the time when the first gellation is observed in the tube is noted and used as a measure of the stability of the blend.

[0092] All the formulations exhibit good to excellent room temperature stability. Some of the formulations, e.g. 3435-16B1, show stability in excess of 9 months at room temperature. Formulations 3435-25 and 3435-29 exhibited stability at 82 00 for up to 3 hours.

Bond Strength Testing [0093] Figures 5 and 6 illustrate tensile shear strength tests for formulations 3435-29 and 3435-25 (see Table 1) respectively.

Procedure for Tensile Shear Tests [0094] Apparatus: Tension testing machine, equipped with a suitable load cell.

Assembly procedure 1. Specimen surface was prepared where necessary. Test specimens were cleaned by wiping with isopropanol and allowed to dry in air before assembly.

2. Bond area on each lap-shear is 322.6 mm2 (0.5 in2). This is marked before applying the adhesive sample.

3. A sufficient quantity of adhesive was applied to the prepared surface of one lap-shear.

4. A second lap-shear was placed onto the adhesive and the assembly was clamped on each side of the bond area.

Test Procedure [0095] At the time specified the shear strength was determined as follows: 1. The test specimen was placed in the grips of the testing machine so that the outer 25.4 mm (1 in.) of each end were grasped by the jaws. The long axis of the test specimen coincided with the direction of applied tensile force through the centre line of the grip assembly.

2. The assembly was tested at a crosshead speed of 2.0 mm/mm or 0.05 in./min., unless otherwise specified.

3. The load at failure was recorded.

[0096] At 24 hours formulation 3435-29 exhibited a bond strength in excess of 7 MPa.

At 24 hours formulation 3435-25 exhibited a bond strength of approximately 4 MPa.

Self Healing [0097] Cu(BF4)2/maltodextrin microcapsules according to the present invention were added to 50 ml of the anaerobic adhesive Loctite 2701 in a concentration range between 1-5 wt%. The suspension was stirred in air for I week to allow an appropriate dispersion and stabilization of the blend. By passing air through/aerating the anaerobic adhesive moderation of cure is achieved, i.e. cure can be suppressed. Thus, the presence of air may help in localising cure of the anaerobic adhesive around the microparticle to provide a polymeric layer on the outersurface of the microparticles without promoting bulk cure.

[0098] The Cu(B F4)2/maltodextrin microcapsules were subsequently filtered and removed from the Loctite 2701 and washed in acetone. The capsules were analysed to observe the extent of self healing.

[0099] Visualization of the filtered microparticles under a fluorescence microscope reveals a fluorescence due to a polymerized adhesive shell (from cured Loctite 2701, which exhibits fluorescence under UV light) cured around the Cu(BF4)2/maltodextrin microparticle. Figure 7 (Scale bar is 50 pm) illustrates the observable fluorescence from a mixture of maltodextrin microparticles submerged in Loctite 2701 compared to non-fluorescing fresh maltodextrin capsules. The fluorescence is represented by the brighter/lighter patches or regions in Figure 7.

Size Distribution [00100] Microparticles of the following composition: 57% Maltodextrin; 29% Kaolin; 9% Cu(BF4)2 and 4.5% APH were prepared by a spray drying process. The particles were subject to size distribution analysis by suspending them in hexane and running them through a laser particle size analyzer -Beckman Coulter LS 13 320. The results of the analysis are illustrated in Figure 8. The mean particle diameter was 81.26 pm.

Analysis of the overall distribution of particle size indicated that 71.8% of the particles were found to be between 36.24 -101.1 pm.

Pressure Testing [00101] Experiments to determine the minimum pressure required to break the particles were conducted as follows. Two aluminium lap shears were charged with the particles and a force was applied to compress the lap shears. Rupture of the particles was observed using an optical microscope. The pressure indicated is the value at which greater than 50 % of the particles are ruptured.

[00102] Two different types of particles were analysed: 3435-14 -Cu(BF4)2/APH/maltodextrin microparticles; mean particle size = 100 pm; prepared by the microemulsion technique disclosed above; and 3435-3OLi -Cu(BF4)2/APH/maltodextrin microparticles; mean particle size = 65 pm; prepared by spray-drying.

[00103] 3435-3OLi refers to solid microparticles prepared by spray-drying with the following composition: 57% wt. Maltodextrin; 29% wt. Kaolin; 9% wt. Cu(B F4)2; 4.5% wt.

APH, 0.5% wt. stabilisers/fillers.

[00104] The tests were carried out using a Digital Force Gauge by Chartillon, model DRC-200N. The test area was 1050 mm2. The pressures required to rupture the particles are indicated below: 3435-1 4: Force = lOON; Pressure = 0.1 MPa 3435-3OLi: Force = 200N; Pressure = 0.2 MPa Cationically Curable Adhesives [00105] A formulation containing the following components was prepared: parts of Daicel Celloxide 2021P -cycloaliphatic epoxy resin; parts of 3435-3OLi (see above).

[00106] Solid particles were finely dispersed in the epoxy resin by mechanical mixing.

Samples of different surface treated mild steel substrates were prepared for tensile shear test.

[00107] The formulation was applied to the substrates (322.6 mm2 (0.5 in2) bond area).

The substrates were assembled as per the assembly procedure above and tested as per the test procedure above. The mating of the mild steel lap shears was sufficient to break the microparticles.

[00108] Samples were left to cure at room temperature. On average, it took 3 days to for the compositions to cure.

[00109] All different mild steel samples tested gave average tensile shear strength of 2 MPa after standard test evaluation indicated above.

[00110] The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[00111] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims

Claims 1. A friable microparticle comprising: a solid matrix; and at least one additional solid material dispersed within the solid matrix, the additional solid material being different from the solid matrix, wherein the additional solid material dispersed within the solid matrix is releasable from or exposable from within the solid matrix to initiate or boost cure of a curable material.
2. A microparticle according to Claim I wherein the at least one additional solid material dispersed in the microparticle matrix comprises at least one reactive component of a cure system for a curable adhesive composition.
3. A microparticle according to Claim 2 wherein the at least one reactive component of a cure system may be selected from the group consisting of one or more metal salts, onium salts, nucleophilic amines, a cure catalyst, a cure accelerator and combinations thereof.
4. A microparticle according to Claim I wherein the at least one additional solid material dispersed in the microparticle matrix comprises a cure catalyst, a cure accelerator and combinations thereof.
5. A microparticle according to Claim 4 wherein the cure catalyst is an ionic solid or salt.
6. A microparticle according to Claim 5 wherein the cure catalyst is at least one metal salt.
7. A microparticle according to Claim 3 or 4 wherein the cure accelerator is selected from the group consisting of amines, imides, hydrazines, phosphines, saccharin, toluidines, maleic acid and combinations thereof.
8. A microparticle according to Claim 3 or 4 wherein the cure accelerator is selected from the group consisting of ethyl carbazate, N-amino rhodanine, acetylphenylhydrazine, para-nitrophenylhydrazine, para-tolylsulfonylhydrazide, N, N-diethyl-p-toluidine, N,N-dimethyl-o-toluidine and combinations thereof.
9. A microparticle according to Claim I wherein the solid matrix of the microparticle matrix is comprised of a polysaccharide, polyvinyl alcohol, polyethylene, polypropylene or combinations thereof.
10. A microparticle according to Claim 9 wherein the polysaccharide is selected from the group consisting of maltodextrin, dextran, cyclodextrin, alginate, alginate-poly(L-lysine), alginate-chitosan and combinations thereof.
11. A microparticle comprising a solid matrix in which at least one reactive component of a cure system for a curable composition is held in solid solution in the solid matrix.
12. A microparticle according to Claim 11 wherein the at least one reactive component of a cure system may be selected from the group consisting of one or more metal salts, onium salts, nucleophilic amines, a cure catalyst, a cure accelerator and combinations thereof.
13. A microparticle according to Claim 11 wherein the at least one reactive component of a cure system is selected from the group consisting of a cure catalyst, an accelerator and combinations thereof.
14. A microparticle according to Claim 12 or 13 wherein the cure catalyst is at least one metal salt.
15. A microparticle according to Claim 12 or 13 wherein the cure accelerator is selected from the group consisting of amines, imides, hydrazines, phosphines, saccharin, toluidines, maleic acid and combinations thereof.
16. A microparticle according to Claim 13 wherein the cure accelerator is selected from the group consisting of ethyl carbazate, N-amino rhodanine, acetylphenylhydrazine, para-nitrophenylhydrazine, para-tolylsulfonylhydrazide, N,N-diethyl-p-toluidine, N,N-dimethyl-o-toluidine and combinations thereof.
17. A microparticle according to Claims 11 to 16 wherein the solid matrix of the microparticle matrix is comprised of a polysaccharide, polyvinyl alcohol, polyethylene, polypropylene or combinations thereof.
18. A microparticle according to Claim 17 wherein the polysaccharide is selected from the group consisting of maltodextrin, dextran, cyclodextrin, alginate, alginate-poly(L-lysine), alginate-chitosan and combinations thereof.
19. A cure system for a curable composition in which at least one reactive component of the cure system is held in solid solution in a microparticle, wherein the microparticle comprises a solid matrix.
20. A cure system according to Claim 19 wherein the at least one reactive component of a cure system may be selected from the group consisting of one or more metal salts, onium salts, nucleophilic amines, a cure catalyst, a cure accelerator and combinations thereof.
21. A cure system according to Claim 19 wherein the at least one reactive component of a cure system is selected from the group consisting of a cure catalyst, an accelerator, and combinations thereof.
22. A cure system according to Claim 20 or 21 wherein the cure catalyst is at least one metal salt.
23. A cure system according to Claim 20 or 21 wherein the cure accelerator is selected from the group consisting of amines, imides, hydrazines, phosphines, saccharin, toluidines, maleic acid and combinations thereof.
24. A cure system according to Claim 21 wherein the cure accelerator is selected from the group consisting of ethyl carbazate, N-amino rhodanine, acetylphenylhydrazine, para-nitrophenylhydrazine, para-tolylsulfonylhydrazide, N,N-diethyl-p-toluidine, N,N-dimethyl-o-toluidine and combinations thereof.
25. A cure system according to Claims 19 to 24 wherein the solid matrix of the microparticle is comprised of a polysaccharide, polyvinyl alcohol, polyethylene, polypropylene or combinations thereof.
26. A cure system according to Claim 25 wherein the polysaccharide is selected from the group consisting of maltodextrin, dextran, cyclodextrin, alginate, alginate-poly(L-lysine), alginate-chitosan and combinations thereof.
27. A curable composition comprising: (i) a curable component; and (ii) a plurality of microparticles according to Claim 1; or (iii) a plurality of microparticles according to Claim 11; or (iv) a plurality of cure systems according to Claim 19.
28. A curable composition according to Claim 27 wherein the microparticles or cure systems are dispersed within the curable component.
29. A curable composition according to Claim 27 wherein the curable component is selected from at least one of a cation ically curable monomer, a radically curable monomer, and an anioincally curable monomer.
30. A curable composition according to Claim 27 wherein the curable component is radically curable and the composition further comprises a radical generating component.
31. A curable composition according to Claim 30 wherein the radical generating component is selected from the group consisting of peroxides, hydroperoxides, hydroperoxide precursors, persulfates and combinations thereof.
32. A curable composition according to Claim 30 wherein the radically curable component has at least one functional group selected from the group consisting of acrylates, methacrylates, thiolenes, siloxanes, vinyls and combinations thereof.
33. A curable composition according to Claim 27 wherein the curable component is cation ically curable.
34. A curable composition according to Claim 33 wherein the cationically curable component has a functional group selected from the group consisting of epoxy, vinyl, vinyl ether, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene and combinations thereof.
35. A curable composition according to Claim 27 wherein the curable component is anionically curable.
36. A curable composition according to Claim 35 wherein the anionically curable component is a cyanoacrylate.
37. A method of bonding comprising: i) applying a curable composition according to Claim 27 to a first substrate; ii) mating the first substrate with a second substrate; and iii) breaking the microparticles or the cure system to initiate or boost cure of the curable composition.
38. A pack comprising: a) a closeable container; and b) a radically curable composition according to Claim 30 held within the container, wherein the container is air permeable.
39. A method of preparing a microparticle according to any preceding Claim comprising the steps of: i) providing a solution of the solid matrix and the least one additional solid material in a first liquid; ii) providing a second liquid, wherein the first and second liquids are immiscible; and iii) adding the solution to the second liquid, wherein the second liquid is heated to a temperature greater than the boiling point of the first liquid such that the first liquid evaporates to provide the microparticles.
40. A method of preparing a microparticle according to any preceding Claim comprising the steps of: i) providing a solution or slurry of the solid matrix and the least one additional solid material in a liquid; ii) dispersing the solution or slurry into a plurality of droplets; and iii) drying the droplets with a hot gas to provide a plurality of microparticles.