CH615363A5 - Double-walled microcapsules with liquid filling material and process for preparing them - Google Patents

Description

The invention relates to double-walled microcapsules with liquid filling material and to a method for producing such microcapsules, the microcapsules being particularly suitable for carbonless paperless copy sets.

In such carbonless carbonless copy sets, the microcapsules with which the papers are coated contain a liquid filling of an initially colorless, but chemically reactive, color precursor compound and a carrier for the latter. The microcapsules can be broken open under pressure.

Carbon paper-free carbonless or impact-sensitive carbonless papers have been in use for a short time. Such papers are usually printed and used as carbonless copies so as to produce a plurality of copies. Pressure on the cover sheet causes a corresponding mark on each of the other sheets in the set.

The paper cover sheet, on which the impact or pressure acts directly, is usually coated on its rear side with microcapsules which contain one of the reaction components which, when reacted, lead to the generation of a label. A receiver sheet which is brought into contact with such a rear side of the cover sheet is coated on its front side with a material which contains a component which is reactive with the contents of the microcapsules, so that when the capsules are broken open as a result of pressure from a writing instrument or by means of a machine type, the initially colorless or essentially colorless content of the broken capsules reacts with the coreactant in the coating of the receiver sheet, and a mark is formed on the latter in accordance with the sign which was pushed through by the writing instrument or the machine type.

In this technique, the pressure-sensitive carbonless papers are designated with the abbreviations CB, CFB and CF, respectively for "coated back", "coated front and back" or "coated front" (coated front) coated on the front). Accordingly, the CB sheet is usually the cover sheet,

That is, which is directly affected by the pressure of the writing instrument, the CFB sheets are the intermediate sheets, each of which is provided with a marking on the front and each simultaneously transfers the contents of the broken capsules from the back to the front of the next sheet , and the CF sheet is the last sheet that is only coated on its front side to form a mark there. The CF sheet is normally not coated on the back because no further transfer is desired.

It is customary to coat the back of each sheet with the capsules and the front of each sheet with the capsule contents Koreagenz, but one could do the reverse if desired; some known systems do not require the use of coatings at all, and the reagents can be contained in the leaves themselves, or one reagent can be embedded in one of the leaves while the other is a surface

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coating is applied. Both reagents can also be contained in microcapsules. Publications describing various such systems are, for example, U.S. Patents 2,299,694, 2,712,507, 3,016,308, 3,429,827 and 3,720,534.

The most commonly used type of carbonless papers, including the type for which the present invention is intended, is described in U.S. Patents 2,712,507 and 3,016,308, respectively. Then microscopic capsules containing a liquid filling, which consists of a solution of an initially colorless chemically reactive color precursor, are applied to the back of the sheet, and a dry coating of a corresponding reagent for the color precursor to form the color is applied to the front of one Receiver sheet applied.

Numerous suitable color precursors are known for carbonless copies. For this, reference is made, for example, to US Pat. No. 3,455,721, in particular to the paragraph at the end of column 5 and at the beginning of column 6. These materials are capable of reacting with a CF coating that contains an acidic material, such as acidic bentonite clay, in accordance with U.S. Patent Application 1,257,075 (1971); the acidic polymer material according to US Pat. No. 3,455,721 is also suitable. Many of the color precursors mentioned in the latter publication can produce the color via an acid-base reaction with an acidic material.

Other known color precursors are the spiro-dipyran compounds according to US Pat. No. 3,293,060, in particular the compounds mentioned there in column 11, line 32 to column 12, line 21. The color precursors of the latter publication as well as US Pat. No. 3,455,721 are initially colorless, but become strongly colored when they are brought into contact with an acid-reacting coating, such as the acidic bentonite clay or an acid-reacting polymer material or the like.

In general, the color precursor materials disclosed in the latter two publications are dissolved in a solvent and the solution is encapsulated. Previously known methods for microencapsulation are disclosed in U.S. Patents 3,016,308, 2,712,507, 3,429,827 and 3,578,605.

Solvents known to be suitable for dissolving color precursors include chlorinated biphenyls, vegetable oils (castor oil, coconut oil, cottonseed oil, etc.), esters (dibutyl adipate, dibutyl phthalate, butyl benzyl adipate, benzyl octyl adipate, tricresyl phosphate, trio etc.), petroleum derivatives (petroleum fractions, kerosene, mineral oil etc.), aromatic solvents (benzene, toluene, etc.), silicone oils or combinations of the aforementioned substances. The alkylated naphthalene solvents according to US Pat. No. 3,806,463 are particularly suitable.

In the above-mentioned staining systems, as is known to those skilled in the art, the color precursors are usually contained in pressure-breakable microcapsules which are in the back coating of the sheets of the carbon copy. It is understood that the acidic coatings are usually used as front-side coatings, the color precursor material dissolved in a solvent being transferred from an adjacent rear-side coating to the acidic front-side coating when the capsules are broken open.

Although microcapsules are already in widespread use in conjunction with carbonless copy sets, there is still a need for products that are more durable and more suitable for use in high speed processing plants. For example, US Pat. No. 3,578,605 discloses double-walled capsules, the outer shell of which is formed by coacervation of a hydrophilic colloid material. US Pat. No. 3,429,827 discloses double-walled capsules in which the outer shell is applied by spray drying or coating with a dry granular substance. The double-walled capsules according to US Pat. No. 3,265,629 comprise an inner shell made of a wax-like material and an outer wall made of a hydrophilic colloid material.

The double-walled capsules according to US Pat. Nos. 2,969,331 and 3,190,837 have an outer shell made of a hydrophilic colloid material and the same applies to US Pat. No. 3,627,693. While the microcapsules disclosed in the latter publications generally have somewhat better properties than single-walled ones Capsules, there are still difficulties and there is still a need for more durable and more manageable microcapsules.

The object of the present invention is to provide a solution to this problem. The solution to the problem according to the invention consists of double-walled microcapsules with liquid filling material, which is characterized in that tiny, discrete droplets of the liquid filling material are made individually from breakable, generally continuous inner walls made of a polycondensate material and the inner walls are made individually from breakable, generally continuous outer shells from one Polycondensate substance are enclosed. The polycondensate substance can be an amino aldehyde polymer.

The process according to the invention for the production of such microcapsules, in which the polycondensate substance is an aminoaldehyde polymer, is characterized in that a two-phase system is produced, comprising an aqueous continuous phase and a dispersed discontinuous phase from tiny units provided as liquid capsule cores, which are used in the continuous Phase are essentially insoluble that a water-soluble aminoaldehyde precondensate of low molecular weight and a water-soluble first polyfunctional reagent, which can carry out polycondensation with a second polyfunctional reagent to produce a polycondensate material, are used in the aqueous continuous phase, that the second polyfunctional reagent is used in the discontinuous Phase is used, wherein the first and second polyfunctional reagent condense at the interface between the phases, so that each core unit in an individual, gener encapsulating the continuous inner polycondensate shell, and thereafter the reaction conditions in the continuous phase are changed so that the precondensate is polymerized to a water-insoluble polymer which fails and envelops each encapsulated core unit with an individual, generally continuous outer aminoaldehyde shell. The reaction conditions in the continuous phase can be changed by lowering the pH to about 5.0 or less. The first and second polyfunctional reagents which can be used are those which react with one another during the interfacial polycondensation to produce a sufficient amount of HCl to lower the pH of the continuous phase. The first polyfunctional reagent can be a diethylene triamine and the second polyfunctional reagent can be terephthaloyl chloride, and the amino aldehyde precondensate can be a urea-formaldehyde resin.

Broadly, the present invention encompasses microcapsules having an inner wall, such as that formed by the interfacial polycondensation described in U.S. Patent No. 3,429,827, and having a hydrophobic outer wall made of an amino aldehyde polymer as disclosed in U.S. Patent No. 3,016,308 there in particular in Example 4, line 17 of column 9. In the preferred method according to the invention

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Hydrochloric acid, produced by the reaction of the terephthaloyl chloride and the diethylenetriamine according to the interfacial polycondensation according to US Pat. No. 3,429,827, is used to lower the pH of the system and to cause the urea-formaldehyde resin from Example 4 of the US Pat. PS 3 016 308 is condensed and precipitated so as to form the outer shell. Accordingly, reference may be made to the latter two publications with regard to the details of the course of the reaction.

Usually, in the interfacial microencapsulation process, an oil containing a diacet chloride, a disulfonyl chloride, a diisocyanate, etc. is emulsified in an aqueous or polar medium containing a monomer such as a diamine or bisphenol or similar. The condensation reaction takes place at or near the interfaces between the dispersed oil phase and the continuous aqueous phase. The concept and principle of the present invention are attractive because the interfacial polycondensation reaction generally proceeds much faster than the acid catalyzed condensation reaction that leads to the formation of the outer shell. This minimizes mixing during shell formation and protects the capsules from damage, rupture or the like caused by demulsification, while maximizing the development of the inner shell wall by interfacial polycondensation. Hydrochloric acid is a useful by-product of the interfacial polycondensation reactions that form the inner shell wall, and an acidic phase is required for the condensation of conventional amino aldehyde precondensates. In addition, an inner shell formed by interfacial polycondensation can be modified to be acidic, basic, very deep, etc., depending on factors such as the type and amount of the monomer and the presence of crosslinking agents or the like during the microencapsulation process. For example, depending on the amount and type of acid chlorides and amines used, the end groups of the polymer chain could be acidic or basic. In addition, the linking groups could be modified in a similar manner.

Another advantage of the invention is that double-walled capsules are formed in a single continuous process, the acid generated by the interfacial polycondensation being used as a catalyst for the condensation of the amino aldehyde precondensate. This does not preclude the use of other chemical additives, heat, mixing processes, etc. to support the reaction or to improve the quality of the outer shell or outer deposit. The double-walled capsules produced according to the present invention have better strength, chemical resistance, hydrophobicity, etc. in comparison with conventional microcapsules. In addition, microcapsules that are produced by conventional interfacial polycondensation processes are elastic in nature and not easily separable, dryable or filterable under normal conditions. According to the present invention, however, free-flowing, dry capsules can be produced very easily, specifically because of the inherent strength and other properties of the crosslinked polycondensate outer shells.

The capsules according to the invention are particularly useful in connection with carbon paper-free copying systems; however, it should be noted that other uses for microcapsules are known to those skilled in the art. If the capsules are used in conjunction with carbonless paperless copying systems, the filler material will usually comprise an initially colorless, chemically reactive color precursor and a carrier for this, such as dibutyl phthalate or one of the alkalized naphthalene solvents according to US Pat. No. 3,806,463.

The inner capsule shell can be any polycondensate formed by interfacial polycondensation at the interface between the dispersed droplets of filler and a continuous phase. For example, various polycondensates are disclosed in US Pat. No. 3,429,827, which include polyamines, polyurethanes, polysulfonamides, polyesters, polyureas, polycarbonates. Particularly useful in connection with the manufacture of the inner shell wall by interfacial polycondensation are those reagents which release an acid as a by-product in the condensation. For example, terephthaloyl chloride and ethylenediamine condense to form a polyamide and release hydrochloric acid as a by-product.

With regard to the outer shell, amino aldehyde resins are generally usable. Melamine formaldehydes, phenolformaldehydes, urea-formaldehyde and urea-acetaldehyde resins are particularly useful. Typically, such materials can be in the form of a water-soluble, low molecular weight precondensate whenever the pH of the system is greater than a certain limit, which in turn is a function of the particular material but is generally around 5. However, if the pH of the system is lowered to or below this particular value, the precondensate is further polymerized to form crosslinks, with the result that a water-insoluble polymer is formed which is precipitated from the solution and thereby particles which can be dispersed in the continuous phase, coated and encapsulated. This phenomenon is described in detail in U.S. Patent 3,516,941, to which reference may be made for further details. This phenomenon is also mentioned in Example 4 of US Pat. No. 3,016,308.

The invention is explained in more detail below on the basis of exemplary embodiments.

example 1

1.00 g of p-toluenesulfinate from Michler's Hydrol (abbreviated PTSMH) is mixed with 37.5 g dibutyl phthalate (abbreviated DBP) and this mixture is heated somewhat on a hot plate until a clear solution (solution A) is obtained. Thereafter, solution A is allowed to cool to room temperature. 3.26 g of terephthaloyl chloride are added to 37.5 g of dibutyl phthalate (DBP), and this mixture is also heated somewhat on a hot plate until a clear solution is obtained (solution B). Solution B is also allowed to cool to room temperature. After preparing solutions A and B, mix: 89.0 g of an aqueous solution containing 1.4% by weight of Hercules-7 L 1 cellulose gum (a commercially available sodium carboxmethyl cellulose product with a degree of substitution of about 0.7 and a molecular weight of less than 45,000) and 18.7 g of URAC Resin 180 solution (a commercial product of the American Cyanamide Company, which is an unmodified urea-formaldehyde resin in water solution, with about 65 % By weight of fat); this mixture is placed in a Waring mixer. Thereafter, solutions A and B are mixed together at room temperature and the resulting solution is added to the aqueous solution of URAC 180 and cellulose gum in the Waring mixer. The mixer is started and shaking with high shear is maintained for 45 seconds until an emulsion results with a dispersed phase, the particle size of which is about 2 to 10 / <m. In this emulsion, the aqueous solution with URAC 180 and cellulose rubber form the continuous phase and the solution of tereph-

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thaloyl chloride and PTSMH in DBP form the dispersed phase. 300 g of water are added to the emulsion and the diluted emulsion is then placed in a suitable container, such as a beaker, and stirred with a mechanical stirrer at different speeds between 300 and 500 rpm, while an aqueous solution containing 1 Contains 5 g of diethylene triamine and 10 g of water is added. Before adding the amine solution, the emulsion was examined and found to have a pH of 6.0; application of the emulsion to a paper substrate was oily and no copy could be obtained on CF paper coated with an acidified bentonite clay coating. This is an indication that there were no capsules in the emulsion before the amine was added. 5 minutes after the addition of the amine solution, the pH of the mixture was 9.4. Microscopic examination of the mixture showed that polyamide capsules had formed. Stirring of the emulsion was continued; after 28 hours the pH of the emulsion had dropped to 2.8. Microscopic examination of the emulsion at this point showed that thicker and stronger urea-formaldehyde walls had formed. The liquid containing the double-walled microcapsules and the cellulose gum binder in the continuous phase was then applied to 12 pound neutral-base printing paper with a coating weight of about 2.34 to 3.04 g / m2, and that coated sheet was dried in an oven at a temperature of 110 ° C for about 30 to 35 seconds. The dry coating of the microcapsules containing PTSMH was then brought into contact with an acidified bentonite clay coating on the surface of another sheet of paper, and when pressure was applied to the back of the sheet coated with microcapsules, the result was a correspondingly more colored one Reproduction of this print pattern immediately on the acidified bentonite clay coating. The rest of the liquid, which was not used for coating the paper as explained above, was filtered through Büchner filters. The filter cake was suspended in 200 ml of distilled water and filtered again. The filter cake was air dried and after drying it was easily fragile. Significant amounts of DBP were squeezed out by squeezing the dry capsules.

Example 2

In this example, the procedure is identical to Example 1, except that in this case R-300 solvent was used as the carrier for the dispersed phase instead of dibutyl phthalate. R-300 solvent is a commercial product of the Kureha Corporation of America; it is a mixture of isomeric diisopropylnaphthalenes as disclosed in US Pat. No. 3,806,463. The amount of R-300 solvent used was identical to the amount of DBP of Example 1 and the amounts of all other materials were also the same as Example 1. A microscopic examination of the liquid immediately after the addition of the diethylenetriamine solution showed that microcapsules had formed and that the capsule size was in the range from about 3 to 20 μm. 15 minutes after the addition of diethylene triamine, the pH of the liquid had dropped to 4.2. The liquid containing these microcapsules (these were mostly single-wall capsules with a polyamide shell at this point) and where cellulose gum was contained in the continuous phase was then placed on a sheet of 12 pound printing paper with a coating weight of approximately 3.5 g / m2, and the coated sheet was oven dried at a temperature of 110 ° C for about 30 to 45 seconds. The dry coating of microcapsules containing PTSMH was then brought into contact with an acidified bentonite clay coating on the surface of another sheet of paper, and when printed on the back of the sheet coated with microcapsules, an analog blue-colored reproduction of such a print pattern resulted immediately on the acidified ben tonite clay coating. Mixing of the microcapsule suspension with the mechanical stirrer was continued for about 5 hours, during which the pH of the liquid dropped to about 2.3. This illustrates the effect of hydrochloric acid, which is generated by the polycondensation of terephthaloyl chloride and diethylene triamine. At this point the microcapsules were agglomerated and a microscopic examination showed that urea-formaldehyde shells had formed around the single-walled capsules that had initially been formed. After stirring for 24 h, the pH of the liquid had dropped further to about 1.95 and a microscopic examination of the suspension at this point showed a clear formation of urea-formaldehyde. The suspension with the double-walled microcapsules and the cellulose gum binder in the continuous phase was then applied to a sheet of 12 pound printing paper with a coating weight of about 3.5 g / m 2 and the coated sheet was oven dried at a temperature of about 110 ° C for about 30 to 45 sec. The dry coating of the PTSMH-containing microcapsules was then brought into contact with an acidified bentonite clay coating on the surface of another sheet of paper, and when pressure was applied to the back of the sheet coated with microcapsules, an analog blue-colored reproduction of such a printing pattern immediately resulted the acidified bentonite clay coating. The rest of the suspension was filtered with a Büchner funnel and the filter cake was suspended in 200 ml of water and filtered again. These microcapsules were then air dried. Filtration of the slurry was possible without difficulty and the dry filter cake was easily broken. In this context it should be noted

that single-wall capsules with a polyamide shell formed by interfacial polycondensation are usually very difficult to filter, and that when the water is evaporated from the slurry, a rubbery mass is often formed which is difficult to break. This is due to the elasticity and tendency of the polyamide films to stick, which are formed by interfacial polycondensation. The outer layer of the solid urea-formaldehyde shell, applied to the inner polyamide wall, eliminates problems such as difficulties in filtering and / or capsules tending to cake, and the double-walled capsules according to the invention can be easily dried, resulting in a free-flowing powder. When the dry capsules made according to this example were squeezed, significant amounts of oil were released.

Example 3

In this example, the procedure was generally the same as that of Example 1, except that in this case the diethylene triamine and the URAC resin 180 were brought together. Solutions A and B were identical to those in Example 1. Here, 80 g of a 1.4% by weight solution of Hercules cellulose gum 7L1 and 36.0 ml of water were used in the Waring mixer and solutions A and B were mixed and in the emulsified in the same way as in Example 1. After the emulsification, 200 g of water was added to the slurry and this was in a beaker

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touched. A solution was prepared from 1.5 g of diethylene triamine, 18.7 g of URAC Resin 180 solution and 50.0 ml of water, and this solution was added to the reaction mixture with continued stirring. Immediately after adding the solution containing the diethylenetriamine and the URAC Resin 180, the pH of the reaction mixture was in the range from about 9 to 10. After 24 hours of stirring, the pH had dropped to 2.3. The color of the mixture was blue and microscopic examination showed a clear formation of urea-formaldehyde walls. A portion of the cellulosic gum-containing slurry containing the microcapsules was then applied to a sheet of 12 pound neutral base printing paper with a coating weight of about 3.5 g / m 2 and the coated sheet was oven dried a temperature of 110 ° C for about 30 to 45 seconds! The dry microcapsule coating with PTSMH content was then brought into contact with an acidified bentonite clay coating on the surface of another sheet of paper and when pressure was applied to the back of the sheet coated with microcapsules, an analog blue colored reproduction of such a print pattern resulted, that immediately appeared on the acidified bentonite clay coating. The rest of the capsule dispersion was filtered, washed and air dried as explained in the previous examples. The dry capsule mixture was easily breakable and significant amounts of liquid fill material were excreted when the dry capsules were squeezed.

Example 4

In this example, the diethylenetriamine was added to the emulsion first and then the URAC 180 resin solution was added. The emulsion was prepared using the same procedure and amounts of materials as described in Example 3. The emulsion was stirred with 250 ml of water and then stirred in a beaker. An aqueous solution containing 1.5 g of diethylene triamine and 10.0 ml of water was then added to the stirred emulsion. Immediately after the diethylenetriamine solution had been added, the pH of the suspension was about 9 to 10. A microscopic examination of the dispersion at this point showed that single-wall capsules with a polyamide shell had been formed by interfacial polycondensation. A few minutes after the diethylene triamine solution was added to the slurry, an aqueous solution containing 18.6 g of URAC Resin 180 solution and 55 ml of water was added to the emulsion. After stirring for 48 h the pH of the mixture had dropped to about 2.1 and this had a light blue color. Microscopic examination of the emulsion showed that the capsule size was between about 10 and 100 μm and a formation of urea-formaldehyde around the polyamide capsules was evident. This slurry was filtered, washed and dried as before. When the dry capsules were squeezed, considerable amounts of liquid filling material were released.

Example 5

In this example, the materials and amounts, as well as the process, are the same as in Example 1, except that in this case, instead of 89 ml of 1.4% Hercules cellulose gum solution, 89 ml of 0.5% Elvanol 50- until 42 solution were used. 50 g of URAC Resin 180 solution were also used. Elvanol 50 to 42 is a polyvinyl alcohol that is 87 to 89% hydrolyzed and has a viscosity of 35 to 45 centipoise in a 4% aqueous solution at 20 ° C. The procedure for the formation of the double-walled microcapsules was correct

in agreement with Example 1. Within 1 min after the addition of the diethylenetriamine solution, the pH of the mixture was about 7.0 and the presence of microcapsules was evident. After 24 hours of mixing, the pH of the emulsion had dropped to 1.9 and microscopic inspection of the emulsion revealed that capsules coated with urea-formaldehyde had been formed. Part of this emulsion was used to make coated paper as in the previous examples. Immediate blue images were produced when such paper was used in conjunction with acidified bentonite clay coatings on CF paper. A sufficient amount of a 20% solution of sodium hydroxide was added to the rest of the emulsion to cure the urea-formaldehyde resin shells. Paper was coated with such hardened capsules and, again, instant blue reproductions were produced when this coated paper was used in conjunction with CF paper coated with acidified bentonite clay. The emulsion was filtered, washed and dried as explained in the previous examples, and the dry filter cake was easy to break open and the dry capsules were powdery and free flowing. When the capsules were squeezed, considerable amounts of liquid filling material were excreted.

Example 6

1.0 g of Michler's Hydrol's methyl ether (MEMH) was mixed with 37.5 g of xylene and this mixture was heated somewhat on a hot plate until a clear solution (solution A) was obtained. Thereafter, solution A was allowed to cool to room temperature. 3.6 g of terephthaloyl chloride was added to 37.5 g of xylene, and this mixture was also warmed slightly on a hot plate until a clear solution (solution B) resulted. Solution B was then also allowed to cool to room temperature. After preparing solutions A and B, 90.0 ml of 0.5 weight percent Elvanol 50-42 solution and 50.0 g URAC Resin 180 solution were placed in a Waring mixer, and then solutions A and B mixed at room temperature and the resulting solution was added to the URAC Resin 180 Elvanol solution in the mixer. The mixer was started and high shear mixing was carried out for about 1 minute until an emulsion was obtained. In this emulsion, the aqueous solution with Elvanol and URAC Resin 180 formed the continuous phase and the solution containing xylene solvents, MEMH and terephthaloyl chloride formed the dispersed phase. This emulsion was diluted with 300 ml of water and the diluted emulsion was then placed in a suitable container, such as a beaker, and stirred with a mechanical stirrer at different speeds of 300 to 500 rpm, while an aqueous solution, the 1st , 5 g of diethylene triamine and 10 ml of water was added. Immediately after adding the diethylenetriamine solution, the pH of the emulsion was in the range of about 6 to 7 and the formation of single-walled capsules with a polyamide shell, formed by interfacial polycondensation, was clear. After stirring for 24 hours, the pH of the liquid had dropped to about 1.9. Coatings with this emulsion gave an immediate copy on CF paper coated with acidified bentonite clay. A sufficient amount of a 20% sodium hydroxide solution was added to raise the pH of the slurry to 9.0. The sodium hydroxide was used to harden the urea-formaldehyde walls of the outer capsules. A portion of this slurry containing the microcapsules with the elvanol polyvinyl alcohol binder in the continuous phase was then reduced to a

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Sheet of 12 pound neutral base printing paper applied with a coating weight of about 3.5 g / m 2 and the coated sheet was oven dried at a temperature of 110 ° C for 30 to 45 seconds. The dry coating on the paper sheet was white. The dry coating of the microcapsules containing MEMH was then brought into contact with an acidified bentonite clay coating on the surface of another sheet of paper, and when pressure was applied to the back of the sheet coated with microcapsules, a corresponding blue-colored reproduction of the printed pattern resulted immediately appeared on the acidified bentonite clay coating. The rest of the dispersion was then filtered, washed and air dried as in the previous examples. The dry filter cake was easily broken and resulted in a free flowing powder of microcapsules, which excreted substantial amounts of liquid filler material when squeezed.

Example 7

1.0 g of PTSMH was mixed with 37.5 g of DBP and this mixture was warmed up slightly on a hot plate until a clear solution (solution A) resulted. The solution was then allowed to cool to room temperature. Then 3.6 g of terephthaloyl chloride was added to 37.5 g of DBP and this mixture was also heated somewhat 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 ml of an aqueous solution containing 0.5% by weight of Elvanol 50 to 42 polyvinyl alcohol and 50 ml of water was put in a Waring mixer, and then solutions A and B were put at room temperature mixed and added to the elvanol solution in the mixer. The mixer was started and mixed under high shear for about 1 minute until an emulsion was obtained. In this emulsion, the polyvinyl alcohol-containing aqueous solution of elvanol formed the continuous phase, and the solution containing DBP solvents, PTSMH and terephthaloyl chloride formed the dispersed phase. The resulting emulsion was then placed in a suitable container, such as a beaker, and diluted with 200 ml of water. 1.4 g of 1,2-ethane dithiol was added to 70 ml of water and a sufficient amount of NaOH was added to the mixture to neutralize the 1,2-ethane dithiol. This mixture was then warmed up a little until a clear solution with a pH of about 9.0 was obtained. 50 g of a 65 weight percent URAC Resin 180 solution was then added to this clear aqueous solution and the resulting solution was added to the dilute emulsion while the latter was being stirred with a mechanical stirrer at varying speeds from 300 to 500 rpm ./min. Stirring was continued for approximately 24 hours. Immediately after adding the solution with the ethanedithiol and the URAC Resin 180 solution, the pH of the emulsion was around 6 to 7 and the formation of single-walled capsules with a polythiolester shell by interfacial polycondensation was clearly evident. A sufficient amount of a 20% sodium hydroxide solution was added to the liquid to raise the pH to about 9.0 while the outer urea-formaldehyde dishes were hardened. A portion of this suspension of the cured microcapsules with the elvanol polyvinyl alcohol binder in the continuous phase was then coated on a sheet of 12 pound neutral base printing paper with a coating weight of about 9.5 g / m 2 and coated Sheet was oven dried at a temperature of 110 ° C for about 30 to 35 seconds. The dry coating on the

Paper sheet was white. The dry coating of microcapsules containing PTSMH was then brought into contact with an acidified bentonite clay coating on the surface of another sheet of paper and when pressure was applied to the back of the sheet coated with microcapsules, one immediately obtained on the acidified bentonite. Clay coating a corresponding blue colored reproduction of the print pattern. The rest of the microcapsules produced according to this example were filtered, washed and dried as in the previously described methods. The filter cake was easily broken and a free flowing powder of microcapsules was obtained. When these microcapsules were squeezed, significant amounts of liquid fill material were excreted.

Although a urea-formaldehyde resin was used to form the outer shell in the above examples, it is to be understood that the invention also encompasses the use of any other type of polymer to form the outer shell wall. However, the monomer for the outer shell must be relatively unresponsive under the conditions which are necessary for the formation of the inner wall by interfacial polycondensation, and moreover the monomer for the outer shell must be water-soluble in its monomeric form, while the polymer formed from it is water-insoluble have to be. Particularly suitable in connection with the invention are the two-stage resins which can exist in a first water-soluble pre-condensate stage and in a cross-linked water-insoluble high-molecular second stage. In particular amino aldehyde resins (or aminoplasts) are useful in connection with the invention. A more detailed explanation of the amino paste and the aminoplast precursors can be found in C.P. Vale, "Aminoplasts", published in 1950 by Inter Science Publishers, Incorporation; reference may be made to this publication for details. The amino aldehyde resins are typically able to exist in a first thermoplastic stage where they are relatively low in molecular weight and water soluble. Catalysis with an acid results in crosslinking of these precondensates and thus a second polymer stage which has a relatively higher molecular weight and which is generally water-insoluble. Once the resin has been converted to its higher molecular weight water-insoluble state, it precipitates out of the aqueous solution and envelops dispersed particles that are in the system. This phenomenon is disclosed and illustrated in U.S. Patent 3,016,308 (particularly Example 4) and U.S. Patent 3,516,941.

As regards the inner wall of the double-walled microcapsules according to the invention, the invention provides for the use of those polymers which are formed by interfacial polycondensation at the interface between a dispersed phase and a continuous phase. Such polymers and processes are fully disclosed in U.S. Patent No. 3,429,827. In this connection it is emphasized that the use of any of these materials is possible according to the present invention. However, those that condense to release an acid are particularly preferred because the pH of the slurry is automatically reduced to a degree during interfacial polycondensation such that the condensation of the aminodehyde precondensates results from their water-soluble first state to their water-insoluble second state without the use of an acid. However, it is emphasized that the invention need not be limited to the automatic generation of an acid during interfacial polycondensation, and that

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Within the broad concept of the present invention, the addition of such acid from an external source is possible.

In accordance with the above, it is summarized once again that, according to the invention, the production of double-walled microcapsules is provided by polymerization processes which are carried out in series. This means that a first polymeric shell is formed around a tiny, discrete drop of filler material by polymerization, and thereafter the conditions in the system are changed such that an outer shell is formed around the inner wall by a second polymerization reaction.

Claims (13)

615 363 2nd PATENT CLAIMS 1. Double-walled microcapsules with liquid filling material, characterized in that tiny, discrete droplets of the liquid filling material are individually enclosed by breakable, generally continuous inner walls made of a polycondensate material and the inner walls are individually enclosed by breakable, generally continuous outer shells made of a polycondensate substance. 2. Microcapsules according to claim 1, characterized in that the polycondensate substance is an amino aldehyde polymer. 3. Microcapsules according to claim 1, characterized in that the polycondensate material is a polyamide. 4. Microcapsules according to claim 1, characterized in that the polycondensate substance is a urea-formaldehyde polymer. 5. Microcapsules according to claim 1, characterized in that the filling material comprises an initially colorless, chemically reactive, color-forming dye precursor. 6. A method for producing microcapsules according to claim 2, characterized in that a two-phase system is produced, comprising an aqueous continuous phase and a dispersed discontinuous phase from tiny units provided as liquid capsule cores which are essentially insoluble in the continuous phase; that a water-soluble aminoaldehyde precondensate of low molecular weight and a water-soluble first polyfunctional reagent, which can carry out a polycondensation with a second polyfunctional reagent to produce a polycondensate material, are used in the aqueous continuous phase; that the second polyfunctional reagent is placed in the discontinuous phase, the first and second polyfunctional reagents condensing at the interface between the phases so as to encapsulate each core unit in an individual, generally continuous inner polycondensate shell, and thereafter the reaction conditions in the continuous phase so be changed; that the precondensate is polymerized to a water-insoluble polymer, which precipitates and envelops each encapsulated core unit with an individual, generally continuous, outer amino aldehyde shell. 7. The method according to claim 6, characterized in that the change in the conditions in the continuous phase is carried out by lowering the pH to about 5.0 or less. 8. The method according to claim 7, characterized in that the first and second polyfunctional reagents used are those which react during the interfacial polycondensation with the generation of a sufficient amount of hydrochloric acid to give the desired lowering of the pH in the continuous phase . 9. The method according to claim 8, characterized in that the first polyfunctional reagent is diethylene triamine and the second polyfunctional reagent is terephthaloyl chloride. 10. The method according to claim 6, characterized in that the aminoaldehyde precondensate is a urea-formaldehyde resin. 11. The method according to claim 10, characterized in that the change in the conditions in the continuous phase by lowering the pH to about 5.0 or less. 12. The method according to claim 11, characterized in that the first and second polyfunctional reagents used are those which react with one another during the interfacial polycondensation to produce a sufficient amount of HCl to lower the pH of the continuous phase. 13. The method according to claim 12, characterized in that the first polyfunctional reagent is a diethylene triamine and the second polyfunctional reagent is terephthaloyl chloride.