EP0464023A4 - Realease assist microcapsules - Google Patents

Realease assist microcapsules

Info

Publication number
EP0464023A4
EP0464023A4 EP19890910356 EP89910356A EP0464023A4 EP 0464023 A4 EP0464023 A4 EP 0464023A4 EP 19890910356 EP19890910356 EP 19890910356 EP 89910356 A EP89910356 A EP 89910356A EP 0464023 A4 EP0464023 A4 EP 0464023A4
Authority
EP
European Patent Office
Prior art keywords
capsule
core material
release
shell
core
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.)
Withdrawn
Application number
EP19890910356
Other versions
EP0464023A1 (en
Inventor
Bruce K. Redding, Jr.
Walter S. Garrison
Arden E. Schmucker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ENCAPSULATION SYSTEMS Inc
Original Assignee
ENCAPSULATION SYSTEMS Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by ENCAPSULATION SYSTEMS Inc filed Critical ENCAPSULATION SYSTEMS Inc
Publication of EP0464023A1 publication Critical patent/EP0464023A1/en
Publication of EP0464023A4 publication Critical patent/EP0464023A4/en
Withdrawn legal-status Critical Current

Links

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
    • B01J13/025—Applications of microcapsules not provided for in other subclasses
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01N—PRESERVATION OF BODIES OF HUMANS OR ANIMALS OR PLANTS OR PARTS THEREOF; BIOCIDES, e.g. AS DISINFECTANTS, AS PESTICIDES OR AS HERBICIDES; PEST REPELLANTS OR ATTRACTANTS; PLANT GROWTH REGULATORS
    • A01N25/00—Biocides, pest repellants or attractants, or plant growth regulators, characterised by their forms, or by their non-active ingredients or by their methods of application, e.g. seed treatment or sequential application; Substances for reducing the noxious effect of the active ingredients to organisms other than pests
    • A01N25/26—Biocides, pest repellants or attractants, or plant growth regulators, characterised by their forms, or by their non-active ingredients or by their methods of application, e.g. seed treatment or sequential application; Substances for reducing the noxious effect of the active ingredients to organisms other than pests in coated particulate form
    • A01N25/28—Microcapsules or nanocapsules
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K9/00—Medicinal preparations characterised by special physical form
    • A61K9/0002—Galenical forms characterised by the drug release technique; Application systems commanded by energy
    • A61K9/0004—Osmotic delivery systems; Sustained release driven by osmosis, thermal energy or gas
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K9/00—Medicinal preparations characterised by special physical form
    • A61K9/48—Preparations in capsules, e.g. of gelatin, of chocolate
    • A61K9/50—Microcapsules having a gas, liquid or semi-solid filling; Solid microparticles or pellets surrounded by a distinct coating layer, e.g. coated microspheres, coated drug crystals
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K9/00—Medicinal preparations characterised by special physical form
    • A61K9/48—Preparations in capsules, e.g. of gelatin, of chocolate
    • A61K9/50—Microcapsules having a gas, liquid or semi-solid filling; Solid microparticles or pellets surrounded by a distinct coating layer, e.g. coated microspheres, coated drug crystals
    • A61K9/5005—Wall or coating material
    • A61K9/5021—Organic macromolecular compounds
    • A61K9/5031—Organic macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polyethylene glycol, poly(lactide-co-glycolide)

Definitions

  • This invention relates to an improved method of effecting the release of an active core from microcapsule ⁇ . Additionally this invention relates to encapsulated fungicides.
  • microcapsule ⁇ There are four main release mechanisms for microcapsule ⁇ available. Conventional microcap ⁇ ules release their active core material through:
  • a microcapsule may be classified as a either a Break On
  • Time Relea ⁇ e i ⁇ a term used to describe a slow release over a period of time of the active core material from the confines of the capsule.
  • Break on Demand microcapsule ⁇ are capsules which generally have thicker shells, allowing little or no relea ⁇ e of the active core material until a physical force or chemical reaction causes the shell to rupture. Such capsules are virtually inert until an outside force effects the breaking or dissolution of the shell.
  • a fungicide is mixed into a can of water based paint, the intent being to provide mildew protection after a surface has been painted.
  • the paint i ⁇ generally used in wet or damp environment ⁇ .
  • the fungicide i ⁇ intended to avoid discoloration of the painted surface.
  • Most fungicides available on the market react with the ingredients in the paint or dissolve while the paint can i ⁇ stored on the shelf, a period of time which can last past one full year.
  • the shelf life reactivity problem leads to a loss of potency for the fungicide.
  • Encapsulation of the fungicide to avoid the chemical reaction problem, can produce either a Reservoir capsule or a Micro-sponge type capsule, a capsule with pores.
  • the Micro-Sponge type capsule allows the fungicide to leak from the capsule while stored on the shelf, thereby having little protection for the active material.
  • the Reservoir construction leads to a capsule with a shell which is so thick as to not allow any leakage of the active or diffusion to occur, avoiding premature reaction during shelf storage, but the shell may also not allow relea ⁇ e after the surface has been painted either.
  • the encapsulation effort is defeated through shelf life and release difficulties.
  • icrocapsules are intended as a means of delivering a catalyst to a particular location or at a particular time in a chemical process, without chemical reaction along the way.
  • Catalysts are isolated within a capsule until the shell is broken of dissolved.
  • Heat, i ⁇ often used to melt away the capsule shell to release the- active catalyst material. In theory this should enable satisfactory controlled delivery of a catalyst.
  • catalyst compounds often react with the shell material, cros ⁇ linking the polymer. This can increase the melt point of the shell material to a level higher than desired or it can lead to a weakening of the shell itself, producing cracks and lesions in the capsule wall.
  • the resultant capsules often have no longevity or actually do not contain the original quality of catalyst.
  • shells which will not react with the catalyst often produce undesirable traits in the resulting product.
  • An example would be the encapsulation of Butyl Tuad ⁇ , a common rubber catalyst, which was desired to be released from the capsule at temperatures below 100° (c) .
  • the chosen shell material which had a melt point of 65° (c) reacted with the catalyst and would release only at 180° (c) .
  • An attempt was made to use a non reactive second polymer which isolated the catalyst properly, but had a temperature melt point of 250 (C) .
  • the problem was: How to get the catalyst to relea ⁇ e in a non-reactive shell at a temperature below 100 (C) ? Conventional microcapsule release methods did not have a suitable effect in this project.
  • the relea ⁇ e function difficultie ⁇ are solved by using a non-reactive polymer as the cap ⁇ ule shell, together with a solvent as a ⁇ econd core.
  • the cataly ⁇ t doe ⁇ not react with the new polymer but the capsule normally ha ⁇ a melt point higher than desired.
  • the addition of the solvent solves this problem.
  • the capsule can be made to release at the desired temperature.
  • the solvent volatilizes completely.
  • the resultant gas then exerts a pressure upon the interiorof the capsule, cau ⁇ ing the capsule to explode outward.
  • the explosion occurs at a temperature lower than that of the shell polymer, and closer to the boiling point of the solvent.
  • the solvent acts as a propellant, providing a Burst Release of the active material when the correct temperature level has been obtained.
  • capsule ⁇ which can have an enhanced relea ⁇ e profile or function u ⁇ ing the Relea ⁇ e Assist approaches defined in this invention.
  • the pre ⁇ ent invention encompa ⁇ e ⁇ encap ⁇ ulation of ⁇ ub ⁇ tances in liquid, solid or slurry form. These substances may be pharmaceutical agents, cataly ⁇ t ⁇ , fungicide ⁇ , pesticides or any other chemical. Encapsulating walls may or may not be permeable to core material or other materials to which the completed capsules may later be added. Capsule ⁇ provided by the present invention may be capable of slow release mechanisms (commonly referred to as "time relea ⁇ e") or may be released in a sudden method caused by heat, ultraviolet light, microwaves, ultrasonics or other energy media or may be released through dissolution of the capsule wall. In each instance of capsule release the release function i ⁇ aided by the u ⁇ e of a propellant material which ha ⁇ been added to the active core material, whereby the propellant acts to accelerate the release of the active.
  • a first object of this invention i ⁇ to provide a microencapsulated product that po ⁇ se ⁇ s a special release function which may be either a Sudden or a Slow relea ⁇ e system which employs the use of a propellant or solvent as an additive to the active core of said microencapsulated product, whereby the release function of the capsule i ⁇ enhanced in some manner through the : u ⁇ e of the propellant additive.
  • a second object of this invention i ⁇ to enable Time Release capsule ⁇ to become stable during shelf storage, beginning their time release function after that function ha ⁇ been triggered by some effective means.
  • a third object of this invention i ⁇ to enable microencapsulated compounds to have a greater utility by providing an expanded selection of polymers for u ⁇ e as capsule wall materials, by enhancing the relea ⁇ e function of the re ⁇ ulting microencapsulated product.
  • a fifth object of the invention i ⁇ to provide a means of fa ⁇ t release at narrow temperature range ⁇ of a confined active core from a microcapsule by providing a propellant additive to the the active core material.
  • FIG. 1 i an illustration of the major capsule forms available through conventional microencapsulation proces ⁇ e ⁇ .
  • FIG. 2 i an illustration of the preferred embodiment of the invention, a cap ⁇ ule containing a propellant additive to the active core material.
  • FIGS. 3 and 4 are graph ⁇ indicating the relea ⁇ e temperature ⁇ of a microcap ⁇ ule containing a cataly ⁇ t active core material, mixed with a solvent, which acts a ⁇ the propellant.
  • FIG. 5 i ⁇ an illustration of one method usable to form microcapsules, called Coacervation.
  • FIG. 4 is ..a chart indicating the bioactivity of cap ⁇ ule ⁇ containing a fungicide compared to capsules containinga Release A ⁇ i ⁇ t mechani ⁇ m employing a heat ⁇ en ⁇ itive propellant material a ⁇ a second core.
  • FIG. 1 illu ⁇ trate ⁇ ⁇ everal conventional forms of microcap ⁇ ule con ⁇ truction.
  • Each con ⁇ truction i ⁇ capable of enhanced relea ⁇ e dynamics using this invention.
  • a Reservoir Capsule construction is indicated by a egg type construction, characterized by a large amount of core material surrounded by a single shell.
  • the Micro-Sponge construction is a capsule with a lower quantity of core material embedded within many shell layers, allowing for a slow release.
  • the Multi-Wall capsule construction involves a Reservoir type microcapsules with more than one shell layer.
  • the liulti-Core cap ⁇ ule is e ⁇ sentially a cap ⁇ ule, or several smaller capsule ⁇ , contained within a larger cap ⁇ ule.
  • Each construction offer unique properties for particular product applications.
  • the normal release mechanism ⁇ involve:
  • FIG. 2 indicates the preferred embodiment of a Relea ⁇ e Assist capsule construction of the present invention 1 using the Reservoir format, whereupon a phase change material or propellant 2 ha ⁇ been added to the core material 3, both contained by a shell layer 4.
  • the illustrated capsule construction of the present invention is a Reservoir type capsule.
  • the present invention may u ⁇ e any of the other capsule forms indicated in FIG. 1.
  • FIG. 2 The embodiment of the invention shown in FIG. 2 is a capsule 1 containing a shell 4 which surrounds a core material combination consisting of a active ingredient 3 which i ⁇ mixed with a propellant 2.
  • the active 3 can be any ⁇ olid, liquid or slurry chemical compound.
  • a partial li ⁇ t of potential active' ⁇ include ⁇ :
  • a number of chemical compounds can be used as the propellant 2 including:
  • the propellant 2 may be any material which will dis ⁇ olve or expand, or convert into a ga ⁇ when heat i ⁇ applied to the cap ⁇ ule 1.
  • the action of the propellant 2 cau ⁇ e ⁇ the Release A ⁇ si ⁇ t function of the invention to take place, in that the propellant 2 acts to cause either a Burst Relea ⁇ e or an Accelerated Release or a Triggered Release function to occur.
  • the propellant may be in either solid, liquid or ga ⁇ eous form.
  • BDRST RELEASE The application of heat to the capsule 1 causes the propellant 2 to expand within the cap ⁇ ule. This can cau ⁇ e the ⁇ hell 4 of the cap ⁇ ule 1 to elongate and expand beyond the ela ⁇ tic li it ⁇ of the polymer, eventually cau ⁇ ing the capsule to explode outward, providing a sudden or burst release effect.
  • the exploding action may be caused by a propellant material 2 which expand ⁇ under heat or pha ⁇ e change ⁇ into a ga ⁇ eous form during heating. The re ⁇ ulting ga ⁇ exerts a pressure against the interior of the shell 4 cau ⁇ ing it to expand outward, eventually exploding the cap ⁇ ule.
  • the propellant 2 expands or pha ⁇ e change ⁇ with heat application but doe ⁇ not generate enough force to actually rupture the shell 4. Instead the pre ⁇ ure generated from the expanding propellant 2 act ⁇ to accelerate the diffu ⁇ ion rate of the active core 3 acro ⁇ the shell membrane 4.
  • the active core can diffu ⁇ e acros ⁇ the shell layer itself.
  • the force of the expanding propellant or its ga ⁇ eous decomposition re ⁇ ult can act to push the active 3 through pores in the capsule ⁇ hell 4, at a rate faster than normal.
  • the propellant under heat can act to accelerate the diffu ⁇ ion rate of the active.
  • cap ⁇ ule ⁇ can be made to have long shelf life stability. Normal time relea ⁇ e cap ⁇ ule ⁇ frequently employ active diffu ⁇ ion function ⁇ or u ⁇ e the sponge approach to allow a generous leakage rate from the cap ⁇ ule.
  • Sponge type cap ⁇ ule ⁇ generally have very short life span ⁇ . Diffu ⁇ ion cap ⁇ ule ⁇ tend to have very thin ⁇ hell ⁇ , thereby affecting their ability to re ⁇ i ⁇ t ⁇ tre ⁇ .
  • Reservoir type cap ⁇ ule ⁇ generally can be made with thicker ⁇ hell ⁇ , allowing them to withstand higher degrees of shear and industrial stre ⁇ . However these type cap ⁇ ule ⁇ have very poor time release functions.
  • Using the heat application to a propellant core 2 can cause the relea ⁇ e to become triggered at a certain point, enhancing the ⁇ helf life ⁇ tability of the cap ⁇ ule product.
  • FIG. 3 is a temperature curve indicating the release point of a microencapsulated capsule containing a catalyst - solvent combination core.
  • the catalyst i ⁇ Butyl Tuads mixed at 50% of the total core volume of the capsule .
  • the solvent i ⁇ cyclohexane and causes the capsule to explode at a point near the boiling point of the solvent. Cyclohexane was mixed at 50% of the total core volume.
  • the ⁇ hell material wa ⁇ ureaformaldehyde which occupied 20 % of the total volume of the cap ⁇ ule while the combination core materials occupied the remaining 80%.
  • the graph is a Differential Scanning Calorimetery te ⁇ t u ⁇ ing a Dupont Model 2000 DSC device.
  • FIG. 4 i ⁇ a graph illu ⁇ trating the Thermogrimetric Analysis of the same sample described in FIG. 3. Both graphs indicate the point at which the capsule shell explode ⁇ , indicated by a sharp peak in the temperature curve profile. Through the ⁇ e graph ⁇ it can be ⁇ een that the cap ⁇ ule ⁇ reach a certain point whereupon the boiling ⁇ olvent, cyclohexane, cause ⁇ the capsule to explode outward. In both thermal studies the release point i ⁇ comparable.
  • FIG. 5 i ⁇ a illu ⁇ tration of the Coacervation method of encapsulation, which was used in this particular ⁇ eries of experi ent ⁇ .
  • the Relea ⁇ e a ⁇ i ⁇ t function can be duplicated through the u ⁇ e of a multitude of encap ⁇ ulation method ⁇ , ⁇ y ⁇ tem ⁇ , technique ⁇ and technologies and the scope of this invention i ⁇ not intended to be limited by the u ⁇ e of ju ⁇ t one such encapsulation proces ⁇ .
  • the Coacervation proce ⁇ is provided only a ⁇ an example of a encapsulation technique employed in the following experiment ⁇ .
  • TABLE 1 i ⁇ a chart illu ⁇ trating the relea ⁇ e rates of two ⁇ ample ⁇ of microencap ⁇ ulated fungicide ⁇ .
  • the chart illu ⁇ trate ⁇ the relea ⁇ e rate of a conventionally encap ⁇ ulated fungicide known a ⁇ Folpet when the cap ⁇ ule na ⁇ been immer ⁇ ed in water compared to the Relea ⁇ e A ⁇ i ⁇ t ⁇ y ⁇ tem of an enhanced encap ⁇ ulated Folpet ⁇ ample.
  • the Relea ⁇ e Assist ⁇ ample u ⁇ e ⁇ a propellant co po ⁇ ed of cyclohexane, an organic ⁇ olvent, when heat i ⁇ applied.
  • TABLE 2 is a table comparing the release results of a particular test conducted using a conventional encapsulation approach to a release assist approach using a common chemical catalyst a ⁇ the active core.
  • SCALE Growth Rate ⁇ cale of 10 to 0 where 10 corresponds to complete coverage of the ⁇ urface of the coated film. Lower number indicate ⁇ reduced Fungi growth activity , and greater efficiency for the fungicide.
  • the Raw fungicide wa ⁇ u ⁇ ed a ⁇ the standard.
  • Fungicide Used was known a ⁇ Folpet, ⁇ upplied by Nuodex Inc., A standard loading of 40 % in latex paint was u ⁇ ed. Samples had been aged for 4 weeks prior to the test.
  • Re ⁇ ult ⁇ indicate that the encap ⁇ ulated fungicide doe ⁇ not have a ⁇ ignificant effect.
  • a second microcapsule batch was produced u ⁇ ing the same coacervation procedure, the same ⁇ hell and the Folpet active, but with a ⁇ econd core con ⁇ i ⁇ ting of a ⁇ olvent known a ⁇ Cyclohexane.
  • the two capsule ⁇ were then compared for ⁇ helf life stability, bio-activity upon release, and relea ⁇ e ef ectiveness.
  • the procedure used to produce the capsule ⁇ was: A pre-condensate of urea - formaldehyde re ⁇ in wa ⁇ fir ⁇ t formed using 120 grams of urea mixed with 325 grams of 37% aqueous formaldehyde containing 15 % methyl alcohol at room temperature. Triethanolamine wa ⁇ added , one drop at a time, to adju ⁇ t the pH -to 8. After 1 hour of agitation , 600 ml of ci ⁇ tilled water was added to the mixture, at room temperature. Then, 130.5 grams of the pre-conden ⁇ ate wa ⁇ further diluted with 200 ml of distilled water, producing a final polymeric solution to be u ⁇ ed a ⁇ the ⁇ hell layer.
  • the capsule ⁇ contained approximately a 25% ⁇ hell volume, and were of the Reservoir type construction.
  • the cap ⁇ ules were then allowed to air dry for 5 days, after which 20 gram ⁇ of the completed capsule ⁇ were then immersed in a beaker of water containing 400 ml of tap water.
  • the capsule ⁇ were then ob ⁇ erved for relea ⁇ e rate activity over a period of 30 days, by testing the amount of Ph change and conductivity change of the tap water over the 30 day period of time, in daily intervals.
  • the capsules were weighed prior to immer ⁇ ion.
  • the weight wa ⁇ then periodically checked to determine the loss rate over the te ⁇ t period. Additionally some of the capsule ⁇ were subjected to fungi for tests of bioactivity.
  • Another batch of microcapsules were produced u ⁇ ing the ⁇ ame ingredien ⁇ and procedure ⁇ listed above except that a second core material wa ⁇ added to the reaction.
  • the ⁇ econd material wa ⁇ a solvent known as cyclohexane, which wa ⁇ applied at a ratio of 20 % of the overall core material.
  • Folpet occupied 80 % of the resulting capsule ⁇ while cyclohexane occupied approximately 20%.
  • the second batch of capsules were well formed, having a Reservoir type construction, and size approximating the first batch, from 5 to 30 microns.
  • the ⁇ econd batch was then filtered and tested u ⁇ ing the same de ⁇ cribed procedures.
  • Thi ⁇ batch was the release assi ⁇ t sample, and contained a thicker shell than the first batch.
  • the capsule ⁇ released at varying rate ⁇ .
  • TABLE 1 (A and B) illu ⁇ trate ⁇ the release rate over the 30 day period for Batch 1 (coacervated Folpet) and Batch 2 (Coacervated Folpet/Cyclohexane) . It can be seen that Batch 1 release ⁇ very quickly compared to Batch 2, which i ⁇ the Relea ⁇ e A ⁇ i ⁇ t cap ⁇ ule product form of thi ⁇ invention.
  • BATCH 1 Encapsulated Folpet fungicide, reservoir type construction using 15% shell (Urea-formaldehyde resin) , 85% active core material, encapsulated through coacervation procedure (interfacial polymerization technique) , a conventional encapsulation product.
  • BATCH 2 Encapsulated Folpet using a reservoir type cap ⁇ ule con ⁇ truction using 25% shell ( ⁇ rea-formaldehyde re ⁇ in ) 75% total core of which 50% i ⁇ Folpet active and 50% i ⁇ cyclohexane ⁇ olvent acting a ⁇ a propellant. BATCH 2 had a thicker ⁇ hell and thereby had a greater shelf life.
  • BATCH 1 did not relea ⁇ e at all during the 30 day trial period.
  • BATCH 2 slowly released as the propellant (Cyclohexane ) phase changed and produced a gas which exerted pressure against the interior surface of the capsule ⁇ hell. The pressure caused cracks and lesion ⁇ to form in the cap ⁇ ule ⁇ hell, through which the active fungicide could escape, yet the release rate wa ⁇ over a prolonged period of time.
  • Table 4 indicates the bioactivity result ⁇ of the above example. Ob ⁇ ervation of the painted surfaces revealed that niether capsule system had broken. The coacervated sample with no ⁇ olvent core, Batch 1 had remained intact with no relea ⁇ e at all. Batch 2, the Relea ⁇ e A ⁇ sist cap ⁇ ule ⁇ , had not exploded or completly broken but photographic analysis revealed that there were several cracks and pore ⁇ in the ⁇ urface of the cap ⁇ ule, which had not been pre ⁇ ent when the capsules were first made. The cracks and pore ⁇ in the ⁇ hell of the cap ⁇ ule were the result of the heating activity, whereupon the expanding propellant forced the fungicide through the weak spots in the capsule construction. EXAMPLE 2
  • a second bath was produced using the Relea ⁇ e A ⁇ i ⁇ t approach whereupon a ⁇ olvent wa ⁇ added to the cap ⁇ ule a ⁇ the ⁇ econd core material.
  • the solvent was added at differing quantities as a ratio of the active catalyst to the solvent.
  • the shell layer remained at a constant 20% of the volume of the overall capsule in each formulation tested. Differing solvents were used to obtain a wide variety of Relea ⁇ e point ⁇ .
  • Stage device to measure the point at which the capsule shell melted under heat The rupturing of the capsule was observed visually under a magnifying lens attached to the heat stage device. In each instance where a solvent was employed as a second core, the capsules were observed to explode when heat was applied to the capsule unit. The capsule ⁇ which contained no solvent ⁇ lowly melted a ⁇ heat wa ⁇ applied whereas the solvent filled capsules tended to expand in size and then explode.
  • the samples were then subjected to DSC ( differential scanning calorimetry ) and TGA ( thermogravimetric analy ⁇ i ⁇ ) te ⁇ t ⁇ to determine the temperature profiles of each sample. The results are shown in TABLE 2:
  • HEX. HEXANE
  • sample 2A the capsule wa ⁇ observed to release through a Melting of the shell.
  • the shell began a slow degradation a ⁇ heat wa ⁇ applied to the capsule.
  • Sample 2C contained a cap ⁇ ule ⁇ hell which had not been cro ⁇ linked into a.hardened form, enabling the vololizing sovent to break the weaker ⁇ hell.
  • the other sa ple ⁇ were cro ⁇ linked into a harder shell formation by adjusting the Ph to a lower level during the final polmerization ⁇ tage of the re ⁇ in ba ⁇ ed ⁇ hell. It is apparent from these test ⁇ that the ⁇ trength of the shell layer is a factor in achieving the desired release temperature.
  • the capsule shell is very thick the ⁇ trength of the wall membrane i ⁇ ⁇ ufficient to resist the expansion force exerted upon it from within the capsule by the gases emitted from the volotilizing propellant or solvent ⁇ econd core.
  • the ⁇ hell i ⁇ hardened through a polymerization or other ⁇ trenghtening process it may also rai ⁇ e the relea ⁇ e temperature of the capsule.
  • Example 2B,2C,2D,2E the capsules exploded ' when they were heated to the indicated release temperature.
  • the release was sudden and complete, in a burst effect which not only destroyed the cap ⁇ ule ⁇ hell but actually expelled the active core from the cataly ⁇ t.
  • the solvent acted to lower the release temperature of the cap ⁇ ule.
  • the ⁇ olvent acted to explode the cap ⁇ ule ⁇ at a very preci ⁇ e release point a ⁇ opposed to an extended relea ⁇ e over a period of time.
  • the ⁇ olvent provided for a ⁇ udden bur ⁇ t release. For each sample the solvents vaporization tended to expel or throw the active material from the cap ⁇ ule once the cap ⁇ ule wa ⁇ broken.
  • the invention provides for a propellant compound to be added to the active core of a microcapsule whereupon the resultant capsule product will provide the following functions:
  • Enable shell to core incompatibility problems to be solved be allowing the use of compatible shell polymers, with adjusted release points through the use of a propellant as a second core to the capsule.
  • the invention may al ⁇ o be practiced u ⁇ ing any other form of cap ⁇ ule manufacture proce ⁇ including but not limited to Coacervation, Thermal Coacervation, Interfacial Polymerization Solvent Evaporation or any mechanical mean ⁇ .

Abstract

The invention is a microcapsule consisting of three components: 1) a shell or wall material layer (4); 2) a core material (3) consiting of an active ingredient; 3) a propellant (2) which is the second core material. The invention is a microcapsule (1) consisting of two core materials, one being an active core ingredient (3) while the other is a propellant (2), both surrounded by an encapsulating shell layer (4). The propellant (2) acts to either explode the capsule (1) or to help accelerate the release of the active core material (3) when the capsule is heated. The capsules have a triggered time release function, caused by heat acting upon the propellant core (2), which then acts to push more of the active ingredient (3) through the wall membrane of the capsule shell, or to explode the capsule from within.

Description

RELEASE ASSIST MICROCAPSDLES
Field of Invention
This invention relates to an improved method of effecting the release of an active core from microcapsuleε. Additionally this invention relates to encapsulated fungicides.
A further relationship exists to encapsulated catalysts.
There are four main release mechanisms for microcapsuleε available. Conventional microcapεules release their active core material through:
1. Diffusion of the active across the shell membrane
2. Leakage of the active core through pores in the structure of the microcapsule
3. Interaction with another chemical, or solvent
4. The use of a force which causes the capsule to break or dissolve. A microcapsule may be classified as a either a Break On
Demand or a Time Release product.
Time Releaεe iε a term used to describe a slow release over a period of time of the active core material from the confines of the capsule. There are several problems with conventional Time
Release icrocapsules:
1. They generally have a short shelf life period, often releasing the core too soon.
2. Most such capsules generally have very fragile shells, making them unsuitable to many industrial applications.
3. They often have pre-mature chemical reactions with the environment they are placed in due to early releaεe of the active core material from the capsule. Break on Demand microcapsuleε are capsules which generally have thicker shells, allowing little or no releaεe of the active core material until a physical force or chemical reaction causes the shell to rupture. Such capsules are virtually inert until an outside force effects the breaking or dissolution of the shell.
The shelf life stability of microencapεulated chemicals has inhibited the application of microencapsulation technology to many fields. In many cases the Time Release capsules release far too early. Using a Break On Demand capsule system can often result in a capsule which does not release at all. Exampleε of such problems can be found through an examination of the encapsulation of catalyεtε and fungicides: HILDE SUPPRESSANT FUNGICIDES FOR PAINT USE
In this project a fungicide is mixed into a can of water based paint, the intent being to provide mildew protection after a surface has been painted. The paint iε generally used in wet or damp environmentε. The fungicide iε intended to avoid discoloration of the painted surface. Most fungicides available on the market react with the ingredients in the paint or dissolve while the paint can iε stored on the shelf, a period of time which can last past one full year. The shelf life reactivity problem leads to a loss of potency for the fungicide. Encapsulation of the fungicide, to avoid the chemical reaction problem, can produce either a Reservoir capsule or a Micro-sponge type capsule, a capsule with pores. The Micro-Sponge type capsule allows the fungicide to leak from the capsule while stored on the shelf, thereby having little protection for the active material.
The Reservoir construction leads to a capsule with a shell which is so thick as to not allow any leakage of the active or diffusion to occur, avoiding premature reaction during shelf storage, but the shell may also not allow releaεe after the surface has been painted either. In this application, where microencapsulation appears to be of potential benefit the encapsulation effort is defeated through shelf life and release difficulties.
ENCAPSULATED CATALYSTS In this field icrocapsules are intended as a means of delivering a catalyst to a particular location or at a particular time in a chemical process, without chemical reaction along the way. Catalysts are isolated within a capsule until the shell is broken of dissolved. Heat, iε often used to melt away the capsule shell to release the- active catalyst material. In theory this should enable satisfactory controlled delivery of a catalyst. In practice however catalyst compounds often react with the shell material, crosεlinking the polymer. This can increase the melt point of the shell material to a level higher than desired or it can lead to a weakening of the shell itself, producing cracks and lesions in the capsule wall. The resultant capsules often have no longevity or actually do not contain the original quality of catalyst. Using substitute shell materials in the capsule construction, shells which will not react with the catalyst, often produce undesirable traits in the resulting product. An example would be the encapsulation of Butyl Tuadε, a common rubber catalyst, which was desired to be released from the capsule at temperatures below 100° (c) . The chosen shell material, which had a melt point of 65° (c) reacted with the catalyst and would release only at 180° (c) . An attempt was made to use a non reactive second polymer which isolated the catalyst properly, but had a temperature melt point of 250 (C) . The problem was: How to get the catalyst to releaεe in a non-reactive shell at a temperature below 100 (C) ? Conventional microcapsule release methods did not have a suitable effect in this project.
To solve theεe problems the use of a secured form of reservoir microcapsule construction is employed, a capsule which does not allow diffusion and does not have poreε which would allow core leakage. Normally such Secured Ilicrocapεules do not have a Time Release Function. Instead these capsules are usually employed in operations whereupon a Break on Demand function is desired. In this instance the Break on Demand capsule iε caused to a have a time release function by using a Triggered Release approach.
In this embodiment of the invention a propellant iε added to the core material to cause the active core to release under certain conditions. The preferred condition iε to employ heat to cause the propellant to accelerate the release of the active material. A propellant iε placed along with the active material aε the core of the icrocapεuleε. When heat is applied the propellant can act to explode the capsule from within, thus providing a burst release function, OR the propellant can act to accelerate the diffusion rate of the active by pushing the active material through the pores in the capsule shell.
In the Fungicide example outlined above the use of a Release Assist Approach was attempted whereby a solvent waε added to the fungicide core material and a Reservoir type sealed capsule waε produced around the combination core. The resultant capsules exhibited a strong resistance to shelf life deteriorate in the paint can. Later after the paint waε applied to a painted εurface the capsules began to releaεe. In this case the painted εurface was the exterior of a house where the heat of sunlight acted to warm the capsules within the paint layer. The heat caused the solvent within the capsule to partially volatilize. The resulting vapors produced a pressure within the capsules which then acted to "push'" the fungicide second core through the shell of the capsule. This push iε triggered by heat and acts to accelerate the release of the capsule. By adjusting the amount of solvent within the core the release rate after the heat trigger can be controlled to take place over a series of days or weekε.
In the catalyst example where the catalyεt core reacted with the shell of the capsule the releaεe function difficultieε are solved by using a non-reactive polymer as the capεule shell, together with a solvent as a εecond core. The catalyεt doeε not react with the new polymer but the capsule normally haε a melt point higher than desired. The addition of the solvent solves this problem. By choosing a solvent with a low enough boiling point the capsule can be made to release at the desired temperature. When the capsule is heated to the boiling point of the solvent second core, the solvent volatilizes completely. The resultant gas then exerts a pressure upon the interiorof the capsule, cauεing the capsule to explode outward. The explosion occurs at a temperature lower than that of the shell polymer, and closer to the boiling point of the solvent. In this manner the solvent acts as a propellant, providing a Burst Release of the active material when the correct temperature level has been obtained.
There are many applications in the prior art where capsules are produced using a wide variety of techniques, capsuleε which can have an enhanced releaεe profile or function uεing the Releaεe Assist approaches defined in this invention.
The preεent invention encompaεεeε encapεulation of εubεtances in liquid, solid or slurry form. These substances may be pharmaceutical agents, catalyεtε, fungicideε, pesticides or any other chemical. Encapsulating walls may or may not be permeable to core material or other materials to which the completed capsules may later be added. Capsuleε provided by the present invention may be capable of slow release mechanisms (commonly referred to as "time releaεe") or may be released in a sudden method caused by heat, ultraviolet light, microwaves, ultrasonics or other energy media or may be released through dissolution of the capsule wall. In each instance of capsule release the release function iε aided by the uεe of a propellant material which haε been added to the active core material, whereby the propellant acts to accelerate the release of the active.
Accordingly , a first object of this invention iε to provide a microencapsulated product that poεseεs a special release function which may be either a Sudden or a Slow releaεe system which employs the use of a propellant or solvent as an additive to the active core of said microencapsulated product, whereby the release function of the capsule iε enhanced in some manner through the :uεe of the propellant additive.
A second object of this invention iε to enable Time Release capsuleε to become stable during shelf storage, beginning their time release function after that function haε been triggered by some effective means. A third object of this invention iε to enable microencapsulated compounds to have a greater utility by providing an expanded selection of polymers for uεe as capsule wall materials, by enhancing the releaεe function of the reεulting microencapsulated product. A fourth object of the invention iε to provide means of encapsulating difficult or very active chemical compouncε by providing a different releaεe mechaniεm, which in turn provideε a greater selection of encapsulating techniques anc technologies. A fifth object of the invention iε to provide a means of faεt release at narrow temperature rangeε of a confined active core from a microcapsule by providing a propellant additive to the the active core material.
Other objects and advantages of the present invention will e obvious from the following eεcriptions, drawings and experiments.
Brief Description Of The Drawings FIG. 1 iε an illustration of the major capsule forms available through conventional microencapsulation procesεeε. FIG. 2 iε an illustration of the preferred embodiment of the invention, a capεule containing a propellant additive to the active core material.
FIGS. 3 and 4 are graphε indicating the releaεe temperatureε of a microcapεule containing a catalyεt active core material, mixed with a solvent, which acts aε the propellant.
FIG. 5 iε an illustration of one method usable to form microcapsules, called Coacervation.
TABLE 1 iε an chart indicating the release rates of capsules containing encapsulated Folpet compared to capsules using the Release Aεεiεt enhancement aε meaεufed by a per centage of weight loεε over a period of time.
TABLE 2 iε a compariεon of the release temperatureε of a catalyεt known aε Butyl Tuadε which haε been encapεulated using a conventional reservoir type conεtruction vs. a release assist construction, whereupon various solventε have been used aε propellantε.
TABLE 3 iε a liεt of potential polymers which may be uεed aε capsule shell materials.
TABLE 4 is ..a chart indicating the bioactivity of capεuleε containing a fungicide compared to capsules containinga Release Aεεiεt mechaniεm employing a heat εenεitive propellant material aε a second core. Detailed Description Of The Invention FIG. 1 illuεtrateε εeveral conventional forms of microcapεule conεtruction. Each conεtruction iε capable of enhanced releaεe dynamics using this invention. In the firεt example a Reservoir Capsule construction is indicated by a egg type construction, characterized by a large amount of core material surrounded by a single shell. The Micro-Sponge construction is a capsule with a lower quantity of core material embedded within many shell layers, allowing for a slow release.
The Multi-Wall capsule construction involves a Reservoir type microcapsules with more than one shell layer. The liulti-Core capεule is eεsentially a capεule, or several smaller capsuleε, contained within a larger capεule. Each construction offer unique properties for particular product applications. The normal release mechanismε involve:
Slow dissolution of the shell layer Permeation of the core active through the shell
Degradation of the shell due to heat, ultrasound, microwave energy, pressure, impact, radiation, ultraviolet light, solvent reactions or Ph adjustments
FIG. 2 indicates the preferred embodiment of a Releaεe Assist capsule construction of the present invention 1 using the Reservoir format, whereupon a phase change material or propellant 2 haε been added to the core material 3, both contained by a shell layer 4.
The illustrated capsule construction of the present invention is a Reservoir type capsule. However, the present invention may uεe any of the other capsule forms indicated in FIG. 1.
The embodiment of the invention shown in FIG. 2 is a capsule 1 containing a shell 4 which surrounds a core material combination consisting of a active ingredient 3 which iε mixed with a propellant 2. The active 3 can be any εolid, liquid or slurry chemical compound. A partial liεt of potential active'ε includeε:
Pharmaceuticalε Pesticideε Catalysts Fungicides
Fragrances Emollients
Lubricants Adhesives
Laundry additiveε Bleaching agents
Dyes and Colorants Essential Oils A number of chemical compounds can be used as the propellant 2 including:
Solvents Phase Change Materials
Waxes Peroxides
Propellants Hydrocarbonous solutions Water Alcohols
Fuels Gaseε The propellant 2 may be any material which will disεolve or expand, or convert into a gaε when heat iε applied to the capεule 1. The action of the propellant 2 cauεeε the Release Aεsiεt function of the invention to take place, in that the propellant 2 acts to cause either a Burst Releaεe or an Accelerated Release or a Triggered Release function to occur. The propellant may be in either solid, liquid or gaεeous form.
BDRST RELEASE The application of heat to the capsule 1 causes the propellant 2 to expand within the capεule. This can cauεe the εhell 4 of the capεule 1 to elongate and expand beyond the elaεtic li itε of the polymer, eventually cauεing the capsule to explode outward, providing a sudden or burst release effect. The exploding action may be caused by a propellant material 2 which expandε under heat or phaεe changeε into a gaεeous form during heating. The reεulting gaε exerts a pressure against the interior of the shell 4 cauεing it to expand outward, eventually exploding the capεule.
ACCELERATED RELEASE FUNCTION The propellant 2 expands or phaεe changeε with heat application but doeε not generate enough force to actually rupture the shell 4. Instead the preεεure generated from the expanding propellant 2 actε to accelerate the diffuεion rate of the active core 3 acroεε the shell membrane 4. In most capεuleε uεing a εingle εhell reservoir type of construction or a sponge type conεtruction the active leakε from the capεule through poreε or crackε in the shell layer of the capεule. Additionally the active core can diffuεe acrosε the shell layer itself. In this application of the invention the leakage rate or the diffuεion rate iε accelerated becauεe of a "push" exerted upon the active 3 by the expanding propellant 2. The force of the expanding propellant or its gaεeous decomposition reεult can act to push the active 3 through pores in the capsule εhell 4, at a rate faster than normal. Additionally the propellant under heat can act to accelerate the diffuεion rate of the active.
In thiε caεe heat actε as the trigger to cause the accelerated release function to take place. By careful choice of the propellant 2 the release function can be controlled so as to only occur when heat is present. When the heat iε removed certain propellants 2 will coalesce back into a neutral form, thereby slowing or ceasing the releaεe rate of the active 3, until heat is applied again.. The releaεe function iε triggered and controlled through the. application of heat to the capsule 1.
TRIGGERED RELEASE FUNCTION Since the propellant acts by heat the capεuleε can be made to have long shelf life stability. Normal time releaεe capεuleε frequently employ active diffuεion functionε or uεe the sponge approach to allow a generous leakage rate from the capεule. Sponge type capεuleε generally have very short life spanε. Diffuεion capεuleε tend to have very thin εhellε, thereby affecting their ability to reεiεt εtreεε. Reservoir type capεuleε generally can be made with thicker εhellε, allowing them to withstand higher degrees of shear and industrial streεε. However these type capεuleε have very poor time release functions. Using the heat application to a propellant core 2 can cause the releaεe to become triggered at a certain point, enhancing the εhelf life εtability of the capεule product. Heat iε uεed aε the trigger, and can be timed to occur at a specific point in a given process.
FIG. 3 is a temperature curve indicating the release point of a microencapsulated capsule containing a catalyst - solvent combination core. The catalyst iε Butyl Tuads mixed at 50% of the total core volume of the capsule .The solvent iε cyclohexane and causes the capsule to explode at a point near the boiling point of the solvent. Cyclohexane was mixed at 50% of the total core volume. In thiε case the εhell material waε ureaformaldehyde which occupied 20 % of the total volume of the capεule while the combination core materials occupied the remaining 80%. The graph is a Differential Scanning Calorimetery teεt uεing a Dupont Model 2000 DSC device.
FIG. 4 iε a graph illuεtrating the Thermogrimetric Analysis of the same sample described in FIG. 3. Both graphs indicate the point at which the capsule shell explodeε, indicated by a sharp peak in the temperature curve profile. Through theεe graphε it can be εeen that the capεuleε reach a certain point whereupon the boiling εolvent, cyclohexane, causeε the capsule to explode outward. In both thermal studies the release point iε comparable.
FIG. 5 iε a illuεtration of the Coacervation method of encapsulation, which was used in this particular εeries of experi entε. It εhould be noted that the Releaεe aεεiεt function can be duplicated through the uεe of a multitude of encapεulation methodε, εyεtemε, techniqueε and technologies and the scope of this invention iε not intended to be limited by the uεe of juεt one such encapsulation procesε. The Coacervation proceεε is provided only aε an example of a encapsulation technique employed in the following experimentε.
TABLE 1 iε a chart illuεtrating the releaεe rates of two εampleε of microencapεulated fungicideε. The chart illuεtrateε the releaεe rate of a conventionally encapεulated fungicide known aε Folpet when the capεule naε been immerεed in water compared to the Releaεe Aεεiεt εyεtem of an enhanced encapεulated Folpet εample. The Releaεe Assist εample uεeε a propellant co poεed of cyclohexane, an organic εolvent, when heat iε applied. TABLE 2 is a table comparing the release results of a particular test conducted using a conventional encapsulation approach to a release assist approach using a common chemical catalyst aε the active core.
TABLE 3 iε a liεting of poly erε known to be uεeful aε εhell materialε for icrocapεuleε uεing the Release Assist approach. 12
TABLE 3
Shell Formulations Are Fluid Film Formers
Including
• Solutions
• Melts
■ Latexes
And May Be Hardened By
10 • Chemical Reaction
• Solvent Extraction
15 • Solvent Evaporation or * Combinations
Some Microencapsulation Matrix And Wall Chemicals
20
Natural Polymers
Carboxymethylcellose Zein Cellulose acetate phthalate Nitrocellulose
25 Et ylcellulose Propylhydroxylcellulose Geiatiπ Shellac Gum Arabic Succinylatec gelatin Starch Waxes, pararfin Ear Proteins
30 Methylcellulose Kraft lignin .ogelactan Natural Rubcer Synthetic Polymers
Polyvϊnyl alcohol Polyvinylideπe chloride
35 Polyethylene Polyvinyl chloride
Polypropylene Polyacryiate
Polystyrene Polyacrylonitrrle
Polyacrylamide Chlorinated polyethylene
Polyether Acetal copolymer
40 Polyester Polyurethane
Pclyarn.de Polyvinylpyrrolidone
Poiyurea Poly (p-xylylene)
Epox'y Polymethyt methacrylate
Eihyier.e-vinyl acetate copolymer Poiyhydroxyεthyl methacrylate
45 Pclyvmv! acetate
Synthetic Elastomers
Poly butadiene Acrylonitrile
Polylsoprene Nstrile
Necpteπe but) i rubber
50 Chloroprene I lj <' IUACI I t
Sty re ne-butύdi s π e rubbe r Hycrin rubbe..
Siϋcone rubber Etr.y!er.e-p.cρylene-dier.e copolymer TABLE 4 is a chart describing a test involving various Fungi whereupon a encapsulated fungicide waε used in an effort to test boiactivity effects upon the target fungi. In one test capsules containing a given fungicide, known aε Folpet, were made by conventional encapsulation techniques aε taught by Noren in the article, Investigation of Microencapsulated Fungicides for uεe in Exterior Trade Sales Paintε, Vol 58, No. 734, March 1986 of the Journal- of Coatings Technology. These capsules, called Batch 1 on the chart, were then compared to capsuleε made in the same manner, except that a propellant waε added to the core material, aεcribing to the teachingε of thiε invention, and indicated on the chart aε Batch 2.
TABLE 4 FUNGAL RESISTANCE TO AQUEOUS PAINT FILMS CONTAINING ENCAPSULATED FUNGICIDE, WITH SAMPLES BEING SUBJECTED TO ARTIFICIAL "SUN LAMP" HEAT TO 90 (F) FOR 30 DAYS AFTER SURFACE WAS COATED
FUNGI RAW BATCH 1 BATCH 2
TYPE FUNGICIDE ENCAPSULATED RELEASE
ASSIST FUNGICIDE FUNGICIDE
MIXED 10
PENICILLIUM 10 FUNICULOSM
ASPERGILLUS 10 NIGER
GLIOCLADIUM 10 VIRENS
SCALE : Growth Rate εcale of 10 to 0 where 10 corresponds to complete coverage of the εurface of the coated film. Lower number indicateε reduced Fungi growth activity , and greater efficiency for the fungicide. The Raw fungicide waε uεed aε the standard.
Fungicide Used was known aε Folpet, εupplied by Nuodex Inc., A standard loading of 40 % in latex paint was uεed. Samples had been aged for 4 weeks prior to the test.
Reεultε indicate that the encapεulated fungicide doeε not have a εignificant effect. The Release Asεiεt capsules, under heat, however did provide decreased bioactivity. for the fungi.
In Table 4 it can be seen that the Batch 2 capεuleε remained stable until heat was applied to them. At thiε point the releaεe function was triggered aε the propellant inεide the capεule began to expand, puεhing the fungicide through crackε which developed in the expanding εhell layer.
EXAMPLE 1 INCREASED SHELF LIFE STABILITY AND ACCELERATED RELEASE THROUGH THE USE OF A RELEASE ASSIST CAPSULE CONSTRUCTION USING A THERMAL TRIGGER TO INITIATE TIME RELEASE FUNCTION A fungicide known aε Folpet, obtained from Nuodex Corporation, was encapsulated using the Coacervation procedure uεing a urea-formaldehyde polymer aε the εhell layer.
A second microcapsule batch was produced uεing the same coacervation procedure, the same εhell and the Folpet active, but with a εecond core conεiεting of a εolvent known aε Cyclohexane.
The two capsuleε were then compared for εhelf life stability, bio-activity upon release, and releaεe ef ectiveness.
The procedure used to produce the capsuleε was: A pre-condensate of urea - formaldehyde reεin waε firεt formed using 120 grams of urea mixed with 325 grams of 37% aqueous formaldehyde containing 15 % methyl alcohol at room temperature. Triethanolamine waε added , one drop at a time, to adjuεt the pH -to 8. After 1 hour of agitation , 600 ml of ciεtilled water was added to the mixture, at room temperature. Then, 130.5 grams of the pre-condenεate waε further diluted with 200 ml of distilled water, producing a final polymeric solution to be uεed aε the εhell layer. Next 10 grams of the above described urea-formaldehyde shell solution was mixed with 40 gra ε of Folpet fungicide supplied by Nuodex Corporation, in 400 ml of water, for 60 minutes, at a temperature of 25 (c) , under rapid agitation. At the end of the 60 minute period the heat was removed to allow the mixture to cool back to room temperature, w.hile the agitation waε maintained. Hydrochloric acid waε added to the mixture to adjust the Ph to slightly less than 6. Once the Ph level had been obtained the mixture waε allowed to air cool for another 2 hourε under moderate agitation. Capεuleε were formed during thiε procedure and hardened by the Ph adjustment into a solidified form. The capsuleε were then filtered from the liquid mixture and examined. The capsuleε contained approximately a 25% εhell volume, and were of the Reservoir type construction. The capεules were then allowed to air dry for 5 days, after which 20 gramε of the completed capsuleε were then immersed in a beaker of water containing 400 ml of tap water. The capsuleε were then obεerved for releaεe rate activity over a period of 30 days, by testing the amount of Ph change and conductivity change of the tap water over the 30 day period of time, in daily intervals. The capsules were weighed prior to immerεion. The weight waε then periodically checked to determine the loss rate over the teεt period. Additionally some of the capsuleε were subjected to fungi for tests of bioactivity.
Another batch of microcapsules were produced uεing the εame ingredien ε and procedureε listed above except that a second core material waε added to the reaction. The εecond material waε a solvent known as cyclohexane, which waε applied at a ratio of 20 % of the overall core material. Folpet occupied 80 % of the resulting capsuleε while cyclohexane occupied approximately 20%. In this batch however 40 gramε of urea-formaldehyde reεin inεtead of 10 gramε waε used in the final capsule mixture.
The second batch of capsules were well formed, having a Reservoir type construction, and size approximating the first batch, from 5 to 30 microns. The εecond batch was then filtered and tested uεing the same deεcribed procedures. Thiε batch was the release assiεt sample, and contained a thicker shell than the first batch. The capsuleε released at varying rateε. TABLE 1 (A and B) illuεtrateε the release rate over the 30 day period for Batch 1 (coacervated Folpet) and Batch 2 (Coacervated Folpet/Cyclohexane) . It can be seen that Batch 1 releaseε very quickly compared to Batch 2, which iε the Releaεe Aεεiεt capεule product form of thiε invention.
TABLE 1 A
WEIGHT LOSS OF ENCAPSULATED FUNGICIDE SAMPLES, WHEN IMMERSED
IN TAP WATER, OVER 30 DAY PERIOD, AT ROOM TEMPERATURE
NO OF DAYS BATCH 1 BATCH 2
WEIGHT LOSS WEIGHT LOSS 0 0 % 0 %
5 2 % 0 %
10 16 % 0 %
15 24 % 0.50 %
20 72 % 0.65 % NO OF DAYS BATCH 1 BATCH 2 WEIGHT LOSS WEIGHT LOSS 25 85 % 0.76 %
30 92 % 1.0 %
BATCH 1 = Encapsulated Folpet fungicide, reservoir type construction using 15% shell (Urea-formaldehyde resin) , 85% active core material, encapsulated through coacervation procedure (interfacial polymerization technique) , a conventional encapsulation product.
BATCH 2 = Encapsulated Folpet using a reservoir type capεule conεtruction using 25% shell (ϋrea-formaldehyde reεin ) 75% total core of which 50% iε Folpet active and 50% iε cyclohexane εolvent acting aε a propellant. BATCH 2 had a thicker εhell and thereby had a greater shelf life.
TABLE 1 B RELEASE RATE OF ENCAPSULATED FOLPET FUNGICIDE WHEN SAMPLE IS SUBJECTED TO HEAT OVER A THIRTY DAY PERIOD TEMPERATURE LEVEL: 90 (F)
NO. OF BATCH 1 BATCH 2 DAYS
0 0 % 0 %
5 0 % 2 %
10 0 % 3.5 %
15 0 % 4.70 %
20 0 % 6.25 % NO. OF BATCH 1 BATCH 2
DAYS
25 0 % 9.75 %
30 0 % 13.00 %
NOTE: BATCH 1 did not releaεe at all during the 30 day trial period. BATCH 2 slowly released as the propellant (Cyclohexane ) phase changed and produced a gas which exerted pressure against the interior surface of the capsule εhell. The pressure caused cracks and lesionε to form in the capεule εhell, through which the active fungicide could escape, yet the release rate waε over a prolonged period of time.
Even though the urea-formaldehyde reεin was supposed to be a water barrier for the microcapsule the Folpet active managed to diffuse or leak from the capsule. Folpet iε a commonly used fungicide for mildew εuppreεεion in houεehold paintε. Thiε test revealed that the product would have released εlowly in the paint can during εhelf εtorage, having no remaining potency after the paint had been applied to itε target εurface. Indeed further examination of the data correεponded with a teεt conducted by Deεoto Paintε on encapεulated Folpet liεted in the reference section of thiε application. The tests conducted by Desoto alεo indicated poor performance for the encapsulated Folpet. Batch 2 had virtually no effective releaεe over the 30 day period, loosing less than 1 % of its weight over the period compared with nearly a 92 % losε rate for the conventionally made capsuleε. Over a year long period the Batch 1 would have leached all of its active from the capsule and would thereby become totally uselesε by the time it waε applied as part of a paint coating to a given surface. Batch 2 would loose less than 12% of itε weight by then however, providing approximately 88% active εtill remaining within the sealed capεule (aεεuming that none of the εhell degraded within the liquid) Theεe teεtε were conducted with the application of water baεed paintε in mind. In the bioactivity teεt the reεults wereremarkably different. Both capsule batches showed no reaction when exposed to Penicilliu Funiculosm; Aspergilluε Niger; Gliocladiu Virenε fungi and a mixture of the three at room te perature. But when "εunlight" exposures were made, whereupon the capsuleε were εubjected to the target fungi under a heat lamp, which approximates a temperature of 85 (f) , the true differences in the batcheε preεented the εelveε. Batch 1 εhowed little or no effective reaction. Batch 2, containing the Releaεe Aεεiεt conεtruction, εhowed a marked ability to kill the fungi. It iε εuggeεted by the inventor that the heat of the lamp caused the cyclohexane εecond core of the capεuleε of Batch number 2 to volatilize. Thiε generated an internal preεεure within the capεuleε and thiε then acted to "push" the Folpet active fungicide through pores in the capεule shell which had developed during immersion in the water. Thiε "puεh" action acted to accelerate the releaεe function, after shelf storage while the capsuleε were immerεed in water, and after the heat trigger was applied by the heat lamp. Batch two waε observed for another 30 dayε to still be effective in destroying the target fungi, indicating that the "push" effect waε not a sudden effective releaεe, but a prolonged releaεe over a period of time.
Table 4 indicates the bioactivity resultε of the above example. Obεervation of the painted surfaces revealed that niether capsule system had broken. The coacervated sample with no εolvent core, Batch 1 had remained intact with no releaεe at all. Batch 2, the Releaεe Aεsist capεuleε, had not exploded or completly broken but photographic analysis revealed that there were several cracks and poreε in the εurface of the capεule, which had not been preεent when the capsules were first made. The cracks and poreε in the εhell of the capεule were the result of the heating activity, whereupon the expanding propellant forced the fungicide through the weak spots in the capsule construction. EXAMPLE 2
SUDDEN ( EXPLOSIVE ) RELEASE THROUGH A THERMAL TRIGGERING OF A RELEASE ASSIST MICROCAPSULE
A batch of Urea-formaldehyde resin waε made according to the procedure outline in Example 1 above. In thiε experiment 40 grams of a chemical catalyεt known aε Butyl Tuadε waε added to the reaction vessel inεtead of the Folpet material uεed in Example 1. The encapεulation procedure waε the same. Capεuleε were produced at approximately 50 - 100 icronε with a Reεervoir type conεtruction. Theεe capεuleε were then filtered from the mixture and allowed to air dry for 24 hourε. •
A second bath was produced using the Releaεe Aεεiεt approach whereupon a εolvent waε added to the capεule aε the εecond core material. The solvent was added at differing quantities as a ratio of the active catalyst to the solvent. The shell layer remained at a constant 20% of the volume of the overall capsule in each formulation tested. Differing solvents were used to obtain a wide variety of Releaεe pointε. Each capεule batch produced waε subjected to a Heat
Stage device to measure the point at which the capsule shell melted under heat. The rupturing of the capsule was observed visually under a magnifying lens attached to the heat stage device. In each instance where a solvent was employed as a second core, the capsules were observed to explode when heat was applied to the capsule unit. The capsuleε which contained no solvent εlowly melted aε heat waε applied whereas the solvent filled capsules tended to expand in size and then explode. The samples were then subjected to DSC ( differential scanning calorimetry ) and TGA ( thermogravimetric analyεiε) teεtε to determine the temperature profiles of each sample. The results are shown in TABLE 2:
TABLE 2
TOL. = TOLUENE CYC. = CYCLOHEXANE HEX. = HEXANE
RELEASE TEMP. = THE RELEASE TEMPERATURE OF THE CAPSULE
U/F = UREA-FORMALDEHYDE RESIK SHELL
In sample 2A the capsule waε observed to release through a Melting of the shell. The shell began a slow degradation aε heat waε applied to the capsule.
Sample 2C contained a capεule εhell which had not been croεεlinked into a.hardened form, enabling the vololizing sovent to break the weaker εhell. The other sa pleε were croεεlinked into a harder shell formation by adjusting the Ph to a lower level during the final polmerization εtage of the reεin baεed εhell. It is apparent from these testε that the εtrength of the shell layer is a factor in achieving the desired release temperature. If the capsule shell is very thick the εtrength of the wall membrane iε εufficient to resist the expansion force exerted upon it from within the capsule by the gases emitted from the volotilizing propellant or solvent εecond core. Likewiεe if the εhell iε hardened through a polymerization or other εtrenghtening process it may also raiεe the releaεe temperature of the capsule.
The temperature profileε indicated in the releaεe curveε of FIG. 3 and FIG. 4, developed by a Differential Scanning Calorimeter and Thermogravimetric Analysis device manufactured by E.I. Du Pont De Nemours Instruments Division, Model 2000, indicate the release tempera-ture of Sample 2 E.
In Examples 2B,2C,2D,2E, the capsules exploded' when they were heated to the indicated release temperature. The release was sudden and complete, in a burst effect which not only destroyed the capεule εhell but actually expelled the active core from the catalyεt.
In thiε example it can be seen that the solvent actε aε a propellant to explode the εhell of the capεule at temperatureε lower than the normally melt point of the polymer uεed in the capsules. In each case the solvent acted to lower the release temperature of the capεule. Additionally the εolvent acted to explode the capεuleε at a very preciεe release point aε opposed to an extended releaεe over a period of time. The εolvent provided for a εudden burεt release. For each sample the solvents vaporization tended to expel or throw the active material from the capεule once the capεule waε broken. Heat iε uεed aε the releaεe trigger but the temperature at which the capεule ruptureε can be adjuεted through the choice of the solvent used and the percentage of solvent used in the capsule as oppoεed to the percentage of active core.
In the above examples several functions of the invention have been described. The invention provides for a propellant compound to be added to the active core of a microcapsule whereupon the resultant capsule product will provide the following functions:
1. Enable a microcapsule to have a thicker εhell conεtruction εo aε to provide an extended shelf life for the product. 2. Enable the sudden release of a microcapsule at a specific temperature level.
3. Enable the acceleration of a active core material through pores or lesionε in the capεule εhell layer after a thermal trigger haε been applied to the capsule.
4. Increase the diffusion rate of of an active core acroεε a εhell membrane after a thermal trigger haε been applied.
5. Enable shell to core incompatibility problems to be solved be allowing the use of compatible shell polymers, with adjusted release points through the use of a propellant as a second core to the capsule.
6. Allow for exploding capsuleε through the uεe of a propellant εecond core, which when heated will cauεe a rapid rupture of the shell layer and a expulsion of the active core from the confines of the capsule. •
In the above examples a batch procesε waε employed uεing Coacervation to produce Reεervoir type microcapεuleε. The invention may alεo be practiced uεing any other form of capεule conεtruction including but not limited to
Micro-sponge or entrapment capsuleε, multi-wall capεules or multi-core capεuleε. The invention may alεo be practiced uεing any other form of capεule manufacture proceεε including but not limited to Coacervation, Thermal Coacervation, Interfacial Polymerization Solvent Evaporation or any mechanical meanε.
While the invention haε been described with reεpect to specific embodiments, it is understood that variationε are possible. The examples given are intended to be illustrative, and not limiting. These and other variations of the invention should be deemed within the spirit and scope of the following clai ε:

Claims

What is claimed is:
1. A microcapεule which comprises: a first core material, and a second core material, said second core material having the property of causing the release of said first core material when heat is applied to the capεule.
2. The microcapεule of claim 1, wherein said firεt and second core materials are encompassed by a shell, said second core material causing said shell to loose itε structural integrity when said heat is applied to the microcapsule, thereby permitting the release of said first core material.
3. The microcapsule of claim 2, wherein the losε of structural integrity of said shell is caused by the volatilization of said second core material due to εaid heat.
4. The microcapεule of claim 3, wherein εaid volatilization of εaid εecond core material cauεeε εaid firεt core material to diffuεe through εaid εhell.
5. The microcapεule of claim 3, wherein εai εhell haε openingε therein and wherein εaid volatilization of εaid second core material causeε said firεt core material to be forced through said openings in said εhell.
6. The microcapεule of claim 3, wherein εaid volatilization of εaid εecond core material iε rapid, thereby cauεing εaid εhell to burεt.
7. The icfocapεule of claim 1, 2, 3, 4, 5, or 6 wherein said first core material iε a biocide selected from the group consisting of fungicides, bactericides, and pesticides. 8. The microcapsule of claim 1, 2, 3, 4, 5, or 6 wherein said first core material is a catalyst.
EP19890910356 1988-09-06 1989-09-06 Realease assist microcapsules Withdrawn EP0464023A4 (en)

Applications Claiming Priority (2)

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US24079488A 1988-09-06 1988-09-06
US240794 1988-09-06

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EP0464023A1 (en) 1992-01-08

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