CA1052195A - Production of dual walled microcapsules by reducing ph to polymerize aminoaldehyde precondensate - Google Patents
Production of dual walled microcapsules by reducing ph to polymerize aminoaldehyde precondensateInfo
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- CA1052195A CA1052195A CA230,762A CA230762A CA1052195A CA 1052195 A CA1052195 A CA 1052195A CA 230762 A CA230762 A CA 230762A CA 1052195 A CA1052195 A CA 1052195A
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- Prior art keywords
- continuous phase
- set forth
- phase
- microcapsules
- solution
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Classifications
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- 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
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
- B41M5/00—Duplicating or marking methods; Sheet materials for use therein
- B41M5/124—Duplicating or marking methods; Sheet materials for use therein using pressure to make a masked colour visible, e.g. to make a coloured support visible, to create an opaque or transparent pattern, or to form colour by uniting colour-forming components
- B41M5/165—Duplicating or marking methods; Sheet materials for use therein using pressure to make a masked colour visible, e.g. to make a coloured support visible, to create an opaque or transparent pattern, or to form colour by uniting colour-forming components characterised by the use of microcapsules; Special solvents for incorporating the ingredients
Abstract
TITLE OF THE INVENTION
DUAL-WALLED MICROCAPSULES AND METHOD
FOR PRODUCING THE SAME
INVENTOR
GEORGE E. MAALOUF
ABSTRACT OF THE DISCLOSURE:
Disclosed is a process for preparing improved dual-walled microcapsules which are useful in connection with carbonless copying systems. Also disclosed are the dual-walled microcapsules themselves which comprise minute discrete drop-lets of liquid fill material including an initially colorless chemically reactive color forming dye precursor and a carrier therefor encapsulated within individual, rupturable, generally continuous shells. The shells comprise inner and outer poly-condensate layers. The process comprises the step of catalyz-ing the reactions whereby the outer shell is formed with the by-products of the reaction by which the inner shell is formed.
DUAL-WALLED MICROCAPSULES AND METHOD
FOR PRODUCING THE SAME
INVENTOR
GEORGE E. MAALOUF
ABSTRACT OF THE DISCLOSURE:
Disclosed is a process for preparing improved dual-walled microcapsules which are useful in connection with carbonless copying systems. Also disclosed are the dual-walled microcapsules themselves which comprise minute discrete drop-lets of liquid fill material including an initially colorless chemically reactive color forming dye precursor and a carrier therefor encapsulated within individual, rupturable, generally continuous shells. The shells comprise inner and outer poly-condensate layers. The process comprises the step of catalyz-ing the reactions whereby the outer shell is formed with the by-products of the reaction by which the inner shell is formed.
Description
BACKGROUND OF THE INVEMTION:
Field Of The Invention:
The present invention relates to carbonless copying systems and in particular to new improved dual-walled microcapsules which are useful in connection with such systems and which comprise minute discrete droplets of liquid fill matèrial including an initially colorless chemically reactive color forming dye precursor and a carrier there~or encapsulated within individual, rupturable, generally continuous dual-wall shell structures made up of inner and outer capsule walls. ~:
` ' r~
': ~'' : ~ ' ~5'~35 ~escrip*ion of The Prior Art:
Impact or pressure sensitive carbonless transfer papers have recently come into wide usage in the United States and throughout the world. Ordinarily, such papers are printed and collated into manifolded sets capable of producing multiple copies. In this connection, pressure applied to the top sheet causes a corresponding mark on each of the other sheets of the set.
The top sheet of paper, upon which the impact or pressure is immediately applied, ordinarily has its back sur-face coated with microscopic capsules containing one of the reactive ingredients which interreact to produce a mark. A
receiver sheet, placed in contact with such back face of the top sheet has its front surface coated with a material having a component which is reactive with the contents of the capsule so that when capsules are ruptured upon impact by stylus or machine key, the initially colorless or substantially color-less contents of the ruptured capsules react with a co-reactant therefor on the receiver sheet and a mark forms on the latter corresponding to the mark impressed by the stylus or machine key.
In the art, impa-t transfer papers are designated by the terms CB, CFB and CF, which stand respectively for "coated back", "coated front and back", and "coated front". Thus, the CB sheet is usually the top sheet and the one on which the impact impression is directly made; the CFB sheets are the intermediate sheets, each of which have a mark formed on the front surface thereof and each of which also transmits the contents of the ruptured capsules from its back surface to the front surface of the next succeeding sheet; and the CF sheet is the last sheet and is only coated on its front surface to have an image formed thereon. The CF sheet is not normally
Field Of The Invention:
The present invention relates to carbonless copying systems and in particular to new improved dual-walled microcapsules which are useful in connection with such systems and which comprise minute discrete droplets of liquid fill matèrial including an initially colorless chemically reactive color forming dye precursor and a carrier there~or encapsulated within individual, rupturable, generally continuous dual-wall shell structures made up of inner and outer capsule walls. ~:
` ' r~
': ~'' : ~ ' ~5'~35 ~escrip*ion of The Prior Art:
Impact or pressure sensitive carbonless transfer papers have recently come into wide usage in the United States and throughout the world. Ordinarily, such papers are printed and collated into manifolded sets capable of producing multiple copies. In this connection, pressure applied to the top sheet causes a corresponding mark on each of the other sheets of the set.
The top sheet of paper, upon which the impact or pressure is immediately applied, ordinarily has its back sur-face coated with microscopic capsules containing one of the reactive ingredients which interreact to produce a mark. A
receiver sheet, placed in contact with such back face of the top sheet has its front surface coated with a material having a component which is reactive with the contents of the capsule so that when capsules are ruptured upon impact by stylus or machine key, the initially colorless or substantially color-less contents of the ruptured capsules react with a co-reactant therefor on the receiver sheet and a mark forms on the latter corresponding to the mark impressed by the stylus or machine key.
In the art, impa-t transfer papers are designated by the terms CB, CFB and CF, which stand respectively for "coated back", "coated front and back", and "coated front". Thus, the CB sheet is usually the top sheet and the one on which the impact impression is directly made; the CFB sheets are the intermediate sheets, each of which have a mark formed on the front surface thereof and each of which also transmits the contents of the ruptured capsules from its back surface to the front surface of the next succeeding sheet; and the CF sheet is the last sheet and is only coated on its front surface to have an image formed thereon. The CF sheet is not normally
- 2 -coated on its back surface as no further transfer is desired.
While it is customary to coat the capsules on theback surface and to coat the co-reactant for the capsule con-tents on the front surface of each sheet, this procedure could be reversed if desired. Further, with some systems, coatings need not be used at all and the co-reactive ingredients may be carried in the sheets themselves, or one may be carried in one of the sheets and the other may be carried as a surface coat-ing. Further, the co-reactive materials may each be micro-encapsulated. Patents illustrative of many of the various kinds of systems which may incorporate such co-reactive ingre- ;
dients and which may be used in the production of manifolded transfer papers include, for example, U. S. 2,~99,694 to Green, U. S. 2,712,507 to Green, U. ~. 3,016,308 to Macaulay, U. S.
While it is customary to coat the capsules on theback surface and to coat the co-reactant for the capsule con-tents on the front surface of each sheet, this procedure could be reversed if desired. Further, with some systems, coatings need not be used at all and the co-reactive ingredients may be carried in the sheets themselves, or one may be carried in one of the sheets and the other may be carried as a surface coat-ing. Further, the co-reactive materials may each be micro-encapsulated. Patents illustrative of many of the various kinds of systems which may incorporate such co-reactive ingre- ;
dients and which may be used in the production of manifolded transfer papers include, for example, U. S. 2,~99,694 to Green, U. S. 2,712,507 to Green, U. ~. 3,016,308 to Macaulay, U. S.
3,42~,827 to Ruus and U. S. 3,720,534 to Macaulay et al.
The most common variety of carbonless impact transfer paper, and the type with which the present invention is uti-lized, is the type illustrated, for example, in Green ('507) and Macaulay ('308) wherein microscopic capsules containing a liquid fill comprising a solution of an initially colorless chemically reactive color forming dye precursor are coated on the back surface of the sheet, and a dry coating of a co-reactant chemical for the dye precursor is coated on the front surface of a receiving sheet.
Many color precursors useful in connection with carbonless copying systems are known to those skilled in the art to which the present invention pertains. For example, specific reference is made to the color precursors mentioned in the patent to Phillips, Jr. et al, U. S. 3,455,721 and par-t~cularly to those li~ted in the paragraph bridging columns5 and 6 thereof. These materials are capable of reacting with a CF coating containing an acidic material such as acid-1~5;Z~
leached bentonite-type clay or the acid-reactant organic polymeric material disclosed in the Phillips, Jr. et al '721 patent. Many of the color precursors disclosed in the '721 patent referred to above are capable of undergoing an acid- -`
base type reaction with an acidic material.
Other previously known color precursors are the spiro-dipyran compounds disclosed in the patent to Harbort, U. S. 3,293,060 with specific reference being made to the dis-closure of the '060 patent extending from column 11, line 32, through column 12, line 21. The color precursors of Harbort, as well as the color precursors of Phillips, Jr. et al are initially colorless and are capable of becoming highly colored when brought into contact with an acidic layer such as an acid-leached bentonite-type clay or an acid-reacting polYmeric material, or the like.
Generally speaking, color precursor materials of the type disclosed by Phillips, JrO et al ('721) and by Harbort ('060) are dissolved in a solvent and the solution is encapsu-lated. Previously known procedures and processes ~or micro-encapsulation are described and disclosed in U. S. 3,016,308 to Macaulay, U. S. 2,712,507 to Green/ U. S. 3,429,827 to Ruus and U. S. 3,578,605 to Baxter.
Solvents known to be useful in connection with dis-solving color precursors include chlorinated biphenyls. vege-table oils (castor oil, coconut oil, cotton seed oil, etc.), esters (dibutyl adipate, dibutyl phthalate, butyl benzyl adi-pate, benzyl octyl adipate, tricresyl phosphate, trioctyl .
phosphate, etc.), petroleum derivatives (petroleum spirits, kerosene, mineral oils, etc.), aromatic solvents (benzene, toluene, etc.), silicone oils, or combinations of the fore-going. Particularly useful are the alkylated naphthalene solven~s disclosed in U. S. 3,806,463 to Konishi et al.
l(~S'~95 .
In the cclor forming systems outlined above, as will be appreciated by those skilled in the art, the color precur-sors are conventionally contained in pressure rupturable microcapsules which are included in the back coatings of the sheets of carbonless copying manifolded sets. Further, it will be appreciated that acidic coatings are generally util-- -ized as front coatings with the color precursor material in a solvent therefor being transferred from an adjacent back ;~
coating to the acidic layer front coating upon rupture of the capsules which contain the color precursor materiaL.
Althouqh microcapsules have been extensively used in connection with carbonless copying systems in the past, those skilled in this art continue to search for products which are more durable and better adapted for handling on high speed processing equipment. U. S. 3,578,605 to Baxter, for example, discloses dual-walled capsules having an outer shell formed from a hydrophilic colloid material by coacervation. U. S.
3,429,827 to Ruus discloses dual-walled capsules wherein the outer shell is applied by spray dryins or coating with a dry 2~ particulate substance. The dual-walled capsules of Jensen disclosed in U. S. 3,265,629 comprise an inner shell of a waxy material and an outer wall of a hydrophilic colloid material.
The dual-walled capsules disclosed by Brynko and Scar-pelli in their patents U. S. 2,969,331 and U. S. 3,190,837 have an outer shell formed from a hydrophilic colloid material as do the multi-layered capsules of Scarpelli disclosed in U. S. ;~
3,627,693. While the microcapsules disclosed in these refer-ences generally possess somewhat better properties than single walled capsules, problems still exist and the search for more ~`~
durable and more easily handled microcapsules continues.
SU~RY OF THE INVENTION:
The present invention provides improved dual-walled _ 5 _ microcapsules wherein the inner shell is formed by an inter-facial polycondensation procedure and thereafter the outer shell is formed thereabout by the polymerization of an initi-ally water-soluble, low molecular weight aminoaldehyde precon-densate. In the preferred form of the invention the reaction leading to the formation of the outer shell is influenced by -conditions created during the initial interfacial polyconden-~
sation of the inner shell. Thus, microcapsules are produced which comprise minute, discrete droplets of a liquid fill material, each surrounded by an individual, rupturable, gener-ally continuous inner wall of a polycondensate material. The capsules also each include an individual, rupturable, gener-ally continuous outer shell of a polycondensate substance encom-passing the outer surface of each of the inner walls. Prefer-ably the polycondensate material is a polyamide which has been formed by interfacial polycondenSation. The preferred poly-condensate substance for the outer shell is a urea-formaldehyde polymer.
Broadly, the microcapsules of the invention are pro-duced by a process which comprises establishing a two-phase system containing an aqueous continuous phase and a dispersed discontinuous phase of minute~intended liquid capsule core en-tities which are substantially insoluble in the cont~nouus phase. Included in the aqueous continuous phase are a water-soluble, low molecular weight aminoaldehyde precondensate and a water soluble first polyfunctional reactant capable of under-go~ng polycondensation with a second polyfunctional reactant to produce a polycondensate material. The second polyfunc-tional reactant is included in the discontinuous phase whereby ;
the first and second polyfunctional reactants condense at the interface between the phases to thereby encapsulate each core I
L9~
entity in an individual, generally continuous polycondensate inner shell. Thereafter the conditions in the continuous -phase are adjusted to cause polymerization of the preconden-sate to a water-insoluble polymer which enwraps each encapsu-lated core entity and forms an individual, generally continu-ous aminoaldehyde outer shell thereabout. Generally speaking, the adjustment of the conditions in the continuous phase com-prises decreasing the pH thereof to about 5.0 or less and preferably such decrease in the pH of the continuous phase is caused by the production of an acid such as HCl during the polycondensation of the first and second reactants. In the most highly preferred form of the invention, the first poly-functional reactant is diethylene triamine, the second poly-functional reactant is terephthaloyl chloride and the aminoal-dehyde precondensate is a urea-formaldehyde resin.
DETAILED DESCRIPTION OF THE INVENTION:
~roadly, the present invention comprises microcapsules having an inner wall such as that produced by the interfacial - polycondensation techniques disclosed in the patent to Ruus, U. S. 3,429,827 and an outer wall of a hydrophobic, aminoalde-hyde polymer such as that produced in accordance with the dis-closure o Macaulay, U. S. 3,016,308, and particularly in accor-dance with Example IV, beginnin~ at line 17 of column 9 of the '308 patent. In the preferred method of the present invention, hydrochloric acid generated by the reaction of terephthaloyl chloride and diethylene triamine in accordance with the Ruus interfacial polycondensation procedure is utilized to decrease the ~H of the system and cause the urea-formaldehyde resin of Example IV of Macaulay to condense and precipitate to thereby form the outer shell. -Usually in interfacial microencapsulation procedures, _ 7 _ ~al5~1~5 an oil containing a diacid chloride, a disulfonyl chloride, a diisocyanate, etc., is emulsified in an aqueous or polar medium containing a monomer such as a diamine or a bisphenol or the like. The condensation reaction takes place at or near the interface between the dispersed oil phase and the continuous aqueous phase. The concepts and principles of the instant invention are attractive because the interfacial polycondensa- -tion reaction is generally much faster than the acid catalyzed condensation reaction leading to the formulation of the outer shell. This minimizes the amount of mixup during shell forma-tion and protects the capsules from distortion. brea~age. or the like~caused by de-emulsification and maximizes the devel-opment of the inner shell wall by interfacial polycondensation.
Hydrochloric acid is a usual by-product of the interfacial polycondensation reactions by which the inner shell wall is formed and an acidic condition is required for condensing conventional aminoaldehyde precondensates. Moreover, an inner shell formed by an interfacial polycondensation procedure could be modified to be acidic, basic, reactive, etc., depending on factors such as the nature and amount of the monomers and the presence of cross-linking agents or the like during the micro-encapsulation process. For example, depending on the amount and nature of the acid chloride and amine used, the end group of the polymer chain could be acidic or basic. Moreover, the ;
connecting groups could be modified similarly.
Another attractive feature of the present invention , is that dual-walled capsules may be formed in a single cbntin-uous procedure wherein the acid generated by the interfacial polycondensation is used to cataly~e the condensation of the aminoaldehyde precondensate. This does not exclude the use I
~sz~s of other chemicals, additives, heat, mixing, etc. to enhance the reaction or improve the quality of the outer shell or deposit. The dual-walled capsules produced in accordance with the present invention have improved strength, chemical resistance, hydrophobicity, etc. when compared with conven-tional microcapsules. Moreover, microcapsules produced by conventional interfacial polycondensation procedures are elas-tic in nature and are not easily separated, dried or filtered under normal conditions. However, in accordance-with tha present invention, free flowing dry capsules are quite easily produced because of the inherent toughness ànd other proper-ties o~ the cross-linked polycondensate outer shell wàll. `~
The capsules of the present invention are pàrticu-`:
larly useful in connection with carbonless copying systems;
however, it shou~d be appreciated that other uses for micro-capsules are well known to those of ordinary skill in this art.
When the capsules are utilized in connection with carbonless copying systems, the fill material will ordinarily include an initially colorless chemically reactive color forming dye pre-cursor and a carrier therefor such as dibutyl phthalate or oneof the alkylated naphthalene solvents disclosed in U. S.
3,806,463 to Konis~i et al.
The inner capsule shell may be any polycondensate formed by interfacial polycondensation at the interface between dispersed droplets of fill material and a continuous phase.
For example, various polycondensates are disclosed in U. S.
3,429,827 to Ruus including polyamides, polyurethanes, polysul-fonamides, polyesters, polyureas, polycarbonates, etc. Par-ticularly useful in connec'cion with the production of the inner shell wall by interfacial polycondensation are those reactants :
~5;~95 which give of~ an acid as a by-product during the condensation.
For example, terephthaloyl chloride and ethylene diamine con-dense to form a polyamide and hydrochloric acid is produced as a by-product.
With regard to the outer shell, aminoaldehyde resins generally are useful. In particular, melamine-formaldehyde, phenol-formaldehyde, urea-formaldehyde and urea-acetaldehyde resins are useful. Typically these materials are capable of existing in a water soluble, low molecular weight preconden-sate form whenever the pH of the system is greater than a par-ticular level which is a fwlction of the specific material and which is generally about 5 or so. However, when the pH of the system is decreased to such particular level or below, the precondensate undergoes further polymerization and cross-linXing to produce a water insoluble polymer which precipi-tates from solution to enwrap and encapsulate particles which might be dispersed in the continuous phase. This phenomena is described in detail in the patent to Matson, U. S. 3,516,941.
This phenomena is also disclosed particularly in Example IV of the patent to Macaulay, U. S. 3,016,308.
EXAMPLE I
l.00 gm of p-toluene sulfonate of Michler's hydrol (PTSMH) were admixed with 37.5 gms of dibutyl phthalate (DBP) and this admixture was warmed slightly on a hot plate until a clear solution (solution A) was obtained. Thereafter, solu-tion A was allowed to cool to room temperature. Then 3.26 gms of terephthaloyl chloride were added to 37.5 gms of dibutyl phthalate (DBP) and this mixture was also warmed slightly on a hot plate until a clear solution (solution B) was obtained.
Solution B was then also allowed tQ cool to room temperature.
After solutions A and B were preparea, 89.0 gms of an aqueous ~5;~ 5 solution containing 1.4 weight percent of the product marketed under the Trade Mark "~ercules 7Ll" cellulose gum (a commerci-ally available sodium carboxymethyl cellulose product having a degree of substitution of approximately 0.~ and a molecular weight of less than 45,000) and 18.7 gms of the product mar-keted under the Trade Mark "URAC Resin 180" solution ~a commer-cial product of American Cyanamide Company which is an unmodi-fied urea-formaldehyde resin in water solution at approximately 65 weight percent solids) were admixed and were placqd in a one quart Waring blender. Then solutions A and B were mixed to-gether at room temperature and the resultant solution was added to the aqueous solution of URAC 180 and cellulose gum in the blender. The blender was activated and high shear agitation was continued for about 45 seconds until an emulsion having a dispersed phase particle size of about 2 to 10 microns was obtained. In this emulsion, the aqueous solution containing the URAC 180 and the cellulose gum formed the continuous phase and the solution of terephthaloyl chloride and PTSMH in DBP
formed the dispersed phase. 300 gms of water were added to the emulsion and the diluted emulsion was then transferred to a suitable container such as a beaker and was stirred with a variable speed mechanical stirrer at 300 to 500 rpm w~ile an aqueous solution containing 1.5 gms of diethylene triamine and 10 gms o water was added thereto. Prior to the addition of the amine solution, the emulsion was examined and the same had a pH of 6Ø A coating of the emulsion on a paper substrate was oilish and no writeoff could be produced on a CF paper coated with a layer of acid-leached bentonite-type clay. This is an indication that there were no capsules in the emulsion prior to the addition of the amine. Five minutes after the amine solution was added thereto, the pH of the mixture was lOS~,G~5 9.4. A microscopic examination of the mixture indicated that polyamide capsules had been formed. Stirring of the emulsion was continued and after 28 hours the pH of the emulsion had dropped to 2.8. A microscopic examination of the emulsion at this point indicated the formation of thicker and stronger urea-formaldehyde walls. The slurry containing the dual-walled microcapsules, and having the cellulose gum binder in the continuous phase, was then drawn down on a 12 pound neutral base continuous bond paper sheet at a coatin~ weight of approx-imately 2.34 to 3.04 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds. The dry coating of microcapsules containing PTSMH
was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the rev~rse side of the sheet -~
coated with microcapsules, a corresponding highly colored re-production of such impression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the slurry which was not utilized Eor coating paper in accordance with the foregoing was filtered using a Buchner filter. The filter cake was slurried in 200 ml of distilled water and was filtered again. The filter cake was air dried and after drying the same was easily broken. Copious amounts of DBP
were exuded when the dry capsules were squeezed.
EXAMPLE II
In this Example, the procedure was identical with that set forth in Example I except that in this instance, the product marXeted under the Trade Mark l'R-300" solvent was util-ized as the carrier for the dispersed phase rather than aibutyl phthalate. R-300 solvent is a commercial product of Kureha Corporation of America which is a mixture of isomeric diisopro--~05~915 pyl naphthaleneS and which is apparently generally disclosed in U. S. 3,806,463 to Konishi et al. The quantity of R-300 solvent utilized was identical to the quantity of DBP utilized in Example I and the quantities of all other materials were identical with Example I. A microscopic examination of the slurry immediately after the addition of the diethylene tria-mine solution revealed that microcapsules had been formed and that the capsule size was within the range of about 3 to about 20 microns. Fifteen minutes after the addition of the di-ethylene triamine, the pH of the slurry had dropped to 4.2.The slurry containing these microcapsules (which at this point were mostly single walled capsules with a poly-amide shell), and having the cellulose gum binder in the continuoùs phase, was then drawn down on a twelve pound continuous bond paper sheet at a coating weight of approximately 3.5 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds. The dry coating of micro-capsules containing PTSMH was then brought into contact with an acid=leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcapsules, a corres-ponding blue colored reproauction of such impression immedi-ately appeared on the acid-leached bentonite-type clay coating.
The mixing of the microcapsule slurry with the mechanical stirrer was continued for about 5 hours by which time the pH
of the slurry had dropped to approximately 2.3. This illus- , trates the effect of the HCl produced by the polycondensation of the terephthaloyl chloride ana the diethylene triamine. At this time the microcapsules had become agglomerated and a microscopic examination of the slurry inaicated that a urea-- formaldehyae shell wall had formed around the previously formed ~1)5;~5 single wall capsules. After stirring for 24 hours the pH of the slurry had decreased further to approximately 1.95 and a microscopic examination of the slurry at this point revealed a definite urea-formaldehyde wall formation. The slurry con-taining the dual-walled microcapsules, and having the cellulose gum binder in the continuous phase, was then drawn down on a 12 pound continuous bond paper sheet at a coating weight of approx-imately 3.5 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds.
The dry coating of microcapsules containing P~SMH was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcapsules a corresponding blue colored reproduction of such impression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the slurry was filtered with a Buchner funnel and the filter cake was slurried in 200 ml of water and was filtered again. These microcap-sules were then air dried. Filtration of the slurry was easily performed and the dried cake was easy to break. In this connection it is to be noted that ~singLe walled capsules having a polyamide shell ~ormed by interfacial polycondensation are usually quite difficult to filter and if the water is evap-~orated from the slurry, a rubbery mass is often formed which is diff.icult to break. This results from the elasticity and the tackiness of the polyamide films formed by interfacial polycon-densation. The outer layer of the tough urea-formaldehyde shell deposited on the inner polyamide wall eliminates problems such as difficult filtration and/or tacky capsules, and the dual-walled capsules of the present invention are easily dried to present a free-flowing powder. When the dry ~apsules pro-i~5~
duced in accoraance with the present Example were squeezed, copious amounts of oll were exuded.
- EXAMPLE III
In this Example, the procedures were generally the same as those of Example I except that in this instance the diethylene triamine and the URAC Resin 180 were added together.
Solutions A and B were identical with those o Example I. In this instance, however, 89 gms of 1.4 weight percent solution of Hercules cellulose gum 7Ll and 36.0 ml of water were placed in the Waring blender and solutions A and B were admixed and emulsified therein in the same manner as in Example I. After emulsification, 200 gms of water were added to the slurry and the same was placed in a stirred beaker. A solution was formed from 1.5 gms of diethylene triamine, 18.7 gms of URAC
Resin 180 solution and 50.0 ml of water and this solution was added to the reaction mixture while the stirring of the same continued. immediately after the addition of the solution containing the diethylene triamine and the URAC Resin 180 solu-tion, the pH of the reaction mixture was within the range of about 9 to 10. After 24 hours of stirring, the pH had dropped to 2.3. ~he color of the mixture was blue and a microscopic examination revealed a definite urea-formaldehyde wall forma-tion. A portion of the slurry containing the microcapsules, and having the cellulose gum binder in the continuous phase, was then drawn down on a 12 pound neutral base continuous bond paper sheet at a coating weight of approximately 3.5 gms per square meter and the coated sheet was oven dried at a tempera-ture of 110C for about 30 to 45 seconds. The dry coating of microcapsules containing PTSMH was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side o~ the sheet coated with microcapsules, a corresponding blue colored reproduction of such impression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the capsule slurry was filtered washed and air dried in accordance with the procedures set forth in the previous Examples. The dry capsule mix was easy to break and copious amounts of liquid fill material were exuded when the dry capsules were squeezed.
EXAMPLE IV
In this Example the diethylene triamine was added to the emulsion first and thereafter the URAC 180 resin solu-tion was added. The emulsion was formed utilizing the same procedures and quantities of materials outlined in Example III ~`
above. The emulsion was diluted with 250 ml of water and was placed in a stirred beaker. An aqueous solution containing 1.5 gms of diethylene triamine and 10.0 ml of water were then added to the stirred emulsion. Immediately after the addi-tion of the diethylene triamine solution, the pH of the slurry was approximately 9 to 10. A microsco~ic examination of the slurry at this point revealed that single walled capsules having a polyamide shell had been formed by interfacial poly-condensation. A few minutes after thè diethylene triamine solution had been added to the slurry, an aqueous solution containing 18.7 gms of URAC Resin 180 solution and 50 ml of water were added to the slurry. After 48 hours of stirring, the pH value of the mix had decreased to approximately 2.1 and the same had a slight blue coloration. A microscopic examin-~ation of the slurry revealed that the capsule size ranged from about 10 to about 100 microns and urea-formaldehyde wall for- -mation around the polyamide capsules was evident. This slurry was filtared, washed and dried as outlined above. When the ~15'~ 5 dry capsules were squeezed, copious amounts of liquid fill material were exuded.
EXAMPLE V
In this Example, the types and quantities of ingre-dients and the procedures utilized were identical with Example I except that in this instance, 89 ml of a 0.5% "Elvanol 50-42" solution ("Elvanol 50-42" being a Trade Mark) were util-ized in lieu of the 89 ml of 1.4~ Hercules cellulose gum solu-tion utilized in Example I. Also, 50 gms of URAC Resin 180 solution were utilized. Elvanol 50-42 is a polyvinyl alcohol with 87 to 89~ hydrolysis and a viscosity of 35 to 45 centi-poises in a 4% aqueous solution at 20C. The procedures for producing the dual-walled microcapsuies were identical with those utilized in Example I. Within a minute after the addi-tion of the diethylene triamine solution, the pH of the mix-ture had become approximately 7.0 and the presence of micro-capsules was apparent. After 2~ hours of mixing the pH of the slurry had decreased to 1.9 and a microscopic examination ~ of the slurry inaicated that urea-formaldehyde coated cap sules had been produced. A portion of this slurry was util-ized to produce coated paper in accordance with the proced-ures set forth above. Instant blue images were produced utilizing such paper in conjunction with acid-leached benton-ite-type clay coated CF paper. A sufficient amount of a 20%
solution of sodium hydroxide was added to the remainder of the slurry to cure and harden the urea-formaldehyde resin shells. Paper was coated with these cured capsules and again instant blue reproductions were created when this coated paper was utilized in con~unction with acid-leached bentonite-type clay coated CF paperO The slurry was filtered, washed and dried in accordance with the procedures set forth - 17 ~
~ .
~, .
~9~5~5 ~:
a~ove and the dried cake was very easy to break and the dry capsules were powdery and ~ree flowing. Upon squeezing the capsules, copious amounts of liquid fill material was exuded.
EXAMPLE VI
1.00 gm of the methyl ether of Michler's hydrol ~MEMH) were admixed with 37.5 gms of xylene and this admixture was warmed slightly on a hot plate until a clear solution ~solution A) was obtained. Thereafter solution A was allowed to cool to room temperature. Then, 3.6 gms of terephthaloyl chloride were added to 37.5 gms of xylene and this mixture was alqo warmed slightly on a hot plate until a clear solution (solution B) was obtained. Solution B was then also allowed to cool to room temperature. After solutions A and B were prepared, 90.0 ml of 0.5 weight percent ~lvanol 50-42 solution and 50.~ gms of URAC Resin 180 solution were placed in a one quart Waring blender and then solutions A and B were mixed to-gether at room temperature and the resultant solution was added to the solution containing URAC Resin 180 and Elvanol in the blender. The blender was activated and high shear agita tion was continued for about one minute until an emulsion was obtained. In this emulsion, the aqueous solution containing the Elvanol and the URAC Resin 180 formed the continuous phase and the solution containing the xylene solvent, the MEMH and terephthaloyl chloride formed the dispersed phase. This emulsion was diluted with 300 ml of water and the diluted emulsion was then transferred to a suitable container such as a beaker and was stirred with a variable speed mechanical stirrer at 300 to 500 rpm while an aqueous solution contain-ing 1.5 gms of diethylene triamine and 10 ml of water were added, Immediately upon addition of the di~thylene triamine solution, the pH of the slurry was in the rangP of from about `
~ 18 - I
-~LO S ~ IL9 5 6 to 7 and the formation of single walled capsules having a polyamide shell formed by interfacial polycondensation became evident. After ~4 hours of stirring, the pH of the slurry had decreased to about l.9. Coatings prepared from this slurry produced an instant blue writeoff on acid-leached bentonite-type clay coated CF paper. A sufficient amount of a 20% solution of sodium hydroxide was added to increase the pH of the slurry to approximately 9Ø The sodium hydroxide is operable to cure and harden the urea-formaldehyde outer capsule walls. A portion of this slurry containing the microcapSules, and having the Elvanol polyvinyl alchohol binder in the continuous phase, was then drawn down on a 12 pound neutral base continuous bond pàper sheet at a coating weight of approximately 3.5 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds. The dry coating on the paper sheet was white. The dry coating of microcapsules containing the MEMH was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcapsules, a corresponding blue colored reproduction of such impression immediately appeared on the acid-leached bentonite~type clay coating~ The remainder of the slurry was then filtered, washed and air dried in accordance with the procedures set forth above. The dry cake was easily broken to produce a free flowing powder of ; microcapsules which exuded copious quantities of liquid fill material whèn squeezed.
EXAMPLE VII ~;
; 30 1.0 gm of PTSMH were admixed with 37.5 gms of DBP
and this admixture was warmed slightly on a hot plate until a ~5'~ 5 clear solution (solution A) was obtained. Thereafter solu-tion A was allowed to cool to room temperature. Then, 3.6 gms of terephthaloyl chloride were added to 37.5 gms of DBP
and this mixture was also warmed slightly on a hot plate until a clear solution ~solution B) was obtained. Solution B was then allowed to cool to room temperature. After solutions A
and B were prepared, 90 ml of an aqueous solution containing 0.5 weight percent Elvanol 50-42 polyvinyl alcohol and 50 ml of water were placed in a one quart Waring blender and then solutions A and B were mixed together at room temperature and the re~ultant solution was added to the Elvanol solution in the blender, The blender was activated and high shear agita-tion was continued for about 1 minutè until an emulsion was obtained. In this emulsion, the aqueous solution containing the Elvanol polyvinyl alcohol formed the continuous phase and the solution containing the DBP solvent, the PTSMH and tereph-thaloyl chloride formed the dispersed phase. The resultant emulsion was then transferred to a suitable container such as a beaker and the same was diluted with 200 ml of water. 1.4 gms of 1,2-ethanedithiol were added to 70 ml of water and a sufficient quantit~ of NaOH was added to the mixture to neu-tralize the 1,2~ethanedithiol. This mixture was then warmed slightly to produce a clear solution having a pH of about 9.O. 50 gms of a ~5 weight percent URAC Resin 180 solution was then added to this clear aqueous solution and the resultant solution was added to the diluted emulsion while the latter was stirred with a variable speed mechanical stirrer at 300 to 500 rpm. Stirring was continued for approximately 24 hours. Immediately after the addition of ` 30 the ~olution containing the ethanedithiol and the URAC Resin 180, the pH of the slurry was approximately 6 to 7 and the formation of single walled capsules having a polythiolester shell formed by interfacial polycondensation was evident. A
sufficient amount of a20% sodium hydroxide solution was added to the slurry to increase the pH to approximately 9.0 whereby the urea-formaldehyde outer ~hells were cured and hardened.
A portion of this slurry containing the hardened microcap6ules, and having the Elvanol polyvinyl alcohol binder in the contin-uous phase, was then drawn down on a 12 pound neutral base con-tinuous bond paper sheet at a coating weight of approximately 3.~ gms per square meter and the coated sheet was then dried at a temperature of 110C for about 30 to 45 seconds. The dry coating on the paper sheet was white. The dry coating o microcapsules containing PTSMH was then brought into contact with an acid-leached bentonite-type clay coating on the sur-face of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcap-sules, a corresponding blue colored reproduction of such im-pression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the microcapsules pro-2~ duced in accordance with this Example were filtered, washedand dried in accordance with the procedures outlined above~
The filter cake was easily broken to present a free flowing powder of microcapsules. When these microcapsules were squeezed, copious amounts of the liquid fill material were exuded.
Although in each of the foregoing Examples a urea-formaldehyde resin was utilized to form the outer shell, it should be understood that the present invention contemplates the utilization of any one of a variety o~ polymers for the formation of the outer shell wall. Critically, the monomer for the outer shell must be relatively non-reactive at the .
conditions necessary for the formation of the inner wall by interfacial polycondensation and moreover, th~ monomer for the outer shell should be water soluble in its monomer form, whereas the polymer formed therefrom should be water insoluble.
Particularly useful in connection with the present invention are the two stage resins capable of existing ln a water soluble, precondensate first stage and in a cross-linked, water insoluble, higher molecular weight second stage. In particular, aminoaldehyde resins (or aminoplasts) are useful in connection with the presentinvention. A discussion of aminoplasts and aminoplast precursors appears in C. P. Vale's book "Aminoplasts" published in 1950 by Inter Science Publi-shers, Inc. The aminoaldehyde resins typically are capable of existing in a thermoplastic first stage where the same are in a relatively low-molecular weight, water soluble form.
Upon catalysis with an acid, these precondensates are cross-linked to present a second stage polymer which is of rela-tively higher molecular weight and is generally water insol-uble. As soon as the resin has been converted into its higher molecular weight, water insoluble form, the same preci-pitates from water solution and enwraps dispersed particles present in the system. This phenomena is fully disclosed and illustrated in U. S. 3j016,308 to Macaulay (see particu-larly Example IV) and in U. S. 3,516,941 to Matson.
With regard to the inner wall of the dual-walled microcapsules of the present invention, the present invention .
contemplate5 the utilization of those polymers which may be formed by interfacial polycondensation at the interface be-tween a dispersed phase and a con~inuous phase. Such poly-mers and processes are fully disclosed in the patent to Ruus, U. S. 3,~29,827. In this connection, it is pointed out that ' . I
:llOS'~95 the present invention contemplates the use of any of these materials; however, those which condense with the evolution of an acid are particularly preferred 50 that the pH of the slurry may be autogenously reduced during the interfacial polycondensation to an extent such that the condensation of the aminoaldehyde precondensate from its water soluble first stage to its water insoluble second stage will proceed with-out further addition of an acid. However, it is pointed out that the present invention is not predicated upon the auto-genous generation of acid during the interfacial polyconden-sation and it is within the broad concepts of the present invention to add such acid from an outside source.
In connection with the foregoing it is stressed that the present invention contemplates the production of a dual-walled microcapsule by polymeri~ation processes which are carried out seriatum. . That is to say, a first polymeric shell,is formed about minute, discrete droplets of fill material by an interfacial polymerization and thereafter the conditions in the system are altered such that an outer shell `
is formed about the inner wall by a secondary polymerization reaction~
The most common variety of carbonless impact transfer paper, and the type with which the present invention is uti-lized, is the type illustrated, for example, in Green ('507) and Macaulay ('308) wherein microscopic capsules containing a liquid fill comprising a solution of an initially colorless chemically reactive color forming dye precursor are coated on the back surface of the sheet, and a dry coating of a co-reactant chemical for the dye precursor is coated on the front surface of a receiving sheet.
Many color precursors useful in connection with carbonless copying systems are known to those skilled in the art to which the present invention pertains. For example, specific reference is made to the color precursors mentioned in the patent to Phillips, Jr. et al, U. S. 3,455,721 and par-t~cularly to those li~ted in the paragraph bridging columns5 and 6 thereof. These materials are capable of reacting with a CF coating containing an acidic material such as acid-1~5;Z~
leached bentonite-type clay or the acid-reactant organic polymeric material disclosed in the Phillips, Jr. et al '721 patent. Many of the color precursors disclosed in the '721 patent referred to above are capable of undergoing an acid- -`
base type reaction with an acidic material.
Other previously known color precursors are the spiro-dipyran compounds disclosed in the patent to Harbort, U. S. 3,293,060 with specific reference being made to the dis-closure of the '060 patent extending from column 11, line 32, through column 12, line 21. The color precursors of Harbort, as well as the color precursors of Phillips, Jr. et al are initially colorless and are capable of becoming highly colored when brought into contact with an acidic layer such as an acid-leached bentonite-type clay or an acid-reacting polYmeric material, or the like.
Generally speaking, color precursor materials of the type disclosed by Phillips, JrO et al ('721) and by Harbort ('060) are dissolved in a solvent and the solution is encapsu-lated. Previously known procedures and processes ~or micro-encapsulation are described and disclosed in U. S. 3,016,308 to Macaulay, U. S. 2,712,507 to Green/ U. S. 3,429,827 to Ruus and U. S. 3,578,605 to Baxter.
Solvents known to be useful in connection with dis-solving color precursors include chlorinated biphenyls. vege-table oils (castor oil, coconut oil, cotton seed oil, etc.), esters (dibutyl adipate, dibutyl phthalate, butyl benzyl adi-pate, benzyl octyl adipate, tricresyl phosphate, trioctyl .
phosphate, etc.), petroleum derivatives (petroleum spirits, kerosene, mineral oils, etc.), aromatic solvents (benzene, toluene, etc.), silicone oils, or combinations of the fore-going. Particularly useful are the alkylated naphthalene solven~s disclosed in U. S. 3,806,463 to Konishi et al.
l(~S'~95 .
In the cclor forming systems outlined above, as will be appreciated by those skilled in the art, the color precur-sors are conventionally contained in pressure rupturable microcapsules which are included in the back coatings of the sheets of carbonless copying manifolded sets. Further, it will be appreciated that acidic coatings are generally util-- -ized as front coatings with the color precursor material in a solvent therefor being transferred from an adjacent back ;~
coating to the acidic layer front coating upon rupture of the capsules which contain the color precursor materiaL.
Althouqh microcapsules have been extensively used in connection with carbonless copying systems in the past, those skilled in this art continue to search for products which are more durable and better adapted for handling on high speed processing equipment. U. S. 3,578,605 to Baxter, for example, discloses dual-walled capsules having an outer shell formed from a hydrophilic colloid material by coacervation. U. S.
3,429,827 to Ruus discloses dual-walled capsules wherein the outer shell is applied by spray dryins or coating with a dry 2~ particulate substance. The dual-walled capsules of Jensen disclosed in U. S. 3,265,629 comprise an inner shell of a waxy material and an outer wall of a hydrophilic colloid material.
The dual-walled capsules disclosed by Brynko and Scar-pelli in their patents U. S. 2,969,331 and U. S. 3,190,837 have an outer shell formed from a hydrophilic colloid material as do the multi-layered capsules of Scarpelli disclosed in U. S. ;~
3,627,693. While the microcapsules disclosed in these refer-ences generally possess somewhat better properties than single walled capsules, problems still exist and the search for more ~`~
durable and more easily handled microcapsules continues.
SU~RY OF THE INVENTION:
The present invention provides improved dual-walled _ 5 _ microcapsules wherein the inner shell is formed by an inter-facial polycondensation procedure and thereafter the outer shell is formed thereabout by the polymerization of an initi-ally water-soluble, low molecular weight aminoaldehyde precon-densate. In the preferred form of the invention the reaction leading to the formation of the outer shell is influenced by -conditions created during the initial interfacial polyconden-~
sation of the inner shell. Thus, microcapsules are produced which comprise minute, discrete droplets of a liquid fill material, each surrounded by an individual, rupturable, gener-ally continuous inner wall of a polycondensate material. The capsules also each include an individual, rupturable, gener-ally continuous outer shell of a polycondensate substance encom-passing the outer surface of each of the inner walls. Prefer-ably the polycondensate material is a polyamide which has been formed by interfacial polycondenSation. The preferred poly-condensate substance for the outer shell is a urea-formaldehyde polymer.
Broadly, the microcapsules of the invention are pro-duced by a process which comprises establishing a two-phase system containing an aqueous continuous phase and a dispersed discontinuous phase of minute~intended liquid capsule core en-tities which are substantially insoluble in the cont~nouus phase. Included in the aqueous continuous phase are a water-soluble, low molecular weight aminoaldehyde precondensate and a water soluble first polyfunctional reactant capable of under-go~ng polycondensation with a second polyfunctional reactant to produce a polycondensate material. The second polyfunc-tional reactant is included in the discontinuous phase whereby ;
the first and second polyfunctional reactants condense at the interface between the phases to thereby encapsulate each core I
L9~
entity in an individual, generally continuous polycondensate inner shell. Thereafter the conditions in the continuous -phase are adjusted to cause polymerization of the preconden-sate to a water-insoluble polymer which enwraps each encapsu-lated core entity and forms an individual, generally continu-ous aminoaldehyde outer shell thereabout. Generally speaking, the adjustment of the conditions in the continuous phase com-prises decreasing the pH thereof to about 5.0 or less and preferably such decrease in the pH of the continuous phase is caused by the production of an acid such as HCl during the polycondensation of the first and second reactants. In the most highly preferred form of the invention, the first poly-functional reactant is diethylene triamine, the second poly-functional reactant is terephthaloyl chloride and the aminoal-dehyde precondensate is a urea-formaldehyde resin.
DETAILED DESCRIPTION OF THE INVENTION:
~roadly, the present invention comprises microcapsules having an inner wall such as that produced by the interfacial - polycondensation techniques disclosed in the patent to Ruus, U. S. 3,429,827 and an outer wall of a hydrophobic, aminoalde-hyde polymer such as that produced in accordance with the dis-closure o Macaulay, U. S. 3,016,308, and particularly in accor-dance with Example IV, beginnin~ at line 17 of column 9 of the '308 patent. In the preferred method of the present invention, hydrochloric acid generated by the reaction of terephthaloyl chloride and diethylene triamine in accordance with the Ruus interfacial polycondensation procedure is utilized to decrease the ~H of the system and cause the urea-formaldehyde resin of Example IV of Macaulay to condense and precipitate to thereby form the outer shell. -Usually in interfacial microencapsulation procedures, _ 7 _ ~al5~1~5 an oil containing a diacid chloride, a disulfonyl chloride, a diisocyanate, etc., is emulsified in an aqueous or polar medium containing a monomer such as a diamine or a bisphenol or the like. The condensation reaction takes place at or near the interface between the dispersed oil phase and the continuous aqueous phase. The concepts and principles of the instant invention are attractive because the interfacial polycondensa- -tion reaction is generally much faster than the acid catalyzed condensation reaction leading to the formulation of the outer shell. This minimizes the amount of mixup during shell forma-tion and protects the capsules from distortion. brea~age. or the like~caused by de-emulsification and maximizes the devel-opment of the inner shell wall by interfacial polycondensation.
Hydrochloric acid is a usual by-product of the interfacial polycondensation reactions by which the inner shell wall is formed and an acidic condition is required for condensing conventional aminoaldehyde precondensates. Moreover, an inner shell formed by an interfacial polycondensation procedure could be modified to be acidic, basic, reactive, etc., depending on factors such as the nature and amount of the monomers and the presence of cross-linking agents or the like during the micro-encapsulation process. For example, depending on the amount and nature of the acid chloride and amine used, the end group of the polymer chain could be acidic or basic. Moreover, the ;
connecting groups could be modified similarly.
Another attractive feature of the present invention , is that dual-walled capsules may be formed in a single cbntin-uous procedure wherein the acid generated by the interfacial polycondensation is used to cataly~e the condensation of the aminoaldehyde precondensate. This does not exclude the use I
~sz~s of other chemicals, additives, heat, mixing, etc. to enhance the reaction or improve the quality of the outer shell or deposit. The dual-walled capsules produced in accordance with the present invention have improved strength, chemical resistance, hydrophobicity, etc. when compared with conven-tional microcapsules. Moreover, microcapsules produced by conventional interfacial polycondensation procedures are elas-tic in nature and are not easily separated, dried or filtered under normal conditions. However, in accordance-with tha present invention, free flowing dry capsules are quite easily produced because of the inherent toughness ànd other proper-ties o~ the cross-linked polycondensate outer shell wàll. `~
The capsules of the present invention are pàrticu-`:
larly useful in connection with carbonless copying systems;
however, it shou~d be appreciated that other uses for micro-capsules are well known to those of ordinary skill in this art.
When the capsules are utilized in connection with carbonless copying systems, the fill material will ordinarily include an initially colorless chemically reactive color forming dye pre-cursor and a carrier therefor such as dibutyl phthalate or oneof the alkylated naphthalene solvents disclosed in U. S.
3,806,463 to Konis~i et al.
The inner capsule shell may be any polycondensate formed by interfacial polycondensation at the interface between dispersed droplets of fill material and a continuous phase.
For example, various polycondensates are disclosed in U. S.
3,429,827 to Ruus including polyamides, polyurethanes, polysul-fonamides, polyesters, polyureas, polycarbonates, etc. Par-ticularly useful in connec'cion with the production of the inner shell wall by interfacial polycondensation are those reactants :
~5;~95 which give of~ an acid as a by-product during the condensation.
For example, terephthaloyl chloride and ethylene diamine con-dense to form a polyamide and hydrochloric acid is produced as a by-product.
With regard to the outer shell, aminoaldehyde resins generally are useful. In particular, melamine-formaldehyde, phenol-formaldehyde, urea-formaldehyde and urea-acetaldehyde resins are useful. Typically these materials are capable of existing in a water soluble, low molecular weight preconden-sate form whenever the pH of the system is greater than a par-ticular level which is a fwlction of the specific material and which is generally about 5 or so. However, when the pH of the system is decreased to such particular level or below, the precondensate undergoes further polymerization and cross-linXing to produce a water insoluble polymer which precipi-tates from solution to enwrap and encapsulate particles which might be dispersed in the continuous phase. This phenomena is described in detail in the patent to Matson, U. S. 3,516,941.
This phenomena is also disclosed particularly in Example IV of the patent to Macaulay, U. S. 3,016,308.
EXAMPLE I
l.00 gm of p-toluene sulfonate of Michler's hydrol (PTSMH) were admixed with 37.5 gms of dibutyl phthalate (DBP) and this admixture was warmed slightly on a hot plate until a clear solution (solution A) was obtained. Thereafter, solu-tion A was allowed to cool to room temperature. Then 3.26 gms of terephthaloyl chloride were added to 37.5 gms of dibutyl phthalate (DBP) and this mixture was also warmed slightly on a hot plate until a clear solution (solution B) was obtained.
Solution B was then also allowed tQ cool to room temperature.
After solutions A and B were preparea, 89.0 gms of an aqueous ~5;~ 5 solution containing 1.4 weight percent of the product marketed under the Trade Mark "~ercules 7Ll" cellulose gum (a commerci-ally available sodium carboxymethyl cellulose product having a degree of substitution of approximately 0.~ and a molecular weight of less than 45,000) and 18.7 gms of the product mar-keted under the Trade Mark "URAC Resin 180" solution ~a commer-cial product of American Cyanamide Company which is an unmodi-fied urea-formaldehyde resin in water solution at approximately 65 weight percent solids) were admixed and were placqd in a one quart Waring blender. Then solutions A and B were mixed to-gether at room temperature and the resultant solution was added to the aqueous solution of URAC 180 and cellulose gum in the blender. The blender was activated and high shear agitation was continued for about 45 seconds until an emulsion having a dispersed phase particle size of about 2 to 10 microns was obtained. In this emulsion, the aqueous solution containing the URAC 180 and the cellulose gum formed the continuous phase and the solution of terephthaloyl chloride and PTSMH in DBP
formed the dispersed phase. 300 gms of water were added to the emulsion and the diluted emulsion was then transferred to a suitable container such as a beaker and was stirred with a variable speed mechanical stirrer at 300 to 500 rpm w~ile an aqueous solution containing 1.5 gms of diethylene triamine and 10 gms o water was added thereto. Prior to the addition of the amine solution, the emulsion was examined and the same had a pH of 6Ø A coating of the emulsion on a paper substrate was oilish and no writeoff could be produced on a CF paper coated with a layer of acid-leached bentonite-type clay. This is an indication that there were no capsules in the emulsion prior to the addition of the amine. Five minutes after the amine solution was added thereto, the pH of the mixture was lOS~,G~5 9.4. A microscopic examination of the mixture indicated that polyamide capsules had been formed. Stirring of the emulsion was continued and after 28 hours the pH of the emulsion had dropped to 2.8. A microscopic examination of the emulsion at this point indicated the formation of thicker and stronger urea-formaldehyde walls. The slurry containing the dual-walled microcapsules, and having the cellulose gum binder in the continuous phase, was then drawn down on a 12 pound neutral base continuous bond paper sheet at a coatin~ weight of approx-imately 2.34 to 3.04 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds. The dry coating of microcapsules containing PTSMH
was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the rev~rse side of the sheet -~
coated with microcapsules, a corresponding highly colored re-production of such impression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the slurry which was not utilized Eor coating paper in accordance with the foregoing was filtered using a Buchner filter. The filter cake was slurried in 200 ml of distilled water and was filtered again. The filter cake was air dried and after drying the same was easily broken. Copious amounts of DBP
were exuded when the dry capsules were squeezed.
EXAMPLE II
In this Example, the procedure was identical with that set forth in Example I except that in this instance, the product marXeted under the Trade Mark l'R-300" solvent was util-ized as the carrier for the dispersed phase rather than aibutyl phthalate. R-300 solvent is a commercial product of Kureha Corporation of America which is a mixture of isomeric diisopro--~05~915 pyl naphthaleneS and which is apparently generally disclosed in U. S. 3,806,463 to Konishi et al. The quantity of R-300 solvent utilized was identical to the quantity of DBP utilized in Example I and the quantities of all other materials were identical with Example I. A microscopic examination of the slurry immediately after the addition of the diethylene tria-mine solution revealed that microcapsules had been formed and that the capsule size was within the range of about 3 to about 20 microns. Fifteen minutes after the addition of the di-ethylene triamine, the pH of the slurry had dropped to 4.2.The slurry containing these microcapsules (which at this point were mostly single walled capsules with a poly-amide shell), and having the cellulose gum binder in the continuoùs phase, was then drawn down on a twelve pound continuous bond paper sheet at a coating weight of approximately 3.5 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds. The dry coating of micro-capsules containing PTSMH was then brought into contact with an acid=leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcapsules, a corres-ponding blue colored reproauction of such impression immedi-ately appeared on the acid-leached bentonite-type clay coating.
The mixing of the microcapsule slurry with the mechanical stirrer was continued for about 5 hours by which time the pH
of the slurry had dropped to approximately 2.3. This illus- , trates the effect of the HCl produced by the polycondensation of the terephthaloyl chloride ana the diethylene triamine. At this time the microcapsules had become agglomerated and a microscopic examination of the slurry inaicated that a urea-- formaldehyae shell wall had formed around the previously formed ~1)5;~5 single wall capsules. After stirring for 24 hours the pH of the slurry had decreased further to approximately 1.95 and a microscopic examination of the slurry at this point revealed a definite urea-formaldehyde wall formation. The slurry con-taining the dual-walled microcapsules, and having the cellulose gum binder in the continuous phase, was then drawn down on a 12 pound continuous bond paper sheet at a coating weight of approx-imately 3.5 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds.
The dry coating of microcapsules containing P~SMH was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcapsules a corresponding blue colored reproduction of such impression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the slurry was filtered with a Buchner funnel and the filter cake was slurried in 200 ml of water and was filtered again. These microcap-sules were then air dried. Filtration of the slurry was easily performed and the dried cake was easy to break. In this connection it is to be noted that ~singLe walled capsules having a polyamide shell ~ormed by interfacial polycondensation are usually quite difficult to filter and if the water is evap-~orated from the slurry, a rubbery mass is often formed which is diff.icult to break. This results from the elasticity and the tackiness of the polyamide films formed by interfacial polycon-densation. The outer layer of the tough urea-formaldehyde shell deposited on the inner polyamide wall eliminates problems such as difficult filtration and/or tacky capsules, and the dual-walled capsules of the present invention are easily dried to present a free-flowing powder. When the dry ~apsules pro-i~5~
duced in accoraance with the present Example were squeezed, copious amounts of oll were exuded.
- EXAMPLE III
In this Example, the procedures were generally the same as those of Example I except that in this instance the diethylene triamine and the URAC Resin 180 were added together.
Solutions A and B were identical with those o Example I. In this instance, however, 89 gms of 1.4 weight percent solution of Hercules cellulose gum 7Ll and 36.0 ml of water were placed in the Waring blender and solutions A and B were admixed and emulsified therein in the same manner as in Example I. After emulsification, 200 gms of water were added to the slurry and the same was placed in a stirred beaker. A solution was formed from 1.5 gms of diethylene triamine, 18.7 gms of URAC
Resin 180 solution and 50.0 ml of water and this solution was added to the reaction mixture while the stirring of the same continued. immediately after the addition of the solution containing the diethylene triamine and the URAC Resin 180 solu-tion, the pH of the reaction mixture was within the range of about 9 to 10. After 24 hours of stirring, the pH had dropped to 2.3. ~he color of the mixture was blue and a microscopic examination revealed a definite urea-formaldehyde wall forma-tion. A portion of the slurry containing the microcapsules, and having the cellulose gum binder in the continuous phase, was then drawn down on a 12 pound neutral base continuous bond paper sheet at a coating weight of approximately 3.5 gms per square meter and the coated sheet was oven dried at a tempera-ture of 110C for about 30 to 45 seconds. The dry coating of microcapsules containing PTSMH was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side o~ the sheet coated with microcapsules, a corresponding blue colored reproduction of such impression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the capsule slurry was filtered washed and air dried in accordance with the procedures set forth in the previous Examples. The dry capsule mix was easy to break and copious amounts of liquid fill material were exuded when the dry capsules were squeezed.
EXAMPLE IV
In this Example the diethylene triamine was added to the emulsion first and thereafter the URAC 180 resin solu-tion was added. The emulsion was formed utilizing the same procedures and quantities of materials outlined in Example III ~`
above. The emulsion was diluted with 250 ml of water and was placed in a stirred beaker. An aqueous solution containing 1.5 gms of diethylene triamine and 10.0 ml of water were then added to the stirred emulsion. Immediately after the addi-tion of the diethylene triamine solution, the pH of the slurry was approximately 9 to 10. A microsco~ic examination of the slurry at this point revealed that single walled capsules having a polyamide shell had been formed by interfacial poly-condensation. A few minutes after thè diethylene triamine solution had been added to the slurry, an aqueous solution containing 18.7 gms of URAC Resin 180 solution and 50 ml of water were added to the slurry. After 48 hours of stirring, the pH value of the mix had decreased to approximately 2.1 and the same had a slight blue coloration. A microscopic examin-~ation of the slurry revealed that the capsule size ranged from about 10 to about 100 microns and urea-formaldehyde wall for- -mation around the polyamide capsules was evident. This slurry was filtared, washed and dried as outlined above. When the ~15'~ 5 dry capsules were squeezed, copious amounts of liquid fill material were exuded.
EXAMPLE V
In this Example, the types and quantities of ingre-dients and the procedures utilized were identical with Example I except that in this instance, 89 ml of a 0.5% "Elvanol 50-42" solution ("Elvanol 50-42" being a Trade Mark) were util-ized in lieu of the 89 ml of 1.4~ Hercules cellulose gum solu-tion utilized in Example I. Also, 50 gms of URAC Resin 180 solution were utilized. Elvanol 50-42 is a polyvinyl alcohol with 87 to 89~ hydrolysis and a viscosity of 35 to 45 centi-poises in a 4% aqueous solution at 20C. The procedures for producing the dual-walled microcapsuies were identical with those utilized in Example I. Within a minute after the addi-tion of the diethylene triamine solution, the pH of the mix-ture had become approximately 7.0 and the presence of micro-capsules was apparent. After 2~ hours of mixing the pH of the slurry had decreased to 1.9 and a microscopic examination ~ of the slurry inaicated that urea-formaldehyde coated cap sules had been produced. A portion of this slurry was util-ized to produce coated paper in accordance with the proced-ures set forth above. Instant blue images were produced utilizing such paper in conjunction with acid-leached benton-ite-type clay coated CF paper. A sufficient amount of a 20%
solution of sodium hydroxide was added to the remainder of the slurry to cure and harden the urea-formaldehyde resin shells. Paper was coated with these cured capsules and again instant blue reproductions were created when this coated paper was utilized in con~unction with acid-leached bentonite-type clay coated CF paperO The slurry was filtered, washed and dried in accordance with the procedures set forth - 17 ~
~ .
~, .
~9~5~5 ~:
a~ove and the dried cake was very easy to break and the dry capsules were powdery and ~ree flowing. Upon squeezing the capsules, copious amounts of liquid fill material was exuded.
EXAMPLE VI
1.00 gm of the methyl ether of Michler's hydrol ~MEMH) were admixed with 37.5 gms of xylene and this admixture was warmed slightly on a hot plate until a clear solution ~solution A) was obtained. Thereafter solution A was allowed to cool to room temperature. Then, 3.6 gms of terephthaloyl chloride were added to 37.5 gms of xylene and this mixture was alqo warmed slightly on a hot plate until a clear solution (solution B) was obtained. Solution B was then also allowed to cool to room temperature. After solutions A and B were prepared, 90.0 ml of 0.5 weight percent ~lvanol 50-42 solution and 50.~ gms of URAC Resin 180 solution were placed in a one quart Waring blender and then solutions A and B were mixed to-gether at room temperature and the resultant solution was added to the solution containing URAC Resin 180 and Elvanol in the blender. The blender was activated and high shear agita tion was continued for about one minute until an emulsion was obtained. In this emulsion, the aqueous solution containing the Elvanol and the URAC Resin 180 formed the continuous phase and the solution containing the xylene solvent, the MEMH and terephthaloyl chloride formed the dispersed phase. This emulsion was diluted with 300 ml of water and the diluted emulsion was then transferred to a suitable container such as a beaker and was stirred with a variable speed mechanical stirrer at 300 to 500 rpm while an aqueous solution contain-ing 1.5 gms of diethylene triamine and 10 ml of water were added, Immediately upon addition of the di~thylene triamine solution, the pH of the slurry was in the rangP of from about `
~ 18 - I
-~LO S ~ IL9 5 6 to 7 and the formation of single walled capsules having a polyamide shell formed by interfacial polycondensation became evident. After ~4 hours of stirring, the pH of the slurry had decreased to about l.9. Coatings prepared from this slurry produced an instant blue writeoff on acid-leached bentonite-type clay coated CF paper. A sufficient amount of a 20% solution of sodium hydroxide was added to increase the pH of the slurry to approximately 9Ø The sodium hydroxide is operable to cure and harden the urea-formaldehyde outer capsule walls. A portion of this slurry containing the microcapSules, and having the Elvanol polyvinyl alchohol binder in the continuous phase, was then drawn down on a 12 pound neutral base continuous bond pàper sheet at a coating weight of approximately 3.5 gms per square meter and the coated sheet was oven dried at a temperature of 110C for about 30 to 45 seconds. The dry coating on the paper sheet was white. The dry coating of microcapsules containing the MEMH was then brought into contact with an acid-leached bentonite-type clay coating on the surface of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcapsules, a corresponding blue colored reproduction of such impression immediately appeared on the acid-leached bentonite~type clay coating~ The remainder of the slurry was then filtered, washed and air dried in accordance with the procedures set forth above. The dry cake was easily broken to produce a free flowing powder of ; microcapsules which exuded copious quantities of liquid fill material whèn squeezed.
EXAMPLE VII ~;
; 30 1.0 gm of PTSMH were admixed with 37.5 gms of DBP
and this admixture was warmed slightly on a hot plate until a ~5'~ 5 clear solution (solution A) was obtained. Thereafter solu-tion A was allowed to cool to room temperature. Then, 3.6 gms of terephthaloyl chloride were added to 37.5 gms of DBP
and this mixture was also warmed slightly on a hot plate until a clear solution ~solution B) was obtained. Solution B was then allowed to cool to room temperature. After solutions A
and B were prepared, 90 ml of an aqueous solution containing 0.5 weight percent Elvanol 50-42 polyvinyl alcohol and 50 ml of water were placed in a one quart Waring blender and then solutions A and B were mixed together at room temperature and the re~ultant solution was added to the Elvanol solution in the blender, The blender was activated and high shear agita-tion was continued for about 1 minutè until an emulsion was obtained. In this emulsion, the aqueous solution containing the Elvanol polyvinyl alcohol formed the continuous phase and the solution containing the DBP solvent, the PTSMH and tereph-thaloyl chloride formed the dispersed phase. The resultant emulsion was then transferred to a suitable container such as a beaker and the same was diluted with 200 ml of water. 1.4 gms of 1,2-ethanedithiol were added to 70 ml of water and a sufficient quantit~ of NaOH was added to the mixture to neu-tralize the 1,2~ethanedithiol. This mixture was then warmed slightly to produce a clear solution having a pH of about 9.O. 50 gms of a ~5 weight percent URAC Resin 180 solution was then added to this clear aqueous solution and the resultant solution was added to the diluted emulsion while the latter was stirred with a variable speed mechanical stirrer at 300 to 500 rpm. Stirring was continued for approximately 24 hours. Immediately after the addition of ` 30 the ~olution containing the ethanedithiol and the URAC Resin 180, the pH of the slurry was approximately 6 to 7 and the formation of single walled capsules having a polythiolester shell formed by interfacial polycondensation was evident. A
sufficient amount of a20% sodium hydroxide solution was added to the slurry to increase the pH to approximately 9.0 whereby the urea-formaldehyde outer ~hells were cured and hardened.
A portion of this slurry containing the hardened microcap6ules, and having the Elvanol polyvinyl alcohol binder in the contin-uous phase, was then drawn down on a 12 pound neutral base con-tinuous bond paper sheet at a coating weight of approximately 3.~ gms per square meter and the coated sheet was then dried at a temperature of 110C for about 30 to 45 seconds. The dry coating on the paper sheet was white. The dry coating o microcapsules containing PTSMH was then brought into contact with an acid-leached bentonite-type clay coating on the sur-face of another sheet of paper and when an impression was made on the reverse side of the sheet coated with microcap-sules, a corresponding blue colored reproduction of such im-pression immediately appeared on the acid-leached bentonite-type clay coating. The remainder of the microcapsules pro-2~ duced in accordance with this Example were filtered, washedand dried in accordance with the procedures outlined above~
The filter cake was easily broken to present a free flowing powder of microcapsules. When these microcapsules were squeezed, copious amounts of the liquid fill material were exuded.
Although in each of the foregoing Examples a urea-formaldehyde resin was utilized to form the outer shell, it should be understood that the present invention contemplates the utilization of any one of a variety o~ polymers for the formation of the outer shell wall. Critically, the monomer for the outer shell must be relatively non-reactive at the .
conditions necessary for the formation of the inner wall by interfacial polycondensation and moreover, th~ monomer for the outer shell should be water soluble in its monomer form, whereas the polymer formed therefrom should be water insoluble.
Particularly useful in connection with the present invention are the two stage resins capable of existing ln a water soluble, precondensate first stage and in a cross-linked, water insoluble, higher molecular weight second stage. In particular, aminoaldehyde resins (or aminoplasts) are useful in connection with the presentinvention. A discussion of aminoplasts and aminoplast precursors appears in C. P. Vale's book "Aminoplasts" published in 1950 by Inter Science Publi-shers, Inc. The aminoaldehyde resins typically are capable of existing in a thermoplastic first stage where the same are in a relatively low-molecular weight, water soluble form.
Upon catalysis with an acid, these precondensates are cross-linked to present a second stage polymer which is of rela-tively higher molecular weight and is generally water insol-uble. As soon as the resin has been converted into its higher molecular weight, water insoluble form, the same preci-pitates from water solution and enwraps dispersed particles present in the system. This phenomena is fully disclosed and illustrated in U. S. 3j016,308 to Macaulay (see particu-larly Example IV) and in U. S. 3,516,941 to Matson.
With regard to the inner wall of the dual-walled microcapsules of the present invention, the present invention .
contemplate5 the utilization of those polymers which may be formed by interfacial polycondensation at the interface be-tween a dispersed phase and a con~inuous phase. Such poly-mers and processes are fully disclosed in the patent to Ruus, U. S. 3,~29,827. In this connection, it is pointed out that ' . I
:llOS'~95 the present invention contemplates the use of any of these materials; however, those which condense with the evolution of an acid are particularly preferred 50 that the pH of the slurry may be autogenously reduced during the interfacial polycondensation to an extent such that the condensation of the aminoaldehyde precondensate from its water soluble first stage to its water insoluble second stage will proceed with-out further addition of an acid. However, it is pointed out that the present invention is not predicated upon the auto-genous generation of acid during the interfacial polyconden-sation and it is within the broad concepts of the present invention to add such acid from an outside source.
In connection with the foregoing it is stressed that the present invention contemplates the production of a dual-walled microcapsule by polymeri~ation processes which are carried out seriatum. . That is to say, a first polymeric shell,is formed about minute, discrete droplets of fill material by an interfacial polymerization and thereafter the conditions in the system are altered such that an outer shell `
is formed about the inner wall by a secondary polymerization reaction~
Claims (8)
1. A process for producing microcapsules comprising:
establishing a two-phase system comprising an aqueous con-tinuous phase and a dispersed discontinuous phase of minute intended liquid capsule core entities which are substantially insoluble in the continuous phase;
initially maintaining the pH of said system above a certain predetermined level;
including in said aqueous continuous phase an amino-aldehyde precondensate capable of existing in a water-soluble, low molecular weight form whenever the pH of the system is above said certain level and capable of undergoing further polymerization and cross-linking to produce a water insoluble polymer whenever the pH of the system is reduced to said certain level or below and a water soluble first polyfunc-tional reactant capable of undergoing polycondensation with a second polyfunctional reactant at a pH greater than said level to produce a polycondensate material;
including said second polyfunctional reactant in said dis-continuous phase whereby said first and second polyfunctional reactants condense at the interfaces between said phases to thereby encapsulate each core entity in an individual, gener-ally continuous polycondensate inner shell; and thereafter, reducing the pH in said continuous phase to cause said further polymerization of the precondensate to occur to produce said water insoluble polymer which thereby precipitates and enwraps each encapsulated core entity to form an individual, generally continuous aminoaldehyde polycondensate outer shell about said inner shell.
establishing a two-phase system comprising an aqueous con-tinuous phase and a dispersed discontinuous phase of minute intended liquid capsule core entities which are substantially insoluble in the continuous phase;
initially maintaining the pH of said system above a certain predetermined level;
including in said aqueous continuous phase an amino-aldehyde precondensate capable of existing in a water-soluble, low molecular weight form whenever the pH of the system is above said certain level and capable of undergoing further polymerization and cross-linking to produce a water insoluble polymer whenever the pH of the system is reduced to said certain level or below and a water soluble first polyfunc-tional reactant capable of undergoing polycondensation with a second polyfunctional reactant at a pH greater than said level to produce a polycondensate material;
including said second polyfunctional reactant in said dis-continuous phase whereby said first and second polyfunctional reactants condense at the interfaces between said phases to thereby encapsulate each core entity in an individual, gener-ally continuous polycondensate inner shell; and thereafter, reducing the pH in said continuous phase to cause said further polymerization of the precondensate to occur to produce said water insoluble polymer which thereby precipitates and enwraps each encapsulated core entity to form an individual, generally continuous aminoaldehyde polycondensate outer shell about said inner shell.
2. A process as set forth in claim 1 wherein the pH in said continuous phase is reduced to about 5.0 or less during said pH reducing step.
3. A process as set forth in claim 2 wherein said first and second reactants interreact, during said interfacial poly-condensation, to produce a sufficient amount of HCl to cause said decrease in the pH of the continuous phase.
4. A process as set forth in claim 2 wherein said first polyfunctional reactant is diethylene triamine and said second polyfunctional reactant is terephthaloyl chloride.
5. A process as set forth in claim 1 wherein said amino-aldehyde precondensate is a urea-formaldehyde resin.
6. A process as set forth in claim 4 wherein the pH in said continuous phase is reduced to about 5.0 or less during said pH reducing step.
7. A process as set forth in claim 6 wherein said first and second reactants interreact; during said interfacial poly-condensation, to produce a sufficient amount of HC1 to cause said decrease in the pH of the continuous phase.
8. A process as set forth in claim 7 wherein said first polyfunctional reactant is diethylene triamine and said second polyfunctional reactant is terephthaloyl chloride.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US50541574A | 1974-09-12 | 1974-09-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1052195A true CA1052195A (en) | 1979-04-10 |
Family
ID=24010214
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA230,762A Expired CA1052195A (en) | 1974-09-12 | 1975-07-04 | Production of dual walled microcapsules by reducing ph to polymerize aminoaldehyde precondensate |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5413874B2 (en) |
| AU (1) | AU502339B2 (en) |
| BE (1) | BE832897A (en) |
| CA (1) | CA1052195A (en) |
| CH (1) | CH615363A5 (en) |
| DE (1) | DE2537238C2 (en) |
| FR (1) | FR2284366A1 (en) |
| GB (1) | GB1502440A (en) |
| IT (1) | IT1047055B (en) |
| NL (1) | NL7510799A (en) |
| ZA (1) | ZA754567B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5547139A (en) * | 1978-09-30 | 1980-04-03 | Mitsubishi Paper Mills Ltd | Improved small capsule |
| NZ196601A (en) | 1980-04-08 | 1982-12-21 | Wiggins Teape Group Ltd | Production of microcapsules |
| JPS56144739A (en) * | 1980-04-10 | 1981-11-11 | Mitsubishi Paper Mills Ltd | Preparation of microcapsule |
| US4601863A (en) * | 1984-02-09 | 1986-07-22 | Kanzaki Paper Manufacturing Co., Ltd. | Process for producing powder of microcapsules |
| JPS60237864A (en) * | 1984-05-08 | 1985-11-26 | Mitsubishi Electric Corp | High voltage thyristor converter |
| ATE235960T1 (en) * | 2000-01-13 | 2003-04-15 | Kureha Chemical Ind Co Ltd | MICRO CAPSULE AND ITS PRODUCTION PROCESS |
| WO2005018795A1 (en) * | 2003-08-26 | 2005-03-03 | Universidade Do Minho | Double walled microcapsules with an outer thermoplastic wall and application process thereof |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH540715A (en) * | 1970-05-26 | 1973-10-15 | Ciba Geigy Ag | Process for the encapsulation of a substance finely divided in a liquid |
| DE2323243C3 (en) * | 1973-05-09 | 1980-02-28 | Robert Bosch Gmbh, 7000 Stuttgart | Method for producing a wear-resistant hard metal layer on a metal object, in particular on the cutting edge of a steel saw blade |
| JPS5813212B2 (en) * | 1973-07-17 | 1983-03-12 | 富士写真フイルム株式会社 | Microcapsules |
-
1975
- 1975-07-04 CA CA230,762A patent/CA1052195A/en not_active Expired
- 1975-07-11 AU AU82961/75A patent/AU502339B2/en not_active Expired
- 1975-07-16 ZA ZA00754567A patent/ZA754567B/en unknown
- 1975-08-20 JP JP10107475A patent/JPS5413874B2/ja not_active Expired
- 1975-08-20 GB GB34627/75A patent/GB1502440A/en not_active Expired
- 1975-08-21 DE DE2537238A patent/DE2537238C2/en not_active Expired
- 1975-08-29 BE BE159591A patent/BE832897A/en not_active IP Right Cessation
- 1975-09-03 FR FR7526985A patent/FR2284366A1/en active Granted
- 1975-09-08 CH CH1163775A patent/CH615363A5/en not_active IP Right Cessation
- 1975-09-09 IT IT51255/75A patent/IT1047055B/en active
- 1975-09-12 NL NL7510799A patent/NL7510799A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| AU502339B2 (en) | 1979-07-19 |
| FR2284366A1 (en) | 1976-04-09 |
| CH615363A5 (en) | 1980-01-31 |
| JPS5147578A (en) | 1976-04-23 |
| GB1502440A (en) | 1978-03-01 |
| IT1047055B (en) | 1980-09-10 |
| JPS5413874B2 (en) | 1979-06-02 |
| AU8296175A (en) | 1977-01-13 |
| ZA754567B (en) | 1976-06-30 |
| BE832897A (en) | 1975-12-16 |
| FR2284366B1 (en) | 1983-04-22 |
| NL7510799A (en) | 1976-03-16 |
| DE2537238A1 (en) | 1976-03-25 |
| DE2537238C2 (en) | 1984-11-08 |
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