CA1045913A - Preparation of microcapsules using dispersed polymer as outer shell - Google Patents
Preparation of microcapsules using dispersed polymer as outer shellInfo
- Publication number
- CA1045913A CA1045913A CA222,367A CA222367A CA1045913A CA 1045913 A CA1045913 A CA 1045913A CA 222367 A CA222367 A CA 222367A CA 1045913 A CA1045913 A CA 1045913A
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- CA
- Canada
- Prior art keywords
- liquid
- polymer particles
- process according
- parts
- microcapsules
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/02—Making microcapsules or microballoons
- B01J13/06—Making microcapsules or microballoons by phase separation
- B01J13/14—Polymerisation; cross-linking
- B01J13/18—In situ polymerisation with all reactants being present in the same phase
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/02—Making microcapsules or microballoons
- B01J13/06—Making microcapsules or microballoons by phase separation
- B01J13/14—Polymerisation; cross-linking
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Dispersion Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Manufacturing Of Micro-Capsules (AREA)
- Cosmetics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Microcapsules useful, for example, in the manufacture of paper and plastics are prepared by dispersing a first liquid, which contains dispersed polymer particles, in a second liquid in the presence of an emulsifying agent, the polymer particles at the liquid-liquid interface being subsequently integrated to form the outer shell of the microcapsules.
Microcapsules useful, for example, in the manufacture of paper and plastics are prepared by dispersing a first liquid, which contains dispersed polymer particles, in a second liquid in the presence of an emulsifying agent, the polymer particles at the liquid-liquid interface being subsequently integrated to form the outer shell of the microcapsules.
Description
~V4LS~3 This inven~iorl relate~s to the preparation of micro-capsules and to the usc of such microcapsules, for example in surface coatlncJ compositions and 1~ the manufac-ture of paper and plastics.
By the term microcapsule we mean a substan-tially spherical capsule having an outer shell comprising polymer and having an average diameter in the range 1~500 micron.
The microcapsule may also comprise gaseoust liquid andjor oth2r solid materials, for example inside the shell or in ~ ~
10 the outer shell itself. -Microcapsules may be prepared by several known ~
processes, for example by forming a polymer shell by poly- -merisation, precipitation or coacervation. One disadvantage o such processes is the difficulty of controlling the thickness of the polymer shell due to limitations in the growth process. In an interfacial polymerisation process, for example, the shell is invariably thin and fragile and ; in a coacervation process the shell is often coarse and thick.
According to this invention we provide a process of producing microcapsules, wherein there is a measure of control over the thickness o the capsule shell, which com-prises the steps: ;
; (a) forming a dispersion of polymer particles in a first liquid which is a non-solvent for the polymer, ;;~
~! ',, ., :
(b) emulsifying said dispersion, in the presence ;
of an emulsifying agent, as a disperse phase of microcapsule -precursors in a second liquid which is immiscible with the first liquid and which is a non-solvent for the polymer, the ~
emulsifying agent being solvated by the second liquid and `~ -30 non-solvated by the first liquid, whereby the disperse polymer ; -"'~''.'.
By the term microcapsule we mean a substan-tially spherical capsule having an outer shell comprising polymer and having an average diameter in the range 1~500 micron.
The microcapsule may also comprise gaseoust liquid andjor oth2r solid materials, for example inside the shell or in ~ ~
10 the outer shell itself. -Microcapsules may be prepared by several known ~
processes, for example by forming a polymer shell by poly- -merisation, precipitation or coacervation. One disadvantage o such processes is the difficulty of controlling the thickness of the polymer shell due to limitations in the growth process. In an interfacial polymerisation process, for example, the shell is invariably thin and fragile and ; in a coacervation process the shell is often coarse and thick.
According to this invention we provide a process of producing microcapsules, wherein there is a measure of control over the thickness o the capsule shell, which com-prises the steps: ;
; (a) forming a dispersion of polymer particles in a first liquid which is a non-solvent for the polymer, ;;~
~! ',, ., :
(b) emulsifying said dispersion, in the presence ;
of an emulsifying agent, as a disperse phase of microcapsule -precursors in a second liquid which is immiscible with the first liquid and which is a non-solvent for the polymer, the ~
emulsifying agent being solvated by the second liquid and `~ -30 non-solvated by the first liquid, whereby the disperse polymer ; -"'~''.'.
- 2 -:: ~
1[)455~3 partlcles are concen~ratecl substantially in the reyion of the inte~Eace oE the first and second liquids, and (c) integxcltiny at least some of the disperse polymer particles in the region of -the irlterface to form microcapsules.
The nature of the initial dipsersion is fundamental to the success of the present process since, for example, the thickness of the shell of the final microcapsule is a function o the size of the polymer particles and the pre-sence of certain materials in the dispersion may be unde-sirable in the subsequent emulsification process. Preferably the particles are monodisperse but polydisperse particles may be used provided that the size distribution is not broad that adequate control o the shell thickness cannot be achieved. In general the average diameter of the polymer particles will be in the range 0.1-2 micron. The final shell will have a thickness of this same order but may not be directly equivalent (due, for example to shrinkage of the polymer) to the presence of materials other than the polymer particles and to only partial integration of the particles.
Preferably the dispersion is prepared by the poly-merisation of appropriate monomers in the first liquid of which the first liquid is comprised. When the first liquid is water or comprises water the polymerisation may be carried out by conventional emulsion polymerisation techniques. When the first liquid is a non-aqueous liquid or comprises a non-aqueous liquid the polymerisation may be carried out by a process oE non-aqueous dispersion polymerisation as described, for example, in British Patents 1,052,241 and 1,221,397.
Stabilisers conventional in such polymerisation
1[)455~3 partlcles are concen~ratecl substantially in the reyion of the inte~Eace oE the first and second liquids, and (c) integxcltiny at least some of the disperse polymer particles in the region of -the irlterface to form microcapsules.
The nature of the initial dipsersion is fundamental to the success of the present process since, for example, the thickness of the shell of the final microcapsule is a function o the size of the polymer particles and the pre-sence of certain materials in the dispersion may be unde-sirable in the subsequent emulsification process. Preferably the particles are monodisperse but polydisperse particles may be used provided that the size distribution is not broad that adequate control o the shell thickness cannot be achieved. In general the average diameter of the polymer particles will be in the range 0.1-2 micron. The final shell will have a thickness of this same order but may not be directly equivalent (due, for example to shrinkage of the polymer) to the presence of materials other than the polymer particles and to only partial integration of the particles.
Preferably the dispersion is prepared by the poly-merisation of appropriate monomers in the first liquid of which the first liquid is comprised. When the first liquid is water or comprises water the polymerisation may be carried out by conventional emulsion polymerisation techniques. When the first liquid is a non-aqueous liquid or comprises a non-aqueous liquid the polymerisation may be carried out by a process oE non-aqueous dispersion polymerisation as described, for example, in British Patents 1,052,241 and 1,221,397.
Stabilisers conventional in such polymerisation
- 3 -1~459~;3 processeg may be employed, together with any appropriate polymerisation catalyst or initiatOr to produce polymer dispersio~s having required characteriSt:iCS such as stability, particle size, an~ molecular weight of polymer. These stabilisers should no-t, however, interfere with the concen-tration of polymer particles at the inte~ace of the first ~-a~d second liquids and in general when a stabiliser is present in the dispersion of polymer particles it is neces-sary that it is substantially non-solvated by the second ~ :
liquid. Thus, for example, an aqueous dispersion of polymer to be emulsified in an aliphatic hydrocarbon may be sakis~
factorily stabilised with an anionic, cationic or non-ionic ; .
surfactant for example sodium di(isobutyl) sulpho-succinates ;.
whereas, for example, a dispersion of polymer in aliphatic hydrocarbon to be emulsified in water may be satisfactorily stabilise~ with a graft copolymer of poly(l2-hydroxy stearic ;
acid)/poly(methyl methacrylate). It is necessary, also, that the concentration o the stabiliser is kept to a low level so :
that excess stab.iliser does not adversely affect the concen- ;~
tration of polymer particles in the region of the liquid-liquid interface. .
Particularly suitable polymers which may be dis- :.
persed as particles in the first liquid are those prepared by the addition polymerisation or copolymerisation of ethyleni-cally unsaturated monomers. Preferably such polymers have a glass transition temperature significantly greater than the mean atmospheric temperature and preferably greater than 40 & .
Particularly suitable monomers or comonomers include the .
lower (Cl 14) alkyl acrylates and lower (Cl 14) aLkyl meth-acrylates, for example, methyl methacrylate, ethyl acrylate, :.
liquid. Thus, for example, an aqueous dispersion of polymer to be emulsified in an aliphatic hydrocarbon may be sakis~
factorily stabilised with an anionic, cationic or non-ionic ; .
surfactant for example sodium di(isobutyl) sulpho-succinates ;.
whereas, for example, a dispersion of polymer in aliphatic hydrocarbon to be emulsified in water may be satisfactorily stabilise~ with a graft copolymer of poly(l2-hydroxy stearic ;
acid)/poly(methyl methacrylate). It is necessary, also, that the concentration o the stabiliser is kept to a low level so :
that excess stab.iliser does not adversely affect the concen- ;~
tration of polymer particles in the region of the liquid-liquid interface. .
Particularly suitable polymers which may be dis- :.
persed as particles in the first liquid are those prepared by the addition polymerisation or copolymerisation of ethyleni-cally unsaturated monomers. Preferably such polymers have a glass transition temperature significantly greater than the mean atmospheric temperature and preferably greater than 40 & .
Particularly suitable monomers or comonomers include the .
lower (Cl 14) alkyl acrylates and lower (Cl 14) aLkyl meth-acrylates, for example, methyl methacrylate, ethyl acrylate, :.
- 4 ~
5~3 butyl methacrylate, vinyl ~sters such as vinyl acetate and vinyl versatate ; ~nd styrene and lts analoyues. Monomers containing cross-linking or cross-linkable groups may also be used in the preparation of the polymers, preferably in minor proportions. Sui-table monomers include methacrylic acid, itaconic acid and its mono-alkyl es-ter, fumaric acid and i-ts monoalkyl ester and maleic acid and its mono-alkyl-ester. The glass transition temperature o any given poly-mer may be varied by the incorporation of minor amounts o plasticing comonomers, for example, ethyl acrylate and 2-ethylhexyl acrylate. Alternatively the effective glass transition temperature o the polymer particles may be varied by the incorporation of A suitable external plasticiser, e.g. dibutyl phthalate.
Other suitable addition polymers include poly(vinyl chloride), poly(vinylidine dichloride), and copolymers of styrene and butadiene. Condensation polymers, for example;
polyamides and polyesters, may also be employed as the poly-mer of the disperse particles.
The disperse polymer particles are preferably sphe-rical and they may comprise materials other than polymer, for example pigment or plasticiser. The Eirst liquid, in which the dispersion of polymer particles is formed, may contain other dispersed or dissolved materials, Eor example, plasti-ciser, pigment, dyestuff, adhesive, blowing agent, catalyst, herbicide, ungicide, insecticide etc. which it is desired to incorporate within the microcapsule.
The selection of the first and second liquids is based primarily upon the immiscibility of the liquids and upon the insolubility of the disperse polymer particles therein.
59~3 In general it wil:l be a matter oE convenience which liquids are most suitclble to the operations which must be performed, for example the convenience of preparing a dispersion in a first liquid of a given polymer and or the convenience of isolating formed microcapsules from a second liquid. A wide range of liquids may be employed for example water, alkanols, ketones, esters, aliphatic and aromatic hydrocarbons.
In some cases the microcapsules may find ultimate : :
use in the form of a slurry in the second liquid or in a .
liquid which comprises the second liquid, so that it is not then necessary for the microcapsules to be isolated and freed from the second liquid. Such cases include the use of an aqueous slurry in the manufacture of paper or aqueous paints and in general in such cases it is not necessary, and may be undesirable, to employ liquids which are relatively volatile.
In other cases it may be necessary to isolate the microcapsules .~ .
and to free them from at least part of the liquids in which :.' :. .
they have been prepared and in such cases, the use of volatile . .
liquids may be advantageous. Other factors affecting the :
20 choice of suitable liquids include, for example, the relative . . ~.:
solubility of materials which it is desired to incorporate .. .
within the microcapsule.
In order to aid the emulsification in the second liquid of the dispersion of polymer particles in the first liquid we employ an emulsifying agent which is solvated by the second liquid and which is substantially non-solvated by the first liquid. In general non-solvation by the first liquid is confirmed by the inability of a satisfactory emul-sifying agent to flush polymer particles from the disperse ~:
30 phase of first liquid into the second liquid. The emulsion ~
1045~31 3 need not be permanently stable since it is oft~n only neces-sary that the microcapsule precursors remain suspended whilst the disperse polymer particles are :integrated, e.g. by addi-tion of coalescing solvent or applicatlon of heat.
In general the emulsion should no-t 'breakl during the formation of the mlcrocapsule precursors. It will be understood by those skilled in the art that the selection of a suitable emulsifying agent must depend upon a number of factors, for example the liquids employed, the siæe of micro-capsule precursors desired and the ultimate use of the micro-capsules.
Preferably there is employed 0.5-5.0~ by weight of emulsifying agent based upon the weight o the second liquid but the precise amount employed will depend, for example, upon the desired size of microcapsule precursor, This amount wlll vary inversely ~ith the size of the microcapsule precursor and with the efficiency of the emulsifying agent. Usually the emulsifying agent will be dissolved in the second liquid before emulsification. ~-Suitable emulsifying agents are illustrated as follows.
When the first liquid is water and the second li~uid is an aliphatic hydrocarbon, suitable emulsifying agents include graft copolymers, for example a copolymer comprising a back-bone of poly(methyl methacrylate/methacrylic acid = 95/5) and side chains of poly(12-hydroxystearic acid) in the weight `~
ratio Backbone/Side Chain - 1/1. When the first liquid is aliphatic hydrocarbon and the second li~uid is water, suitable emulsifying agents include ethoxylated alkyl phenols such as a condensation product of nonyl phenol and 20 moles of ethylene oxide; a sodium salt of an alkyl aryl polyether ~` ' S9:L3 sulphonate such as sodium dodecyl benzene sulphonate; and a partially hydrolysed poly(vinyl acetate).
The size o~ the microsphere precursors produced at the emulsification staye is determined principally by the nature and proportion of the emulsifying agen~ mentioned above and also by the conditions of agitation. Conventional agitators of variable speed may be employed, for example a "Silverson emulsifier"*. Other factors include the relative ViSCQSitieS of the two liquid phases and the temperature of emulsification.
Under the conditions which we have defined for the ;~
process of this invention the polymer particles contained in the disperse phase of the emulsion will move towards the inter-face of the first and second liquids thus forming microcapsule `
precursors. Integration of the polymer particles may be `~
achieved, for example, by using a coalescing solvent for the polymer or by raising the ambient temperature above the glass transition temperature of the polymer. Generally the coales~
cing solvent will be miscible with the second liquid and will be added gradually to the emulsion until the required extent of coalescence is achieved. Typical coalescing solvents in-clude ketones and esters for polymers and copolymers o~ methyl methacrylate, and aromatic hydrocarbons for polymers of styrene and of related monomers.
The shell of the microcapsule, either before or after integration, may be modified by treatment with cross-linking agents, crosslinking catalysts, hardening agents, colouring agents etc. By way of example the shell may be modified with an amino resin which i5 subsequently crosslinked `-by the addition of acid.
' *Registered Trade Mark The microcapsules may b~ isolat~d and dried by conv~n~ional means ~r they may be used in the form of a dispersion or slurry. ~r~Eerably th~ microcapsules have an average diameter of 1-50 microns and an averaye shell thick-ness of 0.1 - 2 micron.
As indicated above the microcapsules may contain ~ ;
a wide range of materials which can be dispersed or dissolved in the first liquid and which remain in the disperse phase at the emulsification stage. The microcapsules are particularly useful in-the manufacture o paper as bulking agents and in the manufacture of paints and plastics wher~ they confer opacity and other characteristics, (e.g. nailability and reduced density).
The invention is illustrated by the following Examples in which parts and percentages are by weight unless otherwise stated.
This example illustrates the preparation of micro- ~
capsules using a coalescing solvent for the polymer particles -of the microcapsule precursors.
(a) Preparation of an aqueous po~y(methyl methacrylate) latex A solution of 1.2 parts of ammonium persulphate in 20 parts of water was added to a stirred mixture of 500 parts of water, 40 parts of methyl methacrylate and 3.2 parts of sodium di(isobutyl) sulphosuccinate. The mixture was heated at 80C for 3 hours, during which time a further 300 parts of methyl methacrylate was added, and after the first and second hours two separate additions were made of a mixture of 0~6 `~
parts ammonium persulphate, 10 parts of water and 0.4 parts of sodium (di-isobutyl) sulphosuccinate (commercially available Manoxol IB*). The resulting latex comprised poly(methyl meth~
*Registered Trade Mark ... . : . : . :
~)45~3 ~
acrylate~ particles o~ 0.2-0.4 micron diameter.
(b) Preparatlon of micro~ere~
5 Parts of a graft copolymer emulsifying agent com-prising a polymer backbone of poly(methyl methacrylate)/
methacrylic acid)= 98/2 of molecular weight 5000 and polymer side chains of poly(12-hydroxy stearic acid) of molecular wei~ht 1500 (prepared by reacting an adduct of poly(l2-hydroxy-stearic acid)/glycidyl me~hacrylate- 1/1.39 with poly(methyl methacrylate/methacrylic acid - 98/2) in a weight ratio of 1/1, was dissolved in a mix-ture of 5 parts ethyl acetate and 200 parts of aliphatic hydrocarbon (boiling range 120 - 160 C).
100 parts of the latex prepared in (a) was emulsified into this solution of emulsifying agent at room temperature using a Silverson emulsifier to produce an emulsion of microcapsule precursors which were of diameter approximately 10 microns.
The stirred emulsion was then treated with 100 parts of ethyl acetate whereby the latex particles oE the microcapsule pre~
cursors were substantially coalesced to form microcapsules which comprised an outer continuous shell of poly(methyl meth-acrylate). The microcapsules settled under gravity, werewashed free from ethyl acetate and were then dried to a fine light powder of density 0.24 g/cc. The microcapsule diameter was approximately 10 microns.
This example illustrates the preparation of micro-capsules using heat to coalesce the polymer particles of the microcapsule precursors.
(a) Preparation of aqueous latex of polymer particles.
~ .
A solution of 1.2 parts of ammonium persulphate in 20 parts of distilled water was added with stirring to a mix-: ' :
- 10 -.
ture of 500 parts of distille~d water, 3~2 parts sodium di-(isobutyl) sulphosuccinat~, 30 p~rts methyl methacry~ate and 10 parts cthyl acrylate and ~he temperature raised to 80C.
After 10 minutes at 80C a mixture of gO parts ethyl acry~
late and 270 parts methyl methacrylate was add~d over 3 hours.
After the first and second hours separate additions were made of 0.6 parts ammonium persulphate, 10 parts distilled water and 0.4 parts sodium di(isobutyl) sulphosuccinate. The re-sulting latex comprised particles of a 25/75 copolymer of ethyl acrylate/methyl methacrylate of 0.2-0.4 micron diameter. The Tg of the polymer was approximately 60C.
(b) Preparation of microcapsules 10 parts of aliphatic hydrocarbon (boiling range 120 - 160C) and 25 parts o the above latex diluted with 25 parts of water was emulsified in this solution at room tempera-ture using a Silverson emulsifier. The microcapsule precursors in the resulting emulsion had a diameter of approximately 10 microns. The temperature of the emulsion was raised to 65 C
to coalesce the polymer particles, the emulsion was cooled, and the resulting microcapsules of diameter approximately 10 microns were isolated froTn the aliphatic hydrocarbon.
The microcapsules of Examples 1 and 2 were useful as bulking agents in the production of paper.
EX~MPLE 3 This example illustra-tes the preparation of micro-capsules containing a pigment.
50 parts of titanium dioxide were dispersed in~200 "~
parts of water containing 2 parts of sodium hexametaphosphate using an ultrasonic bath. 50 parts of this dlspersion were mixed with 50 parts of the aqueous latex of Example 1 and `~,. .'~,',.
~4~9i3 ~ ~
emulsified (usincl a Silverson emulsifier) into 200 parts of aliphatic hydrocarbon (boiling range 120 - 160C) containing 10 parts of the emulsifyiny agent of Example 1. The resulting emulsion comprised mlcrocapsule precursors of diameter less than 40 ~. 100 parts of e-thyl acetate were then added slowly to the emulsion and the mixture stirred for 10 minutes. The resulting microcapsules were washed free from ethyl acetate by decantation using aliphatic hydrocarbon (boiling range 60 - 80C). Microscopic examination indicated that pigment had been encapsulated by the microcapsules. The microcapsules of this example were of diameter approximately 20 microns and were useful in improving the opacity ond other character-istics of paints.
This example illustrates the preparation of micro-capsules using a coalescing solvent to coalesce the polymer particles of microcapsule precursors.
ta) Preparation of a methyl methacrylate/butyl acrylate copolymer dispersion in aliphatic hydrocarbon A graft copolymer dispersion polymerisation stabi-liser was prepared which had a poly(methyl methacrylate.) backbone of molecular weight 5000 and side chains of poly-(12-hydroxy stearic acid) of molecular weight 1500; the weigh~ ratio of side chains to backbone was 1:1Ø73 parts of this stabiliser were mixed with 2.20 parts of methyl meth-acrylate and 0.17 parts of azodiisobutyronitrile and the mix-ture added to a refluxing mixture of 41.45 parts of aliphatic hydrocarbons (boiling range 140-160C). After 20 minutes a mixture of 7.96 parts of the above stabiliser, 0.08 parts of n-octyl mercaptan, 0.11 parts azodiisobutyronitrile, 2.03 -~)4~13 parts b~ltyl acrylate, 36.52 parts of me-thyl methacrylate and 8.72 parts of plasticising polyester tprepared from neopentyl glycol and adipic acid, the terminal hydroxyl groups being reacted with monobutyl phthala~e) was adclecl over 6 hours.
After completion oE the addition the product was refluxed a further 1/2 hour and cooled.
(b) Preparation of microcapsules 50 parts o the me-thyl methacryalte/butyl acrylate (95/5~ copolymer dispersion prepared in (a) were diluted with 50 parts of aliphatic hydrocarbon (boiling range 140-160C).
5 parts of an emulsifyiny agent, nanyl phenol condensed (commercially available as Ethylon 20* 80) with 20 moles of ;~
ethylene oxide, were dissolved in 200 par-ts of water and the above copolymer dispersion emulsified therein (using a Silverson emulsiier) to produce microcapsule precursors of diameter about 10 ~. Whilst stirring, 100 parts o acetone were added gradually to the emulsion and stirring continued for a further 10 minutes. The resulting microcapsules were isolated, washed free from acetone and dried. They were useEul in the manu-acture of paper of reduced density.
, ,' `' ~:
~ ':
~ ~ .
Other suitable addition polymers include poly(vinyl chloride), poly(vinylidine dichloride), and copolymers of styrene and butadiene. Condensation polymers, for example;
polyamides and polyesters, may also be employed as the poly-mer of the disperse particles.
The disperse polymer particles are preferably sphe-rical and they may comprise materials other than polymer, for example pigment or plasticiser. The Eirst liquid, in which the dispersion of polymer particles is formed, may contain other dispersed or dissolved materials, Eor example, plasti-ciser, pigment, dyestuff, adhesive, blowing agent, catalyst, herbicide, ungicide, insecticide etc. which it is desired to incorporate within the microcapsule.
The selection of the first and second liquids is based primarily upon the immiscibility of the liquids and upon the insolubility of the disperse polymer particles therein.
59~3 In general it wil:l be a matter oE convenience which liquids are most suitclble to the operations which must be performed, for example the convenience of preparing a dispersion in a first liquid of a given polymer and or the convenience of isolating formed microcapsules from a second liquid. A wide range of liquids may be employed for example water, alkanols, ketones, esters, aliphatic and aromatic hydrocarbons.
In some cases the microcapsules may find ultimate : :
use in the form of a slurry in the second liquid or in a .
liquid which comprises the second liquid, so that it is not then necessary for the microcapsules to be isolated and freed from the second liquid. Such cases include the use of an aqueous slurry in the manufacture of paper or aqueous paints and in general in such cases it is not necessary, and may be undesirable, to employ liquids which are relatively volatile.
In other cases it may be necessary to isolate the microcapsules .~ .
and to free them from at least part of the liquids in which :.' :. .
they have been prepared and in such cases, the use of volatile . .
liquids may be advantageous. Other factors affecting the :
20 choice of suitable liquids include, for example, the relative . . ~.:
solubility of materials which it is desired to incorporate .. .
within the microcapsule.
In order to aid the emulsification in the second liquid of the dispersion of polymer particles in the first liquid we employ an emulsifying agent which is solvated by the second liquid and which is substantially non-solvated by the first liquid. In general non-solvation by the first liquid is confirmed by the inability of a satisfactory emul-sifying agent to flush polymer particles from the disperse ~:
30 phase of first liquid into the second liquid. The emulsion ~
1045~31 3 need not be permanently stable since it is oft~n only neces-sary that the microcapsule precursors remain suspended whilst the disperse polymer particles are :integrated, e.g. by addi-tion of coalescing solvent or applicatlon of heat.
In general the emulsion should no-t 'breakl during the formation of the mlcrocapsule precursors. It will be understood by those skilled in the art that the selection of a suitable emulsifying agent must depend upon a number of factors, for example the liquids employed, the siæe of micro-capsule precursors desired and the ultimate use of the micro-capsules.
Preferably there is employed 0.5-5.0~ by weight of emulsifying agent based upon the weight o the second liquid but the precise amount employed will depend, for example, upon the desired size of microcapsule precursor, This amount wlll vary inversely ~ith the size of the microcapsule precursor and with the efficiency of the emulsifying agent. Usually the emulsifying agent will be dissolved in the second liquid before emulsification. ~-Suitable emulsifying agents are illustrated as follows.
When the first liquid is water and the second li~uid is an aliphatic hydrocarbon, suitable emulsifying agents include graft copolymers, for example a copolymer comprising a back-bone of poly(methyl methacrylate/methacrylic acid = 95/5) and side chains of poly(12-hydroxystearic acid) in the weight `~
ratio Backbone/Side Chain - 1/1. When the first liquid is aliphatic hydrocarbon and the second li~uid is water, suitable emulsifying agents include ethoxylated alkyl phenols such as a condensation product of nonyl phenol and 20 moles of ethylene oxide; a sodium salt of an alkyl aryl polyether ~` ' S9:L3 sulphonate such as sodium dodecyl benzene sulphonate; and a partially hydrolysed poly(vinyl acetate).
The size o~ the microsphere precursors produced at the emulsification staye is determined principally by the nature and proportion of the emulsifying agen~ mentioned above and also by the conditions of agitation. Conventional agitators of variable speed may be employed, for example a "Silverson emulsifier"*. Other factors include the relative ViSCQSitieS of the two liquid phases and the temperature of emulsification.
Under the conditions which we have defined for the ;~
process of this invention the polymer particles contained in the disperse phase of the emulsion will move towards the inter-face of the first and second liquids thus forming microcapsule `
precursors. Integration of the polymer particles may be `~
achieved, for example, by using a coalescing solvent for the polymer or by raising the ambient temperature above the glass transition temperature of the polymer. Generally the coales~
cing solvent will be miscible with the second liquid and will be added gradually to the emulsion until the required extent of coalescence is achieved. Typical coalescing solvents in-clude ketones and esters for polymers and copolymers o~ methyl methacrylate, and aromatic hydrocarbons for polymers of styrene and of related monomers.
The shell of the microcapsule, either before or after integration, may be modified by treatment with cross-linking agents, crosslinking catalysts, hardening agents, colouring agents etc. By way of example the shell may be modified with an amino resin which i5 subsequently crosslinked `-by the addition of acid.
' *Registered Trade Mark The microcapsules may b~ isolat~d and dried by conv~n~ional means ~r they may be used in the form of a dispersion or slurry. ~r~Eerably th~ microcapsules have an average diameter of 1-50 microns and an averaye shell thick-ness of 0.1 - 2 micron.
As indicated above the microcapsules may contain ~ ;
a wide range of materials which can be dispersed or dissolved in the first liquid and which remain in the disperse phase at the emulsification stage. The microcapsules are particularly useful in-the manufacture o paper as bulking agents and in the manufacture of paints and plastics wher~ they confer opacity and other characteristics, (e.g. nailability and reduced density).
The invention is illustrated by the following Examples in which parts and percentages are by weight unless otherwise stated.
This example illustrates the preparation of micro- ~
capsules using a coalescing solvent for the polymer particles -of the microcapsule precursors.
(a) Preparation of an aqueous po~y(methyl methacrylate) latex A solution of 1.2 parts of ammonium persulphate in 20 parts of water was added to a stirred mixture of 500 parts of water, 40 parts of methyl methacrylate and 3.2 parts of sodium di(isobutyl) sulphosuccinate. The mixture was heated at 80C for 3 hours, during which time a further 300 parts of methyl methacrylate was added, and after the first and second hours two separate additions were made of a mixture of 0~6 `~
parts ammonium persulphate, 10 parts of water and 0.4 parts of sodium (di-isobutyl) sulphosuccinate (commercially available Manoxol IB*). The resulting latex comprised poly(methyl meth~
*Registered Trade Mark ... . : . : . :
~)45~3 ~
acrylate~ particles o~ 0.2-0.4 micron diameter.
(b) Preparatlon of micro~ere~
5 Parts of a graft copolymer emulsifying agent com-prising a polymer backbone of poly(methyl methacrylate)/
methacrylic acid)= 98/2 of molecular weight 5000 and polymer side chains of poly(12-hydroxy stearic acid) of molecular wei~ht 1500 (prepared by reacting an adduct of poly(l2-hydroxy-stearic acid)/glycidyl me~hacrylate- 1/1.39 with poly(methyl methacrylate/methacrylic acid - 98/2) in a weight ratio of 1/1, was dissolved in a mix-ture of 5 parts ethyl acetate and 200 parts of aliphatic hydrocarbon (boiling range 120 - 160 C).
100 parts of the latex prepared in (a) was emulsified into this solution of emulsifying agent at room temperature using a Silverson emulsifier to produce an emulsion of microcapsule precursors which were of diameter approximately 10 microns.
The stirred emulsion was then treated with 100 parts of ethyl acetate whereby the latex particles oE the microcapsule pre~
cursors were substantially coalesced to form microcapsules which comprised an outer continuous shell of poly(methyl meth-acrylate). The microcapsules settled under gravity, werewashed free from ethyl acetate and were then dried to a fine light powder of density 0.24 g/cc. The microcapsule diameter was approximately 10 microns.
This example illustrates the preparation of micro-capsules using heat to coalesce the polymer particles of the microcapsule precursors.
(a) Preparation of aqueous latex of polymer particles.
~ .
A solution of 1.2 parts of ammonium persulphate in 20 parts of distilled water was added with stirring to a mix-: ' :
- 10 -.
ture of 500 parts of distille~d water, 3~2 parts sodium di-(isobutyl) sulphosuccinat~, 30 p~rts methyl methacry~ate and 10 parts cthyl acrylate and ~he temperature raised to 80C.
After 10 minutes at 80C a mixture of gO parts ethyl acry~
late and 270 parts methyl methacrylate was add~d over 3 hours.
After the first and second hours separate additions were made of 0.6 parts ammonium persulphate, 10 parts distilled water and 0.4 parts sodium di(isobutyl) sulphosuccinate. The re-sulting latex comprised particles of a 25/75 copolymer of ethyl acrylate/methyl methacrylate of 0.2-0.4 micron diameter. The Tg of the polymer was approximately 60C.
(b) Preparation of microcapsules 10 parts of aliphatic hydrocarbon (boiling range 120 - 160C) and 25 parts o the above latex diluted with 25 parts of water was emulsified in this solution at room tempera-ture using a Silverson emulsifier. The microcapsule precursors in the resulting emulsion had a diameter of approximately 10 microns. The temperature of the emulsion was raised to 65 C
to coalesce the polymer particles, the emulsion was cooled, and the resulting microcapsules of diameter approximately 10 microns were isolated froTn the aliphatic hydrocarbon.
The microcapsules of Examples 1 and 2 were useful as bulking agents in the production of paper.
EX~MPLE 3 This example illustra-tes the preparation of micro-capsules containing a pigment.
50 parts of titanium dioxide were dispersed in~200 "~
parts of water containing 2 parts of sodium hexametaphosphate using an ultrasonic bath. 50 parts of this dlspersion were mixed with 50 parts of the aqueous latex of Example 1 and `~,. .'~,',.
~4~9i3 ~ ~
emulsified (usincl a Silverson emulsifier) into 200 parts of aliphatic hydrocarbon (boiling range 120 - 160C) containing 10 parts of the emulsifyiny agent of Example 1. The resulting emulsion comprised mlcrocapsule precursors of diameter less than 40 ~. 100 parts of e-thyl acetate were then added slowly to the emulsion and the mixture stirred for 10 minutes. The resulting microcapsules were washed free from ethyl acetate by decantation using aliphatic hydrocarbon (boiling range 60 - 80C). Microscopic examination indicated that pigment had been encapsulated by the microcapsules. The microcapsules of this example were of diameter approximately 20 microns and were useful in improving the opacity ond other character-istics of paints.
This example illustrates the preparation of micro-capsules using a coalescing solvent to coalesce the polymer particles of microcapsule precursors.
ta) Preparation of a methyl methacrylate/butyl acrylate copolymer dispersion in aliphatic hydrocarbon A graft copolymer dispersion polymerisation stabi-liser was prepared which had a poly(methyl methacrylate.) backbone of molecular weight 5000 and side chains of poly-(12-hydroxy stearic acid) of molecular weight 1500; the weigh~ ratio of side chains to backbone was 1:1Ø73 parts of this stabiliser were mixed with 2.20 parts of methyl meth-acrylate and 0.17 parts of azodiisobutyronitrile and the mix-ture added to a refluxing mixture of 41.45 parts of aliphatic hydrocarbons (boiling range 140-160C). After 20 minutes a mixture of 7.96 parts of the above stabiliser, 0.08 parts of n-octyl mercaptan, 0.11 parts azodiisobutyronitrile, 2.03 -~)4~13 parts b~ltyl acrylate, 36.52 parts of me-thyl methacrylate and 8.72 parts of plasticising polyester tprepared from neopentyl glycol and adipic acid, the terminal hydroxyl groups being reacted with monobutyl phthala~e) was adclecl over 6 hours.
After completion oE the addition the product was refluxed a further 1/2 hour and cooled.
(b) Preparation of microcapsules 50 parts o the me-thyl methacryalte/butyl acrylate (95/5~ copolymer dispersion prepared in (a) were diluted with 50 parts of aliphatic hydrocarbon (boiling range 140-160C).
5 parts of an emulsifyiny agent, nanyl phenol condensed (commercially available as Ethylon 20* 80) with 20 moles of ;~
ethylene oxide, were dissolved in 200 par-ts of water and the above copolymer dispersion emulsified therein (using a Silverson emulsiier) to produce microcapsule precursors of diameter about 10 ~. Whilst stirring, 100 parts o acetone were added gradually to the emulsion and stirring continued for a further 10 minutes. The resulting microcapsules were isolated, washed free from acetone and dried. They were useEul in the manu-acture of paper of reduced density.
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Claims (10)
1. A process of producing microcapsules which comprise the steps:
(a) forming a dispersion of polymer particles having an average diameter in the range 0.1-2 microns in a first liquid which is a non-solvent for the polymer, (b) emulsifying said dispersion, in the presence of an emulsifying agent, as a disperse phase of microcapsule precursors in a second liquid which is immiscible with the first liquid and is a non-solvent for the polymer, the emulsifying agent being solvated by the second liquid and non-solvated by the first liquid, whereby the disperse polymer particles are concentrated substantially in the region of the interface of the first and second liquids, and (c) integrating at least some of the disperse polymer particles in the region of the interface to form microcapsules.
(a) forming a dispersion of polymer particles having an average diameter in the range 0.1-2 microns in a first liquid which is a non-solvent for the polymer, (b) emulsifying said dispersion, in the presence of an emulsifying agent, as a disperse phase of microcapsule precursors in a second liquid which is immiscible with the first liquid and is a non-solvent for the polymer, the emulsifying agent being solvated by the second liquid and non-solvated by the first liquid, whereby the disperse polymer particles are concentrated substantially in the region of the interface of the first and second liquids, and (c) integrating at least some of the disperse polymer particles in the region of the interface to form microcapsules.
2. A process according to Claim 1 wherein the polymer particles are monodisperse.
3. A process according to Claim 1 wherein the dispersion of polymer particles is prepared by polymerising appropriate monomers in a medium which comprises the first liquid.
4. A process according to Claim 3 wherein the dispersion of polymer particles is prepared by the addition polymerisation of monomer selected from C1-4 alkyl acrylates or methacrylates, vinyl esters; and styrene and analogues thereof.
5. A process according to Claim 1 wherein the disperse polymer particles are spherical.
6. A process according to Claim 1 wherein the first liquid contains dispersed or dissolved material which is to be incorporated within the microcapsule.
7. A process according to Claim 1 wherein the first liquid or the second liquid is water.
8. A process according to Claim 1 wherein the first liquid or the second liquid is aliphatic hydrocarbon.
9. A process according to Claim 1 wherein there is employed 0.5-5.0% by weight of emulsifying agent based on the weight of the second liquid.
10. A process according to Claim 1 wherein the polymer particles are integrated in the presence of a coalescing agent.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1186374A GB1450665A (en) | 1974-03-18 | 1974-03-18 | Microcapsules |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1045913A true CA1045913A (en) | 1979-01-09 |
Family
ID=9994071
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA222,367A Expired CA1045913A (en) | 1974-03-18 | 1975-03-18 | Preparation of microcapsules using dispersed polymer as outer shell |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1045913A (en) |
| GB (1) | GB1450665A (en) |
| ZA (1) | ZA751627B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7812079B2 (en) | 2001-02-22 | 2010-10-12 | Valspar Sourcing, Inc. | Coating compositions containing low VOC compounds |
-
1974
- 1974-03-18 GB GB1186374A patent/GB1450665A/en not_active Expired
-
1975
- 1975-03-17 ZA ZA751627A patent/ZA751627B/en unknown
- 1975-03-18 CA CA222,367A patent/CA1045913A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU7913775A (en) | 1976-09-23 |
| ZA751627B (en) | 1976-11-24 |
| GB1450665A (en) | 1976-09-22 |
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